Hypochlorite oxidation of cyanate under mildly alkaline conditions

Abstract

Kinetic study was carried out on the hypochlorite oxidation of cyanate, over the pH range of 8.6-10.0 and temperature range from 27 to 50°C. The decomposition reaction was found to be first order each with respect to cyanate, hypochlorite and hydrogen ion concentration. The experimental results indicate that the decomposition reaction may probably follow a series reaction in which the cyanate first hydrolyses to ammonium which then decomposes in alkaline hypochlorite solution to nitrogen. Under the range of pH and hypochlorite/cyanate molar ratio examined in this study, the stoichiometric ratio of hypochlorite to cyanate for the decomposition reaction is found to be approx. 1.5. The conversion of cyanate to nitrate is negligible compared with that to nitrogen. This study suggests that complete treatment of cyanide waste is best carried out in two stages at room temperature and in the presence of excess hypochlorite. The first stage involves the hypochlorite oxidation of cyanide to cyanate at pH 11 and the second stage involves the conversion of the cyanate to nitrogen and other stable inert products at a reduced pH of about 9. © 1987.