GB2184043A

GB2184043A - Separation of particles having different heat capacities and coefficients of thermal conductivity

Info

Publication number: GB2184043A
Application number: GB08629582A
Authority: GB
Inventors: Charlie Maurice Levitt
Original assignee: De Beers Industrial Diamond Division Pty Ltd
Current assignee: De Beers Industrial Diamond Division Pty Ltd
Priority date: 1985-12-11
Filing date: 1986-12-10
Publication date: 1987-06-17
Also published as: GB2184043B; AU6640086A; GB8629582D0; AU581355B2

Abstract

The particles are deposited on a moving body made of a material which is capable of melting under the influence of the particles with the result that some of them melt through the body more quickly than others so that the particles can be collected at different spaced locations beneath the moving body. The moving body may be a sheet of ice (26) formed, and moved from, between a pair of cooled endless belts (10, 12) or formed on a moving stream of water. The particles may be heated (32) before deposition on the moving body. <IMAGE>

Description

SPECIFICATION Separation method and apparatus BACKGROUND TO THE INVENTION THIS invention relates to a separation method, and more particularly to a method for separating a particulate mass into fractions.

A wide range of separation methods are known and used for separating the valuable components of a particulate mineral from the gangue. Each method is tailored to meet the specific requirements of the mineral being treated and the valuable component being sought.

In the case of the separation of diamonds from diamond-bearing particulate materials, the use of a vibrating grease belt is one of the most widely used methods. In this method the diamond-bearing particulate mass is fed in a stream of water on to the vibrating table to which a coat of a sticky substance has been applied. The hydrophobic diamond particles are captured by the sticky coat while the hydrophyllic gangue material is carried away by a stream of water to waste. The diamond particles which have been captured by the sticky substance may then be collected. One of the disadvantages of a grease table is that loss of diamond does occur in the wate stream which carries away the gangue.

SUMMARY OF THE INVENTION One aspect of the invention provides a method of separating a particulate mass conr taining particles which have different heat capacities and coefficients of thermal conductivity in fractions which are distinguished from one another by these characteristics, the method including the steps of providing a moving body made of a material capable of melting in the region of and under the influence of particles of the mass deposited thereon, depositing particles of the mass on the body, allowing the particles to melt through the body and collecting the particles in fractions.

It may be necessary to heat up the particles of the mass before they are deposited on the moving body.

In a preferred version of the invention, the body is a body of ice. The body of ice can be formed and moved by introducing water into a space between two moving belts and cooling the belts, typically by liquid nitrogen sprays.

Alternatively, water may be pumped through a flume with a container of liquid nitrogen arranged at the surface of the water to form a sheet of ice which will then move with the water and be supported by it. In this case, the flume may include an overflow weir at its outlet end over which the sheet of ice will move and be broken up. The melted ice is then recirculated to the inlet end of the flume for re-use.

Another aspect of the invention provides an apparatus for separating a particulate mass containing particles which have different heat capacities and coefficients of thermal conductivity into fractions which are distinguished from one another by these characteristics, the apparatus including means for providing a moving body made of a material capable of melting in the region of and under the influence of particles of the mass deposited thereon, means for depositing the particles of the mass on the moving body so that the particles melt through the body at rates dependent on their coefficients of thermal conductivity, and spaced receptacles for receiving the particles which have melted through the moving body.

Spaced receptacles, for example in the form of bins, removable trays, recessed troughs or hoppers will be provided beneath the moving body to receive particles of the mass which have melted through the moving body.

BRIEF DESCRIPTION OF THE DRA WINGS Figure 1 shows a schematic view of a first apparatus according to the invention; Figure 2.shows a corresponding view of a second embodiment; and Figures 3 and 4 illustrate possible modifications to the Figure 2 apparatus.

DESCRIPTION OF PREFERRED EMBODIMENTS The material will preferably be water thus making the moving body a body of ice. The body will typically be provided in a sheet form with the particulate mass being deposited on one surface thereof.

The temperature of the particulate mass will depend on the melting point temperature of the material from which the moving body is made. In the case of ice, the particulate mass may be at room temperature, but is preferably at a temperature somewhat higher than room temperature.

The invention has particular application to the separation of diamonds from gangue.

One embodiment of the invention will now be described with reference to Figure 1 of the drawings. Referring to this Figure, the apparatus includes a pair of belts 10 and 12 which pass over rollers 14, 16 respectively. Between the belts is provided a space 18 into which water 20 is sprayed through nozzle 22. The water is carried along by the belt 12 and freezes under the influence of liquid nitrogen which is blown on to the belts through nozzles 24. A sheet of ice 26 emerges from the space 18 between the belts.

A particulate mass containing particles of different heat capacities and coefficients of thermal conductivity is passed down a surface 30 and in so doing is heated by means of a heater 32. The particles drop off the surface 30 and on to the sheet of ice 26. The hot particles gradually melt the ice and eventually pass through it. The particles with the highest coefficients of thermal conductivity will be the hottest and so melt the ice and pass through it sooner than the other particles. Thus, these particles will be collected in bin 34 while the other particles, which take longer to pass through the sheet of ice, will be collected in bin 36.

The apparatus of Figure 2 includes an elongate flume 100 of rectangular cross-section.

The flume has an inlet end 102 and an outlet end 104 where there is a weir 106 leading to a vessel 108. A suction pipe 110 leads from the bottom of the vessel 108 to a centrifugal pump 112 which is arranged to pump continuously through a delivery pipe 114 via a control valve 116 and into the inlet end of the flume again.

A pair of perforated baffle plates 118 extend across the flume to promote laminar flow in the water 120 which is pumped through the flume by the pump 112. Just downstream of the baffles is a bath 122 containing liquid nitrogen 124, the underside of the bath being just above the surface of the water 120.

An inclined plate 126 is provided which provides a sloping surface corresponding to the surface 30 of the previous embodiment. A radiant heater 128 heats particles which are placed on the sloping surface before they fall off.

In use, the pump 112 pumps the water around the circuit at a sufficiently slow speed for proper laminar flow to take place in the flume. The surface of the water has a sufficiently long residence time adjacent the bath 122 for a sheet 127 of ice to be formed on the surface of the water, this sheet then being carried downstream along with the water and being supported by the water. In practice, the water will be prechilled to a temperature just above freezing before use of the apparatus.

The heated particles fall off the end of the surface provided by the sloping plate 126 and onto the sheet of ice. As in the previous case, the particles melt through the sheet of ice at rates dependent on their heat capacity and coefficient of thermal conductivity. The hotter particles melt through first and, in the embodiment illustrated in Figure 2, are collected in a shallow tray 130. The cooler particles are collected downstream in a shallow tray 132. Both trays can be removed from the flume when full.

It will be noted that the trays have no upstream lip, the reason being that it is desirable to prevent undue turbulence in the water and possible premature breaking up of the sheet of ice at the water surface.

The water and ice proceed downstream to the weir 106 over which the ice passes. As it passes over the weir into the vessel 108, the ice breaks up and the resulting, melted ice is recirculated by the pump.

Figure 3 illustrates a slight modification of the Figure 2 apparatus. In this case, recessed troughs 140 and 142 are provided to collect the two fractions. This arrangement has the advantage over the tray arrangement of Figure 2 that there will be less turbulence in the water, but has the disadvantage that the troughs cannot be moved about.

In Figure 4, the fraction-receiving receptacles are provided by sunken hoppers 144 and 146 which are served by valves 148 and 150 which can be opened to release their contents under gravity.

It will be noted that there is only a single moving part in the apparatus of Figures 2, 3 and 4, this being the pump.

Claims

1. A method of separating a particulate mass containing particles which have different heat capacities and coefficients of thermal conductivity in fractions which are distinguished from one another by these characteristics, the method including the steps of providing a moving body made of a material capable of melting in the region of and under the influence of particles of the mass deposited thereon, depositing particles of the mass on the body, allowing the particles to melt through the body and collecting the particles in fractions.

2. A method according to claim 1 including the step of heating up the particles of the mass before depositing them on the moving body.

3. A method according to either one of the preceding claims including the step of providing a moving body of ice.

4. A method according to claim 3 including the steps of providing spaced, operatively upper and lower belts, moving the belts in the same direction, introducing water into the space between the belts and cooling the belts so as to freeze the water to form a sheet of ice which is moved by the belts.

5. A method according to claim 4 including the step of cooling the belts by spraying liquid nitrogen onto the belts.

6. A method according to either one of claims 1 or 2 including the step of supporting the moving body on a moving stream of liquid.

7. A method according to claim 6 including the step of forming a sheet of ice on a moving stream of water.

8. A method according to claim 7 including the steps of pumping the water in laminar flow through an elongate flume and cooling the surface of the water to form a sheet of ice on top of the water.

9. A method according to claim 8 including the step of providing an overflow weir at the outlet end of the flume, permitting the sheet of ice to break up on moving over the weir, permitting the ice to melt and returning the melted ice and overflowing water to the inlet end of the flume for re-freezing of its upper surface.

10. A method according to any one of the preceding claims and including the steps of providing two receptacles each for receiving a fraction of the mass, spacing the receptacles apart in the direction of movement of the body and positioning the receptacles for the upstream receptacles to receive particles which have a higher coefficient of thermal conductivity than particles which are received by the downstream receptacle.

11. A method according to any one of the preceding claims for separating a diamondiferous mass of particles into a diamond fraction and a gangue fraction.

12. An apparatus for separating a particulate mass containing particles which have different heat capacities and coefficients of thermal conductivity into fractions which are distinguished from one another by these characteristics, the apparatus including means for providing a moving body made of a material capable of melting in the region of and under the influence of particles of the mass deposited thereon, means for depositing the particles of the mass on the moving body so that the particles melt through the body at rates dependent on their coefficients of thermal conductivity, and spaced receptacles for receiving the particles which have melted through the moving body.

13. An apparatus according to claim 12 and including means for heating up the particles of the mass before they are deposited on the moving body.

14. An apparatus according to claim 12 or claim 13 and including means for forming a moving body of ice.

15. An apparatus according to claim 14 and including spaced, operatively upper and lower belts, means for moving the belts in the same direction, a nozzle for introducing water into the space between the belts, and means for cooling the belts to freeze the water between the belts and form a sheet of ice which is moved by the belts.

16. An apparatus according to claim 1 5 and including a series of spray nozzles arranged to spray liquid nitrogen onto the belts to cool them.

17. An apparatus according to claim 14 and including an elongate flume, a pump for causing water to flow through the flume, in laminar flow, from an inlet end thereof to an outlet end thereof and means for forming a sheet of ice on the surface of the water.

18. An apparatus according to claim 17 and including a container for accommodating liquid nitrogen, the container being positioned adjacent the surface of the water flowing in the flume so that its contents freeze the surface of the water.

19. An apparatus according to either one of claims 17 or 18 and including an overflow weir at the outlet end of the flume over which the sheet of ice moves as it leaves the flume and which causes the sheet of ice to break up, the pump being arranged to return the melted ice to the inlet end of the flume.

20. An apparatus according to any one of claims 1 7 to 19 and including one or more perforated baffles in the flume to promote laminar flow of the water.

21. An apparatus according to any one of claims 17 to 19 wherein the receptacles are located at the base of the flume.

22. An apparatus according to claim 21 wherein the receptacles are in the form of removable trays.

23. An apparatus according to claim 21 wherein the receptacles are in the form of recessed troughs or hoppers at the base of the flume.

24. An apparatus according to any one of claims 12 to 23 and including an inclined surface along which the particles of the mass are moved for deposition on the moving body.

25. An apparatus according to any one of claims 12 to 24 when used for separating a mass of particulate, diamondiferous material into a diamond fraction and a gangue fraction.

26. An apparatus substantially as herein described with reference to Figure 1 or Figures 2,3 and 4 of the accompanying drawings.

27. A method substantially as herein described with reference to Figure 1 or Figures 2,3 and 4 of the accompanying drawings.