Phase Relationship for the CaO–SiO₂–FeO–5 mass%P₂O₅ System with Oxygen Partial Pressure of 10⁻⁸ atm at 1673 and 1623 K

Abstract

Dephosphorization process by using multiphase flux requires smaller slag amount than conventional process, while the high refining efficiency can still be achieved, due to the promotion of the CaO utilization. In order to provide proper phase diagram for understanding the reaction mechanism, the phase relationship for the CaO–SiO₂–FeO–5 mass%P₂O₅ quaternary system has been studied with oxygen partial pressure of 10⁻⁸ atm at 1673 and 1623 K by using chemical equilibration technique. It has been found that the solid solution exists only as 2CaO·SiO₂–3CaO·P₂O₅, and the ratio between both varies with liquid phase compositions. On the other hand, the liquidus for both 1673 and 1623 K that saturated with above solid solution, moves close to the FeO apex comparing with the CaO–SiO₂–FeO_x system equilibrated with iron. Besides, the large phosphorus partition ratio between solid solution and liquid slag has also been found, which agrees well with previous works. Based on the regular solution model, both activities and activity coefficients of P₂O₅ have been discussed.