Photoelectrocatalytic Oxidation of Cu^II–EDTA at the TiO₂ Electrode and Simultaneous Recovery of Cu^II by Electrodeposition

Abstract

The simultaneous decomplexation of Cu–EDTA and electrodeposition recovery of Cu²⁺ ions was attempted in a photoelectrocatalytic (PEC) system using TiO₂/Ti as the anode and stainless steel as the cathode. At a current density of 0.5 mA/cm², removal efficiencies of 0.05 mM Cu–EDTA by photocatalysis, electrooxidation, and PEC processes were determined to be 15, 43, and 72% at 3 h, respectively. Recovery percentages of Cu²⁺ ions were determined to be 10, 33, and 67%, respectively. These results indicated that a synergetic effect in the decomplexation of Cu–EDTA and recovery of Cu²⁺ ions occurred in the PEC process, which favored acid conditions and increased with the current densities. The removal of Cu–EDTA and Cu²⁺ ions can be described by a pseudo-first-order kinetics model. Ca²⁺ ions significantly increase the removal of Cu–EDTA and recovery of Cu²⁺ ions. Intermediates, including Cu–NTA, Cu–EDDA, acetic acid, formic acid, and oxalic acid, were identified, and a decomplexation pathway of Cu–EDTA was proposed. The Cu–EDTA decomplexation at the anode via oxidation of hydroxyl radicals was revealed. On the basis of X-ray photoelectron spectra analysis, a reduction pathway of Cu²⁺ ions at the cathode was discussed. The present study may provide a promising alternative for destruction of the metal complex and recovery of metal ions