Effect of CaO-MgO-FeO-SiO2-xNa2O Slag System on Converter Dephosphorization

Na2O is an alkaline oxide, which can significantly improve the dephosphorization ability of converter slag. The effect of Na2O on the dephosphorization of converter slag was analyzed with a high-temperature dephosphorization experiment in a MoSi2 resistance furnace. We found that the dephosphorization rate increased with the increase of (Na2O) in the dephosphorization slag. The elements of Ca, Si, O, and P in the dephosphorization slag are distributed in the same area, mainly in the form of phosphate minerals, such as Ca2SiO4·0.05Ca3(PO4)2 and 6Ca2SiO4·Ca3(PO4)2. After adding Na2O, part of the Na will replace the Ca in the phosphorus-containing phase to form Ca2SiO4·Ca2Na2(PO4)2. The industrial test showed that the average dephosphorization rate in the early stage of the test heats with the CaO-MgO-FeO-SiO2-0.5%Na2O slag system could reach 62.39%, which was 19.62% higher than that of the conventional heats. The average basicity of the final slag was 0.19% lower than that of the conventional heats, while w(P2O5) increased by 0.36%, and T.Fe decreased by 0.69%. The average consumption of the slagging materials was 35.93 kg/t, which was 7.24 kg/t less than that of the conventional heats. Through thermodynamic calculation, we found that with the increase of (Na2O), the phosphorus distribution ratio between slag and steel increased significantly, the area of the liquid phase zone of the slag system increased continuously, and the viscosity decreased continuously.