BACKGROUND OF THE INVENTION

[0001] This invention relates to the physical separation of solids, using gravity separation devices such as a spiral separator or a shaker table. [0002] A spiral separator consists of an open trough that is twisted helically downward about a vertical central axis. Slurry which is fed to the top of the trough, then flows downwardly in a spiral path, determined by the shape of the trough. Centrifugal and frictional forces acting on the moving slurry create distinct bands or streams of the slurry, with each band containing a respective category of separated solids. A nominal interface zone is formed at the junction of each pair of adjacent streams. Each stream exits from the spiral separator through a respective port. A stream is usually marshalled towards its respective port with the aid of a suitable splitter such as a flap-type splitter, e.g. a mouth organ splitter, located at an end of the trough, or through the aid of an auxiliary splitter, several of which may be located on the surface of the spiral at regular intervals. [0003] Similarly, a shaker table is used to separate solids contained in a slurry. A combined effect of mechanical reciprocating motion of the table and a thin water layer on a sloping surface of the table results in the creation of distinct regions and interface zones, formed between the regions, across the surface. The separated solids are contained in respective distinct streams, which flow over an edge of the surface and which are collected in respective troughs located at the edge. The streams are often marshaled to respective target troughs by means of suitable splitters located at the edge. [0004] The operation of the spiral separator is susceptible to fluctuating feed quality and solid content in the feed slurry and other process variables which may result in changes in the positions of the interface zones. A need therefore exists for the splitter to be adjustable to address changes in the feed conditions. [0005] An incorrect splitter position relative to the position of a target stream results in mineral losses. The position of the splitter should be adjustable to reduce this loss.

[0006] Traditionally the position of the splitter is manually adjusted. This requires regular monitoring and attention via an operator. This is a difficult and repetitive task and is often neglected. The splitter may be in a difficult-to-access location and an appropriate manual adjustment of the splitter might be challenging due to the harsh conditions in which the spiral separator operates.

[0007] Automated actuators have been developed to facilitate an adjustment of a splitter's position. This approach makes use of an optical sensor which, by detecting the position of a stream on the spiral or shaker table surface, controls an actuator which mechanically shifts the splitter from one position to another in response to a signal from the sensor. A high force is required to move the actuator, and frequent movement causes the splitter to become worn due to frictional contact with the surface, thereby increasing cost and complexity.

[0008] An object of the present invention is to address, at least to some extent, the aforementioned situation. SUMMARY OF THE INVENTION

[0009] The invention provides an apparatus for separating particulate material in a slurry which is caused to move to an exit location in at least first and second distinct bands with an interface zone between the first and second bands, the first band generally containing a first category of particles and the second band generally containing a second category of particles, the apparatus at least a first port and a second port at the exit location, and a mechanism for directing at least one jet of pressurized fluid onto or into the slurry upstream of the exit location to influence the position of the interface zone relative to the first port and the second port. [0010] The apparatus may include at least one splitter at the exit location, configured to split the first band from the second band.

[0011] The jet of pressurized fluid may influence the position of the interface relative to the splitter.

[0012] The apparatus finds particular application for use in a system in which the slurry is caused to move to the exit location along an arcuate path generally under gravity action. Thus the apparatus may be employed with benefit in a spiral separator or an equivalent device. In a spiral separator the particles tend to separate from one another, due at least to the effects of centrifugal forces and friction, into first and second generally parallel bands. The first band may contain generally heavier particles and the second band may contain generally lighter particles.

[0013] Alternatively, the apparatus may be employed with a shaker table which causes particles contained in the slurry to separate under the combined effect of a mechanical reciprocating motion and gravity action. The particles tend to separate from one another into, at least, first and second bands extending radially from a feed trough which feeds the slurry onto a surface of the table. The first band may contain generally heavier particles and the second band may contain generally lighter particles. [0014] The pressurized fluid may be pressurised air, pressurised water, pressurised slurry or any other suitable gas or liquid under pressure.

[0015] The apparatus may include a first adjustment device to alter the direction in which the jet impinges on the slurry surface.

[0016] The apparatus may include a second adjustment device to alter the shape of the jet which impinges on the slurry surface.

[0017] The apparatus may include a controller for altering or regulating the flow rate of the fluid in the jet and its pressure. The type of fluid may also be varied according to requirement.

[0018] In one form of the invention use is made of a plurality of nozzles, each of which emits a respective fluid jet onto or into the slurry. Each nozzle could be separately controlled to vary any of the aforementioned parameters. The plurality of nozzles could be in an array which extends at least across a part of the width of the first and second bands, or in an array which extends generally in the slurry flow direction, i.e. towards the exit location. [0019] In a first embodiment of the invention the apparatus includes a spiral separator which includes a spiral chute which defines a slurry passage, an inlet for feeding slurry to the slurry passage, an outlet from the slurry passage, and an off-take assembly located at the outlet, wherein the off-take assembly includes at least one splitter and at least one nozzle used to direct a fluid jet into the slurry passage at a location which is upstream from the splitter. [0020] At least one auxiliary splitter and at least one nozzle which is used to direct a fluid jet into the slurry passage at a location that is upstream from the splitter may be located in the slurry passage. Preferably a plurality of auxiliary splitters, each of which is associated with at least one respective nozzle, are located, at displaced intervals, in the slurry passage. [0021] The nozzle may be movable relative to the splitter thereby to adjust the position at which the fluid jet (in use) impinges on slurry in the slurry passage.

[0022] The splitter may divide the outlet into ports.

[0023] The off-take assembly may include a plurality of splitters with adjacent splitters defining a respective port between them. [0024] The apparatus may include a plurality of nozzles, each of which is used to direct a jet of fluid into the slurry stream at a respective position in the slurry passage.

[0025] In a second embodiment of the invention the apparatus includes a shaker table which includes a deck, mounted in a tilted position on a supporting frame, which defines a surface, a feed for introducing slurry onto the surface located at a feed side of the deck, the surface including a plurality of elongate raised formations, a mechanism for allowing the deck to reciprocally slide along an axis parallel to the raised formations to separate the slurry into at least a first band and a second band, a collection structure at a discharge edge of the deck to collect at least the first and the second band which flows from the edge, and at least one nozzle to direct a fluid jet onto the surface at a location which is upstream from the discharge edge. [0026] The shaker table may include an adjustment device for adjusting a degree of tilt of the deck.

[0027] The shaker table may include at least one splitter, which includes a first side and a second side, located e.g. at an adjacent edge of the deck. The splitter may be associated with the nozzle in such a manner that the fluid jet may be used to direct the first band, at least partially, to the first side of the splitter and the second band, at least partially, to the second side of the splitter.

[0028] The apparatus may include a plurality of splitters, each associated with a respective nozzle. The splitters may be located at spaced intervals along the edge of the deck.

[0029] In each embodiment the apparatus may include a control system which controls the emission of the fluid jet which is emitted by a nozzle, in respect of at least one of the following: the direction of the fluid jet, the time at which the fluid jet is emitted, the duration of a period for which the fluid jet is emitted, the durations of intervals between the emissions of successive fluid jets, the angle of the fluid jet, i.e. its orientation relative to the slurry in the slurry passage, the strength of the fluid jet, i.e. the pressure and the flow rate of the fluid in the jet, and the size or shape of the fluid jet.

[0030] The control system may operate in response to at least one sensor. The sensor may be visually (optically) based and may be used to detect an event or condition in response to which a fluid jet, of defined characteristics, is directed onto a particular location of a slurry stream in the slurry passage. In addition, or alternatively, a sensor may be used to verify that the fluid jet had been correctly emitted.

[0031] The sensor may be responsive to colour contrasts between discrete adjacent slurry streams or to differences in the intensity of light reflected from a surface of each stream. Alternatively, the sensor may be responsive to any other characteristic or characteristic of the material fed to or collected by the spiral or shaker table (as the case may be). Thus the characteristic need not be linked to a particular band but rather to a collection port. For example if the grade is too low the nozzle would exercise an adjusting effect to ensure that less low grade material is collected in a particular collection point (irrespective of the band).

[0032] The invention also extends to a method of using a spiral separator of the aforementioned kind wherein a feed slurry which is passed through the inlet into the slurry passage moves along the slurry passage towards the outlet under gravity action and wherein, due at least to centrifugal forces, the slurry is caused to separate into at least two adjacent streams wherein each stream contains particles generally of a particular density, the method including the step of using a fluid jet to adjust the position of an interface zone between adjacent streams relative to the splitter at the outlet.

[0033] The position of an interface zone between adjacent streams may be determined optically due to contrasts in light reflections from the respective streams. [0034] The invention further extends to a sensor for use in apparatus employed to separate particulate material in a slurry on the basis at least of particle size and particle density wherein, at least due to the effects of centrifugal forces and friction, the slurry is separated into at least two adjacent bands and wherein the sensor optically detects the position of an interface zone between the adjacent first and second bands of slurry by sensing a contrast in colour or reflected light of a surface of the slurry in the first band relative to the colour or reflected light of a surface of the slurry in the second band. [0035] In this specification "streams" and "bands" are used interchangeably.

BRIEF DESCRIPTION OF THE DRAWINGS

[0036] The invention is further described by way of examples with reference to the accompanying drawings in which :

Figure 1 shows a spiral separator according to the invention, Figure 2 depicts components at an outlet from the spiral separator, and Figures 3 and 4 depict aspects of a shaker table according to the invention. DESCRIPTION OF PREFERRED EMBODIMENTS

[0037] Figure 1 shows a spiral separator 10 according to one embodiment of the invention.

[0038] The spiral separator 10 includes a spiral chute 12 of conventional form, which defines a slurry passage 14, an inlet 16 to the chute and an outlet 18 from the chute. A feeding mechanism 20 is used to direct slurry into the inlet 14. An off-take assembly 22 is located at the outlet 18.

[0039] The off-take assembly 22 includes at least one splitter 24. The splitter is in the form of a blade which is positioned in the passage 14 at the outlet 18. The off-take assembly 22 additionally includes nozzles 26 and 28, on opposing sides of the splitter 24 and upstream from the splitter. The nozzles are separately connected to a source 30 of a pressurised fluid. Control valves 32 and 34 are positioned in the connections between the nozzles 26 and 28 and the fluid source 30, respectively. The valves are connected to a controller 36 which controls operation of the valves.

[0040] Auxiliary splitters 38 and 40 (notionally shown), which could be in the form of sliding splitters (non-limiting), are located at displaced locations in the passage 14. Nozzles 42 and 44 are located upstream from the splitters 38 and 40, respectively. The nozzles are separately connected to the source 30 of the pressurised fluid. Control valves 46 and 48, which are controlled by the controller 36, are used to control the flow of fluid from the source 30 to the nozzles 42 and 44.

[0041] An optical sensor 50 is positioned above the slurry passage 14 close to the outlet 18. Optical sensors 52 and 54 are positioned above the slurry close to the positions of the auxiliary splitters 38 and 40. Signals produced by the sensors 50, 52 and 54 are directed to the controller 36.

[0042] Figure 2 is a simplified plan view of the off-take assembly 22 and of the slurry passage 14 at the outlet 18. The optical sensor 50 (shown in dotted outline) extends across a width 56 of the slurry passage 14. The nozzles 26 and 28 are mounted to respective swivel joints 26A and 28A which allow the orientations of the nozzles to be adjusted in an angular sense, vertically relative to a surface of the spiral chute 12 and laterally as is indicated by means of double-headed arrows 26B and 28B respectively. [0043] The invention is described herein with reference to the use of the spiral separator under conditions in which slurry 57 fed into the inlet 16 from the feeding mechanism 20 has a composition in which the slurry is divided due to the action of the spiral separator, in accordance with principles which are well established, into adjacent first and second bands or streams 58 and 60 respectively of the slurry, with an interface zone 62 between the bands. As is known in the art the bands result due to the effects of centrifugal forces and friction as the slurry flows downwardly along the spiral path determined by the spiral chute. Each band generally contains a respective category of particles with each category being characterized by particles in a particular range of particle sizes and in a particular range of particle densities. As the bands generally contain different types of particles, the bands usually take on respective colours associated with the types of particles included in each band. Fluctuating feed quality and changes in the solid content in the feed slurry can affect the colours of the bands and the widths of the bands and hence the position of the interface zone 62 between the bands. [0044] The "interface zone" is a phrase used to define and refer to the junction between adjacent bands of slurry. The zone is not necessarily distinct nor precisely determinable. Also, the zone may lie on a straight, wavy, or curved or other path.

[0045] The invention is described with reference to the use of a spiral separator which produces two bands. This is illustrative only and non-limiting. The principles of the invention can be used with equal effect under conditions in which three or even more bands of slurry are formed in a spiral separator. [0046] The fluid source 30 typically contains water under pressure. This is exemplary only and is non-limiting. Compressed air could be provided by the source. Another possibility is to make use of a slurry under pressure with the slurry being of the same composition as the feed slurry. Ideally the nature of the material in the source should be such that the addition thereof in a limited quantity to the feed slurry does not materially alter the nature of the feed slurry. This aspect can be addressed to some extent by ensuring, as well, that material from the source 30 is added to the feed slurry as close as possible to the splitter 24.

[0047] In use of the spiral separator the optical sensor 50 monitors the intensities of light reflections from the band 58, from the interface zone 62, and from the band 60. The position of the sensor 50 is fixed relative to the spiral chute and the signals which are produced by the sensor 50 are thus in some way physically related to or dependent on the width of each band and the width of the interface zone. This information is fed to the controller 36. An objective is to ensure that, as far as is possible, the splitter 24 is positioned to intercept the downwardly flowing slurry at the interface zone 62 so that only material in the band 58 is directed by the splitter to a first exit path 58A and so that only material from the band 60 is directed by the splitter 24 to a second exit path 60A. The splitter position is however not adjustable.

[0048] If the optical sensor 50 detects that the interface zone 62 is moving laterally across the width 56, ie laterally away from the splitter then this is an indication that efficient splitting of the slurry stream cannot be effected by the splitter 24. The controller 36 detects in which direction the slurry stream is to be moved so that the interface zone 62 is correctly positioned relative to the splitter 24. The controller 36 opens the respective control valve 32 or 34, to an appropriate extent, so that a controlled jet of fluid from the source 30 is directed by the corresponding nozzle 26, 28 onto the surface of the slurry upstream of the splitter 24. The orientation of each nozzle relative to the slurry surface is adjusted manually or automatically according to requirement. The intention is to ensure that at least one jet of fluid with an appropriate flow rate is directed onto the slurry surface, upstream of the splitter 24, to influence the movement of the slurry relative to the splitter and, in the process, to ensure that the interface zone 62 is brought into alignment with the splitter. When this state is achieved effective and efficient splitting of the bands 58 and 60 takes place. [0049] The nozzles 42 and 44 can be used to exert a "splitting" action on the bands 58 and 60 in the passage 14, upstream of the splitter 24, as shown in Figure 2B. The band 60 is directed towards the splitter 38 or 40 (as the case may be) and is taken off the chute 12, as a band 60B, while the band 58 continues down the passage 14, as a band 58B. The optical sensor 52 or 54, in each case detects the position of the interface zone 62. In response to a signal from the respective sensor 52 or 54, the controller 36 opens the corresponding valve 46 or 48 so that the associated nozzle directs a fluid jet onto the slurry surface to move the interface zone relative to the position of the respective auxiliary splitter 38 or 40.

[0050] The control technique is implemented continuously. It may well be that the colour contrast between the bands 58A and 60A, due to differing mineral contents in the bands, is of a transient or short-lived nature. In this event the corrective action of the fluid jet is terminated when the sensor 50 detects that a fluid jet is exerting an over-correcting action. [0051] Figure 2 schematically illustrates the use of two nozzles 26, 28, one above each respective band of slurry which is formed by the separating action of the spiral separator. It is possible to make use of more than two nozzles. For example, an array of nozzles could be positioned stretching across the width 56 of the slurry passage 14. In a variation an array of nozzles is used extending generally in the direction of flow of the slurry in the passage. The displacement force exerted by the nozzles on the slurry flow is accumulative, over the region of the length of the array. The slurry is continuously contacted by the jets of the fluid. Other nozzle configurations are of course possible.

[0052] The invention has been described with reference to the use of an optical sensor 50 to detect mineral bands in a spiral separator. This is exemplary and non-limiting.

[0053] The principles of the invention can also be used in respect of a separator such as a shaker table which does not work on a spirally induced centrifugal process. Figures 3 and 4 show a shaker or riffle table 100, which includes a deck 102 mounted in a tilted position on a supporting frame 104, and a feed trough 106 for introducing slurry 108 onto a tilted surface 1 10 of the deck 102 at a feed side of the deck. A plurality of elongate raised formations, provided by bars or ridges 1 12, are formed on the surface 110. These formations extend transversely from the feed side to the opposed discharge edge.

[0054] A shaker mechanism 1 14 causes reciprocating movement of the deck 102 along an axis which is parallel to the longitudinal dimensions of the formations 1 12. The mechanism 1 14 repeatedly produces a slow forward stroke, followed by a rapid return strike, which can cause the slurry 108 to form adjacent bands 1 16, 118, 120 and 122 of material with respective interface zones 124, 126 and 128 formed between adjacent bands. The interface zones move, relative to respective splitters 132, 134 and 136, according to the composition of each band. Suitable troughs, not shown, are used to collect these bands which flow over the discharge edge. In a manner which is similar to what has been described in connection with Figures 1 and 2, and through the use of similar equipment, the interface zones can be moved by judicious use of respective nozzles 142, 144, 146 and 148 in response to sensors (not shown) which detect the position of each interface zone relative to the associated splitter.