Magnetic Separation of Rare-Earth Ions: Property Database and Kelvin Force Distribution

Abstract

This work bridges two gaps in the magnetic separation of rare-earth ions. (1) A material property database is provided for the solutal expansion coefficient and the magnetic susceptibility of 11 out of 17 trivalent rare-earths. (2) A novel protocol is developed to enhance and resolve the magnetic term of the Kelvin force. For that purpose, an assembly of partition magnets is created where the individual magnets function in the first quadrant of their magnetic hysteresis loop. The mutual reinforcement is quantified in a particle magnetic levitation system. Thus, compared to exisiting magnetic assemblies, an enhancement in ∂B/(2μ0 ∂z) as high as 2 orders of magnitude is realized that covers 90% of the normalized spatial scale and requires 1 order of magnitude less magnet mass. Modeling the energy density field makes it possible to quantify the equilibrium position of the particle cloud at rest, which is attained via magnetophoresis of the particles regardless of their initial position. This enables the magnetic trapping and manipulation of particles with small hydrodynamic diameters. Optically tracking the transient magnetophoresis enables a high-fidelity, sub-mm resolution of ∂B 2/(2μ0 ∂z) which is further used to quantify the magnetic susceptibility of Ho­(III), Tb­(III), Er­(III), and Gd­(III).

A Novel Approach for Quantifying Magnetic Susceptibility of Aqueous and Organic Solutions

“…This is particularly emphasized for rare earth ions utilizing a magnetic field. Numerous works have been dedicated to this topic, focusing on the physicochemical aspects of the potential for separating metal ions based on differences in their magnetic susceptibility. − The key to this concept lies in determining the magnetic susceptibility of individual ions and exploring their possible interactions in the presence of a magnetic field. Assessing the values of these parameters and scrutinizing the phenomena occurring under such conditions could provide significant utility.…”

Magnetic Forces in Paramagnetic Fluids

“…Thermodynamically, the magnetic field hardly affects the chemical potential and the thermodynamic equilibrium remains virtually unchanged [49]. It later became clear that the observed concentration changes in the field gradient could be explained by evaporation of the solvent in a set of experiments [50][51][52][53][54][55][56]. A completely filled and sealed cuvette does not show any inhomogeneity upon exposure to a magnetic field gradient [51].…”

“…Magnetic field gradients of permanent magnets can also act on paramagnetic salt solutions in which the solvent is allowed to evaporate and the top layer of the fluid gains a higher concentration in a distillation process. Several experimental works show that placing a magnet on top of an insufficiently sealed cuvette containing paramagnetic salt solutions levitates the layer of higher concentration above the bulk fluid [50][51][52][53][54][55][56]. Without a magnet close to the liquid surface, this layer sinks in a Rayleigh-Taylor instability and mixes with the bulk solution.…”

70 Jahre Verfahrenstechnik an der TU Dresden

“…Die Grundlagen der magnetischen Separation dieser Ionenklasse einschließlich der damit verbundenen Mikrokonvektion wurden in mehreren Arbeiten, u. a. [114,115] aufgekla ¨rt.…”