Dry beneficiation process of fine and ultrafine iron ores by particle and electrostatic separation

Abstract

Systems and methods for beneficiating fine and very fine particles of iron ore are disclosed. The system includes a first frictional electrostatic belt separator (BSS) that accepts and processes a stream of particles having a median particle size (d50) of less than 75 microns. The system and method are waterless and are conducted in a fully dry metallurgical route. The system also includes at least one air classification device that accepts and processes a stream of particulate feed to provide a stream of particles having a median particle size (d50) of less than 75 microns. The system can also include a dryer and deagglomeration system that accepts a stream of particulate feed and processes the stream of particulate feed to provide a stream of particles having less than 2% moisture.

Description

background

[0001] Invention Field

[0002] This invention relates to a drying, deagglomeration, air classification, and electrostatic separation process for anhydrous iron ore beneficiation.

[0003] Related technical discussions

[0004] U.S. Patent No. 10,207,275 describes a system for dry grinding and dry desliming of iron ore to remove naturally occurring ultrafine particles and ultrafine particles generated during the grinding process. These particles are described as 90% < 37 μm to 90% < 5 μm. However, these particles are lost in the loop as tailings, thus representing a loss in iron recovery.

[0005] U.S. Patent No. 9,327,292 uses a system consisting of a dryer, a series of air classifiers, and a magnetic separator to recover iron ore from low-grade iron ore ranging from coarse to fine. The separator system shows effectiveness for particles smaller than 150 micrometers, but for very fine fractions, such as those below 20 micrometers, there is no separate selectivity data. The inventors acknowledge that for fractions below 150 micrometers, separation is more challenging due to the dragging of non-magnetic fine particles by magnetic particles induced by magnetic lines of force (eddy currents). The inventors describe their invention as providing a high-intensity magnetic roller device specifically designed for separating iron oxide powders with sizes from 150 micrometers to 0 micrometers. However, the system requires particle size separation (or particle size classification), desliming, and multiple operations at different magnetic strength levels to achieve the separation of materials with particle sizes smaller than 45 micrometers.

[0006] U.S. Patent No. 8,757,390 describes a magnetic roller separator device for dry particles, wherein the magnetic roller is covered by a non-magnetic plastic belt. As the roller rotates, the belt separates from the roller, causing the magnetic particles to detach from the belt and fall into a suitable hopper under the influence of gravity and centrifugal force. The system is described as effective for particles between 1,000 micrometers and 50 micrometers.

[0007] U.S. Patent No. 7,041,925 describes an electrostatic separation device for a mixture of particles, based on a difference in electrical conductivity. Through this device, particles are charged and then contacted with a conductive surface, which is a grounded rotating roller. Conductive particles (i.e., iron ore) are neutralized by contact with the roller and are no longer attracted to it by electrostatic forces. Non-conductive particles, i.e., silicates, retain their charge and remain fixed to the rotating roller.

[0008] U.S. Patent No. 6,723,938 describes an electrostatic separator based on conductive inductive charging, characterized in that the electrodes are arranged above a conductive drum, whereby conductive particles contact the drum, transferring charge to or from the drum and rising from the surface of the roller.

[0009] U.S. Patent No. 3,337,328 uses electrostatic separation of iron oxide from silica as part of a large-scale process that includes crushing, grinding, gravity separation or flotation or magnetic separation, followed by electrostatic separation to produce high-grade iron ore. However, this electrostatic process is only suitable for coarse materials with a minimum particle size of 0.003 inches or 75 micrometers. Fine materials are instead processed via froth flotation.

[0010] U.S. Patent Nos. 2,754,965 and 2,805,770 describe methods for beneficiating multi-component ores using electrostatic techniques, with particular interest in phosphate ores. These methods do not describe the beneficiation of iron ore and are limited to particle sizes greater than 200 mesh.

[0011] U.S. Patent No. 2,881,916 describes drying nonmetallic ores prior to electrostatic separation, with a particular focus on phosphate ores. The electrostatic separation process describes the preparation of ores with a particle size preferably in the range of -24 mesh to +100 mesh. Specifically, this invention seeks to limit the fine particles generated during the drying process, which are known to limit effective electrostatic separation.

[0012] U.S. Patent Nos. 4,839,032 and 4,874,507 disclose a belt separator system (BSS). U.S. Patent No. 5,904,253 describes an improved BSS belt geometry and claims a system for processing iron-containing minerals from glass manufacturing raw materials and ceramic precursors. Summary of the Invention

[0013] Various aspects and embodiments of the present invention relate to methods for drying, deagglomeration, air classification, and electrostatic separation in anhydrous beneficiation of fine and very fine iron ores. These aspects and embodiments relate to a method for upgrading iron ore by separating it by particle size using air classification and subsequently by electrostatic separation of one or more particle size fractions, to produce iron ore concentrate from fine and very fine iron ores in a completely dry and anhydrous process. The present invention aims to process fine and very fine iron ores, such as those smaller than 75 micrometers, for example smaller than 70 micrometers, smaller than 50 micrometers, smaller than 25 micrometers, or even smaller than 10 micrometers, which cannot be recovered by conventional technologies, whether wet or dry, otherwise would become waste or tailings. Furthermore, an advantage of the present invention is that the processing is carried out in a completely dry, anhydrous method; therefore, unlike conventional wet tailings, the final waste will be dry and stackable. The present invention is applicable to iron ores containing magnetic minerals, such as magnetite and hematite, and also to non-magnetic minerals, such as goethite and limonite. In some non-limiting embodiments, the iron ore may include one or more of hematite, goethite, and magnetite in varying proportions. In at least some non-limiting embodiments, the iron ore is associated with gangue minerals selected from, but not limited to, quartz, kaolinite, gibbsite, and carbonates. The iron ore may include additional iron minerals, such as siderite and / or lepidocrocite.

[0014] This invention is applicable to the production of marketable iron ore concentrates with 58% Fe or higher, including concentrates with 65% Fe or higher.

[0015] One embodiment of the invention includes an agitated air-purge dryer for drying and de-agglomerated particles, followed by one or more air classifiers or air cyclone separators to separate low-grade iron ore into two or more particle size fractions. In this embodiment, the fine fraction from the air classifier is processed by a belt electrostatic separator system (BSS) to produce a high-grade iron ore concentrate. The term "fine fraction" may be used throughout this document to refer to fine and / or very fine particles as defined herein.

[0016] In another embodiment, the fine and coarse fractions of the iron ore concentrate air classifier are both processed by the BSS as separate streams to maximize the efficiency of the BSS operation.

[0017] These and other features and advantages of the present invention will become more apparent from the following detailed description. Brief description of the attached figures

[0018] The above and other advantages of this application will be more fully understood with reference to the following figures, in which:

[0019] Figure 1A schematic diagram of an embodiment of a system for drying, deagglomerating, particle size separation and belt separation of fine iron ore and / or very fine iron ore is shown.

[0020] Figure 2 A schematic diagram of an embodiment of a system for drying, deagglomeration, particle size separation and belt separation is shown, wherein the ore is classified into multiple particle size streams;

[0021] Figure 3 A schematic diagram of an embodiment of a system for drying, deagglomerating, particle size separation and belt separation of fine iron and / or very fine iron ore and medium-sized ore is shown.

[0022] Figure 4 Another embodiment of a system for drying, deagglomerating, particle size separation, and belt separation of iron ore is shown; and

[0023] Figure 5-9 Other embodiments of a system for drying, deagglomerating, particle size separation, and belt separation of iron ore are shown. Detailed Implementation

[0024] It should be understood that the implementations of the methods and apparatus discussed herein are not limited in application to the details of the construction and arrangement of the components set forth in the following description or shown in the accompanying drawings. These methods and apparatuses can be implemented in other embodiments and can be carried out or performed in various ways. The examples of specific embodiments provided herein are for illustrative purposes only and are not intended to be limiting. Furthermore, the wording and terminology used herein are for descriptive purposes and should not be considered limiting. The terms “including,” “comprising,” “having,” “containing,” “involving,” and variations thereof, as used herein, are intended to cover the items listed thereafter and their equivalents, as well as additional items. References to “or” are to be understood as inclusive, and therefore any term described using “or” may refer to a single, multiple, or any one of all the terms described.

[0025] Anhydrous methods for iron ore beneficiation include magnetic separation and electrostatic separation. Both dry magnetic separation systems and traditional electrostatic separation systems are limited in their ability to handle fine and ultrafine particles. Fine particles are defined as the majority of particles (d50) being less than 75 μm, and ultrafine particles are defined as the majority of particles (d50) being less than 25 μm, and in some cases, mostly less than 10 μm. Anhydrous methods for recovering iron ore from fine particles are highly advantageous for the iron ore industry because this material is typically treated waste, currently stored in large, costly, and potentially disastrous tailings ponds with risks of failure and catastrophic consequences for human life and the environment.

[0026] This economical method for processing fine iron ore particles needs to be highly suitable for handling fine and extremely fine particles, as the particle size distribution of material in iron waste ponds ranges from 60 micrometers to 10 micrometers in the d50 range, meaning a large portion of the material is smaller than 75 micrometers and smaller than 25 micrometers. It is known that such extremely fine particles are difficult or impossible to process using existing technologies such as flotation or magnetic separation. Foam flotation, a wet processing method, is not conducive to processing extremely fine particles because the presence of slime and extremely fine particles adversely affects separation selectivity and reagent consumption. Wet and dry desliming methods for ore have been employed; however, these particles are lost in the loop as tailings, thus representing both a loss in iron recovery and a future environmental responsibility.

[0027] Wet and dry magnetic separators are frequently used in industrial-scale processing of coarse to medium-fine iron ore. Wet magnetic separators have been successfully used for fine particles, but their disadvantages include the production of wet tailings, the need for large amounts of water, and subsequent drying of the final concentrate. Dry magnetic separators are known to be limited for fine particles due to the influence of airflow, particle-particle adhesion, and particle adhesion to the rotor. Fine particles are highly affected by airflow motion, making separation of fine particles impractical by dry magnetic processing methods, where particles must follow a trajectory imposed by the movement of the magnetic belt. Furthermore, for such fine particles, the magnetic force is higher than the centrifugal force that causes unloaded Fe particles to be conducted into the magnetic region. In addition to these disadvantages, magnetic systems also produce mixed fractions, i.e., middlings, which must then be recycled back to the original feed, either as tailings or mixed with the product, thus reducing the final concentrate grade. Magnetic roller separator systems are ineffective for fine particles due to limitations in airflow and particle adhesion.

[0028] Electrostatic separators can be classified according to the charging method used. The three basic types of electrostatic separators include: (1) high-pressure roller (HTR) ionization field separators, (2) electrostatic plate (ESP) and screen electrostatic (ESS) field separators, and (3) triboelectric separators, including belt separator systems (BSS).

[0029] High-pressure roller (HRT) systems are unsuitable for handling fine particles because the particles are affected by airflow and therefore unsuitable for sorting by any method that relies on applied momentum. Furthermore, the inherent limitation of this device in terms of the rate at which it can handle fine particles is due to the requirement that each individual particle must contact the roller. As particle size decreases, the surface area per unit weight of particle increases dramatically, reducing the effective processing rate of this device and making it unsuitable for processing fine particles at commercially relevant rates. In addition to these operational limitations, fine particles present in non-conductive portions are difficult to remove from the rollers once attached due to strong electrostatic forces relative to particle mass. The limitations of this device for fine particles include the difficulty in removing fine particles adhering to the roller surface and the reduced ability of conductive particles to contact the roller. Therefore, this separator is not suitable for extremely fine-grained ores. Electrostatic separation (ES) of iron ore is used only in relatively limited commercial applications and only with relatively coarse particles larger than 75 micrometers.

[0030] Belt separator systems (BSS) are used to separate the components of particulate mixtures based on the charging of different components through surface contact (i.e., the triboelectric effect). BSSs have advantages over HRT, ESP, and ESS electrostatic separators (including free-fall or drum separators) because they are well-suited for processing fine materials, including particulate mixtures containing large amounts of material smaller than 75 μm, 50 μm, 25 μm, and even 10 μm. However, BSSs are limited in their ability to process material streams containing a wide particle size distribution and high moisture content. Furthermore, BSSs require free-flowing and fully released particles, which is not easily achieved when processing waste materials. BSSs rely on triboelectric charging or contact charging, where minerals transfer charge between other components of the mixture due to differences in work function. Therefore, BSSs are most effective when the particulate mixture contains minimal amounts of the main mineral component. For these reasons, BSSs alone are generally considered unsuitable for processing iron ore or extremely fine iron tailings unless specialized pretreatment techniques are employed.

[0031] BSS (Bipolar Separation System) has previously been used to remove iron-bearing minerals, such as pyrite, from glassmaking raw materials and ceramic precursors to improve the color and whiteness of finished ceramic products. This system does not include pretreatment steps such as de-agglomeration drying and pneumatic particle size classification to properly prepare fine-grained iron-bearing minerals for electrostatic treatment. This system has not proven effective for processing iron-bearing minerals from iron ore tailings or waste, where it is desirable to produce a marketable iron ore product with 58% or higher iron content. BSS is most effective when a limited number of major mineral species are present in the feed mixture, or when the major minerals contained in the feed mixture have similar triboelectric charging and work function characteristics. This is the basis of the operation, as mineral species must transfer charge to each other during triboelectric charging. The presence of clay or slime mixed with fine iron ore degrades BSS performance. Aspects and embodiments of this application aim to eliminate this limitation by using pneumatic particle size separation of clay minerals to allow for the selective separation of fine iron from non-clay gangue minerals.

[0032] This application relates to a system for processing fine and very fine iron ores using a completely anhydrous method, such as... Figure 1 As shown. Low-grade iron ore is introduced into a dynamic air classification system or a static cyclone system (03), which separates ore based on particle size. The fine fractions (possibly consisting of fine and / or very fine iron ore particles) (04) from the air classifier are fed into an electrostatic separation system (06), particularly a belt separation system (BSS), in which the ore is separated into an iron concentrate fraction (07) and a dry, stackable waste fraction (08). The coarser fractions (09) from the dynamic air classification system or the air classification system (03) can be further processed using suitable techniques (magnets, flotation, BSS).

[0033] The air classification system (03) can be a static (i.e., a cyclone separator) or dynamic classification system, or a combination of these. Air classification is advantageous because it allows for the production of a dry ore stream with a narrow particle size distribution while controlling the cut size and fineness. In the illustrated embodiment, the air classification system is used to process iron ore, allowing for the production of a fine and / or very fine particle stream. According to one aspect and embodiment, fine particles can be produced by modifying different operating parameters of the pneumatic classification system, thereby obtaining a range of top cut sizes and particle size distributions. For an air classification system comprising a dynamic classifying wheel and a cyclone separator, the particle size distribution and fineness of the product can be controlled by modifying certain variables, such as the speed of the classifying wheel, the airflow, the rate at which material is introduced into the classification system, and the air-to-solids ratio, etc.

[0034] Figure 2Another embodiment of the system and method is shown, in which the ore is completely dried and de-agglomerated using a dryer (22). The system and method involve processing low-grade iron ore fines and waste (20) that are dried and thoroughly de-agglomerated using a stirred dryer (22), such as an air-sweeped tube dryer or other similar flash dryer. The dryer de-agglomerating device (22) reduces the moisture content of the incoming ore, especially in cases where the low-grade iron ore has previously been stored as wet tailings or processed by wet methods. The dryer comprises a tube and a hot gas generator, typically using natural gas or heavy fuel oil as fuel. The hot gas generator dryer operates at temperatures up to 1050 degrees Celsius, with the material outlet temperature maintained below 120 degrees Celsius. Prior to particle size separation and electrostatic separation processes, because the equipment and processes are physical separation processes, it is preferable to use a stirrer or stirred dryer to de-agglomerate the ore when the mineral phases are released or physically separated from each other. The dried iron ore (23) is fed into an electrostatic separation system (25), particularly a belt separation system (BSS), in which the ore is separated into a fine iron fraction (26) and a dry and stackable low-grade iron fraction (27).

[0035] Figure 3 Another embodiment of the system and method is shown, wherein the ore is completely dried and de-agglomerated using a dryer (42) and separated into two particle size fractions by an air classification system (43). The system and method involve processing low-grade iron ore fines or waste (40) and then drying and thoroughly de-agglomerating it using a stirred dryer (42), such as an air-swept tube dryer or other similar flash dryer. The low-grade ore is introduced into a dynamic air classification system or cyclone separator system (43) that separates based on particle size. The fine fraction (which may consist of fine and / or very fine iron ore particles) (44) from the air classifier is fed into an electrostatic separation system (46), particularly a belt separator (BSS), where the ore is sorted into an iron concentrate fraction (47) and a dried and stackable waste fraction (48).

[0036] Figure 4Another embodiment of the system and method is shown, wherein the ore is completely dried and deagglomerated by a dryer (62) and separated into at least three particle size fractions by two or more air classification systems (63, 65). A primary air separator (63) receives the dried output from the dryer and produces a coarser dry ore stream (73), which can be further processed using suitable techniques (magnetic, flotation, BSS). The finer material (64) from the primary air classification system (63) is then separated in a secondary air classification system (65), where a coarser stream (66) containing a large number of fine and very fine particles is processed by a BSS (67) to produce an iron concentrate fraction (68) and a dry and stackable waste fraction (69). The finer material (70) from the secondary air classification system (65) is collected by a fabric filter receiver (71). The dry slime fraction (72) collected in the filter receiver (71) as the finest fraction from the secondary classification system (65) is stackable dry tailings.

[0037] Figure 5 Another embodiment of the system and method is shown, wherein the ore is completely dried and deagglomerated by a dryer (82) and separated into at least three particle size fractions by two or more air classification systems (83, 85). A primary air separator (83) receives the dried output from the dryer and produces a coarser stream of dried ore (93), which can be further processed by a BSS (94). The finer material (84) from the primary air classification system (83) is then separated in a secondary air classification system (85), where a coarser stream (86) containing a large number of fine and very fine particles is processed by a BSS (87), where the ore is sorted into an iron concentrate fraction (88) and a dried and stackable waste fraction (89). The finer material (90) from the secondary air classification system (85) is collected by a fabric filter receiver (91). The dry slime fraction (92) collected in the filter receiver (91) as the finest fraction from the secondary grading system (85) is stackable dry tailings.

[0038] Figure 6Another embodiment of the system and method is shown, wherein the ore is completely dried and deagglomerated by a dryer (103) and separated into at least three particle size fractions by two or more air classification systems (104, 106). A primary air separator (104) receives the dried output from the dryer and produces a coarser stream of dried ore (117), which can be further processed using suitable techniques (magnetic, flotation, BSS). The finer material (105) from the primary air classification system (104) is then separated in a secondary air classification system (106), where a coarser stream (107) containing a large number of fine and very fine particles is processed by a BSS (108), where the ore is sorted into an iron concentrate fraction (109) and a dried and stackable waste fraction (110). The majority of the dry sludge fraction (111), which now contains only clay and iron minerals, is processed by another BSS (113), thus the dry waste (115) is stackable tailings.

[0039] Figure 7 Another embodiment of the system and method is described, wherein the ore is completely dried and de-agglomerated by a dryer de-agglomeration system (142) and separated into at least three particle size fractions (143, 145) by two or more air classification systems. A primary air separator (143) receives the dried output from the dryer and produces a coarser, dried ore stream (156), which can be further processed using suitable techniques (magnetic, flotation, BSS). The finer material (144) from the primary air classification system (143) is then separated in a secondary air classification system (145), and a coarser stream (146) containing a large number of fine and very fine particles is processed by the BSS (147). The dry waste (149) from the primary BSS (147) is processed by the secondary BSS (150), and the product from the BSS (151) is recycled back to the primary BSS (147). The waste fraction from the secondary BSS (150) is dry and stackable. The finer material (153) from the secondary air classification system (145) is collected by a fabric filter receiver (154). The dry slime fraction (155) collected in the filter receiver (154) as the finest fraction from the secondary classification system (145) is stackable dry tailings.

[0040] Figure 8Another embodiment of the system and method is shown, wherein the ore is fully dried and de-agglomerated by a dryer-de-agglomerator system (203) and separated into at least three particle size fractions by two or more air classification systems (204, 206). A primary air separator (204) receives the dried output from the dryer and produces a coarser dry ore stream (216), which is further processed by a BSS (217). The finer material (205) from the primary air classification system (204) is then separated in a secondary air classification system (206), where a coarse stream (207) containing a large number of fine and very fine particles is processed by a BSS (208), wherein the ore is classified into an iron concentrate fraction (209) and a dried and stackable waste fraction (210). The finer material (211) from the secondary air classification system (206) is collected by a fabric filter (212) and processed by another BSS (213), thereby drying the waste (215) into stackable tailings.

[0041] Figure 9 Another embodiment of the system and method is shown, wherein the ore is completely dried and de-agglomerated by a dryer de-agglomeration system (242) and separated into at least three particle size fractions by two or more air classification systems (243, 245). A primary air separator 243 receives the dried output from the dryer and produces a coarser dried ore stream (256), which can be further processed using suitable techniques (magnetic, flotation, BSS). The finer material (244) from the primary air classification system (243) is then separated in a secondary air classification system (245), whereby a coarse stream (246) containing a large number of fine and very fine particles is processed by the BSS (247). The dried waste (249) from the primary BSS (247) is processed by the secondary BSS (250), and the product (251) from the secondary BSS has a sufficiently high iron content to be considered a marketable iron concentrate without further upgrading. The waste fraction (252) from the secondary BSS (250) is dry and stackable. The finer material (253) from the secondary air classification system (245) is collected by a fabric filter receiver (254). The dry slime fraction (255) collected in the filter receiver (254) as the finest fraction from the secondary classification system (245) is stackable dry tailings.

[0042] Predictive Implementation

[0043] To demonstrate the efficiency of the invention, iron ore samples were tested using the new system.

[0044] Example 1:

[0045] In one embodiment, the processing of fine iron ore samples is accomplished via an air classification system followed by a triboelectric strip separator system. The aim of this study is to demonstrate the efficiency of the system and method in processing extremely fine iron ores that would otherwise be unrecoverable using conventional techniques, particularly conventional dry processing methods.

[0046] The main mineral phases of the feed sample are shown in Table 1. The sample exhibits simple mineralogical characteristics. The main iron-recovering mineral in the sample is hematite, and the main gangue mineral exists in the form of quartz.

[0047] Table 1

[0048] minerals Chemical formula weight percentage Hematite Fe2O3 68％ Goethite FeO(OH) 4％ quartz SiO2 24％ Kaolinite Al2Si2O5(OH)4 2％ other --- 2％

[0049] The iron ore samples were processed on a demonstration scale using a novel air classification system and a belt separator system to increase the iron concentration of the extremely fine iron ore, which would otherwise be impossible to recover using conventional techniques. The classification system is a dynamic pneumatic classifier with a rotor speed of 4500 rpm and an air-to-solid mass ratio of 16.3.

[0050] Table 2

[0051]

[0052] The resulting fine fraction has a D50 of 15 micrometers and a D90 of 33 micrometers, which is significantly finer than the effective particle size of conventional iron ore processing technologies. Because the fine particle size of the ore makes it unsuitable for other processing technologies, any concentrate produced is diverted from the waste stream, thus avoiding the need to dispose of it in tailings dams or tailings bins.

[0053] Table 3

[0054]

[0055] The classifier overflow fraction, measured to have a D50 of 65 micrometers, can be processed using a BSS (Body Segmentation System). In this embodiment, the classifier overflow fraction is also processed using a BSS.

[0056] Table 4

[0057]

[0058] Therefore, the embodiments described demonstrate that the pretreatment steps of drying, deagglomeration, and critical air classification improve the separation selectivity of the classifier overflow fraction while allowing the production of a high-grade iron concentrate of +65% from the D50 = 15 micron fraction. Importantly, the BSS does not produce middlings fractions but instead provides marketable concentrates and dried, stackable tailings fractions.

[0059] Example 2:

[0060] In another embodiment, the processing of the fine iron ore sample was completed after a series of air classification stages.

[0061] Table 5

[0062] minerals Chemical formula weight percentage Hematite Fe2O3 48％ Goethite FeO(OH) 29％ Kaolinite Al2Si2O5(OH)4 3％ quartz SiO2 20％

[0063] Air is classified through multiple air classifier stages, with finer grades sent to the BSS.

[0064] Table 6

[0065]

[0066] The fine fractions processed by BSS have D50 = 7 micrometers and D90 = 16 micrometers, which are significantly lower than the effective particle size of conventional iron ore processing technologies.

[0067] Table 7

[0068]

[0069] Example 3:

[0070] In one embodiment, the processing of fine iron ore samples is accomplished by an air classification system followed by a triboelectric belt separator system.

[0071] The iron ore samples were processed on a demonstration scale using a novel air classification system and a belt separator system to increase the Fe concentration in the extremely fine iron ore, which would otherwise be unrecoverable using conventional techniques. The classifier inlet was also treated using a belt separator system to demonstrate the impact of air classification on BSS separation. The classification system was a dynamic pneumatic classifier with a rotor speed of 10,000 RPM.

[0072] Table 8

[0073]

[0074] The D50 of the classifier inlet of the BSS treatment is 5 micrometers and the D90 is 39 micrometers, which is significantly lower than the effective particle size of conventional iron ore processing technology.

[0075] Table 9

[0076]

[0077] The resulting fine fraction has a D50 of 3 micrometers and a D90 of 8 micrometers, and an increased clay content, which reduces the performance of iron ore beneficiation machines, including BSS. The fine fraction is discarded as a slime.

[0078] Measurements showed that the D50 of the deslimed fraction was 28 micrometers, indicating that it contained a large amount of iron-rich material in the range of <20 micrometers. Traditional iron ore processing techniques are ineffective within this range.

[0079] Table 10

[0080]

[0081] Therefore, the embodiments described above demonstrate that the pretreatment steps of drying, deagglomeration, and air classification improve the separation selectivity of the deslimed fraction, thereby allowing the production of a high-grade iron concentrate of +58% from the deslimed fraction with a d50 of 28 microns.

[0082] Example 4:

[0083] In another embodiment, the fine iron ore sample is processed using a triboelectric belt separator system.

[0084] The main mineral phases of the feed sample are shown in Table 11 below. The sample exhibits simple mineralogical characteristics. The main iron-recoverable minerals in the sample are hematite and goethite, and the main gangue minerals exist in the form of quartz.

[0085] Table 11

[0086] minerals Chemical formula weight percentage Hematite Fe2O3 36 Goethite FeO(OH) 14 Kaolinite Al2Si2O5(OH)4 6 quartz SiO2 40 spruce Al(OH)3 2 other --- 2

[0087] Table 12

[0088]

[0089] The BSS-treated samples have D50 = 23 micrometers and D90 = 59 micrometers, therefore containing a large amount of iron-rich material in the range of <20 micrometers, in which traditional iron ore processing technology is ineffective.

[0090] Table 13

[0091]

[0092] Therefore, the embodiments described above demonstrate that the pretreatment steps of drying, deagglomeration, and BSS separation allow for the production of high-grade iron concentrate with a purity of +60% from a sample with a d50 of 23 micrometers.

[0093] Example 5:

[0094] In another embodiment, the processing of iron ore samples containing a large amount of carbonates is accomplished by a triboelectric belt separator system.

[0095] The main mineral phases of the feed sample are shown in Table 14 below. The sample contains a large amount of carbonates (e.g., dolomite). The main iron recovery mineral in the sample is hematite, and the main gangue minerals exist in the form of quartz and carbonates.

[0096] Table 14

[0097] minerals Chemical formula weight percentage Hematite Fe2O3 57 Goethite FeO(OH) 5 magnetite Fe3O4 1 Kaolinite Al2Si2O5(OH)4 2 quartz SiO2 28 other - 7

[0098] Table 15

[0099]

[0100] Samples treated with BSS have a D50 of 62 μm and a D90 of 165 μm and can be treated with BSS.

[0101] Table 16

[0102]

[0103] Therefore, the embodiments described above demonstrate that the pretreatment steps of drying, deagglomeration, and BSS separation allow for the production of high-grade iron concentrate with a purity of +60% from carbonate-containing samples with a D50 of 62 microns.

[0104] Some embodiments of a system for beneficiating very fine iron ore have been described; various changes, modifications, and improvements will be apparent to those skilled in the art. Such changes, modifications, and improvements are intended to fall within the spirit and scope of this application. Therefore, the above description is merely exemplary and not restrictive. This application is limited to what is defined in the following claims and their equivalents.

Claims

1. A beneficiation system for fine and very fine iron ore, comprising: a. At least one air classification device that receives and processes a feed stream of particles to provide a particle stream, wherein the finest particles are concentrate and result in at least one output stream with a median particle size (d50) of less than 75 micrometers. as well as b. A first triboelectric belt separator that receives and processes at least one output particle stream with a median particle size (d50) of less than 75 micrometers from step a to produce iron-rich concentrate. The system and process described therein are anhydrous and are carried out in a dry metallurgical route.

2. The system of claim 1, wherein the system further comprises a dryer and a de-agglomeration system preceding the at least one air grading device, the dryer and de-agglomeration system receiving the feed stream and providing a dried feed stream to the at least one air grading device.

3. The system of claim 1, wherein the system further comprises at least one second air grading device, and wherein the finest fraction of the material from the final air grading device comprises a clay mineral enrichment fraction collected in the fabric filter.

4. The system of claim 3, wherein a second triboelectric belt separator is used to process coarser fractions from one or more air grading units preceding the final air grading unit.

5. The system of claim 4, wherein the finest fraction is processed by the first triboelectric belt separator to recover iron minerals, and wherein the coarser fractions from one or more air classification devices are processed using the second triboelectric belt separator.

6. The system of claim 1, wherein the low-grade iron scrap from the first triboelectric belt separator is processed by the second triboelectric belt separator with a scavenging configuration, wherein the iron-rich product from the second triboelectric belt separator is returned as feed to the first triboelectric belt separator.

7. The system of claim 1, wherein the low-grade iron scrap from the first triboelectric belt separator is processed by a second triboelectric belt separator in a scavenging configuration, wherein the iron-rich product from the second triboelectric belt separator has a sufficiently high iron content to be considered a marketable iron concentrate without additional upgrading.

8. The system of claim 1, wherein the first triboelectric belt separator receives and processes a particle stream having a median particle size (d50) of 70 micrometers or less.

9. The system of claim 1, wherein the first triboelectric belt separator receives and processes a particle stream having a median particle size (d50) of 50 micrometers or less.

10. The system of claim 1, wherein the first triboelectric belt separator receives and processes a particle stream having a median particle size (d50) of 25 micrometers or less.

11. The system of claim 1, wherein the first triboelectric belt separator receives and processes a particle stream having a median particle size (d50) of 10 micrometers or less.

12. The system according to claim 1, wherein the iron ore comprises one or more of hematite, goethite and magnetite in different proportions.

13. The system of claim 1, wherein the iron ore is associated with gangue minerals selected from: quartz, kaolinite, gibbsite, and carbonates.

14. The system of claim 1, wherein the iron ore comprises additional iron minerals, including siderite and / or lepidocrocite.

15. A beneficiation system for fine and very fine iron ore, comprising: a. A dryer and deagglomeration system that receives and processes a particulate feed stream to provide a particulate stream with a moisture content of less than 2%; as well as b. A first triboelectric belt separator that receives and processes a stream of particles with a median particle size (d50) of less than 75 micrometers to produce iron-rich concentrate; The system and process described therein are anhydrous and are carried out in a dry metallurgical route.

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