Removal of Oxyanion Forming Elements from Contaminated Soils through Combined Sorption onto Zero-Valent Iron (ZVI) and Magnetic Separation: Arsenic and Chromium as Case Studies

Mining techniques and waste disposal methods have improved significantly in terms of environment pollution, and this is noticeable primarily in developed countries, where several historic anthropogenic activities have left a legacy of heavily metal-contaminated sites. Current soil remediation techniques are expensive and often not environmental friendly. In this study, using zero-valent iron (ZVI) particles and magnetic separation techniques, laboratory experiments were conducted to remediate soils contaminated with either arsenic (As) or chromium (Cr). In addition to total concentrations, the association of As and Cr with the different geochemical fractions in soils was determined before and after treatment by chemical sequential extraction. The results showed that >73% of initial total As concentration and >92% of Cr were transferred from contaminated soils to ZVI particles, which were then retrieved by magnetic separation with a ZVI recovery efficiency of 99%. Soil's pH had a significant role in controlling As and Cr sorption onto ZVI particles. ZVI application rates (2.5% and 5%) did affect the removal of Cr, but not of As. Using abandoned cattle dipping soils, with an initial arsenic concentration of 24.1 mg/kg, treatment with ZVI and magnetic separation decreased the initial concentration by 60.58%. Overall, in addition to reducing metal pollution in soil and potentially eliminating phytotoxicity, this combination of metal sorption onto ZVI and retrieval by magnetic separation could also help shift away from the current definition of remediation to a new paradigm, which would focus on the recovery of metal resources.