Magnetization Control of Magnetic Liquids for Sink-Float Separations

B. Hu*, K. van Beek, A. Bosman, P.C. Rem, E.J. Bakker, F. Di Maio
Delft University of Technology, Faculty of Civil Engineering and Geosciences, Section Materials and Environment / Recycling Technology, Stevinweg 1, 2628 CN, The Netherlands.

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© 2010 Hu et al.

open-access license: This is an open access article distributed under the terms of the Creative Commons Attribution 4.0 International Public License (CC-BY 4.0), a copy of which is available at: This license permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

* Address correspondence to this author at the Department of Civil Engineering and Geosciences, Delft University of Technology, Delft, The Netherlands; Tel: +31-15-27 82897; Fax: +31-15-27 88162; E-mail:


The cut-density of sink-float separations with water-based magnetic liquids linearly depends on the magnetization of the process liquid. The control of the magnetization of the liquid, by means of measurement followed by extraction of water from the process liquid by membranes or mixing with water or concentrated magnetic liquid, is therefore a critical part of the technology. A potential problem with mixing-in concentrated magnetic liquid is that the process liquid may become inhomogeneous and will segregate in the magnetic field region. Mixing experiments for various scenarios were carried out on a simplified experimental process line and magnetization levels were compared with theoretical models. The results show as process liquid segregation, due to incomplete mixing, can be avoided for all conceivable control strategies by using static mixers. A measurement tool based on a magneto-gravimetric principle was shown to have sufficient sensitivity to detect and control fluctuations of the magnetization of such a fluid in an industrial environment.

Keywords: Magnetic density separation, magnetization, magnetic fluid.