Impact of Impurities on Nickel Sulfate Crystallization and Strategies for Removal: Advancing Toward Battery-Grade Nickel Sulfate Production

The increasing demand for high-purity nickel sulfate, particularly for lithium-ion battery cathode materials, necessitates efficient and effective purification methods. This study investigates the impact of impurities on nickel sulfate crystallization and explores strategies for mitigating these impurities to produce battery-grade nickel sulfate. Through evaporative crystallization, displacement washing, and repulping, we examined the incorporation and removal of various impurities, including magnesium, cobalt, sodium, and calcium. Our findings suggest that Mg and Co are primarily integrated into the crystal lattice via isomorphous substitution and inclusion when present in higher initial concentrations. In contrast, Na and Ca are predominantly adsorbed onto the crystal surface, regardless of their initial concentrations. Repulping, particularly under controlled conditions, proved effective in reducing the levels of Mg and Co, offering a feasible postcrystallization strategy to enhance the purity of nickel sulfate. This research provides critical insights into optimizing nickel sulfate crystallization processes for achieving the high-purity standards required in the battery industry.