Enrichment of phosphorus in reduced iron during coal based reduction of high phosphorus-containing oolitic hematite ore

Abstract

With the objective of phosphorus enrichment in the metallic iron during coal based reduction, high phosphorus oolitic hematite ore was reduced in the presence of coal with the coal/ore molar ratio (C/O, the molar ratio of fixed carbon in coal to oxygen in iron oxides of ore) varying from 1·0 to 2·5 at temperatures ranging from 1473 to 1548 K. The metallic iron was beneficiated from reduction products by magnetic separation. The results showed that the enrichment of phosphorus in the metallic iron improved with increasing temperature and C/O molar ratio. The phosphorus content and the phosphorus enrichment could reach 2·5 and 77·5%, respectively, with a C/O molar ratio of 2·5 at 1548 K and after 60 min reduction. The high phosphorus-containing metallic iron so obtained could then be converted to steel and high phosphorus steelmaking slag that can be used as a phosphate fertiliser. Kinetic analysis demonstrated that the process of phosphorus enrichment in the metallic iron could be divided into two stages, early and late, described by phase boundary controlled reaction and diffusion controlled, respectively. At the early stage, the apparent activation energy and pre-exponential factor of phosphorus enrichment decreased from 182·12 kJ mol−1 and 9509·06 min−1 to 132·60 kJ mol−1 and 395·44 min−1, respectively, when the C/O molar ratio was increased from 1·0 to 2·5. At the later stage, the apparent activation energy and pre-exponential factor were 245·87 kJ mol−1 and 172 818·99 min−1 at a C/O molar ratio of 1·0, respectively, whilst those were reduced to 210·73 kJ mol−1 and 13 930·28 min−1 at a C/O molar ratio of 2·5.