A pre-concentration method of extremely poor magnetite with fine dissemination size

Abstract

This invention relates to the field of mineral processing engineering technology, and particularly to a pre-selection method for extremely lean magnetite with fine-grained disseminated particles. The method includes: a first-stage pre-selection step: dry magnetic separation of the raw ore to obtain a first-stage rough concentrate, a first-stage tailings, and a first-stage middlings; feeding the first-stage middlings into a high-pressure roller mill for roller milling, and returning the roller mill product to the dry magnetic separation step after dispersion to form a first-stage roller mill-dry separation closed-loop cycle; a second-stage pre-selection step: feeding the first-stage rough concentrate into a high-pressure roller mill for roller milling, adding water to the roller mill product to prepare a slurry; wet screening of the slurry to obtain undersize slurry and oversize material; dewatering the oversize material and returning it to the second-stage roller milling step to form a second-stage roller mill-screening closed-loop cycle; wet magnetic separation of the undersize slurry to obtain a second-stage rough concentrate and a second-stage wet tailings. This invention achieves efficient and low-consumption pre-selection of extremely lean magnetite with fine-grained disseminated particles by constructing a first-stage middlings selective closed-loop dry separation and a second-stage full-size forced roller mill-wet screening closed-loop.

Description

Technical Field

[0001] This invention relates to the field of mineral processing engineering technology, and in particular to a pre-selection method for extremely poor magnetite with fine embedded grain size. Background Technology

[0002] my country has long been the world's largest producer of crude steel, resulting in a huge demand for iron ore resources. Although China has abundant iron ore reserves, its resource endowment is poor, generally characterized by low ore grade and extremely fine mineral particle size. For such extremely low-grade magnetite, if the traditional full-size crushing-grinding-magnetic separation process is used, a large amount of surrounding rock is often over-crushed during the grinding process, which not only causes huge energy waste but also produces a large amount of wet fine-grained tailings that are difficult to dewater, resulting in high beneficiation costs and seriously weakening the market competitiveness of domestic mining companies.

[0003] Currently, high-pressure roller mills are widely used in iron ore beneficiation. Utilizing the principle of layered crushing, they significantly reduce grinding energy consumption compared to traditional ball mills. However, in existing pre-selection and tailings disposal processes, the following two technical routes mainly exist: Conventional dry magnetic separation tailings removal process: Due to the fine particle size of extremely poor magnetite, the raw ore that has not been fully liberated is directly subjected to dry magnetic separation. Although some coarse tailings can be removed, the tailings removal rate is low and the improvement of concentrate grade is limited. A large amount of low-grade intergrowth still needs to be processed afterward, which cannot fundamentally solve the problems of large feed volume and high energy consumption. Full-size closed-circuit roller mill-dry separation process: This process returns all middlings and / or tailings after dry separation to the high-pressure roller mill for re-grinding; the disadvantage of this method is that the already liberated gangue minerals (tailings) are subjected to ineffective repeated roller milling, resulting in extremely high load on the high-pressure roller mill, reduced processing capacity, and serious over-grinding, which increases the risk of metal loss in subsequent operations and the difficulty of tailings treatment.

[0004] In summary, existing pre-selection processes struggle to achieve a balance between high tailings rejection, low metal loss, and low grinding energy consumption. Therefore, there is an urgent need to develop a pre-selection method for extremely lean magnetite that can selectively grind, improve pre-selection accuracy, and significantly reduce subsequent operating costs. Summary of the Invention

[0005] In order to overcome the problems of high energy consumption of ineffective grinding, low dry tailings disposal rate, large amount of wet tailings and difficulty in dewatering in the existing pre-selection method for extremely poor magnetite.

[0006] The technical solution of this invention is: a pre-selection method for extremely low-grade magnetite with fine embedded grain size, comprising the following steps: A pre-selection step: Dry magnetic separation is performed on the raw ore to obtain a first-stage rough concentrate, a first-stage tailings and a first-stage middlings; the first-stage middlings are fed into a high-pressure roller mill for roller milling, and the roller mill product is broken up and returned to the dry magnetic separation step to form a first-stage roller mill-dry separation closed-loop cycle; The second-stage pre-selection step involves feeding the first-stage rough concentrate into a high-pressure roller mill for roller milling, adding water to the roller mill product to form a slurry; performing wet screening on the slurry to obtain undersize slurry and oversize material; dewatering the oversize material and returning it to the second-stage roller milling step to form a closed-loop cycle of two-stage roller milling-screening; and performing wet magnetic separation on the undersize slurry to obtain second-stage rough concentrate and second-stage wet tailings.

[0007] Preferably, this method achieves selective roller milling and precise pre-classification of ore by constructing two differentiated closed-loop processes; wherein: In a pre-selection step, unlike the traditional full-scale return, this invention only returns the "first-stage middlings" containing a large amount of undissociated intergrowths to the high-pressure roller mill for regrinding. This "middling closed-loop" architecture allows the fully dissociated gangue (first-stage tailings) to be directly discharged as the final tailings, eliminating the meaningless roller milling of tailings; thereby reducing the circulating load and ineffective energy consumption of the high-pressure roller mill. In the two-stage pre-selection step, for the rough concentrate obtained from the first stage operation, this invention adopts a strategy of "roller milling followed by pulping and screening". The entire particle size of the rough concentrate from the first stage is fed into the second-stage high-pressure roller mill for further fine grinding to improve the degree of liberation. Then, strict particle size control is carried out through wet screening. This closed-loop circulation ensures that the particle size of the material entering the subsequent wet magnetic separation is qualified, effectively preventing coarse intergrowths from entering the beneficiation system and creating the feed particle size conditions for subsequent grinding and beneficiation operations. At the same time, by controlling the particle size entering the mill, the efficiency of subsequent ball milling can be improved and its energy consumption can be reduced.

[0008] Preferably, in the pre-selection step, before the middlings are milled, they are first lifted to the pressure bucket by a bucket elevator and fed to the high-pressure roller mill by their own weight.

[0009] Preferably, the dry magnetic separation in the first pre-selection step is carried out using a drum-type combined magnetic separator, and the first roller mill-dry separation closed-loop cycle operates in a negative pressure sealed environment and collects dust.

[0010] Preferably, the process also includes a dust collection and ash treatment step: combining the collected dust collection and ash with the first-stage rough concentrate, and feeding them together into the high-pressure roller mill of the second-stage pre-selection step for roller milling.

[0011] Preferably, in the two-stage pre-selection step, before the first-stage rough concentrate is subjected to roller milling, it is first fed into the high-pressure roller mill by the material's own weight through a pressure hopper.

[0012] Preferably, in the two-stage pre-selection step, the wet screening step uses a vibrating screen with a screen aperture size of 1 mm.

[0013] Preferably, in the two-stage pre-selection step, the dewatering treatment of the oversize material is carried out using a dewatering screen, and the dewatered oversize material is mixed with the primary rough concentrate that has not undergone the two-stage roller mill in the pressure hopper.

[0014] Preferably, in the two-stage pre-selection step, the wet magnetic separation step is carried out using a medium-intensity wet magnetic separator.

[0015] Preferably, the method also includes a wet tailings classification and utilization step: classifying and recovering the two-stage wet tailings to obtain coarse tailings.

[0016] Preferably, a portion of the tailings in the pre-selection step is discharged directly through a dry discharge device and does not enter the high-pressure roller mill.

[0017] The beneficial effects of this invention are: Compared with existing technologies, the method provided by this invention overcomes the defects of traditional processes involving repeated grinding of liberated gangue. By constructing a combined process of a first-stage selective closed-circuit dry beneficiation of middlings and a second-stage forced roller mill-wet screening closed-circuit process for all particle sizes, it achieves efficient and low-consumption pre-selection of fine-grained, extremely lean magnetite. Specifically, the first stage only grinds the unliberated middlings, reducing the ineffective load on the high-pressure roller mill and achieving selective crushing. The second stage, through forced fine grinding of the coarse concentrate and 1mm wet screening control, not only improves the degree of mineral liberation but also provides an ideal narrow-grade feed for subsequent ball milling operations, reducing ball mill energy consumption. At the same time, this method improves the dry tailings disposal yield and reduces the amount of ore entering the wet system and the final amount of wet tailings, saving energy and material consumption in subsequent grinding and eliminating the need for dewatering a large amount of fine tailings, thus reducing the comprehensive utilization cost of tailings. In summary, this invention synergistically optimizes the three dimensions of grinding source, beneficiation process, and tailings disposal, improving the economic efficiency of the development and utilization of extremely lean magnetite resources. Attached Figure Description

[0018] Figure 1 The diagram shows the detailed steps of the pre-selection method for extremely poor magnetite with fine embedded grain size according to the present invention. Figure 2 The diagram shown is a simplified flow chart of the pre-selection method for extremely poor magnetite with fine intercalation particle size according to the present invention. Detailed Implementation

[0019] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0020] Example 1: Please see Figure 1 and Figure 2This invention provides an embodiment: a pre-selection method for extremely low-grade magnetite with fine embedded grain size, comprising the following steps: The first pre-selection step involves dry magnetic separation of the raw ore to obtain a first rough concentrate, a first tailings, and a first middlings. The first middlings are then fed into a high-pressure roller mill for roller milling. The roller mill product is then broken up and returned to the dry magnetic separation step to form a closed-loop cycle of roller milling-dry separation. The two-stage pre-selection process involves feeding the primary rough concentrate into a high-pressure roller mill for grinding, adding water to the roller mill product to form a slurry, wet screening of the slurry to obtain undersize slurry and oversize material, dewatering the oversize material and returning it to the secondary roller milling process to form a closed-loop cycle of secondary roller milling and screening, and wet magnetic separation of the undersize slurry to obtain secondary rough concentrate and secondary wet tailings.

[0021] This method achieves selective roller milling and precise pre-classification of ore by constructing two differentiated closed-loop processes; wherein: In a pre-selection step, unlike traditional full-scale return, this invention only returns the "first-stage middlings" containing a large amount of undissociated intergrowths to the high-pressure roller mill for regrinding. This "middlings closed-loop" architecture allows the fully dissociated gangue (first-stage tailings) to be directly discharged as the final tailings, eliminating the pointless grinding of tailings; thus reducing the cyclic load and ineffective energy consumption of the high-pressure roller mill. In the two-stage pre-selection step, for the rough concentrate obtained from the first stage operation, this invention adopts a strategy of "roller milling followed by pulping and screening". The entire particle size of the rough concentrate from the first stage is fed into the second-stage high-pressure roller mill for further fine grinding to improve the degree of liberation. Then, strict particle size control is carried out through wet screening. This closed-loop circulation ensures that the particle size of the material entering the subsequent wet magnetic separation is qualified, effectively preventing coarse intergrowths from entering the beneficiation system and creating the feed particle size conditions for subsequent grinding and beneficiation operations. At the same time, by controlling the particle size entering the mill, the efficiency of subsequent ball milling can be improved and its energy consumption can be reduced.

[0022] Furthermore, in a pre-selection step, before the middlings are milled, they are first lifted to the pressure bucket by a bucket elevator and fed to the high-pressure roller mill by their own weight. The stable material column pressure formed by the bucket elevator and the high-positioned pressure bucket ensures that the high-pressure roller mill is always in a "full-cavity feeding" state, giving full play to the high efficiency and low consumption advantages of lamination crushing, and avoiding roller surface wear and equipment vibration caused by feeding fluctuations.

[0023] Furthermore, the dry magnetic separation in the pre-selection step is carried out using a drum-type combined magnetic separator, and the roller mill-dry separation closed-loop cycle operates in a negative pressure sealed environment, collecting dust. Among them, the drum-type combined magnetic separator has a long separation zone, which is conducive to fully dispersing mineral particles and capturing fine-grained magnetic minerals in a dry state, thereby improving separation accuracy. The fully sealed negative pressure operation can effectively collect the fine dust generated during the high-pressure roller mill and dispersion process, which not only meets environmental protection requirements but also recovers this valuable component, which usually has a high iron content.

[0024] Furthermore, the invention includes a dust collection process: the collected dust is combined with the primary coarse concentrate and fed into the high-pressure roller mill of the secondary pre-selection stage for roller milling. The primary dust has fine particle size and high grade, and if it is directly mixed with coarse tailings, it will cause metal loss. This invention combines it with the primary coarse concentrate of similar grade and feeds it into the secondary fine grinding stage, realizing closed-loop recovery of fine-grained magnetic minerals and avoiding waste of resources.

[0025] Furthermore, in the second-stage pre-selection step, before the first-stage rough concentrate is rolled, it is forced to be fed into the high-pressure roller mill by its own weight through a pressure hopper. Similar to the first stage, the pressure hopper is used to ensure stable feeding of the second-stage high-pressure roller mill, ensuring uniform particle size of the roller mill product and avoiding a decrease in processing capacity due to material slippage.

[0026] Furthermore, in the second-stage pre-selection step, the wet screening step uses a vibrating screen with a screen aperture size of 1mm. Wet screening has the advantages of high grading efficiency and no screen clogging. Strictly controlling the screen aperture to 1mm means that materials larger than 1mm are forced to return to the second-stage roller mill for further crushing, while qualified materials smaller than 1mm enter the magnetic separation. This particle size control node is set based on the dissociation characteristics of fine-grained magnetite, which can minimize over-crushing while ensuring the degree of dissociation.

[0027] Furthermore, in the second-stage pre-selection step, the oversize material is dewatered using a dewatering screen. The dewatered oversize material is then mixed with the primary rough concentrate that has not undergone the second-stage roller mill in a pressure hopper. The oversize material produced by the pulping and screening after the second-stage roller mill has a high moisture content, and directly returning it to the dry roller mill would lead to material sticking and blockage. By reducing its external moisture content through the dewatering screen, it is then mixed with the newly fed dry material (primary rough concentrate). This allows the overall moisture content of the mixture to be controlled within a range suitable for the stable operation of the high-pressure roller mill, ensuring the smooth operation of the second-stage closed-loop circulation.

[0028] Furthermore, in the second-stage pre-selection step, the wet magnetic separation step is carried out using a medium-intensity wet magnetic separator. For fine-grained materials, the medium-intensity wet magnetic separator can provide higher magnetic field strength and gradient, which can effectively recover fine-grained magnetite and some weakly magnetic intergrowths that are difficult to capture by conventional weak magnetic separators, thereby reducing the loss of magnetic iron in the second-stage wet tailings.

[0029] Furthermore, it also includes a wet tailings grading and utilization step: the wet tailings from the second stage are graded and recycled to obtain coarse tailings; the present invention reduces the amount of ore entering the subsequent main process, and the amount of wet tailings produced is also reduced accordingly; by performing simple grading treatment on the wet tailings, the coarse-grained part can be recovered and sold as construction sand, reducing the pressure of tailings dam storage and realizing the comprehensive utilization of resources.

[0030] Furthermore, a portion of the tailings from a pre-selection step is directly discharged through a dry discharge device, without entering the high-pressure roller mill. The dry-discharged tailings do not require concentration or dewatering, have a suitable particle size, and can be directly used as building material raw materials or for backfilling, reducing the dewatering energy consumption and processing costs for subsequent resource utilization of tailings.

[0031] Through the above steps, the method provided by this invention achieves efficient and low-consumption pre-selection of extremely lean magnetite with fine particle size by constructing a combined process of a first-stage selective closed-circuit dry separation of middlings and a second-stage forced roller mill-wet screening closed-circuit process. Specifically, the first stage only performs roller milling on the unliberated middlings, reducing the ineffective load on the high-pressure roller mill and achieving selective crushing. The second stage, through forced fine grinding of the coarse concentrate and 1mm wet screening control, not only improves the degree of mineral liberation but also provides an ideal narrow-grade feed for subsequent ball milling operations, reducing ball mill energy consumption. At the same time, this method improves the dry tailings disposal yield and reduces the amount of ore entering the wet system and the final amount of wet tailings, which not only saves energy and material consumption in subsequent grinding but also eliminates the dewatering process for a large amount of fine tailings, thus reducing the comprehensive utilization cost of tailings. In summary, this invention synergistically optimizes the three dimensions of grinding source, separation process, and tailings disposal, improving the economic efficiency of the development and utilization of extremely lean magnetite resources.

[0032] Example 2: Optionally, this embodiment provides a pre-selection method for extremely low-grade magnetite with fine-grained disseminated particles. The raw ore involved in this embodiment and subsequent embodiments is extremely low-grade magnetite with fine-grained disseminated particles produced in a typical mining area. Its raw ore properties are as follows: total iron grade (TFe) is about 18.0%~18.1%, magnetic iron grade (mFe) is about 13.4%~13.5%, the main iron mineral is magnetite, the disseminated particle size is very fine, mostly below 0.05mm, and the gangue minerals are mainly quartz and amphibole.

[0033] Step S1: A pre-selection step The raw ore is fed evenly into the drum-type combined magnetic separator by the feeder for dry magnetic separation; by adjusting the magnetic deflection angle and the position of the ore separating plate of the magnetic separator, the material is separated into three products: a first stage of rough concentrate, a first stage of tailings and a first stage of middlings. One section of tailings, as the final dry tailings, is directly discharged into the tailings shed for storage via a belt conveyor, without entering any grinding process. A section of middlings is lifted by a bucket elevator to a pressure bucket with a height of 4.5m. The material is then fed into a high-pressure roller mill using the pressure of its own weight. The working pressure of the high-pressure roller mill is set at 180MPa and the roller surface linear speed is 1.2m / s. The product (cake) after roller milling is broken up by a breaker and then returned to the drum-type combined magnetic separator at the beginning of step S1 by a belt conveyor. It is then combined with the newly fed raw ore and subjected to dry magnetic separation again, thus forming a closed-loop cycle of roller milling and dry separation.

[0034] Step S2: Two-stage pre-selection step The coarse concentrate obtained in step S1 is transferred to the pressure hopper in the second-stage working area via a belt conveyor. The hopper has a height of 4.5m. The material is then fed into the second-stage high-pressure roller mill by its own weight for the second-stage roller milling operation. The working pressure of the second-stage high-pressure roller mill is set to 200MPa, and the roller surface linear speed is 1.0m / s. After the product from the roller mill is discharged, water is immediately added and stirred to form a slurry with a concentration of 45% to 55%. The slurry flows by gravity to a vibrating screen with a screen size of 1 mm for wet screening. The material on the vibrating screen is mainly coarse intergrowth that has not been fully disintegrated, and its moisture content is relatively high. The material on the screen first enters the dewatering screen for dewatering treatment, reducing its external moisture content to below 5%. Then, it is returned to the pressure hopper of the second-stage high-pressure roller mill at the beginning of step S2 by a belt conveyor. It is mixed with the newly fed first-stage coarse concentrate and then roller milled again to form a closed-loop cycle of two-stage roller mill-screening. The slurry under the vibrating screen flows by gravity to a medium-intensity wet magnetic separator for wet magnetic separation. After one separation, two stages of rough concentrate and two stages of wet tailings are obtained. The rough concentrate is used as the final pre-selected concentrate product and enters the subsequent wet grinding system. The wet tailings are discharged into the tailings treatment system.

[0035] Example 3: Optionally, this embodiment provides further supplementary explanations based on Embodiment 2.

[0036] Additional information for step S1: The entire closed-loop system of roller mill-dry separation, including the feeder, drum-type combined magnetic separator, bucket elevator, high-pressure roller mill and dispersant, is placed in a sealed enclosure and connected to a negative pressure dust collection system. The system is maintained at a slight negative pressure of -100Pa to -200Pa by an induced draft fan. The collected dust-laden gas is purified by a bag filter before being discharged.

[0037] The dust collected by the bag filter was analyzed and found to have a TFe content of 9.64%, an mFe content of 5.03%, and a particle size of -0.074mm accounting for more than 90%. Because the dust particles are fine and contain a certain amount of magnetic iron, direct disposal would result in metal loss.

[0038] Dust collection and ash treatment steps: The collected dust is quantitatively added to the first-stage rough concentrate belt conveyor in step S2 via pneumatic conveying or screw conveyor, so that it is uniformly mixed with the first-stage rough concentrate and fed into the pressure hopper of the high-pressure roller mill in the second-stage pre-selection step for subsequent roller milling-screening-magnetic separation treatment; the remaining steps are the same as in Example 2.

[0039] Example 4: Optionally, this embodiment is a further detailed description based on embodiment 2.

[0040] Step S2 refinement: In step S2, the product from the two-stage roller mill is wet-screened after pulping, with the screen aperture size strictly controlled at 1.0mm × 1.0mm. The oversize material is dewatered using a high-frequency linear dewatering screen with a screen aperture of 0.3mm. The moisture content of the filter cake after dewatering is 8%~10%. The filter cake is unloaded onto the first-stage coarse concentrate conveyor belt via a belt conveyor, where it is mixed with the newly fed first-stage coarse concentrate at the transfer point and in the pressure hopper of the two-stage high-pressure roller mill. By controlling the operating parameters of the dewatering screen, the overall moisture content of the material entering the pressure hopper after mixing is maintained between 2.5% and 3.5%, ensuring stable operation of the high-pressure roller mill without material sticking.

[0041] Steps for the graded utilization of wet tailings: The two-stage wet tailings generated by the strong magnetic wet separation in step S2 are classified; the two-stage wet tailings slurry is fed into a hydrocyclone or spiral classifier for coarse and fine separation to obtain coarse tailings (+0.074mm) with a yield of about 8% to 12% of the original ore; the coarse tailings can be sold as construction sand after being dewatered by a dewatering screen; the overflow fine mud is concentrated in a thickener and then transported to the tailings dam for storage.

[0042] Comparative Example 1: This comparative example adopts a traditional one-stage full-size closed-circuit roller mill-dry separation process, that is, without distinguishing between middlings and tailings, all tailings and middlings after dry magnetic separation are combined and returned to the high-pressure roller mill for regrinding.

[0043] The specific steps are as follows: The raw ore is fed into a dry magnetic separator to obtain a mixed product of rough concentrate and tailings. All the mixed product of tailings and middlings is fed into a high-pressure roller mill via a bucket elevator. The roller mill product is broken up and returned to the dry magnetic separator to form a closed circuit. The rough concentrate is used as the final product. The system also adopts negative pressure dust collection.

[0044] In the operation of Comparative Example 1, the high-pressure roller mill not only processed the undissociated middlings, but also processed a large amount of dissociated gangue minerals. Due to the repeated roller milling of gangue minerals, the high-pressure roller mill had an extremely high cyclic load, and a large amount of energy was consumed in the meaningless crushing of gangue.

[0045] Verification example: Optionally, in order to verify the effectiveness of the technical solution of the present invention, industrial tests were conducted for 72 consecutive hours on Examples 2, 3, 4 and Comparative Example 1; the comparison of stable operation indicators of each process is shown in Table 1.

[0046] Table 1. Comparison of key process parameters for each embodiment and comparative example.

[0047] As can be seen from Table 1, the circulating load rate of Examples 2-4 is only 271.88%, which is much lower than that of Comparative Example 1 (433.12%). The mechanism is that the present invention strictly follows the principle of "rolling only the middlings" and directly throws the dissociated tailings out of the system.

[0048] Let the amount of raw ore be Q_0, and the tailings yield be γ_t. Then, the amount of ore entering the closed-circuit roller mill is only (1-γ_t)·K (K is the circulation coefficient). Since this invention avoids repeated crushing of tailings particles that account for more than 50%, the net tonnage of the material processed by the roller mill is significantly reduced. The energy consumption of the roller mill is positively correlated with the throughput.

[0049] Where E is the total energy consumption, P is the power, Q is the amount of ore passing through, and T is the time; since Q_{Comparative Example} >> Q_{Example} in Comparative Example 1, its unit power consumption is significantly higher than that of the embodiment of the present invention.

[0050] The mFe recovery rate of Example 3 is slightly higher than that of Example 2. This is because Example 3 has a special dust collection and ash treatment step, which recovers the iron-containing dust with extremely fine particle size that is difficult to completely capture by conventional magnetic separation to the two-stage grinding and separation system. This part of the fine particles is effectively recovered in the wet screening and wet magnetic separation process, avoiding the loss of fine iron particles in the dry tailing process.

[0051] Example 4 uses precise dehydration control to keep the moisture content of the feed material in the two-stage roller mill within a reasonable range. High-pressure roller mills are sensitive to feed moisture content. Excessive moisture content can cause the roller surface to slip, the material bite angle to decrease, and consequently, the throughput to decrease and the roller surface to wear more intensely. This invention controls the moisture content of the circulating material through a dehydration screen, ensuring that the high-pressure roller mill is always in a high-efficiency lamination and crushing range.

[0052] In summary, the present invention provides a pre-selection method for extremely poor magnetite with fine embedded particle size. By constructing a differentiated closed-circuit crushing and separation structure, it reduces the ineffective load and system energy consumption of the high-pressure roller mill while ensuring a high magnetic iron recovery rate, and effectively controls the particle size of the subsequent feed product.

[0053] The embodiments of the present invention have been described in detail above with reference to the accompanying drawings. However, the present invention is not limited to the above embodiments. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the spirit of the present invention.

Claims

1. A method for pre-selecting extremely low-grade magnetite with fine-grained disseminated particles, characterized in that: Includes the following steps: A pre-selection step: Dry magnetic separation is performed on the raw ore to obtain a first-stage rough concentrate, a first-stage tailings and a first-stage middlings; the first-stage middlings are fed into a high-pressure roller mill for roller milling, and the roller mill product is broken up and returned to the dry magnetic separation step to form a first-stage roller mill-dry separation closed-loop cycle; The second-stage pre-selection step involves feeding the first-stage rough concentrate into a high-pressure roller mill for roller milling, adding water to the roller mill product to form a slurry; performing wet screening on the slurry to obtain undersize slurry and oversize material; dewatering the oversize material and returning it to the second-stage roller milling step to form a closed-loop cycle of two-stage roller milling-screening; and performing wet magnetic separation on the undersize slurry to obtain second-stage rough concentrate and second-stage wet tailings.

2. The method for pre-selection of extremely low-grade magnetite with fine intercalated grain size according to claim 1, characterized in that: In the aforementioned pre-selection step, before the middlings are milled, they are first lifted to the pressure bucket by a bucket elevator and fed to the high-pressure roller mill by their own weight.

3. The method for pre-selection of extremely low-grade magnetite with fine intercalated grain size according to claim 1, characterized in that: The dry magnetic separation in the first pre-selection step is carried out using a drum-type combined magnetic separator, and the first roller mill-dry separation closed-loop cycle operates in a negative pressure sealed environment and collects dust.

4. The method for pre-selection of extremely low-grade magnetite with fine intercalated grain size according to claim 3, characterized in that: It also includes a dust collection and ash treatment step: the collected dust collection and ash are combined with the first-stage rough concentrate and fed together into the high-pressure roller mill of the second-stage pre-selection step for roller milling.

5. The method for pre-selection of extremely low-grade magnetite with fine intercalated grain size according to claim 1, characterized in that: In the two-stage pre-selection step, before the first-stage rough concentrate is subjected to roller milling, it is first fed into the high-pressure roller mill by the material's own weight through a pressure hopper.

6. The method for pre-selection of extremely low-grade magnetite with fine intercalation grain size according to claim 1, characterized in that: In the two-stage pre-selection steps, the wet screening step uses a vibrating screen with a screen aperture size of 1mm.

7. The method for pre-selection of extremely low-grade magnetite with fine intercalation grain size according to claim 1, characterized in that: In the two-stage pre-selection step, the dewatering treatment of the oversize material is carried out by a dewatering screen, and the dewatered oversize material is mixed with the primary rough concentrate that has not undergone the two-stage roller mill in the pressure hopper.

8. The method for pre-selection of extremely low-grade magnetite with fine intercalated grain size according to claim 1, characterized in that: In the two-stage pre-selection step, the wet magnetic separation step is carried out using a medium-intensity wet magnetic separator.

9. The method for pre-selection of extremely low-grade magnetite with fine intercalated grain size according to claim 1, characterized in that: It also includes a wet tailings grading and utilization step: the two-stage wet tailings are graded and recycled to obtain coarse tailings.

10. The method for pre-selection of extremely low-grade magnetite with fine intercalated grain size according to claim 1, characterized in that: In the first pre-selection step, a portion of the tailings is discharged directly through a dry discharge device and does not enter the high-pressure roller mill.

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