<p>The rotary kiln-electric furnace process, a conventional technology extensively employed for industrial ferronickel production from laterite ores, is currently facing significant overcapacity. Achieving efficient nickel–iron separation is therefore essential to alleviate the oversupply of ferronickel while meeting the growing demand for nickel- and iron-based salts in battery applications. In this study, a sulfuric acid-curing-oxidative decomposition roasting-water-leaching process was developed for the treatment of ferronickel alloys. Under optimized conditions, the recovery efficiencies of Ni, Co, and Mn reached 82.1%, 97.5%, and 94.4%, respectively, whereas the leaching rates of Fe and Cr were limited to 18.2% and 5.7%, respectively. Further enhancement of Ni leaching inevitably led to excessive Fe dissolution (&gt;&#xa0;20%), thereby compromising the overall Ni-Fe separation efficiency. To clarify this trade-off, the roasting mechanism was investigated in detail, revealing that the coexistence of NiFe₂O₄, NiO, and a dense iron sulfate layer synergistically hindered Ni leaching. Moreover, during sulfation roasting, Fe tended to diffuse inward toward the alloy core, whereas Ni migrated outward toward the product layer surface. Overall, the results demonstrate that cyclic sulfation roasting is required to further improve Ni recovery efficiency. This study provides new mechanistic insights into the extraction of nickel from ferronickel alloys.</p>