2024 Kinnunen Direct production of battery grade nickel sulfate

The clean energy transition has increased the global demand of nickel sulfate used in Li-ion batteries. A short-term solution is to refine the nickel sulfate product from nickel intermediates. In the long term, new direct nickel sulfate production technologies are needed. This research focused on the modeling-based concept development of a novel direct hydrometallurgical nickel sulfate process consisting of chemical leaching, impurity removal by precipitation, solvent extraction, and crystallization as an alternative to the conventional nickel sulfate production route via a nickel matte intermediate. The conventional process route with the studied nickel concentrate had lower chemical consumption and waste production compared to direct hydrometallurgical process where approximately 60% of iron was leached consuming oxygen, and the following iron precipitation step consuming calcium carbonate resulted in a high amount of iron precipitate together with gypsum. However, hydrometallurgical alternatives are often suitable for lower ore grades or volumes and can recover copper as by-product metal. The biggest impacts on carbon footprint from chemical consumption in the direct hydrometallurgical process were generated in iron precipitation and oxygen use in leaching. With the studied nickel concentrate, pyrrhotite played a key role in both oxygen use and iron precipitation. In the leaching step, 68% of total oxygen consumption was related to pyrrhotite leaching, while in iron removal 73% of total iron originated from pyrrhotite. Thus, especially pyrrhotite removal prior to leaching needs to be developed to reduce the carbon dioxide footprint, when the pyrrhotite content in the material is high.