Assessment of EDTA-enhanced electrokinetic removal of metal(loid)s from phosphate mine tailings

Electrokinetic remediation (EKR) is a promising technique for the treatment of contaminated soils and sediments. However, the application of EKR to metal(oid)-contaminated mine wastes with varying mineralogy and physicochemical properties has not been fully characterized. This paper evaluates the potential of EDTA-enhanced EKR as a means to remove trace metal(oid)s (Cu, Cd and As) and major metals (Fe, Al and Mg) from a phosphate mine tailings material. Controlled laboratory EKR experiments were performed, in which the electrolyte EDTA concentration was varied between 0.1 and 1 M and the voltage gradient between 24 and 32 V. Migration of the studied contaminants increased proportionally to increasing EDTA concentration and applied voltage gradient, and the obtained average removal efficiencies of Al, Mg, Cu, Cd and As reached up to 29%, 10%, 26%, 28% and 22%, respectively, within a week. Differences in metal mobilization could be explained by their mineral hosts and aqueous speciation under the imposed geochemical conditions during EKR, which were corroborated by aqueous geochemical equilibrium modeling using PHREEQC. Our results suggest that EKR could be a feasible remediation option for select metal(oid)-enriched mine waste fractions following further optimization.