Rare earth elements are used in many technological applications, including electric vehicle batteries and light phosphors. In particular, neodymium iron boron (NdFeB) permanent magnets, which are doped with small amounts of dysprosium, are used in numerous applications including wind turbine generators and magnetic resonance imaging instruments. Extraction of individual rare earth elements for application in these technologies is currently accomplished by counter-current solvent extraction processes that require large amounts of solvent and energy. Previous work by our group has shown that use of a tripodal hydroxylamine ligand [{(2-tBuNO)C6H4CH2}3N]3- (TriNOx3-) resulted in rare earth metal complexes that exhibited a self-association process that was sensitive to small differences in the ionic radius of the rare earth ions involved. By exploiting the differences in solubility between the monomeric RE(TriNOx)(L) and dimeric species [RE(TriNOx)]2 in various organic solvents, separations of early and late combinations can be accomplished by simple filtration in small volumes of benzene. In this work, substitution of the tripodal hydroxylamine ligand with an electron donating group and subsequent complexation resulted in analogous RE(TriNOxOMe) complexes. However, increased electron density at the hydroxylamine arms of the complex led to a larger self-association constant for neodymium, affording higher solubility of Nd(TriNOxOMe) in various organic solvents. As such, Nd/Dy separations were accomplished in similar volumes of toluene, a solvent with significantly lesser health and safety hazards than benzene, a carcinogen banned from industrial use. TriNOxOMe separations were on the same order of magnitude in efficiency in identical amounts of solvent, indicating a substantial improvement in the “greenness” of the separations system.

Molecular approaches to rare earth separations: Tuning ligand electronics for a greener system

255th National Meeting (2018)

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