Fluidity and structure of aluminate slags for smelting high-alumina iron ores: Effect of CaO/SiO2 mass ratio

Slag regulation is crucial for achieving smelting of high-alumina iron ore in blast furnaces. This study investigated the fluidity and structure of CaO-SiO₂–10 wt.%MgO-30 wt.%Al₂O₃ slag by varying the CaO/SiO₂ ratio (1.0–2.0). The results revealed that viscosity decreased with increasing CaO/SiO₂ ratio, while the free running temperature, defined as the temperature at which the slag can flow freely, initially increased and then decreased, peaking at the range of 1.2–1.6. Interestingly, the free running temperature of slag at basicity 2.0 (1392 °C) was lower than that at basicity 1.0 (1398 °C). Spectroscopic analysis demonstrated that increasing basicity facilitated greater charge compensation of Al³⁺ ions, resulting in an increased amount of [AlO₄] tetrahedra. Moreover, increasing free oxygen promoted the depolymerization of [SiO₄] and [AlO₄] tetrahedra, reducing bridging oxygen and increasing non-bridging oxygen. Consequently, the slag's overall polymerization degree decreased. Furthermore, MD simulations identified two distinct fracture mechanisms of bridging oxygen within the Si-O-Si structure.