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Department of Chemical Engineering, University of Kuwait, P.O. Box 5969, Safat 13060, Kuwait

ABSTRACT

In a series of studies on the effect of transition metal ions on the autooxidation of aqueous

S(1V) we have investigated in this study the effect of Cu(II), Fe(II1) and Mn(I1) ions on the oxidation and concluded that in the absence of oxygen, it is possible for the reaction to be completely inhibited due to complex formation. Furthermore it is possible that no synergism exists for the couples Fe(II1) + Cu(I1) and Fe(II1) + Mn(I1) especially at high ratios of these metal ions. We have also investigated the strength of complex formation. The results indicate that in the presence of oxygen, complex S(IV) ions as well as uncomplexed ions are available for oxidation and this is explained in the light of Backstroms mechanism for autooxidation of aqueous S(IV). We have proposed a reaction sequence for the oxidation of aqueous S(1V) in the presence of oxygen. Our conclusion is that in the presence of oxygen, the most effective catalyst is a mixture of Fe(II1) + Mn(I1) which produces almost 1 molar sulphuric acid after 7 hours.