WO2013163678A1

WO2013163678A1 - Recovering mineral from ore

Info

Publication number: WO2013163678A1
Application number: PCT/AU2013/000433
Authority: WO
Inventors: Barry Graham Lumsden
Original assignee: Ausmetec Pty Ltd
Priority date: 2012-04-30
Filing date: 2013-04-29
Publication date: 2013-11-07

Abstract

A method for recovery of magnetisable particles from a flowstream; said method comprising: placing the flowstream into a condition of gentle agitation; causing an attraction surface associated with a magnetic field to be immersed in the flowstream for a predetermined period of time so as to attract to the attraction surface at least some of the magnetisable particles in the flowstream; and following said predetermined period of time, remove from the attraction surface those magnetisable particles that have been attracted thereto during said predetermined period of time. Also disclosed is an apparatus for separating a magnetisable material from a flowstream in a treatment chamber that contains particulate feed material suspended in a liquid; the apparatus including: a magnetic source able to be activated and deactivated; the magnetic source in the flowstream, when enabled for a predetermined period of time, attracting and retaining at least a portion of the magnetisable material in the flowstream as separated magnetisable material; and after said predetermined period of time, a means of removing the separated magnetisable material from the flowstream Also disclosed is a process where the ground ore particles in a sfurry are subjected to flotation, then magnetic separation of the flotation tails or latter stage of the flotation circuit, and the magnetic concentrate is then upgraded with or without regrinding to another stage of separation such as flotation.

Description

RECOVERING MINERAL FROM ORE

[0001] The present invention relates to the field of mineral processing and, more particularly, to methods and apparatus for enhancing the efficiency of extraction of minerals in the form of magnetisable particles from a flowstream, preferably (but not exclusively) in the context of a separation process which does not rely on the magnetic characteristics of the magnetisable particles.

BACKGROUND

[0002] To separate valuable minerals from ore requires that the physical or chemical properties of the valuable minerals are different from the ore. These properties may be the minerals density, its solubility, its chemical properties or some other property. Mineral separation is never absolutely efficient there is always some valuable mineral lost to the ore tailings; and some waste ore that reports to the valuable concentrate.

[0003] For many metals in particular sulphide mineral base metal separation, flotation is the overwhelmingly preferred method. Flotation is a method based on the hydrophobic property (chemically induced or natural) of the metal sulphide that allows the attachment of the metal sulphide to an air bubble, which being less dense than water floats to the surface. Generally, metal sulphide separation is carried out on ores where the metal value of the ore is low (a typical copper ore is 1 % copper or less and so has a metal value of <$100/ton), and so mining and processing costs are minimised.

[0004] In metal sulphide separation flotation metal recovery is generally 75-95%, and the purity of the product produced is generally 60-90% of the sulphide mineral.

Flotation is a relatively efficient and low cost separation method, and because of its efficiency, and the low value of the flotation tails secondary separation methods are generally not cost effective and so not applied.

[0005] Much of the valuable mineral that is lots to the tailings is coarse mineral; that is mineral >100pm. Coarse valuable mineral is lost because it doesn't recover well by flotation and often the coarse mineral is not fully liberated, that is it is a composite of valuable and valueless mineral. This can be seen in Figure 1 from Trahar et al, 1976, which illustrates mineral recovery for different sulphide particle sizes. The other major losses in flotation are the fine particles that float slowly. [0006] Magnetic separation is a mineral separation method based on the magnetic susceptibility of the mineral. It is a highly efficient method for the separation of strongly magnetic minerals with recoveries of 95%-99% possible. Generally, magnetic separation is utilised where the mineral is strongly magnetic and >20microns in size.

[0007] Magnetic separation is not used in metal sulphide mineral separation because base metal sulphides are not strongly magnetic. Many metal sulphides are generally only slightly magnetic defined as paramagnetic. Magnetic separation is not generally used for the recovery of paramagnetic minerals because they are not efficiently recovered or concentrated by magnetic separation. Therefore, magnetic separation is not a suitable method to efficiently recover base metal sulphides.

[0008] Various workers have tried to separate paramagnetic copper sulphides by magnetic separation. Gaudin et al. (1943) used a magnetic separator to separate sulphide minerals from pyrite in the laboratory. Tawil and Morales ( 985) used Wet High Intensity magnetic Separators (WHIMS) to separate chalcopyrite from pyrite. Using WHIMS a final copper concentrate was upgraded from 23.8% copper to 30.2% copper at an 87% copper recovery. It was also possible to separate chalcopyrite from galena, and molybdenite from chalcopyrite. While reasonable magnetic separations were achieved in the laboratory, the method was not seen as a replacement for flotation rather to upgrade flotation

concentrates. Nevertheless, if an operation was to only recover 87% of the copper in its concentrate it would be a very expensive in lost copper. Other operations, particularly those recovering pentlandite actually used magnetic separators to remove waste pyrrhotite from the ore without substantial losses of the paramagnetic sulphides pentlandite and chalcopyrite.

[0009] It is accepted that flotation is an excellent method for recovering mid-sized fractions. Particularly it recovers the 20pm- 00pm minerals, with poorer recovery of the very fine and very coarse particles in the flotation tails (refer Figure 1). Generally it has been shown that magnetic separators are most effective on the +50micron fraction.

[0010] It would be helpful if there were a way to combine the efficiency of the flotation process over its range of fraction sizes with the efficiency of the magnetic separation process over other fraction sizes.

[0011] Therefore, it would be an advantage both technically and financially if a combined flotation/magnetic separation can be carried out. NOTES

[0012] The term "comprising" (and grammatical variations thereof) is used in this specification in the inclusive sense of "having" or "including", and not in the exclusive sense of "consisting only of.

[0013] The above discussion of the prior art in the Background of the invention or elsewhere in this specification is not an admission that any information discussed therein is citable prior art or part of the common general knowledge of persons skilled in the art in any country.

DEFINITIONS

[0014] In this specification, a 'slurry' is a mixture of particles and water, with the particles suspended in, but not dissolved in, the water. Typically, the particles are derived from the grinding of rock ore.

SUMMARY OF INVENTION

[0015] Accordingly, in one broad form of the invention, there is provided a method for recovery of magnetisable particles from a flowstream; said method comprising:

placing the flowstream into a condition of gentle agitation;

causing an attraction surface associated with a magnetic field to be immersed in the

flowstream for a predetermined period of time so as to

attract to the attraction surface at least some of the magnetisable particles in the flowstream; and

following said predetermined period of time, remove from the attraction surface those magnetisable particles that have been attracted thereto during said predetermined period of time.

[0016] Preferably, the predetermined period of time is up to 1 minute.

[0017] Preferably, the predetermined period of time is in the range of 20 to 30 seconds.

[0018] Preferably, the magnetic field has a field strength in the range of 3000 to 5000 Gauss. [0019] Preferably, the agitation is carried out by a rotor operating in the range of 100 to 200 rpm.

[0020] Preferably, agitation is sufficient to suspend the magnetisable particles in the flow stream.

[0021] Preferably, agitation is sufficient to keep the magnetisable particles in the flowstream in suspension during the predetermined period of time.

[0022] Preferably, the magnetisable particles comprise paramagnetic mineral particles

[0023] Preferably, the magnetisable particles comprise paramagnetic and ferromagnetic mineral particles.

[0024] Preferably, the flowstream comprises a slurry.

[0025] Preferably, the step of removal is performed within the flowstream.

[0026] In an alternative preferred form, the step of removal is performed outside the flowstream.

[0027] Preferably, the step of removal is by scraping.

[0028] Preferably, the step of removal is by removal of the magnetic field associated with the attraction surface.

[0029] Preferably, removal of the magnetic field is sufficient to allow the particles to separate from the attraction surface.

[0030] Preferably, the removal is sufficient to permit the particles to fall away from the attraction surface under the influence of gravity.

[0031] Preferably, the attraction surface is immersed in and moved within the flowstream.

[0032] Preferably, the attraction surface attracts paramagnetic and ferromagnetic particles.

[0033] Preferably, the flowstream has passed through at least one flotation cell for separation of particles including the magnetisable particles from the flowstream by a flotation step prior to said step of placing a portion of the flowstream into a condition of gentle agitation.

[0034] Preferably, the gentle agitation is such that the flow forces on the

magnetisable particles in the portion of the flowstream are less than the attractive forces exerted on the magnetisable particles by the attraction surface.

[0035] Preferably, the magnetic field associated with the attraction surface can be activated and deactivated.

[0036] Preferably, the magnetic field is an electromagnetic field.

[0037] Preferably, the magnetic field is a permanent magnet field.

[0038] Preferably, a portion of the flowstream is placed in a flotation cell.

[0039] Preferably, a portion of the flowstream is placed in a tank.

[0040] Preferably, the flowstream comprises flotation tailings.

[0041] Preferably, magnetisable particles in the flowstream comprise one or more of chalcopyrite, bornite, sphalerite, galena or other sulphide mineral.

[0042] Preferably, the mineral particles comprised particles which are candidates for recovery by a flotation process.

[0043] Preferably, the magnetisable particles comprise one or more of gold, silver, platinum or cassiterite particles.

[0044] In a further broad form of the invention, there is provided an apparatus for separating a magnetisable material from a flowstream in a treatment chamber that contains particulate feed material suspended in a liquid including: a magnetic source able to be activated and deactivated

the magnetic source in the flow/stream, when enabled for a predetermined period of time, attracting and retaining at least a portion of the magnetisable material in the flowstream as separated magnetisable material;

after said predetermined period of time, a means of removing the separated magnetisable material from the flowstream.

[0045] Preferably, the flowstream is gently agitated relative to the magnetisable material.

[0046] Preferably, the magnetic source is activated for a predetermined period of time.

[0047] Preferably, the predetermined period of time is a function of the magnetic field strength of the magnetic source.

[0048] Preferably, the predetermined period of time is a function of the magnetic characteristics of the magnetisable material.

[0049] Preferably, the predetermined period of time is a function of the rate of flow of the flowstream.

[0050] Preferably, the means for removing the separated magnetisable material from the flowstream is a scraper.

[0051] Preferably, the means for removing the separated magnetisable material from the flowstream is a conveyor belt.

[0052] Preferably, the means for removing the separated magnetisable material from the flowstream is a magnetised rotating wheel.

[0053] Preferably, the magnetised rotating wheel has magnets placed on the sides of the wheel.

[0054] Preferably, the wheel enters the flowstream. [0055] Preferably, the wheel rotates through the flowstream. [0056] Preferably, the flowstream is in the form of a slurry. [0057] Preferably, the flowstream velocity is low.

[0058] Preferably, the apparatus is a stainless steel tube with a magnet inside and a collection device moving outside the stainless steel tube.

[0059] Preferably, the magnet is only in the part of the tube that is immersed in the slurry.

[0060] Preferably, the collection device scrapes and collects the separated magnetisable material from the surface of the stainless steel tube as collected material.

[0061] Preferably, the collected material is lifted out of the slurry by the collection device.

[0062] Preferably, as the collected material leaves the slurry, it is no longer attracted to the tube because there is no magnet in the non-immersed part of the tube.

[0063] Preferably, the collected material is then washed into a launder for further treatment.

[0064] Preferably, the collected material is further separated as required to increase the concentration of valuable metals derived from the flowstream.

[0065] In yet a further broad form of the invention, there is provided a process where the ground ore particles in a slurry are subjected to flotation, then magnetic separation of the flotation tails or latter stage of the flotation circuit, and the magnetic concentrate is then upgraded with or without regrinding to another stage of separation such as flotation.

[0066] In preferred forms, the above process is performed according to the method described above, and more preferably, utilising the apparatus described above.

[0067] In a particular form, it has been found that magnetic separation of base metal sulphides from flotation tails does increase the total recovery of base metal sulphides. This is done by using magnetic separation to selectively recover the slightly magnetic metal sulphides from the ore stream after flotation, or near the completion of flotation.

[0068] Surprisingly, it is possible to recover some of the very coarse and very fine base metal sulphides from a flotation tails stream by magnetic separation. These are base metal sulphides that are not recovered by flotation. Magnetic separation is a relatively cheap separation method requiring limited inputs and so suitable for use with a very low value tailings stream.

[0069] It might be thought that, operationally, this recovery of the slightly magnetic sulphides is best achieved by treating the flotation tails in a magnetic separator. But as Tawil and Morales (1985) showed magnetic separators even under ideal conditions are not particularly effective in recovering paramagnetic minerals, in fact so poor are they that some operations use magnetic separators to recover magnetic minerals FROM

paramagnetic minerals without large losses of paramagnetic minerals. Because paramagnetic minerals are not strongly magnetic they are not strongly attracted by a magnetic field, therefore in the strong physical flow forces in a standard magnetic separator only strongly magnetic minerals are strongly enough attracted by the magnetic to be efficiently separated from the flowstream. Weakly magnetic minerals are not strongly enough attracted by the magnet and remain in the flowstream.

[0070] Generally, it might be considered that combining magnetic separation with flotation might be accomplished with a dual processing step. That is that the bulk of the copper can be recovered by flotation and then the flotation tails sent to magnetic separators to remove the remaining base metal sulphide that can be recovered by magnetic separation. This may be possible, but two separate operations are more expensive than combining operations together, and magnetic separators are designed to recover strongly magnetic minerals not paramagnetic minerals. Moreover, in magnetic separators there is more turbulent flow as the material passes through the magnetic separator. Turbulent flow reduces the efficiency of magnetic separation particularly of fine mineral because the flow forces are stronger than the magnetic forces of attraction. It is postulated that part of the reason for the effectiveness of the recovery of this fine mineral by magnetic separation is because of the less turbulent fluid in the flotation cell or tailings tank. [0071] Therefore, it would be an advantage both technically and financially if a combined flotation/magnetic separation can be carried out.

[0072] In one form, the magnet separation enhances the recovery of the finest fractions

[0073] In one form, these results are showing it to be very effective on the <20 micron fraction also.

[0074] Surprisingly, it has been found that the magnetic separation is best carried out during the flotation stage. So as not to interfere with the efficient flotation, it is carried out towards the end of the flotation stage.

[0075] While this is a scavenger step, it is nevertheless important not only to recover the metal sulphide minerals, but also to recover them at a sufficiently high concentration so that they can be upgraded to a final product.

BRIEF DESCRIPTION OF DRAWINGS

[0076] Figure 1 illustrates a typical mineral recovery profile for different sulphide particle sizes (prior art).

[0077] Figure 2A illustrates a side section view of a processing apparatus in accordance with a first preferred embodiment of the present invention, at a first stage of operation.

[0078] Figure 2B illustrates a side section view of the processing apparatus of Figure 2A, at a second stage of operation.

[0079] Figure 2C illustrates a side section view of the processing apparatus of Figure 2A, at a third stage of operation.

[0080] Figure 3A illustrates an end section view of a processing apparatus in accordance with a second preferred embodiment of the present invention.

[0081] Figure 3B illustrates a side section view of the processing apparatus of Figure 3A. DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0082] Embodiments of the invention seek to remove magnetisable particles from a flowstream, particularly a portion of a flowstream which has been placed in a condition of gentle agitation, by use of a magnetic field to attract the magnetisable particles followed by a step of release of the magnetisable particles from the influence of the magnetic field; the step of release being a release of the magnetisable particles to an environment outside of the flowstream. Various embodiments disclose apparatus adapted to attract the

magnetisable particles over a predetermined period of time together with an arrangement for releasing the magnetisable particles from the influence of the magnetic field. In one arrangement this is by a mechanical scraping-type operation whilst the magnetic field remains in operation and operable within the environment of the flowstream. In another instance it is by removal of the influence of the magnetic field upon the magnetisable particles at a stage when they have been lifted out of the flowstream whilst under the influence of the magnetic field. In one form the method and apparatus is utilised in an environment where another separation process is also in operation. In particular forms the other separation process is a flotation process.

[0083] With reference to Figures 2A, 2B and 2C, there is illustrated an apparatus 10 suitable to enhance the efficiency of extraction of the magnetisable minerals 15 in accordance with a first preferred embodiment of the invention. In this instance, a high strength rare earth magnet 1 1 is located inside a stainless steel tube 12, in this instance in the form of a sheath. The stainless steel sheath 12 is inserted in the slurry 13 in a gently agitated tank 14, like a flotation cell. In preferred forms, agitation of the flowstream while it is in the tank 14 is performed by a rotating element (not shown) as is commonly used in the industry to assist in flotation. The magnetic and paramagnetic material 15 in the slurry 13 is attracted to the magnet 11 and separated from the slurry 13. A pneumatic cylinder 16 attached to rods 17 is attached to the material collector 18, preferably at or adjacent to lip 22. It is lifted and scrapes the attracted mineral 15 out of the slurry 13 and above the magnet 11. When the magnetic and paramagnetic material 15 is above the slurry 13 and magnet 11, it is washed out of the material collector 18 by a wash water spray 19 and into a launder 20, where it is removed for further processing. In this instance, the magnet 11 remains substantially immersed in the slurry 13, below slurry level 21.

[0084] The magnet 11 is inside a stainless steel sheath 12, with the top of the magnet 11 positioned at the top of the slurry 13 and the stainless steel sheath 12 that is above the slurry 13 not magnetised. This is inserted in the agitated tank 14 containing the slurry 13. There is a material collector 18 that is attached to rods 17 which is then attached to the air cylinder.

[0085] Figure 2A illustrates stage 1 of the process:

[0086] The magnetic and paramagnetic material 15 is attracted to the magnet 11 , and attaches itself to the stainless steel sheath 12 that houses the magnet 11. Because the slurry 13 is relatively gently agitated the paramagnetic material is also attached to the sheath 12. The material collector 18 is in the bottom position.

[0087] Figure 2B illustrates stage 2 of the process:

[0088] The pneumatic cylinder 16 is activated and the material collector 18 that is attached to the air cylinder by rods 17 lifts. Because the inside faces of the material collector 18 scrapes the stainless steel sheath 12, the attached magnetic and

paramagnetic material 15 is moved up in the material collector 18 towards the slurry level 21.

[0089] Figure 2C illustrates stage 3 of the process:

[0090] When the material collector 18, which has scraped the magnetic and paramagnetic material 15 from the stainless steel sheath 12, exits the slurry 13, there is no magnetisation in the top of the sheath 12. Therefore, the collected material 15 in the material collector 18 is free to leave the material collector 18, because there is no longer any attraction to the sheath 2. Wash water is sufficient then to wash out the collected material 15 into a launder 20 that is then removed for further processing.

[0091] With reference to Figures 3A and 3B, there is illustrated a second preferred embodiment of an apparatus 1 0 for enhancing the efficiency of extraction of minerals from a flowstream. In this instance, like components are numbered as for the first embodiment, except in the '100' series.

[0092] Figure 3A shows a side elevation and figure 3B shows an end elevation of a apparatus 110 that is able to remove the magnetic and paramagnetic minerals 115 from the slurry 113. [0093] In the end elevation it can be seen that there is a circular magnet 130 contained within a rotating stainless steel wheel sheath 131. There is a motor 133 associated with a control system 134 that rotates the wheel sheath 131 , but the magnet 130 is fixed in place. The lower half of the wheel sheath 131 is submerged in the slurry 1 3. The magnetic and paramagnetic mineral 115 attaches to the wheel sheath 131. As the wheel sheath 131 rotates in an anticlockwise direction, it lifts the magnetic and paramagnetic material 115 out of the slurry 113. The material 1 5 remains attached to the wheel sheath 131, held to it by the magnet 130. It can be seen from the elevation that the magnet 130 is not a complete disc, but that from about 20 degrees left of the y-axis the magnet 130 stops (i.e. there is a sector 132 where there is no magnet). As the wheel sheath 131 moves material 115 past the position where the magnet 130 stops, there is no longer any magnetic force holding the material 115 to the wheel sheath 131. The magnetic and paramagnetic material 115 then drops into the launder 120 and any material that remains is scraped from the wheel sheath 131 as it passes. This collected and separated material 115 is then washed from the launder 120 for further processing.

[0094] In preferred forms, agitation of the flowstream while it is in the tank 114 is performed by a rotating element (not shown) as is commonly used in the industry to assist in flotation.

IN USE

[0095] In preferred embodiments, the invention relates to a process for removing valuable paramagnetic minerals such as base metal sulphides from a flowstream with a magnet.

[0096] In preferred embodiments, the invention relates to a process for increasing the recovery of paramagnetic minerals in a separation process.

[0097] In preferred embodiments, the invention relates to a process for recovering coarse paramagnetic minerals composited with other minerals that may not be recovered by other methods but have sufficient magnetic susceptibility to be recovered by magnetic separation.

[0098] In preferred embodiments, the invention relates to a method to remove paramagnetic minerals from a flowstream that includes a gently agitated flowstream; a flowstream that contains weakly magnetic paramagnetic minerals; a magnetic device that is suitable to be inserted in a gently agitated flowstream; a magnetic device that can attract the paramagnetic minerals from the non turbulent flowstream; a magnetic device that can remove the separated paramagnetic minerals from the flowstream.

[0099] In the first preferred embodiment described above and with reference to Figures 2A, 2B and 2C, a strong magnet is inserted into a flowstream in a tank. The flowstream contains a mixture of minerals including paramagnetic minerals that are to be separated from the flowstream. The magnet attracts the magnetisable minerals including the paramagnetic minerals and separates them from the flowstream. The separated magnetisable minerals including the paramagnetic minerals that are removed from the flowstream are recovered by being extracted out of the flowstream.

[0100] In particularly preferred embodiments of the invention, it is preferred that the flow forces in the flowstream are not strong so that the magnetic forces on the weakly magnetic paramagnetic minerals are sufficiently strong to separate the paramagnetic minerals from the flowstream. The flowstream must be moving in order to keep the mineral particles suspended in the flowstream, but this movement can be gentle. An example is a flotation cell, or an agitated tank.

[0101] In particularly preferred forms, the flowstream contains weakly magnetic paramagnetic minerals that it is desired to remove these paramagnetic minerals from the flowstream.

[0102] In particularly preferred embodiments, the magnetic device has sufficient magnetic force so that it can separate the weakly magnetic paramagnetic minerals from the flowstream, but that once removed from the flowstream the weakly magnetic minerals can be removed from the magnetic device.

[0103] In particularly preferred embodiments, the device is suitable to be fitted into tanks that are gently agitated.

[0104] An example of use is the removal of the paramagnetic copper sulphide minerals bornite and chalcopyrite from a flotation tailings flowstream. In this example, the flowstream contains about 40% mineral particles by weight, and the mineral particles are about 0.1 % copper and 0.12g/t gold. The flowstream has already undergone flotation separation so this material has been unrecovered by flotation. A magnetic extraction device is inserted into the flowstream in the last flotation cell to attract the paramagnetic and ferromagnetic particles to the magnet. The material is then recovered from the magnet and separated from the flowstream and recovered.

Example 1

[0105] This is a test on the lead tail from a sequential sulphide lead zinc flotation. The lead occurs as galena, the zinc as sphalerite and the iron is a range of sulphide and other iron minerals. The magnetic source was placed in the agitated slurry for 60 seconds, then the material that had been attracted by the magnet was removed. The material recovered and the material remaining was sieved at 63pm and assayed. The fractional recovery by the magnet of the metals is given below. wt %Pb %Zn %Fe %Ag

>63 m 30.4% 40.5% 37.0% 65.1 % 57.8%

<63 m 17.5% 13.3% 6.9% 43.0% 19.3%

[0106] It can be seen that there was excellent recovery from this tails waste stream of all metals particularly the valuable lead, zinc and silver. There was about a 2x upgrade from the feed, so while not at high grade the material was more concentrate than the feed.

[0107] Further separation stages with flotation upgraded the concentrate to high grade:

%Pb %Zn %Fe g/t Ag ·

4.0% 5.0% 32% 320

[0108] This material is significantly higher than the tail feedstock and suitable to be reintroduced into the plant streams to be recovered. The high silver is a very desirable feedstock.

Example 2

[0109] This is a test on the final tail from a sequential sulphide lead zinc flotation. The lead occurs as galena, the zinc as sphalerite and the iron is a range of sulphide and other iron minerals. The magnetic source was placed in the agitated slurry for 60 seconds, then the material that had been attracted by the magnet was removed. The material recovered and the materia! remaining was sieved at 63μηι and assayed. The fractional recovery by the magnet of the metals is given below. wt %Pb %Zn %Fe %Ag

>63μηι 19.7% 27.6% 41.2% 52.7% 37.8%

<63μπι 21.3% 15.8% 18.0% 50.2% 25.9%

[0110] Further magnetic separation to upgrade the concentrate resulted in an upgrade of the concentrate to:

%Pb %Zn %Fe g/tAg

1.2% 0.8% 21 % ^' 91 -

[0111] This material is significantly higher than the tail and suitable to be

reintroduced into plant streams to be recovered. The high silver is a very desirable feedstock.

[0112] Even from very low grade tails, good recoveries were achieved. Example 3

[0113] This test was carried out on a sulphide copper ore that contained gold. The grind was 80% passing 100 μιη, and plant recovery of copper was about 90%. The test work was carried out on the flotation tail in the final flotation cell with a 30second exposure to the magnet. The results were most interesting for the <20μιη mineral, where the recovery over different tests was 6%-10% and the gold recovery 3%-15%.This is a tail sample that assayed about 0.1 %Cu. There was a 3x upgrading in the concentrate for this <20pm mineral fraction. Further upgrading using different separation equipment gave a 1 % copper concentrate with 1g/t gold a 10 times upgrading from the tail.

Example 4

[0114] A plant test was carried out using a single unit of the equipment outlined in Figures 2A-2C. The test was carried out on the final flotation cell and recovered fine gold and copper from this cell. Full scale this equipment would recover 15% of the copper and 14% of the gold now reporting to the tails. The recovered material can be variously upgraded. Further cleaning of this product produced a concentrate that was about 2% copper and 2ppm gold with around 70% recovery that was easily floatable and couid be returned to the plant for final cleaning.

INDUSTRIAL APPLICABILITY

[0115] Embodiments of the present invention can be applied advantageously to improve the recovery of magnetisable minerals from flowstreams in mineral recovery plants, particularly (but not exclusively) flotation-based mineral recovery plants.

REFERENCES

[0116] Gaudin, A and Rush Spedden, H, 1943. Magnetic separation of sulphide minerals, AIME Transactions, 153:563-575 (American Institute of Mining and Metallurgical Engineers Inc).

[0 17] Tawil, M and Morales, M, 1985. Application of wet high intensity magnetic separation to sulphide mineral beneficiation, Complex Sulfides, (ed: A Zunkel), pp 507- 524, (TMS-AIME: Pennsylvania).

[0118] Trahar, W and Warren, L, 1976. The flotability of very fine particles-a review, Int J Miner Process, 3: 103-131.

Claims

1. A method for recovery of magnetisable particles from a flowstream; said method comprising:

placing the flowstream into a condition of gentle agitation;

flowstream for a predetermined period of time so as to

2. The method of claim 1 wherein the predetermined period of time is up to 1 minute.

3. The method of any previous claim wherein the predetermined period of time is in the range of 20 to 30 seconds.

4. The method of any previous claim wherein the magnetic field has^a field strength in the range of 3000 to 5000 Gauss.

5. The method of any previous claim wherein the agitation is carried out by a rotor operating in the range of 100 to 200 rpm.

6. The method of any previous claim wherein the agitation is sufficient to suspend the magnetisable particles in the flowstream.

7. The method of any previous claim wherein the agitation is sufficient to keep the magnetisable particles in the flowstream in suspension during the predetermined period of time.

8. The method of any previous claim wherein the magnetisable particles comprise paramagnetic mineral particles.

9. The method of any previous claim wherein the magnetisable particles comprise paramagnetic and ferromagnetic mineral particles.

10. The method of any previous claim wherein the flowstream comprises a slurry. 1. The method of any previous claim wherein the step of removal is performed within the flowstream.

12. The method of any previous claim wherein the step of removal is performed outside the flowstream.

13. The method of any previous claim wherein the step of removal is by scraping.

14. The method of any previous claim wherein the step of removal is by removal of the magnetic field associated with the attraction surface.

15. The method of any previous claim wherein the removal of the magnetic field is sufficient to allow the particles to separate from the attraction surface. 6. The method of any previous claim wherein the removal is sufficient to permit the particles to fall away from the attraction surface under the influence of gravity.

17. The method of any previous claim wherein the attraction surface is immersed in and moved within the flowstream. 8. The method of any previous claim wherein the attraction surface attracts paramagnetic and ferromagnetic particles.

19. The method of any previous claim wherein the flowstream has passed through at least one flotation cell for separation of particles including the magnetisable particles from the flowstream by a flotation step prior to said step of placing a portion of the flowstream into a condition of gentle agitation.

20. The method of any previous claim wherein the gentle agitation is such that the flow forces on the magnetisable particles in the portion of the flowstream are less than the attractive forces exerted on the magnetisable particles by the attraction surface.

21. The method of any previous claim wherein the magnetic field associated with the attraction surface can be activated and deactivated.

22. The method of any previous claim wherein the magnetic field is an

electromagnetic field.

23. The method of any previous claim wherein the magnetic field is a permanent magnet field.

24. The method of any previous claim wherein a portion of the flowstream is placed in a flotation cell.

25. The method of any previous claim wherein a portion of the flowstream is placed in a tank.

26. The method of any previous claim wherein the flowstream comprises flotation tailings.

27. The method of any previous claim wherein magnetisable particles in the flowstream comprise one or more of chalcopyrite, bornite, sphalerite, galena or other sulphide mineral.

28. The method of any previous claim wherein the mineral particles comprised particles which are candidates for recovery by a flotation process.

29. The method of any previous claim wherein the magnetisable particles comprise one or more of gold, silver, platinum or cassiterite particles.

30. An apparatus for separating a magnetisable material from a flowstream in a treatment chamber that contains particulate feed material suspended in a liquid; the apparatus including:

a magnetic source able to be activated and deactivated;

the magnetic source in the flowstream, when enabled for a predetermined period of time, attracting and retaining at least a portion of the magnetisable material in the flowstream as separated magnetisable material; and

31. The apparatus of claim 30 wherein the flowstream is gently agitated relative to the magnetisable material.

32. The apparatus of claim 30 or 31 wherein the magnetic source is activated for a predetermined period of time.

33. The apparatus of any one of claims 30 to 32 wherein the predetermined period of time is a function of the magnetic field strength of the magnetic source.

34. The apparatus of any one of claims 30 to 32 wherein the predetermined period of time is a function of the magnetic characteristics of the magnetisable material.

35. The apparatus of any one of claims 30 to 32 wherein the predetermined period of time is a function of the rate of flow of the flowstream.

36. The apparatus of any one of claims 30 to 34 wherein the means for removing the separated magnetisable material from the flowstream is a scraper.

37. The apparatus of any one of claims 30 to 34 wherein the means for removing the separated magnetisable material from the flowstream is a conveyor belt.

38. The apparatus of any one of claims 30 to 34 wherein the means for removing the separated magnetisable material from the flowstream is a magnetised rotating wheel.

39. The apparatus of claim 38 wherein the magnetised rotating wheel has magnets placed on the sides of the wheel.

40. The apparatus of claim 38 or 39 wherein the wheel enters the flowstream.

41. The apparatus of any one of claims 38 to 40 wherein the wheel rotates through the flowstream.

42. The apparatus of any one of claims 30 to 41 wherein the flowstream is in the form of a slurry.

43. The apparatus of any one of claims 30 to 42 wherein the flowstream velocity is low.

44. The apparatus of any one of claims 30 to 41 wherein the apparatus is a stainless steel tube with a magnet inside and a collection device moving outside the stainless steel tube.

45. The apparatus of claim 44 wherein the magnet is only in the part of the tube that is immersed in the slurry.

46. The apparatus of claim 44 or 45 wherein the collection device scrapes and collects the separated magnetisable material from the surface of the stainless steel tube as collected material.

47. The apparatus of any one of claims 44 to 46 wherein the collected material is lifted out of the slurry by the collection device.

48. The apparatus of any one of claims 44 to 47 wherein, as the collected material leaves the slurry, it is no longer attracted to the tube because there is no magnet in the non-immersed part of the tube.

49. The apparatus of any one of claims 46 to 48 wherein the collected material is then washed into a launder for further treatment.

50. The apparatus of any one of claims 46 to 49 wherein the collected material is further separated as required to increase the concentration of valuable metals derived from the flowstream.

51. A process where the ground ore particles in a slurry are subjected to flotation, then magnetic separation of the flotation tails or latter stage of the flotation circuit, and the magnetic concentrate is then upgraded with or without regrinding to another stage of separation such as flotation.

52. The process of claim 52 wherein the step of magnetic separation is performed according to the method of any one of claims 1 to 29.

53. The process of claim 52 or 53 wherein the step of magnetic separation is performed using the apparatus of any one of claims 30 to 51.