The efficiency of dephosphorisation is governed by the
thermodynamic behaviour of phosphorus and oxygen in molten
metal, and P2O5 and FeO in slag. The equilibrium distribution
of phosphorus and oxygen, for a wide range of chemical
compositions simulating the evolution of slag composition during
a typical BOF blow, has been experimentally determined. A
mathematical model for estimation of the activity coefficients, as
a function of the chemical composition, was also attempted.