Comminution and ore processing

Abstract

A circuit for preparing ore particles for extracting valuable comprising a feed pump 30 operable to receive ore particles having an F80 of less than 5 mm, a vertical grinding mill 46 in flow communica

Description

Technical Field This disclosure relates to a comminution circuit and a method of using the circuit to prepare ore particles for extracting valuable minerals therefrom. Background to the Disclosure 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. Large amounts of energy and cost are expended generating material of a size required for liberation of valuable minerals. Due to the unselective nature of existing comminution devices like SAG mills, Ball Mills, and to a lesser extent other devices, ore particles finer than what is required for liberation are generated. There is an exponential relationship between the energy consumed and the fineness of particles to be produced. Vast amounts of comminution energy (and therefore operating cost and upfront capital) in mill circuits are needed to generate finer particles as opposed to coarse size reduction, which is relatively efficient. 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 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 ef 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. In a first aspect, the present disclosure provides a circuit for preparing ore particles for extracting valuable minerals therefrom, the circuit comprising: a comminution stage reducing the size of run-of-mine ore to ore particles having an Fso of less than 5 mm; a feed pump operable to receive from the comminution stage ore particles having an Fso of less than 5 mm; a vertical grinding mill in flow communication with the feed pump to receive ore particles therefrom and to output ore particles having a Pso of less than 400 pm; a dual stage hydrocyclone to separate the output ore particles from the vertical grinding mill into an overflow having a Pso of less than 250 pm, and an underflow having a mass proportion of material smaller than 75 pm of less than 15%, to ensure that the particle size is within the optimum particle size operating window of a downstream coarse particle flotation device; and a coarse particle flotation device operable to receive the dual stage hydrocyclone underflow directly therefrom and to separate mineral rich ore particles therein from gangue rich ore particles, and to feed the mineral rich ore particles to the feed pump and to divert the gangue rich ore particles to tailings. Optionally, the underflow has a mass proportion of material smaller than 75 pm of less than 10%. Optionally, the performance alpha parameter is in a range of 2 to 4.7. Optionally, the water split ratio to overflow stream for the hydrocyclone is in a range of 80 to 95%. Optionally, the cut efficiency parameter is selected so that the size range of particles entering the coarse particle flotation device is within a defined range of operation for the coarse particle flotation device. In one embodiment, the preferred particle size range is between 75 pm and 400 pm. The hydrocyclone overflow may have a Pso of less than 200 pm. The vertical grinding mill may comprise a stirred media grinding mill where the stirred effect is caused by rotating grinding discs together with static counter discs situated on a shell surrounding the rotating grinding discs. Optionally, the feed pump receives ore particles having an Fso of less than 3 mm. In a second aspect, the present invention provides a method of preparing ore particles for extracting valuable minerals therefrom, the method comprising: receiving relatively small ore particles from a comminution stage; pumping the received ore particles having an Fso of less than 5 mm to a vertical grinding mill; grinding the pumped ore 09 07 24 particles to a Pso of less than 400 pm; feeding the ground ore particles to a dual stage hydrocyclone to separate the received ore particles into an overflow having a Pso of less than 250 pm, and an underflow having a mass proportion of material smaller than 75 pm of less than 15%, to ensure that the particle size is within the optimum particle size operating window of a downstream process; feeding the underflow ore particles to a coarse particle flotation device; separating mineral rich ore particles therein from gangue rich particles; feeding the mineral rich ore particles to the pumping stage; and diverting the gangue rich ore particles to tailings. An embodiment of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 is a simplified schematic diagram of a mineral processing operation including apparatus for preparing ore particles for extracting valuable minerals therefrom, in accordance with one embodiment of the present invention; Figure 2 is a simplified block diagram of a part (the mineral recovery stage) of the mineral processing operation of Figure 1; and Figure 3 is a simplified block diagram of a part (the comminution stage) of the mineral processing operation of Figure 1. Detailed Description of an Embodiment Reference is now made to the drawings, and particularly to Figure 1, which is a simplified schematic diagram of a mineral processing operation 10 including apparatus 12 for preparing ore particles for extracting valuable minerals therefrom, in accordance with one embodiment of the present invention. The ore preparation apparatus 12 delivers fine ore particles to a mineral recovery stage 14. Run-of-mine (ROM) ore 20 is shown in Figure 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 20 is fed (for example, via a hopper or conveyor (or both) 22) into a comminution stage 24 comprising one or more primary, secondary, and / or tertiary comminution devices, as described in more detail with reference to Figure 3. The output from the comminution stage 24 comprises relatively small ore particles, for example, having a P8o below 3.5mm (in some embodiments, below 2.5 mm or below 2mm), and is mixed with water (at water injection stage 26) to create a slurry (solid ore particles suspended or entrained in liquid, such as water). The remaining processing stages are performed on ore particles suspended in liquid (i.e. wet processing). The slurry is then fed into the ore processing apparatus 12 in any convenient manner, for example, via a pipeline 28, a hose, a spool, or the like. The ore processing apparatus 12 includes a pump 30 (in this embodiment, a centrifugal slurry pump, but in other embodiments a different type of pump may be used). The ore processing apparatus 12 has two outputs 40, 42. The first output (mineral recovery output) 40 is a feed to the mineral recovery (or extraction) stage 14 where the valuable mineral is liberated from the remaining gangue around it using conventional techniques, for example by flotation, leaching, or the like. The mineral recovery stage 14 is shown in more detail in Figure 2, as described below. 09 07 24 The second output (coarse tailings output) 42 is a feed to a coarse tailings processing facility 44. The tailings processing facility 44 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 output from the pump 30 is fed into a vertical grinding mill 46, which in this embodiment comprises a stirred media grinding mill where the stirred effect is caused by rotating grinding discs together with static counter discs situated on a shell surrounding the rotating grinding discs. Suitable vertical grinding mills are provided by Swiss Tower Mills AG (https: / / www stmminers|s.cpm / tproducts), such as the HIGmill (trade mark). The vertical grinding mill 46 grinds the ore particles and produces a ground ore output slurry comprising primarily fine ore particles, in this embodiment having a Pao of less than approximately 450 pm, although in other embodiments the Psomay be smaller (such as approximately 400 pm). The ground ore output slurry is then fed into a hydrocyclone 48, which in this embodiment comprises a dual stage hydrocyclone, such as that described in US 6,758,343. The ground ore output slurry may be gravity fed to the hydrocyclone 48 or there may be an additional process pump (not shown) to pump the slurry thereto. The dual stage hydrocyclone 48 has performance parameters: alpha and water split ratio to overflow stream in a range between 2 to 4.7, and 80-95%, respectively, which ensures a sharp separation between undersize and oversize particles. This sharp separation is helpful to ensure that the particle size is within the optimum particle size operating window of a downstream process, as described below. The hydrocyclone 48 has two outputs: a small particle output at the overflow, which is the mineral recovery output 40; and a large particle output 50 at the underflow. The overflow is a slurry that has a Pso of less than 250 pm (in some embodiments, the overflow has a Pso of less than 200 pm). The underflow is also a slurry and it has a Pso of approximately 450 pm, and a typical particle size distribution between 250 pm and 450 pm. The sharp cut (high separation efficiency, alpha parameter) ensures that less than approximately 15%, preferably less than 10%, of the particles are smaller than 75 pm. The hydrocyclone large particle output 50 feeds a coarse particle flotation device 52, which in this embodiment is a HydroFloat (trade mark) fluidized-bed coarse particle flotation machine available from Eriez Flotation Division (https: / / www.eriez.eu / ). The coarse particle flotation device 52 also has two outputs: a gangue output, which is the coarse tailings output 42; and a mineral rich output 54 which is fed back to the pump 30 to be recirculated into the vertical grinding mill 46 for further size reduction of the ore particles therein. The gangue output 42 comprises a slurry that has ore particles that had insufficient valuable ore to be floated by the coarse particle flotation device 52. Instead of recirculating these particles for further size reduction, they are rejected and diverted to coarse tailings management. Coarse tailings differ from conventional tailings in that they can be used for structural features, such as a wall in a tailings dam. It is therefore an advantageous feature of this ore processing apparatus 12 that it separates coarse tailings from conventional tailings during the ore processing, thereby allowing the coarse tailings to be managed and used separately from the conventional tailings. The minerals recovery operation will now be described with reference to Fig. 2, which is a simplified schematic diagram showing the mineral recovery stage or circuit 14 in more detail. The mineral recovery circuit 14 is conventional and comprises a chemical addition stage 70 that adds the required chemicals to the slurry comprising the mineral recovery output 40 to produce chemically enhanced slurry 72 to assist flotation and removal of the valuable mineral being extracted. The next stage is the mechanical rougher, cleaner, and scavenger stage 74 that receives the chemically enhanced slurry 72. The mineral rich output from the mechanical rougher stage 74 comprises the final concentrate 76, which is the valuable product of the mineral processing operation 10. The low quality (low or no mineral content ore particles) output 78 is fed to a conventional tailing processing facility 80, which may be a TSF. Reference is now made to Figure 3, which is a simplified block diagram of the comminution stage 24. It should be appreciated that the specific details of the comminution stage 24 are not critical, provided an output having an appropriate particle size distribution is created, in this embodiment, a P8o below 3.5mm. The comminution stage 24 includes one or more jaw crushers 82 creating an output having a Pso at or below 150mm, which is fed by a conveyor 83 into one or more cone crushers 84. The cone crusher 84 further reduces the particle size, and a vibrating screen 86 receives the output of the cone crusher 84 and classifies it into an oversize stream 87 that is returned to the cone crusher 84 for further size reduction, and an undersize stream 88 having a Pso at or below 50mm. The undersize stream 88 is choke fed into a high pressure grinding roller (HPGR) machine 90. The HPGR 90 further reduces the particle size, and a vibrating screen 92 receives the output of the HPGR 90 and classifies it into an oversize stream 93 that is returned to the HPGR 90 for further size reduction, and an undersize stream having a Pso at or below 3.5mm. This undersize stream is fed to the water mixing stage 26 and into the pipeline 28. It should now be appreciated that this embodiment has the advantage that it is possible to separate and remove larger particles (having a high gangue concentration) 09 07 24 using a simple and efficient process, without having a high recirculating load. Providing a sharp cut hydrocyclone facilitates the use of coarse particle flotation and increases the efficiency of the mineral processing operation 10. In the foregoing description of certain embodiments, specific terminology has been resorted to 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 “left” and right”, “front” and “rear”, “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. 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. \ In addition, the foregoing describes only some embodiments of the invention(s), and alterations, modifications, additions and / or changes can be made thereto without departing from the scope and spirit of the disclosed embodiments, the embodiments being illustrative and not restrictive. Furthermore, invention(s) have described in connection with what are presently considered to be the most practical and preferred embodiments, it is to be understood that the invention is not to be limited to the disclosed embodiments, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the scope of the invention(s). Also, the various embodiments described above may be implemented in conjunction with other embodiments, e.g., aspects of one embodiment may be combined with aspects of another embodiment to realise yet other embodiments. Further, each independent feature or component of any given assembly may constitute an additional embodiment. Reference Numerals Mineral processing operation 10 Ore preparation apparatus 12 Mineral recovery stage 14 Run-of-mine (ROM) ore 20 Conveyor 22 Comminution stage 24 Water injection stage 26 Pipeline 28 Pump 30 Mineral recovery output 40 Coarse tailings (gangue) output 42 Coarse tailings processing facility 44 Vertical grinding mill 46 Dual stage hydrocyclone 48 Large particle output (of hydrocyclone) 50 Coarse particle flotation (CPF) device 52 Mineral rich output (of CPF device) 54 Chemical addition stage 70 Chemically enhanced slurry 72 Rougher, cleaner, and scavenger stage 74 Final concentrate 76 Low quality output (of rougher) 78 Conventional tailing processing facility 80 Jaw crusher 82 Conveyor 83 Cone crusher 84 Vibrating screen (for cone crusher) 86 Oversize stream 87 Undersize stream 88 High pressure grinding roller (HPGR) machine 90 Vibrating screen (of HPGR) 92 Oversize stream 93

Claims

1. A circuit for preparing ore particles for extracting valuable minerals therefrom, the circuit comprising:(i) a comminution stage reducing the size of run-of-mine ore to ore particles having an Fso of less than 5mm;(ii) a feed pump operable to receive from the comminution stage ore particles having an Fso of less than 5mm;(iii) a vertical grinding mill in flow communication with the feed pump to receive ore particles therefrom and to output ore particles having a Pao of less than 400 pm;(iv) a dual stage hydrocyclone to separate the output ore particles from the vertical grinding mill into an overflow having a Pso of less than 250 pm, and an underflow having a mass proportion of material smaller than 75 pm of less than 15%, to ensure that the particle size is within the optimum particle size operating window of a downstream coarse particle flotation device; and(v) a coarse particle flotation device operable to receive the dual stage hydrocyclone underflow directly therefrom, and to separate mineral-rich ore particles therein from gangue-rich ore particles, and to feed the mineral rich ore particles to the feed pump and to divert the gangue rich ore particles to tailings.

2. A circuit according to claim 1, wherein the vertical grinding mill comprises a stirred media grinding mill where the stirred effect is caused by rotating grinding discs together with static counter discs situated on a shell surrounding the rotating grinding discs.

3. A method of preparing ore particles for extracting valuable minerals therefrom, the method comprising:(i) receiving relatively small ore particles from a comminution stage;(ii) pumping the received ore particles having an Fso of less than 5 mm to a vertical grinding mill;(iii) grinding the pumped ore particles to a Pso of less than 400 pm;(iv) feeding the ground ore particles to a dual stage hydrocyclone to separate the received ore particles into an overflow having a Pso of less than 250 pm, and an underflow having a mass proportion of material smaller thanxt CMCOCM CM75 pm of less than 15% to ensure that the particle size is within the optimum particle size operating window of a downstream process;(v) feeding the underflow ore particles directly to a coarse particle flotation device;(vi) separating mineral rich ore particles therein from gangue rich particles;(vii) feeding the mineral-rich ore particles to the pumping stage; and(viii) diverting the gangue-rich ore particles to a tailings processing facility.

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