Electrokinetic remediation of cadmium-contaminated soil using polarity reversal method: Optimization analysis and mechanism exploration.

Electrokinetic remediation (EKR) has been applied for in-situ removal of Cd from contaminated soil, and the EKR enhanced with polarity reversal has achieved a higher Cd removal efficiency. However, the migration and accumulation mechanisms of Cd in the EKR process have not been investigated. In this paper, the cross-impacts of the voltage gradient, citric acid concentration in the electrolyte, and polarity reversal frequency on the removal efficiency by EKR of Cd and the optimization conditions were investigated. The migration and accumulation mechanisms of Cd were explored by analyzing the changes in electrokinetic process parameters, experimental phenomena, and X-ray diffraction (XRD) analysis. The results showed that the maximum removal efficiency of Cd reached 82.26%. The optimal conditions were determined by fitting the RSM model using the BBD design. In the EKR experiment with polarity reversal, Cd accumulated mainly in the middle part of the soil, attributed to the formation of chemical precipitation focusing area caused by soil pH transition, ion-induced potential gradient well trapping effect (IIPGWTE), or soil compaction induced by water loss. In conclusion, the various parameters have cross-impacts on the EKR of Cd-contaminated soil, and efficient in-situ removal of Cd from the contaminated soil can be achieved by adjusting the parameter conditions.