The thermodynamics of manganese oxide in high-MnO-containing slags was investigated using the chemical equilibrium method in the temperature range of 1623 to 1723 K. MnO-SiO2-Al2O3 slags were brought into equilibrium with molten silver (Ag) under controlled CO/CO2 gas atmos-phere. The equilibrium Mn concentration in the silver was measured by ICP-AES (inductively cou-pled plasma atomic emission spectroscopy) analysis after the experiment. Slag samples were analyzed by EPMA (electron probe microanalyzer) analysis. The obtained activity aMnO and activity coefficient γMnO were derived as a function of the slag composition and temperature. The activity coefficient of MnO within the investigated slag system increased with an increasing MnO/SiO2 ratio. The derived temperature dependence of the activity coefficient and partition ratio of Mn between the metal and the slag was strongly influenced by the slag composition. The thermodynamic assess-ment of the activity and activity coefficient of MnO was carried out by applying the regular solution model (RSM) on the basis of interaction energies of the cations and with FactSage™ 7.3. The theoretical calculations were compared with the experimentally derived values.
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