(368c) Deep Eutectic Solvents Applicable for Nickel Recovery Process from Natural Laterite Ore

In recent years, deep eutectic solvents (DES) have garnered attention as a new type of solvent. DES are obtained by mixing hydrogen bond acceptors (HBAs) and hydrogen bond donors (HBDs) in specific ratios. DES can impart various chemical properties depending on the combination of HBA and HBD, offering high design flexibility and making them applicable in a wide range of fields, including hydrometallurgy. Metal recovery methods using non-aqueous, immiscible solvents like DES have been extensively studied for the recovery of lithium (Li), nickel (Ni), cobalt (Co), and manganese (Mn) from spent lithium-ion batteries (LiBs). However, reports on the use of DES for metal recovery from primary resources such as metal ores are still limited. We hypothesized that incorporating molecules with high affinity for specific metals into hydrophobic deep eutectic solvents (HDES) could enable selective extraction of target metals.

In this study, to address the industrial limitations of high-viscosity DES, we diluted HDES with an organic solvent and, for the first time, applied it for nickel recovery from saprolite ore. To carry out the nickel recovery process, we prepared the HDES using trialkylmethylammonium chloride (TOMAC) as the HBA and decanoic acid (decA) as the HBD. Specifically, by diluting the DES, its viscosity was reduced, improving its operability, shortening the leaching time, and advancing its industrial application. The HDES was prepared by diluting with the industrial diluent Swasol 1800. When hydrochloric acid was added, the HDES exhibited Ni leaching performance comparable to that of conventional sulfuric acid leaching systems, while significantly suppressing Mg leaching. Subsequently, Ni was stripped into the aqueous phase along with other metals and further purified. As a result, impurities were selectively removed through precipitation, and a Ni solution with 97% purity was recovered. Furthermore, the HDES demonstrated excellent reusability over five leaching cycles. These results not only demonstrate the sustainability of metal recovery processes based on HDES but also highlight the potential of saprolite as a source of nickel for LiB applications.