System, method and apparatus for froth flotation

Abstract

A separation system is disclosed for separating selected particles from a mixture of particles in a fluid. The system includes a froth flotation vessel into which in use the mixture of particles and fluid are subjected to an upward flow of an introduced gas to form a froth layer which rises above an interface formed between the froth layer and the mixture of particles and fluid, such that a quantity of the selected particles is conveyed out of the vessel by the froth layer to become a first product of the system. The vessel also has a first outlet arranged in use for receiving a flow of some of the mixture of particles and fluid from the vessel, an entry to the first outlet being located in a region proximate to, but below, the interface. The vessel also has a second outlet arranged in use for receiving a flow of some of the mixture of particles and fluid from a region of the vessel which is located below the first outlet. In use the first outlet receives a quantity of the selected particles which were not conveyed out of the vessel by the froth layer, and the second outlet receives a quantity of the selected particles in a first by-product of the system. The first by-product comprises a relatively higher percentage of solids compared to the flow of particles and fluid in the first outlet. The flow of the mixture of particles and fluid from the vessel via the first outlet passes to a classification device, which separates the flow into two or more fractions on the basis of their size or density or a combination of the two.

Claims

1. A separation system for separating selected particles from a mixture of particles in a fluid, the system comprising: a froth flotation vessel into which in use the mixture of particles and fluid are subjected to an upward flow of an introduced gas to form part of, and to hydraulically support, a fluidized bed of particles suspended in liquid, located in a lowermost region of the vessel; an aerator device arranged in use for aerating the mixture with the introduced gas, to form a froth layer which rises above an interface formed between the froth layer and the mixture of particles and fluid, such that a quantity of the selected particles is conveyed out of an uppermost region of the vessel by the froth layer to become a product of the system; a first outlet arranged in use for receiving a flow of some of the mixture of particles and fluid from the vessel including a quantity of the selected particles which were not conveyed out of the vessel by the froth layer, an entry to the first outlet being located in a region below the interface; a second outlet arranged in use for receiving a flow of some of the mixture of particles and fluid from the fluidized bed, located in the lowermost region of the vessel which is located below the first outlet, the flow comprising a relatively higher percentage of solids compared to the flow of particles and fluid in the first outlet; wherein the froth flotation vessel has a control system comprising a sensing device for measuring a control parameter, which is connected to a flow control device for controlling at least one of: the flow of the mixture of particles and fluid passing through the first outlet for which the control parameter is to maintain the position of the interface in the froth flotation vessel in relation to the first outlet; and the flow of the mixture of particles and fluid passing through the second outlet, for which the control parameter is to maintain a physical parameter of the flow at a stipulated value at that depth of the fluidized bed.

2. A separation system as claimed in claim 1, wherein the flow of particles and fluid in the first outlet passes to a classification apparatus to produce a flow of relatively coarser and/or higher density particles and a separate flow of relatively finer and or lower density particles, and the control system is arranged to control one of the said flows from the classification apparatus.

3. A separation system as claimed in claim 2, wherein the control system controls the amount of the said flow of relatively finer particles and/or relatively lower density particles which is directed either to return to the vessel, or to become a second by-product of the separation system.

4. A separation system as claimed in claim 3, wherein the control system controls a valve which directs the said flows.

5. A separation system as claimed in claim 3, wherein the control system controls a speed control of a variable speed pump, to direct the said flows.

6. A separation system as claimed in claim 4, wherein the control system further includes a sensor which senses the position of the interface in the froth flotation vessel in relation to the first outlet.

7. A separation system as claimed in claim 1, wherein the flow of the mixture of particles and fluid passing through the second outlet is controlled by a valve that is actuated by the sensing device which measures a physical parameter of the flow through the second outlet, to produce a signal to control the valve.

8. A separation system as claimed in claim 1, wherein the physical parameter includes one or more of the group comprising: the percentage of particulates in the fluid, the density of the particulates, and the mass flowrate of the particulates in the mixture of particulates in fluid.

9. A separation system as claimed in claim 1, wherein the flow of the mixture of particles and fluid passing through the second outlet forms a first by-product of the separation system.

10. A separation system as claimed in claim 2, wherein the flow of a relatively coarser and/or higher density particles from the classification apparatus includes a concentrated amount of the selected particles, and becomes a second product of the system.

11. A separation system as claimed in 10, wherein the classification apparatus is one or more of the group comprising: a screen, a sieve bend, a vibrating screen deck, a vibratory screen, a hydrocyclone, a spiral, a gravity table, a teeter bed and a reflux classifier.

12. A separation system as claimed in claim 3, wherein fresh feed of selected particles in a mixture of particles in a fluid is introduced in-line into the flow of relatively finer particles and/or relatively lower density particles which is directed to the vessel so that the resulting mixture of particles and fluid can be returned to, and discharged into, a lowermost region of the froth flotation vessel below the first outlet, to form part of, and to hydraulically support, the fluidized bed of particles suspended in liquid.

13. A separation system as claimed in claim 12, wherein gas for froth flotation separation is introduced by the aerator device in-line into the flow of relatively finer particles and/or relatively lower density particles which is directed to the vessel.

14. A separation system as claimed in claim 3, wherein gas for froth flotation separation is introduced by the aerator device in-line into a flow of particles and fluid which is directed to the vessel, so that the resulting aerated mixture of particles and fluid can be returned to, and discharged into, a lowermost region of the froth flotation vessel below the first outlet, to form part of, and to hydraulically support, the fluidized bed of particles suspended in liquid.

15. A separation system as claimed in claim 14, wherein fresh feed of selected particles in a mixture of particles in a fluid is combined with the flow gas for froth flotation separation which is introduced by the aerator device in-line into a flow of particles and fluid which is directed to the vessel.

16. A separation system as claimed in claim 13, wherein the aerated mixture of particles and fluid along with the introduced gas is discharged into the vessel at a location that is spaced apart sufficiently from, and not placed in immediate fluid communication with, a flow of particles and fluid leaving the vessel via the second outlet, so as to prevent short-circuiting of the aerated mixture therewith.

17. A separation system as claimed in claim 16, wherein the aerated mixture of particles and fluid along with the introduced gas is discharged into the vessel at a location near a lower part of the fluidized bed in the vessel, and the second outlet is located near an upper part of the fluidized bed.

18. A separation system as claimed in claim 16, wherein the aerated mixture of particles and fluid along with the introduced gas is discharged into the vessel via a pipe which is arranged to extend midway into the fluidized bed, and the second outlet is located near a lower part of the fluidized bed.

19. A separation system as claimed in claim 16, wherein the aerated stream of particles and fluid is introduced into the fluidized bed in the form of a downwardly-facing, vertically-oriented, cylindrical cross-section pipe conduit which is located within the vessel, and which discharges the aerated stream of particles and fluid in a downward direction towards the base of the fluidized bed.

20. A separation system as claimed in claim 3, wherein fresh feed of selected particles in a mixture of particles in a fluid, and gas for flotation separation, are introduced at separate locations into the uppermost region of the vessel.

21. A separation system as claimed in claim 20, wherein the gas is introduced near a lower part of the uppermost region in the form of bubbles which rise upwardly through the uppermost region to form the froth layer, and the fresh feed is introduced at a relatively higher location in the uppermost region.

22. A separation system as claimed in claim 20, wherein the second outlet is located below a bed of particles which forms at a lowermost region of the froth flotation vessel, and which comprises the first by-product.

23. A separation system as claimed in claim 1, wherein a chamber located within the froth flotation vessel forms a part of the first outlet, the chamber having an entry which is oriented away from the upward flow of introduced gas in the vessel, in use arranged so that said upward flow of gas is separated from the flow of particles and fluid which is received into the first outlet.

24. A separation system as claimed in claim 1, wherein an uppermost region of the froth flotation vessel is configured to have a region of lower cross-sectional area compared to the remainder of the froth flotation vessel, thereby crowding the rising froth so as to increase the superficial velocity of the selected particles out of the froth flotation vessel.

25. A separation system as claimed in claim 5, wherein the control system further includes a sensor which senses the position of the interface in the froth flotation vessel in relation to the first outlet.

26. A separation system as claimed in claim 15, wherein the aerated mixture of particles and fluid along with the introduced gas is discharged into the vessel at a location that is spaced apart sufficiently from, and not placed in immediate fluid communication with, a flow of particles and fluid leaving the vessel via the second outlet, so as to prevent short-circuiting of the aerated mixture therewith.

27. A separation system as claimed in claim 21, wherein the second outlet is located below a bed of particles which forms at a lowermost region of the froth flotation vessel, and which comprises the first by-product.

Description

DESCRIPTION OF THE FIGURES

(1) The accompanying drawings facilitate an understanding of the various embodiments which will be described:

(2) FIG. 1 is a schematic elevation of a separation system according to one embodiment of the present disclosure;

(3) FIG. 1A is a schematic elevation of a separation system according to another embodiment of the present disclosure;

(4) FIG. 2 is a schematic elevation of a separation system according to another embodiment of the present disclosure;

(5) FIG. 2A is a schematic elevation of a separation system according to another embodiment of the present disclosure;

(6) FIG. 3 is a schematic elevation of a separation system according to a further embodiment of the present disclosure;

(7) FIG. 3A is a schematic elevation of a separation system according to a further embodiment of the present disclosure;

(8) FIG. 4 is a schematic elevation showing a separation system according to yet another embodiment of the present disclosure;

(9) FIG. 5 is a schematic elevation showing a modification to a flotation vessel which is a part of the separation system shown in FIGS. 1, 1A, 2, 2A, 3 and 4; and

(10) FIG. 6 is a schematic elevation showing another modification to a flotation vessel which is a part of the separation system shown in FIGS. 1, 1A, 2, 2A, 3 and 4.

DETAILED DESCRIPTION

(11) The following description is with reference to the drawings, which should be considered in all respects as illustrative and non-restrictive. In the drawings, corresponding features within the same embodiment or common to different embodiments have been given the same reference numerals.

(12) FIG. 1 shows a first embodiment of a flotation separation system 1 which comprises a froth flotation vessel in the form of a column 10, an aerated slurry inlet port 9 located at the lowermost point of the column 10; a first tailings (or by-product) outlet in the form of a discharge port 20 through which a first final tailings (or “tails”) stream is discharged from the column 10; and an outlet in the form of a discharge port 29 which receives a particle and fluid slurry from the column 10, and through which the slurry flows to a classification system 31. The base of the column 10 is conveniently of the shape of an inverted cone 7. At the top end of the column is a lip 40, and a launder 41 which is configured to receive product in the form of froth discharging over the lip 40 from the column 10, and to deliver the froth through a discharge line 42 as a first concentrate CON 1 of the separation system.

(13) For convenience, it will be assumed that the flotation vessel is a column with rotational symmetry about the vertical axis, although columns of square or rectangular section may be used. The liquid feed containing the particles to be separated by flotation is prepared and conditioned with appropriate collector and frother reagents prior to entering the vessel or column 10. Relatively coarse particles in the feed liquid settle in the column, while relatively finer particles may rise. The liquid in the column is rising at a velocity that is sufficient to fluidize a bed of relatively coarse particles in the bottom of column 10.

(14) The flotation column 10 comprises three operational zones: in a lower part, a fluidised bed contact zone 11; in the central part a settling zone 12; and in the top or upper part, a froth zone 13. In the contact zone 11, the flowrate of slurry entering the inlet port 9 is sufficiently high to hydraulically support a majority of the particles, creating a fluidised bed. The slurry is aerated with small bubbles that rise through the fluidised bed, making contact with hydrophobic particles and lifting them upwards into the separation zone. Bubbles with particles attached continue to rise in the separation zone, and any hydrophilic particles that may have been entrained in the wakes of the rising bubbles have an opportunity to fall out of the wakes and return to the fluidised bed. Bubbles with particles attached continue to rise through the separation zone into the froth zone or layer 13. Between the separation and froth zones there is a marked change in the density of the fluid. The density of the slurry in the separation zone underlying the froth is relatively high, since it contains a relatively low proportion of bubbles, while the froth zone has a relatively high proportion of bubbles, and accordingly has a relatively low density. The region between the froth and the underlying pulp or slurry is known as the froth-pulp transition zone, or interface 14. The bubbles rise in the froth zone, because of the continual arrival of new bubbles from below. Froth that is generated by the continual stream of bubbles rising in the column flows over the lip 40 of the column 10 into the launder 41, carrying the attached, selected hydrophobic particles, discharges as the first product concentrate CON 1 from the column through the conduit line 42.

(15) At a level near the top of the fluidised bed, water and particles flow through an outlet in the form of a port 20, under the control of a valve 21 that is actuated by a sensing device 22, to discharge as a first tailings stream through the conduit line 23. The control parameter detected by the sensing device 22 is selected to suit the particular circumstances of the operation. For example, it could measure the percent solids, the density of the solids and/or the mass flowrate of the slurry or the solids in the slurry, as appropriate. The value of the selected parameter measured by the sensing device 22 is converted to a signal that operates the control valve 21 so as to maintain that parameter at a stipulated value.

(16) In some applications, it is desirable to control the level of the top of the fluidised bed contact zone 11 in the column. One way of achieving this is shown in FIG. 1A. A vertically oriented conduit 24 having a per-determined vertical height, is located at about the vertical centreline of the column 10 such that an upwardly facing open end of the conduit 24 is positioned at the desired level of an interface 25 which forms between the fluidised bed contact zone 11 and the settling zone 12 thereabove. The conduit 24 passes downward into the contact zone 11 for a portion of its length, and is then angled toward a side wall of the column 10 so as to pass through an outlet in the column wall in form of a port 20. In use, the flow of material through the conduit 24 is under the control of a valve 21 that is actuated by a sensing device 22, to discharge the said material as a first tailings stream through the conduit line 23 (TAILS1). The control parameter detected by the sensing device 22 is selected to suit the particular circumstances of the operation. For example, it could measure the percent solids, the density of the slurry, and/or the mass flowrate of the slurry or that of the solids in the slurry, as appropriate. The value of the selected parameter measured by the sensing device 22 is converted into a signal that operates the control valve 21 so as to maintain that parameter at a stipulated value. In further embodiments, the vertically-oriented conduit 24 can be of adjustable height, and need not be in a centre region of the fluidised bed contact zone 11. In further embodiments, the outlet in the form of port 20 can be located at other convenient positions along the wall of the column 10.

(17) Under the influence of the liquid rising in the fluidised bed contact zone 11, relatively finer particles will be elutriated from the bed and pass upwards into the settling zone 12. Thus in a continuous operation the bed itself will consist of relatively coarser particles and these will constitute the majority of particles in the first tailings stream flowing in line 23. Rising out of the fluidised bed is a stream consisting mainly of water with elutriated relatively finer particles in suspension and bubble-particle aggregates. The aggregates may consist of single bubbles and single particles, single bubbles whose surfaces are partially or completely covered with a layer of particles, or clusters. Clusters consist of multiplicities of bubbles and particles, and have been described by Ata and Jameson (The formation of bubble clusters in flotation cells, Int J Miner Process 76(1-2), 123-139, 2005.) The clusters in this referenced paper were observed in relatively turbulent mechanical cells, and the size and concentration of such clusters is known to be dependent on the intensity of the turbulence in the cell. It would be expected that in the fluidised bed cell, which is relatively quiescent, the size and number of the clusters would be higher than in previous technologies.

(18) The buoyancy or net upward gravitational force on a cluster of particles and bubbles is given by:
Net upward force=V.sub.bg(ρ.sub.L−ρ.sub.g−V.sub.pg(ρ.sub.p−ρ.sub.L)
where V.sub.b, V.sub.p are the volumes of the bubbles and particles in the cluster, and ρ.sub.g, ρ.sub.L, ρ.sub.p are the densities of the gas, the liquid and the particles respectively. The upward force can be positive if the volume of the gas is sufficiently high, but it can be appreciated that if the ratio of the volumes of the particles to that of the bubbles is too high, the net upward force can be zero or negative. Where there are many interactions between bubbles and particles simultaneously, a fraction of the clusters will have slightly positive upward buoyancy force, so that they can rise to the top of the settling zone 12 but may lack the buoyancy to force their way into the froth zone 13.

(19) Clusters of low net buoyancy gather at the top of the settling zone 12, surrounded by a suspension of relatively finer particles that have elutriated from the fluidised bed, together with hydrophobic selected particles attached to bubbles that may rise into the froth. An outlet in the form of an exit port 29 and a transfer conduit line 30 are provided, through which slurry with bubble-particle aggregates including clusters may be transported to the classification system or device, which in this embodiment is a hydrocyclone 31, as shown in FIGS. 1 and 1A.

(20) One of the exit streams classified by the hydrocyclone 31 discharges through the conduit 32 containing the relatively finer particles. Conduit 32 splits into two branches 33 and 34. The slurry flowing in conduit 33 passes through a control valve 35 and discharges from the system as a second tailings by-product stream through a discharge conduit 36 (TAILS 2). The control valve 35 regulates the flow of the second tailings stream, so as to maintain the level of the froth-pulp interface 14 in the flotation column 10 at a pre-determined level above the exit port 29. In an alternative arrangement, instead of using a control valve to relate the flow of the second tailings stream in the discharge conduit 36, a variable speed pump and controller can be used to control the TAILS 2 flow, and therefore the quantity of slurry material which is recycled or returned to the flotation cell via the conduit 34. There are a number of methods or devices for measuring the interface position, including float gauges, and differential pressure systems that measure the pressures above and below the interface. In the example shown here, a wall-mounted pressure gauge 37 is used. The signal from the gauge is converted into instructions that are transmitted to the control valve 35, which responds accordingly to maintain the interface level 14 at the desired position.

(21) The control systems described hereinabove, as well as in any of the forthcoming embodiments in FIGS. 2, 2A, 3, 3A and 4, ensure that the interface 14 is maintained at the desired operational position so that the exit port 29 is located in a region proximate to, but below, the interface 14. In one embodiment, the exit port 29 is located at a vertical distance below the interface 14 which is equivalent to about one diameter of the column 10 at the interface. In further embodiments, the exit port 29 is located at a vertical distance below the interface 14 which is equivalent to: between 0.5 D to 1.0 D; or between 0.25 D to 0.5 D; or between 0.05 D to 0.25 D, in each case where D is a diameter of the vessel at the interface. The selected proximity of the interface 14 and the exit port 29 is not arbitrary, and will depend on a number of factors to do with the nature of the particulate slurry being subjected to separation, such as particle size, specific gravity, the hydrophobicity of the selected particles, and pulp density of the slurry,

(22) An underflow stream carrying relatively coarse hydrophobic particles from the hydrocyclone 31 discharges through the line 38 as a second flotation concentrate CON 2.

(23) The second conduit 34 carries overflow slurry of relatively fine particles from the hydrocyclone that mixes with a stream of new feed material in a supply conduit 60. The mixture flows to an in-line aeration device 70. In the aerator device 70, gas enters through a supply line 71 and is dispersed into relatively fine bubbles that collide with hydrophobic particles in the feed line 60, and with any hydrophobic particles that may be contained in the slurry from the overflow line 34. The aerated mixture is recycled back to the base of the fluidised bed, entering through the port 9. The aeration device 70 is configured to subject the gas-liquid mixture flowing through it to a relatively high energy dissipation rate, that is favourable to the generation of bubbles of the preferred size, and also to the capture of relatively finer hydrophobic particles in the suspension. Air can be introduced to the slurry in bubble form, or even in a jet form, but broken up into the slurry flow via a static in-line mixer device, for example. The high-energy conditions in the aerator may lead to detachment of relatively coarser particles in the slurry, but such particles will be collected in the fluidised bed contact zone 11 in the column 10.

(24) The purpose of the classification device 31 is to separate a stream of particles in suspension into two or more fractions on the basis of their size or density or a combination of the two. Preferably, the classification device should be able to deliver a first concentrate that consists mainly of the valuable mineral to be separated from the ore. Devices that separate on the basis of size alone are exemplified by various types of screen, such as sieve bends, vibrating screen decks, and high-speed vibratory screens. Hydrocyclones or other devices that utilise centrifugal forces such as centrifuges are widely used to separate on the basis of size alone when the solids are of the same density, but if the densities of the particles are different, small high-density particles will appear in the same product stream as larger particles of lower density. Another general class consists of devices that work on the principle of gravity, and include spirals, tables, teeter beds and the reflux classifier. Any of these classification devices could be used in the present separation system, taking into account the physical properties of the particulate solids to be separated.

(25) It will be appreciated that because there are at least two tailings streams discharging from the separation system, it is possible to control the solids fraction in the first tailings stream (TAILS 1), so that it needs no further dewatering in a downstream thickener, for example. The present disclosure will therefore lead to reduced capital and operating costs for a minerals processing concentrator or coal preparation plant. The excess water removed from the first tailings stream leaves the separation system via the concentrate streams (CON 1 and CON 2) in the conduit lines 42 and 38, or via the second tails stream (TAILS 2) in the conduit line 36.

(26) It will be appreciated by a person skilled in the art that the point at which the new feed enters the flotation system may differ from that shown in FIG. 1. Thus in other embodiments, the feed could be introduced into the fluidised bed contact zone 11 or the settling zone 12.

(27) In the embodiment shown in FIG. 1, bubbles are introduced into the aerator 70 in a recycle conduit 34. It will be understood that bubbles can be introduced into the slurry in other points in the system. Thus, in another embodiment, bubbles are introduced through a gas sparger system that is placed in the settling zone 12 in the column 10, and in yet another embodiment the gas sparger system is immersed in the fluidised bed contact zone 11.

(28) The flotation cell 10 has been shown in FIG. 1 as a vertical column configured to create a fluidised bed of particles in its base. It will be appreciated that it is not essential for a fluidised bed to exist, and the embodiment shown in FIG. 1 leading to the discharge of two or more tailings and concentrate streams can also be implemented in other forms of flotation cell, such as columns and mechanical cells.

(29) In the embodiment depicted in FIG. 1, liquid rises in the column 10 along with bubbles carrying selected particles, which pass into the froth layer 13, along with some entrained liquid. Most of the liquid rising in the column 10 travels via the outlet exit port 29 through the transfer conduit line 30 to the classification device 31. In some circumstances, particularly when the volumetric flow-rate of air bubbles rising in the column 10 is high, a significant number of bubbles are entrained in the transfer conduit line 30, and these bubbles can interfere with the proper operation of the classification device 31.

(30) Surprisingly, it has been found that bubble entrainment can be reduced or eliminated by the provision of a separation chamber associated with the outlet in the form of the exit port 29. In some embodiments, the separation chamber comprises an open-topped collection chamber. In the embodiment of FIG. 2, the separation chamber takes the form of a disengagement chamber 28 that can conveniently be constructed in the form of an inverted cone. The wide mouth open region of the inverted cone is oriented away from the rising flow of bubbles in the column 10, and the mouth, defined by the circumferential lip 27 is located proximate to, but below the interface 14. In this second embodiment, liquid rising in the column 10 passes over the lip 27 and into the disengagement chamber 28. The cross-sectional area of the chamber is chosen so that the downwards superficial velocity of the liquid in the chamber is less than that of the majority of the bubbles rising in the column 10. Accordingly, most of the bubbles will disengage and rise under the influence of gravity into the froth layer 13, while the liquid substantially free of bubbles along with particulate solids discharges through the transfer conduit line 30 to the classification device 31. Any bubble-particle clusters that have low effective buoyancy will be entrained in the down-flowing liquid in the collection chamber and removed from the column. In the absence of a collection chamber, such clusters may burst, so that the particles that have been carried to the top of the liquid in the column 10 may fall back into the fluidised bed 11. This drawback is overcome by the introduction of the collection chamber 28. A further beneficial effect is that particles that may disengage from the froth, so-called drop-back particles, will fall into the open top of the disengagement chamber 28 and be transferred to the classification device 31. In one example, the chamber 28 has a cross-sectional area which is less than half of the cross-sectional area of the vessel at the interface.

(31) Referring now to FIG. 2A, this embodiment is in all respects similar to the embodiment shown and described already in relation to FIG. 2, except it shows a further embodiment of a classification system or device, which is in the form of a sloping deck, vibrating screen 31. One of the exit streams classified by the screen 31 (that is, the screen underflow solids and liquids) discharges through the conduit 32 containing the relatively finer particles. An overflow stream from the screen deck carrying relatively coarse hydrophobic particles discharges through the line 38 as a second flotation concentrate CON2.

(32) FIG. 3 shows another embodiment, which can be used when the feed material contains dense gangue particles that may segregate in the fluidised bed. If such particles are allowed to accumulate they may interfere with the proper operation of the fluidised bed. A solution is provided by the introduction of the aerated stream of new feed and recycled particles in the line 72, into the base of the fluidised bed through an entry port 9, that is configured to include a standpipe 5 that extends part-way into the column 10. The entering particulate slurry leaves the end 6 of the standpipe 5 in the form of a jet in a substantially vertical direction, and as it rises in the column 10, it diffuses laterally and axially, creating a fluidised bed 11. Particles that cannot be supported by the upwards motion of the fluidising liquid fall under gravity to the downwardly sloping sides 7 of the base of the column 10 and discharge through the tails exit port 20 into a transfer line in which the flow is controlled by a valve 21. The control valve 21 responds to signals generated by the sensor 22, so as to maintain the appropriate properties of the first tails stream discharging through the line 23. The control parameters determined and maintained by the sensor 22 and the control valve 21 could include the slurry mass flow rate, the solids flow rate, the fraction of solids in the discharge stream 23 or other appropriate measurements dictated by the characteristics of the ore being processed.

(33) FIG. 3A shows another embodiment which can be used when it is necessary to minimise the overall height of the flotation cell, achieved by eliminating the downwardly facing sides of the column, so that the base of the column is essentially horizontal. The aerated stream of particles and fluid is introduced into the lower region of the flotation cell via the conduit 72, and into the fluidised bed region through an entry in the form of an inlet port 73, which is in turn connected to a downwardly facing, vertically-oriented, cylindrical cross-section duct 74 which is located centrally in the column 10. The duct 74 discharges the aerated stream of particles and fluid downwardly toward the base of the fluidised bed. In one example, the downward velocity of the mixture of particles and air bubbles issuing from the downwardly facing duct 74 is in the range of between 5 to 25 metres per second.

(34) In the embodiments shown in FIGS. 1, 1A, 2, 2A, 3 and 3A, fresh feed of selected particles in a mixture of particles in a fluid, combined with a flow of gas introduced at the aerator device 70, is introduced via an entry port in the form of inlet port 9 (in FIGS. 1, 1A, 2, 2A and 3), or via the inlet port 73 (in FIG. 3A), to form a part of the fluidised bed contact zone 11 of particles suspended in liquid in the lowermost region, through which bubbles of gas flow upwardly in the column 10. In these examples, the inlet port 9, 73 is spaced apart sufficiently from the outlet from the fluidised bed region in the form of the tailings exit port 20. These entry and outlet ports are located near the uppermost and lowermost ends of the fluidised bed contact zone 11 (as shown in FIGS. 1, 2, 2A, 3A), and in the case of FIG. 1A the entry to the outlet port is located at the top of the fluidised bed contact zone 11, so that the fresh feed entering the vessel is not placed in immediate fluid communication with a by-product tailings leaving the vessel via the outlet port, so there is no ‘short-circuiting’ of fresh feed straight out to a tailings output, and there is a chance for bubbles and particles to rise out of the fluidised bed contact zone 11. Similarly, as shown in FIG. 3, the entry port is a standpipe 5 which extends midway into the fluidised bed contact zone 11 of the flotation column 10 and away from the base of the column 10 and the discharge through the tails exit port 20 to prevent short-circuiting flow out of the contact zone 11.

(35) FIG. 4 shows another embodiment, which is applicable to froth flotation columns of conventional design, which operate without a fluidised bed. In the embodiment shown in FIG. 4, a supply of appropriately conditioned new feed slurry enters through a line 80, discharging into the column 10. In this embodiment, the column 10 comprises three operational zones: in an upper part, a froth zone 13; in a central part, a collection zone 15 where hydrophobic particles are collected by bubbles; and in a lower part, a bed of settled solids 16.

(36) A supply of gas is introduced into the column through a line 81, and is distributed to a sparger system 82, which disperses the gas into many small bubbles 83 of a diameter suitable for flotation, typically in the diameter of 0.3 to 3 mm. The bubbles rise under gravity and pass through the slurry in the column, collecting hydrophobic particles as they do so. The bubbles rise through the pulp-froth interface 14 into the froth layer 13, carrying attached hydrophobic particles and water. The froth continues to rise upwards and passes over the lip 40 of the flotation column 10 and into a launder 41, from which it discharges through the duct 42 as a first flotation concentrate CON1.

(37) A first part of the feed that has been introduced through the line 80 descends in the column 10, towards the discharge port 20. The downward velocity of the slurry is sufficiently low to permit gas bubbles to rise upwards, into the froth layer. The feed slurry contains relatively coarse gangue particles that may settle relative to the liquid, and the flotation system in the embodiment shown in FIG. 4 is configured to allow a layer of settled particles to form in the lower part of the column 10. The settled solids accompanied by water discharge through a port 20, under the control of a valve 21 that is actuated by a sensing device 22, to discharge as a first tailings stream through the line 23. The sensing device 22 can conveniently be chosen to measure the percent solids in the first tailings stream, and transmit a signal to the control valve 21 so as to maintain the percent solids at a chosen value. Other control parameters may also be used such as the mass flowrate of the first tailings stream, or of the solids in the first tailings stream.

(38) With reference to FIG. 4, a second stream of slurry containing suspended relatively finer particles, together with bubbles with attached selected hydrophobic particles, rises towards the top of the collection zone 15. At or near the top of the collection zone, beneath the froth-pulp interface 14, an outlet in the form of an exit port 29 and a transfer conduit line 30 are provided through which slurry with particles, bubbles, aggregates of hydrophobic particles and bubbles, and clusters may be transported to the classification system or device, which in this embodiment is a hydrocyclone 31, as shown in FIG. 1.

(39) One of the exit streams classified by the hydrocyclone 31 discharges through the conduit 32 containing the relatively finer particles. The slurry flowing in conduit 32 passes through a control valve 35 and discharges from the system as a second tailings by-product stream through a discharge conduit 36 (TAILS 2). The control valve 35 regulates the flow of the second tailings stream, so as to maintain the level of the froth-pulp interface 14 in the flotation column 10 at a pre-determined level above the exit port 29. In an alternative arrangement, instead of using a control valve to relate the flow of the second tailings stream in the discharge conduit 36, a variable speed pump and controller can be used to control the TAILS 2 flow, and therefore the quantity of slurry material which is recycled or returned to the flotation cell via the conduit 34. There are a number of methods or devices for measuring the interface position, including float gauges, and differential pressure systems that measure the pressures above and below the interface. In the example shown here, a wall-mounted pressure gauge 37 is used. The signal from the gauge is converted into instructions that are transmitted to the control valve 35, which responds accordingly to maintain the interface level 14 at the desired position.

(40) The control systems described hereinabove, ensure that the interface 14 is maintained at the desired operational position so that the exit port 29 is located in a region proximate to, but below, the interface 14. In one embodiment, the exit port 29 is located at a vertical distance below the interface 14 which is equivalent to about one diameter of the column 10 at the interface. In further embodiments, the exit port 29 is located at a vertical distance below the interface 14 which is equivalent to: between 0.5 D to 1.0 D; or between 0.25 D to 0.5 D; or between 0.05 D to 0.25 D, in each case where D is a diameter of the vessel at the interface.

(41) An underflow stream carrying relatively coarse hydrophobic particles from the hydrocyclone 31 discharges through the line 38 as a second flotation concentrate CON2.

(42) The configuration shown in FIG. 4 can provide significant advantages when compared to the operation of conventional froth flotation columns. In conventional flotation column operations, a minor fraction of the water in the new feed passes over the lip of the column and into a launder, from which it discharges as a flotation concentrate. The remainder of the water and non-floating particles discharge through an exit at the base of the column, as the tails. In effect, there is no control of the percent solids in the tails, which in many operations, is quite close to that of the new feed, generally in the range 20 to 45% in base metal operations. In the embodiment shown in FIG. 4 however, the flow rates in the two tailings streams can be balanced to achieve two separate aims; first, to maintain the level of the froth-pulp interface at a desired position, and second, to produce a tailings stream that requires no further de-watering prior to discharge from a concentrator. Thus the percent solids in the first tailings stream could be raised to at least as high as 55 to 65%.

(43) In practical operations, occasions will arise where the new feed to the configuration shown in FIG. 4 contains no coarse particles that could be recovered as concentrate in the classification device 31. It will be appreciated by a person skilled in the art, that there are substantial advantages still to be achieved by dispensing with the classification device and the second concentrate stream altogether, while maintaining the two tailings streams and the concentrate recovered from the froth zone. In such an arrangement, the flotation column could still be operated to achieve the twin aims of controlling the position of the froth-pulp interface and the percent solids in the first tailings stream.

(44) In the embodiments depicted in FIGS. 1, 1A, 2, 2A, 3, 3A and 4, the column 10 is shown as a cylindrical column with rotational symmetry about the vertical axis. In such an arrangement, the cross-sectional area is independent of height, so the rise velocity of the froth will be constant. The superficial velocity of the gas rising in the froth is an important parameter that must be taken into account in the design of flotation columns. It is known that if the gas superficial velocity is relatively low, coarse particles may move downwardly relative in the froth, and may return to the pulp zone 12 below the froth. When the cross-sectional area is constant, the gas superficial velocity must also be constant. A person skilled in the art will recognise that the cross-sectional area of the column in the froth zone may be reduced with advantage, to increase the gas superficial velocity, and thereby to improve the recovery of coarse particles. The area reduction can be accomplished by a number of means. Thus, FIG. 5 shows an embodiment in which a first column 10 is surmounted by a second column 44 of smaller diameter, the two columns being connected by a conical reducer 45. FIG. 6 shows another embodiment in which the column 10 is of constant cross-sectional area, and a body 43 of the shape of an inverted cone is inserted so that as the gas rises in the device, the superficial velocity of the froth increases as it approaches the lip 40, thereby assisting coarse particles in the froth to continue to rise upwardly in the column.

(45) It will further be appreciated that any of the features in the embodiments of the present disclosure can be combined together and are not necessarily applied in isolation from each other. For example, the feature of the disengagement chamber 28 in FIG. 2. can be combined with the feature of standpipe 5 and associated tailings exit port 20 in FIG. 3. Similar combinations of two or more features from the above described embodiments of the separation system and separation apparatus can be considered to fall within the present disclosure.

(46) Experimental Results

(47) Experimental results have been produced by the inventor using the new equipment configuration disclosed herein, to assess whether there are any metallurgically beneficial outcomes during the operation of the separation system and apparatus.

(48) A froth flotation system operating was constructed in accordance with the embodiment shown in FIG. 2A. The system was operated in batch mode (that is, without the addition of fresh feed into conduit 60). A feed material consisting of coal and ash particles up to 2 mm in diameter, was placed in the flotation column. Such a feed size distribution is very wide for coal flotation separation, where normally the ore material is crushed to a top size of no more than 0.5 mm (500 micrometers).

(49) Diesel oil was used as a collector reagent (dosage: 1 kg/tonne of feed solids) and MIBC (methyl isobutyl carbinol) was used as a frother reagent (dosage: 20 ppm in the water). The gas used in the flotation column was air, with a superficial velocity in the column of 1.5 cm/sec. The superficial velocity of the recycle liquid introduced into the base of the flotation column, calculated in terms of the cross-sectional area of the column, was 1.5 cm/sec. The froth depth maintained in the uppermost portion of the flotation column was 100 mm. A wedge-wire sieve bend was used as the classification system, with a nominal gap size of 0.5 mm. The underflow from the sieve bend was collected and returned to the base of the flotation column as recycle, to maintain the fluidisation in the fluidised bed contact zone. The froth product was designated as CON 1 and the oversize from the sieve bend was collected as CON 2. The flotation time was ten minutes of aeration and recirculation flows.

(50) TABLE-US-00001 TABLE 1 Distribution of mass by particle size band Screen size, μm Mass distribution Upper Lower Combined (μm) (μm) Feed Con 1 Con 2 Product Tails 2000 1400 10.4 3.3 3.5 6.8 3.5 1400 1000 18.5 6.9 5.6 12.4 6.1 1000 710 17.9 7.4 5.8 13.2 4.7 710 500 14.3 6.9 4.9 11.8 2.5 500 0 38.9 24.0 6.9 31.0 7.9 Overall: 100.0 48.5 26.7 75.3 24.7

(51) TABLE-US-00002 TABLE 2 Ash in sample, % Screen size, μm Ash (%) Upper Lower Combined (μm) (μm) Feed Con 1 Con 2 Product Tails 2000 1400 34.6 4.5 10.5 7.5 86.9 1400 1000 35.1 4.9 14.8 9.4 87.7 1000 710 33.6 7.0 23.1 14.1 88.1 710 500 29.6 9.8 27.4 17.1 89.4 500 0 35.2 23.3 19.2 22.3 85.1 Overall: 34.0 15.0 19.5 16.6 87.0

(52) TABLE-US-00003 TABLE 3 Combustibles distribution, combustibles recovery, yield Screen size, μm Combustibles distribution Upper Lower Combined Combustibles (μm) (μm) Feed Con 1 Con 2 Product Tails recovery, % Yield, % 2000 1400 10.3 4.8 4.8 9.6 0.7 93.2 65.9 1400 1000 18.2 9.9 7.2 17.1 1.1 93.8 67.1 1000 710 18.0 10.4 6.8 17.2 0.9 95.3 73.7 710 500 15.3 9.5 5.4 14.9 0.4 97.4 82.8 500 0 38.2 27.9 8.5 36.4 1.8 95.3 79.6 Overall: 100.0 62.5 32.6 95.1 4.9 95.1 75.3

(53) Table 1 shows the distribution of mass in various size fractions in the initial feed, in CON1, in CON2, in the combined CON flows and in the tailings by-product stream (TAILS1). Approximately two-thirds of the concentrate was produced as froth product (CON1), while one third was recovered in the classification system (CON2). Inspection of the size-by-size mass distributions shows that in the finest size fractions, the CON1 stream is predominantly composed of the finest particles, but the particles were split evenly between the two product streams as the particle size increased.

(54) Table 2 shows that overall the ash content of CON2 was higher, which is not unexpected, but only marginally so (15% versus 19.5%). The ash content in the tails (TAILS1) was essentially independent of particle size (typically in the range between 85-90%) averaging 87%. This shows that the separation effected by the system was very cleanly done, over a very large range of particle sizes.

(55) Table 3 shows the distributions and recoveries of the combustible coal matter in the various streams. Overall recoveries were very high across all size ranges (between 93-97%), which demonstrates that even for a very coarse size of particulate feed material, the separation system disclosed herein is a very efficient way of yielding both high recoveries of the valuable solids accompanied by a low ash content in the separated product.

(56) Such a result means that the separation system disclosed herein can provide a user with a way of maximising the performance of a flotation separation stage over much higher than normal particulate sizes, which in turn means lower grinding costs in the preceding ore milling stage, which can offer a significant reduction in operating costs overall to a minerals processing operation.

(57) The inventor has discovered that the use of a separation system of the present disclosure can realise optimum (and stable) operating conditions, and has been found to: i) promote better flotation separation recovery and yield of selected (value) particles, but at an overall coarser size distribution, thereby avoiding overgrinding of particles; ii) maximise throughput of product in terms of, for example, tonnage per hour; iii) produce a tailings stream from a lowermost region of, or fluidised bed zone of, a froth flotation cell, which can be discharged direct to a tailings disposal plant avoiding the need for additional dewatering; and iv) maintain the physical separation process parameters at a stable level.

(58) In the foregoing description of certain embodiments, specific terminology has been resorted to for the sake of clarity. However, the disclosure is not intended to be limited to the specific terms so selected, and it is to be understood that each specific term includes other technical equivalents which operate in a similar manner to accomplish a similar technical purpose. Terms such as “top” and “bottom”, “upper” and “lower”, “above” and “below” and the like are used as words of convenience to provide reference points and are not to be construed as limiting terms.

(59) In this specification, the word “comprising” is to be understood in its “open” sense, that is, in the sense of “including”, and thus not limited to its “closed” sense, that is the sense of “consisting only of”. A corresponding meaning is to be attributed to the corresponding words “comprise”, “comprised” and “comprises” where they appear.

(60) The preceding description is provided in relation to several embodiments which may share common characteristics and features. It is to be understood that one or more features of any one embodiment may be combinable with one or more features of the other embodiments. In addition, any single feature or combination of features in any of the embodiments may constitute additional embodiments.

(61) In addition, the foregoing describes only some embodiments of the inventions, and alterations, modifications, additions and/or changes can be made thereto without departing from the scope and spirit of the disclosed embodiments, the embodiments being illustrative and not restrictive.

(62) Furthermore, any inventions which have described in connection with what are presently considered to be the most practical and preferred embodiments, it is to be understood that the invention is not to be limited to the disclosed embodiments, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the inventions. Also, the various embodiments described above may be implemented in conjunction with other embodiments, e.g., aspects of one embodiment may be combined with aspects of another embodiment to realise yet other embodiments. Further, each independent feature or component of any given assembly may constitute an additional embodiment.