PHOTOOXIDATION OF SULFITE IONS IN THE PRESENCE OF SOME IRON-OXIDES

The photocatalytic oxidation of sulfite ions over different iron oxide s samples is investigated. For the different hematite samples tested, the experimental data of sulfite photo-oxidized vs. irradiation time c an be adjusted fairly well to a kinetic equation of the type dx/dt=K(1 -x)/x, where x is the fraction of sulfite reacted at time t. The behav iour described by this equation corresponds to an heterogeneous proces s where the product of reaction is strongly adsorbed on the substrate. The rate constant K obtained for the different hematite samples can b e related to their respective specific surface area. Fe(II) species we re detected in solution when hematite suspensions were irradiated. The se Fe(II) ions are assumed to be formed through photoreduction of latt ice Fe(III). On the contrary, for magnetite and maghemite suspensions no Fe(II) ions were detected in solution after irradiation. In the lat ter case, crystalline phase transformation is assumed to take place.