Influence of redox potential on leaching behavior of a solidified chromium contaminated soil

Cement-based solidification/stabilization (S/S) technology is often used to remediate chromium (Cr) contaminated soils. The valence state and mobility of Cr in soils are closely related with redox potential (E_H). However, Cr mobilization from the solidified soils influenced by E_H has received little attention. In this study, semi-dynamic leaching tests and the toxicity characteristic leaching procedure (TCLP) were performed on a S/S treated Cr contaminated soil under various E_H conditions. The effective diffusion coefficient and leachability index were obtained from the leaching data to investigate the leaching behavior of Cr from the S/S treated soil. Speciation of Cr remained in the sample after the leaching process was obtained through the sequential extraction procedures. The results show that an increase in E_H increases the effective diffusion coefficient of Cr and, therefore, the amount of Cr leached. This result is attributed to immobile Cr(III) being oxidized to highly mobile Cr(VI). The leachability index results indicate that the cement solidification of Cr contaminated soil may not be appropriate under oxidizing conditions. For the TCLP and sequential extraction procedures, the leached amount of Cr exhibits a strong dependence on E_H. As E_H increases, the content of Cr remaining in the soil in unstable phases reduced, and more Cr was released to leachant.