Magnetic-flotation combined beneficiation method for fine-grained low-grade refractory magnetite ore

Abstract

Disclosed is a magnetic-flotation combined beneficiation method for fine-grained low-grade refractory magnetite ore. The method comprises: first, performing first-stage grinding, first-stage classification, and low-intensity magnetic separation; subjecting a resulting first-stage low-intensity magnetic separation concentrate to second-stage pre-classification, second-stage grinding, low-intensity magnetic separation, and magnetic separation column I separation; feeding a resulting magnetic separation column I concentrate into a reverse flotation operation, the reverse flotation operation using one-stage roughing, one-stage scavenging, and three-stage cleaning, and a product remaining in a flotation cell after the third cleaning stage being a final iron concentrate; feeding a magnetic separation column I tailing and a flotation scavenger tailing into third-stage pre-classification, third-stage grinding, low-intensity magnetic separation, and magnetic separation column II separation, and a third-stage low-intensity magnetic separation tailing, a first-stage low-intensity magnetic separation tailing, and a second-stage low-intensity magnetic separation tailing being combined into a final tailing, and the final tailing being used as an iron corrective additive for producing iron-containing silicate cement. The present invention has the advantages of a high iron concentrate grade, a low flotation feed rate, a high flotation feed grade, stable performance indicators, simple production and maintenance, and strong adaptability.

Description

A magnetic levitation combined beneficiation method for fine-grained, low-grade, and difficult-to-process magnetite ore Technical Field

[0001] This invention belongs to the field of iron ore beneficiation technology, specifically relating to a beneficiation method for fine-grained, low-grade magnetite ore. It is particularly suitable for processing magnetite ore with a TFe grade of 20.0%–25.0%, an mFe grade of 10.0%–15.0%, a fine iron mineral distribution (iron minerals can only be liberated when the grinding particle size is in the range of -0.038mm and the content is in the range of 90%–95%), and gangue minerals mainly consisting of quartz, silicates, and carbonates. Background Technology

[0002] Steel is a crucial foundation for national economic development, and China's economic growth is inseparable from the demand for iron ore. In recent years, with the rapid development of China's economy, the demand for iron ore resources has been increasing. However, my country's iron ore resources are relatively poor, with many low-grade ores and few high-grade ones. The ore also contains many associated components, and the minerals are finely distributed. Most iron ore requires beneficiation screening before being smelted in furnaces. Under the current context of supply-side reforms and environmental protection-related production restrictions in the steel industry, improving the utilization rate of iron ore resources is of great significance to the sustainable development of my country's mineral resources and the development of the steel industry.

[0003] The characteristics of my country's iron ore—low grade, fine particle size, and complex composition—determine its difficulty in beneficiation, necessitating continuous advancements in mineral processing technologies. To improve iron grade and recovery rates during beneficiation, and to rationally utilize my country's low-grade, fine-grained, and complexly associated iron ores, we need to process them through crushing, fine grinding, magnetic separation, and flotation. To effectively transform low-grade, fine-grained, and complex-composition ores into high-grade concentrates, flotation is typically required. Before entering the flotation process, appropriate fine grinding and magnetic separation processes are crucial for developing low-grade, fine-grained, disseminated magnetite resources and are key technologies for flotation preparation.

[0004] In magnetic separation, existing weak magnetic separators are efficient and simple wet separation devices for fine-grained strong magnetic minerals. They are characterized by their small size, light weight, and simple operation, and are effective for separating fine-grained strong magnetic minerals. However, the magnetic separation effect of weak magnetic separators is easily affected by factors such as feed particle size and grade, resulting in fluctuating separation performance and unsatisfactory beneficiation indicators such as grade and recovery rate. Due to the limitations of current magnetic separation technology, valuable minerals with significant differences in particle size composition and ore properties cannot be effectively separated, thus failing to provide qualified raw materials for subsequent flotation operations. Consequently, flotation indicators are difficult to guarantee, affecting the grade and recovery rate of the final concentrate product.

[0005] To address the challenges in beneficiation technology for fine-grained magnetite ore, Chinese patent application 201711107180.3 discloses an energy-saving beneficiation method for processing fine-grained magnetite ore. This method involves sequentially subjecting the iron ore to a first-stage grinding and classification, a first-stage weak magnetic separation, a second-stage grinding and classification, a second-stage weak magnetic separation, a first-stage washing and magnetic separation, a third-stage grinding and classification, a third-stage weak magnetic separation, and a second-stage washing and magnetic separation. The resulting concentrates from the first and second stages of washing and magnetic separation are combined to form a total concentrate, and all tailings from the weak magnetic separation are combined to form a total tailings. However, when this beneficiation method is used to process fine-grained, low-grade, and difficult-to-beneficiate magnetite ore with a TFe grade of 20.0%–25.0%, the final iron concentrate has an iron grade of less than 60%, an iron recovery rate of less than 40%, and a magnetic iron recovery rate of less than 60%.

[0006] In addition, Chinese patent ZL201310560636.7 discloses an energy-saving iron ore beneficiation process suitable for fine-grained magnetite ore. The tailings from the first and second stages of weak magnetic separation in the staged grinding and beneficiation process are directly used as the final tailings. The second stage weak magnetic separation concentrate is fed into the reverse flotation operation. The reverse flotation operation adopts a cationic collector reverse flotation process to obtain a portion of qualified iron concentrate in advance. The middlings obtained from the reverse flotation operation are fed into the third stage mill for middlings regrinding and three-stage weak magnetic separation to obtain the third stage weak magnetic separation concentrate. The middlings regrinding fineness is -0.030mm with a content ≥88%. The third stage weak magnetic separation concentrate and the portion of qualified iron concentrate obtained in advance by the reverse flotation operation are combined into a comprehensive iron concentrate. The tailings from the third stage weak magnetic separation are incorporated into the final tailings to obtain the total tailings. However, this mineral processing technology requires a large feed rate and a large amount of flotation reagents, and it is also difficult to process fine-grained, low-grade, difficult-to-process magnetite ores with a TFe grade of 20.0% to 25.0%. Summary of the Invention

[0007] The purpose of this invention is to address the technical challenges in the current beneficiation of fine-grained, low-grade, and difficult-to-process magnetite ores, such as low iron concentrate grade, low iron recovery rate, large flotation feed rate, large reagent consumption, and poor iron separation and enrichment effect. This invention provides a magnetic levitation combined beneficiation method for fine-grained, low-grade, and difficult-to-process magnetite ores. This method, when used to process fine-grained, low-grade, and difficult-to-process magnetite ores, features high iron concentrate grade, low flotation feed rate, high flotation feed grade, stable indicators, simple production and maintenance, and strong adaptability.

[0008] To achieve the above-mentioned objectives of this invention, a magnetic levitation combined beneficiation method for fine-grained, low-grade, and difficult-to-process magnetite ore is provided. This method is used to process fine-grained, low-grade, and difficult-to-process magnetite ore with a TFe grade of 20.0%–25.0%, an mFe grade of 10.0%–15.0%, an Fe-to-TFe ratio in non-recoverable ferrosilicon of 16%–25%, and a grinding particle size of -0.038 mm with a content of 90%–95% of the iron minerals required for individual liberation. The specific process and steps are as follows:

[0009] After the fine-grained, low-grade, and difficult-to-select magnetite ore is crushed, it is first subjected to a first-stage grinding process. The discharge from the first-stage grinding process is fed into a first-stage classification process, and the overflow from the first-stage classification process is discharged. The underflow from the first-stage classification process is returned to the first-stage grinding process. The overflow from the first-stage classification process is fed into a weak magnetic separation process to obtain a weak magnetic separation concentrate, and the weak magnetic separation tailings are discharged.

[0010] S2 Two-stage pre-classification - Two-stage grinding - Weak magnetic separation - Magnetic separation column I separation

[0011] The weak magnetic separation concentrate obtained in step S1 is concentrated. The underflow from the concentrated concentrate is fed into the second-stage pre-classification operation. The underflow from the second-stage pre-classification is fed into the second-stage grinding operation. The discharge from the second-stage grinding operation is returned to the second-stage pre-classification operation, and the overflow from the second-stage pre-classification operation is discharged. The overflow from the second-stage pre-classification operation is fed into the first-stage roughing and first-stage cleaning weak magnetic separation operation, and the tailings from the second-stage weak magnetic separation operation are discharged to obtain the second-stage weak magnetic separation concentrate. The second-stage weak magnetic separation concentrate is then processed by Concentration I. The underflow from Concentration I is fed into Magnetic Separation Column I for separation to obtain Magnetic Separation Column I concentrate, and the tailings from Magnetic Separation Column I are discharged.

[0012] S3 Magnetic Separation Column I Concentrate Reverse Flotation

[0013] The magnetic separation column I concentrate obtained in step S2 is fed into the reverse flotation operation after being concentrated in step II and stirred. The reverse flotation operation consists of one roughing, one scavenging, and three cleaning processes. The flotation scavenging tailings are discharged, and the product in the tank after the third cleaning is the final iron concentrate. The tailings from cleaning step I and the flotation scavenging concentrate are returned to concentration step II.

[0014] S4 Three-stage pre-classification - three-stage grinding - weak magnetic separation - magnetic column II separation

[0015] The tailings from magnetic separation column I discharged in step S2 and the flotation scavenging tailings discharged in step S3 are fed into concentration III for concentration treatment. The underflow from concentration III is fed into the three-stage pre-classification. The underflow from the three-stage pre-classification is fed into the three-stage grinding. The discharge from the three-stage grinding is returned to the three-stage pre-classification, and the overflow from the three-stage pre-classification is discharged. The overflow from the three-stage pre-classification is fed into a two-stage weak magnetic separation operation (one rougher and one cleaner), and the tailings from the three-stage weak magnetic separation are discharged to obtain the three-stage weak magnetic separation concentrate. The three-stage weak magnetic separation concentrate is processed by concentration IV. The underflow from concentration IV is fed into magnetic separation column II for separation to obtain magnetic separation column II concentrate, and the tailings from magnetic separation column II are discharged. The magnetic separation column II concentrate is returned to the concentration II operation in step S3, and the tailings from magnetic separation column II are returned to the concentration III operation. The discharged three-stage weak magnetic separation tailings are mixed with the tailings from the first stage of weak magnetic separation discharged in step S1 and the tailings from the second stage of weak magnetic separation discharged in step S2 to form the final tailings.

[0016] Preferably, in step S1, the first-stage classification operation uses a single spiral classifier; the first-stage grinding uses a grate ball mill, and the grinding particle size is controlled within the range of 50% to 55% of the -0.076mm particle size mass content; the weak magnetic separation operation uses a drum-shaped wet weak magnetic separator, and the magnetic field strength is in the range of 111 to 160 kA / m.

[0017] Preferably, in step S2, the two-stage pre-classification operation uses a single spiral classifier; the two-stage grinding uses a grate ball mill, and the particle size of the two-stage grinding is controlled within the range of 90% to 95% of the mass content of the -0.076mm particle size; in the two-stage weak magnetic separation operation of one coarse and one fine, the magnetic field strength of the coarse separation is in the range of 111 to 160 kA / m, and the magnetic field strength of the fine separation is in the range of 79 to 128 kA / m; the magnetic field strength of the magnetic separation column I is in the range of 11 to 15 kA / m.

[0018] Preferably, in step S3, the reverse flotation operation uses an anionic reverse flotation collector MD, which is prepared by chelation and saponification reaction of organic acid and chelating agent, with an acid value (mgKOH / g) of 90-210, a saponification value (mgKOH / g) of 90-210, and an iodine value of 100-120; the activator used is CaO. The inhibitor used is starch; the modifier used is NaOH; the concentration of the reverse flotation rougher is in the range of 30-35%, and the temperature of the reverse flotation pulp is between 31-36℃; based on the dry ore feed rate, the amount of collector MD used in the reverse flotation rougher is 550-700 g / t, the amount of CaO is 100-250 g / t, the amount of starch is 300-450 g / t, and the amount of NaOH is 950-1150 g / t; the amount of collector MD used in the reverse flotation cleaner is 110-135 g / t; no reagents are added in the reverse flotation scavenging.

[0019] Further, in step S1, the weak magnetic separation operation uses a drum-type wet weak magnetic separator with a magnetic field strength in the range of 135–150 kA / m; in step S2, the two-stage pre-classification operation uses a single spiral classifier; the two-stage grinding uses a grate-type ball mill, and the particle size of the two-stage grinding is controlled within the range of 90%–95% of the -0.076 mm particle size mass content; in the two-stage weak magnetic separation operation of roughing and cleaning, the magnetic field strength of the roughing is in the range of 135–150 kA / m, and the magnetic field strength of the cleaning is in the range of 105–120 kA / m; the magnetic field strength of the magnetic separation column I is in the range of… The concentration ranges from 11.5 to 13.5 kA / m; in step S3, the concentration of the reverse flotation rougher is in the range of 30% to 35%, and the temperature of the reverse flotation pulp is between 34 and 36°C; based on the dry ore feed rate, the amount of collector MD used in the reverse flotation rougher is 660 to 700 g / t, the amount of CaO is 140 to 190 g / t, the amount of starch is 310 to 360 g / t, and the amount of NaOH is 980 to 1060 g / t; the amount of collector MD used in the reverse flotation cleaner is 118 to 132 g / t; no reagents are added in the reverse flotation scavenging.

[0020] The specific values ​​of the above-mentioned grinding particle size, magnetic field strength, reagent dosage, etc. can all be determined based on the properties of the ore through laboratory test results.

[0021] Compared with existing technologies, the magnetic levitation combined beneficiation method for fine-grained, low-grade, and difficult-to-beneficiate magnetite ore of the present invention has the following advantages:

[0022] (1) Under the condition that the particle size of the two-stage grinding reaches more than 90% of -0.076mm, the present invention is generally carried out after conventional magnetic separation; the present invention sets up a magnetic separation column before flotation, which not only improves the flotation grade, but also coarsens the grinding particle size. At the same time, the process adaptability is greatly enhanced, and the fluctuation of ore properties within a certain range has little impact on production indicators.

[0023] (2) In this invention, after two-stage grinding-weak magnetic separation-magnetic column I separation, reverse flotation is used to pre-obtain a portion of qualified iron concentrate products that have been liberated. The remaining unliberated intergrowth iron minerals are further separated by three-stage grinding, which greatly reduces the three-stage grinding load and effectively saves grinding energy.

[0024] (3) The present invention combines the magnetic column I concentrate after two-stage grinding and the magnetic column II concentrate after three-stage grinding into the same flotation system for separation, which simplifies the process flow and reduces equipment investment and land area.

[0025] (4) The present invention adopts a reverse flotation process of roughing-three cleaning-one scavenging, and uses MD as collector, starch as inhibitor, CaO as activator, and NaOH as modifier. The flotation temperature is 31-36℃. Finally, good mineral processing indicators are obtained. The iron concentrate grade can reach more than 62.5%, the effective iron recovery rate (iron in magnetite, hematite, and iron carbonate) can reach more than 70%, and the magnetic iron recovery rate can reach more than 85.0%.

[0026] (5) The iron content in the final total tailings is between 12% and 15%, and it is mainly iron silicate. It can be sold to iron silicate cement plants as a high-quality iron corrective agent, thus realizing 100% full utilization of fine-grained, low-grade, and difficult-to-select magnetite resources, with significant comprehensive benefits.

[0027] (6) The results of industrial application show that the present invention is stable in operation, and is easy to operate and maintain in production. Attached Figure Description

[0028] Figure 1 is a schematic flowchart of the principle process of the magnetic levitation combined beneficiation method for fine-grained, low-grade, and difficult-to-benefit magnetite ore according to the present invention. Detailed Implementation

[0029] To further describe the present invention, the following detailed description, in conjunction with the accompanying drawings and embodiments, provides a magnetic levitation combined beneficiation method for fine-grained, low-grade, and difficult-to-process magnetite ore. It should be noted that any modifications, equivalent substitutions, or improvements made within the technical concept and principles of the present invention should be included within the scope of protection of the present invention.

[0030] In the examples, the fine-grained, low-grade, and difficult-to-process magnetite ore samples were taken from an iron mine in East China. The results of the multi-element chemical analysis of the raw ore are shown in Table 1, and the results of the iron phase analysis are shown in Table 2.

[0031] Table 1. Results of multi-element chemical analysis of the raw ore (%)

[0032]

[0033] Table 2. Results of iron phase analysis in raw ore (%)

[0034]

[0035] This ore is an iron ore primarily composed of magnetite, with a TFe grade of 23.41% and an MFe grade of 13.87%. The SiO2 content is relatively high at 54.18%, while the content of harmful impurities S and P is low. Phase analysis results show that the distribution rate of magnetic iron is 59.13%, and the content of iron silicate is also high, with a distribution rate of 20.78%. Currently, due to limitations in beneficiation technology, this portion of iron cannot be recovered, which will affect the iron concentrate recovery rate. The content of other useful iron minerals is also low.

[0036] As shown in Figure 1, the principle process flow diagram of the magnetic levitation combined beneficiation method for fine-grained, low-grade, and difficult-to-process magnetite ore according to the present invention can be seen, the present invention is implemented by the following steps:

[0037] After crushing, the fine-grained, low-grade, and difficult-to-process magnetite ore with a TFe grade of 23.41%, MFe of 13.87%, iron silicate content as high as 4.85%, and SiO2 content as high as 54.18% undergoes a first-stage grinding process. The discharge from the first-stage grinding is fed into a first-stage classification process, from which the first-stage classification overflow is discharged, and the underflow from the first-stage classification is returned to the first-stage grinding process. The first-stage classification overflow is fed into a weak magnetic separation process to obtain a first-stage weak magnetic separation concentrate, from which the first-stage weak magnetic separation tailings are discharged. The first-stage classification process uses a single spiral classifier, and the first-stage grinding process uses a grate ball mill, with the particle size controlled at -0.076mm particle size and a mass content of 55%. The weak magnetic separation process uses a drum-type wet weak magnetic separator with a magnetic field strength of 143.24 kA / m.

[0038] S2 Two-stage pre-classification - Two-stage grinding - Weak magnetic separation - Magnetic separation column I separation

[0039] The weak magnetic separation concentrate obtained in step S1 is concentrated. The underflow from the concentrated concentrate is fed into the second-stage pre-classification operation. The underflow from the second-stage pre-classification is fed into the second-stage grinding operation. The discharge from the second-stage grinding operation is returned to the second-stage pre-classification operation, and the overflow from the second-stage pre-classification operation is discharged. The overflow from the second-stage pre-classification operation is fed into the two-stage weak magnetic separation operation (roughing and cleaning), and the tailings from the second-stage weak magnetic separation operation are discharged to obtain the second-stage weak magnetic separation concentrate. The second-stage weak magnetic separation concentrate is then processed by Concentration I. The underflow from Concentration I is fed into Magnetic Separation Column I for separation to obtain Magnetic Separation Column I concentrate, and the tailings from Magnetic Separation Column I are discharged. The two-stage pre-classification operation uses a single spiral classifier, and the two-stage grinding uses a grate ball mill. The particle size of the two-stage grinding is controlled at -0.076mm with a mass content of 90%. In the two-stage weak magnetic separation operation of one roughing and one cleaning, the magnetic field strength of the roughing is 143.24kA / m, and the magnetic field strength of the cleaning is 111.41kA / m. The magnetic field strength of the magnetic separation column I is 12.6kA / m.

[0040] S3 Magnetic Separation Column I Concentrate Reverse Flotation

[0041] The magnetic separation column I concentrate obtained in step S2 is fed into the reverse flotation operation after being concentrated in step II and stirred. The reverse flotation operation consists of one roughing, one scavenging, and three cleaning processes. The flotation scavenging tailings are discharged, and the product in the tank after the third cleaning is the final iron concentrate. The cleaning tailings and flotation scavenging concentrate are returned to the concentration II. The reverse flotation operation uses an anionic reverse flotation collector MD, which is prepared by chelation and saponification reaction of organic acid and chelating agent. The acid value (mgKOH / g) is 90-210, the saponification value (mgKOH / g) is 90-210, and the iodine value is 100-120. The activator used is CaO; the depressant used is starch; and the modifier used is NaOH. The roughing concentration in the reverse flotation is in the range of 30-35%, and the pulp temperature is 35℃. Based on the dry ore feed, the dosage of collector MD in the roughing stage is 686 g / t, the dosage of CaO is 160 g / t, the dosage of starch is 326 g / t, and the dosage of NaOH is 1015 g / t. The dosage of collector MD in the cleaning stage is 127 g / t. No reagents are added during the scavenging stage of the reverse flotation.

[0042] S4 Three-stage pre-classification - three-stage grinding - weak magnetic separation - magnetic column II separation

[0043] The tailings from magnetic separation column I discharged in step S2 and the flotation scavenging tailings discharged in step S3 are fed into concentration III for concentration treatment. The underflow from concentration III is fed into the three-stage pre-classification. The underflow from the three-stage pre-classification is fed into the three-stage grinding. The discharge from the three-stage grinding is returned to the three-stage pre-classification, and the overflow from the three-stage pre-classification is discharged. The overflow from the three-stage pre-classification is fed into a two-stage weak magnetic separation operation (one rougher and one cleaner), and the tailings from the three-stage weak magnetic separation are discharged to obtain the three-stage weak magnetic separation concentrate. The three-stage weak magnetic separation concentrate is processed by concentration IV. The underflow from concentration IV is fed into magnetic separation column II for separation to obtain magnetic separation column II concentrate, and the tailings from magnetic separation column II are discharged. The magnetic separation column II concentrate is returned to the concentration II operation in step S3, and the tailings from magnetic separation column II are returned to the concentration III operation. The discharged three-stage weak magnetic separation tailings are mixed with the tailings from the first stage of weak magnetic separation discharged in step S1 and the tailings from the second stage of weak magnetic separation discharged in step S2 to form the final tailings. The three-stage classification uses hydrocyclones, the three-stage grinding uses grate ball mills, and the particle size of the three-stage grinding is controlled at 95% of the -0.038mm particle size; the coarsening magnetic field strength of the two-stage weak magnetic separation operation is 143.24kA / m, and the cleaning magnetic field strength is 111.41kA / m; the magnetic column magnetic field strength of the magnetic separation column II operation is 12.6kA / m.

[0044] Following the above process and steps, the beneficiation of this fine-grained, low-grade, and difficult-to-process magnetite ore yielded an iron concentrate yield of 21.35%, a TFe grade of 63.15%, and an iron recovery rate of 57.59%. The recovery rate of effective iron (iron from magnetite, hematite, and ferric carbonate) was 74.12%, with magnetic iron recovery exceeding 88.7%. The final total tailings iron grade was 12.62%. The total tailings contained more than 65% SiO2, and the main iron mineral was ferrosilicon with a fine particle size. It is a high-quality iron corrective agent for the production of iron-containing silicate cement, with a selling price between 50 and 80 yuan per ton. The method of this invention processes fine-grained, low-grade, and difficult-to-process magnetite ore, achieving 100% full utilization of the magnetite ore resources. The concentrator does not need to build a tailings dam, which not only saves on tailings dam land use and land acquisition costs, as well as tailings dam operating costs, but also avoids the safety risks associated with tailings dam operation. It has achieved unexpected technical and economic effects, with significant economic, environmental, and social (safety) benefits.

[0045] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A magnetic levitation combined beneficiation method for fine-grained, low-grade, and difficult-to-process magnetite ore, used to process fine-grained, low-grade, and difficult-to-process magnetite ore with a TFe grade in the range of 20.0%–25.0%, an mFe grade in the range of 10.0%–15.0%, an Fe-to-TFe ratio in non-recoverable iron silicate between 16% and 25%, and a grinding particle size of -0.038 mm with a particle size content in the range of 90%–95% to achieve individual liberation of iron minerals, characterized in that… The following steps are used to achieve this: S1: One-stage grinding - one-stage classification - weak magnetic separation After the fine-grained, low-grade, and difficult-to-select magnetite ore is crushed, it is first ground in one stage. The discharge from the first stage of grinding is fed into the first stage of classification. The overflow from the first stage of classification is discharged, and the underflow from the first stage of classification is returned to the first stage of grinding. A staged overflow is fed into the weak magnetic separation operation to obtain a staged weak magnetic separation concentrate and a staged weak magnetic separation tailings are discharged. S2 Two-stage pre-classification - Two-stage grinding - Weak magnetic separation - Magnetic separation column I separation The weak magnetic separation concentrate obtained in step S1 is concentrated. The underflow from the concentrated concentrate is fed into the second-stage pre-classification operation. The underflow from the second-stage pre-classification is fed into the second-stage grinding operation. The discharge from the second-stage grinding operation is returned to the second-stage pre-classification operation, and the overflow from the second-stage pre-classification operation is discharged. The overflow from the second-stage pre-classification operation is fed into the first-stage roughing and first-stage cleaning weak magnetic separation operation, and the tailings from the second-stage weak magnetic separation operation are discharged to obtain the second-stage weak magnetic separation concentrate. The second-stage weak magnetic separation concentrate is then processed by Concentration I. The underflow from Concentration I is fed into Magnetic Separation Column I for separation to obtain Magnetic Separation Column I concentrate, and the tailings from Magnetic Separation Column I are discharged. S3 Magnetic Separation Column I Concentrate Reverse Flotation The magnetic separation column I concentrate obtained in step S2 is fed into the reverse flotation operation after being concentrated in step II and stirred. The reverse flotation operation consists of one roughing, one scavenging, and three cleaning processes. The flotation scavenging tailings are discharged, and the product in the tank after the third cleaning is the final iron concentrate. The tailings from cleaning step I and the flotation scavenging concentrate are returned to concentration step II. S4 Three-stage pre-classification - three-stage grinding - weak magnetic separation - magnetic column II separation The tailings from magnetic separation column I discharged in step S2 and the flotation scavenging tailings discharged in step S3 are fed into concentration III for concentration treatment. The underflow from concentration III is fed into the three-stage pre-classification. The underflow from the three-stage pre-classification is fed into the three-stage grinding. The discharge from the three-stage grinding is returned to the three-stage pre-classification, and the overflow from the three-stage pre-classification is discharged. The overflow from the three-stage pre-classification is fed into a two-stage weak magnetic separation operation (one rougher and one cleaner), and the tailings from the three-stage weak magnetic separation are discharged to obtain the three-stage weak magnetic separation concentrate. The three-stage weak magnetic separation concentrate is processed by concentration IV. The underflow from concentration IV is fed into magnetic separation column II for separation to obtain the magnetic separation column II concentrate, and the tailings from the magnetic separation column II are discharged. The magnetic separation column II concentrate is returned to the concentration II operation in step S3, and the tailings from the magnetic separation column II are returned to the concentration III operation. The discharged three-stage weak magnetic separation tailings are mixed with the tailings from the first stage of weak magnetic separation discharged in step S1 and the tailings from the second stage of weak magnetic separation discharged in step S2 to form the final tailings. The final tailings are used as an iron correcting agent in the production of iron-containing silicate cement.

2. The magnetic levitation combined beneficiation method for fine-grained, low-grade, and difficult-to-process magnetite ore as described in claim 1, characterized in that: In step S1, the first-stage classification operation uses a single spiral classifier; the first-stage grinding uses a grate ball mill, and the grinding particle size is controlled within the range of 50% to 55% of the -0.076mm particle size mass content.

3. The magnetic levitation combined beneficiation method for fine-grained, low-grade, and difficult-to-process magnetite ore as described in claim 1, characterized in that: In step S1, the weak magnetic separation operation uses a drum-type wet weak magnetic separator with a magnetic field strength in the range of 111 to 160 kA / m.

4. The magnetic levitation combined beneficiation method for fine-grained, low-grade, and difficult-to-process magnetite ore as described in claim 1, characterized in that: In step S2, the two-stage pre-classification operation uses a single spiral classifier; the two-stage grinding uses a grate ball mill, and the particle size of the two-stage grinding is controlled within the range of 90% to 95% of the mass content of the -0.076mm particle size.

5. The magnetic levitation combined beneficiation method for fine-grained, low-grade, and difficult-to-process magnetite ore as described in claim 1, characterized in that: In step S2, the two-stage weak magnetic separation operation, one coarse and one fine, has a coarse magnetic field strength in the range of 111 to 160 kA / m and a fine magnetic field strength in the range of 79 to 128 kA / m.

6. The magnetic levitation combined beneficiation method for fine-grained, low-grade, and difficult-to-process magnetite ore as described in claim 1, characterized in that: In step S2, the magnetic field strength of the magnetic separation column I is in the range of 11 to 15 kA / m.

7. The magnetic levitation combined beneficiation method for fine-grained, low-grade, and difficult-to-process magnetite ore as described in claim 1, characterized in that: In step S3, the reverse flotation operation uses an anionic reverse flotation collector MD, which is prepared by chelation and saponification reaction of organic acid and chelating agent. The acid value (mgKOH / g) is 90-210, the saponification value (mgKOH / g) is 90-210, and the iodine value is 100-120. The activator used is CaO, the inhibitor used is starch, and the modifier used is NaOH.

8. The magnetic levitation combined beneficiation method for fine-grained, low-grade, and difficult-to-process magnetite ore as described in claim 7, characterized in that: In step S3, the concentration of the reverse flotation rougher is in the range of 30-35%, and the temperature of the reverse flotation pulp is between 31-36℃. Based on the dry ore feed, the amount of collector MD used in the reverse flotation rougher is 550-700 g / t, the amount of CaO is 100-250 g / t, the amount of starch is 300-450 g / t, and the amount of NaOH is 950-1150 g / t. The amount of collector MD used in the reverse flotation cleaner is 110-135 g / t. No reagents are added in the reverse flotation scavenging.

9. The magnetic levitation combined beneficiation method for fine-grained, low-grade, and difficult-to-process magnetite ore as described in claim 2, characterized in that: In step S1, the weak magnetic separation operation adopts a drum-shaped wet weak magnetic separator with a magnetic field strength in the range of 111 to 160 kA / m. In step S2, the two-stage pre-classification operation uses a single spiral classifier; the two-stage grinding uses a grate ball mill, and the particle size of the two-stage grinding is controlled within the range of 90% to 95% of the -0.076mm particle size mass content; in the two-stage weak magnetic separation operation of one coarse and one fine, the magnetic field strength of the coarse separation is in the range of 111 to 160 kA / m, and the magnetic field strength of the fine separation is in the range of 79 to 128 kA / m; the magnetic field strength of the magnetic separation column I is in the range of 11 to 15 kA / m. In step S3, the reverse flotation operation uses an anionic reverse flotation collector MD, which is prepared by chelation and saponification reaction of organic acid and chelating agent, with an acid value (mgKOH / g) of 90-210, a saponification value (mgKOH / g) of 90-210, and an iodine value of 100-120; the activator used is CaO. The inhibitor used is starch; the modifier used is NaOH; the concentration of the reverse flotation rougher is in the range of 30-35%, and the temperature of the reverse flotation pulp is between 31-36℃; based on the dry ore feed rate, the dosage of collector MD used in the reverse flotation rougher is 550-700 g / t, the dosage of CaO is 100-250 g / t, the dosage of starch is 300-450 g / t, and the dosage of NaOH is 950-1150 g / t; the dosage of collector MD used in the reverse flotation cleaner is 110-135 g / t; no reagents are added in the reverse flotation scavenging.

10. The magnetic levitation combined beneficiation method for fine-grained, low-grade, and difficult-to-process magnetite ore as described in claim 9, characterized in that: In step S1, the weak magnetic separation operation adopts a drum-shaped wet weak magnetic separator with a magnetic field strength in the range of 135 to 150 kA / m. In step S2, the two-stage pre-classification operation uses a single spiral classifier; the two-stage grinding uses a grate ball mill, and the particle size of the two-stage grinding is controlled within the range of 90% to 95% of the -0.076mm particle size mass content; in the two-stage weak magnetic separation operation of one roughing and one cleaning stage, the magnetic field strength of the roughing stage is in the range of 135 to 150 kA / m, and the magnetic field strength of the cleaning stage is in the range of 105 to 120 kA / m; the magnetic field strength of the magnetic separation column I is in the range of 11.5 to 13.5 kA / m. In step S3, the concentration of the reverse flotation rougher is in the range of 30-35%, and the temperature of the reverse flotation pulp is between 34-36℃. Based on the dry ore feed rate, the amount of collector MD used in the reverse flotation rougher is 660-700 g / t, the amount of CaO is 140-190 g / t, the amount of starch is 310-360 g / t, and the amount of NaOH is 980-1060 g / t. The amount of collector MD used in the reverse flotation cleaner is 118-132 g / t. No reagents are added in the reverse flotation scavenging.

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