GRAVITATIONAL SEPARATION

Abstract: A shaking table for ore-dressing, having riffles (50) on its deck (10), has circular orbital motion imposed on it to cause the riffles to oscillate, and for a standing wave (71) to be created between the riffles. The continued circular motion acting on the standing waves causes sharp separation of the material fractions which are discharged continuously from the deck. The slope of the deck (10) and riffles (50) and the configuration of the riffles are critical. The slope of the deck is set empirically by estimating the approximate slope appropriate to the parameters of the material being treated and of the motion imparted to the deck; and the final adjustment is made by slewing the deck in its own plane to obtain an optimum result. For a frusto-conical deck (69), the adjustment is made on a flat deck and the frusto-conical deck is constructed accordingly. The deck may have rectilinear or curvilinear motion imparted to it, superimposed upon the circular motion.

Description: FIELD OF THE INVENTION This invention relates to the dressing of particulate ores and / or other material by means of shaking tables. More specifically this invention relates to a method of separating fractions of different density and / or size from a mixture of materials. The invention relates also to apparatus for dressing such material. BACKGROUND OF THE INVENTION Known shaking tables consist of sloped deck, or the upper bight of a moving belt, with or without superficial riffles and with means to vibrate the deck. The collective effect of deck motion, deck slope, deck surface, riffle configuration, rates of flow of material and wash medium, deck geometry and interaction of the material being treated with the wash medium, combine to achieve separation of the material into its components. The behaviour of such tables is in practice unpredictable owing to the inability to alter the variable parameters individually to meet the process conditions. As a result, all shaking tables in current use that are known to the applicant are necessarily a compromise. Where deck motions imposed by linear vibration generate discontinuous shear forces, by the very nature of asymmetric or reciprocal motion, particle deceleration and remixing of the separated fractions occur. Where shaking is caused by rotation of an out-of-balance shaft, an unpredictable elliptical path is imposed on the particles traversing the deck and there is a control problem where the frequency of the oscillatory motion approaches the natural frequency of the table supports. In the latter case, the rate of shear is a function of at least three variables, viz rotational speed, amplitude and total shaken weight. Adjustments to deck pitch are limited to either longitudinal or transverse slope, or both, but do not compensate for change with pitch of the approach angle of the stream of material to the riffles. As far as the applicant is aware, no method has been used which yields an operation under continuous discharge with discrete control of any single variable which influences the separation and concentration of materials containing fractions within a range of densities. Various machinery for separating materials of different specific gravity has been identified in the prior art. In particular document GB-A-22728 discloses such apparatus which comprises a frame mounted, endless elastic belt having raised riffles therein, travelling over powered rollers and imposed upon by circular motion intended to simulate the motion given by a miner to a suspended vanning shovel. The belt is given an inclined disposition of varying amount, transverse to the direction of travel. The raised riffles are oriented substantially in a direction parallel to the travel of the belt. The apparatus is suspended from four adjustable hangers which control a pendular swinging movement and is driven via pivotal linkage and connecting rods by two cams which stabilise the circular motion imposed on the belt, but such that the belt rises and falls in the vertical plane giving rise to an elliptical rocking movement as opposed to planar, circular orbital movement of constant angular velocity. The amplitude of vertical movement increases with the eccentric of the cams. Means are provided for feeding material to the higher part of the belt and wash water along the operative length of the belt. The belt surface in its operative length is characterised by biased slope and increasing transverse slope or cross-fall, giving rise from head to tail to a progressive reduction in the damming back effect of the riffles. Consequent on the net operating movement and the bias of the belt, the slope of the riffles and the angle between deck slope and the riffle slope in operation vary throughout the operative belt surface. Discharge of product is achieved by travel of the moving belt. No significance is attached to the pitch of the riffles in relation to frequency or amplitude of circular movement. The applicant is aware that riffled endless powered belts have been proposed in apparatus for separating ores and does not claim such a device broadly. OBJECT OF THE INVENTION The object of this invention is to propose an operating method and a dressing table to carry out the method, which have advantages over conventional methods and shaking tables. THE INVENTION According to the invention a method of dressing a mixture of particulate ores or other solid materials containing fractions of different density and/or particle size consists in flowing a stream of the mixture carried in a liquid and of a wash liquid onto an inclined deck having riffles therein, characterised by creating a standing wave system in the flowing material in the troughs between the riffles while imposing continuous, uniform, planar, circular orbital motion on the inclined deck, and imposing a shear force on the standing wave system, whereby the components of the mixture are caused to separate from one another into moving fractions; and continuously discharging the fractions from the deck. Preferably, the method is characterised by causing the mobile fractions to remain discrete and continuously discharging the mobile fractions from the deck, tilting said deck about its longitudinal and lateral axes and, while maintaining said deck inclined, slewing the deck in a plane about an axis normal to the deck through an arc of up to 60 degrees to vary the acute angle of approach by the stream of material to the riffles, fixing the deck in that orientation whereby during planar, circular orbital motion of the deck the riffles on the deck will oscillate at a constant acute angle relative to the natural direction of fluid flow. The mobile fractions are continuously discharged from the deck. By "planar" is meant that the deck is moved along a prescribed circular orbital path, and that the path lies within a plane irrespective of the configuration of the deck or of the angular relationship between its axis and the plane. Further according to the invention, a circular orbital motion of constant angular velocity imparted to the deck imposes uniform otherwise described as simple harmonic oscillatory, planar motion on the riffles. The method of the invention has the important distinction compared with known orbital shaking tables in that the discharge of discrete moving fractions is continuous and not discontinuous nor batch-wise. Further according to the invention, the inclination of the riffles is less than the inclination of the natural direction of stream flow, and the acute angle between the two in the plane of the deck is constant throughout the motion of the deck. By Cartesian convention, taking the riffles as the X axis, the acute angle lies in the second quadrant for anticlockwise motion of the deck and the first quadrant for clockwise motion of the deck respectively, when the deck is subjected to uniform, planar, circular orbital motion. Further according to the invention, the acute angle of attack of the fluent stream to the riffles is adjusted by means of slewing the riffled deck in its own plane about an axis normal to the deck surface through an arc of up to 60 degrees and thereafter, imposing uniform, simple harmonic oscillatory, planar motion on the riffles. By "slewing" the deck is meant the deck is rotated in its pre-adjusted plane. The net effect is that the slope of the riffles and the acute angle of approach of stream flow to the riffles are adjusted in the plane of the deck, independently of the slope of the deck. Further according to the invention, the method consists in imposing differential trochoidal motion on a stream of fluent material subjected to planar, circular orbital shear forces to cause a divergent longitudinal advance of mobile fractions of the material along the deck dependent upon the physical characteristics of the particles and to cause the continuous discharge of sharp fractions from the deck. In one form of the invention, asymmetric linear motion, rectilinear or curvilinear, is superimposed upon the continuous and uniform, planar, circular orbital motion of the deck. THE DRAWINGS Embodiments of the invention are shown in the accompanying drawings, in which : Figure 1 is a side elevation, partially sectioned, of the shaking table of the invention; Figure 2 is an enlarged fragmentary side elevation of the tilt and slew mechanism, indicated by the chain line circle in Figure 1; Figure 3 is a perspective view of a portion of the deck; Figure 4 is a plan view of a riffled deck orientated for clockwise planar, circular orbital motion; Figure 5 is a fragmentary section side elevation of the riffles on the decks of Figures 3 and 4; Figures 6 and 7 are respectively a side elevation and a plan view of a deck provided by a moving belt; Figure 8 is a fragmentary section side elevation of a deck showing schematically a progressive wave system in decay; Figure 9 is a view similar to that of Figure 8, showing schematically a standing wave system; Figures 10A to 10H show schematic views of the behaviour of particles; Figure 11 is a plan view of slope geometry; Figure 12 is a representation of the quadrants of the deck according to Cartesian convention; Figure 13 is a side elevation of a frusto-conical deck; Figure 14 is a plan view of the deck of Figure 13; Figure 15 is a schematic plan view of a deck arranged for rectilinear vibration; Figure 16 is a schematic plan view of multiple decks arranged for curvilinear vibration; Figure 17 is a schematic side elevation of a deck with means to amalgamate, trap hydrophobic constituents and separate electro-magnetically shown in one figure for convenience of illustration; and Figures 18A to 18D are plan views of riffle configurations. DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS The shaking table illustrated in Figures 1 and 2 comprises a flat, tilted deck 10 with side walls 11 and 12 (Figure 3). The deck is mounted on a carrier ring 13, which rests on and is contained by three equidistant upwardly directed slide plates 14. The slide plates are mounted on a rigid bearer frame 16. The frame 16 is carried by three upwardly directed jacking bolts 18 equally spaced apart, as is more clearly seen in Fig. 2, and each is provided with a lock nut 19 and a spring washer 21 and let into a screw-threaded and shouldered shaft 20. Each slide plate 14 is tapped to receive a locking screw 22 and a lock nut 24. The shaft 20 is contained within a sleeve 25 of a self-aligning flanged bearing, which is mounted on a movement distributor plate 28. Spacing washers 30 are fitted between the bearing sleeve 25 and the underside of the shoulder of the shaft 20. The sleeve is arranged within a spherical bearing 26 to enable the sleeve to rotate, and which enables the jacking bolts to swivel in their housings 27. The spacing washers 30 are supplied in varying thicknesses in order to return the travel of the shaft screw-threading to within range of the jacking bolts 18. The slope of the deck is adjusted by rotating the shouldered shaft 20 inside the bearings 26 to vary the effective length of the bolts and thus to vary the tilt of the deck in three dimensions. During this adjustment, one of the bolts 18 is left at constant length. The orientation of the deck and carrier ring is held on the tilting bearer frame 16 by the locking bolts 22 and nuts 24 which, when slackened, permit the deck and carrier ring slewing adjustment in the plane of the deck about an axis normal to the deck surface, independently of the tilting bearer frame. The movement distributor plate 28 is connected to three or more (and preferably three) rigid legs 32. Each set of legs has an elastic universal mounting 34 located at one end and another 36 at the other end. The upper universal mounting 34 is bolted to the movement distributor plate and the lower universal mounting 36 to a base frame 38. The movement distributor plate 28 is connected centrally by means of a smooth self-aligning flanged bearing 40 to a motor drive shaft 42 which is releasably engaged with an eccentric bearing or bush 44. A suitable variable speed controlled drive motor 46 is mounted on a rigid independent support 48 fixed to the base frame 38. The motor 46 serves to rotate the drive shaft 42, and the eccentric bush 44 which is interchangeable to give the desired amplitude. The motion of the eccentric offset shaft follows a perimeter defined by a circle which is co-axial with respect to the motor drive shaft, giving a planar, circular orbital motion to the movement distributor plate 28. Thus, rotation of the drive shaft 42 will cause the movement distributor plate 28 at all points to orbit exactly in its own plane. This orbital motion is transmitted to the deck 10 as "planar" circular orbital movement without yawing, pitching or heaving motion. The deck 10 (Figures 3 and 4) has a surface with raised riffles 50 therein, and is served by a feed inlet 52 and peripherally fitted on adjacent sides with wash liquid inlets 54 and 56, each having separate means of flow control (not shown) and a plurality of nozzles. One inlet 54 is mounted along the side 58 of the deck and the other inlet 56, along the upstream side 59 of the deck. A peripheral launder 57 which is transversely partitioned, is located under the remaining two side edges of the deck. The method of the invention requires that, in operation, the deck 10 executes continuous and uniform, planar, circular orbital motion, giving the riffles 50 a simple harmonic planar oscillation. The spatial relationship of the plane to the horizontal and to the vertical, for optimum performance, is dependent upon the nature of the material being handled, and parameters such as amplitude and frequency of oscillation. While it may be theoretically possible to arrive at the optimum relationship of the plane for any particular material, it would, in practice, be impossible. For that reason, the method of the invention provides that the table be adjusted empirically in relation to the horizontal and vertical, by a guesstimate. This having been made, the bolts 18 are adjusted in length to tilt the table accordingly. Samples of the material, together with the fluent wash liquid are then fed on to the deck via the feed inlet 52 and the wash liquid inlets 54 and 56, while the deck is in continuous, planar, circular orbital motion. Adjustments to the deck orientation are made and variations of the other parameters - the rate of feed, the amplitude and frequency of circular orbital motion - are tested, until sharp separation of the particles or other desired result is achieved, when the bolts 18 are locked permanently (as far as that material is concerned). In practice it has been found that optimum separation is readily determined by examination of the fractions discharged from the deck, so that the empirical phase for each material is short. The riffles 50 (Figures 3 and 4) may be straight and parallel or arcuate and coaxial (Figure 18A). They may be inclined to the edge 58 of the deck, or parallel to it (Figure 18B). They may cover part only, or all of the surface of the deck. They may vary in pitch (Figure 18B). They may diverge (Figure 18B). In cross-section, the riffles may be constant, that is rectangular (Figure 5), or they may taper in their height (Figure 18C) or their length (Figure 18D). The deck characteristics for second quadrant operation are illustrated graphically in Figure 3. Here, the deck slope is marked D, the acute angle of fluid approach to the riffles in the second quadrant S, and the anti-clockwise circular orbital movement of the deck A. The deck characteristics for first quadrant operation are illustrated graphically in Figure 4 with appropriate clockwise circular orbital movement B. The applicant has established that the sense of direction of circular orbital motion and slope of the deck with respect to the quadrant are significant, and that the opposite direction to A or B of planar, circular orbital motion may be engaged to advantage. After the optimum orientation of the deck and the various parameters of motion and feed have been established, the particulate material to be dressed is flowed on to the deck at a high position through the feed inlet 52 together with the wash liquid through inlets 54 and 56. It will be appreciated that the table description is simplistic and that there may be multiple decks side by side, or stacked decks. Further, the deck surface (Figure 6) may consist of the upper bight of a moving belt 62 which may move in either direction (Figure 7) and where the belt is supported by the slide plate 68 fixed to the sub-frame integral with the carrier ring 13. One of the two conveyor rollers 64 and 66 is motorised with speed control. The configuration of the individual riffles is such that as a result of the planar oscillatory motion imposed on the riffles 50 an hydraulic progressive wave is created on both sides of a riffle. Beyond particular riffle pitch, deck and riffle slope, and within a particular orbital speed, amplitude or riffle height, the progressive wave system 70 decays before reaching the uppermost of two adjacent riffles 50 (Figure 8). Even under these conditions the mechanism of separation is effective. Figure 10A is a plan view of a deck 10 with parallel ridges 50. The figure includes section lines A-A to E-E to show the position of the particles at various locations across the deck. The behaviour of the particles as they traverse the deck solely by planar trochoidal motion is shown in Figures 10B to 10H. At section AA (Figure 10B), the material is arriving on the deck and the mixture of particles is random. The heavier particles are shown hatched while the lighter are shown in outline. At section B-B (Figure 10C), stratification and sorting resulting from the planar, circular orbital motion is shown. The particles have formed a dilated bed under stable levitation, with the heavier particles below the light and the particles of greater diameter above the fines. Figure 10D is a plan view, at section C-C to indicate the net displacement with time of various strata in the plane of the deck. Figure 10E is a spatial illustration of the trochoidal path A followed on the plane of the deck at different amplitudes by various strata in stable levitation. Figure 10F is a section at D-D of the trochoidal path of progression between riffles in the plane of the deck followed by particles under the influence of dynamic friction forces. In Figure 10G, at section D-D is shown a transitional condition of partially classified particles arranged between successive riffles. It will be seen that classification is complete at the lowermost and uppermost riffles, and incomplete at the intermediate riffles. However, at those intermediate riffles, the heavier particles have descended below the lighter. Figure 10H is a section at E-E and shows the final condition of particles, sorted and classified between the riffles, prior to discharge from the deck. An analysis of the particle behaviour indicates that, by reducing independently the riffle pitch or either the deck or riffle slope, or by increasing either the amplitude or frequency of motion, or the riffle height, the hydraulic motion is compounded of two wave systems 70 progressing in opposite directions. The planar oscillatory motion of the riffles causes an effect similar to vanning, and a series of standing wave systems 71 form intermediate to and parallel to adjacent riffles as shown in Figure 9. With each standing wave system, nodes of instantaneous zero motion occur indigenous to a mean position with respect to the adjacent riffles. Nodal and antinodal zones are imposed upon by planar, circular orbital shear forces. The particles entrained in a nodal zone are influenced by planar orbital shear forces. While nodal zones successively receive feed from upstream, lighter / larger particles in these zones are preferentially displaced by heavier / smaller particles until the inherent lateral transport capacity of the nodal zones is occupied preferentially by relatively heavier / smaller particles. While the particles are encountering antinodal zones of maximum wave motion and surmounting the riffles, successive sorting occurs by the subsequent removal of successively lighter / larger particles. Prior to and subsequent to the formation of the standing wave system, particles move down the deck by the mechanisms of surface washing and differential trochoidal displacement and the lateral, sliding migration of particles in contact or semi-contact with the deck surface intermediate the riffles, along the deck towards the deck perimeter 60 over which they spill into the partitioned launder 57. When they reach the edge 60 (Figures 3 and 4) the particles have been separated into fractions, the concentrates and tailings being discharged from the upper and lower reaches of the deck surface respectively and the middlings intermediately. It is a feature of the process that the separation of the fractions is sharp. The performance of a riffled deck is controlled by both deck and riffle slope as illustrated in Figures 11 and 12 and explained as follows : Consider two superimposed equilateral triangles separated tripodally by adjustable legs the lengths of which are H1, H2, H3, respectively. While the lower triangle remains in a fixed plane, always leaving H1 = 0, the pitch of the upper triangle may be altered by separate adjustments to H2 or H3. For purposes of illustration, assume that H3 will be always greater than or equal to H2 and that for anticlockwise circular orbital motion fluid enters the diagram appropriately in the second quadrant at point A. For any value of H3 and where H2 = H3 fluid will flow orthogonal to H2 - H3 i.e. parallel to and along AB. In the other case, for any value of H3, when H2 = H1 = 0 then fluid will flow orthogonal to H1 - H2 i.e. parallel to and along AC. By inspection, the maximum angular change R in the direction of fluid flow will be 60 degrees or less. In order to maintain a given acute angle of attack S of fluid flow to any riffle, indicated by JAE, the maximum required operating range of angular compensation of the line JAE about the point A will be 60 degrees or less taken in the plane of the deck. For trigonometric reasons, as H2 is varied between H3 and 0 there is for any particular value of H3 relative to H1 = 0 and any particular angle of attack, a fixed ratio between riffle slope and natural slope of fluid flow. Since riffle slope would be altered by slewing, the use of a frusto-conical surface (Figures 13 and 14) requires the deck and riffle slopes to be predetermined and the bearer frame 16 to be equally adjusted to the horizontal. The term frusto-conical surface is intended to mean the upper surface of a frusto-cone the apex of which is uppermost, as well as one of which the upper surface is convex or concave. It will also be appreciated that the operation of the table is dependent upon the characteristics of the material being sorted. The establishment of the parameters of deck tilt, riffle slope, acute angle of attack, amplitude and frequency of planar oscillatory and circular orbital motions, rate of feed to the deck, rate of flow of the wash liquid, and so on are empirically determined, but the particular method of the invention allows the determination of optimum parameters to be established and reproduced with greater precision and accuracy than can be achieved by conventional shaking tables in practice. For example, in the regimes of deck slopes of less than 2,5 degrees and of riffle slopes of less than 1,5 degrees, variable slope geometry as described above offers significant improvement in the control and performance of a riffled deck. The following conclusions are based on test work using beach sand, and increasing independently the listed variables : Advantages may be achieved by imposing directional secondary asymmetric linear (rectilinear / curvilinear) motion C counter to the fluid flow on the deck, superimposed upon the primary planar, circular orbital motion. The result of the combined motions is to enhance the efficiency of the separation and increase the transport capacity of the standing waves. The reason for this advantage is not fully understood but has been demonstrated in practice to be substantial. The means to do this is seen in Figures 15 and 16 where 72 shows a vibrator and 74 shows a second vibrator, arranged to cause mass transport generally counter to the direction of trochoidal movement of the material fractions but insufficient to overcome trochoidal displacement. The advantages of variable slope geometry through slewing are applicable to the operation of the table under asymmetric linear motions as shown in Figures 15 and 16. The driving means for asymmetric linear motion comprises at least one pair of external vibrator motors, each having an adjustable working moment, and mass equally disposed radial to the central vertical axis of the table, motor axes inclined and adjusted in the vertical plane, and the shafts of which contra-rotate. The motor speeds are synchronised and controlled by regulating the frequency and voltage of three phase electrical power through an invertor. Rectilinear directional acceleration (Figure 15) is achieved by disposing the axes of the vibrator motors 72 and 74 at a common angle to the horizontal plane, and curvilinear directional acceleration (Figure 16) by disposing the axes of the vibrator motors 72 and 74 in apposition at an equal angle to the horizontal plane. The amplitude of vibration is varied by adjustment to the working moment of the external vibrator motors. The geometry of table construction and lay-out may require either rectilinear or curvilinear directional acceleration. In the latter case the effective deck surface must occupy the upper surface of a flat deck (Figure 15) or be located entirely in one quadrant of a circle and outside the central vertical axis of the motor axes (Figure 16), such that the lines of acceleration C are generally up-slope and counter to fluid flow D. It is commonly known that with respect to the central vertical axis of curvilinear directional motion as generated by twin vibrators, the amplitude of motion remains constant with increasing radius, and for any frequency the acceleration of the particles increases radially by virtue of interference between the natural resonance of the apparatus and the vibrator motors. The apparatus described provides for one or two motions and particularly the amplitude of either the oscillatory, planar, circular orbital motion or the asymmetric linear motion must be adjusted separately and independently; and the frequency of either motion must be steplessly and independently controlled. Whichever mode of motion or combination of linear and oscillatory, planar, circular orbital motion, the advantages of slewing remain and the separation of fractions is sharp. As an example of the operation of the table, the following range of parameters has been found to be satisfactory : - primary motion : amplitude between 1mm and 50mm; orbital speed between 150 rpm and 300 rpm. secondary motion: frequency between 1200 rpm and 1900 rpm. While the method of the invention has been developed for the separation of particulate materials into fractions, the utility of the method goes further when certain fractions lose their mobility. As shown schematically in Figure 17, the deck surface may be prepared by copper coating K or depressions M to receive mercury for the process of amalgamation; by using the table T as a grease table for trapping hydrophobic valuable constituents such as diamonds, or a mixture of such constituents and gangue; or by the facility of electromagnetic separation by mounting an electro-magnet P over, or one N, under the deck surface 50, with suitable nonmagnetic materials of construction chosen for the apparatus.

Claims: A method of dressing a mixture of particulate ores or other solid materials containing fractions of different density and / or particle size which consists in flowing a stream (70) of the mixture carried in a liquid and of a wash liquid on to an inclined deck (10) having riffles (50) therein, characterised by creating a standing wave system (71) in the flowing material in the troughs between the riffles (50) while imposing continuous, uniform, planar, circular orbital motion on the inclined deck (10), and imposing an orbital shear force on the standing wave system (71) whereby the components of the mixture are caused to separate into moving fractions; and continuously discharging the fractions from the deck (10). The method of Claim 1 further characterised by causing the mobile fractions to remain discrete and continuously discharging the mobile fractions from the deck (10), tilting said deck (10) about its longitudinal and lateral axis and while maintaining said deck (10) inclined, rotating the deck (10) about an axis normal to the deck (10) through an arc of up to 60 degrees to vary the acute angle (S) of approach by the stream of material to the riffles, fixing the deck (10) in that orientation, imparting continuous, uniform, planar, circular orbital motion (A or B) to the deck (10) to cause the riffles (50) on the deck (10) to oscillate at a constant, acute angle (S) relative to the natural flow path (D) of the liquid and wash liquid across the deck (10), imposing differential trochoidal motion on the particulate components to cause divergent longitudinal advance of mobile fractions. The method of Claim 1 or 2, characterised in that the angle (S) between the riffles (50) and the natural flow path (D) of the liquid and the wash liquid across the deck (10) is a constant, acute angle (S) throughout the continuous and uniform, planar, circular orbital motion (A or B) of the deck (10). The method of Claim 1 or 2, characterised in that (by Cartesian convention taking any riffle (50) as the X axis) the acute angle (S) between the riffles (50) and the natural flow path (D) of the liquid and wash liquid across the deck (10), lies in the second quadrant for anti-clockwise planar, circular orbital motion (A) of the deck (10) and in the first quadrant for clockwise planar, circular orbital motion (B) of the deck (10). The method of Claim 1 or 2, characterised in that the feed of material and wash liquid is continuous. The method of Claim 1 or 2, characterised in that the amplitude of continuous planar, circular orbital motion (A or B) is constant over the entire deck (10) with changes in frequency. The method of Claim 1 or 2, characterised in that the operational parameters for the deck (10), which comprises the upper surface or part of the upper surface of a frusto-cone (69) the apex of which is uppermost, are developed initially on a planar surface. The method of Claim 1 or 2, characterised in that continuous asymmetric vibrations are imparted to the deck (10) to impose directional rectilinear or curvilinear movement (C) on the particulate mobile material fractions substantially counter to the direction of the trochoidal movement of the material fractions and lateral to the direction (D) of the liquid and of the wash liquid; the vibrations being superimposed upon the continuous and uniform, planar, circular orbital motion (A or B) of the deck (10). Apparatus for separating a mixture of particulate ores and / or other solid materials containing fractions of different density and / or particle size carried in a liquid over a dressing table comprising a deck (10) with raised riffles (50) therein, a feed inlet (52), wash liquid inlets (54, 56), and a plural of launders (57), characterised by deck rotation means (13, 14, 16) connected to said deck (10) to allow selected rotation of the deck (10), the feed inlet (52), the wash liquid inlets (54, 56) and the launders (57) thereof in a plane, about an axis normal to the deck (10) through an arc of up to 60 degrees; drive means (42, 44, 46) comprising a motor (46) which has an eccentric, offset, shaft (42, 44) to impose planar, circular orbital motion (A or B), which is continuous and uniform, on the deck (10) and to impose planar, simple harmonic oscillatory motion which is continuous and uniform on each riffle (50); riffles (50) adapted to create a standing wave system (71) in the flowing material between the riffles (50), the deck (10) being adapted to impose planar orbital shear forces on the standing wave system (71); deck support means (16, 18, 28, 32) to support the deck (10) and comprising a movement distributor plate (28) having a self-aligned, smooth bearing (40) which receives the eccentric, offset, shaft (42, 44), the movement distributor plate (28) supporting a tripod support means (16, 18, 20, 25, 26, 27) each leg (18) of the tripod support means (16, 18, 20, 25, 26, 27) engaging in a self-aligned smooth bearing (26) mounted on the movement distributor plate (28), the tripod support means (16, 18, 20, 25, 26, 27) permitting selected variation in the tilt of the deck (10) about longitudinal and lateral axes; rotation lock means (22, 24) to lock the deck (10) in a selected rotational position to maintain a selected acute angle (S) between the riffles (50) and the natural flow path (D) of the liquid and wash liquid over the deck (10). An apparatus according to Claim 9, characterised in that the movement distributor plate (28) is mounted on at least three rigid legs (32), each leg (32) having an elastic universal joint (34, 36) at each end. An apparatus according to Claim 9, characterised in that the drive means (42, 44, 46) is supported independently of the movement distributor plate (28). An apparatus according to Claim 9, characterised in that the deck rotation means (13, 14, 16) comprises a carrier ring (13), on which the deck (10) is mounted, and containment means (14, 16) for the carrier ring (13); the carrier ring (13) being rotatable in the containment means (14, 16). An apparatus according to Claim 12, characterised in that the containment means (14, 16) is secured to the deck support means (18). An apparatus according to Claim 12, characterised in that the containment means (14, 16) comprises a planar bearer frame (16) having upwardly directed slide plates (14) slideably engaging the circumferential edge of the carrier ring (13). An apparatus according to Claim 14, characterised in that the rotation lock means (22, 24) comprises a bolt (22) extending through a slide plate (14) and lockable against the carrier ring (13). An apparatus according to Claim 9, characterised in that the deck surface comprises the upper bight of a moving belt (62). An apparatus according to Claim 9, characterised in that the deck surface is frusto-conical, with the apex uppermost (69). An apparatus according to Claim 9, characterised by a frequency variation means (46) to vary the frequency of the circular orbital motion (A or B) at constant amplitude. An apparatus according to Claim 9, characterised in that the wash liquid inlets (54, 56) and launders (57) are attached to the deck (10) and are rotated with the deck (10). An apparatus according to Claim 9, characterised by further comprising vibration means (72, 74) to impart continuous asymmetric vibration to the deck (10) to impose directional rectilinear or curvilinear movement (C) on the particulate mobile material fractions substantially counter to the direction of trochoidal movement of the mobile material fractions and lateral to the direction (D) of flow of the liquid and the wash liquid, the vibration being superimposed upon the continuous and uniform, planar, circular orbital motion (A or B) of the deck (10).

Inventors: FLETCHER, JOHN MAURICE
Applicants: FLETCHER, JOHN MAURICE
Application year: 1987
Main classification: B03B5
IPC codes: B03B5