Desulfurizing Ability of the CaO_satd.-CaCl₂-CaF₂ Slags

Desulfurizing ability of the CaO-CaCl₂-CaF₂ slags saturated with CaO has been investigated from the viewpoint of the sulfide capacity and CaO solubility. The CaO-CaCl₂-CaF₂ slags containing small amounts of Cu₂O and CaS were inserted in a CaO crucible with metallic copper. The CaO crucible was sealed in a nickel holder to prevent the evaporation of CaCl₂, then heated up and kept at temperatures from 1573 K (1300 °C) to 1673 K (1400 °C) for 24 hours, which enabled the system inside the CaO crucible to reach the equilibrium. As expected, the sulfide capacity derived from the data obtained as well as CaO solubility of the slag increase with an increase in temperature at a constant ratio of CaCl₂/CaF₂. The solubility of CaO increases by the replacement of CaF₂ with CaCl₂, whereas the sulfide capacity slightly decreases and the activity coefficient of CaS (γ _CaS) increases. This suggests that CaF₂ has stronger interaction with CaS than CaCl₂. The sulfur distribution ratio between carbon-saturated iron melts and the CaO-CaCl₂ slag has been calculated to be about 10 000 at 1573 K (1300 °C) using the sulfide capacity obtained, which value is still large enough even with the replacement of CaF₂ by CaCl₂.