Thermodynamic analysis of Silico‑Ferrite of Calcium and Aluminum (SFCA) formation via reaction pathways during iron ore sintering and its limitations: Considerations for energy efficiency in sustainable metallurgy

Iron ore sintering is an energy‑intensive agglomeration process whose environmental footprint is strongly influenced by the mineralogical nature of the bonding phases formed during the process. Silico‑ferrite of calcium and aluminum (SFCA) is the dominant bonding phase in industrial sinter and plays a decisive role in determining mechanical strength, reducibility of the iron ore as well as the process efficiency during iron making. In this study, the evolution of Silico-Ferrite of Calcium and Aluminum (SFCA) Ca 2 (Fe,Ca) 6 (Fe,Al,Si) 6 O 20 phase formation has been investigated via CALPHAD‑based FactSage analysis based on existing databases via phase equilibria. Multiple paths starting from raw materials of the sinter mix have been considered through the decomposition of limestone to lime, formation of C 2 (F 1-x A x )/ C 2 F (dicalcium ferrite), CF (monocalcium ferrite, CaO.Fe 2 O 3 ), CFA (brownmillerite, itself with two paths ABC and DEF ) phases using thermodynamic simulations, including analysis of Solidus and Liquidus temperatures, melting pattern as well as reaction of SFCA with Fe-Oxide further to form Fe-rich SFCA phase. Another aspect of this study is to perceive the impact of MgO addition (Dolomite) on SCFA phase formation which leads to the decrement in process temperature from 1156.75 °C to 788.92 °C. Such a temperature decrement not only demonstrates the significant impact of MgO in promoting SFCA phase stability by enabling its formation at a lower temperature but also enhances the energy efficiency of the system. Such modified routes as well as optimization or processing by reducing process temperature can lead to reduced energy demand and associated CO₂ emissions during sintering. Although these thermodynamic calculations indicate that the theoretical formation temperature of SFCA is lowered by MgO additions, a complete study based on non-equilibrium sintering kinetics, melt viscosity, and liquid-phase consolidation is a must in order to quantify energy savings.