Reaction Behavior of Phosphorus in Coal-Based Reduction of an Oolitic Hematite Ore and Pre-Dephosphorization of Reduced Iron

Coal-based reduction followed by magnetic separation is an effective way to recover iron from high phosphorus-containing oolitic hematite ore. Given that high quantities of dephosphorization agent are needed to obtain low phosphorus reduced iron, a novel approach is proposed by the authors. Without prior phosphorus removal, the phosphorus was enriched in the reduced iron during a reduction process, then high-phosphorus reduced iron was refined to low phosphorus molten iron and high phosphorus dephosphorization slag to be used as a phosphate fertilizer. The influences of various parameters, including the reduction temperature, the reduction time, and the C/O molar ratio, on the reaction behavior of phosphorus during reduction process were studied. Experimental results indicate that a higher reduction temperature, a longer reduction time, or a higher C/O molar ratio was favorable for the reduction of apatite to phosphorus and the enrichment of phosphorus in reduced iron. X-ray diffraction (XRD) analysis demonstrated that the apatite was reduced to phosphorus and Ca2SiO4 (or Ca(Al2Si2O8)) in the presence of SiO2 and Al2O3, whilst the phosphorus enriched in reduced iron formed Fe3P. The migration behavior of phosphorus was investigated using line scanning analysis of reduction products at different reduction times. The results show that the phosphorus primarily existed in the slag phase 10 min before reduction, and a large amount of phosphorus migrated into iron phase from slag phase with a reduction time of 40 min. The phosphorus content in the iron phase only slightly changed after 50 min. The pre-dephosphorization of reduced iron was performed at 1873 K, indicating a higher basicity or FetO content of CaO-based slag was beneficial to dephosphorization of the reduced iron.