CONTINUOUS PHOTOCATALYTIC TREATMENT OF Cr(VI) EFFLUENTS WITH SEMICONDUCTOR POWDERS

Abstract

The photocatalytic reduction of Cr(VI) with UV light has been studied using three different semiconductors (TiO₂ ZnO and α-Fe₂O₃) The best yields were obtained using titania as catalyst at pH lower than 2. Experiments have been carried out in a flow system where the Cr(VI) effluent was fed and treated continuously and the catalyst suspension was recycled. Such a device allows the study of the system behaviour at steady and non-steady state and permits to know the influence of the different variables on the reaction rate. In the experimental conditions tested the rate controlling step is the reduction of Cr(Vl). Experimental data obtained at steady state can be fitted to a 1/2 order kinetic equation which do also match the data obtained at non-steady state. The maximum quantum yield obtained was 3.2% referred to the photons entering the photoreactor which are able to be absorbed by titania.