Synergism of citric acid and zero-valent iron on Cr(VI) removal from real contaminated soil by electrokinetic remediation

This study focused on enhanced electrokinetic remediation of Cr(VI) in real contaminated soil. The citric acid (CA) as the electrolyte and Fe(II) released from zero-valent iron (ZVI) under anoxic conditions functioned as the main reducer. They were used for overcoming the high insoluble Cr(VI) fraction in real contaminated soil and high Cr(VI) residue in acidic soil near the anode simultaneously. The synergism of CA and ZVI is that CA helps the release of Cr(VI) to react with the generated Fe(II) and alleviates the hindrance of Fe and Cr co-precipitates in electromigration of Cr; meanwhile, the end product Fe(III) from ZVI catalyzed the Cr(VI) reduction by CA. The removal of Cr(III) and Cr(VI) was significantly improved in real contaminated soil. The optimum result (82.86%) was obtained at a voltage gradient of 2.5 V/cm after 12-day remediation with a 10 g ZVI dose when the catholyte and anolyte were 0.2 mol/L and 0.1 mol/L CA, respectively. This configuration has a significant improvement in overcoming the current obstacles for Cr(VI) electrokinetic remediation from real contaminated soil and prospects for large-scale practical applications.