Rare-earth metals are critical components of electronic materials and permanent magnets. Recycling of consumer materials is a promising new source of rare earths. To incentivize recycling there is a clear need for simple methods for targeted separations of mixtures of rare-earth metal salts. Metal complexes of a tripodal nitroxide ligand [{(2-(t) BuNO)C6 H4 CH2 }3 N](3-) (TriNOx(3-) ), feature a size-sensitive aperture formed of its three η(2) -(N,O) ligand arms. Exposure of metal cations in the aperture induces a self-associative equilibrium comprising [M(TriNOx)thf]/ [M(TriNOx)]2 (M=rare-earth metal). Differences in the equilibrium constants (Keq ) for early and late metals enables simple Nd/Dy separations through leaching with a separation ratio SNd/Dy =359.

Rare earth (RE) metals are critical components of electronic materials and permanent magnets. Recycling of consumer materials is a promising new source of rare REs. To incentivize recycling, there is a clear need for the development of simple methods for targeted separations of mixtures of RE metal salts. Metal complexes of a tripodal hydroxylaminato ligand, TriNOx 3-, featured a size-sensitive aperture formed of its three η 2 -(N,O) ligand arms. Exposure of cations in the aperture induced a self-associative equilibrium comprising RE(TriNOx)THF and [RE(TriNOx)] 2 species. Differences in the equilibrium constants K dimer for early and late metals enabled simple separations through leaching. Separations were performed on RE1/RE2 mixtures, where RE1 = La-Sm and RE2 = Gd-Lu, with emphasis on Eu/Y separations for potential applications in the recycling of phosphor waste from compact fluorescent light bulbs. Using the leaching method, separations factors approaching 2,000 were obtained for early-late RE combinations. Following solvent optimization, >95% pure samples of Eu were obtained with a 67% recovery for the technologically relevant Eu/Y separation. (11)(12)(13)(14). Limitations associated with their beneficiation and separations, especially their solvent-, waste-, and energy intensities, have contributed to the concentration of suppliers in the People's Republic of China. Supply risks for these elements have emerged, particularly in the face of current and growing demand in the next 20 y (15, 16). Because the global marketplace for these elements is dominated by a single source (17), prices for primary rare earth (RE) materials are volatile (18). As a result, the US Department of Energy has classified many of these elements as "critical" (19). There is a clear need to find potential new supplies of these elements.Recent life cycle assessments have indicated that recycling of consumer materials is a promising alternative to conventional production processes (20). Despite this assertion, as recently as 2011, less than 1% of RE-containing materials were being recycled (21). These low recycling rates stem from a combination of sporadic collection procedures and lack of efficient separations and preprocessing steps (22)(23)(24)(25)(26)(27).To contribute to incentivizing the "urban mining" of REcontaining materials, we recently initiated efforts toward new, simplified methods in RE separations (28). Our initial work focused on the separation of neodymium (Nd) and dysprosium (Dy), two key components of neomagnets (Nd 2 Fe 14 B). We disclosed the development of the tripodal nitroxide ligand, [((2-t BuNO)C 6 H 4 CH 2 ) 3 N] 3− (TriNOx 3-), which induced a selfassociation equilibrium between monomeric Nd(TriNOx)THF/ dimeric [Nd(TriNOx)] 2 species. The position of this equilibrium was found to be strongly dependent on the size of the RE cation. We showed proof of concept that differences in the self-association equilibrium constants between Nd and Dy could be exploited to achieve 95% pure materials through a simple leachi...

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Rare-earth metals are critical components of electronic materials and permanent magnets.R ecycling of consumer materials is ap romising new source of rare earths.T o incentivize recycling there is ac lear need for simple methods for targeted separations of mixtures of rare-earth metal salts.M etal complexes of at ripodal nitroxide ligand [{(2-t BuNO)C 6 H 4 CH 2 } 3 N] 3À (TriNOx 3À ), feature as ize-sensitive aperture formed of its three h 2 -(N,O) ligand arms. Exposure of metal cations in the aperture induces as elf-associative equilibrium comprising [M(TriNOx)thf]/ [M(TriNOx)] 2 (M = rare-earth metal). Differences in the equilibrium constants (K eq )f or early and late metals enables simple Nd/Dy separations through leaching with as eparation ratio S Nd/Dy = 359.The rare-earth elements (M), La-Lu, Y, and Sc, are key components of vital materials with diverse applications in electric motors,p hosphors,n ickel-metal-hydride batteries, and catalysts,among others. [1] Their broad, and in many cases irreplaceable,uses result from unique properties arising from their 4f valence electron shell. Neodymium (Nd), typically mixed with praseodymium (Pr), is ak ey component of sintered neodymium magnets (or "neo magnets"; Nd 2 Fe 14 B), which have the highest-energy product (52 MGOe) among commercialized permanent magnets. [2] Te rbium (Tb) and dysprosium (Dy) are also key components of this material which increase its intrinsic coercivity. [3] High-performance neo magnets include up to 9% Dy by total magnet weight. [4] TheU .S.D epartment of Energy has categorized dysprosium and neodymium as "critical materials" because of their supply problems and importance to technology. [5] Ap otential new supply stream of neodymium and dysprosium is end-of-life magnet recycling. In 2007, global in-use stocks for rare-earth metals in neo magnets were estimated to be 62.6 Gg of Nd, 15.7 Gg of Pr and Dy,a nd 3.1 Gg of Tb. [6] In 2011, however, less than 1% of rare-earth metals were recycled. [4] Ar ecent life-cycle assessment sug-gested that end-of-life product recycling is aviable alternative to the mining of rare-earth metals. [7] Recycling processes have been reported for the isolation of mixtures of rare-earth metals from dismantled magnetic materials [4, 8] and significant advances have been made toward processing magnets to produce rare-earth concentrates. [9] However,t he varying blends of Dy,T b, Nd, and Pr necessitate separations of the rare earths for reblending into new sintered magnets in the highest-value recycling schemes.Rare-earth metals are separated commercially using aR hône-Poulenc liquid-liquid extraction process (LLE), an energy-, time-and solvent-intensive process that exploits differences in binding constants of the metals to organic extractants. [10] Recent fundamental studies have worked to enhance the selectivity for one type of rare-earth metal cation over another, based on ionic size,t hrough molecular selfassembly of helical Ln 2 L 3 dimers, [14] or with the use of lanthanide-based metal-organic frameworks...