Effect of Magnetic Susceptibility Gradient on the Magnetomigration of Rare-Earth Ions

Abstract

Magnetomigration of rare-earth ions activated by thermal and evaporation-based gradients was demonstrated with the help of Mach-Zehnder interferometry. Magnetic susceptibility gradients were induced in aqueous solutions of rare-earth ions by local heating/cooling or by evaporation of the solvent. Both methods yielded the enrichment of strongly paramagnetic Dy 3+ ions in the region of the highest magnetic field. Three different orientations of the magnetic field were tested using temperature as the source of magnetic susceptibility gradient. Enhanced magnetomigration was observed when gradients of magnetic field and magnetic susceptibility were non-collinear, indicating that the rotational component of the magnetic force drives the process. Additionally, four rare-earth ions with distinct values of magnetic susceptibility were studied: the diamagnetic ion Y 3+ , and the paramagnetic ions Nd 3+ , Gd 3+ and Dy 3+. A strong correlation between the obtained magnetomigration and the magnetic susceptibility of the rare-earth ions was found. When heating/cooling or evaporation were stopped during magnetization experiments, the magnetic effect gradually faded. This demonstrates that the presence of magnetic susceptibility gradients in the system is crucial for the magnetomigration. These findings are of importance for the development of a magnetic separation process for rare-earth ions.

Neutron Imaging of Paramagnetic Ions: Electrosorption by Carbon Aerogels and Macroscopic Magnetic Forces

“…A density-difference driven vertical concentration gradient of Gd(NO 3 ) 3 was created by the desalination and a magnetic field gradient was able to disturb the hydrostatic stability. The electric driving force from the porous electrodes represents an addition to the previously studied evaporation controlled magnetic enrichment method [10][11][12][13][14][15][16]. Specifically, the customisability of the geometry for the harvesting of ions in a cyclical process is noteworthy.…”

“…Nevertheless, attempts of rare earth ion separation in an inhomogeneous magnetic field were reported by Ida and Walter Noddack in the 1950s [7][8][9]. After a 50 year hiatus, interest in the effects of magnetic field gradients on ionic solutions has been revived [5,6,[10][11][12][13][14][15][16][17][18][19][20][21][22][23]. Magneto-convection only arises when the magnetic field gradient force is rotational, which necessitates a susceptibility gradient and magnetic field gradient that are orthogonal to each other [24].…”

“…Magneto-convection only arises when the magnetic field gradient force is rotational, which necessitates a susceptibility gradient and magnetic field gradient that are orthogonal to each other [24]. Interferometric measurements generated evidence of a magnetic ion enrichment around the surface of an evaporating solution containing a single paramagnetic species [10][11][12][13][14][15][16]. The inhomogeneity in these systems is caused by the input of thermal energy, which is the driving force for the concentration change and essentially a distillation process.…”

Neutron imaging of liquid-liquid systems containing paramagnetic salt solutions

“…This results in a modest long-lived paramagnetic ion enrichment underneath the magnet. The magnetic field gradient force pales in comparison with the force governing diffusion and is unable to appreciably influence the motion of individual ions on these grounds (RT ∇c ≈ 10 10 N/m 3 ≫ F ∇B ≈ 10 4 N/m 3 ; R: gas constant, T : room temperature, and ∇c: concentration gradient) 10 .…”

“…Convection from these paramagnetic liquid tubes is inhibited by the magnetic field gradient force, although mixing by diffusion still prevails on a long time scale. A magnetic field gradient can also initiate magnetothermal convection in a paramagnetic fluid 9,10 .…”