The main challenge for the selective flotation of copper and molybdenum (Cu-Mo) sulfide minerals in seawater is the formation of colloidal precipitates in strongly alkaline conditions. These precipitates hinder the selective separation of copper from molybdenum minerals in seawater by lowering the floatability of Cu-Mo sulfide minerals. The present study aimed to examine the direct utilization of seawater in the selective flotation of Cu-Mo sulfides. Additionally, the effectiveness of sodium metabisulfite (Na2S2O5) as a copper depressant for selective flotation of Cu-Mo sulfides in seawater was studied under weakly acidic, neutral, and moderately alkaline conditions. A complex Cu-Mo concentrate that largely consisted of chalcopyrite and molybdenite, as well as a tiny amount of pyrite and quartz, was used in the flotation tests. The flotation results revealed that treatment with 3.6 kg/t Na2S2O5 in seawater at pH 5.5 significantly lowered the copper recovery from 97% to 11% and caused a modest reduction in the molybdenum recovery from 98% to 94% with a Cu-Mo separation efficiency of 83%. These flotation results demonstrate that Na2S2O5 treatment in seawater selectively depresses the floatability of copper minerals. Consequently, molybdenum can be separated from copper minerals under a weakly acidic condition in seawater. In addition, this study discusses the effects of various pH conditions and dosages of Na2S2O5. The surface properties of Cu-Mo minerals were studied using X-ray photoelectron and infrared spectroscopies, and a mechanism to explain the selective flotation of Cu-Mo using Na2S2O5 treatment in seawater is proposed.

Enargite is typically associated with chalcocite. Owing to the similarity in the flotation behaviors of these minerals, both minerals are reported to concentrate in the conventional flotation circuit. However, inorganic arsenic in enargite can decrease the copper concentrate quality and increase the operating cost of processing this concentrate. Separating these minerals is important for cleaner copper production to avoid these effects. In this context, this study investigated the effect of hydrogen peroxide (H2O2) treatment on the flotation behavior of chalcocite and enargite. Flotation tests of pure and mixed minerals indicated that H2O2 treatment reduced the floatability of chalcocite and enargite by forming sulfate and copper hydroxide on their surfaces. Despite the detrimental effect of the H2O2 treatment, there was a narrow window of H2O2 concentration for separating both minerals, in which enargite floated and chalcocite was depressed. This selective flotation behavior was caused by the rapid adsorption of potassium amyl xanthate (KAX) and lower surface oxidation of enargite compared with that of chalcocite.

Chalcopyrite flotation is selectively depressed by oxidation treatment. The presence of ferric oxyhydroxide on the surface of chalcopyrite after oxidation treatment is a key factor in depressing chalcopyrite flotation. However, there is no concrete evidence that ferric oxyhydroxide has a depressing effect. In addition, the effectiveness of this depressing effect could be enhanced by directly applying ferric oxyhydroxide nanoparticles. This study investigated the effect of goethite (α-FeOOH) nanoparticles on the surface properties and flotation behavior of chalcopyrite. α-FeOOH nanoparticles were produced through chemical precipitation followed by hydrothermal treatment. The crystalline structure of irregular rice grain-shaped α-FeOOH nanoparticles was confirmed by the X-ray diffraction pattern and scanning electron microscope image. Micro-flotation experiments showed that chalcopyrite recovery decreased significantly from 93 % to 13 % when 30 mg/L α-FeOOH nanoparticles was used. This flotation result demonstrated the potential of α-FeOOH nanoparticles as a nanodepressant for the flotation of chalcopyrite. These nanoparticles physically adsorbed on the chalcopyrite surface and rendered its surface hydrophilic, thereby reducing the chalcopyrite flotation recovery. The attractive electrostatic force between the positively charged α-FeOOH nanoparticles and the negatively charged chalcopyrite surface is likely responsible for the adsorption of α-FeOOH nanoparticles on chalcopyrite.

Transition metal quantum dots composites for an electrocatalytic hydrogen evolution reaction.

Over the last few decades, research is being carried out in the field of photocatalysis to investigate for fuels production in sustainable manner. Due to an energy depletion and CO2 emission in the current situation urge us to produce alternative fuels. Water splitting and the reduction of carbon dioxide using various photocatalysts are being developed as promising sustainable methods to obtain eco-friendly energy sources. Conducting polymers (CP) stand out among the current pool of studied photocatalysts due to their high light absorption efficiency, good stability, tunable electronic characteristics, and cost effectiveness. Various CP, such as polyaniline, polythiophene, and polypyrrole have been integrated with different semiconducting nanomaterials to produce photocatalytic composites. Therefore, in this review, we focus on the synthesis of CP and their nanocomposites for application in CO2 photoreduction and water splitting into fuel production using different polymeric composites. Many composite photocatalysts show synergistic effects between the polymeric material and other counterparts in the composite. The improvement in the inactivity of the composite can be attributed to the band configurations of the composite. Improving the separation of excitons, widening the light absorption region, enhancing the substrate adsorption, and preventing photocorrosion conductive polymers can significantly increase the photocatalytic activity under visible light. The addition of conducting polymers with an inorganic materials dramatically change their band positions and may reduce the possiblilty of electron hole recombination. Here, we explain by what means conductive polymeric material can improve the efficiency of the composite in an organized manner, thereby providing a comprehensive reference to the field. Finally, the current challenges and future perspectives of polymeric catalysts have been discussed briefly.

Fe/Mt./TiO2 with Fe-III cation doped on montmorillonite (Mt) and, Mt./Fe-TiO2 with Fe-III cation doped on TiO2 were synthesized at three temperatures. Compared with the influence from the position of Fe-III, the synthesis temperature had moderate interference on the TiO2 formation as was implied by X-ray fluorescence (XRF) and X-ray diffraction (XRD). Characterizations of diffuse reflectance UV-vis spectroscopy (DRS), photoluminescence spectroscopy (PL), photocurrent, and electrochemical impedance spectroscopy (EIS) indicated the more excellent photocatalytic property of Fe/Mt./TiO2 composite than Mt./Fe-TiO2 composite. The energy-resolved distribution of electron traps (ERDT) pattern revealed a distinguished phase composing from the surface to the bulk for both Fe/Mt./TiO2 and Mt./Fe-TiO2 and demonstrated almost the same photocatalytic property of the TiO2 particle surface on both Fe/Mt./TiO2 and Mt./Fe-TiO2. The photocatalytic activities test for phenol decomposition on Fe/Mt./TiO2 was better than Mt./Fe-TiO2 which is consistent with the DRS, PL, photocurrent, and EIS results. A heterojunction between the Mt. and TiO2 in Fe/Mt./TiO2 was proposed to explain the inconsistency of the photocatalytic property and photocatalytic performance for the two composites and the consistency of the photocatalytic property for the surface of TiO2 particles on the composites. To increase the photocatalytic activity of Fe/Mt./TiO2, the electron at the Fermi level on Fe-III-doped Mt. may be coupled with the hole on the valance band of TiO2, resulting in effective separation of electron and hole and reduction and/or avoidance of recombination.

Pharmaceutical organics are a vital milestone in contemporary human research since they treat various diseases and improve the quality of human life. However, these organic compounds are considered one of the major environmental hazards after the conception, along with the massive rise in antimicrobial resistance (AMR) in an ecosystem. There are various biological and catalytic technologies existed to eliminate these organics in aqueous system with their limitation. Advanced Oxidation processes (AOPs) are used to decompose these pharmaceutical organic compounds in the wastewater by generating reactive species with high oxidation potential. This review focused various photocatalysts, and photocatalytic oxidation processes, especially core-shell materials for photo (electro)catalytic application in pharmaceutical wastewater decomposition. Moreover, we discussed in details about the design and recent developments of core shell catalysts and comparison for photocatalytic, electrocatalytic and photo electrocatalytic applications in pharmaceutical wastewater treatment. In addition, the mixture of inorganic and organic core-shell materials, and metal-organic framework-based core-shell catalysts discussed in detail for antibiotic degradation.

CuZn hydroxy double salts (CuZn-HDS) are often used as adsorbent and Fenton-like catalysts. In this work, we report the photocatalytic activity of CuZn-HDS for Cr(VI) reduction. In detail, CuZn-HDS with different Cu/Zn ratios were prepared as photocatalysts through the metal oxide-assisted hydrothermal method. The CuZn-HDS samples were characterized and applied for photocatalytic reduction of Cr(VI), which is a toxic inorganic pollutant in the wastewater. The CuZn-HDS which has the Cu/Zn ratio of about 4 (CuZn-HDS-4) showed the heist photocatalytic Cr(VI) reduction activity more than other samples, especially for copper hydroxy salts (Cu-HS) which have no Zn in the structure. Thus, the Zn-bearing in CuZn hydroxy double can improve the photocatalytic activity for Cr(VI) reduction compared with Cu-HS. The increase in the Cr(VI) reduction activity of the optimized CuZn-HDS-4 was attributed to the excellent separation and transportation of photogenerated electron-holes pairs, as proven by the photoluminescence, photocurrent density, and electrochemical impedance spectroscopy results. Moreover, the atomic structure of the synthesized CuZn-HDS was elucidated by an extended X-ray absorption fine structure technique, which is the first time to report the CuZn-HDS structure. Based on the optical properties, and activity test, a photocatalytic reduction of Cr(VI) over a CuZn-HDS was proposed. Thus, the CuZnHDS can be employed as a potential photocatalyst for the detoxification of Cr(VI) in wastewater.

Over the last few years, photocatalysis using solar radiation has been explored extensively to investigate the possibilities of producing fuels. The production and systematic usage of solar fuels can reduce the use of fossil-based fuels, which are currently the primary source for the energy. It is time for us to exploit renewable sources for our energy needs to progress towards a low-carbon society. This can be achieved by utilizing green hydrogen as the future energy source. Solar light-assisted hydrogen evolution through photocatalytic water splitting is one of the most advanced approaches, but it is a non-spontaneous chemical process and restricted by a kinetically demanding oxidation evolution reaction. Sunlight is one of the essential sources for the photoreforming (PR) of biomass waste into solar fuels, or/and lucrative fine chemicals. Hydrogen production through photoreforming of biomass can be considered energy neutral as it requires only low energy to overcome the activation barrier and an alternate method for the water splitting reaction. Towards the perspective of sustainability and zero emission norms, hydrogen production from biomass-derived feedstocks is an affordable and efficient process. Widely used photocatalyst materials, such as metal oxides, sulphides and polymeric semiconductors, still possess challenges in terms of their performance and stability. Recently, a new class of materials has emerged as organic-inorganic hybrid (OIH) photocatalysts, which have the benefits of both components, with peculiar properties and outstanding energy conversion capability. This work examines the most recent progress in the photoreforming of biomass and its derivatives using OIHs as excellent catalysts for hydrogen evolution. The fundamental aspects of the PR mechanism and different methods of hydrogen production from biomass are discussed. Additionally, an interaction between both composite materials at the atomic level has been discussed in detail in the recent literature. Finally, the opportunities and future perspective for the synthesis and development of OIH catalysts are discussed briefly with regards to biomass photo-reforming.

Photocatalytic treatment is a remarkable process that is popular for the degradation of several organic contaminants in wastewater. In this work, a series of graphitic carbon nitride/ZnTi-mixed metal oxide (CN/ ZnTi-MMO) composites were prepared as photocatalysts through simple calcination. The CN-MMO samples were characterized and applied for photocatalytic degradation of ciprofloxacin (CIP), which is an antibiotic model pollutant. The optimized CN/ZnTi-MMO composite showed complete degradation of CIP within 20 min, leading to a rate constant that is approximately 6 times that of pristine CN and 7 times that of ZnTiMMO. The increase in the degradation rate of the optimized CN/ZnTi-MMO composite was attributed to the excellent separation and transportation of photogenerated electron-holes pairs, as proven by the photoluminescence, photocurrent density, and electrochemical impedance spectroscopy results. Moreover, the energy-resolved distribution of the electron trap (ERDT) pattern of the composite sample suggests the formation of an interfacial electron trap state due to interfacial contraction in the composite, resulting in the excited electrons being trapped and avoiding charge recombination. Based on the optical properties, ERDT results, and activity test, a photocatalytic degradation mechanism of CIP over a CN/ZnTi-MMO composite was proposed. Additionally, the degraded solution showed less bio-toxicity than the original CIP solution. Thus, the CN/ZnTi-MMO composite can be employed as a potential visible-light-driven photo catalyst for the detoxification of pharmaceutical wastewater.(c) 2022 Elsevier B.V. All rights reserved.

Visible active photocatalysts have attracted interest as a potentially efficient and sustainable approach for pollutant degradation treatment. In this work, ZnCr mixed metal oxide/fly ash (ZnCr-MMO/FA) compos-ites were prepared using fly ash (FA) from China coal mining power plants to improve photocatalytic per-formance. The formation of the ZnCr-MMO/FA composites was proved by XRD results which showed the two-phases combination of FA and MMO. Also, the presence of FA in the ZnCr-MMO/FA composite pro-vided a good arrangement of small particles of ZnCr-MMO on the surface of FA and higher light absorp-tion ability with a lower energy bandgap compared with the pure ZnCr-MMO. The photocatalytic performance of the prepared ZnCr-MMO and ZnCr-MMO/FA composites in different FA contents was evaluated by degradation of ciprofloxacin (CIP), which is an antibiotic and often found in pharmaceutical wastes, under visible light irradiation. Clearly, the ZnCr-MMO/FA composites showed higher photocat-alytic decomposition of CIP than pristine ZnCr-MMO, and the highest degradation performance for CIP was obtained from the ZnCr-MMO/FA sample with 0.5 mg FA, which has a reaction rate constant approx-imately four times greater than that of pure ZnCr-MMO. The improved CIP degradation activity of the ZnCr-MMO/FA composite might not only be due to the good arrangement of ZnCr-MMO particles on the FA surface but also high separation and less recombination of photogenerated electrons-holes pairs, proven by the photoluminescence spectra, photocurrent density, and electrochemical impedance spec-troscopy results. The lower recombination of the charge carriers of the ZnCr-MMO/FA composite might be caused by the heterojunction between the ZnCr-MMO as a main photocatalyst and FA. Thus, the pro-posed ZnCr-MMO/FA composite can be used as an effective photocatalyst for wastewater treatment, including the decomposition of organic pollutants, such as discarded pharmaceuticals.(c) 2022 The Korean Society of Industrial and Engineering Chemistry. Published by Elsevier B.V. All rights reserved.

Metal Organic Frameworks (MOFs) with natural clay materials is a relatively new research avenue that appears to reduce high production costs and address the instability issues of pure MOFs. A novel MOF and natural clay composites of MOF@Sp_n (n = 1-4) were fabricated by the in situ precipitation of stable MOF, Zr6O4(OH)(4) (ABDC)(6) (where ABDC = 2-aminobenzene-1,4-dicarboxylic acid), over natural sepiolite (Sp) clay and used as a photocatalysts for elimination of organic dyes in aqueous media. The formation of MOF@Sp_n due to its strong electrostatic interactions between the positively charged MOF and the negatively charged sepiolite. Optimizing the Sp content in the composite strongly influenced the dispersibility, crystallinity of MOFs, resulting in progressively functional hybrid materials with an excellent optoelectronic properties. The composites lessened the shortcomings of the individual components and made them suitable as a visible light-active, highly efficient, standalone photocatalyst material that can degrade RhB.

Zn-Cr layered double oxide/fly ash (ZnCrLDO/FA) composites were synthesized using three different fly ashes (YEM, DAT, PAN) as photocatalysts for the degradation of ciprofloxacin through in situ coprecipitation followed by calcination. Ciprofloxacin (10 mg/L) was completely decomposed more than 98% within 120 min by ZnCrLDO/YEM composites in aqueous conditions, which indicates that the heterojunction between ZnCrLDO and YEM may help electrons move easily to enhance the separation of the electron-hole pairs. Based on the XPS results for the three fly ash samples, the largest Fe and Ti content was detected on the YEM, which suggests that TiO2, Fe2O3 on the surface of fly ash are responsible for the heterojunction. Furthermore, the ERDT pattern of ZnCrLDO/YEM confirmed the formation of new electronic levels that may avoid the recombination of electronhole pairs, which leads to the enhancement of photocatalytic performance. These results show that fly ash is essential as supporting material to avoid the agglomeration of ZnCrLDO particles and as an electron carrier for enhancing the mobility of photogenerated electrons in photocatalyst composites.

Cu-HyS-urea and Cu-HyS-NaOH, which are hydrotalcite-like copper hydroxyl salts, were prepared by two different methods, urea hydrolysis and precipitation, respectively. Both synthesis methods provided the successful formation of a copper hydroxyl salt, Cu2(OH)3NO3. From XRD and UV-DRS results, the product from the urea hydrolysis methods (Cu-HyS-urea) displayed higher crystallinity, small bandgap energy (Eg), and high light absorption ability because of some intercalated carbonate anions. For the Cr(VI) removal test, the Cu-HyS-NaOH showed superior adsorption of Cr(VI) than Cu-HyS-urea due to a higher specific surface area, confirmed by BET analysis. However, the Cu-HyS-urea presented higher photocatalytic Cr(VI) reduction under light irradiation than Cu-HyS-NaOH, owing to narrow Eg, less recombination, and a high transfer of the photogenerated charge carriers, proven by the results from photoluminescence, photocurrent density, and electrochemical impedance spectroscopy. Thus, this work provides a new function of the hydrotalcite-like copper hydroxyl salts (Cu-HyS-urea and Cu-HyS-NaOH) that can be utilized not only for adsorption of Cr(VI) but also as photocatalysts for Cr(VI) reduction under light irradiation.

An intense increase in non-biodegradable plastics and waste metals is an immediate threat to the world and needs to be addressed urgently.

Sodium metabisulfite (MBS) was used in this study for selective flotation of chalcopyrite and molybdenite. Microflotation tests of single and mixed minerals were performed to assess the floatability of chalcopyrite and molybdenite. The results of microflotation of single minerals showed that MBS treatment significantly depressed the floatability of chalcopyrite and slightly reduced the floatability of molybdenite. The results of microflotation of mixed minerals demonstrated that the MBS treatment could be used as a selective chalcopyrite depressant in the selective flotation of chalcopyrite and molybdenite. Furthermore, the addition of diesel oil or kerosene could significantly improve the separation efficiency of selective flotation of chalcopyrite and molybdenite using MBS treatment. A mechanism based on X-ray photoelectron spectroscopy analysis results is proposed in this study to explain the selective depressing effect of MBS on the flotation of chalcopyrite and molybdenite.

Pollutants degradation via visible-light driven photocatalysts have attracted interest as a potentially efficient and sustainable approach for wastewater treatment. In the present study, a series of oxygen-doped hollow porous surface graphitic carbon nitride (OCN) has been prepared by one-pot thermal polycondensation of melamine with different amounts of polyoxyethylene stearyl ether as the oxygen source and template. The prepared OCN samples were utilized for the photocatalytic ciprofloxacin (CIP) degradation, which is a pharmaceutical waste, under visible light irradiation. The highest degradation performance for CIP was obtained from the OCN sample with 1 mg polyoxyethylene stearyl, which was three times greater than that of pristine C3N4. The superior degradation performance of the OCN samples were observed due to the improved light absorption, less recombination rate of photogenerated electron and hole, and enhanced electron transportation, which was proven through the PL, photocurrent density, and EIS results. Thus, the proposed one-pot synthesis of OCN provides an effective method in producing potential photocatalysts for the removal of organic pollutants, such as discarded pharmaceuticals, in wastewater.

Metal-free photocatalysts are widely used to decontaminate aqueous solutions by eliminating toxic and nonbiodegradable compounds. It is desirable to develop a photocatalyst with high charge separation and migration efficiency. The addition of carbon quantum dots (CQDs) to graphitic carbon nitride with polyaniline (PANI) can improve its light absorption abilities and reduce the recombination of holes and electrons. In this study, a novel CQDs decorated on PANI with hollow porous graphitic carbon nitride (CN) was fabricated via an in situ polymerization followed by an ultra-sonication. The optimal CQDs-loaded CN-PANI nanocomposite exhibited the high visible light absorption with a high specific surface area. Furthermore, better photocatalytic degradation of ciprofloxacin (CIP) was achieved under the visible light. The improved photocatalytic activity of CN-PANICQDs (5.0%) can be attributed to its higher charge separation, and destruction of recombination rate through the heterojunction of excited electrons among CN, PANI, and CQDs. This effect was further confirmed by high photocurrent intensity, low photoluminescence emission, and electrical resistance. In addition, different parameters including catalyst weight, initial CIP concentration, and interfering effect of anions during CIP removal were investigated. The main active species in the degradation of CIP were identified to h+, center dot OH, and center dot O-2(-) through the scavenger test. The high reusability and stability of the photocatalyst composite were also verified. The degradation intermediates and reaction pathways were identified. Furthermore, the effectiveness of the photocatalyst was evaluated using different toxic pollutants including imidacloprid, tetracycline, phenol, and rhodamine B under similar conditions. The CQDs-decorated CN-PANI was proved as a promising material for efficient photodegradation of toxic pollutants in water.

Carbon nitride based photocatalysts are widely used to decontaminate aqueous solutions by eliminating toxic and non-biodegradable compounds. It is desirable to develop a photocatalyst with high charge separation and migration efficiency. In this study, synergistic ternary porous carbon nitride-polypyrrole-montmorillonite (CN-PPy-MMt) was successfully synthesized via an in situ oxidative polymerization method. The photocatalytic performance towards mineralization of metronidazole (MZ) under visible light was studied, where the CN-PPy-MMt (10%) nanocomposite exhibited the best performance compared to CN-PPy-MMt (5%, 15%, 20%), CN-PPy, pure CN and other nanocomposites reported. This superior photocatalytic mineralization performance was attributed to synergistic inter-constituent interactions within the CN-PPy-MMt nanocomposite, which effectively enhanced the light absorption capacity and charge transfer, and reduced the recombination of electron-hole pairs. The results were confirmed by UV-DRS, photocurrent, impedance, and photoluminescence measurements. The effect of interfering anions was examined and the results indicated that the MZ mineralization efficiency was significantly inhibited by the addition of HCO3- and PO43-. The reusability and stability of the photocatalyst were excellent even after five repeated photocatalytic reactions. Analysis of the radical scavenger properties indicated that superoxide radicals (O-2(-)) and holes (h(+)) played a major role in the mineralization of MZ. The intermediate products were confirmed using liquid chromatography-mass spectrometry, which provided an insight into the MZ mineralization mechanism. This work suggested that the design of a ternary nanocomposite based on CN with conducting polymers could be an effective strategy to improve the photocatalytic mineralization of antibiotics and energy related applications.

A surfactant-free, low temperature hydrothermal synthesis of Cu2O nanostructures is demonstrated for application to the photocatalytic degradation of trimethoprim (TMP), an environmental xenobiotic. Photophysical properties of different size and shape Cu2O nanostructures were determined by bulk and surface microscopic and spectroscopic analyses. Visible light photoactivity for the oxidative degradation of TMP is sensitive to the rate of photoexcited charge carrier bulk recombination, and therefore the size of Cu2O crystallites. Optimum photodegradation activity was observed for a hierarchical Cu2O nanostructure, comprising 11 nm crystallites nucleated as 50-80 nm particles, themselves coalesced into 400 nm compact agglomerates. The specific activity of 1.12 mu mol.g(-1). min(-1) for a 0.1 mM TMP aqueous solution is comparable to previous reports that required higher energy and/intensity UV irradiation. The stepwise hydroxylation and oxidative cleavage of TMP to form monocylic fragments is driven by hydroxyl radicals photogenerated over the hierarchical Cu2O nanostructure, which exhibits excellent catalytic stability for >25 h.

We report a simple strategy for providing a homogenous TiO2 nanofibre host environment to stabilize Cu2O nanoparticles with an average size of similar to 60 nm and high dispersibility. We found that the small fraction of Cu2O nanoparticles in direct contact/partially submerged with TiO2 nanofibre arrays (diameter similar to 300 nm and length similar to 650 nm) showed excellent synergistic photocatalytic performance for H-2 production rate of 48 mu mol g (-1) h(-1) with an apparent quantum efficiency of 3.6 %. The H-2 production rate was much higher (factor of similar to 6.5 times) compared with unmodified TiO2-NF. In addition, the synergistic Cu2O/TiO2-NF photocatalyst showed significant oxidative-degradation of sulfamethoxazole (7 x 10(-2) mmol g (-1) min(-1)) and was highly stable during five cycles. The small fraction of Cu2O nanoparticles are well dispersed and form heterojunction interfaces to promote charge transfer and provide active sites. This argument is verified by morphology characterisation, band alignment, energy-resolved distribution of electron traps, electrochemical transient photocurrent, and electrochemical impedance (EIS). In addition, a detailed discussion is provided regarding the surface and bulk elemental composition determined by X-ray photoelectron spectroscopy (XPS), X-ray fluorescence (XRF), and X-ray absorption near edge structure (XANES).

The effect of Si/Al molar ratio of geopolymer on the immobilization of Se and As oxyanions was studied through leaching test and solid characterizations including XRD, FTIR, TG, NMR, XAFS, and N adsorption-desorption isotherm. As a whole, the leaching percentages of Se and As oxyanions increased with the increase of the Si/Al molar ratio of geopolymer. Linear combination fitting confirmed that most of selenite, selenate and arsenate ions existed in geopolymers through electrostatic interaction. Thus, Al tetrahedrons in geopolymer structure control the charge stability for these oxyanions to a large extent. Differently, as for arsenate ions, they were recrystallized into an arsenate compound (Na (OH) (H O) )(AsO ) in geopolymers. The additive of these pollutants has an adverse effect on the compactness of geopolymer, then influencing the leaching performance in turn. However, the changes in leaching results did not follow the variation trend of specific surface areas and pore volumes of geopolymers with different Si/Al ratios. The number and distribution of Al tetrahedron and compactness of geopolymer have a synergistic effect on the immobilization of these oxyanions. Besides, the compressive strengths of geopolymer samples are always higher than 20 MPa, which meets the requirement of safe disposal of hazardous waste. 2 3.25 0.25 2 12 4

Zn-Ti layered double hydroxide/montmorillonite (ZTL/MT) and Fe-doped ZTL/MT (ZTL/Fe@MT20%) were prepared as photocatalyst for Cr(VI) reduction. The ZTL/Fe@MT20% exhibited the highest photocatalytic activity, suggesting that a combination of ZTL and Fe-bearing MT could enhance photocatalytic activity by suppressing the recombination of photogenerated electron-hole pairs. On the basis of electronic-structure calculations, a photocatalytic mechanism for Cr(VI) reduction and the effect of Fe3+ on the structure of MT in ZTL/MT composites is proposed by density functional theory approach, whereby Fe impurities in MT generate a new mid-gap state that induce a Z-scheme heterojunction with ZTL, leading to reduced recombination of the photogenerated charge carriers in ZTL. These results establish that MT can not only act as a support material but also play an important role for photocatalytic reaction when Fe impurities are present in its structure.

The elevated level of selenium (Se) in the aqueous system presents long-term ecological risks. Hydroxylated calcined dolomites (HCDs) are considered as potentially sustainable lime sources due to their lower production temperatures and resourceful than lime. In this study, HCDs were developed for the removal of Se contaminated water. The HCDs exhibited a better performance to co-precipitate with Se oxyanions than pure Ca(OH) . Considering that HCDs consisted of Ca(OH) with MgO and Mg(OH) , the function of Mg compounds was also elaborated by various characterization techniques. Mg compounds were proved to enhance the precipitation process and Se removal. STEM-EDX observation revealed that SeO was incorporated into the ettringite structure with Mg compounds, whereas SeO exhibited a affinity to Mg compounds. Extended X-ray absorption fine structure (EXAFS) results for the MgO/Mg(OH) after the reaction proved that both SeO interacted with Mg(OH) and MgO via inner-sphere complexes whereas SeO formed outer-sphere complexes with these Mg compounds. Besides, Mg compounds also influenced the surface charge of solid residues and thus enhanced SeO removal. This study provides a fundamental understanding of the roles of Mg compounds in the removal of Se oxyanions during environmental remediation. Besides, the HCDs were proved to be sustainable Ca sources for waste/wastewater remediation. 2 2 2 3 4 2 3 2 4 3 2– 2– 2– 2– 2–

Electroplating sludge is classified as a hazardous waste due to its extremely high leachability of potentially toxic elements. This study concerns the use of magnesium oxysulfate cement (MOSC) for the stabilisation/solidification (S/S) of Zn-rich electroplating sludge. According to X-ray diffraction and thermogravimetric analyses, Zn was mainly immobilised through both chemical interaction and physical encapsulation in the MOSC hydrates of 5Mg(OH) ·MgSO .7H O (5−1−7) phase. The crystal size analysis, elemental mapping, and extended X-ray absorption fine structure (EXAFS) analysis proved that the Zn was also incorporated in the structure of 5–1–7 phase. Unlike Portland cement system, hydration kinetics, setting time, and compressive strength of the MOSC system were only negligibly modified by the presence of Zn, indicating its superior compatibility. Subsequent S/S experiments demonstrated that the MOSC binder exhibited an excellent performance on immobilisation efficiency of Zn (up to 99.9%), as well as satisfying the requirements of setting time and mechanical strength of sludge S/S products. Therefore, MOSC could be an effective and sustainable binder for the treatment of the Zn-rich industrial wastes. 2 4 2 2+

The development of high-quality photocatalytic materials for the degradation of organic pollutants under visible light irradiation is a vital field of research. In the present study, a composite of natural sepiolite clay and synthetic graphitic carbon nitride (CN) mixed with dispersed palladium nanoparticles was developed for the efficient photocatalytic degradation of ciprofloxacin (CIP) under visible light irradiation. The sepiolite, CN, and composite materials were characterized by several techniques. The sepiolite/CN composite (SC30%) displayed superior activity than pristine sepiolite and CN, resulted from the generation of new electron trap states in the interfacial contract between sepiolite and CN to suppress the charge recombination of CN. Furthermore, the well-dispersed of 1 wt% Pd-nanoparticles in the SC30% composite collectively enhanced CIP degradation by avoiding the recombination of photogenerated electrons and holes. Additionally, the electron trap states on the surface of all samples were studied using novel reversed double-beam photoacoustic spectroscopy to understand electron transfer in the composites related to the photocatalytic degradation mechanism of CIP. The developed sepiolite/CN/Pd(0) composite can act as a potential catalyst for the degradation of organic pollutants in wastewater under visible light irradiation. (C) 2020 Elsevier Inc. All rights reserved.

The catalytic mechanism of activated carbon-assisted bioleaching of enargite concentrate (enargite 37.4%; pyrite 47.3%) was investigated by employing microbiological, electrochemical and kinetic studies. By using moderately thermophilic microorganisms at 45 degrees C, the final Cu dissolution was improved from 36% to 53% at 0.2% (w/v) activated carbon. An excess activated carbon addition showed an adverse effect. The enargite mineral itself favored higher solution redox potential (E-h) for solubilization. However, the dissolution of co-existing pyrite, which also favors high E-h, immediately hindered enargite dissolution through the passivation effect. The surface of activated carbon functioned as an electron mediator to couple RISCs oxidation and Fe3+ reduction, so that elevation of the E-h level was controlled by offsetting microbial Fe3+ regeneration. As long as the E-h level was suppressed at < 700 mV, the dissolution of pyrite was largely avoided, enabling a steady and continuous dissolution of the enargite mineral through the surface chemical reaction model. When the E-h-control by activated carbon becomes no longer sustainable and the E-h hits 700 mV, rapid pyrite dissolution was initiated and the surface chemical reaction of enargite dissolution came to an end. Arsenic species dissolved from enargite was constantly immobilized with an efficiency of 75-90% as amorphous ferric arsenate. However, the sudden initiation of pyrite dissolution also triggered the re-solubilization of ferric arsenate. Therefore, the sustainable E-h-controlling effect was shown to be critical to enable longer Cu dissolution from enargite as well as stabilization of As precipitates.

© 2020 Elsevier Inc. Graphene oxides (GO) and layered double hydroxides (LDHs) were applied to produce alginate beads for the remove of 90Sr2+ and 79SeO42−. The Freundlich isotherm indicated that the Sr2+ sorptions were based on the energetically heterogeneous multilayer surfaces. In contrast, the sorption behavior of SeO42− fitted to the Langmuir adsorption isotherm models, indicating that the removal of SeO42− was caused by the ion-exchange of LDHs. The synthesized LDH/GO alginates beads were also applied for setting up small-bore adsorption columns with loading synthetic SeO42− and Sr2+ contaminated wastewater. Based on the water chemistry, the adsorbed amount of Sr2+ significantly increased after using alginates beads, which was attributed to the functional groups of either GO or alginic acid. The incorporated SeO42− was highly depended on the contents of fabricated LDHs in alginate beads. Specifically, the adsorption capacity of Sr2+ (0.85–0.91 mmol/g) on GO slightly increased after alginates fabrication. Therefore, it was deduced that this layered material was partially exfoliated during the manufacture and thus increased the sorption sites. Applications of LDH/GO alginates beads in the removal of both Sr2+ and SeO42− in water and soil treatment have a significant impact on the environmental remediation.

© 2019 Elsevier B.V. Low-level radioactive wastes are commonly immobilized in cementitious materials, where cement-based material can incorporate radionuclides into their crystal structure. Specifically, ettringite (Ca6Al2(OH)12(SO4)3∙26H2O) is known to stabilize anionic species, which is appealing for waste streams with radioactive iodine (129I) that persists as iodide (I–) and iodate (IO3–) in the cementitious nuclear waste repository. However, the structural information and immobilization mechanisms of iodine species in ettringite remain unclear. The present results suggested minimal I– incorporation into ettringite (0.05 %), whereas IO3– exhibited a high affinity for ettringite via anion substitution for SO42– (96 %). The combined iodine K-edge extended X-ray absorption fine structure (EXAFS) spectra and first-principles calculations using density functional theory (DFT) suggested that IO3– was stabilized in ettringite by hydrogen bonding and electrostatic forces. Substituting IO3– for SO42– was energetically favorable by –0.41 eV, whereas unfavorable substitution energy of 4.21 eV was observed for I– substitution. Moreover, the bonding charge density analysis of the substituted IO3– and I– anions into the ettringite structure revealed the interaction between intercalated ions with the structural water molecules. These results provided valuable insight into the long-term stabilization of anionic iodine species and their migration in cementitious nuclear waste repository or alkaline environments.

© 2019 Elsevier B.V. Geopolymers have been widely adopted to stabilize the cationic pollutants. However, few studies have focused on the immobilization of anionic species. In this study, the immobilization of SeO32– and SeO42– was explored for the first time using geopolymer activated by different alkaline solutions (NaOH and Na2SiO3) with and without calcined hydrotalcite (CHT), characterized by TCLP, XRD, FTIR, TG, NMR, XAFS, and N2 adsorption-desorption isotherm. Na2SiO3-activated geopolymers without CHT additive showed lower leaching percentages of SeO32– and SeO42– (approximately 10 % and 18 %) than NaOH-activated geopolymers (approximately 58 % and 74 %). It has been proven that electrostatic interaction is the main association mode of SeO32– and SeO42– in both NaOH- and Na2SiO3-activated geopolymers. Hence, compactness plays a vital role in the Se leaching from geopolymer. The addition of CHT reduced the compactnesses of both NaOH- and Na2SiO3-geopolymers. Due to the formation of hydrotalcite, the CHT additive contributed to immobilize SeO32– and SeO42– in NaOH-activated geopolymers. However, this phenomenon was not observed in Na2SiO3-activated geopolymers. Thus, the leaching amount of Se greatly increased from Na2SiO3-activated geopolymers with CHT additive. This study provides new insights on the application of geopolymer to immobilize anionic pollutants.

Perchlorate (ClO4-) and pertechnetate (TcO4-) exhibit similar adsorption characteristics on alkyl quaternary ammonium-modified montmorillonite (Mt), and (TcO4-)-Tc-99m normally coexists with Sr-90(2+) in radionuclide-contaminated water. In this study, hexadecyl pyridinium (HDPy)-modified Mt (OMt) was encapsulated in alginate beads to inhibit HDPy release and simultaneously immobilize ClO4- and Sr2+ ions. The release of HDPy was remarkably reduced (78 times) from OMt after alginate encapsulation. Adsorption of ClO4- and Sr2+ on the obtained composite demonstrated synergistic effects, with adsorption capacities reaching 0.542 and 0.484 mmol/g, respectively. Compared to the single-adsorbate system, adsorption capacities of ClO4- and Sr2+ increased significantly. The characterization of solids using X-ray diffraction, Fourier transform infrared spectroscopy, C-13 nuclear magnetic resonance, and X-ray photoelectron spectroscopy, as well as the chemical analysis of the aqueous solution, demonstrated that HDPy+-COO- disintegration accounted for the adsorption synergy. HDPy was extracted from the Mt interlayer space during the synthesis of OMt/alginate and then partially re-intercalated back after interacting with ClO4- during the adsorption of ClO4- and/or Sr2+. In the binary-adsorbate system, the synergy-induced adsorption capacity was superior to many previously reported adsorbents, implying that OMt/alginate beads can be a promising adsorbent for the remediation of aqueous solutions contaminated with multiple radionuclides. (C) 2019 Elsevier Inc. All rights reserved.

We report for the first time to our knowledge the identification of heteroatom-doped and undoped C3N4 with the energy-resolved distribution of electron traps (ERDT) near the conduction band bottom position (CBB) using reversed double-beam photoacoustic spectroscopy. The ERDT/CBB pattern is used to classify the type of elemental doping in C3N4, related to photocatalytic efficiency.

In this study, ZnTi-mixed metal oxides (ZTM), such as ZnTiO3, were synthesized from ZnTi layered double hydroxides by varying the molar ratio of Zn/Ti, calcination temperatures, and synthesis methods (hydrothermal or reflux). The surface electronic characteristics of ZTM were investigated by the energy-resolved distribution of electron traps (ERDTs) using reversed double-beam photoacoustic spectroscopy. The ZTM samples obtained by conducting hydrothermal synthesis at 500 degrees C showed similar ERDT patterns independent of the molar ratio of Zn/Ti, although ZnTiO3 phase was not observed in the X-ray diffraction pattern, when the Zn/Ti ratio was high. When the ERDT patterns demonstrated a high electron accumulation level near the conduction band bottom in hydrothermal products at 500 degrees C, a higher photocatalytic phenol degradation efficiency was observed due to the formation of ZnTiO3 phase. This suggested that the product with the high Zn/Ti molar ratio (Zn/Ti = 6) constituted amorphous ZnTiO3.The enhanced photocatalytic performance of ZTM could be attributed to the heterojunction of electrons among ZnO, TiO2, and ZnTiO3, which enabled electron transfer in the composites, prevented charge recombination, and promoted a wider visible light adsorption by ZnTiO3 phase irrespective of its crystallinity.

Hierarchical Cu2O nanospheres with a Pompon Dahlia-like morphology were prepared by a one-pot synthesis employing electrostatic self-assembly. Nanocomposite analogues were also prepared in the presence of reduced graphene oxide (rGO). Photophysical properties of the hierarchical Cu2O nanospheres and Cu2O/rGO nanocomposite were determined, and their photocatalytic applications evaluated for photocatalytic 4-chlorophenol (4-CP) degradation and H-2 production. Introduction of trace (<1 wt %) rGO improves the apparent quantum efficiency (AQE) at 475 nm of hierarchical Cu2O for H-2 production from 2.23 % to 3.35 %, giving an increase of evolution rate from 234 mu mol.g(-1).h(-1) to 352 mu mol.g(-1).h(-1) respectively. The AQE for 4-CP degradation also increases from 52 % to 59 %, with the removal efficiency reaching 95 % of 10 ppm 4-CP within 1 h. Superior performance of the hierarchical Cu2O/rGO nanocomposite is attributable to increased visible light absorption, reflected in a greater photocurrent density. Excellent catalyst photostability for >6 h continuous reaction is observed.

Solar photocatalytic processes are a promising approach to environmental remediation, however their implementation requires improvements in visible light harvesting and conversion and a focus on low cost, Earth abundant materials. Semiconducting copper oxides are promising visible light photocatalysts for solar fuels and wastewater depollution. Here we report the mild, hydrothermal (template-free) synthesis of core-shell Cu2O(Cu)@CuO photocatalytic architectures for the visible light photocatalytic degradation of N-acetyl-para-aminophenol (APAP). Hollow and rattle-like core-shell nanosphere aggregates with diameters between 200 nm and 2.5 mm formed under different synthesis conditions; all comprised an inner Cu2O shell, formed of 10-50 nm nanoparticles, surrounded by a protective corona of CuO nanoparticles. High reductant and structure-directing agent concentrations promoted the formation of a yolk-like Cu2O/Cu core, associated with improved photophysical properties, notably a high oxidation potential and suppressed charge carrier recombination, that correlated with the highest apparent quantum efficiency (8%) and rate of APAP removal (7 mmol g(-1) min(-1)). Trapping experiments demonstrated hydroxyl radicals were the primary active species responsible for APAP oxidation to quinones and short chain carboxylic acids. Rattle-like core-shell Cu2O/Cu@CuO nanospheres exhibited excellent physiochemical stability and recyclability for APAP photocatalytic degradation.

The thermo-acidophilic archaeon, Sulfolobus tokodaii, was utilized for the production of Pd(0) bionanoparticles from acidic Pd(II) solution. Use of active cells was essential to form well-dispersed Pd(0) nanoparticles located on the cell surface. The particle size could be manipulated by modifying the concentration of formate (as electron donor; e-donor) and by addition of enzymatic inhibitor (Cu2+) in the range of 14-63 nm mean size. Since robust Pd(II) reduction progressed in pre-grown S. tokodaii cells even in the presence of up to 500 mM Cl-, it was possible to conversely utilize the effect of Cl- to produce even finer and denser particles in the range of 8.7-15 nm mean size. This effect likely resulted from the increasing stability of anionic Pd(II)-chloride complex at elevated Cl- concentrations, eventually allowing involvement of greater number of initial Pd(0) crystal nucleation sites (enzymatic sites). The catalytic activity [evaluated based on Cr(VI) reduction reaction] of Pd(0) bionanoparticles of varying particle size formed under different conditions were compared. The finest Pd(0) bionanoparticles obtained at 50 mM Cl- (mean 8.7 nm; median 5.6 nm) exhibited the greatest specific Cr(VI) reduction rate, with four times higher catalytic activity compared to commercial Pd/C. The potential applicability of S. tokodaii cells in the recovery of highly catalytic Pd(0) nanoparticles from actual acidic chloride leachate was, thus, suggested.

Harmful trace elements, which are initially included in the coal fly ash, have the potential to be leached when coal fly ash comes in contact with water. This causes a risk of pollutant species being released, considering the long lifetime of building structures where coal fly ash was applied. Some Ca additives effectively function to suppress the release of anionic pollutants; however, the detailed suppression processes remains unclear. In this work, the influences of various Ca additives on the released anionic pollutants (B, F, S, As, and Cr) was systematically investigated. According to the comprehensive results of solution data with the solid characterization, the 60% hydroxylated calcined dolomite (HCD 60) was the best Ca additive for the suppression of different anionic pollutants since this Ca source not only simply provides an alkaline reagent but also supplies MgO and Mg(OH)(2), which affect the phase transformation that accompanies with hydration. The phase transformation occurs from Ca(OH)(2) to ettringite via hydrocalumite, which is the most important suppression processes of released pollutants. The precipitation of Ca salts is another pathway to immobilize these pollutants. In this scheme, MgO and Mg(OH)(2) were proven to enhance the formation of ettringite and hydrocalumite, respectively.

Fly ash always contains many toxic elements which can be released into environment, thereby easily leading to environmental contaminations. In order to dispose fly ash safely, related strategies are needed. In this investigation, two kinds of hydroxylated calcined dolomites (HCD60 and HCD100) were used as the additives and compared with lime on the leachabilities of anionic species from fly ash. Both additives were found effective in reducing the leaching concentrations of these elements, which was better than that of only lime addition. Mg(OH)(2) and MgO were believed to play important roles in the hydration reaction of fly ash. In the presence of Mg(OH)(2) and MgO, there were more hydration products including calcium silicate hydrate, ettringite, hydrocalumite and other Layered double hydroxides (LDHs) generated which were effective candidates for anion removal. Thus, the final leaching results were controlled by these newly formed phases through adsorption, incorporation or encapsulation. On the other hand, compared with Mg(OH)(2), MgO can promote the formation of hydration products in a larger extent because of the hydration process of MgO into Mg(OH)(2). There was no systematic trend in the promotion of fly ash hydration by Mg(OH)(2) or MgO because it had a close relationship with the properties of original fly ash. Objectively, hydroxylated calcined dolomites can be promising candidate additives for reduction of toxic elements leaching from fly ash. (C) 2019 Elsevier Ltd. All rights reserved.

Selective flotation of chalcopyrite and molybdenite is continuing problem since its selectivity is not perfect and current NaHS process needs closed system flotation plant because of hydrogen sulfide emission on acidic condition. Some alternative additives investigated as chalcopyrite became hydrophilic and molybdenite kept hydrophobic. XPS analysis indicated chalcopyrite became hydrophilic since iron and copper sulphate, hydroxide was covered on the surface whereas molybdenite kept hydrophobic since only molybdenite can be seen. Flotation experiments of chalcopyrite and molybdenite mixture sample indicated excellent separation that 95% of molybdenite can be recovered as froth and 93% of chalcopyrite can be recovered as sink. Flotation experiments with real bulk flotation concentration indicated similar separation result compared with current NaHS additive system. Possible mechanisms and detailed phenomenon were investigated based on the surface analysis and thermodynamic calculation etc. this alternative additive is easy to handle compared with NaHS since it does not emit effluent gas and commercially preferable.

Hydrogen peroxide (H 2 O 2 ) is frequently used as an oxidizing agent in various applications. It has also been reported to reduce the recovery of sulfide minerals. Moreover, the previous work applied H 2 O 2 aqueous solution in selective flotation of chalcopyrite and molybdenite. However, the oxidation method suffered in pilot scale test due to too long conditioning time. Furthermore, the excessive reagent consumption increased the reagent cost, causing the method not economically feasible. Consequently, further improvement is required to reduce the conditioning time and the reagent consumption. The oxidation performance of H 2 O 2 can be improved by using ferrous iron as catalyst, producing a Fenton's reagent which is more powerful oxidizer than the H 2 O 2 itself. Therefore, the effect of Fenton's reagent on the floatability of chalcopyrite and molybdenite was investigated in this study. The flotation test results show that selective flotation of chalcopyrite and molybdenite might be possible at low concentration of H 2 O 2 aqueous solution by adding ferrous iron. Moreover, the conditioning time could be shortened by this improvement. To understand the phenomenon, surface characterization using atomic force microscopy (AFM) along with x-ray photoelectron spectroscopy (XPS) analysis were carried out. The AFM images show that the surface of chalcopyrite was readily covered with mountainous features which alters its hydrophobicity after the oxidation treatment. Meanwhile, the molybdenite surface remained clean and relatively hydrophobic. The XPS results indicate that the mountainous features are various oxidation products (i.e., FeOOH, Fe 2 (SO 4 ) 3 , CuO, Cu(OH) 2 ). Possible mechanisms of this phenomenon were proposed in this work.

Fly ash usually contains a considerable amount of toxic elements that can be leached into the environment, thereby easily leading to serious contaminations. In this work, the leaching behaviors of poisonous elements including boron (B), phosphoms (P), vanadium (V), chromium (Cr) arsenic (As), selenium (Se), inolybdenum (Mo), antimony (Sb), and tungsten (W) from fly ash were explored by sequential' extraction. Importantly, the associations of these elements in fly ash were discussed based on their leaching and X-ray absorption near-edge structure (XANES) results. From the XANES results it was observed that V(IV), Cr(III) As(V), Se(IV), and W(IV) were their main states of existence in fly ash. In terms of leaching results, large amounts of Mo and W were leached into pure water, which indicated their high mobilities. Furthermore, the occurrence of Mo in fly ash was mainly in the form of oxides, and W had complex associations including WX4 (X can be monovalent anions), its reduction state or association with the elements that can be oxidized, and existence in silicates. B was as easily released into the environment as Mo and W. It can have several associations with the other cations, such as Ca2+, Na+, and Mg2+, and occurs in silicates. In contrast, most of the Cr and Sb were locked in silicates, indicating that they were very stable in fly ash. In addition, P, V, and As can exist within the structure of silicates as well. However, a considerable amount of them leached in the reduction step with a low pH. Hence, they can be associated with Ca2+, Na+, Mg2+, or Fe3+. In terms of Se, oxidation processes played an important role in controlling its leaching because of the oxidation of Se(IV) to Se (VI). Calcium selenite should be the predominant form of Se in fly ash.

© 2018, © 2018 Informa UK Limited, trading as Taylor & Francis Group. The effect of controlling the redox potential (Eh) on chalcopyrite bioleaching kinetics was studied as a new aspect of redox control during chalcopyrite bioleaching, and its mechanism was investigated by employing the “normalized” solution redox potential (Enormal) and the reaction kinetics model. Different Eh ranges were established by use of different acidophiles (Sulfobacillus acidophilus YTF1; Sulfobacillus sibiricus N1; Acidimicrobium ferrooxidans ICP; Acidiplasma sp. Fv-AP). Cu dissolution was very susceptible to real-time change in Eh during the reaction. It was found that efficiency of bioleaching of chalcopyrite can be effectively evaluated on the basis of Enormal, since it is normalized for real-time fluctuations of concentrations of major metal solutes during bioleaching. For steady Cu solubilization during bioleaching at a maximum rate, it was important to maintain a redox potential range of 0 ≤ Enormal ≤ 1 (−0.35 mV optimal) at the mineral surface by employing a “weak” ion-oxidizer. This led to a copper recovery of > 75%. At higher Enormal levels (Enormal > 1 by “strong” microbial Fe2+ oxidation), Cu solubilization was slowed by diffusion through the product film at the mineral surface (< 50% Cu recovery) caused by low reactivity of the chalcopyrite and by secondary passivation of the chalcopyrite surface, mainly by jarosite.

The treatment of the geothermal water discharged through mining activity is a critical issue because the rate of discharge is 12,000 m(3) per day and the discharge contains high concentrations of borate (>20 mg/ L) and arsenate (ca.0.4 mg/L) as well as silicate and carbonate. The simultaneous reduction of borate and arsenate concentrations to acceptable levels was successfully performed by co-precipitation with hydroxyapatite (HAp). Although the coexisting high concentrations of carbonate act as a disturbing element, the co-precipitation equilibrium of borate was shifted to lower values by adjusting the P/Ca molar ratio, and the removal rate of borate was accelerated by using A(13+)additives, resulting in the efficient reduction of borate within 1 h. The initially immobilized boron in HAp is in the tetragonal form, which probably occupies the hydroxyl sites in HAp, gradually transforming into the trigonal form in the solid state, as interpreted by H-1 NMR and B-11-NMR. The coexisting silicate was also immobilized in an ellestadite form, as confirmed by Si-29-NMR measurements. Arsenate and silicate were immobilized before borate in geothermal water. A dissolution assay of borate in the solid residues after co-precipitation with HAp verified the acceptable stability of borate, which is independent of the amount of added A1(3+). (C) 2018 Elsevier Ltd. All rights reserved.

This study revealed the importance of SO42- ions during biogenic scorodite crystallization via a two-stage As removal process, using a combination of liquid and solid analyses (chemical digestion, FT-IR, SEM, TG-DTA, particle distribution). The first-stage As-removal was induced by microbial oxidation of Fe2+ and As(III), precipitating SO42- bearing amorphous precursors composed of basic ferric sulfate (MFex(SO4)(y)(OH)(z)) and ferric arsenate (FeAsO4 center dot(2 + n)H2O). This was followed by an induction period (a period of constant concentration), where dissolution-recrystallization of unstable amorphous precursors proceeded: Re-dissolved metal ions became locally concentrated on the surface of precursors, which gave the driving force for the second-stage As removal as secondary layers of crystalline biogenic scorodite (Fe(AsO4)(0.94)(SO4)(0.08)center dot 1.69H(2)O) out of even more dilute and seeded solution. This phase transformation process was also accompanied by continuous dehydration. This two-stage As-removal via SO42- mediated phase transformation was shown to be key to promote biogenic scorodite formation with greater final As-removal from dilute As(III)-bearing solutions.

Hydrogen peroxide (H2O2) has been used as an oxidizing agent in the selective flotation of chalcopyrite and molybdenite. However, this method required relatively high concentration of H2O2 to deliver flotation results (i.e., mineral grades and recoveries) comparable to those obtained by the conventional copper-molybdenum (Cu-Mo) ores flotation using sodium hydrosulfide (NaHS). Therefore, further improvements are needed to reduce the consumption of H2O2 reagent. In this study, ferrous sulfate (FeSO4) was used to enhance the oxidation performance of H2O2 through Fenton-like reactions. Flotation results showed that the consumption of H2O2 reagent could be reduced by the addition of FeSO4 without losing the flotation selectivity. The reason might be caused by increasing of oxidation performance as indicated by the increasing concentration of dissolved oxygen after the addition of FeSO4 into the H2O2 aqueous solution. Surface analysis using X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM) images showed that the surface of chalcopyrite was covered by more hydrophilic precipitates after the oxidation treatment using H2O2 aqueous solution with the addition of FeSO4, thus more hydrophilic surface and lower floatability. On the other hand, the surface of molybdenite was slightly oxidized and its surface remained hydrophobic as confirmed from contact angle results. Flotation tests using Cu-Mo bulk concentrate demonstrated that selective flotation might be possible using a mixture of FeSO4 and H2O2 aqueous solution. Moreover, this new method could be used as an alternative to copper depressant in Cu-Mo selective flotation, replacing the NaHS reagent.

The structural memory effect of layered double hydroxides (LDHs) is one of the important reasons for their extensive use in environmental remediation. In this study, humic acid (HA) was extracted from black soil and sediments and characterized to determine their structures. The regeneration mechanisms of calcinated LDHs (CLDHs) including different divalent metals (Mg-CLDH and Zn-CLDH) in deionized water and different HA solutions were carefully elucidated, and the reasons for the behavior differences in the two materials were explained. The presence of the HAs significantly increased the dissolution rate of Mg2+ ions from Mg-CLDHs and subsequent regeneration of Mg-LDH. Because of the diverse functional groups in the HAs, these groups were complexed with metallic ions such as Mg2+ on the surface of Mg-CLDH in the beginning. During the process, the HAs adsorbed the regenerated LDHs on the surfaces. Therefore, the crystallinity, morphology, and specific surface area of the regenerated Mg-LDH significantly changed, especially in the presence of high concentrations of HA. In the case of Zn-CLDH, the regeneration rate of the LDH increased in the presence of HA, but the surface of Zn-CLDH was covered with regenerated Zn-LDH and HA. Then, the inside of the particles could not transform to LDH, leading to poor crystallinity and a significant increase in the ZnO content of the HA system.

Considering the protocol of "zero-alkaline waste disposal" for green and arsenic-free environment, lanthanum (La3+)-based MOF-like complex materials were designed, and the complex materials have been employed as adsorbent for AsO4 3- adsorption from water. The sucrose-derived porous carbon (SPC)@La-oxalate complex was prepared by a simple one-pot coprecipitation method at room temperature, where oxalate has been used as an organic ligand, and the carbonaceous biomass has been used as a doping material that is naturally a carboxylate-rich functional group derived from a sucrose biomass. In addition to SPC@La-oxalate, bare-SPC, La(OH)3, and SPC@La(OH)3 were also prepared via simple base-addition conventional methods, and their performances in AsO4 3- removal were compared. The FTIR peak at 848 cm-1 confirmed the presence of AsO4 3- on the SPC@La-oxalate complex after adsorption of 1 mM AsO4 3-. The high resolution X-ray photoelectron spectrum for the AsO4 3- adsorbed SPC@La-oxalate showed a peak at EB[As 3d] = 45.2 eV, which could be attributed to As5+. The EXAFS of the As K-edge revealed that there are two distinct atomic shells, As-O with the distance of 1.68 Å and As-La with the distance of 3.32 Å, indicating the formation of monodentate complex of La with AsO4 3-. Additionally, an electrostatic interaction and hydrogen bonding are also possible adsorption mechanism in acidic conditions. The SPC@La-oxalate complex adsorbent showed excellent dearsenate behavior of 1.093 mmol/g, and the maximum AsO4 3- removal was maintained in a wide pH range from 3 to 8. Sorption kinetic data were the best expressed by a pseudo-second-order rate equation, and the maximum adsorption capacity was 1.858 mmol/g based on Langmuir monolayer adsorption. Compared with previous reports, SPC@La-oxalate adsorbent could be easily prepared, and the uptake amounts for AsO4 3- were enriched. Reusability of the material after six cycles is yet another advantage to the present adsorbent. This work will help to facilitate the research on novel complex adsorbents for the removal of AsO4 3- from water.

Because of the Fukushima Daiichi Nuclear Power Plant (FDNPP) accident, radioactive species were leaked out, including selenium isotopes (Se-79). Developing a stable matrix that is suitable for longterm storage is necessary for the decommissioning process of the FDNPP. In the present work, the co-precipitation of SeO42- in cancrinite/sodalite as a potential stable matrix was investigated at various reaction times using a hydrothermal method. Over time, the SeO42- contents in the solid products gradually increased. The XRD patterns revealed that the reaction produced multi-phased precipitates, which were zeolite Na (P), sodalite, and cancrinite. As the SeO42- amount increased, the solid products were transformed to cancrinite. The calculated lattice parameter of sodalite and cancrinite showed an increase in lattice parameter a for sodalite and cancrinite, suggesting SeO42- incorporated into the sodalite/cancrinite structure. XRD, SEM, FTIR, Al-27-NMR, and Si-29-NMR results revealed the phase transformation of the solid products over time. Four stages of the co-precipitation mechanism are proposed, including the formation of zeolite P (Na), hydroxylation of zeolite P (Na), the formation of sodalite, and cancrinite reprecipitation.

Sodium hydrogen sulfide (NaHS) is commonly used as a copper depressant in the selective flotation of copper and molybdenum ores. However, the process is facing health and safety issues because NaHS readily yields toxic hydrogen sulfide gas (H2S) under acidic conditions. In this study, Na2SO3 was proposed as an alternative copper depressant. The effect of Na2SO3 on the surface wettability and floatability of chalcopyrite and molybdenite—typical copper and molybdenum minerals, respectively—was intensively studied using contact angle measurements and flotation tests. Contact angle readings show that the chalcopyrite surface became hydrophilic after the Na2SO3 treatment. Meanwhile, the molybdenite surface was relatively more hydrophobic compared with that of chalcopyrite after the treatment. Flotation tests using pure minerals of chalcopyrite and molybdenite demonstrate that the floatability of chalcopyrite decreased with increasing concentration of Na2SO3. On the other hand, the floatability of molybdenite gradually increased under similar conditions, suggesting that Na2SO3 might have the potential to be used for selective flotation of chalcopyrite and molybdenite. A possible mechanism is proposed in this study to explain the phenomenon using X-ray photoelectron spectroscopy analysis.

In this study, hexadecyl pyridinium chloride (HDPy-Cl) was applied to modify powdery and dispersed montmorillonite (pMt and dMt, respectively). Then, perchlorate (ClO4 −) and methyl red (MR) were selected as representatives of hazardous inorganic and organic pollutants, respectively, to investigate the influence of the dispersion of Mt on their adsorption using the obtained composites (pMt/HDPy and dMt/HDPy). Based on the X-ray diffraction patterns and water chemistry results, pre-dispersion of Mt resulted in a lower crystallinity of the obtained composite with slightly higher contents of HDPy+ (0.93 mmol/g-Mt) and HDPy-Cl (1.41 mmol/g-Mt) compared to the original powdery Mt (0.85 and 1.36 mmol/g-Mt). Moreover, as supported by thermogravimetry results, the amount of HDPy distributed on the external surface of dMt/HDPy was greater than that on pMt/HDPy, which was opposite of the HDPy content in the interlayer space. The adsorption kinetic of ClO4 − and MR on two composites was studied and the results were fitted by three models, where the intra-particle diffusion model fitted the experimental data best. Similar adsorption capacities were obtained, and the slight differences in the adsorption kinetics as supported by the intra-particle diffusion model were ascribed to the differences in the HDPy contents and configuration. The pre-dispersion of Mt is not necessary when a modified composite is planned for use as an adsorbent of pollutants, but it would be beneficial to the synthesis of clay/polymer nanocomposites.

Discharge from accidental nuclear power plants includes boric acid, which is used as a neutron absorbent in nuclear reactors. Co-precipitation of borate with hydroxyapatite (HAp), using Ca(OH)(2), is known to be an effectively fast method for stabilization of borate as well as coexisting radioactive nuclides. To reduce bulky volume of solid residues after co-precipitation, calcination is necessary to investigate the chemical stability of targets. Calcination at 850 degrees C resulted in the high crystalization of HAp with formation of chi CaO center dot B2O as a by-phase in which chi increased with a decrease in the borate contents. After calcination, the lattice parameter a of HAp showed a reentrant curve and c showed a convex curve with an increase in borate contents. A dissolution assay revealed that calcination sometimes increases the borate moiety and that the acceptable B contents in HAp are lower than 1.59 mmol/g-calcined HAp. These results imply that during calcination of HAp, some borate is excluded to form the by-phase chi CaO center dot B2O3 which is relatively insoluble in water, but some other fractions might be additionally emitted from the amorphous phase to weakly bind the calcined products. (C) 2017 Elsevier B.V. All rights reserved.

Seawater has been reported to depress the floatability of molybdenum in copper-molybdenum (Cu-Mo) flotation circuits under alkaline conditions (pH &gt; 9.5). However, the seawater used in the process contains various minerals and flotation reagents, which make it difficult to investigate the depression mechanism. This paper presents a fundamental study into the effect of artificial seawater as a seawater model solution on the floatability of molybdenite and chalcopyrite, which are the main minerals in the Cu-Mo flotation process. Floatability tests in the absence of flotation reagents (Le., frothers and collectors) reveal that artificial seawater adversely affects the floatability of molybdenite and chalcopyrite at pH &gt; 9. This phenomenon can be attributed to the adsorption of hydrophilic Mg(OH)(2) precipitates formed under alkaline conditions on the mineral surfaces, which increases the surface wettability of the mineral particles, as shown by contact angle measurements and atomic force microscopy (AFM) images. The effect of kerosene as a molybdenite collector has also been investigated to assess its potential in the selective flotation of molybdenite and chalcopyrite in artificial seawater.

The co-immobilization of radioactive Sr2+ and SeO4 2- using a multifunctional material is an interesting area of research for the total remediation of radioactive wastes. However, it is rather challenging to target both the anion and cation through the realization of a multifunctional ability of the resultant sorbent. In this work, MgAl-NO3-layered double hydroxides (LDHs) containing graphene oxide (GO) and carbon-dot (C-dot) nanocomposites were synthesized and contrasted for the co-immobilization of Sr2+ and SeO4 2-. Zeta potential measurements and TEM observation of the MgAl-NO3-LDH/C-dot composite indicated that the carbon-nanodot was attached to the surface of LDH nanosheets, while in the MgAl-NO3-LDH/GO composites the LDH nanosheets were decorated on the larger sized GO nanosheets. Adsorption studies found that the normalized Sr2+ adsorption capacity was 1.793 mmol g-1 on MgAl-NO3-LDH/GO, which was nine times higher than that for the MgAl-NO3-LDH/C-dot composite and GO. The enhancement in the Sr2+ adsorption capacity is due to the co-operative effect of the LDH and GO. The adsorption of Sr2+ on the MgAl-NO3-LDH/C-dot occurs by co-ordination with the -COO- group, while ligand exchange and ionic interaction with the alkoxide anion are the dominant mechanisms on the MgAl-NO3-LDH/GO composite. Moreover, the adsorption capacity of both Sr2+ and SeO4 2- increased synergistically in the bi-component system containing both ions. The present technique is promising and offers a sustainable and environmentally friendly multifunctional material for the co-immobilization of both anionic and cationic radioactive surrogates from aqueous solutions.

After accumulation of toxic ions from a contaminated source, spent absorbents and coprecipitation sludge should be stabilized before landfilling for long time storage, especially in the case of absorbed radionuclides. Therefore, development of novel and efficient method to stabilize spent absorbents that contain highly toxic ions is urgently needed. In the present work, the use of industrial by-products as raw materials to produce ceramics to treat toxic waste was investigated. As a typical oxoanion absorbent, selenate-doped ettringite was mixed with granulated blast furnace slag and silica fume and then calcined at various temperatures to produce glass-ceramics. Above 800 A degrees C, the amorphous mixture was converted to glass-ceramics, which were subjected to the toxicity characteristic leaching procedure test. The synthesized ceramics exhibited excellent behavior for immobilization of selenate, and only 0.1 mg/L of selenate was leached out. However, the total concentration of selenate in the mixture was not reduced during calcination. The X-ray photoelectron spectroscopy revealed the stabilization mechanism is based on encapsulation. In addition, the ceramic materials exhibited excellent chemical stability at pH 2-12. These results showed that industrial by-products can be successfully applied to produce ceramics for immobilization and storage of hazardous wastes.

A new one-pot synthesis of highly crystalline MgAl-, CoAl- and ZnAl-layered double hydroxides (LDHs) containing NO3- as interlayer anion along with the surface functionalization of L-arginine was demonstrated by the ecofriendly alkali-free arginine-assisted hydrothermal method to examine the adsorptive reduction of chromate (CrO42-) from aqueous solutions. The amino acid mediated water hydrolysis resulted abundant OH- in the medium, which served as precipitant, and the NO3- from metal precursor acts as an interlayer anion along with surface functionalization of amino acid. Adsorption studies revealed that the removal of CrO42- by anion exchange was the greatest in MgAl-LDH with 1.619mmol-Cr/g of LDH. The mechanism of CrO42- removal was due to the ion-exchange of NO3- from the interlayer as well as the counter anions present on the functionalized arginine cation. The adsorbed CrO42- was partially reduced to nontoxic Cr3+ on the surface of LDH due to the presence of amino acid functionalization. The present technique provides several advantages from the aspect of sustainable chemistry: (i) avoiding hazardous alkali for the preparation of LDH, (ii) removal of CrO42- by ion-exchange and (iii) partial detoxification of CrO42- by reduction to Cr3+ on the surface of the LDH.

Although ettringite is a crucial material in terms of Se immobilization, the immobilization mechanisms, atomic configuration, and intercolumn structure of Se sorbed in ettringite are unclear. The immobilization mechanism of Se oxoanions was evaluated through structural insight into ettringite. It is contrasting between SeO32- and SeO42- in chemical property of the solid residues after immobilization. The oxoanion exchange with structural SO42- is the main mechanism for immobilization of SeO42-. In contrast, SeO32- is easily immobilized to form inner-sphere complexes in ettringite. In addition, it is necessary to reveal the SeO32- complexation sites for understanding the mechanisms in immobilization of SeO32-. Based on the characterization results with the bond valence theory, the location sites of sorbed SeO32- in ettringite structure were proposed. The results obtained in this work are relevant to the understanding of Se and its isotopes immobilized in cement or alkaline environments, especially for nuclear waste management.

Co-immobilization of cationic and anionic radionuclides is highly desirable for total remediation of radioactive wastewater. Carbonaceous nano materials have received much attention in the field of water remediation and pollution control in recent years. However, the handling of these nano materials is challenging due to increased bioavailability and toxicity. In this work, MgAl-NO3 layered double hydroxide (LDH) was synthesized and modified using carbon nanodots (C-dot). The prepared materials were characterized using powder X-ray diffraction (PXRD), Fourier transform infrared (FT-IR), zeta potential, and transmission electron microscopy (TEM) observation. Adsorption of SeO42- and Sr2+ on MgAl-NO3-LDH/C-dot composites showed that the Sr2+ immobilization capacities increased with an increase in the amount of C-dot. The mechanism of Sr2+ adsorption on these composites occurs via coordination with the -COO- group of C-dot, whereas that of SeO42- occurs through ion exchange with NO3- in the interlayer galleries of LDH. The adsorption of Sr2+ and SeO42- was enhanced in both bicomponent (Sr2+ + SeO42-) and tricomponent systems (Sr2+ + SeO42- + M+/M2+ = coexisting cations or A(n-) = coexisting anions) with the presence of other anion and cations. The MgAl-NO3-LDH/C-dot composites demonstrated that the high adsorption efficiency of Sr2+ and SeO42- than most of other materials reported. These results demonstrate that MgAl-NO3-LDH/C-dot composites are an effective adsorbent for total remediation of anionic and cationic radioactive nuclides from wastewater.

Although the Cs adsorption onto soil minerals has been widely studied, the structural factor of Mn oxides affecting the adsorption behavior of trace amounts of Cs is unclear. In order to elucidate the adsorption mechanisms of radioactive Cs at trace levels and the role of Mn oxides on Cs migration in the terrestrial environment, the Cs adsorption onto birnessite and todorokite was investigated for a wide range of concentrations (1 x 10(-10) mol/L to 0.1 mol/L) and an ion-exchange model was used to interpret the adsorption data. Although birnessite showed a higher Cs adsorption capacity than todorokite, most of the Cs adsorbed onto birnessite was desorbed by ion exchange. Two types of adsorption sites were observed for todorokite. Despite low density, the selectivity coefficient was much higher for the T-1 site (Log(Na) K-Cs(sel) = 4.2) than for the T-2 site (LogNa K-Cs(sel)=-0.6). Sequential extraction was carried out at Cs concentrations of 1 x 10(-9) mol/L and 1 x 10(-3) mol/L. At lower concentrations, approximately 34% of the adsorbed Cs was residual in the todorokite after the sequential extraction; this value was much higher than the results for the Cs-adsorbed birnessite as well as the Cs-adsorbed todorokite at higher concentrations. The present results indicate that the structural factors of Mn oxides significantly affect the retention capacity of radioactive Cs. Aside from phyllosilicate minerals, todorokite also contributes to the fixation of radioactive Cs in soils.

Amorphous forms of mixed lanthanum-zirconium oxyhydroxide (ZrxLa1-xOOH) composite materials, containing porous sucrose carbon as a dopant (PSC-ZrxLa1-xOOH), were successfully prepared via co-precipitation and characterized by BET surface area analysis, Fourier transform infrared spectroscopy (FTIR), powder X-ray diffraction (PXRD), scanning electron microscopy (SEM) Energy-dispersive X-ray spectroscopy (EDX) and thermogravimetric analysis (TGA). These synthesized materials were utilized for the simultaneous adsorption of AsO33- and F- from a binary mixture solution in batch tests. The ZrxLa1-xOOH and PSC-ZrxLa1-xOOH composite materials showed both fast adsorption rates and high adsorption capacities towards AsO33- and F- in aqueous solution. Most attractively, ZrxLa1-xOOH and PSC-ZrxLa1-xOOH showed better F- adsorption capacity when the pH was lower than 7, better AsO33- removal when the pH was higher than 9 and were superior to previously reported metallic oxide based sorbents. The mechanism can be interpreted based on the HSAB principle, where the bimetallic oxyhydroxides become "soft acids", while L3+ and Zr4+ are categorized as "hard acids". Moreover, the PSC-ZrxLa1-xOOH adsorbent demonstrated high selectivity for AsO33- in the co-existence of other ions in a triple component system. The fast adsorption kinetics and high capacity make the designed PSC-ZrxLa1-xOOH adsorbent a promising advanced material for the removal of AsO33- and F- from water in practical applications. (C) 2017 Elsevier B.V. All rights reserved.

Precipitation of SeO42--substituted ettringite is an efficient method to immobilize SeO42- under alkaline conditions. The effect of SO42- on SeO42- immobilization was investigated, because SO42- is one of the major ions in aqueous and soil environments and it is easily incorporated in ettringite. We aimed to systemically elucidate the formation mechanisms of SeO42--substituted ettringite with and without SO42-. When SO42- and SeO42- coexisted, both oxoanions were immediately coprecipitated with ettringite after adding a Ca source. Although SO42- was partially substituted by SeO42- in ettringite, no other phases were formed during the process. Without SO42- SeO42--substituted AFm phase was formed as an intermediate, confirmed by X-ray diffraction peak at d 2.878, as well as by scanning electron microscopy with energy dispersive X-ray spectroscopy and zeta potential measurements. It is clear that the incorporation mechanism of SeO42- in ettringite is dependent on coexisting SO42- in aqueous environments.

Montmorillonite (Mt) and illite (lit) were ground for different times under wet condition and sequentially subjected to organic modification by dioctadecyl dimethyl ammonium chloride (DDAC). The influence of the grinding time on the obtained products in terms of DDAC loading and ClO4- adsorption were evaluated. Multiple techniques were used to characterize the changes in structure and morphology before and after mechanical or organic modification. Compared with Ilt, Mt showed a stronger resistance to mechanical treatment due to its swelling property. Silicon nuclear magnetic resonance (Si-29 NMR) spectra and X-ray diffraction (XRD) patterns of samples ground for 30 min indicate the disintegration of Ilt and exfoliation of Mt, resulting in increase of ClO4- uptake by 147% for ont and 13% for OMt. Three stages in the grinding Mt can be proposed, including the separation of large particles into small particles, exfoliation of small particles, and disintegration of exfoliated single layers. In contrast, two stages are involved in the grinding Ilt, which are the destruction/exfoliation of large particles and further disintegration of small exfoliated layers.

Hydrothermal carbonization of sugarcane bagasse using hot-compressed-water was investigated for the treatment of solid material to understand the occurring decomposition reactions. The experiments were performed in 14 ml of batch type reactor in the range of temperatures 200-300 degrees C and reaction times 3-30 min. After separation of solid residues from liquid material, approximately 34-88 wt% of raw material was recovered as solid products. Characterizations show that increased treatment temperature and reaction time causes structural changes of the sugarcane bagasse. When the temperature and reaction time was increased, hemicellulose and cellulose gradually dissolved, leaving a lignin-like acid insoluble residue. The presence of the residue increases the fixed carbon and decreases the volatile matter content of the solid product. Dehydration significantly decreases the oxygen content and slightly decreases the hydrogen content of the treated material. With these changes, the caloric value and of the solid product increases by 1.1-1.9 times that of the raw material. Higher temperature treatment (300 degrees C) produces a material with high caloric value and fixed carbon, with a composition comparable to typical solid fuels such as lignite (or low rank-coal). The hydrothermal carbonization of sugarcane bagasse could be a solution to reduce environmental pollution caused by the combustion of wet stockpiled sugarcane bagasse in the sugar industry. The treated sugarcane bagasse reduces energy loss, smoke and water vapor during the combustion process.

The synthesis of pure nitrate-containing layered double hydroxides (LDHs) via biomolecule-assisted methods is difficult to achieve without producing substantial waste. For the first time, we demonstrated the synthesis of LDHs with a controlled interlayer anion composition using an environmentally friendly L-arginine-assisted hydrothermal method with zero waste disposal. The mechanism of LDH formation was revealed through PXRD, FT-IR, XPS and ion chromatographic (IC) analyses. At low synthesis temperatures (90-110 degrees C), arginine-mediated water decomposition led to OH- and [Arg(+)]-NO3- formation and thus produced pure NO3--containing LDHs. Conversely, at temperatures above 115 degrees C, L-arginine decomposition occurred and produced NH4+ and CO2, which resulted in CO32--bearing LDHs. The FT-IR spectra of the solid residues, which were obtained at lower temperatures, indicated that several amino acids were functionalized on the surface of the LDHs and replaced by CO32-, which was produced at higher temperatures. The sorption of arsenate from an aqueous solution on the resulting LDHs showed maximum sorption capacity values of 1.675 and 1.972 mmol g(-1) for Mg2.3Al-LDH and Mg2Al-LDH synthesised at 100 degrees C, respectively. The arsenate sorption capacity was enhanced by the functionalization of L-arginine compared with conventionally prepared LDHs. The mechanism of arsenate sorption was based on the ion-exchange of interlayer NO3- and functionalized arginine molecules. In summary, the chemical precursor L-arginine (utilized in this study) acts as a multifunctional reagent, including (i) a precipitant for the synthesis of LDH, (ii) an engineer for interlayer anion control, (iii) a functional reagent and (iv) a scavenger for free NO3- that is present in the synthesis medium. The current synthesis method did not utilize a hazardous base during synthesis, and the [Arg(+)]-NO3- byproduct can be used as a chemical source for health/skin care formulations with zero waste disposal, which offers great benefits.

The unique and versatile adsorbents zirconium oxyhydroxide (ZrOOH), aluminum oxyhydroxide (AlOOH), zirconium-aluminum oxyhydroxide (ZrxAl1-xOOH) and chitosan-supported zirconium-aluminum oxyhydroxide (CS@ZrxAl1-xOOH) were synthesized via a simple co-precipitation method. CS was used as a pillar-like support to reinforce the ZrxAl1-xOOH, the resulting material was capable of simultaneously adsorbing both F- and AsO33- because the functional groups of CS facilitated the formation of both ZrOOH and AlOOH nanoparticles. Interestingly, ZrxAl1-xOOH and CS@ ZrxAl1-xOOH had better F- adsorption capacities at pH&lt;7, whereas better AsO33- removal was observed at pH&gt;9. The Langmuir maximum adsorption capacity of CS@ZrxAl1-xOOH was 0.655 and 0.983mmol g(-1) for AsO33- and F-, respectively and the performance was superior to that of previously reported metallic oxide and chitosan-based sorbents. In addition, the presence of coexisting anions revealed that the CS@ZrxAl1-xOOH material selectively removed AsO33- over F- in a binary batch system. The adsorption kinetics of the adsorbents were well fit to the pseudo-second-order model. Due to the simultaneous and quick uptake capacity and cost-effectiveness, CS@ZrxAl1-xOOH nanocomposite have potential application in environmental cleanup.

Porous carbon composites containing varying La contents were synthesized and studied for the sorption of phosphate. The phosphate sorption capacities increased with increasing La content and showed an almost complete La consumption efficiency (P/La molar ratio of 0.936) for the composite containing a La(OH)(3)/porous carbon mass ratio of 0.1 (La-0.1-PC). Phosphate sorption by these composite materials occurred through precipitation of LaPO4 supported by PXRD, XPS and EDS analyses. Kinetic studies revealed that phosphate sorption by the La-0.1-PC composite was rapid and reached equilibrium within 1 h compared to the composites containing higher mass ratio of La(OH)(3). The sorption capacity of phosphate was not reduced in the presence 20 mM chloride and 20 mM sulfate, but was disturbed by 20 mM carbonate. The phosphate sorption in the presence of 25 mg/L humic acid was maintained along with the adsorption of dissolved humic acid by electrostatic adsorption onto the carbon support. Interestingly, the phosphate sorption capacity in seawater was twice that in fresh water, likely because the Ca2+ and Mg2+ ions in seawater enhanced the precipitation of phosphate on the surface of La in the La-PC composite. Column experiments verified that the La-0.1-PC composite was effective for the continuous treatment of phosphate. The current outcome suggests that the La-PC composite can be used as a multifunctional sorbent for the remediation of phosphate along with alkaline metal ions (Ca2+ and Mg2+) as well as the removal of humic substances in wastewaters. Moreover, the spent sorbent could be repurposed as a phosphate plant fertilizer, where it would reduce the cost of disposal and increase the commercial value. (C) 2017 Elsevier B.V. All rights reserved.

Loy Yang lignite with a high water content was dewatered by freeze drying (FD). The drying kinetics of FD was calculated using thin-layer drying models given in the literature. Residual water content, re adsorption or desorption behaviors, and pore size distributions of all of the samples were investigated. Furthermore, coating with different amounts of kerosene by direct mixing or adsorption methods to restrain water re-adsorption was also investigated. The results showed that FD dewatering contained three steps: a fast dewatering period (-2 h), followed by a reduced drying-rate period (2-3 h) and an apparently falling-rate period (&gt;3 h). The Midilli-Kucuk model described the drying process perfectly and could be employed to predict residual water content in the sample at any time during the FD dewatering process. The moisture holding capacity (MHC) of the FD-treated samples was lower than that of raw lignite, which is because of the effect of the water-lignite bond strength and the diffusion adsorption or desorption force. Moreover, adding kerosene by either adsorption or direct-mixing methods can both decrease MHC because kerosene is coated on the surface and in the pores of the lignite. These prevent water re-adsorption. The adsorption method is better than the direct-mixing method because it consumes less kerosene. (C) 2017 Elsevier B.V. All rights reserved.

Fourteen anions were selected to investigate their adsorption capacities and affinities to unwashed and washed hexadecyl pyridinium (HDPy)-modified montmorillonite (HDPy/Mt). Correlations between adsorption characteristics and anionic properties including radius and hydration energy were determined. With the exception of IO3-, H2AsO4-, and CrO42-, monovalent anions showed higher adsorption capacities and affinities to unwashed or washed HDPy/Mt than divalent anions, because the latter possess higher hydration energies. Unwashed HDPy/Mt demonstrated higher selectivity toward poorly hydrated monovalent anions because it presented a more hydrophobic environment, whereas strongly hydrated divalent anions more readily intercalate into the less hydrophobic washed HDPy/Mt. Hydration of the counter ion (Cl-) is the driving force for anion adsorption on HDPy/Mt. Higher energy consumption required to dehydrate divalent anions accounts for their lower affinity. Selectivity of HDPy/Mt to anions depends not only on anion size in different phases (from r(1) in aqueous solution to r(2) in the organic solvent-like HDPy/Mt), but also the dielectric constant of HDPy/Mt (epsilon(2)) after HDPy release. (C) 2016 Elsevier B.V. All rights reserved.

Immobilization of fluoride (F-) in apatite using Ca(OH)(2) as a mineralizer in the presence of phosphate is known to be accompanied by a stagnation period. This is caused by the formation of hydroxyapatite and/or fluoroapatite (HAp/FAp) on the surface of Ca(OH)(2), which inhibits the dissolution of Ca(OH)(2). Al3+ additives effectively eliminated the delay period, leading to the rapid formation of apatites by suppressing the formation of CaCO3. Zeta potential measurements clearly showed that increasing the quantity of Al3+ additives caused not only a decrease in the initial surface charge but also a decrease in the rate of the surface charge of the solid residues during the reaction, indicating that Al3+ additives enhanced the formation of HAp/FAp. 27Al-nuclear magnetic resonance (NMR) studies of the solid residues indicated that the predominant coordination number of Al was always hexagonal ([6]Al) and that the fraction of [6]AI increased with an increase in the molar ratio of F/Al in the solid residues, suggesting that the stable AlF63- complex was easily incorporated into the apatites. In addition, transmission electron microscope- energy dispersive X-ray spectroscopy (TEM-EDX) revealed a uniform distribution of Al in the apatites, which suggests that in the initial stages of the reaction, free Al3+ ions contribute to the formation of apatite crystal seeds independent of Ca(OH)(2) particles, resulting in the efficient growth of apatites containing F-. This result is helpful for the treatment of F--bearing industrial wastewaters in practical applications by using an Al-bearing Ca source, such as ground-granulated blast-furnace slag. (C) 2016 Elsevier B.V. All rights reserved.

© 2016 Elsevier B.V. This study investigated the effect caused by Cu(II) in synthetic As(III)-bearing copper refinery wastewaters, on microbial scorodite (FeAsO4·2H2O) formation using the thermo-acidophilic Fe(II)- and As(III)-oxidizing archaeon, Acidianus brierleyi. Microbial Fe(II) oxidation and cell growth became only marginal in the presence of 8–16 mM Cu(II), with its As(III) oxidation ability being severely inhibited. Consequently, scorodite formation was disabled by Cu(II) addition. However, feeding scorodite seed crystals readily alleviated Fe(II)- and As(III)-oxidation ability of Ac. brierleyi at 8 mM Cu(II), forming crystalline scorodite within 24 days in shake flasks. Zeta potential analysis indicated cell attachment to the scorodite seed crystal surface, implying its role in providing the immediate support for microbial colonization and enabling more robust microbial reactions. Most of Cu(II) was neither adsorbed nor co-precipitated and remained in the solution phase during scorodite crystallization, with or without the presence of seed crystals. Addition of seed crystals at 0.015, 0.03, 0.075 and 0.15% resulted in As immobilization of 96, 97, 97 and 98%, respectively, by day 24. This study demonstrated that despite of its inhibitory effect on Ac. brierleyi cells, scorodite can still be crystallized in the presence of Cu(II) by feeding scorodite seeds from synthetic copper refinery As(III)-bearing wastewaters.

Carbonaceous matter in refractory gold ore is known to be one of the primary causes of gold recovery loss. Model experiments were conducted to simulate the bio-modification of carbonaceous matter using powdered activated carbon (PAC) as a surrogate and cell-free spent medium (CFSM) of Phanerochaete chrysosporium. The CFSM was used because of the lignin peroxidase and manganese peroxidase secreted by the microbe during its incubation. In the present work, an investigation was conducted to determine the physical and chemical alterations in PAC after enzymatic treatment and its effect on Au(CN)(2)(-) uptake. Characterization of the solid residues of PAC by C-13 NMR and N-2 adsorption after bio-modification revealed that the treatment had decomposed poly-aromatic carbons into aliphatic carbons and also reduced the specific surface area from 1430 m(2)/g to 697 m(2)/g in 14 days. As a result, Au(CN)(2)(-) uptake decreased from 100% (0.048 mmol/g) to 43% within 12 h primarily due to the enzyme treatment and adsorption of CFSM components. It further decreased to 26% due to surface passivation by bio-chemicals derived from CFSM and/or decomposed aliphatic hydrocarbons from aromatic carbons between 7 days and 14 days. These findings may contribute to efforts to decrease preg-robbing in hydrometallurgical processing of refractory gold ores. (C) 2016 Elsevier B.V. All rights reserved.

Simultaneous adsorption of Sr2+ and ReO4-, which are surrogates of Sr-90(2+) and (TcO4-)-Tc-99m, on hexadecyl pyridinium (HDPy+)-modified montmorillonite (HDPy/Mt) was investigated. When the amount of HDPy+ corresponding to 0.92 times the cation exchange capacity (CEC) of Mt was added, the obtained composite (HDPy/Mt-0.92) showed considerable adsorption capacities for Sr2+ and ReO4-. Some HDPy+ desorbed from the Mt layer in the presence of ReO4-, providing negatively charged sites on the Mt surface for Sr2+ adsorption. The desorbed HDPy+ interacted with ReO4- and was trapped in the composite in the form of HDPy-ReO4, resulting in adsorption of ReO4-. At high initial concentrations of ReO4-, the HDPy configuration changed after adsorption because of the desorption-adsorption process, which was supported by X-ray diffraction. Based on the results of X-ray photoelectron spectroscopy, in the binary system (i.e., Sr2+ and ReO4-), Sr2+ uptake occurred in the interlayer space, while adsorption of ReO4- occurred on the external surface and probably in the interlayer space. Desorption-adsorption and ion exchange account for Sr2+ uptake, while adsorption of ReO4- was mainly attributed to desorption-adsorption. Compared with the one-adsorbate system, a synergistic effect of simultaneous adsorption of Sr2+ and ReO4- was found in the two-adsorbate system. (C) 2016 Elsevier B.V. All rights reserved.

Various oxidation treatments (i.e., plasma, and ozone) have been applied to separate molybdenite from other sulfide metals. However, plasma and ozone treatments exhibit stronger oxidation on chalcopyrite and molybdenite, reducing the separation selectivity of both minerals in flotation tests. On the other hand, hydrogen peroxide (H2O2) is frequently used as an oxidizing agent in wastewater treatment. It has also been reported to reduce the recovery of sulfide minerals. Therefore, the effect of H2O2 on separation of chalcopyrite and molybdenite was investigated in this study. Contact angle readings and surface images using atomic force microscopy (AFM) showed that chalcopyrite surface was more sensitive to surface oxidation compared to that of molybdenite in H2O2 aqueous solution. The floatability test of single mineral confirmed the contact angle results and AFM images, indicating a possibility for selective separation of chalcopyrite and molybdenite using a H2O2 aqueous solution. In addition, iron was used to improve the oxidation performance of H2O2 and its effect on the selective flotation of chalcopyrite and molybdenite is intensively studied in this work.

The bio-treatment of double refractory gold ores (DRGO) to reduce preg-robbing needs to account for the heterogeneity of the ore so as to acquire a much more complete picture of the system. To this end, the effects of ferrous ion additives on the degradation of powdered activated carbon (PAC) by cell-free spent medium (CFSM) was studied. Au(CN)2- adsorption and Raman spectrometric results suggest that the ferrous salt could have possibly reacted with some biogenic hydrogen peroxide to aid in the degradation of PAC. The bio-treatment produced mixed solid residues containing some partially degraded aromatic compounds which were soluble in alkaline solutions. Ultimately, biodegradation of PAC using CFSM in the presence of 50 µM FeSO4.7H2 O for 7 days followed by washing with 3 mM NaOH reduced Au(CN)2- uptake by 80%.

The selective flotation of chalcopyrite (CuFeS2) and molybdenite (MoS2) was studied using surface oxidation treatments (i.e., ozone (O-3) and hydrogen peroxide (H2O2)). The results indicated that the oxidation treatments had different effects on the wettability of chalcopyrite and molybdenite. Single mineral flotation results showed that the H2O2 treatment had higher separation selectivity for molybdenite and chalcopyrite compared with that of the ozone treatment. The contact angle measurement and X-ray photoelectron spectroscopy (XPS) analysis results showed that the chalcopyrite surface became hydrophilic owing to the surface deposition of oxidized iron and copper after the H2O2 treatment. On the other hand, the contact angle of molybdenite slightly increased following the H2O2 treatment at high concentrations. Possible mechanisms of this phenomenon were proposed in this work. Moreover, the separation selectivity of each oxidation method was discussed. Flotation tests using bulk Cu-Mo concentrate showed that H2O2 could deliver a flotation result comparable to conventional Cu-Mo flotation using NaHS. (C) 2016 Elsevier Ltd. All rights reserved.

©The Mining and Materials Processing Institute of Japan After accumulation of radionuclides from contaminated sources, spent absorbents and co-precipitated sludge is classified into radioactive wastes and should be stabilized before landfilling for long term storage. Therefore, development of efficient technologies to stabilize spent absorbents bearing radionuclides is urgently needed. In the present work, the ultilization of industrial by-products as raw materials to produce ceramics to stabilize radioactive waste was investigated using a surrogate. Selenate-doped ettringite was mixed with granulated blast furnace slag (GBFS) and silica fume (SF) and then calcined at various temperatures to produce glass-ceramics. Above 800 °C, the amorphous mixture was converted to glass-ceramics, which were subjected to the toxicity characteristic leaching procedure (TCLP) test. The synthesized ceramics exhibited excellent results for immobilization of selenate in which less than 0.1 mg/L of selenate was leached out. Moreover, according to the digestion experiment, the quantity loss of selenate in the ceramics was not observed even after calcination. The X-ray photoelectron spectroscopy (XPS) revealed the stabilization mechanism is based on encapsulation. In addition, the ceramic materials exhibited excellent chemical stability in a wide range of pH from 2 to 12. These results showed that industrial by-products can be successfully applied to produce ceramics for not only immobilization but also storage of hazardous wastes.

© 2017 Trans Tech Publications, Switzerland. Silver-catalyzed bioleaching of enargite concentrate with three bacteria (Acidimicrobium ferrooxidans ICP, Sulfobacillus sibiricus N1, Acidithiobacillus caldus KU) and one archaeon (Ferroplasma acidiphilum Y) was conducted in order to elucidate the catalytic mechanism of silver sulfide in enargite bioleaching. Whereas Cu recovery remained relatively low (43%) and Fe dissolved completely without silver sulfide, Cu recovery was greatly enhanced (96%) and Fe dissolution was suppressed (29%) in the presence of 0.04% silver sulfide. In the latter case, 52% of the solubilized As was re-immobilized, in contrast to only 14% As re-immobilization in the former. The silver-catalyzed bioleaching (at 0.04% silver sulfide) proceeded at low redox potentials within the optimal range, which likely promoted enargite dissolution via formation of intermediate Cu2 S. XAFS analysis revealed that As was mainly immobilized as As(V), which was in agreement with the EPMA results detecting ferric arsenate passivation on some enargite grains. Furthermore, formation of trisilver arsenic sulfide (Ag3 AsS4) was detected by XRD and EPMA, covering the surface of enargite particles. An intermediate layer, consisting of (Cu,Ag)3 AsS4, was also observed between the enargite grain and trisilver arsenic sulfide layer, implying that Cu in enargite may be gradually substituted by solubilized Ag. Kinetic study suggested that these secondary minerals do not rate-limit the enargite dissolution. The overall mechanism of silver-catalyzed bioleaching of enargite concentrate will be proposed.

© 2017 Trans Tech Publications, Switzerland. The potential utility of mesophilic/moderately thermophilic acidophiles was investigated for immobilization of arsenic (As) as scorodite (FeAsO4·2H2O) at moderate temperatures (35–45˚C). Here, the acid-tolerant mesophile Thiomonas cuprina Hö5 and acidophilic moderately thermophile Acidimicrobium ferrooxidans ICP were selected as As(III)- and Fe(II)- oxidizers, respectively. Due to a difference in their optimal growth pHs, a 2-step reaction consisting of the 1st As(III) oxidation step followed by the Fe(II) oxidation + precipitation step was studied. In our previous study, the optimal [Fe(II)]ini/[As(III)]ini molar ratio for bioscorodite formation at 70˚C (at [As(III)]ini = 1000 ppm) was shown to be around 1.4. However, setting the same molar ratio at moderate temperatures (35-45˚C) resulted in formation of unstable amorphous ferric arsenate. Lowering the ratio to ≤ 1.0 led to precipitation of crystalline bioscorodite with > 90% As(III) removal at 45˚C.

© 2017 Trans Tech Publications, Switzerland. Arsenic (As) is a major impurity contaminating metal refinery wastewaters. To immobilize As ions, we have previously reported microbial scorodite (FeAsO4·2H2O) crystallization using the thermo-acidophilic iron-oxidizing archaeon, Acidianus brierleyi. In order to extend the applicable range of As(III)-bearing metal refinery wastewaters (especially for dilute As(III) concentrations of 250–1500 ppm), this study investigated the effect of several factors possibly affecting the bioscorodite crystallization efficiency; (i) [Fe(II)]ini/[As(III)]ini molar ratio at different target As(III) concentrations, (ii) initial pH, and (iii) seed scorodite with different morphologies. The [Fe(II)]ini/[As(III)]ini molar ratio strongly affected the bioscorodite crystallization efficiency at each target As(III) concentration. Whilst the [Fe(II)]ini/[As(III)]ini molar ratio of 1.4 was most effective at 500–1500 ppm As(III), the optimal molar ratios for treating more dilute concentrations (< 500 ppm) were shown to be relatively higher. However, further increasing the [Fe(II)]ini/[As(III)]ini molar ratio resulted in formation of unwanted potassium jarosite (KFe3(OH)6(SO4)2) together with scorodite. Lowering the initial pH from 1.5 to 1.2 resulted in earlier scorodite nucleation, but lower overall As immobilization. Feeding chemical- and bio-scorodite seed crystals differently affected the reaction speed and the stability of newly-precipitated bioscorodite. The TCLP test indicated that scorodite formed on bioscorodite seeds is more stable than that formed on chemically-synthesized scorodite seeds.

Electrolysis oxidation of chalcopyrite and molybdenite was investigated, via various electrochemical methods, with the aim of realizing selective flotation of these minerals. Result of potential polarization indicated that oxidation via electrolysis affected only the chalcopyrite surface, owing mainly to the difference in conductivity of these minerals. Also measurements of contact angle after electrolysis indicated that contact angle of chalcopyrite selectively decreased whereas that of molybdenite did not decrease drastically. XPS analyses after electrolysis indicated that chalcopyrite peak decreased whereas iron oxyhydroxide (goethite) and iron sulfate increased, it suggests that these oxidation products covered on the surface of chalcopyrite. On the other hand, molybdenite peak is similar after electrolysis except for molybdenum oxide/oxygen with molybdenite can be seen for oxygen peak. From these results and general knowledge that sulfide hydrophobicity and sulfate/oxyhydroxide hydrophilicity, it can be explained that with electrolysis oxidation, hydrophilic oxihydroxide and sulfate covered on the surface of hydrophobic chalcopyrite then chalcopyrite surface became hydrophilic. On the other hand, molybdenite surface keep hydrophobic since its difficulty of oxidation and it is difficult to stay molybdenum oxide on the surface due to its soluble property. These results revealed that chalcopyrite was selectively oxidized and, hence, selective flotation of chalcopyrite and molybdenite was possible. This electrolysis oxidation methods were compared with those governing other oxidation treatments.

Exfoliation of layeredmaterials has attracted tremendous interest since nanomaterials have become practically applied in many disciplines. In this study, the structural transformation of packed columnar selenate ettringite into nanoscale particles has been investigated. The structural transformation of ettringite has been evidenced based on the results of X-ray diffraction (XRD), Raman spectroscopy, transmission electron microscopy (TEM), and extended X-ray adsorption fine structure (EXAFS). The structural transformation is caused by the electrostatic repulsion between guest sulfate ions and selenate. However, the atomic arrangement of columnar parts of selenate ettringite is still maintained. In addition, a similar phenomenon is more noticeably observed when it is soaked in ethanol. This suggests that this columnar material has the potential to be exfoliated into a single nanoscale column by reactions with polar solvents. Finally, a stable colloidal solution formed when selenate ettringite was soaked in butanol. This is because the surface of the columnar parts in ettringite is surrounded by structural water molecules that can interact with OH groups of strongly polar solvent molecules to form hydrogen bonds that can directly exfoliate selenate ettringite and convert to nanoparticles. It is clear that ettringite could be directly exfoliated to nanoparticles in polar organic solvents, which has potential utility for wide applications.

Here, we developed an enzyme assay of manganese peroxidase (MnP) by capillary electrophoresis using an in-capillary reaction and applied it to a simultaneous assay of MnP and lignin peroxidase (LiP). The enzyme activity of MnP was determined from the peak area corresponding to Mn(III)-malonate produced by the plug-plug reaction between MnP and Mn(II) in a separation capillary. A background electrolyte containing 250 mM malonate buffer (pH 4.5) and 5 mM cetyltrimethylammonium bromide was employed for the separation of Mn(III)-malonate from MnP at -10 kV after a plug-plug reaction for 5 min. Although the assay permitted the determination of purified MnP, we found that both LiP and MnP have similar activities against their substrates, that is, LiP catalyzed the oxidation reaction of Mn(II) as well as MnP, whereas MnP catalyzed the oxidation reaction of veratryl alcohol which was the substrate used in the LiP assay developed previously. Thus, we proposed a method to discriminate MnP from LiP based on the difference in the activities of these enzymes to each substrate. Amounts of MnP and LiP in a mixture were successfully evaluated by the proposed method.

Nanomaterials have gained much interest in water remediation and pollution control in recent years. However, the toxicity associated with nanoparticles remaining in solution after remediation has high impact on the environment. The present study examined the synthesis and characterization of colloidal Mg2Al-NO3 layered double hydroxide (Mg2Al-UD-LDH) nanosheets and their application as adsorbent toward arsenate immobilization. Colloidal LDH nanosheets featured the absence of nanoparticles release in the environment differently from other nanomaterials. The adsorption studies conducted in batch method, revealed that colloidal Mg2Al-UD-LDH nano sheets (obtained by ultrasonic treatment of Mg2Al-NO3-LDH suspension) achieved a higher arsenate adsorption density of 1.21 mmol/g than parent Mg2Al-NO3-LDH (1.16 mmol/g) at a solid-to-solution dosage of 0.78 g LDH/L. The adsorption mechanism of arsenate onto colloidal Mg2Al-UD-LDH nanosheets proceeded through restacking of the nanosheets, besides ion-exchange onto Mg2Al-NO3-LDH and surface adsorption onto Mg2Al-CO3-LDH. Kinetics of arsenate adsorption onto colloidal Mg2Al-UD-LDH nanosheets was rapid, reaching equilibrium within 5 min, whereas equilibrium was reached within 120 min in the presence of Mg2Al-NO3-LDH. The colloidal LDH nanosheets stacking effect was restricted at higher LDH/As ratios owing to electrostatic repulsion among the nanosheets, as determined by zeta potential measurements. Semi-pilot scale static model systems for arsenate adsorption were examined to further investigate the adsorption performance of colloidal Mg2Al-UD-LDH nanosheets in natural water systems such as river, pond, or lake. Arsenate adsorption was rapid onto colloidal Mg2Al-UD-LDH nanosheets owing to their high dispersibility; specifically, 100% adsorption efficiency was achieved within 5 min. Thus, the high adsorption capacity, dispersibility, and fast kinetics of arsenate removal onto colloidal Mg2Al-UD-LDH nanosheets promising for use as an efficient adsorbent for water remediation. (C) 2016 Elsevier B.V. All rights reserved.

An electrode system to study the mechanism of fine microgram powder sulfide mineral dissolution was developed by using a relatively simple method that enables the attachment of micrograms of fine powder to a platinum plate surface. This system yields highly reproducible results and is sensitive compared with conventional electrode systems for various sulfide minerals such as pyrite, chalcopyrite, chalcocite, enargite, and tennantite. The leaching behavior of chalcopyrite was re-examined in a test of the application of this electrode system. Chalcopyrite dissolution is enhanced in specific potential regions because it is believed to be reduced to leachable chalcocite, but this result is inconclusive because it is difficult to detect the intermediate chalcocite. Powder chalcopyrite in the new powder electrode system was held at 0.45 V in the presence of copper ion and sulfuric acid media followed by an application of potential in the anodic direction. Besides the chalcopyrite oxidation peak, a small peak resulted at similar to 0.55 V; this peak corresponds to reduced chalcocite, because it occurs at the same potential as the chalcocite oxidation peak.

The combustion characteristics and kinetics of hydrothermal treatment (HT) without addition of extra water and of HT coupled with mechanical expression (HT-ME) were investigated using thermogravimetric analysis at various heating rates. The relationships between various physicochemical properties, i.e., amounts of volatile matter and fixed carbon, specific surface area, and pore volume, and combustion performance were also investigated. The activation energy was calculated using the Kissinger-Akahira-Sunose isoconversional method. The results showed that for samples treated using HT and HT-ME, the ignition temperatures and temperatures at which the mass loss rates were at maximum, mainly because of char combustion, were significantly higher than those for raw lignite. They increased slightly with increasing processing temperature, suggesting that HT and HT-ME decrease the reactivity of Loy Yang lignite. The maximum combustion rates of the treated samples were higher than those of raw lignite and the values for the HT and HT-ME samples differed slightly from each other. The higher maximum combustion rates indicate that HT and HT-ME modify the combustion intensity of Loy Yang lignite. Furthermore, the combustion of raw lignite can be described by multistep kinetics, whereas single rate-limiting step kinetics can be used to describe the kinetics of the other samples. Average activation energies of samples treated using HT and HT-ME at 200 degrees C reached the maximum values.

We investigated the influence of initial arsenate concentration (C-0) in the 5th order of magnitude on removal of arsenate by hydrocalumite (bimetallic layered double hydroxide, LDH) and Mg-doped hydrocalumite (trimetallic LDH) from aqueous solution. These hydrocalumites were prepared by the microwave-assisted hydro thermal treatment. There is a trend that the larger adsorption density of arsenate (Q(e)) values is observed with bimetallic LDH under low C-0 values and with trimetallic LDH under high C-0 values. The transitional C-0 values ranged at 2.10-2.96 mM. Comprehensively understanding characterization results for the solid residues after adsorption of arsenate by X-ray diffraction, Al-27-nuclear magnetic resonance, and scanning electron microscopy energy dispersive X-ray, the mechanism to remove arsenate was dependent on arsenate concentrations. At low arsenate concentration, partial intercalation and dissolution-reprecipitation (DR) happened together. With increasing C-0, full intercalation and DR happened to bring out one phase of arsenate-bearing hydrocalumite. Under the very high C-0, DR mechanism happened at the edge sites of LDH sheets, leading that the newly formed massive precipitates block the further intercalation with nitrate. As a result, two phases of LDH were observed. The greater Q(e) with bimetallic LDH in low concentration comes from high crystallinity to enhance partial ion-exchange, and greater Q(e) with trimetallic LDH in high concentration is derived from more fragile properties to enhance DR mechanism. (C) 2016 Elsevier B.V. All rights reserved.

A powdery lithium ion sieve (HMO) derived from biogenic birnessite was homogeneously integrated in sodium alginate (AL) beads. The composite beads were then characterized and their Li+ adsorption properties were investigated. Scanning electron microscopy-energy dispersive spectroscopy analysis showed that the HMO particles were homogeneously dispersed in the AL beads even after drying. The adsorption isotherm of Li+ adsorption to HMO encapsulated in AL beads (HMO-AL) was well fitted by the linear Langmuir model, and the beads showed a maximum adsorption capacity of 3.61 mmol/g based on HMO, which is comparable with the value of the original powdery HMO. Kinetic studies revealed that adsorption of Li+ follows a pseudo-second-order model with rate constant k(2) = 2.8-11.9 x 10(-3) g/(mmol min) for the initial Li+ concentration range 2.56-4.23 mM. Diffusion of Li+ from aqueous solution to the HMO particle through the Ca-AL network is the rate-limiting step for Li+ adsorption to HMO-AL beads. The HMO-AL beads enhanced the handling efficiency for Li+ adsorption and reused without significant reduction of Li+ adsorption efficacy. (C) 2016 Elsevier B.V. All rights reserved.

In this study, freeze-drying was applied in the synthesis of nanocrystalline layered double hydroxides (LDHs), and the properties of resulting LDHs along with their efficacies for the removal of fluoride were evaluated. Nano crystalline NO3- and Cl-type LDHs were produced by freeze-drying using liquid N-2. The solid properties of the freeze-dried LDHs were compared with those of LDHs dried at 100 degrees C. Both NO3- and Cl-type LDHs were analyzed via X-ray diffraction (XRD), Fourier transform infrared spectroscopy, Raman spectroscopy, and scanning electron microscopy (SEM). XRD analysis confirmed that the LDHs dried by liquid N-2 were hydrotalcite-like compounds with lower degrees of crystallinity compared with those dried at 100 degrees C. SEM images showed agglomerated nano particles in the freeze-dried LDHs. No significant difference was observed between the NO3- and Cl-type LDHs. However, all characterization results suggested that the freeze-drying method resulted in small nanoparticle sizes. Moreover, bimetallic oxides produced by the calcination of LDHs were affected by the crystallinities of starting materials. Fluoride (F-) sorption experiments on the synthesized LDHs indicated that the freeze-dried LDHs and resulting bimetallic oxides were better sorbents compared with the LDHs prepared at 100 degrees C. The sorption capacities of F- on the LDHs and bimetallic oxides from freeze drying were 0.78-0.87 mM and 4.34 mM, respectively. (C) 2016 Elsevier B.V. All rights reserved.

A novel method is reported for surfactant modification of montmorillonite (Mt), and then the performance of the surfactant-modified Mt was investigated for the removal of perchlorate (ClO4 center dot-). Mt was first modified with dimethyl dioctadecyl ammonium chloride (DDAC) under microwave irradiation, which was followed by a second modification with benzyl octadecyl dimethyl ammonium chloride (BODAC). The influence of the added amount of DDAC in terms of ClO4- adsorption to the modified Mt was intensively investigated. In addition, sequential and simultaneous-mixing methods were compared for preparation of the modified Mt in terms of ClO4- removal performance. Using sequential modification, addition of DDAC corresponding to 0.05 times the cation exchange capacity of Mt significantly increased BODAC uptake, resulting in the highest adsorption capacity for ClO4- (1.08 mmol/g). This can be explained by the good balance between the decrease of steric hindrance and the formation of a hydrophobic interface because of adsorbed DDAC. In contrast, for a composite synthesized with the same ratio of DDAC to BODAC, the simultaneous-mixing method resulted in modified Mt with much poorer ClO4- removal performance than the sequential modification method because of the negligible contribution of DDAC to BODAC uptake by Mt. Moreover, a high binding affinity of ClO4- to the sequentially modified composite was obtained because of hydrophobicity of interlaced alkyl chains. (C) 2015 Elsevier Inc. All rights reserved.

Seawater flotation has been applied to mineral processing in areas located far from fresh water resources. However, as seawater has a detrimental effect on molybdenite floatability under alkaline conditions (pH &gt; 9.5), its application in the conventional copper and molybdenum (Cu-Mo) flotation circuit is hindered. A fundamental study of the effect of two divalent cations in seawater, Mg2+ and Ca2+, on the floatability of chalcopyrite and molybdenite is presented in this paper. Floatability tests showed that both MgCl2 and CaCl2 solutions depress the floatability of chalcopyrite and molybdenite at pH values higher than 9. Furthermore, Mg2+ exerts a stronger effect than Ca2+ owing to the adsorption of Mg(OH)(2) precipitates on the mineral surfaces, as indicated by dynamic force microscopy images. The floatability of chalcopyrite was significantly depressed compared with that of molybdenite in a 10(-2) M MgCl2 aqueous solution at pH 11. This phenomenon is likely due to the adsorption of hydrophilic complexes on the mineral surface, which reduces the surface hydrophobicity. A reversal of the zeta potential of chalcopyrite in MgCl2 and CaCl2 solutions at pH 11 and 8, respectively, indicated the adsorption of precipitates onto the surface. In contrast, the zeta potential of molybdenite decreased" continuously under the same conditions. The floatability test of chalcopyrite and molybdenite in mixed systems showed that selective separation of both minerals should be possible with the addition of emulsified kerosene to a 10(-2) M MgCl2 solution at pH 11. A mechanism is proposed to explain this phenomenon. (C) 2016 Elsevier Ltd. All rights reserved.

Biogenic birnessite (BB) is a stable form of manganese oxide. It is widely distributed in the natural environment and originates from microbial oxidation. It has potential applications in functional material fabrication because of its unique morphology. Using a microwave-assisted hydrothermal method, nano-sized lithium-ion sieves were prepared from BB with a short reaction time. A combination of sorption experiments and structural characterization was used to compare Li uptake by nanoparticles with that by microparticles. X-ray diffraction (XRD) patterns showed that the nano-and microparticles had similar fundamental structures, but the lattice parameter of nanopartides is smaller than micropartides. Mn K-edge X-ray absorption fine structure (XAFS) spectroscopy showed that the oxidation state of Mn increased from 3.50 to 3.69 with decreasing crystal size, and the Mn-Mn atomic distance decreased from 2.92 to 2.89 angstrom. Li extraction resulted in significant cleavage of the micropartide surfaces. The oxidation state of Mn increased to 4.0, and the Mn-Mn atomic distance decreased to 2.86 angstrom. XRD showed that dissolution of the polycrystalline phase of the nanopartides occurred during acid washing. However, the EXAFS spectrum was similar to that of the original material before acid washing. The specific surface areas and U-sorption capacities of the nano-sized lithium-ion sieves prepared from manganese carbonate were significantly higher than those of a similarly prepared micro-sized lithium-ion sieve. The results obtained in this work suggest that BB is a promising starting material for the energy-saving fabrication of functional materials for highly efficient Li recovery. (C) 2015 Elsevier B.V. All rights reserved.

The combustion characteristics and activation energy of the microwave irradiation (MI) treated lignite were investigated by thermogravimetric analysis at different heating rates. Effects of the changes in physicochemical properties (amounts of volatile matter and fixed carbon, specific surface area, and pore volume) on the combustion performance were also discussed. The activation energy was calculated using the Kissinger-Akahira-Sunose isoconversional method. The results showed that ignition temperature of the MI treated samples increased significantly relative to that of raw lignite, and it gradually increased with increasing MI time, indicating that MI treatment decreases the reactivity of lignite, which progressively decreases as MI time increases. The maximum combustion rates of the treated samples were higher than that of raw lignite, suggesting that MI treatment modifies the combustion intensity of Loy Yang lignite. Moreover, the combustion processes of samples treated by MI for 5 and 7 min were single rate-limiting step kinetics, whereas raw lignite and samples treated by MI for 3 and 9 min followed multistep kinetics. Average activation energy for sample treated using MI for 5 min was the maximum value, and it decreased with further increasing MI time because of the increased effect of diffusion. (C) 2016 Elsevier B.V. All rights reserved.

Hydroxylated calcined dolomite (HCD) is used as a mineralizer to immobilize borates by co-precipitation with hydroxyapatite (HAp). HCD sometimes includes appreciable quantities of MgO depending on the degree of hydroxylation of the calcined dolomite. In this work, the interfacial effects of MgO in HCD on the removal kinetics of borates were examined using Ca(OH)(2) and HCDs with different degrees of hydroxylation. As the fraction of MgO phases within the HCD increased, the borate immobilization rate stagnated because the formation of hydroxyapatite (HAp) was inhibited. This effect arose from the interaction of boric acid (H3BO3) with the MgO in HCD, followed by hydroxylation to cover the Ca(OH)(2) surfaces with newly formed Mg(OH)(2). In the presence of borate, the unstable intermediate [MgB(OH)(4)](+) complex was formed through ligand-promoted dissolution of MgO in the HCD. B-11 NMR spectra revealed that the stagnation in immobilization of tetragonal boron (NB) species was observed for up to 45 min, accompanied by the suppression of HAp formation. TEM images of the HCD suggested that Ca(OH)(2) was partially associated with MgO and Mg(OH)(2) phases within the HCD and hydroxylation of MgO led to a thin covering of the surface of Ca(OH2 with the newly formed gel phases comprising Mg(OH)(2)/H3BO3 that hinders the dissolution of Ca(OH)(2). However, when MgO was completely hydroxylated in the HCD this delay was not observed. This was supported by zeta potential measurements on the solid residues during co-precipitation. The results suggest that the degree of hydroxylation of the calcined dolomite in HCD markedly influences the co-precipitation kinetics of borates in industrial water treatment. (C) 2016 Elsevier B.V. All rights reserved.

OBJECTIVE: To investigate the bioreduction of toxic pentavalent vanadium [vanadate; V(V)] in the acidophilic, Fe(III)-reducing obligately heterotrophic bacterium, Acidocella aromatica PFBC. RESULTS: Although the initial lag-phase of growth became extended with increasing initial V(V) concentrations, the final cell density during aerobic growth of A. aromatica PFBC was unaffected by up to 2 mM V(V). While strain PFBC is an aerobe, growth-decoupled PFBC cell suspensions directly reduced V(V) using fructose, both micro-aerobically and anaerobically, under highly acidic (pH 2) and moderately acidic (pH 4.5) conditions. Bio reduced V(IV) was subsequently precipitated even under micro-aerobic conditions, mostly by encrusting the cell surface. An anaerobic condition at pH 4.5 was optimal for forming and maintaining stable V(IV)-precipitates. Recovery of approx. 70 % of V(V) from the solution phase was made possible with V(V) at 1 mM. CONCLUSIONS: The first case of direct V(V) reducing ability and its subsequent V recovery from the solution phase was shown in acidophilic prokaryotes. Possible utilities of V(V) bioreduction in acidic conditions, are discussed.

The formation of stable bubble-particle aggregates is essential to the froth flotation process. To form such aggregates, bubbles and particles must collide, the intervening liquid film must be drained below its critical rupture thickness, and three-phase contact (TPC) formation must occur. A good understanding of the interaction mechanism between bubbles and particles during collision and attachment is important. We herein investigated the effects of emulsified kerosene in a 0.01 M MgCl2 solution (a model seawater component) on bubble interactions with pure molybdenite (MoS2) and chalcopyrite (CuFeS2) surfaces. In 0.01 M MgCl2 at pH 6 and 11, kerosene retarded the bubble surface mobility and reduced the bubble rise velocity. In the presence of kerosene at pH 6, the TPC formed more rapidly on both mineral surfaces. This was due to the increase in surface hydrophobicity caused by kerosene. In addition, TPC formation was more rapid on the molybdenite surface than on the chalcopyrite surface due to the effect of the adsorbed kerosene and the low surface homogeneity of molybdenite. Finally, floatability tests demonstrated that the separation of molybdenite and chalcopyrite should be possible by adding emulsified kerosene in a 0.01 M MgCl2 solution at pH 9. (c) 2016 Elsevier B.V. All rights reserved.

Catalytic effects of silver on the dissolution of arsenic-containing copper sulfides such as enargite in acidic media were investigated. Leaching experiments showed that silver increased the enargite dissolution rate, and that the dissolution behavior was potential-dependent. The addition of silver ions and silver sulfide greatly enhanced enargite dissolution. Such behavior can be explained based on the following reaction model: enargite dissolution is enhanced by silver as the silver ions remove the hydrogen sulfide produced during enargite reduction, giving the more amenable copper sulfide. Thermodynamic calculations suggested that the addition of silver ions and controlling the potential would maintain a high enargite dissolution rate. Leaching experiments were therefore performed with the addition of silver sulfide and potential control using an automatic titration apparatus. Experimental results showed that a combination of these two factors gave high enargite dissolution; i.e., 75% copper was dissolved in 24 hat 0.750-0.850 V vs. the standard hydrogen electrode at 303 K. (C) 2016 Elsevier B.V. All rights reserved.

Needle- and sponge-shaped hydroxyapatite (HAp) particles were synthesized from calcined tuna fish bone (Tn1000) and commercially available HAp reagent (ChemHAP) by a urea-assisted hydrothermal treatment using 0.1-1.0 M urea solution at 160 degrees C for 3 h. The Sr2+ sorption capacity of the synthesized HAp was also investigated using 0-50 mM Sr2+ solution at 25 degrees C for 72 h to evaluate its performance as a sorbent for environmental remediation. Sponge-shaped HAp was formed under hydrothermal conditions with a urea concentration of 1.0 M. With decreasing urea concentration, the morphology of HAp changed from sponge-shaped to needle shaped crystals, regardless of the starting material. Some calcium carbonate and/or beta-tricalcium phosphate impurities were formed from Tn1000 at 0.1-0.5 M urea concentration. The Sr2+ sorption mechanism of the synthesized HAp was estimated using Ca ion-exchange reaction and precipitation of SrCO3. The sponge-shaped HAp crystals, which had high specific surface area and CO32- content, exhibited a large ion-exchange capacity with Sr2+ In contrast, the ion-exchange ratio of needle-shaped HAp dramatically decreased with increasing initial Sr concentration. No clear difference in Sr2+ sorption behaviour caused by the choice of HAp synthesis starting material was observed. These results indicate that the Sr sorption mechanism of HAp is influenced by not only its composition but also its crystal morphology. (C) 2016 Elsevier B.V. All rights reserved.

© 2016 Elsevier B.V. All rights reserved. Saprolitic ores from Sulawesi Island (SS ore) contain serpentine and goethite as major minerals, whereas the main minerals in saprolitic ore from Halmahera Island (SH ore) are talc and goethite. Most of the nickel was incorporated in a magnesium-silica-containing mineral. The effects on nickel extraction of leaching temperature, citric acid concentration, and ore particle size were determined to investigate the leaching performances and leaching kinetics of the two saprolitic ores. Nickel leaching efficiency from SS ore is always higher than that from SH ore under the same leaching conditions. The mineral contents of the ores significantly affected the leaching performances and mineral dissolution behaviors of the samples. The results of nickel leaching efficiency and analysis of the solid residues suggest that all dissolved nickel originated from serpentine, which is more easily leached than goethite and talc. The rate of nickel extraction for SS ore was faster than that for SH ore. Nickel leaching from SS ore and SH ore followed the shrinking-core model and was controlled by diffusion of a reactant or product through the solid product layer.

Here we describe the application of an in-capillary enzyme assay using micellar electrokinetic chromatography (MEKC) in the determination of enzyme activity in a crude culture medium containing lignin peroxidase released from Phanerochaete chrysosporium (P. chrysosporium). The method consists of a plug-plug reaction between lignin peroxidase and its substrate, veratryl alcohol, the separation of the product, veratraldehyde, from the other components including the enzyme and the culture medium, and the determination of the enzyme activity from the peak area of veratraldehyde produced by the plug-plug reaction. This method is more sensitive than conventional spectrophotometry since the background originates from the enzyme and the culture medium can be removed via MEKC separation. Veratraldehyde was separated at-10 kV in a background electrolyte containing 50mM tartrate buffer (pH 2.5) and 50 mM sodium dodecyl sulfate (SDS) after a plug-plug reaction in the capillary for 5 min. The calibration curve of veratraldehyde was linear up to 4pmol (500 mu M) with a limit to quantification of 0.026 pmol (3.211 mu M) (SN = 10). The activity of lignin peroxidase was directly measured from the peak area of veratraldehyde. The activity of lignin peroxidase released from P. chrysosporium into the medium for 7 days was successfully determined to be 3.40 UL-1. (C) 2016 Elsevier B.V. All rights reserved.

Adsorption of perchlorate (ClO4-) onto hexadecylpyridinium-modified montmorillonite (OMt) was investigated by in situ and ex situ methods. For the in situ method, ClO4- was initially bound by hexadecylpyridinium (HDPy+) in the form of HDPy-ClO4 which together with the excess HDPy+ were simultaneously captured by Mt. The ex situ strategy was performed by adding synthesized OMt into ClO4- bearing solution, where conventionally dried OMt (II-OMt) and innovative OMt (I-OMt) without drying and washing procedure were compared as adsorbents. The adsorption capacity of CLOT and amount of HDPy released into equilibrium solution were evaluated, where surfactant release was rarely addressed in previous publications. I-OMt showed relatively high adsorption capacity of ClO4- and negligible release of HDPy. The lower adsorption capacity of ClO4- onto II-OMt was caused by the washing procedure which removed the unstably anchored HDPy. Inhibition of HDPy release of I-OMt was explained by reconfiguration of HDPy after ClO4- adsorption as supported by results of X-ray diffraction and attenuated total reflection Fourier transform infrared spectroscopy. In addition, for anion adsorption onto conventionally synthesized OMt, the difference between the amounts of released counter ion and that of entrapped target anion is generally ignored. Such phenomenon was critically considered in this study, and the results showed that the difference between adsorbed ClO4- and released Cl- decreased with an increase of HDPy loading and was more significant in I-OMt. This is rationalized by the desorption of HDPy+ and formation of HDPy-ClO4- according to the results of C-13 nuclear magnetic resonance spectra and the adsorption energy evaluated by the Dubinin-Radushkevich model. (C) 2016 Elsevier B.V. All rights reserved.

Co-precipitation of borate in a wide range of concentration with hydroxyapatite (HAp) was investigated using Ca(OH)2 as a mineralizer in the presence of phosphate. The sorption data of borate was fitted to Freundlich model. The maximum sorption density of B/Ca to maintain a mono-phase of HAp was found around 0.40. In higher B concentrations, borate was still immobilized, however, the crystalization of hydroxyapatite was inhibited, where the solid residues were accompanied with amorphous CaB2O4, as well as HAp. Based on 11B-NMR and elemental analysis for solid residues in addition to solution chemistry, the removal mechanism of high concentration borate can be explained by the surface complexation of triborate on Ca(OH)2, subsequently decomposition of triborate into monoborate to release [CaB(OH)4]+ and B(OH)4 -, followed by co-precipitation with HAp. These tetragonal B species were immobilized in the solid residues including amorphous HAp. During the process there was a trend to eliminate carbonate from the solid phase. TEM images suggested that the HAp particles precipitated at room temperatures were in a fibrous shape consisting of a number of short rods when borate species are not added. When borate species were immobilized, the HAp particles have gotten swelled with losing fibrous shapes. When further higher borate concentrations were encapsulated in co-precipitated products, the morphologies were dramatically changed, that is, nano-sized and less crystalline HAp particles were enveloped by possibly amorphous CaB2O4.

The separation of a spent sorbent from treated water after remediation is one of the major difficulties associated with industrial scale water treatment methods. Fe3O4 particles offer an easy magnetic method for the separation of used sorbent from water. Due to its low sorption capacity, magnetic Fe3O4 particles were first modified with Mg2Al-NO3-LDH prior to use in phosphate remediation. The Fe3O4/Mg2Al-NO3-LDH composite materials showed a maximum sorption capacity of 33.4 mgP/g while Fe3O4 particles alone recovered only 4.6 mgP/g. The kinetics of phosphate sorption onto Fe3O4/Mg2Al-NO3-LDH follows the pseudo-second order kinetic model supported by the best linear regression coefficient value (R2 - 1.00). Sorption isotherm studies indicated that it follows the Langmuir monolayer sorption isotherm. The effect of pH and competing anion studies indicate that this material is highly efficient in a wide pH range (pH 3-10). Selective sorption of phosphate on Fe3O4/Mg2Al-NO3-LDH was observed in the presence of excess sulfate, as well as from sea water enriched with phosphate. Fe3O4/Mg2Al-NO3-LDH composite material offers easy separation of spent sorbents due to magnetic property. The retention of sorption capacity in a wide pH range, and selectivity in the presence of competing anion, as well as from sea water suggests that these composite magnetic materials will be effective for wastewater remediation.

Hydroxylated calcined dolomite (HCD) is practically used as a mineralizer to immobilize fluoride by co-precipitation with hydroxyapatite (HAp) and precipitation as fluoroapatite (FAp). It has an advantage to remove fluoride without stagnation, which is always observed with Ca(OH)(2) alone. HCD includes a certain content of MgO and Mg(OH)(2) as well as Ca(OH)(2). In the present work, the mechanism to explain the enhancing role of Mg components on removal kinetics of fluoride was aimed to elucidate. Nano-domain observation approaches were conducted by TEM when Ca(OH)(2) is added as a Ca source in the presence of different Mg2+ concentrations, instead of HCD. With increase in Mg2+ concentrations in the presence of Ca (OH)(2), removal rate of fluoride was enhanced. The enhancement was also observed with HCD. Mg2+ and [Mg(OH)](+) species, which can be derived from HCD, are adhered to the negatively charged c-plane of freshly formed amorphous HAp/FAp and CaCO3. As a result, the surface of Ca(OH)(2) particles are gotten rid of hetero-coagulation with HAp/FAp and CaCO3 in the presence of Mg2+ and [Mg(OH)](+) species, and maintained to release Ca2+ and OH- ions, facilitating to precipitate HAp and FAp for immobilization of fluoride. Without Mg2+ additives the Ca(OH)(2) surfaces are blocked by insoluble HAp/FAp through hetero-coagulation. This interpretation is also supported by TEM observation, which is well consistent with XRD results. The findings indicate that MgO and Mg(OH)(2) contents in HCD influence the removal kinetics of fluoride by (co-)precipitation as apatites in industrial water treatment. Understanding the surface science in nano-domain is important in parallel reactions of dissolution and precipitation. (C) 2015 Elsevier B.V. All rights reserved.

Seawater has been reported to depress molybdenite in a copper-molybdenum (Cu-Mo) flotation process at high pH due to the precipitation of Mg(OH)2. Meanwhile, to improve mineral recoveries, collectors are usually added into the flotation cells, thus adding the complexity to the mechanism of bubble-particle interactions involved in Cu-Mo flotation. Therefore, understanding the interaction mechanism in seawater flotation and in the presence of collectors is important to explain the minerals depression. The present work investigated the effect of kerosene on the bubble collision and attachment to pure chalcopyrite and molybdenite surfaces in MgCl2 solution as one of the seawater major components at pH 6 and 11. Mineral surfaces were characterized using atomic force microscopy (AFM). In addition, minerals floatability in the same system were tested in a column flotation. The study of bubble-particle interactions shows that following several collisions, bubble could displace the intervening liquid layer on the mineral surfaces, forming a three-phase contact (TPC). A TPC formed more rapidly in the presence of emulsified kerosene in a 0.01 M MgCl2 solution at pH 6 for both minerals. The reason is kerosene increased the surfaces hydrophobicity and destabilized the intervening liquid layer on the surfaces. Moreover, the average time required to form a TPC was shorter on molybdenite surface. This can be attributed to the effect of adsorbed kerosene on molybdenite surface and molybdenite surface roughness.

Selective flotation of chalcopyrite and molybdenite was studied using various surface treatment methods such as electrolysis, ozone treatment, and plasma. Oxidation via electrolysis method indicated that only chalcopyrite surface is affected by electrolysis due to conductivity difference with molybdenite. Oxidation treatments and XPS analyses indicated that chalcopyrite became hydrophilic due to deposition of oxidized iron on its surface. Various oxidizing methods also showed that chalcopyrite was selectively oxidized and this can apply selective flotation of chalcopyrite and molybdenite. The possible mechanisms are proposed in this work based on surface analyses and thermodynamic calculations.

Recycling high-purity rare earths from the waste in fluorescent lamps will assist in preserving rare earth resources. However, the present recovery from the waste in fluorescent lamps is very low at around 30%, and most waste fluorescent lamps are reclaimed. In this study we attempted to reduce one cause of difficulty in recycling lamps, namely the identification of rare earths in plastic-covered lamps, which is conventionally executed by human operators. Using the Acoustic Emission (AE) signal of the collision sound between lamps and an AE sensor head, we first carried out waveform analysis, and frequency analysis using the discrete Fourier transform. We extracted six feature values for each analysis and differentiated the plastic-covered lamps using thresholds. The least error rates were 4.85% and 6.67% for the waveform and frequency analyses, respectively. Second, we applied discriminant analysis on the six feature values from each analysis, resulting in error rates of 3.03% and 5.45%, respectively. Third, we extracted six feature values from the time-frequency analysis using the discrete Wavelet transform and Fractal dimensioning, and applied discriminant analysis on the six feature values, resulting in an error rate of 4.24%. Finally, we examined all the results from the three analyses to find the best combination of feature values, applied discriminant analysis to 12 feature values from the time analysis and time-frequency analysis, and succeeded in reducing the error rate to 0%.

The changes in the gaseous, liquid, and solid products obtained from hydrothermally treated lignite and hydrothermally treated solid products treated by the following mechanical expression were investigated. Furthermore, a microscopic description of the changes was present. Gaseous, liquid, and solid products were characterized by gas chromatography, total organic carbon analyzer, inductively coupled plasma atomic emission spectroscopy, high-performance liquid chromatography, and Fourier transform infrared spectrometer, respectively. The results showed that at temperatures above 173 degrees C for hydrothermal treatment, freezable water, and some organic and inorganic compounds were removed from lignite, and acidic groups first dissolved and decomposed at 100 degrees C. For the following mechanical expression treatment, freezable and nonfreezable water and organic and inorganic compounds were removed, and the concentration of acidic groups changed little. Within temperatures range 175-250 degrees C, for hydrothermal treatment, nonfreezable water and inorganic and organic compounds continued to be removed, and the detection of CO2 is because of decarboxylation. For the following mechanical expression treatment, the main removed water was nonfreezable water, and changes in organic and inorganic compounds, acidic groups, and volatile matter were similar to that of samples treated by mechanical expression at temperatures below 173 degrees C.

The changes in the hydrogen bonds (HBs) of three types of Indonesian lignite during low-temperature heating were investigated. The amount of water loss was determined by weighing the samples before and after heating in an oven. The changes in the number of the different types of HBs were determined using Fourier transform infrared spectroscopy coupled with types of water in lignite. The number of peak positions and absorption bands in each spectrum was determined by curve-fitting analysis with a Gaussian function. The quantified integrated area of aromatic hydrogen atoms was used to accurately investigate the changes in the HBs. The results show that at low temperatures (T50 degrees C), free water is mainly removed, and the HBs broken are those between free water molecules. However, at medium temperatures (50 &lt;T 100 degrees C), bound water is mainly removed. The number of HBs significantly changes because of the breaking of bound water molecule HBs and bound water cluster-carboxyl group HBs, and the formation of nonfreezable moisture HBs. At high temperatures (100 &lt;T&lt;125 degrees C), nonfreezable moisture can be released. The number of HBs changes as a result of competition between the removal of nonfreezable moisture and the increase in the number of carboxyl groups. At higher temperatures (T125 degrees C), the moisture remaining in lignite is thermal decomposition moisture. In addition, the rate of decomposition of carboxyl groups is higher than the rate of generation, which means that the number of HBs markedly decreases at higher temperatures.

© 2015 Elsevier Ltd. All rights reserved. Comparison effect of chemical citric acid and other leaching reagents including inorganic acid and other organic acid on nickel extraction from low-grade Indonesian saprolitic ores was evaluated. Two saprolitic ores from two different mining areas (Sulawesi Island and Halmahera Island) in Indonesia were used to investigate the leaching performance and mineral dissolution behaviors of different ore samples using different leaching reagents. Leaching was performed using citric, sulfuric, nitric, hydrochloric, lactic, and oxalic acids. The saprolitic ore from Sulawesi Island (SS) has higher serpentine and lower goethite contents than the saprolitic ore from Halmahera Island (SH). These differences significantly affect the leaching performances and metal dissolution behaviors. Citric acid and sulfuric acid were more effective than other acid solutions for nickel extraction from both samples. Citric acid was very effective for dissolving nickel from serpentine, but did not recover nickel from goethite. In contrast, inorganic acids, namely sulfuric, nitric, and hydrochloric acids, can extract nickel from lateritic ores by dissolving goethite as well as serpentine, but the nickel recoveries achieved with sulfuric acid were higher than those achieved with other inorganic acids. A comparison of the leaching performances of the two samples shows that nickel recovery from SS was higher than that from SH when citric acid leaching was used, but the samples gave similar nickel recoveries in all inorganic acid and lactic acid leaching processes. Moreover, oxalic acid is the least effective reagent for nickel extraction from both samples, because of nickel oxalate precipitation after nickel dissolution. In addition, the effect of a sulfuric acid-citric acid mixture on the nickel dissolution rate was investigated to confirm the individual influences of citric acid and sulfuric acid on the leaching behavior of each sample. The results show that an increase in the amount of sulfuric acid affected the dissolution rate of nickel in leaching of SH much more than that in leaching of SS. In general, the effect of citric acid in the mixture of sulfuric acid and citric acid is attractive. Moreover, citric acid offers not only high nickel recovery and high selectivity of leaching but also an environmentally safe process and low acid consumption.

Measurements of equilibrium water contents (EWCs) in samples obtained from hydrothermal treatment (HT) and HT coupled with mechanical compression (HT-MC) were undertaken across a range of relative humidities (RHs) to investigate the performance of EWC and its mechanism. The changes in the concentrations of carboxyl groups and mesopore volume were measured by an improved barium ion exchange and N-2 adsorption-desorption isotherms methods, respectively. The results showed that EWCs decreased with progressively severe HT and HT-MC conditions and EWCs of HT-MC samples were lower than those of HT samples, indicating that HT and HT-MC can upgrade lignite by reducing water loading capacity and HT-MC was better than HT. At low RHs (RH &lt;= 10%), the factor that controls EWC is water molecules-active sites interactions and one to two water molecules are associated with each carboxyl group, while at medium RHs (10 &lt; RH &lt;= 92%) the amount of monolayer water and mesopore volume gain in significance and ca. two multilayer water molecules are bound to each monolayer water molecule. At high RHs (RH &gt; 92%), EWC is determined by comprehensive factors such as macropores and cracks. Furthermore, EWC can be either higher or lower than residual water content (RWC) based on the RH within a threshold residual water level (ca. 5 to 16%). EWC was generally higher than RWC below a RWC of ca. 5% and the opposite relationship was observed for samples with RWC above ca. 16%. These provide information for the operation of lignite dewatering technique, the control of its water re-adsorption, and storage.

© 2015 Elsevier B.V. Pyrite is a mineral sulfide found extensively in acid mine drainage; this is one of the most serious environmental problems in the mining industry. Suppression of pyrite oxidation via carrier microencapsulation (CME) with silicon (Si) and organic carriers has been proposed. In the present study, use of the hydrothermal treatment liquid (HTL) produced from low-rank coal as a carrier in CME was investigated. In dissolution tests for 51 days with pyrite and iron-oxidizing bacteria, treatment with a mixture of HTL and a silicon reagent (Si-HTL) lowered the ferric ion concentration and limited bacterial attachment compared with untreated pyrite. This might be caused by catechol present in the HTL. A mixture of catechol and a silicon reagent (Si-Cat) was also used, and the coatings obtained using Si-HTL and Si-Cat were compared. The electrochemical behavior of the treated pyrite samples showed oxidative decomposition of the Si-Cat complex and formation of an encapsulating layer at 690 mV for Si-HTL and 550 mV for Si-Cat. The two semi-circular curves in the Nyquist plot simulations showed that the total impedances of the treated pyrite samples increased. Microscopic observations showed that the oxidative layer was silica rich. These data indicate that a silica-quinone coating is created and the pyrite oxidation rate can be suppressed by pretreatment with either Si-HTL or Si-Cat for 1 h.

The removal mechanism of polymeric borate by calcined layered double hydroxides is not clear. In this work, layered double hydroxides containing different divalent metals were synthesized and calcined to produce calcined layered double hydroxides (Zn-, Mg-, and Ca-CLDH). Then, Zn-, Mg-, and Ca-CLDH were applied to remove polymeric borate. Zn-CLDH showed better performance for the removal of borate than Ca-CLDH, and hardly any borate was removed by Mg-CLDH. Based on the characterization results, the detailed removal process of polymeric borate by different calcined layered double hydroxides is discussed. Because there is little H3BO3 that can act as a trigger, and ligand promoted dissolution of the complex H3BO3 and MgO is prevented. Therefore, Mg-CLDH could not transform to the layered structure to immobilize the borate. For the Zn-CLDH, Zn-CLDH transformed into Zn-LDH, and polymeric borate was absorbed into the interlayer of layered double hydroxides, which is the dominant mechanism of borate removal by Zn-CLDH. Reconstruction of the Ca-LDH from the Ca-CLDH was more rapid than the other calcined layered double hydroxides. However, formation of borate-containing ettringite was the main removal mechanism in the first stage. With increasing reaction time, the reaction between CO32- and Ca2+ released from ettringite, and the regeneration of Ca-LDH to form CaCO3 were the main reasons for borate removal in the second stage. (C) 2015 Elsevier B.V. All rights reserved.

In this paper, prevention of pyrite oxidation by carrier microencapsulation (CME) was investigated. A possible layer structure was suggested following analysis with electrochemical and surface analysis techniques. Electrochemical study of treated pyrite samples showed that treatment with silicon catechol (Si-Cat) for 6h at an initial pH of 9.5 gave the best barrier properties and suppression of the samples. Scanning electron microscopy with energy-dispersive X-ray, and Fourier transform infrared (FUR) analyses confirmed the presence of a silicate layer on the surface of treated pyrite. X-ray photoelectron spectroscopy indicated that the coating layers on the treated pyrite samples consisted of a network of Fe-O-Si and Si-O-Si units bonded to the surface of pyrite. The Si-O-C asymmetric stretching mode was also observed in FTIR spectra. Detailed spectroscopic analyses confirmed the formation of a silicate polymer on a silica quinone layer, which resulted in the effective suppression effect shown by Si-Cat-treated pyrite at increasing pH.

A high adsorption capacity (0.90 mmol/g) of perchlorate was achieved on organo-montmorillonites (organo-MMTs) through modification by benzyloctadecyldimethylammonium chloride (BODMA-Cl), which typically possesses a long alkyl chain and a benzene ring. With increase in the amount of BODMA-Cl added, the XRD and FTIR results showed that the BODMA(+)/BODMA-Cl achieved a lateral bilayer, pseudo-trilayer and tilted paraffin-like bilayer configurations in the MMT interlayer space with improvement of ordered arrangement, and the formation of bilayers and/or micelles on the external surface also was demonstrated by TG-DTA and zeta potential curves. The EDX spectra of resultant products and adsorption isotherms of perchlorate on organo-MMTs suggested that a larger content of BODMA-Cl resulted in synthesized adsorbent with a greater adsorption capacity, because neutral BODMA-Cl is predominantly responsible for ion exchange with perchlorate. The maximum adsorption capacity was attained not only by enhanced affinity between BODMA(+) and metallic layer of MMT, but also by increasing density of intercalated BODMA-Cl which is caused by hydrophobic interactions through long alkyl chains and pi-pi interactions through benzene rings among BODMA+/BODMA-Cl. It was also emphasized that the high adsorption capacity of perchlorate on organo-MMTs was achieved with a rapid adsorption rate and stably maintained against variations in temperature, initial solution pH and co-existing competitive anion. (C) 2015 Elsevier B.V. All rights reserved.

A series of organo-montmorillonites (organo-Mt) was synthesized using various cationic surfactants with different alkyl-chain lengths, head groups, and alkyl-chain numbers, which were systematically examined for perchlorate adsorption. The products were characterized by the specific surface area, field-emission scanning electron microscopy, X-ray diffraction, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy. In addition, the surfactant loadings and surface charges were investigated by CHN analysis and zeta potential measurements. The greatest adsorption capacity of 0.95 mmol/g-composite was obtained on benzyloctadecyldimethylammonium-modified Mt. Increasing the alkyl-chain length significantly enhanced the capacity and selectivity for perchlorate adsorption, but resulted in decrease of adsorption rate. Compared with trimethylammonium and pyridinium with the same alkyl-chain length, the benzyldimethylammonium as a head group showed better performance in terms of adsorption capacity and selectivity of perchlorate because of higher hydrophobicity. Moreover, increasing the alkyl-chain number decreased adsorption rate, but enhanced adsorption capacity, because of dense packing of alkyl chains and high driving force for entrapment of counter ion-accompanying surfactant. The perchlorate adsorption performance of organo-Mt was synergistically influenced by the alkyl-chain length, head group and alkyl-chain number of the surfactants used for modification. (C) 2015 Elsevier B.V. All rights reserved.

The changes in the hydrogen bonds (HBs) of Loy Yang lignite during low-temperature pyrolysis were investigated. The water content of all of the samples was determined by weighing the samples before and after heating in an oven. The changes in the number of the different types of HBs were determined using diffuse reflectance Fourier transform infrared spectroscopy considering the forms of water in lignite. The number of absorption bands, their peak positions, and the area of each peak in each spectrum were determined by curve-fitting analysis with the mixed Gaussian and Lorentzian function. The quantified integrated area of aromatic hydrogen atoms was used to accurately investigate the changes in the HBs. The results showed that the freezable and nonfreezable water contents of the total water weight in raw lignite were 84.8% and 15.2%, respectively. At low temperatures (T &lt;= 100 degrees C), the main removed water was freezable water. The number of OH-lignite interactions decreased compared with raw lignite, which can be attributed to the breaking of bound-water-cluster-lignite HBs. The removal of free water induced a decrease in the number of OH-OH interactions, and then the transition of free water to bound water increased the number of OH-OH interactions. At medium temperatures (100 &lt; T &lt; 200 degrees C), bound and nonfreezable water were mainly removed. The number of OH-lignite and OH-OH interactions changed because of the competition between the transition of bound water to nonfreezable water and desorption of bound and nonfreezable water. At higher temperatures (200 &lt; T &lt;= 250 degrees C), nonfreezable water was the main form of water removed, and carboxyl groups started to drastically pyrolyze. OH-lignite interactions changed as a result of the removal of nonfreezable water and the pyrolysis of carboxyl groups.

Mg-Al bimetallic oxides produced via the calcination of hydrotalcite-like compounds ([(Mg0.75Al0.25(OH)(2)](A(n-))(0.75/n)center dot mH(2)O, where A is an anionic species) exhibited high potential for the removal of boron from aqueous solutions. X-ray diffraction patterns for the produced bimetallic oxides revealed that MgO was the primary phase within the range of investigated calcination temperatures. In addition, B-11 NMR spectral analyses indicated that the Mg-Al bimetallic oxides captured trigonal B (B-[3]) and tetrahedral B (B-[4]) after the sorption of boron, regenerating hydrotalcite-like compounds. As the initial concentration of boron increased, the percentage of tetrahedral B-[4] in solid residues after the sorption of boron increased. The B-[4]/B-[3] ratios in the solid residues increased with time along with the regeneration of hydrotalcite-like compounds. Furthermore, the Mg-Al bimetallic oxides produced from hydrotalcite-like compounds were more favorable than other bimetallic oxides and effective than single-phase MgO produced from MgCO3 at the same temperature, indicating that Mg-Al bimetallic oxides are stable materials with the potential for use in the remediation of contaminated sites and water. (C) 2015 Elsevier B.V. All rights reserved.

Copyright 2015, Society for Mining, Metallurgy & Exploration Inc. The kinetics of leaching of a saprolitic ore from Indonesia by citric acid solution under atmospheric pressure was investigated. An examination of the effects of leaching temperature, citric acid concentration, pulp density and ore particle size on the dissolution rate of nickel found that they all had significant influence on the rate. The highest nickel recovery (95.6 percent) was achieved under the leaching conditions of ore particle size of 212-355 microns, citric acid concentration of 1 M, leaching time of 15 days, pulp density of 20 weight/volume percent, leaching temperature of 40°C and shaker speed of 200 rpm. The shrinking core model was found to be appropriate for describing the leaching kinetics of this ore in citric acid solutions at atmospheric pressure. The experimental data were well interpreted by this model with rate of reaction controlled by diffusion through the solid product layer. Using the Arrhenius expression, the apparent activation energy for nickel dissolution was evaluated as 12.38 kJ/mol. Finally, on the basis of the shrinking core model, a proposed empirical kinetic model for the leaching of nickel from this Indonesian saprolitic ore was expressed as a mathematical model, which was verified as consistent with the observed experimental results.

© 2015, Copyright © Taylor & Francis Group, LLC. Effectiveness of different pure and mixed cultures of three moderately thermophilic, extremely acidophilic bacterial strains (Acidimicrobium ferrooxidans ICP, Sulfobacillus sibiricus N1, Acidithiobacillus caldus KU) were investigated for biooxidation of highly refractory polymetallic gold ore concentrates. Despite of its complex mineralogy and the presence of a mixture of potentially inhibitory metals and metalloids, the concentrate was readily dissolved in defined mixed cultures including both iron and sulfur oxidizers, releasing as much as 80% of soluble Fe and 61% of soluble As. Factors to affect microbial mineral dissolution efficiencies (i.e. microbial As(III) oxidation ability, formation of secondary mineral precipitation (e.g. jarosite, elemental sulfur, scorodite, anglesite), and microbial population dynamics during biooxidation) were studied, based on which roles of individual microbes and their synergistic interactions during biooxidation were discussed. Applying the biooxidation pretreatment using the most efficient mixed cultures containing all three strains significantly improved the recovery of both Au (from 1.1% to 86%) and Ag (from 3.2% to 87%). Finally, this study provides one of the very few available comparisons of the effectiveness of different pretreatment techniques for refractory gold ore concentrates: Compared with other abiotic pretreatment approaches (roasting, pressure oxidation, and alkali dissolution), biooxidation was shown to be one of the most effective options in terms of the recovery of Au and Ag.

Layered double hydroxides (LDHs) have the property to remove different anions due to their high anion exchange ability. Synthesis of LDHs using natural earth resources is highly desired in environmental concern. Single phases of Mg&lt
inf&gt
2.3&lt
/inf&gt
Al-, Mg&lt
inf&gt
2.9&lt
/inf&gt
Al- and Mg&lt
inf&gt
4&lt
/inf&gt
Fe-LDHs were successfully synthesized from calcined dolomite (CaO·MgO) as Mg source as well as precipitant through optimization of microwave-assisted hydrothermal aging. Sorption data of arsenate over these LDHs were well fitted to non-linear Langmuir adsorption isotherm. Among the materials studied Mg&lt
inf&gt
2.3&lt
/inf&gt
Al-LDH showed not only superior arsenate sorption capacity but also superior coverage of arsenate. This suggests there are some additional factors other than charge density to influence the sorption density. Mechanism of arsenate sorption was probed by different characterization techniques of solid residues after sorption such as X-ray diffraction, X-ray photoelectron spectroscopy, Fourier transformed infrared, extended X-ray absorption fine structure analysis. Sorption of arsenate over MgAl-LDHs mediated through ion-exchange as well as surface adsorption, depending on charge density of metallic layers. However, sorption of arsenate over MgFe-LDH occurred through ion-exchange along with the formation of inner surface complexes, which leads disturbed layer stacking.

LDHs with different divalent metals (Zn-LDH, Mg-LDH and Ca-LDH) have been synthesized and produced calcined LDHs (Zn-CLDH, Mg-CLDH and Ca-CLDH) for borate removal. Based on XRD, SEM, BET, Al-27 NMR, CO2-TPD, and B-11 NMR, detailed characterization of different CLDHs before and after reaction with the boron species was systematically performed. The surface area, basicity and the particle charge of the different CLDHs, which are related to the hydration and regeneration, were markably influenced by the nature of the divalent metals. Transformation of crystal phases and the types of boron species adsorbed by the different CLDHs varied as time changed. The regeneration of Ca-CLDH required the shortest time. However, Ca-LDH decomposed to release Ca2+ ions, forming ettringite with borate. Zn-CLDH also rapidly transformed into Zn-LDH. During this reconstruction, B(OH)(4)(-) was intercalated into the interlayer of ZnLDHs, which is the predominant mechanism of borate removal by Zn-CLDH. Increase in the initial pH caused a competition between borate and OH- so that the removal efficiency of borate by Zn-CLDH decreased. For Mg-CLDH, surface complexation and electrostatic attraction were included in the first stage, immobilizing boric acid into mg(OH)(2) and attracting borate as interlayer anionic species into the new forming Mg-LDHs in the second stage. (C) 2015 Elsevier Inc. All rights reserved.

Hydrocalumite (Ca-Al-layered double hydroxide (LDH)) was prepared and applied for the removal of borate. The properties of Ca-Al-LDH calcined at different temperatures were diverse, which affected the sorption density and mechanism of boron species. The sorption density increased with increase in calcined temperature and the sample calcined at 900 degrees C (Ca-Al-LDH-900) showed the maximum sorption density in this work. The solid residues after sorption were characterized by B-11 NMR, Al-27 NMR, SEM, and XRD to investigate the sorption mechanism. Dissolution-reprecipitation was the main mechanism for sorption of borate in Ca-Al-LDH. For Ca-Al-LDH calcined at 300 and 500 degrees C, regeneration occurred in a short time and the newly forming LDHs were decomposed to release Ca2+ ions and formed ettringite with borate. Two stages occurred in the sorption of boron by Ca-Al-LDH calcined at 900 degrees C. In the first stage, boron species adsorbed on the alumina gel resulting from the hydration of calcined products. In this stage, borate was included as an interlayer anion into the newly forming LDHs in the following stage, and then immobilized as HBO32- into the interlayer, most the LDHs. (C) 2015 Elsevier B.V. All rights reserved.

The extremely acidophilic, Fe(III)-reducing heterotrophic bacterium Acidocella aromatica strain PFBC was tested for its potential utility in bioreduction of highly toxic heavy metal, hexavalent chromium, Cr(VI). During its aerobic growth on fructose at pH 2.5, 20 µM Cr(VI) was readily reduced to Cr(III), achieving the final Cr(VI) concentration of 0.4 µM (0.02 mg/L), meeting the WHO drinking water guideline of 0.05 mg/L. Despite of the highly inhibitory effect of Cr(VI) on cell growth at higher concentrations, especially at low pH, Cr(VI) reduction activity was readily observed in growth-decoupled cell suspensions under micro-aerobic and anaerobic conditions. Strain PFBC was not capable of anaerobic growth via dissimilatory reduction of Cr(VI), such as reported for Fe(III). In the presence of both Cr(VI) and Fe(III) under micro-aerobic condition, microbial Fe(III) reduction occurred only upon complete disappearance of Cr(VI) by its reduction to Cr(III). Following Cr(VI) reduction, the resultant Cr(III), supposedly present in the form of cationic Cr (III) (OH2) 6 (3+) , was partially immobilized on the negatively charged cell surface through biosorption. When Cr(III) was externally provided, rather than microbially produced, it was poorly immobilized on the cell surface. Cr(VI) reducing ability was reported for the first time in Acidocella sp. in this study, and its potential role in biogeochemical cycling of Cr, as well as its possible utility in Cr(VI) bioremediation, in highly acidic environments/solutions, were discussed.

A rapid and efficient method based on microwave-assisted treatment has been developed for preparing layered double hydroxides (LDHs) using natural dolomite as a magnesium source. The aging temperature was 120 degrees C and the total synthetic time was only within 6 h. The product was fully characterized by elemental composition, powdery X-ray diffraction, and scanning electron microscopy, to be highly pure hydrotalcite with a flaky shape. The synthesized adsorbent exhibited the sorption capacity of 1.34 mmol/kg which is comparable to boron-specific resin. Based on B-11 MAS NMR and XRD results, the principal mechanism for borate immobilization on the LDHs is ion-exchange followed by transformation of polyborate into monoborate in a process of drying.

Atomic hole type of bio-templated lithium ion sieve was synthesized to supply for adsorption of Li⁺ in simulated geothermal waters at 70<tt>℃</tt>. Sorption data was fit to linearlized Langmuir isotherm and the maximum sorption density was not largely influenced by coexisting ions including larger amounts of Na⁺ in simulated geothermal waters. The sorption kinetic data was fit to the first order rate, and the kinetic constant was not also influenced by coexisting ions as mentioned above. Temperature elevation accelerated the sorption rate. The activation energy obtained from Arrhenius plots was estimated 4.34 ~ 4.67 kcal/mol, implying that the adsorption is controlled by interparticle diffusion. The enthalpy change was evaluated 2.3 kcal/mol, which is larger than the previously reported value with the atomic hole type of ion sieve. It might be due to the unique morphologies of the present bio-templated ion sieve.

© 2015 The Japan Institute of Metals and Materials. The copper refinery process produces Se(VI)-bearing wastewater with a high content of Cl- and SO<inf>4</inf>^2- ions. To overcome the negative effect caused by Cl- and SO<inf>4</inf>^2- ions on Se(VI) reduction and its following removal, this study investigated the possible synergistic effect of the combination of Se(VI)-reducing bacterium, Thaurea (T.) selenatis and zero-valent iron (ZVI). In the presence of SO<inf>4</inf>^2- (200mM) and Cl-(300 mM), the following was observed: (i) ZVI alone was unable to remove Se both under strictly aerobic and micro-aerobic conditions. (ii) Se(VI) reduction by T. selenatis alone was severely inhibited under anaerobic conditions (and thus no microbial growth was observed). (iii) On the other hand, T. selenatis was capable of growth and Se(VI) reduction under micro-aerobic conditions. (iv) Combining T. selenatis and ZVI under micro-aerobic conditions showed a synergistic effect on Se(VI) reduction, readily facilitating Se removal. This synergistic effect was optimized by adjusting the pH to near neutral (optimal for T. selenatis growth), but by adjusting the temperature to 35°C (sub-optimal for T. selenatis growth): Se removal of 55% by T. selenatis alone, was significantly improved to 98% by combining T. selenatis and ZVI. The proposed key process to display the synergistic effect on Se removal under micro-aerobic conditions is as follows: (i) Using the remaining dissolved O<inf>2</inf> (DO) during the first hours, T. selenatis can overcome the inhibitory effect of Cl- and SO<inf>4</inf>^2- by growing with more energy-gaining aerobic respiration, (ii) ZVI indirectly serves as a reducing agent to maintain low DO levels, consequently readily switching from aerobic to anaerobic Se(VI) respiration by T. selenatis. (iii) ZVI may also be acting directly for Se deposition by reducing microbially-produced intermediate Se(IV), which is more reactive than original Se(VI). The present findings could be used as a basis for developing an economically feasible and environmentally harmless bio-treatment technology for Se(VI) containing copper refinery wastewaters.

Biogenic birnessite is a stable form of manganese oxide found in nature that originates from microbial oxidation. Its unique structural properties provide potential for materials scientists to fabricate new functionalized materials. This study used a manganese-oxidizing fungus, Paraconiothyrium sp. WL-2, as a bio-oxidizer and biotemplate to prepare a lithium ion-sieve in the shape of a microtube through a solid-state transformation by calcination. The effect of calcination temperature was studied in terms of chemical composition, structure, and morphology. The results showed that the calcination temperature affects not only the weight fraction but also the crystallinity of the lithium manganese oxide spinel, which significantly influences the adsorption capacity of lithium ions.

Microbial catalysis, a primary pathway for the generation of Mn oxides in most natural environments, provides potential to fabricate new materials. A microtube-type lithium manganese oxide (LMO-MT) was synthesized through a solid-state transformation using Mn-oxidizing fungus, Paraconiothyrium sp. WL-2. Compared with abiotic precursors, the lithium-ion sieve microtube (HMO-MT) showed better performance for Li+ recovery. In order to clarify the formation process of LMO-MTs, in situ high-temperature X-ray diffraction was used to compare with three synthetic references. The effects of calcination temperature on crystal phase, composition, particle size and lattice parameters of the LMO-MTs were systematically discussed. It was found that the poorly crystalline structure of biogenic precursor as well as high content of organic matter facilitated the formation of highly crystalline LMO-MTs at low temperature. The unique structural properties of LMO-MTs, including high crystallinity and small lattice constant, are attributed to the high Li+ sorption capacity of HMO-MTs. (c) 2014 Elsevier B.V. All rights reserved.

For pretreatment of selective flotation, plasma treatment of chalcopyrite and molybdenite was applied then the minerals were washed by solution at pH 9 with oxygen bubbling. Surface characteristics of these minerals were investigated with AFM, XPS, zeta potential and contact angle measurements. Contact angle of chalcopyrite and molybdenite decreased a lot by plasma treatment. When they were washed with pH 9 solution with oxygen bubbling, contact angle of molybdenite increased whereas chalcopyrite one kept low. Adhesion force measurements indicated similar behavior. Result of flotation experiments indicated low recovery of both chalcopyrite and molybdenite after plasma treatment and only molybdenite recovery became higher after washing. Selective flotation of chalcopyrite and molybdenite could be achieved with this process. However, flotation of mixture of chalcopyrite and molybdenite after these treatments indicated both chalcopyrite and molybdenite were depressed. Addition of emulsified kerosene changed the flotation results where molybdenite was floated and chalcopyrite was depressed. Possible mechanism of selective flotation was proposed from the results of XPS, AFM, etc. (C) 2014 Elsevier Ltd. All rights reserved.

Adsorption of Cs+ on biogenic birnessite was investigated and compared with (ad)sorption of other heavy metals and also with (ad)sorption on chemically synthesized birnessite. The adsorption density of Cs+ on biogenic birnessite was smaller than that on chemically synthesized birnessite; however, the (ad)sorption densities of Co2+ and Ni2+ on biogenic birnessite were larger than on chemically synthesized birnessite. These phenomena can be interpreted by considering the distinctive nano-structure of biogenic birnessite, which is not only poorly crystalline and includes organic matter but also according to EXAFS contains a greater proportion of vacant central metal sites than is found in synthetic birnessite. Adsorbed Cs+ ions on both birnessites were mainly in the form of outer sphere complexes, which cannot easily occupy vacant central metal sites in biogenic birnessite. Biogenic birnessite has a greater specific surface area and more fine pores than synthetic birnessite, but these factors do not necessarily lead to more adsorption sites for Cs+ ions. (C) 2014 Elsevier B.V. All rights reserved.

To obtain basic information on how microbial cells absorb cadmium from aqueous solution, we examined cadmium absorption in various micro-organisms. Of 51 micro-organism strains tested, we found that some Gram-positive bacteria, such as, Arthrobacter nicotianae and Bacillus subtilis, and some actinomycetes, such as, Streptomyces flavoviridis and S. levoris were highly capable of absorbing cadmium from an aqueous solution. A. nicotianae absorbed the largest amount of cadmium, over 800 mu mol cadmium per gram of dry wt. cells. However, cadmium absorption by A. nicotianae was affected by the solution pH, cadmium concentration, and cell density. The absorption of cadmium was very rapid. Some factors that affected cadmium absorption by A. nicotianae cells were also discussed.

Animal bones are waste materials that can be developed as effective ionic exchangers after appropriate calcination treatment. Calcination of fish bones improves the crystallinity and purity of hydroxyapatite (HAp), but is sometimes accompanied with the formation of by-products and changes in the lattice parameters of HAp. In the present study, naturally derived HAp was obtained by calcination of fish bones that had different impurity contents, and the influence of calcination on the Sr2+ ion-exchange efficiency of the resulting HAp materials was investigated. Calcination of natural fish bones with high Mg contents led to the formation of beta-tricalcium phosphate, which did not contribute to the sorption of Sr2+, and those with high carbonate contents led to the formation of CaO, which increased the solution pH, thus facilitating ion-exchange with Sr2+. The specific surface area of the calcined fish bones played a trivial role in the sorption densities of Sr2+. Fish bones calcined at 1000 degrees C displayed a smaller HAp a-lattice when compared with the theoretical a-lattice parameter because of decarbonation. High Sr2+ sorption densities were obtained with natural HAp containing low Mg and high CO32- contents. This finding is practically useful to apply natural animal bones to sorbents in groundwater remediation. (C) 2014 Elsevier Ltd and Techna Group S.r.l. All rights reserved.

Hydroxyapatite (HAp) which has ion-exchange properties is a useful sorbent for heavy metals and radionuclides. Ion-exchange capacity is influenced by the composition and crystallinity of HAp. In this study, synthesis of HAp from calcined fish bones was investigated, focusing on the effects of major trace elements. The HAp formed by calcination of fish bones is most likely B-type carbonated HAp. Even when we include the Na, K and Mg contents, the molar ratio of (Ca+ substituted cation)/P of fish bones was about similar to 5% lower than the theoretical one (Ca/P=1.67). X-ray diffraction and EXAFS analysis results indicated that the crystallinity of Horse mackerel bones (Hm) is the lowest. Calcined Hm had the highest Mg content, accompanied with the formation of beta-tricalcium phosphate and the least crystalline HAp of the fish bones studied. In calcination of Tuna bones (Tn), which had a high Ca/P ratio and low Mg content, highly crystalline HAp and calcium oxide were formed at temperatures above 800 degrees C. The findings are useful for application of calcined fish bones as green materials for water remediation, because these factors strongly affect the efficiency of ion exchange in HAp and the pH changes in solutions after HAp immersion. (C) 2014 Elsevier Ltd and Techna Group S.r.l. All rights reserved.

Sugarcane bagasse, the solid waste material produced in the sugar industry, was subjected to treatment in hot compressed water. The experiments were performed in a batch-type reactor containing slurry of 10 ml of water and 1.2 g of solids. The reactor was heated to temperatures ranging between 200 degrees C and 300 degrees C for reaction times of 3 to 30 min. The product was separated into liquid and solid fractions. Each fraction was analyzed to investigate the alteration of the main lignocellulosic polymers by hot compressed water. Results for the liquid fractions showed that increased temperatures and reaction times completely dissolved hemicellulose and cellulose in the water, leaving lignin in the solid product. During treatment, hemicellulose and cellulose gradually decomposed into simple sugars, which were then degraded and decomposed into furfural, 5-(hydroxymethyl)furfural (5-HMF) and organic acids. However, the yield of furans and some organic acids decreased and became undetectable at 300 degrees C and with increasing reaction time. The solid fraction was also characterized before and after treatment. Results showed that the hydrogen and oxygen content of the solids decreased with increased reaction conditions, due to dehydration and decarboxylation reactions. The reactions also increased the carbon content of the treatment products by 1.2-1.6 times that in the raw material, suggesting that the hot compressed water treatment of sugarcane bagasse can be considered for the provision of valuable chemicals for biofuel and high-carbon-content material (biochar).

Geochemical characteristics of shallow groundwaters and core sediments are studied to better understand the sources and transportation process responsible for As and Mn enrichment in Singair Upazila of Manikgonj District in Bangladesh. Results demonstrate that the groundwater is mostly of Ca-HCO3 and Ca-Mg-HCO3 types. Concentrations of As in groundwater ranged from 1 to 159 mu g/L, with about 59% of these exceeded the WHO drinking water guideline of 10 mg/L. In addition, all groundwater samples had higher concentrations of Mn (0.6-5.7 mg/L) and Fe (0.9-16.5 mg/L) than the WHO drinking water guidelines (0.4 and 0.3 mu g/L, respectively). Most groundwaters contained both As(III) and As(V) species in which the concentration of As(III) was generally higher than that of As(V). High concentration of As (23 mg/kg) with elevated levels of FeO, MnO and TOC were found within the upper 15 m of silty clay sediments. Multivariate geostatistical analysis showed that dissolution of the Fe-Mn oxides was the dominant process of As and Mn release in groundwater. Geochemical modeling suggested that the concentrations of As, Mn, Fe and PO43- in groundwaters were also influenced by secondary minerals phases in addition to redox processes.

The thermoacidophilic iron-oxidizing archaeon Acidianus brierleyi is a microorganism that could be useful in the removal of inorganic As from wastewater, because it simultaneously oxidizes As(III) and Fe(II) to As(V) and Fe(III) in an acidic culture medium, resulting in the immobilization of As(V) as FeAsO₄. To investigate the oxidation mechanism, speciation of the As species in both the cells and its culture media is an important issue. Here we describe the successive determination of As(III), As(V), and total As in A. brierleyi and its culture medium via a facile method based on inductively coupled plasma-optical emission spectroscopy (ICP-OES) with a flow injection pretreatment system using a mini-column packed with an anion-exchange resin. The flow-injection pretreatment system consisted of a syringe pump, a selection valve, and a switching valve, which were controlled by a personal computer. Sample solutions with the pH adjusted to 5 were flowed into the mini-column to retain the anionic As(V), whereas As(III) was introduced into ICP-OES with no adsorption on the mini-column due to its electrically neutral form. An acidic solution (1 M HNO₃) was then flowed into the mini-column to elute As(V) followed by ICP-OES measurement. The same sample was also subjected to ICP-OES without being passed through the mini-column in order to determine the total amounts of As(III) and As(V). The method was verified by comparing the results of the total As with the sum of As(III) and As(V). The calibration curves showed good linearity with limits of detection of 158, 86, and 211 ppb for As(III), As(V), and total As, respectively. The method was successfully applicable to the determination of the As species contained in the pellets of A. brierleyi and their culture media. The results suggested that the oxidation of As(III) was influenced by the presence of Fe(II) in the culture medium, i.e., Fe(II) enhanced the oxidation of As(III) in A. brierleyi. In addition, we found that no soluble As species was contained in the cell pellets and more than 60% of the As(III) in the culture medium was oxidized by A. brierleyi after a 6-day incubation.

Permeable reactive barrier (PRB) column tests for removal of borate were carried out over 287 days corresponding to 76 pore volumes (pv), using MgO agglomerates as the primary reactive material, with and without boron-specific resin (CRB05). Adding 3 (% v/v) CRB05 increased the column shelf life (the time until effluent contains the maximum boron concentration for drinking water) by about 50%, and increased boron accumulation within the column by 15% over 76 pv. The quantities of boron captured were 15-17 mg/g-CRB05, and 1-2 mg-B/g-MgO, decreasing with increasing distance along the column. Rietveld refinement of X-ray diffraction patterns from solid residues after 76 pv revealed that 69-78% of the MgO was transformed into Mg(OH)(2) independent of distance along the column, implying that hydration of MgO is not always associated with integration of borate. B-11-NMR spectra demonstrated that trigonal B (B-[3]) is predominantly immobilized in Mg(OH)(2) in both columns, while tetragonal B (B-[4]) is largely trapped in the added CRB05. The complexed forms of B-[4] with the N-methylglucamine group after 76 pv were mostly bischelate, with some monodentate. CRB05 contributed to immobilization of B-[4] (which is difficult to react with MgO), however, the resin surface was gradually covered with Mg(OH)(2) and inactivated. (C) 2013 Elsevier B.V. All rights reserved.

Scorodite (FeAsO4·2H2O) is a thermodynamically stable mineral with advantages as an arsenic disposal compound. With an aim to immobilize highly toxic As(III) contained in the copper refinery process solution, eventually in the form of crystalline scorodite, the use of thermo-acidophilic iron-oxidizing archaeon, Acidianus brierleyi, was investigated. The extent of As(III) oxidation by Ac. brierleyi became greater at elevated culture As(III) concentrations, especially in the presence of yeast extract. Microbial growth on yeast extract was also implied to facilitate As(III) oxidation by Fe(III) on cell surface. When the initial Fe(II)/As(III) ratio was set at 1.4 in the presence of yeast extract, both ions were readily oxidized and 86-100% of As was precipitated as crystalline scorodite. The molar ratio of microbially-oxidized Fe(II) and As(III) was an important factor to determine the type of the secondary mineral formed. Phosphate concentration was another critical factor for scorodite biomineralization. Biogenic scorodite was crystallized with almond-shaped polyhedron habit of 1 μm in size. This study demonstrates the applicability of a one-step bioprocess which enables treatment of As(III)-bearing copper refinery process solution by producing biogenic crystalline scorodite. © 2014 Elsevier B.V.

Boric acid is known to be difficult to immobilize because it has a pK(a) of 9.23, which means it is present in a molecular form in most aqueous environments and can be changed in the structure and nature with the change of the environmental conditions. Layered double hydroxides (LDHs) are potential sorbents for borate. However, the drawbacks of using LDHs for borate removal are that they are affected by the presence of other anions and are difficult to separate from water. In the present work, novel composites of Mg-Al type of LDH, synthesized onto filter papers and then intercalated with gluconate (F-LDH-G) were prepared. LDH with interlayer of carbonate form was first immobilized onto the surface of filter paper (F-LDH-CO3) by in situ hydrothermal crystallization, and then ion-exchanged sequentially with chloride (F-LDH-Cl) followed by gluconate. The influence of the molar ratio of gluconate/LDH and reaction time on F-LDH-G synthesis was explored. Products were characterized by X-ray diffraction, scanning electron microscopy, Fourier transform infrared spectroscopy and nuclear magnetic resonance as well as measurements of borate sorption. The optimal molar ratio of gluconate/LDH and reaction time for preparing F-LDH-G from F-LDH-Cl were 40 and 24 h (F-LDH-G-40-24 h), respectively. F-LDH-G-40-24 h had higher sorption density and greater stability than both the original filter paper and the filter papers containing other LDHs, even in the presence of other anions. B-11 NMR and XRD results indicate that the principal mechanism for borate immobilization on F-LDH-G-40-24 h is complexation of gluconate with borate in both bischelate and monodentate forms. The novel composite is boron-specific and facilitates solid/liquid separation. (C) 2013 Elsevier B.V. All rights reserved.

The sorption of borate by ion exchange using a traditional layered double hydroxide (LDH) is affected by external conditions such as coexisting anions. Hydrotalcite intercalated with d-gluconate (G-LDH) was synthesized through a one-step microwave-assisted treatment and characterized by XRD, TEM, FTIR, TG/DTA and two-dimensional B-11 NMR. Several factors that influence sorption of borate were investigated: gluconate content in the LDH, G-LDH dosage, coexisting anions, initial pH of borate solution and sorption temperature. The synthesized adsorbent exhibited a greater borate sorption rate than the traditional hydrotalcite (NO3-LDH) or a boron-specific resin. The maximum sorption capacity was 1.27 mmol/g (obtained by fitting to the Langmuir model). The G-LDH sorption density increased with increasing initial borate concentration and adsorbent dosage. In the presence of 50 mM sulfate, sorption of borate by NO3-LDH significantly decreased and no obvious sorption could be observed, whereas the sorption of borate by G-LDH was maintained at similar to 0.57 mmol/g. B-11 NMR indicated that the sorption mechanism of borate by G-LDH is mainly through bischelate and monodentate types of complexation with borate. This mechanism is similar to that of CRB05, and fundamentally different from that of NO3-LDH. (C) 2014 Elsevier B.V. All rights reserved.

We investigated co-precipitation using magnesium (Mg) salt as a cost efficient method of removing B from wastewater. To clarify the mechanism of co-precipitation and the effect of precipitation rate against B sorption mechanism, we conducted co-precipitation experiments changing reaction time at different temperatures. For these experiments, we carried out sorption isotherm formation and XRD analysis to clarify how co-precipitation of B with magnesium hydroxide (Mg (OH) ₂) occurred. The sorption isotherm of co-precipitation was a BET type, while the XRD peak shift occurred as the initial B/Mg molar ratio increased. These results suggested that the mechanism of B uptake was a combination of surface precipitation and surface complexation, and the later mechanism became more apparent as the initial B/Mg molar ratio increased. XRD spectrum of co-precipitated residues was relatively similar to that of hydromagnesite, which indicated that structure of surface precipitation is similar to that of hydromagnesite. Co-precipitation experiments for 6 hours revealed that Mg precipitation rate was faster at the higher temperature, while sorption density became worse as the temperature increased. At 40<tt>℃</tt> and 60<tt>℃</tt>, XRD peak shift did not occur when the initial B/Mg molar ratio was0.063, which suggests that fast precipitation rate disturbed production of surface precipitation. In addition, the initial B/Mg molar ratio in which B sorption mechanism changed from formation of surface compexation to production of surface precipitation became larger as Mg precipitation rate increased.

Bimetallic oxides were synthesized from hydrotalcite using increasing calcination temperatures (873, 1073,1273 K). These bimetallic oxides were fully characterized and the sorption density of F- was investigated. X-ray diffraction patterns for the produced bimetallic oxides showed that MgO was the primary phase within the range of investigated calcination temperatures, but MgO crystallinity increased with calcination temperature and an additional MgAl2O4 phase was formed. In the process of F- sorption, the bimetallic oxides were primarily transformed into hydrotalcite with intercalation of F-.
The Higher calcination temperature increased the MgAl2O4 phase, which did not contribute to the immobilization of F-. These findings show that optimizing the calcination temperature can be used to maximize the sorption density of this material for F- removal. (C) 2013 Elsevier Ltd. All rights reserved.

Magnesia (MgO), which can be obtained by calcination of natural magnesite, is one of the most effective known sorbents for borate in aqueous solutions. Here we examine the effect of calcination temperature on sorption of borate for MgO-rich phases produced by calcination of magnesite at 873-1373 K. Calcination at or above 1273 K produced a single magnesium oxide phase, whereas basic magnesium carbonates (mMgCO(3)center dot nMg(OH)(2)center dot xH(2)O) formed in association with magnesium oxide at or below 1073 K. Calcination temperature directly affected the efficiency of decarbonation of magnesium carbonate, and the solubility and basicity of magnesium oxide in the resultant calcined products. These factors (along with the boron concentration) essentially control the immobilization mechanism of borate on the calcined MgO-rich phases. After sorption of borate on products calcined at lower temperatures, different types of basic magnesium carbonates were formed that are less effective at immobilizing borate. At low borate concentrations, under saturation for magnesium borate hydrate (Mg7B4O13 center dot 7H(2)O), co-precipitation of borate with Mg(OH)(2) predominates. However, as magnesium borate hydrate becomes supersaturated, both precipitation of Mg7B4O13 center dot 7H(2)O and co-precipitation with Mg(OH)(2) contribute significantly to borate immobilization. Calcination temperature is a key practical factor affecting the borate sorption efficiency by changing the immobilization mechanism. (C) 2013 Elsevier Ltd and Techna Group S.r.l. All rights reserved.

Trace metals were analyzed in water and sediment samples from Barapukuria coal mine area of Bangladesh in order to evaluate their mobility and possible environment consequences. Cadmium is the most mobile element with an average partition coefficient (log K (d) ) of 2.95 L/kg, while V is the least mobile element with a mean log K (d) of 5.50 L/kg, and their order of increasing mobility is: V &lt; As &lt; Pb &lt; Fe &lt; Cr &lt; Se &lt; Mn &lt; Ni &lt; Zn &lt; Cu &lt; Ba &lt; Sr &lt; Cd. Contents of organic carbon in sediment samples shows strong positive correlations with most trace metals as revealed by the multivariate geostatistical analysis. The overall variation in concentration is mainly attributed to the discharge of effluents originating from the coal mining activities around the study area. Compared to their background, Ni and Cu are the most enriched while significant enrichment of As, Mn, Ba, Sr, Cr, and Pb is also observed in the sediments. Geoaccumulation indices (I (geo) ) suggest sediments are moderately to heavily polluted with respect to Ni and Cu. The metal pollution index (MPI) varied from 91.91 to 212.01 and the highest value is found at site CM03 that is close to discharge point. The sediment quality guideline index (SQG-I (Intervention) ) values (0.56-1.52) suggest that the sediments at the study area have moderate to high ecotoxicological risk.

Microbial transformations, a primary pathway for the Mn oxides formation in nature, provide potential for material-oriented researchers to fabricate new materials. Using Mn oxidizing fungus Paraconiothyrium sp. WL-2 as a bio-oxidizer as well as a bio-template, a special lithium ion sieve with microtube morphology was prepared through a solid-state transformation. Varying the calcination temperature from 300 to 700°C was found to influence sample properties and consequently, the adsorption of Li+. Lithium manganese oxide microtube (LMO-MTs) calcined at different temperatures as well as their delithiated products (HMO-MTs) were characterized by X-ray diffraction (XRD), X-ray absorption fine structure (XAFS) spectroscopy, scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Calcination temperatures affect not only the content but also the crystal structure of LMO spinel, which is important in Li+ adsorption. The optimized sample was obtained after calcination at 500°C for 4h, which shows higher Li+ adsorption capacity than particulate materials. © 2013 Elsevier B.V.

Oxidation of Co by Mn oxide has been investigated using abiotically synthesized Mn oxide. However, oxidation of Co by biogenic Mn oxide is not well known. In this study, we isolated a Mn-oxidizing bacterium (Pseudomonas sp.), designated as strain NGY-1, from stream water. Sorption experiments on Co were carried out using biogenic Mn oxide produced by strain NGY-1. Similar sorption experiments were also conducted using a synthetic analogue of δ-MnO2. Sorption of Co on δ-MnO2 was faster and stronger than that on biogenic Mn oxide, which was possibly due to their structural difference and/or the presence of bacterial cells in biogenic Mn oxide. X-ray absorption near-edge structure spectra clearly demonstrated that Co was oxidized from the divalent to the trivalent state on biogenic Mn and δ-MnO2. The oxidation property of both the biogenic Mn oxide and δ-MnO2 was stronger under circumneutral conditions than under acidic conditions. Linear combination fitting using divalent and trivalent Co reference materials suggested that ∼90% of Co was oxidized at pH ∼ 6, whereas ∼80% was oxidized at pH ∼ 3. Oxidation properties of the biogenic Mn oxide and δ-MnO2 were similar, but Co(II) oxidation by biogenic Mn oxide was slower than that by δ-MnO2. The difference of Co oxidation may be caused by the coexisting bacterial cells or structural differences in the Mn oxides. Supplemental materials are available for this article. Go to the publisher's online edition of Geomicrobiology Journal to view the supplemental file. © 2013 Copyright Taylor and Francis Group, LLC.

The formation and structural evolution of fungal mediate biogenic birnessite are dynamic processes. Although the associations of Zn with the pre-formed biogenic Mn oxides are relatively well understood, the reactivity of the intermediate precipitate at the initial stage of Mn bio-oxidation appears to differ from the final precipitate. In the present work, Zn sorption during precipitation of biogenic Mn oxides was investigated contrasting Zn sorption to pre-formed biogenic Mn oxides, using the Mn-oxidizing fungus Paraconiothyrium sp. WL-2. A substantially higher Zn uptake was found during precipitation of biogenic Mn oxides compared to Zn sorption to pre-formed biogenic Mn oxides. The presence of Zn during Mn oxidation resulted in a biogenic Mn oxide with reduced ordering in the c-axis. The precipitate was identified by X-ray diffraction (XRD) as a layer-type Mn oxide with structural properties similar to hexagonal birnessite. Extended X-ray absorption fine structure (EXAFS) spectroscopy showed that Zn forms triple-corner-sharing tetrahedral coordination ((TCS)-T-IV-Zn) complexes on the surface of birnessite, which may inhibited layer stacking of birnessite in the final products. This study emphasizes the importance of the intermediate precipitates on Zn sorption, and provides insight regarding the dynamic interaction between Zn and Mn oxide in the process of microbiological oxidation. Supplemental materials are available for this article. Go to the publisher's online edition of Geomicrobiology Journal to view the supplemental file.

There has been an increasing interest in the application of Mn(II) oxidizing microbes for Mn(II) containing waste water treatment, as well as biogenic Mn oxides for remediation of a number of toxic metals. Sambe hot spring in Shimane Prefecture, Japan is known for its Mn-rich spring water, and Mn oxide sediments are widely distributed over an area of 60 m x 80 m of this region. With an aim to find out Mn(10 oxidizing bacteria involved in this massive Mn(11) oxide deposit formation, culture enrichment was undertaken. Pseudomonas sp. strain MM1 was isolated as dominant Mn(II) oxidizing bacterium from the site. Biogenic Mn oxide formed by strain MM1 was shown to be poorly-crystalline birnessite, having the large specific surface area of 90 m(2).g(-1). Mn(II) was readily oxidized by strain MM1 during the stationary phase and initial Mn(II) concentrations of up to 1.0 mmol.dm(-3) (55 mg.dm(-3)) went well below the effluent standard of dissolved manganese (10 mg.dm(-3); set by Japanese Ministry of Environment). Strain MM1 grew heterotrophically and Mn(II) did not serve as the sole electron donor. Nano-sized (3050 nm) Mn oxide particles were produced by strain MM1, which later chained or aggregated to form larger Mn oxide minerals. Cells were observed eventually encrusted inside the Mn oxides. This study showed the important role of strain MM1 in the production of massive Mn oxide deposits at Sambe hot spring. The Mn(II) oxidizing ability of this strain is potentially applied for bioremediation of toxic metals.

Biogenic birnessite (BB), a stable form of manganese in the natural environment that originates from microbial oxidation, could be use as a starting material to prepare nanocrystalline lithium manganese oxide (LMO) by solid-state reaction for Li+ recovery. In this work, the effects of calcination temperature on Li+ adsorption density were investigated by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, N-2 adsorption-desorption isotherms, and If ion sorption isotherms. An increase in calcination temperature causes a phase transformation that results in changes in crystal compositions. The formation of Li4Mn5O12 was observed at 350 degrees C. An increase in calcination temperature from 350 to 450 degrees C results in a decrease in the Li4Mn5O12 phase quantity, an increase in the Li2MnO3 phase quantity, and a decrease in Li+ sorption density from 4248 to 2789 mmol/kg. The sorption density of Li+ is mainly affected by the Li4Mn5O12 phase content. LMOs prepared from BB show a higher Li+ sorption density compared with acidic birnessite. Phase transformation on poorly-crystalline BB at a relatively lower calcination temperature facilitates formation of the Li4Mn5O12 phase, which is the main contributor to Li+ sorption from aqueous solution. (C) 2013 Elsevier Inc. All rights reserved.

A hydrotalcite-like compound prepared through chemical deposition using calcined dolomite as the magnesium source (D-LDH) was applied to remove borate. D-LDH calcined at different temperatures was characterized by specific surface area measurements, scanning electron microscope images, X-ray diffraction (XRD) patterns, and Fourier transform infrared (FTIR) spectra to optimize the calcination temperature and maximize the sorption capacity of borate. Greater sorption density of borate was observed at higher calcination temperature, and the sample calcined at 700 degrees C showed the maximum sorption density. In addition, the sorption density of borate by D-LDH calcined at 700 degrees C decreased with increasing initial pH. The solid residues after the sorption of borate were characterized by FTIR, B-11 NMR ((11)Boron nuclear magnetic resonance), and XRD to explore the sorption mechanism of the calcined product at 700 degrees C. (c) 2013 Elsevier B.V. All rights reserved.

Natural dolomite was calcined at 700-900 degrees C under air and an Ar gas flow atmosphere to characterize its sorbency potential for borate. A sequential decarbonation occurred with increase in calcination temperature, that is, transformation of CaMg(CO3)(2) to MgO and CaCO3 up to 700 degrees C and CaCO3 to CaO from 700 to 900 degrees C. The surface molar ratio of Ca/Mg decreased from 1.6 to 0.6 by calcination at more than 700 degrees C, owing to the crystal growth of MgO toward the surfaces. MgO crystal growth is responsible for hydration leading to borate co-precipitation. The sorption density of borate was greater with the calcined products at 700 degrees C than 800-900 degrees C and under an Ar gas flow system rather than for static air at the same temperatures. The surface reactivity of the calcined dolomite with borate in the aqueous phase was affected by CO2 emitted in the decarbonation at higher temperatures. (C) 2012 Elsevier Inc. All rights reserved.

Microbiological contribution to the formation of the manganese deposits in Sambe hot springs, Shimane, was investigated in combination with water chemistry, characterization of sediments and microbial community structure. Analysis of bacterial and fungal community structure based on DNA extracted from a Mn-oxidizing enrichment culture indicated close matches with Pseudomonas putida, Phoma sp. and Plectosphaerella cucumerina, all Mn-oxidizing microorganisms. These sediments were poorly crystalline and formed at neutral pH values, which is characteristic of biogenic precipitates. The EPMA results demonstrated a positive correlation between Mn and Ba contents in well-crystalline Mn oxide grains. Substantial Ba contents were observed inside Mn oxide grains. These findings indicated that Ba contents in sediments are influenced by not only aqueous Ba2+ concentrations but also crystallinity of biogenic birnessite. Barium would be incorporated in birnessite during biomineralization. © 2013 The Society of Resource Geology.

The use of a thermophilic acidophilic iron-oxidizing archaeon, Acidianus brierleyi, was investigated for oxidation and immobilization of As(III) from acidic refinery waste water. Some As(III) oxidation was measured in all Ac. brierleyi cultures independently of the presence or concentration of Fe(II) in bulk solution; the exception was at initial Fe(II) concentration ([Fe(II)] ini) of 1000 mg l-1 where As(III) oxidation became markedly facilitated and consequently approximately 70% of As was immobilized as amorphous ferric arsenate. Providing 1000 mg l-1 Fe(III) instead of Fe(II) did not show the same effect, implying the importance of Fe(III) be microbially-produced and complexed in the archaeal EPS (extracellular polymeric substances) region for effective As(III) oxidation. The reaction towards secondary mineral formation shifted from ferric arsenate to jarosite at [Fe(II)]ini of >1000 mg l-1. Furthermore addition of jarosite seed crystals retarded the As(III) oxidation rate at [Fe(II)] ini of 1000 mg l-1. The observations indicate that by setting the appropriate bulk Fe(II)/As(III) ratio in Ac. brierleyi culture to achieve a certain concentration of Fe(III) within the EPS region, but at the same time to avoid jarosite formation, it is possible to maximize the As(III) oxidation rate and thus As immobilization efficiency. This study describes for the first time microbially-mediated simultaneous oxidation and immobilization of As(III) as ferric arsenate, using a thermoacidophilic iron-oxidizing archaeon, Ac. brierleyi. © 2012 Elsevier Ltd. All rights reserved.

Natural dolomite was calcined at different temperatures in the range 873-1373K and characterized by X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, and N2 adsorption/desorption isotherm. The calcination temperature had considerable effect on the surface chemical composition, crystallinity, and basicity of CO2 gas sorption of each component in the calcined products. The sorption isotherm of both in low and high concentrations of fluoride (F-) was investigated for selected calcination products. The sample calcined at 973K was found to show the highest sorption density for F- at equilibrium concentrations lower than 0.5mM, which was equivalent to the maximum concentration limit of F-. In this range, the principle of F- removal is mainly based on destructive hydration of MgO. At equilibrium concentrations of F- higher than 0.5mM, the sorption process was controlled by precipitation of CaF2 and co-precipitation with Ca(OH)2 due to excess liberation of Ca2 ions from CaO. In this concentration region the products of calcination at higher temperatures are profitable for the immobilization of F-. Additionally, the effect of CO2 gas derived from carbonates on the reactivity of MgO to remove F- during calcination of natural dolomite was also discussed. © 2012 Elsevier B.V.

Plasma treatment of activated carbon (AC) was found to be an efficient method to enhance phenol removal by ozonation in a three-phase fluidized-bed reactor. The plasma treatment extended porous structure, changed surface morphologies, and produced oxygen functional groups on the surface of AC. Plasma-treated activated carbon together with O3 gave the best removal result, in which phenol was completely decomposed within 10 min (with pseudo first-order rate constant k = 0.286 min-1), while untreated AC without O3 showed the worst result (k = 0.024 min-1). Consequently, AC modified by plasma was shown to be a good material for removal of organic pollutants and yield superb performance in an integrated process with ozone in a fluidized-bed reactor. © (2013) Trans Tech Publications, Switzerland.

The CO2-blown integrated coal gasification combined cycle (IGCC) is a promising electric power generation technology that will reduce CO 2 emission, due to its high efficiency. Recent studies have found that base metals improve the coal char gasification in cases when they can interact with the char matrix at an atomic level. In this paper, we clarified the effect of heavy medium separation, which is one of the most popular coal cleaning technologies, on the CO2 char gasification. Before sink and float test and thermogravimetric analysis, Datong Coal from China was ground to below 20 mesh, which is a size usually used for a coal cleaning process. The float and sink test revealed that the highest separation efficiency would be obtained at a specific gravity of 1.45. The ash content would be reduced dramatically from 10.2% to ca. 4% and about 85% of combustibles would be recovered. The chars derived from different specific gravity fractions showed different gasification reactivity
the char from heavier fraction has gasification reactivity higher than the lighter fraction-derived char. This tendency agrees with the ash content
the heavier fraction has a higher ash content. Removal of ash from well-ordered holes in Fusinite and Semi-fusinite in Inertinite might increase the gasification reactivity. © 2012 Elsevier Ltd. All rights reserved.

The reaction mechanism of H3BO3/B(OH)(4)(-) with MgO in aqueous phase was investigated using sorption isotherm, XRD, B-11-NMR and FTIR. Release of Mg2+ was observed soon after contact of MgO with H3BO3 and maximum released Mg2+ was proportional to the initial boron concentration, suggesting ligand-promoted dissolution of MgO by H3BO3. The molecular form of H3BO3 was more reactive with MgO in releasing Mg2+ ions than B(OH)(4)(-). B-11-NMR results indicated that trigonal B (B-[3]) was predominant over tetrahedral B (B-[4]) in solid residues after sorption of H3BO3. The molar ratio of B-[4]/B-[3] increased with H3BO3 sorption density. XRD patterns for the solid residues were assigned to Mg(OH)(2) and peaks broadened with increasing H3BO3 sorption density, except for (hk0) planes due to c-axis lattice strain induced by incorporation of H3BO3 between layers. These results indicated that H3BO3 interfered in the c-axis stacking of in Mg(OH)(2). Molecular H3BO3 acted as a trigger when reacting with the MgO surface, releasing Mg2+ to produce an unstable complex leading to the precipitation formation of Mg(OH)(2), which is a sink for the immobilization of H3BO3/B(OH)(4)(-).

Geomimetics, taking lessons from nature's biogenic mineralization mechanisms, can provide powerful tools for advancing biohydrometallurgical processing. Microbial transformations are largely responsible for the Mn oxides found in nature. In this research biogenic birnessite was produced by a manganese-oxidizing fungus, Paraconiothyrium sp. WL-2, at pH 6.5 under room temperature, and characterized by XRD and TG-DTA. Abiotic (chemically synthesized) acidic birnessite was also prepared hydrometallurgically and subjected to a similar battery of characterization techniques. Following thermal treatment the sorption characteristics of these two materials were compared. The biogenic precursor showed several advantages to produce more effective Li-ion sieve than the chemically synthesized precursor. First, a shorter calcination period was required to produce Li4Mn5O12 without other phases; second, a greater content and higher crystallinity of H4Mn5O12 were obtained from the biogenic precursor. These advantages might be caused by poorer crystallinity and around 20 wt% organic matter in biogenic birnessite. While sorption density of Li+ in mmol/g was basically dependent on contents of H4Mn5O12 phase, the unique morphologies and sorption density were maintained with biogenic precursor even after repetition of sorption/desorption of Li+.

The formation and consumption of elemental S were investigated in the bioleaching of chalcopyrite within and without a CE dialysis membrane in Acidithiobacillus caldus cultures. The bacteria were supplemented with tetrathionate outside the membrane. XPS analysis showed that monosulfide species and elemental S were formed on CuFeS2 surface regardless of the enclosure in the dialysis membrane. They diminished over time in the inoculated systems. In the membrane enclosure, colloidal S partially dissolves and can pass the dialysis membrane for bacterial oxidation to sulfuric acid. Anaerobic pre-oxidation of CuFeS2 by Fe3+ produced S-rich deposition on mineral surface. The solubilization of Cu from membrane-enclosed pre-oxidized chalcopyrite in the A. caldus culture was much slower as compared to direct contact with bacteria. The difference is attributed to slow diffusion through the dialysis membrane as well as clogging caused by polymerized S on the inside of the membrane. (C) 2012 Elsevier B.V. All rights reserved.

Use of MgO for repeated calcination with regard to its sorption density for F- and chemical stability was examined. Magnesium oxide was produced by the calcination of MgCO3 at 1273 K for 1 h. The sorption of 9.82 mM F- on the calcined product and the calcinations of solid residues were carried out five times to evaluate trends in sorption density for F- and the stability of the chemically regenerated sorbents. The order of sorption density of F- (Q/mol g(-1)) apparently seems to depend on the specific surface area. However. Q' values after normalization of the sorption density for the specific surface area (Q'/mmol m(-2)) were found to be correlated with the solid basicities of the calcined products which were derived from CO2-TPD curves for the calcined products. The number of weak base sites, calculated from the peak intensity at 373 K in CO2-TPD, was considered to be responsible for the removal of F- through hydration. Large quantities of NaMgF3 and elemental Mg were evaporated by the calcination at 1273 K of the solid residues formed after sorption of F-. (c) 2012 Elsevier B.V. All rights reserved.

With the recent Fukushima incident, there is an urgent need to find cost effective and workable permeable reactive barrier (PRBs) for the remediation/retardation of problematic radionuclides. Catfish bones were calcined at various temperatures (400-1100 degrees C) to remove the organic matter (87.1 mg-g(-1)) and to change the structural properties of the hydroxyapatite (HAP). Increasing temperatures increased the HAP crystallinity as indicated by a decrease in lattice strain (0.0098 to 0.00135) and an increase in crystallite sizes (5.0 x 10(-8) to 7.7 x 10(-8) m). There was also an observed decrease in specific surface areas (98.9 to 0.99 m(2)-g(-1)) and increase in particle sizes (50 to 1000 nm). The sorption densities of Sr2+ decreased with increasing calcination temperatures, from 0.34 to 0.05 mmol.g(-1). However, once normalized for surface area, the sorption densities increased from 1.8 to 5.9 mmol.m(-2). Overall, this research has important implications for the design of hydroxyapatite PRBs with higher calcination temperatures producing a more reactive material with larger particle sizes for increased permeability. Lower calcination temperatures produced amorphous HAP material, which released more aqueous PO43- and resulted in the precipitation of strontium phosphates, ultimately reducing the permeability of PRBs. [doi:10.2320/matertrans.M-M2012813]

The surface reactivity of biogenic birnessite is attributed to its structure. However, structural control of heavy metal adsorption on biogenic birnessite is not well understood. Here a poorly-crystalline birnessite was produced by the fungus Paraconiothyrium sp. WL-2 strain under ambient pH and temperature conditions. The structure was characterized by X-ray absorption spectroscopy and X-ray diffraction. Sorption behaviors of Co2+ were compared with Zn2+. The primary product of the Mn bio-oxidation is hexagonal birnessite with a turbostratic structure. XAFS analysis demonstrated that the biogenic birnessite consists of octahedral sheets with Mn(IV) as the central metal and some vacant sites. Mn(III) atoms are coordinated to some of the vacant sites in the interlayer. The adsorption of Co2+ by the biogenic birnessite is higher than Zn2+. The excess adsorption of Co2+ than Zn2+ is nearly the same as the excess release of Mn from the biogenic birnessite. These results strongly suggested that the interlayer Mn(III) can oxidize the adsorbed Co2+ to Co3+, resulting in excess adsorption of Co2+ compared to Zn2+ by biogenic birnessite. (C) 2012 Elsevier B.V. All rights reserved.

Application of microorganisms as surface modifiers in flocculation has generated a great deal of interest in recent times. The surface properties such as zeta-potential and hydrophobicity of minerals and microorganisms play a major role in determining the adsorption of microorganisms onto the minerals and hence the efficiency of flocculation. The utility of microorganisms, including Escherichia coli (wild-type and genetically modified strain Sip), Arthrobacter nicotianae, Bacillus licheniformis, and Pseudomonas maltophilia, has been evaluated by measuring their zeta-potentials and carrying out adsorption and flocculation experiments. Of the tested microorganisms, adsorption of E. coli strain Sip significantly modified the quartz surface. The zeta-potential of the quartz became highly positive at acidic pH, and its IEP (isoelectric point) was shifted from pH < 2 to pH 4.3. Moreover, the settling velocity of the bio-treated quartz reached its maximum value at this pH. The number of cells adsorbed onto quartz was low at pH above the IEP due to the identical surface charges of the mineral and bacterial cells. This led to a repulsive force between the mineral particles and bacterial cells, which hindered the adsorption process. For all of the studied strains, the settling velocity of bio-treated quartz was high at their respective IEPs. An interaction model of microorganisms is proposed to explain the flocculation behavior of bio-treated quartz. Potential energies were calculated using the DLVO theory, and the results were found to be in good agreement with the flocculation tests. The settling velocity of the bio-treated quartz was maximized at pH close to the IEP of microbial cells. Interaction between cells is identified as the most likely cause of flocculation of bio-treated quartz. © 2011 Elsevier B.V. All rights reserved.

In this study, the effects of sodium thiosulphate on chalcopyrite and tennantite at various pH values were investigated. Contact angle, flotation (Hallimond tube), zeta potential and X-ray photoelectron spectroscopy were used to observe these effects and to investigate the mechanisms involved. The addition of sodium thiosulphate depressed both chalcopyrite and tennantite at all pH values. Further addition of diethyl dithiophosphate significantly increased the notability of chalcopyrite at all pH values as well as tennanite in acidic conditions, but not tennantite in alkaline conditions. In light of the zeta potential measurements and due to the stability of thiosulphate over the pH range, the coverage of sulphate resulting from the oxidation of thiosulphate was responsible for the depression of both chalcopyrite and tennantite in acidic conditions. Adsorption of diethyl dithiophosphate species on the mineral surface resulted in notability of tennantite which was almost as high as that of chalcopyrite. In alkaline conditions, coverage of the copper thiosulphate complex was responsible for the depression. The copper thiosulphate complex inhibited adsorption of diethyl dithiophosphate species on the mineral surface. Higher coverage of the copper thiosulphate complex on tennantite caused an insignificant increase in its notability in comparison to that of chalcopyrite which allowed the separation of tennantite from chalcopyrite. The XPS spectra supported the proposed mechanism of thiosulphate depression on these minerals. (C) 2011 Elsevier B.V. All rights reserved.

During the process for the bioleaching of sulfides, the surface of the target mineral is sometimes covered with intermediates, and the final products that interfere with the extraction of the target metal. Understanding the characterization and formation order of the secondary minerals responsible for passivation is a key to resolving the passivation mechanism. The present article reviews identification of secondary minerals and intermediates in a process of bioleaching of several sulfides by X-ray photoelectron spectroscopy, Raman spectroscopy', identification of the jarosite group minerals using Raman spectroscopy, and expectation of the formation order of the secondary minerals by SEM-EDX and TEM. The TEM observation in a nano-domain provides useful information about amorphous the secondary minerals. A passivation model was proposed to keep maximizing Cu recovery and minimizing As solubilization for the bioleaching of arsenic-bearing copper sulfides using super-thermophilic archaea, which are expected to be new target minerals in the near future.

Numerical modeling was developed in one dimensional solute transport including chemical reaction to simulate the permeable reactive barrier column results, in which arsenite (As(III)) was removed using zero-valent iron (ZVI). Removal principles of As(Ill) includes oxidation of As(III) to As(V), sorption of As(III) and sorption of As(V) at least. Each kinetic parameter was drawn in preliminary batch tests to integrate the simulation.The column simulation results show that As(V) adsorption rate was faster than the As(III) adsorption rate and that they are affected by the available mass of Fe(III) in the system. The model can be used to design and predict the long term performance of ZVI permeable reactive barriers (PRBs). (C) 2011 Elsevier Inc. All rights reserved.

The kinetics of diethyl dithiophosphate adsorption on chalcopyrite and tennantite has been studied by UV-visible spectroscopy at pH values of 4, 6, and 9. The concentration of diethyl dithiophosphate in the solution has been monitored as a function of time and pH for both minerals. It was found that the adsorption tendency of diethyl dithiophosphate on both minerals decreased with the increasing pH treatments. This is due to the existence of metal hydroxide species onto the mineral surface in more alkaline condition inhibiting the adsorption of diethyl dithiophosphate species. In comparison to that of chalcopyrite, tennantite possessed slightly higher adsorption of diethyl dithiophosphate in acid condition, while vice versa correlation observed at other pH treatments at where the coverage of metal hydroxide species obtained higher than that of chalcopyrite showing that the rate oxidation of tennantite is higher. An adsorption mechanism has been proposed and tested against the experimental kinetic data. Both the kinetic data and flotation studies are consistent with the proposed mechanism.

Bioleaching of enargite by the thermophilic iron-oxidizing archaea, Acidianus brierleyi, at 70 degrees C for 27 days yielded a 90.9% recovery of Cu and 5.9% recovery of As. The preferential dissolution of Cu compared to As was mainly achieved by the formation of crystalline scorodite (FeAsO(4)center dot 2H(2)O). Although the chemical valence of As in enargite was confirmed to be As(III), most of the dissolved As was in the compound H(3)As(V)O(4). This indicates that the H(3)As(III)O(3) released from the enargite was immediately oxidized to H(2)As(V)O(4)(-) in solution via a catalytic reaction on the surface of the enargite. During the bioleaching process, dissolved Fe(3+) was consumed through the formation of precipitates, such as scorodite and jarosite ((M(+))Fe(3)(SO(4))(2)(OH)(6)), as well as the oxidation of enargite. Even after the formation of scorodite had stopped due to the consumption of Fe(3+), As was further passivated in the absence of Fe(3+). The co-sorption of Cu(2+) and H(2)As(V)O(4)(-) on jarosite led to the formation of copper arsenate by a seed-forming effect. Subsequent secondary mineral precipitation resulted in the formation of multi-precipitation layers consisting of scorodite, potassium jarosite, elemental sulfur and copper arsenate, after most of the Cu had been recovered from the enargite by microbially induced leaching. Crown Copyright (C) 2011 Published by Elsevier B.V. All rights reserved.

To maximize Cu recovery and minimize As release during the bioleaching of enargite (Cu3AsS4) by Acidianus brierleyi at 70 degrees C, the initial Fe2+ ion concentration and pulp density were investigated in batch tests. A maximum Cu recovery of 91.0 +/- 0.5% was obtained with an initial Fe2+ ion concentration of 1.8-2.7 g/L and a pulp density of 1.0%. As the immobilization of As depended on the formation of scorodite (FeAsO4 center dot 2H(2)O) and cupric arsenate, a more rapid and stable As immobilization was achieved with an initial Fe2+ ion concentration of 2.7 g/L Thus the initial Fe2+ concentration of 2.7 g/L and 1.0% pulp density provided for a combination of As precipitation and &gt;90% Cu recovery. When the initial Fe2+ concentration was increased, K-jarosite (KFe3(SO4)(2)(OH)(6)) precipitated, leading to passivation of the enargite surface. When the initial Fe2+ concentration was lowered, the Cu recovery was incomplete due to insufficient oxidation. Elevating the pulp density to 2.0% showed that the increase in Eh significantly lagged behind the exponential phase in the planktonic cell growth curve. Pulp density also clearly affected the makeup of secondary minerals in solid residues after the bioleaching of enargite. There is a tendency for dissolved Fe3+ ions to readily precipitate as potassium jarosite at relatively smaller pulp densities and as scorodite at relatively larger pulp densities. (C) 2011 Elsevier B.V. All rights reserved.

Atomic force microscopy (AFM) has been used to observe the morphology and surface characteristics of chalcopyrite and tennantite treated at pH 4 and 9. Mineral treated with DTP at pH 9 was also observed. It was found that new surface "islands" were formed on the minerals after these treatments. The occurrence of these islands as a product of reaction was amplified with increasing treatment time. Adhesion force measurements revealed that the formation of islands under acidic conditions (pH 4) lowered the adhesion force value compared to that under alkaline conditions (pH 9), thus rendering the surfaces of the minerals more hydrophobic. A similar tendency was observed in the adhesion force value of minerals surface-treated with DTP at pH 9. This phenomenon arose as a result of a propensity for the formation of elemental sulfur or metal-deficient sulfur-rich species at pH 4 and DTP species at pH 9. The more hydrophilic surfaces of both minerals indicated by higher values of the adhesion force after treatment at pH 9 may be attributed to the occurrence of metal hydroxide moieties. From the morphology images and adhesion force, it is apparent that the coverage of islands on the surface of a mineral determines its hydrophobicity or hydrophilicity. Moreover, it also shows the relative reactivities of the minerals, with tennantite being more reactive than chalcopyrite. Furthermore, the microscopic observation by AFM was consistent with the macroscopic observations of contact angle and flotability studies. (C) 2011 Published by Elsevier B.V.

Biomineral hydroxyapatite (Bio-HAp) produced by Serratia sp. has the potential to be a suitable material for the remediation of metal contaminated waters and as a radionuclide waste storage material. Varying the Bio-HAp manufacturing method was found to influence hydroxyapatite (HAp) properties and consequently the uptake of Sr 2+ and Co 2+. All the Bio-HAp tested in this study were more efficient than the commercially available hydroxyapatite (Com-HAp) for Sr 2+ and Co 2+ uptake. For Bio-HAp the uptake for Sr 2+ and Co 2+ ranged from 24 to 39 and 29 to 78 mmol per 100 g, respectively. Whereas, the uptake of Sr 2+ and Co 2+ by Com-HAp ranged from 3 to 11 and 4 to 18 mmol per 100 g, respectively. Properties that increased metal uptake were smaller crystallite size (&lt
40 nm) and higher surface area (&gt
70 m 2 g -1). Organic content which influences the structure (e.g., crystallite arrangement, size and surface area) and composition of Bio-HAp was also found to be important in Sr 2+ and Co 2+ uptake. Overall, Bio-HAp shows promise for the remediation of aqueous metal waste especially since Bio-HAp can be synthesized for optimal metal uptake properties. © 2011 American Chemical Society.

Attempts to produce high-grade fuel from biomass and low rank coal are important from the viewpoint of renewable energy and the utilization of unused resources. In this paper, the authors reported on the hydrothermal treatment of biomass and low rank coal at 300 degrees C using a bench scale continuous apparatus and a batch autoclave. The results show that coalification takes place during the hydrothermal treatment of both the low rank coal and biomass, and the upgraded solid products show similar chemical compositions, gross calorific value and effective calorific value, independent of the mixing ratio. The solid product also becomes hydrophobic and unable to re-adsorb the lost moisture. The characteristics of the solid produced by the bench scale continuous apparatus can be predicted by the results of the batch process. Thermogravimetric analysis shows that the solid product has a wide-range of molecular weight but the thermally stable heavy molecules are found more in the treated coal as opposite to the thermally unstable light molecules, more of which are found in the treated biomass. This may correlate with that the solid product of higher biomass mixing ratio has a higher volatile matter content. Polymerization is synergistically promoted during mixed hydrothermal treatment of low rank coal and biomass. (C) 2011 Elsevier Ltd. All rights reserved.

The effect of calcination temperature during production of magnesium oxide-rich phases from MgCO(3) on the sorption of F(-) ions in the aqueous phase has been investigated. Magnesium oxide-rich phases were formed by calcination at over 873 K for 1 h. Higher calcination temperatures produced more crystalline MgO with smaller specific surface area and provided larger values of the total basicity per unit surface area. The higher calcination temperatures lead to slower F(-) removal rate, and lower equilibrium F(-) concentrations, when the equilibrium F(-) concentrations are less than 1 mmol dm(-3). Larger total basicity per unit surface area made the reactivity with F(-) ions in aqueous phase more feasible, resulting in a greater degree of F(-) sorption. For equilibrium F(-) concentrations more than 1 mmol dm(-3), lower calcination temperatures favored the co-precipitation of F(-) with Mg(OH)(2), probably leading to the formation of Mg(OH)(2-x)F(x), and the achievement of larger sorption density. This is the first paper which describes the relationship between the solid base characteristics obtained by CO(2)-TPD for MgO with different calcination temperatures as a function of the reactivity of F(-) sorption in the aqueous phase. (C) 2011 Elsevier B.V. All rights reserved.

This study investigated the mechanisms involved in removing arsenic from water using zero-valent iron (ZVI) as sorbent. Relatively limited information is available on the kinetics aspects of sorption of arsenic compounds onto ZVI. In order to gain an understanding of the sorption kinetics, a detailed study was conducted in a controlled batch test and developed sorption kinetic model.The effects of different arsenic concentrations on the kinetics sorption rates of arsenic(V) and arsenic(III) were investigated. Arsenic(V) was removed by two mechanisms-surface adsorption and co-precipitation with Fe(III) on ZVI, while arsenic(III) was removed by adsorption on ZVI and oxidized to arsenic(V). Reaction rate constants were calculated for arsenic(V) and arsenic(III) at different concentrations by a second-order kinetic model.The results indicate that ZVI could be employed as sorbent materials to enhance the adsorption and co-precipitation processes to improve the removal rate of arsenic from water. The results also showed that the arsenic(III) oxidized to arsenic(V), while the analyses indicated that there was no measurable reduction of arsenic(V) to arsenic(III).

Effective immobilization of boron in groundwater is a major challenge. Permeable reactive barrier (PRB) column tests for removal of borate have been investigated using MgO agglomerates as the primary reactive material over 40 weeks. Additionally, saw dust was also blended with MgO agglomerates to facilitate for borate removal in this system. Boron accumulation was more than 1.6 times greater in the presence of saw dust, although MgO alone performed well. Increased boron accumulation in the presence of saw dust was primarily due to higher porosity of the PRB column, decreasing the impact of secondary Mg(OH)(2) passivating layers and leaving more reactive sites on MgO agglomerates. In addition, Mg(2+) ions released from MgO agglomerates are complexed with carboxylic acids leached from saw dusts. This sequestration prevents the formation of bulky Mg(OH)(2) which is an ineffective sorbent for borate and covers the surfaces and passivating reactive sites on the MgO agglomerates. The morphologies of Mg(OH)(2) precipitated in the PRB column were also significantly affected by the presence of saw dust, with crystallization of needle-like particles of Mg(OH)(2) was prevented by Mg(2+) ions-organic ligand complexation. (C) 2010 Elsevier B.V. All rights reserved.

This paper describes experimental research and a fundamental study of alkaline hydrothermal treatment of high-sulfur, high-ash coal from Banten, Java-Indonesia. Experiments were carried out on a laboratory-scale 0.5 L batch reactor. The alkaline hydrothermal treatment gave upgraded clean coal with low sulfur content (about 0.3 wt.%) and low ash content (about 2.1 wt.%). A zero carbon dioxide and pure hydrogen gas were produced at 330 degrees C by introducing an alkali (sodium hydroxide, NaOH) to the hydrothermal treatment of raw coal. X-ray diffraction (XRD) and X-ray fluorescence (XRF) techniques were used to test for the removal or reduction of major, inorganic elements in the coal, and changes in carbon-functional groups and their properties were determined by Fourier transform infrared spectroscopy (FTIR) and Carbon-13 of nuclear magnetic resonance ((13)C NMR) tests on the product of the hydrothermal upgrading and demineralization process. (C) 2010 Elsevier Ltd. All rights reserved.

Cenospheres recovery is one of the coal fly ash beneficiations, providing economic as well as environmental benefits. Current techniques, such as lagoon or other wet-separation processes, consume large amounts of water and add to water pollution due to leaching of toxic materials from fly ash. The other possible disadvantage is the need for a wide operational area, which is unsuitable for densely populated countries. As wet-separation processes have some disadvantages, an improved and/or sustainable alternative recovery technique is required. An air classifier is one of the alternative techniques. In this study, two types of air classifiers, namely a closed-type pneumatic separator and a micron separator, have been investigated. In terms of separation efficiency, it was found that the micron separator has the potential to be applied in cenospheres recovery from coal fly ash, giving a Newton&apos;s efficiency of 0.44, as compared to a value of about 0.26 for the closed-type pneumatic separator. The cenospheres recoveries of both pieces of equipment at their optimum Newton&apos;s efficiencies were similar at over 60 wt.%. The separation performance was further assessed from the particle distributions of the overflow and underflow products obtained from both pieces of equipment, as well as from SEM images. It was found that the lower Newton&apos;s efficiency of the closed-type pneumatic separator was due to the re-concentration of fine particles in the underflow product at air-flow rates higher than 2.2 m/s (the underflow product yield was about 55 wt.%).
In order to further confirm the applicability of this technique, the micron separator, which had provided higher separation efficiency and cenospheres recovery, was deployed in a cenospheres recovery unit prior to the use of a wet-separation process (float and sink tank). About 80% of the cenospheres was recovered, with an 87.8% reduction in the total mass of fly ash to be separated in the float and sink tank. Consequently, much less water was needed for the process of cenospheres recovery. Moreover, it was also confirmed that the micron separator could yield higher quality fly ashes, that is. fly ash types I and II, from lower feed quality of fly ash type IV, which is the lowest category in commercial classification of fly ash according to JIS A6201. (C) 2010 Elsevier B.V. All rights reserved.

This paper describes a study of the effects of hydrothermal dewatering of raw tropical peat from Pontianak, West Kalimantan-Indonesia, on the amounts of organic compounds released into and gaseous products. Hydrothermal upgrading and dewatering of the peat was carried out in a batch-type autoclave reactor at temperatures between 150 and 380 degrees C at a maximum pressure of 25.1 MPa for 30 min. It was found that the extent of decomposition of organics during hydrothermal dewatering depended on temperature increase.
Wastewater from hydrothermal dewatering was found to contain organic carbon (TOC) ranging from 800 ppm at low temperatures, to 7504 ppm at high temperatures. A number of sugars and furans were detected in the wastewater at 250 degrees C, and organic acids and alcohols at all temperatures. Phenol and phenolic derivatives were observed at 250 degrees C, and significant amounts of CO(2), CO and H(2) were detected at all temperatures studied; CH(4) was detected only at 380 degrees C, but at this temperature CO(2) was no longer detected.
A simplified schematic diagram of the decomposition behavior of tropical peat in the hydrothermal dewatering process is discussed with respect to the change in the concentration of organics in wastewater and gaseous products as determined by TOC, GC, GC-MS and (13)C NMR analyses of the solids produced. (C) 2010 Elsevier Ltd. All rights reserved.

In this study, upgrading of agricultural waste, in the form of oil palm fronds and trunks, into solid biofuel was investigated using hydrothermal treatment. A slurry of 300 mL of water and 30 g of material was treated in a 500-mL batch autoclave equipped with stirrer, thermometer, and pressure sensor. Experiments were conducted in the temperature range 200-350 degrees C at an initial pressure of 2.0 MPa. The slurry was gradually heated to the target temperature and held for a further 30 min. Approximately 35-65% of the original material was recovered as a solid product with favorable solid fuel characteristics. The gross calorific value ranged from 19.9 to 29.7 MJ/kg and the equilibrium moisture content was 7.6-4.5 wt%. The carbon content varied from 51.4 to 78.5 wt% and the oxygen content was 42.1-16.1 wt% after upgrading. Changes in the solid composition and carbon functional groups following upgrading were identified by FTIR and C-13 NMR. In addition, analyses on the liquid product (by GC-MS) and the gas product (by GC) were carried out to clarify the decomposition behavior of material.

The purpose of this study was to characterize secondary minerals that were formed in the bioleaching of enargite (Cu(3)AsS(4)) by Acidithiobacillus ferrooxidans. Two parallel cultures were used: one was adapted to arsenic in the growth medium and the other was wild-type. The progress of the solubilization of As in A. ferrooxidans cultures was stepwise and different from that observed in the non-adapted culture. In contrast, the bioleaching of Cu and Fe from enargite was not affected by prior adaptation of the culture. Minor presence of jarosite was observed by X-ray diffraction (XRD) in solid residues after the bioleaching, and no other peaks of secondary crystalline minerals were detected. The relative intensities of As 3d and Fe 2p to Cu 2p in X-ray photoelectron spectroscopy (XPS) for the solid residues were at maximum at 46 days after the bioleaching with As-adapted A. ferrooxidans. The results from the examination of solid residues with XPS, transmission electron microscopy with energy-dispersive microprobe (TEM-EDS) and XRD after 46 days of contact with As-adapted A. ferrooxidans showed the presence of metastable, amorphous ferric arsenate as an intermediate on the surface of enargite and minor amounts of jarosite. The amorphous ferric arsenate phase did not appear to have an adverse effect of the dissolution of Cu from enargite. Crown Copyright (c) 2010 Published by Elsevier B.V. All rights reserved.

The adhesion behavior of Ferroplasma acidiphilum archaeon to pyrite mineral was investigated experimentally and theoretically. F. acidiphilum showed high affinity to adhere to pyrite surface at acidic regions, however low affinity was observed at neutral and alkaline regions. The microbe-mineral adhesion was assessed by the extended DLVO theory. Hamaker constants, electron donors, electron acceptors and surface charges for the microbe and the mineral were experimentally determined. The extended DLVO theory was used to explain the adhesion results. Significant changes to the pyrite surface properties after being treated with the microbial cells were observed. Pyrite lost its hydrophobic nature and became hydrophilic, the contact angle of untreated pyrite was 61 degrees and this decreased to 36 degrees after the treatment. As a consequence, the flotation experiment results showed that F. acidiphilum strain could act as a good depressant for pyrite in xanthat flotation; where in absence of F. acidiphilum cells, over 95% of pyrite can be recovered as a float. However, when the mineral was pretreated with F. acidiphilum cells, less than 20% can be recovered as a float. (C) 2010 Elsevier Inc. All rights reserved.

Forty-six deep groundwater samples from highly arsenic affected areas in Bangladesh were analyzed in order to evaluate the processes controlling geochemical constituents in the deep aquifer system. Spatial trends of solutes, geochemical modeling and principal component analysis indicate that carbonate dissolution, silicate weathering and ion exchange control the major-ion chemistry. The groundwater is dominantly of Na-Cl type brackish water. Approximately 17% of the examined groundwaters exhibit As concentrations higher than the maximum acceptable limit of 10 mu g/L for drinking water. Strong correlation (R(2) = 0.67) of Fe with dissolved organic carbon (DOC) and positive saturation index of siderite suggests that the reductive dissolution of Fe-oxyhydroxide in presence of organic matter is considered to be the dominant process to release high content of Fe (median 0.31 mg/L) in the deep aquifer. In contrast, As is not correlated with Fe and DOC. Boron concentration in the 26% samples exceeds the standard limit of 500 mu g/L, for water intended for human consumption. Negative relationships of B/Cl ratio with Cl and boron with Na/Ca ratio demonstrate the boron in deep groundwater is accompanied by brackish water and cation exchange within the clayey sediments. (C) 2010 Elsevier B.V. All rights reserved.

The degree of separation in the recovery of cenospheres from coal fly ash has been estimated for both wet and dry separation processes by applying the terminal velocity concept of particles. Particle diameter and density were determined by sieving industrial cenospheres and coal fly ash type IV, the model particles. This information was then utilized to calculate the terminal velocity needed to estimate the separation performances of both the wet and dry separation processes. Based on this estimation, the dry separation process performed similarly to the wet separation process, with an optimum Newton&apos;s efficiency of 0.54, only slightly lower than that of the wet separation process of 0.6. Moreover, it was observed that the cenospheres were concentrated in the underflow product, whereas for the wet separation process the reverse was true. The findings of this assessment were verified using a micron separator. Similar tendencies in the concentration of cenospheres in the underflow products were obtained. An optimum Newton&apos;s efficiency as high as 0.44 was achieved, with 66% recovery of the cenospheres. The recovery of the cenospheres was only 4% lower than the estimated value (70%), from which we conclude that dry separation processes are interesting technologies to apply to the recovery of cenospheres from coal fly ash because of their high efficiencies. (C) 2010 Elsevier B.V. All rights reserved.

In this study, hydrothermal upgrading and dewatering of raw tropical peat derived from Pontianak, West Kalimantan-Indonesia was evaluated at temperatures ranging from 150 to 380 degrees C, a maximum final pressure of 25.1 MPa and a residence time of 30 min. The moisture content of the raw peat was approximately 90 wt.%. Raw peat was hydrothermally upgraded without the addition of water in the laboratory scale. The yield of the solid products was between 53.0 and 99.7 wt.% and the effective calorific value of hydrothermally dewatered peat was between 17,290 and 29,209 kJ/kg following hydrothermal upgrading. In addition, the oxygen content in the solid product was varied from 38.4 to 15.6 wt.% after upgrading, while the carbon content from 55.2 to 77.8 wt.%. The hydrothermally upgraded peat fuel product also had an equilibrium moisture content of 2.3 wt.% and a maximum equilibrium moisture content of 17.6 wt.%. Upgraded peat is characteristically resistant to moisture adsorption at high humidity, which makes it promising for fuel based combustion. The change in the carbon-functional groups and their properties, as determined by FTIR and C-13 NMR, are discussed in terms of the hydrothermal upgrading and dewatering process. (C) 2009 Elsevier Ltd. All rights reserved.

Effluents from bioleaching processes cause severe problems if dispersed in the environment since they typically have very low pH values and high sulfate and ferric iron concentrations. Dissolved iron may also interfere with the metal recovery. In the bioleaching circuit, partial removal of dissolved iron and sulfate is needed to alleviate process disturbances. In this study, an integrated, bench-scale process comprising a fluidized-bed reactor (FBR) and a gravity settler was developed for controlled biological oxidation of ferrous iron and precipitative removal of ferric iron and sulfate for use in waste management of heap bioleaching processes. The FBR for iron oxidation by an enrichment culture dominated by Leptospirillum ferriphilum was operated at 37 +/- 2 degrees C. The FBR recycle liquor was partially neutralized with 10 M KOH or 50 g/L CaCO(3) slurry to promote ferric iron and sulfate precipitation. With 6 +/- 1.5 g Fe(2+)/L in the feed and KOH-adjusted pH 3.5, the oxidation rate of Fe(2+)/L was 3.7 g/L h and 99% precipitation of ferric iron was achieved in the process. Adjustment with CaCO(3) to pH 3.2 slightly decreased the oxidation rate to 3.3 g/L h and 98% of ferric iron precipitated. With 15 g Fe(2+)/L in the feed, the oxidation rate was 7.0 g Fe(2+)/L h coupled with 96% precipitation of ferric iron. A solid solution of jarosite was the main product of ferric iron precipitation with KOH adjustment and with minor amounts of goethite at the higher pH range. Adjustment of the pH with CaCO(3) precipitated ferric iron also as a solid solution of jarosite, and sulfate precipitated also in the form of gypsum (CaSO(4)center dot 2H(2)O) especially at the higher pH values. (C) 2009 Elsevier B.V. All rights reserved.

Decomposition behavior of each part of oil palm residue (EFB, fiber, trunk, frond) using a hot-compressed water (HCW) at 200°C in batch and semi-batch treatment was examined. As a result, the water insolubles in batch treatment was more than that in semi-batch treatment. On the other hand, in both treatment, most of hemicellulose was solubilized, while most of cellulose remained in the residue. These behaviors did not depend on feed materials. However, in case of lignin, solubilization ratio in batch treatment was less than that in semi-batch treatment.

Decomposition behavior of each part of oil palm residue (EFB, fiber, trunk, frond) using a hot-compressed water (HCW) flow type reactor at 200℃ was examined. Approximately, 40〜60mg% of the samples was decomposed. Particularly, Most of hemicellulose was solubilized, while most of cellulose remained in the residue. These behaviors did not depend on feed materials. However, in case of lignin, solubilization ratio depended on them. That is, lignin in Trunk and Frond was easy to solubilize in comparison with that in EFB and Fiber.

Chalcopyrite (CuFeS2) occurs sometimes in association with As-bearing copper ores, such as enargite (Cu3AsS4) and tennantite (Cu12As4S13), especially in deep ore bodies. To employ oxidative pretreatment for recovering copper resources from these minerals, it is important to characterize the surface properties of enargite and tennantite as well as chalcopyrite. The minerals were oxidized in 0.013% H2O2 with O-2 bubbling at pH 2.5, and 11 followed by analysis with X-ray photoelectron spectroscopy. Elemental sulfur was formed most significantly at pH 2 in all sulfide mineral samples. Enargite was the most stable under the oxidative conditions. Arsenic in enargite was partly oxidized at pH 5. Substantial proportion of copper in tennantite was oxidized from Cu(I) to Cu(II) at pH 11. The dissolution rate of Cu from tennantite at pH 2 was by far the fastest, and incongruent dissolution of Cu occurred with suppression of As and S in tennantite. These selective differences in the oxidation may be of use in designing a flotation process for separation of these sulfide minerals. (C) 2009 Elsevier B V All rights reserved.

The adhesion of Escherichia coli onto quartz, hematite and corundum was experimentally investigated. A strain of E. coli was used that had the genes for expressing protein for silica precipitation. The maximum cell adhesion was observed at pH &lt; 4.3 for quartz and at pH 4.5-8.5 for corundum. For hematite, cell adhesion remained low at all pH values. The microbe-mineral adhesion was assessed by the extended DLVO theory approach. The essential parameters for calculation of microbe-mineral interaction energy (Hamaker constants and acid-base components) were experimentally determined. The extended DLVO approach could be used to explain the results of the adhesion experiments. The effect of E. coli on the floatability of three oxide minerals was determined and the results showed that E. coli can act as a selective collector for quartz at acidic pH values, with 90% of the quartz floated at 1.5 x 10(9) cells/ml. However, only 9% hematite and 30% corundum could be floated under similar conditions. By using E coli and no reagents, it was possible to separate quartz from a hematite-quartz mixture with Newton&apos;s efficiency of 0.70. Removal of quartz from the corundum mixture was achieved by E coli with Newton&apos;s efficiency of 0.62. (C) 2009 Elsevier B.V. All rights reserved.

Preferential sorption of Co2+ ions over Ni2+ ions was achieved using biogenic Mn oxides produced by the Mn-oxidizing fungus Paraconiothyrium sp. WL-2 strain with a maximum selectivity coefficient (alpha(Co)) of 18. The selective sorption was based on different sorption mechanism for Co2+ and Ni2+ and unique properties of biogenic Mn oxides. The octahedral Co2+ ions occupy vacancies of central metal sites and edge sites in the octahedral Mn oxide unit structures of biogenic Mn oxides, where they are immobilized by oxidation to CoOOH by Mn(III). In contrast, Ni2+ ions are sorbed primarily on layer edges at circumneutral pHs without oxidation. Selective sorption of Co2+ over Ni2+ on the biogenic Mn oxides results from more vacant sites, higher Mn(III) contents, and larger specific surface areas compared to synthetic Mn oxides. [doi: 10.2320/matertrans.M-M2009821]

Unique properties of biogenic Mn oxides were applied to a fundamental study of separation and recovery of rare earth elements. Selective sorption of Ce(3+) over La(3+) ions was achieved at neutral pH values using biogenic Mn oxides produced by Paraconiothyrium sp. WL-2 strain. The selective coefficient for Ce(3+) (alpha(Ce)) was Much greater with biogenic and synthetic Mn oxides than those for La(3+) (alpha(La)). Ce(3+) ions were oxidized to CeO(2) by Mn(III, IV) in Mn oxides under anaerobic conditions resulting in the release of Mn(2+) ions, while La(3+) ions were sorbed without a redox reaction. With an increase in coexisting La(3+) ions, sorption of Ce(3+) oil both Mn oxides was significantly suppressed, especially with synthetic Mn oxides. The edges of the structure are competitive sites because of fewer numbers of vacant sites in synthetic Mn oxide layers. The preferential sorption oil the edge sites of Mn oxides is in the order of La(3+) &gt; Ce(3+). These phenomena call be expanded to separation and recovery of other rare earth elements from natural and anthropogenic Sources.

Acidithiobacillus ferrooxidans was acclimatized to 1000 mg/L arsenic(V) and then used for the bioleaching of enargite (Cu3AsS4) at pH 2. Secondary minerals formed during the bioleaching of enargite were characterized by X-ray diffraction, FT- infrared spectroscopy, Raman spectroscopy and X-ray photoelectron spectroscopy. Oxidative dissolution of enargite resulted in the formation of elemental sulfur, arsenate and oxidized sulfur species including jarosites and possibly also schwertmannite at pH 2.

A permeable reactive barriers (PRBs) column test was carried out to remove arsenic (As) and manganese (Mn) from groundwater using zero valent iron (ZVI), sheep manure, compost and woodchips as reactive materials. Arsenic was mainly immobilized through sorption and co-precipitation with iron-bearing minerals, and also possibly precipitation as FeAsO4. The presence of sulfate-reducing bacteria (SRB) in the inoculated column was suggested by decrease of sulfate concentrations and increase of delta S-34 in the effluent. Arsenic was more effective to immobilize in the inoculated than in the sterilized column due to co-precipitation with sulfides formed by reduction of sulfate in addition sorption and/or co-precipitation with carbonates. The Mn was mainly immobilized through adsorption onto compost and ZVI, and partly by precipitation as carbonates. Manganese was more effectively immobilized in the sterilized than in the inoculated column. Since compost is biodegraded, the capability of compost to immobilize Mn 2(+) decreased in the inoculated column. The result demonstrates that As is more effective to immobilize using mixture of sheep manure with ZVI than only ZVI as reactive materials in PRBs. [doi: 10.2320/matertrans.M-MRA2008827]

Permeable reactive barriers (PRBs) column tests were performed to investigate the contribution of anaerobic microbial community in sheep manure on the removal of As from groundwater. The column was packed with zero valent iron (ZVI), sheep manure, compost, wood chips, glass beads and gravels. All materials were sterilized except for sheep manure that contains anaerobic bacteria. Decrease in sulfate concentration was observed at the maximum rate of 0.26 mmol dm(-3) day(-1). In addition, the sulfur isotopic ratio of delta S-34 increased from the influent (-4.3 parts per thousand) to the effluent (0.2 parts per thousand), suggesting that there was sulfate-reducing activity in the microbial community. Arsenate was more effectively immobilized on ZVI than arsenite. Bacterial community analysis using polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) on 16S rRNA sequences suggested that majorities of bacteria were several Clostridium species and one species of Proteobacteria, Geobacter metallireducens GS-15, independently of PRBs column heights. Some of them might have contributed to the removal of arsenic. [doi: 10.2320/matertrans.M-MRA2008826]

The potential for immobilization of Se in mine drainage water using a permeable reactive barrier was investigated by a column study, in which the reactive components were zero valent Fe, municipal leaf compost, sawdust, and wood chips. These components were mixed with silica sand and gravel. Trace amounts of creek sediment were added to serve as a source of anaerobic bacteria. The influent concentration (40 mg L-1) of SeO42 - decreased to less than 2 mg L-1 within one week and to less than 0.014 mg L-1 within 1 month during passage through the column. In the column, the concentrations of SO42 - also were reduced from 620 to 220 mg L-1. After 2 months, cell populations of SO42 --reducing bacteria, estimated using the MPN method, were in the range of 106-107 cells g-1. Isotopic analysis of S showed δ34S = -9.19‰ for the input solution, and δ34S = -4.69‰ for the output solution. This change in isotopic ratio is attributed to the preferential utilization of 32 SO42 - over 32 SO42 - by SO4-reducing bacteria in the column. Geochemical calculations indicate that SeO42 - is stable in the influent water, and that conditions within the column favour reduction of SeO42 - to metallic Se or SeO32 -, and the reduction of SO42 - to S2-. © 2008 Elsevier Ltd. All rights reserved.

Immobilization of arsenate in groundwater impacted by acid mine drainage was investigated using a permeable reactive barrier (PRB) column bearing granulated blast furnace slag (GBFS) to compare with iron granules which are commonly used. Sorption capacity of arsenate onto the GBFS was quite lower than iron granules in the amount of sorbed arsenate per unit surface area of sorbents (mmol/m(2)) at the equilibrium, Q', in two orders of magnitude in batch tests, however, the amount of sorbed arsenate per unit amount of sorbents (mmol/kg) at the equilibrium, Q, were comparative to each other, because of much higher porosity in the GBFS. Results of column performance showed that 15 mg/L of As was decreased to be less than 0.4 mg/L for more than 18 pore volumes (pv) in the GBFS-PRB by sorption, co-precipitation and presumably formation of hydrated calcium arsenate, and less than 0.04 mg/L for more than 17 pv in the iron bearing PRB probably by co-precipitation with iron (oxyhydro)oxides. Additionally 15 mg/L of Mn2+ ions was also decreased to less than 0.3 mg/L and 0.03 mg/L, respectively, in iron bearing and the GBFS bearing PRB columns, probably caused by sorption and precipitation of oxides and carbonates. The GBFS has advantages to compensate its low reactivity with high porosity, to facilitate the industrial handling with low density, and to utilize industrial wastes for more valuable applications, emphasizing a potential of alternative reactive materials instead of iron granules in PRB for immobilization of arsenic and manganese in acid mine drainage.

A Mn-oxidizing fungus, Phoma sp. strain KY-1, showed a Mn-oxidizing activity of more than 1.82 mol m(-3) of Mn(II) at an optimum pH 6.8. Controlling the pH at between 6.5 and 7.3 was necessary for fungal oxidation of Mn(II). This is probably due to inactivation of the Mn-oxidizing enzyme by decrease in pH during the reaction. Carbon fiber was found to catalyze the oxidation of Mn(II), most significantly under more unfavorable conditions such as high Mn concentrations, coexisting inhibitive components, or lacking nutrients. Examinations of fungus used for actual Mn-rich mine drainage containing more than 1.46 mol m(-3) of Mn showed that organic nourishments and pH-buffering agents are both essential to obtain acceptable Mn removal rates and that the time required to attain the 10 mg dm(-3) (0.182 mol m(-3)), which is the maximum acceptable concentration of Mn in discharged wastewater in Japan, was about 170 h in the presence of carbon fiber.

Zeta potential measurements of silica-induced protein (SIP) Escherichia coli and quartz showed that the former are positively charged under acidic condition and negatively charged under neutral and alkaline conditions, with an isoelectric point (IEP) at pH 4.5, while the quartz was always negatively charged. Adsorption experiments with bacteria cells on quartz were conducted under different conditions. The results show that at pH values lower than the IEP of the cells, more cells were adsorbed due to electrostatic forces. However, at pH &gt; 4.5, the amount of adsorbed cells decreased as a result of electrostatic repulsion forces. Zeta potentials of quartz showed that at pH 2.5 a significant change in the surface chemistry of quartz occurred after bacterial treatment. The degree of this change was related to the initial SIP E. coli concentration; at 5 x 10(7) cells/ml the average zeta potential of biotreated quartz shifted from -30 mV to 0 mV and at higher concentrations the zeta potential shifted to the positive direction and reached a similar value to that of the bacterial cells. SIP E. coli showed hydrophobic properties at pH lower than the IEP, with approximately 60% of the cells moving to the organic phase from aqueous phase. Bioflotation of quartz using SIP E coli alone at pH 2.5 gave approximately 60% recovery because at this pH more bacteria adsorb onto the quartz surface and the bacterial surface is hydrophobic. In anionic flotation of quartz using sodium dodecyl sulfate, SIP E. coli cells act as a surface modifier, with an increase in flotation recovery from 28% to 85%. This is because the bacterial cells confer hydrophobic properties to the quartz and the biotreated quartz is positively charged, so a large amount of the collector was adsorbed and the recovery increased. (C) 2007 Elsevier Ltd. All rights reserved.

A Paraconiothyrium sp. WL-2 of Mn-oxidizing fungus is highly tolerant to Mn2+ ions, and capable of oxidizing more than 380 mg dm(-3) of Mn2+ ions, leading to the formation of a large amount of insoluble Mn(III, IV) oxides. The biogenic Mn oxides were characterized by X-ray diffraction, FT-Infrared spectroscopy, elemental analysis, measurement of specific surface area, scanning electron microscopy, and measurement of zeta potential, in comparison with the synthetic Mn oxides. It was found that the biogenic Mn oxide is poorly crystalized birnessite, with higher porosity and much more weakly bounded Mn(II) on the surface than the synthetic Mn oxide. Cobalt(II) ions were sorbed and incorporated as Co(III) into the structure of the biogenic Mn oxide. Sorption efficiency in the biogenic Mn oxide was 5.6 times as high as that in the synthetic ones. Relation of the relased Mn2+ ions to the immobilized Co suggested that Mn(IV) is preferentially used as oxidants over Mn(III) in the biogenic Mn oxide, and emphasized that the existence of Mn(III) in the biogenic Mn oxide activates the geochemical cycles of Mn and the other involved elements in environments.

Mt. Sanbe is an active volcano located in the Shimane prefecture, Japan. At south slope of Mt. Sanbe, hot springs (max 39.0°C) dissolved significant Fe2+ and Mn2+ discharge (Fe2+=0.9-6.9ppm, Mn2+=1.1-1.6ppm). Iron precipitates (Fe=68.9-76.4 %) and manganese precipitates (Mn=71.3-79.2 %) are distributed in 1m of central discharge point of hot springs. At 20-100m east of hot springs, many cold springs (11.8-20.1°C) dissolved Mn2+ (max 0.6ppm) discharge at several points. Manganese precipitates \(Mn=0.48-80.9%\) are widely distributed under flowing cold springs. We studied chemical and microbial precipitation process.

The purpose of this work was to isolate Cu-tolerant sulfate-reducers that could be used to produce copper sulfides under pure culture conditions. Three sulfate-reducing bacteria were isolated from wastewater effluents of a zinc-smelter in the Urals and their tolerance to copper varied between 325 and 2600 mg Cu l(-1). Analysis of 16S rRNA gene sequences placed the isolates in the genus Desulfovibrio. The isolates showed pronounced saccharolytic growth. Growing cultures precipitated Cu2+ as covellite (CuS) within less than a week. Extended incubation for 1 month lead to the formation of chalcocite (Cu2S) and chalcopyrite (CuFeS2).

The potential for Se removal from mine drainage water using permeable reactive materials was evaluated by a laboratory column experiment. The column materials, organic carbon and zero valence iron (ZVI), were exposed to mine drainage containing 630 mg L-1 SO42-. The influent water was spiked with 40 mg L-1 Se(VI) to assess the potential for Se removal. This high Se(VI) concentration was selected to ensure that there would be a sufficient mass of Se-bearing reaction products available for mineralogical characterization. The experiment was conducted in an anaerobic chamber to replicate the anaerobic conditions that prevail in permeable reactive barrier systems. After loading 10.8 pore volumes of input solution, the column effluent contained &lt;0.002 mg L-1 Se and &lt;300 mg L-1 SO42-. After the column experiments was complete the reactive materials were sampled in the anaerobic chamber and examined using scanning electron microscopy (SEM) coupled with energy dispersion X-ray analysis (SEM-EDAX), X-ray photoelectron spectroscopy (XPS) and by Raman spectroscopy. Sulfate was reduced to sulfide and elemental sulfur, which accumulated on the surfaces of the column materials. Se-bearing precipitates were observed at the base of column. Scanning electron microscopy (SEM) showed the presence of elemental Se, suggesting that Se(VI) was partly reduced to metallic Se(0). The XPS results revealed that selenate was reduced mainly to iron selenide (FeSe and/or FeSe2) on the surface of the column substances. These observations suggest that both chemical reduction and biologically mediated reduction of Se(VI) occurred.

A fundamental investigation on the extraction from biomass, low rank coal and their mixture during hydrothermal treatment was conducted by using a circulative equipment having a 10 cm³ cell. Beluga coal from Alaska, and Cryptomeria Japonica and empty fruit bunch of oil palm (EFB) were used as material samples of low rank coal and biomass, respectively. Biomass started to be decomposed at a temperature lower than that of low rank coal, which suggests that amorphous cellulose and hemicellulose were hydrolyzed. Frans such as furfural and 5-hydroxymethyl-2-furaldehyde (HMF) extracted from biomass were unstable as compared to phenol, and therefore decomposed and partially cyclized. It was considered that low rank coal adsorbed extracts from biomass due to the porous morphology. The possibility to predict the TOC from an on-line monitoring of the absorbance intensity in UV region during hydrothermal treatment was also shown.

Sorption of Co(II) on the biogenic Mn oxide produced by a Paraconiothyrium sp.-like strain was investigated. The biogenic Mn oxide, which was characterized to be poorly crystalline birnessite ((Na4Mn6Mn(IV))-Mn-(III) O-8(27)center dot 9H(2)O) bearing Mn(III) and Mn(IV) in the structure, showed approximately 6.0-fold higher efficiency for Co(II) sorption than a synthetic Mn oxide. XP-spectra of Co 2p for the biogenic and synthetic Mn oxides after Co(II) sorption indicate that Co was immobilized as Co(III) on the surface of Mn oxides, clearly suggesting that redox reaction occurs between Co(II) ions and each Mn oxides, The Co(II) ions would be initially sorbed on the vacant sites of the surface of biogenic Mn oxide, and then oxidized to Co(III) by neighbor Mn(III/IV) atoms to release Mn(II). For the synthetic Mn oxide, release of Mn(II) was negligibly small because the oxidant is only Mn(IV) in ramsdellite (gamma-MnO2). The Mn(II) release from the biogenic Mn oxide during Co(II) adsorption would be not only from weakly bounded Mn(II), but also from redox reaction between Mn(III/IV) and Co(II) ions.

Oxidation of Mn(II) ions in model drainages by a fungus genetically related to Phoma sp. was carried out in the presence of polyacrylonitrile-based carbon fiber, pitch-based carbon fibers formed at different heat treatment temperatures, and bamboo charcoal, aiming to understand the morphological effect of carbon materials on the microbiological activity of the manganese-oxidizing fungus. From the experimental results obtained so far, it was reasonably concluded that only carbon fiber accelerates the oxidation of dissolved Mn(II) ions by this fungus. When the carbon fiber shortened below certain length, the promoting effect was lost. The results strongly suggest that the shape of carbon, specifically the fibrous shape having flexibility, is a crucial factor in the promoting effect on the manganese oxidation by the present fungus.

The purpose of this study was to characterize Ni- and Zn-sulfides precipitated in sulfate-reducing bacterial cultures. Fe-free media containing 58 mM SO42- were amended with Ni and Zn chloride followed by inoculation. Precipitates were sampled from cultures after two weeks of incubation at 22, 45, and 60 degrees C. Abiotic controls were prepared by reacting bacteria-free liquid media with Na2S solutions under otherwise identical conditions. Precipitates were collected anaerobically, freeze-dried and analyzed by x-ray diffraction (XRD), scanning electron microscopy, and for total Ni, Zn, and S. In Ni-containing media, biogenic sulfide precipitates were mostly heazelwoodite (Ni3S2), whereas abiotic precipitates were mixed heazelwoodite and vaesite (NiS2). The biogenic Ni-precipitates were better crystalline than the corresponding abiotic samples. Sphalerite (ZnS) was identified by XRD in precipitates sampled from Zn-containing media. Scanning electron microscopy revealed disordered morphological features for the sulfides, which occurred mostly as aggregates of fine particles in biogenic samples, whereas abiotic precipitates contained more plate- and needle-like structures.

Three strains of Mn-oxidizing fungi were isolated from manganese-rich aquatic environments: sediment in a stream (Komanoyu) in Mori-machi and inflow to an artificial wetland in Kaminokuni-cho, Hokkaido, Japan. The characteristics of each strain were then established. Genetic analysis based on the ribosomal RNA (rRNA) gene was performed to clarify their classification. The sequences of the 18S rRNA and internal transcribed spacer (ITS1)-5.8S rRNA-ITS2 genes showed that all three strains are Ascomycetes. Based on its morphology, it seems probable that the KY-1 strain from Mori-machi belongs to the genus Phoma or Ampelomyces. The phylogenetic analysis indicates that this strain belongs to Phoma rather than Ampelomyces. Morphological identification of WL-1 and WL-2 strains from Kaminokuni-cho was impossible because of the lack of a sexual stage and specific organs. Phylogenetic analysis of the sequence in the ITS1-5.8S rRNA-ITS2 gene suggests that the WL-1 strain corresponds to Paraconyothyrium. sporulosum? and that WL-2 also belongs to the genus Paraconiothyrium. Because the ability to oxidize Mn has not been evaluated for most species of Phonza or Paraconiothyrium (Coniothyrium), further study is needed to confirm the status of these three strains.

Sulfate-reducing bacteria (SRB) play a major role in the precipitation of metal sulfides in the environment. In this work, biogenic copper sulfide formation was examined in cultures of SRB and compared to chemically initiated Cu sulfide precipitation as a reference system. Mixed cultures of SRB were incubated at 22, 45, and 60 degrees C in nutrient solutions that contained copper sulfate. Abiotic reference samples were produced by reacting uninoculated liquid media with Na2S solutions under otherwise identical conditions. Precipitates were collected anaerobically by centrifugation, frozen in liquid N-2, and freeze-dried, followed by analysis using X-ray diffraction (XRD), X-ray fluorescence, and scanning electron microscopy. Covellite (CuS) was the only mineral found in the precipitates. Covellite was less crystalline in the biogenic precipitates than in the abiotic samples based on XRD peak widths and peak to background ratios. Poor crystallinity may be the result of slower precipitation rates in bacterial cultures as compared to the abiotic reference systems. Furthermore, bacterial cells may inhibit the nucleation steps that lead to crystal formation. Incubation at elevated temperatures improved the crystallinity of the biotic specimens.

Hydrothermal treatments of mixtures of Beluga coal and Cryptomeria Japonica were conducted by using a slurry of 10wt% density, fed at 10 kg/h rate in the reactor of a bench-scale continuous equipment, the temperature and pressure of which were set at 300°C and 12 MPa, respectively. The reaction time was 30 minutes. It was found that, during the hydrothermal treatment, the yield of solid phase decreased and the total organic carbon (TOC) of liquid phase increased as the biomass-mixing ratio increased. That means that the biomass was more decomposable than the coal. Besides, volatile matter in the material sample showed a higher decomposability, as compared with fixed carbon, and part of the decomposed volatile matter was considered to produce new aromatic compounds and carboxylic acids through repolymerization to fixed carbon. As a consequence, the gross calorific value of the solid phase of the hydrothermally treated mixture became higher with increasing biomass-mixing ratio on a dry basis. Considering ash content, the solid phase showed negligible change in gross calorific value, independent of the mixing ratio; it was ca. 7300 kcal/kg on a dry ash-free basis. In addition, it is worth mentioning that a five-hour run using a bench-scale continuous equipment was conducted successfully.

A Mn-oxidizing fungus was isolated from a constructed wetland of Hokkaido (Japan), which is receiving the Mn-impacted drainage, and genetically and morphologically identified as Paraconiothyrium sp.-like strain. The optimum pHs were 6.45-6.64, where is more acidic than those of previously reported Mn-oxidizing fungi. Too much nutrient inhibited fungal Mn-oxidation, and too little nutrient also delayed Mn oxidation even at optimum pH. In order to achieve the oxidation of high concentrations of Mn like mine drainage containing several hundreds g-m(-3) of Mn, it is important to find the best mix ratio among the initial Mn concentrations, inocolumn size and nutrient concentration. The strain has still Mn-tolerance with more than 380 g-m(-3) of Mn, but high Mn(II) oxidation was limited by pH control and supplied nutrient amounts. The biogenic Mn deposit was poorly crystallized birnessite. The strain is an unique Mn-oxidizing fungus having a high Mn tolerance and weakly acidic tolerance, since there has been no record about the property of the strain. There is a potentiality to apply the strain to the environmental bioremediation.

Morphological characterization of jarosite groups formed from Fe(III) biologically oxidized with different numbers of Acidithiobacillus ferrooxidans was conducted using FE-SEM. The higher population of A. ferrooxidans resulted in more distinct jarosite mineral shape, and stronger Raman intensities for potassium jarosite, ammoniojarosite and argentojarosite. The morphology of the jarosites might he dependent oil iron-oxidizing activity of A. ferrooxidans.
The technique was applied to identify jarosite compounds formed during microbially mediated dissolution of arsenopyrite by A ferrooxidans. It is difficult to identify this jarosite compound by X-ray diffraction and Raman spectroscopy because amounts are typically low and the crystallization is poor in minerals formed by microbially mediated oxidation. However, FE-SEM image provided helpful information for identification of jarosite compounds.
The results suggest that morphology would provide useful information for identification and history of jarosite minerals as geochemical samples.

Zeta-potential measurements were made to determine the electric state of phosphor materials on the basis of which a feasibility study could be performed for the use of flotation in the recovery of fine (d50 &lt; 13 gm) rare earth phosphors from waste fluorescent lamps. Tests were carried out with pure specimens of white (calcium halo-phosphate), red, green and blue (rare earth) phosphors, with a 17: 1 : 1 : I ratio of their mixture, and with actual waste phosphor materials. The effects of a cationic (dodecyl ammonium acetate, DAA) and two anionic (sodium dodecyl sulfate (SDS) and sodium oleate (NaOl)) collectors on the floatability of materials, as well as that of Na2SiO3 dispersant on the separation characteristics, were investigated at different pH ranges. The process, applied to actual discarded waste phosphors gave, in a two-stage separation scheme, sink products assaying 17.7-23.8% and 21.5-25.9% rare earth phosphors for DAA and SDS flotation, respectively. The recovery and Newton's efficiency were about 70-90% and 0.26-0.37, 66-82% and 0.18-0.20, respectively for DAA and SDS flotation. (c) 2005 Elsevier B.V. All rights reserved.

Experiments were carried out with waste phosphors collected during the recycling of end-of-life fluorescent lamps to obtain a highly enriched phosphors product as starting material for the better extraction of rare earth elements. The aim of this work was therefore to separate low-density calcium halo-phosphate phosphors from high-density rare earth-activated phosphors through dense-medium centrifugation (with di-iodomethane as organic dense-medium). The feasibility of the process and the conditions for a good separation (higher Newton's efficiency) appear to be a function of the rotation speed of the centrifugal separator, the pulp concentration and the adsorption of a surfactant (sodium oleate, NaOl) during the pre-treatment stage. The effect of the centrifugation time was less pronounced. Through this study, a sink product assaying 48.61% of rare earth-activated phosphors could be recovered from waste phosphor materials pre-treated with 5 x 10(-5) mol/dm(3) of sodium oleate (NaOl) surfactant. The Newton's efficiency and recovery of the separation were 0.84 and 97.34%, respectively. The process feasibility was reinforced by the possibility to recover, through laboratory batch tests, more than 99.8% of the di-iodomethane (CH2I2). (C) 2005 Elsevier B.V. All rights reserved.

Manganese-oxidizing microorganisms are distributed in a wide range of environments. Amorphous biogenic manganese oxides play a significant role in the control of trace phase distribution in aquatic system. Some of them, which are tolerant to extremely high concentrations of Mn and have optimum pH less than 7, can be practically applied to treatment high Mn water, such as Mn-rich mine drainage. Additionally, the biogenic Mn deposits are poorly crystalline and significantly porous, providing highly efficient reaction fields in the environments, which are approached for decomposition and molecular size reduction of organic compounds like humic substances, oxidants, adsorbents of toxic metals, and so on.

Despite the use of scallop shells for soil improvement and as bed materials in oyster cultivation, or as culvert fitting materials and food additive, a huge amount of this waste is stockpiled or discarded to land filling sites every year. Recently, the depletion of land filling sites, the sudden increase in the treatment cost of waste materials and the new environmental regulations are pushing for a continuous improvement of recyclable materials. The synthesis of needle like crystals of aragonite from pulverized scallop shells, mainly made of the calcite form calcium carbonate, to get a product that could be used as filler for plastics, rubber, paper, follows this objective.
In the present study aimed at the synthesis of crystals of different size and different aspect ratio of the aragonite form calcium carbonate, scallop shells were pulverized, calcined, and then hydrated, to have mainly Ca(OH)(2) as starting material. The conversion of calcite into aragonite form was made by treating in one stage or two stage chemical process the dissolved Ca(OH)(2) with MgCl2 and CO2 at relatively low temperature, 35 degrees C and 60 degrees C respectively. Parameters such as pulp density and pH, MgCl2 concentration, CO2 flow rate and mixing conditions were investigated through the study. SEM and XRD analyses of dried precipitates indicate that crystals of 1.36-12.33 mu m in length and 0.10-0.49 mu m in width, with an aspect ratio of 7.15-25.16 could be obtained by these methods. Besides ultrasonic waves stirring was suggested to prevent synthesized crystals Z aggregating.

A manganese-oxidizing fungus was isolated from a hot spring in Japan. The fungus was increasingly effective at oxidizing Mn(II) ions as the concentration of organic carbon sources in the growth medium was decreased. The fungus oxidized 50 ppm of Mn(II) ions within 160 h in a pH 7.3 medium at 25°C. The presence of carbon fiber shortened the time to 80 h, and promoted steady oxidation. The oxidation products were identified by XPS and XRD to be poorly crystallized and amorphous MnO2, both with and without the fiber. These results suggest that the fiber participates in kinetically limited oxidation. The fungus was entangled with and clung to the fibers, and the oxidized Mn species accumulated on the fungus. Similarly shaped polyethylene telephthalate fiber did not enhance the oxidation, nor was adhesion of the fungus observed. Although the mechanism is still unknown, the present work shows that removal of Mn from solution through the precipitation and accumulation of Mn-oxides on the fungus in the presence of carbon fiber is a promising improvement for water treatment. © 2004 Wiley Periodicals, Inc.

In hydrothermal treatment Cryptomeria Japonica (gymnosperm) was treated at temperatures of 270-330 °C in the presence of liquid water for 30 minutes using an autoclave of 10 L capacity. The solid product having heating values of 7,000-7,200 kcal / kg (dry basis) was obtained at yields of 48-55 %. The FT-IR, proximate and ultimate analysis results of this solid product were similar to those of the solid product obtained by hydrothermal treatment of Acacia Mangium (dicotyledonous angiosperm) reported in our previous paper. The liquid product is composed of mainly methyl alcohol, acetic acid, ...

Liquid products produced in a hot water drying (HWD) process of Beluga low rank coal were characterized by GC/MS, HPLC, GPC, TOC measurement and cyclic voltammetry. The Beluga coal was treated at three different temperatures, namely 270, 300 and 330°C. The ability of the liquid products to reduce Cr(VI) was investigated by analyzing the solution containing the liquid and Cr(VI), using Fluorescence Spectrometry. With increasing treatment temperature TOC concentration of the liquid products became larger. The liquid product at 270°C contained acetic acid, acetic acid-methyl ester and oligome...

The vertical distributions of heavy metals and other elements in sediment core samples in a landfill of abandoned mine tailings were examined. Core samples were analyzed by XRF and XRD, and further examined by ICP-AES measurements after acid-sequential extraction with HCl, HE and HNO3. According to XRD, the sediments contained alpha-quartz as the main component, and sericite, chlorite, rhodochrosite. pyrite, jarosite, sphalerite, and galena as minor components. A complete decomposition method using sequential extraction for the mine tailings sediments was established at ambient temperatures. Acid sequential extraction was useful for the analysis of minerals in mine tailings which are difficult to detect by XRD. Rhodochrosite and chlorite were dissolved by HCl-extraction, quartz and sericite by HF-extraction, and sulfides by HNO3-extraction. Rhodochrosite was the main source of high concentrations of Mn in mine drainage, highly distributed below the - 100 cm zone in the mine tailings, combined with pyrite but not with sericite and quartz. The distributions of most heavy metals were related to those of pyrite.

Aragonite type of calcium carbonate was synthesized via amorphous calcium carbonate from calcined scallop shell. The effect of aging and Mg²⁺ ion addition on polymorphism of the product was determined, and the mechanism of formation of aragonite is discussed. Aging of amorphous calcium carbonate first led to the formation of calcite and unstable vaterite, and the vaterite was then converted to aragonite with the longer aging. The addition of Mg²⁺ ions further enhanced the formation of aragonite. The elemental analysis by atomic absorption spectrometry and the characterization of the products by EPMA and XRD showed that Mg²⁺ ions were preferentially adsorbed on the calcite nucleus, then involved in the growing calcite (not needlelike crystal like aragonite). This adsorption inhibited the growth of calcite, leading to aragonite formation.

To clarify the formation mechanism of acid mine drainage and to propose a method to alleviate this environmental problem, the microbially-mediated dissolution of pyrite and its suppression was investigated. First, the dissolution of pyrite with the iron-oxidizing bacteria, Thiobacillus ferrooxidans, was investigated by both a solution analysis (ICP-AES) and a mineral-surface analysis (XRD, XPS, FTIR, and XMA). A microbial attack on pyrite by T. ferrooxidans proceeds mainly by the "indirect contact mechanism". An abiotic dissolution of pyrite with Fe(III) ions around pH 2 was found to be suppressed by the complexation of Fe(III) ions with anionic ligands, such as oxalate, and also by a preferential adsorption of Cu(II) and Fe(II) ions. Tannic and fulvic acids were found to be more effective inhibitors of T. ferrooxidans and T. thiooxidans than oxalic acid, reported by others. Finally, originally isolated fulvic acids were used to elucidate the suppression of the microbially mediated dissolution of pyrite by T. ferrooxidans and T. thiooxidans. The suppression was due to the inhibition of microorganisms by organic acids and their adsorption to active sites of the pyrite surface, as well as the reduction and complexation of Fe(III) ions by them. The results indicate that humic substances would be useful for the remediation and prevention of damage caused by acid mine drainage

Bacterial leaching is often applied to recover useful metallic elements from low grade ores; an understanding of the leaching mechanism is necessary to improve the efficiency of this process. In the present work, surface analysis by XPS was carried out on pyrite (FeS2) after leaching with Thiobacillus ferrooxidans for 1 to 11 d. The measured complex spectra were analyzed by the concept of differential charging effects; it was found that Fe(II, III), S, SO4(2-), and probably SO3(2-), are formed on the pyrite. The accumulation of K+ ions was also found with more than 6 d of leaching. Although the observed elemental S is considered to be an intermediate product in the indirect leaching mechanism, the formation on pyrite particles during the bacterial leaching has not been directly observed. The assignment of the SO3(2-) peak is still conditional but, as a metabolic intermediate, the formation of SO3(2-) ions in the cell has been proposed by others. The time variations in the mole ratios of species of S or K vs. Fe in the surface products are helpful to understand the leaching mechanism. The accumulation of Fe(III), SO4(2-), K+ and OH- ions on the surface with leaching suggests the formation of insoluble compounds, such as jarosite (chemical formula: K[Fe3(SO4)2(OH)6]).

In the previous report, the authors considered the leaching mechanism of chalcopyrite concentrate by Thiobacillus ferrooxidans, and pointed out that leaching rate was mainly controlled by the deposition of elemental sulphur on the mineral surface. In this report, the effect of the coexistence of Thiobacillus thiooxidans, whose energy source is elemental sulphur, with Thiobacillus ferrooxidans on the leaching of a chalcopyrite concentrate was investigated. During the culture of both species the relation between the surface tension of the culture medium and cell number was examined, and the phospholipid which is one of the extracellular substances in the culture of both microorganisms were qualitatively analyzed by thin layer chromatography. The leaching efficiency of a chalcopyrite was conspicuously improved by the coexistence of Thiobacillus thiooxidans with Thiobacillus ferrooxidans. The results indicated that in order to make efficient the leaching of chalcopyrite concentrate, it is necessary that the reactions of equations (1) to (3) or (4) mentioned in the text must consecutively proceed. However, the initially high leaching rate of chalcopyrite did not continue to the complete dissolution of chalcopyrite. The reason is that the growth of Thiobacillus thiooxidans was depressed by the increase of ferrous ion concentration, and that it became impossible to keep the sequence in the above mentioned reactions. Accordingly it is indicated that in order to improve further the efficiency of leaching it is necessary to artificially control the chemical constituents of the leaching solution. As the cell number increased, the surface tension of the culture medium decreased. Phosphatidylethanolamine and phosphatidylglycerol were detected as phospholipid. The phospholipid is polar-nonpolar substance, accordingly these extracellular substances would affect the leaching rate.