A device and method for extracting iron from red mud solid waste

Abstract

The present application relates to solid waste resource recycling technical field, disclose a kind of from red mud solid waste extraction iron device and method, including red mud raw material is obtained by drying and microwave treatment pretreatment red mud, pretreatment red mud is sorted by high gradient magnetic separator and obtains iron element enrichment, iron element enrichment is mixed and granulated after preheating and depth reduction roasting, by reducing atmosphere cooling and water cooling treatment obtains reduction pellet, reduction pellet is ground to monomer dissociation particle size by crushing system, and reduction crushed material is sent into multistage wet magnetic separator group and is classified and collected iron mineral product by magnetic separation.The present application generates microcracks by microwave reactor induced thermal stress and improves monomer dissociation degree, high gradient magnetic separator rejects silicon aluminum impurities and reduces reduction energy consumption, reduction roasting furnace promotes metal iron aggregation and growth and recovers high temperature and flue gas waste heat, water cooling tank prevents secondary oxidation of metal iron, and multistage wet magnetic separator group realizes iron product grading recovery and improves total recovery rate of iron element.

Description

Technical Field

[0001] This invention relates to the field of solid waste resource recycling technology, specifically to an apparatus and method for extracting iron from red mud solid waste. Background Technology

[0002] Red mud is a solid waste generated during the alumina production process. Red mud stockpiling occupies land resources and pollutes the ecological environment. Red mud contains iron, which is a potential iron resource. Red mud has a complex chemical composition and is highly alkaline. The iron minerals have low crystallinity and fine particle size. The close symbiosis between iron minerals and gangue minerals makes it difficult to extract iron from red mud.

[0003] Existing red mud iron extraction technologies include direct magnetic separation, acid leaching, and roasting magnetic separation. Direct magnetic separation has a low iron recovery rate, while acid leaching consumes a large amount of acid and corrodes production equipment, generating acidic wastewater that increases environmental treatment costs. Traditional roasting magnetic separation has a high reduction temperature and a long reduction time, resulting in high energy consumption and poor magnetic separation and grading effects, leading to low iron product purity. Existing technologies struggle to balance iron extraction efficiency with production costs, and the difficulty in treating secondary waste residue limits the industrial application of these technologies.

[0004] The red mud mudification effect makes it difficult to separate iron minerals from impurities. Conventional pretreatment methods cannot simultaneously achieve magnetic enhancement, alkali removal, and mud removal. The lack of a waste heat recovery and utilization mechanism in the reduction roasting process leads to heat energy waste. High-temperature reduction products are prone to secondary oxidation during the cooling process, resulting in a decrease in iron recovery rate. The single crushing process leads to insufficient dissociation of elemental iron from gangue minerals, making it difficult to achieve graded extraction based on the magnetic differences of different iron phases, resulting in the loss of high-quality iron resources. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides an apparatus and method for extracting iron from red mud solid waste, which solves the problems of difficulty in separating iron minerals from gangue minerals due to the red mud mudification effect, high energy consumption of traditional reduction roasting process, easy secondary oxidation of high-temperature reduction products during cooling process, low iron element recovery rate and low iron product purity in existing technologies.

[0006] To achieve the above objectives, the first aspect of the present invention provides an apparatus for extracting iron from red mud solid waste, comprising: The dryer has its dry material outlet connected to the microwave reactor's feed inlet. The microwave reactor is used to perform microwave modification treatment on dried red mud. The discharge port of the microwave reactor is connected to the feed port of the vibrating screen. The vibrating screen has its undersize outlet connected to the feed inlet of a high-gradient magnetic separator. A high-gradient magnetic separator, the magnetic concentrate outlet of which is connected to the solid feed inlet of a mixer; The mixer's mixture outlet is connected to the feed inlet of the disc granulator (briquetting machine); The discharge port of the disc granulator (briquetting machine) is connected to the feed port of the preheating kiln; The preheating kiln has its preheated material outlet connected to the feed inlet of the reduction roasting furnace. The reduction roasting furnace has a high-temperature roasting material outlet connected to the feed end of the water cooling tank. The reduction roasting furnace is equipped with a high-temperature flue gas exhaust port, which is connected to the hot gas inlet of the preheating kiln through a heat-resistant pipe. The heat-resistant pipe is used to introduce the waste heat flue gas generated by reduction roasting into the interior of the preheating kiln. The water-cooled tank has its discharge end connected to the feed inlet of the crushing system. The crushing system has its discharge port connected to the feed port of the multi-stage wet magnetic separator. The crushing system consists of a jaw crusher, a cone crusher, and a ball mill connected in series. The multi-stage wet magnetic separator unit includes a first-stage wet magnetic separator, a second-stage wet magnetic separator, and a third-stage wet magnetic separator connected in series. The first-stage tailings outlet of the first-stage wet magnetic separator is connected to the feed inlet of the second-stage wet magnetic separator. The second-stage tailings outlet of the second-stage wet magnetic separator is connected to the feed inlet of the third-stage wet magnetic separator. The weak magnetic product outlet of the third-stage wet magnetic separator is connected to the medium magnetic product outlet of the second-stage wet magnetic separator through a pipeline.

[0007] A second aspect of the present invention provides a method for extracting iron from red mud solid waste, comprising the following steps: The red mud raw material is sent to a dryer for drying, and the dried red mud is sent to a microwave reactor for microwave treatment. The microwave-treated red mud is then screened by a vibrating screen to obtain pretreated red mud. During microwave treatment, the microwave reactor utilizes the difference in dielectric constant between iron minerals and gangue minerals in red mud. Iron minerals have a higher microwave absorption capacity than gangue minerals. Microwave radiation causes the iron minerals to heat up at a higher rate than the gangue minerals, creating a temperature gradient between them. This temperature gradient induces thermal stress at the grain boundaries of the iron and gangue minerals. The thermal stress causes microcracks to form at these grain boundaries. These microcracks reduce the energy consumption of subsequent crushing operations and increase the degree of mineral dissociation. Simultaneously, microwave treatment removes interlayer water and adsorbed water from the red mud, thus disrupting its colloidal properties. The pretreated red mud is fed into a high gradient magnetic separator for combined gravity and magnetic separation. The high gradient magnetic separator uses the difference in the specific magnetic susceptibility between iron minerals and clay minerals to remove some silicon and aluminum impurities and non-magnetic impurities, resulting in iron enrichment. Removing silicon and aluminum impurities improves the iron grade of the material fed into the furnace. Iron element enrichment, reducing agent, slag-forming agent and binder are added to a mixer and mixed evenly to obtain a mixture. The mixture is then processed into spherical particles by a disc granulator. Spherical particles are fed into a preheating kiln for preheating, and then into a reduction roasting furnace for deep reduction roasting. Inside the furnace, a carbothermic reduction reaction occurs, where the reducing agent vaporizes at high temperature to produce carbon monoxide and hydrogen. The carbon monoxide and hydrogen then progressively reduce the hematite and limonite in the red mud, following the sequence of hematite to magnetite, magnetite to ferrous oxide, and ferrous oxide to metallic iron. Meanwhile, a slagging agent reacts with gangue components in the red mud at high temperature to generate a low-melting-point silicate liquid phase. The process promotes the migration, aggregation, and growth of metallic iron particles into iron particles. The high-temperature flue gas generated by the reduction roasting furnace is introduced into the preheating kiln. The heat carried by the high-temperature flue gas is transferred to the spherical particles in the preheating kiln. The heat transfer process reduces the heating energy consumption of the reduction roasting furnace. After the deep reduction roasting is completed, the spherical particles are cooled in the reducing atmosphere. The cooled spherical particles are sent to the water cooling tank for water cooling treatment to obtain reduced pellets. The water cooling tank rapidly reduces the temperature of the high-temperature reduced pellets to room temperature, which rapidly reduces the temperature to prevent metallic iron from re-oxidizing into iron oxide in the air. The reduced pellets are crushed and ground by a crushing system to the size of the monomers, resulting in reduced crushed material; The reduced crushed material is prepared into a slurry, which is then fed into a multi-stage wet magnetic separator for grading and magnetic separation. The multi-stage wet magnetic separator separates different iron phases based on their magnetic differences, collecting different iron mineral products. The grading and magnetic separation process achieves graded recovery of iron products and improves the total recovery rate of iron elements.

[0008] Furthermore, the red mud raw material is dried to a moisture content of 2%-10%, the microwave power for microwave treatment is 300 watts-500 watts, the microwave treatment time is 15 minutes-30 minutes, and the screen size used in the vibrating screen is 100 mesh-150 mesh.

[0009] Furthermore, the magnetic field strength of the high-gradient magnetic separator is set to 1.0 Tesla-1.4 Tesla for dry magnetic separation.

[0010] Furthermore, the mixture is made from raw materials comprising the following parts by weight: 100 parts of iron enrichment; 4-10 parts of reducing agent; 3-6 parts of slagging agent; and 1-3 parts of binder. The reducing agent is made by mixing coke powder and anthracite in a mass ratio of 1:1 to 1:2. The slagging agent is made by mixing lime (stone) and quartz sand in a mass ratio of 2:1. The binder is bentonite or starch. The moisture content of the mixture is adjusted to 10%-20%.

[0011] Furthermore, the preheating kiln introduces the residual heat from the reduction roasting furnace, preheating the spherical particles to 200-300 degrees Celsius and holding them at that temperature for 20-30 minutes. Nitrogen gas with a flow rate of 0.5-1.0 cubic meters per hour is introduced into the reduction roasting furnace as a protective gas, and the spherical particles are roasted at 900-1050 degrees Celsius for 3-5 hours. The reducing atmosphere consists of carbon monoxide and carbon dioxide gases generated by the reducing agent, and the atmosphere is precisely controlled (CO2 / CO=0.15-0.25). After cooling to 100-300 degrees Celsius in the reducing atmosphere, the spherical particles enter the water cooling tank.

[0012] Furthermore, the crushing system includes a jaw crusher, a cone crusher, and a ball mill connected in series; the jaw crusher coarsely crushes the reduced pellets to a particle size of less than or equal to 20 mm; the cone crusher medium crushes the reduced pellets to a particle size of less than or equal to 5 mm; and the ball mill finely grinds the reduced pellets to a particle size of less than or equal to 0.015 mm.

[0013] Furthermore, the multi-stage wet magnetic separator unit includes a first-stage wet magnetic separator, a second-stage wet magnetic separator, and a third-stage wet magnetic separator connected in sequence. The first-stage wet magnetic separator is a weak magnetic drum type magnetic separator, and the magnetic field strength of the first-stage wet magnetic separator is set to 0.12 Tesla-0.2 Tesla. The first-stage wet magnetic separator is used to separate and collect strongly magnetic products to obtain elemental sponge iron and highly magnetic iron oxide. The magnetic field strength of the second-stage wet magnetic separator is set to 0.5 Tesla-0.7 Tesla. The second-stage wet magnetic separator is used to separate and collect moderately magnetic products to obtain high-grade iron minerals. The third-stage wet magnetic separator is a strong magnetic separator, and the magnetic field strength of the third-stage wet magnetic separator is set to 0.8 Tesla-1.0 Tesla. The third-stage wet magnetic separator is used to recover weakly magnetic iron components, which are then merged into the moderately magnetic products.

[0014] This invention provides an apparatus and method for extracting iron from red mud solid waste, which has the following beneficial effects: 1. This invention utilizes a microwave reactor to pretreat red mud raw materials using microwave. The microwave reactor uses the difference in dielectric constant between iron minerals and gangue minerals to induce thermal stress and generate microcracks at the grain boundaries of iron minerals and gangue minerals. Microwave pretreatment removes interlayer water and adsorbed water from the red mud and destroys the colloidal properties of the red mud. The microcracks reduce the energy consumption of the crushing system and increase the degree of mineral liberation. A high-gradient magnetic separator is used to pre-enrich the microwave-treated red mud. The high-gradient magnetic separator uses the difference in specific magnetization coefficient to remove silicon and aluminum impurities and increase the iron grade of the material entering the furnace. Increasing the iron grade of the material entering the furnace reduces the heating energy consumption and reagent consumption of the subsequent reduction roasting furnace.

[0015] 2. This invention uses a carbothermic reduction reaction in a reduction roasting furnace to gradually reduce hematite and limonite into magnetic iron oxide and metallic iron. The slag-forming agent generates a low-melting-point silicate liquid phase at high temperature, which promotes the aggregation and growth of metallic iron particles into iron particles. The preheating kiln is introduced into the reduction roasting furnace to discharge high-temperature flue gas and recover waste heat. The waste heat recovery reduces the heating energy consumption of the reduction roasting furnace. The high-temperature reduction pellets are quenched using a water-cooling tank in conjunction with a reducing atmosphere cooling process to reduce the temperature of the high-temperature reduction pellets. The temperature reduction prevents the metallic iron from being re-oxidized into weakly magnetic iron oxide in the air.

[0016] 3. This invention grinds the reduced pellets to the size of the individual particles using a crushing system. The multi-stage wet magnetic separator classifies and separates the iron phases based on their magnetic differences. The multi-stage wet magnetic separator collects strongly magnetic elemental sponge iron, medium magnetic high-grade iron minerals, and weakly magnetic iron intergrowths. The graded magnetic separation process achieves graded recovery of iron products and improves the total iron recovery rate. The total iron recovery rate and the purity of the iron products are superior to those of traditional single magnetic separation processes. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the device structure of the present invention; Figure 2 This is a flowchart of the method of the present invention.

[0018] The components include: 1. Dryer; 2. Microwave reactor; 3. Vibrating screen; 4. High gradient magnetic separator; 5. Mixer; 6. Disc granulator; 7. Preheating kiln; 8. Reduction roasting furnace; 9. Water cooling tank; 10. Jaw crusher; 11. Cone crusher; 12. Ball mill; 13. Primary wet magnetic separator; 14. Secondary wet magnetic separator; 15. Tertiary wet magnetic separator. Detailed Implementation

[0019] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0020] See attached document Figure 1 This invention provides an apparatus for extracting iron from red mud solid waste. The apparatus includes: Dryer 1 is equipped with a wet material inlet and a dry material outlet to reduce the moisture content of red mud raw materials. The dry material outlet of dryer 1 is connected to the feed inlet of microwave reactor 2. Microwave reactor 2 is equipped with a microwave generating component for microwave modification treatment of dried red mud. The discharge outlet of microwave reactor 2 is connected to the feed inlet of vibrating screen 3. Vibrating screen 3 is equipped with a screen for separating materials according to particle size. Vibrating screen 3 is equipped with an oversize material outlet and an undersize material outlet.

[0021] The undersize outlet of the vibrating screen 3 is connected to the feed inlet of the high-gradient magnetic separator 4. The high-gradient magnetic separator 4 is equipped with a magnetic concentrate outlet and a magnetic tailings outlet. The magnetic concentrate outlet of the high-gradient magnetic separator 4 is connected to the solid feed inlet of the mixer 5. The mixer 5 is equipped with a liquid addition inlet and a binder addition inlet for mixing iron element enrichment, reducing agent, slagging agent and binder. The mixture outlet of the mixer 5 is connected to the feed inlet of the disc granulator 6. The disc granulator 6 is used to prepare the mixture into spherical particles.

[0022] The discharge port of the disc granulator 6 is connected to the feed port of the preheating kiln 7. The preheating kiln 7 is equipped with a hot gas inlet, a waste gas outlet, and a preheated material outlet. The preheated material outlet of the preheating kiln 7 is connected to the feed port of the reduction roasting furnace 8. The reduction roasting furnace 8 is equipped with a heating component and an inert gas protection system. The reduction roasting furnace 8 is equipped with a high-temperature roasted material outlet and a high-temperature flue gas exhaust port. The high-temperature flue gas exhaust port of the reduction roasting furnace 8 is connected to the hot gas inlet of the preheating kiln 7 through a heat-resistant pipe, so that the waste heat flue gas generated by reduction roasting enters the interior of the preheating kiln 7. The high-temperature roasted material outlet of the reduction roasting furnace 8 is connected to the feed end of the water cooling tank 9. The water cooling tank 9 is equipped with a cooling water circulation system for rapid cooling of the high-temperature reduced pellets.

[0023] The discharge end of the water-cooled tank 9 is connected to the feed inlet of the jaw crusher 10, the discharge outlet of the jaw crusher 10 is connected to the feed inlet of the cone crusher 11, and the discharge outlet of the cone crusher 11 is connected to the feed inlet of the ball mill 12. The jaw crusher 10, the cone crusher 11 and the ball mill 12 are connected in series to form a three-stage crushing system. The ball mill 12 is used to grind the reduced pellets to the size of the individual dissociated particles.

[0024] The discharge port of the ball mill 12 is connected to the feed port of the primary wet magnetic separator 13. The primary wet magnetic separator 13 is equipped with a strong magnetic product outlet and a primary tailings outlet. The primary tailings outlet of the primary wet magnetic separator 13 is connected to the feed port of the secondary wet magnetic separator 14. The secondary wet magnetic separator 14 is equipped with a medium magnetic product outlet and a secondary tailings outlet. The secondary tailings outlet of the secondary wet magnetic separator 14 is connected to the feed port of the tertiary wet magnetic separator 15. The tertiary wet magnetic separator 15 is equipped with a weak magnetic product outlet and a tertiary tailings outlet. The weak magnetic product outlet of the tertiary wet magnetic separator 15 flows through a pipeline to the medium magnetic product outlet of the secondary wet magnetic separator 14 for merging and collecting iron ore products. The tertiary tailings outlet of the tertiary wet magnetic separator 15 is connected to the interface of the subsequent valuable metal recovery process.

[0025] See attached document Figure 1 When the red mud raw material enters the microwave reactor 2 and is irradiated with microwaves, the microwave reactor 2 utilizes the difference in dielectric constant between iron minerals and gangue minerals in the red mud. Iron minerals have a higher microwave absorption capacity than gangue minerals. Microwave radiation causes the iron minerals to heat up at a higher rate than the gangue minerals, creating a temperature gradient between them. This temperature gradient induces thermal stress at the grain boundaries of the iron minerals and gangue minerals. The thermal stress causes microcracks to form at the grain boundaries of the iron minerals and gangue minerals. These microcracks reduce the energy consumption of subsequent crushing operations and increase the degree of mineral dissociation. At the same time, microwave treatment removes interlayer water and adsorbed water from the red mud, destroying its colloidal properties.

[0026] The high-gradient magnetic separator 4 pre-enriches the microwave-treated red mud. The high-gradient magnetic separator 4 uses the difference in the specific magnetic susceptibility between iron minerals and clay minerals to remove some silicon and aluminum impurities, thereby improving the iron grade of the material entering the furnace.

[0027] Carbothermic reduction reaction is carried out in reduction roasting furnace 8. A mixture of coke powder and anthracite is used as a reducing agent. The reducing agent is gasified at high temperature to produce carbon monoxide and hydrogen. The carbon monoxide and hydrogen reduce hematite and limonite in red mud step by step. The reduction process follows the sequence of hematite to magnetite, magnetite to ferrous oxide, and ferrous oxide to metallic iron. Limestone and quartz sand are used as slagging agents. The slagging agents react with gangue components in red mud at high temperature to generate a low-melting-point silicate liquid phase. The low-melting-point silicate liquid phase promotes the migration, aggregation and growth of metallic iron particles into iron particles.

[0028] The high-temperature flue gas generated by the reduction roasting furnace 8 is introduced into the preheating kiln 7. The heat carried by the high-temperature flue gas is transferred to the spherical particles in the preheating kiln 7. The heat transfer process reduces the heating energy consumption of the reduction roasting furnace 8.

[0029] The water-cooled tank 9 performs quenching treatment on the high-temperature reduced pellets. The water-cooled tank 9 rapidly reduces the temperature of the high-temperature reduced pellets to room temperature, and the rapid temperature reduction prevents the metallic iron from being re-oxidized into iron oxide in the air.

[0030] The multi-stage wet magnetic separator separates iron phases based on their magnetic differences. The first-stage wet magnetic separator 13 uses a magnetic field strength of 0.12 Tesla to 0.2 Tesla to adsorb strongly magnetic elemental sponge iron. The second-stage wet magnetic separator 14 uses a magnetic field strength of 0.5 Tesla to 0.7 Tesla to adsorb moderately magnetic iron minerals. The third-stage wet magnetic separator 15 uses a magnetic field strength of 0.8 Tesla to 1.0 Tesla to recover weakly magnetic iron intergrowths. The graded magnetic separation process achieves graded recovery of iron products and improves the total recovery rate of iron elements.

[0031] To verify the practical application effect of the device for extracting iron from red mud solid waste according to the present invention, the following description is provided in conjunction with specific embodiments.

[0032] Examples 1-3: Example 1:

[0033] See attached document Figure 2 This embodiment provides a method for extracting iron from red mud solid waste, including the following steps: S1. The red mud raw material is fed into dryer 1 and dried to a moisture content of 2%. The dried red mud is then fed into microwave reactor 2 for microwave treatment. In this embodiment, for laboratory-scale verification, the microwave power of microwave reactor 2 is set to 400 watts and the microwave treatment time is set to 22 minutes. The microwave-treated red mud is then fed into vibrating screen 3 for cooling. Vibrating screen 3 uses a 120-mesh screen to screen the red mud. Vibrating screen 3 removes large particles of impurities to obtain pretreated red mud.

[0034] S2. The pretreated red mud is fed into a high gradient magnetic separator 4. The magnetic field strength of the high gradient magnetic separator 4 is set to 1.2 Tesla. The high gradient magnetic separator 4 performs a combination of gravity separation and magnetic separation on the pretreated red mud. The high gradient magnetic separator 4 removes clay-like substances and non-magnetic impurities from the pretreated red mud to obtain iron element enrichment. The iron element grade in the iron element enrichment is 45%.

[0035] S3. Add 100 parts by weight of iron element enrichment, 7 parts by weight of reducing agent, 7.5 parts by weight of slag-forming agent and 2 parts by weight of binder to mixer 5 and mix evenly to obtain a mixture. The reducing agent is made by mixing coke powder and anthracite in a mass ratio of 1:1.5. The slag-forming agent is made by mixing limestone and quartz sand in a mass ratio of 2:1. The binder is bentonite. Add deionized water to mixer 5 to adjust the moisture content of the mixture to 15%. Feed the mixture into disc granulator 6. Disc granulator 6 makes the mixture into spherical particles with a diameter of 10 mm.

[0036] S4. Deep Reduction Roasting: The spherical particles are fed into the preheating kiln 7, which introduces the residual heat from the reduction roasting furnace 8. The preheating kiln 7 preheats the spherical particles to 250 degrees Celsius and holds them at that temperature for 25 minutes. The preheated spherical particles are then fed into the reduction roasting furnace 8, where a reducing agent is burned to produce CO2 and CO. The atmosphere is precisely controlled (CO2 / CO = 0.15–0.25). The reduction roasting furnace 8 performs deep reduction roasting on the spherical particles at 980 degrees Celsius and holds them at that temperature for 4 hours. After deep reduction roasting, the spherical particles are cooled to 200 degrees Celsius in a reducing atmosphere (CO2 / CO = 0.15–0.25). The cooled spherical particles are then fed into a water-cooling tank 9 for water cooling. The water-cooling tank 9 yields reduced pellets with a moisture content of 6.5%.

[0037] S5. The reduced pellets are fed into the jaw crusher 10, which coarsely crushes the reduced pellets to a particle size of less than or equal to 20 mm. The coarsely crushed reduced pellets are then fed into the cone crusher 11, which medium crushes the reduced pellets to a particle size of less than or equal to 5 mm. The medium crushed reduced pellets are then fed into the ball mill 12, which finely grinds the reduced pellets to a particle size of less than or equal to 0.015 mm to obtain the reduced crushed material.

[0038] S6. The reduced crushed material is prepared into a slurry with a concentration of 28%. The slurry flow rate is controlled at 0.8 m / s during the extraction process. The slurry is fed into the primary wet magnetic separator 13. In order to prioritize the extraction of strongly magnetic elemental iron and avoid magnetic agglomeration, the primary wet magnetic separator 13 is a weak magnetic drum type magnetic separator with a magnetic field strength set to 0.15 Tesla. The primary wet magnetic separator 13 separates and collects strongly magnetic products to obtain elemental sponge iron and highly magnetic iron oxide. The primary tailings generated by the primary wet magnetic separator 13 are fed into the secondary wet magnetic separator 1. 4. The magnetic field strength of the secondary wet magnetic separator 14 is set to 0.6 Tesla. The secondary wet magnetic separator 14 separates and collects the magnetic products to obtain high-grade iron minerals. The secondary tailings generated by the secondary wet magnetic separator 14 are sent to the tertiary wet magnetic separator 15. The tertiary wet magnetic separator 15 uses a strong magnetic separator with a magnetic field strength set to 0.9 Tesla. The tertiary wet magnetic separator 15 recovers the weakly magnetic iron components and merges them into the medium magnetic products. The tertiary tailings of the tertiary wet magnetic separator 15 enter the subsequent valuable metal recovery process.

[0039] Example 2:

[0040] This embodiment provides a method for extracting iron from red mud solid waste, including the following steps: S1. The red mud raw material is fed into dryer 1 and dried to a moisture content of 10%. The dried red mud is then fed into microwave reactor 2 for microwave treatment. In this embodiment, for laboratory-scale verification, the microwave power of microwave reactor 2 is set to 500 watts and the microwave treatment time is set to 30 minutes. The microwave-treated red mud is then fed into vibrating screen 3 for cooling. Vibrating screen 3 uses a 150-mesh screen to screen the red mud. Vibrating screen 3 removes large particles of impurities to obtain pretreated red mud.

[0041] S2. The pretreated red mud is fed into the high gradient magnetic separator 4. The magnetic field strength of the high gradient magnetic separator 4 is set to 1.4 Tesla. The high gradient magnetic separator 4 performs a combination of gravity separation and magnetic separation on the pretreated red mud. The high gradient magnetic separator 4 removes clay-like substances and non-magnetic impurities from the pretreated red mud to obtain iron element enrichment. The iron element grade in the iron element enrichment is 55%.

[0042] S3. Add 100 parts by weight of iron element enrichment, 10 parts by weight of reducing agent, 10 parts by weight of slag-forming agent and 3 parts by weight of binder to mixer 5 and mix evenly to obtain a mixture. The reducing agent is made by mixing coke powder and anthracite in a mass ratio of 1:2. The slag-forming agent is made by mixing limestone and quartz sand in a mass ratio of 2:1. The binder is bentonite. Add deionized water to mixer 5 to adjust the moisture content of the mixture to 20%. Feed the mixture into disc granulator 6. Disc granulator 6 makes the mixture into spherical particles with a diameter of 12 mm.

[0043] S4. The spherical particles are fed into the preheating kiln 7, which introduces the residual heat from the reduction roasting furnace 8. The preheating kiln 7 preheats the spherical particles to 300 degrees Celsius and holds them at that temperature for 30 minutes. The preheated spherical particles are then fed into the reduction roasting furnace 8, where a combustion reducing agent is introduced to generate CO2 and CO. The atmosphere is precisely controlled (CO2 / CO = 0.15–0.25). The reduction roasting furnace 8 performs deep reduction roasting on the spherical particles at 1050 degrees Celsius and holds them at that temperature for 5 hours. After deep reduction roasting, the spherical particles are cooled to 300 degrees Celsius in a reducing atmosphere (CO2 / CO = 0.15–0.25). The cooled spherical particles are then fed into the water-cooling tank 9 for water cooling treatment. The water-cooling tank 9 yields reduced pellets with a moisture content of 8%.

[0044] S5. The reduced pellets are fed into the jaw crusher 10, which coarsely crushes the reduced pellets to a particle size of less than or equal to 20 mm. The coarsely crushed reduced pellets are then fed into the cone crusher 11, which medium crushes the reduced pellets to a particle size of less than or equal to 5 mm. The medium crushed reduced pellets are then fed into the ball mill 12, which finely grinds the reduced pellets to a particle size of less than or equal to 0.015 mm to obtain the reduced crushed material.

[0045] S6. The reduced crushed material is prepared into a slurry with a concentration of 30%. The slurry flow rate is controlled at 1.0 m / s during the extraction process. The slurry is fed into the primary wet magnetic separator 13. In order to preferentially extract strongly magnetic elemental iron and avoid magnetic agglomeration, the primary wet magnetic separator 13 is a weak magnetic drum type magnetic separator with a magnetic field strength set to 0.2 Tesla. The primary wet magnetic separator 13 separates and collects strongly magnetic products to obtain elemental sponge iron and highly magnetic iron oxide. The primary tailings generated by the primary wet magnetic separator 13 are fed into the secondary wet magnetic separator 1. 4. The magnetic field strength of the secondary wet magnetic separator 14 is set to 0.7 Tesla. The secondary wet magnetic separator 14 separates and collects the medium magnetic products to obtain high-grade iron minerals. The secondary tailings generated by the secondary wet magnetic separator 14 are sent to the tertiary wet magnetic separator 15. The tertiary wet magnetic separator 15 uses a strong magnetic separator with a magnetic field strength set to 1.0 Tesla. The tertiary wet magnetic separator 15 recovers the weak magnetic iron components and merges them into the medium magnetic products. The tertiary tailings of the tertiary wet magnetic separator 15 enter the subsequent valuable metal recovery process.

[0046] Example 3:

[0047] This embodiment provides a method for extracting iron from red mud solid waste, including the following steps: S1. The red mud raw material is fed into dryer 1 and dried to a moisture content of 8%. The dried red mud is then fed into microwave reactor 2 for microwave treatment. In this embodiment, for laboratory-scale verification, the microwave power of microwave reactor 2 is set to 300 watts and the microwave treatment time is set to 15 minutes. The microwave-treated red mud is then fed into vibrating screen 3 for cooling. Vibrating screen 3 uses a 100-mesh sieve to screen the red mud. The vibrating screen 3 removes large particles of impurities to obtain pretreated red mud.

[0048] S2. The pretreated red mud is fed into a high gradient magnetic separator 4. The magnetic field strength of the high gradient magnetic separator 4 is set to 1.0 Tesla. The high gradient magnetic separator 4 performs a combination of gravity separation and magnetic separation on the pretreated red mud. The high gradient magnetic separator 4 removes clay-like substances and non-magnetic impurities from the pretreated red mud to obtain iron element enrichment. The iron element grade in the iron element enrichment is 25%.

[0049] S3. Add 100 parts by weight of iron element enrichment, 4 parts by weight of reducing agent, 3 parts by weight of slag-forming agent and 1 part by weight of binder to mixer 5 and mix evenly to obtain a mixture. The reducing agent is made by mixing coke powder and anthracite in a mass ratio of 1:1. The slag-forming agent is made by mixing limestone and quartz sand in a mass ratio of 2:1. The binder is bentonite. Add deionized water to mixer 5 to adjust the moisture content of the mixture to 10%. Feed the mixture into disc granulator 6. Disc granulator 6 makes the mixture into spherical particles with a diameter of 8 mm.

[0050] S4. The spherical particles are fed into the preheating kiln 7, which introduces the residual heat from the reduction roasting furnace 8. The preheating kiln 7 preheats the spherical particles to 200 degrees Celsius and holds them at that temperature for 20 minutes. The preheated spherical particles are then fed into the reduction roasting furnace 8, where nitrogen gas at a flow rate of 0.5 cubic meters per hour is introduced as a protective gas. The reduction roasting furnace 8 performs deep reduction roasting on the spherical particles at 900 degrees Celsius and holds them at that temperature for 3 hours. After deep reduction roasting, the spherical particles are cooled to 100 degrees Celsius in a reducing atmosphere with precise control of the reducing atmosphere (CO2 / CO = 0.15~0.25). The cooled spherical particles are then fed into the water cooling tank 9 for water cooling treatment. The water cooling tank 9 yields reduced pellets with a moisture content of 5%.

[0051] S5. The reduced pellets are fed into the jaw crusher 10, which coarsely crushes the reduced pellets to a particle size of less than or equal to 20 mm. The coarsely crushed reduced pellets are then fed into the cone crusher 11, which medium crushes the reduced pellets to a particle size of less than or equal to 5 mm. The medium crushed reduced pellets are then fed into the ball mill 12, which finely grinds the reduced pellets to a particle size of less than or equal to 0.015 mm to obtain the reduced crushed material.

[0052] S6. The reduced crushed material is prepared into a slurry with a concentration of 25%. The slurry flow rate is controlled at 1.2 meters per second during the extraction process. The slurry is fed into the primary wet magnetic separator 13. In order to prioritize the extraction of strongly magnetic elemental iron and avoid magnetic agglomeration, the primary wet magnetic separator 13 is a weak magnetic drum type magnetic separator with a magnetic field strength set to 0.12 Tesla. The primary wet magnetic separator 13 separates and collects strongly magnetic products to obtain elemental sponge iron and highly magnetic iron oxide. The primary tailings generated by the primary wet magnetic separator 13 are fed into the secondary wet magnetic separator 1. 4. The magnetic field strength of the secondary wet magnetic separator 14 is set to 0.5 Tesla. The secondary wet magnetic separator 14 separates and collects the medium magnetic products to obtain high-grade iron minerals. The secondary tailings generated by the secondary wet magnetic separator 14 are sent to the tertiary wet magnetic separator 15. The tertiary wet magnetic separator 15 uses a strong magnetic separator with a magnetic field strength set to 0.8 Tesla. The tertiary wet magnetic separator 15 recovers the weak magnetic iron components and merges them into the medium magnetic products. The tertiary tailings of the tertiary wet magnetic separator 15 enter the subsequent valuable metal recovery process.

[0053] Comparative Examples 1-4: Comparative Example 1: Compared with Example 1, the difference is that the microwave treatment process was not set in the red mud pretreatment of S1. In Comparative Example 1, the red mud raw material was sent to the dryer 1 to dry to a moisture content of 2% and then directly sent to the vibrating screen 3 for screening. The proportions and steps of the remaining raw materials were the same as those in Example 1.

[0054] Comparative Example 2: Compared with Example 1, the difference is that the S2 magnetic enrichment pretreatment process was not set. In Comparative Example 2, 100 parts by weight of the pretreated red mud after S1 treatment was directly added to the mixer 5 as the iron source material in the S3 reduction pelletizing process. The other raw material ratios and steps are the same as those in Example 1.

[0055] Comparative Example 3: Compared with Example 1, the difference is that in the S6 multi-stage magnetic separation extraction, the first-stage wet magnetic separator 13, the second-stage wet magnetic separator 14 and the third-stage wet magnetic separator 15 are replaced with a single high-intensity magnetic separator. The magnetic field strength of the single high-intensity magnetic separator is set to 1.0 Tesla. The single high-intensity magnetic separator performs one-time sorting and collection of magnetic products from the reduced crushed material. The remaining raw material ratios and steps are the same as in Example 1.

[0056] Comparative Example 4: Compared with Example 1, the difference is that the reducing atmosphere cooling section and the water cooling tank 9 quenching process were not set in the deep reduction roasting of S4. In Comparative Example 4, the spherical particles were allowed to cool naturally to room temperature with the reduction roasting furnace 8 after the deep reduction roasting was completed. The other raw material ratios and steps were the same as those in Example 1.

[0057] Test Example 1-2: Test Example 1: This test case is mainly used to verify the effect of microwave modification pretreatment on the dissociation of iron minerals in red mud and the subsequent magnetic separation enrichment effect. The solid products produced by the high gradient magnetic separator 4 in S2 of Examples 1, 2, 3 and Comparative Example 1 were selected as iron element enrichment test samples, and the untreated red mud raw material was selected as the raw ore control sample.

[0058] 500 grams of iron enrichment was extracted from the production process of Example 1, Example 2, Example 3 and Comparative Example 1 respectively, and another 500 grams of raw ore control sample was taken.

[0059] Each sample to be tested and the raw ore control sample were placed in a constant temperature drying oven and dried at 105 degrees Celsius to constant weight. The dried samples were then ground to a particle size of less than 0.074 mm.

[0060] The total iron content of each sample was determined according to the national standard GB / T6730.5-2007 "Determination of Total Iron Content in Iron Ore by Potassium Dichromate Titration after Reduction with Titanium Trichloride". Each sample was measured in triplicate and the arithmetic mean was taken.

[0061] The enrichment ratio is calculated based on the measurement results. The formula for calculating the enrichment ratio is: the total iron content of the iron element enrichment divided by the total iron content of the original ore reference sample.

[0062] The experimental results are as follows: The specific data obtained from the test are recorded in Table 1.

[0063] Table 1. Test data on red mud pretreatment and magnetic enrichment effect.

[0064] Note: A value of 0 in the microwave power and processing time column of the table indicates that no microwave treatment was performed on this group; a value of "nothing" in the total iron content and enrichment ratio column of the enriched material indicates that this group was only used as a reference for the chemical composition of the raw ore and no subsequent magnetic separation enrichment process was performed, therefore there are no enriched products and no calculated enrichment ratio.

[0065] The results and conclusions are as follows: According to Table 1, the total iron content of the iron element enrichment obtained in Examples 1, 2 and 3 is higher than that of the iron element enrichment obtained in Comparative Example 1. The enrichment ratio of Example 1 reaches 1.95, indicating that the iron grade is nearly doubled after microwave and high gradient magnetic separation treatment.

[0066] The iron minerals in the red mud raw material are mainly embedded in the aluminosilicate gangue in the form of micron-sized particles. The red mud raw material has mud-like characteristics and colloidal properties. Comparative Example 1 only uses conventional heat conduction drying. Conventional heat conduction drying transfers heat from the sample surface to the interior. Under conventional heat conduction drying, the mineral particles are heated relatively uniformly. Conventional heat conduction drying cannot generate enough stress between different mineral phases to destroy the grain boundary bonding. In the subsequent high gradient magnetic separation process, the iron minerals and gangue minerals in Comparative Example 1 are still in a dense intergrowth state. The intergrowth causes a large number of gangue minerals to enter the magnetic components along with the iron minerals. The intergrowth reduces the grade of iron element enrichment.

[0067] Examples 1 to 3 introduce microwave modification treatment. Microwave heating is based on the principle of dielectric loss. Iron minerals such as hematite and limonite in red mud have high dielectric constants and dielectric loss factors, while gangue minerals such as quartz and aluminosilicates have low dielectric constants. The microwave radiation field causes iron minerals to absorb microwave energy and heat up rapidly, while gangue minerals absorb less microwave energy and heat up more slowly. A temperature gradient is formed between iron minerals and gangue minerals. The temperature gradient causes the volume expansion of iron minerals and gangue minerals to be inconsistent. The inconsistent volume expansion induces shear thermal stress at the grain boundaries of iron minerals and gangue minerals. When the shear thermal stress exceeds the bonding strength between minerals, intergranular microcracks are generated. Intergranular microcracks weaken the mechanical interlocking force between iron minerals and gangue minerals and promote monomer dissociation in the subsequent high-gradient magnetic separation process. Microwave treatment destroys the colloidal double-layer structure of red mud and reduces the non-selective adsorption of iron minerals by fine gangue particles.

[0068] Therefore, Examples 1 to 3 can remove silicon and aluminum impurities and obtain high-grade iron element enrichment. In Example 2, the microwave power was too high and the time was too long, which caused some local overheating and sintering, slightly hindering the decomposition. Therefore, the index was slightly lower than that of Example 1. In Example 3, the microwave energy input was insufficient and the thermal stress crack propagation was not sufficient. Therefore, the enrichment effect was between that of Example 1 and Comparative Example 1.

[0069] Test Example 2: This test case is mainly used to comprehensively evaluate the impact of different process conditions on the final product quality and iron recovery efficiency. The test objects cover the magnetic concentrates finally produced by the production processes of Examples 1, 2, and 3, as well as Comparative Examples 1, 2, 3, and 4. The test indicators focus on examining the purity, metallization degree of the sponge iron product, and the comprehensive recovery capacity of the entire process for iron resources.

[0070] For Examples 1 to 3, according to the modified magnetic separation process logic, primary sponge iron samples are collected at the strong magnetic product outlet of the primary wet magnetic separator 13 (weak magnetic drum magnetic separator), and secondary iron ore powder samples are collected at the medium magnetic product outlet (including the tertiary combined material) of the secondary wet magnetic separator 14.

[0071] For Comparative Examples 1, 2 and 4, the primary sponge iron sample and the secondary iron ore powder sample were obtained using the same collection method as in Example 1.

[0072] For Comparative Example 3, a mixed concentrate sample was collected at the magnetic product outlet of a single high-intensity magnetic separator.

[0073] All collected wet samples were placed in a vacuum drying oven and dried at 60 degrees Celsius until the moisture content was less than 0.5%. The dried samples were then reduced in size and ground to a particle size of less than 0.074 mm.

[0074] According to the YB / T5338-2006 standard "Sponge Iron", the metallic iron content of each group of primary sponge iron samples and mixed concentrate samples was determined by the ferric chloride-potassium dichromate titration method.

[0075] The total iron content of all samples in each group was determined according to the GB / T6730.5-2007 standard.

[0076] The formula for calculating the metallization rate is: the metallic iron content divided by the total iron content multiplied by 100%.

[0077] The formula for calculating the total iron recovery rate is: the sum of the iron mass in all magnetic separation concentrates divided by the total iron mass in the red mud raw material multiplied by 100%.

[0078] The experimental results are as follows: The specific data obtained from the test are recorded in Table 2.

[0079] Table 2. Test data on final product quality and process recovery indicators

[0080] Note: The product of Comparative Example 3 is a mixed concentrate, and the data is entered in the corresponding column of Primary Sponge Iron for comparison.

[0081] The results and conclusions are as follows: According to Table 2, the total iron recovery rate of Example 1 is as high as 89.24%, and the iron metallization rate of the primary sponge reaches 97.49%. Comparative Example 1 did not use microwave treatment, and Comparative Example 2 did not use magnetic separation enrichment. The product indicators of Comparative Example 1 and Comparative Example 2 are lower than those of Example 1.

[0082] The mechanism is as follows: Red mud raw materials contain a large amount of quartz and aluminosilicates. During the reduction roasting process, quartz and aluminosilicates react with flux to generate liquid slag. Excessive liquid slag will encapsulate iron oxide particles. The slag encapsulation increases the resistance to the diffusion of reducing gas into the iron oxide. The slag encapsulation also hinders the aggregation and growth of fine metallic iron grains generated during reduction. In Example 1, microwave-induced cracking combined with high-gradient magnetic separation removes a large amount of gangue components before entering the furnace. Pre-removal of tailings reduces the amount of slag during the reduction roasting process. The low slag environment optimizes the thermodynamic and kinetic conditions, allowing iron particles to be rapidly reduced and aggregated into dense large particles with less liquid phase obstruction. Large iron particles and slag phase are more easily liberated in the subsequent grinding process. Therefore, Example 1 obtained a higher metallization rate and separation index. In contrast, Comparative Example 2 had a low furnace grade and excessive slag, resulting in insufficient reduction and iron particles being tightly encapsulated by the slag phase, making grinding and liberation difficult, ultimately affecting the recovery rate and grade.

[0083] Example 1 uses a three-stage series magnetic separation process, and the total iron grade of the first-stage sponge iron in Example 1 reaches 93.42%. Comparative Example 3 uses a single-stage strong magnetic separation, and the total iron grade of the mixed concentrate in Comparative Example 3 is only 82.15%.

[0084] Three types of substances with different properties exist in the reduction grinding products: elemental metallic iron (strongly magnetic), iron-rich intergrowths (medium magnetic), and gangue (weakly magnetic or non-magnetic). Elemental metallic iron has a high grade but is prone to magnetic agglomeration, while iron-rich intergrowths contain some undissociated gangue and have a lower grade. Comparative Example 3 uses a single strong magnetic field for full recovery. The strong magnetic field simultaneously adsorbs elemental metallic iron and iron-rich intergrowths into the concentrate. The inclusion of iron-rich intergrowths dilutes the iron content in the concentrate, leading to a decrease in the grade of the final product. Example 1 utilizes the difference in the specific magnetic susceptibility of different iron phases. The first stage strictly controls the weak magnetic field strength of 0.15 Tesla to prioritize the extraction of high-purity elemental iron and avoid the inclusion of intergrowths. The second and third stages use medium to high magnetic field strengths (0.6 Tesla and 0.9 Tesla) to scavenger and recover intergrowths. This staged extraction achieves high quality and high utilization, and tiered recovery, obtaining a high-value-added, high-quality sponge iron product while ensuring the overall recovery rate.

[0085] A comparison of Example 1 and Comparative Example 4 shows that the total iron content of the two is similar, but the metallic iron content and metallization rate of Comparative Example 4 show a sharp drop, with the metallization rate of Comparative Example 4 being only 74.99%.

[0086] The newly formed metallic iron produced by reduction roasting has high chemical activity and a large specific surface area. Under high temperature conditions, metallic iron is prone to reverse oxidation reaction in an oxygen-rich environment to generate iron(II,III) oxide or iron oxide. In Comparative Example 4, natural cooling was used, and the material remained in the medium temperature range of 500°C to 300°C for too long. This prolonged residence caused some metallic iron to undergo secondary oxidation with adsorbed oxygen or trace amounts of oxidizing gases in the environment. In Example 1, direct quenching was performed in a water-cooled tank. Water-cooled quenching reduced the material temperature to below 100°C within seconds. This rapid cooling exceeded the temperature range where iron oxidation kinetics were most active. The water-sealed environment isolated the material from air contact. Therefore, Example 1 retained the metallic iron phase obtained from high-temperature reduction.

Claims

1. An apparatus for extracting iron from red mud solid waste, characterized in that, include: The dryer (1) has its dry material outlet connected to the feed inlet of the microwave reactor (2), and the discharge outlet of the microwave reactor (2) is connected to the feed inlet of the vibrating screen (3). The undersize outlet of the vibrating screen (3) is connected to the feed inlet of the high gradient magnetic separator (4), the magnetic concentrate outlet of the high gradient magnetic separator (4) is connected to the solid feed inlet of the mixer (5), and the mixed material outlet of the mixer (5) is connected to the feed inlet of the disc granulator (6). The discharge port of the disc granulator (6) is connected to the feed port of the preheating kiln (7), the preheating material outlet of the preheating kiln (7) is connected to the feed port of the reduction roasting furnace (8), and the high-temperature roasting material outlet of the reduction roasting furnace (8) is connected to the feed end of the water cooling tank (9). The discharge end of the water-cooled tank (9) is connected to the feed port of the crushing system, and the discharge port of the crushing system is connected to the feed port of the multi-stage wet magnetic separator.

2. The apparatus for extracting iron from red mud solid waste according to claim 1, characterized in that, The reduction roasting furnace (8) is equipped with a high-temperature flue gas exhaust port. The high-temperature flue gas exhaust port is connected to the hot gas inlet of the preheating kiln (7) through a heat-resistant pipe. It is used to introduce the waste heat flue gas generated by reduction roasting into the interior of the preheating kiln (7). The crushing system is composed of a jaw crusher (10), a cone crusher (11), and a ball mill (12) connected in series.

3. The apparatus for extracting iron from red mud solid waste according to claim 1, characterized in that, The multi-stage wet magnetic separator unit includes a first-stage wet magnetic separator (13), a second-stage wet magnetic separator (14), and a third-stage wet magnetic separator (15) connected in series. The first-stage tailings outlet of the first-stage wet magnetic separator (13) is connected to the feed inlet of the second-stage wet magnetic separator (14). The second-stage tailings outlet of the second-stage wet magnetic separator (14) is connected to the feed inlet of the third-stage wet magnetic separator (15). The weak magnetic product outlet of the third-stage wet magnetic separator (15) is connected to the medium magnetic product outlet of the second-stage wet magnetic separator (14) through a pipeline.

4. A method for extracting iron from red mud solid waste, characterized in that, An apparatus for extracting iron from red mud solid waste according to any one of claims 1-3, comprising the following steps: The red mud raw material is sent to the dryer (1) for drying, and then sent to the microwave reactor (2) for microwave treatment. The treated red mud is screened by the vibrating screen (3) to obtain pretreated red mud. The pretreated red mud is fed into a high gradient magnetic separator (4) for combined gravity and magnetic separation to remove clay-like substances and non-magnetic impurities, and iron-rich material is obtained. The iron element enrichment, reducing agent, slag-forming agent and binder are added to the mixer (5) and mixed evenly to obtain a mixture. The mixture is then processed into spherical particles by a disc granulator (6). The spherical particles are fed into a preheating kiln (7) for preheating, and then sent to a reduction roasting furnace (8) for deep reduction roasting. After roasting, they are cooled in a reducing atmosphere and then sent to a water cooling tank (9) for water cooling treatment to obtain reduced pellets. The reduced pellets are crushed and ground by a crushing system to the monomer dissociation particle size to obtain reduced crushed material; The reduced crushed material is prepared into a slurry and fed into a multi-stage wet magnetic separator for grading and magnetic separation, collecting iron ore products of different qualities.

5. The method for extracting iron from red mud solid waste according to claim 4, characterized in that, The red mud raw material is dried to a moisture content of 2%-10%, the microwave power of the microwave treatment is 300 watts-500 watts, the treatment time is 15 minutes-30 minutes, and the screen size used in the vibrating screen (3) is 100 mesh-150 mesh.

6. The method for extracting iron from red mud solid waste according to claim 4, characterized in that, The magnetic field strength of the high gradient magnetic separator (4) is set to 1.0 Tesla-1.4 Tesla, the slurry concentration is 25%-30%, and the slurry flow rate is controlled to be 0.8 m / s-1.2 m / s.

7. The method for extracting iron from red mud solid waste according to claim 4, characterized in that, The mixture is made from raw materials comprising the following parts by weight: Iron concentrate: 100 parts; Reducing agent: 4-10 parts; Slag-forming agent: 3-10 parts; Adhesive: 1-3 parts; The reducing agent is a mixture of coke powder and anthracite in a mass ratio of 1:1 to 1:2; the slag-forming agent is a mixture of limestone and quartz sand in a mass ratio of 2:1; the binder is bentonite; and the moisture content of the mixture is adjusted to 10%-20%.

8. A method for extracting iron from red mud solid waste according to claim 4, characterized in that, The preheating kiln (7) introduces the residual heat from the reduction roasting furnace (8) to preheat the spherical particles to 200-300 degrees Celsius and keep them at that temperature for 20-30 minutes. The reduction roasting furnace (8) is supplied with nitrogen gas at a flow rate of 0.5 cubic meters per hour to 1.0 cubic meters per hour as a protective gas, and the spherical particles are roasted at 900 degrees Celsius to 1050 degrees Celsius for 3 to 5 hours. The reducing atmosphere consists of carbon monoxide with a volume fraction of 30%-40% and carbon dioxide with a volume fraction of 60%-70%. The spherical particles are cooled to 100-300 degrees Celsius in the reducing atmosphere and then enter a water-cooling tank (9).

9. A method for extracting iron from red mud solid waste according to claim 4, characterized in that, The crushing system includes a jaw crusher (10), a cone crusher (11), and a ball mill (12) connected in series. The jaw crusher (10) coarsely crushes the reduced pellets to a particle size of less than or equal to 20 mm; The cone crusher (11) crushes the reduced pellets to a particle size of less than or equal to 5 mm; The ball mill (12) grinds the reduced pellets to a particle size of less than or equal to 0.015 mm.

10. A method for extracting iron from red mud solid waste according to claim 4, characterized in that, The multi-stage wet magnetic separator unit includes a first-stage wet magnetic separator (13), a second-stage wet magnetic separator (14), and a third-stage wet magnetic separator (15) connected in sequence. The first-stage wet magnetic separator (13) is a weak magnetic drum magnetic separator with a magnetic field strength set to 0.12 Tesla-0.2 Tesla, used to separate and collect strongly magnetic products to obtain elemental sponge iron and highly magnetic iron oxide. The magnetic field strength of the secondary wet magnetic separator (14) is set to 0.5 Tesla-0.7 Tesla, which is used to separate and collect magnetic products to obtain high-grade iron minerals; The three-stage wet magnetic separator (15) is a strong magnetic separator with a magnetic field strength set to 0.8 Tesla-1.0 Tesla, used to recover weakly magnetic iron components, which are then incorporated into the medium magnetic products.

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