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

概要

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In a previous study, the authors found that phosphorus exhibits remarkable segregations in industrial hot metal pretreatment slag where it exists as a Ca3P2O8–Ca2SiO4 solid solution together with a FeO–CaO–SiO2–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–SiO2–MnO–MgO with less P2O5, 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 slag in a hot-metal dephosphorization process have potentially great environmental and economic benefits.