抄録
The reductive dissolution of Mn (III) or Mn (IV) oxides with ferrous ion, which is produced by oxidation of iron sulfides, such as pyrite, is considered as a a cause of dissolution of manganese ion into mine waters. The dissolution of manganite and pyrolusite with ferrous ion has been investigated from this point of view. In this experiment, pH of solution was kept at constant values by using a pH stat.
The reaction of manganite and pyrolusite with ferrous ion in sulfuric acid solution were supposed to be expressed as :
2MnOOH+2FeSO4+3H2SO4=2MnSO4+Fe2 (SO4) 3+4H2O (pH<3)
2MnOOH+2FeSO4+2H2O=2MnSO4+2Fe (OH) 3 (pH>3)
MnO2+2FeSO4+2H2SO4=MnSO4+Fe2 (SO4) 3+2H2O (pH<3)
and
MnO2+2FeSO4+4H2O=MnSO4+2Fe (OH) 3+H2SO4 (pH>3)
The dependencies of hydrogen ion concentration on the dissolution rates of manganite were 0.5th order below pH 3. On the other hand, the dissolution rates of pyrolusite were 2nd order with respects to hydrogen ion concentration at pH 2 to 3 and constant below pH 2. Also, the dissolution rates of pyrolusite were considerably higher than those of manganite below pH 3, but, the former were lower than the latter above pH 3.
The dependencies of ferrous ion concentration on the dissolution rates were 0.5th order for manganite and 1st order for pyrolusite.
The activation energies for the reductive dissolution were 15.2 kcal/mole for manganite and 4.9 kcal/mole for pyrolusite. From these values for activation energies, the overall reactions were supposed to be controlled by chemical reaction for manganite and by diffusion process for pyrolusite.
