A device and method for reducing iron from red mud without combustion and heating

Abstract

The present invention discloses an apparatus and method for reducing and extracting iron from red mud without the need for combustion and heat. Hydrogen is used as a reducing agent and fluidizing gas, and low-temperature cold plasma fluidization is employed to solid-state reduce the iron oxide in the red mud. Ferromagnetic material is then obtained by magnetic separation, with an iron recovery rate of ≥80%. A high-gas-velocity graded microwave fluidized bed with a built-in inert granular bed material is employed to dry, break up, and transport the red mud. Low-temperature cold plasma hydrogen reduces the iron oxide to ferromagnetic material without the need for combustion and heat. Microwave heating and drying are clean and efficient, and collisions between the inert granular bed material in the fluidized bed and between the particles and the inner wall of the reactor can effectively disperse the red mud particles. The process equipment of the present invention is simple, easy to operate, and has low energy consumption. It can process high-moisture, high-viscosity red mud materials, has a wide range of raw material applications, is environmentally friendly, and can achieve large-scale, clean, and efficient iron extraction from red mud, with good economic and social benefits.

Description

Technical Field

[0001] The present invention relates to the field of chemical nonferrous metallurgy and environmental protection, and in particular to a device and method for extracting iron by reducing red mud without combustion and heat supply. Background Art

[0002] Red mud is an industrial solid waste generated during the alkaline leaching of bauxite to produce alumina. It is characterized by high alkalinity, high moisture content, high viscosity, and radioactivity. Existing disposal methods primarily rely on dry damming and stockpiling, which not only consumes significant land resources but also poses significant safety hazards and harm to surrounding soil and water resources over long periods of storage. Red mud contains a high iron content and can be used as a secondary resource for iron recovery. Separating and recovering the iron in red mud is a key approach to its resource utilization and reduction.

[0003] Chinese patent application CN102628097A discloses a method for producing iron ore concentrate from red mud using a fluidized bed reduction magnetization process. The red mud is dried and preheated in a drum, then subjected to magnetization reduction roasting in a circulating fluidized bed using reducing gas of a specified composition, yielding iron ore concentrate with an iron grade of 61%-65%. While this method can recover iron from the red mud, drum drying is only suitable for low-moisture, low-viscosity red mud. High-moisture, high-viscosity red mud tends to clump and adhere to the wall during drum drying, making it difficult to operate continuously.

[0004] Chinese patent application CN107523686A discloses an apparatus for producing iron ore concentrate by suspended roasting of red mud. The apparatus first dries and pulverizes the red mud to produce red mud ore with a moisture content of less than 15%. This ore concentrate then undergoes fluidized preheating, fluidized oxidation, fluidized reduction, and cooling magnetic separation to yield an iron ore grade of 50%-68%. This solution can achieve an iron recovery rate of 60-90% in the red mud. However, it uses ambient temperature water for indirect heat exchange cooling of the heat-reduced raw material, failing to effectively recycle the preheated raw material within the system, resulting in wasted system energy. Furthermore, the apparatus does not specifically describe the drying and pulverizing method for the red mud, making it difficult to effectively utilize the high-moisture, high-viscosity red mud.

[0005] Chinese patent application CN1300348A discloses a method for recovering iron from red mud. Red mud with a moisture content of 10-20% is mixed with coal and sponge iron powder, extruded, and dried. The mixture is then mixed with industrial coal and fed into a rotary kiln for reduction roasting at 1100-1200°C. The roasted product is cooled and magnetically separated to produce sponge iron powder. Chinese patent application CN102839249A discloses a method for producing iron ore concentrate by direct reduction of high-iron red mud in a rotary hearth furnace. The red mud is dried in a chain grate using preheated air to a moisture content of less than 12%. The mud is then mixed with coke or coal powder and pressed into green pellets. The green pellets are dried, screened, and refined to 8-12mm in size before being fed into a rotary kiln for reduction roasting at 1000-1400°C. The roasted product is cooled, crushed, and magnetically separated to produce iron ore concentrate with an iron grade exceeding 60%. Chinese patent application CN103805726A discloses a method for comprehensively utilizing high-iron red mud using a rotary hearth furnace pelletized iron process. The method involves mixing high-iron red mud, coal powder or coke powder, and a certain amount of additives, forming pellets, and then reducing and roasting them in a rotary hearth furnace at 1350-1450°C. The roasted product is cooled, crushed, and magnetically separated to produce pelletized iron. Chinese patent application CN107254583A discloses a method for comprehensively utilizing red mud based on direct reduction roasting and magnetic separation in a rotary kiln. The method uses red mud as the raw material, coal powder as the reducing agent, titanomagnetite as an additive, and starch and bentonite as binders to form pellets, dry them, and then directly reduce and roast them in a rotary kiln at 1280-1300°C. The roasted product is cooled and magnetically separated to produce direct reduced iron with an iron grade exceeding 92%. The above technical solutions all achieve the recovery of iron resources in red mud through reduction roasting. However, all use coal powder or coke powder as the reducing agent, and the roasting process emits a large amount of carbon dioxide and introduces other impurities into the roasted products. In addition, the reduction roasting temperature of the above inventions is above 1000°C, which consumes a lot of energy. Summary of the Invention

[0006] In view of the shortcomings of the existing technology, the present invention aims to provide a device and method for reducing red mud to extract iron without combustion and heat supply.

[0007] In order to achieve the above object, the present invention adopts the following technical solutions:

[0008] A device for reducing red mud to extract iron without combustion and heat supply, comprising a silo, a feeder, a variable-diameter fluidized bed, a microwave generator, an inert granular bed material, a first-stage cyclone separator I, a standpipe, a discharge valve I, a second-stage cyclone separator I, a feed valve, a fluidized bed reactor, a low-temperature cold plasma generator, a first-stage cyclone separator II, a cyclone separator return valve, a second-stage cyclone separator II, a discharge valve II, a magnetic separation system, and a dust removal and dehydration system;

[0009] The silo, feeder, and variable diameter fluidized bed are sequentially connected along the direction of material flow; the air inlet at the bottom of the variable diameter fluidized bed is connected to an air pipeline, and the air outlet is connected to the air inlet of the primary cyclone separator I; the diameter of the lower portion of the variable diameter fluidized bed is larger than that of the upper portion, and a microwave generator is provided at the lower portion, and an inert granular bed material is loaded inside the lower portion;

[0010] The air outlet at the top of the first-stage cyclone separator 1 is connected to the air inlet of the second-stage cyclone separator 1, and the discharge port at the bottom is connected to the feed port of the discharge valve 1 through a vertical pipe, and the discharge port of the discharge valve 1 is connected to the feed port of the feed valve; the air outlet at the top of the second-stage cyclone separator 1 is connected to the tail gas treatment system, and the discharge port at the bottom is connected to the feed port of the feed valve; the discharge port of the feed valve is connected to the feed port of the fluidized bed reactor;

[0011] The discharge port of the fluidized bed reactor is connected to the feed port of the discharge valve II, and the air outlet is connected to the air inlet of the primary cyclone separator II; a low-temperature cold plasma generating device is provided at the lower part of the fluidized bed reactor;

[0012] The air outlet of the first-stage cyclone separator II is connected to the air inlet of the second-stage cyclone separator II, and the discharge port is connected to the feed port of the cyclone separator return valve; the discharge port of the second-stage cyclone separator II is connected to the feed port of the cyclone separator return valve, and the air outlet is connected to the inlet of the dust removal and dehydration system; the discharge port of the cyclone separator return valve is connected to the cyclone return port of the fluidized bed reactor; the air inlet at the bottom of the fluidized bed reactor is connected to the hydrogen pipeline; the discharge port of the discharge valve II is connected to the inlet of the magnetic separation system, and the outlet of the dust removal and dehydration system is connected to the hydrogen pipeline.

[0013] Furthermore, the air inlet at the bottom of the discharge valve I, the air inlet at the bottom of the feed valve, and the air inlet at the bottom of the discharge valve II are all connected to a nitrogen pipeline.

[0014] Furthermore, the air inlet at the bottom of the return valve of the cyclone separator is connected to a hydrogen pipeline.

[0015] Furthermore, the inert particle bed material is one or a combination of spherical zirconia, spherical alumina, spherical silicon carbide, and spherical silicon nitride; and the diameter of the inert particle bed material is 1-5 mm.

[0016] The present invention also provides a working method of the above device, the specific process is as follows:

[0017] Red mud is stored in a silo and enters a variable-diameter fluidized bed through a feeder. Air is introduced into the variable-diameter fluidized bed from the bottom, causing the inert granular bed material to be bubbling fluidized or turbulently fluidized. The red mud is dispersed by the inert granular bed material. The red mud is simultaneously dried by microwave heating generated by a microwave generator. The dried and dispersed red mud is rapidly fluidized and enters the upper part of the variable-diameter fluidized bed, and then enters a primary cyclone separator 1 and a secondary cyclone separator 1 for separation. The red mud separated by the primary cyclone separator 1 passes through a riser, a discharge valve 1, and a feed valve to enter a fluidized bed reactor. The red mud separated by the secondary cyclone separator 1 passes through a feed valve to enter the fluidized bed reactor, and the separated tail gas enters a tail gas treatment system.

[0018] In the fluidized bed reactor, hydrogen is introduced from the bottom of the fluidized bed reactor, and the hydrogen generates hydrogen low-temperature cold plasma under the action of the low-temperature cold plasma generator, which reduces the iron oxide in the red mud; the material obtained by the reduction enters the magnetic separation system through the discharge valve II, and ferromagnetic material and aluminum-containing slag are obtained through magnetic separation; the reduction tail gas passes through the outlet of the first-level cyclone separator II and the second-level cyclone separator II in sequence for separation, and the materials separated by the first-level cyclone separator II and the second-level cyclone separator II are returned to the lower part of the fluidized bed reactor through the cyclone separator return valve. The tail gas separated by the second-level cyclone separator II enters the dust removal and dehydration system for purification to obtain hydrogen purified gas and return to the hydrogen pipeline.

[0019] Furthermore, in the above method, nitrogen is introduced from the bottom of the discharge valve I, the feed valve and the discharge valve II.

[0020] Furthermore, in the above method, hydrogen is introduced from the bottom of the return valve of the cyclone separator.

[0021] Furthermore, in the above method, the solid content of the red mud is 20%-90%.

[0022] Furthermore, in the above method, the reduction time of red mud in the fluidized bed reactor is 0.1-0.5h.

[0023] Furthermore, in the above method, the temperature of microwave drying in the variable diameter fluidized bed is 100-300°C.

[0024] Furthermore, in the above method, in the fluidized bed reactor, the dry red mud particles are in a bubbling fluidization state or a turbulent fluidization state.

[0025] Furthermore, in the above method, the recovery rate of iron is ≥80%.

[0026] The beneficial effects of the present invention are:

[0027] 1. This invention uses fluidized bed low-temperature cold plasma hydrogen to solid-state reduce iron oxide in red mud, eliminating the mixing, pelletizing, pellet drying, and combustion heating steps, resulting in a simple process. The hydrogen activated by the low-temperature cold plasma has high reducing activity and can reduce the iron oxide in red mud to produce ferromagnetic material at low or room temperature, achieving high reduction efficiency and low energy consumption.

[0028] 2. The present invention uses microwave heating to provide the heat required for red mud drying, resulting in high energy utilization. The mass and heat transfer rates between the gas and the fine red mud particles in the fluidized bed are fast, resulting in high drying efficiency.

[0029] 3. This invention utilizes a high-velocity, graded fluidized bed with an internal inert granular bed material to dry, break up, and transport red mud, requiring minimal equipment. Under microwave heating and drying, the internal inert granules collide with each other and with the inner wall of the fluidized bed reactor, breaking up the red mud, making operation simple and convenient.

[0030] 4. In the present invention, the solid phase processing processes of red mud drying, breaking up, conveying and reduction of iron oxide in red mud all adopt a gas-solid fluidized bed, which is convenient for continuous operation and large-scale treatment. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 This is a schematic structural diagram of the device for reducing iron from red mud without combustion for heat supply in Example 1 of the present invention. DETAILED DESCRIPTION

[0032] The present invention will be further described below in conjunction with the accompanying drawings. It should be noted that this embodiment is based on the technical solution and provides a detailed implementation method and specific operation process, but the protection scope of the present invention is not limited to this embodiment.

[0033] Example 1

[0034] This embodiment provides a device for reducing red mud to extract iron without combustion heat supply, such as Figure 1 As shown, it includes a silo 1, a feeder 2, a variable diameter fluidized bed 3, a microwave generator 31, an inert granular bed material 32, a primary cyclone separator I 4, a standpipe 5, a discharge valve I 6, a secondary cyclone separator I 7, a feed valve 8, a fluidized bed reactor 9, a low-temperature cold plasma generator 91, a primary cyclone separator II 10, a cyclone separator return valve 11, a secondary cyclone separator II 12, a discharge valve II 13, a magnetic separation system 14 and a dust removal and dehydration system 15;

[0035] The silo 1, feeder 2 and variable diameter fluidized bed 3 are connected in sequence along the direction of material flow; the air inlet at the bottom of the variable diameter fluidized bed 3 is connected to the air pipeline, and the air outlet is connected to the air inlet of the primary cyclone separator 14; the diameter of the lower part of the variable diameter fluidized bed 3 is larger than the diameter of the upper part, and a microwave generator 31 is provided at the lower part, and the interior of the lower part is loaded with inert granular bed material 32.

[0036] The air outlet at the top of the first-stage cyclone separator 14 is connected to the air inlet of the second-stage cyclone separator 17, and the discharge port at the bottom is connected to the feed port of the discharge valve 16 through the riser 5, and the discharge port of the discharge valve 16 is connected to the feed port of the feed valve 8; the air outlet at the top of the second-stage cyclone separator 17 is connected to the tail gas treatment system, and the discharge port at the bottom is connected to the feed port of the feed valve 8; the discharge port of the feed valve 8 is connected to the feed port of the fluidized bed reactor 9;

[0037] The discharge port of the fluidized bed reactor 9 is connected to the feed port of the discharge valve II 13, and the air outlet is connected to the air inlet of the primary cyclone separator II 10; a low-temperature cold plasma generator 91 is provided in the lower part of the fluidized bed reactor 9;

[0038] The air outlet of the first-stage cyclone separator II 10 is connected to the air inlet of the second-stage cyclone separator II 12, and the discharge port is connected to the feed port of the cyclone separator return valve 11; the discharge port of the second-stage cyclone separator II 12 is connected to the feed port of the cyclone separator return valve 11, and the air outlet is connected to the inlet of the dust removal and dehydration system 15; the discharge port of the cyclone separator return valve 11 is connected to the cyclone return port of the fluidized bed reactor 9; the air inlet at the bottom of the fluidized bed reactor 9 is connected to the hydrogen pipeline; the discharge port of the discharge valve II 13 can be connected to the inlet of the magnetic separation system 14 through a conveying device, and the outlet of the dust removal and dehydration system 15 is connected to the hydrogen pipeline.

[0039] In this embodiment, the air inlet at the bottom of the discharge valve I 6, the air inlet at the bottom of the feed valve 8, and the air inlet at the bottom of the discharge valve II13 are all connected to the nitrogen pipeline.

[0040] In this embodiment, the air inlet of the cyclone separator return valve 11 is connected to the hydrogen pipeline.

[0041] Example 2

[0042] This embodiment provides a working method of the device described in Embodiment 1, and the specific process is as follows:

[0043] Red mud is stored in a silo 1 and enters a variable diameter fluidized bed 3 through a feeder 2. Air is introduced into the variable diameter fluidized bed 3 from the bottom thereof, causing the inert granular bed material to be bubbling fluidized or turbulently fluidized. The red mud is dispersed by the inert granular bed material. The red mud is simultaneously dried by microwave heating generated by a microwave generator 31. The dried and dispersed red mud rapidly fluidizes and enters the upper portion of the variable diameter fluidized bed 3, and then sequentially enters a primary cyclone separator 14 and a secondary cyclone separator 17 for separation. The red mud separated by the primary cyclone separator 14 sequentially passes through a riser 5, a discharge valve 16, and a feed valve 8 to enter a fluidized bed reactor 9. The red mud separated by the secondary cyclone separator 17 passes through a feed valve 8 to enter the fluidized bed reactor 9, and the separated tail gas enters a tail gas treatment system.

[0044] In the fluidized bed reactor 9, hydrogen is introduced from the bottom of the fluidized bed reactor 9. Under the action of the low-temperature cold plasma generator 91, the hydrogen generates hydrogen low-temperature cold plasma, which reduces the iron oxide in the red mud. The reduced material enters the magnetic separation system 14 through the discharge valve II 13, and is magnetically separated to obtain ferromagnetic material and aluminum-containing slag. The reduced tail gas passes through the outlet of the first-stage cyclone separator II 10 and the second-stage cyclone separator II 12 for separation. The materials separated by the first-stage cyclone separator II 10 and the second-stage cyclone separator II 12 are returned to the lower part of the fluidized bed reactor 9 through the cyclone separator return valve 11. The tail gas separated by the second-stage cyclone separator II 12 enters the dust removal and dehydration system 15 for purification to obtain purified hydrogen gas, which is then returned to the hydrogen pipeline.

[0045] In this embodiment, nitrogen is introduced from the bottom of the discharge valve I 6, the feed valve 8 and the discharge valve II 13.

[0046] In this embodiment, the inert particle bed material is spherical zirconia with a diameter of 1 mm.

[0047] In this embodiment, hydrogen is introduced from the bottom of the return valve 11 of the cyclone separator.

[0048] In this embodiment, the reduction time of red mud in the fluidized bed reactor 9 is 0.5 h.

[0049] In this embodiment, the microwave drying temperature in the variable diameter fluidized bed 3 is 100°C.

[0050] In this embodiment, the solid content of the red mud is 20%.

[0051] In this embodiment, in the fluidized bed reactor, the dry red mud particles are in a bubbling fluidization state or a turbulent fluidization state.

[0052] Through the above method, the recovery rate of iron in red mud is 83%.

[0053] Example 3

[0054] This embodiment is basically the same as Example 2, and the similarities are not described again. The differences are: the solid content of the red mud is 90%, the microwave heating and drying temperature is 300°C, the inert particle bed material is spherical alumina with a diameter of 5 mm, low-temperature cold plasma hydrogen reduction is performed for 0.1 h, and a ferromagnetic material is obtained after magnetic separation, with an iron recovery rate of 87%.

[0055] Example 4

[0056] This embodiment is basically the same as Example 2, and the similarities are not described again. The differences are: the solid content of the red mud is 40%, the microwave heating and drying temperature is 200°C, the inert particle bed material is spherical silicon carbide with a diameter of 3 mm, low-temperature cold plasma hydrogen reduction is performed for 0.3 h, and a ferromagnetic material is obtained after magnetic separation, with an iron recovery rate of 85%.

[0057] Example 5

[0058] This embodiment is basically the same as Example 2, and the similarities are not described again. The differences are: the solid content of the red mud is 60%, the microwave heating drying temperature is 250°C, the inert particle bed material is spherical silicon nitride with a diameter of 2 mm, low-temperature cold plasma hydrogen reduction is performed for 0.2 h, and a ferromagnetic material is obtained after magnetic separation, with an iron recovery rate of 89%.

[0059] In the above embodiments, all percentages not specified are by mass.

[0060] The process parameters (such as temperature, time, etc.) of the present invention can realize the method by taking upper and lower limits and interval values, and the embodiments are not listed here one by one.

[0061] Those skilled in the art can make various corresponding changes and modifications based on the above technical solutions and concepts, and all of these changes and modifications should be included in the scope of protection of the claims of the present invention.

Claims

1. A device for reducing iron from red mud without combustion and heat supply, characterized in that: The invention comprises a silo (1), a feeder (2), a variable diameter fluidized bed (3), a microwave generator (31), an inert granular bed material (32), a primary cyclone separator I (4), a vertical pipe (5), a discharge valve I (6), a secondary cyclone separator I (7), a feed valve (8), a fluidized bed reactor (9), a low-temperature cold plasma generator (91), a primary cyclone separator II (10), a cyclone separator return valve (11), a secondary cyclone separator II (12), a discharge valve II (13), a magnetic separation system (14) and a dust removal and dehydration system (15); The silo (1), the feeder (2) and the variable diameter fluidized bed (3) are connected in sequence along the direction of material flow; the air inlet at the bottom of the variable diameter fluidized bed (3) is connected to an air pipeline, and the air outlet is connected to the air inlet of the primary cyclone separator I (4); the diameter of the lower part of the variable diameter fluidized bed (3) is larger than the diameter of the upper part, the lower part is provided with a microwave generating device (31), and the interior of the lower part is loaded with inert granular bed material (32); The air outlet at the top of the first-stage cyclone separator I (4) is connected to the air inlet of the second-stage cyclone separator I (7), and the discharge port at the bottom is connected to the feed port of the discharge valve I (6) through a vertical pipe (5), and the discharge port of the discharge valve I (6) is connected to the feed port of the feed valve (8); the air outlet at the top of the second-stage cyclone separator I (7) is connected to the tail gas treatment system, and the discharge port at the bottom is connected to the feed port of the feed valve (8); the discharge port of the feed valve (8) is connected to the feed port of the fluidized bed reactor (9); The discharge port of the fluidized bed reactor (9) is connected to the feed port of the discharge valve II (13), and the air outlet is connected to the air inlet of the first-stage cyclone separator II (10); a low-temperature cold plasma generating device (91) is provided in the lower part of the interior of the fluidized bed reactor (9); The air outlet of the first-stage cyclone separator II (10) is connected to the air inlet of the second-stage cyclone separator II (12), and the discharge port is connected to the feed port of the cyclone separator return valve (11); the discharge port of the second-stage cyclone separator II (12) is connected to the feed port of the cyclone separator return valve (11), and the air outlet is connected to the inlet of the dust removal and dehydration system (15); the discharge port of the cyclone separator return valve (11) is connected to the cyclone return port of the fluidized bed reactor (9); the air inlet at the bottom of the fluidized bed reactor (9) is connected to the hydrogen pipeline; the discharge port of the discharge valve II (13) is connected to the inlet of the magnetic separation system (14), and the outlet of the dust removal and dehydration system (15) is connected to the hydrogen pipeline.

2. The device for reducing iron from red mud without combustion and heat supply according to claim 1 is characterized in that: The air inlet at the bottom of the discharge valve I (6), the air inlet at the bottom of the feed valve (8) and the air inlet at the bottom of the discharge valve II (13) are all connected to the nitrogen pipeline.

3. The device for red mud reduction and iron extraction without combustion and heat supply according to claim 1 is characterized in that: The air inlet at the bottom of the cyclone separator return valve (11) is connected to the hydrogen pipeline.

4. The device for reducing iron from red mud without combustion and heat supply according to claim 1, characterized in that: The inert particle bed material is one or a combination of spherical zirconia, spherical alumina, spherical silicon carbide, and spherical silicon nitride; the diameter of the inert particle bed material is 1-5 mm.

5. A method for operating the device according to any one of claims 1 to 4, characterized in that: The specific process is: The red mud is stored in a silo (1) and enters a variable diameter fluidized bed (3) through a feeder (2); in the variable diameter fluidized bed (3), air is introduced from the bottom of the variable diameter fluidized bed (3), so that the inert granular bed material is bubbling fluidized or turbulent fluidized; the red mud is dispersed under the action of the inert granular bed material; the red mud is simultaneously dried under the action of microwave heating generated by a microwave generator (31); the dried and dispersed red mud is rapidly fluidized and enters the upper part of the variable diameter fluidized bed (3), and then enters the first-stage cyclone separator I (4) and the second-stage cyclone separator I (7) in sequence for separation; the red mud separated by the first-stage cyclone separator I (4) passes through a riser (5), a discharge valve I (6), and a feed valve (8) in sequence and enters a fluidized bed reactor (9); the red mud separated by the second-stage cyclone separator I (7) passes through a feed valve (8) and enters a fluidized bed reactor (9), and the separated tail gas enters a tail gas treatment system; In the fluidized bed reactor (9), hydrogen is introduced from the bottom of the fluidized bed reactor (9), and the hydrogen generates hydrogen low-temperature cold plasma under the action of the low-temperature cold plasma generator (91), thereby reducing the iron oxide in the red mud; the reduced material enters the magnetic separation system (14) through the discharge valve II (13), and the ferromagnetic material and aluminum-containing slag are obtained through magnetic separation; The reduction tail gas is separated in sequence through the outlet of the first-stage cyclone separator II (10) and the second-stage cyclone separator II (12). The materials separated by the first-stage cyclone separator II (10) and the second-stage cyclone separator II (12) are returned to the lower part of the fluidized bed reactor (9) through the cyclone separator return valve (11). The tail gas separated by the second-stage cyclone separator II (12) enters the dust removal and dehydration system (15) for purification, and then the purified hydrogen gas is obtained and returned to the hydrogen pipeline.

6. The method according to claim 5, characterized in that Nitrogen is introduced from the bottom of the discharge valve I (6), the feed valve (8) and the discharge valve II (13).

7. The method according to claim 5, characterized in that Hydrogen is introduced from the bottom of the cyclone separator return valve (11).

8. The method according to claim 5, characterized in that The solid content of the red mud is 20%-90%.

9. The method according to claim 5, characterized in that The reduction time of red mud in the fluidized bed reactor (9) is 0.1-0.5h.

10. The method according to claim 5, characterized in that In the variable diameter fluidized bed (3), the microwave drying temperature is 100-300°C.

11. The method according to claim 5, characterized in that In the fluidized bed reactor (9), the dry red mud particles are in a bubbling fluidization state or a turbulent fluidization state.

12. The method according to claim 5, characterized in that The iron recovery rate is ≥80%.

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