GB2024184A

GB2024184A - Heavy liquids

Info

Publication number: GB2024184A
Application number: GB7917131A
Authority: GB
Original assignee: De Beers Industrial Diamond Division Pty Ltd
Current assignee: De Beers Industrial Diamond Division Pty Ltd
Priority date: 1978-07-03
Filing date: 1979-05-16
Publication date: 1980-01-09
Also published as: IL57316A0; DE2920859C2; AU4699479A; AU522181B2; GB2024184B; ZA783808B; DE2920859A1; BR7904165A

Abstract

A heavy liquid for densimetric separations, particularly the densimetric separations of diamond from gangue, comprises a suspension of finely divided metal carbide powder in a liquid base which is compatible with the carbide and which has a density of greater than 1,5. The metal carbide is preferably tungsten carbide and the liquid base is preferably tetrabromoethane, bromoform or di- iodomethane.

Description

SPECIFICATION Heavy liquids This invention relates to heavy liquids for use in densimetric separations.

For the separation of diamond from concentrates, two liquids are required, one of density 3,60 and another of density 3,45, diamond having a density of 3,52 + 0,02. This narrow density range excludes most heavy minerals in diamond concentrates. The three most common liquids at present used in this regard all suffer practical disadvantages. The first and the most common is a suspension of ferrosilicon in water. Its main disadvantage is its instability which makes it unsuitable for static bath use. The second is lead sulphamate.

This liquid is useable only above 60"C, to which temperature diamond-bearing gravel must be heated before being treated to obviate solidification of the liquid on the cooler gravel. Its preparation is also tedious. The third is Clerici solution, which is commercially available with densities variable up to 4,2. The main drawback of Clerici solutions is cost. Moreover, being thallium compounds, they are dangerous cumulative poisons.

They require special disposal, recovery and handling precautions.

There are other liquids, but these are all very costly and require very specialised manufacturing and handling techniques.

It is an object of the present invention to provide a novel heavy liquid for densimetric separations, particularly densimetric separations of diamond concentrates.

According to the invention, there is provided a heavy liquid for densimetric separations comprising a suspension of finely divided metal carbide powder in a liquid base compatible with the carbide and having a density of greater than 1.5. The liquid base must be compatible with the carbide in the sense that it must not react with the carbide.

The density of the liquid base is preferably in the range 2,80 to 4,00 and more preferably in the range 2,85 to 3,50. Particularly suitable liquid bases are tetrabromoethane, bromoform and di-iodomethane.

The heavy liquid of the invention can be made to any specified pulp density according to the following equation: x = pp- pr p, Ps-P1 pp x = Weight fraction of solids in pulp.

pp = Pulp density (gum~3) p1 = Liquid density (gum~3) ps = Solid density (gum~3) By use of this equation it is possible to determine the amount of powder required for a particular pulp density.

The metal carbide powders have a relatively high density so it is possible to produce appropriate pulp densities without producing an unacceptably high viscosity. Tungsten carbide powder is the preferred powder. Tungsten carbide powder is preferred over other carbides such as tantalum carbide, niobium carbide and vanadium carbide because of its relatively high density (15,7) and its availability.

The powder as mentioned above is finely divided, i.e. it is of micron size. The average particle size of the metal carbide powder will generally be less than 5 microns, preferably less than 2 microns.

The heavy liquids of the invention are stable over long periods of time and can therefore be used in both continuous and static bath processes. Furthermore, they are relatively non-toxic and have low viscosities.

The heavy liquids of the invention may be made by mixing the powder with the liquid base. It is preferable to wet the surface of the powder, for example by mixing the powder with a little acetone, prior to mixing it with the liquid base. Wetting the powder achieves a better distribution ofthe powder in the liquid base and a better suspension. If the powder is mixed directly with the liquid there may be a tendency for some of it to lump and float to the surface as a scum. The amount of powder added can be determined according to the equation given above. By way of illustration the table below indicates the weight fraction of solids of various densities which are required to achieve various pulp densities using tetrabromoethane as liquid base.

Solid p5 Mass fraction values, x density gum~3 Pulp Density pp = 3,0 Pulp Density pp = 4,0 6 0,301 0,513 +6,8 0,273 0,460 7 0,267 0,451 8 0,245 0,413 9 0,230 0,387 10 0,219 0,369 11 0,211 0,356 12 0,205 0,345 13 0,200 0,337 14 0,196 0,330 15 0,192 0,324 *15,7 0,190 0,320 16 0,189 0,319 17 0,187 0,315 18 0,185 0,311 + Density of Ferrosilicon * Density of Tungsten Carbide The invention has particular application to the densimetric separation of diamond particles from gangue.

Prior art methods for such separations have generally been applicable only to particles of size greater than 6 mm. The heavy liquid of this invention can be used for the successful densimetric separation of diamond particles of size greater than or smaller than 6mm. Indeed, the heavy liquid of the invention has application particlarly to particles in the size range 0,6 mm to 6 mm. Such diamonds are of ever increasing commercial importance.

As mentioned above, the heavy liquid may be used in a static bath process or in a continuous process. By way of example only, without in any way limiting the scope and application of the invention, a static bath process suitable for separating diamond particles from gangue using a heavy liquid of the invention will now be described with reference to the accompanying drawing which illustrates diagrammatically in Figures 1 to 4 the four steps in the process.

Referring to the drawing, there is shown a container 10 divided into compartments 12, 14 separated from each other by dividing wall 16. The container has a head volume 18 in which is located a cylinder 20 which is movable across the two compartments. The cylinder may be positioned in register with either compartment.

Outlets 22, 24 are located at the lower ends of the compartments. These outlets are closed by means of suitable valves. The outlets are located above screens 26, 28.

In use, the heavy liquid is poured into the container so that it fills the two compartments, the head volume and the cylinder to a point just below the top of the cylinder. The cylinder is moved to a position in which it is in register with the compartment 12, as illustrated by Figure 1. Particulate diamond-containing gravel is poured on to the liquid surface of in the cylinder. The light fraction 30, i.e. the gangue, floats, while the heavy fraction 32, i.e. the diamond, sinks, as illustrated by Figure 2. After separation of the fractions in the liquid, the cylinder is moved to a position in which it is in register with compartment 14, as illustrated by Figure 3.

The valves are then opened and the liquid in both compartments drained through the screens. The diamonds 32 are collected on the screen 26, while the gangue 30 is collected on the screen 28.

By way of further illustration the following example is provided.

Example 1 kilogram quantity of a heavy liquid of density 3,75 gem~3 was made by first mixing 255 g of tungsten carbide powder of average particle size less than 2 microns with a small amount of acetone to produce a black viscous fluid. This fluid was then added to 745 g of tetrabromoethane and thoroughly mixed. The resulting suspension had the required density and a viscosity of about 15 centipoise. The suspension was found to be stable with no measurable change in density over a period of 30 minutes. The suspension was ideally suitable as a heavy liquid for the densimetric separation of diamond from gangue.

Claims

1. A heavy liquid for densimetric separations comprising a suspension of finely divided metal carbide powder in a liquid base compatible with the carbide and having a density of greater than 1,5.

2. A heavy liquid according to claim 1 wherein the density of the liquid base is in the range 2,80 to 4,00.

3. A heavy liquid according to claim 1 wherein the density of the liquid base is in the range 2,85 to 3,50.

4. A heavy liquid according to any of the preceding claims wherein the metal carbide has an average particle size of less than 5 microns.

5. A heavy liquid according to any one of claims 1 to 3 wherein the metal carbide has an average particle size of less than 2 microns.

6. A heavy liquid according to any one of the preceding claims wherein the metal carbide powder is tungsten carbide powder.

7. A heavy liquid according to any one of the preceding claims wherein the liquid base is tetrabromoethane, bromoform or di-iodomethane.

8. A heavy liquid according to claim 1 substantially as hereinbefore described.

9. A heavy liquid, comprising a suspension of tungsten carbide particles in tetrabromoethane, substantially as hereinbefore described in the Example.

10. A heavy liquid according to any one of the preceding claims for use in the densimetric separation of diamond from gangue.

11. A method for the densimetric separation of diamond particles from gangue employing a heavy liquid in accordance with any one of the preceding claims.

12. A method for the densimetric separation of diamond particles from gangue substantially as herein before described with reference to the accompanying drawings.

13. Apparatus for the densimetric separation of diamond particles from gangue employing heavy liquid in accordance with any one of claims 1 to 10, substantially as hereinbefore described with reference to the accompanying drawings.