Feasibility Study of Dephosphorization of Slag Generated from Basic Oxygen Furnace of an Integrated Steel Plant

Basic oxygen furnace slag (BOF slag) is an unavoidable by-product of steelmaking process of basic oxygen furnace. The main chemical constituents of BOF slag are CaO, FeO, Al2O3, SiO2 and MgO. Due to its high metallic value (FeO: 16-20%) and lime content (CaO: 45-50%), it is possible to use in iron making and steelmaking process to replace lime and recover iron and CaO. But it also contains some P2O5 around 2 – 3% which is too high for recycling. The objective of this study is to investigate the removal of phosphorus by magnetic separation technique. The slag generally contains a Ca19Fe2(PO4)14 (phosphorus enriched phase) with FeO-CaO-SiO2 matrix phase. X-ray fluorescence (XRF), X-ray diffraction (XRD) and Scanning electron microscope (SEM) analysis were carried out for characterizing different property of BOF slag. The slag was then crushed and heated at several rates and dwell time up to 1500°C. Afterward it was cooled to 1400°C at the rate of 1°C/min with holding period of 240 min and then quenched with water. The cooled slag was then crushed, milled and separated by wet magnetic separation method. Since the magnetic properties differ for different phases, it is possible to separate each phase with the aid of magnetic separation. By applying magnetic field to the crushed slag sample, phosphorus lean and rich phases may be notably separated.