Effects of additives in BaO-BaF2-MnO slag on phosphate and manganese capacities

The effects of various additives (CaO, MgO, SiO2, CaF2, and Al2O3) in BaO-BaF2-MnO slags on the distribution ratios of phosphorus and manganese between the slags and ferro manganese have been studied at 1300 degrees C. The dephosphorization ability of BaO-BaCl2-MnO slag is also investigated. It is found that replacement of BaO with CaO or MgO causes a decrease in the phosphate capacity and an increase in the manganese capacity, and that substitution of BaF2, with CaF2, or SiO2, results in a poor dephosphorizing ability and more losses of manganese from metal to slags. CaF2, in BaO-BaF2-MnO slags strongly reduces the BaO activity, which diminishes the beneficial action of BaO in the slags on dephosphorization. Comparing with BaO-BaCl2-MnO slags, BaO-BaF2-MnO slags give a higher dephosphorizing capacity. Critical contents of different additives in BaO-BaF2-MnO slags to achieve an effective dephosphorization have been given. Based on the fact that the relationships between optical basicity and the phosphate and manganese capacities are only valid in a restricted range of slag compositions, the relationships between the capacities and optical basicity a nd slag composition have been derived by considering the interaction of slag components and analyzing a host of experimental data from different authors. These relationships are expected to be useable in a wider range of slag compositions and temperatures and to predict the phosphorus and manganese contents in metal without serious error.