Electrokinetic remediation of a Cu contaminated red soil by conditioning catholyte pH with different enhancing chemical reagents

The effect of enhancement reagents on the efficiency of electrokinetic remediation of Cu contaminated red soil is evaluated. The enhancement agents were a mix of organic acids, including lactic acid + NaOH, HAc–NaAc and HAc–NaAc + EDTA. The soil was prepared to an initial Cu concentration of 438 mg kg−1 by incubating the soil with CuSO4 solution in a flooded condition for 1 month. Sequential extraction showed that Cu was partitioned in the soil as follows: 195 mg kg−1 as water soluble and exchangeable, 71 mg kg−1 as carbonate bound and 105 mg kg−1 as Fe and Mn oxides. The results indicate that neutralizing the catholyte pH maintains a lower soil pH compared to that without electrokinetic treatment. The electric currents varied depending upon the conditioning solutions and increased with an increasing applied voltage potential. The electroosmotic flow rate changed significantly when different conditioning enhancing reagents were used. It was observed that lactic acid + NaOH treatments resulted in higher soil electric conductivities than HAc–NaAc and HAc–NaAc + EDTA treatments. Ultimately, enhancement by lactic acid + NaOH resulted in highest removal efficiency (81% Cu removal) from the red soil. The presence of EDTA did not enhance Cu removal efficiencies from the red soil, because EDTA complexed with Cu to form negatively charge complexes, which slowly migrated toward the anode chamber retarding Cu2+ transport towards the cathode.