Evaporation-Assisted Magnetic Separation of Rare-Earth Ions in Aqueous Solutions

Abstract

This work aims to answer the question of why an enrichment of paramagnetic ions can be observed in a magnetic field gradient despite the presence of a counteracting Brownian motion. For that purpose, we study a rare-earth chloride (DyCl 3 ) solution in which weak evaporation is adjusted by means of small differences in the vapor pressure. The temporal evolution of the refractive index field of this solution, as a result of heat and mass transfer, is measured by means of a Mach−Zehnder interferometer. We develop a numerical algorithm that splits the refractive index field into two parts, one space-dependent and conservative and the other time-dependent and transient. By using this algorithm in conjunction with a numerical simulation of the temperature and concentration field, we are able to show that 90% of the refractive index in the evaporation-driven boundary layer is caused by an increase in the concentration of Dy(III) ions. A simplified analysis of the gravitational and magnetic forces, entering the Rayleigh number, leads to a diagram of the system's instability. Accordingly, the enrichment layer of elevated Dy(III) concentration is placed in a spatial zone dominated by a field gradient force. This leads to the unconditional stability of this layer in the present configuration. The underlying mechanism is the levitation and reshaping of the evaporation-driven boundary layer by the magnetic field gradient.

Experiments on the magnetic enrichment of rare-earth metal ions in aqueous solutions in a microflow device

“…Work [17] presents results connected with the analysis of the magnetomigration of Dy(III) and Y(III) ions. Work [23] analyzed the mechanism of Dy(III) ion transportation under the gradient of the magnetic field. It ascertained that the enrichment of the concentration in the upper part of the solution is connected with the evaporation of water.…”

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

“…27 To summarize, the magnetomigration in external magnetic fields proceeds as a magnetically induced motion inside paramagnetic solutions resulting in local ionic enrichment due to the activation of ∇ × F ∇B . 8,20,21,23 In experiments with thermal gradients demonstrated in this paper, regions of ∇χ sol are created in the solution due to the temperature dependence of χ m (Eq. 4).…”

“…4). In the presence of an external magnetic field, these gradients are expected to activate the rotational component of the magnetic field gradient force, inducing the magnetomigration of paramagnetic species 8,23. To test this assumption with the help of MZI, experiments were performed in a 1.0 mol dm −3 Dy 3+ solution.…”

Magnetic‐Field‐Manipulated Growth of Flow‐Driven Precipitate Membrane Tubes

“…The front propagation speed of an other prominent reaction, the Belousov–Zhabotinsky‐reaction was also investigated in a magnetic field, and the magnet caused acceleration and deceleration manifested also in the shape of the front . The magnetic field dependent diffusion of paramagnetic ions can be applied for the separation of solutes; also, labeled living cells can be sorted this way …”

“…[19] The magnetic field dependentd iffusion of paramagnetic ions can be appliedf or the separation of solutes;a lso, labeled living cellsc an be sorted this way. [20][21][22] Not only solutes and cells, but also entire jets of conducting liquids can be directed within the framework of magnetohydrodynamics. Furthermore, if ap recipitation reaction is taking place between the reactant solutions the motion of which is manipulated by magnetic field, solid 3D structures may be obtained with tailored properties.…”