A microwave suspension magnetization roasting process for complex and refractory limonite

Abstract

The application provides a complex and refractory limonite microwave suspension magnetization roasting system and process flow, and belongs to the field of mineral processing. The limonite is subjected to dehydration roasting and magnetization roasting, and uniform iron concentrate powder is obtained. Meanwhile, the different mineral phases have different heat stress differences in the absorption of microwaves, so that the content of gangue minerals in the product can be reduced, and the efficient separation of the complex and refractory limonite can be realized. The equipment and process of the application are mature, friendly to the environment, selective, uniform in heating, high in heat utilization, and simple in process and easy to realize industrialization.

Description

Technical Field

[0001] This invention belongs to the field of mineral processing, and specifically relates to a microwave suspension magnetization roasting system and process flow for complex and difficult-to-process limonite. Background Technology

[0002] Iron is an important strategic resource, and its efficient development and utilization are crucial to national development. In nature, iron mainly exists in the form of compounds. Based on the state of iron occurrence in ores, the main states of iron ore resources include: hematite, ferric sulfide, magnetic iron, ferrosilicon, and ferric carbonate. Hematite, limonite, and siderite are the primary raw materials for iron extraction in nature. However, with the continuous depletion of high-quality mineral resources, easily beneficiated iron ore resources are constantly decreasing. To compensate for the gradual depletion and shortage of resources, the development and utilization of complex and difficult-to-beneficial limonite resources has attracted great attention. However, limonite ore is characterized by its complex mineral composition, coexistence of multiple iron minerals, fine grain size, high water content, loose and porous surface, small crystal size, large porosity, and tendency to become muddy, making its beneficiation extremely difficult. It is a typical complex and difficult-to-beneficial mineral resource, and its beneficiation indicators are currently low during the development and utilization process.

[0003] Currently, methods for separating complex and difficult-to-process limonite mainly include magnetic separation, flotation, and gravity separation. However, these methods suffer from numerous problems, such as poor product indicators, complex separation processes, high costs, large equipment footprint, high reagent consumption, limited processing of limonite with relatively singular properties, and environmental pollution. In recent years, extensive research has been conducted on the beneficiation of complex and difficult-to-process limonite, gradually recognizing that the complexity of limonite's properties is the primary reason for its difficulty in beneficiation. Patent CN202310043687.6 relates to a pellet production method with a high proportion of hematite, which involves mixing raw ore and hematite concentrate in a certain mass ratio, grinding them, and then adding bentonite to the mixed concentrate for pelletizing. However, the limonite pelletizing process still needs further discussion regarding its effectiveness in improving subsequent beneficiation indicators and has certain drawbacks. Patent CN202210601759.X relates to a combined beneficiation and smelting method for low-grade tungsten-bearing limonite. The main beneficiation process includes: first, pre-enrichment by direct flotation, where the raw ore is ground and gangue inhibitors and compound anionic collectors are added to obtain a rough concentrate containing iron and tungsten through direct flotation; second, regrinding of the rough concentrate, adding alkaline leaching reagents and grinding again; alkaline leaching and solid-liquid separation of the regrinded ore sample to obtain a tungsten-containing leachate and an iron-containing leaching residue; finally, magnetic separation of the leaching residue to obtain an iron concentrate. However, this process suffers from problems such as complex reagent formulation, long production cycle, high beneficiation cost, environmental pollution from alkaline reagents, and low iron concentrate recovery rate. Therefore, efficient recovery and utilization of limonite has become a major challenge restricting the beneficiation and utilization of limonite. Given the current limitations of efficient and environmentally friendly processes in the comprehensive utilization of limonite, it is of great significance to develop technologies and equipment that are low-cost, have high processing capacity, are environmentally friendly, have high iron concentrate recovery rates and grades, and are easy to industrialize. Summary of the Invention

[0004] To address the aforementioned problems in existing complex and difficult-to-process limonite beneficiation processes, this invention provides a microwave suspension magnetization roasting system and process flow for complex and difficult-to-process limonite. This system dehydrates and magnetizes limonite during roasting to obtain uniform iron concentrate. Because microwaves serve as a heat source, this process is simple, has a fast reaction rate, short reaction time, good product indicators, is easy to operate, and has low production costs. Furthermore, the difference in microwave absorption between different ores creates thermal stress differences, which can reduce the content of gangue minerals in the product, thus achieving efficient separation of complex and difficult-to-process limonite.

[0005] A microwave suspension magnetization roasting system for complex and difficult-to-process limonite includes a first silo 1, a screw feeder 2, a cyclone preheater 3, a first cyclone separator 4, a pre-reduction suspension roasting furnace 5, a strong reduction suspension roasting furnace 6, a first burner 7, a second burner 8, a water cooling device 9, a second cyclone separator 10, a bag filter 11, a blower 12, a chimney 13, a stirred mill 14, and a magnetic separator 15. The outlet of the first silo 1 is connected to the inlet of the screw feeder 2, the outlet of the screw feeder 2 is connected to the inlet of the cyclone preheater 3 via a pipe, the outlet of the cyclone preheater 3 is connected to the inlet of the first cyclone separator 4, and the outlet of the first cyclone separator 4 is connected to the inlet of the pre-reduction suspension roasting furnace 5. The pre-reduction suspension roasting furnace 5 has an air inlet, and the bottom air inlet is connected to the first burner 7. The top discharge port pipe of the original suspension roasting furnace 5 is connected to the feed port of the strong reduction suspension roasting furnace 6. The strong reduction suspension roasting furnace 6 has an air inlet, and the bottom air inlet is connected to the first burner 8. The bottom discharge port pipe of the strong reduction suspension roasting furnace 6 is connected to the feed port of the water cooling device 9. The discharge port of the water cooling device 9 is connected to the feed port of the second cyclone separator 10. The dust outlet of the second cyclone separator 10 is connected to the inlet of the bag filter 11. The discharge port of the second cyclone separator 10 is connected to the feed port of the stirred mill 14. The discharge port of the stirred mill 14 is connected to the feed port of the magnetic separator 15. The dust outlet of the bag filter 11 is connected to the feed port of the pre-reduction suspension roasting furnace 5. The flue gas outlet of the bag filter 11 is connected to the air inlet of the blower 12. The air outlet of the blower 12 is connected to the air inlet of the chimney 13.

[0006] In the above system, the gas introduced into the first burner 7 is nitrogen; the gas introduced into the second burner 8 is nitrogen and carbon monoxide.

[0007] In the above system, the pre-reduction suspension roasting furnace 5 and the strong reduction suspension roasting furnace 6 are equipped with microwave heating devices inside.

[0008] In the above system, the water cooling device 9 is equipped with water cooling pipes.

[0009] In the above system, the second cyclone separator 10 is provided with two outlet pipes, which include a dust outlet and a material outlet; the bag filter 11 is provided with two outlet pipes, which include a dust outlet and a flue gas outlet. In the above system, an ash hopper is provided between the bag filter 11 and the pre-reduction suspension roasting furnace 5.

[0010] A process flow for a microwave suspension magnetization roasting system for complex and difficult-to-process limonite is carried out according to the following steps:

[0011] Step 1: Feed the complex and difficult-to-select limonite raw material after crushing and grinding into the first silo 1. The particle size of the crushed and ground raw material is less than 1 mm.

[0012] Step 2: The crushed raw material enters the cyclone preheater 3 through the screw feeder 2 for preheating. The temperature of the material after preheating by the cyclone preheater is 300~450℃. The cyclone preheater 3 sends the preheated material to the first cyclone separator 4 through airflow. The outlet of the first cyclone separator 4 is connected to the inlet of the pre-reduction suspension roasting furnace 5. The material flows into the pre-reduction suspension roasting furnace 5. The first burner 7 is started and nitrogen is introduced into the first burner 7 to form high-temperature flue gas. The high-temperature flue gas is fed into the bottom of the pre-reduction suspension roasting furnace 5. The material will be in a suspended state under the action of the rising airflow. The microwave heating device of the pre-reduction suspension roasting furnace 5 is turned on. The dehydration reaction of the material in the pre-reduction suspension roasting furnace 5 occurs at a reaction temperature of 500~550℃ and the dehydration reaction lasts for 5~10 minutes. After that, the material enters the strong reduction suspension roasting furnace 6 for microwave magnetization roasting.

[0013] Step 3: Turn on the microwave roasting device in the strong reducing suspension roasting furnace 6. The microwave magnetization roasting temperature is 500~550℃ and the time is 5~10 min. Start the second burner 8 and introduce nitrogen and carbon monoxide into the second burner 8 to form a reducing atmosphere and carry out microwave suspension magnetization roasting of complex and difficult-to-process limonite.

[0014] Step 4: After being magnetized and roasted in the strong reduction suspension roaster 6, the minerals are cooled to 50°C by the water cooling device 9 and then pass through the second cyclone separator 10. The dust outlet of the second cyclone separator 10 is connected to the inlet of the bag filter 11. The dust collected by the bag filter is returned to the pre-reduction suspension roaster 5. The returned material continues to enter the separation system along with the newly fed minerals. The discharge port of the second cyclone separator 10 is connected to the feed port of the stirred mill 14.

[0015] Step 5: The roasted product, after being cooled by the water cooling device 9, enters the stirred mill 14 through the outlet of the second cyclone separator 10 and is ground until 70-75% of the particles are smaller than 0.045 mm. Then, it enters the weak magnetic separator 15 for magnetic separation to finally obtain iron concentrate.

[0016] In the above method, the dust from the first cyclone separator 4 and the second cyclone separator 10 enters the bag filter 11 for primary dust removal. An ash hopper is provided between the bag filter 11 and the pre-reduction suspension roasting furnace 5. The dust in the ash hopper contains fine particles of useful minerals and is returned to the pre-reduction suspension roasting furnace 5. The flue gas is discharged through the chimney 13.

[0017] In step 5 above, the magnetic field strength of the magnetic separation operation is 120 kA / m, and the time is 5 to 10 minutes.

[0018] In step 2 above, the main reaction formula for the dehydration reaction of the preheated material is:

[0019] 2FeOOH = Fe₂O₃ + H₂O(g) (1)

[0020] In step 3 above, the main chemical reaction that occurs is as follows:

[0021] 3Fe2O3+CO(g)=2Fe3O4+CO2(g) (2).

[0022] In step 4 above, the temperature of the cooled material after passing through the cooler is ≤60 ℃.

[0023] Compared with existing processes, the beneficial effects of this invention are as follows:

[0024] (1) In this invention, since the complex and difficult-to-process limonite has a high water content, its own moisture will be removed by cyclone preheating and microwave suspension magnetization roasting, which will cause the limonite to undergo a dehydration reaction and decompose into hematite at high temperature. While the material is being heated, it will undergo microwave magnetization roasting reaction with reducing gas CO in the microwave suspension roasting furnace, which will lead to the weak magnetic minerals in the complex and difficult-to-process limonite being transformed into strong magnetic magnetite. After the roasted product is cooled, it will be effectively prevented from re-oxidizing. At the same time, due to the effect of airflow, the fine particles of useful minerals in the material will be lost. In order to fully recover and utilize resources, the dust particles are recovered and returned to the pre-reduction suspension roasting furnace. The roasted product is then ground and magnetically separated to obtain the final iron concentrate.

[0025] (2) The equipment of the present invention has mature technology, is environmentally friendly, selective, has uniform heating, high heat utilization, and simple process that is easy to industrialize. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of the microwave suspension magnetization roasting system for complex and difficult-to-process limonite of the present invention;

[0027] In the diagram, 1. First silo, 2. Screw feeder, 3. Cyclone preheater, 4. First cyclone separator, 5. Pre-reduction suspension roasting furnace, 6. Strong reduction suspension roasting furnace, 7. First burner, 8. Second burner, 9. Water cooling device, 10. Second cyclone separator, 11. Bag filter, 12. Blower, 13. Chimney, 14. Stirred mill, 15. Magnetic separator. Detailed Implementation

[0028] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0029] To facilitate understanding of the present invention, a more comprehensive description of the invention will be given below with reference to the accompanying drawings, and several embodiments of the invention will be provided. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided so that the disclosure of the present invention will be more thorough and complete.

[0030] The complex and difficult-to-process limonite used in this embodiment of the invention has an iron grade of 27.03~32.89% and contains, by weight percentage, 33~41% SiO2, 1.46~2.8% Al2O3, 1.8~3% CaO, 0.35~1.3% MgO, and 0.2~0.4% S.

[0031] A schematic diagram of the microwave suspension magnetization roasting system for complex and difficult-to-process limonite in this embodiment of the invention is shown below. Figure 1 As shown.

[0032] Example 1

[0033] A microwave suspension magnetization roasting system for complex and difficult-to-process limonite includes a first silo 1, a screw feeder 2, a cyclone preheater 3, a first cyclone separator 4, a pre-reduction suspension roasting furnace 5, a strong reduction suspension roasting furnace 6, a first burner 7, a second burner 8, a water cooling device 9, a second cyclone separator 10, a bag filter 11, a blower 12, a chimney 13, a stirred mill 14, and a magnetic separator 15.

[0034] The discharge port of the first silo 1 is connected to the inlet of the screw feeder 2. The discharge port of the screw feeder 2 is connected to the inlet of the cyclone preheater 3 via a pipe. The discharge port of the cyclone preheater 3 is connected to the inlet of the first cyclone separator 4. The discharge port of the first cyclone separator 4 is connected to the inlet of the pre-reduction suspension roasting furnace 5. The pre-reduction suspension roasting furnace 5 has an air inlet, and the bottom air inlet is connected to the first burner 7. The top discharge port pipe of the pre-reduction suspension roasting furnace 5 is connected to the inlet of the strong reduction suspension roasting furnace 6. The strong reduction suspension roasting furnace 6 has an air inlet, and the bottom air inlet is connected to the first burner 8. The bottom discharge pipe of the roasting furnace 6 is connected to the inlet of the water cooling device 9. The discharge port of the water cooling device 9 is connected to the inlet of the second cyclone separator 10. The dust outlet of the second cyclone separator 10 is connected to the inlet of the bag filter 11. The discharge port of the second cyclone separator 10 is connected to the inlet of the stirred mill 14. The discharge port of the stirred mill 14 is connected to the inlet of the magnetic separator 15. The dust outlet of the bag filter 11 is connected to the inlet of the pre-reduction suspension roasting furnace 5. The flue gas outlet of the bag filter 11 is connected to the inlet of the blower 12. The outlet of the blower 12 is connected to the inlet of the chimney 13.

[0035] The gas introduced into the first burner 7 is nitrogen, and the gas introduced into the second burner 8 is nitrogen and carbon monoxide. Microwave heating devices are installed inside the pre-reduction suspension roasting furnace 5 and the strong reduction suspension roasting furnace 6. The second cyclone separator 10 has two outlet pipes; the dust outlet of the second cyclone separator 10 is connected to the inlet of the bag filter 11, and the discharge port of the second cyclone separator 10 is connected to the feed inlet of the stirred mill 14. An ash hopper is installed between the bag filter 11 and the pre-reduction suspension roasting furnace 5. The bag filter 11 has two outlet pipes; the dust outlet of the bag filter 11 is connected to the feed inlet of the pre-reduction suspension roasting furnace 5, and the flue gas outlet of the bag filter 11 is connected to the air inlet of the blower 12.

[0036] A process flow for a microwave suspension magnetization roasting system for complex and difficult-to-process limonite is carried out according to the following steps:

[0037] The complex and difficult-to-process limonite used in this embodiment of the invention has an iron grade of 32.89% and contains, by weight percentage, 33.88% SiO2, 1.46% Al2O3, 1.83% CaO, 0.35% MgO, and 0.22% S.

[0038] Step 1: The complex and difficult-to-select limonite raw material after crushing and grinding is fed into the first silo 1. The particle size of the crushed and ground raw material is less than 1 mm. The screw feeder 2 continuously feeds the material to the cyclone preheater 3 for preheating. The temperature of the preheated material is 350 ℃.

[0039] Step 2: Cyclone preheater 3 sends the material to the first cyclone separator 4 through airflow. The outlet of the first cyclone separator 4 is connected to the inlet of the pre-reduction suspension roasting furnace 5. The material flows into the pre-reduction suspension roasting furnace 5. The first burner 7 is started and nitrogen is introduced into the burner 7 to form high-temperature flue gas. The high-temperature flue gas is fed into the bottom of the pre-reduction suspension roasting furnace 5. The material will be in a suspended state under the action of the rising airflow. The microwave heating device of the pre-reduction suspension roasting furnace 5 is turned on. The material is heated to 500°C in the pre-reduction suspension roasting furnace 5 and stays in the pre-reduction suspension roasting furnace 5 for 10 minutes. At this time, the limonite in the pre-reduction suspension roasting furnace undergoes a dehydration reaction and is converted into hematite. Then the material enters the strong reduction suspension roasting furnace 6 for microwave magnetization roasting.

[0040] Step 3: Turn on the microwave roasting device in the strong reducing suspension roasting furnace 6. Once the strong reducing suspension roasting furnace reaches 500℃, start the second burner 8 and introduce nitrogen and carbon monoxide into the burner 8 to create a reducing atmosphere. Carbon monoxide and nitrogen are introduced into the strong reducing roasting furnace, and the material is suspended by the upward airflow. After roasting for 5 minutes at 500℃ and 550 W microwave power, the obtained material is the final roasted product. The magnetized roasted minerals are cooled by a water-cooling device after passing through a cyclone separator.

[0041] Step 4: After being magnetized and roasted in the strong reduction suspension roasting furnace 6, the minerals are cooled to 50°C by the water cooling device 9 and then pass through the second cyclone separator 10. The dust outlet of the second cyclone separator 10 is connected to the inlet of the bag filter 11. The dust is collected by the bag filter and returned to the pre-reduction suspension roasting furnace 5. The returned material continues to enter the separation system along with the newly fed minerals. The discharge port of the second cyclone separator 10 is connected to the feed port of the stirred mill 14.

[0042] Step 5: After being cooled by the water-cooling device 9, the roasted product enters the stirred mill 14 through the outlet of the second cyclone separator 10. The roasted product is ground to a particle size of less than 0.045 mm (75%) and then enters the weak magnetic separator 15 for magnetic separation. The magnetic separation is carried out in a weak magnetic field with a magnetic field strength of 120 kA / m for 5 minutes. Finally, the iron concentrate has a grade of 57.91%, a recovery rate of 90.07%, and a SiO2 content of 3.55%.

[0043] In the above method, the dust from the cyclone separator 4 and the second cyclone separator 10 enters the bag filter 11 for primary dust removal. An ash hopper is provided between the bag filter 11 and the pre-reduction suspension roasting furnace 5. The dust in the ash hopper contains fine particles of useful minerals and is returned to the pre-reduction suspension roasting furnace 5. The flue gas is discharged directly through the chimney 13. During the heating process, the minerals undergo a dehydration reaction, generating a large number of pores. At the same time, the presence of microwaves causes a heat difference in the minerals themselves during the heat absorption process, which promotes the formation of a large number of cracks between different mineral phases. This is beneficial for the diffusion of reducing gas into the interior of the particles to recover useful minerals and is also beneficial for the separation of gangue minerals.

[0044] Example 2

[0045] The system and steps are the same as in Example 1, except that:

[0046] (1) The complex and difficult-to-process limonite used in the embodiments of the present invention has an iron grade of 29.24% and contains, by weight percentage, 37.19% SiO2, 1.73% Al2O3, 1.94% CaO, 0.47% MgO, and 0.2% S;

[0047] (2) The temperature of the material after preheating by the cyclone preheater is 300 ℃, the temperature at which the preheated material undergoes dehydration reaction in the pre-reduction suspension roasting furnace is 500 ℃, and the residence time of the preheated material in the pre-reduction suspension roasting furnace is 10 min.

[0048] (3) The roasting temperature in the strong reducing suspension roasting furnace is 510 ℃, the microwave power is 500W, and the roasting time is 5.5 min;

[0049] (4) The temperature of the cooled material after passing through the cooler is 60 ℃;

[0050] (5) The roasted product was ground to a size of less than 0.045 mm, accounting for 71%, and then magnetically separated for 3 minutes in a weak magnetic field with a magnetic field strength of 140 kA / m. The final iron concentrate had a grade of 56.87%, a recovery rate of 88.74%, and a SiO2 content of 3.94%.

[0051] Example 3

[0052] The system and steps are the same as in Example 1, except that:

[0053] (1) The complex and difficult-to-process limonite used in the embodiments of the present invention has an iron grade of 30.31% and contains 34.53% SiO2, 2.01% Al2O3, 2.21% CaO, 0.21% MgO, and 0.27% S by weight percentage;

[0054] (2) The temperature of the material after preheating by the cyclone preheater is 330 ℃, the temperature at which the preheated material undergoes dehydration reaction in the pre-reduction suspension roasting furnace is 520 ℃, and the residence time of the preheated material in the pre-reduction suspension roasting furnace is 8 min.

[0055] (3) The roasting temperature in the strong reducing suspension roasting furnace is 540 ℃, the microwave power is 510W, and the roasting time is 6min;

[0056] (4) The temperature of the cooled material after passing through the cooler is 45 ℃;

[0057] (5) The roasted product was ground to a size of less than 0.045 mm, accounting for 72%, and then magnetically separated for 4.5 min in a weak magnetic field with a magnetic field strength of 150 kA / m. The final iron concentrate had a grade of 57.64%, a recovery rate of 89.31%, and a SiO2 content of 4.31%.

[0058] Example 4

[0059] The system and steps are the same as in Example 1, except that:

[0060] (1) The complex and difficult-to-process limonite used in the embodiments of the present invention has an iron grade of 27.65% and contains 38.44% SiO2, 2.53% Al2O3, 2.37% CaO, 0.46% MgO, and 0.31% S by weight percentage;

[0061] (2) The temperature of the material after preheating by the cyclone preheater is 320 ℃, the temperature at which the preheated material undergoes dehydration reaction in the pre-reduction suspension roasting furnace is 530 ℃, and the residence time of the preheated material in the pre-reduction suspension roasting furnace is 7.5 min;

[0062] (3) The roasting temperature in the strong reducing suspension roasting furnace is 530 ℃, the microwave power is 540W, and the roasting time is 7min;

[0063] (4) The temperature of the cooled material after passing through the cooler is 40 ℃;

[0064] (5) The roasted product was ground to a size of less than 0.045 mm, accounting for 74%, and then magnetically separated for 4 minutes in a weak magnetic field with a magnetic field strength of 130 kA / m. The final iron concentrate had a grade of 58.28%, a recovery rate of 88.49%, and a SiO2 content of 2.76%.

Claims

1. A process flow for a microwave suspension magnetization roasting system for complex and difficult-to-process limonite, characterized in that, The complex and difficult-to-process limonite microwave suspension magnetization roasting system includes a first silo, a screw feeder, a cyclone preheater, a first cyclone separator, a pre-reduction suspension roasting furnace, a strong reduction suspension roasting furnace, a first burner, a second burner, a water cooling device, a second cyclone separator, a bag filter, a blower, a chimney, a stirred mill, and a magnetic separator. The discharge port of the first silo is connected to the inlet of the screw feeder, the discharge port of the screw feeder is connected to the inlet of the cyclone preheater through a pipe, the discharge port of the cyclone preheater is connected to the inlet of the first cyclone separator, and the discharge port of the first cyclone separator is connected to the inlet of the pre-reduction suspension roasting furnace. The pre-reduction suspension roasting furnace has an air inlet, and the bottom air inlet is connected to the first burner. The top discharge port pipe of the pre-reduction suspension roasting furnace is connected to the feed port of the strong reduction suspension roasting furnace. The strong reduction suspension roasting furnace has an air inlet, and the bottom air inlet is connected to the first burner. The bottom discharge port pipe of the strong reduction suspension roasting furnace is connected to the feed port of the water cooling device. The discharge port of the water cooling device is connected to the feed port of the second cyclone separator. The dust outlet of the second cyclone separator is connected to the inlet of the bag filter. The discharge port of the second cyclone separator is connected to the feed port of the stirred mill. The discharge port of the stirred mill is connected to the feed port of the magnetic separator. The dust outlet of the bag filter is connected to the feed port of the pre-reduction suspension roasting furnace. The flue gas outlet of the bag filter is connected to the air inlet of the blower. The air outlet of the blower is connected to the air inlet of the chimney. Follow these steps: Step 1: Feed the complex and difficult-to-select limonite raw material after crushing and grinding into the first hopper. The particle size of the crushed and ground raw material is less than 1 mm. Step 2: The crushed raw material is fed into the cyclone preheater through a screw feeder for preheating. The temperature of the material after preheating in the cyclone preheater is 300~450℃. The cyclone preheater sends the preheated material to the first cyclone separator through airflow. The outlet of the first cyclone separator is connected to the inlet of the pre-reduction suspension roasting furnace. The material flows into the pre-reduction suspension roasting furnace. The first burner is started and nitrogen is introduced into the burner to form high-temperature flue gas. The high-temperature flue gas is fed into the bottom of the pre-reduction suspension roasting furnace. The material will be in a suspended state under the action of the rising airflow. The microwave heating device of the pre-reduction suspension roasting furnace is turned on. The reaction temperature of the material in the pre-reduction suspension roasting furnace is 500~550℃. The dehydration reaction lasts for 5~10 minutes. After that, the material enters the strong reduction suspension roasting furnace for microwave magnetization roasting. Step 3: Turn on the microwave roasting device in the strong reducing suspension roasting furnace. The microwave magnetization roasting temperature is 500~550℃ and the time is 5~10 min. Start the second burner and introduce nitrogen and carbon monoxide into the burner to form a reducing atmosphere and carry out microwave suspension magnetization roasting of complex and difficult-to-process limonite. Step 4: After being magnetized and roasted in the strong reduction suspension roasting furnace, the minerals are cooled to 50 ℃ by a water cooling device and then pass through the second cyclone separator. The dust outlet of the second cyclone separator is connected to the inlet of the bag filter. The dust is collected by the bag filter and returned to the pre-reduction suspension roasting furnace. The returned material continues to enter the separation system along with the new minerals. The discharge port of the second cyclone separator is connected to the feed port of the stirred mill. Step 5: The roasted product, after being cooled by the water cooling device, enters the stirred mill through the outlet of the second cyclone separator and is ground until 70-75% of the particles are smaller than 0.045 mm. Then, it enters the weak magnetic separator for magnetic separation to finally obtain iron concentrate.

2. The process flow of a microwave suspension magnetization roasting system for complex and difficult-to-process limonite according to claim 1, characterized in that, The gas introduced into the first burner is nitrogen; the gas introduced into the second burner is nitrogen and carbon monoxide.

3. The process flow of a microwave suspension magnetization roasting system for complex and difficult-to-process limonite according to claim 1, characterized in that, The pre-reduction suspension roasting furnace and the strong reduction suspension roasting furnace are equipped with microwave heating devices inside.

4. The process flow of a microwave suspension magnetization roasting system for complex and difficult-to-process limonite according to claim 1, characterized in that, The water-cooling device is equipped with water-cooling pipes.

5. The process flow of a microwave suspension magnetization roasting system for complex and difficult-to-process limonite according to claim 1, characterized in that, The second cyclone separator is provided with two outlet pipes, which include a dust outlet and a material outlet; the bag filter is provided with two outlet pipes, which include a dust outlet and a flue gas outlet; and an ash hopper is provided between the bag filter and the pre-reduction suspension roasting furnace.

6. The process flow of a microwave suspension magnetization roasting system for complex and difficult-to-process limonite according to claim 1, characterized in that, The dust from the first and second cyclone separators enters the bag filter for primary dust removal. An ash hopper is provided between the bag filter and the pre-reduction suspension roasting furnace. The dust in the ash hopper contains fine particles of useful minerals and is returned to the pre-reduction suspension roasting furnace. The flue gas is discharged through the chimney.

7. The process flow of the microwave suspension magnetization roasting system for complex and difficult-to-process limonite according to claim 1, characterized in that, In step 5, the magnetic field strength of the magnetic separation operation is 120 kA / m, and the time is 5 to 10 minutes.

8. The process flow of the microwave suspension magnetization roasting system for complex and difficult-to-process limonite according to claim 1, characterized in that, In step 2, the main reaction formula for the dehydration reaction of the preheated material is: 2FeOOH = Fe₂O₃ + H₂O(g) (1) In step 3 above, the main chemical reaction that occurs is as follows: 3Fe2O3+CO(g)=2Fe3O4+CO2(g) (2).

9. The process flow of the microwave suspension magnetization roasting system for complex and difficult-to-process limonite according to claim 1, characterized in that, In step 4, the temperature of the cooled material after passing through the cooler is ≤60 ℃.

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