Hot metal desulfurization by CaO-SiO₂-CaF₂-Na ₂O slag saturated with MgO

The effect of CaF₂ and Na₂O on the sulfide capacity of the CaO-SiO₂-CaF₂-MgO_satd (-Na₂O) slags for hot metal desulfuhzation was investigated at 1 623 and 1 723 K by taking the role of MgO as an important refractory component into account. The liquidus line of the MgO-saturated system was similar to the CaO-SiO ₂-CaF₂ ternary slag system. The silica content for the 2CaO·SiO₂-saturation was slightly decreased with MgO saturation. Although the sulfide capacity at MgO-saturation is lower than that of the CaO_satd -SiO₂-CaF₂ slag system, it is greater than the ternary slag system saturated with 2CaO· SiO₂ phase. This suggests that MgO can increase the activity of free O^2- ions under conditions of relatively low CaO activity. Near the composition of 3CaO SiO₂-saturation, MgO decreased the sulfide capacity of the slag because MgO is less basic than CaO in highly basic compositions. In addition, the addition of 5 mass% Na₂O significantly increases the sulfide capacity of the MgO-saturated slag especially in the composition of low 'CaO+CaF₂' This suggests that the input amounts of 'CaO+CaF ₂' can be reduced from 95 to 75 mass% for maintaining the sulfide capacity of 0.01 at 1 623 K, which is important considering the reduction of CaO and CaF₂ consumption in hot metal desulfurization process with MgO saturation.