The electrochemical oxidation of alkaline copper cyanide solutions

A systematic investigation of the electrochemical oxidation of copper cyanide was carried out. At low pH, cyanide destruction is believed to be catalyzed by the heterogeneous reaction involving adsorbed Cu(CN)₃]²⁻ and possibly Cu(CN)₄]³⁻. At high pH, rapid oxidation of cyanide was observed around 0.75 V versus Hg/HgO with the formation of a black copper oxide film. This enhanced electrocatalytic activity is believed to be related to the formation of an active copper(III) species. The transition point between low and high pH as a function of cyanide and copper concentrations is discussed. Bulk electrolysis of a copper cyanide solution at 0.90 V oxidized most of the cyanide to cyanate. Prolonged electrolysis further oxidized the cyanate to nitrate. The copper oxide film is found to be catalytic, capable of electro-oxidizing hydroxide to oxygen and cyanate to nitrate.