A thermodynamic study of dephosphorization using BaO-BaF₂, CaO-CaF₂, and BaO-CaO-CaF₂ systems

Abstract

Phosphorus partition ratios between BaO-BaF₂ fluxes and copper-phosphorus alloys have been measured as a function of slag composition at 1400 °C. A molybdenum sleeve has been used to avoid contact between the slag and the crucible in order to prevent the absorption of slag by the graphite crucible. The effects of additions of BaO to the CaO-CaF₂ system have been investigated by measuring the phosphorus partition ratios between these fluxes and Fe-C_sat-P alloy as a function of slag composition at 1400 °C. Also, the activity of BaO as a function of slag composition at 1400 °C has been determined by equilibrating a silver-barium alloy with the BaO-CaO-CaF₂ fluxes and CO in a graphite crucible. The results indicate that phosphorus partition ratios with carbon-saturated iron, L_P, for the BaO-BaF₂ system are relatively high, going up to 400, even for oxygen partial pressure as low as 7.8 × 10⁻¹⁶ atm. The phosphate capacity and the activity coefficient of PO_2.5 for this system were calculated from the experimental results using the available thermodynamic data. No effects of barium oxide addition in lime-based fluxes were observed for BaO contents less than 40 pct. One of the reasons for this phenomenon is that BaO activity in a lime-based flux is very small for BaO content less than 46 pct. However, for high BaO contents,$C_{PO4^{3 - } }$ increases significantly, as does the activity of BaO.