Field of the Invention This invention relates to a device and method for the recovery of at least one mineral from an ore body. More specifically, the device and method can be used for improving the recovery of a mineral product in a froth flotation process. Alternatively, the device and method can be used for reducing the amount of unwanted mineral in the concentrate stream of a flotation cell by ensuring that a greater portion of the unwanted mineral reports to a tailing stream.

When the term"mineral"is used in the present specification, it refers to one or more metal or non-metal compounds that may be subjected to a froth flotation process including ores, concentrates, semi-refined metal compounds, metal oxides and sulfides, flue dust etc.

Background Art Currently the flotation process, as practiced in industry, is used to recover minerals from a mineral ore by ensuring that the mineral is hydrophobic so that it may float in an aerated flotation cell. Typically, the ore is mined prior to undergoing a comminution process whereby it is first crushed and then ground in a mill, usually in the presence of water, to a fine size so as to form a slurry.

The pH may be adjusted and chemicals added as required during the milling or subsequent operations.

The slurry then usually undergoes cycloning so that the solids in the slurry are of the required size for flotation.

After the cycloning stage, the fine particle slurry is generally fed to a flotation chamber where further chemicals, such as for example pine oil or MIBC, may be added to act as a frothing agent which produces a stable froth.

Other chemicals may also be added prior to the flotation process to act as collecting agents, depressants or promoters. Examples families of chemical collectors include Xanthates and Dithiophosphates which react with the mineral to make its surface hydrophobic so that it may attach to the surface of bubbles as they travel through the flotation cell to a froth phase. The efficiency at which the collector attaches to the mineral will be one factor which affects the performance of a flotation operation.

Other reagents may be added to the flotation process to adjust surface potential and particle surface interactions, such as for example sodium hydrogen sulfide (NaSH).

The selection of the particular frothing or collecting agent will depend upon the mineral undergoing flotation and the desirable surface potential and flotation conditions.

Once the collector, frother and other agents are added to the slurry, the mixture is then subjected to aeration within an agitated chamber known as a flotation cell. Air or other gases are introduced to the flotation cell to create a froth on the surface of the mixture. Hydrophobic minerals attach to the bubbles of the mixture transferring to a froth phase on the surface of the process fluid. Non- hydrophobic gangue is discharged and does not enter the froth phase but reports to a tailings stream at the bottom end of the flotation cell.

As this is an equilibrium process, it will be appreciated by those skilled in the art that the process does not recover all of the desired mineral and a quantity is lost as tailings, particularly for fine sized mineral particles.

During flotation, the collected mineral is in equilibrium between a froth phase and a liquid phase. This is typically represented by the following equation:

Mineral (liq) + Collector (liq) H Mineral-Collector-Complex (froth) Flotation is used for many mineral recovery processes such as for the recovery of copper, molybdenum, nickel, lead and zinc. Furthermore, flotation may be used in a number of other separation processes, such as for cleaning coal.

It would be advantageous if the present invention provided an improvement in the performance of a flotation process. By improving the recovery or quality of product from a mineral flotation process, significant increases in productivity from mineral processing plants are possible which would produce an increase in revenue.

Summary of the Invention According to a first aspect of the present invention, there is provided an apparatus for flotation of at least one mineral included in a slurry, the apparatus including: -a flotation treatment enclosure in which the mineral is included in the slurry with a gas phase, the mineral being subjected to a flotation process; and -magnetic means arranged to apply a magnetic field to the mineral.

The magnetic means may be located within the flotation treatment enclosure or outside of the flotation treatment enclosure.

In one form of the invention the magnetic means may be in the form of a movable magnetic structure. In another form of the invention, the magnetic means may be in the form of a fixed magnetic structure. Preferably these structures are capable of orientation, either simultaneously or separately, to encourage movement of mineral particles in a particular direction due to the application of a magnetic field.

In one aspect, the movable magnetic structure may be in the form of a motive structure within a sealed

protective housing which is placed in contact with the mineral slurry and/or froth interface. Preferably this apparatus will have a mechanism for the movement of magnetic means within the housing to allow discharge of fine mineral accumulated on the surface of the housing.

In another aspect the movable magnetic structure may be in the form of a motive structure in direct contact with the mineral slurry and the froth interface. Preferably this apparatus will have a mechanism capable of scraping and discharging the fine mineral accumulated from the surface of the magnetic means.

Preferably the magnetic field is applied by means of a magnet. More preferably the magnet is either an electromagnet or a permanent magnet.

Preferably the flotation treatment enclosure will consist of a tank fitted with a mechanism to provide gas phase dispersion in the form of bubbles.

According to a second aspect of the present invention, there is provided a method for flotation of at least one mineral included in a slurry, the method including the steps of: -subjecting the mineral to a flotation process wherein, the mineral is suspended in a slurry with a gas phase and then subjected to a flotation process; and -applying a magnetic field to the mineral when located within the enclosure.

Preferably the mineral has undergone a mineral comminution operation so that when it enters the flotation treatment enclosure it is in fine particle form.

Preferably reagents or other additives have been included in the milling. More preferably the mineral particles undergo a mineral comminution operation so that the size distribution of the mineral particles is 80% smaller than 200 micrometers in size.

In one form of the invention the mineral may be capable of being ferromagnetic or paramagnetic so that when the magnetic field is applied to the flotation enclosure, the mineral particles move towards a froth phase. More advantageously upon application of the magnetic field the finer sized mineral particles attract to other particles, so forming larger particles which report to a froth phase.

In another form of the invention the mineral may be capable of being ferromagnetic or paramagnetic so that when the magnetic field is applied to the flotation enclosure, the mineral moves away from a froth phase. More advantageously upon application of the magnetic field a substantial portion of the mineral reports to a tailing stream.

Typically the flotation treatment enclosure is a flotation cell, column or chamber which is used for a flotation process.

Typically, the gas phase in the flotation treatment enclosure is substantially evenly dispersed throughout the slurry of the flotation treatment enclosure. More typically, gas phase is in the form of bubbles which are dispersed throughout the slurry and aerate the slurry to produce bubbles. Typically the gas phase is air supplied to the flotation treatment enclosure.

Preferably chemicals are added to the flotation treatment enclosure so that with the bubbles and magnetic field, the mineral particles tend to travel towards a froth phase which forms on top of the slurry. More preferably these chemicals would include collectors, frothers, surface potential modifiers and the like. More preferably other particulate additives could be included such as iron powder.

Brief Description of the Drawings Notwithstanding any other forms which may fall within the scope of the present invention, a number of preferred

embodiments and variations thereof will now be described by way of example only, with reference to the accompanying drawings in which: Figure 1 is a diagrammatic horizontal section through a flotation cell with two sets of magnets, one set of magnets being placed inside the flotation cell while the other set of magnets are placed outside the flotation cell; Figure 2 is a diagrammatic elevation showing an embodiment of the present invention in which there are a series of magnets which move within an enclosure that is inside a flotation cell; Figure 3 is a diagrammatic elevation showing an embodiment of the present invention in which there are a series of magnets which move within an enclosure that is inside a flotation cell so that the mineral particles are attracted away from a froth phase; Figure 4 is a diagrammatic elevation showing a series of magnets that are inside a tubular enclosure, the tubular enclosure being placed inside and towards the top of a flotation cell; Figure 5 is a diagrammatic elevation showing a magnet inside a flotation cell in which the gradient of the magnetic field induced by the magnet is greater towards the top of the flotation cell; Figure 6 is a diagrammatic elevation showing a plurality of magnets which are deployed at the interface of the liquid and froth phase so as to ensure the magnetic field is applied across upper surface of the flotation cell; Figure 7 is a diagrammatic sectional plan view showing a cross-section of a self-cleaning magnetic tube; Figure 8 is a similar view to Figure 7 showing the tube being cleaned on one side so that the particles move from the surface of the tube; and

Figure 9 is a similar view to Figure 7 showing the alternative side being cleaned and the particles being removed from the tube.

Figure 10 is a diagrammatic elevation showing an embodiment of the present invention using a rotating drum magnet to directly draw magnetisable material from the froth.

Modes for Carrying Out the Invention Although the magnetic field may be applied to a flotation cell in many different ways, a number of specific examples will now be described.

Referring to Figure 1, this diagram shows examples of two possible arrangements in which a magnetic field may be imparted to a flotation treatment enclosure. In this example, there is provided a flotation treatment enclosure in the form of flotation cell 10 in which one set of magnetic means in the form of permanent magnets 14 are placed throughout the flotation cell 10 in parallel, equally spaced rows.

In another form of the invention as disclosed in Figure 1, there is provided magnetic means in the form of electromagnets 16 on the outside of the flotation cell 10.

As will be apparent from Figure 1, the minerals shown in the form of the mineral particles 12 are, in this example of the invention, ferromagnetic or paramagnetic.

As the permanent magnets 14 or electromagnets 16 impart a magnetic field to the flotation slurry within flotation cell 10, the mineral particles become magnetized particles 13 and coagulate as they are attracted to each other.

During flotation, the surfaces of the mineral particles are reacted with a collector chemical for example with a functional group such as Xanthate. The magnetized particles 13 are subjected to a flotation process wherein they attach to bubbles 15 and move towards the froth phase 18.

It will be obvious to those skilled in the art that the permanent magnets 14 and the electromagnets 16 could be used upon a flotation cell 10 either together, as in this example, or individually so as to achieve the desired effect. Furthermore, the electromagnets 16 may be placed within the flotation cell 10 and the permanent magnets 14 may be placed outside of the flotation cell 10. Such examples and variations are encompassed by the invention.

Referring to Figure 2, this diagram demonstrates another example of the means by which a magnetic means can be imparted to a flotation treatment enclosure. In this example, there is a flotation treatment enclosure in the form of a flotation cell 10 within which there is a protective housing 20.

The protective housing 20 is placed inside the flotation cell 10. The protective housing 20 is enclosed so that slurry cannot enter. Inside the protective housing 20, there is provided in this example, two rows of permanent magnets 14 which rotate on two belts 22. The belts 22 enable the magnets 14 to travel around the protective housing 20 as they are moved by two rollers 24.

The rollers 24 are, in this example, directly aligned underneath each other so that the belts 22 can travel substantially throughout the height of the flotation cell 10. Hence, a magnetic field is imparted throughout the height of the flotation cell 10 and in a direction which moves towards the froth phase 18.

The small mineral particles 12 under a magnetic field, are attracted to each other forming magnetized particles 13 which move as the belts 22 move towards the surface of the froth phase 18. The general flow path of the magnetized particles is represented by flow lines 19. In this example, the two belts which are placed inside the protective housing 20 are placed at equally spaced

distances on the belt so that movement of the magnetized particles is towards the froth phase 18.

Referring to Figure 3, this example is a similar device to that shown in Figure 2, however there is a single belt 22 which rotates about two rollers 24 on the outside of the flotation cell 10. Hence, it will be apparent to those persons skilled in the art that such a belt could be placed on any side of the flotation cell so that a magnetic field is imparted to the slurry. In this example the magnetized particles are travelling towards the tailings stream 21.

Referring to Figure 4, this diagram shows a flotation treatment enclosure in the form of a flotation cell 10 in which there is a magnetic means in the form of permanent magnets 14 that rotate within a protective housing 20. The protective housing includes a cylindrical tube 26 and rotating wheel 28. In this example, the rotating wheel 28 rotates within the cylindrical tube in a clockwise direction. The rotating wheel 28 has attached on its outer surface a plurality of stems 30. On the periphery of the stems 30 are the magnets 14 which rotate about the inner surface of the cylindrical tube 26 during the flotation process.

On one side of the cylindrical tube 26, there is a magnetic bridge 32 which ensures that the magnetic field is shunted from the flotation cell 10 as the magnets 14 rotate past the magnetic bridge 32. This ensures that the mineral particles 12 are maintained in the froth phase and not carried over back into the slurry phase as the rotating wheel 28 moves in a clockwise direction within the flotation cell 10. In this example the general path of the magnetized particles can be shown by flow lines 21.

Referring to Figure 5, in this example of the present invention, there is a magnetic means in the form of a magnet 14 which is located within a flotation treatment

enclosure in the form of a flotation cell 10. The gradient of the magnetic field or the rate of change of magnetic field strength over the length of the flotation cell, is greater towards the surface of the mixture as shown by magnetic field lines 23. This encourages the mineral particles 12 to move towards the froth phase 18. In this example the general path of the magnetized particles can be shown by flow lines 19.

Referring to Figure 6, this example of the present invention shows the magnetic means in the form of a plurality of circular-shaped magnets 14 configured in a grid-like pattern on the surface of the slurry, so as to establish a magnetic field in the region of the slurry- froth interface. The slurry is contained by the flotation treatment enclosure in the form of flotation cell 10. Any sort of grid arrangement can be used, but in this arrangement the grids are arranged in a series of squares so that there is an interface of magnets with overlapping field areas 15. The mineral particles 12 which are either ferromagnetic, paramagnetic or diamagnetic particles, are circulated throughout the chamber by an agitator and/or by the gas phase in the form of bubbles 34 supplied to the flotation cell 10. As a result of agitation, all types of particles enter the magnetic grid formed by overlapping areas 15. The magnetic particles 12 are encouraged to stay in the magnetic grid areas 15 and move into the froth phase 18 for separation from the slurry phase. The diamagnetic particles continue to circulate under the influence of the mixer and a portion of these diamagnetic particles enter a tailing stream (not shown).

The magnets 14 can be placed in either the slurry itself or partially in the froth phase above the slurry, without departing from the features of the present invention as disclosed herein.

It will be apparent to those skilled in the art that, some of the mineral particles that become magnetized, may attach permanently to any of the surfaces of the above- mentioned magnetic means, rather than proceeding to the froth. Over time, the build up of particles reduces the efficiency of the magnetic device in imposing a magnetic field to the flotation treatment enclosure, hence there is provided a device to overcome the problems associated with the build up of magnetic particles.

For example in Figure 6 there is shown a cross-section of a number of magnets which are in a grid arrangement on the surface of the mixture. In this example, it can be shown that the magnets 14 collect fine, strongly magnetic particles that may be present in or have been introduced to the grinding process.

Referring to Figure 7, this diagram shows a self- cleaning tube magnet 36 which can be used in the place of the magnets 14 and which includes a plurality of magnet elements 40 enclosed within a tubular section 38. The magnetic elements may be any type of magnet but in this example, they are permanent magnets. The magnetic elements are spaced within the tubular section 38 at even intervals so that between each magnet element 40 there is a compartment 42.

At the ends of the tubular section 38, there are provided plugs 44 which insert into the ends of the tubular section 38. Additionally there is also provided a conduit 46 which is attached to an air supply tube 48.

Furthermore, a discharge disc 50 is positioned in the middle section of the tubular section and is made from any type of diamagnetic material.

In operation, the tubular section 38 imparts a magnetic field 15 substantially along the length of the tubular section 38 so as to impart a magnetic field to the slurry solution.

Over long periods of time, fine particles 52 may accumulate on the outer surface of the tubular section, hence when the tubular section 38 is to be cleaned, an air supply is provided at one end via air supply tube 48 which imparts a pressure force of air to the conduit 46. This force acts against the seal 54 which moves the magnet elements to one end of the tubular section 38 as shown in Figure 8.

Those fine particles 52 which are on the surface of the tubular section 38, move until they contact the discharge disc 50. At the discharge disc 50 there is no longer a magnetic field being imparted to the tubular section 38, hence the fine particles 52 are removed from the surface of the tubular section 38 and the self-cleaning tube magnet 36 becomes clean.

When the other end of tubular section 38 is to be cleaned, an air supply is provided at one end via air supply tube 49 which imparts a pressure force of air to the conduit 46. This force acts against the seal 54 which moves the magnet elements to one end of the tubular section 38 as shown in Figure 9.

Those fine particles 52 which are on the surface of the tubular section 38, move until they contact the discharge disc 50. At the discharge disc 50 there is no longer a magnetic field being imparted to the tubular section 38, hence the fine particles 52 are removed from the surface of the tubular section 38 and the self-cleaning tube magnet 36 becomes clean.

It is to be noted that the device may be of any particular shape and that the magnetic elements could be easily substituted into a single unit.

Referring to Figure 10, this diagram shows a cross sectional diagram of a flotation treatment enclosure in the form of a flotation cell 10 in where there is a magnetic means in the form of a permanent magnet 54 that rotates in

direct contact with the mineral slurry 56 and the froth layer above the slurry 18 and which has some clearance over the top of the froth layer 62. The general flow paths of the magnetised particles are represented by flow lines 19.

The magnetic means 54 is circular in configuration and arranged for rotation about a horizontal axis with the lower part of the magnetic means immersed in the mineral slurry 56 and/or froth layer 18 above.

It will be apparent to those skilled in the art that, some of the mineral particles 12 that become magnetized, may attach permanently to any of the surfaces of the above- mentioned magnetic means 54, rather than proceeding to recovery in the froth 18. Over time, the build up of particles 58 reduces the efficiency of the magnetic device 54 in imposing a magnetic field to the flotation treatment enclosure 10, hence there is a requirement for a physical surface cleaning provided a device to overcome the problems associated with the build up of magnetic particles 58. A scraper 60 is positioned on the upper side of the magnetic means 54 in order to detach accumulated mineral material minerals 58 from the surface of said magnetic means.

Experimental Results (A) As an example of the improvements that this method and apparatus has provided over that of the prior art, laboratory results produced using conventional froth flotation and the invention are shown in Table 1.

The results are for the flotation of a copper (Cu) mineral (chalcopyrite) from an ore using two test runs.

Test 1 are the results of flotation using a standard flotation cell, Test 2 are the results of flotation using the present invention.

Both Test 1 and Test 2 were carried out in duplicate under the same test conditions and using the same feed stock.

Table 1 TEST 1 TEST 2 Cu recovery % (wt) 89.3 95.8 Cu in concentrate % (wt) 18.8 19.8 Cu in tailings % (wt) 2.2 0.93 Cu in feed % (wt) 10.4 10.6

As can be seen in the results, the Cu recovery using the present invention is significantly increased over that of the prior art using conventional flotation techniques.

It has been found that improvements in the recovery of Cu using the present invention are in the order of 5-6 % wt.

(B) As a further example of the improvements that this method and apparatus has provided over that of the prior art, laboratory results produced using conventional froth flotation and the invention are shown in Table 2.

The results are for the flotation of a nickel (Ni) mineral (pentlandite) from an ore using two test runs. Test 3 are the results of flotation using a standard flotation cell, Test 4 are the flotation results using the present invention.

Both Test 3 and Test 4 were carried out in under the same test conditions and using the same feed stock.

Table 2 Condition Ni Flotation Recovery TEST 3 Ni recovery % (wt) 92.1 No magnetic means present TEST 4 Ni recovery % (wt) 96.1 magnetic means present As can be seen in the results, the Ni recovery using the present invention is significantly increased over that of the prior art using conventional flotation techniques.

It has been found that the improvement in the recovery of Ni using the present invention is in the order of 4 % wt.

(C) As a further example of the improvements that this method and apparatus has provided over that of the prior art, laboratory results produced using conventional froth flotation and the invention are shown in Table 3.

The results are for the flotation of a nickel (Ni) mineral (pentlandite) from an ore using two test runs, which correspond to the test runs given in the previous example (B). Test 3 are the results of flotation using a standard flotation cell, Test 4 are the flotation results using the present invention.

Both Test 3 and Test 4 were carried out under the same test conditions and using the same feed stock. Some of the mineral particles that become magnetized may attach permanently to any of the surfaces of the above-mentioned magnetic means, rather than proceeding to the froth.

Recovery I is the recovery of mineral during flotation, and Recovery II is the recovery from the magnet itself during flotation. Use was made of a device to overcome the problems associated with the build up of magnetic particles. The magnets collect fine, strongly magnetic particles that may be present in the flotation cell. The fine particles which are on the surface of the tubular section of the magnetic means are removed from the surface of this tubular section at the discharge disc and the self- cleaning tube magnet becomes clean. A size analysis of the copper-containing mineral reporting to concentrate was conducted.

As can be seen in the results, the Ni recovery using the present invention is significantly increased over that of the prior art using conventional flotation techniques, across the particle size range. In use a self-cleaning magnetic device partially located within the flotation cell

significantly augments flotation recovery of mineral.

Depending upon the particle size range, it has been found that improvements in the recovery of Ni using the present invention are in the order of 3-5 % wt.

Table 3 Condition Recovery Recovery Recovery Recovery I I II II >38 <38 >38 <38 micro-micro-micro-micro- meters meters meters meters TEST 3 Ni recovery % 93.3 89.5 (wt) No magnetic means present TEST 4 Ni recovery % 91.7 91. 0 7. 3 2. 3 (wt) magnetic means present (D) As a further example of the improvements that this method and apparatus has provided over that of the prior art, laboratory results produced using conventional froth flotation and the invention are shown in Table 4.

The results are for the flotation of a copper (Cu) mineral (chalcopyrite) from an ore using two test runs.

Test 5 are the results of flotation using a standard flotation cell, Test 6 are the flotation results using the present invention.

Both Test 5 and Test 6 were carried out in under the same test conditions and using the same feed stock. A size-by-size analysis of the copper containing mineral reporting to concentrate was conducted.

As can be seen in the results, the Cu recovery using the present invention is significantly increased over that of the prior art using conventional flotation techniques, across the particle size range. Depending upon the particle size range, it has been found that improvements in

the recovery of Cu using the present invention are in the order of 9-10 % wt.

Table 4 Condition +75-75+53-53+38-38 micro-micro-micro-micro- meters meters meters meters TEST 5 Cu recovery % (wt) 89.2 98. 5 99. 3 87.8 No magnetic means present TEST 6 Cu recovery % (wt) 98.3 99. 4 99. 6 96.1 magnetic means present (E) As a further example of the improvements that this method and apparatus has provided over that of the prior art, laboratory results produced using conventional froth flotation and the invention are shown in Table 5.

The results are for the flotation of a copper (Cu) mineral (chalcopyrite) from an ore using two test runs.

Test 7 are the results of flotation using the present invention, Test 8 are the flotation results using the present invention with the inclusion of a finely ground magnetic material in the pulp (in this case, iron powder), introduced previously in the milling stage. Magnetic means were available in both instances.

Table 5 Condition Cu Flotation Recovery TEST 7 Cu recovery % (wt) 95.0 no iron powder present TEST 8 Cu recovery % (wt) 96.7 iron powder present Both Test 7 and Test 8 were carried out in under the same test conditions and using the same feed stock.

As can be seen in the results, the Cu recovery using the present invention is significantly increased over that of the prior art using the same new flotation techniques.

It has been found that improvements in the recovery of Cu using the present invention are in the order of 1-2 % wt.

(F) As a further example of the improvements that this method and apparatus has provided over that of the prior art, laboratory results produced using conventional froth flotation and the invention are shown in Table 6.

The results are for the flotation of a copper (Cu) mineral (chalcopyrite) from an ore using two test runs.

Test 9 are the results of flotation using the present invention, Test 10 are the flotation results using the present invention with the inclusion of a reductant (reducing agent) in the flotation cell (in this case, sodium hydrogen sulfide). Magnetic means were available in both instances.

Table 6 Condition Cu Flotation Recovery TEST 9 Cu recovery % (wt) 95.0 no reductant present TEST 10 Cu recovery % (wt) 96.3 reductant present Both Test 9 and Test 10 were carried out in under the same test conditions and using the same feed stock.

As can be seen in the results, the Cu recovery using the present invention is significantly increased over that of the prior art using the same new flotation techniques.

It has been found that improvements in the recovery of Cu using the present invention are in the order of 1 % wt.

Whilst the invention has been described with reference to a number of preferred embodiments, it should be appreciated that the invention can be embodied in many other forms and that the above disclosure has been by one of the many examples that may be used to carry out the present invention. Furthermore, it should be noted that a magnetic

field can also be applied to the slurry solution from the lower part of the flotation treatment enclosure so as to encourage any ferromagnetic or paramagnetic materials to report to the tailing stream. Such obvious adaptations of the present invention are within the scope of the above disclosure without departing from the invention as herein disclosed.

It should also be noted that the flotation treatment enclosure relates to any device for flotation, such as a flotation cell or flotation column.