Removal of cadmium in contaminated kaolin by new-style electrokinetic remediation using array electrodes coupled with permeable reactive barrier

Electrokinetics is an in-situ soil remediation technique by which the flow direction of the pollutants can be controlled and soil with low permeability can be treated. In this study, the remediation of cadmium (Cd) contaminated kaolin by a new-style electrokinetics using an-ay electrodes (AEEK) coupled with permeable reactive barrier (AEEK-PRB) process was investigated and the effects were compared. Zeolite and zero-valent iron (ZVI) were used as the PRB material. The investigation firstly evaluated voltage gradients and soil moisture conditions, which ranged from 1.5-3.0 V/cm and 25%-40%, respectively. The best combination of parameters was a voltage gradient of 2.0 V/cm and a moisture content of 30%. The integration of PRB with AEEK could more effectively remove Cd from kaolin with citric acid as the electrolyte. The average removal rate reached the highest at 93.1%, when the initial Cd2+ concentration was 300 mg/kg. Morphological analysis of Cd before and after remediation showed AEEK-PRB could effectively remove most of the exchangeable Cd fraction and the carbonate fraction, as well as some of the organic matter-bound and Fe-Mn oxide-bound fraction, thus reducing the mobility and toxicity of Cd in soil. Cd-polluted soil remediation of AEEK-PRB was comparable to that of previously conducted electrokinetics.