Atmosphere-Temperature Dual-Driven Activation of Ferronickel Enables Metal Extraction via Sulfuric Acid Leaching

The emerging new energy industry has significantly increased the demand for iron phosphate and nickel–cobalt precursors in lithium-ion batteries. Using crude ferronickel derived from the smelting of laterite ores to produce these precursors enables the efficient valorization of Fe, Ni, and Co. However, the limited leaching efficiency of ferronickel necessitates strategies to enhance its acid leaching properties. This study proposes a synergistic approach using a roasting atmosphere and temperature to activate water-quenched ferronickel. With increasing roasting temperature, the face-centered cubic (FCC) Ni–Fe phase transformed into the body-centered cubic (BCC) phase. When the temperature exceeded 800 °C, however, the newly formed BCC phase reverted to the FCC phase in a N₂ atmosphere. Carbon in ferronickel could be removed by roasting in a CO₂ atmosphere, thereby preventing phase reversion. After roasting at 800 °C for 1 h under a N₂ atmosphere, the leaching efficiencies of Ni, Co, and Fe were 92.88, 91.88, and 89.20%, respectively, with the unleached portion consisting of cementite and an unconverted FCC phase. Following roasting at 1000 °C for 1 h in a CO₂ atmosphere, the corresponding leaching efficiencies increased to 99.65, 99.37, and 96.75%, respectively, achieving near-complete leaching due to phase elimination.