Method for microwave-enhanced biomass-based pellet direct reduction process

Abstract

The invention provides a method for extracting Fe by using microwaves and biomass energy, which comprises the following steps: mixing mineral powder with biomass accounting for 30-40% of the mass of the mineral powder to obtain a mixed raw material; the mixed raw materials are subjected to pelletizing treatment, the forming pressure of pelletizing treatment is larger than 15 MPa, the pressure maintaining time is larger than 2 min, and the diameter of pellets obtained through pelletizing treatment ranges from 10 mm to 16 mm; the pellets are subjected to microwave heating treatment, the microwave power ranges from 3 KW to 4 KW, the heating temperature ranges from 800 DEG C to 1000 DEG C, the reduction time ranges from 30 min to 50 min, and a reduction product is obtained; and carrying out magnetic separation on the reduction product to obtain an iron product. According to the method, microwave is used for replacing carbon heating in the whole process, and meanwhile biomass is used for replacing coke and pulverized coal. Compared with a conventional direct reduction ironmaking process, the method is low in temperature, short in time, good in reduction effect, high in yield, low in energy consumption and low in carbon emission, and has the huge potential of replacing carbon with hydrogen and increasing the green electricity use ratio.

Description

Technical Field

[0001] The present application relates to the field of metallurgy, and in particular, to a method for extracting Fe using microwaves and biomass energy, and more particularly, to a method for microwave-enhanced biomass-based pellet direct reduction process. Background Art

[0002] Under the "dual carbon" goal, higher requirements are placed on low-carbon green production in the steel industry, and traditional blast furnace ironmaking technology faces challenges. As a clean and renewable energy source, biomass has the advantages of carbon neutrality and high reactivity, and has begun to be used in ironmaking as a fuel and reducing agent.

[0003] my country is rich in iron ore resources, but most of them are low-grade composite co-existing ores, showing the four characteristics of "abundant, poor, fine and mixed". Among them, the iron grade is low, and the overall level of development and utilization is not high. Traditional magnetic roasting and smelting processes are not effective in treating composite co-existing ores. In contrast, the direct reduction-magnetic separation method is effective in separating slag iron at low temperatures, but it has high requirements for metallization rate and iron particle size, and high temperature will reduce the selective reduction range. Therefore, it is urgent to find a process that can be quickly reduced at a lower temperature to improve the production efficiency of direct reduced iron, while reducing energy consumption and carbon emissions.

[0004] Therefore, the current direct reduction method for extracting Fe, especially the biomass-based direct reduction method for extracting Fe, still needs to be improved. Summary of the invention

[0005] The present application aims to provide a method for extracting Fe by direct reduction to solve or alleviate one or more technical problems in the related art. The method proposed in the present application utilizes the high efficiency and environmental protection characteristics of microwave heating, combines biomass to replace conventional carbon reducing agents, and realizes the high efficiency and low consumption reduction of iron ore resources. Through the magnetic separation process, the separation and enrichment of iron and other elements can be realized, providing a new way for the green and sustainable development of the steel industry.

[0006] This application is based on the method of reducing Fe by biomass, which has many disadvantages such as high reduction temperature, need to pre-treat biomass into biochar, and complex operation. In order to improve production efficiency and reduce energy consumption, it is imperative to optimize the reduction process. The inventor found that microwave heating technology has the advantages of selective heating, fast heating rate, clean production and green pollution-free. It can supplement the heat loss caused by hydrogen reduction in the process of biomass energy smelting, and can also significantly increase the reaction speed, shorten the reaction time, reduce energy consumption and improve product quality. In addition, compared with the thermal reduction process using non-renewable resources such as coal as fuel, biomass-based pellets have a lower carbon content than coal and other materials on the one hand, so they naturally have a lower carbon characteristic. On the other hand, biomass will undergo pyrolysis during low-temperature solid-state reduction, and pyrolysis releases a large amount of hydrogen-rich gas to participate in reduction. At the same time, a large number of gas channels are generated, making the pellets loose and porous, thereby improving the kinetic conditions of gas-solid reaction. In addition, biomass is rich in alkaline earth metals such as K and Na, which can catalyze the solid-state reduction of iron minerals. In summary, this method has a better reduction effect and a higher metallization rate.

[0007] Therefore, in one aspect of the present application, the present application proposes a method for extracting Fe by direct reduction using microwaves and biomass-based pellets. The method comprises: mixing mineral powder with biomass, wherein the mass of the biomass accounts for 30-40% of the mass of the mineral powder, to obtain a mixed raw material; subjecting the mixed raw material to a pelletizing treatment, wherein the molding pressure of the pelletizing treatment is greater than 15MPa, the pressure holding time is greater than 2min, and the diameter of the pellets obtained by the pelletizing treatment is 10-16mm; subjecting the pellets to a microwave reduction treatment, wherein the microwave power is 3-4KW, the heating temperature is 800-1000℃, and the reduction time is 30-50min, to obtain a reduction product; subjecting the reduction product to magnetic separation to obtain an iron product. The method can easily use microwaves to reach the required reduction temperature, and obtain a better reduction effect, and the yield of the obtained iron product is high.

[0008] According to an embodiment of the present application, the biomass includes at least one of forestry waste, straw, distiller's grains, and rice husks, and the mineral powder includes at least one of concentrate powder, low-grade mineral powder, composite mineral powder, and mine dust. Thus, the cost of the method can be further reduced.

[0009] According to an embodiment of the present application, the mixed raw material further includes a binder and a solvent, the content of the solvent is 6-8% of the total mass of the mixed raw material, the content of the binder is 0.18-0.24% of the total mass of the mixed raw material, the binder includes at least one of water glass, bentonite, and polyvinyl alcohol, and the solvent includes water. Thus, the uniformity of the raw material mixing can be further improved.

[0010] According to an embodiment of the present application, the pellets after the pelletizing process are further dried before the microwave heating process, and the drying process is to keep the temperature at 100-110° C. for 12-15 hours. Thus, the quality of the pelletizing can be further improved.

[0011] According to an embodiment of the present application, the biomass is pre-treated before being mixed with the mineral powder, and the pre-treatment includes: washing and drying the biomass, thereby removing impurities such as surface dust, and further improving the quality of the biomass used for pelletizing.

[0012] According to an embodiment of the present application, the particle sizes of the mineral powder and the biomass in the mixed raw material are independently d=-48 μm to -74 μm, thereby improving the reduction effect.

[0013] According to an embodiment of the present application, the microwave power is 3.5-3.8KW, thereby improving the reduction effect.

[0014] According to an embodiment of the present application, the heating rate of the microwave heating treatment is 25-35° C. / min, and the heating temperature is 800-1000° C. Thus, the reduction effect can be improved.

[0015] According to one embodiment of the present application, the magnetic field strength of the magnetic separation is 0.15-0.2 T. Thus, the efficiency and effect of the magnetic separation can be further improved.

[0016] According to one embodiment of the present application, the method further comprises: recovering the waste gas and tar generated during the microwave reduction treatment.

[0017] The above summary is for the purpose of description only and is not intended to be limiting in any way. In addition to the illustrative aspects, embodiments and features described above, further aspects, embodiments and features of the present application will be readily apparent through the following detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 A schematic flow chart of a method according to an embodiment of the present application is shown;

[0019] Figure 2 A device structure diagram of a method according to an embodiment of the present application is shown. DETAILED DESCRIPTION

[0020] In the following, only some exemplary embodiments are briefly described. As those skilled in the art will appreciate, the described embodiments may be modified in various ways without departing from the spirit or scope of the present application, and different embodiments may be combined arbitrarily without conflict. Therefore, the following description is considered to be exemplary and non-restrictive in nature.

[0021] The method proposed in this application is described below by means of specific examples. The methods used in the following examples are conventional methods unless otherwise specified, and the reagents used are commercially available reagents unless otherwise specified.

[0022] The present application proposes an innovative process for microwave-enhanced direct reduction of biomass-based pellets, which cleverly combines environmental protection concepts and efficient energy utilization technology. This method uses biomass renewable energy to replace conventional carbon reducing agents, which not only reduces dependence on fossil fuels, but also effectively reduces CO2 emissions, thereby reducing environmental pollution. It is a new type of hydrogen-rich low-carbon ironmaking process. The introduction of a microwave field in the direct reduction process of biomass-based pellets can reduce the reduction temperature, improve the reaction efficiency, and achieve rapid reduction at low temperatures. Through the method described in the present invention, microwave heating replaces conventional heating as a heat source, and biomass replaces conventional carbon as a reducing agent, which can effectively overcome the shortcomings of the direct reduction ironmaking process of internal carbon pellets, such as long reduction time, high reduction temperature, low reduction efficiency, and large CO2 emissions, and improves the economy and environmental protection of the entire process, and has good application prospects.

[0023] Specifically, refer to Figure 1 , the method proposed in this application may include the following steps:

[0024] S100 mixes mineral powder with biomass to obtain mixed raw materials

[0025] In this step, mineral powder and biomass are first mixed in a certain proportion to obtain a mixed raw material.

[0026] Among them, biomass may include forestry waste, straw, distiller's grains, rice husks and other raw materials, and mineral powder may be one or more of low-grade ore, composite mineral powder, and mine dust. The above raw material costs are relatively low, which can reduce the raw material cost of the method. In addition, the aforementioned biomass raw materials such as straw and rice husk are wastes from various industries, but have a certain organic matter content, and can release reducing gases through the decomposition of organic matter in the subsequent microwave reduction process, so they have good potential for use as reducing agents: the use of the above substances to form pellets can reduce production costs on the one hand, save other industrial and agricultural processes to treat waste operations, and can also reduce the overall carbon emissions of the method: As mentioned above, compared with traditional reduction raw materials such as coal, the carbon content of biomass itself is relatively low, so the carbon discharged by the entire process can also be greatly reduced, which is more in line with the requirements of energy conservation and emission reduction, and becomes an effective way to reduce carbon emissions and achieve carbon neutrality.

[0027] In some embodiments, the mass of the biomass in the mixture accounts for 30-40% of the mass of the mineral powder, for example, it can be 35-40%. Regarding the raw material ratio, as the amount of biomass added increases from 10% to 40%, the metallization rate of the method gradually increases. Increasing the biomass increases the concentration of the reducing atmosphere and promotes the reduction of iron oxides in the mineral. However, when the amount of biomass added increases from 40% to 50%, the metallization rate does not increase significantly, and the amount of biomass added is too much, resulting in a waste of resources.

[0028] In order to further improve the mixing quality of mineral powder and biomass and make them fully contact, the particle sizes of mineral powder and biomass can be independently: d = -48μm to -74μm. In order to better perform pelletizing in subsequent steps, the mixed raw materials can further include a binder and a solvent. Specifically, the solvent content is 6 to 8% of the total mass of the mixed raw materials, and the binder content is 0.18 to 0.24% of the total mass of the mixed raw materials. The binder can include at least one of water glass, bentonite, and polyvinyl alcohol, and the solvent can be water.

[0029] The method proposed in the present application can use raw material powder of lower quality because it adopts appropriate raw material ratio and efficient heating method.

[0030] In order to further improve the effect of this method, raw materials such as biomass can also be pretreated before mixing:

[0031] The biomass may be washed with water, specifically, firstly by washing to remove surface dust and other impurities, and then by drying.

[0032] S200 pelletizing process

[0033] In this step, the mixed raw materials are pelletized to obtain raw material pellets. The molding pressure of the pelletization process is greater than 15 MPa, the pressure holding time is greater than 2 minutes, and the diameter of the pellets obtained by the pelletization process is 10 to 16 mm.

[0034] The pellets after the pelletizing process can be further dried before the subsequent microwave heating process to improve the effect of the subsequent microwave heating process. The drying process is to keep the temperature at 100-110°C for 12-15 hours. Thus, fully dried pellets are obtained.

[0035] S300 Microwave Reduction Process

[0036] According to the embodiment of the present application, in this step, the pellets are subjected to a microwave reduction process. Specifically, the pellets are subjected to microwave heating. The microwave power is 3-4KW, the heating temperature can be 800-1000°C, and the reduction time is 30-50min to obtain a reduced product.

[0037] As an electromagnetic field of a specific frequency, the application of microwaves has brought revolutionary changes to material preparation. Microwaves can not only heat materials quickly and evenly, but also interact with microscopic particles such as ions and molecules in the materials, accurately regulating their motion state and reaction process, thereby achieving precise control of material properties.

[0038] In the field of high magnetic field material science, the application of microwaves provides strong support for the preparation of new materials with excellent performance. The process of microwave-enhanced reduction mainly relies on the unique heating mechanism of microwaves. Under the action of an external electromagnetic field, the polar molecules in the medium change from a disordered random state to an arrangement in the direction of the electric field. Since the molecular arrangement orientation changes periodically with the frequency of the electric field, violent collisions will occur during the movement, thereby generating heat. By utilizing the wave-absorbing characteristics of the material, the sample can be quickly and comprehensively heated in a short period of time, providing the required heat for reduction. This heating method has the advantages of rapid temperature rise, overall heating and no heating inertia. The use of microwave heating not only solves some inherent problems in traditional heating, such as the "cold center" technical problem, but also improves the reduction efficiency: the aforementioned special mechanism of microwave heating determines that the raw material is not a heat conduction process that gradually penetrates from the surface to the inside of the material under the action of microwave heating. Compared with the traditional contact heat transfer process, microwave heating can fully heat the material more evenly and quickly. In this way, the temperature difference caused by different heat transfer rates at different positions in the material can be avoided, thereby improving the uniformity of the heating environment at different positions inside the pellets, allowing the reduction reaction to proceed in a more efficient and uniform manner.

[0039] In addition, microwaves have different effects on materials with different absorption capabilities. Gangue minerals such as carbonates and silicates have lower dielectric constants and less sensitivity to temperature changes. This means that they have weaker absorption capabilities in the microwave field and therefore absorb less microwave energy. Such materials can maintain a relatively low temperature during microwave heating. Iron-containing minerals have higher dielectric constants and dielectric loss factors, which make them have stronger absorption capabilities in the microwave field. When iron-containing minerals absorb microwave energy, they heat up rapidly and reach higher temperature levels. This high temperature helps to accelerate the reduction reaction and improve the reduction efficiency. At the same time, this temperature difference between iron-containing minerals and gangue minerals under the action of microwaves produces thermal stress between the two, which helps the two dissociate. For iron ore, especially the large-scale polymetallic co-existing composite iron ore, the mineral types are complex. By utilizing the differences in the absorption capabilities of different minerals under the action of microwaves, selective heating between multiple minerals can be achieved, which not only promotes the dissociation of useful minerals from gangue, but also increases the effective reaction area of ​​useful minerals. A larger reaction area means that more reduction reactions can occur on the mineral surface, thereby improving the overall reduction efficiency. Therefore, the application of microwaves in material preparation shows great potential and advantages.

[0040] As mentioned above, during the microwave reduction process, a large amount of gas is produced due to the decomposition of organic matter in biomass. Therefore, after microwave intensification, the material structure becomes looser. After a certain amount of gas generated by the decomposition of organic matter accumulates in the pellets, it will overflow the surface of the pellets. Therefore, this process will form a variety of gas channels inside the pellets. The formation of these gas channels can make the pressed material looser, enhance the contact between the reducing gas and the mineral powder, and improve the kinetic conditions. This method places the biomass-based pellets in a microwave reduction furnace, and through the special heating mechanism of microwaves, it can achieve efficient and rapid heating of the materials, thereby strengthening the reduction reaction process.

[0041] In this step, 2 to 3 layers of the pellets prepared in the previous steps can be spread flat on a material tray and placed in a microwave reduction furnace with a microwave power of 3.6 KW, a heating rate of 30°C / min, a temperature rise to 800 to 1000°C, and a reduction time of 30 to 50 minutes.

[0042] S400 Magnetic Separation Process

[0043] In this step, the product obtained by solid phase reduction can be subjected to magnetic separation to obtain a magnetic phase product and a non-magnetic phase residual material. The magnetic field intensity during the magnetic separation process is 0.18T.

[0044] Furthermore, the waste gas and tar generated during the reduction process can be recycled through a waste gas recovery and treatment device.

[0045] For example, refer to Figure 2 , Figure 2 The schematic diagram of the structure of a device for Fe separation using the method proposed in the present application is shown. Among them, 1 is a display, 2 is a microwave switch, 3 is a touch screen, 4 is a quartz tube, and microwave reduction is realized in the quartz tube. 5 is a heating area, 6 is a heating cavity, 7 is a microwave source, 8 is a Forma wheel, 9 is a condensation water tank, 10 is a conical flask, 11 is a gas flow meter, and 12 is a gas collection bottle.

[0046] The conical flask 11 and the gas collecting bottle 12 can effectively treat the gas and tar generated by the experiment, ensure the safety of the experimental environment by introducing inert protective gas, realize the condensation and separation of tar by a three-stage condensation device, monitor the gas flow and composition in real time by a gas flow analyzer, and finally collect gas samples by a gas collecting device for subsequent analysis.

[0047] In general, this application can have the following beneficial effects:

[0048] (1) The reducing agent raw material used in the present invention is biomass, which is a typical hydrogen-rich renewable energy that is "rich, diverse, green and sustainable", including wood chips, straw, distiller's grains, and rice husks. The main components of these biomass raw materials are hydrocarbons, with relatively few impurities, and they are good substitutes for coke pulverized coal in the ironmaking process.

[0049] (2) The present invention introduces the role of microwaves in the direct reduction process of biomass-based pellets. Through the unique heating mechanism of microwaves, the wave-absorbing characteristics of the material are utilized to achieve a fast and efficient reduction process, achieving a reduction effect that cannot be achieved under conventional conditions. In the hydrogen-rich smelting process, the heat loss caused by hydrogen reduction is supplemented, and the reaction speed can be significantly increased, the reaction time can be shortened, the energy consumption can be reduced, and the product quality can be improved. Microwave heating replaces fossil energy heating.

[0050] (3) Through the method of the present invention, the solid phase reduction temperature can be reduced to below 900°C and can be quickly reduced to more than 80%. The reduction time is shortened. Under the action of microwaves, the biomass-based pellets can achieve a metallization rate of more than 90% within 50 minutes, thereby improving production efficiency. After microwave enhancement, the material structure is looser, further achieving efficient selective reduction and separation of iron and valuable metal elements in the ore.

[0051] (4) Microwave heating is used instead of conventional heating as the heat source, and biomass is used instead of conventional carbon reducing agent, and the two environmentally friendly methods are combined to reduce mineral powder.

[0052] The technical solution of the present invention is further described in detail below in conjunction with specific examples:

[0053] The Baiyunebo mineral powder with a particle size of d=-48μm to -74μm is used as the mineral powder, and the chemical composition is shown in Table 1. The biomass particle size of d=-48μm to -74μm liquor lees is used as the reducing agent.

[0054] Table 1 Chemical composition of Bayan Obo mineral powder / %

[0055]

[0056] The ore sample was taken from the Bayan Obo Mine in Inner Mongolia, with a total iron grade of 47.5%, mainly enriched in hematite. The biomass used was liquor lees, which accounted for 3.74% ash, 76.64% volatile matter, and 14.73% fixed carbon in industrial analysis.

[0057] (1) Raw material processing: The wine lees are washed with clean water to remove surface dust and other impurities, and then dried to obtain biomass B.

[0058] (2) Raw material ratio: Mix the mineral powder and distiller's grains B in a certain ratio. Raw material requirements: particle size d = -48μm to -74μm; the mixing ratio is 40% of distiller's grains B by mass of the mineral powder. After mixing evenly, add the binder and water, the amount of each added is 0.24% and 8% of the total mass of the raw materials.

[0059] (3) Pellet preparation: The mixture is prepared into biomass-based pellets by a pelletizing machine or a pelletizing machine at a molding pressure of 15 MPa, and the pressure is maintained for 2 minutes. The pellet diameter is 10 to 16 mm. The pressed pellets are dried for use. The drying method is to keep the temperature at 100 ± 5 ° C for 12 to 15 hours.

[0060] (4) Solid phase reduction: 2 to 3 layers of biomass-based pellets are spread flat on a tray and placed in a microwave reduction furnace. The microwave power is 3.6KW, the heating rate is 30℃ / min, the temperature is raised to 900℃, and the reduction time is 50min. After the reduction is completed, magnetic separation is performed to obtain a direct reduced iron product.

[0061] After magnetic separation, a direct reduced iron product with a metallization rate of 94.3% is obtained.

[0062] Embodiment 2:

[0063] The remaining operations are the same as those in Example 1, except that the microwave power used is 3.0 KW and the metallization rate is 55.6%.

[0064] Embodiment 3:

[0065] The remaining operations are the same as those in Example 1, except that the biomass particle size is -74 μm to -80 μm, and the metallization rate is 25.0%.

[0066] Embodiment 4:

[0067] The remaining operations are the same as those in Example 1, except that the mixing ratio is 30% by mass of lees C to the mineral powder, and the metallization rate is 25.6%.

[0068] Comparative Example 1:

[0069] (1) Raw material processing: The wine lees are washed with clean water to remove surface dust and other impurities, and then dried to obtain biomass B.

[0070] (2) Raw material ratio: Mix the mineral powder and distiller's grains B in a certain ratio. Raw material requirements: particle size d = -48μm to -74μm; the mixing ratio is the percentage of distiller's grains B in terms of the mass of the mineral powder, i.e. 40%. After mixing evenly, add the binder and water, the amounts of each added being 0.24% and 8% of the total mass of the raw materials.

[0071] (3) Pellet preparation: The mixture is prepared into biomass-based pellets by a pelletizing machine or a pelletizing machine at a molding pressure of 15 MPa, and the pressure is maintained for 2 minutes. The pellet diameter is 10 to 16 mm. The pressed pellets are dried for use. The drying method is to keep the temperature at 100 ± 5 ° C for 12 to 15 hours.

[0072] (4) Solid phase reduction: 2 to 3 layers of biomass-based pellets are spread flat on a tray and placed in a non-microwave tubular reduction furnace. The temperature is raised to 900°C at a rate of 30°C / min for 50 minutes. After the reduction is completed, magnetic separation is performed to obtain a direct reduced iron product.

[0073] After magnetic separation, a direct reduced iron product with a metallization rate of 20.3% is obtained.

[0074] It can be seen from the comparison that the microwave-enhanced direct reduction process of biomass-based pellets of the present invention significantly improves the reduction efficiency. Under the action of microwaves, the metallization rate of biomass-based pellets is increased by 3.65 times compared to when there is no microwave action. This innovation not only significantly improves the reduction efficiency of biomass-based pellets, but also reduces the reduction temperature to below 1000°C, effectively supplementing the heat loss during the hydrogen reduction process, thereby reducing the overall energy consumption. In addition, the process flow of the present invention is easy to operate, and by using biomass as a reducing agent, it effectively reduces CO2 emissions, thereby reducing environmental pollution.

[0075] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include one or more of the features. In the description of this application, the meaning of "plurality" is two or more, unless otherwise clearly and specifically defined.

[0076] The above application provides many different embodiments or examples to realize the different structures of the present application. In order to simplify the present application, the parts and settings of specific examples are described above. Of course, they are only examples, and the purpose is not to limit the present application. In addition, the present application can repeat reference numbers and / or reference letters in different examples, and this repetition is for the purpose of simplification and clarity, which itself does not indicate the relationship between the various embodiments and / or settings discussed.

[0077] The above are only specific implementations of the present application, but the protection scope of the present application is not limited thereto. Any technician familiar with the technical field can easily think of various changes or substitutions within the technical scope disclosed in the present application, which should be included in the protection scope of the present application. Therefore, the protection scope of the present application should be based on the protection scope of the claims.

Claims

1. A method for extracting Fe by direct reduction using microwaves and biomass-based pellets, It is characterized in that include: Mixing mineral powder with biomass, wherein the mass of the biomass accounts for 30-40% of the mass of the mineral powder, to obtain a mixed raw material; The mixed raw materials are subjected to a pelletizing process, wherein the molding pressure of the pelletizing process is greater than 15 MPa, the pressure holding time is greater than 2 minutes, and the diameter of the pellets obtained by the pelletizing process is 10 to 16 mm; The pellets are subjected to microwave reduction treatment, wherein the microwave power is 3-4KW, the heating temperature is 800-1000°C, and the reduction time is 30-50min to obtain a reduction product; The reduction product is subjected to magnetic separation to obtain an iron product.

2. The method according to claim 1, It is characterized in that The biomass includes at least one of forestry waste, straw, distiller's grains, and rice husks. The mineral powder includes at least one of concentrate powder, low-grade mineral powder, composite mineral powder and mine dust.

3. The method according to claim 1 or 2, It is characterized in that The mixed raw material further includes a binder and a solvent, wherein the content of the binder is 0.18-0.24% of the total mass of the mixed raw material, and the content of the solvent is 6-8% of the total mass of the mixed raw material. The binder includes at least one of water glass, bentonite and polyvinyl alcohol. The solvent includes water.

4. The method according to claim 1, It is characterized in that The pellets after the pelletizing treatment are further dried before the microwave heating treatment, and the drying treatment is carried out by keeping the temperature at 100-110° C. for 12 to 15 hours.

5. The method according to claim 1, It is characterized in that The biomass is pre-treated before being mixed with the mineral powder, and the pre-treatment includes: The biomass is washed with water, The washed biomass is dried.

6. The method according to claim 1, It is characterized in that The particle sizes of the mineral powder and the biomass in the mixed raw material are independently d=-48 μm to -74 μm.

7. The method according to claim 1, It is characterized in that The microwave power is 3-4KW.

8. The method according to claim 1, It is characterized in that The heating rate of the microwave heating treatment is 25-35°C / min, and the heating temperature is 800-1000°C.

9. The method according to claim 1, It is characterized in that The magnetic field strength of the magnetic separation is 0.15-0.2T.

10. The method according to claim 1, It is characterized in that Further including: The waste gas and tar generated during the microwave reduction process are recovered and processed.

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