REACTION KINETICS OF HYDROGEN PEROXIDE WITH REDUCED-SULFUR COMPOUNDS IN AQUEOUS MEDIUM (MECHANISMS, HYDROLYSIS, CATALYSIS, SULFATE PRODUCTION)

Reduced-sulfur compounds are the main source of obnoxious odors and corrosion in municipal sewage systems and many chemical industries. The contributions of the oxidation of these compounds to precipitation acidity, sulfate production in clouds, and acidification of lakes and other surface waters may be significant. Still, the kinetics and mechanisms of oxidation of these compounds in aqueous solutions by various environmental oxidants are not well understood.;The oxidation of CS(,2) by H(,2)O(,2) to sulfate in alkaline medium (pH (LESSTHEQ) 11) is controlled by the hydrolysis step. The reaction of CS(,2) with OH('-) is rate-controlling and proceeds by the formation of a complex. The linear increase as a function of OH('-) ion concentration for the pseudo-first order rate constants for both the formation and decomposition of this complex leads to the concept of bimolecular course for both steps. The formation of sulfate increases exponentially and is dependent on the rate of hydrolysis; thus an increase in pH results in increased sulfate production rates. The productions of sulfate also shows large induction periods; suggesting formation by secondary reactions. The results of CS(,2) oxidation is applied to the oxidation of OCS.;Oxidation of CH(,3)SCH(,3) by H(,2)O(,2) is bimolecular and is subject to acid catalysis. The observed rate coefficient is fairly constant between pH 2 and 6, increases drastically at pH 1 and below, and decreases substantially at pH 7. For solutions of the same normality, the catalytic power of HCP is double that of H(,2)SO(,4) at 20(DEGREES)C. Differences in activation energies in acidic (pH < 7) and neutral (pH = 7) solutions suggest two different mechanisms are operative.;Rate expressions are obtained experimentally for the oxidation of CS(,2), OCS and CH(,3)SCH(,3) by hydrogen peroxide in aqueous medium. Mechanisms which are consistent with the observed rate laws are also given. In addition, a comprehensive literature review of the solution chemistry of the reduced-sulfur compounds of environmental interest (H(,2)S, CS(,2), OCS, CH(,3)SCH(,3), CH(,3)SSCH(,3)), and their chemical oxidation by O(,2), H(,2)O(,2), O(,3), Cl(,2) and Br(,2) is included.