Optimization analysis and mechanism exploration on the removal of cadmium from contaminated soil by electrokinetic remediation

Cadmium (Cd) contamination in soil poses a serious threat to human health, and it is necessary to explore an insitu effective method to remove Cd from contaminated soil. In this study, electrokinetic technology was applied to achieve Cd removal and accumulation in soil. The cross-impact of voltage gradient, initial soil moisture content, and citric acid concentration of the electrolyte on the removal efficiency of Cd by electrokinetic remediation and the optimization condition were investigated. In addition, the migration mechanism of Cd in soil was explored by X-ray diffraction (XRD). The results show that the best removal rate of Cd from the anode region of soil (P1) could reach 97.32% through the electromigration and electroosmotic which was positively affected by the voltage gradient and the citric acid concentration. The removal rate of Cd in P2 was negatively correlated with the voltage gradient and the citric acid concentration due to the formation of soil-bound Cd (Cd-Soil) and cadmium citrate complexes (Cd-Cit) and the migration of Cd from the P1 region. The accumulation of Cd appeared in the cathode region (P3), which was increased as the voltage gradient increased, due to the formation of precipitates, and decreased as the citric acid concentration increased, due to its ability to neutralize OH- produced by electrolysis. In this study, the optimal conditions considering optimization were at voltage gradient = 1.4 V/cm; initial soil moisture content = 20%; citric acid concentration = 0.07 mol/L. This study demonstrated the in-situ removal of Cd from soil can be effectively achieved by electrokinetic technology, and the accumulation of Cd in part of soil can achieve the reduction of contaminated soil, which is conducive to the subsequent centralized treatment.