Electrochemical separation and reuse of EDTA after extraction of Cu contaminated soil

Abstract

Recycling chelant is a precondition for cost-effective EDTA-based soil washing remediation technologies. Soil contaminated with 290 mg kg −1 Cu was extracted with 40 mmol EDTA per kg of soil. The spent washing solution (containing 73 ± 1 mg L −1 of Cu and 8.4 ± 0.0 g L −1 of EDTA) was treated in a single-compartment electrolytic cell using a sacrificial Al anode, at current density 96 mA cm −2 and pH 6, 10 and pH left unregulated. Electrochemical treatment at pH 10 efficiently separated metal from chelant; 99% of Cu was removed from the solution, mostly by electro-deposition on the stainless steel cathode, while almost all the EDTA was preserved in the solution. The Cu in the EDTA complex was presumably replaced by Al electro-corroded from the anode after electro-reduction of the EDTA at the cathode. After trans-complexation, the EDTA in the treated washing solution retained from 82 to 69% of the Cu extraction potential. Reusing the washing solution in several soil extraction and EDTA recycling steps reduced the Cu soil concentration to 70 mg kg −1, while a single use of EDTA solution removed less than half of the Cu from the soil.