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

The photocatalytic oxidation of sulfite ions over different iron oxides samples is investigated. For the different hematite samples tested, the experimental data of sulfite photo-oxidized vs. irradiation time can 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 behaviour described by this equation corresponds to an heterogeneous process where the product of reaction is strongly adsorbed on the substrate. The rate constant K obtained for the different hematite samples can be related to their respective specific surface area. Fe(II) species were detected in solution when hematite suspensions were irradiated. These Fe(II) ions are assumed to be formed through photoreduction of lattice Fe(III). On the contrary, for magnetite and maghemite suspensions no Fe(II) ions were detected in solution after irradiation. In the latter case, crystalline phase transformation is assumed to take place.