Magnetic suspension combined beneficiation method for micro-fine particle low-grade refractory magnetite ore

Abstract

The invention discloses a magnetic suspension combined beneficiation method for micro-fine particle low-grade refractory magnetite, which comprises the following steps: first-stage ore grinding, first-stage grading and low-intensity magnetic separation are carried out, the obtained first-stage low-intensity magnetic separation concentrate is subjected to second-stage pre-grading, second-stage ore grinding, low-intensity magnetic separation and magnetic separation column I separation, and the obtained magnetic separation column I concentrate is subjected to reverse flotation operation; one-time roughing, one-time scavenging and three-time concentration are adopted in reverse flotation operation, products in a groove after third-time concentration are final iron ore concentrate, tailings of a magnetic separation column I and flotation scavenging tailings are fed into a magnetic separation column II to be subjected to three-section pre-classification, three-section ore grinding, low-intensity magnetic separation and separation, and the tailings of the third-section low-intensity magnetic separation, the tailings of the first-section low-intensity magnetic separation and the tailings of the second-section low-intensity magnetic separation are mixed to be final tailings. The final tailings are used as an iron correcting agent for producing the iron-containing Portland cement. The method has the advantages of being high in iron ore concentrate grade, small in flotation feeding amount, high in flotation feeding grade, stable in index, easy and convenient to produce and maintain, high in adaptability and the like.

Description

Technical Field

[0001] The invention belongs to the technical field of iron ore dressing, and specifically relates to a method for dressing fine-grained low-grade magnetite ore, which is particularly suitable for processing magnetite ore with a TFe grade in the range of 20.0% to 25.0%, an mFe grade in the range of 10.0% to 15.0%, a fine iron mineral embedded particle size (the grinding particle size is in the range of -0.038mm particle size content 90% to 95% for the iron mineral to be dissociated monomerically), and gangue minerals mainly being quartz, silicate, and carbonate. Background Art

[0002] Steel is an important foundation for the development of the national economy, and economic growth is inseparable from the demand for iron ore. In the context of the current reform of the steel industry and environmental protection restrictions, improving the utilization rate of iron ore resources is of great significance to the sustainable development of mineral resources and the development of the steel industry.

[0003] In order to improve the iron grade and recovery rate in the ore dressing process and make reasonable use of low-grade, fine-grained, complex and difficult-to-select iron ore, it is necessary to crush, finely grind, magnetically separate and flotate the iron ore. In order to effectively select low-grade, finely embedded and complex ore into high-grade concentrate, it is usually necessary to flotate the ore. Before entering the flotation operation, reasonable fine grinding and magnetic separation processes are critical for the development of low-grade fine-grained magnetite ore resources, and are key technologies for flotation preparation operations.

[0004] In terms of magnetic separation, the existing weak magnetic separator is an efficient and simple wet separation equipment for fine-grained strong magnetic minerals. It has the characteristics of small size, light weight, and simple operation. It is effective for the separation of fine-grained strong magnetic minerals, but the magnetic separation effect of the weak magnetic separator is easily affected by the particle size and grade of the feed, and the magnetic separation effect is prone to fluctuations. The mineral processing indicators such as grade and recovery rate are not ideal. Due to the limitations of magnetic separation technology at this stage, useful minerals with large differences in particle size composition and ore properties cannot be effectively separated, and thus cannot provide qualified raw materials for subsequent flotation operations. As a result, flotation indicators are difficult to guarantee, affecting the grade and recovery rate of the final concentrate product.

[0005] In order to solve the technical problem of beneficiation of fine-grained magnetite, Chinese patent application 201711107180.3 discloses an energy-saving beneficiation method for processing fine-grained magnetite: the iron ore is sequentially subjected to the first stage of grinding and classification, the first stage of weak magnetic separation, the second stage of grinding and classification, the second stage of weak magnetic separation, the first stage of washing and magnetic separation, the third stage of grinding and classification, the third stage of weak magnetic separation, and the second stage of washing and magnetic separation. The first stage of washing and magnetic separation concentrate and the second stage of washing and magnetic separation concentrate are combined into a total concentrate, and all the weak magnetic separation tailings are combined into a total tailings. However, when this beneficiation method is used to process fine-grained low-grade and difficult-to-select magnetite ore with a TFe grade of 20.0% to 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-extracting ore dressing process suitable for the dressing of fine-grained magnetite ore. The first-stage weak magnetic separation tailings and the second-stage weak magnetic separation tailings of the stage grinding process are directly used as the final tailings, and the second-stage weak magnetic separation concentrate obtained by the second-stage weak magnetic separation is fed to the reverse flotation operation; the reverse flotation operation adopts a cationic collector reverse flotation process to obtain part of the qualified iron concentrate in advance, and the middlings obtained by the reverse flotation operation are fed to the third-stage mill for re-grinding of the middlings after magnetic separation and dehydration - the three-stage weak magnetic separation obtains the three-stage weak magnetic separation concentrate, the grinding fineness of the re-grinded middlings is -0.030mm and the content is ≥88%, the three-stage weak magnetic separation concentrate and the part of the qualified iron concentrate obtained in advance by the reverse flotation operation are combined into a comprehensive iron concentrate, and the three-stage weak magnetic separation tailings are incorporated into the final tailings to obtain the total tailings. However, this mineral processing process requires a large amount of flotation feed and a large amount of flotation reagents, and is also difficult to process fine-grained, low-grade, difficult-to-select magnetite ores with a TFe grade of 20.0% to 25.0%. Summary of the invention

[0007] The purpose of the present invention is to provide a magnetic flotation combined beneficiation method for fine-grained low-grade difficult-to-select magnetite, in view of the technical difficulties in the current beneficiation of fine-grained low-grade difficult-to-select magnetite, such as low iron concentrate grade, low iron recovery rate, large flotation feed amount, large amount of reagent used, and poor iron separation and enrichment effect. When the magnetic flotation combined beneficiation method is used to process fine-grained low-grade difficult-to-select magnetite, it has the characteristics of high iron concentrate grade, small flotation feed amount, high flotation feed grade, stable indicators, simple production and maintenance, and strong adaptability.

[0008] To achieve the above-mentioned purpose of the present invention, the present invention provides a magnetic flotation combined beneficiation method for fine-grained low-grade refractory magnetite ore, which is used to process the original ore TFe grade in the range of 20.0% to 25.0%, the mFe grade in the range of 10.0 to 15.0%, the ratio of Fe to TFe in the unrecoverable iron silicate between 16% and 25%, the grinding particle size in the range of -0.038mm particle content of 90% to 95%, and the iron mineral can be dissociated into monomers. The method is specifically implemented by the following processes and steps:

[0009] S1 one-stage grinding-one-stage classification-weak magnetic separation

[0010] 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 after the first-stage grinding process is fed into a first-stage classification process, and a first-stage classification overflow is discharged. The underflow after the first-stage classification process 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, and a first-stage weak magnetic separation tailings is discharged.

[0011] S2 two-stage pre-classification - two-stage grinding - weak magnetic separation - magnetic column I separation

[0012] The first-stage weak magnetic separation concentrate obtained in step S1 is concentrated, and the concentrated underflow is fed into the second-stage pre-classification operation, and the underflow after the second-stage pre-classification is fed into the second-stage grinding. The discharge after the second-stage grinding is returned to the second-stage pre-classification, and the second-stage pre-classification overflow is discharged; the second-stage pre-classification overflow is fed into a two-stage weak magnetic separation operation of a coarse and a fine, and the second-stage weak magnetic separation tailings are discharged to obtain a second-stage weak magnetic separation concentrate; the second-stage weak magnetic separation concentrate is treated with concentration I, and the concentration I underflow is fed into magnetic separation column I for separation to obtain a magnetic separation column I concentrate, and the magnetic separation column I tailings are discharged;

[0013] S3 Magnetic Separation Column I Concentrate Reverse Flotation

[0014] The magnetic column Ⅰ concentrate obtained in step S2 is concentrated Ⅱ and stirred before being fed into reverse flotation operation. The reverse flotation operation adopts 1 roughing, 1 scavenging and 3 concentrating, and the flotation scavenging tailings are discharged. The product in the tank after the third concentrating is the final iron concentrate, and the concentrating Ⅰ tailings and flotation scavenging concentrate are returned to concentration Ⅱ;

[0015] S4 three-stage pre-classification - three-stage grinding - weak magnetic separation - magnetic column II separation

[0016] The tailings of magnetic separation column I discharged from step S2 and the tailings of flotation scavenging discharged from step S3 are fed to concentration III for concentration treatment, the bottom flow of concentration III is fed to three-stage pre-classification, the bottom flow after three-stage pre-classification is fed to three-stage grinding, the discharge after three-stage grinding is returned to three-stage pre-classification, and the overflow of three-stage pre-classification is discharged; the overflow of three-stage pre-classification is fed to two-stage weak magnetic separation operations of one coarse and one fine, and three-stage weak magnetic separation tailings are discharged to obtain three-stage weak magnetic separation concentrate; the three-stage weak magnetic separation concentrate is treated by concentration IV, and the bottom flow of concentration IV is fed to magnetic separation column II for separation to obtain magnetic separation column II concentrate, and magnetic separation column II tailings are discharged; the magnetic separation column II concentrate is returned to the concentration II operation in step S3, and the magnetic separation column II tailings are returned to the concentration III operation; the discharged three-stage weak magnetic separation tailings are mixed with the first-stage weak magnetic separation tailings discharged from step S1 and the second-stage weak magnetic separation tailings discharged from step S2 to form the final tailings.

[0017] Preferably, in step S1, the first stage classification operation adopts a single spiral classifier; the first stage grinding adopts a grate ball mill, and the first stage grinding particle size is controlled within the range of 50% to 55% mass content of the -0.076 mm particle size; the weak magnetic separation operation adopts a drum-type wet weak magnetic separator, and the magnetic field strength is within the range of 111 to 160 kA / m.

[0018] Preferably, in step S2, the two-stage pre-classification operation adopts a single spiral classifier; the two-stage grinding adopts a grate ball mill, and the second-stage grinding particle size is controlled within the range of 90% to 95% of the mass content of the -0.076 mm particle size; in the two-stage weak magnetic separation operation of one coarse and one fine, the coarse selection magnetic field strength is within the range of 111 to 160 kA / m, and the fine selection magnetic field strength is within the range of 79 to 128 kA / m; the magnetic field strength of the magnetic separation column I is within the range of 11 to 15 kA / m.

[0019] Preferably, in step S3, the reverse flotation operation uses an anionic reverse flotation collector MD, which is prepared by chelating and saponifying an organic acid and a 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 regulator used is NaOH; the reverse flotation roughing concentration is in the range of 30-35%, and the reverse flotation The temperature of the mineral processing pulp is between 31 and 36°C; according to the amount of dry ore fed to the flotation, the dosage of the collector MD used in the reverse flotation roughing is 550-700g / t, the dosage of CaO is 100-250g / t, the dosage of starch is 300-450g / t, and the dosage of NaOH is 950-1150g / t; the dosage of the collector MD used in the reverse flotation concentration is 110-135g / t; and no drug is added in the reverse flotation scavenging.

[0020] Furthermore, in step S1, the weak magnetic separation operation adopts a drum-shaped wet weak magnetic separator, and the magnetic field strength is in the range of 135-150 kA / m; in step S2, the second stage pre-classification operation adopts a single spiral classifier; the second stage grinding adopts a grid ball mill, and the second stage grinding particle size is controlled in the range of -0.076 mm particle mass content 90% to 95%; in the two-stage weak magnetic separation operation of one coarse and one fine, the roughing magnetic field strength is in the range of 135-150 kA / m, and the fine magnetic field strength is in the range of 105-120 kA / m; the magnetic field strength of the magnetic separation column I is 11.5~13.5kA / m range; in step S3, the reverse flotation roughing concentration is in the range of 30~35%, and the reverse flotation pulp temperature is between 34-36℃; according to the dry ore amount of flotation feed, the amount of collector MD used in the reverse flotation roughing is 660~700g / t, the amount of CaO is 140~190g / t, the amount of starch is 310~360g / t, and the amount of NaOH is 980~1060g / t; the amount of collector MD used in the reverse flotation concentration is 118~132g / t; and no drug is added in the reverse flotation scavenging.

[0021] The specific values ​​of the above parameters such as grinding particle size, magnetic field strength, reagent dosage, etc. can all be determined based on the properties of the ore and through laboratory test results.

[0022] Compared with the prior art, the magnetic flotation combined beneficiation method of fine-grained low-grade difficult-to-be-selected magnetite ore of the present invention has the following advantages:

[0023] (1) In the present invention, under the condition that the particle size of the second-stage grinding reaches more than 90% of -0.076mm, flotation is generally performed after conventional magnetic separation; in the present invention, a magnetic separation column operation is arranged before flotation, which not only improves the flotation grade, but also can reduce the coarse 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 obvious effect on production indicators.

[0024] (2) After the second-stage grinding-weak magnetic separation-magnetic column I separation, the present invention uses reverse flotation to pre-acquire a portion of qualified iron concentrate products that have been monomerically dissociated from the concentrate in the magnetic column I, and continues to perform the third-stage grinding and re-separation of the remaining unmonomerized conjoined iron minerals, which greatly reduces the load of the third-stage grinding and effectively saves grinding energy consumption.

[0025] (3) The present invention combines the concentrate of magnetic column I after the second stage of grinding and the concentrate of magnetic column II after the third stage of grinding and enters the same flotation system for separation, thereby simplifying the process flow and reducing equipment investment and floor space.

[0026] (4) The present invention adopts a reverse flotation process of one coarse-three fines-one sweep, and uses MD as a collector, starch as a depressant, CaO as an activator, NaOH as a regulator, and a flotation temperature of 31-36° C., and finally obtains good mineral processing indicators, the iron concentrate grade can reach more than 62.5%, the effective iron (iron in magnetite, hematite (limonite), and iron carbonate) recovery rate can reach more than 70%, and the magnetic iron recovery rate can reach more than 85.0%.

[0027] (5) The iron grade in the final total tailings is between 12% and 15%, and is mainly iron silicate, which can be sold to iron-containing silicate cement plants as a high-quality iron corrector, thereby achieving 100% full quantitative utilization of fine-grained, low-grade, difficult-to-select magnetite resources, with significant comprehensive benefits.

[0028] (6) The industrial application results show that the present invention is stable in operation, easy to operate and maintain in production. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 The present invention is a process flow chart of the principle of a magnetic flotation combined beneficiation method for fine-grained, low-grade, difficult-to-select magnetite ore. DETAILED DESCRIPTION

[0030] To further describe the present invention, the magnetic flotation combined beneficiation method for fine-grained low-grade refractory magnetite ore of the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be noted that any modification, equivalent replacement, improvement, etc. made within the technical ideas and principles of the present invention should be included in the protection scope of the present invention.

[0031] In the examples, the fine-grained, low-grade, refractory magnetite ore samples were taken from an iron mine in East China. The results of the chemical multi-element analysis of the raw ore are shown in Table 1, and the results of the iron phase analysis are shown in Table 2.

[0032] Table 1 Results of chemical multi-element analysis of raw ore (%)

[0033] Test items TFe S P CaO MgO <![CDATA[SiO2]]> content 23.41 0.26 0.064 3.49 1.99 54.18 Test items <![CDATA[Al2O3]]> <![CDATA[TiO2]]> <![CDATA[V2O5]]> MnO <![CDATA[K2O]]> <![CDATA[Na2O]]> content 3.54 0.09 0.005 0.17 0.73 0.35 Test items C NiO Cu ZnO Burning MFe content 0.61 0.004 Not detected 0.008 2.56 13.87

[0034] Table 2 Analysis results of iron phase of raw ore (%)

[0035] Iron Phase Iron content Occupancy magnetite 13.80 59.13 Hematite 2.50 10.71 Iron carbonate 1.89 8.10 Iron silicate 4.85 20.78 Iron sulfide 0.30 1.28 Full Iron 23.34 100.00

[0036] The ore is mainly composed of magnetite, with a TFe grade of 23.41% and MFe of 13.87%; the SiO2 content is as high as 54.18%, and the harmful impurities S and P are relatively low. The results of phase analysis show that the distribution rate of magnetic iron is 59.13%. In addition, the content of iron silicate is relatively high, with a distribution rate of 20.78%. Currently, due to the limitation of the level of mineral processing technology, this part of iron cannot be recovered, which will affect the recovery rate of iron concentrate. The content of other useful iron minerals is relatively low.

[0037] Depend on Figure 1 As shown in the process flow chart of the principle of the magnetic levitation combined beneficiation method for fine-grained low-grade and difficult-to-select magnetite ore of the present invention, the present invention is implemented by the following steps:

[0038] S1 one-stage grinding-one-stage classification-weak magnetic separation

[0039] After crushing the fine-grained low-grade and difficult-to-select magnetite ore with a TFe grade of 23.41%, MFe of 13.87%, an iron silicate content of up to 4.85%, and a high SiO2 content of 54.18%, a first-stage grinding is carried out, and the discharge after the first-stage grinding is fed into a first-stage classification operation, and a first-stage classification overflow is discharged, and the bottom flow after the first-stage classification returns to the first-stage grinding; the first-stage classification overflow is fed into a weak magnetic separation operation to obtain a first-stage weak magnetic separation concentrate, and a first-stage weak magnetic separation tailings is discharged. The first-stage classification operation adopts a single spiral classifier, the first-stage grinding adopts a grid-type ball mill, and the first-stage grinding particle size is controlled at a mass content of 55% at a particle level of -0.076mm; the weak magnetic separation operation adopts a drum-shaped wet weak magnetic separator, and the magnetic field strength is 143.24kA / m.

[0040] S2 two-stage pre-classification - two-stage grinding - weak magnetic separation - magnetic column I separation

[0041] The first-stage weak magnetic separation concentrate obtained in step S1 is concentrated, and the concentrated underflow is fed to the second-stage pre-classification operation. The underflow after the second-stage pre-classification is fed to the second-stage grinding. The discharge after the second-stage grinding is returned to the second-stage pre-classification, and the second-stage pre-classification overflow is discharged; the second-stage pre-classification overflow is fed to two-stage weak magnetic separation operations of one coarse and one fine, and the second-stage weak magnetic separation tailings are discharged to obtain the second-stage weak magnetic separation concentrate; the second-stage weak magnetic separation concentrate is treated with concentration I, and the underflow of concentration I is fed to magnetic separation column I for separation to obtain magnetic separation column I concentrate, and the magnetic separation column I tailings are discharged. The two-stage pre-classification operation adopts a single spiral classifier, the two-stage grinding adopts a grid ball mill, and the second-stage grinding particle size is controlled at -0.076mm particle size with a mass content of 90%; in the two-stage weak magnetic separation operation of one coarse and one fine, the coarse selection magnetic field strength is 143.24kA / m, and the fine selection magnetic field strength is 111.41kA / m; the magnetic field strength of the magnetic separation column I is 12.6kA / m.

[0042] S3 Magnetic Separation Column I Concentrate Reverse Flotation

[0043] The magnetic column Ⅰ concentrate obtained in step S2 is concentrated Ⅱ and stirred before being fed into reverse flotation operation. The reverse flotation operation adopts 1 roughing selection, 1 scavenging selection and 3 concentrating selections, and the flotation scavenging tailings are discharged. The product in the tank after the third concentrating is the final iron concentrate, and the concentrating Ⅰ tailings and flotation scavenging concentrate are returned to concentration Ⅱ. The reverse flotation operation adopts anionic reverse flotation collector MD, which is prepared by chelating and saponifying 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 adopted is CaO; the inhibitor adopted is starch; the adjusting agent adopted is NaOH; the reverse flotation roughing concentration is in the range of 30-35%, and the reverse flotation pulp temperature is 35°C; according to the dry ore amount of flotation feed, the amount of collector MD adopted in the reverse flotation roughing is 686g / t, the amount of CaO is 160g / t, the amount of starch is 326g / t, and the amount of NaOH is 1015g / t; the amount of collector MD adopted in the reverse flotation concentration is 127g / t; and no drug is added in the reverse flotation scavenging.

[0044] S4 three-stage pre-classification - three-stage grinding - weak magnetic separation - magnetic column II separation

[0045] The tailings of magnetic separation column I discharged from step S2 and the tailings of flotation scavenging discharged from step S3 are fed to concentration III for concentration treatment, the bottom flow of concentration III is fed to three-stage pre-classification, the bottom flow after three-stage pre-classification is fed to three-stage grinding, the discharge after three-stage grinding is returned to three-stage pre-classification, and the overflow of three-stage pre-classification is discharged; the overflow of three-stage pre-classification is fed to two-stage weak magnetic separation operations of one coarse and one fine, and three-stage weak magnetic separation tailings are discharged to obtain three-stage weak magnetic separation concentrate; the three-stage weak magnetic separation concentrate is treated by concentration IV, and the bottom flow of concentration IV is fed to magnetic separation column II for separation to obtain magnetic separation column II concentrate, and magnetic separation column II tailings are discharged; the magnetic separation column II concentrate is returned to the concentration II operation in step S3, and the magnetic separation column II tailings are returned to the concentration III operation; the discharged three-stage weak magnetic separation tailings are mixed with the first-stage weak magnetic separation tailings discharged from step S1 and the second-stage weak magnetic separation tailings discharged from step S2 to form the final tailings. The three-stage classification adopts a hydrocyclone, the three-stage grinding adopts a grid ball mill, and the three-stage grinding particle size is controlled at 95% of the -0.038mm particle size content; the roughing magnetic field strength of the two-stage weak magnetic separation operation is 143.24kA / m, and the fine magnetic field strength is 111.41kA / m; the magnetic field strength of the magnetic separation column of the magnetic separation column II operation is 12.6kA / m.

[0046] According to the above process and steps, the fine-grained low-grade refractory magnetite ore is beneficiated to obtain an iron concentrate yield of 21.35%, a TFe grade of 63.15%, an iron recovery rate of 57.59%, a recovery rate of effective iron (iron in magnetite, hematite (limonite), and iron carbonate) of 74.12%, of which the magnetic iron recovery rate is more than 88.7%, and the final total tailings iron grade is 12.62%. The SiO2 content in the total tailings is greater than 65%, the iron minerals are mainly iron silicate, and the particle size is fine, which is a high-quality iron corrector for the production of iron-containing silicate cement, and the selling price is between 50 and 80 yuan per ton. By processing fine-grained low-grade difficult-to-select magnetite ore through the method of the present invention, 100% full-quantity utilization of fine-grained low-grade difficult-to-select magnetite ore resources is achieved, and the ore dressing plant does not need to build a supporting tailings pond, which not only saves the land occupation and land acquisition costs of the tailings pond and the operating costs of the tailings pond, but also avoids the safety risks caused by the operation of the tailings pond, and achieves unexpected technical and economic effects, and the economic benefits, environmental benefits, and social (safety) benefits are remarkable.

[0047] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the invention, which should be covered by the protection scope of the present invention.

Claims

1. A magnetic flotation combined beneficiation method for fine-grained low-grade refractory magnetite ore, which is used to process the original ore TFe grade in the range of 20.0% to 25.0%, the mFe grade in the range of 10.0 to 15.0%, the ratio of Fe to TFe in the unrecoverable iron silicate between 16% and 25%, the grinding particle size in the range of -0.038mm particle content of 90% to 95%, and the iron mineral can be dissociated into monomers. It is characterized by This is accomplished using the following steps: 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 subjected to a first-stage grinding process. The discharge after the first-stage grinding is fed into a first-stage classification operation, and the overflow of the first-stage classification is discharged. The underflow after the first-stage classification is returned to the first-stage grinding process. The overflow of the first stage classification is fed into the weak magnetic separation operation to obtain a weak magnetic separation concentrate and discharge a weak magnetic separation tailings; S2 two-stage pre-classification - two-stage grinding - weak magnetic separation - magnetic column I separation The first-stage weak magnetic separation concentrate obtained in step S1 is concentrated, and the concentrated underflow is fed into the second-stage pre-classification operation, and the underflow after the second-stage pre-classification is fed into the second-stage grinding. The discharge after the second-stage grinding is returned to the second-stage pre-classification, and the second-stage pre-classification overflow is discharged; the second-stage pre-classification overflow is fed into a two-stage weak magnetic separation operation of a coarse and a fine, and the second-stage weak magnetic separation tailings are discharged to obtain a second-stage weak magnetic separation concentrate; the second-stage weak magnetic separation concentrate is treated with concentration I, and the concentration I underflow is fed into magnetic separation column I for separation to obtain a magnetic separation column I concentrate, and the magnetic separation column I tailings are discharged; S3 Magnetic Separation Column I Concentrate Reverse Flotation The magnetic column Ⅰ concentrate obtained in step S2 is concentrated Ⅱ and stirred before being fed into reverse flotation operation. The reverse flotation operation adopts 1 roughing, 1 scavenging and 3 concentrating, and the flotation scavenging tailings are discharged. The product in the tank after the third concentrating is the final iron concentrate, and the concentrating Ⅰ tailings and flotation scavenging concentrate are returned to concentration Ⅱ; S4 three-stage pre-classification - three-stage grinding - weak magnetic separation - magnetic column II separation The tailings of magnetic column I discharged from step S2 and the tailings of flotation scavenging discharged from step S3 are fed to concentration III for concentration treatment, the bottom flow of concentration III is fed to three-stage pre-classification, the bottom flow after three-stage pre-classification is fed to three-stage grinding, the discharge after three-stage grinding is returned to three-stage pre-classification, and the overflow of three-stage pre-classification is discharged; the overflow of three-stage pre-classification is fed to two-stage weak magnetic separation operations of one coarse and one fine, and three-stage weak magnetic separation tailings are discharged to obtain three-stage weak magnetic separation concentrate; the three-stage weak magnetic separation concentrate is treated by concentration IV, and the bottom flow of concentration IV is fed to magnetic column II for separation to obtain magnetic separation column II concentrate, and magnetic separation column II tailings are discharged; the magnetic separation column II concentrate is returned to the concentration II operation in step S3, and the magnetic separation column II tailings are returned to the concentration III operation; the discharged three-stage weak magnetic separation tailings are mixed with the first-stage weak magnetic separation tailings discharged from step S1 and the second-stage weak magnetic separation tailings discharged from step S2 to form the final tailings, and the final tailings are used as an iron corrector for the production of iron-containing silicate cement.

2. The magnetic flotation combined beneficiation method for fine-grained low-grade and difficult-to-be-selected magnetite according to claim 1, characterized in that: In step S1, the first stage classification operation adopts a single spiral classifier; the first stage grinding adopts a grid-type ball mill, and the first stage grinding particle size is controlled within the range of 50% to 55% of the mass content of the -0.076 mm particle size.

3. The magnetic flotation combined beneficiation method for fine-grained low-grade refractory magnetite ore according to claim 1, characterized in that: In step S1, the weak magnetic separation operation adopts a drum-shaped wet weak magnetic separator, and the magnetic field strength is in the range of 111 to 160 kA / m.

4. The magnetic flotation combined beneficiation method for fine-grained low-grade refractory magnetite ore according to claim 1, characterized in that: In step S2, the second stage pre-classification operation adopts a single spiral classifier; the second stage grinding adopts a grid ball mill, and the second stage grinding particle size is controlled within the range of 90% to 95% of the mass content of the -0.076 mm particle size.

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

6. The magnetic flotation combined beneficiation method for fine-grained low-grade refractory magnetite ore according to 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 flotation combined beneficiation method for fine-grained low-grade refractory magnetite ore according to claim 1, characterized in that: In step S3, the reverse flotation operation adopts anionic reverse flotation collector MD, which is prepared by chelating and saponifying reaction of organic acid and chelating agent, with acid value (mgKOH / g) of 90-210, saponification value (mgKOH / g) of 90-210, and iodine value of 100-120; the activator adopted is CaO; the inhibitor adopted is starch; and the adjusting agent adopted is NaOH.

8. A magnetic flotation combined beneficiation method for fine-grained low-grade refractory magnetite ore as claimed in claim 7, characterized in that: In step S3, the reverse flotation roughing concentration is in the range of 30-35%, and the reverse flotation pulp temperature is between 31-36°C; according to the dry ore amount of flotation feed, the amount of collector MD used in the reverse flotation roughing is 550-700g / t, the amount of CaO is 100-250g / t, the amount of starch is 300-450g / t, and the amount of NaOH is 950-1150g / t; the amount of collector MD used in the reverse flotation concentration is 110-135g / t; and no drug is added in the reverse flotation scavenging.

9. The magnetic flotation combined beneficiation method for fine-grained low-grade refractory magnetite ore according to claim 2, characterized in that: In step S1, the weak magnetic separation operation adopts a drum-shaped wet weak magnetic separator, and the magnetic field strength is in the range of 111 to 160 kA / m; In step S2, the two-stage pre-classification operation adopts a single spiral classifier; the two-stage grinding adopts a grid ball mill, and the second-stage grinding particle size 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 coarse selection magnetic field strength is within the range of 111 to 160 kA / m, and the fine selection magnetic field strength is within the range of 79 to 128 kA / m; the magnetic field strength of the magnetic separation column I is within the range of 11 to 15 kA / m. In step S3, the reverse flotation operation adopts an anionic reverse flotation collector MD, which is prepared by chelating and saponifying an organic acid and a 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 regulator used is NaOH; the reverse flotation roughing concentration is in the range of 30-35%, and the reverse flotation ore The slurry temperature is between 31-36°C; according to the dry ore amount of flotation feed, the dosage of collector MD used in the reverse flotation roughing is 550-700g / t, the dosage of CaO is 100-250g / t, the dosage of starch is 300-450g / t, and the dosage of NaOH is 950-1150g / t; the dosage of collector MD used in the reverse flotation concentration is 110-135g / t; no drug is added in the reverse flotation scavenging.

10. A magnetic flotation combined beneficiation method for fine-grained low-grade refractory magnetite ore as claimed in claim 9, characterized in that: In step S1, the weak magnetic separation operation adopts a drum-shaped wet weak magnetic separator, and the magnetic field strength is in the range of 135 to 150 kA / m; In step S2, the two-stage pre-classification operation adopts a single spiral classifier; the two-stage grinding adopts a grid ball mill, and the second-stage grinding particle size 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 coarse selection magnetic field strength is within the range of 135 to 150 kA / m, and the fine selection magnetic field strength is within the range of 105 to 120 kA / m; the magnetic field strength of the magnetic separation column I is within the range of 11.5 to 13.5 kA / m. In step S3, the reverse flotation roughing concentration is in the range of 30-35%, and the reverse flotation pulp temperature is between 34-36°C; according to the dry ore amount of flotation feed, the amount of collector MD used in the reverse flotation roughing is 660-700g / t, the amount of CaO is 140-190g / t, the amount of starch is 310-360g / t, and the amount of NaOH is 980-1060g / t; the amount of collector MD used in the reverse flotation concentration is 118-132g / t; and no drug is added in the reverse flotation scavenging.

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