AU628133B2

AU628133B2 - Sorting method and apparatus

Info

Publication number: AU628133B2
Application number: AU49999/90A
Authority: AU
Inventors: Kevin Peter Ashby; Charlie Maurice Levitt; Roger Clyde Randall
Original assignee: De Beers Industrial Diamond Division Pty Ltd
Current assignee: De Beers Industrial Diamond Division Pty Ltd
Priority date: 1989-02-20
Filing date: 1990-02-20
Publication date: 1992-09-10
Anticipated expiration: 2010-02-20
Also published as: GB2229116A; AU4999990A; GB2229116B; GB9003803D0

Description

|i i i 628 33 COMMONWEALTH OF AUSTRALIA PATENTS ACT 1952 COMPLETE SPECIFICATION NAME ADDRESS OF APPLICANT: De Beers Industrial Diamond Division (Proprietary) Limited Main Street Johannesburg Transvaal Republic of South Africa S NAME(S) OF INVENTOR(S): Kevin Peter ASHBY S* Charlie Maurice LEVITT Roger Clyde RANDALL ADDRESS FOR SERVICE: DAVIES COLLISON Patent Attorneys 1 Little Collins Street, Melbourne, 3000.

COMPLETE SPECIFICATION FOR THE INVENTION ENTITLED: Sorting method and apparatus The following statement is a full description of this invention, including the best method of performing it known to me/us:t- Insert place and date of signature.

Signature of declarant(s) (no attestation required) Note: Initial all alterations.

Declared at SANDTON this 15TH day of FEBRUARY, 1990 y p- -M E

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2 BACKGROUND TO THE INVENTION S. S

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*5 THIS invention relates to a sorting method and apparatus. In one application of the invention, it may be used to sort diamondiferous particles from non-diamondiferous particles.

It is known that diamonds have a much higher thermal conductivity than the non-diamondiferous material with which they are normally associated in the natural enviroment. The invention seeks to use such differences in thermal properties in a method and apparatus of sorting particles.

;i -3- SUMMARY OF THE INVENTION

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S. S S S *5 According to the invention there is provided a method of sorting particles having different thermal conductivities into fractions, the method comprising wetting the particles with a liquid, bringing the particles into contact with a surface which has a temperature at or below the freezing point of the liquid, and separately recovering from the surface particles which are and are not adhered to the surface after a specified time period.

The method is time and temperature dependent. These parameters may, on the one hand, be set such that during the specified time period, all particles adhere to the surface by reason of the liquid with which they are wetted freezing, those particles having a higher coefficient of thermal conductivity releasing heat rapidly enough to melt the frozen liquid with the result that they are released from the surface by the end of the specified time period, while other particles having a lower coefficient of thermal conductivity are not able to release heat rapidly enough to melt the frozen liquid by the end of the specified time period and thus remain adhered to the surface.

On the other hand, the time parameters may be set such that the particles with the higher coefficient of thermal conductivity lose heat more rapidly to prevent freezing of the liquid, such particles thus not adhering at all to the surface, while the other particles with the lower coefficient of thermal conductivity do not lose sufficient heat within the specified time period to prevent freezing of the liquid and thus are adhered to the surface when the liquid does freeze.

4 The method may, in one example, be used to sort diamondiferous material from non-diamondiferous material, diamond having a higher coefficient of thermal conductivity than the gangue material with which it is normally associated. In this case, the separation of the particles into fractions may take place after a time period sufficient for the diamond particles to melt the frozen liquid and be released from the surface.

The invention also provides apparatus for use in the method, the apparatus comprising a surface which can be maintained at a temperature at or below the freezing point of a liquid S with which particles to be sorted have previously been wetted, means for bringing the particles into contact with the surface, and means for separately recovering from the surface, after a specified time period, particles which are S and are not adhered to the surface.

The liquid which is used may be water, in which case the surface, possibly the cylindrical surface of a drum rotating about a horizontal axis, is at a temperature of 0°C or less.

BRIEF DESCRIPTION OF THE DRAWING The invention will now be described in more detail, by way of example only, with reference to the accompanying drawing which illustrates the method and apparatus of the invention schematically.

L 5 SPECIFIC DESCRIPTION In the drawing, a drum 10 rotates about a horizontal axis 12 and has a round cylindrical surface 14. The drum is internally cooled such that the surface 14 has a temperature of 0 0 C or less. Particles 16 to be sorted, in this case diamondiferous particles 18 and non-diamondiferous gangue particles 20, are at ambient temperature and are fed by a chute 22 onto the moving surface of the drum. Prior to this, all the particles are wetted with water.

By the term "diamondiferous particles" is meant particles which are either pure diamonds or particles which have a relatively high diamond content, say 50% or more.

o Soon after the particles contact the cold surface 14 of the drum, the water with which they are wetted freezes. The

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freezing of the water results in the particles adhering to the surface 14.

The diamondiferous particles 18, having a higher coefficient of thermal conductivity than the gangue particles 20, are able to lose more heat more quickly to the ice which adheres them to the surface 14. Thus the ice adhering the diamondiferous particles melts more quickly than the ice adhering the non-diamondiferous particles. This in turn means that the diamondiferous particles are released from the surface of the drum more quickly than the gangue particles and are the first to fall off the drum under S* gravity. The particles which are the first to fall off the drum collect in a bin 24 while particles which fall off subsequently collect in a bin 26. A splitter plate 28 ensures efficient separation of the particles into the relevant fractions.

1 6 In this embodiment, the non-diamondiferous particles, which adhere to the surface 14 for the longer period of time, fall off under gravity. It may in some cases be preferable to physically remove the adhering particles, for example with a hot air blast or with a scraper or the like.

It will be appreciated that the method described above is time and temperature dependent. In the specific example given above, these parameters are set such that the diamondiferous particles are not stuck to the surface of the drum at the end of a specified time period, while non-diamondiferous particles are. In other examples of the invention, different parameters may be used. For instance, the parameters may be such that diamondiferous particles Slose heat so rapidly that they prevent any freezing of the *@9 liquid by the time separation of the particles is to take place while non-diamondiferous particles do not lose sufficient heat in this period of time to prevent freezing of the liquid.

O**0 ~A further possibility would be that the diamondiferous particles lose heat to melt the liquid and then retain insufficient heat to prevent refreezing of the liquid, with S* the result that these particles are adhered to the surface at a specified time. The non-diamondiferous particles, on the other hand, lose heat to melt the liquid, but still S retain sufficient heat to prevent refreezing of the liquid.

The invention is not confined to sorting diamondiferous from non-diamondiferous particles. Particles having different thermal conductivities may be sorted into a number of fractions on the basis of their different thermal conductivities, using the method and apparatus of the invention.

Claims

2. A method according to claim 1 wherein the temperature of the surface and the time period are set such that particles with a higher thermal conductivity are not adhered to the surface o at the end of the time period while particles with a lower *thermal conductivity are adhered to the surface at the end of the time period.
3. A method according to claim 1 wherein the temperature of the surface and the time period are set such that particles with "a low thermal conductivity are adhered to the surface at the end of the time period while particles with a lower thermal conductivity are not adhered to the surface at the end of the time period.
4. g A method according to any one of the preceding claims when used to sort particulate material into diamondiferous and non-diamondiferous fractions. i 8 A method according to any one of the preceding claims wherein adhering particles are rscovered from the surface by means of a hot air blast or by means of a scraper.
6. Apparatus for sorting particles having different thermal conductivities into fractions, the apparatus comprising a surface, means for maintaining the surface at a temperature at or below the freezing point of a liquid with which particles to be sorted have previously been wetted, means for bringing the wetted particles to be sorted into contact with the surface, and means for separately recovering from the surface, after a specified time period, particles which are and are not adhered to the surface.
7. Apparatus according to claim 6 in which the liquid is water and wherein the temperature maintenance means operate to maintain the surface at a temperature of 0° or less.
8. cfl^ G a r Cf da Apparatus according to zithcr on-cf olaim 7 wherein the surface is the cylindrical surface of a drum rotatable about a horizontal axis.
9. Apparatus according to claim 8 wherein the drum is internally cooled. 6 or- c/atA Apparatus according to eithezr e if .lai:mo 9 and comprising a chute for feeding wetted particles to be sorted onto the cylindrical surface of the drum. 4r, l-_-ilXI -q I1IC 9
11. Apparatus according to claim 10 and comprising first and second bins located beneath the drum for collecting particles which are not adhered to the surface of the drum at the end of the time period and which fall off the surface of the drum, and for collecting particles which are adhered to the surface of the drum at the end of the time period and which are subsequently caused or allowed to fall off the surface of the drum.
12. Apparatus according to any one of claims 6 to 12 when used to sort diamondiferous and non-diamondiferous particles into fractions.
13. A sorting method substantially as herein described with reference to the accompanying drawing.
14. Sorting apparatus substantially as herein described with reference to the accompanying drawing. 6 oo/]r v F The st0.eps, -features, compositions and eempoundas disclosed herein or referred to or indicat e specification and/or clai is application, individua collectively, and any and all combinations oef-a-ny--two or mere of said steps or featuros. 00* 0 0 DATED this TWENTY-SECOND day of MARCH 1990 De Beers Industrial Diamond Division (Proprietary) Limited by DAVIES COLLISON Patent Attorneys for the applicant(s) S @5 *5 S 0@ S 0 S S. S. 5* 5 5* 5S