Sulfuric acid leaching of ferronickel and preparation of precursor materials for power batteries: Strategy of enhanced leaching through thermal activation and its mechanism

With the development of the new energy industry, the demand for iron phosphate and nickel–cobalt hydroxide precursor materials in the power battery industry has increased sharply. Ferronickel with low content of other impurities, derived from electric furnace smelting of laterite nickel ore, contains iron, nickel, and cobalt components used for the production of two kinds of power batteries. In this study, the sulfuric acid leaching behaviors of the water quenched ferronickel particles under atmospheric pressure was investigated. Practically, the direct leaching performance of these ferronickel particles in sulfuric acid is unsatisfactory. The leaching of Ni, Co and Fe was only 4.52 %, 3.58 % and 3.83 %, respectively, at the initial acid concentration of 3 mol/L, liquid–solid ratio of 12 mL/g, leaching temperature of 95 °C and time of 4 h. However, through thermal activation, the face-centered cubic (FCC) Fe-Ni phase was transformed into the body-centered cubic (BCC) structure, which significantly improved its acidic leaching activity. Under the thermal activation at 800 °C for 2 h, the leaching of Ni, Co and Fe reached 91.27 %, 90.12 % and 89.19 %, respectively, at the same leaching conditions. After oxidizing the Fe(II) in lixivium to Fe(III) using hydrogen peroxide, 89.3 % of Fe was selectively precipitated into battery-grade iron phosphate by adding phosphoric acid and coordinating solution pH. Nickel and cobalt in residual solution was then recovered to nickel–cobalt hydroxide by precipitation after removing impurity ions in advance. This study provides a new pathway for the value-added utilization of ferronickel in the power battery industry, not only in the production of stainless steel.