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

The photocatalytic oxidation of free cyanide ions was carried out in aqueou s 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 dep endence of cyanide photo-oxidation rate on the following parameters: (1) cy anide 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 reactio n pathway was also investigated: cyanate, nitrite, nitrate and carbonate we re found to be the main oxidation products. The mass balance of nitrogen wa s achieved only in strongly oxidant conditions; this insight suggests that some volatile nitrogen-containing species are formed at mild oxidation cond itions. (C) 1999 Elsevier Science B.V. All rights reserved.