Thermodynamic study on phase equilibria in the liquid Fe-S-O system

The phase equilibria and thermodynamic properties of the Fe-S-O melt at 1273 - 1573 K were investigated by employing thermochemical equilibration technique. The γ-Fe+liquid region was extended to higher sulphur content region than that of literature. The solubility of FeS in slags decreased with increasing the activity of FeO and the solubility slightly decreased with increasing temperature. The activity of FeO exhibited a negative deviation from ideality in the composition with a molar mass fraction of less than about 60 % FeO, while a positive deviation was observed at X_FeO ≥ 0.6. However, the activity of FeS exhibited a positive deviation from ideality at 1273 K, and a nearly ideal behaviour at 1573 K, respectively. The enthalpy changes of mixing were calculated to be some positive value. The sulfur content in reduced solid iron decreased from about 110 to 70 ppm at 1273 K as the ratio FeO/FeS in slag increased up to the composition doubly saturated by Fe/FeO, while the sulfur content decreased from about 400 to 150 ppm at 1573 K. The oxygen content in reduced solid iron increased to about 3 ppm at 1273 K with increasing FeO/FeS ratio up to the composition saturated by FeO.