Magnetic Field Directed Rare-Earth Separations

The separation of rare-earth ions from one another is challenging due to their chemical and physical similarities. Nearly all rare-earth separations rely upon small changes in ionic radii to direct speciation or reactivity. Herein, we show that the intrinsic magnetic properties of the rare-earth ions impact the separations of light/heavy and selected heavy/heavy binary mixtures. Using TriNOx^3- ([{(2-^t BuNO)C₆ H₄ CH₂ }₃ N]^3- ) rare-earth complexes, we efficiently and selectively crystallized heavy rare earths (Tb-Yb) from a mixture with light rare earths (La and Nd) in the presence of an external Fe₁₄ Nd₂ B magnet, concomitant with the introduction of a concentration gradient (decrease in temperature). The optimal separation was observed for an equimolar mixture of La:Dy, which gave an enrichment factor of EF_La:Dy =297±31 for the solid fraction, compared to EF_La:Dy =159±22 in the absence of the field, and achieving a 99.7 % pure Dy sample in one step. These results indicate that the application of a magnetic field can improve performance in a molecular separation system for paramagnetic rare-earth cations.