A method for combined magnetic and floatation beneficiation of fine-grained low-grade refractory magnetite ore

Abstract

The application discloses a kind of micro fine particle low-grade refractory magnetite ore's magnetic suspension combined beneficiation method, first stage grinding-grading-weak magnetic separation is carried out, and the first stage weak magnetic separation concentrate obtained is carried out second stage pre-classification-second stage grinding-weak magnetic separation-magnetic separation column I separation, the magnetic separation column I concentrate obtained is given to reverse flotation operation, reverse flotation operation adopts 1 roughing, 1 cleaning, 3 times concentration, and the in-tank product after third concentration is final iron concentrate, magnetic separation column I tailings, flotation cleaning tailings are given to three-stage pre-classification-three-stage grinding-weak magnetic separation-magnetic separation column II separation, and three-stage weak magnetic separation tailings, first stage weak magnetic separation tailings, second stage weak magnetic separation tailings are mixed as final tailings, and final tailings are used as iron correction agent for producing iron-containing Portland cement.The application has the advantages of high-grade iron concentrate, less flotation feed, high-grade flotation feed, stable index, simple production and maintenance, strong adaptability and the like.

Description

Technical Field

[0001] The present invention belongs to the technical field of iron ore beneficiation, and specifically relates to a beneficiation method for fine-grained low-grade magnetite ore. The method 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 of 90% to 95% for the iron mineral to be dissociated into monomers), and gangue minerals mainly consisting of quartz, silicate and carbonate. Background Art

[0002] Steel is an important foundation for the development of the national economy. Economic growth is inseparable from the demand for iron ore. 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 iron grade and recovery rate during the beneficiation process and make rational use of low-grade, fine-grained, complex and difficult-to-process iron ore, iron ore needs to be crushed, finely ground, magnetically separated, and flotated. In order to effectively convert low-grade, finely embedded, and complexly composed ores into high-grade concentrates, flotation is usually required. Before entering the flotation operation, reasonable fine grinding and magnetic separation processes are crucial for the development of low-grade, finely embedded magnetite ore resources and are key technologies for flotation preparation.

[0004] In terms of magnetic separation, existing weak magnetic separators are highly efficient and simple wet-process equipment for separating fine-grained, strongly magnetic minerals. These separators are characterized by their small size, light weight, and simple operation, making them effective for separating fine-grained, strongly magnetic minerals. However, their separation efficiency is easily affected by factors such as feed size and grade, leading to fluctuations in separation efficiency and unsatisfactory mineral separation performance indicators such as grade and recovery. Due to the limitations of current magnetic separation technology, useful minerals with widely varying particle size compositions and ore properties cannot be effectively separated, thus failing to provide qualified raw materials for subsequent flotation operations. Consequently, flotation performance indicators are difficult to guarantee, impacting the grade and recovery of the final concentrate product.

[0005] In order to solve the technical problem of fine particle magnetite ore dressing, Chinese patent application 201711107180.3 discloses an energy-saving ore dressing method for processing fine particle magnetite: the iron ore is sequentially subjected to first-stage grinding classification, first-stage low-intensity magnetic separation, second-stage grinding classification, second-stage low-intensity magnetic separation, first-stage elutriation magnetic separation, third-stage grinding classification, third-stage low-intensity magnetic separation, and second-stage elutriation magnetic separation. The first-stage elutriation magnetic separation concentrate and the second-stage elutriation magnetic separation concentrate are combined to form a total concentrate, and all the low-intensity magnetic separation tailings are combined to form a total tailings. However, when this ore dressing method is used to process fine particle low-grade refractory 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 a Fe-enhancing energy-saving ore dressing process suitable for fine particle magnetite ore dressing. The tailings of the first-stage low-intensity magnetic separation and the tailings of the second-stage low-intensity magnetic separation of the stage grinding and separation process are directly used as the final tailings. The second-stage low-intensity magnetic separation concentrate is fed into a reverse flotation operation. The reverse flotation operation adopts a cationic collector reverse flotation process to obtain part of the qualified iron concentrate in advance. The middlings obtained from the reverse flotation operation are subjected to a magnetic separation and dewatering operation and then fed into a third-stage mill for middlings regrinding and third-stage low-intensity magnetic separation to obtain third-stage low-intensity magnetic separation concentrate. The grinding fineness of the middlings regrinding is greater than or equal to 88% of -0.030 mm. The third-stage low-intensity magnetic separation concentrate and the part of the qualified iron concentrate obtained in advance from the reverse flotation operation are combined to form a comprehensive iron concentrate. The tailings of the third-stage low-intensity magnetic separation are combined with the final tailings to form a total tailings. However, this ore dressing process has a large amount of flotation feed and a large amount of flotation reagent, and it is also difficult to process fine particle low-grade refractory magnetite ore with a TFe grade of 20.0% to 25.0%. SUMMARY

[0007] The purpose of the present application is to solve the technical problems of low-grade iron concentrate, low iron recovery rate, large amount of flotation feed, large amount of reagent, poor iron separation and enrichment effect, etc. in the current fine particle low-grade refractory magnetite ore dressing, and to provide a magnetic-flotation combined ore dressing method for fine particle low-grade refractory magnetite ore. When this method is used to process fine particle low-grade refractory magnetite ore, it has the characteristics of high-grade iron concentrate, small amount of flotation feed, high-grade flotation feed, stable indicators, simple production and maintenance, and strong adaptability.

[0008] To achieve the above-mentioned object of the present invention, a magnetic flotation combined beneficiation method for fine-grained, low-grade, refractory magnetite ore is provided. The method is used to process fine-grained, low-grade, refractory magnetite ore having a TFe grade of 20.0% to 25.0%, an mFe grade of 10.0% to 15.0%, a ratio of Fe to TFe in unrecoverable ferrosilicate of 16% to 25%, a grinding particle size of -0.038 mm, and a content of 90% to 95% of the iron mineral fraction required for the separation of the iron minerals. The method is specifically implemented by the following process and steps:

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

[0010] After the fine-grained, low-grade, and difficult-to-select magnetite ore is crushed, it undergoes a first-stage grinding process. The discharge from the first-stage grinding process is fed into a first-stage classification process, and the first-stage classification overflow is discharged. The underflow after the first-stage classification process returns 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 the first-stage weak magnetic separation tailings are 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. 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 overflow of the second-stage pre-classification is discharged; the overflow of the second-stage pre-classification is fed into two-stage weak magnetic separation operations, 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 subjected to concentration I treatment, and the underflow of concentration I is fed into magnetic separation column I for separation to obtain magnetic separation column I concentrate, and the magnetic separation column I tailings are discharged;

[0013] S3 magnetic column I concentrate reverse flotation

[0014] The magnetic column I concentrate obtained in step S2 is concentrated II, stirred, and then fed into the reverse flotation process. The reverse flotation process adopts one roughing process, one scavenging process, and three cleaning processes. The flotation scavenging tailings are discharged. The product in the tank after the third cleaning process is the final iron concentrate. The cleaning I tailings and the flotation scavenging concentrate are returned to the 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 flotation scavenging tailings 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 returns to the concentration II operation in step S3, and the magnetic separation column II tailings return to the concentration III operation; the discharged three-stage weak magnetic separation tailings are mixed with the one-stage weak magnetic separation tailings discharged from step S1 and the two-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% of the 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 second-stage pre-classification operation adopts a single spiral classifier; the second-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 magnetic field strength is within the range of 111 to 160 kA / m, and the fine 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.; based on the dry ore amount of the flotation feed, the dosage of the collector MD used in the reverse flotation roughing is 550 to 700 g / t, the dosage of CaO is 100 to 250 g / t, the dosage of starch is 300 to 450 g / t, and the dosage of NaOH is 950 to 1150 g / t; the dosage of the collector MD used in the reverse flotation cleaning is 110 to 135 g / 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-type ball mill, and the second stage grinding particle size is controlled in 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 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 in the range of The reverse flotation roughing concentration is in the range of 11.5 to 13.5 kA / m; in step S3, the reverse flotation roughing concentration is in the range of 30 to 35%, and the reverse flotation pulp temperature is between 34 and 36°C; based on the dry ore content of the flotation feed, the amount of collector MD used in the reverse flotation roughing 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 cleaning is 118 to 132 g / 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, and reagent dosage can be determined based on the properties of the ore and the results of laboratory tests.

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

[0023] (1) Under the condition that the particle size of the second-stage grinding reaches more than 90% of -0.076mm, the present invention generally performs flotation after conventional magnetic separation; the present invention sets a magnetic separation column operation 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-obtain a portion of qualified iron concentrate products that have been monomerically dissociated from the magnetic column I concentrate, and the remaining conjoined iron minerals that have not been monomerically dissociated continue to be subjected to the third-stage grinding and re-separation, which greatly reduces the third-stage grinding load and effectively saves grinding energy consumption.

[0025] (3) The present invention combines the concentrate from magnetic column I after the second stage of grinding and the concentrate from 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. Finally, good mineral processing indicators are obtained, 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 composed of 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 illustrate the present invention, a magnetic flotation combined beneficiation method for fine-grained, low-grade, refractory magnetite ore is described in further detail below, with reference to the accompanying drawings and examples. It should be noted that any modifications, equivalent substitutions, and improvements made within the technical concepts and principles of this invention are intended to be included within the scope of protection of this invention.

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

[0032] Table 1 Chemical multi-element analysis results of raw ore (%)

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

[0034] Table 2 Results of iron phase analysis of raw ore (%)

[0035] Iron phase Iron phase content Occupancy rate Magnetite 13.80 59.13 Hematite (limonite) 2.50 10.71 Iron carbonate 1.89 8.10 Iron silicate 4.85 20.78 Iron sulfide 0.30 1.28 Total iron 23.34 100.00

[0036] This ore is primarily magnetite, with a TFe grade of 23.41% and an MFe grade of 13.87%. It also contains a high SiO2 content of 54.18%, while the harmful impurities S and P are relatively low. Phase analysis indicates a 59.13% distribution of magnetic iron. Furthermore, the iron silicate content is high, at 20.78%. Due to current limitations in mineral processing technology, this iron cannot be recovered, impacting the iron concentrate recovery rate. The content of other useful iron minerals is relatively low.

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

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

[0039] After crushing, the fine, low-grade, refractory magnetite ore, with a TFe grade of 23.41%, an MFe content of 13.87%, an iron silicate content of up to 4.85%, and a high SiO2 content of 54.18%, undergoes primary grinding. The discharge from primary grinding is fed to a primary classification process, where overflow from the primary classification process is discharged, and the underflow from the primary classification process returns to the primary grinding process. The overflow from the primary classification process is fed to a weak magnetic separation process to produce a primary weak magnetic separation concentrate, which is then discharged as a primary weak magnetic separation tailings. The primary classification process utilizes a single spiral classifier, while the primary grinding process utilizes a grate ball mill. The primary grinding process controls the particle size to a -0.076mm particle size fraction of 55% by mass. The weak magnetic separation process utilizes a drum-type wet weak magnetic separator with a magnetic field strength of 143.24 kA / 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 into the second-stage pre-classification operation. 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 overflow of the second-stage pre-classification is discharged; the overflow of the second-stage pre-classification is fed into two-stage weak magnetic separation operations, 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 into magnetic separation column I for separation to obtain magnetic separation column I concentrate, and the magnetic separation column I tailings are discharged. The second-stage pre-classification operation adopts a single spiral classifier, the second-stage grinding adopts a grate ball mill, and the second-stage grinding particle size is controlled at a mass content of 90% of the -0.076mm particle size; in the two-stage weak magnetic separation operation of one coarse and one fine, the coarse magnetic field strength is 143.24kA / m, and the fine magnetic field strength is 111.41kA / m; the magnetic field strength of the magnetic separation column I is 12.6kA / m.

[0042] S3 magnetic column I concentrate reverse flotation

[0043] The magnetic column I concentrate obtained in step S2 is concentrated II and stirred before being fed into the reverse flotation operation. The reverse flotation operation adopts 1 roughing, 1 scavenging and 3 cleaning operations, and the flotation scavenging tailings are discharged. The product in the tank after the third cleaning is the final iron concentrate, and the cleaning I tailings and the flotation scavenging concentrate are returned to the concentration II. 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; and the adjusting agent used is NaOH. The reverse flotation roughing concentration is in the range of 30-35%, and the reverse flotation slurry temperature is 35°C. Based on the dry ore content of the flotation feed, the amount of the collector MD used in the reverse flotation roughing is 686g / t, the amount of CaO used is 160g / t, the amount of starch used is 326g / t, and the amount of NaOH used is 1015g / t. The amount of the collector MD used in the reverse flotation cleaning is 127g / t. No drugs are 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 flotation scavenging tailings 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 returns to the concentration II operation in step S3, and the magnetic separation column II tailings return to the concentration III operation; the discharged three-stage weak magnetic separation tailings are mixed with the one-stage weak magnetic separation tailings discharged from step S1 and the two-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 grate 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] After the fine and low-grade refractory magnetite ore is beneficiated by the process and steps, the iron concentrate yield is 21.35%, the TFe grade is 63.15%, the iron recovery rate is 57.59%, the recovery rate of effective iron (iron in magnetite, hematite (limonite) and iron carbonate) is 74.12%, the recovery rate of magnetic iron is more than 88.7%, and the final total tailings iron grade is 12.62%. The SiO2 content in the total tailings is more than 65%, the iron mineral is mainly silicate iron, and the particle size is fine, which is a high-quality iron correction agent for producing iron-containing silicate cement, and the selling price is between 50-80 yuan per ton. Through the method, the fine and low-grade refractory magnetite ore is processed, the 100% full utilization of the fine and low-grade refractory magnetite ore resources is realized, the tailings pond is not needed for the concentrator, not only the land occupation and land acquisition fees and the tailings pond operation cost are saved, but also the safety risk caused by the tailings pond operation is avoided, unexpected technical effects, economic effects, environmental benefits and social (safety) benefits are achieved.

[0047] The above merely describes the preferred embodiments of the present application, but the protection scope of the present application is not limited thereto, any person skilled in the art can make equivalent replacements or changes to the technical solutions and the inventive concept of the present application within the technical range disclosed by the present application, which should be covered within the protection scope of the present application.

Claims

1. A magnetic flotation combined beneficiation method for fine-grained, low-grade, refractory magnetite ore, characterized in that the ore has a TFe grade of 20.0% to 25.0%, an mFe grade of 10.0% to 15.0%, a ratio of Fe to TFe in unrecoverable ferrosilicate of 16% to 25%, a grinding particle size of -0.038 mm, and a content of 90% to 95% of iron minerals that can only be separated into individual components. This is accomplished using the following steps: S1 first stage grinding-first 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 material after the first-stage grinding is fed into a first-stage classification process, 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 process to obtain the first stage weak magnetic separation concentrate and discharge the first stage 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. 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 overflow of the second-stage pre-classification is discharged; the overflow of the second-stage pre-classification is fed into two-stage weak magnetic separation operations, 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 subjected to concentration I treatment, and the underflow of concentration I is fed into magnetic separation column I for separation to obtain magnetic separation column I concentrate, and the magnetic separation column I tailings are discharged; S3 magnetic column I concentrate reverse flotation The magnetic column I concentrate obtained in step S2 is concentrated II, stirred, and then fed into the reverse flotation process. The reverse flotation process adopts one roughing process, one scavenging process, and three cleaning processes. The flotation scavenging tailings are discharged. The product in the tank after the third cleaning process is the final iron concentrate. The cleaning I tailings and the flotation scavenging concentrate are returned to the concentration II. S4 three-stage pre-classification - three-stage grinding - weak magnetic separation - magnetic column II separation The tailings of magnetic separation column I discharged from step S2 and the flotation scavenging tailings discharged from step S3 are fed to concentration III for concentration treatment, the underflow of concentration III is fed to three-stage pre-classification, the underflow after three-stage pre-classification is fed to three-stage grinding, the discharge after three-stage grinding is returned to the three-stage pre-classification, and the overflow of the three-stage pre-classification is discharged; the overflow of the three-stage pre-classification is fed to two-stage weak magnetic separation operations of one coarse and one fine, and the tailings of the three-stage weak magnetic separation are discharged to obtain three-stage weak magnetic separation concentrate; the three-stage weak magnetic separation concentrate is treated by concentration IV, and the underflow of concentration IV is fed to magnetic separation column II for separation to obtain magnetic separation column II concentrate, and the tailings of magnetic separation column II are discharged; the concentrate of magnetic separation column II is returned to the concentration II operation in step S3, and the tailings of magnetic separation column II are returned to the concentration III operation; the discharged three-stage weak magnetic separation tailings are mixed with the one-stage weak magnetic separation tailings discharged from step S1 and the two-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, refractory magnetite ore 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 grate 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-type 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 to 160 kA / m, and the fine magnetic field strength is in the range of 79 to 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 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; and the adjusting agent used is NaOH.

8. The magnetic flotation combined beneficiation method for fine-grained, low-grade, refractory magnetite ore according to 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; based on 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 cleaning 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-type wet weak magnetic separator with a magnetic field strength in the range of 111 to 160 kA / m; In step S2, the second stage pre-classification operation adopts a single spiral classifier; the second 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 low-weak magnetic separation operation of one coarse and one fine, the coarse magnetic field strength is within the range of 111 to 160 kA / m, and the fine 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 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 ore The slurry temperature is between 31-36°C; based on the dry ore content of the flotation feed, 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 cleaning is 110-135g / t; and no drug is added in the reverse flotation scavenging.

10. A magnetic flotation combined beneficiation method for fine-grained, low-grade, refractory magnetite ore according to claim 9, 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 135 to 150 kA / m; In step S2, the second stage pre-classification operation adopts a single spiral classifier; the second 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 low-weak magnetic separation operation of one coarse and one fine, the coarse magnetic field strength is within the range of 135 to 150 kA / m, and the fine 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; based on 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 cleaning is 118-132g / t; and no drug is added in the reverse flotation scavenging.

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