GB2233759A - "Particulate ore sorting" - Google Patents

Abstract

Particulate ore material which is to be sorted is mixed with a liquid to form a slurry. This is done in a header tank 12 which is connected to a vertical duct 10 through which the slurry flows under gravity. The static head of slurry in the header tank is maintained constant (16, 18). During its flow through the duct, the slurry is irradiated (24) and the responses of the particles in the slurry to the radiation is detected (26) and analysed to form the basis for a subsequent step of sorting the particles into fractions in accordance with their responses. Typically the method is used to sort diamonds for diamondiferous particles from non- diamondiferous particles and the radiation is either laser radiation designed to produce detectable Raman spectral activation in the diamond particles or X-radiation designed to produce detectable luminescence in the diamond particles. <IMAGE>

Description

BACKGROUND TO THE IIN'VEN'TIONT THIS invention relates to ore particle sorting.

It has already been proposed to cause particulate material which is to be sorted to flow in slurry form along an open chute. While on the chute, the slurry is subjected to a chosen excitation and detection equipment is used to detect the response of the particles of the material to the excitation and thereafter to initiate a separation step in which desired material is separated from undesired material.

The use of a chute has some disadvantages, one being the possibility of irregular flow on the chute and "bumping" of particles against the chute walls. leading to velocity and positional errors.

SUMMARY OF THE INVENTION A first aspect of the invention provides a method of sorting particulate ore material, the method comprising the steps of providing a vertical duct connected below a header tank, forming a fluent slurry of the ore material which is to be sorted in the header tank, maintaining a constant static head of slurry in the header tank while allowing the slurry to flow full under gravity through the duct, irradiating the slurry as it flows through the duct, detecting and analysing the responses of the particles in the slurry to the radiation, and sorting the particles into fractions in accordance with their responses.

The method may comprise the steps of irradiating the slurry through one or more windows in the duct and of detecting the responses of the particles to the radiation through one or more windows of the duct.

The slurry may be formed by mixing the particulate ore material with water in the header tank.

The method according can be used for sorting diamond or diamondiferous particles from non-diamondiferous particles, in which case the slurry is irradiated witch laser radiation and the particles are sorted into fractions in accordance with their Raman spectral activation. Alternatively, the slurry is irradiated with X-radiation and the particles are sorted into fractions in accordance with their luminescence response to the X-radiation.

A second aspect of the invention provides apparatus for sorting particulate ore material, the apparatus comprising a header tank, a vertical duct connected below the header tank, means for feeding particulate ore material which is to be sorted, and water, into the header tank for mixture therein to form a slurry which is then able to flow full under gravity through the duct, means for maintaining a constant static head of slurry in the header tank, means for irradiating the slurry as it flows through the duct, means for detecting and analysing the responses of the particles to the radiation and means for sorting the particles into fractions in accordance with their responses.

Preferably, the duct is rectangular in cross-section. Preferably also, the width of the duct is substantially greater than the depth thereof and the irradiating means is arranged to irradiate the slurry in a direction normal to the width of the duct.

The duct may include one or more windows through which the slurry is irradiated and through which detection of the responses of the particles takes place.

Preferably, the or each window is flush with the inner surface of the duct.

The header tank should have a substantially greater cross-sectional area than the duct and may be connected to the duct through a tapered transition conduit.

When the apparatus is used to sort diamond and diamondiferous particles from non-diamondiferous particles, the means for irradiating the slurry as it flows through the duct may comprise a laser source and the means for detecting the responses of the particles to the laser radiation may be responsive to Raman spectral activation. Alternatively, the means for irradiating the slurry as it flows through the duct may be a source of X-radiation and the means for detecting the responses of the particles to the X-radiation may be responsive to luminescence of the particles.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will now be described in more detail, by way of example only, with reference to the accompanying drawings in which: Figure 1 illustrates apparatus of the invention; and Figure 2 illustrates a window at a larger scale than in Figure 1.

DESCRIPTION OF AN EMBODIMENT Figure 1 shows a vertical, tubular duct 10 of rectangular cross-section. The upper end of the duct 10 communicates, via a frusto-conical transition conduit, with a header tank 12 having a substantially larger cross-sectional area than the duct.

Vertical baffles 14 are provided in the header tank as illustrated. Inlet pipes 16 are arranged to feed water into the header tank. A level controller 18 is provided to ensure that a constant static head is maintained in the header tank. Although shown only schematically, the level controller 18 can take any one of a number of conventional forms, such as a level probe system, with fast-acting valves (not shown) being provided in the pipes 16 to control the inflow of water through those pipes in response to the level controller.

An inclined chute 20 feeds particulate ore material which is to be sorted into the header tank 12. The baffles 14 only extend for a part of the depth of the header tank and permit some turbulence to take place in the header tank to promote disagglomeration of the particulate feed material and thorough dispersion and mixing of the particles in the water to form a slurry.

The slurry of particles in water which is formed in the header tank 12 is able to leave the header tank and flow full under gravity through the duct 10. As a result of the so-called Magnus effect, the particles in the slurry are caused to migrate towards the central axis of the duct 10.

By the time the particles reach a pair of opposing windows 22 in the wall of the duct 10, they are fairly well centralised in the duct and are spread out fairly evenly from one another.

As illustrated in the drawing, the duct 10 has a marked rectangular shape. In a typical example, the duct may have dimensions of 250mm by 16mm in crosssection. In such a case, the particles in the slurry will, by the time they reach the windows, have arranged themselves into a generally planar "curtain" extending parallel to the longer sides of the duct and centralised with respect to the shorter sides.

Only one window 22 is visible in Figure 1 but it will be understood that a similar window is provided on the opposite side of the duct 10 as well.

In one specific application of the invention, where it is desired to sort diamond and diamondiferous particles from other particles using the Raman technique described in international patent application publication No WO 88/01378, a laser source 24 is positioned opposite the far side window 22 and is used to project a laser beam through the window to impinge on the slurry. Diamondiferous particles cause Raman spectral activation to take place and this is detected using suitable spectral detection equipment 26 focussed on the slurry through the near side window 22.

Signals from the detection equipment are analysed using an appropriate microprocessor (not shown) and a determination is made as to whether the detected radiation is indicative of a diamond or diamondiferous particle.

The slurry, having passed bv the windows 22, issues from the duct 10 in a falling stream. In response to a positive determination by the microprocessor, a downstream separation apparatus (not shown) is used to eject or otherwise separate the desired particles in the falling stream from other, undesired particles.

Although specific mention has been made of sorting taking place on the basis of Raman response to an incident laser beam, it should be understood that the apparatus could also be used in other sorting techniques. Once example would be the use of X-radiation to generate detectable luminescence in diamonds and diamondiferous particles.

A major advantage of the apparatus described above when compared to the open chute system proposed by international application publication No. WO 88/01378 resides in the fact that the particles in the slurry, by the time the excitation and detection station is reached, are fairly closely confined to a known central region of the duct so that positioning problems are less pronounced. High speed filming studies have shown that with particles having a size in the range 3mm to 6mm, substantially no particle "overlap" occurs at feed rates of 3 to 6 tons per hour through a duct having a width of 250mm. This is despite the fact that the particles occupy a substantial portion, typically 22% of the width of the duct. Additionally, the particle flow velocities are stabilised by the flow regime and by the incompressible carrier liquid.The particle velocities which are possible are higher than in the case of falling, dry particles. For instance, in the high speed filming studies mentioned previously, particle velocities of 5m/s with a small standard deviation of only 0,3m/s have been observed, compared to equivalent values of 4,2m/s and 0,7m/s for drv particles falling freely under gravity, i.e. with no carrier liquid, through an equivalent vertical distance and between parallel constraining plates. Naturally, uniformity in the particle velocities contributes to accuracy in the subsequent sorting procedure. Yet another advantage when compared to an open chute is the fact, that, optically, there is a depth of field which is defined accurately by the width of the duct at the excitation and detection station.

As stated previously, the duct may have a shape which causes the particles to descend in the slurry in a planar "curtain". In this case, it may be necessary to provide a plurality of radiation sources and detectors spaced out to irradiate and view the particles in the curtain.

Figure 2 shows a flush-fitting window 22 in which the inner surface 30 of an inner window pane 22A is flush with the inner surface of the duct wall 32. An outer glass pane 22B is laminated at 36 to the inner pane 22A, the outer plane being clamped relative to the duct by means of a clamping plate 38 with a resilient gasket 40 interposed between the clamping plate and the pane 22B. With the proposed, flush-fitting windows, it will be possible to detect low intensity light signals and focus them accurately without the focussing problems experienced with a turbulent slurry surface in an open chute.

Claims (16)

1.

A method of sorting particulate ore material, the method comprising the steps of providing a vertical duct connected below a header tank, forming a fluent slurry of the ore material which is to be sorted in the header tank, maintaining a constant static head of slurry in the header tank while allowing the slurry to flow full under gravity through the duct, irradiating the slurry as it flows through the duct, detecting and analysing the responses of the particles in the slurry to the radiation, and sorting the particles into fractions in accordance with their responses.

2.

A method according to claim 1 comprising the steps of irradiating the slurry through one or more windows in the duct and of detecting the responses of the particles to the radiation through one or more windows in the duct.

3.

A method according to any one of the preceding claims wherein the slurry is formed by mixing the particulate ore material with water in the header tank.

4.

A method according to any one of the preceding claims for sorting diamond or diamondiferous particles from non-diamondiferous particles, wherein the slurry is irradiated with laser radiation and the particles are sorted into fractions in accordance with their Raman spectral activation.

5.

A method according to any one of claims 1 to 3 for sorting diamond or diamondiferous particles from non-diamondiferous particles, wherein the slurry is irradiated with X-radiation and the particles are sorted into fractions in accordance with their luminescence response to the X-radiation.

6.

Apparatus for sorting particulate ore material, the apparatus comprising a header tank, a vertical duct connected below the header tank, means for feeding particulate ore material which is to be sorted, and water, into the header tank for mixture therein to form a slurry which is then able to flow full under gravity through the duct, means for maintaining a constant static head of slurry in the header tank, means for irradiating the slurry as it flows through the duct, means for detecting and analysing the responses of the particles to the radiation and means for sorting the particles into fractions in accordance with their responses.

7.

Apparatus according to claim 6 wherein the duct is rectangular in cross-section.

8.

Apparatus according to claim 7 wherein the width of the duct is substantially greater than the depth thereof and wherein the irradiating means is arranged to irradiate the slurry in a direction normal to the width of the duct.

9.

Apparatus according to any one of claims 6 to 8 wherein the duct includes one or more windows through which the slurry is irradiated and through which detection of the responses of the particles takes place.

10.

Apparatus according to claim 9 wherein the or each window is flush with the inner surface of the duct.

11.

Apparatus according to any one of claims 6 to 10 wherein the header tank has a substantially greater cross-sectional area than the duct and is connected to the duct through a tapered transition conduit.

12.

Apparatus according to any one of claims 6 to 11 wherein the means for maintaining a constant static head of slurry in the header tank comprises a level controller responsive to the level of slurry in the header tank.

13.

Apparatus according to any one of claims 6 to 12 for sorting diamond and diamondiferous particles from non-diamondiferous particles, wherein the means for irradiating the slurry as it flows through the duct comprises a laser source and wherein the means for detecting the responses of the particles to the laser radiation is responsive to Raman spectral activation.

14.

Apparatus according to any one of claims 6 to 12 for sorting diamond and diamondiferous particles from non-diamondiferous particles, wherein the means for irradiating the slurry as it flows through the duct is a source of X-radiation and wherein the means for detecting the responses of the particles to the X-radiation is responsive to luminescence of the particles.

15.

A method of sorting particulate ore material substantially as herein described with reference to the accompanying drawings.

16.

Apparatus for sorting particulate ore material substantially as herein described with reference to the accompanying drawings.