Bifunctional hydrophobic deep eutectic solvents for selective recovery of Sm and Co from waste SmCo permanent magnets

Abstract

The application of hydrophobic deep eutectic solvent (HDES) to single-use separation of valuable metal ions in waste samarium-cobalt permanent magnets has been a significant challenge. Trioctylphosphine oxide and 3-benzoyl-1,1,1-trifluoroacetone were combined to prepare a bifunctional HDES that was investigated for green, efficient and safe recovery Sm and Co. Firstly, internal hydrogen bond interaction was verified by DSC, TGA, NMR, FT-IR and molecular dynamics study. Then, a various of optimization experiments were carried out to discovery extraction behaviors on different metal ions. The findings indicated that the acidity has a significant impact on the effectiveness of the extraction process. The maximum extraction capacities were measured as 98.8 g/L Sm(III), 64.8 g/L Co(II), 52.4 g/L, Fe(III) and 75.1 g/L Cu(II), respectively. After that, combined with UV–vis, FT-IR and XPS, the neutral complex extraction mechanism was proposed. Finally, the competitive extraction experiments at different acidity provided the theoretical underpinnings for a three-stage separation strategy that, through acidity control and the use of various stripping agents, was able to efficiently recover 97.8% Sm(III), 99.1% Co(II), 99.5% Fe(III) and 95.6% Cu(II). The whole recycling process has no need additional organic solvents, enabling cleaner and sustainable engineering production.