Recycling Effects of Residual Slag after Magnetic Separation for Phosphorus Recovery from Hot Metal Dephosphorization Slag

摘要

In a previous study, the authors found that phosphorus exhibits remarkable segregations in industrial hot metal pretreatmerrt slag where it exists as a Ca_3P_2O_8-Ca_2SiO_4 solid solution together with a FeO-CaO-SiO_2-MnO-MgO matrix. Since the magnetic property of each phase is significantly different, it is possible to separate the phases with the aid of a superconducting strong magnetic field. By applying a strong magnetic field of 0.5 to 2.5 T to the crushed slag, more than 60 % of the concentrated phosphorus phase in the slag was recovered. If most of the phosphorus can be removed from the slag, the residual slag will comprise FeO-CaO-SiO_2-MnO-MgO with less P_2O_5, and thus may be recycled to iron- and steel-making processes, such as sintering, hot-metal desiliconization, and hot-metal dephosphorization processes. In the present work, the recycling effect of subjecting the residual slag to the dephosphorization process was simulated based on a mass balance calculation. A significant reduction in total slag generation and CaO input was demonstrated by the mathematical model considering phosphorus recovery and recycling of residual slag as a dephosphorization agent. Using the waste input-output model, it was shown that phosphorus recovery from dephosphorization slag and the recycling of residual s!ag in a hot-metal dephosphorization process have potentially great environmental and economic benefits.