Effects of Al2O3 content on the properties of BF slag and suitable fluxing regime for BF ironmaking with high Al2O3 content

The difficulty of smelting high-alumina iron ore is that the Al2O3 content in the slag is too high, affecting the smooth running of the blast furnace. This work employed a combination of physical experiments and thermodynamic calculations to investigate the effect of Al2O3 content on blast furnace slag properties, including phase transition, viscosity, liquidus temperature, and slag structure. The results showed that a spinel phase appeared when the Al2O3 content was increased from 15wt% to 17wt%, and the liquidus temperature and viscosity of the BF slag were of therefore increased. For 17wt% to 20wt% Al2O3 content, the viscosity, liquidus temperature, and the ratio of complex structure content to simple structure content increased rapidly owing to slag structure polymerisation. Additionally, the viscosity and liquidus temperature of high-alumina blast furnace slag were negatively correlated with TiO2 content, but positively correlated with basicity. At approximately 5wt% TiO2 content, Ti(C, N) with a high melting point appeared in the molten iron, resulting in a rapid increase in the viscosity. Thus, it is recommended that the TiO2 content in the slag be less than 5wt% when the high-alumina iron ore is the main raw material of BF.