Activity of MnO in MnO‐CaO‐MgO‐SiO2‐Al2O3 Slags at 1500 °C

A thermodynamic study was made on the MnO‐CaO‐MgO‐SiO₂‐Al₂O₃ slags that are typical of the production of ferromanganese in submerged arc furnaces. The Al₂O₃ content of the slags was kept constant at 5 per cent by mass. The activity‐composition relationship in Pt‐Mn binary alloys were re‐determined for calibration purposes at 1300, 1400 and 1500°C and po₂ values between 5.40×10^?6 and 4.54×10^?13 atm. A linear regression equation was derived to predict the activity coefficients of manganese, in Pt‐Mn alloys at 1500°C. The effect of concentration, basicity ratio and CaO‐to‐MgO ratio on MnO activities in above mentioned complex slags was investigated at 1500 °C and at two different po₂ values of 4.76×10^?7 and 5.80×10^?8 atm. It was found that a_Mno values increase with increasing MnO, and tend to increase with an increasing CaO‐to‐MgO ratio. The a_MnO values also increase with increasing basicity ratio. The activity coefficient of MnO increases with an increase in its mole fraction in the slag. Quadratic multivariable regression model equations which represent the activity data successfully and which can be used to predict the MnO activities in the compositional range of this study were developed. The MnO activity data was interpreted in terms of a slag model which describes the thermodynamic properties of the slag successfully.