Thermodynamics of MnO-SiO2-Al^sub 2^O3-MnS Liquid Oxysulfide: Experimental and Thermodynamic Modeling

The activities of MnO and MnS in a MnO-SiO2-Al^sub 2^O3(or AlO^sub 1.5^)-MnS liquid oxysulfide solution were investigated by employing the gas/liquid/Pt-Mn alloy chemical equilibration technique under a controlled atmosphere at 1773 K (1500 °C). Also, the sulfide capacity, defined as C ^sub S^ = (wt pct S)(pO2/pS^sub 2^)^sup 1/2^, in MnO-SiO2-Al^sub 2^O3 slag with a dilute MnS concentration was obtained from the measured experimental data. As X ^sub SiO2^/(X ^sub MnO^ + X ^sub SiO2^) in liquid oxysulfide increases, the activity coefficient of MnO decreases, while that of MnS first increases and then decreases. As X(AlO^sub 1.5^) in liquid oxysulfide increases, the activity coefficient of MnS increases, while no remarkable change is observed for the activity coefficient of MnO. The behavior of the activity coefficient of MnS was qualitatively analyzed by considering MnO + A^sub x^S^sub y^(SiS^sub 2^ or Al^sub 2^S^sub 3^) = MnS + A^sub x^O^sub y^(SiO2 or Al^sub 2^O3) reciprocal exchange reactions in the oxysulfide solution. The behavior was shown to be consistent with phase diagram data, namely, the MnS saturation boundary. Quantitative analysis of the activity coefficient of the oxysulfide solution was also carried out by employing the modified quasichemical model in the quadruplet approximation.[PUBLICATION ABSTRACT]