AU623406B2 - Particle sorting apparatus and method - Google Patents

Description

I m COMMONWEALTH OF4USTRAMS PATENTS ACT 1952 (COMPLETE SPECIFICATION NAME ADDRESS OF APPLICANT: De Beers Industrial Diamond Division (Proprietary)Limited Main Street Johannesburg Transvaal Republic of South Africa NAME(S) OF INVENTOR(S): Henry Joseph COPPENS ADDRESS FOR SERVICE: DAVIES COLLISON Patent Attorneys 1 Little Collins Street, Melbourne, 3000.

o a 4 o a0c o o 0 0 t*0 0 0 0 0 o o a o o0 0 00o o e COMPLETE SPECIFICATION FOR THE INVENTION ENTITLED: Particle sorting apparatus and method The following statement is a full description of this invention, including the best method of performing it known to me/us:o o o 4o 0 0 0 o 04 0 o0a 1v~ 0Y10 0 8 0 t Q a I~ I~ Al- 2 BACKGROUND TO THE INVENTION 0 09 00 9 0090 9I 0i 99 0 9 99 9 THIS invention relates to a particle sorting apparatus and method.

A number of known particle sorting apparatuses, particularly those used in the ore sorting industry, have a conveyor system which transports the particles successively through an excitation zone, a detection zone and an ejection zone.

In the excitation zone, the particles are subjected to some or other exciting influence, typically X-radiation in the case of diamond sorting, which causes certain of the particles to exhibit some or other detectable response which can be detected in the detection zone. In the case of diamond sorting, the response which is excited in diamond particles by the incident X-radiation is luminescence which can be detected in the detection zone using appropriate photodetectors.

Signals from the detection appparatus, and also from apparatus used to determine sizes and locations of the particles, are fed to a processor which actuates, at the appropriate instant, an ejector system in the ejection zone.

Typically the ejector system has a bank of air blast ejectors which are actuated to blast selected particles out of the main stream of particles, which are usually in free flight at this stage.

o o 9999 o 00 0 0 4 I 9 9 (9 Generally, the particles which are ejected from the main stream are the desired particles, since they will usually be far less numerous than undesired particles. Thus in a diamond sorting machine operating in the manner outlined above, diamond particles which have luminesced under Xradiation are ejected from the main stream and fall into one bin while other particles of gangue are allowed to continue unimpeded into a reject bin.

SUMMARY OF THE INVENTION A first aspect of the invention provides a method of sorting ore particles into a desired fraction containing desired particles and a gangue fraction containing gangue .0 15 particles, the method comprising the steps of causing a stream of particles which are to be sorted to move along 'a normal path through a deflection zone, directing a liquid blast at the stream in the deflection zone to deflect gangue particles away from the normal path for S0: 20 collection as a gangue fraction, and interrupting the liquid blast whenever a desired particle arrives at the deflection zone so that the desired particles continue moving along the normal path for collection as a desired fraction.

o: Advantageously, the gangue particles are deflected by .means of a water blast directed at the stream of So particles. It is preferred that the stream of particles be projected from the end of a moving conveyor such that they fall in free flight past liquid blast means which deflects the gangue particles from the normal path of the falling stream.

The invention also extends to an apparatus for sorting a stream of ore particles into a desired fraction containing desired particles and a gangue fraction S containing gangue particles, the apparatus comprising 920224,PHHSPE.02,dcbcersspe,3 Il~-u~ ii i i -4means for moving the particles which are to be sorted along a normal path through a deflection zone, means for directing a liquid blast at the stream in the deflection zone so that gangue particles are deflected away from the normal path for collection as a gangue fraction, and means for interrupting the liquid blast whenever a desired particle arrives at the deflection zone so that the desired particles are able to continue moving along the normal path for subsequent collection as a desired fraction.

In one embodiment of the apparatus, the liquid which is used is water. The means for directing the blast at the stream comprises one or more blast nozzles through which 15 the liquid is passed under pressure. In this case, the means for interrupting the liquid blast may comprise i, means for introducing a volume of gas, possibly air, t under pressure into the liquid such that a gap is formed S:j: in the liquid blast, the desired particle then passing through the gap without being deflected along with the gangue particles. Typically, the pressure of the gas is approximately the same as that of the liquid.

4, 4 44 BRIEF DESCRIPTION OF THE DRAWINGS ,o The invention will now be described in more detail, by way of example only, with reference to the accompanying drawings in which Figures 1 to 5 show successive stages in the practice of the invention, used in this case for sorting diamond particles from gangue particles.

920224,PHHSPE.021,debers.spe,4 5 SPECIFIC DESCRIPTION t ll 4 I: 1 I~ I 14 41 I eI 11 44s In the Figures a conveyor belt is designated with the reference numeral 10. A mass of ore articles, including gangue particles 12 and diamond particles 14, is deposited on the belt to form a stream which is conveyed from left to right in the Figures. At the end of the belt, where it passes over a discharge pulley 16, the stream of particles is projected in free flight such that the particles fall along a normal, parabolic path.

The particles in the stream 18 are, prior to reaching a deflection zone 20, subjected to X-radiation which causes the diamond particles to luminesce. The luminescence is detected by appropriate photodetectors (not shown) which issue signals to a processing unit (not shown). The processing unit also receives signals from a line scan camera 22.

Under the control of the processing unit, one or more water blast nozzles 24 in the deflection zone issue a blast 26 of water under a pressure of, in this case, 100kPa. The water blast is continuous whenever gangue particles reach the deflection zone. The water blast impinges on the falling stream of particles and deflects the gangue particles 12 away from the normal path such that they fall into a waste bin 28.

At the appropriate instant when a diamond particle 14 reaches the deflection zone, the blast of liquid is interrupted, again under the control of the processing unit.

Accordingly, the desired diamond particles are not deflected along with the gangue particles, and are able to continue 6 falling along the normal path into a diamond bin The periodic interruption of the water blast is achieved using compressed air. A nipple 32 enters the water blast nozzle 24 at a point near its discharge end. The pressure of the air is about the same as that of the water, namely 100kPa, and is controlled by a solenoid valve or the like which operates under instructions from the processing unit.

A short duration blast of the compressed air enters the nozzle 24 through the nipple, forming a small pocket of air 34 in the water stream in the nozzle. This pocket 34 establishes a gap 36 in the water stream as it leaves the nozzle.

The diamond particles arriving at the deflection zone 20 are able to pass through the gaps in the water blast and hence are able to continue unimpeded along the normal path to the diamond bin Note that the use of a water blast as opposed to an air blast as used in conventional sorting machines is advantageous in that it will be possible to deflect undesired particles from the falling stream which are too large and heavy to be deflected by compressed air. Thus it is believed that the invention will be suitable for sorting large particles of, say, kimberlite, from large particles of gabbro.

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Claims (13)

1. A method of sorting ore particles into a desired fraction containing desired particles and a gangue fraction containing gangue particles, the method comprising the steps of causing a stream of particles which are to be sorted to move along a normal path through a deflection zone, directing a liquid blast at the stream in the deflection zone to deflect gangue particles away from the normal path for collection as a gangue fraction, and interrupting the liquid blast whenever a desired particle arrives at the deflection zone so that the desired particles continue moving along the normal path for collection as a desired fraction.

2. A method according to claim 1 wherein the liquid blast is interrupted by introducing a volume of gas into the liquid blast. O 4 4 4

3. A method according to claim 2 wherein the liquid blast is interrupted by introducing a volume of compressed air into the liquid blast. o

4, A method according to any one of the preceding claims wherein the gangue particles are deflected away from the normal path by a water blast.

A method according to any one of the preceding claims wherein the particles which are to be sorted are projected in free flight along the normal path from the end of a moving conveyor.

6. Apparatus for sorting a stream of ore particles into a desired fraction containing desired particles and a gangue fraction containing gangue particles, the apparatus comprising means for moving the particles which are to be sorted along a normal path through a deflection zone, means for directing a liquid blast at the stream in the deflection zone so that gangue particles are deflected away from the normal path for collection as a gangue fraction, and means for interrupting the liquid blast whenever a desired particle arrives at the deflection zone so that the desired particles are able to continue moving along the normal path for subsequent collection as a desired fraction.

7. Apparatus according to claim 6 and comprising one or more blast S nozzles through which the liquid is passed under pressure. i 0

8. A.AA Apparatus according to claim 7 wherein the means for interrupting AA the liquid blast comprises means for introducing a volume of gas under pressure into the liquid such that a gap is formed in the liquid blast, the desired particles then passing through the gap A without being deflected along with the gangue particles.

9. Apparatus according to claim 8 wherein the gas is air and the i liquid is water.

Apparatus according to claim 9 wherein the means for directing the liquid blast and for introducing the volume of gas into the liquid blast are arranged such that the pressures of the liquid and of the gas are approximately the same. i i i I i 9

11. Apparatus according to any one of claims 6 to 10 and comprising a conveyor for conveying the particles and for projecting the particles in free flight along the normal path.

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

13. Apparatus for sorting ore particles substantially as herein described with reference to the accompanying drawings. DATED this 24th day of February, 1992. DE BEERS INDUSTRIAL DIAMOND DIVISION (PROPRIETARY) LIMITED By its Patent Attorneys DAVIES COLLISON CAVE