Physicochemical Properties of CaO-SiO2-MgO-Al2O3-Na2SiO3 Slag: Dependence on Al2O3 Content

The influence of Al2O3 on the viscosity, desulfurization, and alkali removal properties of CaO-SiO2-MgO-Al2O3-Na2SiO3 slag was explored based on the high-temperature experiments, X-ray photoelectron spectroscopy analysis (XPS), and thermodynamic calculation. With an increase in Al2O3 content, the viscosity tended to increase, but the molten slag still had the satisfactory fluidity at 1500 degrees C. The viscosity of the slag was 0.36 Pa<middle dot>s when Al2O3 content was as much as 17.5wt.%. Al2O3 promoted the generation of more Al-O bonds and [AlO4]-tetrahedron. The amount of bridging oxygen (O0) increased, while that of non-bridging oxygen (O-) and free oxygen (O2-) decreased, consistent with the changes in the corrected optical basicity. The sulfur partition ratio (Ls) and sulfur capacity (CS) of the slag decreased because the overall basicity of the slag decreased and more Ca2+ was occupied for charge compensation of [AlO4]. As the Al2O3 content increased, the alkali removal rate and alkali capacity of the slag increased because of the decrease of O2- content and the increase of Na+ stability, which inhibited the reaction between Na+ and carbon. In conclusion, the viscosity and desulfurization performance of high-Al2O3 slag met the smelting requirements of BF, but the alkali capacity of the slag was improved, which was conducive to the application of alkali-bearing raw materials from this perspective.Graphical AbstractThe phase diagram of the slag at 1400 degrees C from FactSage 8.3