Synergistic chemical reduction, photochemical reduction and ion-exchange driving forces within a FeS2/red soil–analcime zeolite composite for effective Cr(vi) remediation in groundwater

Abstract

Reduction and stabilization of hexavalent chromium (Cr(VI)) in groundwater are essential for mitigating environmental and human health risks. In this work, we demonstrate the development of FeS₂/Re-ANA composites (PM/RAs), a multifunctional material that integrates the chemical and photochemical reduction function within FeS₂ with the ion-exchange capacity of the red soil-converted ANA type of zeolites for effective reduction and stabilization of Cr(VI) in groundwater. The PM/RA-3 composite material obtained an impressive Cr(VI) removal rate of 98.90% in a solution with 1 mg L⁻¹ Cr(VI), reducing the residual concentration to 0.011 mg L⁻¹, which complies with the WHO standards for drinking water quality. A detailed mechanistic investigation reveals that FeS₂ facilitates both chemical and photoreduction of Cr(VI) to Cr(III), which is subsequently either adsorbed onto the FeS₂ surface or immobilized through an ion-exchange process within the zeolite microporous channels. Furthermore, fixed-bed column studies using groundwater samples contaminated with Cr(VI) from a chromate production facility double confirmed the material's effectiveness in meeting discharge standards under environmentally relevant water conditions. This work highlights the potential of employing FeS₂/Re-ANA composites as a promising material for treating Cr(VI)-polluted groundwater in permeable reactive barriers, offering a significant advancement for the control of the widespread Cr(VI)-contaminated groundwater pollution.