GB2109708A - Materials separation system and method - Google Patents

Abstract

In a materials separation system a distributor (13A, 13B) for jigs (14A, 14B, 14C) used in the separation of heavy minerals, also diamonds, from pulp dredged up from a body of water (and separated by a trommel (10A, 10B) according to size) functions to supply all of the finer material, including sand which is not rejected by the trommel, to the feed boxes of the jigs, but when the material delivered by the dredge and trommel contains excessive sand, the sand is caused to overflow (at 17) to, if desired, one or more secondary distributors (18) and jigs (25). In this way the primary jig or jigs and the dredge can be kept operating at full dredge capacity. <IMAGE>

Description

SPECIFICATION Materials separation system and method This invention relates to a distributor for a jig employed to recover heavy minerals by gravity concentration. The invention is also applicable to the recovery of diamonds which, although not heavy minerals, separate by gravity due to their non-wetting characteristic. The jig employed with the distributor of the present invention is preferably a circular jig, such as that described in the specification of my copending British Patent Application No.8117112, Serial No. 2077627.

However, the distributor may be employed with other types of jigs, such as rectangular jigs.

In the separation of heavy minerals, such as gold, platinum, tin ore, diamonds, etc. from sand and gravel in placer mining operations, it is common to dredge up the alluvial material (sand, gravel, etc.) from 3 pond in which the dredge operates. This material is then sized in a trommel, which is a rotating cylinder with perforated side plates. In the trommel the dredged material is scrubbed with jets of water. Typically, such a trommel will reject material of some 1.6 cms in diameter and greater and will deliver the finer material, generally known as the pulp, to a distributor which divides the pulp into as many portions as there are jigs, For the jigs to operate efficiently each should be fed as equally as possible, not only as regards volume but also as regards pulp density, grain size, and recoverable values.Naturally, the greater the number of jigs, the greater the difficulty in feeding them all properly.

The problem is further complicated by the fact that normally there is a wide variation in the character of the solids in a placer deposit, ranging from mostly sand in some spots to mostly boulders nearby. When only sand is encountered, there is no oversize material for the trommel to reject, therefore it is normally necessary to reduce the digging rate of the dredge to prevent overloading both the distributoi and the jigs. Such reduction in the rate of digging reduces the dredge's throughput and increases unit operation costs. To design a treatment plant capable of coping with maximum sand conditions would result in such a plant being vastly underloaded and inefficient for most of the time.

Probably the most successful means so far for coping with this problem is by a rather involved system of splitters which require much additional headroom and thus significantly increases dredge weight and operating costs.

The present invention will make it possible for the dredgs to dig at maximum capacity most of the time without overloading either the distributors or the jigs. This significant improvement in dredging practice is obtained by taking advantage of the fact that rarely do the valuable minerals occur in those portions of the deposit which are entirely sand. Thus, by applying the "boil box" principle of my aforesaid Patent Application for circular jigs, the distributor under consideration becomes a concentrator from which the lighter fractions of the barren sand overflow and are thereby removed from the pulp being delivered to the jigs. At the same time the amount of pulp passing to each jig can be controlled to prevent overloading the jigs.Thus by upgrading the pulp and controlling the pulp volume, jig efficiency is improved and the overall capacity of the dredge is determined by digging rather than by treatment capacity; According to the present invention there is provided a materials separation system comprising a size separator serving to receive an aqueous mixture of solids of varying size and density and to pass finer solids up to a certain size and to reject solids exceeding such size, a density separator serving to receive from the size separator an aqueous pulp containing such finer solids, to separate the finer solids according to density, and/or wetting characteristics, and to create an overflow of less dense or less wetted solids, and a distributor means interposed between the size separator and the density separator, such distributor means functioning during normal operation while the sand component of such pulp is not excessive to pass the pulp to the density separator but functioning, during periods when such sand component is excessive, to create and maintain an overflow of the pulp and to divert it from the density separator.

To ensure maximum recovery of values, the sand or other material boiled over from the main distributor can be retreated on second or third distributors which feed scavenger jigs, under conditions where again neither the distributors nor the jigs are overloaded and all barren material eventually passes over the stern or the dredge as do the tailings from the jigs.

According to another aspect of the invention there is provided a method of size and density classification of mixtures of sand, gravel and denser mineral values comprising (a) subjecting an aqueous mixture of such mixture dredged from a body of water to size classification to separate coarser from finer solids and producing an aqueous pulp of finer solids including sand and denser or less wetted mineral values, (b) subjecting such pulp to density classification to separate denser or less wetted mineral values from lighter material such as sand, and (c) interposing between steps (a) and (b) a control step whereby during periods of operation of the dredge when said aqueous pulp contains normal amounts of sand, substantially the entire solids of the pulp is introduced into step (b) but during periods of operation when the dredge is delivering excessive quantities of sand at least a substantial portion of the solids is diverted from step (b).

One embodiment of the invention is shown by way of an example in the accompanying drawings, in which: Figure 1 is a schematic view of an installation including a trommel, a circular jig and a distributor embodying the present invention; Figure 2 is a top plan view of a system employing a double trommel, three circular jigs, and two distributors; Figure 3 is a top plan view of one of the distributors; Figure 4 is a view in vertical section along the line 4-4 of Figure 3; Figure 4A is a fragmentary view on a larger scale than that of Figure 4, showing valve means for controlling flow of material from the distributor into sluices and to the jigs of Figure 2; Figure 5 is a fragmentary view in vertical section showing the manner in which water may be supplied to a distributor in the event that there is a shut-down of power; and Figure 6 is a schematic view showing how the flow of puip from a pair of trommels is distributed among the three jigs of Figure 2.

Referring now to the drawings and preliminariiy to Figure 1, a trommel 10 is shown provided with a helper 11 and with a funnel 12 to direct pulp to a distributor 1 3. The distributor 1 3 is shown as overlying a circular jig 14 which may be of the same construction as described in my Patent Application above mentioned.

Referring now to Figure 2, a double trommel 1 OA and 1 OB is shown provided with a hopper 11.

The trommel 1 OA overlies a distributor 1 3A and the trommel 1 OB overlies a distributor 1 3B. Three circular jigs 1 4A, 1 4B and 1 4C are shown, each having a feed box 1 5. Overflow from each of the distributors 1 3A and 1 3B flows through a sluice or other conduit 17, into a secondary distributor 18, which may be constructed identically to the distributors 1 3A and 1 3B. Overflow of the ligher material from the secondary distributors 1 8 would normally go to waste, although it may receive further treatment, as with another jig (not shown).

The underflow of heavier material from each of the secondary distributors 1 8 passes through a sluice or other conduit 1 9 to a jig feed box 20 of a scavenger jig 25.

Referring now to Figures 3 and 4, one of the distributors (that indicated in Figure 2 at 1 3B) is shown. The distributor 1 3B is in the form of an inverted cone 30 having an open top and provided with an overflow sluice 31 which varies in depth so as te flow into one of the sluices 1 7. The cone 30 is formed with three rows of holes 34, spaced 1 20 degrees apart. Each row of holes 34 overlies a sluice so that one third of the underflow passes into a sluice 41, one third into a sluice 42 and one third into a sluice 43. Sluice 41 conveys the underflow or pulp to the jig feed box 1 5 of center jig 1 4B. The sluices 42 and 43 join and deliver pulp to a common sluice 44 which conveys the pulp to feed box 1 5 of jig 1 4C.Similarly the distributor 1 3A delivers two thirds of its underflow to jig 1 4A and one third to jig 1 4B. Therefore one third of the underflow or pulp is delivered to each of the three jigs 1 4A, 1 4B and 1 4C. This system of distribution is shown in Figure 6.

It will be understood that a single jig may be used with a single distributor and a single trammel; two jigs may be employed with a single distributor, etc. The particular combination of jig or jigs and distributor or distributors will depend upon particular circumstances.

Referring to Figure 4A, one of the holes of cone 30 is there shown and connected to it a length of tubing 45, for example hose material, and a valve is incorporated at 46. such being, for example, a pinch valve which is a clamp which can pinch the hose 45 and control the outflow of material. There will be such connections to some or all of the holes 34 of the two cones 30.

In operation, and with reference to Figures 2, 3 and 4, pulp is delivered by each of the trommels 1 OA and 1 OB to the respective distributors 1 3A and 1 3B and by the distributors to the three jigs 1 4A, 1 4B and 1 4C as described above. Overflow from each distributor will flow from the sluice 31 into a sluice 1 7 thence to a secondary distributor 1 8 for further concentration. This overflow will consist largely of water, and the finer particles having the lowest specific gravity.

As noted above, difficulty is encountered when a dredge brings up an excessive quantity of sand.

The valves 46 are adjusted so that under the worst possible conditions, that is to say, a condition where the solid material brought up by the dredge consists entirely of sand, the lighter fraction of the solid material will overflow into the sluices and eventually into the tailings behind the dredge.

None of the jigs will be overloaded. Once the pinch valves 46 have been adjusted for maximum sand conditions they may be repiaced by fixed spigots (not shown) of similar capacity.

If such seems justified, further stages of the procedure outlined above are readily possible. The overflow process results in a minimum loss of overhead between stages. But in case more headroom is needed such could be obtained by pumping the final overflow to provide whatever headroom is required. In any event, it would not be necessary either to slow down the rate of digging nor to overload the jigs.

Referring to Figure 5, an additional feature is shown including â tube 50 provided with a valve 51. The tube enters the bottom of the cone 30 and is deflected and distributed by a distributor member 52. This auxiiiary source of water will be used in case it is desirable to dilute the pulp or in case of a blockage that might result from a power failure. The valve may be operated manually or automatically to supply water when and in the volume needed.

Claims (8)

1. A materials separation system comprising a size separator serving to receive an aqueous mixture of solids of varying size and density and to pass finer solids up to a certain size and to reject solids exceeding such size, a density separator serving to receive from the size separator an aqueous pulp containing such finer solids, to separate the finer solids according to density, and/or wetting characteristics, and to create an overflow of less dense or less wetted solids. and a distributor means interposed between the size separator and the density separator, such distributor means functioning during normal operation while the sand component of such pulp is not excessive to pass the pulp to the density separator but functioning, during periods when such sand component is excessive, to create and maintain an overflow of the pulp and to divert it from the density separator.

2. A system according to claim 1, wherein the size separator is a trommel and the density separator is a jig.

3. A system according to claim 1 or 2, wherein the distributor means is in the form of a vessel having openings through which pulp is delivered to the jig and also has overflow means which function during abnormal conditions to cause overflow of the lighter fraction of the pulp.

4. A system according to claim 3, including adjustable valve means positioned to adjust the rate of flow of pulp into the density separator.

5. A system according to claim 1, 2, 3 or 4, including means for supplying water to the distributor vessel to prevent clogging of the distributor by excessive amounts of sand.

6. A method of size and density classification of mixtures of sand, gravel and denser mineral values comprising (a) subjecting an aqueous mixture of such mixture dredged from a body of water to size classification to separate coarser from finer solids and producing an aqueous pulp of finer solids including sand and denser or less wetted mineral values, (b) subjecting such pulp to density classification to separate denser or less wetted mineral values from lighter material such as sand, and (c) interposing between steps (a) and (b) a control step whereby during periods of operation of the dredge when said aqueous pulp contains normal amounts of sand, substantially the entire solids of the pulp is introduced into step (b) but during periods of operation when the dredge is delivering excessive quantities of sand at least a substantial portion of the solids is diverted from step (b).

7. A materials separation system constructed and arranged to operate substantially as herein described with reference to and as illustrated in the accompanying drawings.

8. A method of size and density classification of sand, gravel and minerals substantially as hereinbefore described with reference to the accompanying drawings.