Thermodynamic Modelling of Phosphorus in Steelmaking Slags

This study reviews and assesses published phase diagrams of key P2O5-containing systems relevant to steelmaking slags and experimental data on phosphorus partitioning between liquid iron and a complex composition of slags. A set of reliable experimental data was carefully selected to optimize the generalized central atom (GCA) model parameters for phosphorus-containing slag systems. The developed database effectively represents the liquidus temperature of key P2O5-containing systems and the phosphorus distribution ratio between steelmaking slags and liquid iron. The GCA model was employed to model the dephosphorization reaction under varying operating conditions such as slag chemistry and temperature. Results indicate that the phosphorus distribution ratio exhibits a maximum point with changes in the FeOx content of the slag, and that phosphorus deportment to the slag is enhanced by lowering the operating temperature and MgO content while increasing the CaO/SiO2 ratio. A comparison with commercial basic oxygen steelmaking (BOS) furnace data reveals that current operating conditions do not achieve phosphorus equilibrium contents, and the degree of P dis-equilibrium increases with higher slag viscosities.