Challenges in Use of Chemical Reagents in Hydrometallurgical Pathways for Production of Sulphates of Nickel and Cobalt

Nickel sulphate (NiSO₄.6H₂O) and cobalt sulphate (CoSO₄.7H₂O) crystals are key components of precursor cathode-active materials (P-CAM) used in lithium-ion batteries. Following increasing demand in recent years for electric vehicles (EV), there has been an upsurge in the production of nickel sulphate and cobalt sulphate crystals of high purity. Feedstocks for the production of these crystalline materials include various forms of pure metal, concentrates, oxides, and hydroxides. The sulphate hydrometallurgical process plants typically include pressure oxidation, leaching, neutralization, precipitation, solid-liquid separation, solvent extraction, ion exchange, and crystallization. Choice of chemical reagents and their required quantities for these process schemes is a major consideration in the design and operation of sulphate refineries. Provision and application of reagents in the hydrometallurgical plant to meet stringent product grades and in the treatment of effluent streams to meet environmental regulations call for special attention to process chemistry and test work. Potential challenges are the need for optimization and reduction of excessive reagent quantities, reduction of operating costs and adverse impacts of reagent reactions on other process steps, introduction of impurities to process streams and final product, extent of engineering and equipment required for safe introduction of chemical reagents at the various stages of the process, potential availability of reagents in the current supply-chain environment, and handling of by-products. This paper discusses some of these challenges as encountered in several hydrometallurgical process schemes for the production of nickel sulphate and cobalt sulphate crystals and points to possible conceptual process solutions for mitigating the difficulties encountered.