Successful defense of the dissertation of Barbara Fritzsche "Magnetic Separation of Rare Earth Ions"

On December 05, 2022 Barbara Fritzsche successfully defended her dissertation entitled "Magnetic Separation of Rare Earth Ions".

Rare earth elements are highly relevant due to their unique catalytic, optic, and magnetic properties. The current processing methods require a multi-stage process which is associated with high consumption of environmentally harmful solvents. While the rare earths hardly differ chemically, the differences in their magnetic moment are more pronounced. Magnetic separation of ions can therefore be a very advantageous complementary step in beneficiation and recycling. Although the magnetic manipulation of ions seemed to be impossible, the robust enrichment of some paramagnetic rare earth ions was found in the vicinity of the magnet. The studies in recent years have resolved the physical paradox of why there is a reproducible enrichment of paramagnetic rare earth ions in magnetic field gradients despite the Brownian motion of the ions. The underlying mechanism includes presence of a trigger process, in this case evaporation of the solvent water which generates a concentration gradient underneath the surface of the solution. This concentrated layer of paramagnetic ions can be levitated by the magnetic field gradient force, also called Kelvin force.

A significant influence of the magnetic gradient field on the shape of the surface and the flow inside the liquid were revealed for different rare earth solutions, i.e. different magnetic properties of the solution. We were able to verify our hypothesis that the energy barrier must be located inside the solution for a successful magnetic separation. This is the key result of this work which helps to predict the feasibility of magnetic separation for rare earth ions as the position of the energy barrier can be easily computed for a given magnetic separation system. We believe this thesis will stimulate future research of implementing the magnetic separation step into rare earth extraction to make it environmentally friendlier and more efficient.