During an investigation on the dcstruction of cyanide in waste waters by chlorination it was observed that, even in strongly alkaline solution, the first product of the reaction of a cyanide wirh a hypochlorite is cyanogen chloride ; this then undergoes hydrolysis, possihly with formation of a cyanate. Thc ratc of formation of cyanogen chloride is extremely rapid, but hydrolysis, as has bccn shown by Price ef a/,,' proceeds at a measurable rate, given by the equation :T h e value of kl was cstimatcd by Price to be 600 I./mol. min. at 25" c.In treatment of waste waters containing cyanidc the object is to convcrt the cyanide to relatively non-toxic substances ; cyanogcn chloride, which is toxic, is thcreforc an undcsirable intermediate product and it is important to know how quickly it will disappear from solutions undergoing treatment. T h c rates of hydrolysis of cyanogcn chloride 3t tcmpcratiircs ranging from oo to 30" c. were thcrcfore determined in solutions bufkrcd Z t the pII value of 1 1 , which has been found most suitahlc for chlorination of ivastc waters containing cvanidc; the effect of the presence of small concentrations of h-pochloritc was also investigated, since it had been noted in preliminary experiments that a slight cxccss of chlorinating agent appcnrcd to accclerate hydrolysis.
ExperimentalPreparation of soltitions of cyartogeit chloride.-To avoid the inconvenience of working with pure cyanogen chloride, stock solutions were prepared when required in the apparatus shown in Fig. I. Flask A was charged with 50 ml. of 5~-sulphuric acid, 200 ml. of distilled water, and 250 ml. of a solution containing approximately 4000 p.p.m. potassium thiocyanate ; to this mixture was added the volume of standardized hypochlorite solution required for production of cyanogen chloride according to the equation :After mixing and addition of 30 ml. of a 2% solution ofarsenious oside to remove any trace of excess hypochlorite, the flask was closed and air was blown through the solution by means of a sintered glass diffuser plate to carry cyanogen chloride vapour through a solution of arsenious oxide in the Dreschel bottle B, and a spray trap C containing cotton wool, into distilled water in the absorption vessel D. Air leaving D was recirculated by a small diaphragm pump; this was necessary because owing to the ~olatility of cyanogen chloride it was not possible to build up a sufficient concentration of the compound in D if the stream of air was passed to waste. By circulating air for one hour it was possible to obtain a solution containing about 300 p.p.m. cyanogen chloride. Although potassium thiocyanate rather than potassium cyanide was used for production of cyanogen chloride to minimize the possibility of production of hydrogen cyanide, traces of this compound could in fact be detected in the solutions produced.
Analysis of soltrriotts oJ cyarrogeir cliloridcThe concentration of cyanogen chloride in the stock solutions was determined according to the methods of Mauguin and Simon.? One value was obtained by addit...
A study of the reactions of sodium and calcium hypochloritcs with buffered alkaline solutions of potassium cyanide indicated that the first product was always cyanogen chloride, which was npidly hydrolysed at pi, XI or above without funher absorption of available Chlorine. At lower pIt values additional chlorine was absorbed up to a total of 5.75 gnm-atoms per gnm-molecule of cyanide. At pH I I the reaction of hypochloritcs with the complex cyanides of zinc and cadmium was similar to that with potassium cyanide ; cuprocyanide was also rapidly attacked, with oxidation of cuprous copper to the cupric state, but nickelocyanidc was ody slowly attacked.A process was developed for treating electroplating wasrcs, or other waste waters containing cyanide, by reaction with calcium hypochlorite at pH I I. The process would be applicable to liquids containing simple cyanides and !he complex cyanides of zinc, udmium, and copper, but not to solutions containing nickel.
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