Electrochemical decomposition of cyanides on tin dioxide electrodes in alkaline media

Abstract

The electrochemical oxidation of cyanide in alkaline media was studied at different pH levels on SnO₂ doped with Sb supported on titanium, at 25 °C. The electrooxidation of CN^– at constant current follows a first-order rate law with a half life of t_½= 35 min on SnO₂—SbO_x electrodes and t_½= 69 min on SnO₂—SbO_x—RuO₂ electrodes, in K₂SO_4(aq), pH 12. The reaction rate increases with the applied current and tends to reach a plateau when j > 20 mA cm^–2. In the pH range 10–13.5 the reaction rate diminishes as pH is increased owing to an increasing competition between CN^– and OH^– ions for the electrode surface. Addition of chloride to the solution does not alter the rate law but increases the reaction rate. A mechanism is proposed to explain the observed behaviour.