EP0484611B1 - Ultrasonic industrial sorting of diamonds - Google Patents

Description

The present invention relates to a method for sorting diamonds from a mixture containing inter alia diamonds to be recovered, in which said mixture is brought to a detection system, one or more diamonds to be recovered are detected by said system and the control is carried out. a device for separating the diamond or diamonds to be recovered from the mixture when one or more diamonds to be recovered has been detected.

• séchage coûteux du minerai ;
• coût important des systèmes à rayons X ;
• faible discernabilité due à la fluorescence d'autres pierres telles que le zircon ;
• rejet de diamants non fluorescents ou de diamants d'une granulométrie inférieure à trois millimètres.

Until now, diamond detection has been done by X-ray fluorescence. Such methods have many drawbacks, namely:

• costly drying of ore;
• high cost of X-ray systems;
• poor discernibility due to the fluorescence of other stones such as zircon;
• rejection of non-fluorescent diamonds or diamonds with a grain size less than three millimeters.

The known methods do not therefore allow, on the one hand, total recovery of the diamonds contained in the mixture and, on the other hand, recovery of diamonds of pure crystalline form.

The present invention aims to remedy these drawbacks. In particular, the present invention relates to a method making it possible to recover diamonds from a wet mixture, to recover all the diamonds contained in the mixture or ore to be treated and / or to recover diamonds of pure crystalline form only.

It has thus been noted that these remarkable results could be obtained by a method according to the invention in which one or more diamonds to be recovered from the mixture are detected by emitting an acoustic wave or waves of frequency greater than 10 MHz and by picking up one or more acoustic waves reflected by said mixture.

According to a particular feature of the method according to the invention, the acoustic wave emitted is focused so as to reduce the useful section of the beam of the acoustic wave, preferably to a value less than the surface of a facet of the diamond or diamonds to be detect or crystallites of minerals contained in the mixture.

Advantageously, acoustic waves are emitted towards the mixture in planes perpendicular to each other and waves reflected in said planes are picked up so as to neutralize anisotropy effects.

In one embodiment of the method according to the invention, in which the mixture to be treated is moved substantially in a plane, the acoustic wave or waves are emitted in a direction making an angle between 5 ° and 35 °, preferably approximately 20 ° with respect to a perpendicular to said plane and waves reflected by the mixture are captured in a direction making an angle between 15 ° and 25 °, preferably between 16.5 ° and 23.5 ° with said perpendicular to said plane.

According to the invention, ultrasonic or ultrasonic waves of frequency greater than 10 MHz, and advantageously greater than 20 MHz, are used. The use of high frequency waves as well as the focusing of the waves allow, on the one hand, the treatment of wet ore seen a weak attenuation of the acoustic waves in wet environment, and, on the other hand, the examination of stones ore in small areas (areas of section less than 5.10 ^-2 , preferably about 1.5.10 ^-2 mm ² ).

In a method according to the invention, the separation device is controlled when a reflected wave with a sound power greater than 3 dB is detected, preferably at 5 dB for a sound wave with a power between 80 and 85 dB.

The applicant noted that by changing the detection threshold, it was possible to sort the diamonds according to their quality.

Thus, for a detection threshold between 3.2 and 3.6 dB, it has been noted that all of the ilmenite and limonite are eliminated while 95 to 100% of the diamonds contained in the mixture and only 20 to 30% of the pyropes are recovered. .

For a detection threshold of the order of 5dB, only diamonds of a pure crystalline form are recovered. The method according to the invention therefore allows quality sorting, which was by no means possible with known methods.

The present invention also relates to a device or apparatus for implementing a method according to the invention. This device comprises a means of supplying the mixture to a detection system controlling a device for separating one or more diamonds to be recovered, the detection system consisting of an emitter of acoustic waves of frequency greater than 10 MHz and an acoustic wave receiver, the latter being intended to capture acoustic waves reflected by the mixture.

According to a feature of a device according to the invention, it comprises a first set of transceiver and a second set of transceiver, said sets being located in perpendicular planes.

In one embodiment, the supply means comprises at least one part intended for the displacement of the mixture substantially in a plane, the transmitter emits acoustic waves in a direction making an angle between 5 ° and 35 °, preferably, about 20 ° with respect to a perpendicular to said plane, while the receiver picks up waves reflected by the mixture making an angle between 15 ° and 25 ° with said perpendicular to said plane.

In an advantageous embodiment of the device according to the invention it comprises a focusing device intended to focus the acoustic waves substantially at one point of the mixture. Such a focusing device is for example a focusing device of the IPS type ref. 129.320 sold by Krautkrämer.

• d'une trémie d'alimentation d'un mélange à une table mise en mouvement par un moteur, ledit mélange tombant, par l'effet de la gravité, d'un bord de ladite table ;
• d'un moyen de séparation de diamants lors de la chute du mélange ;
• d'une trémie pour récupérer les diamants séparés du mélange, et
• d'une trémie pour récupérer le mélange après récupération de diamants, cette trémie étant la trémie d'alimentation de l'étage inférieur.

In a particular embodiment, the device according to the invention comprises at least one, preferably 2 to 3, stages made up:

• a hopper for feeding a mixture to a table set in motion by a motor, said mixture falling, by the effect of gravity, from an edge of said table;
• a means for separating diamonds when the mixture falls;
• a hopper to recover the diamonds separated from the mixture, and
• a hopper to recover the mixture after recovery of diamonds, this hopper being the feed hopper of the lower stage.

• un moteur entraînant en rotation un arbre portant une série de disques sur lesquels repose éventuellement une table circulaire, et
• une série de paires de trémies dont la section supérieure est circulaire, la section supérieure d'une première trémie de chaque paire est inférieure ou sensiblement égale à la section circulaire du disque ou table, tandis que la section circulaire de la seconde trémie est supérieure à la section circulaire du disque ou table, chaque paire de trémies étant située en-dessous d'un disque ou table et présentant une ouverture livrant passage audit arbre, une trémie de chaque paire située au-dessus d'un disque ou table présentant un passage pour amener une partie du mélange sur ce disque ou table, des canons a eaux étant disposés, pour chaque disque, à un niveau inférieur au niveau du disque ou table mais supérieur au niveau des trémies destinées à recueillir le mélange tombant du disque ou table.

According to a detail of this particular embodiment, it comprises:

• a motor driving in rotation a shaft carrying a series of discs on which possibly rests a circular table, and
• a series of pairs of hoppers whose upper section is circular, the upper section of a first hopper of each pair is less than or substantially equal to the circular section of the disc or table, while the circular section of the second hopper is greater than the circular section of the disc or table, each pair of hoppers being located below a disc or table and having an opening providing passage to said shaft, a hopper of each pair located above a disc or table having a passage for bringing part of the mixture onto this disc or table, water cannons being arranged, for each disc, at a level below the level of the disc or table but above the level of the hoppers intended to collect the mixture falling from the disc or table.

Other features and details of the invention will emerge from the following detailed description in which reference is made to the accompanying drawings.

• la figure 1 représente schématiquement un procédé suivant l'invention, et
• les figures 2 et 3 montrent des formes de réalisation de dispositifs suivant l'invention.

In these drawings:

• FIG. 1 schematically represents a method according to the invention, and
• Figures 2 and 3 show embodiments of devices according to the invention.

In the method of sorting diamonds from a mixture containing inter alia diamonds to be recovered, namely in the particular case described below a wet diamondiferous ore coming from the mine of Mbujimayi (Zaire), the ore was deposited on a table 1 and this was brought to a table edge 1 by means of a pusher so that said ore fell from the table and was brought to a detection system 2.

Diamonds present in the ore were detected by emitting and focusing acoustic waves with frequencies close to 25 MHz and by picking up waves reflected by ore with frequencies close to 20 - 22 MHz, and a water cannon 3 was ordered when a diamond has been detected, so as to bring it into a tank 4.

The ore after treatment was collected in a tank 5.

The detection of diamonds in the ore was carried out by emitting and capturing acoustic waves in two planes perpendicular to each other so as to neutralize the effects of crystalline anisotropy.

The ore was moved substantially in a vertical plane A-A and the focused waves made an angle α between 20 ° ± 15 ° with a perpendicular B to said plane A-A. Waves reflected by the ore were captured which made an angle β between 16.5 ° and 23.5 ° with said perpendicular B.

After adjusting the power of the emitted wave to around 80 dB, we studied the influence of the sound threshold controlling the separation of a diamond or a particle from the ore.

It was thus determined, for different thresholds, the% of particles recovered relative to those present in the mixture. threshold from which the water cannon was ordered (dB) % of ilmenite recovered % of limonite recovered % of pyrope recovered % of diamond recovered 3 0 33 40 100 3.2 0 16.5 30 100 3.4 0 0 30 95 3.6 0 0 20 95 5 0 0 0 36

This table shows, on the one hand, that by using a process according to the invention, it is possible to recover from 95 to 100% of the diamonds present in the ore, while recovering only about 20 to 30% of pyrope present in the ore; and, on the other hand, that by using a process according to the invention, it is possible to eliminate all of the diamond accompaniments in the ore and to keep only diamonds with pure crystalline forms.

Given these results, a device has been developed which makes it possible, on the one hand, to recover all the diamonds present in the ore and, on the other hand, to make a first sorting to separate the diamonds with pure crystalline forms from the other diamonds.

This device is shown diagrammatically, in perspective and partially in section, in FIG. 2.

This device comprises means 6 for supplying a mixture containing diamonds to a detection system 7 controlling a device 8 for separating diamonds from the mixture.

The means 6 is a vibrating table having a series of channels 9 in which the stones move in the direction of the arrow X. The vibrations of the table are obtained by means of a vibrator connected by arms to the table 6 (not represented).

Table 6 has a slot 12 intended to allow the detection of the diamonds contained in the mixture. To carry out this detection, the device comprises a system 7 consisting of two sets of transmitters 13 - receivers 14 of acoustic waves, these sets being mounted on a slide 15 and located in planes perpendicular to each other.

The slide 15 is connected by a set of crank-rod 16 to a motor 17 and is guided by rails 18. The rotation of the motor shaft 17 causes the slide to move in a direction Y parallel to the slot 12.

The acoustic waves generated by a generator 10 which are reflected by a diamond in the mixture are picked up by the receiver 14, amplified by an amplifier 19, filtered in a filter 20 so as to keep only the reflected waves of a determined frequency, preferably high frequency.

The waves thus amplified and filtered are then sent to a comparator 21 of the intensity of the wave. If this intensity is greater than 5 dB, a unit value is given to the two outputs 22, 23 of the comparator while if this intensity is less than 5 dB, a zero value is given to output 22 of the comparator and a zero value is given at output 23 if the intensity is less than 3.6 dB. Doors "or" 24,24 ′ make it possible to determine whether the intensity of a wave received by a receiver 14 is greater than 5 dB, or is less than 5 dB but greater than 3.6 dB.

When a unit value leaves a comparator, a suction device 25 connected to recovery tanks 26, 27 extended by a horn 28 extending to the vicinity of the slot 12 is actuated so as to recover one or more diamonds of the said mixture or to obtain diamond concentrates.

A valve 29 mounted in the horn 28 is controlled when a unit value leaves the door 24 'so that the detected diamond or diamonds are sucked up.

A door "and" 30 compares the values leaving the doors "or" 24,24 'and controls a hatch 31 intended to direct the diamond or diamonds sucked towards the tank 26 when a unit value leaves the door "and" 30 and to tray 27 in other cases.

The table 6 has at one of its ends an inclined plane 32 intended to bring the treated mixture to another vibrating table 6.

Another device which can be used for implementing a method according to the invention is shown in FIG. 3.

• d'une trémie d'alimentation 32, 33 d'un mélange à une table 35, 36, cette table étant soumise à des vibrations par un vibrateur électromécanique 38 ;
• d'un moyen de séparation des diamants lors de leur chute, ce moyen étant un canon à eau 39 commandé par un système de détection 40 ;
• d'une trémie 41, 42 pour récupérer les diamants séparés du mélange, et
• d'une trémie 44, 33, pour récupérer le mélange après une opération de séparation de diamants, la trémie 33 étant la trémie d'alimentation de l'étage inférieur.

This device comprises a series of stages consisting of:

• a feed hopper 32, 33 of a mixture at a table 35, 36, this table being subjected to vibrations by an electromechanical vibrator 38;
• means for separating the diamonds during their fall, this means being a water cannon 39 controlled by a detection system 40;
• a hopper 41, 42 to recover the diamonds separated from the mixture, and
• a hopper 44, 33, for recovering the mixture after a diamond separation operation, the hopper 33 being the feed hopper of the lower stage.

In the embodiment of the device shown in Figure 3, the device comprises 2 stages.

• un bâti 45 portant la trémie d'alimentation supérieure 32 et la table 35 ;
• un arbre 46 portant une série de disques 47, 36, le disque supérieur 47 étant destiné à transmettre les vibrations du vibrateur 38 à la table 35 tandis que le disque 36 constituent également une table pour amener le mélange à un système de détection 40 ;
• un moteur 48 monté sur un plateau relié au vibrateur 38, ce moteur entraînant en rotation ledit arbre 46, et
• une série de paires de trémies 33, 41 ; 44, 42 solidaires de l'arbre 46 par des bras, la section supérieure circulaire d'une première trémie 41, 42 de chaque paire étant sensiblement égale à la section circulaire du disque ou table tandis que celle de la seconde trémie 33, 44 de chaque paire est supérieure à la section circulaire d'un disque ou table placé au dessus de ladite paire.

The device advantageously comprises:

• a frame 45 carrying the upper feed hopper 32 and the table 35;
• a shaft 46 carrying a series of discs 47, 36, the upper disc 47 being intended to transmit the vibrations of the vibrator 38 to the table 35 while the disc 36 also constitutes a table for bringing the mixture to a detection system 40;
• a motor 48 mounted on a plate connected to the vibrator 38, this motor driving said shaft 46 in rotation, and
• a series of hopper pairs 33, 41; 44, 42 secured to the shaft 46 by arms, the circular upper section of a first hopper 41, 42 of each pair being substantially equal to the circular section of the disc or table while that of the second hopper 33, 44 of each pair is greater than the circular section of a disc or table placed above said pair.

The hopper 33 has a passage 50 for bringing part of the mixture onto a disc or table 36 located under said hopper 33; the latter being therefore a hopper for supplying said disc or table.

Between each disc 47, 36 and the hoppers for recovering the diamonds or the treated mixture are arranged the water cannons 39.

The hoppers 41, 42 for recovering the diamonds from said mixture are extended by a conduit 51 whose free end is distant from the shaft 46 by a distance at least equal to the largest radius of the upper section of the hoppers. The diamonds or the diamond concentrate leaving said hoppers are then harvested in a circular tank or a collector 52, while the mixture after treatment leaves the lower hopper 44 via a conduit 53 and is brought into a tank 54.

Claims (13)

1. A sorting process for a mixture in which the mixture is brought into contact with a system of detection, with this system detecting one or several particles, which are to be recovered, by emitting one or several sound waves in the direction of the mixture and where the mixture picks up one or several reflected waves, with control of a particle separation device when one or several particles, which are to be recovered, are detected, this being characterized by the fact that ultrasonic waves or ultrasound of a frequency in excess of 10 MHz, preferably 20 MHz, are used to detect the above-mentioned diamond-bearing mixture.
2. A process in accordance with claim 1., characterized by the fact that a separation device is used when picking up reflected sound waves of more than 3dB, preferably 5dB, for an emitted wave of between 80 and 85 dB.
3. A process in accordance with claim 1 or 2, characterized by the fact that the diamond-bearing mixture is displaced on a plane, and by the fact that the sound wave or sound waves is/are emitted in an angle of between 5° and 35°, preferably more or less 20° perpendicular to the aforementioned plane, and by the fact that the mixture picks up the reflected wave within an angle of between 15° and 25°, preferably between an angle of 16.5° and 23.5° perpendicular to the aforementioned plane.
4. A process in accordance with whatsoever of the above-mentioned claims, characterized by the fact that the useful section of the beam is reduced to less than the surface value of one facet of the diamond or diamonds to be detected or of the mineral crystallite contained in the mixture, with this value preferably being less than 5.10^-2 mm².
5. A process in accordance with whatsoever of the above-mentioned claims, characterized by the fact that sound waves are emitted perpendicularly to the mixture and by the fact that the waves reflected from these (perpendicular) planes are picked up in such a way that they neutralize the effects of crystal anisotropy.
6. A device for implementing a process in accordance with whatsoever of the above-mentioned claims, with this device including a supply system (6) of the mixture to the detection system (7), controlling a separation device (8) of the diamond or diamonds to be recovered, with the detection system including an emitter (13) of ultrasonic waves or ultrasound of frequencies over and above 10 MHz, preferably 20 MHz, and a receiver (for the sound waves) (14), with the latter being designed to pick up the sound waves reflected by the mixture.
7. A device in accordance with claim 6, characterized by the fact that it comprises two sets of emitters-receivers, with both sets being perpendicular to each other.
8. A device in accordance with claim 6 or 7, characterized by the fact that the supply system (6) is made up at least of an element designed to displace the mixture mainly in a plane, with the emitter (13) emitting sound waves in an angle of preferably between 5° and 35°, more or less 20° perpendicular to the aforementioned plane, while the receiver (14) picks up the waves reflected by the mixture in an angle of between 15° and 25° with the aforementioned perpendicular (angle) to the plane.
9. A device in accordance with whatsoever of the above-mentioned claims 6 to 8, characterized by the fact that it includes a focalizer to focus the sound waves on a given point of the mixture.
10. A device in accordance with whatsoever of the above-mentioned claims 6 to 9, characterized by the fact that it includes at least one working level, preferably 2 to 3, made up as follows :

    - a feed hopper (32, 33) supplying the mixture to the table (35, 36) which is activated by a motor, the aforementioned mixture falling off one side of the table thanks to gravity;

    - a diamond separation device (39) where the mixtures falls from the table (35, 36);

    - a recovery hopper (41, 42) for the diamonds which have been separated from the mixture, and

    - a recovery hopper (44, 33) for the mixture after the diamonds have been recovered, with this hopper being the feed hopper on the lower working level, when the device is made up of several working levels.
11. A device in accordance with claim 10, characterized by the fact that it includes a vibrator (38) designed to vibrate the table (35, 36).
12. A device in accordance with whatsoever of the above-mentioned claims 10 and 11, characterized by the fact that it includes the following :

    - a motor (48) rotating an axle (46) fitted with a series of disks (47, 36), to which a circular table may possibly be attached, with the motor being preferably mounted on a plate which is vibrated (38) and

    - a series of twin hoppers (33, 41; 44, 42) whose upper section is circular, with the upper section of the first hopper (41, 42) of each pair of hoppers being smaller or essentially equal to the circular section of the disk or the table, while the circular section of the second hopper (33, 44) is greater than the circular section of the disk or the table, each pair of hoppers being located under a disk or a table and presenting an opening giving access to the aforementioned axle, with one hopper (33) of each pair located under the disk or the table (36) giving access (50) to part of the mixture being supplied to the disk or the table, and with water jets (39) for each disk being mounted below the level in question but above the hoppers designed to collect the falling mixture (from the disk or the table).
13. A device in accordance with claim 12, characterized by the fact that the separation devices, preferably water jets (39), are controlled by a receiver (14) when the latter picks up the sound waves reflected by the mixture so as to ensure that the diamonds are separated from the mixture and are fed into a hopper (41, 42) whose upper section is smaller or equal to the section of the disk or the table (35, 36) from which the mixture is falling, these hoppers (41, 42) preferably being extended at the bottom by a pipe (51) in order to feed the separated diamonds to a collector (52).

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