Thermodynamic and experimental study of external hot-metal dephosphorisation using calcium ferrite-based reagents

This study aims to develop a novel flux reagent for cost-effective, energy-efficient hot metal external dephosphorisation. Thermodynamic simulations using FactSage 8.3 were used to design and evaluate five reagent systems based on primary constituents, including CaO, FeO, Fe₂O₃, CaF₂, Na₃AlF₆, and B₂O₃. Laboratory-scale dephosphorisation experiments using these designed reagents were subsequently performed in a 5 kg coreless induction furnace at 1350 °C using hot metal containing 0.18 wt.% phosphorus. A calcium ferrite–based reagent (43% CaO, 54% Fe₂O₃, and 3% CaF₂) exhibited the highest experimental phosphorus removal efficiency (76%) with only 7% reagent addition in 10 min at 1350 °C under manual stirring. XRD analysis of the slags after dephosphorisation revealed that around 81% phosphorus was fixed in dicalcium silicate–tricalcium phosphate (2C₂S–C₃P, where C₂S = 2CaO·SiO₂ and C₃P = 3CaO·P₂O₅) solid solutions, particularly Ca₇P₂Si₂O₁₆. The above reagent also caused minimal refractory dissolution and a significant desiliconisation, highlighting the strong potential of the designed reagent for industrial hot-metal pretreatment with minimal reagent addition.