Phase Equilibrium for the CaO–SiO₂–FeO–5mass%P₂O₅–5mass%Al₂O₃ System for Dephosphorization of Hot Metal Pretreatment

Abstract

Recently, after the restriction of the use of CaF₂, dephosphorization process often generates large amount of slag, due to the neglect of refining functions of solid phases. Consequently, this brings environmental issues and influences refining. In order to improve the utilization efficiency of solid CaO and its compounds in the dephosphorization slag, multiphase flux refining has been proposed by considering the enrichment of phosphorus within the solid phases. As to provide theoretical fundamentals for both understanding on the reaction mechanism of phosphorus and practical slag control, phase relationship for the CaO–SiO₂–FeO–5mass%P₂O₅–5mass%Al₂O₃ system has been studied based on chemical equilibration technique with oxygen partial pressure of 10⁻¹⁰ atm at 1673 K. In current work, the liquidus saturated with P₂O₅-rich solid solution has been firstly deduced on the CaO–SiO₂–FeO ternary system, and the discussions on the relationship between solid solution and liquid phase has been proceeded. It has been found that the existence of Al₂O₃ enlarges the liquid phase area, but does not affect the composition of solid solution. On the other hand, the equilibrium solid phase has been confirmed as 2CaO·SiO₂–3CaO·P₂O₅ solid solution, while the ratio between both varies along with liquidus. As expected, the large equilibrium partition ratio of phosphorus between solid solution and liquid slag has also been found and discussed.