Biochar with high adsorption performance as well as preparation, application and recycling method thereof

Abstract

The invention belongs to the technical field of biochar, and particularly relates to biochar with high adsorption performance as well as preparation, application and recycling methods thereof, the preparation method comprises the following steps: 1) uniformly mixing agricultural straw with livestock and poultry manure to obtain a mixture A; 2) sequentially adding a biomass binder and a composite catalyst into the mixture A, and uniformly mixing to obtain a mixture B; and 3) carrying out two-stage microwave-induced pyrolysis on the mixture B to obtain the high-adsorption-performance biochar. The biochar is prepared from the agricultural straw and the livestock and poultry manure based on a two-stage microwave induced pyrolysis method, the problem of treatment of the agricultural straw and the livestock and poultry manure can be effectively solved, recycling of resources is achieved, and the prepared biochar has high adsorption performance on heavy metal ions such as Pb < 2 + >, Cd < 2 + > and Cr < 3 + > in wastewater and has wide application prospects.

Description

Technical Field

[0001] This invention belongs to the field of biochar technology, specifically relating to a high-adsorption-performance biochar and its preparation, application and recycling methods. Background Technology

[0002] In today's society, agricultural production activities generate a large amount of waste, among which the disposal of agricultural straw and livestock manure is particularly prominent. With the advancement of agricultural modernization, the planting area of ​​crops continues to expand, and straw production increases year by year. At the same time, the development of large-scale livestock farming has also led to a sharp increase in the discharge of livestock manure. If agricultural straw is not properly treated and is discarded or burned at will, it will not only waste resources but also cause serious environmental pollution problems. Open burning of straw produces large amounts of smoke and harmful gases, such as sulfur dioxide, nitrogen oxides, and particulate matter, leading to a decline in air quality, harming human health, and easily causing fires that threaten life and property. If livestock manure is directly discharged into the environment, it will pollute the soil, water bodies, and air. The large amounts of organic matter, nitrogen, phosphorus, and other nutrients contained in manure can lead to eutrophication of water bodies, causing algae to proliferate and disrupting the aquatic ecological balance; at the same time, manure may also carry pathogens and parasite eggs, spreading diseases and posing a threat to public health and safety. Therefore, how to efficiently and environmentally treat agricultural straw and livestock manure and realize resource reuse has become an important issue that urgently needs to be addressed in the current agricultural sector.

[0003] Biochar, as a carbonaceous material with unique structure and properties, has shown great application potential in wastewater treatment, soil improvement, and energy storage in recent years. Utilizing agricultural straw and livestock manure to prepare biochar holds promise as a solution to the problem of agricultural straw and livestock manure treatment. However, biochar is typically obtained through the pyrolysis of biomass under anaerobic or hypoxic conditions. Traditional pyrolysis techniques suffer from drawbacks such as slow heating rates, high energy consumption, and long pyrolysis times, resulting in low biochar preparation efficiency, high production costs, and unstable quality with inconsistent adsorption performance. Therefore, it is necessary to develop new preparation methods to overcome the technical bottlenecks of traditional processes, obtain biochar with high adsorption performance, promote the resource utilization of agricultural waste, and contribute to achieving the dual goals of agricultural ecological environmental protection and efficient resource utilization. Summary of the Invention

[0004] The technical problem this invention aims to solve is to address the shortcomings of existing technologies by providing a high-adsorption-performance biochar and its preparation, application, and recycling methods. This invention utilizes agricultural straw and livestock manure to prepare biochar via a two-stage microwave-induced pyrolysis method. This not only effectively solves the problem of agricultural straw and livestock manure treatment and achieves resource reuse, but also enhances the adsorption capacity of the prepared biochar for Pb in wastewater. 2+ Cd 2+Cr 3+ Heavy metal ions exhibit high adsorption performance and have broad application prospects.

[0005] To address the technical problem proposed in this invention, this invention provides a method for preparing biochar with high adsorption performance, comprising the following steps: S1, mix agricultural straw and livestock manure evenly to obtain mixture A; S2, add biomass binder and composite catalyst to mixture A in sequence and mix evenly to obtain mixture B; S3, the mixture B is subjected to two-stage microwave-induced pyrolysis to obtain biochar with high adsorption performance.

[0006] In the above scheme, the agricultural straw is one or more of corn straw, wheat straw, and rice straw.

[0007] In the above scheme, the particle size of the agricultural straw is 1.0~2.0mm and the moisture content is 15%~25%.

[0008] In the above scheme, the agricultural straw is pretreated with alkaline solution before use. The steps include: soaking the agricultural straw in a compound alkaline solution of potassium hydroxide and sodium carbonate, taking it out, washing it, and drying it.

[0009] Furthermore, the mass fraction of potassium hydroxide in the composite alkaline solution is 1% to 3%, and the mass fraction of sodium carbonate is 4% to 6%.

[0010] Furthermore, the agricultural straw is soaked in a sufficient amount of compound alkaline solution, with each kilogram of agricultural straw soaked in no less than 20 liters of compound alkaline solution.

[0011] Furthermore, the soaking time is 12-24 hours.

[0012] Furthermore, the washing process involves rinsing with water until neutral, and the drying process involves drying until the moisture content is 15% to 25%.

[0013] In the above scheme, the livestock and poultry manure is one or more of chicken manure, pig manure, and cow manure.

[0014] In the above scheme, the particle size of the livestock and poultry manure is 0.5~1.5mm and the moisture content is 8%~18%.

[0015] In the above scheme, the mass ratio of agricultural straw to livestock manure is (3~5):1.

[0016] In the above scheme, the biomass binder is a mixture of bituminous rock and lignin.

[0017] Furthermore, the mass ratio of the asphalt rock to lignin is (1~2):1.

[0018] In the above scheme, the particle size of the biomass binder is 3~30μm.

[0019] In the above scheme, the amount of biomass binder added is 1% to 3% of the mass of mixture A.

[0020] In the above scheme, the composite catalyst is a mixture of Fe2TiO4, Fe2CoO4, Co3O4 and NiO.

[0021] Furthermore, the composite catalyst comprises the following raw materials in the following mass percentages: Fe2TiO4 30%~40%, Fe2CoO4 25%~35%, Co3O4 15%~25%, and NiO 10%~20%.

[0022] In the above scheme, the particle size of the composite catalyst is 20~80nm.

[0023] In the above scheme, the amount of the composite catalyst added is 2% to 5% of the mass of mixture A.

[0024] In the above scheme, the microwave power of the two-stage microwave-induced pyrolysis is 550~850W.

[0025] In the above scheme, the pyrolysis pressure of the two-stage microwave-induced pyrolysis is 0.3~0.7MPa.

[0026] In the above scheme, the first stage of the two-stage microwave-induced pyrolysis has a pyrolysis temperature of 200~300℃ and a pyrolysis time of 20~40min; the second stage has a pyrolysis temperature of 450~650℃ and a pyrolysis time of 40~70min.

[0027] Furthermore, the heating rate to the first pyrolysis temperature is 3~7℃ / min, and the heating rate to the second pyrolysis temperature is 5~10℃ / min.

[0028] In the above scheme, the two-stage microwave-induced pyrolysis uses a mixture of N2 and NH3 as the pyrolysis atmosphere.

[0029] Furthermore, the volume ratio of N2 to NH3 is 9:1 to 7:3.

[0030] The present invention also provides a high-adsorption biochar, which is prepared by the above method.

[0031] In the above scheme, the high-adsorption biochar has a particle size of 100~200μm and a specific surface area of ​​900~950m². 2 / g, total pore volume 0.7~0.8cm2 / g, average pore size 2.6~3.0nm, pH value 9.7~10.3.

[0032] This invention also provides an application of high-adsorption-performance biochar in the treatment of wastewater containing heavy metals. The application method is as follows: add high-adsorption-performance biochar to the wastewater, adjust the pH, and then adsorb heavy metal ions in the wastewater under stirring or shaking conditions.

[0033] In the above scheme, the pH is adjusted to 4.5~5.5.

[0034] In the above scheme, the amount of high-adsorption biochar added is 0.05~0.15% of the wastewater mass.

[0035] In the above scheme, the adsorption temperature is 20~30℃ and the adsorption time is 15~30h.

[0036] In the above scheme, the heavy metal ions in the wastewater include Pb. 2+ Cd 2+ Cr 3+ One or more of them.

[0037] This invention also provides a method for recycling high-adsorption-performance biochar, specifically a method for regenerating high-adsorption-performance biochar, comprising the following steps: after the used high-adsorption-performance biochar is washed once, desorbed, and washed a second time, it is dried to obtain regenerated high-adsorption-performance biochar.

[0038] In the above scheme, the used high-adsorption biochar is recovered from the water by an external magnetic field.

[0039] In the above scheme, the washing process involves rinsing with water for 5 to 10 minutes each time, and rinsing 3 to 5 times to remove impurities and unadsorbed heavy metal ions attached to the surface.

[0040] In the above scheme, the desorption solution used for desorption is a mixture of 0.1~1.0 mol / L nitric acid solution and 0.01~0.1 mol / L ethylenediaminetetraacetic acid solution in a volume ratio of (1~5):1.

[0041] In the above scheme, the used high-adsorption biochar and the desorption solution are mixed at a solid-liquid ratio of 1g:(20~50)mL and desorbed by stirring at a rate of 150~200rpm at 25~35℃.

[0042] In the above scheme, the desorption time for a single desorption is 3-6 hours. After one desorption is completed, the biochar is separated, and then a new desorption solution is added for the next desorption. A total of 2-3 desorptions are performed.

[0043] In the above scheme, the secondary rinsing is performed with water until the pH value of the rinsing solution is neutral, so as to remove residual desorption solution and heavy metal ions.

[0044] In the above scheme, the drying is carried out at 50~80℃ until constant weight.

[0045] This invention also provides a method for recycling high-adsorption-performance biochar, specifically a method for recovering composite catalysts from high-adsorption-performance biochar, comprising the following steps: after the used high-adsorption-performance biochar is subjected to primary washing, desorption, and secondary washing, it is then calcined, and the calcined product is ground and depolymerized, and the biomass ash is removed by air classification to obtain the regenerated composite catalyst.

[0046] In the above scheme, the processes of primary washing, desorption, and secondary washing are the same as those for regenerating high-adsorption-performance biochar.

[0047] In the above scheme, the calcination temperature is 650~750℃ and the calcination time is 1~2h.

[0048] This invention also provides a method for recycling high-adsorption-performance biochar, specifically a method for recovering components of a composite catalyst from high-adsorption-performance biochar, comprising the following steps: 1) After the high-adsorption biochar is washed, desorbed and washed twice, it is roasted. The roasted product is ground and depolymerized, and the biomass ash is removed by air classification. Then, a mixture containing Fe2TiO4 and Fe2CoO4 is recovered from the roasted product by applying an external magnetic field. 2) After the residue separated by the magnetic field is mixed with dilute nitric acid solution, the mixture is stirred and reacted. Then, ammonia water is added to adjust the pH to 8-9, the precipitate is collected, and after washing, drying and calcination, Co3O4 is obtained. Sodium carbonate solution is added to the remaining solution, the precipitate is collected, and after washing, drying and calcination, NiO is obtained.

[0049] In the above scheme, the processes of primary cleaning, desorption, secondary cleaning, and calcination are the same as those for regenerating the composite catalyst.

[0050] In the above scheme, the magnetic field strength of the external magnetic field is 0.8~1.0T.

[0051] In the above scheme, the concentration of the dilute nitric acid solution is 1.0~2.0mol / L, the mass ratio of the residue after magnetic separation to the volume ratio of the dilute nitric acid solution is 1g:(50~100)mL, the stirring reaction temperature after mixing is 60~80℃, and the stirring reaction time is 120~180min.

[0052] In the above scheme, in step 2), the calcination temperature of the obtained Co3O4 is 400~500℃ and the calcination time is 1~3h.

[0053] In the above scheme, the concentration of the sodium carbonate solution is 0.5~1.0 mol / L, and it is added until no more precipitate is formed.

[0054] In the above scheme, in step 2), the calcination temperature of NiO is 400~500℃ and the calcination time is 1~3h.

[0055] In the above scheme, the mixture of Fe2TiO4 and Fe2CoO4 can be further used to recover Fe2TiO4 and Co3O4. The specific steps are as follows: mix the mixture with dilute sulfuric acid solution, stir and filter, the filter residue is Fe2TiO4; add H2O2 solution to the filtrate to oxidize ferrous ions to ferric ions, and adjust the pH to 3.5~4.5 with NaOH solution to remove the precipitate; add sodium carbonate solution to the remaining filtrate, collect the precipitate, and obtain Co3O4 after washing, drying and calcining.

[0056] Furthermore, the concentration of the dilute sulfuric acid solution is 0.5~1.0 mol / L, the mass ratio of the Fe2TiO4 and Fe2CoO4 mixture to the volume ratio of the dilute sulfuric acid solution is 1 g: (50~100) mL, the stirring temperature after mixing is 60~80℃, and the stirring time is 60~120 min.

[0057] Furthermore, the concentration of the sodium carbonate solution is 0.5~1.0 mol / L, and it is added until no more precipitate is formed.

[0058] Furthermore, the calcination temperature for obtaining Co3O4 is 400~500℃, and the calcination time is 1~3h.

[0059] The main technical concept and technical principles of this invention are as follows: 1) This invention addresses the shortcomings of traditional pyrolysis technology by proposing a two-stage microwave-induced pyrolysis process. Microwave-induced pyrolysis differs from traditional microwave pyrolysis. Although it also has a thermal effect that can raise the temperature, its core function is to achieve high dispersion of pyrolysis raw materials, activation of active sites, and pore expansion through high-frequency oscillation. Therefore, it is called microwave-induced pyrolysis.

[0060] In the first stage of microwave-induced pyrolysis, the high-frequency oscillation of microwaves helps to better disperse the catalyst in the mixed raw materials, activates the active sites on the catalyst surface, achieves catalyst activation and raw material pretreatment, and enhances the catalyst's catalytic ability for subsequent pyrolysis reactions. Simultaneously, the high-frequency oscillation of microwaves helps to break some weaker chemical bonds between raw material molecules, making the molecular structure of the raw materials more loose, creating favorable conditions for subsequent pyrolysis reactions. At this stage, some volatile components can also be removed; low-boiling-point organic matter and moisture will volatilize first. Removing these volatile components from the reaction system in a timely manner prevents them from undergoing secondary reactions during subsequent pyrolysis, which could affect the quality of the final product. Using an N2 / NH3 atmosphere, NH3 will undergo an acid-base neutralization reaction with acidic groups in the raw materials at this stage (e.g., R-COOH + NH3 → R-COONH4), thereby changing the chemical composition and structure of the raw materials and providing more active sites for subsequent pyrolysis reactions. Furthermore, some unstable chemical bonds in the raw materials will gradually break under the combined effects of microwaves and temperature, such as some ether bonds (-O-) and ester bonds (-COO-).

[0061] In the second stage of microwave-induced pyrolysis, the main reactions occurring are thermal cracking, catalytic reforming, and nitrogen doping. Within this higher temperature range, the raw materials undergo deep pyrolysis under the catalysis of the catalyst. The high-frequency oscillation of the microwaves further promotes the movement and collision of raw material molecules, accelerating the pyrolysis reaction. Simultaneously, microwaves allow pyrolysis products to diffuse more easily from the raw material, improving the efficiency of the pyrolysis reaction and achieving a pore-expanding effect. During pyrolysis, a series of cracking, reforming, and condensation reactions occur between raw material molecules, generating various pyrolysis products, such as gases (H2, CH4, CO, CO2, etc.), liquids (tar), and solids (coke). The composite catalyst can also selectively promote certain reactions, increasing the yield and quality of the target product while inhibiting tar formation. At higher temperatures, nitrogen atoms produced by the decomposition of NH3 can be incorporated into the structure of biochar, increasing the nitrogen content of the coke and enhancing its adsorption performance.

[0062] 2) This invention, by introducing a composite catalyst with a specific formulation, can jointly improve the efficiency of the pyrolysis reaction and the adsorption performance of biochar. The composite catalyst of this invention comprises Fe2TiO4, Fe2CoO4, Co3O4, and NiO. Specifically, during the catalytic pyrolysis reaction, Fe2TiO4 can lower the activation energy of the biomass pyrolysis reaction and promote the breaking of chemical bonds in biomass molecules; Fe2CoO4 contains Fe... 3+ / Fe 2+ and Co 3+ / Co 2+The redox pairs can regulate the electron cloud density in the reaction system by gaining and losing electrons, thereby promoting the thermal decomposition of biomass. The acidic sites on the surface of Co3O4 can act as proton donors, promoting the protonation reaction of biomass molecules and optimizing the pyrolysis pathway. NiO helps catalyze the nitrogen-doped pyrolysis reaction of biomass, optimizing the quality and adsorption performance of biochar by increasing the nitrogen doping amount. These components synergistically reduce the activation energy of the pyrolysis reaction, optimize the pyrolysis reaction pathway, and thus improve the efficiency of the pyrolysis reaction. Regarding improving the adsorption performance of biochar, Fe2TiO4 can provide abundant adsorption sites; its surface hydroxyl groups and oxygen vacancies can interact with Pb. 2+ Cd 2+ Cr 3+ Heavy metal ions are bound together through ion exchange and coordination complexation, thus immobilizing them on the biochar surface. Fe₂TiO₄ exhibits strong catalytic activity, catalyzing the reaction between functional groups on the biochar surface and heavy metal ions, accelerating the adsorption process. Fe₂CoO₄ contains Fe... 3+ / Fe 2+ and Co 3+ / Co 2+ Redox pairs can undergo electron transfer with heavy metal ions, altering their form and thus improving the effectiveness of targeting the heavy metal ion Pb. 2+ Cd 2+ Cr 3+ The adsorption capacity of the composite biochar is high. Co3O4 has certain acidic sites on its surface, which can undergo ion exchange reactions with heavy metal ions, promoting their adsorption. Furthermore, the acidic environment can inhibit some chemical reactions on the biochar surface that are detrimental to adsorption, thus improving the adsorption effect. NiO has good chemical stability, which can improve the stability and durability of the composite biochar to a certain extent. In complex wastewater environments, NiO can protect other components from excessive corrosion and dissolution, ensuring the long-term performance of the composite biochar. The four components provide different types and numbers of adsorption sites, which synergistically and mutually cooperate to form a complex and rich adsorption network, thereby improving the adsorption capacity and selectivity for various heavy metal ions.

[0063] 3) Regarding raw material processing, this invention precisely controls the particle size and moisture content of agricultural straw and livestock manure, ensuring the uniformity and stability of subsequent mixing and pyrolysis processes. By optimizing the particle size and moisture content of the raw materials, the contact area between biomass and the catalyst can be increased, promoting the pyrolysis reaction and thus improving the yield and performance of biochar. Furthermore, a composite alkaline solution of potassium hydroxide and sodium carbonate is used to pretreat agricultural straw. Potassium hydroxide, with its strong alkalinity and high solubility, can rapidly penetrate the cell wall structure of straw during soaking, effectively disrupting the bonds between lignin, cellulose, and hemicellulose. This loosens the straw's structure, laying a good foundation for the formation of biochar pores during subsequent pyrolysis and helping to improve the specific surface area and porosity of biochar. However, potassium hydroxide alone may excessively corrode the straw, leading to excessive dissolution and loss of some organic components, affecting the yield and quality of biochar. Sodium carbonate, with its relatively weak alkalinity and buffering capacity, can regulate the alkalinity of the composite solution, preventing excessive corrosion of the straw by potassium hydroxide. Simultaneously, when reacting with straw, sodium carbonate undergoes exchange and precipitation reactions with some metal ions, helping to remove impurities and some minerals from the straw. Moreover, sodium carbonate promotes the formation of functional groups on the surface of biochar during pyrolysis, enhancing its adsorption activity. Therefore, the synergistic treatment of both can significantly improve the adsorption performance and overall quality of biochar.

[0064] Compared with the prior art, the beneficial effects of the present invention are as follows: 1) This invention employs a two-stage microwave-induced pyrolysis method to prepare biochar. The first stage mainly involves catalyst activation, raw material pretreatment, and removal of some volatile components. The second stage involves a deep pyrolysis reaction. By controlling the temperature and reaction conditions stepwise, targeted reaction control is achieved in different temperature ranges, improving reaction selectivity, reducing side reactions, and making the composition and properties of the pyrolysis products more stable, thereby increasing the yield of the target product. Furthermore, the two-stage microwave-induced pyrolysis method can better utilize the high-frequency oscillation and pore-expanding effect of microwaves. The high-frequency oscillation of microwaves in the first stage loosens the raw material structure, creating better conditions for pore expansion in the second stage, which is conducive to the formation of biochar with rich pore structure and surface functional groups, improving biochar quality and adsorption performance. In addition, the first stage uses a lower temperature for pretreatment, reducing the time and energy consumption of high-temperature heating. At the same time, in the second stage of pyrolysis, since the raw materials have already been pretreated, the pyrolysis reaction is easier to carry out, which helps to reduce energy consumption and improve energy utilization efficiency.

[0065] 2) This invention introduces a composite catalyst. The hydroxyl groups, oxygen vacancies, and acidic sites on the surfaces of Fe2TiO4, Fe2CoO4, Co3O4, and NiO can specifically adsorb different heavy metal ions, thereby improving the adsorption capacity and selectivity for various heavy metal ions. Furthermore, the Fe and Co elements in Fe2CoO4 and Co3O4 have variable oxidation states, and they can undergo redox reactions to form a redox cycle system. This redox synergy can promote the oxidation, reduction, and transformation of heavy metal ions, making them easier to adsorb and remove by changing their existing form. In addition, both Fe2TiO4 and Fe2CoO4 are magnetic, and their combined action can significantly enhance the magnetism of the composite biochar. This synergistic magnetic effect makes the separation of biochar in a magnetic field more efficient and thorough, which is beneficial for the recovery and recycling of biochar. At the same time, the strong magnetism can also promote the dispersion and aggregation of biochar in wastewater, increase the contact opportunities with heavy metal ions, and improve the adsorption efficiency.

[0066] 3) This invention uses agricultural straw and livestock manure as the main raw materials. It uses a composite alkaline solution of potassium hydroxide and sodium carbonate to pretreat the agricultural straw. Potassium hydroxide mainly destroys the internal structure of the straw, creating conditions for the formation of pores during pyrolysis. Sodium carbonate helps to regulate the reaction process, protect the organic components of the straw, optimize the surface properties of biochar, and improve the adsorption performance and overall quality of biochar. Attached Figure Description

[0067] Figure 1 The high-adsorption-performance biochar prepared in Example 8, after five regeneration cycles, effectively adsorbed heavy metal ions (Pb) from wastewater. 2+ Cd 2+ Cr 3+ The change in adsorption amount. Detailed Implementation

[0068] To better understand the present invention, the following embodiments further illustrate the content of the present invention, but the content of the present invention is not limited to the following embodiments.

[0069] In the following examples, the Fe2TiO4 used was prepared by chemical coprecipitation, and the specific steps are as follows: 1) Weigh 80.8g of ferric nitrate nonahydrate, dissolve it in 500mL of deionized water to prepare a 0.4mol / L iron salt solution; measure 23.4mL of tetrabutyl titanate, slowly add it dropwise to 200mL of anhydrous ethanol, and stir until homogeneous to obtain a titanium salt ethanol solution. 2) Under magnetic stirring, slowly add the titanium salt ethanol solution to the iron salt solution at a rate of 1~2 drops / second, and continue stirring for 30 minutes to ensure that the two solutions are fully mixed and the temperature is controlled at 25℃. 3) Add 1.0 mol / L NaOH solution dropwise to the above mixed solution to adjust the pH value of the solution to 10. At this time, a precipitate will be formed. Continue to stir the reaction at 25°C for 2 hours to allow the precipitation reaction to proceed fully. 4) Centrifuge to separate the precipitate, wash the precipitate 3 times with deionized water, then wash it 2 times with anhydrous ethanol, and dry the washed precipitate at 80℃ for 12h to obtain precursor powder. 5) Place the precursor powder into a muffle furnace, heat it to 900℃ at a heating rate of 5℃ / min, and calcine it at this temperature for 3h to obtain Fe2TiO4 powder.

[0070] In the following examples, the Fe2CoO4 used was prepared by chemical coprecipitation, and the specific steps are as follows: 1) Weigh 80.8g of ferric nitrate nonahydrate and 29.1g of cobalt nitrate hexahydrate, dissolve them in 1000mL of deionized water to prepare a mixed salt solution, wherein the concentration of ferric ions is 0.2mol / L and the concentration of cobalt ions is 0.1mol / L; 2) Under magnetic stirring, add 10% ammonia solution at a rate of 1-2 drops / second to the mixed salt solution to adjust the pH value of the solution to 9. At this time, a precipitate will be formed. Continue stirring at 30°C for 1.5 hours to allow the precipitation reaction to proceed fully. 3) Centrifuge to separate the precipitate, wash the precipitate 4 times with deionized water, and dry the washed precipitate at 90℃ for 15h to obtain precursor powder; 4) The precursor powder was placed in a muffle furnace and heated to 700°C at a heating rate of 5°C / min, and calcined at this temperature for 3 hours to obtain Fe2CoO4 powder.

[0071] In the following examples, the Co3O4 used was prepared by chemical coprecipitation, and the specific preparation method is as follows: 1) Weigh 58.2g of cobalt nitrate hexahydrate, dissolve it in 500mL of deionized water to prepare a 0.4mol / L cobalt salt solution; weigh 21.2g of sodium carbonate, dissolve it in 300mL of deionized water to prepare a 0.67mol / L sodium carbonate solution. 2) Under magnetic stirring, the sodium carbonate solution is slowly added to the cobalt salt solution at a rate of 1~2 drops / second. At this time, a precipitate will be formed. Continue stirring at 35°C for 1.5 hours to allow the precipitation reaction to proceed fully. 3) Centrifuge to separate the precipitate, wash the precipitate three times with deionized water, and dry the washed precipitate at 85℃ for 18h to obtain precursor powder; 4) The precursor powder was placed in a muffle furnace and heated to 400°C at a heating rate of 5°C / min, and calcined at this temperature for 3.5 h to obtain Co3O4 powder.

[0072] In the following examples, the NiO used is from Shanghai Aladdin Biochemical Technology Co., Ltd., with a purity of AR (≥99%); the lignin used is sulfonate lignin, specifically calcium lignin sulfonate, which is from Shanghai Aladdin Biochemical Technology Co., Ltd.; the microwave pyrolysis furnace used is equipped with an electric heating device, and the heating rate can be adjusted by the electric heating device.

[0073] Example 1 A method for preparing biochar with high adsorption performance includes the following steps: 1) Raw material processing: Select corn stalks, crush them to a particle size of 1.0 mm, and reduce the moisture content to 15% by sun-drying and baking. Then, according to the ratio of 1 kg corn stalks to 20 L compound alkaline solution, soak the corn stalks in a compound alkaline solution with a potassium hydroxide mass fraction of 2% and a sodium carbonate mass fraction of 5% for 18 hours. After soaking, remove them, rinse them with deionized water until neutral, and then dry them to a moisture content of 15%. Select chicken manure, crush it to a particle size of 0.5 mm, and dehydrate it to reduce the moisture content to 8%. 2) Raw material mixing: Mix corn stalks and chicken manure evenly at a mass ratio of 3:1, then add 2% of the total mass of corn stalks and chicken manure biomass binder and mix evenly, then add 2% of the total mass of corn stalks and chicken manure composite catalyst and mix evenly; wherein, the biomass binder is a mixture of asphalt rock and lignin at a mass ratio of 1:1, with a particle size of 3~30μm; the composite catalyst includes the following raw materials in the following mass percentages: Fe2TiO4 30%, Fe2CoO4 35%, Co3O4 25%, NiO 10%, with a particle size of 20~80nm; 3) Microwave-induced pyrolysis: The above mixed raw materials are placed in a microwave pyrolysis furnace, and a N2 and NH3 mixed gas with a volume ratio of 9:1 is introduced. The furnace pressure is controlled at 0.3MPa, and the microwave power is adjusted to 550W. The temperature is first raised to 200℃ at a heating rate of 3℃ / min and held for 40min. Then, the temperature is raised from 200℃ to 450℃ at a heating rate of 5℃ / min and held for 70min. 4) Biochar collection: After the pyrolysis reaction is completed, the biochar is naturally cooled to room temperature and collected to obtain high adsorption capacity biochar.

[0074] Example 2 A method for preparing biochar with high adsorption performance includes the following steps: 1) Raw material processing: Select wheat straw, crush it to a particle size of 1.5mm, and reduce the moisture content to 20% through sun-drying and baking. Then, according to the ratio of 1kg wheat straw to 20L compound alkaline solution, soak the wheat straw in a compound alkaline solution with a mass fraction of 1% potassium hydroxide and 4% sodium carbonate for 20 hours. After soaking, take it out, rinse it with deionized water until neutral, and then dry it to a moisture content of 20%. Select pig manure, crush it to a particle size of 1.0mm, and dehydrate it to reduce the moisture content to 13%. 2) Raw material mixing: Wheat straw and pig manure are mixed evenly at a mass ratio of 4:1. Then, 2% of the total mass of wheat straw and pig manure biomass binder is added and mixed evenly. Then, 3% of the total mass of wheat straw and pig manure composite catalyst is added and mixed evenly. The biomass binder is a mixture of asphalt rock and lignin at a mass ratio of 1:1, with a particle size of 3~30μm. The composite catalyst includes the following raw materials in the following mass percentages: Fe2TiO4 35%, Fe2CoO4 30%, Co3O4 20%, NiO 15%, with a particle size of 20~80nm. 3) Microwave-induced pyrolysis: The above mixed raw materials are placed in a microwave pyrolysis furnace, and a N2 and NH3 mixed gas with a volume ratio of 8:2 is introduced. The furnace pressure is controlled at 0.5MPa, and the microwave power is adjusted to 650W. The temperature is first raised to 250℃ at a heating rate of 5℃ / min and held for 30min. Then, the temperature is raised from 250℃ to 550℃ at a heating rate of 7℃ / min and held for 55min. 4) Biochar collection: After the pyrolysis reaction is completed, the biochar is naturally cooled to room temperature and collected to obtain high adsorption capacity biochar.

[0075] Example 3 A method for preparing biochar with high adsorption performance includes the following steps: 1) Raw material processing: Select rice straw, crush it to a particle size of 2.0 mm, and reduce the moisture content to 25% by sun-drying and baking. Then, according to the ratio of 1 kg rice straw to 20 L compound alkaline solution, soak the rice straw in a compound alkaline solution with a mass fraction of 2% potassium hydroxide and 5% sodium carbonate for 18 hours. After soaking, take it out, rinse it with deionized water until neutral, and then dry it to a moisture content of 25%. Select cow dung, crush it to a particle size of 1.5 mm, and dehydrate it to reduce the moisture content to 18%. 2) Raw material mixing: Mix rice straw and cow manure evenly at a mass ratio of 5:1, then add 1% of the total mass of rice straw and cow manure biomass binder and mix evenly, then add 5% of the total mass of rice straw and cow manure composite catalyst and mix evenly; wherein, the biomass binder is a mixture of asphalt rock and lignin at a mass ratio of 1:1, with a particle size of 3~30μm; the composite catalyst includes the following raw materials in the following mass percentages: Fe2TiO4 40%, Fe2CoO4 25%, Co3O4 15%, NiO 20%, with a particle size of 20~80nm; 3) Microwave-induced pyrolysis: The above mixed raw materials are placed in a microwave pyrolysis furnace, and a N2 and NH3 mixed gas with a volume ratio of 7:3 is introduced. The furnace pressure is controlled at 0.7MPa, and the microwave power is adjusted to 850W. The temperature is first raised to 300℃ at a heating rate of 7℃ / min and held for 20min. Then, the temperature is raised from 300℃ to 650℃ at a heating rate of 10℃ / min and held for 40min. 4) Biochar collection: After the pyrolysis reaction is completed, the biochar is naturally cooled to room temperature and collected to obtain high adsorption capacity biochar.

[0076] Example 4 A method for preparing biochar with high adsorption performance includes the following steps: 1) Raw material processing: Corn stalks and wheat stalks were mixed in a 1:1 mass ratio and crushed to a particle size of 1.2 mm. The moisture content was reduced to 17% by sun-drying and baking. Then, the straw mixture was soaked in a compound alkaline solution with a mass fraction of 2% potassium hydroxide and 5% sodium carbonate for 18 hours at a ratio of 1 kg straw mixture to 20 L compound alkaline solution. After soaking, the mixture was taken out, rinsed with deionized water until neutral, and then dried to a moisture content of 17%. Chicken manure and pig manure were mixed in a 1:1 mass ratio and crushed to a particle size of 0.8 mm. The moisture content was reduced to 10% by dehydration. 2) Raw material mixing: Mix the straw mixture and manure mixture at a mass ratio of 3.5:1 until homogeneous. Then add 2% of the total mass of the straw mixture and manure mixture as a biomass binder and mix until homogeneous. Finally, add 2.5% of the total mass of the straw mixture and manure mixture as a composite catalyst and mix until homogeneous. The biomass binder is a mixture of asphalt rock and lignin at a mass ratio of 1:1 with a particle size of 3~30μm. The composite catalyst includes the following raw materials in the following mass percentages: Fe2TiO4 30%, Fe2CoO4 35%, Co3O4 25%, NiO 10%, with a particle size of 20~80nm. 3) Microwave-induced pyrolysis: The above mixed raw materials are placed in a microwave pyrolysis furnace, and a N2 and NH3 mixed gas with a volume ratio of 8.5:1.5 is introduced. The furnace pressure is controlled at 0.4MPa, and the microwave power is adjusted to 600W. The temperature is first raised to 220℃ at a heating rate of 4℃ / min and held for 35min. Then, the temperature is raised from 220℃ to 480℃ at a heating rate of 6℃ / min and held for 65min. 4) Biochar collection: After the pyrolysis reaction is completed, the biochar is naturally cooled to room temperature and collected to obtain high adsorption capacity biochar.

[0077] Example 5 A method for preparing biochar with high adsorption performance includes the following steps: 1) Raw material processing: Wheat straw and rice straw were mixed at a mass ratio of 2:1 and crushed to a particle size of 1.8 mm. The moisture content was reduced to 22% by sun-drying and baking. Then, the straw mixture was soaked in a compound alkaline solution with a mass fraction of 1% potassium hydroxide and 4% sodium carbonate for 20 hours at a ratio of 1 kg straw mixture to 20 L compound alkaline solution. After soaking, the mixture was taken out, rinsed with deionized water until neutral, and then dried to a moisture content of 22%. Pig manure and cow manure were mixed at a mass ratio of 1:2 and crushed to a particle size of 1.2 mm. The moisture content was reduced to 15% by dehydration. 2) Raw material mixing: Mix the straw mixture and manure mixture at a mass ratio of 4.5:1 until homogeneous. Then add 2% of the total mass of the straw mixture and manure mixture as biomass binder and mix until homogeneous. Finally, add 4% of the total mass of the straw mixture and manure mixture as composite catalyst and mix until homogeneous. The biomass binder is a mixture of asphalt rock and lignin at a mass ratio of 1:1 with a particle size of 3~30μm. The composite catalyst includes the following raw materials in the following mass percentages: Fe2TiO4 35%, Fe2CoO4 30%, Co3O4 20%, NiO 15%, with a particle size of 20~80nm. 3) Microwave-induced pyrolysis: The above mixed raw materials are placed in a microwave pyrolysis furnace, and a N2 and NH3 mixed gas with a volume ratio of 7.5:2.5 is introduced. The furnace pressure is controlled at 0.6MPa, and the microwave power is adjusted to 800W. The temperature is first raised to 280℃ at a heating rate of 6℃ / min and held for 25min. Then, the temperature is raised from 280℃ to 620℃ at a heating rate of 8℃ / min and held for 45min. 4) Biochar collection: After the pyrolysis reaction is completed, the biochar is naturally cooled to room temperature and collected to obtain high adsorption capacity biochar.

[0078] Example 6 The only difference between Example 6 and Example 1 is that, during the corn stalk pretreatment, the mass fraction of potassium hydroxide in the compound alkaline solution is 1%, the mass fraction of sodium carbonate is 4%, and the soaking time is 12 hours.

[0079] Example 7 The only difference between Example 7 and Example 2 is that when mixing the raw materials, the amount of biomass binder added is 3% of the total mass of wheat straw and pig manure.

[0080] Example 8 The only difference between Example 8 and Example 3 is that when mixing the raw materials, the mass ratio of rice straw to cow dung is 3:1, and the amount of composite catalyst added is 3% of the total mass of rice straw and cow dung.

[0081] Example 9 The only difference between Example 9 and Example 4 is that during microwave-induced pyrolysis, the atmosphere and pressure remain unchanged, the microwave power is adjusted to 650W, the temperature is first increased to 200℃ at a heating rate of 3℃ / min and held for 40min, and then increased from 200℃ to 500℃ at a heating rate of 5℃ / min and held for 60min.

[0082] Example 10 The only difference between Example 10 and Example 5 is that the formulation of the composite catalyst is adjusted to include the following raw materials in the following mass percentages: Fe2TiO4 32%, Fe2CoO4 32%, Co3O4 20%, NiO 16%.

[0083] Comparative Example 1 Biochar prepared by conventional pyrolysis of chicken manure, purchased from a certain company, was used as a comparison.

[0084] Comparative Example 2 Biochar prepared by conventional pyrolysis of wheat straw, purchased from a certain company, was used as a comparison.

[0085] It is understood that the conventional method for preparing biochar by pyrolysis is as follows: cleaned chicken manure or wheat straw is placed in an oven at 105℃ and dried for 24 hours. After cooling, it is crushed and passed through a 0.038mm sieve to obtain powder. 20.0g of the above powder is placed in a tube furnace filled with N2 and heated to 500℃ at 5℃ / min and kept at the temperature for 2 hours. After naturally cooling to room temperature, it is ground and passed through a 100-mesh sieve to obtain conventional pyrolytic biochar.

[0086] Comparative Example 3 The only difference between Comparative Example 3 and Example 5 is that the composite catalyst is replaced with Fe2TiO4.

[0087] Comparative Example 4 The only difference between Comparative Example 4 and Example 5 is that no composite catalyst is added.

[0088] Comparative Example 5 The only difference between Comparative Example 5 and Example 5 is that the N2 and NH3 mixture is replaced with pure N2 gas.

[0089] The physicochemical properties of the biochar in each embodiment and comparative example were tested, and the results are shown in Table 1.

[0090] Table 1 Comparison of physicochemical properties characterization results of biochar

[0091] As shown in Table 1, compared to the comparative example, the BET specific surface area of ​​the examples is at a higher level, indicating more surface active sites and potentially better performance in adsorption and catalysis. The examples also have a larger total pore volume, suggesting a more developed pore structure within the biochar, which is beneficial for adsorbate storage and transport, and has better application potential in adsorption and separation processes. Furthermore, the average pore size of the examples is relatively stable and within a suitable range, which may enhance the biochar's ability to adsorb Pb. 2+ Cd 2+ Cr 3+ The examples exhibit better selectivity and efficiency in the adsorption and separation of heavy metal ions. Overall, the examples show significant performance improvements in multiple physicochemical properties compared to the comparative examples. The examples have more uniform average particle size, larger BET specific surface area and total pore volume, stable and suitable average pore size, and relatively stable pH value.

[0092] The biochar from each embodiment and comparative example was applied to treat wastewater containing heavy metals. The specific application steps were as follows: 0.1 g of biochar was weighed into a 150 mL Erlenmeyer flask, and 100 mL of simulated wastewater (simulated wastewater with Pb content...) was added. 2+ Cd 2+ Cr 3+ All concentrations were 50 mg / L. The pH of the solution was adjusted to 5.0 with nitric acid or sodium hydroxide solution. The conical flask was placed in a constant temperature shaking incubator and shaken at 25℃ and 150 r / min for 24 h to allow adsorption to reach equilibrium. After shaking, the supernatant was collected by centrifugation and the remaining Pb was determined using inductively coupled plasma mass spectrometry (ICP-MS). 2+ Cd 2+ Cr 3+ The concentration of heavy metals was used to calculate the adsorption capacity of biochar for heavy metals. Q e (mg / g), the results are shown in Table 2.

[0093] Table 2. Effects of biochar on heavy metal ions (Pb) in simulated wastewater 2+ Cd 2+ Cr 3+ Adsorption capacity comparison

[0094] As shown in Table 2, the biochar prepared in the embodiments of the present invention has a positive effect on the heavy metal ion Pb in simulated wastewater. 2+ Cd 2+ Cr 3+ The adsorption capacity of the biochar in Comparative Examples 1 and 2 was significantly higher than that in the comparative examples. The biochar prepared by conventional pyrolysis in Comparative Examples 1 and 2 showed adsorption capacities far lower than those in the embodiments of this invention and other comparative examples, fully demonstrating the significant effects of the two-stage microwave-induced pyrolysis process of this invention. Parameters such as heating rate, pyrolysis temperature, atmosphere, and pressure all affect the performance of biochar. Different heating rates and pyrolysis temperatures affect the pore structure and surface properties of biochar. Higher pyrolysis temperatures may make the pores of biochar more developed, but may also destroy some surface functional groups. Different ratios of N2 / NH3 mixed gas also affect the properties of biochar. Comparative Example 5, which introduced pure N2 gas, showed a different adsorption capacity compared to the examples introduced with mixed gas, indicating that the presence of NH3 may have participated in the surface modification of biochar during pyrolysis, increasing the adsorption active sites for heavy metals. The pressure during pyrolysis also affects the structure of biochar. Different pressure conditions may lead to different pore sizes and distributions in biochar, thus affecting its adsorption capacity for heavy metals. Comparative Example 3, which used only Fe2TiO4 as a catalyst, showed a significantly lower adsorption capacity than the example using the composite catalyst. Comparative Example 4, which did not add any catalyst, showed an even greater reduction in adsorption capacity. This indicates that a composite catalyst with appropriate content and ratio can significantly improve the adsorption capacity of biochar for heavy metals.

[0095] Example 1 of recycling The used high-adsorption-performance biochar (Example 8) was subjected to five regeneration and cyclic adsorption experiments. The regeneration steps were as follows: First, the used high-adsorption-performance biochar was rinsed with deionized water for 8 minutes each time, and rinsed three times to remove surface impurities and unadsorbed heavy metal ions. Second, a desorption solution was prepared by mixing 0.5 mol / L nitric acid solution and 0.05 mol / L ethylenediaminetetraacetic acid solution at a volume ratio of 3:1. The biochar and desorption solution were mixed at a solid-liquid ratio of 1 g:30 mL and stirred at 200 rpm for 5 hours at 30°C. After one desorption cycle, the biochar was filtered and separated, and new desorption solution was added for the next desorption cycle, for a total of two desorption operations. After desorption was completed, the biochar was repeatedly rinsed with deionized water until the pH of the rinsing solution was close to neutral to remove residual desorption solution and heavy metal ions. Finally, the washed biochar was dried at 80°C to constant weight to obtain the regenerated high-adsorption-performance biochar. Figure 1 It can be observed that after five cycles of adsorption experiments, the high-adsorption-performance biochar effectively reduced the adsorption of heavy metal ions (Pb) in the simulated wastewater. 2+ Cd 2+Cr 3+ The adsorption capacity remains at a very high level, with its adsorption performance decreasing by only about 1%.

[0096] Example 2 of recycling The composite catalyst was recovered from the used high-adsorption-performance biochar (Example 8). The specific steps were as follows: the used high-adsorption-performance biochar was washed, desorbed, and washed twice according to the steps of recycling Example 1. Then, it was calcined in air at 700°C for 1.5 hours at a rate of 8°C / min. After the temperature inside the furnace cooled to less than 80°C, the calcined product was taken out. The calcined product was thoroughly ground and deagglomerated to a particle size of <200µm. Then, it was air-classified in a fume hood using a vertical air-classifying column with an inner diameter of 50mm and a height of 1.0m. The bottom of the air-classifying column was pressurized with air intake, and the top was connected to a cyclone separator and a filter bag. The apparent upward air velocity was set to 1.5m / s, and the feed was uniformly fed at a feed rate of 10g / min. The light gray powder collected at the top was biomass ash, and the dark dense powder collected at the bottom was the target product. This product is the regenerated composite catalyst, which can be used again to prepare high-adsorption-performance biochar.

[0097] Example 3 of recycling The specific steps for recovering the components of the composite catalyst from the used high-adsorption-performance biochar (Example 8) are as follows: 1) Following the steps of recycling example 2, the used high-adsorption biochar was subjected to a first washing, desorption, a second washing, calcination, grinding, and air separation to obtain a dark-colored dense powder collected at the bottom. By applying an external magnetic field of about 1.0T, a mixture containing Fe2TiO4 and Fe2CoO4 was magnetically separated from the dark-colored dense powder. The mixture was mixed with 0.5 mol / L dilute sulfuric acid solution at a ratio of 1 g: 80 mL, stirred at 65 °C for 90 min, and filtered. The filter residue was washed and dried to obtain Fe2TiO4. Excess H2O2 solution was added to the filtrate to oxidize ferrous ions to ferric ions. Then, the pH was adjusted to 4.0 ± 0.1 with NaOH solution. After aging for 20 min, the Fe(OH)3 / FeOOH / basic ferric sulfate precipitate was removed by filtration. Then, 1.0 mol / L sodium carbonate solution was added dropwise to the remaining filtrate until no more precipitate was formed. The precipitate was collected, washed, dried, and calcined at 450 °C for 2 h to obtain Co3O4. 2) The residue after magnetic separation of the dark dense powder was mixed with 1.0 mol / L dilute sulfuric acid solution at a ratio of 1 g: 80 mL. The mixture was stirred at 70 °C for 150 min. Then, ammonia was added to adjust the pH to 8.5 ± 0.1. The precipitate was collected, washed, dried, and calcined at 450 °C for 2 h to obtain Co3O4. 1.0 mol / L sodium carbonate solution was added dropwise to the remaining solution until no more precipitate was formed. The precipitate was collected, washed, dried, and calcined at 450 °C for 2 h to obtain NiO.

[0098] The above embodiments are merely examples for clear illustration and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations, and any obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A method for preparing biochar with high adsorption performance, characterized in that, Includes the following steps: S1, mix agricultural straw and livestock manure evenly to obtain mixture A; S2, add biomass binder and composite catalyst to mixture A in sequence and mix evenly to obtain mixture B; S3 uses a mixture of N2 and NH3 as the pyrolysis atmosphere to perform two-stage microwave-induced pyrolysis on mixture B. The first stage pyrolysis temperature is 200~300℃ and the pyrolysis time is 20~40min. The second stage pyrolysis temperature is 450~650℃ and the pyrolysis time is 40~70min, resulting in biochar with high adsorption performance.

2. The method for preparing high-adsorption biochar according to claim 1, characterized in that, The microwave power of the two-stage microwave-induced pyrolysis is 550~850W, the pyrolysis pressure is 0.3~0.7MPa, the heating rate to the first stage pyrolysis temperature is 3~7℃ / min, the heating rate to the second stage pyrolysis temperature is 5~10℃ / min, and the volume ratio of N2 to NH3 in the pyrolysis atmosphere is 9:1~7:

3.

3. The method for preparing high-adsorption biochar according to claim 1, characterized in that, The agricultural straw is one or more of corn straw, wheat straw, and rice straw, with a particle size of 1.0~2.0mm and a moisture content of 15%~25%; the livestock and poultry manure is one or more of chicken manure, pig manure, and cow manure, with a particle size of 0.5~1.5mm and a moisture content of 8%~18%; the mass ratio of the agricultural straw to the livestock and poultry manure is (3~5):

1.

4. The method for preparing high-adsorption biochar according to claim 1, characterized in that, The agricultural straw undergoes alkaline pretreatment before use, the steps of which include: soaking the agricultural straw in a compound alkaline solution of potassium hydroxide and sodium carbonate for 12-24 hours, then taking it out, washing it, and drying it; the mass fraction of potassium hydroxide in the compound alkaline solution is 1%-3%, and the mass fraction of sodium carbonate is 4%-6%.

5. The method for preparing high-adsorption biochar according to claim 1, characterized in that, The biomass binder is composed of asphalt rock and lignin in a mass ratio of (1~2):1, with a particle size of 3~30μm, and is added at 1%~3% of the mass of mixture A; the composite catalyst includes the following raw materials in the following mass percentages: Fe2TiO4 30%~40%, Fe2CoO4 25%~35%, Co3O4 15%~25%, NiO 10%~20%, with a particle size of 20~80nm, and is added at 2%~5% of the mass of mixture A.

6. A high-adsorption-performance biochar prepared by the method according to any one of claims 1 to 5, characterized in that, The high-adsorption biochar has a particle size of 100-200 μm and a specific surface area of ​​900-950 m². 2 / g, total pore volume is 0.7~0.8cm³ 2 / g, with an average pore size of 2.6~3.0nm and a pH value of 9.7~10.

3.

7. The application of the high-adsorption-performance biochar as described in claim 6 in the treatment of heavy metal-containing wastewater, characterized in that, The application method is as follows: add high-adsorption biochar to wastewater, adjust the pH to 4.5~5.5, and then adsorb heavy metal ions in the wastewater under stirring or shaking conditions.

8. The application of the high-adsorption biochar according to claim 7 in the treatment of heavy metal-containing wastewater, characterized in that, The high-adsorption biochar is added at a rate of 0.05-0.15% of the wastewater mass, the adsorption temperature is 20-30℃, and the adsorption time is 15-30 hours; the heavy metal ions in the wastewater include Pb. 2+ Cd 2+ Cr 3+ One or more of them.

9. A method for recycling high-adsorption biochar as described in claim 6, characterized in that, Includes the following steps: After the used high-adsorption biochar is washed once, desorbed, and washed twice, it is dried to obtain regenerated high-adsorption biochar. The desorption solution is composed of 0.1~1.0 mol / L nitric acid solution and 0.01~0.1 mol / L ethylenediaminetetraacetic acid solution in a volume ratio of (1~5):

1.

10. A method for recycling high-adsorption biochar as described in claim 6, characterized in that, Includes the following steps: After the high-adsorption biochar was washed, desorbed and washed again, it was calcined at 650~750℃. The calcined product was ground and depolymerized, and the biomass ash was removed by air classification to obtain the regenerated composite catalyst. The roasting temperature is 650~750℃, and the roasting time is 1~2h.

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