Copper removal from diluted cyanide wastewater by electrolysis

Metal electroplating processes can use cyanide as reagent, generating large amounts of industrial wastewaters containing cyanide and heavy metals. These wastewaters are usually treated by chemical precipitation, generating toxic slugs consisting of metallic hydroxides and sulfides. This work aims at developing an electrolytic cell in order to recover the copper from diluted solutions simulating the wastewaters from the rinsing of copper electroplated disks, for coins manufactured in the Brazilian Mint, and, as a secondary target, to oxidize the free cyanide at the same time. The influence of some process variables was evaluated by thermodynamic and voltammetric studies. The solution flow rate and temperature increase favor copper deposition. It was also verified, by voltammetric and electrolytic tests, that the presence of copper oxide on the anode surface catalyses cyanide oxidation. The best results were obtained for a temperature of 50°C, a solution flow rate of 0.37 mL/s, and after a 3-h electrolysis, when the copper and free cyanide concentrations were, respectively, 0.70 and 0.08 mg/L, for an electric current of 1.5 A, and, respectively, less than 0.50 and 0.08 mg/L, for an electric current of 2.0 A. © 2011 American Institute of Chemical Engineers Environ Prog, 32: 52–59, 2013.