Enhanced Photoelectrocatalytic Oxidation of Cu(CN)32- and Synchronous Cathodic Deposition of Cu by Peroxydisulfate

Abstract

Oxidation of Cu-cyanides by a photoelectrocatalytic method was enhanced by adding peroxydisulfate (PS). In the photoelectrocatalytic system (PEC), graphitic carbon nitride (g-C3N4) thin films prepared by a liquid-based reaction and graphitic carbon felt (GCF) were used as the photoanode and cathode, respectively. First, various processes, including PEC, PS oxidation, and PEC with PS addition (PEC/PS), were compared for Cu-cyanide removal. The addition of PS improved greatly the photoelectrocatalytic efficiency for the oxidation of CN- and the recovery of Cu on the cathode. The effect of the amount of K2S2O8 was investigated in detail. The removal efficiency of CN- and Cu recovery can reach up to 86.23% and 82.11%, respectively, with 1 mmol·L-1 K2S2O8 at 1.0 V bias potential. Combined with the SEM, EDS, and XPS analysis of the electrode surface, it was concluded that the free Cu+ was oxidized and existed in the precipitation and photoanode in the form of CuO. Conversely, the liberated Cu+/Cu2+ ions were electrochemically reduced to elemental Cu on the surface of the graphitic carbon felt cathode. As a result, metal Cu was recovered from the wastewater of the copper cyanide complexes. Electron spin resonance and radical quenching experiment analysis showed that the oxidation of CN- is assigned to sulfate radical oxidation and non-radical oxidation processes.