Destruction of cyanide in waste waters by chlorination

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Abstract
A study of the reactions of sodium and calcium hypochlorites with buffered alkaline solutions of potassium cyanide indicated that the first product was always cyanogen chloride, which was rapidly hydrolysed at pH II or above without further absorption of available chlorine. At lower pH values additional chlorine was absorbed up to a total of 5·75 gram‐atoms per gram‐molecule of cyanide. At pH II the reaction of hypochlorites with the complex cyanides of zinc and cadmium was similar to that with potassium cyanide; cupro‐cyanide was also rapidly attacked, with oxidation of cuprous copper to the cupric state, but nickelocyanide was only slowly attacked.A process was developed for treating electroplating wastes, or other waste waters containing cyanide, by reaction with calcium hypochlorite at pH II. The process would be applicable to liquids containing simple cyanides and the complex cyanides of zinc, cadmium, and copper, but not to solutions containing nickel.