Electrolytic Oxidation of Cyanide on Bare and Manganese Dioxide Coated 304 Stainless Steel Electrodes

Bare and manganese dioxide coated ANSI-304 stainless steel anodes were evaluated for use in electrolytic cyanide waste effluent treatment using bicarbonate buffered electrolytes. Cyclic voltammetry of 10 mM carbonate pH 10 buffered electrolytes showed evidence of mass transfer limited cyanide oxidation just prior to the onset of oxygen gas evolution for both electrode types, and a reaction mechanism in which cyanide is oxidized via reaction with hydroxyl radical containing higher oxidation state species on electrode surfaces is proposed. The results of galvanostatic experiments, conducted in the same base electrolyte with addition of 250 mg L -1 cyanide at a current density of 2 mA cm -2 , were fit to a pseudo-first order model of mass transfer limited cyanide oxidation with little difference in cyanide oxidation performance between bare steel and the MnO 2 coated electrodes. However, addition of 10 mg L -1 of dissolved copper to the electrolyte was found to enhance the kinetics of cyanide oxidation when employing bare stainless steel electrodes, but had no appreciable effect on cyanide oxidation performance for cells employing manganese dioxide coated electrodes.