Magnet configurations for improved separations of magnetic and non-magnetic materials

S. Khushrushahi¹ - T. A. Hatton² - M. Zahn¹

¹ Massachusetts Institute of Technology, Department of Electrical Engineering and Computer Science, Laboratory for Electromagnetic and Electronic Systems, Research Laboratory of Electronics, Cambridge, MA 02139, USA
² Massachusetts Institute of Technology, Department of Chemical Engineering, Cambridge, MA 02139, USA

Abstract
Magnetic separation of a mixture of magnetic and non-magnetic liquid phases is needed for such applications as cleaning up oil spills by separating oil and water liquid phases, or by separating magnetic materials from non-magnetic materials in biomedical and microfluidic applications. Most magnetic separation techniques work on the single principle of applying a non-uniform magnetic field in a single flow channel to direct the magnetic phase/particles to one side of the channel for separation. Inlet velocity/pressure, phase volume fraction and viscosities, magnetization of the magnetic phase and applied magnetic field strength are some of the parameters for efficient separation. A varying concentration of either the magnetic or non-magnetic components in the mixture adds to the difficulty of separation and can result in contamination of the separated components. The Kelvin magnetization force density that drives separation requires a spatial non-uniformity in the magnetic field. Non-uniform magnetic fields can be generated but are also inherent to edges of permanent magnets. This work describes using non-uniform magnetic fields, generated by edges of permanent magnets, for the magnetic separation in a mixture of non-magnetic and magnetic liquid phases. In addition, this work describes the use of a one-sided magnetic flux configuration (Halbach array) to increase the efficiency of separations. Figs 7, Refs 12.