Dissolution Behavior and Phase Evolution During Aluminum Oxide Dissolution in BOF Slag

Basic oxygen furnace (BOF) slag is a byproduct in the steel making process and is produced in considerable amounts. Thus, its valorization is important. Additives such as Al₂O₃ can be utilized to modify the composition and mineralogy of the slag provided that a fast and effective dissolution of these additives in molten slags can be ensured. With this in mind, the dissolution of Al₂O₃ particles in molten BOF slag has been investigated between 1500 and 1600 °C. In all cases, a dissolution zone forms around the dissolving particle which limits the dissolution rate in the melt under natural convection conditions. The dissolution in the current system is found to be an indirect process, wherein crystalline reaction products like CaAl₄O₇ (CA₂) and CaAl₂O₄ (CA) form on the surface of the particles. CA forms at 1500 °C and CA₂ at 1600 °C. These reaction products form a continuous layer on the surface of the dissolving particles but the thickness of this reaction layer remains limited. The experimental data have been utilized to evaluate the dissolution paths. Near the Al₂O₃/slag interface, the inter-diffusion of Al₂O₃ and CaO occurs due to which the dissolution path shifts towards the Al₂O₃-CaO binary system. A phenomenological model is presented to explain the evolution of the dissolution process in the current system, wherein the kinetics of the process is used to explain the reaction products formed at 1500 °C and 1600 °C.