Froth flotation cells are known in the chemical field, particularly in the metallurgical field, for separation of components from a slurry.

A froth flotation cell of the type known in the art is shown in Figure 1. The flotation cell 10 includes a tank 12 for receiving slurry 14, which typically is introduced into the bottom of the tank. The flotation cell 10 also includes a rotor 16 which is connected to an electric motor 17 via a pulley 19. The rotor agitates the slurry and draws it upwards within the tank by means of a draft tube 20 extending from a false bottom 21. In practice the relationship between the diameter of the rotor 16 and the diameter of the draft tube 20 is an important variable in controlling the movement of slurry within the tank, which is shown by the arrows in Figure 1.

Separation of the slurry occurs by introducing bubbles 22 into the slurry so as to generate a froth 24 which rises to the surface of the slurry and can be removed by overflow into a launder 26. Certain components within the slurry are selectively carried with the froth and thus are separated by flotation from the rest of the slurry. Chemicals may be added to the slurry in order to activate the specific components which are to be selectively floated with the froth.

Typically, the bubbles are introduced into the slurry by means of a compressed-air line. However, generating compressed air is costly and the generators tend to be bulky.

In some froth flotation cells, for example the flotation cell illustrated in Figure 1, bubbles are introduced into the slurry by generating a vortex 28 within a sealed standpipe 30 which extends below the surface of the slurry.

The vortex is generated as a consequence of rotation of the rotor 16 within the slurry, and creates a vacuum in the area 34 above the slurry. The vacuum draws atmospheric air into the standpipe via an air-inlet line 32, and this air is drawn into the slurry to create the bubbles 22 as the slurry is forced through a disperser 36 and a disperser hood 38 by the rotor 16.

With this method, it is possible to generate bubbles without compressed air.

It is an object of the present invention to provide an impeller for enhancing the vortex and improving the generation of bubbles within the slurry.

SUMMARY OF THE INVENTION In this specification, the terms rotor and impeller are used to distinguish different components which have similar features and operate in substantially the same way. The use of different terms is intended to avoid confusion and not to distinguish the features or method of operation of the different components.

According to a first aspect of the invention there is provided an impeller for a froth floatation cell of the type including a draft tube extending from a false bottom, a disperser depending from a standpipe, and a rotor located at least partly within the disperser, the impeller being connectable to the rotor or to a drive shaft for the rotor and comprising: a hub, and at least one spoke formation extending radially from the hub; wherein the diameter defined by the impeller is larger than the diameter defined by the rotor.

In a preferred embodiment of the invention, the hub of the impeller is connectable to the drive shaft of the rotor so that at least a portion of each spoke formation extends axially between blades of the rotor.

Typically, each spoke formation comprises a first deflecting formation connected to the hub, and a second deflecting formation extending from the first deflecting formation.

In one embodiment of the invention, each first deflecting formation defines a first deflecting surface which is substantially vertical, in use. Alternatively, the first deflecting surface may be inclined to the vertical, in use.

Ideally, the second deflecting formation defines a second deflecting surface which is inclined relative to the first deflecting surface.

In a particularly preferred arrangement, the first deflecting formation defines a blade, and the second deflecting formation extends radially outwardly from the blade. In this arrangement, the second deflecting formation may include and upper portion and a lower portion, wherein the upper portion defines two opposed surfaces which slope outwardly and downwardly from an upper edge of the second deflecting formation, and the lower portion defines two opposed surfaces which slope outwardly and upwardly from a lower edge of the second deflecting formation.

In another embodiment, the first deflecting formation defines a blade, and the second deflecting formation extends along a lower edge of the blade.

In this case, the second deflecting formation may comprise an inverted V- shaped channel connected to a lower edge of the blade along an upper edge of the inverted V-shaped channel. Alternatively, the second deflecting formation may comprise a blade which is connected to the lower edge of the first deflecting formation so as to be inclined relative to the first deflecting formation.

The first and/or second deflecting formations may include one or more openings therein.

In another embodiment of the invention, each spoke formation comprises a blade defining a pair of opposed surfaces which slope outwardly and downwardly from an upper edge of the blade.

In yet another arrangement, each spoke formation comprises an elongate limb such as a round bar or the like.

Preferably, the diameter defined by the impeller is marginally smaller than the inner diameter of the standpipe and/or the disperser so that a relatively small gap is defined between the free ends of the spoke formations on the impeller and the inner surface of the standpipe and/or disperser.

The hub may include a locking mechanism for securing the impeller to the rotor or to the drive shaft.

According to a second aspect of the invention there is provided a rotor for a froth floatation cell of the type including a draft tube extending from a false bottom, a disperser depending from a standpipe, and a rotor located at least partly within the disperser, the rotor comprising: a hub, a first rotor formation including at least one rotor blade extending radially from the hub, and a second rotor formation including at least one spoke formation extending radially from the hub, wherein the diameter defined by the second rotor formation is larger than the diameter defined by the first rotor formation.

Preferably, each spoke formation includes at least one deflecting formation extending radially from the hub.

The spoke formations may each include a first deflecting formation and a second deflecting formation. In this arrangement, the first deflecting formation typically comprises a blade which is substantially vertical or inclined relative to the vertical, and the second deflecting formation extends radially outwardly from the first deflecting formation or along a lower edge thereof.

In a preferred arrangement, the second deflecting formation includes an upper portion and a lower portion, wherein the upper portion defines two opposed surfaces which slope outwardly and downwardly from an upper edge of the second deflecting formation, and the lower portion defines two opposed surfaces which slope outwardly and upwardly from a lower edge of the second deflecting formation.

The second deflecting formation may comprise an inverted V-shaped channel connected to a lower edge of the blade along an upper edge of the inverted V-shaped channel. Alternatively, the second deflecting formation may comprise a blade which is connected to the lower edge of the first deflecting formation so as to be inclined relative to the first deflecting formation.

Typically, at least a portion of each spoke formation extends axially between each rotor blade.

Preferably, the first rotor formation is offset axially from the second rotor formation, and each spoke formation is offset radially from each rotor blade.

In one embodiment of the invention, each rotor blade and each spoke formation includes a pair of opposed surfaces which taper inwardly from a free end of the rotor blade or spoke formation towards the hub.

The invention extends to a froth flotation cell including an impeller or a rotor as described above.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will now be described in more detail, by way of example only, with reference to the accompanying drawings in which: Figure 1 shows, diagrammatically, a cross-sectional view of a froth flotation cell of the type known in the art; Figure 2 shows a side view of a first embodiment of an impeller according to a first aspect of the present invention, connected to a drive shaft of a rotor; Figure 3 shows a plan view of the impeller illustrated in Figure 2; Figure 4 shows a perspective view of the impeller illustrated in Figure 2; Figure 5 shows a perspective view of an impeller according to a second embodiment of the invention; Figure 6 shows a perspective view of an impeller according to a third embodiment of the invention; Figure 7 shows a perspective view of an impeller according to a fourth embodiment of the invention; Figure 8 shows a perspective view of the impeller of Figure 7 attached to a rotor; and Figure 9 shows a perspective view of a rotor according to a second aspect of the invention.

DETAILED DESCRIPTION OF THE INVENTION Figure 2 of the drawings illustrates an impeller 50 which is connectable to a drive shaft 18 of a rotor 16 for a froth flotation cell 10 of the type known in the art, for example the froth floatation cell described above with reference to Figure 1.

The impeller 50 includes a hub 52 in the form of an elongate metal tube, and eight spoke formations designated generally with the reference numeral 56. The diameter of the hub 52 is selected so that it can be located over the drive shaft 18, and two locking bolts 54 protrude through the wall of the hub so as to lock the impeller 50 to the drive shaft. The locking bolts 54 are arranged on opposed sides of the hub 52 to ensure that the hub is properly balanced. It will be appreciated that various other locking mechanisms could be used to lock the impeller 50 to the drive shaft 18, and that the impeller could also be locked to the rotor 16 rather than to the drive shaft.

The hub 52 is coated in a high-density polyurethane material to protect it from corrosion inside a froth flotation cell. Alternatively, the hub could be formed from a material which is resistant to corrosive attack so as to eliminate the need for the coating.

As can be seen more clearly in Figure 3, the spoke formations 56 are arranged at regular intervals around the circumference of the hub 52, and each spoke formation is located between a pair of adjacent rotor blades 40.

Although the embodiment of the invention illustrated in Figures 2 and 3 of the accompanying drawings illustrates eight spoke formations, it will be understood that the impeller 50 could include a different number of these formations, for example 2,3 or 6. It will also be appreciated that the number of spoke formations could vary depending on the number of rotor blades, which need not be eight. The diameter defined by the impeller 50 is seen in Figure 3 to be larger than the diameter defined by the rotor 16.

In this embodiment, the diameter of the spoke formations 56 is marginally smaller than the inner diameter of the disperser 36 so that a relatively small gap is defined between the free ends of the spoke formations on the impeller 50 and the inner surface of the disperser.

Similarly to the hub 52, each spoke formation 56 is formed from metal and is coated in a high-density polyurethane. However, as indicated above, the spoke formations could be formed from a material which is resistant to corrosive attack so as to eliminate the need for the coating.

Figures 2 to 4 illustrate an embodiment of the impeller wherein each spoke formation 56 comprises a first deflection formation in the form of a blade 58, and a second deflection formation in the form of an inverted V-shaped channel 60 which is connected to a lower edge of the blade 58 along an upper edge 62 thereof. Each blade 58 defines a first deflecting surface 59 which is substantially vertical, in use. The blades extend axially along the hub, as shown, and the height of the blades is selected to enhance the vortex in a particular application. Each blade is seen in Figure 4 to define a recess 64 at an inner end thereof so that a portion of each spoke formation 56 can extend axially between two adjacent rotor blades 40. The axial depth to which the spoke formations extend between adjacent rotor blades depends upon the application of the impeller, and can be altered to a certain extent by changing the position of the hub on the drive shaft.

The second deflecting formations could have other shapes to that illustrated in Figures 2 to 4. For instance, one corner of a length of square tubing could be connected to a lower edge of each blade 58 to define a diamond configuration in cross section. Alternatively, one side of the square tubing could be connected to the lower edge of the blade so as to define a square configuration in cross section.

It will be appreciated that the Figures 2 to 4 embodiment of the impeller presents the same deflecting formations regardless of the direction of rotation of the impeller. This is particularly advantageous in that it allows the direction of rotation of the drive shaft to be alternated so as to prevent excessive wear on one side only of the rotor 16 and the impeller 50.

Figure 5 illustrates another embodiment of the impeller according to the invention. As can be seen, in this embodiment each spoke formation 156 comprises a first deflecting formation in the form of a blade 158 and a second deflecting formation in the form of a blade 166. Each blade 158 is connected to a hub 152 at an inner end thereof, and defines a first deflecting surface 159 which is inclined to the vertical, as shown. The blades 166 define second deflecting surfaces 168 which are inclined with respect to the first deflecting surfaces 159.

In this embodiment, the arrangement of the blades 158 and 166 is such that the impeller is designed to rotate only in the direction indicated by the arrow A in Figure 5, and the impeller will not function as effectively if the direction of rotation is reversed.

In Figure 6 there is shown an impeller 250 according to another embodiment of the invention, which is similar to the impellers illustrated in Figures 4 and 5 of the drawings except that each blade 258 defines a pair of opposed surfaces 259 which extend downwardly and outwardly from an upper edge 260, as shown. In this embodiment, the blades are solid and are cast from a high-density polyurethane.

Figures 7 and 8 illustrate a preferred embodiment of the impeller according to the invention. In this embodiment, the impeller 350 is seen to include a hub 352 and eight spoke formations 356 extending radially from the hub.

Each spoke formation includes a first deflecting formation in the form of a blade 358 and a second deflecting formation 366 which is connected to the blade so as to extend radially outwardly from the blade.

The blades 358 define first deflecting surfaces 359, as shown, and each second deflecting formation 366 is seen to include an upper portion 368 which defines a pair of opposed surfaces 370 extending downwardly and outwardly from an upper edge 372 thereof, and a lower portion 374 which defines a pair of opposed surfaces 376 extending upwardly and outwardly from a lower edge 378 thereof.

Similarly to the Figure 6 embodiment, the spoke formations 356 are solid and are cast from a high-density polyurethane.

Figure 8 illustrates the impeller 350 connected to a rotor 380 with eight rotor blades 340. As can be seen, the spoke formations 356 are arranged to extend axially between adjacent rotor blades 340 in a similar manner to that described above with reference to the other embodiments of the invention.

Although not illustrated, one or more blades on the spoke formations of the impeller could include openings in the form of a plurality of holes. Also, in another non-illustrated embodiment of the invention, each spoke formation comprises an elongate limb, for example a round bar or a length of round tubing.

Figure 9 shows a rotor 470 for a froth flotation cell of the type illustrated in Figure 1, according to another aspect of the invention. The rotor 470 includes a hub 472 which is connectable to the drive shaft (not shown) of the rotor.

A first rotor formation 474 is connected to the hub 472 and, in a typical embodiment, includes eight rotor blades 478 which are located at regular intervals around the circumference of the hub 472, as shown. A second rotor formation 476 is also connected to the hub 474 and, in a typical embodiment, includes eight rotor blades 480 which are located at regular intervals around the circumference of the hub.

Although the blades 478 and 480 are regularly spaced around the hub, it will be appreciated that the blades could be offset circumferentially. Also, it will be understood that the first rotor formation 474 and the second rotor formation 476 could have different numbers of rotor blades. In the illustrated embodiment, the first and second rotor formations are formed in one piece. However, these formations could form two discrete pieces and could be spaced apart axially from one another. In addition, each rotor blade 478 and corresponding rotor blade 480 could lie in the same plane, i. e. extend axially one above the other along the one piece rotor formation.

Furthermore, it should be understood that the rotor blades 480 could have any of the shapes of the spoke formations described above with reference to Figures 2 to 8 of the drawings.

The rotor 470 may be formed from metal with a high-density polyurethane material coating to protect it from corrosion, or it may be formed from a material which is resistant to corrosive attack so as to eliminating the need for the coating.

As can be seen, the diameter defined by the second rotor formation 476 is larger than the diameter defined by the first rotor formation 474.

In tests conducted by the applicant, a standard froth flotation cell of the type illustrated in Figure 1 was used to determine the difference in aeration between froth flotation using a standard rotor of the type illustrated in Figure 1 and froth flotation using the same rotor with an impeller of the type illustrated in Figure 7.

A 6m3 round tank was used with a no. 84 size flotation mechanism. The rotor, which included eight rotor blades, was connected to a 15kW electric motor running at 380 rpm, and the slurry used in the tests had a specific gravity of 1.5. The engagement, i. e. the extent to which the rotor extended into the draft tube 20, was 100 mm, and the submergence, i. e. the distance between the top of the rotor and the top of the tank 12, was 370 mm. The impeller was arranged on the rotor so that the second deflection formations 366 extended 50 mm into the standpipe 30, and 90 mm into the disperser 36.

When the standard rotor was used, the average of ten readings on an aerometer connected to the air-inlet line 32 was 9.29 m/s and the Amperage on the electric motor was between 14A and 15A.

When the impeller was connected to the rotor, the readings on the aerometer increased to 22.27 m/s and the Amperage on the electric motor increased to between 28A and 29A. In addition, the surface of the froth within the cell rose by 260 mm.

Other embodiments of the impeller according to the invention were also tested, and in each case the impeller effected an increase in the air supplied to the vortex and in the surface level of the froth within the froth celt..

It will be appreciated that by increasing the amount of froth within the flotation cell, the separation effected by the cell, and hence the efficiency of the cell, is increased.

Although the invention has been described above with reference to certain embodiments, it will be appreciated by those skilled in the art that the advantages of the invention could be achieved by various other embodiments falling within the scope of the invention as defined in the appended claims.