GB1576469A

GB1576469A - Sand separator

Info

Publication number: GB1576469A
Application number: GB12655/77A
Authority: GB
Original assignee: National Research Development Corp UK; National Research Development Corp of India
Current assignee: National Research Development Corp UK; National Research Development Corp of India
Priority date: 1977-03-25
Filing date: 1977-03-25
Publication date: 1980-10-08
Also published as: SG76883G; HK30184A; AU3480478A; ZA781616B; AU518515B2; CA1115663A; MY8500219A

Description

(54) SAND SEPARATOR (71) We, NATIONAL RESEARCH DEVELOPMENT CORPORATION, a British Corporation established by Statute, of Kingsgate House, 66 - 74 Victoria Street, London, S.W. 1, do hereby delcare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This 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 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, there is described a gravity separator which was developed primarily to handle tin bearing slimes to recover residual tin which at the time could not be recovered with existing equipment of conventional type. Apparatus in accordance with U.K. Patent Specification No. 1,174,405 has been available and extensively used for some years and has given excellent performance enabling very considerable savings 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 shaking motion of variable amplitude and frequency in order to cause heavier material to remain on a moving 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 unbalancedweight drive which, although simple 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 invention, a separator for particles of differing densities has all the following features (a) to (e): (a) Two sloping surfaces each have a supply inlet to their upper regions for passing a supply 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 and side-by-side and are arranged to be moved by a positive drive so as 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.

(d) The motion is imparted to the surfaces by the positive drive causing the motion to follow a path independent of the weight on the surfaces.

(e) The separator has timing means controlling it 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 a change in shear conditions on that other surface 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 being arranged to present different compartments to receive different time-intervals of particles draining into them.

Thus, in general terms, the present invention provides a gravity separator designed to apply an oscillatory motion in a transverse direction relative to the progressive movement down a slope of a flowing suspension and capable 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. This apparatus comprises two sloping separating surfaces each receiving material to be treated, hereinafter termed "decks", mounted side by side and 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 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 resuspended 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.The 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. However, 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 other, each receiving its own supply of material to be treated, but each discharging into a drain common 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 2.20, 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 600, e.g.

30 to 450.

The invention will now be described with reference to the accompanying drawings, in which Figure 1 is a plan view, 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 embodiment, Figure 5 is a perspective schematic view of a third embodiment, and Figure 6 is an end elevation of the embodiment of Figure 5, in its rest position.

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 side edges. The decks A and B are mounted side by side on support sub-frames 1 suspended by vertical support wires 2 from a support frame 3. A single subframe 1 common to both decks is also possible. If under certain operating conditions there appears 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 sub-frames 1 to the support frame 3 so that the sub-frame 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 mounted 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 drain 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.

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 appropriate frequency, amplitude and slope to collect (bank) a deposit of material comprised of 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 13/4 coarser than 50 mesh BS 1.10Hz 14-15cm 13/40 In general, the finer the particles, the high 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. Meanwhile wash water is supplied to deck A (which continues at the previous frequency, 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) 13/4 to 400 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) throughout which frequency and amplitude conveniently remain unchanged, as follows: Time (minutes) Deck A Deck B 0 - 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 water Supplied with feed.

7 - 8 Deck slope increased and concentrate flushed off Supplied with feed.

8 Deck restored to slight slope. 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 sub-frame 22 which is suspended by suspension wires 23 from a support frame 24. Fixed to the sub-frame 22 is a bracket 25 to which there is attached a connecting rod 26 which actuates the sub-frame 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 be 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 numberal 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 its 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 timers which may be variable pneumatic timers which may be variable to permit variation of the total cycle time and the individual components of it.

Instead of single decks A and B, vertically stacked banks of decks A and B 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.

Each feature of any one of the embodiments shown may be adapted for use in relation to any of the other embodiments.

WHAT WE CLAIM IS: 1. A separator for particles of differing densities, having all the following features (a) to e a Two sloping surfaces each have a supply inlet to their upper regions for passing a supply 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 and side-by-side and are arranged to be moved by a positive drive so as to perform a repetitious non-discontinuous horizontal motion generally orthogonal to their slope.

(e) The lower ends of the surfaces drain into separate collecting arrangements.

(e) The separator has timing means controlling it 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 a change in shear conditions on that other surface to flush off the particles still remaining on it, the second phase being a reversal of roles of the surface the two phases alternating, the collecting arrangements being arranged to present different compartments to receive different time-intervals of particles draining into them.

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

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

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

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

6. A separator according to claim 1 wherein the motion has an amplitude of 20 em or more.

7. A separator according to any preceding claim, wherein the motion is simple harmonic motion.

8. A separator according to any preceding claim, wherein the change in shear conditions is achieved by increasing the slope, and wherein the two surfaces share a common drive subframe.

9. A separator according to any preceding claim, wherein the slope (when receiving the suspension and suspending liquid) is from 1.3 to 2.5 .

10. A separator according to claim 9, wherein the slope is 1.5 to 2.2".

11. A separator according to claim 9, wherein the slope is 1.6 to 20.

12. A separator according to any preceding claim wherein the frequency of the motion is from 0.8 to 3Hz.

13. A separator according to claim 12, wherein the frequency of the motion is from 1.5 to 2Hz.

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

15. A separator according to claim 1 and substantially as hereinbefore described with reference to and as shown in Figures 1 - 3, or Figure 4, or Figures 5 and 6. of the accompanying drawings.

16. A method of separating particles of differing densities, comprising using a separator according to any preceding claim.

17. A method according to claim 16 and substantially as hereinbefore described.

18. Particles separated from other particles by the method of claim 16 or 17.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. two funnels 13a, 13b depending on the deck slope. Each feature of any one of the embodiments shown may be adapted for use in relation to any of the other embodiments. WHAT WE CLAIM IS:

1. A separator for particles of differing densities, having all the following features (a) to e a Two sloping surfaces each have a supply inlet to their upper regions for passing a supply of particles to be separated in the form of a flowing suspension in a liquid.

(e) The lower ends of the surfaces drain into separate collecting arrangements.

10. A separator according to claim 9, wherein the slope is 1.5 to 2.2".

11. A separator according to claim 9, wherein the slope is 1.6 to 20.

17. A method according to claim 16 and substantially as hereinbefore described.

18. Particles separated from other particles by the method of claim 16 or 17.