Enhanced Photoelectrocatalytic Decomplexation of Cu–EDTA and Cu Recovery by Persulfate Activated by UV and Cathodic Reduction

In order to enhance Cu–EDTA decomplexation and copper cathodic recovery via the photoelectrocatalytic (PEC) process, S2O8 2– was introduced into the PEC system with a TiO2/Ti photoanode. At a current density of 0.2 mA/cm2 and initial solution pH of 3.0, the decomplexation ratio of Cu complexes was increased from 47.5% in the PEC process to 98.4% with 5 mM S2O8 2– addition into the PEC process (PEC/S2O8 2–). Correspondently, recovery percentage of Cu was increased to 98.3% from 47.4% within 60 min. It was observed that nearly no copper recovery occurred within the initial reaction period of 10 min. Combined with the analysis of ESR and electrochemical LSV curves, it was concluded that activation of S2O8 2– into SO4 ·– radicals by cathodic reduction occurred, which was prior to the reduction of liberated Cu2+ ions. UV irradiation of S2O8 2– also led to the production of SO4 ·–. The generated SO4 ·– radicals enhanced the oxidation of Cu–EDTA. After the consumption of S2O8 2–, the Cu recovery via cathodic reduction proceeded quickly. Acidification induced by the transformation of SO4 ·– to OH· favored the copper cathodic recovery. The combined PEC/S2O8 2– process was also efficient for the TOC removal from a real electroplating wastewater with the Cu recovery efficiency higher than 80%.