Magnetic Separation: Industrial and Lab Scale Applications
Magnetic Separation: Industrial and Lab Scale Applications Magnetic Separation: Industrial and Lab Scale Applications
Magnetic separation, particularly the high gradient magnetic separation (HGMS), is the method of entrapping magnetic particles from a non-magnetic medium by the virtue of high gradient magnetic fields. The high gradients are obtained as a consequence of distortion of the magnetic field by ferromagnetic wire matrix present in a separation column. b. Comparison to magnetic separation and applications which could not be done by normal magnetic separation. HGMS methods have been successful in separating weakly paramagnetic materials of the order of microns, efficiently unlike traditional magnetic separation techniques (Parker 1981). HGMS has been successfully applied to remove cells (Safarik, 1999) and proteins (Bucak 2003), organic (Moeser 2002) and inorganic contaminants using functionalized magnetic materials, all of which will be exemplified in the related applications sections. c. Physics and Fluid dynamics of the method. Magnetic separation occurs on account of the force balance between the various competing forces acting on a magnetic particle like hydrodynamic drag arising due to the flow velocity, magnetic force due the applied field, diffusion force and inter-particle forces like Helmotz double layer interaction, dipole-dipole interaction and Van Der Waals attraction. The diffusion forces become important in the nanometer regime because the energy required to move a particle, attains comparability with the thermal
energy of the Brownian motion, hence setting up a number density gradient (Fletcher 1998). Hence, the magnetic, dipole-dipole interaction and Van Der Waals forces aid the process of separation, whereas, diffusion, double layer interaction and drag force act against the separation. Since the magnitude of magnetic (Fm), drag (Fh) and diffusional (Fd) forces are prominent, we shall consider these for the force balance. Fm + Fh + Fd = 0 Fm = μ VpMp o ∇ H where µo is the permeability of free space, Vp is the particle volume, Mp is the core magnetization of the particle and grad H is the magnetic field gradient(order of Ms/a - Parker 1981) in the vicinity of a capture center (e.g Ferromagnetic wire) (Gerber and Birss, 1983). Fh = 6πηbv Where η is the viscosity of the solvent in which the nanosized magnetite particles are dispersed, b is the particle radius and v is the flow velocity.
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energy of the Brownian motion, hence setting up a number density gradient (Fletcher<br />
1998). Hence, the magnetic, dipole-dipole interaction <strong>and</strong> Van Der Waals forces aid the<br />
process of separation, whereas, diffusion, double layer interaction <strong>and</strong> drag force act<br />
against the separation.<br />
Since the magnitude of magnetic (Fm), drag (Fh) <strong>and</strong> diffusional (Fd) forces are<br />
prominent, we shall consider these for the force balance.<br />
Fm + Fh + Fd = 0<br />
Fm = μ VpMp<br />
o ∇<br />
H<br />
where µo is the permeability of free space, Vp is the particle volume, Mp is the core<br />
magnetization of the particle <strong>and</strong> grad H is the magnetic field gradient(order of Ms/a -<br />
Parker 1981) in the vicinity of a capture center (e.g Ferromagnetic wire) (Gerber <strong>and</strong><br />
Birss, 1983).<br />
Fh = 6πηbv<br />
Where η is the viscosity of the solvent in which the nanosized magnetite particles are<br />
dispersed, b is the particle radius <strong>and</strong> v is the flow velocity.
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