Classifying – separating – and assorting solids – Magnetic – Paramagnetic
Patent
1985-04-08
1987-05-05
Reeves, Robert B.
Classifying, separating, and assorting solids
Magnetic
Paramagnetic
209212, 209232, B03C 100
Patent
active
046630295
DESCRIPTION:
BRIEF SUMMARY
ticle's susceptibility (.chi..sub.p) times the field (H) times the particle size or volume (Vp) is hereinafter referred to as the "magnetic moment" of the particle. A magnetized wire or rod extends adjacent to the canister. The term "adjacent" is meant to encompass a wire within or outside the canister. The wire is magnetized by a magnetic field H.sub.o to create a magnetization component transverse to its longitudinal axis. A field gradient extends within the canister and exerts a radial force on particles passing through the canister. Depending upon the orientation of the magnetic field, vis-a-vis the canister, diamagnetic particles in the slurry can be attracted toward the wire and paramagnetic particles repelled (diamagnetic capture mode of operation); or vice-versa, for a magnetic field usually rotated by 90.degree. with respect to the plane of the canister (paramagnetic capture mode of operation). Two or more laterally spaced outlets are provided at the bottom of the canister to collect the separated particles.
In the diamagnetic capture mode, the diamagnetic particles are obtained from the innermost outlets, that is, the outlet(s) nearer the wire, and the paramagnetic particles from the remote outlets. The converse obtains for the paramagnetic capture mode.
The apparatus of the invention permits continuous separation. Unlike conventional magnetic separators wherein particles are captured on the ferromagnetic wire, no wash-off process to clean up the filter is necessary after a certain collection period. The process is capable of handling a high concentration slurry, e.g., whole blood with a cell (red, white, etc.) concentration of about 50% by volume. Magnetic separation of low magnetic susceptibility materials can be performed with relatively high flow rate. For example, CuO particles of about 5.5 .mu.m in radius, can be separated (one outlet clear) at 3.6 cm/sec flow velocity. With the apparatus of the invention, it is possible to use a permanent magnet to produce the magnetic field since it is not necessary to interrupt the field. Also, it is easy to perform a multi-stage operation to increase the selectivity.
By way of contrast with the Kelland-type separator, it may be deduced from the above, that the Kelland device does not utilize a purely radial force component for separation, but relies on a vector force which is a combination of radial and azimuthal components. Kelland's separator can separate paramagnetic from diamagnetic particles and vice versa; but because of the influence of the azimuthal force, it cannot effectively separate several species of paramagnetic (or diamagnetic) particles from each other.
On the other hand, because the azimuthal force in the present device is essentially zero, the apparatus of the present invention is capable of separating several paramagnetic (or diamagnetic) species from each other, in accordance with the susceptibility of each species or in accordance with their size if all the particles have the same magnitude and sign of susceptibility.
In a further embodiment of the invention, the single wire radial force apparatus of the invention is extended to an efficient technique of selective separation of particles, according to the particles magnetic susceptibility only; independent of density, size and shape of the particles. In this embodiment, a family of fluid streams are fed into a canister. Each stream differs from each other stream by the magnetic susceptibilities of the fluids in the family of streams. Thus, a susceptibility gradient is established in the canister, which may be used to separate particles in the stream. This method does not use the relatively slow technique of allowing a colloidal suspension of magnetic particles to sit in a magnetic field to establish a magnetic susceptibility gradient. Instead, the gradient is established before passing the fluids through the canister.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic perspective representation of a diamagnetic capture mode magnetic separator of the invention with a generall
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The Government has rights in this invention pursuant to Grant No. 8120442-CPE, awarded by the National Science Foundation.
Kelland David R.
Takayasu Makoto
Hajec Donald T.
Massachusetts Institute of Technology
Reeves Robert B.
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