REMEDIATION OF METAL-CONTAMINATED SOIL BY EDTA INCORPORATING ELECTROCHEMICAL RECOVERY OF METAL AND EDTA

Removal of toxic heavy metals from a soil matrix by the addition of ethylenediamine tetraacetic acid (EDTA) is an effective means of remediation. The liquid stream containing the metal and chelating agent is amenable to further treatment by electrolysis in which the metal can be separated from the chelating agent. This provides a separated metal that can be removed for reuse or treated for final disposal by conventional technologies and a reclaimed EDTA stream that can be used again for treatment of contaminated soil. Under the diffusion controlled conditions of polarography or voltammetry, we observed reduction of cadmium, copper and lead ions and their protonated EDTA complexes (MHY-), but not of the non-protonated EDTA complexes (MY2-). Potentials applicable for metal deposition and, consequently, regeneration of the EDTA were established. To prevent electrochemical oxidation of EDTA during electrolysis we used a cell in which the anode and cathode compartments were separated by a cation exchange membrane. Tests with Pb-EDTA demonstrated that over 95 percent recovery of both EDTA and lead could be achieved by electrolysis. The lead that was deposited onto a copper electrode was a mixture of hydrolysis products and salts and the lead could be recovered by dissolution in acid. EDTA was equilibrated with soil before addition of lead. When electrolyzed, this sample released EDTA and deposited Pb to approximately the same extent as did the samples that had not been equilibrated with soil.