In order to clarify the effect of the MgO/Al2O3 ratio on the fluidity of a low-alumina blast furnace slag system, the influence law of slag fluidity with different MgO/Al2O3 ratios was studied based on the composition of blast furnace slag through a viscosity experiment and themodynamic software. By studying the effect of the MgO/Al2O3 ratio on the activation energy of viscous flow of slag combined with FT-IR, the effect of the MgO/Al2O3 ratio on the thermal-stability of low-aluminum slag was interpreted from the microstructure level. Results indicated that the viscosity and the melting temperature of slag both showed a gradual downward trend due to the increase of the MgO/Al2O3 ratio. Besides, the temperature stability of the low aluminum slag became more stable due to the depolymerization of the complex structure of slag. Considering the actual operating conditions of blast furnace, the MgO/Al2O3 ratio of slag was suggested to be controlled to 0.60 and the basicity to be no higher than 1.20 under the conditions of this investigation. Industrial test results showed that the coke rate could be saved as 3.49 kg/t when the MgO/Al2O3 ratio decreased from 0.70 to 0.58.
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