Kinetics of the autoxidation of sulfui(IV) in unbuffered and acetate-buffered aqueous silica and copper (II) oxide suspensions appear to be surface mediated, and the suggested mechanism requires the adsorption of both dioxygen and sulfur(IV) on the particle surface involving solid-liquid-gas interactions.
Autoxidation of S(IV), in buffered solutions,conforms the rate law (1). The increase in buffer concentration has a
R obsd=k5[CdO][S(IV)]2[H+]−1.22 (1)
rate decreasing effect. On the other hand, in unbuffered solutions the kinetics obey a different rate law (2).
R obsd=(k10+k11[CdO])[S(IV)][H+]−0.5 (2)
In both situations, the dissolution of CdO accompanies the autoxidation. A heterogeneous catalytic mechanism involving adsorption of both dioxygen and sulfur(IV) on the surface of CdO particle has been proposed.
The kinetics of the reaction (1) obey the rate law (2) in acetate buffered solutions. A comparison with HZOP and S Z O~' shows the reactivity order to be HPOZ < HS05-> SzO8'-. 0 1992
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