US EPA

1710207 

Journal Article 

Role of manganese dioxide in the oxidation of aqueous sulphur(IV) in oxic and anoxic suspensions 

Gupta, KS; Singh, R; Saxena, D; Manoj, SV; Sharma, M 

1999 

1 

Indian Journal of Chemistry. Section A
ISSN: 0376-4710
EISSN: 0975-0975 

38 

11 

1129-1138 

WOS:000084927400007 

The kinetics of direct oxidation of sulphur(IV) by MnO2 has been studied in stirred suspensions in nitrogen atmosphere and that of autoxidation reaction in stirred suspensions in equilibrium with atmospheric oxygen. Sulphate has been detected to be the only oxidation product of sulphur(IV) in both the cases. In the pH range 4.6-5.8, the kinetics of direct oxidation of sulphur(IV) in anoxic suspesions agreed with the rate law (I). On the other hand at pH 7.9 for the same reaction a much simpler rate law (II) is obeyed.



-d[S(IV)]/dt={(A[H+](-1)+B)[MnO2](0)[S(IV)](0)}/{1+C[S(IV)](0)[H+](-1)} ...(I)



-d[S(IV)]/dt = {k(3)K(3)[MnO2](0)[S(IV)](0)}/{1+K-3[S(IV)](0)} ...(II)



At 30 degrees C, the values of empirical constants are: A = 4.8x10(-10) mol g(-1)s(-1); B = 2.8x10(-5) L g(-1) s(-1); C = 1.1 x 10(-3); k(3) = 9.3 x 10(-7)s(-1) and K-3 = 34. For MnO2 catalysed autoxidation in oxic suspensions the rate data pertaining to pH range 4.6-5.8 fitted Eq. (III) and those



-d[S(IV)]/dt = k(5)[MnO2](0)[S(IV)](0)[H+](-0.34) ...(III)



-d[S(IV)]/dt = k(8)[MnO2](0)[S(IV)](0)[H+](-0.4) ...(IV)



in the pH range 6.5-7.0 fitted Eq. (IV). At 30 degrees C, k(5) and k(8) have values of 1.4 x 10(-4) L-0.66 g(-1) mol(-0.34) s(-1) and 3.2 L-1.4 g(-1) mol(-0.4) s(-1). The rate of autoxidation is independent of oxygen partial pressure. The atmospheric conversion rates at 30 degrees C have been calculated.