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Magnetic migration (magnetophoresis) and extraction of Dy 3+ ions by magnetite (Fe 3 O 4 ) nanoparticles functionalized with diethylenetriaminepentaacetic acid (MagNP@DTPA) were probed , using an analytical balance and an external weighing device comprising a miniature neodymium (Nd 2 Fe 14 B) magnet and a Lego ® system. Contrary to our expectation, when the paramagnetic Dy 3+ ions were captured by the superparamagnetic nanoparticles, the overall magnetization decreased, due to the anti-ferromagnetic dipolar interactions between the lanthanide ion and the superparamagnetic core. This finding allowed to monitor, in real time, the lanthanide extraction process (nanohydrometallurgy) and the nanoparticles migration in the magnetic field.

The extraction of dysprosium (Dy3+) ions from aqueous solution was carried out successfully, using magnetite (Fe3O4) nanoparticles functionalized with diethylenetriaminepentaacetic acid (MagNP@DTPA). The process was monitored by energy dispersive X-ray fluorescence spectroscopy, as a function of concentration, proceeding according to a Langmuir isotherm with an equilibrium constant of 2.57 × 10-3 g(MagNP) L-1 and a saturation limit of 63.2 mgDy/gMagNP. The presence of paramagnetic Dy3+ ions attached to the superparamagnetic nanoparticles led to an overall decrease of magnetization. By imaging the nanoparticles surface using scanning transmission electron microscopy equipped with high resolution elemental analysis, it was possible to probe the binding of the Dy3+ ions to DTPA, and to show their distribution in a region of negative magnetic field gradients. This finding is coherent with the observed decrease of magnetization, associated with the antiferromagnetic coupling between the lanthanide ions and the Fe3O4 core.

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