Kinetic Aspects of Aluminum Oxide Dissolution in Molten BOF Slag

The valorization of Basic Oxygen Furnace (BOF) slag is important as the global annual production of this slag amounts to about 200 million tonnes. Al2O3 can be added to modify the composition and mineralogy of the slag. Al2O3 dissolution can provide long term volumetric stability to the solidified slag and tailor its microstructure/mineralogy for high-added value non-binder applications e.g., aggregates. To ensure the effectiveness of this modification, a fast dissolution of the additives is required. In this study, the dissolution of alumina particles in molten BOF slag between 1500 °C and 1600 °C was experimentally investigated. The alumina particles dissolve indirectly in the BOF slag. A continuous layer of CaAl4O7 (CA2) and CaAl2O4 (CA) solids are formed at the alumina/slag interface. Its thickness remains between 3 and 7 µm. The dissolution process starts rapidly wherein the initial particle diameter is reduced from 1092 µm to almost half within 60 seconds after particle addition. The dissolution rate however then drops rapidly due to the formation of an alumina enriched zone around the dissolving particle. The diffusion coefficient of Al2O3 in liquid slag varies from 1.5 × 10−3 mm2/s at 1600 °C to 9.8 × 10−5 mm2/s at 1500 °C. The activation energy of the Al2O3 dissolution process is determined to be 751 ± 54 kJ mol−1 under the present experimental conditions. Clustering of dissolving particles is observed between 1550 °C and 1500 °C, which has an adverse effect on the dissolution rate.