An Operationally Simple Method for Separating the Rare-Earth Elements Neodymium and Dysprosium

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-(BuNO)-Bu-t)C6H4CH2}(3)N](3-) (TriNOx(3-)), feature a size-sensitive aperture formed of its three (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 (K-eq) for early and late metals enables simple Nd/Dy separations through leaching with a separation ratio S-Nd/Dy=359.