Experiments have been made to study the phosphorus distribution between liquid iron and MgO saturated CaO-MgO-FeO_x-SiO₂ slags containing 1 to 4% CaF₂ in the temperature range 1550 to 1650°C. The effect of CaF₂ on the equilibrium quotient k_p(=(%P₂O₅)/{[%P]²(%FeO)⁵}) was found to be nearly equal to that of CaO on the weight percentage base. The equilibrium quotient k_p is expressed as logk_p=8.22log[(%CaO)+(%CaF₂)+0.3(%MgO) -0.05(%FeO)]+21460/T-27.02 or logk_p=0.156[(%CaO)+(%CaF₂)+0.3(%MgO)] +20730/T-19.48
The effect of CaF₂ on the activity coefficient of P₂O₅ was also studied by the Turkdogan and Pearson's treatment. The following expression for the activity coefficient of P₂O₅ is given for the slags containing CaF₂. logγ_P2O5=-1.01(23N_CaO+21N_CaF2+17N_MgO+8N_FeO) -26300/T+11.24
It was found from the plot of the activity coefficient of FeO vs. the mole fraction of SiO₂ that the activity of FeO increases with the addition of CaF₂.