WO2004106592A1

WO2004106592A1 - A process for the recovery of synthetic diamonds

Info

Publication number: WO2004106592A1
Application number: PCT/IB2004/001745
Authority: WO
Inventors: Jozef Leopold Stankiewicz
Original assignee: Jozef Leopold Stankiewicz
Priority date: 2003-05-30
Filing date: 2004-05-27
Publication date: 2004-12-09
Also published as: WO2004106592A8

Abstract

Apparatus (1) for the recovery of synthetic diamonts from capsules includes a plurality of enclosures (2), in this embodiment bags, formed from an ion permeable membrane (3) each having a plate-like anode (5) centrally positioned therein. Plate-like cathodes (6) are located on either side of each bag (2) to form a alternating series of cathodes (6) and anodes (5). These are suspended in a container (8) which is partly filled with an electrolyte (9). The capsules (10), each formed from a mixture of graphite and a meal catalyst (5) and containing synthetic diamonds, are loaded into the bags (2) in contact with the anodes (5). The capsules (10) can be whole or in a fragmented form. A DC current is then passed through the anodes (5) and cathodes (6). The electrolyte (9) is selected to have a pH range suitable for the deposition of (10) the metal catalyst on to the cathodes (6) and is usually made up of one or more of hydrochloric acid, sulphuric acid, nitric acid and hydrofluoric acid. Passing an electrical current through the electrodes causes dissolution of the metal catalyst and migration of the metal ions through the ion permeable membrane (3) to the cathodes (6) where they deposit as a metal. On completion of the process, graphite and diamonds are left in the bags (2). This mixture is removed from the bags (2) and the diamonds separated out.

Description

A PROCESS FOR THE RECOVERY OF SYNTHETIC DIAMONDS

FIELD OF THE INVENTION

This invention relates to a process for the recovery of synthetic diamonds.

BACKGROUND TO THE INVENTION

Synthetic diamonds are typically formed by creating a capsule from a mixture of graphite and a catalyst, often a metal such as nickel, and then subjecting the capsule to high pressure and high temperature. This causes diamond crystals to nucleate at many sites in the capsule. The capsule is then cooled and the diamonds separated from the rest of the mixture. This is typically achieved by crushing the capsule and dissolving the metals using strong acids to leave the diamonds and graphite. The diamonds are then separated from the graphite.

Although fairly effective, this process does suffer a number of disadvantages. These include the generation of an acid effluent which requires further

COWFIRftr ION copy processing prior to disposal and which is environmentally unacceptable in an unprocessed state, and the use of large quantities of chemicals.

OBJECT OF THE INVENTION

It is an object of this invention to provide a process for the recovery of synthetic diamonds which will at least partially alleviate some of the abovementioned problems.

SUMMARY OF THE INVENTION

In accordance with this invention there is provided a process for the recovery of synthetic diamonds from a graphite and metal capsule which includes oxidising the metal and graphite of the capsule to expose diamonds contained therein.

Further features of the invention provide for the oxidising agent to include a halogen, preferably chlorine; and for oxidation to occur by electrolysis.

Further features of the invention provide for electrolysis to occur in an acidic electrolyte, preferably hydrochloric acid; for each anode to be surrounded by an ion permeable, preferably semi-anionic, membrane; and for electricity to be passed directly through the capsules into the electrolyte.

Still further features of the invention provide for the metal to be recovered by electroplating; for the electrolyte to be circulated to a further cell for electroplating to occur; and for the further cell to include capsules or to contain no capsules.

Further features of the invention provide for the capsule to be placed in an enclosure; for the enclosure to be at least partly formed from an ion permeable membrane; for an anode to be located within the enclosure; for a cathode to be located outside the enclosure; and for the electrical current to cause deposition of the metal on the cathode.

Yet further features of the invention provide for the electrolyte to be selected to suit the deposition of the metal on the cathode; and for the electrolyte to be an acid, preferably one or more of hydrochloric acid, sulphuric acid, nitric acid and hydrofluoric acid.

Still further features of the invention provide for the electrical current to be direct current (DC); for there to be a plurality of alternating anodes and cathodes; for an enclosure formed from an ion permeable membrane to separate each anode from the cathodes; and for each enclosure to be in the form a bag.

Further features of the invention provide for the diamonds and a portion of the graphite to be removed from the enclosure after deposition of the metal on the cathode; and for the diamonds and graphite to be separated.

BRIEF DESCRIPTION OF THE DRAWINGS

One embodiment of the invention will be described, by way of example only, with reference to Figure 1 which is a schematic illustration of a process for the recovery of synthetic diamonds.

DETAILED DESCRIPTION OF THE DRAWINGS

Apparatus (1) for the recovery of synthetic diamonds from capsules is shown in Figure 1 , and includes a plurality of enclosures (2), in this embodiment bags, formed from an ion permeable membrane (3) each having a plate-like anode (5) centrally positioned therein. Plate-like cathodes (6) are located on either side of each bag (2) to form an alternating series of cathodes (6) and anodes (5). These are suspended in a container (8) which is partly filled with an electrolyte (9).

The capsules (10), each formed from a mixture of graphite and a metal catalyst and containing synthetic diamonds, are loaded into the bags (2) in contact with the anodes (5). The capsules (10) can be whole or in a fragmented form. A DC current is then passed through the anodes (5) and cathodes (6).

The electrolyte (9) is selected to have a pH range suitable for the deposition of the metal catalyst onto the cathodes (6) and is usually made up of one or more of hydrochloric acid, sulphuric acid, nitric acid and hydrofluoric acid.

Passing an electrical current through the electrodes causes dissolution of the metal catalyst and migration of the metal ions through the ion permeable membrane (3) to the cathodes (6) where they deposit as a metal.

On completion of the process, graphite and diamonds are left in the bags (2). This mixture is removed from the bags (2) and the diamonds separated out. There may be a small amount of metal left in the capsule which can be removed with an acidic mixture of, for example, nitric and sulphuric acid. The metal catalyst deposited on the cathodes (6) can be sold.

The mechanics of the process to which capsules are subject can in general terms be described as follows.

When the capsules are submerged in the electrolyte, for present purposes hydrochloric acid, and have an electric current passed through them, both the metal and the graphite of the capsules becomes oxidised. The metal dissolves in the acid and migrates through the semi-anionic membrane to the cathodes. It can either be plated out at the cathodes or the solution circulated to a further cell or cell bank for electroplating. Circulation to a further cell has the advantage that electroplating conditions can be more closely controlled and optimised and the further cell can either have no capsules in it or can also have capsules.

Where electroplating occurs in a further cell the solution is circulated back to the original cell to maintain a stable supply of electrolyte.

Importantly, the chlorine formed by electrolysis of the hydrochloric acid reacts with the graphite of the capsules to make them more porous to further expose the capsule for more metal to dissolve into the electrolyte. This reaction takes place as the capsules act as electrodes and have electricity passing directly through them by virtue of being in direct contact with the anodes.

As the graphite becomes oxidised and so consumed, the capsules become increasingly porous and further exposed to reaction.

The chlorine involved in the reaction is not consumed and is available for further reaction. This makes the process highly cost effective as a minimal input of reagents is required whilst metal is recovered and the graphite effectively transformed into a harmless gas. Chlorine gas production can occur where most of the metal has been dissolved but can be controlled by adjusting the potential and current strength.

Importantly, the capsules themselves, preferably uncrushed, can be used as the electrode by, for example, stacking them in the container and putting them under pressure via a conductive material. This would obviate the need for an electrode with which they are to be kept in contact. Alternatively, crushed capsules can be applied to a magnetised sheet which is in contact with the anode.

The process is highly efficient and has the advantage that no effluent is generated, that minimal quantities of chemicals are used, that minimal labour is required and in that the capsules do not have to be crushed. The process is also much more cost-effective than existing processes and has the further advantage that the metal catalyst is recovered and can be sold at a relatively high price because it is in the form of a metal, which can be a combination of metals depending on the catalysts used in the capsule, for example, nickel and iron.

It will be appreciated that the parameters of the process will largely depend on the catalyst used in the capsules, especially as regards the electrolyte. Also, any suitable apparatus configuration can be used. It may for example be unnecessary to use an ion permeable membrane in the process. Where ion permeable membranes are used these can be semi-anionic. Additionally, or alternatively, the capsules could be placed in a bag, such as a polypropylene bag, directly in the electrolyte or in an ion permeable membrane. The use of polypropylene bags would serve at least to make handling of the end product easy. Furthermore, the speed of the process can be modified by changing various parameters, for example, by maximising the surface area of the anode in contact with crushed capsule and for the crushed capsule to be of a fairly uniform size so that the reaction will be completed at all the anodes at the same time.

It will be appreciated by those skilled in the art that other methods exist of oxidising the graphite and metal which fall within the scope of the invention, particularly as far as apparatus configuration and process parameters are concerned. For example, it is possible to use an alternating current (AC) instead of DC. In this case it is unnecessary to use a membrane to control the pH as with DC. An AC potential of up to 24V is applied between the electrodes as described above with capsules in contact with the electrodes. Hydrogen is released as a gas and anions are formed in the vicinity of the capsules resulting in the dissolution of the metals and partial destruction of the graphite. Fresh electrolyte can be added until the solution becomes saturated at which time it can be removed and the metals crystallized out. Alternately, the saturated electrolyte can be transferred to a further bath where the metals can be electrolytically recovered using DC with or without a membrane about the anodes. However, solvent extraction, precipitation or any other suitable method could also be used to recover the metals from solution whether AC or DC is used.

Claims

1. A process for the recovery of synthetic diamonds from a graphite and metal capsule which includes oxidising the metal and graphite of the capsule to expose the diamonds contained therein.

2. A process as claimed in claim 1 in which the oxidising agent includes a halogen.

3. A process as claimed in claim 2 in which the oxidising agent is chlorine.

4. A process as claimed in any one of the preceding claims in which oxidation occurs by electrolysis.

5. A process as claimed in claim 4 in which electrolysis occurs in an acidic electrolyte.

6. A process as claimed in claim 5 in which the electrolyte is hydrochloric acid.

7. A process as claimed in any one of claims 4 to 6 in which each anode is surrounded by an ion permeable membrane.

8. A process as claimed in claim 7 in which each membrane is semi- anionic.

9. A process as claimed in any one claims 4 to 8 in which electricity is passed directly through the capsules into the electrolyte.

10. A process as claimed in any one claims 4 to 9 in which the metal is recovered by electroplating.

11. A process as claimed in claim 10 in which the electrolyte is circulated to a further cell for electroplating.

12. A process as claimed in claim 11 in which the further cell has capsules therein.

13. A process for the recovery of synthetic diamonds from a graphite and metal capsule which includes placing the capsule in an electrolyte in contact with at least one of a number of electrodes inserted therein and passing an electrical current between the electrodes to cause the metal to be deposited thereon.

14. A process as claimed in claim 13 in which the capsule is placed in an enclosure.

15. A process as claimed in claim 14 in which the enclosure is at least partly formed from an ion permeable membrane.

16. A process as claimed in claim 14 or claim 15 in which an anode is located within the enclosure.

17. A process as claimed in claim 16 in which a cathode is located outside the enclosure.

18. A process as claimed in claim 17 in which the electrical current causes deposition of the metal on the cathode.

19. A process as claimed in any one of claims 13 to 18 in which the electrolyte is an acid.

20. A process as claimed in claim 19 in which the acid is selected from one or more of hydrochloric acid, sulphuric acid, nitric acid and hydrofluoric acid.

21. A process as claimed in any one of claims 13 to 20 in which the electrical current is DC.

22. A process as claimed in any one of claims 13 to 21 in which a plurality of alternating anodes and cathodes are inserted into the electrolyte.

23. A process as claimed in claim 22 in which an enclosure formed from an ion permeable membrane separates each anode from the cathodes.

24. A process as claimed in claim 23 in which each enclosure is a bag.

25. A process as claimed in claim 23 or claim 24 in which the diamonds and a portion of the graphite are removed from each enclosure after deposition of the metal on the cathodes.

26. A process as claimed in claim 25 in which the diamonds and graphite are separated after removal from the enclosures.

27. A process as claimed in any one of claims 14 to 28 in which the or each capsule is in either of a whole or fragmented form.

28. A process for the recovery of synthetic diamonds from a graphite and metal capsule substantially as herein described and as illustrated with reference to Figure 1.