Abstract
Rare earth (RE) elements (scandium, yttrium, and the lanthanides) are critical for their role in sustainable energy technologies. Problems with their supply chain have motivated research to improve separations methods to recycle these elements from end of life technology. Toward this goal, we report the synthesis and characterization of the ligand tris[(1-hydroxy-2-oxo-1,2-dihydropyridine-3-carboxamido)ethyl]amine, H31·TFA (TFA = trifluoroacetic acid), and complexes 1·RE (RE = La, Nd, Dy). A high-throughput experimentation (HTE) screen was developed to quantitatively determine the precipitation of 1·RE as a function of pH as well as equivalents of H31·TFA. This method rapidly determines optimal conditions for the separation of RE mixtures, while minimizing materials consumption. The HTE-predicted conditions are used to achieve the lab-scale separation of Nd/Dy (SFNd/Dy = 213 ± 34) and La/Nd (SFLa/Nd = 16.2 ± 0.2) mixtures in acidic aqueous media.
Highlights
Rare earth (RE) elements are critical for their role in sustainable energy technologies
H31·trifluoroacetic acid (TFA) was synthesized without any protection/deprotection steps commonly used in the synthesis of HOPO-based ligands, which improved atom economy and minimized the total number of steps required[47]
H31·TFA exhibits high stability under acidic conditions required for solubilizing RE oxides
Summary
Rare earth (RE) elements (scandium, yttrium, and the lanthanides) are critical for their role in sustainable energy technologies. A high-throughput experimentation (HTE) screen was developed to quantitatively determine the precipitation of 1·RE as a function of pH as well as equivalents of H31·TFA This method rapidly determines optimal conditions for the separation of RE mixtures, while minimizing materials consumption. Opportunities remain to improve selectivity for individual rare earths over a single extraction and stripping step Toward these goals, researchers have developed novel ligands[13], ionic liquids[14,15], and extractants[16,17,18]. High-throughput experimentation (HTE) refers to running multiple reactions in parallel[27] Such methods have been used extensively in catalysis to rapidly screen reaction conditions (e.g., metal ion, ligand, solvent) and require a fraction of the time and materials resources necessary for lab-scale methods[28,29,30]. The hydroxylamine moieties required the use of strong bases—incompatible with water—to coordinate the RE ions
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