Magnetic Separation of Phosphorus Enriched Phase from Multiphase Dephosphorization Slag

Abstract

The authors have found that phosphorus exhibits remarkable segregation in exhausted actual hot-metal pretreatment slag (dephosphorization slag), and it exists as a 3CaO·P₂O₅–2CaO·SiO₂ solid solution with the FeO–CaO–SiO₂ matrix. Since their magnetic properties are significantly different, it is possible to separate them with the aid of a superconducting strong magnetic field. To investigate the effects of magnetic field strength, the particle size of the slag, etc., an experiment on magnetic separation has been carried out using simulated dephosphorization slag (18.1Fe_tO–45.9CaO–20.3SiO₂–6.6P₂O₅–2.5MnO–5.5MgO in mass%) and a superconducting magnet with 0.5–2.5 T. In a stronger magnetic field, the quality of the recovered slag becomes better due to less contamination of the Fe_tO matrix phase, while its quantity worsens and the amount of recovered slag declines. However, the quantity of the recovered slag can be improved by repeating the procedure. In the present experiment, about 65% of the phosphorus enriched phase can be recovered with less than 10% of Fe_tO matrix phase contamination at conditions of 0.5 T, a particle size of less than 35 μm, and a water/slag ratio of 32 with a single procedure. The P₂O₅ content in the recovered slag is close to that in the phosphorus-enriched phase in the initial slag, and the FeO content decreases markedly with magnetic separation.