AU4443602A - Flotation cells with devices to enhance recovery of froth containing mineral values - Google Patents

Description

AUSTRALIA

Patents Act 1990 COMPLETE SPECIFICATION STANDARD PATENT Applicant(s): BAKER HUGHES INCORPORATED Invention Title: FLOTATION CELLS WITH DEVICES TO ENHANCE RECOVERY OF FROTH CONTAINING MINERAL VALUES The following statement is a full description of this invention, including the best method of performing it known to me/us: 2 FLOTATION CELLS WITH DEVICES TO ENHANCE RECOVERY OF FROTH CONTAINING MINERAL VALUES BACKGROUND OF THE INVENTION Field of the Invention This invention relates generally to froth flotation cells and more particularly to froth flotation cells that include devices, such as baffles and radial launders for improved recovery of mineral values from mineral waste.

Background Art Froth flotation cells are used to separate mineral values from mineral wastes. An ore is finely ground and suspended as.' a water-based slurry or pulp in a flotation cell. An impeller or rotor is turned at a high speed in the slurry to suspend the mineral particulates and to distribute or disperse air bubbles into the slurry. The mineral values attach to the air bubbles. The bubbles with the entrained mineral values rise to form a froth atop the pulp or slurry pool. The froth overflows a weir and is collected in a launder for further processing. Examples of flotation cells are described in U.S. Patent No. 5,611, 917 to Degner, U.S. Patent No. 4,737,272 to Szatkowski et al., U.S.

Patent No. 3,993,563 to Degner, U.S. Patent No.

5,219,467 to Nyman et al., U.S. Patent No. 5,251,764 to Niitti et al., and.U.S. Patent No. 5,039,400 to Kallioinen et al. In the flotation apparatus of some of these references, air is supplied to the pulp or slurry via a separate pumping mechanism.

During flotation cell operation, the rotation of the impeller imparts rotational energy to the pulp or slurry pool. This rotational energy is transferred to 3 the froth phase which can develop a substantial angular velocity of the pulp. This angular velocity increases the time it takes to remove the froth and can cause the mineral values to drop back into the pulp phase, thus reducing the efficiency of the flotation cell. It is thus desirable to reduce the angular velocity of the slurry or pulp.

The flotation cells usually include a circumferential launder to collect the mineral-rich froth.

Such cells are limited in their froth removing capabilities, as the froth must travel to the periphery of the cells before being collected by the launder. It is thus deemed desirable to provide mechanisms to more effectively collect froth. The present invention addresses to above-noted deficiencies of floatation cells and provides baffles in the cell which reduce the angular velocity of the pulp and structures to more quickly and effectively remove the froth compared to cells only utilizing a central launder.

As noted above, commercially available flotation cells are limited in their ability to quickly remove froth. If froth is not removed quickly and efficiently, mineral values tend to drop back into the pulp phase and then either attach once again to air bubbles or are discharged with the mineral waste. The present invention provides devices in addition to the commonly used central launder at the inner periphery of the flotation cells in the flotation cell to relatively quickly remove the froth regardless of the froth flow characteristics.

According to the present invention, there is provided a flotation cell for removing mineral values present in a slurry, comprising: a tank for holding a mass of the slurry containing said mineral values; \\melb-files\home$\MCooper\Keep\Speci\81954 .98-Div.doc 28/05/02 4 a mechanism in the tank introducing gas into the slurry and generating froth near the top of the mass of the slurry; a launder adjacent a periphery of the tank constituting an outer launder, said outer launder removing froth from the tank during operation of the flotation cell; an inner launder in the tank that is of a size smaller than the outer launder and disposed generally toward the center of the tank said inner launder collecting froth from the tank; and at least one radial launder in the tank, said radial launder extending from adjacent said outer launder generally inwardly toward an inner portion of said tank, said at least one radial launder receiving froth from the tank and is in fluid flow communication with the outer launder and the inner launder to enhance recovery of froth from the tank.

According to the present invention, there is also provided a flotation cell for recovering mineral values contained in a slurry, comprising: a tank for receiving and holding a mass of the slurry; a mechanism in the tank adjacent the middle of the tank introducing gas and creating froth containing mineral values near top of the slurry mass in the tank; an launder adjacent a periphery of the tank constituting an outer launder, said outer launder removing froth from the tank during operation of the flotation cell; an inner launder in the tank, said inner launder substantially surrounding said mechanism, said inner launder receiving froth from the tank and discharging the received froth from the tank to enhance removal of the froth from the tank; and at least one radial launder in the tank, said \\melb_files\homeS\MCooper\Keep\Speci\81954.98-Div .doc 28/05/02 5 radial launder extending from adjacent said outer launder generally inwardly toward an inner portion of said tank, said at least one radial launder receiving froth from the tank and in fluid flow communication with the outer launder and the inner launder to enhance recovery of froth from the tank.

According to the present invention, there is also provided a froth flotation cell, comprising: a tank; a mechanism disposed in the tank for suspending mineral particulates and dispersing air bubbles in a pulp phase or slurry in said tank, thereby aiding in a generation of forth from the pulp phase or slurry; a central launder at the periphery of the tank, the central launder being adapted to remove froth from the tank during operation of the flotation cell; and a secondary launder in the tank, said secondary launder discharging froth from within the tank to a selected location during operation of the flotation cell.

The present invention provides a network of launders in the flotation cell tank to effectively remove froth. These launders may be used with or without the baffled plates described above. The network of launders may include a plurality of radial launders. The radial launders extend inwardly from the central launder. A secondary launder may be placed inside of the central launder. The radial launders preferably are connected to both the central launder \\melb-files\homeS\MCooper\Keep\Speci\81954 98-Div.doc 28/05/02 and the secondary launder, forming a network of launders in the tank.

The launders are preferably fastened together in a manner so that the secondary launder is in fluid communication with the radial launders, and, in turn, the radial launders are in fluid communication with the central launder. Thus, a network of fluid channels is created, all leading to the central launder for disposal of the collected froth. Preferably, the radial launders are circumferentially equispaced.

In the present invention, a wash assembly may be placed so as to introduce a sprayed liquid in the radial launders. The spray is introduced near the point of connection between the radial launders and the secondary launder. The introduction of a liquid at this point facilitates a more rapid flow of the froth traveling through 'e rad.al laiunders to- the central launder, thus accelerating the overall removal of the froth.

In the present invention, all of the launders are provided with a froth overflow lip which determines the level of the froth in the tank. The launders are assembled so as to make their associated overflow lips coplanar throughout the tank. In a separate embodiment, the overflow lips could be arranged in a non-coplanar fashion in order to take advantage of fluid froth flow dynamics associated with a particular flotation cell design.

A crowder device may be used to direct froth flow radially outward in the tank. Tank baffles, as described earlier, may be utilized for controlling flow dynamics of the pulp phase or slurry as well as the froth.

7 BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a partial side elevational view, partially in phantom lines, of a froth flotation cell in accordance with the present invention, showing one of a plurality of froth baffle plates attached to a side wall of a flotation tank.

Fig. 2 is a partial top plan view of the froth flotation cell of Fig. 1, showing the plurality of froth baffle plates.

\\melbfiles\homne$\MCper\Keep\Speci\81954 .98-Div.doc 28/05/02 -s- Fig. 3 is a front elevational view of a bracket assembly for attaching the baffle plates of Figs. 1 and 2 to the side wall of the'flotation tank.

Fig. 4 is a top plan view of the bracket assembly of Fig. 3.

Fig. 5 is a side elevational view of the bracket assembly of Fig. 3.

Fig. 6 is a partial side elevational view, partially in phantom lines, of a froth flotation cell in accordance with the present invention, showing a central launder, two of a plurality of radial launders, a secondary circumferential launder, and a wash assembly Fig. 7 is a partial top plan view of the froth flotation cell of Fig. 1, showing the plurality of radial launders.

Fig. 8a is an elevational view along the axis of a radial launder showing the connection between a radial launder and the central launder.

Fig. 8b is a side elevational view, perpendicular to the axis of a radial launder, again showing the connection between a radial launder and the central launder.

Fig. 9 is a side elevational view, perpendicular to the axis of a radial launder showing the connection of a radial launder to the secondary circumferential launder, the connection of the secondary launder to the standpipe of the flotation cell and a wash assembly positioned in the radial launder.

9 DESCRIPTION OF THE PREFERRED EMBODIMENTS Figs. 1-5 illustrate an embodiment of a froth flotation cell with a plurality of baffles, the subject of AUA 81954/98, and Figs. 6-9 illustrate an embodiment of a froth flotation cell with launders according to the concept of the present invention. As illustrated in Fig.

i, a froth flotation cell comprises a tank 10 and an impeller or rotor 12 rotatably disposed in the tank 10 for generating froth from a pulp phase or slurry in the tank.

Impeller 12 includes a plurality of vertical vanes or propeller blades 14 disposed in a cylindrical configuration about a rotation axis 16. Impeller 12 is connected to a vertically oriented drive shaft 18 which is drivingly coupled at an upper end to a drive assembly including a conventional motor, transmission belts, and bearings (none shown).

A lower end of the impeller 12 is surrounded by an upper end of cylindrical draft tube extension or spacer element 21 which is coupled at a lower end to a conical draft tube 22. Draft tube 22 is spaced from a lower wall or panel 24 of tank 10 by a plurality of supports 26.

Supports 26 define a plurality of openings 28 through which pulp or slurry is drawn into the draft tube 22.

An upper end of impeller 12 is surrounded by a fenestrated disperser 30 which is coaxially aligned with drive shaft 18 and acts to facilitate shearing of air bubbles and to eliminate vortexing of the pulp phase.

Positioned over and about the disperser 30 is a perforated conical hood 32 for stabilizing the pulp surface.

Impeller 12 is positioned near the top of the fluid volume 11 and hood 32 functions to calm the turbulent fluid 11.

\\melbfiles\home$\MCooper\Keep\Speci\81954 .98-Div.doc 28/05/02 10 A crowder device 34 is provided above hood 32 and impeller 12. Crowder device 34 is coaxially disposed relative to shaft 18. The structure and function of crowder device 34 is described in U.S. Patent No.

5,611,917 to Degner, the disclosure of which is hereby incorporated by reference. The disclosures of U.S.

Patent No. 4,737,272 to Szatkowski et al. and U.S.

Patent No. 3,993,563 to Degner are also incorporated by reference.

As illustrated in Figs. 1 and 2, the froth flotation cell also includes a plurality of substantially radially oriented stationary baffle plates 36 disposed:in tank 10 for reducing angular momentum of a froth phase while enhancing radial momentum thereof. Each baffle plate 36 preferably extends through a substantial portion of the froth and into the pulp phase or slurry pool in a lower end portion of tank 10. As illustrated in Fig. 2, baffle plates 36 are preferably circumferentially or angularly equispaced.

A plurality of braces 37 (see Figs. 1 and 2) are each connected at opposite ends to baffle plates 36 for reinforcing the baffle plates against the tangential forces exerted by the rotating froth and slurry. Each baffle plate 36 is supported in a tangential direction by a pair of braces 37 on opposite sides of the respective baffle plate. Braces 37 are preferably connected to baffle plates 36 along radially inner edges thereof and may be angle pieces, L-shaped in cross-section. In the froth flotation cell of Figs. 1 and 2, braces 37 are located below hood 32. Of course, other points of attachment of braces 37 to baffle plates 36 are possible, for example, at different vertical or radial locations.

-Hl Baffle plates 36 are fastened to a wall 38 of flotation cell tank 10 and extend radially inwardly from that wall. Wall 38 is an inner wall of a froth overflow weir or launder 40. In an alternative embodiment of the invention (not illustrated), baffle plates for froth momentum or velocity control are instead fastened to disperser 30 and extend radially outward therefrom.

Baffle plates 36 have upper edges 42 disposed at approximately an upper level or surface of a froth layer (not shown) located atop the pulp phase or slurry pool (not shown) during operation of the froth flotation cell. The froth level is defined or determined by an overflow lip 44 of launder 40 and is generally located slightly above the vertical position of that lip. Lower edges 46 of baffle plates 36 are disposed sufficiently below a lower end of impeller 12 to substantially arrest rotational motion of the pulp phase or slurry mass or at least in an upper outer annular portion thereof.

As shown in Fig. 1, each baffle plate 36 is provided along a radially inner side with a centrally located cutout 48. A lower end of hood 32 extends into the cutout. In the embodiment of Figs. 1 and 2, baffle plates 36 are spaced from hood 32, as well as from disperser 30, draft tube 21, and tube extension 22.

This spacing is preferably sufficiently great, particularly above the lower end of hood 32, to permit the removal of hood 32, disperser 30 and impeller 12 for maintenance purposes. In a simplified embodiment of a flotation cell, the froth control baffle plates are rectangular and have a width less than the radial distance between the lower end of hood 32 and the inner surface of wall 38.

As illustrated in Figs. 1 and 3-5, a simple bracket assembly 52 for mounting baffle plates 36 to wall 38 of flotation cell tank 10 includes a slotted vertical member or post 54 attachable to the tank wall, a horizontal member or arm 56 attached to the vertical member, and an angled member or brace 58 connected at opposite ends to vertical and horizontal members 54 and 56. Members 54, 56, and 58 are formed as angle members.

In assembling the flotation cell of Figs. 1 and 2, baffle plates 36 are attached to flotation cell tank so that the baffle plates each extend in a substantially vertical and radial orientation in the tank and so that each baffle plate 36 extends downwardly through a substantial portion of the froth and a substantial distance into the pulp phase.or slurry pool. More specifically, baffle plates 36 are attached to flotation cell tank 10 so that upper edges 42 are disposed at approximately froth level, at approximately the vertical position of overflow lip 44.

In addition, baffle plates 36 are preferably attached to inner wall 38 of tank 10 via respective bracket assemblies 52.

Baffle plates 36 increase the removal of froth from the flotation cell and improve mineral recovery.

Generally, each flotation cell is provided with from four to eight baffle plates 36. However, more or fewer baffle plates could be used in different applications.

In a baffled flotation cell, froth moves to launder approximately twice as fast as in a nonbaffled cell.

In general mineral recovery is generally increased more than four percent.

Figs. 6-9 show a froth flotation cell with a plurality of launders for enhancing the recovery of froth. Fig. 6 shows a schematic elevational view of a flotation cell 100 that includes a froth flotation cell comprising a tank 110 and an impeller or rotor 112 rotatably disposed in the tank for generating froth from a pulp phase or slurry in the tank. Impeller 112 includes a plurality of vertical vanes or propeller blades 114 disposed in a cylindrical configuration about a rotation axis 116. Impeller 112 is connected to a vertically oriented drive shaft 118 which is drivingly coupled at an upper end to a drive assembly 120, which may include a conventional motor, transmission belts, and bearing (none shown). For clarity and simplicity, the flotation cells of Figs. 6- 9 are shown without the baffles described above.

A lower end of impeller 112 is surrounded by an upper end of a cylindrical draft tube extension or spacer element 121 which is coupled at a lower end to a conical draft tube 122. Draft tube 122 is spaced from a lower wall or panel 124 of tank 110 by a plurality of supports 126. Supports 126 define a plurality of openings 128 through which pulp or slurry moves and is drawn into extension 122.

An upper end of impeller 112 is surrounded by a perforated dispenser 130 which is coaxially aligned with drive shaft 118 and acts to facilitate shearing of air bubbles and to eliminate vortexing of the pulp phase. Positioned over and about disperser 130 is a perforated conical hood 132 for stabilizing the pulp surface. Impeller 112 is positioned near the top of the fluid volume and hood 132 functions to calm the turbulent fluid.

While not shown in the current embodiment, a crowder device may be placed above the hood 132 and impeller 112.

Above the disperser 130 is a standpipe 134 through which air is mixed into the pulp or slurry. The -14 impeller 112 creates a vortex within the standpipe 134 which allows for mixing and entrainment of air into the pulp or slurry.

As illustrated in Figs. 6 and 7, the froth flotation cell also includes a central launder 140.

The central launder 140 is fixed near the upper end around the inside periphery of the tank 110. An overflow lip 144 of launder 140 defines or determines the froth level, which is generally located slightly above the vertical position of the overflow lip 144.

Radial launders 136 are shown to be connected at one end to the central launder 140, extend inward, and are circumferentially or angularly equispaced. Each radial launder 136 also has an overflow lip 138 similar to the central launder's overflow lip 144. The central overflow lip 144 and each radial overflow lip 138 are aligned in a coplanar fashion so that the definition or determination of the froth level initially set by the central overflow lip 144 is unchanged.

Each radial launder 136 has a second end which is connected to a secondary launder 150. The secondary launder 150 is concentric with and of smaller diameter than the central launder 140. The secondary launder 150 also having an overflow lip 154 which is aligned to be coplanar with the radial overrlow lips 138 and the central overflow lip 144. The secondary launder 150 is structurally attached to the standpipe 134 by using a plurality of brackets 160 shown in Fig 4.

Referring to Figs 8a and 8b, the radial launders 136 are connected to the central launder 140 by means of a flange type bracket 162. At this point of connection there is a cutout 164 in the wall of central launder 140 in order to create a continuous fluid path from radial launder 136 to central launder 140. In between the radial launder 136 and the central launder 140 is a gasket 166 to prevent fluid from leaking either in or out of the launders.

Referring to Fig 9, the radial launder 136 is similarly connected to the secondary launder 150 by means of another flange type bracket 170 and a gasket 172 to prevent leakage. The connection between radial launder 136 and secondary launder 150 also includes a cutout (not shown) to allow for a continuous fluid path between the two launders.

Referring back to Fig 6, the radial launder 136 is shaped so that it has a greater vertical depth at the connection with the central launder 140 than it has at the connection with the secondary launder 150. This creates a slope in the bottom of radial launder 136 which begins at the secondary launder 150 and continues downward until the connection at the central launder 140.

The interconnection of launders 136, 140, and 150 creates a network of launders which are in continuous fluid communication. Froth which has build up inside the tank 110 pours into the various launders via the overflow lips 138, 144, and 154. Depending on where the froth initially overflows into the launders, it may follow any of the various paths to reach the central launder 140 and ultimately exit through a discharge pipe 146. For example, if the froth initially collects in the secondary launder 150, it will travel from the secondary launder 150 through one or more radial launders 136 and then to the central launder 150. The froth is carried from one launder to the next by gravity based on the slope of the radial launders 136.

To further aid in the removal of the froth, a wash assembly 180 is provided. The wash assembly 180 contains a plurality of spray nozzles 182, which are placed so as to introduce a fluid in the radial launders 136 at approximately the point of connection of the radial launder 136 to the secondary launder 150, (see Fig The introduction of a fluid at these locations, in essence, reduces the viscosity of the froth and allows the froth to travel more rapidly from the radial launder 136 to the central launder 150.

Thus, the use of a wash assembly 180 expedites the removal of froth collected in the radial launders 136 and also allows for a more shallow slope of the radial launder 136 if desired.

An advantage of setting up a network of launders, such as described above, is that the froth is removed efficiently regardless of the froth flow characteristics. For example, if froth flows with an angular momentum, then it is captured by the radial launders 136. Likewise, if the flow of the froth is either radially outward from the center of the tank, or radially inward towards the.center of the. tank, the froth is collected by either the central launder 140 or the secondary launder 150 respectively.

Although.the invention has been described in terms of particular embodiments and applications, one of ordinary skill in the art, in light of this teaching, can generate.additional embodiments and modifications without departing from the spirit of or exceeding the scope of the claimed invention. For example, rather than having froth control baffles connected solely to the sidewall of the flotation cell tank, baffle plates may be attached also to the disperser. Such baffle plates would extend radially outward from the disperser. The hood may be modified or entirely omitted to facilitate proper operation of the disperser-carried baffles.

Also, it is to be noted that the present invention is applicable to any type of froth flotation cell regardless of the mechanism a pump) used to suspend mineral particulates and disperse air bubbles into the slurry. Thus, a froth flotation cell without a rotating impeller, draft tube, disperser, hood, or crowder device can benefit from baffle plates as described herein.

Accordingly, it is to be understood that the drawings-and descriptions herein are offered by way of example to facilitate comprehension of the invention and should not be construed to limit the scope thereof.

Claims (26)

1. A flotation cell for removing mineral values present in a slurry, comprising: a tank for holding a mass of the slurry containing said mineral values; a mechanism in the tank introducing gas into the slurry and generating froth near the top of the mass of the slurry; a launder adjacent a periphery of the tank constituting an outer launder, said outer launder removing froth from the tank during operation of the flotation cell; an inner launder in the tank that is of a size smaller than the outer launder and disposed generally toward the center of the tank said inner launder collecting froth from the tank; and at least one radial launder in the tank, said radial launder extending from adjacent said outer launder generally inwardly toward an inner portion of said tank, said at least one radial launder receiving froth from the tank and is in fluid flow communication with the outer launder and the inner launder to enhance recovery of froth from the tank.

2. The flotation cell of claim i, further comprising a plurality of radial launders disposed in the tank.

3. The flotation cell of claim 2, wherein said radial launders are arranged circumferentially equispaced.

4. The flotation cell of claim i, wherein said outer launder includes an upper lip that defines the level of the froth in the tank.

The flotation cell of claim 4, wherein the at \\melb-files\home$\MCoper\Keep\Speci\S1954.9B-Div.doc 28/05/02 19 least one radial launder includes a lip coplanar with the lip of the outer launder.

6. The flotation cell of claim 1, wherein at least one radial launder discharges the received froth into the outer launder.

7. The flotation cell of claim i, wherein said radial launder, inner launder, and outer launder each have a generally coplanar lip defining the level of froth in the tank.

8. The flotation cell of claim 1, wherein the inner launder discharges the froth into the at least one radial launder.

9. The flotation cell of claim i, further having a device for delivery of wash liquid to at least one of the inner or radial launders to enhance flow of froth through the radial launder.

The flotation cell of claim 2, further comprising a device for delivery of wash liquid to at least one of the outer or radial launders to enhance flow of froth through said radial launder.

11. A flotation cell for recovering mineral values contained in a slurry, comprising: a tank for receiving and holding a mass of the slurry; a mechanism in the tank adjacent the middle of the tank introducing gas and creating froth containing mineral values near top of the slurry mass in the tank; an launder adjacent a periphery of the tank constituting an outer launder, said outer launder removing froth from the tank during operation of the flotation cell; \\melb fies\homeS\MCooper\Keep\Speci\81954 .98-Div.doc 28/05/02 20 an inner launder in the tank, said inner launder substantially surrounding said mechanism, said inner launder receiving froth from the tank and discharging the received froth from the tank to enhance removal of the froth from the tank; and at least one radial launder in the tank, said radial launder extending from adjacent said outer launder generally inwardly toward an inner portion of said tank, said at least one radial launder receiving froth from the tank and in fluid flow communication with the outer launder and the inner launder to enhance recovery of froth from the tank.

12. The flotation cell of claim 1, further comprising a plurality of generally radially oriented vertical baffles mounted in said tank for reducing angular momentum of said froth while enhancing radial momentum thereof.

13. The flotation cell of claim i, further comprising at least one opening toward a lower end of said tank for delivery of slurry to said tank.

14. The flotation cell of claim i, further comprising an impeller mounted for rotation in said tank, with said impeller being positioned generally toward an upper end of said tank and suspending solid particulates in the slurry upon rotation and inducing radial and angular motion of the slurry away from said impeller.

The flotation cell of claim 14, wherein said mechanism comprises an upper conduit for delivery of gas to said impeller for dispensing gas bubbles into the slurry to generate a froth of air, liquid and solid particulates that is of lower density than the slurry and thus raises toward the top of said tank. \\melbfiles\home$\MCooper\Keep\Speci\81954.9a-Div.doc 28/05/02 21

16. The flotation cell of claim 14, further comprising a dispenser around said impeller and defining together with the inner periphery of said tank a flow channel for flow of the froth from said dispenser up to said outer launder.

17. The flotation cell of claim 1, wherein said at least one radial launder comprises a plurality of radial portions extending from adjacent said tank periphery generally toward the center of said tank.

18. The flotation cell of claim 12, wherein said baffles are mounted in said tank independent of direct attachment to the interior periphery of said tank.

19. The flotation cell of claim 12, wherein said baffles extend to an upper end and generally above a dispenser in said tank and a lower end generally below said dispenser.

The flotation cell of claim 13, wherein said opening is positioned below a baffle and a impeller.

21. The flotation cell of claim 14, further comprising a draft tube extending from adjacent said lower end tank up to said impeller.

22. A froth flotation cell, comprising: a tank; a mechanism disposed in the tank for suspending mineral particulates and dispersing air bubbles in a pulp phase or slurry in said tank, thereby aiding in a generation of forth from the pulp phase or slurry; a central launder at the periphery of the tank, the central launder being adapted to remove froth from the tank during operation of the flotation cell; and a secondary launder in the tank, said secondary \\melbfiles\homeS\MCooper\Keep\Spei\81954.98-Div.dec 28/05/02 22 launder discharging froth from within the tank to a selected location during operation of the flotation cell.

23. The flotation cell as defined in claim 22, further comprising at least one radial launder in fluid communication with said central launder and the secondary launder to enhance the recovery and discharge of the froth from the tank.

24. The flotation cell as defined in claim 22, further comprising at least one baffle plate disposed in the tank for reducing the angular motion of the froth in the tank.

25. The flotation cell as defined in claim 23, wherein said central launder, secondary launder and the radial launder each have an upper surface coplanar with the other launders.

26. A flotation cell according to any one of claims 1 to 25 substantially as described herein with reference to and as illustrated in Figures 6 to 9 of the accompanying drawings. Dated this 2 9 th day of May 2002 BAKER HUGHES INCORPORATED By their Patent Attorneys GRIFFITH HACK Fellows Institute of Patent and Trade Mark Attorneys of Australia \\melb_files\home$\MCoper\Keep\Speci\81954 .98-Div.doc 28/05/02