Study on the Combination of Composite Additives and Electric Remediation of Hexavalent Chromium Contaminated Soil

This study focused on hexavalent chromium-contaminated soil, investigating the effects and mechanisms of a composite additive composed of tartaric acid (TA) and potassium chloride (KCl) on electrokinetic remediation. The research first established different KCl concentrations (0.02-0.06 mol/L) combined with a fixed TA concentration (0.1 mol/L) to screen the optimal ratio, then compared it with single additives (TA or KCl) and a deionized water control group, analyzing changes in soil physicochemical properties, heavy metal speciation, and removal efficiency. The results showed that the composite additive significantly enhanced hexavalent chromium removal efficiency. The experimental group with TA and 0.04 mol/L KCl (FH-3) achieved an average hexavalent chromium removal rate of 86.45%, which was 23.45% higher than the control group, 4.01% higher than the TA-only group, and 16.97% higher than the KCl-only group. The total chromium removal rate also slightly increased, surpassing the control group of 3.50%. In terms of heavy metal speciation, post-remediation soil exhibited a dynamic shift between iron-manganese oxide-bound and residual chromium fractions, with an increased proportion of residual chromium in the cathode region, enhancing chromium stabilization and reducing bioavailability. Current intensity initially rose rapidly, with the composite additive group showing higher peak current than the control group, indicating that soluble ion concentration in the soil increased, promoting hexavalent chromium migration and transformation. Soil pH initially decreased and then rebounded, with slower recovery in the composite additive group, particularly in the anode region, which might be related to the adsorption of H⁺ and K⁺ from TA by the soil. Soil electrical conductivity significantly improved in the composite additive group, confirming enhanced ion migration. Overall, TA and KCl as a composite additive can effectively promote hexavalent chromium desorption and migration under electric fields, improve electrokinetic remediation efficiency, enhance soil physicochemical properties, thus having promising application potential.