Metal recovery and EDTA recycling from simulated washing effluents of metal-contaminated soils

The recovery of EDTA (ethylenediaminetetraacetic acid) and metals such as Cu-II, Pb-II, Cd-II and Zn-II from simulated washing effluents of metal-contaminated soils was investigated using a two-chamber electrolytic cell, which was separated by a cation exchange membrane Neosepta CIM-I. The iridium oxide coated on titanium electrode and stainless steel were used as the anode and cathode, respectively. An equimolar solution of EDTA and total metals was selected. All experiments were carried out at a fixed current density (185 A/m(2)) and concentration ratio among metals, but at different initial catholyte pH values (1.47-6.0) and total metal concentrations (10.4-31.1 mM). It was shown that the initial catholyte pH played the most important role in metal recovery. Metal recovery generally decreased in the order Cu-II > Pb-II > Cd-II > Zn-II, which was related to the reduction tendency of free metal ions. The effect of added supporting electrolytes such as NaCl and Na2SO4 on electrolytic recovery was also investigated. (C) 2000 Elsevier Science Ltd. All rights reserved.