Utilization of multiphase fluxes for the dephosphorization of hot metal

Although steelmaking slags have been usually treated and studied as homogeneous liquids, they are actually mixtures of a liquid and solids in practical processes. CaO-based refining flux that does not contain fluxing agents such as CaF₂ inevitably forms a heterogeneous slag in normal cases, and hence, it is defined as a "multiphase flux." Efficient utilization of this type of flux would decrease the consumption of resources and the emission of CO₂, and thus, would reduce the load on the environment. Metallurgical studies on multiphase fluxes are limited, however, the physical chemistry and reaction kinetics of the same are important for the development of advanced refining processes. The reaction mechanism of dephosphorization using a multiphase flux at hot metal temperatures was investigated in this study. The reaction of a P₂O₅- containing slag with solid CaO was studied by immersing a CaO disc in the slag. A CaO-FeO layer was formed near the interface, and a solid solution of Ca ₂SiO₄-Ca₃P₂O₈ was observed in this layer. The Fe-P-Si alloy reacted with calcium ferrites at 1673 K, and the samples were analysed by XMA. The same solid solution (Ca ₂SiO₄-Ca₃P₂O₈) was observed near the slag-metal interface, which suggests that the phosphorus removed from the metal gets concentrated in the solid phase. The experimental results were reproduced with a kinetic simulation model. The simulation program was also applied to the reaction of the CaO-FeO droplet in a hot-metal bath.