Impurity Uptake During Cooling Crystallization of Nickel Sulfate

Abstract

Battery production for electric vehicles has increased rapidly in the last decade, and the projections show an ever-increasing demand for the next years. This leads to a need for recycling of valuable metals used in batteries, such as nickel, for a sustainable development. Nickel can be recovered from process streams or side streams in hydrometallurgical industry as nickel sulfate by crystallization , in order to obtain high-purity products for applications like battery-grade nickel sulfate . In this work, NiSO₄·6H₂O was precipitated by cooling crystallization in a temperature-controlled batch reactor, and uptake of Na, Cl, and Mg, impurities commonly found in hydrometallurgical industries, were investigated. Increasing the initial impurity concentrations in the reactor caused increased impurity content in the precipitates, and the highest uptake was provided by Mg. Characterization of final products with X-ray diffraction (XRD) showed that the precipitating polymorph was altered at high impurity concentration. The results of partial dissolution studies indicated that uptake of Cl was negligible, and Na was weakly adsorbed on the crystal surface, while Mg was also incorporated in the bulk of the crystals, possibly explained by the similar properties of Mg and Ni.