Effect and mechanism of cyanide degradation and Cu/Zn recovery by photoelectro-catalytic oxidation

Abstract Cyanide wastewater contains highly toxic substances such as cyanide and metals. A simple and efficient photoelectro-catalytic oxidation method was proposed. Effect and mechanism of cyanide degradation and Cu/Zn recovery by photoelectro-catalytic oxidation were investigated. The experimental results show the degradation efficiency of total cyanide and removal efficiencies of copper and zinc reached 96.90%, 99.76% and 90.56%, respectively, under the optimum conditions of 2.5 V external bias voltage and 4.0 h with air and lighting. An external electric field can significantly improve the migration and separation of photo-generated electrons (e–) and holes (h+), thereby increasing the photocatalytic efficiency. Simultaneously, the surface potential of semiconductor is lower than the body under the action of bias voltage and leads to energy band bending. XPS analysis indicates that cyanide is finally degraded into carbon oxide and nitrogen. Cu and Zn are mainly recovered as elementary substance.