Processing crushed ore

Abstract

Method of processing crushed ore to separate ore having a high gangue concentration from ore having a high valuable mineral concentration. The method comprises classifying 40 the crushed ore into at l

Description

04 04 25 PROCESSING CRUSHED ORE FIELD OF INVENTION The invention relates to improvements in or relating to processing crushed ore, and particularly to separation of ore having a high gangue concentration from ore having a high valuable mineral concentration using dry separation. One particular application relates to pre-sorting crushed ore particles based on the concentration of valuable mineral contained in each particle to avoid having to process ore having a low concentration of valuable mineral. BACKGROUND OF THE INVENTION Mined ore, also known as run-of-mine (“ROM”) ore, is conveyed to a mineral processing plant (also called a “mill” or “concentrator”) to extract valuable minerals (such as metals) from the waste material in the ore (referred to as gangue). Processing ROM ore involves reducing its size (comminution) and then mineral recovery (for example, using flotation or leaching) and waste disposal (for example, to a tailings storage facility). Processing ROM ore is very expensive, and much of the ore processed is actually waste (gangue). There is no economic or environmental benefit in processing gangue. It would be advantageous if gangue could be rejected early in the processing stage to avoid wasting energy on processing such gangue. It is among the objects of an embodiment of the present invention to overcome or mitigate one or more of the above disadvantages or other disadvantages of the prior art, or to provide a useful alternative. SUMMARY OF THE INVENTION This summary is provided to introduce a selection of concepts that are further described in the detailed description below. This summary is not intended to identify indispensable features of the claimed subject matter, nor is it intended for use as an aid in limiting the scope of the claimed subject matter. In this application relative terms are used, such as front, rear, up, down, etc., only for ease of the description and understanding of the embodiments, not by way of limitation. Ordinal numbers (first, second, third, etc.) are assigned arbitrarily herein, and are used to differentiate between parts, and do not indicate a particular order, sequence or importance. According to a first aspect there is provided a method of processing crushed ore to separate ore having a high gangue concentration from ore having a high valuable mineral concentration, where the mineral has a first density and the gangue has a second density, significantly different from the first density, the method comprising: (i) classifying the crushed ore into at least two dry streams, (a) a large particle dry stream consisting essentially of particles larger than a defined size and (b) a small particle dry stream consisting essentially of particles smaller than a defined size; (ii) routing the small particle 04 04 25 dry stream through a first air classifier configured to split the small particle dry stream based on weight so that heavier particles are routed through to a first processing stream, and lighter particles are diverted to a second processing stream; (iii) routing the processing stream from step (ii) that most closely matches the first density to a mineral extraction 5 stage, (iv) routing the other processing stream from step (ii) to tailings; (v) routing the large particle dry stream from step (i) to a second air classifier configured to split the large particle dry stream based on weight so that heavier particles are routed through to a third processing stream, and lighter particles are diverted to a fourth processing stream; and (vi) routing the processing stream from step (v) that most closely matches the first density to a 10 comminution stage then the classifying stage of step (i), and routing the other processing stream from step (v) to tailings; thereby pre-sorting both the small and large particle dry streams based on particle density to reduce the amount of gangue that has to be crushed or otherwise processed. Optionally, the first density is different from the second density by at least 1 gem’3. 15 Optionally, the particles in the large particle dry stream have a dso of at least 1mm. Optionally, the particles in the small particle dry stream have a dso of less than 1mm. Optionally, the first air classifier comprises a static air classifier. Alternatively, or additionally, the first air classifier comprises a dynamic air classifier. Optionally, the second air classifier comprises a static air classifier. Alternatively, or 20 additionally, the second air classifier comprises a dynamic air classifier. Optionally, the large particle stream is comminuted (for example, crushed, milled or ground) to reduce its size. Optionally, the large particle stream is classified to create a dry stream within a narrow size range (for example, having a d8o between 2mm and 5mm). The method may further 25 comprise (i) routing the narrow size range dry particle stream through a further air classifier configured to split the particle stream based on weight so that heavier particles are routed through to a fifth processing stream, and lighter particles are diverted to a sixth processing stream; and (ii) routing the processing stream (fifth or sixth) that most closely matches the first density to a mineral extraction stage, and routing the other processing stream to tailings; 30 thereby pre-sorting the narrow size range dry particle stream to reduce the amount of gangue that has to be crushed or otherwise processed. Suitable minerals may include: iron ore, chromite (chromium ore), and lithium. It will now be appreciated that this aspect has the advantage of being able to separate small particles by density (or weight) and thereby avoid having to process particles that are 35 solely, or almost entirely, gangue. By constraining a stream of dry particles within a relatively small size envelope it is possible to distinguish between an ore particle having a high gangue concentration and an LD CM 04 04 25 ore particle having a high valuable mineral concentration based on the weight of the ore particle. According to a second aspect there is provided apparatus for processing crushed ore having a high gangue concentration from ore having a high valuable mineral concentration, where the mineral has a first density and the gangue has a second density, significantly different from the first density, the apparatus comprising: (i) a first classifier for classifying the crushed ore into at least two dry streams, (a) a large particle dry stream consisting essentially of particles larger than a defined size and (b) a small particle dry stream consisting essentially of particles smaller than a defined size; (ii) a first air classifier configured to split the small particle dry stream based on weight so that heavier particles are routed through to a first processing stream, and lighter particles are diverted to a second processing stream; and (iii) a first transporter for routing the processing stream from the first air classifier that most closely matches the first density to a mineral extraction stage; (iv) a second transporter for routing the other processing stream from the first air classifier to tailings; (v) a second air classifier configured to split the large particle dry stream from the first classifier based on weight so that heavier particles are routed through to a third processing stream, and lighter particles are diverted to a fourth processing stream; (vi) a third transporter for routing the processing stream from the second air classifier that most closely matches the first density to a comminution stage then to the first classifier; and (vii) a fourth transporter for routing the other processing stream from the second air classifier to tailings, thereby pre-sorting both the small and large particle dry streams based on particle density to reduce the amount of gangue that has to be crushed or otherwise processed. Optionally, the first classifier comprises a screen (such as a vibrating screen). Using a screen allows the crushed ore to be handled without adding any water. Alternatively, but less preferred, the first classifier may comprise a hydrocyclone. Optionally, the first transporter may include a conveyor, a hopper, or the like. Optionally, the second transporter may include a conveyor, a hopper, or the like. According to an unclaimed aspect there is provided a method of ore sorting to reject ore having a high gangue concentration at an early stage, the method comprising: producing a small dry particle stream, splitting the small dry particle stream, using air separation based on weight, so that heavier particles are routed through to a first processing stream, and lighter particles are diverted to a second processing stream; routing the processing stream that most closely matches the valuable mineral density to a mineral extraction stage, and routing the other processing stream to tailings. According to an unclaimed aspect there is provided a method comprising: (i) classifying crushed ore into at least two dry streams, (a) a large particle dry stream consisting essentially of particles larger than a defined size and (b) a small particle dry stream consisting essentially of particles smaller than a defined size; (ii) routing the small particle dry stream 5 through a first air classifier configured to split the particle stream based on weight so that heavier particles are routed through to a first processing stream, and lighter particles are diverted to a second processing stream; (iii) routing the processing stream that most closely matches a LD CM desired valuable mineral density to a mineral extraction stage, and (iv) routing the other processing stream to tailings. The step of (or apparatus for) classifying crushed ore into at least two dry streams according to any of the above aspects may comprise a large particle dry stream consisting essentially of particles with a first size range, and (b) a small particle dry stream consisting essentially of particles with a second size range, where the upper size of the second size range is smaller than the lower size of the first size range. The first size range may be between 2mm and 5mm, or between 2.5mm and 4.5mm, or between 3mm and 4mm. The second size range may be between 0.5mm and 1.5mm, or between 0.8mm and 1.2mm, or between 0.9mm and 1.1mm. BRIEF DESCRIPTION OF THE DRAWINGS These and other aspects of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which: Fig. 1 is a simplified schematic diagram of a mineral processing operation including apparatus for processing crushed ore in accordance with one embodiment of the present invention; Fig. 2 is a simplified schematic diagram of a mineral processing operation including apparatus for processing crushed ore in accordance with another embodiment of the present invention; and Fig. 3 is a flowchart illustrating a generalised method of processing crushed ore according to an embodiment of the present invention. DETAILED DESCRIPTION OF EMBODIMENTS Reference is now made to the drawings, and particularly to Fig. 1, which is a simplified schematic diagram of a mineral processing operation 10 including apparatus 12 for processing crushed ore in accordance with one embodiment of the present invention. The ore processing apparatus 12 is suitable for use with valuable mineral that has a significantly lower density than the gangue surrounding the valuable mineral. This means that for a given ore particle size, the lighter the particle the more valuable mineral it contains, and the heavier the particle the more gangue it contains. In this embodiment, the valuable mineral comprises lithium (having a density of approximately 0.53 gem-3), and the gangue comprises pegmatite (having a density of approximately 2.7 gem-3). As a result, for particles of approximately the same size, lighter particles will contain more lithium (the valuable mineral) and heavier particles will contain more pegmatite (the gangue), which allows sorting and segregation of the crushed ore based on valuable mineral concentration as inferred from the weight of the crushed ore particles. Run-of-mine (ROM) ore 14 is shown in Fig. 1 as a stockpile, but it may be provided in any desired form, for example, on a conveyor belt, from a load haul dump (LHD) truck, or a hopper or in any other convenient manner. The ROM ore 14 is fed (for example, via a hopper or conveyor (or both) 15) into a comminution stage 16 comprising one or more dry comminution devices (i.e. a comminution device that does not require the addition of any water, or only minimal water). In this embodiment, the comminution stage 16 comprises a primary crusher, a secondary crusher, and a dry tertiary crusher, if desired. Such comminution devices are well known. The output from the comminution stage 16 is relatively small, for example, having a Pso below 6mm. The output from the comminution stage 16 is fed into the ore processing apparatus 12 in any convenient manner, for example, via a conveyor 18, a hopper, or the like. The ore processing apparatus 12 has three outputs 20, 22, 24. The first output (mineral recovery output) 20 is a feed to a mineral recovery (or extraction) operation 30 where the valuable mineral is liberated from the remaining gangue around it using conventional techniques, for example by flotation, leaching, or the like. The second output (tailings output) 22 is a feed to a tailings processing facility 32. The tailings processing facility 32 may comprise a tailings storage facility (“TSF”) or alternatively (or additionally) it may comprise equipment (a pump, thickeners, transport trucks, conveyors, or the like) for transporting the high gangue concentration ore to a TSF. The third output (regrind output) 24 is a feed that routes the crushed ore back to the comminution stage 16 for further size reduction. The ore processing apparatus 12 comprises an initial classification stage 40, which in this embodiment comprises a vibrating screen. The initial classification stage 40 has two outputs: a small particle output 42, and a large particle output 44. These outputs 42, 44 comprise conveyors in this embodiment, but other transportation mechanisms are possible. Those particles that passed through the apertures in the vibrating screen 40 are directed to the small particle output 42; whereas, those particles that did not pass through the apertures in the vibrating screen 40 are directed to the large particle stream 44. The small particle output 42 feeds a first static dry classifier 50. The static classifier 50 includes an air input 52, and it acts by passing an air flow across a stream of falling particles in-between a cascading track of louver plates 54, thereby blowing the light particles out of the falling stream and through a light particle exit 56 at an upper portion of the classifier 50 to a collector 58 (for example, a dust cyclone and bag house). The light particles from the collector 58 are fed onto the mineral recovery output 20 and from there they are delivered to the mineral recovery operation 30. The heavier particles are discharged through a heavy particle exit 60 at the bottom of the classifier 50. By variation of air flow and angle of inclination of the louver plates 54, different separation cut sizes can be obtained, generally varying between 80 and 1,500 pm. The heavier particles are then discharged onto the tailings output 22. The particles on the large particle stream 44 (i.e. those particles that did not pass through the apertures in the vibrating screen 40) are sent to a second static dry classifier 70. The second static dry classifier 70 operates in a similar way to the first static dry classifier 50 in that the lighter particles are blown out (by air input 72) of the falling stream and through a light particle exit 76 to a collector (not shown) and then back to the comminution stage 16 (for example, a tertiary crusher or grinder) for further size reduction, via the regrind output 24. The heavier particles are diverted through a heavy particle exit 80 at the bottom of the classifier 70. The heavier particles are then discharged onto the tailings output 22. It should now be appreciated that this embodiment has the advantage that it is possible to separate and remove heavier particles (having a high gangue concentration) without requiring any wet comminution on such particles, or any further mineral extraction processing. This reduces the energy involved in recovering the valuable mineral and uses less water. Reference is now made to Fig. 2, which is a simplified schematic diagram of a mineral processing operation 110 including apparatus 112 for processing crushed ore in accordance with another embodiment of the present invention. Whereas in the first embodiment, the ore processing apparatus 12 is suitable for use with valuable mineral that has a significantly lower density than the gangue surrounding the valuable mineral. In this embodiment, the ore processing apparatus 112 is suitable for use with valuable mineral that has a significantly higher density than the gangue surrounding the valuable mineral. In this embodiment, the valuable mineral comprises iron (having a density of approximately 7.8 gem-3), and the gangue comprises banded iron formations (having an average density of approximately 3.5 gem’3). As a result, for particles of approximately the same size, heavier particles will contain more iron (the valuable mineral) and lighter particles will contain more banded iron formations (the gangue), which allows sorting and segregation of the crushed ore based on valuable mineral concentration. The primary differences between the ore processing apparatus 12 and the ore processing apparatus 112 are that the light particles in the ore processing apparatus 112 are diverted to tailings and the heavy particles are sent to mineral extraction; whereas, in the ore processing apparatus 12, the light particles are diverted to mineral extraction and the heavy particles are sent to tailings. In the ore processing apparatus 112, the heavier particles in the first dry static classifier 50 are routed to the mineral recovery output 20 and then delivered to the mineral recovery operation 30. The heavier particles in the second dry static classifier 70 are routed to the regrind output 24 and then delivered to the comminution stage 16. In contrast, the lighter particles in the first dry static classifier 50 are routed to the tailings output 22 and then delivered to the tailings processing facility 32. Similarly, the lighter particles in the second dry static classifier 70 are also routed to the tailings output 22 and then delivered to the tailings processing facility 32. Fig. 3 is a flowchart 200 illustrating a generalised method of processing crushed ore according to an embodiment of the present invention. In this embodiment, the valuable mineral has a first density and the gangue has a second density, significantly different (in this embodiment more than 0.8 gem-3)from the first density. The first step (initial classifying 202) is classifying the crushed ore into at least two dry streams, (a) a large particle dry stream consisting essentially of particles larger than a defined size (in this embodiment above 1mm) and (b) a small particle dry stream consisting essentially of particles smaller than a defined size (in this embodiment equal to or smaller than 1mm). The small particle stream may comprise a size envelope between 0.5mm and 1mm. The second step (first dry classifying 204) is splitting the small particle stream based on weight. The next step is routing the heavier particles through to a first processing stream (heavy particle routing 206), and routing the lighter particles to a second processing stream (light particle routing 208). In preferred embodiments, the heavy particle routing 206 and the light particle routing 208 steps are performed simultaneously, but this is not essential. The next step is the density matching step (210) in which the processing stream that most closely matches the first density is routed to a mineral extraction stage (step 212 or step 222), and routing the other processing stream (that does not match the first density) to tailings (step 214 or step 220). Various modifications may be made to the above embodiments within the scope of the present invention. For example, in other embodiments, a different or additional dry classifier may be used, for example, a dynamic classifier. It will be appreciated that these embodiments may be used with other types of valuable minerals, such as gold, copper, platinum, chromite, and the like. In the foregoing description of certain embodiments, specific terminology has been used for the sake of clarity. However, the disclosure is not intended to be limited to the specific terms so selected, and it is to be understood that each specific term includes other technical equivalents which operate in a similar manner to accomplish a similar technical purpose. Terms such as "upper" and "lower", "above" and "below" and the like are used as words of convenience to provide reference points and are not to be construed as limiting terms, nor to imply a required orientation of the seal assembly. The word “or" is used to indicate that one or more of the words listed may be present, unless the context requires the disjunctive use. In this specification, the word “comprising” is to be understood in its “open” sense, that is, in the sense of “including”, and thus not limited to its “closed” sense, that is the sense of “consisting only of’. A corresponding meaning is to be attributed to the corresponding words “comprise", "comprised" and "comprises" where they appear. The preceding description is provided in relation to several embodiments which may share common characteristics and features. It is to be understood that one or more features of any one embodiment may be combined with one or more features of the other embodiments. In addition, any single feature or combination of features in any of the embodiments may constitute additional embodiments. In addition, the foregoing describes only some embodiments of the inventions, and alterations, modifications, additions and / or changes can be made thereto without departing from the scope of the disclosed embodiments, the embodiments being illustrative and not restrictive. List of reference numerals: Mineral processing operation 10, 110 Ore processing apparatus 12, 112 Run-of-mine (ROM) ore 14 Hopper or conveyor 15 Comminution stage 16 Conveyor 18 First (mineral recovery) output 20 Second (tailings) output) 22 Third (regrind) output 24 Mineral recovery operation 30 Tailings processing facility 32 Initial classification stage (e.g. vibrating screen) 40 Small particle output (of initial classification stage) 42 Large particle output (of initial classification stage) 44 First static dry classifier 50 Air input 52 Louver plates 54 Light particle exit 56 Collector 58 Heavy particle exit 60 Second static dry classifier 70. 5 Air input 72 Light particle exit 76

Claims

04 04 251. A method of processing crushed ore having a high gangue concentration from ore having a high valuable mineral concentration, where the mineral has a first density and the gangue has a second density, significantly different from the first density, the method 5 comprising:(i) classifying the crushed ore into at least two dry streams, (a) a large particle dry stream consisting essentially of particles larger than a defined size and (b) a small particle dry stream consisting essentially of particles smaller than a defined size;10 (ii) routing the small particle dry stream through a first air classifier configuredto split the small particle dry stream based on weight so that heavier particles are routed through to a first processing stream, and lighter particles are diverted to a second processing stream;(iii) routing the processing stream from step (ii) that most closely matches the 15 first density to a mineral extraction stage,(iv) routing the other processing stream from step (ii) to tailings;(v) routing the large particle dry stream from step (i) to a second air classifier configured to split the large particle dry stream based on weight so that heavier particles are routed through to a third processing stream, and lighter 20 particles are diverted to a fourth processing stream; and(vi) routing the processing stream from step (v) that most closely matches the first density to a comminution stage then the classifying stage of step (i), and routing the other processing stream from step (v) to tailings;thereby pre-sorting both the small and large particle dry streams based on 25 particle density to reduce the amount of gangue that has to be crushed orotherwise processed.

2. The method according to claim 1, wherein the first density is different from the second density by at least 0.7 gem’3.

3. The method according to claim 1, wherein, the first density is different from 30 the second density by at least 1 gem-3.

4. The method according to any preceding claim, wherein the particles in the large particle dry stream have a dso of at least 1mm.

5. The method according to any preceding claim, wherein the particles in the small particle dry stream have a dso of less than 1mm.04 04 256. The method according to any preceding claim, wherein routing the small particle dry stream through a first air classifier comprises routing the small particle dry stream through a static air classifier.

7. The method according to any of claims 1 to 5, wherein routing the small 5 particle dry stream through a first air classifier comprises routing the small particle dry stream through a dynamic air classifier.

8. Apparatus for processing crushed ore to separate ore having a high gangue concentration from ore having a high valuable mineral concentration, where the mineral has a first density and the gangue has a second density, significantly different from the first 10 density, the apparatus comprising:(i) a first classifier for classifying the crushed ore into at least two dry streams, (a) a large particle dry stream consisting essentially of particles larger than a defined size and (b) a small particle dry stream consisting essentially of particles smaller than a defined size;15 (ii) a first air classifier configured to split the small particle dry stream based onweight so that heavier particles are routed through to a first processing stream, and lighter particles are diverted to a second processing stream;(iii) a first transporter for routing the processing stream from the first air classifier that most closely matches the first density to a mineral extraction stage, and20 (iv) a second transporter for routing the other processing stream from the firstair classifier to tailings;(v) a second air classifier configured to split the large particle dry stream from the first classifier based on weight so that heavier particles are routed through to a third processing stream, and lighter particles are diverted to a 25 fourth processing stream; and(vi) a third transporter for routing the processing stream from the second air classifier that most closely matches the first density to a comminution stage then to the first classifier; and(vii) a fourth transporter for routing the other processing stream from the second 30 air classifier to tailings;thereby pre-sorting both the small and large particle dry streams based on particle density to reduce the amount of gangue that has to be crushed or otherwise processed.

9. Apparatus according to claim 8, wherein the first classifier comprises a screen.

10. Apparatus according to claim 8 or 9, wherein the first transporter includes a conveyor or a hopper.

11. Apparatus according to any of claims 8 to 10, wherein the second transporter includes a conveyor or a hopper.5 12. Apparatus according to any of claims 8 to 11, wherein the first air classifiercomprises a static air classifier.LDCM

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