Closed-circuit magnetic separation of nanoparticles on a packed bed of spheres

Cécilia Magnet (1) , Mesferdon Akouala (1) , Pavel Kuzhir (1) , Georges Bossis (1) , Norman Wereley (2)

1 LPMC - Laboratoire de physique de la matière condensée
2 University of Maryland [College Park]

In this work, we consider magnetic separation of iron oxide nanoparticles when a nanoparticle suspension (diluted ferrofluid) passes through a closed-circuit filter composed of a packed bed of microspheres magnetized by an externally applied magnetic field. Recent studies on isolated magnetic collectors have shown that the capture of nanoparticles of a size as small as 50 nm is still very efficient if the magnetic interactions between them is sufficiently strong to induce a phase separation in the nanoparticle suspension [Magnet et al. (2012, 2014)]. In the present case of the packed bed of magnetizable spheres, such phase separation (manifesting by appearance of droplike aggregates of nanoparticles) is easily achieved at magnetic fields as low as 15 kA/m. We show that the key parameter governing the capture of magnetic nanopartilces in the present system is the Mason number - the ratio of hydrodynamic-to-magnetic forces exerted to nanoparticles. The capture efficiency, λ, defined through a ratio of the inlet-to-outlet concentration shows a power-law dependency on Mason number, λ∝Ma-0.8, in the range Ma<104. We developed a theoretical model based on the trajectory analysis of particle motion in a concentric-sphere representative cell of the porous filter. This model allows a correct prediction of the Mason number dependency of the capture efficiency. The obtained results could be of potential interest for water purification systems based on chemical adsorption of micro-pollutants on magnetic nanoparticles, followed by a magnetic separation on the considered type of magnetic filter. Preliminary results on nickel ion adsorption on oleate-covered iron oxide nanoparticles have already been obtained and are also reported in this work.

Domaines: Mécanique des fluides [physics.class-ph]

Cécilia Magnet, Mesferdon Akouala, Pavel Kuzhir, Georges Bossis, Norman Wereley. Closed-circuit magnetic separation of nanoparticles on a packed bed of spheres. 59th Annual Conference on Magnetism and Magnetic Materials, 2014, Honolulu, United States. ⟨hal-01304867⟩