Drum magnetic separator

Magnetic separators introduction

By creating an environment comprimizing a magnetic force (Fm), a gravitational force (Fg) and a drag force (Fd) magnetic particles can be separated from nonmagnetic particles by Magnetic separators.

Magnetic separation – Magnetic attraction force (Fm)
Fm = V x X x H x grad H
V = particle volume (determined by process)
X = magnetic susceptibility (see table below)
H = magnetic field (created by the magnet system design) in mT
(milliTesla) or kG (kiloGauss) 1 kG = 100 mT = 0.1 T
grad H = Magnetic field gradient (created by the magnet system design) in mT/m

Magnetic field and magnetic gradient are equally important factors for creating the magnet attraction force.

Magnetic separation – Competing forces

    • Gravitational force (Fg) is determined by particle size and density.
    • Drag force (hydrodynamic, aerodynamic), Fd, is determined by particle size, shape, fluid density, viscosity, turbidity and velocity.
    • Centripetal force (Fc).
    • Adhesion
    • Electrostatic forces etc.

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Magnetic Separation

Magnetic separations take advantage of the magnetic properties of minerals. All minerals will have one of three magnetic properties: ferromagnetic, paramagnetic, and diamagnetic. Ferromagnetic minerals (i.e., magnetite and pyrrhotite) are magnetic and are easily separated from other minerals, since they will be attracted to the poles of a magnet. Paramagnetic and diamagnetic minerals are not magnetic, but differ in how they interact with magnetic fields. Paramagnetic minerals are weakly attracted whereas diamagnetic minerals are weakly repelled along lines of magnetic forces. Thus, if a mixture of paramagnetic and diamagnetic minerals is passed through a magnetic field; the paramagnetic minerals will be pulled into the field and the diamagnetic minerals will be repelled or separated from the field. Furthermore, paramagnetic minerals have different degrees of paramagnetism that can also be used to effect separations.

Magnetic fields of various intensities can be provided by permanent or electromagnets. Generally, magnetic separators are classified as low or high intensity and whether they work in wet or dry applications. In concurrent separators, slurry flows in the same direction as the rotation of the drum surrounding the magnets.