A mixed surface reaction kinetic model for the reductive leaching of manganese dioxide with acidic sulfur dioxide
Senanayake, G. (2004) A mixed surface reaction kinetic model for the reductive leaching of manganese dioxide with acidic sulfur dioxide. Hydrometallurgy, 73 (3-4). pp. 215-224.
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Previous researchers have rationalised the kinetics of dissolution of manganese dioxide in acidic sulfur dioxide solutions on the basis of either the adsorption of reactants followed by reactions with HSO3- and SO2 or a two-electron surface electrochemical reaction with H+ and HSO3-, the species involved in the equilibrium: SO2(aq)+H2O=H++HSO 3-. This paper revisits the reported rate data for the dissolution of MnO2 in the form of plates [Herring and Ravitz, Trans. SME/AIME 231 (1965) 191] or particles [Miller and Wan, Hydrometallurgy 10 (1983) 219] to show that the rate of dissolution can be rationalised on the basis of a fast redox reaction: (i) MnO2(s)+SO2(aq)+H 2O=MnOOH(s)+HSO3(aq) followed by one of the two rate determining redox reactions: (ii) MnOOH(s)+HSO3(aq) = MnSO 40(aq)+H2O or Mn(OH)HSO4(s), (iii) MnOOH(s)+SO2(aq) = MnO(s)+HSO3(aq) depending on the pH of the medium. Whilst the rate equation for (iii) agrees with the electrochemical kinetic model reported previously, the dissolution of the solid Mn(OH)HSO 4 or the direct reaction: (iv) MnO2(s)+SO2(aq) = MnSO40(aq) also appear to be rate controlling. The two rate constants k1 and k2 based on a shrinking sphere kinetic model: 1-(1-X)1/3 = k1K0.5[SO 2]0.5(t/rρ)+k2[SO2](t/rρ), for the leaching of monosized pyrolusite and electrolytically prepared MnO 2 particles, are in reasonable agreement with k1 and k2 based on the dissolution kinetics of MnO2 plates.
|Publication Type:||Journal Article|
|Murdoch Affiliation:||Parker Cooperative Research Centre for Integrated Hydrometallurgy Solutions|
|Copyright:||© 2003 Elsevier B.V.|
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