Photocatalytic oxidation of cyanide in aqueous TiO2 suspensions irradiated by sunlight in mild and strong oxidant conditions

The photocatalytic oxidation of free cyanide ions was carried out in aqueous aerated suspensions containing polycrystalline TiO2 (anatase) irradiated by sunlight. The influence of the presence of an organic compound (phenol) or of a strong oxidant (H2O2) on the photoprocess was also studied. The dependence of cyanide photo-oxidation rate on the following parameters: (1) cyanide concentration; (2) catalyst amount; and (3) phenol concentration was investigated. At the used experimental conditions, the kinetics of cyanide photo-oxidation is independent of the initial cyanide concentration and of the catalyst amount while it is affected by the phenol concentration and by the presence of H2O2. The Langmuir-Hinshelwood kinetic model has been used for phenomenologically describing the photoreactivity results. The reaction pathway was also investigated: cyanate, nitrite, nitrate and carbonate were found to be the main oxidation products. The mass balance of nitrogen was achieved only in strongly oxidant conditions; this insight suggests that some volatile nitrogen-containing species are formed at mild oxidation conditions. (C) 1999 Elsevier Science B.V. All rights reserved.