CN119162399A

CN119162399A - A method for microwave-enhanced direct reduction of biomass-based pellets

Info

Publication number: CN119162399A
Application number: CN202411471610.XA
Authority: CN
Inventors: 金永丽; 赵增武; 柴轶凡; 康杰
Original assignee: Inner Mongolia University of Science and Technology
Current assignee: Inner Mongolia University of Science and Technology
Priority date: 2024-10-21
Filing date: 2024-10-21
Publication date: 2024-12-20

Abstract

The application provides a method for extracting Fe by using microwaves and biomass energy, which comprises the steps of mixing mineral powder with biomass, wherein the mass of the biomass accounts for 30-40% of that of the mineral powder, obtaining mixed raw materials, carrying out pelleting treatment on the mixed raw materials, wherein the forming pressure of pelleting treatment is more than 15MPa, the dwell time is more than 2min, the diameter of pellets obtained by pelleting treatment is 10-16 mm, carrying out microwave heating treatment on the pellets, the power of the microwaves is 3-4KW, the heating temperature is 800-1000 ℃ and the reduction time is 30-50 min, obtaining reduction products, and carrying out magnetic separation on the reduction products, thus obtaining iron products. The method uses microwaves to replace carbon for heating in the whole process, and simultaneously uses biomass to replace coke and coal dust. Compared with the conventional direct reduction ironmaking process, the method has the advantages of low temperature, short time, good reduction effect, high yield, low energy consumption and low carbon emission, and has great potential of replacing carbon with hydrogen and improving the green electricity use ratio.

Description

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

Technical Field

The application relates to the field of metallurgy, in particular to a method for extracting Fe by using microwaves and biomass energy, and more particularly relates to a method for a direct reduction process of microwave-reinforced biomass-based pellets.

Background

Under the 'double carbon' target, higher requirements are put on low-carbon green production in the steel industry, and the traditional blast furnace ironmaking technology faces challenges. Biomass, which is a clean and renewable energy source, has the advantages of neutrality of carbon, high reactivity and the like, has been beginning to be applied to iron making as fuel and reducing agent.

The iron ore in China is rich in resources, but is mostly low-grade composite associated ore, and has four characteristics of more, lean, fine and miscellaneous, wherein the grade of iron is low, and the overall level of development and utilization is not high. The traditional magnetizing roasting and melting technology has poor effect in treating the composite associated ore. In contrast, the direct reduction-magnetic separation method has good effect of separating slag iron at low temperature, but the metallization rate and the iron particle size are required to be high, and the high temperature can reduce the selective reduction range. It is therefore desirable to find a process that can be rapidly reduced at lower temperatures to increase the efficiency of direct reduced iron production while reducing energy consumption and carbon emissions.

Thus, current methods of direct reduction extraction of Fe, particularly biomass-based methods of direct reduction extraction of Fe, remain to be improved.

Disclosure of Invention

The application aims to provide a method for directly reducing and extracting Fe, which solves or alleviates one or more technical problems in the related art. The method provided by the application utilizes the characteristics of high efficiency and environmental protection of microwave heating, combines biomass to replace a conventional carbon reducer, realizes high-efficiency and low-consumption reduction of iron ore resources, can realize separation and enrichment of iron and other elements through a magnetic separation process, and provides a new way for green sustainable development of the steel industry.

The method for reducing Fe based on biomass has the defects of high reduction temperature, need of pretreatment of biomass to biomass charcoal, complex operation and the like. In order to improve the production efficiency and reduce the energy consumption, optimization of the reduction process is imperative. The inventor finds that the microwave heating technology has the advantages of selective heating, high heating rate, clean production, green pollution-free and the like, can supplement heat loss caused by hydrogen reduction in the biomass energy smelting process, can obviously improve the reaction speed, shortens the reaction time, reduces the energy consumption and improves the product quality. In addition, compared with a thermal reduction process using non-renewable resources such as coal and the like as fuel, biomass-based pellets have lower carbon content than substances such as coal and the like on one hand, so that the biomass-based pellets have the characteristic of lower carbon naturally, and on the other hand, biomass can be pyrolyzed in a low-temperature solid reduction process, and a large amount of hydrogen-rich gas is released to participate in reduction by pyrolysis. Simultaneously, a large number of gas channels are generated, so that the pellets become loose and porous, and the dynamic conditions of gas-solid reaction are improved. In addition, the biomass is rich in alkaline earth metals such as K, na and the like, and can catalyze the solid-state reduction of iron minerals. In conclusion, the method has better reduction effect and higher metallization rate.

Thus, in one aspect of the application, the application proposes a method for direct reduction extraction of Fe using microwaves and biomass-based pellets. The method comprises the steps of mixing mineral powder with biomass, wherein the mass of the biomass accounts for 30-40% of that of the mineral powder, obtaining mixed raw materials, carrying out pelletizing on the mixed raw materials, wherein the forming pressure of the pelletizing is greater than 15MPa, the pressure maintaining time is greater than 2min, the pellet diameter obtained by the pelletizing is 10-16 mm, carrying out microwave reduction on the pellet, the power of microwaves is 3-4KW, the heating temperature is 800-1000 ℃, the reduction time is 30-50 min, obtaining reduction products, and carrying out magnetic separation on the reduction products, thus obtaining iron products. The method can simply and conveniently utilize microwaves to reach the required reduction temperature, and obtain better reduction effect, and the obtained iron product has higher yield.

According to one embodiment of the application, the biomass comprises at least one of forestry waste, straw, distillers grains, rice hulls, and the mineral powder comprises at least one of concentrate powder, low-grade mineral powder, composite mineral powder, and mine dust. Thereby, the cost of the method can be further reduced.

According to one embodiment of the application, the mixed raw material further comprises a binder and a solvent, wherein 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 comprises at least one of sodium silicate, bentonite and polyvinyl alcohol, and the solvent comprises water. Thus, the uniformity of mixing of the raw materials can be further improved.

According to one embodiment of the application, the pellets subjected to the pelletizing treatment are further subjected to a drying treatment before being subjected to the microwave heating treatment, wherein the drying treatment is carried out by preserving heat for 12-15 hours at 100-110 ℃. Thus, the quality of the pelletization can be further improved.

According to one embodiment of the application, the biomass is subjected to a pretreatment prior to mixing with the mineral powder, the pretreatment comprising washing the biomass with water and drying. Thus, impurities such as surface dust can be removed, and the quality of biomass for pelletizing can be further improved.

According to one embodiment of the application, the particle sizes of mineral powder and biomass in the mixed raw material are respectively and independently d= -48 μm to-74 μm. This can enhance the reduction effect.

According to one embodiment of the application, the microwave power is 3.5-3.8KW. This can enhance the reduction effect.

According to one embodiment of the application, the heating rate of the microwave heating treatment is 25-35 ℃ per minute, and the heating temperature is 800-1000 ℃. This can enhance the reduction effect.

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

According to one embodiment of the application, the method further comprises recycling the exhaust gas and tar produced during the microwave reduction treatment.

The foregoing summary is for the purpose of the specification 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 become readily apparent from the following detailed description.

Drawings

FIG. 1 shows a schematic flow diagram of a method according to one embodiment of the application;

Fig. 2 shows a block diagram of a device of a method according to an embodiment of the application.

Detailed Description

Hereinafter, only certain exemplary embodiments are briefly described. As will be recognized by those of skill in the pertinent art, the described embodiments may be modified in various different ways, and the different embodiments may be combined arbitrarily without conflict, without departing from the spirit or scope of the present application. The following description is, therefore, to be taken in an illustrative and not a limiting sense.

The method according to the application is illustrated by means of specific examples. The methods used in the examples described below are conventional methods unless otherwise indicated, and the reagents used are commercially available reagents unless otherwise indicated.

The application provides an innovative technological method for directly reducing the microwave-enhanced biomass-based pellets, which skillfully integrates the environment-friendly concept and the high-efficiency energy utilization technology. The method uses biomass renewable energy to replace conventional carbon reducing agent, thereby not only reducing the dependence on fossil fuel, but also effectively reducing the emission of CO ₂, further reducing the environmental pollution, and belonging to a novel hydrogen-rich low-carbon ironmaking process. The microwave field is introduced into the biomass-based pellet direct reduction process, so that the reduction temperature can be reduced, the reaction efficiency is improved, and the rapid reduction at low temperature is realized. According to the method, microwave heating is used for replacing conventional heating and biomass is used for replacing conventional carbon as a reducing agent, so that the defects of long reduction time, high reduction temperature, low reduction efficiency, large CO ₂ emission and the like in the direct reduction iron-making process of the internally-matched carbon pellets can be effectively overcome, the economy and environmental friendliness of the whole process are improved, and the method has a good application prospect.

Specifically, referring to fig. 1, the method proposed by the present application may comprise the steps of:

S100, mixing mineral powder and biomass to obtain a mixed raw material

In the step, firstly, mineral powder and biomass are mixed according to a certain proportion to obtain a mixed raw material.

The biomass can comprise forestry waste, straw, vinasse, rice hulls and other raw materials, and the mineral powder can be one or more of low-grade ore, composite mineral powder and mine dust. The raw material cost is low, and the raw material cost of the method can be reduced. Moreover, the biomass raw materials such as straw, rice husk and the like are wastes in various industries, but have a certain organic matter content, and can release reducing gas through the decomposition of organic matters in the subsequent microwave reduction process, so that the biomass raw materials have better potential for being used as a reducing agent: the adoption of the substances to form the pellets can reduce the production cost, save the operation of treating wastes in other industrial and agricultural processes, and reduce the whole carbon emission of the method: as described above, compared with the conventional reduction raw materials such as coal, the biomass has a lower carbon content, so that the carbon discharged by the whole process can be greatly reduced, and the method meets the requirements of energy conservation and emission reduction, and becomes an effective way for reducing carbon emission and realizing carbon neutralization.

In some embodiments, the mass of biomass in the mixture is 30-40% of the mass of the ore fines, which may be, for example, 35-40%. Regarding the raw material ratio, the metallization rate of the method gradually increases as the biomass addition amount increases from 10% to 40%. Increasing the biological quality improves the concentration of the reducing atmosphere and promotes the reduction of iron-containing oxides in minerals. However, when the biomass addition amount is increased from 40% to 50%, the metallization rate is not improved significantly, and the biomass addition amount is excessive, so that the resource waste is caused.

In order to further improve the mixing quality of the mineral powder and the biomass, the mineral powder and the biomass are fully contacted, and the particle sizes of the mineral powder and the biomass can be respectively and independently d= -48 mu m to-74 mu m. For better pelletization in the subsequent step, a binder and a solvent may be further included in the mixed raw materials. Specifically, the content of the solvent is 6-8% of the total mass of the mixed raw materials, and the content of the binder is 0.18-0.24% of the total mass of the mixed raw materials. The binder may include at least one of water glass, bentonite, and polyvinyl alcohol, and the solvent may be water.

The method provided by the application adopts a proper raw material proportion and a high-efficiency heating mode, so that raw mineral powder with lower quality can be adopted.

In order to further improve the effect of the method, the raw materials such as biomass and the like may be pretreated before mixing:

the biomass may be subjected to a water wash treatment. Specifically, surface dust and other impurities may be removed first by a water washing treatment, and then a drying treatment may be performed.

S200 pelletizing process

In this step, the mixed raw material is subjected to pelletization treatment to obtain raw material pellets. The forming pressure of the pelletizing treatment is more than 15MPa, the dwell time is more than 2min, and the diameter of the pellets obtained by the pelletizing treatment is 10-16 mm.

The pellets subjected to pelletization may be further subjected to a drying treatment before being subjected to a subsequent treatment, i.e., a microwave heating treatment, so as to improve the effect of the subsequent microwave heating treatment. And the drying treatment is to keep the temperature at 100-110 ℃ for 12-15 h. Whereby a sufficiently dry pellet is obtained.

S300 microwave reduction process

According to an embodiment of the application, the pellets are subjected to a microwave reduction process in this step. Specifically, the pellets are subjected to microwave heating treatment. The power of the microwaves is 3-4KW, the heating temperature can be 800-1000 ℃, and the reduction time is 30-50 min, so that the reduction product is obtained.

The application of microwaves as an electromagnetic field of a specific frequency brings a revolutionary revolution to the preparation of materials. The microwaves can not only rapidly and uniformly heat the material, but also interact with microscopic particles such as ions, molecules and the like in the material, and accurately regulate and control the motion state and the reaction process of the material, thereby realizing accurate control of the material properties.

In the field of strong magnetic field material science, the application of microwaves provides powerful support for preparing novel materials with excellent properties. Wherein the microwave enhanced reduction process mainly depends on a unique heating mechanism of microwaves. Under the action of the externally applied electromagnetic field, polar molecules in the medium are converted from a disordered random state to be arranged along with the direction of the electric field. Since the molecular alignment orientation periodically changes reciprocally with the frequency of the electric field, severe collisions occur during the movement, thereby generating heat. By utilizing the wave-absorbing property of the material, the sample can be quickly and comprehensively heated in a short time, and the required heat is provided for reduction. The heating mode has the advantages of rapid temperature rise, integral heating, no heating inertia and the like. The adoption of microwave heating not only solves some inherent problems in the traditional heating, such as the technical problem of 'cold center', but also improves the reduction efficiency, namely the special mechanism of microwave heating determines the heat conduction process that the raw materials are not gradually permeated into the material from the surface under the action of microwave heating. Compared with the traditional contact type heat transfer process, the microwave heating mode can heat materials more uniformly and rapidly. Therefore, temperature difference caused by different heat transfer rates at different positions in the material can be avoided, so that the uniformity of heating environments at different positions in the pellet can be improved, and the reduction reaction can be performed in a more efficient and uniform manner.

In addition, microwaves have different effects on substances with different wave absorbing capacities. Gangue minerals such as carbonates, silicates, etc. have a lower dielectric constant and less sensitivity to temperature changes. This means that they have a weaker absorption capacity in the microwave field and thus absorb less microwave energy. Such materials can be kept at relatively low temperatures during microwave heating. Whereas iron-containing minerals have a higher dielectric constant and dielectric dissipation factor, which makes them more absorptive in the microwave field. When iron-bearing minerals absorb microwave energy, they rapidly warm up and reach higher temperature levels. The high temperature is helpful to accelerate the reduction reaction and improve the reduction efficiency. Meanwhile, the temperature difference of the iron-containing minerals and gangue minerals under the action of microwaves generates thermal stress between the iron-containing minerals and the gangue minerals, so that the iron-containing minerals and the gangue minerals are beneficial to dissociation, and for iron ores, particularly a large amount of multi-metal co-associated composite iron ores, the mineral species are complex, selective heating among various minerals can be realized by utilizing the difference of wave absorption capacities of different minerals under the action of microwaves, the dissociation of useful minerals and the gangue is promoted, the effective reaction area of the useful minerals is increased, and a larger reaction area means that more reduction reactions can occur on the surfaces of the minerals, so that the overall reduction efficiency is improved. Thus, the use of microwaves in the preparation of materials presents great potential and advantages.

As described above, the biomass is decomposed by the organic matters in the microwave reduction process to generate a large amount of gas, so that after the microwave reinforcement, the material structure is more loose, and the gas generated by the decomposition of the organic matters can overflow the surface of the pellet after accumulating a certain amount in the pellet, so that a plurality of gas channels can be formed in the pellet in the process. The formation of the gas channels can loosen the pressed materials, enhance the contact between the reducing gas and the mineral powder, and improve the dynamic conditions. According to the method, biomass-based pellets are placed in a microwave reduction furnace, and the materials are heated efficiently and rapidly by a special heating mechanism of microwaves, so that the reduction reaction process is enhanced.

In the step, 2-3 layers of pellets prepared in the previous step can be tiled in a tray, and placed in a microwave reduction furnace, wherein the microwave power is 3.6KW, the heating rate is 30 ℃ per minute, the temperature is increased to 800-1000 ℃, and the reduction time is 30-50 minutes.

S400 magnetic separation process

In the 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 strength during magnetic separation was 0.18T.

Furthermore, the waste gas and tar generated in the reduction process can be recycled through the waste gas recycling device.

For example, referring to fig. 2, fig. 2 shows a schematic view of an apparatus for Fe separation using the method according to the present application. Wherein, 1 is the display, 2 is the microwave switch, 3 is the touch screen, 4 is the quartz capsule, realizes microwave reduction in the quartz capsule. 5 is a heating area, 6 is a heating cavity, 7 is a microwave source, 8 is a condensation water tank, 9 is a conical flask, 11 is a gas flowmeter, and 12 is a gas collecting bottle.

Through erlenmeyer flask 11 and gas collecting bottle 12, can handle the gas and the tar that experiment produced effectively, guarantee the security of experimental environment through inert shielding gas's the letting in, realize the condensation separation to the tar through syllogic condensing equipment, monitor gas flow and composition in real time through the gas flow analyzer, collect the gas sample through the gas collecting device so that follow-up analysis at last.

In general, the present application may have the following beneficial effects:

(1) The raw materials of the reducing agent used in the invention are biomass, and the biomass is used as a typical hydrogen-rich renewable energy source, is rich and various, and is green and sustainable, and comprises wood chips, straws, vinasse and rice hulls. The main component of the biomass raw materials is hydrocarbon, the impurity components are relatively few, and the biomass raw materials are good coke coal powder substitutes in the ironmaking process.

(2) The invention introduces the action of microwaves in the biomass-based pellet direct reduction process, and realizes a rapid and efficient reduction process by utilizing the wave-absorbing characteristics of materials through a unique heating mechanism of the microwaves, thereby realizing the reduction effect which cannot be achieved under the conventional conditions. The heat loss caused by hydrogen reduction is supplemented in the hydrogen-rich smelting process, the reaction speed can be obviously improved, the reaction time is shortened, the energy consumption is reduced, the product quality is improved, and the microwave heating replaces fossil energy heating.

(3) By the method, the solid phase reduction temperature is reduced to below 900 ℃ and can be reduced to more than 80 percent rapidly. The reduction time is shortened, under the action of microwaves, the biomass-based pellets can enable the metallization rate to reach more than 90% within 50min, and the production efficiency is improved. After microwave reinforcement, the material structure is looser, and the selective reduction and separation of iron and valuable metal elements in the ore are further efficiently achieved.

(4) The microwave heating is used for replacing the conventional heating as a heat source, the biomass is used for replacing the conventional carbon reducing agent, and two environment-friendly methods are combined for reducing the mineral powder.

The technical scheme of the invention is further described in detail below with reference to specific examples:

The baiyunebo mineral powder with the particle size of d= -48 mu m to-74 mu m is used as mineral powder, and the chemical compositions are shown in the table 1 below. The distilled spirit vinasse with the biomass particle size of d= -48 mu m to-74 mu m is used as a reducing agent.

TABLE 1 chemical composition/%

The ore sample is taken from inner Mongolia white Yun E blogs, the full iron grade is 47.5%, and the ore sample is mainly enriched in hematite. The biomass used is distilled spirit vinasse, ash content in industrial analysis is 3.74%, volatile content in industrial analysis is 76.64%, and fixed carbon content is 14.73%.

(1) Raw material treatment, namely washing the distilled grain with clear water, removing surface dust and other impurities, and drying to obtain biomass B.

(2) The raw materials are proportioned that the mineral powder and the vinasse B are mixed uniformly according to a certain proportion. The raw material requirement is that the grain diameter d= -48 mu m to-74 mu m, the mixing proportion is that the vinasse B is uniformly mixed according to the mass percentage of the mineral powder of 40%, and then the binder and the water are added, wherein the addition amounts are 0.24% and 8% of the total mass of the raw material.

(3) The preparation of pellets, namely preparing the mixture into biomass-based pellets by adopting a pelletizer or a ball press, wherein the molding pressure of the biomass-based pellets is 15MPa, the pellet diameter is 10-16 mm when the pressure is maintained for 2min, and the pressed pellets are dried for standby, and the drying method is carried out for 12-15 h at 100+/-5 ℃.

(4) And (3) solid phase reduction, namely flatly laying 2-3 layers of biomass-based pellets in a material tray, placing the material tray in a microwave reduction furnace, wherein the microwave power is 3.6KW, the heating rate is 30 ℃ per minute, the heating is up to 900 ℃, and the reduction time is 50 minutes. And after the reduction is finished, carrying out magnetic separation to obtain a direct reduced iron product.

And (3) obtaining a direct reduced iron product with a metallization rate of 94.3% after magnetic separation.

Example 2:

the rest of the procedure was as in example 1, except that a microwave power of 3.0KW was used and the metallization rate was 55.6%.

Example 3:

The rest of the operations were the same as in example 1, except that the biomass particle size was-74 μm to-80 μm and the metallization rate was 25.0%.

Example 4:

The rest of the operations are the same as in example 1, except that the mixing ratio is 30% of distillers grains C by mass of mineral powder and the metallization rate is 25.6%.

Comparative example 1:

(2) The raw materials are proportioned that the mineral powder and the vinasse B are mixed uniformly according to a certain proportion. The raw material requirement is that the grain diameter d is between 48 and 74 mu m below zero, and the mixing proportion is 40 percent of the vinasse B according to the mass percentage of the mineral powder. After being evenly mixed, the adhesive and water are added, and the addition amounts of the adhesive and the water are 0.24 percent and 8 percent of the total mass of the raw materials.

(4) And (3) solid phase reduction, namely flatly laying 2-3 layers of biomass-based pellets in a material tray, placing the material tray in a microwave-free tubular reduction furnace, heating to 900 ℃ at a temperature rising rate of 30 ℃ per minute, and reducing for 50 minutes. And after the reduction is finished, carrying out magnetic separation to obtain a direct reduced iron product.

And (3) obtaining a direct reduced iron product with a metallization rate of 20.3% after magnetic separation.

Compared with the prior art, the method for directly reducing the microwave-enhanced biomass-based pellets remarkably improves the reduction efficiency. Under the action of microwaves, the metallization rate of the biomass-based pellets is improved by 3.65 times compared with the metallization rate without the action of microwaves. The innovation not only remarkably improves the reduction efficiency of biomass-based pellets, but also reduces the reduction temperature to below 1000 ℃, effectively supplements the heat loss in the hydrogen reduction process, and further reduces the overall energy consumption. In addition, the process flow is simple and convenient to operate, and the emission of CO ₂ is effectively reduced by using biomass as a reducing agent, so that the environmental pollution is reduced.

Furthermore, the terms "first," "second," and the like, are used for descriptive purposes only and are not to be construed as indicating or implying a relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defining "a first" or "a second" may explicitly or implicitly include one or more such feature. In the description of the present application, the meaning of "a plurality" is two or more, unless explicitly defined otherwise.

The above application provides many different embodiments or examples for implementing different structures of the application. The components and arrangements of specific examples have been described above in order to simplify the present disclosure. They are, of course, merely examples and are not intended to limit the application. Furthermore, the present application may repeat reference numerals and/or letters in the various examples, which are for the purpose of brevity and clarity, and which do not themselves indicate the relationship between the various embodiments and/or arrangements discussed.

The foregoing is merely illustrative of the present application, and the present application is not limited thereto, and any person skilled in the art will readily recognize that various modifications and substitutions are possible within the scope of the present application. Therefore, the protection scope of the application is subject to the protection scope of the claims.

Claims

1. A method for extracting Fe by direct reduction using microwaves and biomass-based pellets, comprising:

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, characterized in that the biomass comprises 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, characterized in that the mixed raw material further comprises a binder and a solvent, the binder content is 0.18-0.24% of the total mass of the mixed raw material, and the solvent content 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 is characterized in that the pellets after the pelletizing treatment are further dried before the microwave heating treatment, and the drying treatment is to keep warm at 100-110°C for 12 to 15 hours.

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

The biomass is washed with water,

The washed biomass is dried.

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

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

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

10. The method according to claim 1, further comprising: recovering the waste gas and tar generated during the microwave reduction process.