Thermodynamic properties of manganese oxide in BOF slags

It is necessary to understand the thermodynamic properties of MnO in steelmaking slags for the smelting reduction of Mn ore in BOF process. Studies of the manganese distribution between CaO-SiO₂-Fe_tO-MnO slags and liquid silver in equilibrium with solid Fe in the temperature range of 1 623 to 1 723 K were carried out under a CO/CO₂ atmosphere. The Fe_tO content in (32.4∼36.3)%CaO-(31.6∼44.0)%SiO₂- (9.9∼24.1)%FeO-(0.4∼2.6)%Fe₂O₃-(8.9∼10.8)% MnO slags was found to have a linear relationship with oxygen partial pressure. The values of Fe³⁺/Fe²⁺ in the same slag system increase by increasing the Fe_tO content. The Mn distribution ratio between slag and metal, (%MnO)/[%MN]_Fe-Csat, increases with FeO content in a linear relationship over the measured FeO concentration range (6.7-24.1 mass%). The Mn distribution ratio decreases with increasing CaF₂, which is believed to have the effect of increasing the activities of MnO and FeO. Temperature dependence of equilibrium manganese distribution at p_O2 = 6.6 × 10^-12 atm in the temperature range of 1 623 to 1 723 K can be expressed as follows: log (MnO)/[%Mn]_Fe-Csat = 14 270/T - 6.55 The relative partial heat of solution of MnO into (32.7∼39.1) %CaO-(32.7∼38.8)%SiO₂-(10.2∼20.2∼20.78)%FeO- (1.0∼2.4)%Fe₂O₃-(9.4∼10.8)%-MnO slags was estimated to be 198 kJ/mol.