Wet magnetic separation of phosphorus containing phase from modified BOF slag

Basic oxygen furnace slag was modified by addition of SiO2, remelted and cooled to 1400°C at a rate of 1°C min, then held for 240 min at this temperature, then quenched in water. The solidified slag was crushed, milled and then separated by a wet magnetic method at 0·35 T. X-ray fluorescence, X-ray diffraction, scanning electron microscopy and image analysis were used to investigate the separation of phosphorus containing phase from the slag. Results show that nearly all the phosphorus was enriched in the C2S phase in the modified slag which was separated into two layers, top and bottom (termed as modified slag-1 and slag-2), after solidification. The P2O5 in the non-magnetic materials from slag-1 is greater than 4%, which is almost twice than that of modified slag. C2S mineral particles in slag-1 have a larger mean size of 51 μm and most of them are well liberated, which were recovered efficiently at 0·35 T. It was also found that in slag-2, C2S minerals have limited separation owing to the highly interlinked mineral phases and a lower liberation degree resulting from their smaller crystal size. Compared with original slag, the phosphorus containing phase (i.e. C2S) with larger size in modified slag-1 will be picked up effectively. In conclusion, compared with original slag, modified slag not only obtained phosphorus concentrating phase whose phosphorus content is three times more than original slag, but also improved the separation performance at weak magnetic field by precipitation of spinel-ferric carrier mineral.