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Sulfur dioxide in aqueous solutions a t low pH levels exists both in molecular SOz(aq) and in hydrolyzed ionic form HSOa-. Experiments indicate that only HS03is the reacting species in the oxidation catalyzed by activated carbon, while SOz(aq) deactivates by competing with HS03for the active sites of the catalyst particles. A mechanism is proposed and a rate model is developed that also accounts for the effect of sulfuric acid (product of the oxidation) on the solubility of sulfur dioxide. It predicts first order in HS03-, half order in dissolved oxygen, and a linear deactivation effect of SOz(aq), which are confirmed by experimental data. The deactivation reaches a constant level corresponding to saturation of the active sites by SOAaq). Activation energy for the oxidation is 93.55 kJ mol-l and for deactivation is 21.4 kJ mol-l.

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