Comparison of approaching and fixed anodes for avoiding the 'focusing' effect during electrokinetic remediation of chromium-contaminated soil

Approaching anode is used to decrease the 'focusing' effect during electrokinetic (EK) remediation of chromium-contaminated soils from a chromite ore processing residue (COPR) deposition site. Four EK remediation experiments were performed to compare the effect of approaching and fixed anodes. Various parameters, including current, pH, removal of chromium (Cr) and variation of Cr chemical fractionation were used to evaluate the process. Results show that approaching anode EK remediation (AA-EK) enhanced the current and decreased the pH of the soil. It improved not only the removal of Cr(VI) (92.50%) but also Cr(total) (35.96%). Citric acid as the catholyte was more suitable for reducing the 'focusing' effect and enhancing removal rate of Cr(total). After remediation, the four fractions of Cr(total) achieved broader distribution changes. AA-EK decreased the content of BCR2. BCR3 and BCR4 near the cathode. However, it increased the ratio of BCR1 in the sections near the anode, especially with citric acid as the electrolytes. The results indicate that the approaching anode method in the presence of citric acid is an advisable choice for remediation of chromium-contaminated soil. (C) 2012 Elsevier B.V. All rights reserved.