Effect of Calcium Fluoride on Phosphorus Distribution between MgO-saturated Slags of the System CaO-MgO-FeO_x-SiO₂ and Liquid Iron

Abstract

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 from 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 a weight percentage base. The equilibrium quotient k_p is expressed as log k_p-8.22log[(%CaO)+(%CaF₂)+0.3(%MgO)-0.05(%FeO)]+21460/T-27.02
or log k_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 TURKDOGAN and PEARSON'S treatment. The following expression for the activity coefficient of P₂O₅ was given for CaF₂-containing slags.
logγP₂O₅=-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 versus mole fraction of SiO₂ that activities of FeO increased with addition of CaF₂.