Focus on factors affecting pH, flow of Cr and transformation between Cr(VI) and Cr(III) in the soil with different electrolytes

To evaluate the extraction of Cr from contaminated soil by electrokinetics and study the factors affecting pH and the transformation between Cr(VI) and Cr(III), electrokinetic remediation (EKR) experiments were performed with different electrolytes under constant electric potential. The results indicated that the maximum difference in the pH of anolytes/catholytes in the experiments with the selected electrolytes was <0.8/1.2 after 25 h. Electrolyte pH is closely related to the current and electroosmotic flow (EOF). Soil pH almost remained above 7 due to the high acid buffering capacity of the soil. When the electrolytes was ultra-pure water, 0.1 M KCl and 0.1 M citric acid, Cr concentration in the real contaminated soil decreased by an average of 138.13 mg/kg, −45.04 mg/kg and 494.44 mg/kg, respectively. Material flows showed 13.07% of Cr removed out of the artificially contaminated soil, and the total Cr concentration reduced in artificially contaminated soil was almost twice of real contaminated soil when the same electrolyte was used. Cr in the anolytes with high Cr concentration returned to the soil. Based on the mass balance analysis more Cr(VI) reduced to Cr(III) than the oxidation of Cr(III) to Cr(VI) when citric acid and ultra-pure water were used as electrolytes.