Reduction and migration behavior of phosphorus in coal-based reduction of high-phosphorus oolitic iron ore
摘要
Phosphorus tends to migrate into metallic iron during the direct reduction of high-phosphorus oolitic iron ore, leading to undesirable phosphorus enrichment in metallic iron. However, the underlying reduction and migration mechanisms remain poorly understood. Phosphorus behavior during coal-based reduction was systematically investigated through theoretical modeling and experimental approaches. Thermodynamic analysis revealed that the carbon reduction of solid Ca3(PO4)2 to gaseous P2 requires temperatures exceeding 1400 °C. Notably, this threshold significantly decreases to 1130.5 °C in the presence of SiO2 and Al2O3. Further investigations demonstrated that Ca3(PO4)2 co-reduces with FexOγ in the presence of SiO2–Al2O3–FexOγ, forming Fe3P (instead of gaseous P2) at a markedly lower temperature of 778.7 °C. Mechanistic studies indicate that the inherent thermal stability of Ca3(PO4)2 inhibits the generation of reactive [P2O5]. However, SiO2–Al2O3 coexistence destabilizes Ca3(PO4)2 while exponentially enhancing [P2O5] activity. This synergistic effect dramatically promotes the phosphorus mineral reduction. Characterization confirmed that Ca3(PO4)2 migrated into the slag phase (4FeO·Al2O3·3SiO2·CaO·P2O5). Subsequently, the reactive P2O5 in slag is reduced with metallic iron to form Fe3P, which further dissolves into the α-Fe matrix through solid-state diffusion, ultimately generating Fe–P solid solutions.