CA1136582A - Separator for particles of differing densities in suspension on repetitiously moved sloping surfaces - Google Patents

Abstract

ABSTRACT
A separator is disclosed for separating particles of differing densities by treatment of suspensions of the particles in a liquid. The separator comprises two sloping separating surfaces for receiving materials to be treated mounted side-by-side and arranged to perform a repetitious non-discontinuous horizontal motion. A cycle of operation is so organized that at any one time one of the surfaces is functioning as a collecting surface on which banking of heavy deposits is taking place, whilst on the other surface previously banked material is being further separated and is removed by alteration of the shear conditions thereon to cause banked material to be resuspended in a stream of washing liquid.

Description

`" 11365~2 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 -B

11365~2 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.

(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 :
` ~s 11365~Z

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, 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 ~136~582 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.

~136582 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 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 1~365B2 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.

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.

~13658Z

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.

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.

11365~Z

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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Claims (19)

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1. A separator for particles of differing densities which comprises:
(a) two sloping surfaces each having a supply to the upper regions thereof of particles to be separated, in the form of a flowing suspension in a liquid;
(b) the two surfaces being mounted side-by-side with the 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 arranged to perform a repetitious non-discontinuous horizontal motion generally orthogonal to their slope;
(c) the lower ends of the surfaces draining into separate collecting arrangements or into gutters draining into tailings collection means;
(d) motion being imparted to the surfaces by a positive drive causing the motion to follow a path independent of the weight on the surfaces;
(e) the separator being arranged to follow a cycle of operations, with the motion applied to the surfaces throughout, in a first phase of which one surface is receiving the suspension while the other surface receives 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.

2. A separator according to Claim 1, wherein the motion has an amplitude of at least 1 cm.

3. A separator according to Claim 1, wherein the motion has an amplitude of 4 to 18 cm.

4. A separator according to Claim 1, wherein the motion has an amplitude of 5 to 15 cm.

5. A separator according to Claim 1, wherein the motion has an amplitude of 6 to 12 cm.

6. A separator according to Claim l, wherein the motion has an amplitude of 20 cm or more.

7. A separator according to Claim 1, wherein the motion is simple harmonic motion.

8. A separator according to Claim 1, wherein each surface has full-length riffles substantially parallel to the horizontal motion.

9. A separator according to Claim 8, wherein the riffles are in groups separated along the sloping direction by unriffled portions of the surface.

10. A separator according to Claim 9, wherein the partitioning of the collecting arrangements corresponds with the grouping of the riffles.

11. A separator according to Claim 8, 9 or 10, wherein the riffles are 1 to 3 inches apart.

12. A separator according to Claim 8. 9 or 10, wherein the riffles are 0.01 to 0.1 inches high.

13. A separator according to Claim 1, wherein the slope (when receiving the suspension and suspending liquid) is from 1.3 to 2.5°.

14. A separator according to Claim 13, wherein the slope is 1.5 to 2.2°.

15. A separator according to Claim 13, wherein the slope is 1.6 to 2°.

16. A separator according to Claim 1, 7 or 8, wherein the frequency of the motion is from 0.8 to 3Hz.

17. A separator according to Claim 1, 7 or 8, wherein the frequency of the motion is from 1.5 to 2Hz.

18. A separator according to Claim 1, wherein in place of each of the two surfaces there is a stack of parallel surfaces fixed above each other, each surface receiving its own supply of particles to be separated, but each discharging into a collecting arrangement common to that stack.

19. A method of separating particles of differing densities comprising:
flowing in the form of a suspension in a liquid particles to be separated to the upper regions of two sloping surfaces each having their own supply with the two surfaces being mounted side-by-side with the sloping directions parallel or the upper edges of the surfaces are adjacent with the surfaces sloping downwardly away from each other with the sloping directions being in line and the surfaces being arranged to perform a repetitious non-discontinuous horizontal motion generally orthogonal to their slope; draining the lower ends of the surfaces into separate collecting arrangements or into gutters which drain into tailings collection means; imparting motion to the surfaces in a manner to cause the motion to follow a path independent of the weight on the surfaces;
following a cycle wherein one surface receives the suspension while the other surface receives the suspending liquid with no particles followed by tilting that other surface about a line parallel to the sloping direction to flush off the particles which remain and a second phase of the cycle being a reversal of roles of the surfaces, the phases being carried out alternately with the collecting arrangement lying alongside the lower edge, when tilted, of each surface parallel to the sloping direction and partitioned to separately collect particles which at the instant of tilting have travelled different distances down the sloping direction.