In-Situ Investigation of Phosphorus Transformation and Distribution During Gas-Based Reduction of High-Phosphorus Oolitic Hematite

High-phosphorus oolitic hematite is recognized as one of the most refractory iron ores due to the intergrowth of phosphorus and iron, making traditional separation techniques ineffective. Gas-based direct reduction followed by magnetic separation is of significance to realize the efficient recovery of iron from low-grade iron ore, accompanying the reduction of phosphorus. However, the transformation and migration behavior of phosphorus during the reduction process remains unclear. To simulate the direct reduction of this ore, the initial heating followed by the reduction experiments were performed. Using confocal laser scanning microscopy (CLSM), this study first investigated the phosphorus transformation under a high-purity Ar atmosphere heating from 25 °C to 1500 °C. The results indicate that fluorapatite (Ca₅(PO₄)₃F) underwent a sequence of defluorination, partial dissolution, and complete dissolution, corresponding to solid (Ca₃(PO₄)₂), solid-liquid coexistence, and liquid phases (P₂O₅), respectively. Subsequently, the migration behavior of three kinds of phosphorus in different states during CO reduction was clarified through a quantitative mass balance analysis. At 1200 °C, solid Ca₃(PO₄)₂ was not reduced by CO. By 1300 °C, (P₂O₅) in the melt was reduced, and more than half of phosphorus escaped to the gas phase. The increase in dissolved (P₂O₅) in the melt accelerated the reduction of phosphorus at 1400 °C, resulting in an increase of phosphorus in the iron phase. Finally, inhibiting (P₂O₅) dissolution in the melt via Al₂O₃ addition could decrease phosphorus content in the iron phase, providing a visible strategy to promote the utilization of high-phosphorus iron ores.