The Effect of Na₂O and Al₂O₃ on Dephosphorization of Molten Steel by High Basicity MgO Saturated CaO-FeO_x-SiO₂ Slag

Abstract

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 FeO_1.5 were also determined. The phosphate capacity for MgO saturated CaO-FeO_x-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 1823 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-FeO_x-SiO₂ system increases the phosphate capacity of the slags. Alumina in the MgO saturated CaO-FeO_x-SiO₂ system decreases the phosphate capacity of the slags. The addition of Na₂O to the MgO saturated CaO-FeO_x-SiO₂ system decreases the activity coefficients of FeO and FeO_1.5 and those of P₂O₅. The activity coefficients of FeO and FeO_1.5 show that they all behave as an acidic oxide in MgO saturated CaO-FeO_x-SiO₂ system.