Stability criterion for the magnetic separation of rare-earth ions

Magnetic forces in paramagnetic fluids

An overview of the effect of a magnetic field gradient on fluids with linear magnetic susceptibilities is given. It is shown that two commonly encountered expressions, the magnetic field gradient force and the concentration gradient force for paramagnetic species in solution are equivalent for incompressible fluids. The magnetic field gradient and concentration gradient forces are approximations of the Kelvin force and Korteweg-Helmholtz force densities, respectively. The criterion for the appearance of magnetically induced convection is derived. Experimental work in which magnetically induced convection plays a role is reviewed.

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

The electrosorption of Gd³⁺ ions from an aqueous 70 mM Gd(NO₃)₃ solution in monolithic carbon aerogel electrodes was recorded by dynamic neutron imaging. The aerogels have a bimodal pore size distribution consisting of macropores and mesopores centered at 115 and 15 nm, respectively. After the uptake of Gd³⁺ ions by the negatively charged surface of the porous structure, an inhomogeneous magnetic field was applied to the system of discharging electrodes. This led to a convective flow and confinement of Gd(NO₃)₃ solution in the magnetic field gradient. Thus, a way to desalt and capture paramagnetic ions from an initially homogeneous solution is established.

Oscillatory surface deformation of paramagnetic rare-earth solutions driven by an inhomogeneous magnetic field

The deformation of the free surface of a paramagnetic liquid subjected to a nonuniform magnetic field is studied. A transient deformation of the surface caused by the interplay of gravity, magnetic field, and surface tension is observed when a permanent magnet is moved vertically downward to the free surface of the liquid. Different concentrations of rare-earth-metal salt (DyCl_{3}) are used and different magnet velocities are studied. The deformation of the interface is followed optically by means of a microscope and recorded with a high-speed camera. The experimental results are compared and discussed with complementary numerical simulations. Detailed results are given for the static shape of the deformed surface and the temporal evolution of the surface deformation below the center of the magnet. The frequency of the surface oscillations is found to depend on the concentration of the salt and is compared with analytical findings. Finally, a potential application of the effects observed is presented.