Enhancing Electrokinetic Remediation of Cadmium- Contaminated Soils with Stepwise Moving Anode Method

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Abstract
This paper proposed an innovative approach by stepwise moving anode towards cathode to enhance the cadmium (Cd) removal from soil during the process of electrokinetic (EK) remediation. Fixed anode tests and moving anode tests were carried out for 60 hours to compare their performances. The anode-cathode spacing was 21 cm. Constant voltage grade of 1.0 V cm− 1 was applied in this study. The parameters included pH, electrical conductivity, current, Cd concentration and speciation distributions, energy consumptions, etc. It was found that the pH values in the moving anode tests were relatively lower than those of the fixed tests. In the moving anode test, the removal efficiency of Cd in the soils at the fraction of S4 was enhanced by 54.9% compared with that of the fixed anode tests. After 60 hours of treatment, approximately 80% of the spiked soils (100.63 mg · kg− 1 of Cd) in the system were successfully remedied in the moving anode tests; and the mean removal efficiency was 73% for actual field-contaminated soil (54.26 mg · kg−1 of Cd). It is effective to remedy actual contaminated soils. In addition, the cumulative energy consumptions were 59.29 kWhm− 3 and 31.52 kWhm− 3 for the fixed and moving tests, respectively. The results revealed that the Cd removal efficiency was improved by the moving anode method. Moreover, less energy was consumed in the moving test. The proposed approach does not need to introduce extra chemicals nor adjust the pH in the system to enhance the Cd removal by EK remediation. The basic idea proposed in this paper provides a novel and environmental friendly method to enhance the EK remediation of heavy metals contaminated soils.

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