Experimental study on remediation of Cd-contaminated soil by electrokinetic permeable reaction barrier coupling

Coupled remediation by electrodynamic permeable reaction barrier (EK-PRB) could effectively remove heavy metal ions from contaminated soil in coal mine areas as this technology combines the advantages of both electrokinetic remediation and permeable reaction barrier. Taking Cd-contaminated soil as the research object, this study conducted physical simulation experiment of EK-PRB coupled remediation to investigate the evolution patterns of pH value of electrolyte and soil, Cd2+ removal efficiency, current and total electric energy consumption in coupled remediation. We found that the pH value of the electrolyte and current exhibited cyclic variations during the remediation process: the pH value of anode decreased while that of cathode increased, the current first increased and then decreased within the cycle. After remediation, the pH value and Cd2+ enrichment index of contaminated soil increased successively from anode to cathode. When a mixture of citric acid and NaCl was used as electrolyte, Cd2+ removal efficiency and current increased significantly, demonstrating maximum remediation efficiency. Montmorillonite as PRB active filling material could effectively reduce the OH- concentration and migration rate produced by cathodic electrolysis, showing higher removal efficiency of Cd2+, lower electric energy consumption, and maximum remediation efficiency. The voltage gradient is positively correlated with Cd2+ removal efficiency and electric energy consumption. Given factors such as Cd2+ removal efficiency, electric energy consumption and cost-effectiveness, the remediation efficiency reaches its maximum when the voltage gradient is 2.5 V/cm.