Distribution of P2O5 between Solid Dicalcium Silicate and Liquid Phases in CaO–SiO2–Fe2O3 System

Abstract

In most cases, the slag used in hot metal dephosphorization is saturated with dicalcium silicate (C2S) and contains two phases—solid C2S and liquid. It is known that C2S and tricalcium phosphate (C3P) form a solid solution over a wide range of composition. The distribution ratio of P2O5 between the solid solution and the liquid slag phase has been reported to be very high. In order to determine the maximum possible concentration of P2O5 in the solid solution, the distribution ratio of P2O5 in slag containing a high concentration of P2O5 was measured in this study, and the influence of MgO and MnO on the distribution ratio was also investigated. CaO–SiO2–Fe2O3 slag containing up to 18% P2O5 was melted at 1873 K and then cooled to 1673 K at a rate of 10 K/min. During cooling, the solid solution of C2S and C3P precipitated from the liquid slag. A linear relationship, which was independent of the lime/silica ratio and P2O5 content, was found to exist between the distribution ratio of P2O5 and the T·Fe content. On the contrary, the concentration of P2O5 in the solid solution was strongly influenced by the lime/silica ratio and P2O5 content. If the P2O5 content was high enough and the T·Fe content was controlled to show the high distribution ratio, the concentration of C3P in the solid solution can be increased to 100%. No significant change was observed in the distribution ratio upon the addition of MgO and MnO.