Antisolvent crystallization of battery grade nickel sulphate hydrate in the processing of lateritic ores

Abstract

Lithium-ion batteries are a crucial part in the rapid, on-going electrification of the global vehicle fleet, which is essential in enabling a transition to a society based on renewable energy. By combining metals including lithium, nickel, cobalt, and manganese in different proportions, cathode active materials with different properties can be obtained. Nickel sulphate hexahydrate, which is of great importance to the battery industry, can be produced by hydrometallurgical processing of lateritic and sulphide ores. Antisolvent crystallization is examined as an alternative to conventional crystallization methods for the production of high-grade nickel sulphate hexahydrate in the processing of lateritic nickel ores from Turkey. The ore has been leached under atmospheric pressure followed by purification by ion exchange resulting in a solution enriched with respect to nickel together with a range of impurity metals from which NiSO4·6H2O can be obtained by antisolvent crystallization. Separate antisolvent crystallization experiments have been carried out for nickel, cobalt and iron sulphate systems, which are the main metals present in the solution, and solubility data has been determined for key conditions. Acetone and isopropanol have been evaluated as antisolvents. Antisolvent crystallization experiments have also been carried out using synthetic solutions and the effect of addition rate of antisolvent, addition of diluted antisolvent and seeding on the purity of the crystals has been investigated. Acetone gives the best product quality in terms of purity and shape. Seeding and a slow rate of addition of dilute antisolvent gives the highest purity of the NiSO4·6H2O crystals. Under optimised conditions, crystals containing 22.3% Ni with a purity of 99.8% by mass have been obtained with a crystallization yield of 63.5%.