Recovery of cobalt from lithium-ion battery cathode material by combining solvoleaching and solvent extraction

The recycling of cobalt from lithium-ion batteries (LIBs) is crucial for sustainability reasons. During hydrometallurgical recycling of LIBs, the cathode material is usually separated from the current collectors aluminium and copper at initial process stages. A common type of cathode material is lithium cobalt oxide (LCO) and recovery of cobalt from this source requires reduction of cobalt(iii) to cobalt(ii), often done by adding a separate reducing agent. This work aims to recover cobalt from LCO via a simple, Green and safe process whose novelty is based on using the current collectors themselves as reducing agents, and combining leaching and solvent extraction of cobalt into a single step. The acidic extractant di-(2-ethylhexyl)phosphoric acid (D2EHPA) was used to leach cobalt from LCO in the presence of metallic aluminium and copper. After optimisation, quantitative leaching of cobalt, copper and lithium was achieved, while aluminium remained unaffected. This observation demonstrates that copper can act as an effective reducing agent for cobalt(iii) in LCO, which simplifies the process by avoiding the pre-separation of the current collectors. Compared to conventional sulphuric acid leaching, the proposed process was more selective and avoided the formation of explosive hydrogen gas. Furthermore, direct leaching with D2EHPA gave a cobalt-loaded organic phase from which cobalt was selectively stripped by controlling the equilibrium pH. This approach reduced the number of steps to recover cobalt compared to traditional methods, also decreased the volume of aqueous waste and could be a greener concept for future metal recovery processes.