AU601053B2

AU601053B2 - Apparatus for noble metal recovery

Info

Publication number: AU601053B2
Application number: AU18819/88A
Authority: AU
Inventors: Bruce Maddison
Original assignee: Individual
Current assignee: Individual
Priority date: 1987-07-07
Filing date: 1988-07-07
Publication date: 1990-08-30
Anticipated expiration: 2008-07-07
Also published as: AU1881988A

Description

COMMONWEALTH OF AUSTRALIA Patents Act 1952 COMPLETE SPECIFICATION (Original) SO5 3 FOR OFFICE USE Application Number: P12964 Lodged: 07-07-87 Complete Specification Lodged: Ac'cpt ed: Published: Class Int. Class f 4 4F f i I t t o 4 4. i 44* t* II 44 4 44 9 Priority: This document contains the amendmn i'its made undur Section 49 and is correct for printing.

I^1 iiHK iM WH M Related Art: TO BE COMPLETED BY APPLICANT Name of Applicant: BRUCE MADDISON Address of Applicant: 11c Blackadder Road, Swanview, in the State of Western Australia, Commonwealth of Australia Actual Inventor: Bruce Maddison Address for Service:- Wray Associates Primary Industry House 239 Adelaide Terrace Perth Western Australia 6000. aJ P)0002 0 6 0 7/07/88 Complete Specification for the invention entitled: "APPARATUS FOR NOBLE METAL RECOVERY" The following statement is a full description of this invention, including the best method of performing it known to me:- -1 I i -2- THIS INVENTION relates to an apparatus for noble metal recovery from friable material and to a trommel means and a riffle means used in a dry blower apparatus.

In accordance with one aspect of the present invention, there is provided a trommel means comprising:a rotatable cylinder having a feed inlet at one end through which friable material may be fed into said cylinder, a discharge outlet at the other end through which remaining friable material may be discharged from said cylinder, and an intermediate barrel along which said friable material may pass from said inlet to said outlet; a series of successive annular grinding faces disposed at spaced apart locations axially along said barrel for grinding and reducing the size of said friable material during its passage along said barrel; a series of successive annular screens disposed at spaced apart locations axially along said barrel for screening and discharging sufficiently small particulate material from said barrel during its passage therealong; said annular screens and grinding faces being arranged alternately along said barrel; a plurality of retentioner vanes arranged in a series of annular formations disposed at a junction between a successive grinding face and screen ati a screen at the anterior end of the screen and the posterior end of the grinding face; and a plurality of feeder vanes arranged in a series of annular formations disposed at a junction between a successive screen and grinding face at the anterior 3- -3end of the grinding face and the posterior end of the screen; wherein said vanes each extend radially inwardly along the inner circumference of said barrel a marginal distance and are particularly positioned with respect to adjacent vanes, such that during rotation of said cylinder and the feeding of friable material therethrough, said retentioner vanes are adap.ted to partially retain larger size friable material within portions of said barrel circumscribed by said grinding faces and pass smaller size friable material therebetween onto an adjacent screen for screening and discharge as appropriate from said barrel; and wherein said feeder vanes are adapted to feed remaining friable material from portions of the barrel circumscribed by said screens to successive portions of the barrel circumscribed by said grinding faces.

In accordance with another aspect of the present invention, there is provided an apparatus for noble metal recovery from friable material comprising:a feeding means for feeding friable material; a trommel means of the type defined in the first aspect of the invention for receiving said friable material at the feed inlet end thereof from said feeding means and discharging sufficiently particulate material from the screens of the barrel thereof; conveying means for conveying said particulate material from said trommel means; and dry blowing means for receiving said particulate material from said conveying means and recovering noble metal from said particulate material.

1_ I lr S- 4- Preferably, said dry blowing means comprises a riffle means for dry blowing particulate material, said riffle means comprising:a housing having an upper opening over which said particulate material may pass, and a lower air inlet through which a compressed air flow may be introduced into said housing to be expelled through said opening; a plurality of baffles to be arranged in a tiered formation within said housing to divide the interior of said housing into a plurality of layered compartments extending in succession from said inlet to said opening, said inlet being disposed to communicate with the lowermost compartment; a plurality of riffles to be disposed upon the uppermost baffle proximate said opening to extend froio one end of said housing to an opposite end, said one end being intended to be slightly elevated relative to the other to define a slight gradient down which said particulate material is intended to travel; and a fine mesh screen to be disposed between said i riffles and said uppermost baffle; wherein said baffles are provided with a plurality of apertures through which said compressed air flow is intended to pass, said apertures being graded in size such that in a said baffle, the apertures of larger cross section are disposed generally towards said one end of the housing as opposed to apertures of smaller cross section.

The invention will be better understood in the light of the following description of one specific embodiment thereof. The description is made with reference to the accompanying drawings, wherein:- Figure 1 is an end view of the hopper; Figure 2 is a side view of the apparatus; Figure 3 is an end view showing the location of the riffle boxes relative to the riffle conveyor; Figure 4 is an end view of the trommel cylinder from the feed end; Figure 5 is a side view of the trommel showing the supporting wheels and driving wheels in position; Figure 6 is an end view of figure 5 taken from the discharge end; SFigure 7 is a longitudinal sectional view of the i trommel cylinder; Figure 8 is a sectional view of the trommel cylinder taken along section 8-8 of figure 7; Figure 9 is a sectiohal view taken along section 9-9 of figure 7; Figure 10 is a sectional view along section 10-10 of figure 7; Figure 11 is a sectional view taken along section 11-11 of figure 7; Figure 12 is a sectional view taken along section 12-12 of figure 7; Figure 13 is a sectional view taken along section 13-13 of figure 7; Figure 14 is a schematic view showing the relative positioning of the retentioner vanes for the grinding sections of the trommel; -I d -6- Figure 15 is a schematic view showing the relative spacing of the feeder vanes for the screening sections of the trommel; Figure 16 is an end view of the lower opening of the riffle box; and Figure 17 is a sectional side view of the riffle box.

i The embodiment is directed towards an apparatus for noble metal recovery and is particularly suited for recovering alluvial gold from auriferous friable material.

j The apparatus 11 generally comprises a hopper 13, a trommel feed conveyor 15, a trommel 17, a trommel discharge conveyor 19, a riffle feed conveyor 21, a riffle means 23, and a discharge chute 25. The apparatus is mounted on a mobile chassis 27 having a pair of wheels 28 to facilitate transport from one location to another.

The hopper 13 is provided with an entry grating 29 mounted at an inclined attitude upon a series of springs and to which is attached a vibrator 30. The grating performs a primary screening operation on material which is deposited into the hopper to be fed onto the trommel feed conveyor The grating 29 is inclined towards one transverse side of the apparatus to facilitate feeding the hopper with a front end loader or the like from one side of the 4 apparatus. The hopper outlet is provided with an outlet chute 31 which directs material passed through the hopper onto the trommel feed conveyor The trommel feed conveyor 15 extends on an incline from the bottom of the hopper 13 to an elevated position at the

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1 ,i 7feed end of the trommel 17. The conveyor belt (not shown) of the feed conveyor 15 is provided with a series of transverse slats therealong and a pair of frills either side of the belt to confine and convey material discharged from the outlet chute 31 of the hopper upwardly to the inlet of the feed end of the trommel 17.

4 4 4 1 4e 0 4 00 04 0* 0 #4 The trommel 17 comprises a rotatable cylinder having a feed inlet 17a at one end adjacent to the end of the trommel feed conveyor 15, a discharge outlet 17b at the opposite end adjacent the discharge shoot 25 and an elongate barrel 33 extending from the inlet to the outlet.

The trommel 17 is supported for rotation upon rolling elements such as two sets of wheels 35 positioned axially along either side of the barrel 33 so that the central axis of the trommel is disposed at a slight decline of approximately 6° extending from the inlet end to the outlet end of the trommel.

4 i6 4t One set of wheels 35a comprise the drive wheels which are disposed co-axially in tandem pairs along an axle 37. The t axle is disposed parallel to the central axis ,f the trommel and is spaced from the outer circumference of the barrel 33 to enable the wheels 35a to contact the barrel Speriphery at axially spaced locations along the barrel.

The other set of wheels comprise idler wheels 35b which are similarly mounted in tandem pairs co-axially along a second axle (not shown). The idler wheels and second axial are positioned on the opposite side of the trommel to the drive wheels 35a and axle 37 thereof so that the idler wheels may engage the opposite side of the barrel to enable it to be supported upon the sets of wheels.

WI 4r o w N4 0 f-8 The drive axle 37 is in turn connected by a differential 39 to a motor drive and gear box (not shown) for providing motive power to the wheels for the purposes of rotating the trommel.

The feed inlet 17a of the trommel is provided with wall means in the form of an annular flange 41 concentrically disposed about the central axis of the trommel, to define a constricted central opening 43 of the trommel and an outer collar 45 which projects radially outwardly beyond the circumference of the barrel 33. The opening 43 is of sufficient size to receive friable material into the trommel from the upper end of the feed conveyor 15. The collar 45, on the other hand, is of sufficient size to define a track along the inner axial side thereof adjacent to the barrel 33 to enable a pair of retainer wheels 47 or other rolling elements to run therealong. The retainer wheels 47 are positioned at opposite sides of the barrel for rotation about a substantially transverse axis relative to the barrel to engage the inner side of the collar. Each retainer wheel is connected to a fixed mounting (not shown) supporting a rotatable shaft about which the wheels may rotate. Consequently, the wheels provide a counteractive force to axial movement of the trommel as a result of its rotation about a declined axis and consequently, retain the axial position of the trommel.

The discharge outlet 17b is also formed with a concentrically disposed flange 49. However, this flange 49 is of lesser radial extent than the flange 41 of the feed inlet and thus defines a central constricted opening 51 of greater diameter than the constricted opening 43, and a peripheral lip 53 having a marginal radial extent beyond the outer circumference of the barrel 33 adjacent thereto.

;i .I 9 The constricted opening 51 is provided to discharge extraneous material passed through the trommel onto the discharge chute 25 for conveyance away from the apparatus.

The interior of the barrel 33 is divided up into a number of different regions at different axial locations along the barrel, namely an inlet region 55, an intermediate region 61 and a discharge region 91. The inlet region is proximate the feed inlet 17a and comprises a series of axial inlet vanes 57 extending from the inner side of the flange 41 to an entry position 59 spaced a first axial distance therefrom. The inlet vanes 57 each extend radially inwardly from the barrel at radially spaced locations around the inner circumference. Each vane is formed with a leading deflector portion 57a at the leading end thereof, a trailing deflector portion 57b at the trailing end thereof, and an intermediate axial portion 57c. The leading deflector portion 57a engages the inner side of the flange 41 and is disposed to deflect friable material deposited through the constricted opening 43 inwardly onto the intermediate axial portion 57c towards the entry position 59. The trailing deflector portions 57b are provided to further deflect material deposited within the region axially beyond the entry position 59.

Consequently, the leading portions 57a are angled towards the inner side of the flange 41 to lead the intermediate portions 57c of the vanes during rotation of the barrel and the trailing portions 57b are angled to trail the intermediate portions 57c of the vanes during rotation.

The intermediate portions 57c of the vanes consequently function to scoop friable material received within the first region in a circular motion up to an elevated position towards the top of the barrel, whence the material may fall, pursuant to a weakening of the centrifugal force applied thereto by appropriate selection of the rotational speed of the I i i ~I i ~i cylinder, down to the bottom of the region, thereby Sperforming an initial impact crushing treatment upon the material in order to reduce it down in size.

The intermediate region 61 of the barrel comprises a series of successive annular grinding face selection and screening sections, alternating axially along the barrel interior. The arrangement of the grinding face sections and screening sections is such that an annular grinding face 63 is provided initially, followed by an annular screen 65 which combine to form a first subregion 67. This subregion is subsequently followed by a succession of similar subregions along the entire axial extent of the intermediate region 61. Each subregion is separated from an adjoining subregion by a plurality of feeder vanis 69 arranged in a series of annular formations disposed at a junction between the annular screen 65 of a preceding region and the annular grinding face 63 of a succeeding subregion.

The feeder vanes 69 are each fixedly mounted to the inner circumference of the barrel and extend radially inwardly a marginal portion to define an inner passage 71 through which material may pass. Additionally, each feeder vane 69 is spaced apart from an adjacent vane to define a series of feeder spacings 77, and is disposed obliquely to the right section of the barrel extending through the annular formation in a similar direction to the leading portions and trailing 57a and 57b of the axial vanes 57. Thus, the leading edge of each feeder vane is disposed on the screen side adjacent thereto and the trailing edge is disposed on the grinding face side with respect to the direction of rotation of the barrel. Accordingly, the feeder vanes function to axially deflect material passed across the c i .I -11 preceding annular screen 65 of one subregion towards the adjacent grinding face 63 of a succeeding subreg.> n The grinding face 63 and screen 65 within each subregion are separated from each other by a plurality of retentioner vanes 73 arranged in an annular formation at the junction between the grinding face and screen. The retentioner vanes 73 are similar to the feeder vanes 69 except they are of a much smaller size and extend radially inwardly from the outer circumference of the barrel a lesser marginal distance than the feeder vanes. The retentioner vanes 73 are much more closely spaced and are disposed at a much more acute angle to the right section the barrel passing therethrough. Consequently, the retentioner spacings 75 between adjacent retentioner vanes permit only relatively small particles to pass therethrough from the grinding face 63 to the screen 65 of a subregion, as opposed to the spacings 77 between adjacent feeder vane 69 which permit much larger particles Sto pass therethrough. In order to support the small retentioner vanes 73 in opposition, an annular rim 79 is fixedly attached to the innermost radial extent of each i retentioner vane 73 within an annular formation, and consequently defines another inner passage 81 through which larger material may pass within a subregion. The annular grinding faces are each formed of a series of quilted, hard facing segments 83 which are fixedly mounted to the inner surface of the barrel. Each annular screen comprises a series of openings formed around the circumference of the barrel, each covered by a screen segment 87 of a prescribed mesh size, The screen segment may be of any suitable construction such as perforated plate or wire mesh. The size and shape of each grinding face and screen segment is the same for all of the subregions of the second region 61, apart from the first i -i -12 subregion 67 and the last subregion 85. Moreover,. the grinding face segments 83 in these intermediate subregions are each derived from the portions of the barrel which are cut out to provide the openings for the screen segments 87. Consequently, succeeding grinding face and screen segments 83 and 87 respectively, are arranged rectilinearly along the barrel, and are of same size and shape within the intermediate subregions.

With regard to the first and last subregions 67 and respectively, the grinding face segments 83 of the first subregion have a longer axial extent than the grinding face segments of the remaining subregions and the screen segments of the last subregion 85 are of a similarly longer axial extent being larger than that of the remaining screen segments. Moreover, the grinding face segments 83 of the first subregion 67 are obtained from the barrel portions removed to provide the screen openings I, of the screen segments 87 of the last subregion 85. In this manner material. deposited within the first subregion 67 may be exposed to a longer period of residence within the annular grinding face section thereof, and similarly material. deposited within the lacot subregion may be subjected to a longer period of residence within the annula screening section thereof. This achieves increased grinding or crushing of material at the feeding end, of the intermediate reqion 61 and greater screening of material at the discharge. end thereof.

In order to strengthen the barrel along iLs axial extent, there are provided a series of axial ribs 89 extending from the entry position 59 of the barrel to the discharge outlet end, in radially spaced positions between the grinding face and screen segments. The mesh size of each 13 Teen is approximately 3mm except for the last annular screen which is of approximately The discharge region 91 of the barrel extends marginally inwardly from the discharge end flange 49 to adjoin the intermediate region 61 at the trailing end of the last annular screen 65. The discharge region 91 has a series of axial outlet vanes 93 disposed at spaced apart radial locations around the inner circumference of thee end of the barrel. These axial outlet vanes 93 need to extend radially inwardly and are respectively mounted upon the axial reinforcing ribs 89 of the barrel. The axial outlet vanes 93 are provided to scoop extraneous material which has not been sufficiently reduced in size during passage through the trommel to be screened, to an elevated position for subsequent feeding to the discharge chute for removal from the trommel.

The discharge cute 25 is connected to a series of riffles mounted upon a vibrating platform over which material discharged from the trommel is passed prior to discharge from the apparatus in order to trap heavier material for further scrutiny.

The trommel discharge conveyor 19 is disposed directly beneath the trommel cylinder 17 and extends the entire axial extent thereof to convey material discharged through the annular screening sections of the trommel. The conveyor belt of this conveyor is troughed to contain material within the confines of the belt duringconveyance therealong.

The riffle fee conveyor 21 is disposed to receive material from the trommel discharge conveyor 19 and convey this material to an elevated position from which it may be fed i _i -1to the riffle means 23. Accordingly, the riffle conveyor 21 is of a similar design to the feed conveyor 21 is adapted to discharge material at its elevated end 21 onto a Z-shaped deflector plate arrangement 97 which is provided to deflect material to riffle means provided either side of the conveyor. The Z-shaped deflector plate arrangement comprises a pair of outwardly disposed first plates 97a which initially deflect material either side of the conveyor, and a pair of inwardly disposed second plates 97b which receive material from the first plates 97a and direct it inwardly towards the riffle means. In i this manner the riffle means can be disposed relatively close to each other to facilitate attending to either.

The riffle means 23 comprises a pair of riffle boxes 99, f one positioned each side of the conveyor to receive material from the deflector plate 97.

As shown in figure 17, each riffle box comprises an outer wooden housing 101 in the shape of a box having an upper opening 103 and a lower air inlet 105. The box is disposed at an incline to one side or the other of the apparatus and is suspended in such a manner as to enable vibration of the box. Moreover, the bottom of the elevated end 101a of the housing is connected to the top of a vertical compression spring 107 and the lower end 101b of the housing is suspended by a coil spring and chain 109 connected in series. A vibrator 111 is mounted to the bottom of the housing 101 and is arranged to provide an upward vibratory motion to the box.

The upper edge 103a of the upper opening 103 is connected to an entry chute 113 along its entire horizontal extent in order to guide material deflected by the deflector plates into the upper opening 103.

Li The interior of the housing 101 is provided with a plurality of baffles 115 arrange din a tiered formation which divide the interior into a plurality of layered compartments 117. These compartments extend in succession from the inlet 105 to the upper opening 103. The baffles 115 are evenly spaced to define compartments 117 of substantially similar volume.

In the present embodiment three baffles are provided, namely a lower baffle l15a, an intermediate baffle 115b, 1" 0 and an upper baffle 115c. The lower l15a is spaced from the bottom of the housing 101 to define a lower compartment 117a which communicates with the air inlet o105. The intermediate baffle l15b is spaced from the first 4 baffle 115a to define an intermediate compartment 117b, and the upper baffle 115c is spaced from the intermediate baffle 115b to define the third compartment 117c. Each baffle 115 is slidably received within complementary grooves 119 provided at successive locations along the interior walls of the housing 101.

Each baffle is provided with a plurality of apertures 121 of varying sizes depending upon the particular baffle and relative location of the apertures with respect to the upper and lower ends 101a and 101b of the housing.

Moreover, the apertures 121 in the lower baffle l15a are arranged in an even array about the entire area of the baffle to provide an even distribution of compressed air introduced into the lower compartment 117a into the intermediate compartment 117b. On the other hand, the apertures 121b provided in the intermediate baffle 115b are graded and vary in size in a prescribed manner.

Moreover, the lower third of the baffle is not provided with any apertures at all and the remainder of the baffle

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j 16 is provided with an array of apertures extending in size from a relatively small diameter near the lower end of the baffle to a relatively large diameter towards the top end of the baffle. Consequently, these apertures tend to concentrate a stronger air flow towards the top of the upper compartment 117c from compartment 117b, and a lesser concentration of air follow down towards the bottom of compartment 117c. The third baffle 115c has apertures 121c provided therein, which are arranged in groups extending t0 from the top of the baffle 115c are of a slightly larger diameter than those in groups towards the lower end of the Sbaffle. The variation in sizes is evenly graded from the top group to the bottom group.

a Disposed upon the upper baffle 115c are a series of riffles 123 which extend laterally across the opening 103 at successive locations extending from the top of the opening down towards the bottom. The riffles 123 are interconnected by a series of spaced longitudinal braces 125 which extend similarly from the top of the opening 123 down towards the bottom of the opening at spaced apart lateral locations. Interposed between the riffles 123 and the upper baffle 115c is a cloth screen 128 which covers the entire area of the opening 103. The screen is of approximately 30 micron through which compressed air may pass whilst permitting most of the particulate material to transverse along the outer face thereof.

The grouping of the apertures 121c provided in the top baffle 115c are disposed to align with each of the regions interposed between successive riffles. Additionally, the top group of apertures 121c are each partially countersunk at their upper ends to provide venturis which increase air flow passing therethrough. This stronger air flow is required near the top end 101a of the upper opening to 17 fluidise the large amount of material deposited thereon from the entry chute 113 compared with material received lower down the opening.

The lower compartment 117a is provided with a series of spacing pegs 127 positioned at intermediate locations of the compartment to rest the intermediate portion of the lower baffle l15a thereon, thereby maintaining the spacing between the baffle and the bottom of the housing 101. The intermediate and upper compartments 117b and 117c respectively, are each provided with a series of elongate partitions 129'extending longitudinally from the upper end 101a of the housing to the bottom end 101b of the housing at laterally spaced apart locations. These partitions 129 Sprovide the dual function of maintaining the spacing between adjacent baffles defining the compartments and also partitioning the compartments into separate divisions to resist lateral spreading of air within the compartments as a result of the occurrence of blinding of adjacent portions of the cloth screen 128 directly above.

S 20 The air inlets 105 of the riffle boxes are connected to respective branch ducts 106 which are in turn connected to a primary duct 108 by way of a control valve 110. The primary duct 108 is connected to a source of air under pressure such as an air pump 112. The control valve 110 is arranged in use to direct air from the primary duct 108 alternatively to each branch duct 106. The control valve also has the facility to regulate the flow rate of air delivered to each riffle box. Air delivered to each riffle box enters the bottom compartment through inlet 105 and subsequently passes up through the remaining compartments to fluidise particulate material deposited within the upper opening. Consequently, material will gradually traverse over the riffles 123 down towards the bottom of U- 18the opening allowing heavier material to remain or be trapped within the grooves defined by the riffles.

The feed conveyors 15 and 21 may be at least partially enclosed along at least part of their lengths with shrouds or other enclosure means if so desired.

Now describing the operation of the apparatus, the apparatus is positioned so that an operator may load the hopper 13 with auriferous friable material from the upwind side of the apparatus. Material of appropriate size may pass through the screen 29, into the hopper 13 and be deposited by the outlet chute 31 onto the feed conveyor The material is conveyed along the feed conveyor for discharge into the trommel at the feed inlet end 17a I thereof, through the constricted opening 43.

1 The trommel is rotated by means of drive imparted to the barrel by the drive wheels 35a so that material is scooped up by the inlet vanes within the inlet region 55 of the trommel on the drive side. This material is subjected to an initial impact crushing operation by rotating the trommel at approximately 37% of the critical speed which is the speed sufficient for centrifugal action to take affect. In practice this is in the order of 13 r.p.m.

Consequently, material will be lifted by the axial inlet vanes 57 upwardly towards the top of the trommel whereupon material will fall under the action of gravity, and impact with other material on the bottom of the trommel in this region.

Material is eventually deflected beyond the entry position 59 of the intermediate region 61 of the trommel, whereupon it is subjected to a grinding action by the annular grinding face 63 within the first subregion 67. Material -19is retained within this subregion by the action of the retentioner vanes 73 until it is reduced to a sufficient size to pass through the gap 75 of the vanes or excessive material is built up to pass over the inner periphery of the rim 79 through the opening 81 onto the annular screen.

The fine particulate material passed through the spacings of the retentioner vanes 73 subsequently falls through the annular screen 65 for discharge onto the trommel discharge conveyor 19. Additionally, this material forms an effective bed to cushion the screen mesh from larger material passed through the orifice 81. Subsequently, the material which is not discharged through the annular screening section of the first subregion is deflected axially further by the action of the feeder vanes into the next subregion. This operation is repeated for each successive region until extraneous material is received

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within the discharge subregion 91.

The annular screen section of the discharge subregion is of a larger size than previous screening sections to permit discharge of a large quantity material sufficiently small to be screened which has avoided discharge through the previous screens. Any extraneous material passing through the last screen 65 is subsequently scooped up by the axial outlet vanes 93, for discharge into the discharge chute 25 for subsequence conveyance out from the trommel. Prior to discharge from the apparatus, however this material is passed over a series of vibrating riffles the crushing operation of the trommel.

The screened material received by the trommel discharge conveyor 19, is subsequently conveyed via the riffle feed conveyor 21 to the riffle means 23, whereupon the material is passed over the upper opening 103 of the riffle boxes A 20 to form a fluidised bed from which any nobel metals may be retained within the grooves of the riffles 123.

It should be appreciated that an important feature of the trommel in the present embodiment, is that a number of alternate annular grinding face sections and screening sections are used each having a relatively small axial extent in preference to a single grinding face section and screening section, both having a larger axial extent.

Accordingly, by adopting the present arrangement, optimization of grinding and screening of material is achieved.

It should be appreciated that the scope of the present invention is not limited to the particular embodiment herein described.

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Claims

1. A trommel means comprising:- a rotatable cylinder having a feed inlet at one end j through which friable material may be fed into said cylinder, a discharge outlet at the other end through which remaining friable material may be discharged from said cylinder, and an intermediate barrel along which said friable material may pass from said inlet to said outlet; a series of successive annular grinding faces disposed at spaced apart locations axially along said barrel for grinding and reducing the size of said friable material during its passage along said barrel; a series of successive annular screens disposed at spaced apart locations axially along said barrel for screening and discharging sufficiently small i particulate material from said barrel during its passage therealong; said annular screens and grinding faces being arranged alternately along said barrel; a plurality of retentioner vanes arranged in a series of annular formations disposed at a junction between a successive grinding face and screen at the anterior end of the screen and the posterior end of the grinding face; and a plurality of feeder vanes arranged in a series of annular formations disposed at .a junction between a successive screen and grinding face at the anterior end of the grinding face and the posterior end of the screen; i _i _i i i 22 wherein said vanes each extend radially inwardly along the inner circumference of said barrel a marginal distance and are particularly positioned with respect to adjacent vanes, such that during rotation of said cylinder and the feeding of friable material therethrough, said retentioner vanes are adapted to partially retain larger size friable material within portions of said barrel circumscribed by said grinding faces and pass smaller size friable material therebetween onto an adjacent screen for screening and o.'o Sdischarge as appropriate from said barrel; and wherein said feeder vanes are adapted to feed remaining friable "1 material from portions of the barrel circumscribed by said i screens to successive portions of the barrel circumscribed *by said grinding faces.

2. A trommel means according to claim 1 wherein said annular grinding faces each comprise a plurality of quilted hard facing segments fixedly mounted on the inner i| face of the barrel.

3. A trommel means according to claim 1 or 2 wherein said annular screens each comprise a plurality of openings formed around the circumference of the barrel and each S* covered by perforate material.

4. A trommel means according to any one of the preceding claims wherein the annular grinding face closest to the face inlet of the rotatably cylinder has a longer axial extent than the remaining annular grinding faces. A trommel means according to any one of the preceding claims wherein the annular screen closest to the discharge outlet of the rotatable cylinder has a longer axial extent than the remaining annular screens. c 1 i' I 23

6. A trommel means according to any one of the preceding claims further comprising crushing means disposed ahead of said series of grinding faces and screens for performing a crushing operation on friable material delivered into the rotatable cylinder.

7. A trommel means according to claim 6 wherein said crushing means comprises at least one vane extending generally along the cylinder, said vane including a first deflector portion at the leading end of the vane, a second deflector portion at the trailing end of the vane and a third portion intermediate the first and second portions, the third portion being disposed axially within thet cylinder and the first and second portions being inclined to the third portion such that during rotation of the cylinder the first portion leads the third portion and the second portion trails the third portion.

8. A trommel means according to claim 7 wherein a wall i means is provided at the feed inlet end of the cylinder and an opening is provided in the wall means to define the feed inlet.

9. A trommel means according to claim 8 wherein said at least one vane extends into the rotatable cylinder from the inner face of said wall means. A trommel means according to claim 8 or 9 wherein said wall means and said opening are together defined by an annular flange mounted concentrically on the cylinder and having a portion extending outwardly beyond the periphery of the cylinder. 24

11. A trommel means according to claim iO wherein the cylinder is rotatably supported by a plurality of spaced rolling elements.

12. A trommel means according to claim 11 wherein the cylinder is disposed in an inclined position with the feed inlet end uppermost and wherein there is provided at least one rolling element in rolling engagement with said portion of the flange extending beyond the cylinder thereby to retain the axial position of the cylinder.

13. A trommel means according to any one of the preceding claims wherein a wall means is provided at the discharge outlet end of the cylinder and an opening is provided in the wall means to define the discharge outlet.

14. A trommel means according to claim 13 further comprising at least one axial vane mounted in the cylinder adjacent the discharge outlet to facilitate discharge of material through said outlet. A trommel means substantially as herein described with reference to the accompanying drawings.

16. Apparatus for noble metal recovery from friable material comprising:- a feeding means for feeding friable material; a trommel means according to any one of the preceding claims for receiving said friable material at the feed inlet end thereof from said feeding means and discharging sufficiently particulate material from the screens of the barrel thereof; conveying means for conveying said particulate a 25 material from said trommel means; and dry blowing means for receiving said particulate material from said conveying means and recovering noble metal from said particulate material.

17. Apparatus according to claim 16 wherein said conveying means comprises an endless belt conveyor disposed beneath the trommel means. S18. Apparatus according to claim 16 or 17 wherein the dry blowing means is in the form of a riffle means comprising: a housing having an upper opening over which said particulate material may pass, and a lower air inlet through which a compressed air flow may be introduced into said housing to be expelled through said opening; a plurality of baffles to be arranged in a tiered formation within said housing to divide the interior of said housing into a plurality of layered compartments extending in succession from said inlet to said opening, said inlet being disposed to communicate with the lowermost compartment; a plurality of riffles to be disposed upon the uppermost baffle proximate said opening to extend from one end of said housing to an opposite end, said one end being intended to be slightly elevated relative to the other to define a slight gradient down which said particulate material is intended to travel; and a fine mesh screen to be disposed between said riffles and said uppermost baffle; 7/. L-II__l-I.I _LII- QPI, I- 26 wherein said baffles are provided with a plurality of apertures through which said compressed air flow is intended to pass, said apertures in at least some of the baffles being graded in size such that the apertures of larger cross section are disposed generally towards said one end of the housing as opposed to apertures of small cross section.

19. Apparatus according to claim 18 wherein the o apertures-in the lowermost baffle are arranged in a substantially even array over substantially the entire surface ahead of the baffle. re Apparatus according to claim 18 wherein there are three said baffles being a lowermost baffle, an intermediate baffle and an uppermost baffle and wherein the apertures in the lowermost baffle are arranged in substantially even array substantially to the entire surface ahead of the baffle.

21. Apparatus according to claim 20 wherein the apparatus in the intermediate baffle are arranged in an array spaced from the lower end of the baffle such that the region of the baffle adjacent said lower end is devoid of apertures and the apertures in said array are graded in size from a relatively small diameter at the lower end of the array to a relatively large diameter at the upper end of the array.

22. Apparatus according to claim 20 or 21 wherein the apparatus in the uppermost baffle are arranged in groups, the groups being in alignment with the regions between successive riffles. L -27-

23. Apparatus according to claim 22 wherein the size of apertures in gro-ups disposed towards the upper end of the uppermost baffle are larger than the size of apertures in groups disposed towards the lower end of the uppermost baffle.

24. Apparatus according to any one of claims 20 to 23 wherein the compartments below the intermediate and uppermost affles are each provided with at least one partition extending longitudinally between the upper and lower ends of the compartment to inhibit lateral spreading of air introduced into the compartment. Apparatus for noble metal recovery from friable material substantially as hereindescribed with reference to the accompanying drawings. DATED this THIRTEENTH day of JUNE 1990. BRUCE MADDISON Applicant. Wray Associates, Perth, Western Australia, Patent Attorneys for Applicant.