Evaporationassisted magnetic separation of rare earth ions in aqueous solutions
Evaporationassisted magnetic separation of rare earth ions in aqueous solutions
Lei, Z.; Fritzsche, B.; Eckert, K.
Abstract
This work aims to answer the question of why an enrichment of paramagnetic ions can be observed in a magnetic field gradient [1] despite the presence of a counteracting Brownian motion. For that purpose, we study a rare earth chloride (DyCl3) solution in which weak evaporation is adjusted by means of small differences in the vapor pressure in a specially developed cell, see Fig. 1.
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 MachZehnder interferometer. We develop a numerical algorithm which splits the refractive index field into two parts, one spacedependent and conservative and the other timedependent 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 evaporationdriven 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 field. The underlying mechanism is the levitation and reshaping of the evaporationdriven boundary layer by the magnetic field gradient [2].
[1] X. Yang, K. Tschulik, M. Uhlemann, S. Odenbach, K. Eckert, J. Phys. Chem. Lett. 3 (2012), 3559–3564.
[2] Z. Lei, B. Fritzsche, K. Eckert, submitted to J. Phys. Chem. C (2017).
Keywords: magnetic separation; rare earth; interferometry

Lecture (Conference)
International Conference on MagnetoScience 2017 (ICMS 2017), 23.27.10.2017, Reims, Frankreich
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