Photocatalytic oxidation of cyanide in aqueous titanium dioxide suspensions: Effect of ethylenediaminetetraacetate

The kinetics of the photocatalytic oxidation of cyanide in aqueous TiO2 suspensions was investigated as a function of catalyst loading (0.1–5.0 g l−1), air-flow rate (0.2–1.1 l min−1), and the concentration of ethylenediaminetetraacetate, EDTA (0.4–40 mM) at pH 13.0. The cyanide oxidation rate did not vary with the TiO2 loading while a slight increase in the degradation rate with an increase in the air-flow rate was found. Cyanate (NCO−) was the only product of the cyanide decomposition. The effect of EDTA on the photocatalytic oxidation of cyanide was examined at different molar ratios of EDTA to cyanide (0.1–10.5) by keeping the initial cyanide concentration at 3.85 mM. EDTA retarded the photocatalytic oxidation of cyanide and the decrease in the oxidation rate was not proportional to the molar ratio of EDTA to cyanide. The first-order rate constant, k (min−1) for the oxidation of cyanide in the presence of EDTA may be expressed as k = 3.38 × 10−3 × ([EDTA]/[CN−])−0.23. A mechanism of the oxidation of cyanide by a photocatalytic process in absence and presence of EDTA is presented.