Oxidation-Reduction Equilibria of Manganese in MntO-CaO-SiO2-Al2O3 Melts

The redox equilibrium between Mn3+ and Mn2+ in MntO-CaO-SiO2-Al2O3 melts at temperatures ranging from 1 245 to 1 450°C was investigated as a function of composition, oxygen partial pressure close to thatof air.In the composition range studied, the concentration ratio (%Mn3+)/(%Mn2+) increased with an increase in basicity and in MnO content. As a result, Mn2O3 is inferred to behave as an oxoacid ion such as MnOx(2x-3)- in slag melts. The above mentioned ratio increased proportionally to the approximate fourth root of oxygen partial pressure, as predicted theorically. The enthalpy change of oxidation of Mn2+ to Mn3+was found to be -9 150 cal/mol Mn2+.In the light of these findings, Mn3+ content in sintered manganese ores and slags for ferromanganese production was discussed in terms of equilibration with the environment.