Removal and immobilization of heavy metals in contaminated soils by chlorination and thermal treatment on an industrial-scale

Abstract

Heavy metals contaminated soils are a potential exposure hazard to the public. This study demonstrated the application of chlorination and thermal treatment for remediation of heavy metals-contaminated soils on a full-industrial scale. Five soil samples were treated at a soil remediation factory equipped with an internally-heated rotary kiln (length: 17 m; diameter: 4 m; rotating speed: 0.60 rpm). The target soil temperature was set at about 950 °C. During treatment, calcium chloride was added to facilitate chlorination. The chlorination and thermal treatments effectively removed Pb and Cd and led to the slight removal of Cu and Zn but was not effective for Cr and Ni. Chlorination and thermal treatment also significantly reduced the bioaccessibility of heavy metals in soils, particularly Pb and Cd. The results of sequential extraction revealed that thermal treatment generally decreased the carbonate (C2), Fe/Mn oxide (F3) and organic matter (O4) fractions but tended to increase the residual (R5) fractions of heavy metals, indicating that the chlorination and thermal treatment also favored the immobilization of heavy metals. Overall, the results of this study suggest that remediation of heavy metals-contaminated soils by chlorination and thermal treatment is technologically feasible and that there is great potential for practical application of this method.