WO2000051743A1

WO2000051743A1 - Flotation cell with vortex stabilizer

Info

Publication number: WO2000051743A1
Application number: PCT/US2000/004986
Authority: WO
Inventors: Hayward B. Oblad; Dariusz Lelinski
Original assignee: Baker Hughes Incorporated
Priority date: 1999-03-05
Filing date: 2000-02-28
Publication date: 2000-09-08
Also published as: AU3709000A

Abstract

In a froth flotation cell including a tank (62), a rotor or impeller (10) disposed in the tank (62) for rotation about a substantially vertical axis, and a disperser (22) disposed in the tank (62) about the rotor (10) and the axis, a vortex stabilizing member (46) is disposed in the tank (62) proximate to an upper end of the rotor (10) and an upper end of the disperser (22) so as to limit upward travel of a slurry vortex (38) generated by rotation of the rotor (10). The vortex stabilizing member (46) generally takes the form of a flat or curved ring secured to a lower end of a standpipe (28) above the rotor (10) and the disperser (22).

Description

FLOTATION CELL WITH VORTEX STABILIZER

BACKGROUND OF THE INVENTION This invention relates to froth flotation cells. This invention also relates to an associated vortex stabilizer for froth flotation cells and to a method for stabilizing a vortex in a froth flotation cell.

Froth flotation cells are used to separate mineral values from mineral wastes. Finely divided ores are suspended as water-based slurries 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 distribute or disperse air bubbles into the slurry. Some of the minerals attach to the air bubbles. The bubbles with the entrained minerals then 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. The balance of the minerals in the slurry exit the cell and may also be further processed. 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 machines of some of these references, air is supplied to the pulp or slurry via a separate pumping mechanism.

The rotor is designed to simultaneously draw slurry upwardly from the pool and suck air downwardly through a standpipe disposed above the rotor. The slurry and air are forced by rotation of the rotor radially outwardly through a disperser disposed about the rotor. During flotation cell operation, the rotation of the impeller imparts rotational energy to the pulp or slurry pool. This rotational energy generates a vortex inside the disperser and the standpipe. A problem with the vortex is its instability. Unavoidable irregularities in operating parameters such as air pressure and overpumping by the impeller or rotor cause the vortex to periodically rise and fall, producing surface waves in the slurry outside of the disperser. Every time the vortex falls, a wave crest is produced on the surface of the slurry pool. Conversely, the rising of the vortex along the inside surface of the standpipe generates a trough on the surface of the slurry pool. The surface waves in the slurry pool are sometimes considered undesirable. More particularly, some operators of froth flotation cells believe that the waves are detrimental to metallurgical performance and profitability when it is necessary to operate the flotation cell with a thin froth. Surface waves containing pulp tend to wash over the weir with the froth concentrate and degrade the separation effected.

The unstable vortex can also contribute to machine vibration. Sometimes, the vibration, caused also by rotor rotation itself, can become pronounced, thus dissipating the vibrational energy throughout the flotation cell superstructure or a portion thereof Parts of the rotor and superstructure may fatigue and fail after prolonged, severe vibration. SUMMARY OF THE INVENTION

The present invention is directed to the problem of stabilizing the vortex produced in the slurry pool of a froth flotation cell between the rotor and the disperser. The invention basically inserts a vortex stabilizing member at the upper end of the rotor and the disperser, which acts like a dam, preventing or at least inhibiting the rotating slurry from rising significantly above the disperser, inside the standpipe, up the wall thereof. This measure not only reduces wave motion of the slurry pool but also reduces lateral shifts in the vortex, thus generally stabilizing the vortex.

A froth flotation cell comprises, in accordance with the present invention, a tank, a rotor or impeller disposed in the tank for rotation about a substantially vertical axis, a disperser disposed in the tank about the rotor and the axis, and a vortex stabilizing member disposed in the tank proximate to an upper end of the rotor and an upper end of the disperser so as to limit upward travel of a slurry vortex generated by rotation of the rotor. The rotor and the disperser cooperate to suspend mineral particulates and disperse air bubbles in a pulp phase or slurry in the tank, thereby aiding in a generation of froth from the pulp phase or slurry.

The vortex stabilizing member is preferably fixed relative to the disperser. The vortex stabilizing member may be connected directly to an upper end of the disperser. Alternatively, the vortex stabilizing member may be integral with or attached to a standpipe in turn connected to the disperser.

Where the flotation cell tank is provided with a standpipe connected to the disperser and extending upwardly therefrom, the vortex stabilizing member may be disposed inside the standpipe at a lower end thereof. The vortex stabilizing member may be bolted to the standpipe or press-fit against an inwardly turned flange thereof by steel struts. These methods of attachment are particularly effective where the vortex stabilizing member is being retrofitted to an existing machine. Alternatively, in the case of a new machine, the vortex stabilizing member may be integrally formed with (e.g., welded to) the standpipe and/or the disperser. Preferably, the vortex stabilizing member extends inwardly from a wall of the standpipe and defines a central opening larger than the rotor so as to enable removal of the rotor from the tank via the opening. Alternatively, the central opening in the vortex- stabilizing member may be smaller than the rotor. In that case, the rotor is removed as part of an assembly including the standpipe and the vortex-stabilizing member. In a specific implementation of this alternative construction, the standpipe is a tubular member which surrounds the rotor's drive shaft and is provided at a lower end with a flange functioning as the vortex stabilizing member. The flange extends outwardly from the lower end of the standpipe and is connected along a radially outer periphery to the disperser.

The standpipe may be formed of an upper part and a lower part connected to one another along respective annular flanges. In that case, the vortex stabilizing member is disposed inside, and connected to, the lower part.

Preferably, the vortex stabilizing member is an annular metal body coated with a layer of protective abrasion-resistant material such as rubber. Although perforations may be provided in the annular body, for example, to reduce the weight thereof, the annular body is preferably a solid ring. That ring may be planar or, alternatively, a toroidal section having an annular concave lower surface. In other configurations of the vortex stabilizing member contemplated by the present invention, the vortex stabilizing member is made of multiple parts connected at least indirectly to the disperser. In a particular embodiment of the invention, the standpipe is shortened and includes an upper wall extending generally transversely to an axis of rotation of the rotor. The upper wall serves as the vortex stabilizing member.

The present invention is also directed to a retrofit assembly for a froth flotation cell having a tank, a rotor disposed inside the tank, and a disperser disposed about the rotor. The retrofit assembly comprises a vortex stabilizing member and fastener components for fixing the vortex stabilizing member at least indirectly to the disperser at an upper end thereof, so that the vortex stabilizing member is disposed inwardly from the upper end of the disperser so as to limit upward travel of a slurry vortex generated by rotation of the rotor inside the disperser.

The vortex-stabilizing member is preferably an annular body, i.e., a vortex stabilizing ring. The ring may be a unitary structure or, alternatively, made of a plurality of connected parts. The ring may be planar, conical, or a toroidal section having an annular concave lower surface. The concave lower surface serves in part to turn a rising vortical flow inwardly into an upper end of the rotor, thereby recirculating the slurry.

Where a pre-existing froth flotation cell selected for a retrofit includes a standpipe disposed in the tank above the rotor and the disperser, the vortex-stabilizing member generally has predetermined external dimensions smaller than internal dimensions of the standpipe. The attachment components are adapted to connect at least indirectly to the standpipe so that the vortex-stabilizing member is disposed inside the standpipe.

In one preferred embodiment of the invention, the vortex-stabilizing member is a metal ring-shaped plate provided with a coating of a wear-resistant material such as rubber or polytetrafluoroethylene and having a central opening larger than the rotor so as to enable removal of the rotor from the tank via the opening. A related method for improving the operation of a froth flotation cell wherein a rotor rotates inside a disperser comprises, in accordance with the present invention, providing a vortex stabilizing member and fixing that member at least indirectly to the disperser proximate to an upper end thereof, so that the vortex stabilizing member extends inwardly from the upper end of the disperser so as to limit upward travel of a slurry vortex generated by rotation of the rotor inside the disperser.

In an associated method for operating a froth flotation cell, a rotor is rotated inside a disperser of the froth flotation cell, the disperser and the rotor being disposed in a tank containing a slurry. By virtue of rotor rotation, a vortex is generated inside said disperser from the slurry. Proximate to an upper end of the disperser, upward travel of the vortex is blocked to thereby stabilize motion of the vortex. The blocking of the vortex is achieved by fixing a vortex stabilizing member proximately to an upper end of the disperser and inwardly from the disperser . A vortex stabilizing member or assembly in accordance with the present invention serves to stabilize and calm the vortex which appears between the rotor and the disperser. The vortex stabilizing member or assembly functions like a dam to restrict the ability of the vortex to climb along the inner surface of the standpipe. Surging and oscillation of the vortex are substantially reduced, if not eliminated. Concomitantly, surface waves in the slurry pool are significantly reduced. Separation of mineral values is enhanced, particularly where the machine is operated with a thin layer of froth on the surface of the slurry pool. In addition, machine integrity is preserved over a relatively long period owing to a reduction in machine vibration.

A vortex stabilizing member or assembly in accordance with the present invention is extremely simple in concept, design, and function. The member or assembly is easy to build, transport, and install.

BRIEF DESCRIPTION OF THE DRAWING Fig. 1 is a partial diagrammatic side elevational view of operating structures of a conventional froth flotation cell, indicating a slurry vortex and movement thereof during flotation cell operation.

Fig. 2 is a schematic side elevational view, partially in cross-section, of operating structures of a froth flotation cell with a vortex stabilizing ring in accordance with the present invention. Fig. 3 is a schematic perspective view of the vortex stabilizing ring of Fig. 2 and attachment or mounting struts.

Fig. 4 is a schematic perspective view of another vortex stabilizing ring in accordance with the present invention. Fig. 5 is a schematic side elevational view similar to Fig. 2, showing the vortex stabilizing ring of Fig. 3 installed in structures of the froth flotation cell of Fig. 2 in place of the vortex stabilizing ring of Figs. 2 and 3.

Fig. 6 is a diagrammatic side elevational view of operating structures of a modified froth flotation cell in accordance with the present invention, showing a vortex stabilizing ring as illustrated in Figs. 2 and 3.

Fig. 7 is a diagrammatic side elevational view similar to Fig. 6, showing a vortex stabilizing ring as illustrated in Figs. 4 and 5.

Fig. 8 is a diagrammatic side elevational view of operating structures of a further modified froth flotation cell in accordance with the present invention. Fig. 9 is a schematic side elevational view of operating structures of froth flotation cell with a vortex-stabilizing member extending outwardly from a lower end of a narrow standpipe, in accordance with the present invention.

Fig. 10 is a schematic side elevational view similar to Fig. 9, showing a modification of the froth flotation cell of that drawing figure. Fig. 11 is a schematic side elevational view similar to Fig. 9, showing another modification of the froth flotation cell of that drawing figure.

Fig. 12 is a schematic side elevational view similar to Fig. 9, showing yet another modification of the froth flotation cell of that drawing figure.

Identical structural elements in the various drawing figures are identified by the same reference numerals.

DESCRIPTION OF THE PREFERRED EMBODIMENTS As illustrated in Fig. 1, a froth flotation cell generally includes a rotor or impeller 10 fastened to a lower end of a drive shaft 12 in turn connected to an output shaft 14 of a motor 16 via a plurality of belts 18 and sheaves 20. An annular disperser 22 is disposed about rotor 1, generally coaxially with a rotation axis 23 thereof, and is provided with apertures 24 through which a mixture of air and mineral laden water passes, as indicated by arrows 26, so as to generate a bubbly froth. Disperser 22 is fastened to and suspended from a lower end of a vertical standpipe 28 in turn mounted to a cross beam (not shown) positioned across upper edges of tank walls (not shown). An upper end of disperser 22 is surrounded by a conical hood 29 which, like disperser 22 is attached to a flange (not shown) at a lower end of standpipe 28.

As indicated by an arcuate arrow 30, rotor 10 is rotated at a high speed in a slurry pool to suspend the mineral particulates and to cooperate with disperser 22 to distribute or disperse air bubbles into the slurry. Certain minerals attach to the air bubbles. The bubbles with the entrained minerals then rise to form a froth (not illustrated) overlying an upper surface 32 of a pulp or slurry pool (not separately designated) . 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 Ny an 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., the disclosures of which are all hereby incorporated by reference.

Rotor 10 is designed so as to simultaneously draw slurry upwardly from the pool and suck air downwardly through standpipe 28. Standpipe 28 is provided with an air inlet 34 for the introduction of air, as represented by an arrow 36. The slurry and air are forced by rotation of rotor 10 radially outwardly through apertures 24 in disperser 22.

During flotation cell operation, rotation of rotor 10 generates a vortex 38 inside disperser 22 and standpipe 28. Vortex 38 rises and falls along an inner surface (not separately designated) of standpipe 28, as indicated by an arrow 40, between an upper position 42 and a lower position 44, concomitantly producing waves in surface 32 of the slurry outside of disperser 22.

Fig. 2 shows the flotation cell of Fig. 1 with a vortex stabilizing ring 46 installed inside standpipe 28 at a lower end thereof. Ring 26 functions as a barrier which limits upward travel of vortex 38 along the inner surface of standpipe 28. This restriction on vortex 38 inside disperser 22 and standpipe 28 stabilizes the vortex and substantially inhibits, if not eliminates, vertical oscillations of the vortex. In addition, lateral migrations or shifting of the vortex is decreased. The result of stabilization of vortex 38 is that waves in slurry pool surface 32 (Fig. 1) are significantly reduced, as symbolically represented at 48 in Fig. 2.

Vortex stabilizing ring 46 is basically a barrier or dam which serves to prevent or at least inhibit the rotating slurry from rising significantly above disperser 22, up a sidewall 50 of standpipe 28. Ring 46 is preferably disposed inside standpipe 28 just above rotor 10.

Ring 46 is generally made of rubber coated metal. However, other abrasion- resistant materials may be used to coat the metal body to provide protection against wear. As illustrated in Figs. 2 and 3, ring 46 is pressed or clamped against a lower flange (not shown) of standpipe 28 by a plurality of steel struts 52 secured at an upper end against an upper wall 54 of standpipe 28. Ring 46 is formed of two parts 56 and 58 connected to one another via flanges 60. The two part construction facilitates a retrofit installation of ring 46 in an existing froth flotation cell defined along a periphery by a tank 62.

Various alternative modes of fixing ring 46 to standpipe 28 will occur to those skilled in the art. For example, ring 46 may be provided with a plurality of upstanding tabs 64 (Fig. 3) which may be bolted to sidewall 50 of standpipe 28. Welding, particularly in new machines, is also possible. In that case, the rubber coating on ring 46 is preferably applied after the welding operation.

Ring 46 is provided with a central opening or aperture 65 with a diameter which is larger than the diameter of rotor 10. It is then possible to remove rotor 10 from tank 62 via opening 65 without removing ring 46 or standpipe 28. Thus, manual access to rotor 10 for repair or maintenance purposes is facilitated.

As depicted in Figs. 4 and 5, another vortex stabilizing member 66 for a froth flotation cell takes the form of a toroidal section having an annular convex upper surface 68 and an annular concave lower surface 70. Vortex-stabilizing member 66 may be conceptually formed by slicing a doughnut-shaped hollow torus along a plane oriented peφendicularly to an axis of the torus. Mathematically, member 66 is formed by revolving a shallow C or U shape about a toroidal axis. Fig. 5 shows toroidal vortex-stabilizing member 66 installed inside standpipe 28 at a lower end thereof, just above disperser 22 and rotor 10. Member 66 is attached to standpipe 28 by any of various techniques including bolting, welding, and clamping. To facilitate retrofit installation in existing flotation cells, member 66 may be made of two parts 72 and 74. Tabs 76 may be provided on member 66 for bolting the member to standpipe 28. Annular or toroidal vortex-stabilizing member 66 is formed with a central opening or aperture 78 with a diameter which is larger than the diameter of rotor 10, for enabling extraction of rotor 10 from tank 62 without necessitating removal of member 66 or standpipe 28. Thus, manual access to rotor 10 for repair or maintenance purposes is facilitated. Fig. 6 illustrates a modified froth flotation cell utilizing vortex stabilizing ring 46 described above with reference to Figs. 2 and 3. Standpipe 28 of Fig. 2 is replaced by a standpipe 80 having an upper part 82 and a lower part 84 connected to one another via respective flanges 86 and 88 and bolts 90. Vortex stabilizing ring 46 is fixedly secured to lower standpipe part 84. As depicted in Fig. 7, another modified froth flotation cell utilizes toroidal member

66, disclosed above with reference to Figs. 4 and 5, and further incoφorates two-part standpipe 80, discussed above with reference to Fig. 6. Thus, standpipe 28 of Fig. 5 is replaced by standpipe 80 which comprises upper part 82 and lower part 84 interconnected by flanges 86 and 88 and bolts 90. Toroidal member 66 is fixedly secured to lower standpipe part 84.

In yet another vortex-stabilized froth flotation cell, shown in Fig. 8, disperser 22 is attached to a lower end of a shortened standpipe 92. Standpipe 92 has a sidewall 94 of reduced height, which brings an upper wall 96 into sufficient proximity to rotor 10 and the upper end of disperser 22 to effectively limit upward migration of a slurry vortex, thereby stabilizing the vortex and reducing surface waves in slurry, as symbolically represented at 48. Upper wall 96 thus functions as a barrier or dam restricting upward movement of a vortex generated by rotation of rotor 10. Upper wall 96 is provided with an air inlet 98 for air introduction at 100. Upper wall 96 may be provided with an optional seal (not shown) about drive shaft 12. The seal, however, is not critical, inasmuch as air is necessarily being drawn into standpipe 92 via inlet 34.

In an experiment testing the invention, a vortex stabilization ring fabricated from a plastic plate was mounted inside a standpipe of a WEMCO^® flotation machine. Prior to the installation of the vortex stabilization ring, the wave on the surface of the slurry pool in the flotation cell had an amplitude of approximately 6 inches and was highest when the rotor speed was about 180 rpm. After installation of the vortex stabilization ring, the amplitude of the wave was reduced to 1 inch or less and the surface of the slurry pool was concomitantly flattened. The outer diameter of this vortex stabilization ring was 31 inches, while the inner diameter was approximately 19 inches and the thickness was approximately 1/4 inch. The vortex stabilization ring was positioned at the bottom of the standpipe of the flotation cell, parallel to the floor. The ring was supported on a 1-inch ledge on the inner circumference of the standpipe and held down with steel struts. As illustrated in Fig. 9, a modified froth flotation cell includes a standpipe 102 in the form of a tubular member having a diameter substantially smaller than the diameter of rotor 10. At a lower end, standpipe 102 is provided with an outwardly extending planar flange 104 connected to an upper end of disperser 22 and to hood 29. Flange 104 functions as a vortex-stabilizing member which blocks upward motion of a slurry vortex and thereby reduces waves in a slurry pool outside of the disperser 22.

As shown in Fig. 10, a narrow tubular standpipe 106 is provided at a lower end with an outwardly extending conical flange 108 connected to an upper end of disperser 22 and to hood 29 via a cylindrical skirt 110. Conical flange 108 also serves as a vortex- stabilizing member which limits upward migration of a slurry vortex, thereby stabilizing the vortex and reducing wave motion in a slurry pool outside of the disperser 22.

Fig. 11 depicts a froth flotation cell with a narrow tubular standpipe 112 provided at a lower end with an outwardly extending conical flange 114 connected to an upper end of disperser 22 and to hood 29. Conical flange 114 tapers in an upward direction, whereas conical flange 108 tapers in a downward direction.

According to Fig. 12, a narrow tubular standpipe 116 is provided at a lower end with a toroidal section 118 concave in a downward direction. Toroidal section 118 is connected along an inner periphery to tubular standpipe 116 and along an outer periphery to an upper end of disperser 22 and to hood 29.

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

Claims

WHAT IS CLAIMED IS:

1. A froth flotation cell comprising: a tank; a rotor disposed in said tank for rotation about a substantially vertical axis; a disperser disposed in said tank about said rotor and said axis, said rotor and said disperser cooperating to suspend mineral particulates and disperse air bubbles in a pulp phase or slurry in said tank, thereby aiding in a generation of froth from said pulp phase or slurry; and a vortex stabilizing member disposed in said tank proximate to an upper end of said rotor and an upper end of said disperser so as to limit upward travel of a slurry vortex generated by rotation of said rotor.

2. The flotation cell defined in claim 1 wherein said vortex stabilizing member is fixed relative to said disperser.

3. The flotation cell defined in claim 2 wherein said vortex stabilizing member is disposed above said rotor and said disperser.

4. The flotation cell defined in claim 3 wherein said tank is provided with a standpipe connected to said disperser and extending upwardly therefrom, said vortex stabilizing member being disposed inside said standpipe at a lower end thereof.

5. The flotation cell defined in claim 4 wherein said vortex stabilizing member extends inwardly from said standpipe and defines a central opening larger than said rotor so as to enable removal of said rotor from said tank via said opening.

6. The flotation cell defined in claim 5 wherein said vortex stabilizing member is an annular body.

7. The flotation cell defined in claim 6 wherein said vortex stabilizing member has an annular concave lower surface.

8. The flotation cell defined in claim 2 wherein said vortex stabilizing member extends radially inwardly from said disperser.

9. The flotation cell defined in claim 1 wherein said tank is provided with a standpipe connected to said disperser and extending upwardly therefrom, said vortex stabilizing member being disposed inside said standpipe at a lower end thereof.

10. The flotation cell defined in claim 9 wherein said vortex stabilizing member extends inwardly from said standpipe and defines a central opening larger than said rotor so as to enable removal of said rotor from said tank via said opening.

11. The flotation cell defined in claim 9 wherein said standpipe includes an upper part and a lower part connected to one another along respective annular flanges, said vortex stabilizing member being disposed inside said lower part.

12. The flotation cell defined in claim 1 wherein said tank is provided with a standpipe disposed above said rotor, said vortex stabilizing member extending outwardly from a lower end of said standpipe.

13. The flotation cell defined in claim 12 wherein said vortex stabilizing member extends substantially annularly about an axis of rotation of said rotor, said vortex stabilizing member being connected on a radially inner side to said standpipe and on a radially outer side to said disperser.

14. The flotation cell defined in claim 1 wherein said vortex stabilizing member is an annular body.

15. The flotation cell defined in claim 14 wherein said vortex stabilizing member includes a toroidal section having an annular concave lower surface.

16. The flotation cell defined in claim 1 wherein said vortex stabilizing member is disposed above said rotor and said disperser.

17. The flotation cell defined in claim 1 wherein said vortex stabilizing member is a ring.

18. The flotation cell defined in claim 1 wherein said vortex stabilizing member includes a metal part coated with a layer of protective wear-resistant material.

19. The flotation cell defined in claim 1 wherein said tank is provided with a standpipe connected to said disperser and extending upwardly therefrom, said vortex stabilizing member being an upper wall of said standpipe.

20. An assembly for a froth flotation cell having a tank, a rotor disposed inside said tank, and a disperser disposed about said rotor, comprising: a vortex stabilizing member; and fastener components for fixing said vortex stabilizing member at least indirectly to said disperser at an upper end thereof, so that said vortex stabilizing member is disposed inwardly from the upper end of said disperser so as to limit upward travel of a slurry vortex generated by rotation of said rotor inside said disperser.

21. The assembly defined in claim 20 wherein said vortex stabilizing member is an annular body.

22. The assembly defined in claim 19 wherein said vortex stabilizing member includes a toroidal section having an annular concave lower surface.

23. The assembly defined in claim 20 wherein said froth flotation cell includes a standpipe disposed in said tank above said rotor and said disperser, said vortex stabilizing member having external dimensions smaller than internal dimensions of said standpipe, said attachment components being connectable at least indirectly to said standpipe so that said vortex stabilizing member is disposed inside said standpipe

24. The assembly defined in claim 20 wherein said vortex stabilizing member includes a metal body provided with a coating of a wear-resistant material.

25. The assembly defined in claim 20 wherein said vortex stabilizing member defines a central opening larger than said rotor so as to enable removal of said rotor from said tank via said opening.

26. The assembly defined in claim 20 wherein said vortex stabilizing member is a ring.

27. The assembly defined in claim 20 wherein said vortex stabilizing member is a plate.

28. A method for improving operation of a froth flotation cell having a rotor rotating inside a disperser, comprising: providing a vortex stabilizing member; disposing said vortex stabilizing member proximately to an upper end of the disperser and inwardly from said disperser; fixing said vortex stabilizing member at least indirectly to said disperser proximate to the upper end thereof, so that said vortex stabilizing member is disposed inwardly from the upper end of said disperser so as to limit upward travel of a slurry vortex generated by rotation of said rotor inside said disperser.

29. The method defined in claim 28 wherein said froth flotation cell includes a standpipe disposed above said rotor and said disperser, the fixing of said vortex stabilizing member including attaching said vortex stabilizing member to said standpipe so that said vortex stabilizing member is disposed inside said standpipe.

30. A method for operating a froth flotation cell, comprising: rotating a rotor inside a disperser of the froth flotation cell, said disperser and said rotor being disposed in a tank containing a slurry; by virtue of the rotating of said rotor, generating, inside said disperser, a vortex from said slurry; and blocking upward travel of said vortex to thereby stabilize motion of said vortex.

31. The method defined in claim 30 wherein the blocking of said vortex includes fixing a vortex stabilizing member proximately to an upper end of said disperser and inwardly from said disperser .