Manganese(II) catalyzed sulfur dioxide oxidation in aqueous solution at environmental concentrations

Abstract

Manganese(II) catalyzed SO 2 oxidation in aqueous solution at atmospheric concentrations over the wide pH range from 3 to 8 has been studied by using a continuously flowing stirred reactor. The S(IV) oxidation rate is proportional directly to both Mn(II) and S(IV) concentration in the solution with a rate constant of k = (5.1 +- 0.5) × 10 3 / mole −1 s −1 at 23.7†C. The rate constant is constant over the range of pH from 3 to 6, while it sharply decreases below pH = 3 and above pH = 6. The activation energy is obtained to be 17.8 kcal mole −1. This pH dependence is discussed in terms of the solution chemistry of both S(IV) and Mn(II) as a function of pH and in terms of the complex formation of Mn(II) with S(IV) species on the basis of the observed anion effect on the reaction rate.