AU649512B2 - Self-clearing riffle-box - Google Patents

Description

AUSTRALIA 049 12 Patents Act 1990 COMPLETE SPECIFICATION FOR A STANDARD PATENT .s Os

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APPLICANT: Lawrence Douglas Shepherd ADDRESS: 15 Duke St, Goulburn, NSW ACTUAL INVENTOR: Lawrence Douglas Shepherd ADDRESS FOR SERVICE: Paul A Grant and Associates P0 Box Fisher, ACT 2611 INVENTION TITLE: SELF-CLEARING Ra41PLERIFFLE-B0X ASSOCIATED PROVISIONAL APPLICATION Nos. PK8920 and PK9380 The following statement is a full description of this invention, including the best method of performing it known to me:-

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S 56 SS 0 S 50 TECHNICAL FIELD This invention relates wet ippleriffie-boxes for use in the recovery of fine particles of gold, tin or other heavy valuables from aqueous slurries of sand and gravel. It is also concerned with simple, portable and efficient tppleriffle-boxes suitable for use by amateur fossickers.

For the sake of descriptive convenience, this invention will described with reference to gold recovery, though it will be appreciated that it is also intended for use in the recovery of other finely divided heavy metals, precious stones or minerals from lighter sand and gravel slurries. For the same reason, it will be assumed that a rppitriffle-box comprises a rppleriffle-plate or base having transverse linear grooves or ridges over which the slurry flows and sides to prevent the slurry from flowing off the sides of the plate, the longitudinal dimension of the box being aligned with the slurry flow so that the rippriffles run transversely across the box.

Though it is usual for a 4ppleriffle-box to be longer than it is wide, this is not essential and the use of the terms "longitudinal" and "transverse" does not imply otherwise.

BACKGROUND TO THE INVENTION itppleritfle-plates and 4ppleriffle-boxes have been widely use for centuries in recovering fine gold from slurries of sands and gravels, and many variations of the basic idea are known. A 4ppleriffle plate generally consists "00° of an elongate board or plate, inclined in the longitudinal direction, down 25 which the sand and gravel is washed with water, the plate having p ritleriffles comprising indents or ridges formed transversely thereon to disturb the flow of the slurry in such a way that the lighter gangue particles are carried over the Appleriffles but the heavier gold particles are retained.

While the design of the ripperiffle-plate requires care, the prior art recognises that there are many important operational parameters which must also be addressed; for example: /I the degree to which the gold-bearing sand and gravel is pre-treated by trommelling, sieving or admixing with surfactants; the proportion of water in the slurry; the slope of the fppleriffle-plate; the rate of flow of the slurry down the rippleriffle-plate; the frequency with which the slurry flow is stopped and the concentrate (ie, the material including the fine gold deposited at or in the rippleriffles) is removed; the method by which the concentrate is removed from the 4ppleriftes; and the method by which the gold is separated from the concentrate.

Given that the use of many shallow rippleriffles is preferred by the art, it will be necessary to remove the concentrate at frequent intervals. The method by which the concentrate is removed from the rippteriffles therefore becomes an important, if not critical, factor in determining the overall efficiency of gold recovery (in terms of percentage of the total fine gold in 20 a given quantity of slurry recovered per unit of time).

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The simplest method of removing the concentrate is to stop the flow of the slurry and wash the plate using a large and vigorous flow of water, sometimes increasing the slope of the plate for the purpose. The concentrate and wash water are collected in a suitable container which, after settling, is decanted to leave the wet concentrate for further processing.

This method is costly in terms of rippleriftle-box down-time, water consumption and gold recovery from the wash water.

30 A common technique which addresses this problem involves the use of matting on the fippleriffle-plate (often placed under the ripperiffles) to trap the fine gold and to allow the removal of the gold from the rippleriffle-box by 0, removing the matting and, thus, eliminating the need to wash the gold out of the rippleriffle box. This allows fresh matting to be laid in place and the rippleriffle-plate quickly returned to operation. But the use of the matting adds considerably to the complexity and cost of the frppleriffle-box, as it must be held in place under the ripperiffles but on top of a base plate and it must be easily replaceable. It also adds to the operational expense of the system, as the matting has a relatively short life and is often burnt in order to allow recovery of the gold entrained therein.

In short, while ippleriffle-plate gold-recovery systems are well known, those that are effective in removing gold tend to have many rippleriffles, use retaining mats and are generally too large, cumbersome and expensive to be portable or suited for amateur use. On the other hand, those which are portable have only a few rppleriffles and are not very effective in separating the gold from the slurry. What is needed is a simple, short 4tppleriffle box which can remove gold effectively with relatively few fippleritfles; such a frppleriffle-box would find wide application in both commercial and amateur operations.

S 20 OBJECTIVES OF THE INVENTION It is the objective of the present invention to provide a simple and effective ri4pplteriffle-box for use in the recovery of fine gold and other heavy valuables 0:0o from sand and gravel slurries. More particularly, the invention seeks to provide a rippleriffle-box or fippleriffle-plate which is not only effective in S 25 separating gold from slurry but is self-clearing in that, after becoming loaded with gold, it can be easily, quickly and thoroughly cleared by washing with a small volume of water.

*0 It is desirable that the t4ppleriffle-box system should be capable of being 30 built in a small, compact and portable form suitable for amateur fossickers with limited water supplies, as well as being built in large, permanent installations for commercial users.

S o OUTLINE OF INVENTION This invention is based upon the realisation that the flow of slurry and water over a ippleriffle is capable of wide control by the use of a moveable flowcontrol element arranged along the length of the rippleriffle, so that depending upon the position of the element, the retention of gold will be enhanced or all particulate matter trapped by the rippleriffle can be quickly flushed out. More particularly, the interaction of the element and the ripplriffle can be such that a bed of particulate material is retained at the rippleriffle and kept agitated by the flow of slurry past the rippleriffle. Such a bed is well suited to trapping relatively fine particles of gold as it acts like the ragging in a jigged-bed concentrator. A Fippleriffle-box making use of this principle can therefore be designed as a compact and portable unit as it need have only a few relatively large rippleriffles and can be very short in length in comparison to conventional iippleriffle-boxes of the same efficiency.

The element should thus be movable from a first position (or range of positions), in which the collection of fine gold from a slurry is facilitated, to a second position (or range of positions) in which the washing of all material 20 over or out of the x4ppleriffle is facilitated. However, it is also envisaged that f..t fine adjustment of the position of the element within the first range of 4'00 positions could be effected to compensate for variations in the nature of the slurry, while fine adjustment of the element within the second range of positions could be effected to compensate for variation in the slope of the S 25 fippleriffle-plate (and other factors).

As noted above, the invention is also based upon the appreciation of the need to form an "active" bed of appropriately-sized particles (usually, but not necessarily drawn from the slurry) at each rippleriffle within which the fine 30 gold is entrapped. By moving the element to its second position, the entire bed (formed at each fippleriffle) can be rapidly flushed into a collection vessel using little wash-water.

b From one aspect, therefore, the invention comprises a ripple-plate or ripplrifle-box for use in recovering x finelydivided gold or other heavy valuables fro slurries of sand ad gravel, comprising a ritfle-plate having a at least one transverse riffle formed as sridge or depression terein ,nd comprising a t ove ablse transverse oflow pontrol elerent adrrang t tbo each ripffi, each element being moveable (when t riffe-box is in hiuse)h it aus a fi position in which it is adapted to cause a bed of particulate material to be retained in or against the riffle (to taid 15n against thrippl (t entrap the vauabls) to a second position in wic it allws the bed and h it anyaus th bd (and th entrapped goldvaluables) to be flushed fom the riffe.

ripplThe iffls may be ormed as ridges or indents in the plate. Eachcovering finely-divided gold or other heavy valuables from slurries of sand and gravel, cmoveable element may be pivoted a at least one transverse axis running paralleld as with and in close proximity to its and comprising moveabifle so that it can be flow controtated between its firstanged abovnd secnd positions, orff each element ngcan be moved bodily backwards and forwards in the longitudinal direction between (wheits two positions The moveable elementriffle-box is n use) from a first position in whichurved n the manner cause an aerofoil so thicuat it is more effective tain perfd in or againg its two distinct 25 functions in cooperation with its associated rippleriffle. In one convenient 15 entrap the moveable element to a second posists of a cyin which er arranged transverselyd (and anyit toward and away frombles) to be traling or down-stream edge of the riffleerif DECRIPTIN OF EXAMPLES Having broadly portrayed th e nature of the pres indent invention, particularc S embodiments thereof will now be p ivoted about a transverse axis running paralle and 20 with and in close proximity to its associated Aipplerilfle so that it can be rotated between its first and second positions, or each element can be sees moved bodily backwards and forwards in the longitudinal direction between its two positions. The moveable element is preferably curved in the manner of an aerofoil so that it is more effective in performing its two distinct 25 functions in cooperation with its associated 4ppleriffle. In one convenient 00** form, the moveable element consists of a cylinder arranged transversely 0 j *00 above the flpplkriffle so as to be rotatable about an eccentric axis to move it toward and away from the trailing or down-stream edge of the fippleriff le.

30 DESCRIPTION OF EXAMPLES Having broadly portrayed the nature of the present Invention, particular 0. g: embodiments thereof will now be described by way of example and illustration only. In the following description, reference will be made to the accompanying drawings in which: Figure 1 is a diagrammatic longitudinal section depicting a rippleriffle plate with raised rippleriffles having pivoted plate-like moveable elements associated therewith, Figure 2 is a similar diagrammatic longitudinal section depicting a rippleriffle plate with depressed rippleriffles having pivoted plate-like moveable elements associated therewith, Figure 3 is a similar diagrammatic longitudinal section depicting a r4ppteriffle plate with depressed ippleriffles having slidable plate-like moveable elements associated therewith, Figure 4 is a diagrammatic longitudinal section depicting a rippleriffle plate with depressed 4ppleriffles having pivoted cylindrical moveable elements associated therewith, Figure 5 is a diagrammatic side elevation of a fippleriffle-box, employing the rippleiffle-plate system of Figure 4, suitable for amateur use, and

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*5S S. S 5 S. 0 Figure 6 is a plan view of the rippleriffle-box of Figure Referring now to Figure 1, a portion of a fippleriffle-plate 10 is shown in longitudinal section, plate 10 being inclined from left to right so that the input or up-stream end 10a is on the left and the discharge or down-stream end is on the right. Conveniently, plate 10 is formed from pressed or folded 30 steel sheet material and, in the portion illustrated, two raised rippleriffles 12 and 14 are shown as being formed Integrally with the body of the plate.

4ppleriffles 12 and 14 are of smoothly-curved triangular section and run transversely of the plate in spaced parallel relation to one another.

tipplriffle-plate 10 forms the base of a rppGeriffle box having longitudinal side walls 16, only one of which is shown in this Figure.

In this first example, the moveable elements associated with the 4rpperiffles comprise elongate steel strips 18 and 20 arranged transversely of the plate and in close proximity to their respective rippleriffls 12 and 14, each strip being curved downwardly (in section) and extending the full length of its associated 4ppleriffle. Strips (or elements) 18 and 20 are mounted upon and supported by respective transverse shafts 22 and 24 that pass through holes (not shown) formed in the side plates 16 of the rippleriffle box so that the strips can be rotated about the shaft between their two positions. For the sake of convenience of description, strip 18 is shown in the first position and strip 20 is shown in the second position.

To place it in the first position, strip 18 is rotated clockwise to bring its trailing edge 18a into contact with the top of rippleriffle 12 so as to hold a bed 26 of particulate material beneath it and against the leading edge of the ri4ppleri[fle, trapping fine particles of gold 28 in the bed. Strip 20 is placed 20 in the second position by turning shaft 24 anti-clockwise from outside of the ritppleriffle-box to raise its trailing edge and lower its leading edge. This causes water flowing down plate 10 to be channelled between strip 20 and iftppleriffle 14 scouring-out any particulate materials (including gold) from the leading edge of rippleriffle 14.

In operation and during the phase when the gold is being concentrated, strips 18 and 20 are placed in the first position (as shown for strip 18) and the gold-bearing sand and gravel slurry is fed down plate 10. A bed of sand and gravel becomes trapped under the strips and ahead of the rppleriffles, 30 as shown for rppleriffie 12 where the bed is indicated at 26 and the particles of gold at 28. After a period of time operating like this, the slurry C.e flow is cut off and replaced with a flow of water and strips 18 and 20 are moved to their second positions (as shown for strip 20). This channels the water between the strips and the rippleriffles to wash the bed and gold particles (26 and 28) over the ripplerifiles and down the plate 10 for collection.

Figures 2 to 4 illustrate various arrangements in which the rippleriffles are formed as depressions in the rippleriffle plate, an arrangement which is generally preferred to that of Figure 1, though the principle of operation is as described with respect to Figure 1.

Referring more particularly to Figure 2, it will be seen that essentially the same form of pivoting strip as described with respect to Figure 1 is employed, but the strip is mounted toward the down-stream side of the 4ppleriffle rather than the up-stream side. Plate 30 is formed from steel sheet and indented ifppleriffles 31 and 32 are pressed into the sheet.

Moveable strip 33 is supported by shaft 34 above and along ppleriftle 31, while moveable strip 35 is similarly supported above rippleriffle 32 by shaft S* 36. As in the case of Figure 1, strip 33 is shown in the first position and strip 35 is shown in the second position for the purpose of illustration.

In operation, a bed of sand and gravel (37) builds up in the rppleriftles when their strips are in the first position (as shown for rippleriffle 31 and strip 33) trapping the heavier gold particles but this bed and the gold can be washed cleanly out of the rippleriflles by simply rotating the strips to the second position (as shown for strip 35 and fippleriffle 32).

S The example of Figure 3 employs depressed tippleriftes 41 and 42 in a plate 40 and elongate steel strips 43 and 44 similar to the previous examples, but in this case, the strips are arranged to slide up and down the plate rather than to pivot about shafts. In the first position (as shown for strip 43), the leading edge of the fSppleriffle (42) is covered by the strip and its raised and curved profile results in a vortex being formed along its trailing edge which retains bed 45 in the ippleriffle and deposits fine gold particles 46 in the bed. With the strip moved to a position (the "second" position) where the leading edge of the fpperiffle is no longer covered by the strip (as shown for strip 44), water enters the ippleriffle (42) along its leading edge and flows out between the trailing edges of the strip and the rippleriffle destroying the vortex and scouring the rppleriffle of its bed and accumulated gold.

In the example of Figure 4, a plate 50 with depressed fippleriffles 51 and 52 is also used, but the moveable elements are transversely-extending cylinders 53 and 54 mounted for eccentric rotation about respective shafts (or trunnions) 55 and 56, the cylinders being located toward the trailing or down-stream edge of the fippleriifles. In this Figure, cylinder 53 is shown in the first position where a bed of sand and grave! 57 is trapped under it in fippleriffle 51 so as to collect the fine gold 58 in the bed, while cylinder 54 is shown in the second position in which it is moved clear of the trailing edge of r4ppleriffle 52 so that the flow of water down plate 50 will scour the bed and the entrapped gold from the f4ppleriffle 52.

9 20 The frppieriffle-plate s, 2'em of the last example is shown incorporated in a opractical small-scale prospector's 0ppleriffle-box in the example illustrated by Figures 5 and 6. Only three 4rppleriffles are shown in the Figures and, while this will be adequate in many situations, up to about eight rippleriffles may be used.

Referring more particularly to Figures 5 and 6, an elongate 4ppleriffle-box 100, incorporating the rippleriftle plate 102 (of the type shown in Figure 4) as its base, is supported by two transverse beams 104 and 106. Each end of each beam is fitted with a tubular guide 108 through which a respective leg 110 is slipped and clamped into place by clamp-bolt 112, each leg being provided with a ball-jointed foot 114. This support arrangement allows the fippleriffle-box 100 to be quickly set at the desired angles on uneven *5 ground; it also raises the box to a convenient working height, allowing the discharge end to be positioned above the level of a collecting bucket 116.

Three sides of the input or up-stream end of the rippleriffle box are raised to form a hopper 120 for the gold-bearing sand and gravel, the downstream end of the hopper being formed by a gate-plate 122 that can be raised and lowered vertically to meter the flow of slurry from the hopper 120 onto the rippleriffle plate 102. Gate-plate 122 can be clamped in the desired position by clamp-bolt 124. Water from a suitable container (not shown) is metered into the end of hopper 120 by the combination of valve 126 and spreaderplate 128 (shown dotted).

The cylinders 130 (shown dotted) associated with each depressed rippleriffle 132 are eccentrically mounted on shafts 134 that project through the sides 136 of rippleriffle box 100, the outer ends of the shafts carrying levers or handles 138 by which the cylinders may be rotated between their first and second positions. Handles 138 can be linked together if it is wished to operate the cylinders in unison.

s 20 In operation, the fippleriffle-box is set up so that it is level from side to side, the fippleriffle plate 102 slopes at about 5 to 80 toward the discharge end and there is room to position the collection bucket 116 under the discharge end. Valve 126 is connected via hose 140 to a tank of water and turned on to allow enough water to flow to just cover the ri pleriffle plate from side to side, legs 110 being adjusted to give an even depth of water across the plate. Cylinders 130 are moved to their first positions and a small quantity of selected and sifted particulate bed material is fed into hopper 120 until all f4ppleriffles 132 are full of the bed material, any excess being collected S* and retained for future use.

The gold-bearing sand and gravel mix is then added to hopper 120 and the metering plate 122 and water valve are adjusted to give the desired rate of slurry flow down the rippleriffle-plate 102 and (ii) ensure that the upper surface of the bed material in each ippleriffle is "active" that is, agitated by the water flow. The active surface of the bed, together with the leakage of water from between the down-stream edge of the rppleriffle and the associated cylinder, combine to efficiently entrap gold particles being carried along the bottom of the rippleriffle-plate. The efficiency of entrapment can be considerably enhanced by selecting bed materials having a specific gravity significantly greater than that of the gold-bearing sand and gravel material but still significantly less than that of gold. Crushed zircon, garnet, rutile, ilmenite and magnetite are examples of suitable bed materials, but sieved coarse sand can also be used to good effect where few high-density gangue minerals are present in the slurry. The particle size of the bed material should be a few standard-mesh sizes below that of the slurry materials, though a range of particle sizes is preferred.

The frequency with which the gold concentrate should be washed out of the rippleriffles must be determined by the nature of the slurry and the bed materials being used. The bed can become clogged by clay or excessive fine 'heavies' in the slurry, or when rich slurries are being used, there is a S 20 danger of gold filling the bottom of the fippleriffles and being washed out by the agitation of the bed. When it is judged necessary to collect the concentrate, the sand and gravel in the hopper is allowed to run out and the flow of clean water maintained for a seconds. Then, the concentrate bucket is placed beneath ihe discharge-end of the ippleriffle-box and the cylinders rotated to their second positions to allow the beds to be scoured out of the rippleriftle depressions. The cylinders can be rotated in unison or in any dc ired order, but, where they are not rotated in unison, it has been found preferable to operate them in order from the down-stream end to the upstream end. An advantage of the eccentric cylinder arrangement is that sny large pieces of gravel caught between a cylinder and the fippleriffle plate can be crushed by rotating the cylinder backwards and .forwards.

While the examples of the invention described above meet the objects and advantages set out at the beginning of this specification, allowing efficient and rapid recovery of gold from sand and gravel slurries with the minimum of effort and cost using equipment suited to the amateur prospector, those skilled in the art will understand that many variations and modifications can be made to the invention as disclosed without departing from its spirit or scope as defined by the following claims. The invention has considerable potential in full-scale commercial gold recovery systems as well as in smallscale portable prospector's equipment. The examples of moveable element and r-pplerifle combinations are not intended to be exhaustive and many other configurations are possible.

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