Thermodynamic Study on Redox Equilibrium of Manganese in CaO–SiO<SUB>2</SUB>–Mn<SUB>t</SUB>O–MgO<SUB>sat</SUB>

Abstract

Experiments were carried out to determine the ratio of Mn 3+ /Mn 2+ at equilibrium in CaO-SiO 2 -Mn t O-MgO slag under various slag compositions and oxygen partial pressures in temperature range of 1350∼1450°C. As magnesia crucibles were used, the solubility limit of MgO could also be determined. Results indicate that the Mn 3+ /Mn 2+ ratio increases with slag basicity as well as with Mn t O content. The solubility of MgO, on the other hand, decreases as the slag basicity increases and also with increasing Mn t O content. The ratio (%Mn 3+ )/(%Mn 2+ ) does not change in the oxygen partial pressure between 10 -12 atm and 10 -6 atm. At the constant oxygen partial pressure, the value of log(%Mn 3+ )/(%Mn 2+ ) does not change with the slag basicity less than 0.9. On the other hand, the value of log(%Mn 3+ )/(%Mn 2+ ) decreases with increasing basicity of slag more than 0.9. Although there is small deviation in the value of log (%Mn 3+ )/(%Mn 2+ ), the value does not change in the slag composition containing more than 16% Mn t O. Temperature dependence of the ratio (%Mn 3+ )/(%Mn 2+ ) at 5.1x10 -9 atm in the temperature range of 1350 to 1450°C can be expressed as follows. From the expression, the reaction enthalphy was calculated to be -75kcal/mol. ...Formula math....