A combined roasting system and beneficiation method for iron ore

Abstract

A combined roasting system for iron ore comprises a rotary kiln and a fluidized bed roasting system. The rotary kiln tail is connected to a cyclone dust collector, and an intermediate bin is provided at the bottom of the cyclone dust collector. The fluidized bed roasting system comprises a cyclone preheater, a fluidized bed reactor, a gas-solid separator, and a hot blast furnace. The hot blast furnace is used to supply heat to the fluidized bed reactor. The intermediate bin, cyclone preheater, fluidized bed reactor, and gas-solid separator are sequentially connected via pipelines. A method for beneficiating iron ore based on the combined roasting system comprises: using weakly magnetic iron ore as raw material, roasting and magnetizing it in a rotary kiln, collecting the flue gas in the rotary kiln and introducing it into the fluidized bed roasting system for calcination, and grinding, grading, magnetic separation, or flotation of the obtained rotary kiln-roasted ore and fluidized bed roasted ore to obtain iron concentrate. The present invention combines a rotary kiln and a fluidized bed roasting furnace as equipment for magnetic roasting. Raw materials of different particle sizes are roasted in their respective suitable roasting equipment, which effectively overcomes the shortcomings of using these two methods separately.

Description

Technical Field

[0001] The present invention belongs to the field of ore dressing, and in particular relates to a method and device for jointly roasting weakly magnetic iron ore using a rotary kiln and a fluidized bed furnace. Background Art

[0002] my country currently has a large amount of complex, difficult-to-separate, weakly magnetic iron ore resources, including low-grade, fine-grained hematite, siderite, and limonite. Conventional separation methods, such as magnetic separation, gravity separation, flotation, or combined beneficiation, result in low concentrate grades and iron recoveries. Magnetic roasting is the most effective method for processing this complex, difficult-to-separate iron ore. Rotary kiln magnetic roasting followed by magnetic separation, or flash (fluidized) magnetic roasting followed by magnetic separation, are commonly used to separate these ores. However, these methods have their drawbacks.

[0003] Due to the constant tumbling of materials within the rotary kiln, the kiln flue gas entrains a large amount of fine mineral powder. During the countercurrent flow, much of this fine material is not subjected to high-temperature roasting. Consequently, the weakly magnetic iron minerals within them do not have time to transform into strongly magnetic iron minerals and are subsequently discharged from the rotary kiln with the flue gas at the kiln tail. These fine particles cannot be recovered through weak magnetic separation and must be collected and discarded as tailings, reducing raw material utilization and polluting the environment.

[0004] The raw material for the flash (fluidized) magnetization roasting method is powder ore with a particle size of less than 1mm. If the raw ore is processed, it needs to be pre-treated for powdering. However, the investment in the construction of the powdering system is large and the energy consumption of the powdering process is high, which will inevitably increase the production cost of the product. Summary of the Invention

[0005] The present invention aims to solve the problems of low utilization rate of fine-grained powder and potential dust pollution in the rotary kiln magnetization roasting method, large investment in the construction of the powder making system and insufficient utilization of tail gas waste heat in the fluidized bed magnetization roasting method, and proposes a method and device for jointly roasting weakly magnetic iron ore in a rotary kiln and a fluidized bed furnace.

[0006] In order to solve the above technical problems, the technical solution of the present invention is:

[0007] An iron ore combined roasting system includes a rotary kiln for roasting raw iron ore and a fluidized roasting system for roasting fine iron ore collected by a cyclone dust collector at the tail of the rotary kiln.

[0008] The rotary kiln is connected to a raw material bin at the kiln tail, so that iron ore enters the rotary kiln from the kiln tail for roasting. The kiln tail of the rotary kiln is also connected to a cyclone dust collector for collecting fine-particle iron ore, and an intermediate bin for storing fine-particle iron ore is provided at the bottom of the cyclone dust collector; the kiln head of the rotary kiln is provided with a burner for supplying heat to the rotary kiln, and the kiln head of the rotary kiln is also provided with a cooling bin for cooling the roasted ore;

[0009] The fluidized bed roasting system includes a cyclone preheater, a fluidized bed reactor, a gas-solid separator and a hot blast furnace; the hot blast furnace is used to provide heat for the fluidized bed reactor. According to the flow direction of the fine-particle iron ore, the intermediate bin is connected to the cyclone preheater, the fluidized bed reactor and the gas-solid separator in sequence through pipelines.

[0010] Preferably, the cyclone preheater is a two-stage cyclone preheater, the air outlet of the second-stage cyclone preheater is connected to the cooling bin and connected to the air inlet of the first-stage cyclone preheater; the air outlet of the first-stage cyclone preheater is connected to the bag dust collector; the air outlet of the gas-solid separator is connected to the discharge port of the first-stage cyclone preheater and to the feed port of the second-stage cyclone preheater, and the material discharged from the discharge port of the first-stage cyclone preheater is brought into the second-stage cyclone preheater through a pipeline by the airflow for heat exchange.

[0011] Preferably, air lock valves are installed on the pipes between the cyclone preheater and the cooling bin, on the pipes between the intermediate bin and the cyclone preheater, and on the pipes between the air outlet of the second-stage cyclone preheater and the cooling bin. The air volume entering the cooling bin and the first-stage cyclone preheater is controlled by adjusting the opening of the fixed valves on the relevant pipes.

[0012] Preferably, the cooling bin and the gas-solid separator are respectively connected to a stirring barrel for cooling the sintered ore discharged from the cooling bin and the gas-solid separator.

[0013] Based on the same inventive concept, the present invention provides a method for beneficiating iron ore, comprising the following steps:

[0014] (i) Weakly magnetic iron ore is crushed and weighed as raw material before being fed into a rotary kiln from the kiln tail. Pulverized coal and air are supplied to the kiln head and burned in the kiln. The coarse iron ore in the kiln tumbles as the kiln rotates, flowing from the kiln tail to the kiln head. During this process, it is heated and converted into strongly magnetic iron ore, thus obtaining rotary kiln roasted ore. The fine iron ore in the kiln flows out of the kiln from the kiln tail along with the flue gas generated by the combustion, is collected by a cyclone dust collector, and is stored in an intermediate bin.

[0015] (ii) preheating the fine iron ore collected in step (i) through a cyclone and then transporting it to a fluidized bed reactor for roasting to convert it into a strongly magnetic iron ore, and obtaining a fluidized bed roasted ore after gas-solid separation;

[0016] (iii) The rotary kiln roasted ore and the fluidized bed roasted ore obtained in step (ii) are cooled and then combined or subjected to grinding, classification, magnetic separation or flotation separately to obtain an iron ore concentrate product.

[0017] Preferably, in step (i), the particle size of the weakly magnetic iron ore is -20 mm; the weakly magnetic iron ore may be a mixed ore of one or more of hematite, limonite, siderite, etc.

[0018] Preferably, in step (ii), a hot blast furnace is used to supply heat to the fluidized bed reactor, and the tail gas discharged from the fluidized bed reactor is used to transport and preheat the fine iron ore.

[0019] Preferably, in step (ii), the tail gas discharged from the cyclone preheater is first used to cool the ore roasted in the rotary kiln, is further heated after gas-solid heat exchange, and is then introduced into the rotary kiln as combustion air for further roasting.

[0020] Preferably, in step (iii), the cooling method for the rotary kiln roasted ore is: first cooling with tail gas from the fluidized bed reactor, and then water cooling, and the fluidized bed roasted ore is directly cooled with water.

[0021] The specific mineral processing method and principle of the present invention are as follows:

[0022] Iron ore is crushed to a particle size of -20mm and fed into the rotary kiln from the kiln tail after metering, according to a coal mine ratio of 0-30%. A movable pulverized coal burner is installed at the kiln head. The temperature and atmosphere inside the rotary kiln are controlled by adjusting the burner's coal injection rate, air volume, and air pressure. The pulverized coal and air supplied by the kiln head burner burn inside the kiln, providing heat and reducing agents for the ore.

[0023] The ore material (coarse-grained iron ore) in the kiln keeps rolling with the rotation of the rotary kiln, and slowly moves from the kiln tail to the kiln head. In this process, the ore is preheated and magnetized, and the weakly magnetic iron minerals are transformed into strongly magnetic Fe3O4 and flow out of the rotary kiln.

[0024] The combustion flue gas draws in the dust generated by the tumbling of the ore. Since the flue gas flows in the countercurrent to the ore, some fine-grained materials are drawn into the flue gas at the tail of the rotary kiln without undergoing high-temperature roasting. The weakly magnetic iron minerals in them do not have time to be converted into strongly magnetic iron minerals and flow out of the rotary kiln with the flue gas.

[0025] The dust (i.e., fine iron ore particles) that exit the rotary kiln with the flue gas is collected in an intermediate bin by a dust collector. The flue gas after dust removal is discharged into the atmosphere. The dust is then fed by a screw pump and pneumatically conveyed to the fluidized bed roasting system for roasting. The weakly magnetic iron minerals in the dust are converted into highly magnetic Fe3O4.

[0026] The roasted ore flowing out of the rotary kiln is first cooled by the tail gas of the fluidized roasting system, and then the air-cooled roasted ore is water-cooled to obtain the rotary kiln roasted ore; the roasted ore after fluidized roasting is directly water-cooled to obtain the fluidized roasted ore.

[0027] The rotary kiln roasted ore and fluidized bed roasted ore are ground, classified and magnetically separated to finally obtain iron ore concentrate products.

[0028] The fluidized bed reactor is heated by a hot blast stove, and the atmosphere in the roasting furnace is controlled by adjusting the amount of fuel supplied from the lower part of the reactor to ensure that the tail gas discharged from the fluidized bed roasting system is a neutral atmosphere.

[0029] The feed for fluidized bed roasting is the fine-grained material collected by the cyclone dust collector at the tail of the rotary kiln. This solves the problem of recycling the fine powder collected by the cyclone dust collector of the rotary kiln magnetized roasting on the one hand, and on the other hand eliminates the dry pulverizing operation in the raw material preparation process of fluidized bed magnetized roasting.

[0030] The air used for pneumatic conveying is the exhaust gas from the fluidized bed roasting system, which can ensure that the heat loss of dust is minimized during the transportation process. While reducing the energy consumption of fluidized bed roasting, it can ensure that a small amount of magnetized iron minerals in the dust will not be secondary oxidized, thereby increasing the magnetic susceptibility of the fluidized bed roasting process.

[0031] The air source for the air-cooling of the roasted ore flowing out of the rotary kiln is the exhaust gas from the fluidized bed roasting system. The roasted ore is cooled after the gas-solid heat exchange, thereby reducing the subsequent water cooling intensity. At the same time, the flue gas after the gas-solid heat exchange is used to assist the combustion of the pulverized coal at the kiln head, thereby recovering part of the waste heat from the roasted ore.

[0032] The movement path of the iron ore and flue gas / exhaust gas of the present invention is as follows: the iron ore enters the rotary kiln from the raw material bin and enters from the kiln tail. The coarse-grained iron ore is roasted in the rotary kiln and discharged from the kiln head. The fine-grained iron ore is discharged from the kiln tail along with the flue gas generated by the rotary kiln and enters the cyclone dust collector. The fine-grained iron ore is collected and enters the intermediate bin. The fine-grained iron ore in the intermediate bin is transported to the cyclone preheater by the exhaust gas of the roasting furnace for preheating. After preheating, it enters the fluidized bed reactor for roasting. The heat source of the fluidized bed reactor is provided by the hot blast furnace. After the roasted material (fluidized bed reactor ore) is separated by gas and solid, the solid is directly water-cooled, and the gas is the exhaust gas after roasting, which is used to transport fine-grained iron ore and can achieve preheating of the material. In addition, the exhaust gas after roasting can also be used to cool the ore roasted in the rotary kiln. After the temperature of the exhaust gas rises, it enters the rotary kiln to recycle part of the heat, thereby reducing the heat consumption of the rotary kiln.

[0033] Compared with the prior art, the advantages of the present invention are:

[0034] (1) The present invention combines a rotary kiln and a fluidized bed reactor as equipment for magnetized roasting. Raw materials of different particle sizes are roasted in their respective suitable roasting equipment, which effectively overcomes the shortcomings of the two methods used alone. While solving the environmental pollution problem of fine-grained materials collected by dust removal at the tail of the rotary kiln for magnetized roasting and realizing resource utilization of fine-grained materials, the powder making process in the raw material pretreatment process of fluidized bed magnetized roasting is omitted, which greatly reduces the infrastructure investment and production cost of fluidized bed roasting. It has important practical significance for the economic and rational development and utilization of low-grade, complex, difficult-to-select, weakly magnetic iron ore resources.

[0035] (2) The present invention uses part of the fluidized roasting tail gas to cool the rotary kiln roasted ore, and the flue gas is used as the combustion-supporting gas for the rotary kiln combustion after heat exchange. This method of utilizing the waste heat from roasting ore greatly reduces production energy consumption.

[0036] (3) The present invention can control the amount of fuel added to the fluidized bed reactor to ensure that the exhaust gas of the fluidized bed reactor is neutral. The neutral partially fluidized roasting exhaust gas is used to transport the fine powder collected at the tail of the rotary kiln to the cyclone preheater. This recovers the heat in the fluidized roasting exhaust gas while avoiding the secondary oxidation of the partially reduced fine powder, which is beneficial to improving the magnetic susceptibility of the fluidized magnetic roasting process. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 Schematic diagram of a rotary kiln-fluidized bed furnace combined roasting system for refractory iron ore in an embodiment of the present invention.

[0038] Legend:

[0039] 1. Raw material bin; 2. Rotary kiln; 3. Pulverized coal bin; 4. Screw conveyor; 5. Burner; 6. Cooling bin; 7. First mixing barrel; 8. First air lock valve; 9. Cyclone dust collector; 10. Intermediate bin; 11. First-stage cyclone preheater; 12. Second-stage cyclone preheater; 13. Gas-solid separator; 14. Fluidized bed reactor; 15. Second mixing barrel; 16. Hot blast furnace; 17. Second air lock valve; 18. Third air lock valve. DETAILED DESCRIPTION

[0040] To facilitate understanding of the present invention, the present invention will be described in more comprehensive and detailed form below in conjunction with the accompanying drawings and preferred embodiments. However, the scope of protection of the present invention is not limited to the following specific embodiments.

[0041] Unless otherwise defined, all technical terms used hereinafter have the same meanings as those generally understood by those skilled in the art. The technical terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the scope of protection of the present invention.

[0042] Unless otherwise specified, various raw materials, reagents, instruments and equipment used in the present invention can be purchased from the market or prepared by existing methods.

[0043] Example 1

[0044] like Figure 1 As shown, this embodiment provides a combined iron ore roasting system, comprising a rotary kiln 2 for roasting raw iron ore and a fluidized roasting system for roasting fine iron ore collected by a cyclone dust collector at the tail of the rotary kiln.

[0045] The tail of the rotary kiln 2 is connected to a raw material bin 1, which allows iron ore to enter the rotary kiln from the tail of the rotary kiln 2 for roasting and magnetization. The tail of the rotary kiln 2 is also connected to a cyclone dust collector 9 for collecting fine-particle iron ore, and an intermediate bin 10 for storing fine-particle iron ore is provided at the bottom of the cyclone dust collector 9; the head of the rotary kiln 2 is provided with a burner 5 (specifically: a movable pulverized coal burner) for providing heat for the rotary kiln 2, and the head of the rotary kiln 2 is also provided with a cooling bin 6; the fuel of the rotary kiln 2 is coal, which is stored in the pulverized coal bin 3 and transported to the movable pulverized coal burner by a screw conveyor 4. The movable pulverized coal burner mixes the coal transported by the screw conveyor 4 with air and sends it into the rotary kiln 2 for combustion.

[0046] The fluidized bed roasting system includes two cyclone preheaters (a first-stage cyclone preheater 11 and a second-stage cyclone preheater 12), a fluidized bed reactor 14, a gas-solid separator 13, and a hot blast furnace 16. The hot blast furnace 16 provides heat for the fluidized bed reactor 14. The intermediate bin 10 is connected to the cyclone preheater, the fluidized bed reactor 14, and the gas-solid separator 13 in sequence via pipes, in the direction of fine iron ore flow. The air outlet of the second-stage cyclone preheater 12 is connected to the cooling bin 6 and to the air inlet of the first-stage cyclone preheater 11. The air outlet of the gas-solid separator 13 is connected to the discharge port of the first-stage cyclone preheater 11 and to the feed port of the second-stage cyclone preheater 12. The airflow carries the material discharged from the discharge port of the first-stage cyclone preheater 11 through pipes into the second-stage cyclone preheater 12 for heat exchange.

[0047] The cooling bin 6 is connected to the first mixing barrel 7, and the gas-solid separator 13 is connected to the second mixing barrel 15. The air outlet of the first stage cyclone preheater 11 and the air outlet of the cyclone dust collector are both connected to the bag dust collector to further collect dust and avoid environmental pollution.

[0048] A first air lock valve 8 is provided on the pipe between the cyclone preheater and the cooling bin 6; a third air lock valve 18 is provided on the pipe between the intermediate bin 10 and the cyclone preheater; a second air lock valve 17 is provided on the pipe between the air outlet of the second-stage cyclone preheater 12 and the cooling bin 6. The air lock valve can adjust the air volume as needed for easy control.

[0049] The iron ore combined roasting system of this embodiment operates as follows: the iron ore is crushed and fed into the rotary kiln 2 from the kiln tail after being measured according to the coal ore content. A movable pulverized coal burner 5 is installed at the kiln head of the rotary kiln 2. The temperature and atmosphere within the rotary kiln 2 are controlled by adjusting the coal injection rate, air volume, and air pressure of the burner 5. The pulverized coal and air supplied by the burner 5 are burned within the kiln, providing heat and reducing agents for the ore.

[0050] The ore material (coarse-grained iron ore) in the kiln tumbles continuously with the rotation of the rotary kiln 2 and slowly moves from the kiln tail to the kiln head. In this process, the ore is preheated and magnetized, and the weakly magnetic iron minerals are transformed into strongly magnetic Fe3O4 and flow out of the rotary kiln, which is the rotary kiln roasting ore.

[0051] The combustion flue gas draws in the dust generated by the tumbling of the ore. Since the flue gas flows in the countercurrent to the ore, some fine particles are drawn into the flue gas at the tail of the rotary kiln without undergoing high-temperature roasting. The weakly magnetic iron minerals in them do not have time to be converted into strongly magnetic iron minerals and flow out of the rotary kiln with the flue gas 2.

[0052] The dust (i.e., fine iron ore particles) that exits the rotary kiln 2 with the flue gas is collected by a cyclone dust collector 9 and stored in an intermediate bin 10. The cleaned flue gas is then discharged into the atmosphere. The dust is then fed by a screw pump and pneumatically conveyed to the fluidized bed roasting system for roasting. The weakly magnetic iron minerals in the dust are converted into highly magnetic Fe₃O₄.

[0053] The fluidized bed reactor 14 is heated by a hot blast stove 16, and the atmosphere in the roasting furnace is controlled by adjusting the amount of fuel supplied from the lower part of the reactor to ensure that the tail gas discharged from the fluidized bed roasting system is a neutral atmosphere.

[0054] The feed for fluidized roasting is the fine-grained material collected by the cyclone dust collector 9 at the tail of the rotary kiln 2. On the one hand, this solves the problem of recycling the fine powder collected by the cyclone dust collector 9 of the magnetic roasting in the rotary kiln 2, and on the other hand, it eliminates the dry powder making operation in the preparation process of the raw materials for fluidized magnetic roasting.

[0055] The air used for pneumatic conveying is the exhaust gas from the fluidized bed roasting system, which can ensure that the heat loss of dust is minimized during the transportation process. While reducing the energy consumption of fluidized bed roasting, it can ensure that a small amount of magnetized iron minerals in the dust will not be secondary oxidized, thereby increasing the magnetic susceptibility of the fluidized bed roasting process.

[0056] The roasted ore exiting rotary kiln 2 is first cooled using the exhaust gas from the fluidized roasting system. The air-cooled ore is then water-cooled to produce rotary kiln-roasted ore. The fluidized roasted ore is directly water-cooled to produce fluidized roasted ore. In this process, the air-cooled ore exiting rotary kiln 2 is cooled using the exhaust gas from the fluidized roasting system. The air-solid heat exchange cools the roasted ore, reducing the subsequent water cooling intensity. Simultaneously, the flue gas after the air-solid heat exchange is used to support the combustion of pulverized coal at the kiln head, recovering some of the waste heat from the roasted ore.

[0057] Finally, the rotary kiln roasted ore and the fluidized bed roasted ore are ground, classified, magnetically separated or flotation separated to obtain the iron ore concentrate product.

[0058] Example 2:

[0059] The refractory red iron ore treated in this embodiment has useful minerals mainly siderite, and also contains a small amount of hematite, limonite and pseudo-hematite; the gangue minerals are mainly quartz and sericite, with a small amount of feldspar, kaolinite, barite, apatite and other scattered minerals. The siderite minerals are well crystallized, and the grains are often euhedral and semi-euhedral granular of varying sizes, some of which are irregular in shape. The embedded particle size is generally between 0.02 and 0.35 mm, and the fine ones can be less than 0.01 mm. The content of hematite and limonite is not high, and the two are closely embedded, often existing in the form of aggregates, with an aggregate particle size of generally 0.02 to 0.20 mm. The chemical multi-element analysis results of the raw ore are shown in Table 1.

[0060] Table 1 Multi-element analysis results of raw ore (%)

[0061] project TFe FeO <![CDATA[Fe2O3]]> <![CDATA[SiO2]]> <![CDATA[Al2O3]]> CaO MgO content 24.68 23.71 8.95 34.21 8.67 0.27 2.26 project MnO <![CDATA[Na2O]]> <![CDATA[K2O]]> P S Ig TFe / FeO content 0.56 0.13 2.66 0.10 0.72 16.84 1.04

[0062] The roasting system of device embodiment 1 is used for treatment, controlling the roasting temperature in the rotary kiln to about 750°C and the roasting atmosphere to a weak reducing atmosphere, the temperature in the fluidized bed reactor to about 650°C and the roasting atmosphere to a weak reducing atmosphere, the roasted ore grade after magnetic roasting in the rotary kiln is 29.33% TFe and the magnetic susceptibility is 89.93%; the fine powder after fluidized bed magnet roasting has a roasted ore grade of 24.57% and a magnetic susceptibility of 93.72%; the roasted ore in the rotary kiln is ground in the first stage to a fineness of 70% to 75% of -0.075 mm, and then combined with the roasted ore from the fluidized bed roasting to enter a first weak magnetic separation, the first weak magnetic coarse concentrate is then subjected to second and third stage grinding, second and third stage weak magnetic separation to obtain a weak magnetic separation concentrate, and the weak magnetic concentrate is then subjected to a reverse flotation process to obtain the final iron ore concentrate product. After the roasted ore is separated by stage grinding-weak magnetic process, the concentrate grade TFe is 60.08% and the iron recovery rate is 86.39%.

[0063] Example 3:

[0064] The iron minerals in the refractory red iron ore treated in this embodiment are mainly limonite, followed by a small amount of hematite. Other metallic minerals include pyrolusite and rutile; the gangue minerals are mainly quartz, followed by silicate minerals such as sericite, feldspar and kaolinite. Limonite is mainly produced in two forms: one is a massive aggregate with extremely irregular shapes; the other is a grid-like and irregular granular form. Hematite is a relatively minor iron mineral in the ore and only appears in a few block ores. It is mostly a product of the dehydration of limonite, often in irregular or granular form and closely intergrows with limonite. The chemical multi-element and iron phase analysis results of the original ore are shown in Table 2 and Table 3 respectively.

[0065] Table 2 Results of multi-element analysis of raw ore (%)

[0066]

[0067] Table 3 Analysis results of iron phase of raw ore (%)

[0068]

[0069] The roasting system of Example 1 was used for processing, with the roasting temperature in the rotary kiln controlled at approximately 750°C and the CO gas content at approximately 3% by volume, and the temperature in the fluidized bed reactor controlled at approximately 650°C and the CO gas content at approximately 5% by volume. The ore from the rotary kiln was ground in the first stage to a fineness of -0.075 mm (70% to 75%), and then combined with the ore from the fluidized bed roasting to enter a first stage of weak magnetic separation. The first stage of weak magnetic coarse concentrate was then subjected to second and third stage grinding and second and third stage weak magnetic separation to obtain a weak magnetic separation concentrate. The final grinding fineness of the third stage was -0.045 mm (80% to 85%). The weak magnetic concentrate was then subjected to a reverse flotation process to obtain the final iron ore concentrate product. After treatment with the combined roasting and beneficiation method, the final iron ore concentrate yield was 56.27%, the TFe grade was 60.47%, and the iron recovery rate was 92.86%.

Claims

1. A combined roasting system for iron ore, characterized in that: It comprises a rotary kiln (2) for roasting iron ore raw materials and a fluidized roasting system for roasting fine iron ore discharged from the kiln tail of the rotary kiln (2); The rotary kiln (2) is connected to a cyclone dust collector (9) for collecting fine iron ore particles, and an intermediate bin (10) for storing fine iron ore particles is provided at the bottom of the cyclone dust collector (9); The fluidized bed roasting system comprises a cyclone preheater, a fluidized bed reactor (14), a gas-solid separator (13) and a hot blast furnace (16), wherein the hot blast furnace (16) is used to supply heat to the fluidized bed reactor (14) and regulate the atmosphere in the roasting furnace by adjusting the amount of fuel supplied from the lower part of the reactor (14) to ensure that the tail gas discharged from the fluidized bed roasting system is a neutral atmosphere; the intermediate bin (10), the cyclone preheater, the fluidized bed reactor (14) and the gas-solid separator (13) are connected in sequence through pipelines; the cyclone preheater is a two-stage cyclone preheater, including a first-stage cyclone An air preheater (11) and a second-stage cyclone preheater (12); the air outlet of the second-stage cyclone preheater (12) is connected to the cooling bin (6) through a pipeline, and is connected to the air inlet of the first-stage cyclone preheater (11); part of the tail gas discharged from the second-stage cyclone preheater (12) is first used to cool the ore roasted in the rotary kiln, and is further heated after gas-solid heat exchange, and then introduced into the rotary kiln (2) as combustion-supporting air for roasting again; the carrier gas introduced into the pipeline between the intermediate bin (10) and the first-stage cyclone preheater (11) is the tail gas discharged from the fluidized bed reactor (14).

2. The combined roasting system according to claim 1, characterized in that: The kiln head of the rotary kiln (2) is provided with a burner (5) for supplying heat to the rotary kiln (2), and the kiln head of the rotary kiln (2) is also provided with a cooling bin (6).

3. The combined roasting system according to claim 2, characterized in that: The air outlet of the first-stage cyclone preheater (11) is connected to the bag dust collector; The air outlet of the gas-solid separator (13) is connected to the discharge port of the first-stage cyclone preheater (11) and to the feed port of the second-stage cyclone preheater (12). The material discharged from the discharge port of the first-stage cyclone preheater (11) is brought into the second-stage cyclone preheater (12) through the pipeline by the airflow for heat exchange.

4. The combined roasting system according to claim 3, characterized in that: A first air lock valve (8) is provided on the pipeline between the cyclone preheater and the cooling bin (6); a third air lock valve (18) is provided on the pipeline between the intermediate bin (10) and the cyclone preheater; and a second air lock valve (17) is provided on the pipeline between the air outlet of the second-stage cyclone preheater (12) and the cooling bin (6).

5. The combined roasting system according to any one of claims 2 to 4, characterized in that: The cooling bin (6) is connected to the first stirring barrel (7), and the gas-solid separator (13) is connected to the second stirring barrel (15); the kiln tail of the rotary kiln (2) is connected to the raw material bin (1).

6. A method for beneficiating iron ore based on the combined roasting system according to any one of claims 1 to 5, characterized in that: The following steps are involved: (i) Using weakly magnetic iron ore as raw material, the raw material is crushed and measured, and then fed into the rotary kiln (2) from the kiln tail of the rotary kiln (2) and roasted and magnetized in the rotary kiln (2). The roasted ore is collected at the kiln head of the rotary kiln (2). Fine particles of iron ore in the rotary kiln (2) flow out of the rotary kiln (2) from the kiln tail along with the flue gas generated by combustion, are collected by a cyclone dust collector (9), and are stored in an intermediate bin (10); (ii) the fine iron ore collected in step (i) is preheated in a cyclone preheater and then transported to a fluidized bed reactor (14) for roasting to convert it into a strongly magnetic iron ore, and fluidized bed roasted ore is obtained after gas-solid separation; (iii) cooling the rotary kiln roasted ore obtained in step (i) and the fluidized bed roasted ore obtained in step (ii) and then combining them or subjecting them to grinding, classification, magnetic separation or flotation to obtain an iron ore concentrate product.

7. The mineral processing method according to claim 6, wherein: In step (i), the particle size of the weakly magnetic iron ore is -20 mm; the weakly magnetic iron ore is a mixed ore of one or more of hematite, limonite, and siderite.

8. The mineral processing method according to claim 6, wherein: In step (i), a hot blast furnace (16) is used to supply heat to the fluidized bed reactor (14), and the tail gas discharged from the fluidized bed reactor (14) is partially used to transport and preheat fine iron ore after gas-solid separation.

9. The mineral processing method according to claim 6, wherein: In step (ii), part of the tail gas discharged from the second stage cyclone preheater (12) is first used to cool the ore roasted in the rotary kiln, is further heated after gas-solid heat exchange, and is then introduced into the rotary kiln (2) as combustion air for further roasting.

10. The mineral processing method according to claim 6, wherein: In step (iii), the rotary kiln roasted ore is cooled by first cooling the exhaust gas discharged from the cyclone preheater and then water cooling. The fluidized bed roasted ore is directly cooled by water.

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