Electrowinning of copper from copper cyanide solutions at low pH

The electrodeposition of copper from solutions containing free cyanide is difficult under alkaline conditions, but can be substantially enhanced by decreasing the pH due to the formation of the more electroactive aqueous species, Cu(CN)(2)(-). The optimum pH for electrowinning is pH 5, and the electrodeposition of copper is significantly enhanced in an acetate solution due to the minimization of interfacial pH change. Cu(CN)(2)(-) was found to be readily oxidized at potentials more positive than 550 mV, and an anode material has yet to be found that promoted oxygen evolution over the oxidation of copper cyanide. At pH 5, the current efficiency increases as the cathode potential shifts to more positive potentials, whilst the copper recovery rate decreases as the potential becomes more positive than -600 mV. The optimum operating cathode potential is between -500 and -600 mV, giving a current efficiency of 90 - 100 % and an average energy consumption of 0.85 - 1.00 kWh (kg Cu)(-1).