Classifying – separating – and assorting solids – Magnetic – Paramagnetic
Patent
1996-04-01
1999-02-09
Bollinger, David H.
Classifying, separating, and assorting solids
Magnetic
Paramagnetic
209215, 209224, 209232, B03C 100
Patent
active
058682570
DESCRIPTION:
BRIEF SUMMARY
This invention relates to magnetic separation devices, in particular to the type of device in which magnetic particles are removed from a stream of material by feeding the stream on or through stationary magnetic material, the magnetic particles being held or "trapped" by the magnetic material and therefore extracted from the stream.
One form of magnetic separation device which functions by magnetic particle entrapment is generally referred to as a High Gradient Magnetic Separator or HGMS. An HGMS comprises a canister containing a liquid-permeable packing of magnetizable material between the canister inlet and outlet. The packing material may be paramagnetic or ferromagnetic and may be in particulate or filamentary form, for example, it may comprise wire wool, wire mesh, knitted mesh or steel balls. The packing may be in the form of a single block which essentially fills the canister or it may be in other forms, for example, concentric cylinders or rectangular plates. The term "matrix" is generally employed to refer to the packing and this is used, in the case where the packing is divided into a number of elements, by some in the industry to refer to the individual elements and by others to refer to the totality of the packing. The term will be employed herein in the latter way.
The canister is surrounded by a magnet which serves to magnetise the matrix contained therein, the magnet generally being arranged to provide a magnetic field in the direction of the cylindrical canister axis. With the matrix magnetized, a slurry of fine mineral ore, for example, clay dispersed in water, is fed into the inlet of the canister. As the slurry passes through the canister the magnetizable particles in the slurry are magnetized and captured on the matrix. Eventually, the matrix becomes substantially filled with magnetisable particles and the rate of capture decreases so that the quantity of magnetizable particles in the treated slurry leaving the outlet of the canister reaches an unacceptably high level. The slurry feed is then stopped and the canister rinsed with water to remove all non-magnetic material from the matrix. The magnetic field acting on the matrix is reduced to a sufficiently low value to enable the magnetic material to be washed off the matrix elements with a high speed stream of water.
The reduction in the magnetic field may be achieved by de-energizing the magnet. HGMS systems operated in this way are referred to as switched HGMS systems. With large diameter canisters, slow slurry velocities and fairly infrequent flushing operations switched HGMS systems are relatively efficient. However with stronger magnets having higher magnetic fields, processing velocities can be increased giving an overall decrease in cycle time. The flushing operation then becomes an increasingly large element of the cycle time. The cycle efficiency drops owing to wasted magnet time which can be significant even with a magnet capable of fast field reduction and subsequent increase, referred to as a "fast ramp" magnet. The percentage of time during which separation is taking place, known as a the "duty factor" of the separator, is typically less than 50%. Further, the ramping of the magnet causes increased heating of the coil by eddy currents which must be compensated for by providing larger and more expensive cooling. Ramping increases power consumption and, if it is to be fast, necessitates a large and expensive power supply.
These disadvantages can be overcome by use of a process in which the saturated matrix containing canister is pulled out of the magnet into a region of low field where flushing takes place. At the same time a second canister is moved into the field so that separation can be carried out there during flushing of the first canister. The only "dead time" is during movement of the canisters and this can be made very short so that the duty factor of the separator can approach 100%. An HGMS system operated in this way is referred to as a reciprocating canister HGMS or RCHGMS.
Removal of a canister containing a ferro
REFERENCES:
patent: 4054513 (1977-10-01), Windle
patent: 4110222 (1978-08-01), Watson
patent: 5076914 (1991-12-01), Garaschenko et al.
IEEE Transactions on Magnetics, vol. 17, No. 6, Nov. 1981, New York US pp. 3299-3301, P.W. Riley et al.
Book: Magnetic Methods For the Treatment of Minerals, 1987, Elsevier, Amsterdam, NL, pp. 201-203, J. Svoboda.
Bollinger David H.
Carpco, Inc.
Yeager Arthur G.
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