Kinetics of Mn2O3 digestion in H2SO4 solutions

The kinetics of Mn2O3 digestion in various H2SO4 solutions (0.5–2.0 M) and at various temperatures (ambient to 80 °C) to form solid γ-MnO2 and soluble Mn(II) have been examined using X-ray diffraction. Using a modified first-order Avrami expression to describe digestion kinetics, rate constants in the range 0.02–0.98 h−1 were found for Mn2O3 disappearance, and 0.03–0.42 h−1 for γ-MnO2 formation, with higher H2SO4 concentrations and temperatures leading to faster conversion rates. Also, for a particular set of experimental conditions, the rate of γ-MnO2 formation was always slower than Mn2O3 disappearance. This was interpreted in terms of the solubility and stability of the soluble Mn(III) intermediated formed during the digestion. Activation energies for Mn2O3 dissolution and γ-MnO2 formation were also determined.