Practical Limits of Ionic Magnetophoresis for Rare-Earth Separation

Magnetic separation has been proposed as an attractive alternative to the current chemistry-based purification processes of rare-earths because it is envisioned to be much more environmentally friendly. To evaluate its practical viability, we present a physics-based assessment of the magnetic separation of rare-earth elements (REE). Our approach is based on a standard quantum-statistical model for paramagnetic ions combined with transport estimates and magnetostatic simulations of permanent magnets, superconducting coils, and high-gradient magnetic separation (HGMS) matrices. When these methods are applied to REE ions, we find the level of enhancement and the separation time are impractical even for the highest fields (over 30 T) and most magnetic ions (Dy3+and Ho3+). In terms of time, HGMS provides the best-case scenario, but even here the degree of enrichment remains well below the sub-percent range. These realities dictate that for magnetic separation to be useful in REE processing it must be pursued in hybrid strategies that also involve controlled clustering, selective adsorption, or other chemical and physical processes.