Study on Phosphorus Removal of High-Phosphorus Oolitic Hematite by Coal-Based Direct Reduction and Magnetic Separation

Abstract

In this article, mineralogical phase changes and structural changes of iron oxides and phosphorus-bearing minerals during the direct reduction roasting process were investigated by X-ray diffraction (XRD) and scanning electron microscope (SEM). It has been found that the reduction of hematite follows the following general pathway: Fe2O3 → Fe3O4 → FeO → Fe. The last step of the reduction process contains two side reactions: either FeO → Fe2SiO4 → Fe or FeO → FeAl2O4 → Fe depending on the micro mineralogical makeup of the ore. In the reduction process of FeO → Fe, oolitic structure was destroyed completely and fluorapatite was diffused into gangue while metallic phase is coarsening at temperatures below 1200°C. Therefore, the separation of phosphorus-bearing gangue and metallic iron can be achieved by wet grinding and magnetic separation, and low phosphorus content metallic iron powder can be obtained. However, when the temperature reached 1250°C and beyond, some of the fluorapatite was reduced to elemental P and diffused into the metallic iron phase, making the P content higher in the metallic iron powder.