Remediation of chromium(VI) in contaminated soil by schwertmannite: Leachability, long-term stability, and stabilization mechanism

It has been demonstrated that schwertmannite (Sch) has a strong adsorption ability for hexavalent chromium (Cr(VI)) in wastewater. However, the stabilization of Cr(VI) in soil by Sch has not been studied. In this study, Sch was first applied to the remediation of Cr(VI) contaminated soil. The stabilization effectiveness of Cr(VI) in soils was evaluated by the toxicity leaching tests. A pH-dependent leaching test was used to study the changes in leaching behavior when pH changed on site. The long-term stability of Cr(VI) by Sch was investigated through an up-flow column percolation test. The products of Cr(VI) adsorbed by Sch were characterized, and the stabilization mechanism of Cr(VI) on Sch was discussed. The results showed that in high and low concentrations of Cr-contaminated soil, a 10% addition of Sch reduced the leached- Cr(VI) concentration by 79.96% and 86.59%, respectively. The maximum leachable rate of Cr(VI) was reduced by 20.23% after 10% Sch treatment. The cumulative release rate of Cr(VI) was decreased by 85.79% when the cumulative liquid-solid ratio reached 20. The stabilization of Cr(VI) on Sch was mainly due to the ion exchange of CrO42- with SO42- and the formation of inner-sphere complexes. The results demonstrated that Sch has a significant stabilization effect and long-term stability on soil Cr(VI).