Oxidation of cyanide in aqueous solution by chemical and photochemical process

Cyanide waste is found predominantly in industrial effluents generated from metallurgical operations. The toxicity of cyanide creates serious environmental problems. In this paper, oxidation of cyanide in aqueous solution was investigated using chemical and photochemical process. Chemical oxidation was studied at room temperature using H2O2 as oxidant and Cu2+ as catalyst. Photochemical oxidation was studied in an annular type batch photoreactor of 1l capacity using 25 W low-pressure (81.7% transmission at 254 nm wavelength) ultraviolet (UV) lamp along with H2O2 as oxidant. The effect of Cu2+ catalysis was also studied. It was observed that in absence of UV source, the degradation of cyanide by H2O2 alone was very slow, whereas copper ions accelerated the rate of reaction thereby acting as catalyst. Copper formed a complex with cyanide ion, i.e. tetracyanocuprate which had greater affinity for H2O2. Cyanate hydrolysis was also favoured by copper ions. As Cu2+ ion concentration was increased, rate of degradation also increased. Photochemical oxidation by H2O2 and Cu2+ was found to be the best system for cyanide degradation. CN- (100 mg/l) was degraded to non-detectable level in 9 min at pH 10.0 with optimum H2O2 dose of 35.5 mM and Cu2+ dose of 19 mg/l. Reaction kinetics of cyanide oxidation was found to be pseudo-first order and the rate constant has been determined for different processes.