Phosphorus distribution between Mn-Si Melts and CaO-SiO₂-MnO-CaF₂ slags

Experiments were carried out to investigate the equilibrium distribution ratio of phosphorus (L_P) between CaO-SiO₂-MnO-CaF₂ melts and carbon saturated Mn-Si alloy as a function of oxygen partial pressure, alloy and slag compositions at 1,300°C. The results demonstrate that L_P increases with increasing basicity of slag, silicon concentration and oxygen partial pressure. In order to understand quantitatively the effect of silicon concentration on L_P, the phosphorus activity coefficient was measured and the interaction parameter, Mn at 1,300°C was found to be 10.7. The CaO equivalent of MnO for dephosphorization was 0.4±0.1 in terms of weight percent. By measuring the manganese activity, the activity coefficient of MnO in the range of the slag composition was calculated to be in the range of 0.42 to 0.62. The critical oxygen partial pressure between the stability of phosphate and phosphide in this slag system was about 10^-18.4 atm at 1,300°C.