Abstract: The photocatalytic oxidation of pollutant SO₂ in aqueous suspension of ZnO·WO₃ under visible light irradiation was investigated and an air flowing was proposed to treatconcentrated SO₃^2- solution. The SO₃^2-,contained in an aqueous solution of 0.15 mol/L,was almost photocatalytically oxidized to produce SO₄^2- within 2h irradiation.In photoassisted spontaneous oxidation of SO₃^2-,such coexistent reactions as spon-taneous,heterogeneously catalytic,photochemical and photocatalytic reactions hclVe beencompared by experiments.Gram molecular ratio 0.5 ZnO·WO₃ was chosen to be the opti-mal doping ratio.The effect of the heat treatment of photocatalyst,air flowing and pH onphotocatalytic activity has been determined and pH7.5 was identified to be the optimal.Solar photocatalytic oxidation of SO₃^2- shows the faster reaction rate than that in indoorexperimentst which develops a better prospects for the application of solar photocatalysisto environmental protection,All experimental results are explained in theory.A reactionmechanism has been proposed in detail.

Key words: pollutant SO₂ sulfite, sulfate, photocatalytic oxidation