AU5185798A - Centrifugal separator with injection of fluidizing liquid between non-fluidized recesses - Google Patents

Description

CENTRIFUGAL SEPARATOR WITH INJECTION OF FLUIDIZING LIQUID BETWEEN NON-FLUIDIZED RECESSES

This invention relates to a centrifugal separator of the type having a plurality of axially spaced annular recesses on a peripheral wall of a rotatable bowl.

In U.S. Patents 4,608,040, 4,776,833, 5,222,933 and 5,338,284 the present applicant discloses a number of different arrangements of centrifugal separator of the type including a rotatable bowl having a peripheral wall of generally frusto-conical shape on which is provided a plurality of axially spaced, annular recesses. The particulate material containing fractions of different specific gravity to be separated is fed in slurry form through a feed duct to a position at or adjacent a base of the bowl so that the feed materials pass over the peripheral wall with heavier particulate materials collecting in the annular recesses while lighter particulate materials escape from the bowl through the open mouth. In the above patents, all of the annular recesses are fluidized by the injection of fluidizing water through holes in the peripheral wall at the respective recesses thus acting to fluidize the collecting material within the recesses.

A further arrangement is disclosed in U.S. Patent 5,586,965, issued December 24th, 1996 of the present inventor in which the number of recesses is reduced and a frusto-conical lead-in section of the bowl is provided which is free from fluidized recesses so that the feed material is deposited onto the lead-in section and flows over that lead-in section prior to reaching the first annular recess.

Fluidized recesses have the potential disadvantage that it is necessary for the supply of the additional water for providing the fluidizing action within the recesses. In some cases where water is in short supply it is desirable to provide a reduction in the quantity of fluidizing water necessary for running the machine. Fluidized recesses also have the disadvantage that they should be relatively deep and wide with a consequential large volume so that the total volume of material in the concentrate is relatively large and only some of this is the required heavier material. Thus the ratio of heavier in the collected concentrate is relatively low in many cases requiring a further concentration step before the heavier material is in sufficient concentration for direct use, for example smelting.

It is one object of the present invention to provide an improved centrifugal separator of the above general type in which the quantity of fluidizing water can be reduced and the richness of the concentrate can be increased.

According to a first aspect of the invention, therefore, there is provided an apparatus for separating intermixed particulate materials of different specific gravity in a slurry comprising: a centrifuge bowl having a base and a peripheral wall surrounding an axis passing through the base and generally upstanding from the base to an open mouth; means mounting the bowl for rotation about the axis; a feed duct for feeding the intermixed particulate materials in the slurry into the bowl so that during rotation of the bowl the intermixed particulate materials flow over the peripheral wall for collection of heavier particulate materials on the peripheral wall and for discharge of the lighter particulate materials in the slurry from the open mouth; a launder for collecting the lighter particulate materials in the slurry discharged from the open mouth; a plurality of annular non-fluidized recesses on the peripheral wall at axially spaced positions over which the materials pass so that the heavier particulate materials collect in the recesses, each non-fluidized recess being defined by a surface portion of the peripheral wall between two axially spaced land portions of the peripheral wall which surface portion of the peripheral wall is substantially imperforate such that fluidizing liquid is prevented from entering into the recess by passing through the surface portion of the peripheral wall; and, between the surface portion of at least one non-fluidized recess and the next, an annular fluidizing area of the peripheral wall which contains a plurality of angularly spaced fluidizing openings for adding fluidizing liquid to the materials as they pass over the recesses.

Preferably between each non-fluidized recess and the next is provided a respective one of a plurality of annular fluidizing areas.

According to a second aspect of the invention there is provided an apparatus for separating intermixed particulate materials of different specific gravity in a slurry comprising: a centrifuge bowl having a base and a peripheral wall surrounding an axis passing through the base and generally upstanding from the base to an open mouth; means mounting the bowl for rotation about the axis; a feed duct for feeding the intermixed particulate materials in the slurry into the bowl so that during rotation of the bowl the intermixed particulate materials flow over the peripheral wall for collection of heavier particulate materials on the peripheral wall and for discharge of the lighter particulate materials in the slurry from the open mouth; a launder for collecting the lighter particulate materials in the slurry discharged from the open mouth; a plurality of annular non-fluidized recesses on the peripheral wall at axially spaced positions over which the materials pass so that the heavier particulate materials collect in the recesses, each non-fluidized recess being defined by a surface portion of the peripheral wall between two axially spaced land portions of the peripheral wall which surface portion is substantially imperforate; and at least one annular fluidizing recess axially spaced from each of the non-fluidizing recesses, the or each fluidizing recess having a plurality of angularly spaced fluidizing openings for injection of fluidizing liquid through the peripheral wall for adding fluidizing liquid to the materials therein.

Preferably between at least one of the non-fluidizing recesses and a next adjacent one is provided at least one of the fluidizing recesses for adding fluidizing liquid to the materials passing over said at least one and said next non- fluidizing recesses.

Preferably the non-fluidized recesses each have a depth less than that of the fluidized recesses.

Preferably the fluidized recesses and the non-fluidized recesses are arranged substantially alternately.

Preferably the recess closest to the open mouth is a fluidized recess.

Preferably one or more recesses closest to the base are non- fluidized recesses.

Preferably above the plurality of the non-fluidized recesses closest to the base is provided a plurality of fluidized recesses closest to the mouth.

According to a third aspect of the invention there is provided an apparatus for separating intermixed particulate materials of different specific gravity in a slurry comprising: a centrifuge bowl having a base and a peripheral wall surrounding an axis passing through the base and generally upstanding from the base to an open mouth; means mounting the bowl for rotation about the axis; a feed duct for feeding the intermixed particulate materials in the slurry into the bowl so that during rotation of the bowl the intermixed particulate materials flow over the peripheral wall for collection of heavier particulate materials on the peripheral wall and for discharge of the lighter particulate materials in the slurry from the open mouth; a launder for collecting the lighter particulate materials in the slurry discharged from the open mouth; a plurality of annular non-fluidized recesses on the peripheral wall at axially spaced positions over which the materials pass so that the heavier particulate materials collect in the recesses, each non-fluidized recess being defined by a surface portion of the peripheral wall between two axially spaced land portions of the peripheral wall which surface portion is substantially imperforate; and, between at least one non-fluidized recess and the next, an annular land area of the peripheral wall which is raised inwardly toward the axis from surface portions of the adjacent recesses and which carries a plurality of angularly spaced fluidizing openings for adding fluidizing liquid to the materials as they pass over the recesses.

Preferably between each non-fluidized recess and the next is provided a respective one of a plurality of land areas, each of which is raised inwardly toward the axis from the adjacent recesses and which carries a plurality of angularly spaced fluidizing openings for fluidizing the materials as they pass over the recesses.

Preferably there is provided at least one annular fluidizing recess axially spaced from the non-fluidizing recesses and arranged adjacent the mouth of the bowl for receiving the material after passing over the non-fluidized recesses, the or each fluidizing recess having a plurality of angularly spaced fluidizing openings for injection of fluidizing liquid through the peripheral wall for fluidizing the materials therein.

Preferably at least one of the fluidized recesses includes a first side wall adjacent the mouth, a second side wall adjacent the base and an annular base interconnecting the side walls so as to define a volume therebetween and wherein the recess contains fixed elements therein which reduce the volume of the recess so as to reduce the quantity of separated materials contained therein.

Preferably the elements comprise a plurality of inwardly projecting axially space annular rings contained within the recess with fluid injection openings between each ring and the next.

Preferably at least some of the non-fluidized recesses include a surface portion which is parallel to the axis.

Preferably on a side of each non-fluidized recess adjacent the mouth the adjacent land portion defines a shoulder lying substantially in a radial plane of the axis.

Preferably below the non-fluidized recesses closest to the base of the bowl is provided a frusto-conical wall portion having a wall angle for directing the materials across the recesses and wherein the feed duct is arranged to feed the materials so that they pass onto the frusto-conical portion.

Preferably each fluid injection opening includes a fluid injection duct formed through the wall of the bowl and having a second duct portion at the interior of the bowl which is of larger diameter than a first duct portion supplying the second duct portion so as to reduce the velocity of the liquid as it passes to the bowl.

Preferably the peripheral wall increases in diameter from the base to the open mouth such that each recess closer to the open mouth has a diameter greater than one closer to the base and such that an uppermost recess has a largest diameter and wherein there is provided an annular restricting member provided on the bowl at or adjacent the open mouth and extending from the peripheral wall to an inner edge of the restricting member spaced inwardly toward the axis for causing the lighter material and the slurry to escape from the open mouth at a position spaced inwardly toward the axis relative to the uppermost recess.

Preferably the annular restricting member comprises an imperforate ring.

Preferably the inner edge lies on an imaginary cylinder which intersects with the peripheral wall at a position thereon at or below a fluidized recess which is the second from the open mouth.

One embodiment of the invention will now be described in conjunction with the accompanying drawings in which:

Figure 1 is vertical cross-sectional view through a first embodiment of centrifugal separator according to the present invention.

Figure 2 is a cross-sectional view through a part of the bowl only of figure 1 on an enlarged scale.

Figures 3, 4 and 5 are cross-sectional views through the bowl only of respectively a second, third and fourth embodiment of an apparatus according to the present invention, the remainder of the apparatus being the same as that shown in figure 1.

The general arrangement of the centrifugal separator shown in Figure 1 is taken from the above U.S. patent 5,222,933 of the present inventor and therefore will described only briefly in regard to the points of importance. The disclosure of the above patents of the present inventor are incorporated here in by reference for further details which may be necessary for a full understanding. The apparatus therefore comprising a bowl generally indicated at 10 having a base generally indicated at 11 and a peripheral wall 12 standing upwardly from the base to an open mouth 13. The bowl can rotate around an axis 15 on a support shaft 16.

A feed duct 17 carries feed materials 18 in the form of a mixture of heavier and lighter particulate materials in a water slurry through the open mouth to a position adjacent to the base so the feed materials can be deposited onto a horizontal guide plate 11A at the base 11 and can move therefrom onto the peripheral wall 12 for separation of the heavier materials into a plurality of recesses 19 on the peripheral wall while the lighter materials in the slurry pass over the peripheral wall to the open mouth for discharge. The recesses are annular and are axially spaced. The peripheral wall is frusto-conical so that the diameter of the recesses increases from a first recess at the base to a last recess at the open mouth. Material exiting from the open mouth is collected by a launder 20 for discharge.

Around the bowl 10 is provided a jacket 21 having a peripheral wall 22 and a base 23 both of which are connected to the respective elements of the bowl so as to form a compartment 21 A fed with fluidizing water from a central duct 24 of the shaft 16 through connecting ducts (not shown). The compartment 21 A therefore receives fluidizing water under pressure which is communicated through openings 25 in the peripheral wall 12 into the recesses for adding fluidizing water into the material collecting in the recesses.

The separation and collection process is a batch process so that the heavier material is collected in the recesses for subsequent wash down and collection. The collected materials when washed down to the base pass through a discharge opening 26 into a second collection system 27 for collecting the concentrate. The feed duct 17 comprises a cylindrical tube carried on a cover 28 of the launder 20. Thus the tube forming the feed duct is in fixed position and remains stationary as the bowl rotates around the axis 15.

The apparatus described above is substantially as shown in the prior patent and is modified in accordance with the present invention by the shape and arrangement of the bowl and particularly the recesses and peripheral wall thereof as described in detail hereinafter.

In the arrangement shown in figures 1 and 2 a first series 30 of the recesses 19 as indicated at 30A to 30 F provides recesses which are of the conventional nature previously described particularly in U.S. Patents 4,776,833 and 4,608,040 of the present inventor.

A second series 40 of recesses indicated at 40A to 40D provides recesses which are modified relative to the previously described recess arrangement so that the recesses are significantly reduced in depth and are free from connection to the chamber 21 A.

It will be noted in Figure 1 that the recesses 30 and the recesses 40 are arranged alternately so that the uppermost one of the recesses is of the fluidized type indicated at 30A, the second of the recesses is of the shallower, non- fluidized type indicated at 40A et cetera through to the lowermost two recesses 30E and 30F which are both of the fluidized type.

It will be appreciated that the size of the bowl can be varied in accordance with requirements so that the number of recesses is determined in effect by the height of the bowl and a diameter of the recesses is determined by the diameter of the bowl.

Also the bowl type is not limited to one which include the central opening 26 and another known type includes an opening offset to one side (not shown) which allows the discharge of the material after collection. In addition the attachment of the bowl to the surrounding jacket is again not shown but it will be appreciated that the outside flange 50 mounted at the outer periphery of the upper part 51 of the bowl allows the bowl to be attached to the jacket 21 to define the injection water receptacle 21A for passage of injection water through the openings 25 into the recesses 30.

As described in the previous patents, the bowl is formed from a suitable elastomeric material which is molded to define the recesses 30 and 40. The elastomeric material can be supported by a metal shell as shown in Figure 1 or can be unsupported.

The recesses 30 are molded into the resilient material so as to define a generally V shape of the recess with side walls 31 and 32 converging outwardly to a flat outer base 33. The side walls define innermost edges 34 and 35 respectively. The uppermost portion 51 of the bowl defines a flat inner surface 36 between the innermost edge 34 of the upper side wall 31 and the mouth of the bowl. The openings 25 communicate with the base 33 substantially at a mid point across the base with the openings being spaced around the base. The base is narrower than the width between the edges 34 and 35. The recesses have a depth between the inner edges 34 and the base 33 which is generally greater than the width of the recess at the mouth of the recess. The openings 25 are arranged at an angle to the radius of the axis so as to tend to direct the injected angularly around the recess.

The recesses 40 have a base 41 and side walls 42 and 43, the side walls each having an innermost edge 44 and 45 respectively. The side wall 42 between the base surface 41 of the recess and the edge 44 forms a shoulder lying in a radial plane of the axis 15 and thus acts to help in trapping the materials as they flow over the bowl wall. A wall or land portion between the inner edge 35 and the inner edge 44 is straight and parallel to the axis of the bowl so as to form an annular band. The inner edges 34, 35 and 45 etc. lie generally on a frusto conical surface including the upper most edge of the bowl at the top of the wall 36 and this forms generally the inner surface of the bowl from which the recesses are recessed outwardly of the axis of the bowl.

The side walls 42 and 43 are parallel and lie in radial planes of the axis. The base 41 is at right angles to the side walls. The depth of the recess 40 as defined by the distance from the inner edges 44 and 45 to the base 41 is very much less than the depth of the recess 30. The recess 40, and its defining surfaces 41 , 42 and 43, is not in any way connected with the outside surface of the bowl so that there is no communication of fluidizing liquid to the interior of the recess 40.

The material flowing over the periphery of the bowl thus generally passes over the inner surface of the bowl defined by the edges of the recesses and provides a separation action at the interface between the material in the recesses and the material passing over the peripheral surface.

It will be noted that the width from the innermost edge 35 of the lower side wall 32 to the innermost edge 34 of the side wall 31 of the next adjacent recess is greater than the width of the recesses between the edges 34 and 35. This width is necessarily greater than the width of the recess itself since the recess 40 is substantially the same width as the recess 30 and there is provided the wall portions between those recesses as previously described.

The depth of the recess 40 is just sufficient to allow collection of some material in the recess so that the surface between the innermost edge 45 and the innermost edge 35 is defined in effect by the collected materials lying on the conical surface which acts as the separation surface for the materials flowing over the conical surface of the bowl. As the depth of the recesses 40 is very much less than that of the recesses 30, the volume of material contained therein is very much reduced. The majority of heavier material collected at the recess is collected at the separation surface with material outside of that being formed by the initial material fed into the bowl at start up. As the volume is thus reduced, the ratio or richness of heavier material to start up material in the non-fluidized shallower recesses 40 is very much increased.

In essence the present arrangement using the shallower recesses 40 in replacement for some of the recesses 30 of the conventional system allows the system to use approximately 40% less water for fluidizing. This reduction in fluidizing water has a significant improvement in the operation of the machine and overcomes some problems in the processing of the slurry.

The arrangement of the present invention allows the material to be fluidized in every second recess between the non-fluidized recesses, that is the alternate recesses 30 and this fluidization in the alternate recesses allows the material to pass from one fluidizing recess over the non-fluidized recess to the next fluidizing recess without allowing the material to dry (squeeze the water out) in a short space between the fluidizing recesses.

At the same time each shallow recess 40 will allow some material to be retained on the face of each recess area and this now sets up a textured surface defined by the inside surface of the collected material where fine gold particles (heavier materials) will have the ability to be trapped in the natural interstices created between the particles.

The reduction in depth of the recesses 40 will also create a smaller amount of concentrate to be treated in secondary treatment. In addition, if the same total amount of materials to be collected is contained within the smaller amount of concentrate then the concentrate is increased in grade providing a further bonus. The modification does not decrease the ability of the bowl to handle large volumes of throughput. Other proposals for reducing the number of fluidized recesses sometimes provides the problem that the material can dry on the wall of the bowl and as soon as the material dries it tends to collect in a stationary mass thus interfering with the proper operation of the bowl. The replacement of the fluidizing recesses at the alternate positions by the non-fluidized recesses 40 allows the material to properly flow through the bowl without the drying effect of the material on the bowl causing loading or imbalance.

Turning now to Figure 3 there is shown an alternative bowl construction for use in the apparatus of Figure 1. The bowl is of the construction substantially as previously described including a plurality of fluidized recesses 51 through 56 and a plurality of non-fluidized recesses 61 through 68. Each of the fluidized recesses has an opening 57 allowing injection of fluid into the recesses for fluidizing the materials as previously described.

In this embodiment the arrangement is modified in that the bottom three recesses are all of the non-fluidized type. The top recess is of the fluidized type. In between these recesses, the remaining recesses alternate between fluidized and non-fluidized types.

The bottom three recesses are arranged so that the lowermost recess is slightly deeper than the second recess 62 and the third recess 63. Thus in one example the lowermost recess 61 is 1/2 in depth, the second recess 62 is 1/4 inch in depth and the remaining recess is of 1/8 inch in depth.

The bowl of Figure 3 is further modified by the addition of a restricting member 70 in the form of annular imperforate ring attached to the open mouth of the bowl by bolts 71 which clamp an outer part of the ring to the bowl beyond the open mouth with an inner part of the ring projecting inwardly from the mouth to an inner edge 73 of the ring which is spaced inwardly from the peripheral wall at the uppermost recess. It will be noted that each of the recesses is of course defined by inwardly projecting ribs and the ribs project inwardly to a height which is substantially equal throughout each of the recesses so that as the peripheral wall increases in diameter so the diameter of each recess increases.

The inner edge 73 is circular in plan thus lying on an imaginary cylinder 74 surrounding the axis 15 of the bowl. The cylinder 74 intersects the peripheral wall at the rib 76 which is at one of the recesses spaced downwardly from the uppermost recess and in the embodiment shown is the lower rib of the fifth recess from the top which is recess 54. The imaginary cylinder is thus spaced inwardly from the fluidized recesses 54, 55 and 56.

In operation, the bowl of Figure 3 allows a significant reduction in the quantity of water while preventing or significantly reducing escape of water outwardly from the bowl through the injection openings 57 which could otherwise carry fine gold or heavier particles through into the jacket where they are lost.

The provision of the non-fluidized recesses significantly reduces the number of fluidized recesses relative to a conventional bowl in which all of the recesses are fluidized so that the amount of fluid necessary to maintain the fluidized recesses fluidized is significantly reduced.

The recesses at the base of the bowl are all non-fluidized recesses. These recesses are aggressively impacted by the entering materials so there is a significant tendency for those recesses to be scoured or washed. The provision of the shallower non-fluidized recesses at this point significantly reduces the escape of water and particles in these recesses.

The shallow recesses do not themselves contain a significant volume of the start up materials. However the shallow recesses do collect some particulate materials and thus define a layer of the particulate materials on the inside surface of the bowl. Additional particulate materials flowing over the surface of the bowl impact upon the particles already in place thus acting as a frictional surface to slow those particles closest to the wall which are the heavier particles and allow them to enter into the next fluidized recess. While the number of fluidized or collecting recesses is therefore reduced, the overall collection efficiency is not significantly reduced and may be enhanced due to the effect of the intervening strips or bands of particulate material which improve the separation when the material reaches the collecting or fluidized recess.

The restricting member which is ring 70 at the open mouth closes the material to take up a path indicated at the dash line 80 in which the material is thus spaced inwardly from the recesses above the recess 66. In this way material collects in the zone outwardly of the line of material 80. Additional collection occurs in this zone due to the fluidization in the recesses 54, 55 and 56. This ring 70 if used with a conventional bowl in which all of the recesses are of the fluidized type can also have an improving effect in that the ring can also reduce escape of water and small particles in the lower recesses of this type of bowl.

As the bowl is frusto-conical, there tends to be a higher injection pressure at the upper recesses than at the lower recesses. Thus in a conventional bowl the significant in diameter between the lowermost recess and the uppermost recess causes a significant increase in injection pressure at the uppermost recess. In the event that insufficient water is supplied, there is a tendency for water and fine particles to escape from the recesses at the base so as to feed the increase in water being injected in the upper recesses. Any such particles entering into the jacket are of course lost from collection. Conventionally the jacket includes ejection openings which allow any particulates entering the jacket to escape so that the jacket does not become clogged. Such particulates enter into the slurry with the escaping material and thus are lost. In the present invention, therefore, the provision of the three recesses at the base which are non-fluidized reduced the differential in pressure since the differential is now obtained by comparing the pressure at recess 51 with the preset pressure at recess 56. Yet further the addition of the restriction member 70 tends to decrease the excess pressure at the recess 56 so that it is substantially equal to the excess pressure at the recess 54. The differential therefore in pressure is obtained by comparing the pressure at recess 51 with that of recess 53 and this differential is significantly reduced since the difference in diameter is significantly reduced. This bowl therefore has a reduced tendency for fluid and fine particles to escape from the recess 51.

In a situation therefore where there is insufficient water supply available to provide the required amount of fluidizing water for the bowl the provision of the reduced number of fluidizing recesses and the addition of the restriction member allows the bowl to operate without significantly reducing the collection of the concentrate.

Turning now to Figure 4 there is shown a further modified bowl arrangement utilizing the principles described hereinbefore.

In this arrangement the bowl has a peripheral wall formed of three sections including a first section 80, a second section 81 and a third section 82.

In the first section 80 the bowl is smooth, imperforate and frusto- conical at an angle to the axis which is common to the remainder of the bowl wall and is at a shallow angle generally less than 15°.

In the second section of the bowl there is provided a plurality of shallow non-fluidized recesses 83. In the embodiment shown there are four such recesses extending from an upper end 85 of the frusto-conical portion 80 and terminating at an upper most land portion 86 at which the bowl portion 82 commences. The bowl portion 82 comprises a plurality of fluidized recesses 87 and in the embodiment shown there are two such recesses. Each of the recesses is divided from the next by a land portion 86A identical to the land portion 86. The land portions 86A and 86 lie on a common cone which is at the same angle as the frusto-conical portion 80. The land portions are raised slightly inwardly of a cone containing the frusto conical portion 80.

Each of the recesses 83 comprises a shoulder 88 lying in a radial plane of the axis and intersecting with the land on the upper side of the recess. A second surface 89 of the recess lies in a cylindrical surface surrounding the axis and parallel to the axis. A third portion 90 of the recess is a frusto conical surface which is inclined inwardly from a lower edge of the surface 89 to intersect with the land on the lower side of the recess. Thus there is no shoulder corresponding to the shoulder 88 adjacent the lower land.

Each land portion 86A has a series of openings 91 at angularly spaced positions around the land portion. The openings connect with duct portions 92 communicating from the opening to a second opening 93 on the outside surface of the bowl so that water from the receptacle 21 A can pass through the duct 92 and the opening 91 to communicate additional fluidizing water into the materials as they pass over the wall of the bowl and as they pass from each recess to the next. Thus additional fluidizing water is added to the materials as they flow across the bowl wall to ensure that the materials do not dry on the wall and in the non fluidized recesses. Each non fluidized recess as defined by the shoulder 88 and the surfaces 89 and 90 is imperforate so that no water enters the recess through the bowl wall at this location within the recess. Each duct 92 includes two duct portions first of which connects with the outside opening 93 and the second of which connects with the inside opening 91. The first duct portion is narrower than the second duct portion so as to control the amount of liquid which passes from the receptacle 21 A into the duct. The second duct portion is wider or of greater diameter so as to reduce the velocity of the liquid flowing through the duct 92 while of course the flow rate remains unchanged and controlled by the first narrower duct portion. In this way the jetting effect of the liquid entering through the land portion is reduced so as to avoid impacting and disturbing the particulate materials as they flow over the land portion.

The recesses in the bowl portion 82 are of the fluidized type. Each recess is defined between the respective land portions 86 and includes side walls 94 and 95 which converge to a base 96 of the recess. The recess is modified relative to the recesses previously described in that the recess includes a plurality of annular ribs or rings 97 which project inwardly from the base to an innermost edge 98 which lies outside of an imaginary conical line containing the lands 86. Thus the ribs or rings 97 reduce the volume of the recess 87 between the side walls and inwardly of the base. Between each ring and between the rings and the sidewalls are provided fluid injection ducts 99 of the type previously described. The ducts are inclined to the radius of the bowl as previously described so as to tend to inject the material around the recess. The recesses 87 are therefore deeper than the recesses 83 and provide a bed of generally fluidized material which thus acts more effectively to trap heavier materials and also to trap larger particles. In the event that heavier materials and larger particles therefore roll over the shallow recesses 83, these particles are collected in the fluidized recesses and are therefore maintained in the bowl and prevent from escaping with the slurry. The lands 86 are not fluidized and contain no openings.

In an alternative embodiment (not shown), only alternate ones of the lands 86A are fluidized so as to further reduce the quantity of additional fluidizing water. However the amount of fluidizing water is maintained sufficient so as to ensure that the materials are fluidized in a movement across the wall. The number of non fluidized recesses and the number of fluidized recesses can of course vary and may be increased in larger size bowls.

The reduction in volume of the fluidized recesses in conjunction with the shallow depth and rich concentrate of the non fluidized recesses ensures that their collective concentrate is of very high ratio and in some cases will allow smelting of the concentrate directly without further concentration.

Turning now to Figure 5 there is shown a further alternative construction of bowl. This is modified relative to the construction of Figure 4 in that it includes a first bowl portion 80A similar to the bowl portion 80 and the second bowl portion 81 A similar to the bowl portion 81 but does not include a bowl portion 82 and thus does not contain any fluidized recesses. Thus the bowl consists solely of the frusto-conical portion 80A and the recesses 83A of the portion 81 A.

The bowl portion 81 A includes lands 86B of the same construction as the lands 86A. However the recesses are of a modified shape in that they include a shoulder 88A and a portion 90A but between those portions there is provided two further shoulders 88B and 88C and two inclined portions 89A and 89B thus forming a zig-zag shape with additional shoulders for engaging the materials as they flow over the bowl wall.

Alternative shapes of the non fluidized recess can be used. In another example (not shown) the recesses are of the same shape as shown in Figure 2 with the lands between the non fluidized recesses being fluidized with openings identical to the openings 91 of the embodiment of Figure 4. In each embodiment, the shallow, non fluidized recesses define a surface portion which is recessed from the adjacent lands so as to provide an area in which the particles can collect for separation of the heavier particles from the lighter particles and slurry as previously described. As shown in figure 4, the recesses 83 are wholly imperforate from the land 91 to the next land 91 , that is, the shoulder 88 and the surfaces 89 and 90 are wholly imperforate so that no fluidizing liquid enters the recess at all through these surfaces. Thus the whole of the fluidizing liquid is injected through the land portions 91. The land portions lie on imaginary surfaces which are cylindrical or at a slight cone angle matching the cone angle of the bowl. It is also possible in an alternative arrangement (not shown) that the injection openings be provided on a surface which is at an angle inclined upwardly and outwardly relative to the land surface and immediately in advance of the main surfaces of the recess. In this way the recess itself is not fluidized but fluidizing liquid is added to the materials as they pass over the peripheral wall and particularly over the recesses.

Claims (22)

I CLAIM:

1. An apparatus for separating intermixed particulate materials of different specific gravity in a slurry comprising: a centrifuge bowl having a base and a peripheral wall surrounding an axis passing through the base and generally upstanding from the base to an open mouth; means mounting the bowl for rotation about the axis; a feed duct for feeding the intermixed particulate materials in the slurry into the bowl so that during rotation of the bowl the intermixed particulate materials flow over the peripheral wall for collection of heavier particulate materials on the peripheral wall and for discharge of the lighter particulate materials in the slurry from the open mouth; a launder for collecting the lighter particulate materials in the slurry discharged from the open mouth; a plurality of annular non-fluidized recesses on the peripheral wall at axially spaced positions over which the materials pass so that the heavier particulate materials collect in the recesses, each non-fluidized recess being defined by a surface portion of the peripheral wall between two axially spaced land portions of the peripheral wall which surface portion of the peripheral wall is substantially imperforate such that fluidizing liquid is prevented from entering into the recess by passing through the surface portion of the peripheral wall; and, between the surface portion of at least one non-fluidized recess and the next, an annular fluidizing area of the peripheral wall which contains a plurality of angularly spaced fluidizing openings for adding fluidizing liquid to the materials as they pass over the recesses.

2. The apparatus according to claim 1 wherein between each non-fluidized recess and the next is provided a respective one of a plurality of annular fluidizing areas.

3. An apparatus for separating intermixed particulate materials of different specific gravity in a slurry comprising: a centrifuge bowl having a base and a peripheral wall surrounding an axis passing through the base and generally upstanding from the base to an open mouth; means mounting the bowl for rotation about the axis; a feed duct for feeding the intermixed particulate materials in the slurry into the bowl so that during rotation of the bowl the intermixed particulate materials flow over the peripheral wall for collection of heavier particulate materials on the peripheral wall and for discharge of the lighter particulate materials in the slurry from the open mouth; a launder for collecting the lighter particulate materials in the slurry discharged from the open mouth; a plurality of annular non-fluidized recesses on the peripheral wall at axially spaced positions over which the materials pass so that the heavier particulate materials collect in the recesses, each non-fluidized recess being defined by a surface portion of the peripheral wall between two axially spaced land portions of the peripheral wall which surface portion is substantially imperforate; and at least one annular fluidizing recess axially spaced from each of the non-fluidizing recesses, the or each fluidizing recess having a plurality of angularly spaced fluidizing openings for injection of fluidizing liquid through the peripheral wall for adding fluidizing liquid to the materials therein.

4. The apparatus according to claim 3 wherein between at least one of the non-fluidizing recesses and a next adjacent one is provided at least one of the fluidizing recesses for adding fluidizing liquid to the materials passing over said at least one and said next non-fluidizing recesses.

5. The apparatus according to Claim 3, or 4 wherein the non- fluidized recesses each have a depth less than that of the fluidized recesses.

6. The apparatus according to Claim 3, 4 or 5 wherein the fluidized recesses and the non-fluidized recesses are arranged substantially alternately.

7. The apparatus according to Claim 3, 4, 5 or 6 wherein the recess closest to the open mouth is a fluidized recess.

8. The apparatus according to Claim 3, 4, 5, 6 or 7 wherein the recess closest to the base is a non-fluidized recess.

9. The apparatus according to Claim 8 wherein a plurality of the recesses closest to the base are non-fluidized recesses.

10. The apparatus according to Claim 9 wherein above the plurality of the non-fluidized recesses closest to the base is provided a plurality of fluidized recesses closest to the mouth.

11. An apparatus for separating intermixed particulate materials of different specific gravity in a slurry comprising: a centrifuge bowl having a base and a peripheral wall surrounding an axis passing through the base and generally upstanding from the base to an open mouth; means mounting the bowl for rotation about the axis; a feed duct for feeding the intermixed particulate materials in the slurry into the bowl so that during rotation of the bowl the intermixed particulate materials flow over the peripheral wall for collection of heavier particulate materials on the peripheral wall and for discharge of the lighter particulate materials in the slurry from the open mouth; a launder for collecting the lighter particulate materials in the slurry discharged from the open mouth; a plurality of annular non-fluidized recesses on the peripheral wall at axially spaced positions over which the materials pass so that the heavier particulate materials collect in the recesses, each non-fluidized recess being defined by a surface portion of the peripheral wall between two axially spaced land portions of the peripheral wall which surface portion is substantially imperforate; and, between at least one non-fluidized recess and the next, an annular land area of the peripheral wall which is raised inwardly toward the axis from surface portions of the adjacent recesses and which carries a plurality of angularly spaced fluidizing openings for adding fluidizing liquid to the materials as they pass over the recesses.

12. The apparatus according to claim 11 wherein between each non-fluidized recess and the next is provided a respective one of a plurality of land areas, each of which is raised inwardly toward the axis from the surface portion of the adjacent recesses and which carries a plurality of angularly spaced fluidizing openings for fluidizing the materials as they pass over the recesses.

13. The apparatus according to claim 11 wherein there is provided at least one annular fluidizing recess axially spaced from the non-fluidizing recesses and arranged adjacent the mouth of the bowl for receiving the material after passing over the non-fluidized recesses, the or each fluidizing recess having a plurality of angularly spaced fluidizing openings for injection of fluidizing liquid through the peripheral wall for fluidizing the materials therein.

14. The apparatus according to any one of claims 3 to 13 wherein at least one of the fluidized recesses includes a first side wall adjacent the mouth, a second side wall adjacent the base and an annular base interconnecting the side walls so as to define a volume therebetween and wherein the recess contains fixed elements therein which reduce the volume of the recess so as to reduce the quantity of separated materials contained therein.

15. The apparatus according to claim 14 wherein the elements comprise a plurality of inwardly projecting axially space annular rings contained within the recess with fluid injection openings between each ring and the next.

16. The apparatus according to any preceding claim wherein at least some of the non-fluidized recesses include a surface portion which is parallel to the axis.

17. The apparatus according to any preceding claim wherein on a side of each non-fluidized recess adjacent the mouth the adjacent land portion defines a shoulder lying substantially in a radial plane of the axis.

18. The apparatus according to any preceding claim wherein below the non-fluidized recesses closest to the base of the bowl is provided a frusto-conical wall portion having a wall angle for directing the materials across the recesses and wherein the feed duct is arranged to feed the materials so that they pass onto the frusto-conical portion.

19. The apparatus according to any preceding claim wherein each fluid injection opening includes a fluid injection duct formed through the wall of the bowl and having a second duct portion at the interior of the bowl which is of larger diameter than a first duct portion supplying the second duct portion so as to reduce the velocity of the liquid as it passes to the bowl.

20. The apparatus according to any preceding claim wherein the peripheral wall increases in diameter from the base to the open mouth such that each recess closer to the open mouth has a diameter greater than one closer to the base and such that an uppermost recess has a largest diameter and wherein there is provided an annular restricting member provided on the bowl at or adjacent the open mouth and extending from the peripheral wall to an inner edge of the restricting member spaced inwardly toward the axis for causing the lighter material and the slurry to escape from the open mouth at a position spaced inwardly toward the axis relative to the uppermost recess.

21. The apparatus according to Claim 20 wherein the annular restricting member comprises an imperforate ring.

22. The apparatus according to Claim 20 wherein the inner edge lies on an imaginary cylinder which intersects with the peripheral wall at a position thereon at or below a fluidized recess which is the second from the open mouth.