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.