Medium-scale ex suit electrokinetic remediation of Cd and Zn polluted soil enhanced by EDTA, tartaric acid, citric acid and acetic acid

Abstract

Abstract:The effect of enhancement agents on the efficiency of electrokinetic (EK) remediation of contaminated soils has been extensively studied in the past few years. However, the larger scale ex suit EK remediation with enhancement agents has been rarely reported. In this study, medium-scale EK remediation tests (20 kg dry soil at a single test) enhanced by EDTA, tartaric acid, citric acid and acetic acid were carried out to remove Cd and Zn from the contaminated soil. The removal efficiencies of Cd and Zn were enhanced by EDTA, tartaric acid and citric acid, and the enhanced effect of acetic acid on removal efficiencies of Cd and Zn was less. The highest removal efficiencies of Cd and Zn were 22.2% (citric acid) and 23.3% (tartaric acid), respectively. Low removal efficiencies were ascribed to the accumulations of Cd and Zn in F1 (exchangeable) and F2 (carbonate-associated) fractions in the middle section soils after EK remediation for all tests. After EK remediation, the F3 (reducible) concentrations of Cd and Zn, lower than initial concentrations, increased with the distance from the anode for all tests. The results suggested that F3 fraction can be transformed into F1 and F2 fractions, and F1, F2 and F3 fractions were removable during the EK remediation. Comparing with the control test (CT), more variations of total concentration and speciation of Cd and Zn were found, indicating apparent effects of enhancement agents on heavy metal removal during EK remediation. The results are significant for the enlargement of ex suit EK remediation.