AU2011350656A1

AU2011350656A1 - Flotation machine

Info

Publication number: AU2011350656A1
Application number: AU2011350656A
Authority: AU
Inventors: Don J. Foreman; Jouko Kallioinen
Original assignee: FLSmidth AS
Current assignee: FLSmidth AS
Priority date: 2010-12-28
Filing date: 2011-12-28
Publication date: 2013-07-11
Also published as: BR112013016633A2; WO2012090167A2; WO2012090167A3; ZA201304793B

Abstract

A flotation machine for extracting floatable minerals from a slurry by simultaneously agitating and aerating the material while continuously diluting the slurry in the area of the machine where it is being agitated.

Description

WO 2012/090167 PCT/IB2011/055988 FLOTATION MACHINE Background of the Invention 5 This invention relates to an improved flotation separation apparatus for separating valuable minerals from slurries received from grinding mills, cyclone or the like. In a flotation separation process utilized to separate a valuable mineral from its ore, the ore is initially crushed to a fine powder and is then mixed with a liquid such as water to form a finely 10 ground, solid/liquid, flowable mixture called a slurry or pulp. Wetting agents are added to the slurry which selectively wet the surface of the mineral sought to be separated. This slurry is introduced to a flotation separation vessel where it is agitated and aerated. Air is dispersed in the slurry during agitation and minerals which have been wetted by the added agent attach to small air bubbles and rise in the vessel, eventually to accumulate in a froth near the top of the slurry 15 mass. The froth is withdrawn from the vessel generally through an upper outlet and the non floatable tailings of residue components are withdrawn generally through a lower outlet. The tailings contain coarse material which is typically sent for regrinding. In one form of flotation vessel, a rotor-stator assembly is positioned near the bottom of the vessel. 20 There are numerous forms of rotor-stator assemblies known. As one example, the rotor comprises a plurality of radially extending blades which are rotated in a central space or cavity defined by an annular array of stator blades. In any form of rotor-stator combination, the circular motion of the rotor agitates and establishes a flow of slurry. An aeration system is also provided to disperse air under pressure into the agitator and hence into the slurry- generally through an 25 axially extending, substantially vertical, central passageway located within the hollow drive shaft of the rotor. As the bubbles from the aerated slurry rise toward the surface of the vessel they carry with them floatable particles which form the mineral enriched froth. The slurry introduced into the vessel will have a heterogeneous mixture of solid material, and in 30 flotation vessels of the type described above there will be areas within the vessel in which there are concentrations of slurry having different densities. Typically there will be a concentration of higher density slurry, that is, a slurry containing a comparatively high percentage of solids, near the bottom of the vessel in the vicinity of the rotor and stator, and under such conditions the WO 2012/090167 PCT/IB2011/055988 process of the particles attaching to the bubbles is hampered with a resulting loss of operating efficiency. A prior art solution is to dilute, that is decrease the solids content of, the slurry introduced into 5 the vessel by adding water to an upstream grinding stage to achieve acceptable pulp density. This can result in decreasing the effectiveness and capacity of the grinding circuit. By employing this solution the operator has to compromise in part between the grinding capacity of the upstream mill and the efficiency of the flash flotation process. Furthermore, the slurry that moves toward the bottom of the vessel near the rotor/stator will still have significantly higher solids content than 10 slurry located further up in the vessel. An alternative prior art solution is to remove a portion of slurry from the flotation vessel, add water to this slurry and re-circulate it to the cell to dilute the cell sufficiently to achieve good flotation. This is not an ideal solution in that it requires equipment, piping and controls to 15 accomplish and it reduces the residence time in the flotation cell. It is an object of the present invention to provide an improved flotation separation vessel and process that overcomes the above disadvantages of the prior art. 20 The above object and other advantages of the present invention are achieved by selectively diluting the slurry in the vicinity of the rotor, for example within the confines of the stator, preferably by transporting lower density slurry from another area of the flotation cell to the vicinity of the rotor. In one embodiment of the invention there is provided a slurry delivery conduit that serves to both (1) support the stator component, that is, the delivery conduit extends 25 downward into the flotation vessel with its lower end attached to and supporting the stator; and (2) deliver comparatively low density slurry from the upper areas of the flotation vessel to mix with and thereby dilute the solids content of the higher density slurry in the vicinity of the rotor. Brief Description of the Drawing 30 The invention is described in more details in the following drawings wherein Figure 1-3 illustrate various embodiments of the invention as schematic cut away side-views. 2 WO 2012/090167 PCT/IB2011/055988 Throughout the specification and drawings identical reference numerals refer to identical or similar parts. The drawings are not drawn to scale. Detailed Description of the Invention 5 Referring to Figure 1, the invention provides a flotation apparatus 100 comprising a vessel or tank 11 to contain a slurry having minerals to be extracted. The tank is defined by generally cylindrical side walls 12, a bottom section 13, which as depicted is conical, but which can be other shapes, including straight, parabolic or arc shaped. An agitator means is closer to the bottom than the top of the vessel to impart net a rotational force to the contents of the vessel about a vertical axis of 10 the vessel and thereby mix the slurry within the tank. In the depicted embodiment the agitator comprises a rotor 14 supported for rotation within a surrounding stator 15, which in one embodiment comprises an annular array of blades extending transversely to a central axis and forming a central cavity. Rotor 14 is supported by and rotated by a hollow drive shaft 16 that extends downwardly into the tank and rotates about a vertical axis of the tank. Rotor 14 is 15 attached to a bottom portion of the drive shaft. The top portion of drive shaft 16 is attached above the slurry level, such as onto the overhead supporting structures of the vessel, and is rotated by motor 18. During rotary motion of rotor 14, an aeration system is utilized to convey a gas to the rotor from a 20 source, not shown, via an axial passageway 17 in drive shaft 16. The gas flows down passageway 17 preferably to a location adjacent rotor 14 and the rotation of the rotor forces the gas and slurry radially outwardly through stator 15. While various gases may be utilized, a preferred gas is air. 25 The feed slurry comprising an ore water mixture into which there has been inserted a wetting or frothing agent of a kind and in a quantity well known in the art is introduced into tank 11 via a slurry inlet 19 preferably located in the side wall of tank 11. Coarser and denser particles fall from suspension as they enter the cell, for removal through a discharge outlet 20 in the bottom of tank 11, through which they are discharged from the tank in the form of slurry tailings that are 30 residue rock, clay or sand. The distribution of the slurry in the vessel begins immediately upon its introduction, with the larger and denser solids beginning to settle toward the bottom of the tank. When the slurry is agitated by rotary motion of rotor 14, slurry in the vicinity of the agitator is drawn into the rotor by suction and is then impelled outwards, between the blades of the stator 15, 3 WO 2012/090167 PCT/IB2011/055988 into a dispersion zone that surrounds the agitator. The slurry is further distributed in the tank and particles in the slurry are classified so that the floatable and fine particles are suspended, whereas the unattached and coarser particles sink directly to the bottom of the tank. The combined agitation and aeration creates bubbles and froth which migrate progressively upwardly towards 5 the surface 32 in which there is collected floatable mineral particles suspended in the feed slurry. Near the surface 32, the froth forms an upper layer which flows out tank outlet 21 where it is recovered as flotation concentrate. The coarse and dense components of the slurry form a lower slurry area containing a relatively 10 high pulp density slurry that impedes the ability of minerals to attach to bubbles. The percent by weight solids at which such impedance becomes pronounced to thereby affect froth formation will depend on the nature of the ore being processed, the specific gravity and viscosity of the slurry and other factors. In copper flotation processes the percent by weight solids will typically range from about 65-70% in the vicinity of the rotor and between 35-55% in the upper areas of 15 the flotation cell. Reducing the percent solids by as little as 5%, that is, to about 60-65% percent by weight solids, in the vicinity of the rotor can result in significant benefits to the flotation process As one feature of the invention, stator 15 is supported from above by hollow slurry delivery pipe 20 24, which has an upper end 24b that has a point of attachment located outside the tank, which as depicted is overhead support plate 26. In one embodiment drive shaft 16 is disposed within slurry delivery pipe 24 and is coaxial thereto. Slurry delivery pipe 24 has no required cross sectional shape, and may be configured, for example, with a circular, square, rectangular, oval or trapezoidal cross sectional shape. Drive shaft 16 is spaced apart from delivery pipe 24 to thereby 25 form an annular internal slurry passageway 27 within and coaxial with slurry delivery pipe 24. Slurry passageway 27 has an upper area 27a that is accessible to low density slurry within the tank and a lower area 27b accessible to and above the vicinity of the agitator means. It is a feature of the present invention that the froth producing capacity of the system and 30 therefore its efficiency can be increased by decreasing the undesirable high degree of pulp density in the vicinity of the rotor by continuously introducing slurry that is directly transported from another, lower density, area of the vessel and to thereby have a continuous dilution process. In one embodiment of the invention, the above is accomplished by having at least one slurry inlet 28 in delivery pipe 24 through which low density slurry from area 23, which is in a comparatively 4 WO 2012/090167 PCT/IB2011/055988 upper region of the tank, will enter delivery pipe 24 and thereafter be drawn by the rotor's operation through internal passageway 27 to the vicinity of rotor 14. The direction of movement of slurry from lower density areas of the vessel into conduit 27 and thereafter to the vicinity of the rotor is depicted by arrows 22. The low density slurry will intermix with and dilute the high 5 density slurry located in the vicinity of the rotor to facilitate the ability of particles to adhere to froth bubbles. The size and number of the slurry inlets 28 and the size of passageway 27 and the rate of introduction of low density slurry in the vicinity of the rotor will all depend on factors such as the 10 output of the flotation machine, the pulp density of the slurry near the rotor prior to the introduction of the low density slurry, the size and rate of rotation of the rotor and are adjustable by the skilled practitioner. In one embodiment of the invention, an upper portion of the delivery pipe 24 is positioned within, 15 and is coaxial with, hollow circulating pipe 29, which may be employed to initialize the mixture of the slurry. Circulating pipe 29 has an upper end 29a and is attached, such as by being bolted or welded, to support structure located outside the tank, which as depicted is support plate 26, and an open lower end 29b that extends partially into the tank and is located in vessel area 23 where there is comparatively low density slurry. Circulating pipe 29 is spaced apart from delivery pipe 20 24 to thereby form a passageway for slurry that enters between lower end 29b and pipe 24, is drawn by the pulling force of the circulating rotor upward through the passageway, through slurry inlets 28, into delivery pipe 24 and then downward through pathway 27 to the vicinity of rotor 14. When circulating pipe 29 is not utilized slurry from area 23 will directly enter pipe 24 through inlets 28. Circulating pipe 29 is generally tubular but does not necessarily have a circular 25 horizontal cross section and can alternatively have, for example, a square or hexagonal cross section. For maintenance purposes, the entire mixing mechanism with along with tubes 24 and 29 can be lifted out of the tank as a whole as whole and quickly replaced with a substitute mechanism. The 30 removed mechanism can then be repaired on floor level thus allowing for rapid repair work. Figure 2 depicts an alternative embodiment in which stator 15 is not attached to and supported by delivery pipe 24. Rather, stator 15 is supported on platform 24 which in turn is supported from the bottom section 13 of tank 11. The horizontal cross sectional area of platform 24 is relatively 5 WO 2012/090167 PCT/IB2011/055988 small compared to the horizontal cross sectional area of the vessel at the level where platform 24 is deployed. Consequently, there is amble room at such level for coarse material to fall around platform 24 and settle to the bottom of the vessel. Since delivery pipe 24 is not connected to stator 15 its lower area 27b is open and adjacent to and directly above rotor 14. 5 In another embodiment as shown in Figure 3, diluting fluid compatible for mixing with the slurry, such as water, is directed from outside the vessel to delivery pipe 24 by conduit 40 and thereafter to the vicinity of rotor 14. The delivery rate will be metered by the skilled practitioner to produce slurry in the vicinity of the rotor that will be of a desired solids content to promote particle 10 attachment to the froth bubbles. While there has been described a particular embodiment of the invention, it will be apparent to those skilled in the art that variations may be made thereto without departure from the spirit of the invention and scope of the appended claims. 15 20 25 30 6

Claims

1. A flotation machine for extracting floatable minerals from a slurry containing a frothing agent, the flotation machine comprising: 5 (i) a vessel for holding the slurry; (ii) means to agitate the slurry positioned in the vessel and disposed to agitate the slurry in its vicinity by imparting net rotational force to such slurry; (iii) means to dilute the solids content of the slurry in the vicinity of the agitator means by directing a diluting fluid to such vicinity; 10 (iv) an aeration means to aerate the slurry in the vicinity of the agitator means during agitation to produce floatable material in the form of a froth; and (v) means for removing the froth from the vessel.

2. The flotation machine of Claim 1 wherein the means to dilute operates continuously. 15

3. The flotation machine of Claim 2 wherein the means to dilute comprises a conduit that transports comparatively low solids content slurry from another area of the vessel to the vicinity of the agitator means. 20

4. The flotation machine of Claim 2 wherein the means to dilute comprises a conduit that transports a diluting fluid from outside the vessel to the vicinity of the agitator means.

5. The flotation machine of Claim 4 wherein the diluting fluid is water. 25

6. The flotation machine of Claim 1 wherein the means to agitate comprises (i) a rotor-stator assembly; (ii) a support means for supporting the rotor within a cavity formed by the stator; and (iii) means for rotating the rotor in the vessel. 30

7. A flotation machine for separating a material from a slurry comprising: (i) a tank to hold the slurry, said tank having an upper region and a lower region; (ii a rotor-stator assembly located in the lower region of the tank for mixing the slurry; (iii) means for supplying a gas to the vicinity of the rotor during mixing; and (iv) a hollow support member extending downward into the tank for supporting the stator; and 7 WO 2012/090167 PCT/IB2011/055988 (v) means to transport slurry from a comparatively lower slurry density area located in the upper region of the tank to the vicinity of the assembly to thereby dilute the slurry located in said vicinity. 5

8. The flotation machine of claim 7, wherein the means to transport comprises a conduit for low density slurry located within the support member and coaxial therewith and having a lower end adjacent to the assembly.

9. The flotation machine of claim 8, wherein the support member has at least one slurry inlet to 10 the conduit, said at least one inlet being located in the upper region of the tank adjacent to a low density slurry area within the tank.

10. The flotation machine of Claim 7 wherein the air supply means comprises (i) a hollow rotatable drive shaft extending into said tank from above and having an air 15 passageway therein, with said rotor being suspended from a bottom portion of said shaft; (ii) means to direct air into and through said air passageway and adjacent said rotor and (iii) means to rotate the drive shaft.

11. The flotation machine of Claim 10 wherein the drive shaft is disposed within said stator 20 support member and is coaxial thereto.

12. A method of extracting floatable minerals from a slurry comprising: (i) introducing a slurry containing a frothing agent into a vessel; (ii) simultaneously and continuously, in an agitation area of the vessel, 25 (a) agitating the slurry, (b) aerating the slurry, and (c) diluting the solids content of the slurry, to produce floatable material in the form of a froth; and (iii) removing the froth from the vessel. 30

13. The method of claim 12 wherein the diluting step comprises introducing a comparatively low solids content slurry to the agitation area. 8 WO 2012/090167 PCT/IB2011/055988

14. The method of claim 13 wherein the comparatively low solids content slurry is transported from another area of the vessel to the agitation area.

15. The method of claim 12 wherein the diluting step comprises introducing water to the 5 agitation area.

16. The method of claim 15 wherein water is transported to the agitation area from outside of the vessel. 10 15 20 25 30 o