AU2010235964B2 - Mineral Separating Means - Google Patents

Abstract

The present invention relates to a mineral separating means adapted to detect desirable phosphorescent minerals such as opal in material which includes other phosphorescent matter. In its broadest form the arrangement includes a source of light to induce phosphorescence in the opal and the other phosphorescent matter which may be present, and a detection means adapted to detect such phosphorescence when the other phosphorescent matter is no longer significantly phosphorescing. There is a means to controllably direct the material such that matter which is identified as non-phosphorescing or not significantly phosphorescing is directed along a first path, and matter which is identified as phosphorescing is directed along a second path. This invention is useful because it has been found by experiment that the main minerals which phosphoresce have a much more rapid phosphorescent decay rate than opal potch.

Description

EDITORIAL NOTE APPLICATION NUMBER - 2010235964 This specification does not contain a page 1 2 Mineral separating means The present invention relates to a mineral separating means and in particular to an apparatus and method for the separation of opal from other materials. BACKGROUND OF THE INVENTION In a number of other previous patent applications the applicant has described various improved apparatus for the separation of opal from other materials. These improvements all relate to the fact that opal possesses a somewhat unique characteristic in that it absorbs electromagnetic radiation in the ultra-violet part of the spectrum that is then re-radiated as visible light at a wavelength typically around 470 nm. The half-life time of this re-radiation is some 4 seconds. The basic technique of thus detecting opal from other material, and which can be gleaned from the above identified patent applications, involves the removal of dust from the host material, typically sandstone, using either trommels or vibrating screens, grading the material into a range of stone sizes, and placing the stones on a moving wide flat conveyor belt contained in a light tight enclosure. At the start of the belt the material is irradiated with ultraviolet light after which the material moves to a darkened region where an array of optical fibres across the belt detects the resulting phosphorescence of the opal potch and transmits the light to an array of photomultiplier tubes. Subsequent electronics analyses the signal from the photomultipliers causing a deflection mechanism to remove the opal potch from the main stream of material. The opal potch remains in the light tight enclosure and the remaining material is extracted from the room via a moving conveyor through a light tight exit port. Such an apparatus has been found to be most effective eliminating the need for human operators to work in a dark room and remove the opal by hand. In addition the efficiency of this technique, called noodling, has been found to increase substantially. However, it has been discovered that many other minerals in addition to opal potch phosphoresce. For example some common materials found with opal that phosphoresce are Barite and Alunite. These minerals often occur in a quantity greatly exceeding the occurrence of opal potch and the resulting shunting or collection of material from the belt that their phosphorescence causes makes the quantity of separated material so large that economic operation is not possible.

3 The applicant has tried various solutions to the problem of separating phosphorescing materials from each other. Given that the phosphorescent colour of these materials is slightly different optical filters were tried as a means of separation. This however was not found to be practical since the optical emission bands of the various materials and opal overlapped. Although each posses a unique spectra, full spectral analysis is not possible due to the cost and low light level. Furthermore Alunite has a spectrum that is very similar to opal. Thus rejection using optical filters would have results in opal potch also being rejected. It is therefore an object of the present invention to overcome at least some of the above mentioned problems or provide for a useful alternative by providing an apparatus and method for the separation of opal potch from other material at least some of which is phosphorescing material. SUMMARY OF THE INVENTION It has been found by experiment that the main minerals that phosphoresce have a much more rapid phosphorescent decay rate than opal potch. Although this was based upon data from one opal field only there is no reason to suspect that this property is not common across most if not all opal fields. Experimentally, the decay time constant for opal is approximately 6 seconds and for the minerals Alunite and Barite it is approximately 2.5 seconds. These decay times are represented by I = I0 exp(-t / 6) and I = I. exp(-t / 2.5) respectively so the ratio R of opal brightness to mineral brightness as a function of time is R = exp(t / 2.5 - t / 6) = exp(2.3t). The ratio increases exponentially with time so although one time constant is only 2.4 times longer than the other the ratio of brightness is 10 after 10 seconds. Therefore in one form of the invention though this need not be the only or indeed the broadest form there is proposed an arrangement for detection of a phosphorescent mineral from material which includes other phosphorescent matter, said arrangement including: at least one source of light to induce phosphorescence in said phosphorescent mineral and said other phosphorescent matter; at least one detection means adapted to detect such phosphorescence when said other phosphorescent matter is no longer significantly phosphorescing; and a means to controllably direct said material such that matter which is identified as non- 4 phosphorescing or not significantly phosphorescing is directed along a first path, and matter which is identified as phosphorescing is directed along a second path. Preferably said means to controllably direct said material includes a flipper mechanism operative in response to a control means, said flipper mechanism being movable between a first position directing matter along said first path, and a second position directing matter along said second path. In preference said arrangement further includes transport means adapted to transport said material to said flipper mechanism, said transport means including a sensor capable of measuring the speed of the transport means. In preference the control means operate in connection with the means to controllably direct the matter, the detection means and the sensor means to thereby select a speed and trajectory for the phosphorescent matter. Preferably said source of light is one or more lamps which emit ultraviolet radiation onto said material. In preference said detection means detects the amount of light emitted from the material that has been subjected to ultraviolet radiation. In preference the phosphorescent decay time of said phosphorescent mineral is greater than that of said other phosphorescent matter. Preferably said phosphorescent mineral is opal, and said other phosphorescent matter includes Alunite and/or Barite. Preferably the position of said flipper mechanism is changed using an air solenoid controlled by said control means. In preference said assembly further includes a plurality of said flippers. Advantageously said transport means is a conveyor belt. In a further form of the invention there is proposed an arrangement for detection of opal in material including: a sorting means having a first ultraviolet source of light to induce phosphorescence of opal and other phosphorescing matter in said material, a detection means adapted to detect such phosphorescence, and a shunting means adapted to shunt such detected phosphorescing material away from non-phosphorescing material; and 5 a transport means adapted to transport said material so that it is subjected to the ultraviolet source of light, then the detection means, and then the shunting means, said transport means configured to move at a speed which ensures that detection of phosphorescence takes place when said other phosphorescing matter is no longer significantly phosphorescing. In a still further form of the invention there is proposed an arrangement for detection of opal in material including: a sorting means having a first ultraviolet source of light to induce phosphorescence of opal and other phosphorescing matter in said material, a detection means adapted to detect such phosphorescence, and a shunting means adapted to shunt such detected phosphorescing material away from non-phosphorescing material; and a transport means adapted to transport said material so that it is subjected to the ultraviolet source of light and then the detection means, which are spaced apart enough to ensure that detection of phosphorescence takes place when said other phosphorescing matter is no longer significantly phosphorescing. In a yet further form of the invention there is proposed an arrangement for detection of opal in material including: a first sorting means having a first ultraviolet source of light to induce phosphorescence of opal and other phosphorescing matter in said material, a first detection means adapted to detect such phosphorescence, and a first shunting means adapted to shunt such detected phosphorescing material away from non-phosphorescing material onto a second sorting means, said second sorting means having a second detection means adapted to detect such phosphorescence and having a second shunting means adapted to shunt such phosphorescing material away from other material that is no longer significantly phosphorescing. Preferably said first sorting means includes a conveyor belt for transporting said material such that it is first subjected to the ultraviolet source of light, then the first detection means, and then the first shunting means. In preference said second sorting means includes a conveyor belt for transporting phosphorescing material which has been shunted from the first conveyor belt, so that it is subjected to the second detection means, and then the second shunting means. Alternatively said second sorting means includes a rotating table adapted to receive phosphorescing material which has been shunted from the first conveyor belt, and rotating said 6 material so that it is sequentially subjected to the second detection means and second shunting means. Advantageously said second sorting means includes a second ultraviolet source of light. BRIEF DESCRIPTION OF THE DRAWINGS The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate several implementations of the invention that together with the description serve to explain the advantages and principles of the invention. In the drawings, Figure 1 is a time plot diagram of the phosphorescent intensity of opal (series 2) and the minerals Alunite or Barite (series 1) after initial illumination with ultraviolet light; and Figure 2 is a schematic diagram illustrating the operation of an apparatus embodying the present invention. DESCRIPTION OF THE PREFERRED EMBODIMENTS The following detailed description of the invention refers to the accompanying drawings. Although the description includes exemplary embodiments, other embodiments are possible, and changes may be made to the embodiments described without departing from the spirit and scope of the invention. Wherever possible, the same reference numbers will be used throughout the drawings and the following description to refer to the same and like parts. Figure shows the phosphorescent intensity of opal (series 2) and the minerals Alunite or Barite (series 1) after initial illumination with Ultraviolet light. Both the opal and the mineral are assumed to have the same brightness initially with the brightness of the opal decreasing to one fifth after 10 seconds. However the opal is some 10 times brighter than the minerals so with a sufficiently sensitive optical sensing system small opal stones can be distinguished from even larger mineral stones. The ratio of the brightness is depicted as series 3 in Figure 1. Since the stones are typically graded in size on the conveyor belt this leads to efficient separation for there are no issues of a bigger mineral being brighter just because of its size. There are several embodiments of an apparatus that can lead to efficient separation of the opal potch from other matter including phosphorescing minerals once it is understood that the brightness of similar size material decays at a different rate. These are: 7 (a) Ensuring that the time between irradiation of the material with ultraviolet light to detection of the phosphorescing is of the order of some 10 seconds (b) Making the conveying belt considerably longer than current apparatus (c) Having a two-stage separation process, where the two-stage process would firstly remove most phosphorescing material, and then given that more time has elapsed, the second stage would remove or shunt mainly opal material. We deal with each embodiment in term. Slowing the belt down has been found to operate well. However, given that one needs to ensure that opal potch is not buried the total amount of material put through must be reduced. As such this embodiment is probably the least satisfactory of the three for it leads to less production, but in certain situation, such as shunting already separated opal potch and minerals may work adequately well. The second embodiment of greatly extending the length of the belt means that the total throughput of material does not decrease. This solution of a long conveyor belt leads to the material being thinly spread on the belt and provides results in a long delay time from illumination with ultraviolet light. In the apparatus that has been identified earlier, the typical belt is of the order of some 7 meters long. Moving at a speed of just under 1 meter per second, this provides a time delay of some 7-9 seconds between illumination with ultraviolet light and detection of re-radiated visible light using photomultipliers. In instances where the belt can move faster or the degree of contaminating (phosphorescing) minerals is not great, the ultraviolet source may be movable so as to position it at the most appropriate location to control the delay time between irradiation and detection. The third embodiment includes separating the material using two separating systems. The first separating system operates in the manner as described in the above-identified patent applications. However, instead of the shunted or collected material then deposited into a bin, it is actually shunted onto a second conveyor belt that need be much smaller than the first. This is illustrated in Figure 2 and will now be discussed. There is shown an opal sorting table 10 including a frame 12 and supporting legs 14 having feet 16 which help to distribute the weight of the table 10 on a floor. Although not shown, the table may also include support beams extending between each adjacent leg.

8 A first conveyor belt 18 extends along the table 10 and is supported by rollers 20 and 22 at either end, one of the rollers coupled to and rotatably driven by a motor (not shown) to drive the belt. Typically the motor is a hydraulic motor although it may equally well be an electric motor. Located above and extending perpendicularly above one end of the belt 18 is a longitudinal hopper 24 that is loaded with material 26 to be sorted. A third roller 28 extends longitudinally with the hopper 24 and is in contact with the material 26. A gap 30 in between the roller 28 and the hopper 24 allows material to pass from the hopper and drop onto the belt 18. By controlling the speed of the roller the operator is able to control the rate of material that drops onto the belt 18. As with the conveyor belt 18, the roller 28 is driven by a suitable motor. The speed of the conveyor belt is limited to the flippers as discussed below. The material that passes through the gap 30 and drops into belt 18 is exposed to ultraviolet radiation by the use of longitudinal lamps 32 located above the belt 18. A shield 34 extends over the lamps to minimise the amount of radiation that is scattered outside of the shielded area, the lamps 32 and the shield 34 held in place by the use of arms (not shown) attached to the frame 12. Any phosphorescent material then absorbs the ultraviolet radiation and re-radiates it in the visible part of the spectrum. Located above and towards the other end of the belt 18 are optical sensing devices extending longitudinally across the belt. The devices typically include optical detectors 36 that collect radiated light and feed it into an optical to electrical signal converter, such as a photomultiplier tube 38. The optical sensing device is in fact an optical fibre cable. Any detected signal from the photomultiplier 38 is assessed by a suitable control device 40, supplied power from source 42 that is operatively connected to a mechanical flipper or shunter 44 by control cable 46. To avoid contaminating light from being detected by the photomultipliers, a shield 48 is used to cover the optical componentry that extends into the shield 48. The optical componentry, typically the ends of the optical fibres are housed in cover 50 having a transparent glass or plastic window 52 that protects the detector 36 from any dust or unwanted material and is typically adapted to be easily removable for cleaning. The window 52 may also include filters adapted to filter out the ultraviolet light that is used to excite the opal in the first instance. It is obviously quite integral to the operation of the whole of the table 10 that the light that is sensed reaching each optical detector 36 be localised to allow for the fine control of each 9 flipper. For that reason inside the shield 48 that extend towards the centre of the belt 18 are curtains 54 and 56 that further ensure that no light reaches the optical detector 36. Although the curtains are designed to extend downwardly they are very light and can easily be swayed to ensure that they do not cause material to be held back on the belt. The curtains are typically constructed of two layers of material, the first layer being of a resiliently flexible material to provide the strength of the curtain, the second layer providing for the required absorption characteristics. At times up to four curtains may be used to cut out intrusive light. Each optical sensing device includes its own photomultiplier tube that in turn controls its own mechanical flipper. The photomultiplier tubes may be separately cooled to improve their sensitivity. Furthermore, the use of the optical fibre cable allows them to be separated from the rest of the table 10 thereby removing any unwanted vibrations. Typically there are some 20 flippers extending below the and across the front of the belt 18 each one shunting material of different sizes. The flippers are adjacent to each other so that there is a minute gap there in-between, typically the order of 1-2 millimetres. The flippers are designed to very quickly pivot around pivot point 58. Their position is chosen so that when the flipper has not been activated material transported on belt 18 is cause to fall in trajectory 60 whilst when the flipper has been activated it rotates inwardly and upwardly to deflect material into trajectory path 62. Thus material 10 is deposited onto the first conveyor belt 18 at the beginning of which it is irradiated with ultraviolet light through use of lamps 32 shielded by shield 32. The material is then transported at speed passing under shield 48 where the phosphorescence is detected with detectors 36. The signal is collected and amplified by the photomultiplier tube before it is fed into the control device 40. The device is semi-intelligent and can calculate, based upon the speed of the belt that it typically measures by the use of appropriate sensors or timing pulse 63, precisely when it needs to activate the shunter 44 to cause that material that the optical detector 36 has detected to radiate visible light, to be ejected onto a second conveyor 64. Each flipper 44 is activated by the use of an air solenoid 66 which is fed air by the use of hoses 68 and 70 that control the air solenoid to extend and retract as desirable. An air supply is provided through regulator 72 as is well known in the art. Those skilled in the art will appreciate that with a row of flippers 44 extending across the belt 18, different flippers will be caused to operate to ensure that any detected material is ejected onto the second conveyor belt 64. Other material that is non-radiating then drops into a further 10 conveyor belt 74 to be transported away from the table, typically to an area that is some distance away. Alternatively, the inert material may simply fall into a bin (not shown) to be disposed of in a suitable manner. The shunting process typically occurs less than once per second on average so that shunted material which is deposited onto the second belt 64 is widely spaced. The second conveyor belt 64 is configured similarly to the first and includes a second set of ultraviolet lamps 76, which are also shielded with shield 78, and a second optical detecting means 80 which is shielded by shield 82. Located at the end of the conveyor is a single shunt 84. It is to be understood that these parts are similar to those which have been described above and so their working will not be described again in detail. When the light emitting material drops onto the second conveyor belt 64, it passes under the second set of ultraviolet lamps 76. Again, any phosphorescent material absorbs the ultraviolet radiation and re-radiates it in the visible part of the spectrum. Given that the majority of material conveyed on the second conveyor belt 64 is widely spaced, it can be moved at a much slower rate so that the delay time between radiation and eventual detection by the optical detectors 80 on this belt is between 8 to 9 seconds. Those skilled in the art would realise that in prolonging the delay time in this way, opal potch can be distinguished from other phosphorescent material on the belt which has a more rapid phosphorescent decay rate. Thus the use of a second ultraviolet source to excite the spaced shunted material and the associated time delay ensures that only opal potch will be detected by the detector 80. As mentioned, there is only one shunt 84 on this belt 64 because the material is widely spaced on the belt and therefore only single stones are selected. The opal potch 86 is then collected in a secure bin 88 whilst non-opal material 90 is again either transported away using a further belt 92 or disposed of in a suitable manner. Although not shown, it is to be understood that detectors 80 and shunter 84 of the second conveyor belt may be controlled using the same control device as the first conveyor belt 18 whereby when opal potch is detected, the shunter 84 is activated and moves to a position to direct the material into bin 64. Of course, the second conveyor belt could include its own means for controlling the shunt 84 according to the material that is detected. The reader will therefore appreciate that the above twin separation system provides for an opal detecting apparatus and method that is a great improvement on the current state of the art. By effectively double selecting any opal and moving it slowly enough so that other 11 phosphorescent material is rejected, the collected opal is generally free from being contaminated with other minerals. An alternative system for the second sorting process, although not shown, is to use a rotating table. In this case material from the first belt is directed onto the perimeter of a slowly rotating table (say one revolution every 14 seconds). The material is illuminated by ultraviolet light as it is placed on the table and continues to be carried around in the dark as the table rotates. At a later time of about 8 to 9 seconds the fluorescence is detected and the material is shunted off the table. The remaining material is shunted a little later onto a slide or conveyor and added to the reject material from the first table or conveyor belt. This system results in a compact system situated below the main conveyor belt. The result of either of these systems is that mainly opal potch is recovered ready to be hand sorted. The removal of the large quantity of additional material (up to five hundred time more than the amount of opal) at the mining site rather than by hand at a later time means that the automatic sorting of opal potch from the host material is an economic mining procedure. It is to be understood that the main advantage of the present system is that it is a two stage detection process. In the first stage generally any phosphorescing material is collected and removed from inert material. The collected material is then placed onto a second sorting system. The second sorting system need only have a second detection and shunting means. Although preferably it also includes a second source of ultraviolet light, under some circumstances the second light source may not be necessary if the material reaches the detectors quickly enough. Thus in operation it may be that the first belt sorting takes some 4 seconds, and that the material then travels along the second belt over another 4-5 seconds. During this time the brightness of non-opal phosphorescing material would have effectively reduced to zero. Further advantages and improvements may very well be made to the present invention without deviating from its scope. Although the invention has been shown and described in what is conceived to be the most practical and preferred embodiment, it is recognized that departures may be made therefrom within the scope and spirit of the invention, which is not to be limited to the details disclosed herein but is to be accorded the full scope of the claims so as to embrace any and all equivalent devices and apparatus.

12 Opdetech Pty Ltd By their Patent Attorneys LESICAR PERRIN

Claims (11)

1. An arrangement for detection of opal in material including: a first sorting means having a first ultraviolet source of light to induce phosphorescence of opal and other phosphorescing matter in said material, a first detection means adapted to detect such phosphorescence, and a first shunting means adapted to shunt such detected phosphorescing material away from non-phosphorescing material onto a second sorting means, said second sorting means having a second detection means adapted to detect such phosphorescence and having a second shunting means adapted to shunt such phosphorescing material away from other material that is no longer significantly phosphorescing.

2. An arrangement as in claim 1 wherein said first sorting means includes a conveyor belt for transporting said material such that it is first subjected to the ultraviolet source of light, then the first detection means, and then the first shunting means.

3. An arrangement as in claim 1 or 2 wherein said second sorting means includes a conveyor belt for transporting phosphorescing material which has been shunted from the first conveyor belt, so that it is subjected to the second detection means, and then the second shunting means.

4. An arrangement as in 1 or 2 wherein said second sorting means includes a rotating table adapted to receive phosphorescing material which has been shunted from the first conveyor belt, and rotating said material so that it is sequentially subjected to the second detection means and second shunting means.

5. An arrangement as in any one of the above claims wherein said second sorting means includes a second ultraviolet source of light.

6. An arrangement as in claim I wherein each said shunting means to controllably direct said material includes a flipper mechanism operative in response to a control means, said flipper mechanism being movable between a first position directing matter along said first path, and a second position directing matter along said second path.

7. An arrangement as in claim 1 wherein said arrangement further includes transport means adapted to transport said material to said flipper mechanism, said transport means including a sensor capable of measuring the speed of the transport means. 13

8. An arrangement as in any one of the above claims wherein the phosphorescent decay time of said phosphorescent mineral is greater than that of said other phosphorescent matter.

9. An arrangement as in any one of the above claims wherein said phosphorescent mineral is opal, and said other phosphorescent matter includes Alunite and/or Barite.

10. An arrangement as in claim 6 wherein the position of said flipper mechanism is changed using an air solenoid controlled by said control means.

11. An arrangement as in claim 6 wherein said assembly further includes a plurality of said flippers. 14 THIS PAGE IS INTENTIONALLY LEFT BLANK 15