Study on the Performance and Mechanism of S-nZVI Loaded with Chitosan and Biochar to Efficiently Remove Cd²⁺ from Wastewater

Cadmium (Cd) pollution in aqueous solution has caused great threat to human health. A novel chitosan and biochar supported sulfide-modified nZVI composite (CB-S-nZVI) was synthesized by liquid phase reduction method and applied to the removal of Cd²⁺ from wastewater. The synthesized materials were characterized by SEM, BET, XRD, FTIR, and zeta potential. Batch experiments showed that the optimum synthesis conditions of CB-S-nZVI were the S/Fe molar ratio of 0.56 and the Fe/BC mass ratio of 2. The removal capacity of Cd²⁺ by CB-S-nZVI increased with the increase of pH and reached the maximum of 249.92 mg/g at pH of 9. Among the competitive cations, Pb²⁺ and Cu²⁺ had a strong inhibition to the removal of Cd²⁺. The removal process of Cd²⁺ conformed to the pseudo-second-order kinetic model and the Freundlich model, and it was exothermic. XPS analysis suggested that the removal mechanism of Cd²⁺ was mainly through electrostatic attraction, precipitation, and complexation. Overall, these findings provide new insights into the development of new nZVI-modified material, and CB-S-nZVI is promising in removing heavy metals from wastewater.