Deep eutectic solvent-assisted selective extraction of valuable metals from waste lithium-ion batteries

A novel synergistic extractant consisting of a deep eutectic solvent (DES) and tri-n-butyl phosphate (TBP) is proposed for selective extraction of valuable metals from waste lithium-ion batteries (LIBs). The extraction efficiencies of Ni2+, Co2+, and Mn2+ were 99.8%, 99.1%, and 95.9%, respectively, and high-purity Li+ was enriched in the raffinate after the single-stage extraction. Valuable metal salts, lithium carbonate (92.3 wt%) and cobalt oxalate (94.9 wt%), were obtained. The DES + TBP extractant retained its high extraction performance even after multiple regeneration cycles. The extraction process followed the so-called "cation exchange mechanism" with thermodynamic properties of Delta H < 0, Delta G < 0, and Delta S < 0. The molecular-level extraction mechanism demonstrated that the extraction process was dominated by both electrostatic and coordination interactions between the metal ions and DES/TBP, based on quantum chemical calculations. This study aims to provide a new strategy for recycling valuable metals from waste LIBs.