Salt ions affect the remediation of Cr(VI)-contaminated groundwater using a simulated permeable reactive barrier filled with sulfidated nano-scale zerovalent iron (S-nZVI)

Hexavalent chromium (Cr(VI)) posts a great risk to humans and living organisms. In recent years, sulfidated nano-scale zerovalent iron (S-nZVI) has gained increasing attention for its potential in Cr(VI) removal due to its exceptional physical and chemical properties. However, limited studies have explored the application of S-nZVI in remediating groundwater polluted by Cr(VI), particularly the effects of salt ions on S-nZVI-based permeable reactive barrier (S-nZVI/PRB) reactors. To address this gap, both experimental and computational approaches were employed in this study to investigate the performance of S-nZVI/PRB reactors for Cr(VI) treatment under background solutions with various salt ions. The results demonstrated 1.2–2.0 times higher Cr(VI) removal efficiencies with the existence of Ca²⁺ and Mg²⁺ (introduced as CaCl₂ and MgCl₂) compared to pure water and NaCl solutions. In contrast, CO₃²⁻ (introduced as Na₂CO₃) exhibited a strong inhibitory effect with a Cr(VI) removal capacity of only 34 mg g⁻¹, lower than the 104 mg g⁻¹ observed in NaCl solution. Density functional theory calculations revealed that different ionic species influenced the interaction between Cr(VI) and S-nZVI by occupying active adsorption sites and altering the free energy of intermediate reduction products. These findings deepen our understanding on how various ionic species in groundwater influence the Cr(VI) removal by S-nZVI. This study provides essential scientific insights to support the application of S-nZVI/PRB reactors for in-situ remediation of groundwater polluted by heavy metal and also provides reference for environmental management strategy.