In response to recent industrial demands for refining hot metals without using halides at the lowest CaO consumption, the possibility of hot metal dephosphorization by CaO-SiO₂-Fe_tO slags of low CaO content has been assessed in this study. In order to clarify the dephosphorization behavior of hot metals, equilibrium distribution ratios of phosphorus between CaO-SiO₂ -Fe_tO slags and solid iron strips have been measured as a function of slag composition at 1573 K, avoiding CO gas evolution if carbon-saturated iron is used. The obtained distribution ratios have been converted to those for hot metals using available thermodynamic data of phosphorus in solid and liquid irons.
Phosphorus distribution ratio strongly depends on CaO content but not so much on Fe_tO content of the slag. It increases with an increase in CaO content when Fe_tO content is kept constant, while it slightly decreases when total Fe content is increased from 18-24 to 55 mass% at the (mass%CaO)/(mass%SiO₂) rario of around unity.
Phosphate capacities have also been estimated using activity data for FeO in this slag system, being considerably affected by CaO content of the slag. They show a good correlation with slag basicity.