As a fundamental study on the thermodynamic properties of Na₂O-based slags, the sulfide capacities of the Na₂O-SiO₂ slags with and without CaO, MnO, MgO, or Al₂O₃ were measured at 1500°C by conducting a method of gas/slag equilibration, and the effects of CaO, MnO, MgO, and Al₂O₃ on the sulfide capacities of Na₂O-SiO₂ slags were investigated in connection with slag basicity.
The results show that the additive oxides of CaO, MnO, and MgO increase the sulfide capacities of Na₂O-SiO₂ slags, but that of Al₂O₃ decreases it. From the evaluation of these contributions the sulfide capacities of Na₂O-SiO₂ slags can be expressed as a function of the modified slag basicity B' as follows.
logC_S=4.64B'–6.88 (1500°C)
B'={(Na₂O)+m(MO)}/{(SiO₂)+m'(MO')} [mole ratio]
m=0.7 for MO=CaO, 0.4 for MnO, 0.3 for MgO
m'=0.5 for MO'=Al₂O₃.In addition, the relation between sulfide capacity and theoretical optical basicity for Na₂O-SiO₂ slags was also investigated in comparison with that for CaO-based slags. As a result, the present correlation can be expressed by logC_S=27.0Λ_th–21.2 (1500°C)
and is not in agreement with that previously developed for CaO-based slags.