Roles of MgO and Al2O3 in Viscous and Structural Behavior of Blast Furnace Primary Slag with C/S = 1.4

Permeability is crucial for stable operation and strengthening of smelting in blast furnace ironmaking, especially for the current utilization of low-grade iron ore. The viscosity of the primary slag is an important factor affecting permeability. In this study, the roles of MgO and Al₂O₃ in the viscous and structural behavior of CaO-MgO-Al₂O₃-SiO₂-10 mass pct FeO (CaO/SiO₂ weight ratio of 1.4) primary slag were investigated. The results showed that slag viscosity initially decreased and subsequently increased when Al₂O₃ content was increased from 6 to 16 mass pct, having the lowest value at 10 mass pct Al₂O₃. The reduction in viscosity with increase in Al₂O₃ content from 6 to 10 mass pct was attributed to the effect of solid crystals dissolving into the liquid phase caused by the decrease in the liquidus temperature, while the increase in viscosity at higher Al₂O₃ contents up to 16 mass pct was caused by the network-forming role of Al₂O₃ owing to its acidic nature. The viscosity fluctuated with increase in MgO content from 6 to 16 mass pct, which was related to the variation in the equilibrated primary phase field. The MgO and Al₂O₃ in the molten slag network structure functioned as network modifier and network former, respectively, to change the silicate network, as verified by Fourier transform infrared (FTIR) and Raman spectroscopy.