Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
`" 11365~2
14393
SAND SEPARATOR
The invention relates to a separator for separating particles
of different densities, by treatment of suspensions of the
particles in a liquid, and concerns separation of suspensions
containing material distributed over a range of density and/or
05 particle size. The invention is especially concerned with the
treatment of suspended material of very small particle size such
as for example sand tailings from mineral dressing equipment which
in current practice are normally discharged to waste even though
they contain valuable metalliferous components. For example,
sand tailings from a typical mill might range from 20 British
Standard mesh to 400 mesh with small proportions even finer.
In our U.K. Patent Specification No. 1,174,405 of Oct. 3/67 to
National Research Development Corporation there is described a gravity
separator which was developed primarily to handle tiD bearing slimes to
recover residual tin which at that tim~ could piot be recovered with existing
equipment of conventional type. Apparatus in accordance with U.K. Patent
Specification ~o. 1,174,4~5 has ~een avail~ble and extensively used for some
years and has given excellent performance enabling very considerable
~avings to be made in the tin mining and other industries. The
principle of operation of the apparatus of U.K. Patent Specification
No. 1,174,405 is that of adjusting shear conditions in a flowing
suspension by applying a Rhaking motion of variable amplitude and
frequency in order to cause heavier material to remain on a moving
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surface, and form a close packed deposit or bank, whilst the
finer particles remain in suspension and advance along the surface.
The decks are freely suspended and are moved by a vibratory shaking
action using an unbalanced-weight drive which 9 although simple
o5 and reliable, is such that the path traced out by the decks with
a given weight rotating at fixed radius will undesirably vary
according to the total shaken weight. In certain applications,
it has also become necessary to employ lower frequencies and
then, particularly when the frequency employed approaches the
natural frequency of the apparatus, control problems can arise.
According to the present invention, a separator for particles of
differing densities has all the following features (a) to (e)
(a) Two sloping surfaces each have a supply to their upper
regions of particles to be separated, in the form of a flowing
suspension in a liquid.
(b) The two surfaces are mounted side-by-side with their
sloping directions parallel or the upper edges of said surfaces
are adjacent with the surfaces sloping downwardly away from each
other with the sloping directions being in line, and the surfaces
are arranged to perform a repetitious non-discontinuous
horizontal motion generally orthogonal to their slope.
(c) The lower ends of the surfaces drain into separate
collecting arrangements or into gutters draining into tailings
collection means.
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(d) The motion is imparted to the surfaces by a positive
drive causing the motion to fo]low a path independent of the
weight on the surfaces.
(e) The separator is arranged to follow a cycle of operations~
05 with the motion applied to the surfaces throughout, in a first
phase of which one surface is receiving the suspension while the
other surfacereceives at a comparable rate the suspending liquid
without particles, followed by tilting that other surface about a
line parallel to the sloping direction to flush off the particles
still remaining on it, the second phase being a reversal of roles
of the surfaces, the two phases alternating, the collecting
arrangements lying alongside the (when tilted) lower edge of
each surface parallel to the sloping direction and partitioned
to collect separately particles which at the instant of tilting
have travelled different distances down the sloping direction.
Thus, in general terms, the pre#ent invention provides a modification
of Cdn. Patent 1,115,663 of Jan 5/82 to ~ational Research Development Corpora-
tion which relates to a gravity separator designed to apply an oscillatory
motion in a transverse direction relat~ve to the ~rogressive
movement down a slope of a flowing suspension and capa'ble of
operating at high amplitudes, e.g. at least 1 cm and possibly as
large as 20 cm or more, and preferably from 4 to 18 cm, for
example 5 to 15 cm, or 6 to 12 cm. Thls apparatus comprises
two sloping separating surfaces each receiving material to be
treated, hereinafter termed "decks", mounted side by side and
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arranged to perform a repetitious non-discontinuous horizontal
motion e.g. linear, orbital or other oscillatory motion, preferably
simple harmonic motion, in a generally transverse direction relative
to the slope of the deck. Jerky motion must be avoided. The
05 decks are driven by a positive drive which causes their motion to
follow a path independent of the weight of material deposited on
them from the suspension being treated. The positive drive also
avoids problems of loss of control at lower frequencies. In
the gravity separator according to the present invention the
cycle of operations is so organised that at any one time one of
the decks is functioning as a collecting surface on which banking
of heavy deposits is taking place, whilst on the other deck
previously banked material is being further separated and is then
removed by alteration of the shear conditions thereon to cause
banked material to be re~uspended in a stream of washing liquid.
Consequently~ the apparatus entails means for adjusting the shear
conditions on each of the decks preferably by alteration of slope
and/or by adjustment of amplitude and/or by adjusting frequency
of oscillation, the last-named for example by interchangeable drive
belts or a gearbox. 1`he simplest arrangement is one in which the
two decks share a common subframe and thus are driven by a common
drive means and shear conditions are altered by adjustment of
slope. ~owever, because the two decks are operated for the most
part in sequence, they may be arranged to be driven independently
thus giving more flexibility in selecting running conditions,
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e.g. amplitude and frequency. To save floor space, there may be
in place of each deck a stack of (for example 4 or 6) decks
fixed on top of each other9 each receiving its own supply of
material to be treated9 but each discharging into a drain common
05 to that stack.
The slope (when running as a collecting surface) is preferably
within the range 1.3 to 2.5 , more preferably 1.5 to 2.2 9 most
preferably 1.6 to 2 . The frequency of oscillation is preferably
within the range of 0.8 to 3 Hz, more preferably 1.5 to 2 Hz.
If the step of flushing (removal of banked solids) entails
altering the slope, the slope then may be 10 to 60 , e.g. 30
to 45.
The invention in Canadian Patent Application 299669 is
repeated in the accompanying drawings, in which
Figure 1 is a plan view7 Figure 2 an elevation and Figure 3
an end elevation of one embodiment of a separator according to
the invention,
Figure 4 is an elevation of part of a second embodimentl
Figure 5 is a perspective schematic view of a third embodimen-t
and
Figure 6 is an end elevation of the embodiment of Figure 5,
in its rest position,
Figure 7 illustrales the modified invention the subject of the
present application.
Turning to Figures 1 - 3, the separator comprises two plane
decks A and B of width 1~5m and of length 1~2m and with upturned
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side edges. The decks A and B are mounted side by side on
support subframes 1 suspended by vertical support wires 2 from
a supportframe 3. A single subframe 1 common to both decks is
also possible. If under certain operating conditions there appears
05 a tendency for the wires 2 to spring or slacken cyclically,
causing the decks to bounce, the wires can be augmented or replaced
by floor-mounted pneumatic stiffening rocking struts. Horizontal
longitudinal restraining wires 4 also connect the subframes 1 to
the support frame 3 so that the subframes 1, and hence the decks~
cannot move in the longitudinal direction. The wires 4 may be
augmented or replaced by transverse rails welded to the subframes 1,
the rails running between floor-mounted roller guides. The decks
A and B are molmted on pivots 5 and are adjustable in slope by
means of tilt pistons 6.
The decks are driven by a common drive comprising pusher
rods 7 driven by a cranked drive shaft 8 off a motor 9.
At the top end of the sloping decks, shown on the right in
Figure 3, is mounted a suspension feed device comprising a feed
pipe 10 supplying a two compartment feedbox 11 leading through
flexible ducting 12 to the top ends of the decks A and B.
At the bottom end of the decks, receiving material flowing
off the bottom of each deck~ is a dra;n in the form of a funnel 13
feeding through a splitter device 14 into appropriate channels 15
for the further disposition of concentrate, middlings and tailings.
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In typical operation, a suspension of tin-bearing sand is
initially fed into one compartment of the feedbox 11 and hence
to the upper end of deck A which is oscillated with appropr1ate
frequency, amplitude and slope to collect (bank) a deposit of
05 material comprised of the particles of a higher density.
Suitable conditions, as a guide, have been found to be as
follows, subject to the finding that the wider the deck, the
larger should be the amplitude and the slower the frequency.
Particle size to be collected Frequency Amplitude Slope
finer than 300 mesh BS 1.72Hz 7.5cm 1~
coarser than 50 mesh BS 1.10Hz 14-15cm 13
In general, the finer the particles, the higher the frequency
and the lower the amplitude.
Perhaps 10% of the solids feed may thus be banked until a
reasonable thickness of bank, perhaps 0.5 cm - 2 cm thick, is
built up. The feed is next diverted through the second compartment
of feedbox 11 to the upper edge of deck B which then starts
operating in the manner just described for the first deck. Mean-
while wash water is supplied to deck A (which continues at the
previous freguency, amplitude and slope) and the splitter 14 is
set first to direct the product of deck A to tails~ then when the
grade of the deck A product approaches the feed grade it may be
directed to middlings, and to deck B (possibly with thickening
by a cyclone). Wash water flow (and feed flow) may be adjusted
for optimum performance, and are preferably from 1 to 2 litres per
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minute, for example 1.51/min. The third phase of the cyclical
operation is the discharge of the banked, washed concentrate on
deck A into its drain. This is achieved by operating the tilt
pistons for deck A to increase the slope from (say) 1~ to 40
05 and adjusting the flow of wash water until the banked material is
effectively dislodged on the deck (flushed off, in other words)
and passes through the splitter device to recovery. Other ways
of removing the concentrate would be by greatly increasing the
frequency or amplitude or both. A typical repeated cycle may
involve an 8 minute period (could be say 6 to 10 minutes) through-
out which frequency and amplitude conveniently remain unchanged, as
follows:
Time (minutes) Deck A Deck B
O - 3 Supplied with feed Irrigated with wash
water.
3 - 4 Supplied with feed Deck slope increased
and concentrate
flushed off.
4 - Deck restored to
slight slope.
4 - 7 Irrigated with wash Supplied with feed.
water.
7 - 8 Deck slope increased Supplied with feed.
and concentrate
flushed off.
8 Deck restored to
slight slope
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Referring now to Figure 4, the drawing shows one arrangement
for varying the amplitude of oscillation. The deck 20 is supported
by tilt mechanisms 21 on a subframe 22 which is suspended by
suspension wires 23 from a support frame 24. Fixed to the
05 subframe 22 is a bracket 25 to which there is attached a
connecting rod 26 which actuates the subframe 22 to perform a
linear reciprocating motion. The connecting rod 26 is secured
at its other end to a block 27 which is slidable along an arm 28
connected at its lower end to a fixed pivot 29. At its upper
end the arm 28 is hinged to a link 20 which is connected to a
crank 31. The crank 31 is driven by means of a variable speed
750W motor 32 through a belt drive arrangement indicated generally
by reference numeral 33. The motor 32 is secured to the support
frame 24. Block 27 is movable along the arm 28 by means of a
pneumatic cylinder and piston assembly 34. In operation the arm
28 performs an oscillatory angular movement about the fixed
pivot 29 and therefore the throw of the connecting rod 26 and
hence the amplitude of movement of the deck 20 is dependent upon
the position of the block 27 on the arm 28. The above
arrangement can be duplicated for each deck and the other deck
(not shown) can therefore be independently varied as regards
amplitude and frequency of oscillation through it own independent
drive system. Variation of amplitude can be achieved through
operation of the piston and cylinder assembly 34 without
stopping operation of the equipment.
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Initiation of the changeovers every few minutes may be by
linked pneumatic times which may be variable pneumatic timers which
may be variable to permit variation of the total cycle time and the
individual components of it.
05 Instead of single decks A and B, vertically stacked banks of
decks A and ~ are envisaged to provide increased throughput, as
in Figures 5 and 6. Each deck has its own materials feed 12, and
the clean-water feed (for wash water and also for flushing) is
separately fed through individual flexible tubes 12a. The latter
feed 12a need only be to a single point in the upper region of
each deck. The former feed 12 is distributed over the width of
each deck, but that it is always suspension, not alternating with
clean water, gives advantages in switching and in keeping issuing
jets unblocked.
All the decks in a bank drain via a collecting board 40 common
to that one bank into one of two funnels 13a, 13b depending on the
deck slope.
During the step when that separator is receiving the suspending
liquid without particles, various densities of particles separate
out down the slope. This phenomenon is exploited in the present
invention by modifying that separator in the following ways--
Feature (b): The sloping directions may be in line, theupper edges being adjacent and the surfaces sloping downwardly away
from each other.
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Feature (c): The lower ends of the surfaces may, instead,
each have a gutter affixed to its respective surface, the gutters
draining into tailings collection means.
Feature (e): The change in shear conditions consists in
05 that the surface is tilted, the line on which the surface pivots
being parallel to the sloping direction. The collecting
arrangements are not arranged to separate different time-intervals
of particles, but lie alongside the (when tilted) lower edge of
each surface parallel to the sloping direction and are partitioned
to collect separately particles which at the instant of tilting
have travelled different distances down the sloping dirbction.
Preferably, each surface has full-length riffles substantially
parallel to the horizontal motion.
Preferably, the riffles are in groups separated along the
sloping dire~tion by unriffled portions of the surface.
Preferably, the partitioning of the collecting arrangements
corresponds with the grouping of the riffles.
The riffles may be ~" to ~" wide by 10 thou to 100 thou
(thousandths of an inch) high, spaced by 1 to 3 inches.
20The invention extends to a method of using the present
separator and to the particles separated by it.
The invention of the present Application will now be
discussed by way of example.
The words 'slope' and 'tilt' are used to designate different
directions. The invention is illustrated by Figure 7 of the
accompanying drawings.
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With the sideways tilting, riffles do assist and may be in
say three groups of 3 - 5, the groups being intended to retain
high-grade conce"trate (for which low riffles 71, e.g. 30 thou
high, are suitable), medium-grade concentrate (slightly higher
05 riffles 72 - the riffles generally should be slightly higher
than the coarsest particles to be collected thereat) and middlings
(riffles 73) respectively.
A sideways flushing water supply (not shown) is provided to
allow the particles to be rinsed off when the surface is tilted
by pneumatic cylinders 76, to say 40 , consequent on which the
upturned lips at the edges 74 of the surfaces parallel to the
sloping direction should be of a somewhat smaller angle of upturn,
~ay 30.
The launder 75 which collects the particles during the
sideways tilting is partitioned 75a corresponding to the above
groups of riffles. The launder may either be common to both
surfaces (or stacks) with separate feeds of flushing water, or
said feeds may be common, with separate launders. Where the
whole surface is riffled, the partitioning of the launders may
be made movable, so that fractions of any desired range of
characteristics may be collected separately.
The change in shear conditions in Canadian Patent 1,115,663
may be a rapid tilt perpendicular to the sloping direction, additional
suspending fluid being applied along the side which has been tilted
up. The 1~ slope interferes relatively little if the tilt is
around 40 , and may thus conveniently be left alone.
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Turning to the riffles, these are applied to the deck
surfaces and extend the full length parallel to the horizontal
motion. Their height and spacing are related to the feed
characteristics but are usually grouped as above. Their heights
05 and widths are as above. The riffle spacing, conveniently 2", and
the number of riffles in each group are chosen to provide sufficient
catchment appropriate to the amount of liberated or free heavies
arriving on the surface during a feed period.
The riffle dimensions being tailored to their proposed
function~ the second group of riffles may for example be required
to reproduce the first group and be of the same height and spacing,
or they may be successively higher down the slope to catch the
intermediate den~ity particles (which are usually of larger size).
The tilt now being sideways (rather than as in Cdn. Patent 1,115,663 being a
mere increase in the tilt used in the feed cycle, with all products
discharging over the same lip), it is now possible to collect
~eparately particles of different grades (which previously were
all mixed up), so as to equal the performance of a shaking table
in which high grade products are made.
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