Dissolution Behavior of Solid 5CaO·SiO₂·P₂O₅ in CaO-SiO₂-FeO_x Slag

Abstract

In order to clarify the dissolution behavior of solid P₂O₅ rich phase in slag, the solid phosphate compound silicocarnotite 5CaO·SiO₂·P₂O₅ being the representative of P₂O₅ rich phase was dipped into the molten CaO-SiO₂-FeO_x slag at 1573 and 1673 K. Since the initial slag was free of P₂O₅, the increase of P₂O₅ content in the slag is the indication of the dissolution behavior of solid 5CaO·SiO₂·P₂O₅. Therefore, the concentration profile of P₂O₅ across the interface between solid 5CaO·SiO₂·P₂O₅ and slag was analyzed to evaluate the dissolution behavior.
The results show that the dissolution of solid 5CaO·SiO₂·P₂O₅ into slag can be divided into the following stages: interaction of solid phase with slag, disintegration of solid phase, reaction between disintegrated solid phase and surrounding slag, and diffusion of CaO and P₂O₅ from solid sample to slag. The diffusivity of P₂O₅ in the liquid slag was calculated. It was found that higher temperature is favored for the diffusion in some cases, whereas larger CaO/SiO₂ ratio of the slag restrains the diffusion.