Optimization of blast furnace slag chemistry for sustainable ironmaking using high alumina burdens

Critical issues with slag fluidity, thermal balancing, and hot metal quality arise from the growing usage of high-alumina iron ores and agglomerates in blast furnace (BF) operations. Under such circumstances, conventional methods often result in increased slag production, higher coke consumption, and reduced productivity. By analysing CaO–SiO₂–AlO₃–MgO interactions, this study systematically explores the optimization of slag chemistry to minimize these effects. Laboratory characterization and plant-scale experiments show that controlled MgO addition through flux charging (7–8 wt%) and precise basicity adjustment by regulating limestone and flux proportions within the range of 1.15–1.20 reduced slag viscosity by over 15% and decreased the liquidus temperature by roughly 35–40 °C. These modifications improved hot metal quality, stabilised furnace permeability, and increased fluidity. Industrial trials revealed a decrease in coke rate by 25–30 kg/thm, an increase in pulverised coal injection (PCI) utilisation, and a 2–3% increase in productivity. Optimised slag chemistry led to lower CO₂ emissions, supporting sustainable and energy-efficient ironmaking. The findings provide blast furnace operators with practical guidance for effectively managing high-alumina burdens through controlled adjustment of flux addition and burden composition using existing charging system, without additional capital investment, thereby enabling greater process stability, reduced fuel consumption, and more sustainable steel production.