Method and device for sorting a spodumene-containing ore

Abstract

A method and sorting device for sorting grains (8) from an ore stream of a spodumene-containing ore, wherein the ore stream is moved through an exposure zone (9) and illuminated, wherein spodumene is detected by determining the light intensity of light emitted by the grains (8), wherein a detection signal is generated and a grain (8) is identified as a spodumene-containing grain when this detection signal exceeds a reference value, wherein the exposure time is at least 5 ms and light incident has a wavelength between 200 nm and 540 nm, wherein the light intensity of light emitted by the grains (8) is determined in at least one wavelength band between 500 nm and 1000 nm.

Description

[0001]

[0002] Method and device for sorting a spodumene-containing ore

[0003] The invention relates to a method for sorting grains from an ore stream of a spodumene-containing ore, wherein fractions of this ore are formed on the basis of a measured spodumene content of the grains in the ore stream. This ore stream is moved in a direction of motion and with a stream width through an exposure zone where the grains are exposed to light during an exposure time.

[0004] The spodumene may comprise, for example, kunzite or hiddenite, while the material to be separated from the spodumene may be, for example, quartz, feldspar, muscovite, or other stony materials.

[0005] Spodumene is detected in said grains by determining the intensity of light emitted by the grains using a detection device. Depending on the specific light intensity of said emitted light, a detection signal is generated, with a grain being identified as a spodumene-containing grain when the detection signal exceeds a reference value. Spodumene-containing grains identified in this way are directed to one and the same fraction in the ore stream, while other grains are directed to at least one other fraction.

[0006] Spodumene is a mineral with the chemical formula LiAl(SiO3)2, which is an important source for lithium extraction.

[0007] At present, ores containing spodumene are primarily subjected to crushing and / or grinding and flotation treatments to separate a fraction rich in spodumene from the other ore grains. The invention aims to improve the separation of spodumene from other components such as quartz, feldspar, etc. To this end, according to the invention, optical sorting is applied to the spodumene-containing ore. This optical sorting may be preceded or followed by known separation techniques such as flotation, for example.

[0008] According to the invention, the exposure time in the exposure zone is at least 5 ms, while the light striking the ore stream in the exposure zone has a wavelength between 200 nm and 540 nm, preferably between 255 nm and 540 nm.

[0009] According to the invention, the light intensity of light emitted by the grains is determined in at least one wavelength band between 500 nm and 1000 nm, preferably between 500 nm and 800 nm.

[0010] Preferably, the wavelength band in which the intensity is determined by means of the detection device is 610 nm, and this wavelength band preferably has a minimum width of 50 nm.

[0011] According to a preferred embodiment of the method according to the invention, the detection of spodumene using the detection device is performed after said grains have been in the exposure zone for at least 5 ms.

[0012] According to a particular embodiment of the method according to the invention, the detection is performed using the detection device no later than 5 ms after the grains have left the exposure zone.

[0013] Advantageously, the detection device is shielded from light with a wavelength similar to the incident light.

[0014] According to an interesting embodiment of the method according to the invention, the detection of spodumene is performed at least at two different points in time.

[0015] According to a preferred embodiment of the method according to the invention, the detection of spodumene takes place at least at two different point in time and the detection signal is generated by comparing the light intensities determined each time.

[0016] The invention also relates to a sorting apparatus for separating an ore stream of a spodumene-containing granular ore into at least two fractions on the basis of a measured spodumene content of the grains in the ore stream. This sorting apparatus has an exposure zone, a detection device, a control unit and a removal device.

[0017] In the sorting apparatus, the ore stream moves through the exposure zone in a direction of motion, wherein at least one light source is provided which allows grains of the ore stream to be exposed to light having a wavelength between 255 nm and 540 nm for an exposure time of at least 5 ms.

[0018] The detection device is designed to determine the light intensity emitted by the grains in a wavelength band between 500 nm and 1000 nm, in particular between 500 nm and 800 nm, following exposure to light from the aforementioned light source.

[0019] Furthermore, the control unit allows a detection signal to be generated depending on the magnitude of the determined light intensity of the emitted light in the aforementioned at least one wavelength band. A grain is identified as a spodumene-containing grain by the control unit when this detection signal exceeds a reference value.

[0020] The control unit controls a removal device in the sorting apparatus to direct spodumene-containing grains to one and the same fraction of the ore stream and to direct other grains to at least one other fraction.

[0021] According to an interesting embodiment of the sorting apparatus according to the invention, the detection device is sensitive to light in a wavelength band that includes 610 nm and said wavelength band preferably has a minimum width of 50 nm.

[0022] Other particularities and advantages of the invention will become clear from the following description of several specific embodiments of the method and the sorting apparatus according to the invention. This description is given by way of example only and does not limit the scope of the claimed protection in any way; the reference numbers used below refer to the figures appended hereto.

[0023] Figure l is a schematic perspective view of a sorting apparatus with an exposure zone, a detection device and a removal device according to an interesting embodiment of the invention.

[0024] Figure 2 is a schematic graph of the light intensity (I) as a function of time (t) of light emitted by spodumene in response to exposure during an exposure time (ta).

[0025] Figure 3 is a schematic perspective view of a variant of the sorting apparatus from Figure 1.

[0026] Figure 4 is a schematic representation of a part of the detection device of the sorting apparatus from Figure 3 according to the invention.

[0027] Figure 5 is a schematic graph of the light intensity (I) as a function of time (t) of light emitted by spodumene in response to exposure during an exposure time (ta), wherein the intensity of light emitted by spodumene is measured at two points in time.

[0028] Figure 6 is a schematic graph of the intensity of light incident on an exposure zone of a sorting apparatus according to the invention, originating from the light source, with this intensity being shown as a function of the distance in the direction of motion of the ore stream.

[0029] In the various figures, the same reference numbers refer to the same or similar elements.

[0030] The invention generally concerns a method and a sorting apparatus for sorting spodumene-containing ores, making use of the optical properties of spodumene. Indeed, it has been found that when spodumene is exposed to a light source with certain wavelengths, the spodumene will emit light at other wavelengths. However, this light emission does not occur immediately upon exposure, but with a slight delay.

[0031] It is assumed that this persistent luminescence property is caused by the presence of Cr and / or Mn atoms in the spodumene.

[0032] Luminescence is the phenomenon whereby a material takes up energy by absorbing incident light from an excitation source. This energy is re-emitted in the form of light, usually with a different wavelength than the incident light. When the material continues to emit light for a limited time after the incident light from the excitation source is no longer present, this is referred to as persistent luminescence. This continued emission of light after the energy source has been removed is also called afterglow.

[0033] Thus, the spodumene in most spodumene-containing ores exhibits persistent luminescence when the excitation source causes light to strike the spodumene in one of the wavelength bands 200 nm-290 nm, 350 nm-370 nm, 395 nm- 420 nm and / or 515 nm-540 nm. The light emitted by spodumene can then be observed in a wavelength band between 500 nm and 1000 nm, but mainly between 500 nm and 800 nm, with a peak usually around 610 nm.

[0034] Thus, the spodumene in most spodumene-containing ores exhibits persistent luminescence when the excitation source makes light in one of the wavelength bands 200 nm-290 nm, 350 nm-370 nm, 395 nm-420 nm and / or 515 nm- 540 nm strike the spodumene. The light emitted by spodumene can then be observed in a wavelength band between 500 nm and 1000 nm, but mainly between 500 nm and 800 nm, with a peak usually around 610 nm.

[0035] In addition, it has been found that when spodumene is exposed to light from one of these wavelength bands, light will not be immediately emitted by spodumene as a result of this luminescence, but the intensity of this emitted light will gradually increase, as shown in Figure 2.

[0036] Figure 2 shows a graph illustrating light intensity (I) as a function of time (t) when a spodumene mineral is exposed to an exciting light source for an exposure time ta. The lower curve 1 of the graph shows the light intensity of the light source, while the upper curve 2 shows the measured intensity of light emitted by the spodumene mineral as a result of exposure to the light source.

[0037] The height ratio of curves 1 and 2 shown in this graph is for illustrative purposes only and does not reflect the actual intensity ratio of curve 1 to curve 2.

[0038] The light source in this case is, for example, a laser source generating light with a wavelength of 405 nm, while the light emitted by spodumene is detected in a wavelength band around 600 nm, for example from 525 nm to 750 nm.

[0039] Thus, after approximately 10 ms of exposure of the spodumene, 95% of the maximum intensity Imax of the light emitted by the spodumene is reached. After an exposure of approximately 20 ms, the maximum intensity Imax of the emitted light is reached and there will be no further increase with longer exposure.

[0040] When the exposure of the spodumene is terminated after an exposure time ta, the intensity of the emitted light will gradually decrease until it is virtually zero after approximately 10 ms.

[0041] In general, the spodumene mineral emits light in at least a wavelength band between 500 nm and 1000 nm with an intensity curve as shown in the graph in Figure 2 when exposed to light with a wavelength between 200 nm and 540 nm.

[0042] It appears that the intensity of the light falling on the spodumene has virtually no effect on the course of curve 2 but it does influence the magnitude of the intensity of the emitted light. It was thus found that, as the intensity of the light incident on the spodumene increases, the intensity of the light emitted by the spodumene in the relevant wavelength band also increases. However, the time course is virtually unaffected, so that, regardless of the intensity of the incident light, the emitted light reaches a maximum intensity Imax after approximately 20 ms of exposure.

[0043] Figure 1 schematically shows an interesting embodiment of a sorting apparatus for spodumene-containing grains in an ore stream. In this sorting apparatus, exposure and detection of light emitted by the grains as a result of the exposure, as briefly described above, are used to sort spodumene-containing ore grains.

[0044] The sorting apparatus 3 thus has a feed device 4 for moving an ore stream past a detection device 5. In the proposed sorting apparatus 3, the feed device 4 consist of a wide conveyor belt 6 which is followed downstream by an inclined plane 7. The ore grains leaving the feed device have a homogeneous speed, while the ore stream has a thickness there which corresponds approximately to a single grain 8.

[0045] The spodumene-containing granular ore to be sorted is placed on the conveyor belt 6, where the ore grains 8 are moved in the form of an ore stream at a speed determined by the speed of the conveyor belt 6 towards the inclined plane 7. The grains 8 then move downwards over this inclined plane 7 under the influence of gravity, so that the ore grains 8 leave the inclined plane 7 in a wide stream having a thickness of approximately one grain 8 and move through an exposure zone 9 of the sorting apparatus 1 at approximately the same homogeneous speed.

[0046] Alternative ways of feeding the ore grains 8 through the exposure zone 9 can also be provided, of course. For example, the inclined plane 7, as shown in Figure 1, may not be present. In that case, the grains 8 are thrown off the conveyor belt 6 at a speed that is sufficiently high to move the grains 8 in free flight at a virtually uniform speed through the exposure zone 9. Such a supply of grains 8 to the exposure zone 9 is represented, for example, in Figure 1 of documents US 4723659 or US 4634881.

[0047] According to yet another method of supplying the grains 8 to the exposure zone 9, they are allowed to move in free fall through the exposure zone 9. In this case, the grains 8 are supplied, for example, onto a curved plate whose surface approximates a parabolic trajectory of the grains 8 by means of a vibrating table. Upon leaving the plate, the grains 8 move through the exposure zone 9 in a single layer at a virtually uniform speed. This is described, for example, in document WO 98 / 31477 or WO 2014 / 013421. Said plate is not necessarily curved but may also be straight.

[0048] The grains 8 of the ore stream typically have a diameter in the order of 1 cm to 5 cm. However, the invention can also be applied to an ore stream containing grains 8 having a diameter of, for example, 1 mm. Preferably, however, the diameter of the grains 8 in an ore stream is of the same order of magnitude.

[0049] In general, the exposure zone 9 preferably extends transversely to the direction of motion 10 of the ore stream and over a distance L in the direction of motion 10 of the grains 8 of the ore stream. In Figure 1, the exposure zone 9 is schematically represented by a plane that is substantially parallel to the ore stream.

[0050] Opposite the exposure zone 9 extends a light source 11 that allows the ore grains 8 to be irradiated with light as they move through the exposure zone 9. The light source 11 is mounted such that light from this light source 11 illuminates at least the entire width of the ore stream in said exposure zone 9 over the aforementioned distance L. The exposure zone 9 therefore corresponds to the zone where light from the light source 11 strikes the ore stream.

[0051] Thus, the exposure zone 9 comprises the area onto which light from the light source 11 strikes and through which the ore stream moves over a distance L. The length L of the exposure zone 9 in the direction of motion 10 of the ore stream corresponds to the zone in which the intensity of the light from the light source 11 falling on the ore stream is at least 50% of the maximum intensity Imax of the light from the light source 11, as shown schematically in Figure 6. In the graph of this Figure 6, the horizontal axis corresponds to the distance x in the direction of motion 10 of the ore stream, while the vertical axis represents the intensity I of light from the light source 11 falling on the ore stream.

[0052] In other embodiments of the invention, this length L may, of course, be defined based on a different percentage of Imax. For example, it is possible for the length L to correspond to the zone in which the intensity of the light from light source 11 falling on the ore stream is at least approximately 10%, 20%, 30%, or 40% of the intensity Imax. This percentage depends, for example, on the type of light source and / or the sensitivity of the sensors in the detection device 5.

[0053] Preferably, the light source 11 generates light with a wavelength between 200 nm and 540 nm. Interesting light sources 11 generate light in a wavelength band around 365 nm, 405 nm and / or 532 nm, for example.

[0054] According to an interesting embodiment of the invention, the light from the light source 11 that falls on the ore stream is preferably collimated. Thus, the light from the light source 11 strikes the grains 8 moving through the exposure zone 9 in the form of a collimated light beam. This ensures, for example, that the intensity of the light from the light source 11 falling on the ore grains 8 is virtually independent of the distance between the light source 11 and the grains 8. This makes it possible to sort ore grains 8 of different sizes without the measured light intensity being influenced by the size of the ore grains 8.

[0055] Moreover, the use of a collimated light beam ensures that the intensity of the light from the light source 11 falling on the ore grains 8 remains virtually constant as it passes through the exposure zone 9.

[0056] Generally, the light source 11 illuminates the ore grains 8 by generating a continuous light curtain that extends across the entire width of the ore stream.

[0057] Furthermore, the sorting apparatus comprises the aforementioned detection device 5 which allows the intensity of light emitted by the grains 8 to be measured as a result of the light from the light source 11 falling on the grains 8. The detection device 5 thus allows the light intensity to be measured in at least one wavelength band between 500 nm and 1000 nm, preferably between 500 nm and 800 nm.

[0058] In the embodiment of the sorting apparatus 3 shown in Figure 1, the detection device 5 comprises, for example, a line scan camera 12, such as a TDI camera, whose field of view 13 extends in a substantially straight line in the aforementioned exposure zone 9, and substantially perpendicular to the aforementioned direction of motion 10 of the ore grains 8. This line scan camera 12 cooperates with a control unit 14 that processes the data generated by the camera. It goes without saying that an area scan camera can also be used instead of a line scan camera 12.

[0059] In general, the detection device 5 is provided downstream of the light source 11, as shown in Figure 1. However, in certain embodiments of the invention, it may be advantageous to place the detection device 5 upstream of the light source 11, for example. In such a case, the camera’s field of view will intersect the light source’s luminous flux.

[0060] The position of the line corresponding to the field of view 13 of the detection device 5, for example of the line scan camera 12, is represented in Figure 2 by a vertical dashed line 15. Thus, as shown in this Figure 2, the intensity of the light emitted by a grain 8 as a result of exposure by the light source 11 is measured by the detection device 5 while this grain 8 is still in the aforementioned exposure zone 9. More specifically, the ore grains 8 move through the exposure zone 9 for at least 5 ms while light from the light source 11 falls on them before the intensity of the light emitted by the grains 8 is measured by means of the detection device 5.

[0061] The exposure time of the ore grains 8 in the exposure zone 9 is, for example, at least 7 ms and preferably at least 10 ms. This ensures that the speed of the ore grains moving through the exposure zone 9 is adjusted so that they are illuminated by the light source 11 for a sufficiently longtime. Optionally, the distance L over which the exposure zone 9 extends in the aforementioned direction of motion 10 can be adjusted by making the light source’s light beam sufficiently wide in this direction of motion 10.

[0062] According to the invention, the light emitted by the grains will be detected after they have been exposed for at least 5 ms. When the grains 8 move through the exposure zone 9 at a speed of, for example, 3 m / s, this means that detection of the light intensity emitted by the grains occurs after the grains have travelled at least a distance of 1.5 cm through the exposure zone 9.

[0063] In the example from Figure 1, where line 15 of the field of view 13 of the line scan camera 12 is shown in Figure 2, this means that detection of the light intensity emitted by the ore grains 8 occurs 45 ms after the start of the exposure or, in other words, after the grains 8 have travelled a distance of 13.5 cm at 3 m / s through the exposure zone 9.

[0064] In general, ore grains 8 are moved through the exposure zone 9 at a speed that is usually between 2 m / s and 4 m / s. In general, the ore grains 8 of the ore stream can be moved at a speed between 1 m / s and 5 m / s, depending on the type of feed device 4 or, possibly, depending on the type of light source 11. The light intensity emitted by the grains 8 is measured by the detection device 5 after the grains 8 have been exposed to the light source 11 for at least 5 ms, which, depending on the speed of the grains 8, corresponds to a movement through the exposure zone 9 over a distance of 0.5 to 10 cm. However, it is preferably made sure that said distance is less than 10 cm and is, for example, between 1 cm and 5 cm in order to obtain a compact sorting device, for example. Said detection device 5 thus cooperates with the control unit 14 to process the signals generated by the detection device 5 to determine the intensity of light emitted by the grains 8. More specifically, a detection signal is generated depending on the magnitude of the determined light intensity of the light emitted by the grains 8. This detection signal is normally proportional to the magnitude of the intensity of the light emitted by the grains 8. A grain 8 is therefore identified as a spodumene-containing grain when the detection signal exceeds a reference value for this grain 8. The choice of the magnitude of this reference value depends, among other things, on the intensity of the light from the aforementioned light source 11 that is incident on the grains 8.

[0065] This reference value may, for example, be chosen by a person skilled in the art by first measuring the detection signal for grains with a known high concentration of spodumene and grains with a known low concentration of spodumene. The level of the reference value is then chosen such that it becomes possible to distinguish spodumene-containing grains with a desired minimum spodumene content from grains without spodumene or with a spodumene concentration that is too low.

[0066] The detection device 5 thus allows a detection signal to be generated depending on the magnitude of the determined light intensity of the light emitted by the grains 8 in at least one wavelength band. A grain 8 is identified as a spodumenecontaining grain when said detection signal exceeds the reference value for this grain.

[0067] Furthermore, a removal device 16 is provided downstream of the exposure zone 9. This removal device 16 is preferably controlled by the control unit 14 on the basis of signals obtained from the detection device 5 and it allows selected grains 8a to be removed from the ore stream and separated into one and the same fraction, while the remaining grains 8b move further into another fraction of the ore stream.

[0068] In this way, grains identified as spodumene-containing grains are directed to one and the same fraction of the ore stream, while the remaining grains are directed to at least one other fraction.

[0069] The removal device 16 comprises, for example, a row of compressed air valves extending across the entire width of the ore stream. When the presence of a selected grain 8a in the ore stream is detected by the detection device 5, the control unit 14 will activate the removal device 16 to remove this grain 8a from the ore stream. To this end, the control unit 14 activates a compressed air valve of the removal device 16 opposite the selected grain 8a so that a short air flow is created which blows the selected grain 8a out of the ore stream. These blown-out grains 8a form a fraction of the ore stream which is discharged separately from the other grains 8b.

[0070] In certain embodiments of the invention, selected grains 8a contain a high concentration of spodumene for which the detection signal is higher than the aforementioned reference value and thus exceeds it, whereas in other embodiments of the invention, selected grains 8a contain a low amount of spodumene for which, for example, the detection signal is lower than the reference value.

[0071] In the above embodiment of the sorting apparatus 3 according to the invention, the light intensity of the light emitted by the grains 8 is measured while these grains 8 are still in the exposure zone 9. For certain ore streams, however, it may be useful to determine the light intensity after the grains 8 have left the exposure zone 9. If this light intensity is determined within 5 ms after irradiation by the light source 11 has ended, in other words within 5 ms after leaving the exposure zone 9, sufficient light will still be emitted by the grains as a result of the previous exposure by the light source 11 to determine its intensity by means of the detection device 5.

[0072] This offers the advantage, for example, that light coming directly from the light source 11 can hardly influence the measurement of the light intensity emitted by the grains 8. In addition, this may be relevant if certain ore grains exhibit some fluorescence as a result of exposure to the light source 11 due to the presence of other minerals such as quartz or feldspar. Since the fluorescence of these other minerals disappears as soon as the light from the light source 11 is removed, only the intensity of the light emitted by spodumene can be determined in this way.

[0073] Figure 3 shows a variant of the sorting apparatus from Figure 1 in which the detection device 5 contains a rotating polygon mirror 17. This polygon mirror 17 cooperates with a detector 18 that is sensitive to light emitted by the grains 8 as a result of exposure to the light source 11. This detector is therefore sensitive in a wavelength band ranging, for example, between 500 nm and 1000 nm. For example, in a wavelength band between 500 nm and 800 nm that includes 610 nm. This wavelength band has, for example, a minimum width of 50 nm. Light emitted by the ore grains 8 strikes the polygon mirror 17 and reaches the detector 18 via an intermediate mirror 19. As a result of the rotation of the polygon mirror 17 around its central axis, the field of view of the detector 18 is shifted across the width of the ore stream. Consequently, in this way, the detector 18 scans the width of the ore stream as shown by line 13 in Figure 3.

[0074] The detector 18 is formed, for example, by a PMT detector, an APD detector, a SiPM detector (Silicon Photomultiplier) or a photodiode cooperating with the control unit 14 to process the signals generated when determining the intensity of light emitted by the grains 8, as already described above with respect to Figure 1.

[0075] Preferably, the detection device 5 is shielded from light having a wavelength similar to the light incident on the grains 8 originating from the light source 11. In the sorting apparatus shown in Figures 3 and 4, an optical filter 20 is provided to this end, located in the optical path between the grains 8 and the detector 18. In the example of Figure 4, this optical filter 20 is mounted, for example, between the mirror 19 and the detector 18.

[0076] For the sake of completeness, it should be noted that it is known to those skilled in the art to provide a background element 25 when the ore stream is scanned across its width using a polygon mirror 17, so that the ore stream extends between this background element 25 and the polygon mirror 17. Such a background element 25 emits light having, for example, the same wavelength as spodumene within the wavelength band measured by the detector 18.

[0077] It is also possible that the possible background element 25 emits light with a different wavelength, for example a wavelength outside the fluorescence spectrum of spodumene. In such a case, the background element 25 cooperates with a detector sensitive to light emitted by the background element 25 to generate a presence signal when an ore grain 8 is located between this background element 25 and the detector. Consequently, in the positions opposite the background element 25 where such a presence signal is thus generated, there will be an ore grain 8. In this way, the detection device 5 preferably only detects spodumene for the positions for which a presence signal is generated.

[0078] In certain cases, it may be useful to combine the detection of spodumene, as described above, with other optical detection methods. This may be relevant, for example, when distinguishing spodumene-containing grains from other stony grains in the ore stream. These other grains may contain mainly quartz, feldspar or muscovite, for example.

[0079] In such a case, the detection device 5 contains one or more additional detectors. Figure 4 thus shows a detection device that also allows ore grains 8 to be characterised on the basis of the measurement of the scattering of laser light in the grains 8.

[0080] To this end, the detection device 5 contains a laser source 21 which causes a laser beam 22 with a wavelength between 365 nm and 1500 nm to strike the grains 8 via the rotating polygon mirror 17. This laser source 21 generates, for example, a laser beam 22 with a wavelength of 532 nm or 405 nm. Preferably, it is made sure that the laser beam 22 is incident on the ore stream at a position corresponding to the position of the field of view of the detector 18. When the laser beam 22 strikes a grain 8, the light from the laser beam 22 will be scattered in the grain 8. This scattered light is detected by a second detector 23 of the detection device 5. A mirror 24 with a central opening is provided in the optical path of the laser beam 22 between the polygon mirror 17 and the laser source 21. Thus, the laser beam 22 passes through this central opening and strikes the polygon mirror 17 to be directed towards the grains 8. Due to the central opening in the mirror 24, only light from the laser beam 22 that is scattered by the grains 8 reaches the detector 23. Light from the laser beam that is reflected directly by the grains 8 is not directed to the detector 23, as it disappears in the central opening of the mirror 24.

[0081] Since certain minerals that often occur together with spodumene, such as quartz, exhibit greater scattering of the laser beam 22 than spodumene, such detection of the scattering of a laser beam allows for an additional distinction to be made between spodumene and these minerals. Other materials, such as basalt, for example, exhibit less scattering of the laser beam 22 than spodumene, so that they can also be distinguished from spodumene by detecting the scattering of the laser beam.

[0082] When generating said detection signal, it is preferable to also consider the measured scattering of the laser beam in the grains in order to identify grains 8 as spodumene-containing grains and to thus direct them to one and the same fraction of the ore stream as described above.

[0083] In addition to detecting the scattering of the laser beam 22 by the grains 8, it is also possible to measure the direct reflection of the laser beam by the grains 8. Such a detection method is also known to those skilled in the art and allows, for example, minerals or ores that do not contain spodumene to be identified. In this case, the wavelength of the laser beam 22 is, for example, in the infrared range between 750 nm and 1000 nm.

[0084] It goes without saying that, as is also the case for the embodiment of the sorting apparatus 3 shown in Figure 1, the detection device 5 can be designed such that the light intensity emitted by the grains 8 is detected immediately upon leaving the exposure zone 9, in particular, preferably within 5 ms after leaving the exposure zone 9. In such a case, the light emitted by the grains 8 is detected in a detection zone 13 located downstream of the exposure zone 9.

[0085] If the light emitted by the grains 8 is detected in a detection zone 13 downstream of the exposure zone 9, a screen may be placed between the exposure zone 9 and the detection zone 13 to ensure that the incidence of light from the light source 11 in the detection zone is limited as much as possible. This screen may, for example, be formed by a plate extending almost directly above the ore stream across its entire width and transversely to the direction of motion 10. In this way, the detection zone is shielded from light from the exposure zone 9.

[0086] According to an interesting embodiment of the sorting apparatus or method according to the invention, more than one spodumene detection is performed. This can be done, for example, at different points in time by placing different detection devices downstream, one after the other. The different detection devices can, for example, be coordinated so that the different measurements are performed for the same ore grain zone.

[0087] For example, during an initial spodumene detection, the emitted light intensity of an ore grain 8 can be measured in the aforementioned exposure zone 9, while a second measurement is performed after the grain 8 has left the exposure zone. However, this second measurement is performed during the so-called afterglow of the spodumene, i.e. within a period of 5 ms. The detection signal is then generated on the basis of a ratio or sum of the two determined intensities si and S2 of light emitted by the grain 8 and compared with a reference value. Figure 5 shows, by way of illustration, the point in time of the first detection 26 and the point in time of the second detection 27 of the light intensity emitted by a grain 8. In this way, it is therefore possible to distinguish a grain containing spodumene and exhibiting persistent luminescence from a material that may be luminescent but does not exhibit persistent luminescence, such as quartz, for example. By comparing the thus generated detection signal with the aforementioned reference value, the light intensities si and S2 determined at these points in time are compared with each other.

[0088] Not only can the light intensity emitted by the grains 8 be detected at one, two, or more points in time, but it is also possible to take multiple measurements of the intensity of light emitted by a grain 8, possibly even at the same point in time. To this end, the intensity of light emitted by the grains 8 is determined in two or more separate wavelength bands ranging from 500 nm to 1,000 nm. In such a case, the detection device 5 may be equipped with, for example, multiple cameras 12 or multicolour cameras, or a detector 18 for each measured wavelength band. Said detection signal is then generated, for example, on the basis of a ratio or sum of the determined intensities of the measured wavelength bands and compared with a selected reference value. Determining the intensity of the light emitted by the grains in multiple wavelength bands in this way allows materials that also exhibit luminescence but have a different emission spectrum than spodumene, to be distinguished from spodumene. This may be relevant for separating quartz, feldspar, muscovite or other minerals from spodumene-containing grains.

[0089] In general, the detection device may contain five colour cameras or multispectral cameras to detect different wavelengths of light emitted by the grains, in particular by spodumene. It is also possible, for example, to incorporate five prisms, dichroic mirrors or bandpass filters in the detection device, which ensure that the light emitted by the grains is split into different wavelengths or wavelength bands and thus directed to a corresponding detector. Alternatively, an RGBI or RGBI camera can be used, for example, which not only allows spodumene to be identified by measuring the light emitted by the grains, but also allows other minerals to be identified.

[0090] In an interesting way, the fluorescence spectrum of the light emitted by the ore grains as a result of UV-light exposure can. By comparing the different wavelength bands from this spectrum, the aforementioned detection signal can be generated, or other minerals can be recognised. This is possible, for example, by using an RGB colour camera in the detection device 5. According to an interesting embodiment of the method according to the invention, a grain 8 is identified as a spodumene-containing grain when, for a part of the surface area of the grain 8, the light intensity of the emitted light in the relevant wavelength band or wavelength bands exceeds a predetermined reference value or reference values, respectively.

[0091] A spodumene value is then assigned to the spodumene-containing grain. This spodumene value is associated with a proportion of the surface area of the image of said part of the spodumene-containing grain where spodumene is detected relative to the surface area of the image of the spodumene-containing grain.

[0092] When this spodumene value exceeds a desired spodumene value, the relevant grain will be directed to a fraction rich in spodumene, whereas when this spodumene value does not exceed the desired value, the grain will be directed to a fraction poor in spodumene.

[0093] In general, the detection device 5 allows the intensity of light emitted by the grains 8 to be determined pixel by pixel. An intensity value is thus determined for each pixel. The detection signal can thus be generated on the basis of the intensity values determined for multiple pixels for a grain 8.

[0094] According to one possible embodiment, the intensity value of each pixel is compared, for example, with a reference pixel value. The number of contiguous pixels that exceed this reference pixel value is then determined. This number of pixels then forms a detection signal that is compared with the reference value, and when the number of pixels exceeds the reference value, the relevant grain is identified as a spodumene-containing grain.

[0095] In another embodiment of the invention, it is possible, for example, to determine the number of pixels that are close to each other and have an intensity value exceeding the reference pixel value. Here, nearby pixels are defined, for example, as pixels that are 1 to 3 pixels apart. The number of pixels selected in this way then forms the detection signal that is compared with the reference value in order to potentially identify the grain as a spodumene-containing grain.

[0096] According to yet another embodiment, an average value of the intensity value of each pixel is calculated within a specific area or within a part of a grain’s surface. This average intensity value of the relevant pixels forms the detection signal and is compared with a reference value. If this detection signal, or in other words the average intensity value of the pixels, is greater than the reference value for a grain, this grain will be identified as a spodumene-containing grain.

[0097] According to a further variant, for example, the surface area of a grain occupied by pixels having an intensity value higher than the reference pixel value is compared with the total surface area of this grain. The proportion of the surface area occupied by these pixels relative to the total surface area of the grain then constitutes, for example, the detection signal. When this ratio, i.e. the detection signal, exceeds a selected reference value, the grain will be identified as a spodumene-containing grain.

[0098] Although Figures 1 and 3 show a sorting apparatus 3 containing only a single light source 11 and a single detection device 5, it is usually advantageous to provide multiple light sources 11 that cooperate with multiple detection devices 5. For example, a light source 11 with a corresponding exposure zone 9 and a detection device 5 can be provided both at the top and at the bottom of the ore stream. This makes it possible to detect the presence of spodumene on opposite sides of the ore grains. The control unit 14 can thus consider the determined intensity of the emitted light on both sides of the same grain via the corresponding detection device 5. This prevents, for example, that an ore grain 8 on which spodumene is visible on only one side would not be selected as a spodumene-containing grain.

Claims

CLAIMS1. Method for sorting grains (8) from an ore stream of a spodumene-containing granular ore by forming fractions of this ore on the basis of a measured spodumene content of the grains (8) of the ore stream, wherein the ore stream is moved in a direction of motion (10) and with a stream width through an exposure zone (9) in which grains (8) of said ore stream are exposed for an exposure time to light incident on the ore stream, wherein spodumene is detected by determining the light intensity of light emitted by the grains (8) as a result of said exposure by means of a detection device (5), wherein, depending on the magnitude of the determined light intensity of said emitted light in said at least one wavelength band, a detection signal is generated, whereby a grain (8) is identified as a spodumene-containing grain when this detection signal exceeds a reference value for this grain, wherein grains (8) identified as spodumene-containing grains are directed to one and the same fraction of the ore stream, while other grains are directed to at least one other fraction, characterised in that said exposure time is at least 5 ms, whereas the light incident on the ore stream has a wavelength between 200 nm and 540 nm, wherein the light intensity of light emitted by the grains (8) is determined in at least one wavelength band between 500 nm and 1000 nm, preferably between 500 nm and 800 nm.

2. Method according to claim 1, wherein said detection of spodumene by means of the detection device (5) is performed after the grains have been in the exposure zone (9) for at least 5 ms.

3. Method according to claim 1 or 2, wherein said detection by means of the detection device (5) is performed at the latest 5 ms after said grains have left the exposure zone (9).

4. Method according to any one of claims 1 tot 4, wherein the wavelength band in which said intensity is determined by means of the detectiondevice (5) comprises 610 nm and wherein said wavelength band preferably has a minimum width of 50 nm.

5. Method according to any one of claims 1 tot 4, wherein said detection device (5) is shielded from light having a wavelength of the incident light.

6. Method according to any one of claims 1 tot 5, wherein the detection of spodumene is performed at least at two different points in time.

7. Method according to claim 6, wherein the detection of spodumene is performed at least at two different points in time, wherein the detection signal is generated by comparing the light intensity determined for each of these points in time.

8. Method according to any one of claims 1 to 7, wherein said exposure of the grains (8) is performed with light from at least one of the wavelength bands 200 nm-290 nm, 350 nm-370 nm, 395 nm-420 nm and / or 515 nm-540 nm.

9. Method according to any one of claims 1 to 8, wherein said exposure time is at least 7 ms, and preferably at least 10 ms.

10. Method according to any one of claims 1 to 9, wherein, when performing said detection, said light intensity in two or more distinct wavelength bands between 500 nm and 1,000 nm is determined by means of said detection device (5).

11. Method according to any one of claims 1 to 10, wherein said ore stream is moved through said exposure zone (9) in a single layer of grains (8) extending across the stream width in the aforementioned direction of motion (10) which is substantially transverse to the stream width, whereby the ore stream is exposed across the entire stream width.

12. Method according to any one of claims 1 tot 11, wherein said exposure is performed by creating a continuous light curtain across the entire width of the ore stream.

13. Method according to any one of claims 1 to 12, wherein the grains (8) of the ore stream are exposed to collimated light as they move through the exposure zone (9).

14. Method according to any one of claims 1 to 13, wherein the detection is performed in a detection zone (13) located downstream of the exposurezone (9), wherein the detection zone (13) is shielded from light from the exposure zone (9).

15. Method according to any one of claims 1 to 14, wherein said detection is performed using a camera (12), such as a line scan camera, a TDI camera or an area scan camera.

16. Method according to any one of claims 1 to 15, wherein said detection is performed by scanning said ore stream across its width using a polygon mirror (17) rotating around a central axis thereof in order to direct light emitted by said grains (8) via the polygon mirror to a light detector (18), such as, for example, a PMT detector, an APD detector, a SiPM detector (Silicon Photomultiplier) or a photodiode.

17. Method according to any one of claims 1 to 16, wherein the ore stream is moved in the direction of motion (10) at a speed between 1 m / s and 5 m / s, preferably between 2 m / s and 4 m / s, wherein said exposure takes place over a distance (L) along said direction of motion (10) between 10 mm and 100 mm, for example between 10 mm and 50 mm.

18. Method according to any one of claims 1 to 17, wherein a grain (8) is identified as a spodumene-containing grain when, for a part of the surface area of the grain (8), the light intensity of said emitted light in said at least one wavelength band exceeds a predetermined reference value, wherein a spodumene value is assigned to the spodumene-containing grain, which spodumene value is associated with a proportion of the surface area of the image of said part of the spodumene-containing grain relative to the surface area of the image of the spodumene-containing grain, wherein the grain (8) is directed to a fraction rich in spodumene when said spodumene value exceeds a desired spodumene value and to a fraction poor in spodumene when this value does not exceed the desired value.

19. Sorting apparatus for separating an ore stream of a spodumene-containing granular ore into at least two fractions as a function of a measured spodumene content of the grains (8) in the ore stream,with an exposure zone (9) through which the ore stream moves in a direction of motion (10), wherein at least one light source (11) is provided which allows grains (8) of the ore stream to be exposed for an exposure time of at least 5 ms with light having a wavelength between 200 nm and 540 nm, with a detection device (5) for determining the light intensity of light emitted by the grains (8) in a wavelength band between 500 nm and 1000 nm, in particular between 500 nm and 800 nm, with a control unit (14) which is designed to generate a detection signal as a function of the magnitude of the determined light intensity of said emitted light in said at least one wavelength band, wherein a grain (8) is identified as a spodumenecontaining grain by the control unit (14) when this detection signal exceeds a reference value, wherein the control unit (14) controls a removal device (16) to direct spodumene-containing grains to one and the same fraction of said ore stream and to direct other grains to at least one other fraction.

20. Sorting apparatus according to claim 19, wherein said detection device (5) is sensitive to light in a wavelength band comprising 610 nm, wherein said wavelength band preferably has a minimum width of 50 nm.

21. Sorting apparatus according to claim 19 or 20, wherein the light source (11) generates light that strikes the grains (8) of the ore stream in at least one of the wavelength bands 200 nm-290 nm, 350 nm-370 nm, 395 nm-420 nm and / or 515 nm-540 nm.

22. Sorting apparatus according to any one of claimsl8 to 21, wherein the exposure time is at least 7 ms, and preferably at least 10 ms.

23. Sorting apparatus according to any one of claims 18 to 22, wherein the detection device (5) is configured to determine the light intensity of the emitted light at the end of the exposure time, no later than 5 ms after the end of the exposure.

24. Sorting apparatus according to any one of claims 18 to 23, wherein the light source (11) is designed to generate collimated light.

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