Application of sulfide-modified nanoscale zerovalent iron electrodes for electrokinetic remediation of chromium-contaminated soil in a three-dimensional electrode system

A modified electrokinetic remediation (EKR) system was designed to remediate Cr-contaminated soil using sulfidated nano-scale zerovalent iron (S-nZVI) as the third electrode. This study systematically compared the technological parameters and remediation efficiencies of three-dimensional (3D) electrokinetic systems using different materials as the third electrodes. The comparative experiment showed that the 3D EKR could effectively increase current efficiency, balance voltage distribution, alleviate excessive acidification or alkalization of soils and effectively improve the removal efficiency of Cr. Compared with other 3D electrodes, the S-nZVI electrode led to the higher currents and the more uniform voltage distribution; additionally, the leaching toxicities were reduced by 50.0-66.7%, and the removal efficiencies of total Cr (Cr(tot)) and hexavalent Cr (Cr(VI)) were increased by at least 15.4% and 22.6%, respectively. Cr(VI) was removed mainly resulting from the electrokinetic migration. Meanwhile, a small amount of Cr(VI) was converted to FeCr2O4 and Cr3+OOH after reacting with SnZVI in the middle region of the 3D EKR system. Due to the active layer of iron sulfides, S-nZVI was more stable and its electrokinetic efficiency was higher than other 3D electrodes, resulting in higher overall removal efficiencies. 3D EKR with S-nZVI can effectively decrease the toxicological effect of Cr contaminated soil at an experimental scale. The experimental findings from this study may provide a reference for guiding the development of more efficient methods for Cr-contaminated soil treatment.