BACKGROUNDART It is well known that diamonds are mined from the sea bed in certain parts of the world such as the South African and Namibian west coasts. These diamonds may be trapped in sea shells and further processing of the shells are required to prevent such entrapped diamonds from being treated as waste together with the shells.

Up to now, these shells are processed through a preparation plant and in some cases are mechanically disintegrated or crushed whereafter the material is sieved to separate the resulting waste in the form of disintegrated shells from the diamonds. A problem with this process is that the diamonds are damaged or destroyed during the necessary communition step, to liberate the diamonds.

OBJECT OF THE INVENTION Accordingly, it is an object of the present invention to provide an alternative method and system for disintegrating diamond bearing material to recover the diamonds therefrom and with which the applicant believes the aforementioned disadvantages may at least be alleviated.

SUMMARY OF THE INVENTION According to the invention there is provided a method of recovering diamonds from diamond bearing material, the method comprising the steps of: - subjecting the material to a contactless disintegration stage; and - causing the material to be disintegrated into particles smaller than the diamonds, thereby facilitating separation of the particles and the diamonds.

The method may also include a further step of separating the particles and the diamonds. The separating step may be performed by a screening or size classification step.

In some embodiments the material may be kimberlite ore and in other embodiments it may be sea shells.

The material may be subjected to at least one pressure pulse, to disintegrate the material.

The at least one pressure pulse may be a shockwave or burst of ultra- sound and may be generated by applying high voltage signals between electrodes in an energy converter.

The method may also include the step of repeatedly subjecting the material to pressure pulses, thereby to disintegrate the material while the diamonds remain intact.

According to another aspect of the present invention there is provided a system for recovering diamonds from diamond bearing material, the system comprising: means for generating pressure pulses ; means for subjecting the diamond bearing material to the pulses to disintegrate the material into particles, while leaving the diamonds intact; and means for separating the particles and the diamonds.

The means for generating pressure pulses may comprise an electricity to pressure pulse converter.

The pressure pulses may comprise be high voltage generated shockwaves.

The system may comprise a train of converters and means for feeding batches of the material in sequential manner past the converters.

Each converter may comprise an electrode arrangement which may be submerged in a body of water in a suitable vessel.

BRIEF DESCRIPTION OF THE ACCOMPANYING DIAGRAMS The invention will now further be described, by way of example only, with reference to the accompanying diagrams wherein: figure 1 is a schematic representation of a first embodiment of a diamond recovery plant ; figure 2 is a diagrammatic representation of a contactless disintegration stage according to the invention and forming part of the diamond recovery plant ; and figure 3 is a schematic representation of a second embodiment of the plant according to the invention.

DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION A first embodiment of a marine diamond recovery system is generally

designated by the reference numeral 10 in figure 1.

The system comprises a first screening stage 12 where mined alluvium 14 comprising sea shells, some of which may entrap diamonds, is received. Particles bigger than a first size S, (S1 = 19mm say) are separated from smaller particles and the bigger particles 16 are fed to waste.

The particles 18 equal to and smaller than the first size is fed to a second screening stage 20. Here particles smaller than a second size S2 (S2 = 2mm say) are separated from a product 24 which has a particle size p wherein: S2 < p < S1' In a conventional marine diamond recovery system, the aforementioned product 24 would have been fed to a mechanical disintegration or crushing stage (not shown) or directly to a FeSi addition stage, thereafter to a dense media separation stage and then to a final recovery stage, as will hereinafter be described. These conventional systems have the disadvantages referred to in the introduction of this specification.

The system 10 according to the invention comprises a contactless disintegration stage 26 for the product 24. The contactless disintegration 26 stage is shown in more detail in figure 2.

The stage 26 comprises an endless conveyor 28 carrying a plurality of equi-spaced containers 30.1 to 30. n for batches of the product 24. As stated hereinbefore, the product 24 comprises shells having a particle size p wherein S1 # p # S2 and some of which may entrap marine diamonds.

The conveyor is mounted about rollers 32.1,32.2 and 32.3 and has a top run 28.1 and a return run 28.2. Just below the top run 28.1 there are provided a plurality of spaced electric to pressure pulse energy converters 34.1 to 34.4. The spacing between adjacent converters is equal to the spacing between adjacent containers 30.1 to 30. n.

Each converter comprises a steel vessel 36 and an electrode arrangement 38 extending into a body of water 40 in the vessel. A top end of the vessel is closed by a membrane 42. The electrode arrangements are energized by respective capacitors (not shown) in a capacitor bank 31. When energized, an arc is formed between the

electrodes of an arrangement. This generates a pressure pulse 33 propagating through the water towards the membrane 42 and the aforementioned containers holding the product 24. The pressure pulse may be in the form of a shockwave or burst of ultra-sound. The converters may be of the kind described in a pamphlet of a company TZN of Unterluss, Germany and entitled"High Performance Pulsed Power Technology (HP3T)-Contactless disintegration of compound materials." The top ends of containers 30.2 to 30.5 are closed off by a lid arrangement 35.

In use, the conveyor moves in a clockwise direction. As the containers 30.1 to 30. n move past charging point A, batches of product 24 are charged into the containers.

When a container 30.2 is located opposite converter 34.1, the electrode arrangement of that converter is energized. The resulting pulse 33 causes the shells at least partially to disintegrate. The conveyor then moves on, so that container 30.1 is opposite converter 34. 1, container 30. 2 is opposite converter 34.2 and container 30. n is opposite changing point A. The electrode arrangements of converters

34.1 and 34.2 are then energized either simultaneously or sequentially, to further disintegrate the shells. This procedure is repeated until each batch of the product 24 has been subjected to a desired number of pulses. The number of pulses will depend on the diamond bearing material. For sea shells, it is presently believed that four to five pulses or stages should suffice.

As shown in the container 30.6, with the apparatus 26 hereinbefore described and the method, the shells are disintegrated to particles 47 having a size of less than 1mm or even 0.5mm, depending on the parameters of the pulse such as frequency, repetition rate, energy, pulse shape etc. The diamonds 45 remain intact and are released by the disintegrated shells.

Referring again to figure 1, the product 44 of the disintegration stage 26 is fed to a third screening stage 46. Here particles smaller than a third size S3 (S3 = 2mm say) are separated from larger particles. The smaller particles 48 are fed to waste.

The larger particles 50 are fed to the aforementioned and known FeSi addition stage 52. Thereafter a dense media separation stage 54 is used to separate particles that float and particles that sink. The

floating particles 56 are fed to waste and the particles 58 that sank are fed to an X-ray sorter and final recovery stage 60. Between stages 54 and 60, the FeSi is recovered for recycling. It is believed that the system and method according to the invention would use less FeSi than the known systems and methods.

In stage 60 the diamonds 45 are separated from waste 64 in known manner.

In the second embodiment of the plant shown at 100 in figure 3, the contactless disintegration stage 26 is provided downstream of the FeSi stage 52 and the dense media separation stage 54. A return path for recovered FeSi is shown at 102 in figure 3.

It will be appreciated that there are many variations in detail on the system and method according to the invention without departing from the scope and spirit of the appended claims.