Effect of vermiculite modified with nano-iron-based material on stabilization of lead in lead contaminated soil

Lead (Pb) contamination arising from the production of lead-acid batteries is getting more severe, and research on its treatment technology reflects the increasing concern worldwide. Vermiculite is a mineral with a layered structure, containing hydrated magnesium aluminosilicate and has high porosity and large specific surface area. Vermiculite has the ability of improving soil permeability and water retention performance. However, in recent studies, vermiculite is shown to be less effective than other stabilizing agents in immobilizing heavy metal Pb. Nano-iron-based materials have been widely used to adsorb heavy metals in wastewater. Therefore, vermiculite has been modified with two nano-iron-based materials-nanoscale zero-valent iron (nZVI) and nano-Fe₃O₄ (nFe₃O₄) to improve its immobilization effect for the heavy metal lead. SEM and XRD analysis confirmed that nZVI and nFe₃O₄ were successfully loaded on the raw vermiculite. XPS analysis was applied to further understand the composition of VC@nZVI and VC@nFe₃O₄. The stability and mobility of nano-iron-based materials were improved after being loaded on raw vermiculite, and the Pb immobilization effect of modified vermiculite on Pb-contaminated soil was evaluated. Adding nZVI-modified vermiculite (VC@nZVI) and nFe₃O₄-modified vermiculite (VC@nFe₃O₄) increased the immobilization effect and decreased the bioavailability of Pb. Compared with raw vermiculite, adding VC@nZVI and VC@nFe₃O₄ increased the amount of exchangeable Pb by 30.8% and 6.17%. After leaching ten times in soil column leaching experiments, the total concentration of Pb in the leachate of the soil with VC@nZVI and VC@nFe₃O₄ were reduced by 40.67% and 11.47%, compared with raw vermiculite. These results prove that the modification with nano-iron-based materials enhances the immobilization effect of vermiculite, in which the effect of VC@nZVI is significantly better than VC@nFe₃O₄. Vermiculite was modified with nano-iron-based materials, resulting in a better fixing effect of the modified curing agent. This study provides a new approach for the remediation of Pb-contaminated soil, but further research is needed for soil recovery and utilization of nanomaterials.