The effect of Na2O and Al2O3 on dephosphorization of molten steel by high basicity MgO saturated CaO-FeOx-SiO2 slag

Highly basic CaO based slags saturated with MgO have been studied with respect to the phosphate capacity by measuring the phosphorous distribution ratio between slag and metal under controlled oxygen partial pressure at 1823 K and 1873 K. The effect of Na2O and Al2O3 addition and the activity of FeO and FeO1.5 were also determined. The phosphate capacity for MgO saturated CaO-FeOx-SiO2 slag containing 0 to 5 mass% Al2O3 and 0 to 1.75 mass% Na2O at 1873 K are in the range of 10(18.37) to 10(19.00) and that containing 4.1 to 5.0 mass% Al2O3 and 0 to 2.37 mass% Na2O at 1 823 K are in the range of 10(18.53) to 10(18.62). For the slags containing 21.28 to 23.59 mass% Al2O3 and 0 to 4.25 mass % Na2O at 1823 K are in the range of 10(17.84) to 10(18.15). The addition of Na2O to the MgO saturated CaO-FeOxSiO2 system increases the phosphate capacity of the slags. Alumina in the MgO saturated CaO-FeOxXSiO2 system decreases the phosphate capacity of the slags. The addition of Na2O to the MgO saturated CaO-FeOxSiO2 system decreases the activity coefficients of FeO and FeO15 and those of P2O5. The activity coefficients of FeO and FeO15 show that they all behave as an acidic oxide in MgO saturated CaO-FeOxSiO2 system.