Mechanism-Guided Transformation of Hematite to Battery-Grade FePO

A novel low-carbon route was developed to synthesize high-purity FePO4 from natural hematite (α-Fe2O3). To overcome the inherently low solubility of α-Fe2O3, a mild carbothermal reduction (0.8 wt % carbon, 650 °C, 15 min) was applied before leaching. This pretreatment partially reduced Fe2O3 to Fe3O4, disrupted the lattice, and generated microcracks, significantly enhancing structural reactivity. Thermodynamic analysis confirmed progressive reduction and in situ CO formation under carbon-rich conditions. The reduced samples were leached using an HCl-H3PO4 system (H3PO4/Fe = 1.05, H2O2/Fe = 0.3), where proton attack and ligand complexation promoted Fe3+ dissolution. Under identical leaching conditions, the reduced sample achieved 85.82% Fe3+ leaching within just 2 h, matching the nonreduced counterpart at 8 h, and reached 90.88% at 3 h, demonstrating good leaching efficiency. Kinetic analysis showed that the leaching behavior followed the Valensi-Carter model, with a high correlation (R2 = 0.9968) and an apparent activation energy of 21.89 kJ/mol, indicating a mixed control mechanism governed by both solid-state diffusion and surface chemical reaction. Subsequent precipitation at pH 2.0, 60 °C for 20 min yielded FePO4 with Fe/P = 0.989 and >99.60 wt % purity, meeting HG/T 4701-2021 standards. This work establishes a highly efficient, structurally driven hydrometallurgical route for producing battery-grade FePO4 from refractory iron ores under low-carbon conditions.