Phase Relationship of CaO-SiO2-FeO-5 mass pct P2O5 System with Low Oxygen Partial Pressure at 1673 K (1400 °C)

Abstract

Dephosphorization by using multiphase flux could considerably decrease the consumption of CaO and prevent the addition of fluorite. However, the equilibrium phase relationship within this system, which is of significant importance for understanding the formation mechanism of multiphase flux, remains unclear. Thus, it is required to provide reliable phase diagrams of the basic slag system of multiphase flux. In this research, the phase relationship of the CaO-SiO2-FeO-5 mass pct P2O5 system at 1673 K (1400 °C) with $$ {P}_{{{\text{O}}_{2} }} $$ of 9.24 × 10−11 atm has been studied by using the chemical equilibration method. It has been found that solid solution consists mainly of 2CaO·SiO2-3CaO·P2O5, but occasionally it contains 3CaO·SiO2. Liquidus saturated with solid solution shrinks toward the FeO corner compared with the isothermal at 1673 K (1400 °C) of the CaO-SiO2-FeO system equilibrated with metallic iron. Thermodynamically stable CaO-FeO phase is confirmed, which could promote the condensation of 3CaO·P2O5 into the solid solution and increase the phosphorus partition ratio between the solid solution and molten slag. Based on the regular solution model, the effect of T.Fe and CaO content in the liquid phase on the phosphorus partition ratio between the solid solution and molten slag is discussed.