TECHNICAL FIELD

[0001] The present invention relates to a centrifugal concentrator.

[0002] More particularly, the present invention relates to a centrifugal concentrator capable of continuous operation when harvesting concentrate.

BACKGROUND ART

[0003] The following discussion of the background art is intended to facilitate an understanding of the present invention only. The discussion is not an acknowledgement or admission that any of the material referred to is or was part of the common general knowledge as at the priority date of the application.

[0004] Centrifugal concentrators are commonly used to recover heavy metals and minerals from slurry.

[0005] Conventional concentrators include a frusto-conical bowl which is rotated at speed to produce a centrifugal force at the bowl wall.

[0006] Slurry containing heavy metal or mineral particles is entered into the bowl near the base and is driven up the wall by the centrifugal force.

[0007] The wall comprises at least one riffle, being a rib or lip on the bowl wall where heavier particles collect as the slurry flows over. Typically, a number of riffles are included within the wall.

[0008] The rotating bowl allows high centrifugal forces to be applied to maximise the particle collection.

[0009] A centrifugal concentrator can be operated on a batch and continuous basis.

[0010] A first centrifugal concentrator design, described as the manual operation concentrator and involving batch operation, comprises numerous riffles to maximise particle collection. However, to collect the deposited particles, the concentrator must be fully stopped and manually cleaned. Such cleaning may be carried out by an operator using a hose for example. The cleaning operation takes time and is not appropriate for a large weight pull (i.e. concentrator weight to feed weight).

[0011] A second continuous concentrator has remotely operated discharge valves that release the concentrate without stopping the machine. In one design, the collection of deposited particles is achieved using a series of pneumatic valves arranged around the perimeter of the bowl under a single riffle. The pneumatic valves are opened just long enough for the deposited particles to be extracted, allowing the collection of concentrate whilst the concentrator is operating. Such continuous concentrators, in themselves, are complex, expensive and prone to failure. Furthermore, the single riffle arrangement - where used - limits the volume of collectable concentrate per instance of collection.

[0012] Any requirement to stop operation of a concentrator is undesirable, as it must be done frequently and stopping is also likely to require the interruption of upstream machinery, such as the slurry feed.

[0013] The present invention attempts to overcome at least in part the aforementioned disadvantages of previous centrifugal concentrators by providing a concentrator capable of continuous operation at a lower cost than known designs.

SUMMARY OF INVENTION

[0014] In accordance with one aspect of the present invention, there is provided a centrifugal concentrator comprising: a bowl having a frusto-conical wall; a slurry inlet; and a basket comprising a series of riffles; wherein the basket is moveable between a first configuration and a second configuration; and wherein, when in the first configuration, the riffles are seated against the wall; and, when in the second configuration, the riffles are offset from the wall.

[0015] Preferably, the concentrator further comprises: a slurry discharge and a concentrate discharge; wherein the basket comprises an upper ring configured to direct slurry to the slurry discharge when the basket is in the first configuration, and to direct concentrate to the concentrate discharge when the basket is in the second configuration.

[0016] Preferably, the bowl and basket are configured to rotate around an axis.

[0017] Preferably, the bowl and basket are configured to rotate together at substantially the same speed.

[0018] Preferably, the concentrator comprises an actuator to move the basket between the first and second configurations.

[0019] Preferably, the concentrator comprises a plurality of stabilisers to maintain the basket’s axial position when in the second configuration.

[0020] Preferably, the slurry inlet is configured to provide slurry to a base of the bowl.

[0021] Preferably, the concentrator comprises at least one spray directed at the wall of the bowl, wherein the spray is configured to spray liquid to wash the wall when the basket is in the second configuration.

[0022] Preferably, the slurry inlet comprises a bund or reservoir configured to store sufficient slurry for the duration of the particle collection operation.

[0023] In accordance with a further aspect of the present invention, there is provided a method of operating a centrifugal concentrator comprising: a bowl having a frusto-conical wall; a slurry inlet; a slurry discharge; a concentrate discharge; and a basket wherein the basket comprises a series of riffles and an upper ring; wherein the basket is moveable between a first configuration and a second configuration; and wherein, when in the first configuration, the riffles are seated against the wall and the upper ring is configured to direct slurry to the slurry discharge; and, when in the second configuration, the riffles are offset from the wall and the upper ring is configured to direct concentrate to the concentrate discharge; wherein the concentrator is operated to collect concentrate according to the following method steps: a. inserting slurry, whilst the bowl is rotating, causing the slurry to flow up the wall, causing heavier particles to concentrate and collect against the riffles and directing barren slurry to the slurry discharge; b. moving the basket from the first configuration to the second configuration, creating a gap between the riffles and the wall, closing the slurry discharge and opening the concentrate discharge; c. allowing the concentrate to flow out of the bowl into the concentrate discharge; d. moving the basket from the second configuration to the first configuration, causing the riffles to locate against the surface, opening the slurry discharge and closing the concentrate discharge.

[0024] Preferably, the method comprises the following steps after steps a and d; ai. diverting flow of slurry to a bund so that slurry can continue to be pumped for the duration that the basket is in the second configuration; di. diverting flow of slurry from the bund to the bowl, so that concentrate collection may continue.

[0025] Preferably, the method comprises the following additional step after step c: ci. spraying the bowl wall to assist with removal of concentrate.

[0026] In a further aspect, there is provided a basket for use in the above described centrifugal concentrator or method of operation of the centrifugal concentrator. The bowl and/or basket are desirably replaceable components.

BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Further features of the centrifugal concentrator of the present invention are more fully described in the following description of several non-limiting embodiments thereof. This description is included solely for the purposes of exemplifying the present invention. It should not be understood as a restriction on the broad summary, disclosure or description of the invention as set out above. The description will be made with reference to the accompanying drawings in which:

[0028] Figure 1 is a cross-section view of a centrifugal concentrator according to one embodiment of the present invention in which the concentrator is depicted with the basket in the first configuration.

[0029] Figure 2 is a cross-section view of the centrifugal concentrator according to one embodiment of the present invention in which the concentrator is depicted with the basket in the second configuration.

[0030] Figure 3 is a close-up cross-section view of the bowl wall of the centrifugal concentrator of Figure 1.

[0031] Figure 4 is a close-up cross-section view of the bowl wall of the centrifugal concentrator of Figure 2.

DESCRIPTION OF PREFERRED EMBODIMENTS

[0032] Referring to the Figures, there is shown a centrifugal concentrator 10 according to the present invention, the concentrator 10 comprising: a bowl 20 having a frusto- conical wall 30; a slurry inlet 50; and a basket 40 comprising a series of riffles 42; wherein the basket 40 is moveable between a first configuration and a second configuration; and wherein, when in the first configuration, the riffles 42 are seated against the wall 30 and, when in the second configuration, the riffles 42 are offset from the wall 30. Centrifugal concentrator 10 may, in an embodiment, be used in a precious metals extraction process, such as for recovery of gold bearing particles.

[0033] The centrifugal concentrator 10, as shown, further comprises: a slurry discharge 60 and a concentrate discharge 70: wherein the basket 40 comprises an upper ring 45 configured to direct slurry to the slurry discharge 60 when the basket 40 is in the first configuration and to direct concentrate to the concentrate discharge 70 when the basket 40 is in the second configuration.

[0034] The bowl 20 and basket 40 may be configured to rotate around an axis, in this case a vertical axis.

[0035] The bowl 20 and basket 40 may be configured to rotate together at substantially the same speed.

[0036] The concentrator 10 may comprise an actuator 80 to move the basket 40 between the first and second configurations.

[0037] The concentrator 10 may comprise a plurality of stabilisers 90 to maintain the basket’s 40 axial position when in the second configuration.

[0038] The slurry inlet 50 may be configured to provide slurry to a base of the bowl 20.

[0039] The concentrator 10 may comprise at least one spray (not shown) directed at the wall 30 of the bowl 20, wherein the sprays are configured to spray liquid to wash the wall 30 when the basket 40 is in the second configuration.

[0040] The slurry inlet 50 may comprise a bund or reservoir (not shown) configured to store sufficient slurry for the duration of a collection operation.

[0041] In an embodiment, the centrifugal concentrator 10 comprises: a bowl 20 having a frusto-conical wall 30, a slurry inlet 50, a slurry discharge 60, a concentrate discharge 70 and a basket 40. The basket 40 comprises a series of riffles 42 and an upper ring 45.

[0042] Basket 40 is movable between a first configuration and a second configuration. [0043] When in the first configuration, as shown in Figures 1 and 3, the riffles 42 are seated against the wall 30 of bowl 20. The upper ring 45 is, in this first configuration, configured to direct slurry to the slurry discharge 60.

[0044] When in the second configuration, as shown in Figures 2 and 4, the riffles 42 are offset from the wall 30 of bowl 20. The upper ring 45 is, in this second configuration, configured to direct collected concentrate to the concentrate discharge 70.

[0045] The operation of centrifugal concentrator 10 may proceed, in one embodiment, as follows.

[0046] Slurry is inserted or fed into the centrifugal concentrator 10 at a base of bowl 20 whilst the bowl 20 is rotating at a determined operating speed causing the slurry to flow up the wall 30. Under centrifugal force, which is a function of the determined operating speed, heavier particles from the slurry are caused to concentrate and collect against the riffles 42. In an embodiment where centrifugal concentrator 10 is used to recover gold bearing particles, the heavier particles, i.e. having higher specific gravity than gangue material, would be expected to be gold bearing.

[0047] In one embodiment, barren slurry from which substantially all particles have been separated is directed to the slurry discharge 60. In other embodiments, particles of different size ranges may be separated using a plurality of centrifugal concentrators 10, each operated with a determined operating speed and centrifugal force to separate particles of selected particle size in each centrifugal concentrator 10.

[0048] Following collection of particles, basket 40 may be moved from the first configuration to the second configuration, creating a gap between the riffles 42 (where particles have collected), closing the slurry discharge 60 and opening the concentrate discharge 70.

[0049] The concentrate bearing the collected particles are allowed to flow out of the bowl 20 into the concentrate discharge 70. This step involves a batch discharge of concentrate without the need to stop the centrifugal concentrator 10.

[0050] The basket 40 is then moved from the second configuration to the first configuration, causing the riffles 42 to locate against the wall 30, opening the slurry discharge 60 and closing the concentrate discharge 70. [0051] The operating cycle, as described above may repeat on a continuous basis without need for stopping of operation of the centrifugal concentrator 10 other than for scheduled maintenance. Thus, the operating cycle is time and cost efficient.

[0052] In another embodiment, the operating cycle may include additional steps as follows.

[0053] In a step ai, a flow of slurry may be diverted to a bund (not shown) so that slurry can continue for the duration that the basket 40 is in the second configuration.

[0054] When basket 40 is returned to the first configuration, the flow of slurry is diverted from the bund to the bowl 20, in a step di, so that concentrate collection can continue as above described.

[0055] If necessary, spray(s) may be provided to spray wall 30 of bowl 20 to assist with removal of concentrate in a step ci.

[0056] In use, with the basket 40 in the first configuration, the concentrator 10 operates conventionally. Slurry is provided or fed to the base of the bowl 20 and centrifugal force forces the slurry outwards and up the wall 30, where particles of greater density collect and form a concentrate at the interfaces between each riffle 42 and the wall 30.

[0057] To collect the concentrate, the basket 40 is raised into the second configuration, creating a gap 43 between each riffle 42 and the wall 30 of the bowl 20.

[0058] The gap 43 allows the concentrate to flow up the wall 30 of the bowl 20.

[0059] When in the second configuration, the upper ring 45 at the top of the basket 40 closes the slurry discharge 60, and opens the concentrate discharge 70, allowing the concentrate to be collected separately from the barren slurry.

[0060] Where sprays (not shown) are provided, these assist with cleaning the concentrate from the bowl 20 and optimising particle recovery. In one example, spraying water on the wall 30 loosens and frees concentrate which may be stuck to the wall 30 or riffles 42.

[0061] The moveable basket 40 allows the centrifugal concentrator 10 to operate continuously, thus overcoming a problem associated with one commonly known design. [0062] The moveable basket 40 further enables the collection of concentrate over a greater number of riffles 42, thus overcoming a problem associated with known concentrators capable of continuous operation.

[0063] The upper ring 45 of the basket 40, which is used to redirect the flow of the contents of the bowl 20, from slurry being directed to a slurry discharge 60 when in the first configuration, to concentrate being directed to a concentrate discharge 70 when in the second configuration, overcomes a problem associated with known concentrators capable of continuous operation, being the complexity of the concentrate discharge mechanism.

[0064] The centrifugal concentrator 10 of the invention therefore provides a more reliable and cheaper alternative to known continuous operation centrifugal concentrators.

[0065] Modifications and variations to the centrifugal concentrator as described herein will be apparent to the skilled reader and are deemed to be within the scope of the present invention.

[0066] Throughout this specification, unless the context requires otherwise, the word "comprise" or variations such as "comprises" or "comprising", will be understood to imply the inclusion of a stated integer or group of integers but not the exclusion of any other integer or group of integers.