Enhanced reduction of Cr(VI) in UV/EKR system by organic acids: Focus on Cr(VI) desorption and Fe(III) catalysis

Reducing highly toxic and mobile Cr(VI) to environmentally less hazardous Cr(III) is vital research for remediating Cr-contaminated soil. In this study, a UV/EKR system, which combined electrokinetic remediation (EKR) technology with ultraviolet (UV) photoreduction, was employed to investigate the enhanced reduction of Cr(VI) in actual contaminated soil by oxalic, malic, and tartaric acids. The results demonstrated that the introduction of UV radiation resulted in the removal of 99.49% of Cr(VI) from the anolyte and further enhanced the removal efficiency of high-concentration Cr(VI) in the near-anode soil layer by 14.83% compared to traditional EKR. Among the three acids, malic acid exhibited superior performance, as it alleviated the clogging caused by precipitates, provided more photocatalyst Fe(III), and reduced the retention of the reduction product Cr(III) in the soil. This resulted in the removal rates of 90.38%, 83.82%, and 27.14% of water-soluble, weakly bound, and strongly bound Cr(VI), respectively in the near-anode soil layer. Therefore, the combination of organic acids and the UV/EKR technique shows high compatibility, offering a promising solution to the poor reduction efficiency of Cr(VI) in actual soil in the field of EKR. This approach provides new insights for the in-situ remediation of Cr-contaminated soil.