Perfluorooctanoic acid (PFOA) contamination poses serious environmental risks due to its persistence and mobility. Conventional ex situ method using preformed layered double hydroxides (LDHs) shows limited performance, particularly under complex leachate conditions. This study developed an effective in situ Zn/Al LDH strategy for enhanced PFOA removal. Batch experiments, solid-phase characterization, and theoretical simulations were conducted to elucidate the adsorption mechanism and the effect of fluoride ion (F−). The results demonstrated that the in situ method exhibited superior performance in the presence of fluoride, achieving a PFOA adsorption density of up to 54.93 mmol/mol-Al, which is significantly higher than that of the ex situ method (26.76 mmol/mol-Al). Unlike the competitive adsorption observed in the ex situ method, the in situ process relies on synergistic mechanisms: F− participates in LDH formation as an interlayer anion and coordinates with Zn2+ and Al3+ to regulate LDH growth, thereby optimizing the surface chemical environment for PFOA capture. Molecular dynamics (MDs) and density functional theory (DFT) further showed that preferentially adsorbed F− affects hydrogen-bond networks and stabilizes PFOA through inner and outer sphere complexation. Overall, these findings clarify the fluoride-regulated adsorption mechanism and demonstrate the potential of in situ LDH coprecipitation for PFAS remediation in leachates.

Abstract

This study explores the potential of acrylonitrile butadiene styrene (ABS) resin, a bromine-containing plastic, for selectively separating PbO from a ZnO-PbO mixture. Thermodynamic calculations suggested the susceptibility of both PbO and ZnO to bromination by HBr from ABS resin. Initial trials showed limited PbO and ZnO volatilization. Combusting ABS resin and dust mixtures converts approximately 40 wt% of PbO to PbBr₂, but PbO volatilization selectivity remains below 30% due to concurrent ZnO volatilization. This low selectivity is due to the inhibiting effect of char and CO gas on PbBr₂ volatilization and the enhancement of ZnO volatilization. To improve PbO volatilization selectivity, operational parameters were varied. Increasing ABS resin size, decreasing pellet size, and altering the heating method raised PbO volatilization selectivity by over three times, with more than 60 wt% PbO volatilized. Microscopic analysis confirmed PbO bromination and volatilization as lead bromide compound (e.g., PbBr₂), while ZnO underwent direct volatilization through a carbothermic reaction. This study shows that optimizing operational parameters can selectively separate heavy metals using bromine-containing plastics. For practical application in steelmaking dust, it is crucial to examine the effects of coexisting Fe compounds.