For a better understanding of phosphorus removal from hot metal, the Gibbs free energies of solid solutions between dicalcium silicate and tricalcium phosphate were derived through applications of solutions models. The regular solution model with the parameters determined in this study gave the activities of the compo nents thermodynamically consistent with the literature data and the phase diagrams. Fig. 2: Schematic illustration of solid solution between Ca 2 SiO 4 and Ca 3 P 2 O 8 .