Chromium removal from contaminated soil using a novel FeOx/granular activated carbon-based three-dimensional electrokinetic system

Abstract

A novel three-dimensional electrokinetic remediation (3D EKR) system, with FeOx/granular activated carbon (GAC) composite constituting a third electrode was investigated for the removal of Cr from a real contaminated soil. Such third electrode particles were distributed evenly throughout the contaminated soil and their additional presence enabled the generation of a higher and more stable current density and reduced acid-base polarization of the soil, when compared against a conventional 2D EKR (cathode-anode) system. This resulted in a higher Cr removal, which was primarily driven by enhanced oxidation of Cr(III) to more mobile Cr(VI) aqueous complexes, which electromigrated towards the anode and into the anolyte. Analysis of FeOx/GAC and soil samples before and after EKR using XRD, FTIR, SEM-EDS, and XPS confirmed that: (i) both oxidation of Cr(III) and reduction of Cr(VI) occurred simultaneously on particle electrode surfaces; and (ii) aqueous Cr transport governed by electromigration was enhanced by Electro-Fenton reactions and hydrolysis on FeOx/GAC. A further benefit of 3D EKR was the promotion of residual Cr(III), in proximity to the cathode, to barely soluble crystalline silicate phases, therefore further decreasing the overall toxicity of the soil. This study therefore provides a highly promising first insight into the use of 3D EKR for the removal of Cr from contaminated land. Future work will seek to examine this emerging new technology at large scale and for different contaminated land scenarios, therefore further developing it towards a potential commercial application.