Patent Description:
In the separation of valuable minerals from an ore, whether by flotation separation or gravity separation or some other method, it has been found that fine minerals, those less than <NUM> are the hardest to recover - refer <FIG> which illustrates mineral recovery by flotation for different sulphide particle sizes (Ahmed et al.

Primarily, the sulphide minerals of base metals are recovered by flotation. These <<NUM> minerals are valuable and increased recovery of these minerals significantly enhances the profitability of these operations.

Recent research has shown that magnetic conditioning of flotation feed increases the recovery of these <<NUM> minerals (Englehardt et al <NUM>, Holloway et al <NUM>, Lacouture et al <NUM>, Wilding and Lumsden <NUM>, Musuku et al <NUM>, Rivett et al <NUM>, Zoetbrood et al <NUM>). This technology was patented in <NUM> (<CIT>) and has been installed in many plants throughout the world.

In a typical plant operation the mined ore is ground in a ball mill, sag mill and/or fine grinding mill to produce small minerals where the valuable minerals can be separated from the ore by flotation. As existing ores are depleted mining companies are forced to process more complex ores of lower grade. Also, the economics and technology for fine grinding technology is improving so the combination of these two factors leads to finer grinding in flotation plants to optimize the separation of valuable minerals from the ore.

However, very fine minerals are harder to recover. Moreover, even detecting these very fine minerals in plant flowstreams is more difficult. Plants collect flowstream samples from their process streams to measure the performance of their plant. However, the standard filter paper in use has a <NUM>-<NUM> pore size. Therefore, it is probable that some <<NUM> mineral in process flowstreams is passing through the filter paper undetected, not being recovered in the filter cake so not being detected in the plant flowstreams. Obviously a magnetic aggregation technology that aggregates fine minerals would aggregate some of the <<NUM> minerals to ><NUM> and therefore they are filtered and detected in the plant flowstreams.

Mineral processing plants also have other separation processes downstream of flotation that may be inefficient in removing <<NUM> mineral from the process. In particular there are dewatering processes - the settling (or thickening) then filtration of the flotation concentrate and the thickening of the flotation tailings. The water recovered from these dewatering processes report back to the grinding circuit or other parts of the process upstream of the flotation. These dewatering processes are not <NUM>% efficient so the process water does retain some of the finer mineral. Filter cloth manufacturers claim only <NUM>% recovery of <<NUM> minerals when concentrate is being filtered.

Magnetic conditioning has been in use in plants for many years. There is a relationship between magnetic field strength and the size of particle that can be aggregated. This can be seen in <FIG> from Svoboda, <NUM>. As magnetic field strength (B) increases smaller paramagnetic particles can be aggregated.

The diagram also makes clear that at fields of 3000gauss (3x10-1T) even very small <<NUM> paramagnetic particles with similar magnetic susceptibility to haematite would aggregate. So the aggregation of a <NUM> particle with a <<NUM> particle would be assured. There is no necessity of stronger fields for this size particle aggregation of similar magnetic susceptibility (many base metal sulphides have similar magnetic susceptibility to haematite). Of course this is a theoretical graph based on some reasonable assumptions including about particles shape, particle homogeneity but nevertheless they give a reasonable indication of paramagnetic particle interaction.

<FIG> depicts a generalised description of the total energy of interaction for paramagnetic ultrafine particles as a function of particle size (a) and magnetic induction B (Svoboda, <NUM>). The publication <NPL> discloses a flotation recovery circuit according to prior art.

Notwithstanding the issues involved in extracting the very fine mineral portions in plant flowstreams it is desirable to improve the proportion of recovery of the fine portion - particularly as ore bodies of lesser quality are processed. It would also be desirable to reprocess tailings of previously processed ore bodies.

It is an object of the present invention to address the above issues or at least provide a useful alternative.

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".

The above discussion of the prior art in the Background of the invention, 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.

Fine Mineral: In this specification "fine mineral" means ore particles after grinding or other processing step in the size range predominantly between zero and substantially <NUM> and more preferably between zero and substantially <NUM>.

An object of the invention is a method of increasing recovery of a metal portion from a predetermined quantity of ore in a flotation recovery circuit which comprises a grinding stage, a flotation recovery stage, a dewatering stage and a filter stage according to claim <NUM>.

Another object of the invention is a system for increasing recovery of a metal portion from a predetermined quantity of ore in a flotation recovery circuit which comprises a grinding stage, a flotation recovery stage according to claim <NUM>.

Preferred embodiments are the subject-matter of dependent claims.

Embodiments of the present invention will now be described with reference to the accompanying drawings wherein:.

It has become apparent in recent testwork that magnetic conditioning is changing the paramagnetic mineral detected in different flowstreams UPSTREAM of the magnetic conditioning installation. It is postulated that the only mechanism by which this could occur is if the magnetic conditioning is impacting the process water from the dewatering separations that are downstream of the magnetic conditioning, where the water is recycled and then reports upstream of the magnetic conditioning. This is not to say it is impacting the H2O molecules but it is impacting the minerals that are suspended in the water. Therefore, suspended paramagnetic minerals and very fine paramagnetic minerals are impacted as they pass the magnetic conditioning so that the content and characteristics (size via being aggregated or not aggregated) are different when they are recycled in the process water, compared to when no magnetic conditioning is employed. This difference is either in concentration or in particles size of these suspended paramagnetic minerals in the recycled process water.

Where magnetic conditioning has been installed two different impacts UPSTREAM of the magnetic conditioning have been measured to very high statistical confidence. Firstly, a decrease in the amount of paramagnetic mineral has been detected in the UPSTREAM process. The most likely mechanism for this would be that the magnetic conditioning is aggregating the very fine <<NUM> paramagnetic minerals and in the downstream processes these aggregated concentrate minerals dewater (filter and settle) more efficiently, report to the final saleable product rather than the process water and so their concentration in the recirculating plant water is reduced.

Secondly, there has been a measured increase in paramagnetic mineral in the UPSTREAM process. The possible reason for this is that magnetic conditioning is aggregating very fine paramagnetic minerals (chalcopyrite CuFeS2), sphalerite (Zn/FeS) or other valuable paramagnetic sulphide minerals). So when the process water recirculates containing these fine minerals where magnetic aggregation has been operating, these minerals have been aggregated from <<NUM>-<NUM> size to ><NUM>-<NUM> size; they are now filtered out of the process streams, recovered to the filter cake and so detectable in the plant flowstreams. Whereas, when magnetic conditioning is not operating, the <<NUM>-<NUM> mineral remains <<NUM>-<NUM>, is not filtered out from the process stream and so not detected in the plant. The mineral is there but because it is not aggregated it is not filtered and therefore not detected.

There are then two mechanisms postulated about how magnetic conditioning can impact the UPSTREAM plant assays. The two mechanisms have an opposite effect on the paramagnetic mineral recirculating in the process water. One mechanism reduces and one increases the detectable (and in fact recoverable) metal in the process streams. Both mechanisms are at work, but one may predominate over the other. Therefore, in a plant with poor thickening and filtering of the fine mineral in its concentrate, the reduction in mineral recirculating to the UPSTREAM process in the process water may predominate. But in a plant with good thickening and filtering of its concentrate and less paramagnetic mineral in its process water then the aggregating of the<<NUM>-<NUM> mineral to a filterable ><NUM>-<NUM> with magnetic conditioning may increase the filtration and detection of fine mineral in its UPSTREAM process.

At a mine in Australia that grinds to very fine size (concentrate is <NUM>%<<NUM>) the magnetic conditioning reduced the concentration of Zn and Ag in the feed by up to <NUM>%. The table below gives the %Zn and Ag in the plant feed upstream of the magnetic conditioning. The results are to an extremely high level of confidence.

At a mine in Canada that grinds quite coarse (<NUM>%<<NUM>)the magnetic conditioning increased the Cu in feed by about <NUM>%. It can be seen that the increase causes a significant and very beneficial increase in saleable Cu recovered to the concentrate.

At a mine in Africa that grinds quite coarse (<NUM>%<<NUM>) the magnetic conditioning increased the %Cu in feed by about <NUM>% over a <NUM>-month period.

At a mine in Asia that also grinds quite coarse (<NUM>%<<NUM>) an evaluation of magnetic conditioning was carried out. There was no re-circulating water from the Copper concentrate thickener or the Copper filter back to the grinding circuit. During this test no increase in %Cu in the feed with the magnetic conditioning to a high level of confidence was measured, but the magnetic conditioning still increased the Cu recovery.

At the same mine when the magnetic conditioning was tested in an identical position, the only difference being that now water from the downstream filtering and thickening processes was recirculated back to the grinding circuit magnetic conditioning not only increased the Cu recovery but also there was a measured increase in the %Cu in feed by about <NUM>%.

If with magnetic conditioning there is a higher rate of recovery and a higher amount of metal in the feedstream this is a much better production of metal for payment; rather than an equally higher recovery with the same amount of metal in the feedstream.

At one site the %Zn in flowstream <NUM> feed increased by <NUM>% when magnetic conditioning was ON to high confidence.

At another site the %Cu in flowstream <NUM> feed increased when magnetic conditioning was ON by about <NUM>%.

This is a surprising result. Firstly, it is surprising that the magnetic conditioning can be impacting a process UPSTREAM of its location in the process. This is unexpected and was not anticipated. Secondly, it is surprising because there are many steps between the magnetic conditioning and the upstream process, all of which would be expected to break some aggregates. And thirdly, it is surprising that there is significant amounts of <<NUM> mineral in the process water, this is not expected, if it was plants would be using filter papers with smaller pore sizes because they are trying to measure the true process effect. The magnitude of the change with magnetic conditioning is very surprising.

A possible reason why this UPSTREAM impact is being detected now, whereas, it wasn't detected previously is that the magnetic fields used for magnetic conditioning have increased and it can be seen from <FIG> that the stronger the field the smaller the particles that will aggregate. In the early magnetic conditioners the field strength on the face had a maximum field of <NUM>-4000gauss. However, because of developments in the magnetic arrays the magnetic field strengths of the current magnetic conditioners are more than 5000gauss and some are as high as <NUM>-8000gauss. This increase, while not appearing significant from the <FIG>, may be very significant in real process conditions, given the assumptions of the Svoboda model and the reality of process plants.

It has been established that in an environment where water is returned from the flotation recovery process using stronger magnets it does indeed improve the aggregation and/or flotation of the <<NUM> micron paramagnetic minerals.

In a current plant installation magnets with lower magnetic field strengths of around <NUM> gauss were compared with a stronger magnets with magnetic field strengths of around <NUM> gauss. The zinc recovery as measured at the output filter cake <NUM> from the filtration stage <NUM> increased by <NUM>%, and this was achieved with a purer final concentrate as measured at point <NUM> in <FIG> prior to entry into the filtration stage <NUM>; so less waste was being recovered to the concentrate.

This clearly shows the benefits of stronger magnetic field strengths in aggregating very fine paramagnetic minerals that occur either in flotation slurries, process water or in improving settling and filtering of fine paramagnetic minerals.

Embodiments of the invention relate to using stronger magnetic fields to carry out magnetic conditioning in a flotation recovery circuit which returns recovered process water to the grinding stage and in so doing not only impacting the flotation recovery but the magnetic conditioning of the flotation circuit also impacting a surprising change in the UPSTREAM feed grade due to magnetic conditioning.

With reference to <FIG> there is illustrated a block diagram of a mineral processing circuit applicable to embodiments of the present invention.

With reference to <FIG> there is illustrated an alternative apparatus for inducing magnetism in the flowstream.

The apparatus illustrated and described with reference to <FIG> may be located in the magnetic conditioning stage <NUM> illustrated in the process diagram of <FIG>. The apparatus causes the magnetic source <NUM> to apply an increased range of magnetic field strength to the ground ore portion during this stage thereby to cause increased recovery by improved recovery at the flotation stage <NUM> arising from the increased range of magnetic field strength; the process interacting with the recovered process water in which the ground ore portion is contained.

In a preferred form, the magnetic field strength applied is at least <NUM> Gauss. More preferably the magnetic field strength is at the range of <NUM> to <NUM> Gauss. More preferably, the magnetic field strength is in the range of <NUM> to <NUM> Gauss.

In a further aspect with reference to the discussion in the background art, there will now be described apparatus and a methodology to maximize the magnetic induction in the slurry flowstream by maximizing the magnetic induction strength of the magnetic source and by minimizing the distance between the magnetic source and the slurry flowstream with a ferromagnetic cleaning mechanism that maintains the magnetic source in a stationary position within the flowstream to maximize slurry residence time in the magnetic field.

The importance of the higher field strength due to wiper cleaning and the greater residence time in the magnetic field due to continuous activation of the magnetic source in the slurry flowstream allows for greater magnetization and aggregation of the mineral particles and reduced equipment requirements, therefore improving the overall process. This is represented diagrammatically in <FIG> illustrates the effect of equipment sizing on using wiper magnetising. In the cleaning process the magnet may be deactivated for <NUM>%-<NUM>% of the time to clean the magnet. With this invention because deactivation of the magnetic source does not occur, the number of magnetic sources can be reduced by <NUM>%-<NUM>%.

In this instance the arrangement of <FIG> shows an arrangement of magnetic sources <NUM> in an array within a predetermined treatment volume <NUM>. In this instance there are nine sources intended to achieve a predetermined level of magnetic irradiation of a flowstream <NUM> passing there through.

<FIG> illustrates the same predetermined treatment volume <NUM> this time with magnetic sources <NUM> having associated therewith wipers (refer later description) which mechanically clean the exterior of the sources <NUM> whilst the sources <NUM> are retained within the flowstream <NUM> on a continuous basis. As has been described above and with reference to the later described embodiments a smaller number of sources <NUM> can achieve the same level of magnetic irradiation for the same predetermined treatment volume <NUM>.

In a further aspect, again with reference to the discussion in the background art, there will now be described alternative apparatus and methods for cleaning the magnetic source housing that does not require the deactivation of the magnetic source by movement of the magnetic source in and out of the slurry and so allows the magnetization of the slurry flowstream to be maximized.

A wiping mechanism to wipe off the build-up of the ferromagnetic minerals.

This method of cleaning has these advantages:.

This preferred method with reference to <FIG>, <FIG>, <FIG> works by the magnetic source <NUM> being housed in a stainless steel housing <NUM> with a very thin abrasion resistant rubber lining and a rubber lined stainless steel scraper <NUM> on a piston <NUM> moving vertically up and down the external face <NUM> of the magnetic housing <NUM>. The magnetic source <NUM> in the housing <NUM> with the scraper <NUM> attached is located in the slurry flowstream <NUM>. As the scraper <NUM> moves over the face of the magnetic housing <NUM> it disturbs and dislodges the ferromagnetic material <NUM> that has built, while still attracted to the magnet. The force of the moving flowstream <NUM> is sufficient to force the magnetic material <NUM> back into the flowstream <NUM> and away from the magnetic source <NUM>, thus cleaning the build-up of magnetic material <NUM> on the magnetic housing <NUM>.

A wiping mechanism combined with the flowstream washing to wipe off the build-up of the ferromagnetic minerals.

<FIG> illustrates the slurry magnetising equipment according to a preferred embodiment of the invention. Like components are numbered as for the embodiment described above with reference to <FIG>.

<FIG> shows the effect of the combined wiping and flowstream movement in wiping the magnetic housing clean and removing the build-up of magnetised material including ferromagnetic material into the flowstream.

This method (refer <FIG>) works by the magnetic source <NUM> being housed in a thin stainless steel housing <NUM> (<NUM>) with a very thin rubber lining (<NUM>) and one or more rubber lined stainless steel wipers or scrapers <NUM> mounted on a piston <NUM> which moves vertically up and down the external face <NUM> of the magnetic housing <NUM>. The magnetic source <NUM> in the housing <NUM> with the scraper <NUM> attached is located in the slurry flowstream <NUM>. As the scraper <NUM> moves over the face <NUM> of the magnetic housing <NUM> it disturbs and dislodges the ferromagnetic material <NUM> that has built-up, while still attracted to the magnet. The force of the moving flowstream <NUM>, which is generally and most advantageously perpendicular to the wiper movement combined with the action of the wiping mechanism is sufficient to force the magnetic material <NUM> back into the flowstream and away from the magnetic source <NUM>, thus cleaning the build-up of magnetic material <NUM> on the magnetic housing <NUM>.

Flow rates will vary depending on the plant. Typical flow rates can be in the range from 20m3/hr to 5000m3/hr.

With reference to <FIG>, <FIG> and <FIG>, there is illustrated diagrammatically possible usage scenarios for one or more embodiments previously described. In use in a typical ore processing plant a flowstream <NUM> containing particles of valuable ore passes into a magnetic conditioning stage in this instance in the form of processing chamber <NUM> having at least one magnetic source <NUM> located therein. The source <NUM> has a high strength magnetic field <NUM> which can fall away sharply with distance from the source as illustrated in the inset graph of <FIG>. To this end a thin walled housing <NUM> having an external face <NUM> only a relatively short distance from the magnetic source <NUM> is utilised so as to maximise the high strength field to which the flowstream <NUM> is exposed as it passes through the chamber <NUM>. In one form the magnetic source <NUM> is fitted with a scraper <NUM> (refer <FIG>, <FIG>) or similar arrangement thereby to periodically dislodge material which may have accumulated on face <NUM>. The flowstream <NUM> and a substantial portion of the valuable ore particles entrained within it including any dislodged material <NUM> continues on to a further treatment tank <NUM> where valuable ore may be separated from the flowstream <NUM> by a flotation process wherein aggregated weakly magnetic particles <NUM> are actively floated in the froth <NUM>. The amount of target particles is maximised and the amount of non-target particles entrained in the froth may be minimised. In a further particular embodiment those aggregated weakly magnetic particles not selected by the flotation process in tank <NUM> nor entrained in the froth can pass to a further treatment tank or tanks 19A, 19B (refer to <FIG>) where a further flotation process may be instigated and wherein a different target particle may be selected for flotation, or the aggregated weakly magnetic particles may pass to a settling tank <NUM> for dewatering and to tailings <NUM>. It will be appreciated that the magnetic conditioning stage should be placed so as to operate on the flowstream <NUM> before significant processing occurs in the flotation process in order to optimize the effect of the magnetic conditioning stage <NUM>.

In this instance placing the magnetic conditioning stage very early in the flotation recovery stage supports a method of increasing recovery of the metal portion from the predetermined quantity of ore; said method comprising applying a magnetic field to the ground ore portion in a magnetic conditioning stage while it is contained in the recovered process water subsequent to the grinding stage and prior to the flotation recovery stage.

With reference to <FIG> there is illustrated a specific arrangement of processing chamber <NUM> having at least one magnetic source <NUM> placed in the circuit between the grinding stage and prior to the flotation recovery stage. In this instance eight such magnetic sources <NUM> are placed within a first flotation cell <NUM> and distributed evenly throughout. In this instance the first flotation cell <NUM> contains an agitator <NUM> which assists in circulating the slurry within the first flotation cell <NUM>. Any concentrate <NUM> is passed to the filter stage <NUM> the balance, in this instance, is sent to a further flotation cell 19A and from there, in this instance, to yet a further flotation cell 19B.

With reference to <FIG> filtrate <NUM> from the flotation recovery process <NUM> effected within the flotation recovery stage <NUM> or at least a portion thereof may be recirculated via return line <NUM> to the grinding stage <NUM>.

Filter cake <NUM> arising from filtration stage <NUM> exits the process as saleable product.

The tailings dewatering stream <NUM> from the flotation recovery process <NUM> or at least a portion thereof also passes to return line <NUM> as part of the process water recirculation system. Dewatered, settled solids <NUM> from the dewatering process <NUM> exit to a tailings dam <NUM> or like repository.

It is postulated that there are two effects in operation Upstream Flowstream <NUM> of the magnetic conditioning due to the increased magnetic field strength.

These effects are postulated to have the following impacts: where magnetic conditioning has been installed two different impacts UPSTREAM of the magnetic conditioning have been measured to very high statistical confidence in the plant feed <NUM>.

Firstly, for a constant incoming feed composition a decrease in the amount of paramagnetic mineral has been detected in the UPSTREAM process when magnetic conditioning is on compared with when magnetic conditioning is off. The most likely mechanism for this would be that the magnetic conditioning is aggregating the very fine <<NUM> paramagnetic minerals and in the downstream processes these aggregated concentrate minerals dewater (filter and settle) more efficiently and so their concentration in the recirculating plant water stream <NUM> is reduced. [this postulation is exemplified by example <NUM> earlier in the specification - despite reduced paramagnetic mineral in the UPSTREAM feed the amount of useful metal portion recovered at the output <NUM> of the process is increased - refer <FIG>].

Secondly, for a constant incoming feed composition there has been a measured increase in paramagnetic mineral has been detected in the UPSTREAM process when the magnetic conditioning is on compared with when magnetic conditioning is off. The possible reason for this is that magnetic conditioning is aggregating very fine paramagnetic minerals (chalcopyrite CuFeS2), sphalerite (Zn/FeS) or other valuable paramagnetic sulphide minerals). So when the process water recirculates <NUM> containing these fine minerals where magnetic aggregation has been operating, these minerals have been aggregated from <<NUM>-<NUM> size to ><NUM>-<NUM> size; they are now filtered out of the process streams, recovered to the feed sample (<NUM>) filter cake and so detectable in the plant flowstreams. Whereas, when magnetic conditioning is not operating, the <<NUM>-<NUM> mineral remains <<NUM>-<NUM>, is not filtered out from the process stream and so not detected in the plant. The mineral is there but because it is not aggregated it is not filtered and therefore not detected in the plant sampler (<NUM>) [this postulation is exemplified by example <NUM> - <NUM> earlier in the specification - increased paramagnetic mineral in the UPSTREAM feed provides increased opportunity for re-recovery of the metal portion whereby the amount of useful metal portion recovered at the output <NUM> of the process is increased - refer <FIG>].

In summary it is postulated that there are then two mechanisms as to how magnetic conditioning can impact the UPSTREAM plant assays. The two mechanisms have an opposite effect on the paramagnetic mineral recirculating in the process water. One mechanism reduces and one increases the detectable (and in fact recoverable) metal in the process streams. Both mechanisms are at work, but one may predominate over the other.

The apparatus illustrated and described may be located in the magnetic conditioning stage <NUM> illustrated in the process diagram of <FIG>. The apparatus causes the magnetic source <NUM> to apply an increased range of magnetic field strength to the ground ore portion during this stage thereby to cause increased recovery by improved recovery at the flotation stage <NUM> arising from the increased range of magnetic field strength; the process interacting with the recovered process water in which the ground ore portion is contained.

In a preferred embodiment, the present invention provides an apparatus <NUM> for inducing magnetism in a flow stream <NUM> of an at least partially magnetisable particulate feed material <NUM> suspended in a liquid. The feed material typically includes a mixture of paramagnetic and ferromagnetic particulates present with other nonmagnetic or diamagnetic gangue minerals in a water slurry. Paramagnetic particulates usually require a high gradient magnetic field in order to become magnetised. Some sulfide minerals containing copper (such as chalcopyrite), zinc (such as sphalerite contaminated with iron) or other transition metals are paramagnetic. Ferromagnetic particulates include iron oxide minerals (such as magnetite) and metallic iron particles (from worn grinding media, for example).

Referring to <FIG>, the apparatus <NUM> includes a treatment chamber in the form of an annularly shaped vessel <NUM> with an uppermost inlet <NUM> and a lowermost outlet <NUM> through which a flow stream of the aforementioned mineral mixture can flow respectively into and out of the vessel <NUM> with some residence time therein. The apparatus can also be used in 'batch' mode, and does not require a continuous flow stream of the mineral slurry mixture. Furthermore, either the uppermost inlet <NUM> or the lowermost outlet <NUM> can be an inlet or outlet - which is to say flow can be reversed in the apparatus <NUM>.

The chamber vessel incorporates a central elongate recess <NUM>. A magnetic source is able to be selectively activated to induces magnetism in at least some of the particulate feed material <NUM> located in the vessel <NUM> by movement of the magnetic source into and out of proximity with the vessel <NUM>. In one preferred embodiment the magnetic source is at least one permanent magnet mounted on a motive means in the form of a piston which is connected to a drive so that the piston can be reciprocatingly moved into and out of the recess <NUM>. In one preferred embodiment the piston <NUM> is cylindrically shaped, having a diameter of approximately <NUM> millimetres and is fitted with a number of inset permanent magnets <NUM> that are square in shape and have a side dimension of <NUM> millimetres, made of neodymium or other materials. The diameter of the recess <NUM> in the vessel <NUM> is <NUM> millimetres.

In further embodiments the permanent magnets can be of any shape, size or material and the piston need not be cylindrical, but can be square or triangular in crossection for example, and of any overall length. The means by which the piston is moved reciprocatingly with respect to the vessel can include any type of drive including a cam, a spring, an air cylinder (<NUM>, as illustrated) or an occentrically rotatable shaft etc..

In still further embodiments the relative movement of the vessel and the magnetic source need not involve a piston being received into a recess in a vessel. The magnetic source need only be brought into proximity to the vessel, for example by being moved close to one side of a vessel so that a magnetic field can magnetise the particulate materials located in the vessel. In other embodiments the vessel itself may be able to be moved in relation to a stationary magnet. The vessel can be of any particular shape, size and orientation to facilitate the magnetic source coming into proximity to the vessel contents.

The apparatus <NUM> described allows the introduction of a high gradient magnetic. field to effectively magnetise both the weakly and strongly magnetic particulates <NUM> for subsequent removal of all particulates by enhanced gravity settling or separation of the weakly magnetic particulates by techniques such as flotation. When the piston <NUM> carrying the magnets <NUM> is moved into the recess <NUM> of the vessel <NUM>, both the weakly and strongly magnetic particulates <NUM> are attracted and migrate toward the portion of the interior face of the vessel <NUM> which adjoins the internal elongate recess <NUM>. The particles then become, at least in part, magnetised. When the piston <NUM> carrying the magnets <NUM> is moved out of the recess <NUM>, deposits of magnetised particulate material <NUM> are no longer held to the interior face by magnetic attraction and are mostly dissipated by the flow stream <NUM> of feed material in the vessel <NUM>. Depending on the location and orientation of the inlet and outlet ports, the vessel contents can develop a swirling fluid motion (illustrated in the drawing by an arrow in the vessel <NUM>).

The dissipation of solids can reduce the possibility of any flow restrictions developing in the vessel and improve the efficiency of the magnet/s.

In still further embodiments a magnetic source can be selectively activated to induces magnetism in at least some of the particulate feed material located in the vessel by use of electromagnet/s located proximal to the vessel. The supply current fed to the electromagnet/s can be switched on and off repeatedly to provide the same effect as if a permanent magnet was moved in and out of proximity with the vessel. In still further embodiments the field of a permanent magnet can be shunted or blocked by moving a magnetic field barrier in between the permanent magnet and the vessel containing the magnetisable particulates.

The cycle or frequency of movement of the magnetic source may be initiated by a timing device or by sensors that detect the mass of accumulated particles <NUM>. The measurement of this mass may be made by determining the interference to the magnetic field or by measuring the resistance to flow of the particulate slurry as the mass of particles <NUM> increases.

In the case of the paramagnetic feed material, the inventors have surprisingly discovered that the induced magnetism can cause at least some of the magnetised paramagnetic particles to become aggregated in the liquid flow stream. The inventors have observed that the aggregated paramagnetic particles remain aggregated for at least several hours and that the aggregated particles can survive further treatment steps in a mineral separation process such as pumping and agitation. In a feed with particulate materials of a range of magnetic susceptibilites, the preferred apparatus is able to be operated in a manner to facilitate the subsequent separation of the magnetised paramagnetic feed material fraction from the magnetised ferromagnetic feed material fraction. The magnetised paramagnetic feed fraction is also separable from the non-magnetic or diamagnetic gangue minerals.

In the experimental work, a flotation separation process was used on several finely ground mineral ores (typically with <NUM>% of the ore particles of a particle size less than <NUM> micrometres in diameter) in order to separate the magnetised paramagnetic feed material into a froth phase.

The experimental results have demonstrated good increases in sulfide mineral recovery by flotation due to the use of the magnetisation treatment step prior to the flotation step. The inventors believe that the very fine (eg. <<NUM> micrometre diameter) paramagnetic particles, which ordinarily exhibit poor flotation rates and recoveries, once magnetised, can become aggregated to give an 'effective' (coagulated) particle diameter of greater than <NUM> micrometres. Such aggregates can exhibit good flotation rate and recovery characteristics due to hydrodynamic reasons such as better attachment to rising air bubbles in a flotation cell.

The use of sulfide mineral collector reagents such as xanthates or dithiophosphates can ensure that the surfaces of the paramagnetic mineral particles become hydrophobic and more readily attach to the surface of the rising air bubbles in the flotation cell. Typically the ferromagnetic particles in a particulate mixture of paramagnetic and ferromagnetic minerals are rejected in a flotation process (having no affinity for xanthate or dithiophosphate collectors) and report to gangue or tailings. In the experiments conducted, the sulfide mineral collector reagents used were present in the magnetisation treatment vessel <NUM> prior to any subsequent flotation step. In experiments where no magnetic treatment step was applied prior to the flotation step, the feed to flotation containing sulfide mineral collector was still passed through the vessel <NUM> prior to being passed to the subsequent flotation apparatus. The flotation apparatus used can comprise any standard type of agitated flotation cell, flotation column or flotation circuit.

As an example of the improvements that this apparatus and process have provided over that known in the prior art, experimental results produced using conventional froth flotation with and without the pretreatment step of the invention are now presented.

The present apparatus can allow the introduction of a very high gradient magnetic field to effectively magnetise the both weakly and strongly magnetic particulates. When the magnetic source is activated both the weakly and strongly magnetic particulates are attracted toward that magnetic source and become, at least in part, magnetised. Previous apparatus and methods have not allowed the use of very high gradient magnetic fields because of the problem of deposition of magnetised feed material around the magnetic source and the low degree of magnetisation of the weakly magnetic particulates.

The vessel and piston can be made of any suitable materials of construction which wear appropriately and that can be shaped, formed and fitted in the manners so described, such as a metal, metal alloy, hard plastics or ceramic.

It is to be understood that, if any prior art information is referred to herein, such reference does not constitute an admission that the information forms a part of the common general knowledge in the art, in Australia or any other country.

Whilst the invention has been described with reference to preferred embodiments it should be appreciated that the invention can be embodied in many other forms.

The above describes only some embodiments of the present invention and modifications can be made thereto without departing from the scope of the appended claims.

Claim 1:
A method of increasing recovery of a metal portion from a predetermined quantity of ore in a flotation recovery circuit which comprises a grinding stage (<NUM>), a flotation recovery stage (<NUM>), a dewatering stage (<NUM>) and a filter stage (<NUM>) and which effects the steps of:
grinding a predetermined quantity of ore in the grinding stage (<NUM>) to a predetermined size while irrigating the ore with water including recovered process water thereby to form a ground ore portion;
conveying the ground ore portion mixed with the recovered process water to the flotation recovery stage (<NUM>);
the recovered process water recovered after the flotation recovery stage (<NUM>) from the dewatering stage (<NUM>) or the filter stage (<NUM>);
applying flotation recovery via the flotation stage to the ground ore portion thereby to extract a recovered metal portion from a mix of the recovered process water and the ground ore portion;
returning at least a portion of the recovered process water to the grinding stage (<NUM>);
said method comprising applying a magnetic field to the ground ore portion in a magnetic conditioning stage (<NUM>) while it is contained in the recovered process water subsequent to the grinding stage (<NUM>) and prior to the flotation recovery stage (<NUM>) for improving recovery of the desired paramagnetic minerals by aggregation of the para-magnetic minerals ;
and wherein the magnetic field strength applied to the ground ore portion in the magnetic conditioning stage (<NUM>) is at least <NUM> Gauss.