Hot Metal Desulfurization by CaO–SiO2–CaF2–Na2O Slag Saturated with MgO

Abstract

The effect of CaF2 and Na2O on the sulfide capacity of the CaO–SiO2–CaF2–MgOsatd.(–Na2O) slags for hot metal desulfurization was investigated at 1623 and 1723 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–SiO2–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 CaOsatd.–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 O2− 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+CaF2’ can be reduced from 95 to 75 mass% for maintaining the sulfide capacity of 0.01 at 1623 K, which is important considering the reduction of CaO and CaF2 consumption in hot metal desulfurization process with MgO saturation.