Interfacial charge-transfer-driven uptake and reduction of hexavalent chromium on amine-functionalized bentonite:...

Developing remediation agents that are both highly efficient and environmentally compatible remains a major focus for mitigating hexavalent chromium (Cr(VI)) contamination, particularly in mining-impacted soils. In this study, bentonite (Bent), attapulgite (ATP), and diatomite (DE) were modified with APTES, and solution-phase screening identified amine-modified bentonite (NH₂-Bent) as the best-performing agent, achieving a Cr(VI) removal efficiency of 95.3% was amine-modified bentonite (NH₂-Bent). Multidimensional structural and electrochemical analyses showed that the bentonite interface changed from anion-repulsive to highly electropositive with reduced electron-transfer resistance due to amine modification. This interfacial transformation shifted Cr(VI) removal from diffusion-limited adsorption toward adsorption-assisted interfacial processes involving enhanced electron exchange. Density functional theory calculations indicated that the introduction of amine groups strengthened Cr(VI) binding at the mineral interface and facilitated directional electron transfer from amine nitrogen atoms to chromium species. When applied to Cr(VI)-contaminated mining soils, NH₂-Bent reduced Cr(VI) bioavailability by 92.8% at a 3% amendment rate, markedly outperforming unmodified bentonite, while promoting the recovery of soil biochemical functions, as evidenced by increases in urease and sucrase activities by 157.1% and 102.2%, respectively. Therefore, NH₂-Bent emerges as a promising and environmentally compatible mineral amendment for mitigating Cr(VI) contamination in mining soils.