Dephosphorization of Hot Metal Containing High Phosphorus Using F-free CaO–SiO2–Al2O3–Fe2O3 Slag

With the extensive usage of domestic low-grade iron ore with high phosphorus, abundant high (> 0.35%) phosphorus hot metal generates in China. To solve the dephosphorization issue of high-P hot metal under the premise of avoiding the environmental problem caused by CaF2 flux agent, a type of F-free CaO–SiO2–Al2O3–Fe2O3 slag was designed for the dephosphorization of high-P hot metal and systematically tested and analyzed combined with FactSage software under 1400 °C in this paper. The results show that it is an effective approach to remove phosphorus from hot metal-containing high phosphorus using F-free CaO–SiO2–Al2O3–Fe2O3 slag. The major driving force for this dephosphorization comes from the precipitation of $${\text{Ca}}_{{2}} {\text{SiO}}_{{4}} \cdot n{\text{Ca}}_{{3}} {\text{(PO}}_{{4}}^{{}} {)}_{{2}}$$ (C2S-C3P) phase which lowers the activity of phosphorus in liquid slag by providing a site to stabilize phosphorus in slag. The increase of basicity enhances the dephosphorization process by promoting the precipitation of the P-rich C2S-C3P phase. The Fe2O3 in slag favors the removal of phosphorus from hot metal-containing high phosphorus using CaO–SiO2–Al2O3–Fe2O3 slag by improving the oxidability of slag. The Al2O3 in slag will compete with P2O5 to combine with CaO and SiO2, which inhibits the formation of C2S-C3P and thus weakens the dephosphorization ability of slag.