Immobilization of high concentration hexavalent chromium via core-shell structured lightweight aggregate: A promising soil remediation strategy

Abstract

Among industrially polluted soils, chromium contaminated sites, especially hexavalent chromium (Cr6+) contaminated C6+ sites, are particularly difficult to manage. The Cr6+ in such soils is usually at a high concentration. Several studies show that sintering and solidification are effective ways to treat Cr6+ in soil. In this study, a core-shell lightweight aggregate (CS-LWA) was prepared using Cr6+ contaminated soil as the core and clean bulk materials as a shell to seal the Cr6+ pollutant in the core, and the shell prevents it from leaching out. A reductant, pulverized coal, was added to assist the solidification and improve chromium immobilization . The results show that this method can effectively reduce the leaching of chromium in polluted soil with varying chromium content, and that chromium leaching can be further reduced by increasing the amount of coating material. The chromium in leachate from coated CS-LWA mixed with 8% pulverized coal was only 0.02 mg/L, much lower than 1042.8 mg/L in leachate from untreated chromium-contaminated soil. Moreover, the strength, density, and water absorption characteristics of CS-LWA met the Chinese national standards, enabling its use as a lightweight aggregate for construction.