Effect of CaCl2 Addition on Phosphorus Distribution Between CaO-SiO2-FeOx-P2O5 Slag and Carbon-Saturated Iron at Steelmaking Temperature

To understand the effect of CaCl2 addition on the dephosphorization ability of steelmaking slags, laboratory experiments were carried out to study the phosphorus distribution between CaO-SiO2-FeOx-P2O5-CaCl2 slags and carbon-saturated iron at steelmaking temperature. The phosphorus distribution ratio between slag and pure iron foil (L-P(Fe-gamma)) was measured by equilibrium experiments and converted into the phosphorus distribution ratio between slag and carbon-saturated iron (L-P(Fe-C)) using thermodynamic calculations. The influential mechanism of CaCl2 was also discussed based on the phases in the slags. It was found that the addition of CaCl2 is beneficial for the improvement of L-P(Fe-C). In the slag with basicity (R = [w(CaO)/w(SiO2)]) of 1.0, the P content in the liquid slag was increased by the addition of CaCl2. When the basicity is sufficiently high (e.g., R >= 1.5), the addition of CaCl2 enhances the generation of P-rich solid phases, including both 2CaO center dot SiO2-3CaO center dot P2O5 (C2S-C3P) and Ca5Cl(PO4)(3). Compared with CaCl2-free slags, CaCl2 addition in BOF slags doesn't evidently change the effects of slag basicity and FeOx content. With the increase of slag basicity (1.0 to 2.0), the amount of C2S-C3P solid solution in the slag climbs obviously, resulting in a higher L-P(Fe-C) both in CaCl2-added slags and CaCl2-free slags, while L-P(Fe-C) increases first and then decreases when the FeOx content varies from 15 to 35 pct in this study.