Note: Descriptions are shown in the official language in which they were submitted.
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--1--
GRAVI'I'Y ~ GNETIC ORE SEPI~R~'rORS
Technical Field_ _ _ _
This invention relates to apparatus for separat-
ing magnetic or weakly magnetic minerals from feed mate-
rials such as ores, beach san~s and gravels and more par-
ticularly, for enhancing the separating capability of con
ventional gravity separators through the addition of
magnetic forces which are substantially codirectional with
the gravity force.
This application is a division of application
Serial No. 431,397 filed June 29, 1983.
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Background Art
In conventional gravity separators, differences
in the specific gravities of the different individual min-
erals or phases making up the mixrure known as the feed
material are used to accomplish the separation.
Generally, a stream of the feed material flows over a
downward sloping surface under the influence of the force
of ~ravity. Typically, the surface is an inclined plane
or cone, or spiral. The higher specific gravity particles,
which generally become the concentrate (e.g. wolframite,
magnetite, tin, gold), tend to settle near the bottom of
the stream of feed material, while the lower specific
gravity particles, which generally become the tailings,
tend to congregate near the top of the stream.
Alternatively, in particular applications, it is the
particles which congregate near the top of the stream
which are saved while the particles which settle near the
bottom are discarded. Various means, some of which are
described below, are used to divide the top of the stream
from the bottom of the stream so as to separate the
tailing and concentrate.
In practice, many minerals such as wolframite, a
source of tungsten, are magnetic or weakly magnetic and
have a high specific gravity. Wolframite is usually
separated from its ore in two distinct stages, the first
stage being gravity separation and the second stage being
magnetic separation. More particularly, the first stage
typically involves wet gravity separation of ground
wolframite ore using one of the conventional gravity sepa-
rators e.g. cones, spirals, shaking tables, pinchedsluices, etc. The wet gravity concentrate is then dried
and subjected to dry magnetic separation to produce a
tungsten concentrate. Such dry magnetic separation may be
accomplished with the magnetic and gravity forces working
against or opposite one another.
The per~ormance of a conventional gravity sepa-
rator in separating high specific gravity magnetic or
weakly magnetic minerals from their ores can be improved
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by combining the gravity force with codirectionally acting
magnetic forces. The reason for this is that the resul-
tant of the gravity and magnetic forces is more effective
in causing high specific gravity magnetic or weakly
magnetic particles to settle at the bottom of a stream of
eed rnaterial than is the gravity force acting alone. One
resulting advantage is the cecovery of relatively
fine-sized magnetic or weakly magnetic particles which are
often difficult to recover using a conventional gravity
1 separatorO While not eliminating the need for the separate
magnetic separation stage in the above described process
for recovering wolframitet adding magnetic forces to a
conventional gravity separator improves both the capacity
of the gravity separator and the grade of concentrate pro-
duced by the gravity separator.
An ore separator in which substantiallycodirectional magnetic and gravitational forces are used
to concentrate magnetic or weakly magnetic minerals is
disclosesd in Martinez, "The Concentration of Weakly
Magnetic Minerals", The Pennsylvania State College
~epartment of Mineral Engineering, Masters Thesis, 1953, a
lone copy of which was deposited in the library of
Pennsylvania State College. In this separator, a plurality
of stationary permanent magnets is located beneath and
along the length of an inclined planar surface which is
formed by the uphill moving portion of a continuously
moving endless belt. Wet ore is fed onto the belt and
tends to move downhill. However, the magnetic or weakly
magnetic particles in the ore are attracted by the magnets
3o located beneath the moving belt and are moved uphill by
the moving belt. In this ore separator, the tailing is
collccted at the bottom of the incline and the concentrate
is collectcd near the top of the incline. 'rhe belt is
used so as to continuously move the m3gnetic or weakly
magnetic part;cles away from the magnets to which they are
attracted. If this is not done, the rnagnetic or weakly
magnetic particlcs will bllild up on thc separator surface
at sites corrcsponding to the locations of the magncts and
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( will in time upset the concentration process by selectively
blocking ~low of the we~ ore, thereby ereating undesirable
eddy currents. In addition, the build up of magnetic or
weakly magnetic particles on the separator surface may
ultimately distort or shield the magn~tic field. In
addition to including the desired magnetic or weakly
magnetic particles, the unwanted build up may also inelude
other types of magnetie or weakly magnetic partieles.
The proeessing of most ores eontaining desirable magnetie
or weakly magnetie minerals requires erushing and grinding of
the feed material to a fine size~ Crushing and grinding
introduces into the ore mill iron, abraded from the erusher,
grinding mill liners, rods, and balls. This material is
highly magnetie. In addition, ~any ores eontaining desirable
magnetie or weakly magnetie minerals also eontain magnetie
or weakly magnetie minerals, sueh as pyrrhotite (FeS), whieh
may be eonsidered gangue or worthless material. The mill
iron, as well as the worthless magnetie and weakly magnetie
minerals will be attraeted by the magnetie field and will,
if a means is not used to allow them to be removed from the
separator surface, build up near the magnets. An alternative
solution to the problem o~ build up of magnetic partieles ~s
diselosed in Japanese patent 143967 of T. Shibuya published
~eptember ll, 1979. The Japanese patent discloses a
separator in whieh a slurry o~ eoal and iron ore flows along
the bottom of a separation tank while the slurcy is agitated
by water eolning from sprinklers. The iron ore sticks to the
bottom of ~he tank whieh is magnetized by electcomagnetic
coils while the non-magnetic materials are washed away.
Scrapers are used to remove the built up iron ore ~rom the
tank bottom.
While the above described gravity-magnetic ore
separatoes may, under certain circumstances, exhibit
inproved concentration capability for ,nagnetic or weakly
magnetic minerals, no means has hereto~ore been disclosed
for providing conventional gravity separators such as Wright
concentratocs, cones, pinched sluices, spirals,
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shaking tables, etc. with rnagnetic forces so as to improve
the ote concentrating capabilities of such standard grav-
ity separators. One reason for this is that no adequate
solution to the problem of preventing build up of magnetic
materials on the flow surace of a conventional gravity
separator equipped with magnetic force applying means has
neretofore been proposed. Accordingly, it is an object of-
the present invention to provide means for modifying con-
ventional already existing gravity separatots with
magnetic force applying means so as to improve their ore
concentrating capabilities while at the same time inhibit-
ing the build of magnetic materials.
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Dlsclosure of the Invention
The present invention consists of an apparatus
for separating magnetic or weakly magnetic material from
non-magnetic material having a lower specific gravity than
said magnetic or weakly magnetic material, said magnetic
or weakly magnetic material and said non-magnetic material
heing combined in a mixture with a non-magnetic liquid,
said apparatus being effective for separating magnetic or
weakly magnetic particles, said apparatus comprising: a
spiral-shaped surface over which said mixture flows under
the influence of the force of gravity for achieving at
least a partial gravity separation of said magnetic or
weakly magnetic material from said non-magnetic material
as said mixture flows downwardly over said surface under
the influence of gravity; means for applying a magnetic
force beneath said surface for augmenting said gravity
separation with magnetic separation by attracting said
magnetic or weakly magnetic material toward said surface,
there being no other forces applied to said magnetic or
weakly magnetic material in opposition to said magnetic
and gravity forces; means for intermittently reducing said
magnetic force to prevent the build-up of said magnetic or
weakly magnetic material on said surface by permitting
downward motion of said magnetic or weakly magnetic
material; and, means for separating the higher specific
gravity ~s~-magnetic or weakly magnetic material comprising
a portion of the material adjacent sai.d surface from the
pl~t~r~l
lower specific gravity non-magnetic~ comprising a portion
of the material riding above said material adjacent said
surface.
~s~
The invention also consists of a method for
separating magnetic or weakly magnetic material from a
non-magnetic material having a lower specific gravity than
said magnetic or weakly magnetic material, said method
being effective for separating magnetic or weakly magnetic
particles, the method comprising: forming a mixture by
combining said magnetic or weakly magnetic material and
said non-magnetic material with a non-magnetic liquid;
feeding said mixture onto the raised end of a downwardly
sloping spiral-shaped surface of sufficient length to
achieve at least partial gravity separation between said
magnetic or weakly magnetic material and said non-magnetic
material as said mixture flows over said surface under the
influence of the force of gravity; applying a magnetic
force beneath said spiral surface while said mixture flows
thereover for augmenting said gravity separation by
magnetic separation by attracting said magnetic or weakly
magnetic material toward said surface, there being no
other forces applied to said magnetic or weakly magnetic
material in opposition to said magnetic and gravity forces;
intermittently reducing the magnetic force to prevent the
build-up of said magnetic or weakly magnetic material on
said surface by permitting downward motion of said magnetic
or weakly maanetic material; and separating the higher
specific gravity magnetic or weakly magnetic material
comprising a portion of the material ad~acent said surface
from the lower specific gravity non-magnetic material
comprising a portion of the material riding above said
material adjacent said surface.
Brief Descri~tion o~ the Drawings
_ _ . . _ _ _ _ _ _ . . _ , . . _ . _ _ _ , , . _
FIG. 1 is a partly diagrammatic and partly in
sectlon illustration of a conventional Wright Concentrator
modified with magnet means in accordance with the princi-
ples of the present invention;
FIG. 2 is a partly diagrammatic and pattly in
section illustration of a concentration plate modified
with magnets and shielding means in accordance with an
illustrative embodiment of the invention;
1~ FIG. 3 is a partly diagrammatic and partly in
section illustration of a concentration p~ate modified
with electromagnets in accordance with an illustrative
embodiment of the invention;
FIG. 4 is a view partly in perspective and par-
tly in section illustrating a conventional spiral separa-
tor modified with magnet means in accordance with the
principles of the present invention;
FIG. 5 diagrammatically illustrates a cross sec-
tional view of a conventional cone type separator modified
2 with magnet means in accordance with the principles of the
present invention;
FIG~ 6 di2grammatically illustrates in perspec-
tive a portion of a conventional shaking table separator
which has been modified with magnetic means in accordance
with an iilustrative embodiment of the invention. - . .
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Best Mode For Carrying Out The Invention
he following is a description of several con-
vent;onal gravity separators which have been .nodified
through the use of magnets in accordance with the princi-
ples of the present invention.
_ Wr~ht_Concentrator
FlG. 1 illustrates a multistage Wright gravity
concentrato~ 10 modified through the use of time varying
magnetic forces to increase concentration capability. The
1 Wright Concentrator comprises a plurality of concentration
plates 12, 14, 16, 18. A feed stream of a wet feed mate-
rial 20 which includes one or more magnetic or weakly
~agnetic minerals is fed onto the surface 13 of the plate
12 from feed unit 22. Particle guiding panel 24 which
1$ forms an approximately right angle with the plate 12
seeves to guide the eed stream 20 onto the plate 12.
Eelow the plate 12, mounted on a support such as a sheet
25 is a magnet means, here shown as a plurality of
magnets, such as permanent magnets 26. As the feed stream
20 flows over the plate 12, the downward acting gravity
force and the downward acting magnetic force produced by
the magnets 26 cause the high specific gravity magnetic or
weakly magnetic particles to settle near the bottom of the
feed stream 20 while the non-magnetic low specific gravity
particles congregate near the top of the feed stream 20.
To prevent build up of magnetic particles on the
surface 13, the sheet 25 is intermittently pivotted about
axle 28 by a motor means 27 away from the plate 12 to vary
the magnetic force in order to free any built up m2gnetic
material. Of course, instead of permanent magnets mounted
on a rotatable sheet, any other of the permanent or
electromagnet arranaements described herein may be used to
provide the time varying magnetic forces.
The application of the magnetic and gravity
forces will tend to stratify stream 20 into an ore~ rich
lower zone and a tailing rich upper zone. After the feed
stream 20 flows to the end of the plate 12, baffle 30
divides l:he stream 20 into streams 20a and 20b. Stream
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20a comprises the predominantly low specific gravit~
non-magnetic particles, while the stream 20b comprises the
predominantly high specific gravity magnetic or weakly
magnetic particles. Baffle 30 along with guiding panels
32, 34 and 36 serve to guide stream 20a onto surface 19 of
plate 18 although magnet means could be positioned below
the plate 18. Similarly, baffle 30 along with guiding
panel 38 guides stream 20b onto surface 15 of plate 14.
In the embodiment of the Wright concentrator
shown in FIG. 1, stream 20a after separation from stream
20b undergoes only gravity separation while flowing over
the plate 18. Stream 20b, however, undergoes both gravity
and magnetic separation while flowing over the plate 14.
Magnetic forces are applied to stream 20b through the use
of the permanent magnets 40 which are mounted on the end-
less belt 42. Rulleys 44 and 46 are used to cause the
endless belt to move in the clockwise direction to prevent
build up of magnetic material on surface 15, at least one
of the pulleys being driven by a motor means 43. The end-
less belt 42 is moved by motor means 43 in t`he clockwise
direction in order to ease the transport of the magnetic
particles along the surface 15.
The application of gravity and magnetic forces to
stream 20b stratifies that stream, in the manner in which
stream 20 was stratified. Baffle 50 serves to separate
stratified feed stream 20b into two streams 20c and 20d.
Stream 20c is the concentrate which comprises largely high
specific gravity magnetic or weakly magnetic particles.
Note this concentrate (stream 20c) has been formed as a
result of two gravity-magnetic separation stages taking
place at plates 12 and 14. At this point it passes to a
suitable collector (not shown). Similarly, baffle 52
divides stream 20a into streams ?Oe and 20f. Guiding
panels 54, 55, 58 along with baffles 50 and 52 serve to
direct streams 20d and 20f onto surface 17 of plate 16
where they combine to form stream 20g. Baffle 52 along
with guiding panels 56 and 57 serve to direct stream
20e which comprises tailing out of the concentrator
apparatus.
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Stream 20g undeegoes a third stage of
gravity-magnetic separation. In this stage, the downward
magnetic force results from two groups of permanent
magnets 60 and 62. The magnets 60 are mounted on wheel 6~
and the magnets 62 are mounted on wheel 66. Wheels 64 and
66 are rotated in the clockwise direction by motor means
65 and 63 respectively to prevent the build up of magnetic
mateeials on surface 17 and to ease the transport of the
magnetic materials along surface 17. The combined gravity
and magnetic forces cause any high specific gravity
magnetic or weakly magnetic particles remaining in the
stream 20g to settle near the bottom of stream 20g while
lighter, non-magnetic particles congregate near the top of
the stream 20g. Thus, when baffle 70 divides the stream
20g into strearns 20h and 20i, stream 20i becomes the
middling, that is material which has a lower concentration
of high specific gravity magnetic particles than the
concentrate, but a higher concentration of such particles
than the tailing. Stream 20h becomes a portion of the
tailing and is guided out of the Wright Concentrator by
panels 72 and 74 as well as baffle 70.
In FIG. 1, three means for providing varying
magnetic forces are illustrated. These are permanent
magnets rnounted on a rotatable sheet, permanent magnets
mounted on an endless belt, and permanent magnets mounted
on rotatable wheels. All of these arrangements are
designed to cause magnetic forces to act on the stream of
source material while at the same time preventing a build
up of magnetic material on the concentration plates.
Numerous other arrangements may be used to achieve these
objectives. For example, permanent magnets may be mounted
on sheets which can be raised or lowered toward or away
from the concentrator surfaces. Alternatively, the
magnets may be permanently mounted and shields may be
intermittently inserted between the magnets and the con-
- centrator surfaces to prevent build up of magnetic
material on the concentrator surfaces. For example, FIG. 2
shows a concentration plate 83 of the type discussed above
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equipped with diagrammatical;y illustrated magnet means 85
for applying magnetic forces to feed material 87 as the
feed material flows over the plate 83. Shield 89 is
intermittently positioned between the plate 83 and the
magnet means 85 to vary the magnetic force on the source
material, thereby preventing the build up of magnetic
material on plate 83. Finally, conventional electro-
magnets May be used, in which case a conventional control
circuit is utilized to periodically turn off or vary the
magnetic field to prevent unwanted build up of magnetic
material. For example, FIG. 3 shows a concentration plate
91 equipped with diagrammatically illustrated conventional
electromagnets 93 for applying magnetic forces to feed
material 95 as it flows over the plate 91. Typically,
each of the magnets 93 comprises a current carrying coil
surrounding a magnetic core. Diagrammatically iLlustrated
conventional control circuit 97 is used to vary the
current flowing in the electromagnets 93 so as to vary the
magnetic forces and prevent build up of magnetic material
on plate 91. In particular cases, all of the magnets 93
may be turned off at once or the magnets 93 may be turned
off sequentially. It will be recognized that the three
magnetic means 26, 40 and 60 empolyed in Fig. 1 are all
differently mounted. Of course, in practice, they may all
be the same, as may be preferable for sake of simplicity,
or two may be of one type and one of the other. Some may
be made of permanent magnets and others of electro
magnets. The configuration shown in Fig. 1 and described
above is just one of a large group of different possible
arrangements.
II Spiral Separator
Turning to FIG. 4, the separator 100 includes a
spiral trough 102 of curved cross section. Feed material
containing a high specific gravity magnetic or weakly
magnetic mineral is introduced into the trough 102 near
-- the top of the spiral. As the source material flows down
the spiral trough 102 gravity separation takes place.
Heavy material is removed through ports 106 spaced along
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the bottom 103 of the trough 102, that is near the center
of the spiral 102. The highest grade of concentrate
emanates from the ports at and near the top of the spiral,
whereas the ports near the lower end of the spiral trough
discharge middling. Materials discharged by the ports 106
enter a circular cylindrical pipe 107 which runs down the
center of the spiral. The tailing flows out of the lower
end of the spiral trough 102.
In order to improve the mineral concentrating
capabilities of the spiral separator 100, means 110 for
producing a varying magnetic force may be positioned
beneath the sprial trough 102 at various locations along
the spiral. In Fig. 2, four such means 110 for producing
a time varying magnetic force are diagrammatically
illustrated only. However understood that any of the
means for producing a varying magnetic force described
above ln connection with the Wright concentrator (Fig. 1)
are suitable for use in connection with the spiral. These
means include permanent magnets suitably mounted on
rotatable sheets, continuous belts, or rotatable wheels
for varying the position of the magnets relative to the
spiral to prevent the buildup of magnetic particles on the
surface of the spiral. Alternatively, conventional
electromagnets in conjunction with a conventional control
circuit may be used to produce the varying magnetic
forces. In or to have a significant effect on the
separation of magnetic and weakly magnetic particles from
the feed material, it is desirable that the means 110 be
positioned underneath the bottom portion 103 of the trough
102 near the pipe 107 as most of the feed material flows
over the bottom portion 103 of the trough 102. In
addition, it should be noted that although only four means
110 for producing a time varying magnetic force are shown
in Fig. 4, in particular embodiments of the invention
means for producing a time varying magnetic force may be
located adjacent one another along the spiral trough 102
so that feed material flowing down the spiral trough 102
is under the influence of time varying magnetic forces
along most of the length of the spiral trough 102.
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It should be noted that many of the spirals
currently in use are made of iron or fiberglass reinforced
plastic. In the case of the iron spirals, it may be
necessary to replace sections of the spiral lying directly
over the magnet means with a non-magnetic material such as
fiberglass reinforced plastic, as iron will shield the
source material from the magnetic forces.
III Cones and Pinched Sluices
-
In addition to Wright concentrators and spirals,
another conventional gravity separator which may be
modified with ~agnets to improve its concentration
capability is the cone. While the discussion hereinafter
refers only to cones, it should be noted that this
discussion is applicable to pinched sluices as well. With
pinched sluices the magnets may be placed on the sides as
well as underneath the separating surface~
Turning to ~igure 5, separator 300 comprises
three separator stages 302, 304, 306, stage 302 being a
double cone concentrator, stage 304 being a single cone
concentrator, and stage 306 being a tray concentrator.
The double cone stage 302 comprises two cones 310 and 312
while the single cone stage 304 comprises only a single
cone 314. In order to enter thé cones 310 and 312, the
feed material 316 flows over surface 320 of feed
distributor 322. While the feed 316 flows over the sur-
face 320, gravity separation takes place. In order to
enhance the separation of magnetic and weakly magnetic
particles from the feed 316, means 324 for producing time
varying downward acting magnetic forces is mounted below
the feed distributor 322. The magnetic forces should be
varied to prevent buildup of magnetic material on surface
320.
In Figure 5, the means 324 for applying time
varying downward acting magnetic forces is diagrammati-
cally illustrated only. These magnetic forces may be
-- applied using conventional electromagnets or permanent
magnets. As previously indicated, in the case of electro-
magnets, the magnetic force is varied through use of a
conventional control circuit which intermittently varies
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the current flowing in the coils comprising the
electromagnets. In the case of permanent magnets, the
magnetic force on the feed can be varied by continuously
or intermittently moving the magnets or by intermittently
shielding the magnets from the feed, as has already been
described with other embodiments.
After flowing down the surface 320, annular
splitter 325 enables part of the feed 316a to flow through
annular orifice 328 into upper cone 312 of separator stage
302 and the remainder of the feed 316b to flow past
orifice 328 and through annular orifice 330 into lower
cone 310 of separator stage 302. Source material 316a
contains a higher concentration of high specific gravity
magnetic or weakly magnetic particles than does source
material 316b as a result of separation which took place
while the feed was flowing over surface 320.
While source materials 316a and 316b flow down
the inner surfaces of cones 312 and 310, respectively,
further gravity and magnetic separation occurs. The
downward actins time varying magnetic forces are applied
by diagrammatically illustrated magnet means 326, of any
of the forms previously shown and/or described. At the
bottom of cones 310 and 312, the light weight tailing 329
is removed while the concentrate 331 enters onto the outer
surface 332 of distributor 334 through annular openings
336 and 338. The concentrate 331 flows down surface 332
and enters cone 314 via annular opening 340. Gravity
separation takes place while the concentrate material 331,
resulting from separation stage 302, flows down surface
332 and surface 333 which is the inner surface of cone
314. Middlings 342 is removed at the bottom of cone 314
while concentrate 344 resulting from the second separation
stage 304 enters tray concentrator 306 through passageway
346. As concentrate 344 flows down surface 348 of tray
concentor 306 further gravity separation takes place.
- Concentrate 350 from the separation stage 306 is collected
at orifice 352 while the middlings 354 is removed from the
tray concentrator at the end 360 of surface 348. It
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should be noted that while stages 304 and 306 use only
gravity separation they could be modified in accoedance
with the principles of the present invention so that both
gravity and magnetic separation are utilized with either
one or both of them.
IV. _Shaking Table
Turning to Figure 6, shaking table 400 comprises
a generally rectangular deck 402 which slopes gradually
downward from the feed end 404 to the tailing end 406.
Extending longitudinally along the upper surface 410 of
the deck is a plurality of spaced apart riffles 412 which
serve to form a plurality of troughs 414. The deck 410 is
able to undergo reciprocating motion in a direction
parallel to the longitudinally extending riffles.
Source material containing a high specific
gravity magnetic or weakly magnetic mineral flows downward
over the surface 410 of the deck 402 from the feed end 404
to the tailing end 406. The fundamental principle of
operation of the shaking table is vertical stratification
according to specific gravity. That is, high specific
gravity particles are generally trapped behind the riffles
whereas low specific gravity particles are able to flow
over the riffles and are removed at the tailing end. It
should be noted, however, that very fine particles of
heavy material may not be trapped between the riffles of
conventional shaking tables and may be lost.
The particles trapped between the riffles are
removed as a result of the longitudinal reciprocation of
the deck 402. Roughly what happens is that the deck 402
is moved slowly in the direction of arrow 420 and then
snapped backwards relatively fast. The inertia of the
particles trapped between the riffles causes them to
continue moving in the direction of arrow 420 when the
deck 402 is snapped backward. Eventually the particles
trapped behind the riffles come to the end of the deck
where they are removed as concentrate.
Diagrammatically illustrated means 430 for pro-
ducing a varying magnetic force are placed under the table
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- 17 -
surface and troughs 414 in order to trap magnetic and
weakly magnetic particles in the troughs 414 formed by the
riffles 412. Use of the magnetic force in addition to t'ne
gravity force enables the trapping of particles which
would be lost if a conventional shaking table were used.
Varying the magnetic force can be accomplished with perma-
nent or electromagnets in the manners previously
described. As is true with the other embodiments varying
the magnetic field prevents the buildup of magnetic parti-
cles on the surface 410 deck 402 of the shaking table
400. In a possible alternative embodiment on the
invention, the riffles themselves might be formed from
magnetic material to enhance the trapping of magnetic and
weakly magnetic particles.
Finally, it is to be understood that the
above-described embodiments of the invention are intended
to be illustrative only and that numerous alternative
embodiments of the invention may be constructed by those
skilled in the art without departing from the scope and
spirit of the claims which follow.
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