A magnetic biochar, its preparation method and application, and a preparation method of an organic fertilizer

Abstract

The present invention belongs to the technical field of adsorption materials, and specifically relates to a magnetic biochar and its preparation method and application, as well as a preparation method of organic fertilizer. The present invention provides a preparation method of magnetic biochar, which comprises the following steps: mixing farmland sludge and plant residues, and performing carbonization to obtain sludge biochar; mixing the sludge biochar, an activator and water, and performing soaking to obtain an activated biochar system; mixing iron salt, an alkaline reagent and water, and sequentially performing precipitation reaction and dehydration to obtain magnetic particles; mixing the magnetic particles, a surfactant and water, and performing modification under an alkaline environment to obtain modified magnetic particles; mixing the modified magnetic particles, a complexing agent and water to obtain a magnetization agent; mixing the activated biochar system and the magnetization agent, and performing magnetization to obtain the magnetic biochar. The magnetic biochar obtained by the method provided by the present invention has good adsorption effects on harmful substances such as bisphenol A, antibiotics, and heavy metals.

Description

Technical Field

[0001] The present invention belongs to the technical field of adsorption materials, and specifically relates to a magnetic biochar, a preparation method and application thereof, and a preparation method of an organic fertilizer. Background Art

[0002] Agricultural waste composting is an economical, effective and environmentally friendly technical means, which can effectively solve the prominent contradictions such as the large amount of agricultural waste and the difficulty in utilization. However, the compost pile often contains harmful substances such as endocrine disruptors (EDCs), antibiotics, heavy metals, pesticides, microplastics, etc. When the compost is applied to the soil again, it will have an adverse impact on plants and the soil. Bisphenol A (BPA) is a typical EDC. According to relevant biological and toxicological studies, BPA entering the environment will have an adverse impact on human health. If there is a suitable method to remove it, the safety of applying compost to the soil can be improved, and the high-quality development of agriculture can be promoted. In view of this problem, at present, there are a large number of studies on technical processes such as pretreatment before composting, compost additives and secondary fermentation. Biochar is one of the hot topics.

[0003] The raw materials of biochar (Biochar, BC) are relatively wide, such as solid wastes such as dead branches and leaves, rice straw and other agricultural and forestry wastes, livestock and poultry breeding wastes, sludge, domestic garbage, etc. Its main components are lignin, cellulose, hemicellulose and mineral elements. BC shows a certain adsorption effect on endocrine disruptors due to its characteristics such as rich carbon content, relatively high specific surface area and developed pore structure, but its adsorption effect is limited, and it is difficult to separate endocrine disruptors. Summary of the Invention

[0004] The purpose of the present invention is to provide a preparation method of magnetic biochar. The magnetic biochar (MBC) obtained by the method provided by the present invention has good adsorption and separation effects on endocrine disruptors in compost.

[0005] In order to achieve the above purpose, the present invention provides the following technical solutions:

[0006] The present invention provides a preparation method of magnetic biochar, comprising the following steps:

[0007] Mix farmland sludge and plant residues, and perform carbonization to obtain sludge biochar (SBC);

[0008] Mix the sludge biochar, an activator and water, and perform soaking to obtain an activated biochar system;

[0009] Mix an iron salt, an alkaline reagent and water, and perform a precipitation reaction and dehydration in sequence to obtain magnetic particles;

[0010] Mix the magnetic particles, surfactant and water, and perform modification under an alkaline environment to obtain modified magnetic particles;

[0011] Mix the modified magnetic particles, complexing agent and water to obtain a magnetizing agent;

[0012] Mix the activated biochar system and the magnetizing agent, and perform magnetization to obtain the magnetic biochar.

[0013] Preferably, the farmland sludge is fruit and vegetable plant farmland sludge; the water content of the farmland sludge is 60 - 80%; the plant residues are fruit and vegetable plant residues; the mass ratio of the farmland sludge to the plant residues is 1 - 6:2 - 8;

[0014] The temperature of carbonization is 300 - 600 °C, and the time is 2 - 8 h.

[0015] Preferably, the activator is 5,5 - dimethyl - 1 - pyrroline - N - oxide; the mass ratio of the sludge biochar to the activator is 10 - 50:1;

[0016] The soaking time is 2 - 3 h.

[0017] Preferably, the iron salts include divalent iron salts and trivalent iron salts; the divalent iron salts include one or more of ferrous sulfate, ferrous nitrate and ferrous chloride; the trivalent iron salts include ferric chloride and / or polyferric chloride; the alkaline reagents include one or more of ammonia water, calcium hydroxide and sodium carbonate;

[0018] The time of the precipitation reaction is 1 - 6 h; the dehydration is heating dehydration; the temperature of the heating dehydration is 60 - 80 °C, and the time is 20 - 40 min.

[0019] Preferably, the surfactant includes anionic surfactant and / or cationic surfactant; the mass ratio of the magnetic particles to the surfactant is 150:0.1 - 0.8;

[0020] The pH value of the alkaline environment is 7 - 8; the temperature of the modification is 90 - 100 °C, and the time is 40 - 50 min.

[0021] Preferably, the complexing agent includes one or more of sodium isobutyl tripolyphosphate, ethylenediaminetetraacetic acid, citric acid and tartaric acid; the mass ratio of the modified magnetic particles to the complexing agent is 100:0.5 - 1.

[0022] Preferably, the mass ratio of the sludge biochar in the activated biochar system to the modified magnetic particles in the magnetizing agent is 5 - 10:1;

[0023] The temperature of the magnetization is 80 - 90 °C, and the time is 2 - 3 h.

[0024] The present invention also provides the magnetic biochar obtained by the preparation method described in the above technical solution. The particle size of the magnetic biochar is 74-150 μm, and the specific surface area is 215.25-305.1 m 2 ·g - ⁻¹.

[0025] The present invention also provides the application of the magnetic biochar described in the above technical solution in the preparation of fertilizers.

[0026] The present invention also provides a preparation method of an organic fertilizer, comprising the following steps:

[0027] Mixing compost raw materials and magnetic biochar, and performing composting to obtain the organic fertilizer; the magnetic biochar is the magnetic biochar described in the above technical solution.

[0028] The present invention provides a preparation method of magnetic biochar, comprising the following steps: mixing farmland sludge and plant residues, and performing carbonization to obtain sludge biochar; mixing the sludge biochar, an activator and water, and performing soaking to obtain an activated biochar system; mixing iron salt, an alkaline reagent and water, and performing precipitation reaction and dehydration in sequence to obtain magnetic particles; mixing the magnetic particles, a surfactant and water, and performing modification under an alkaline environment to obtain modified magnetic particles; mixing the modified magnetic particles, a complexing agent and water to obtain a magnetizing agent; mixing the activated biochar system and the magnetizing agent, and performing magnetization to obtain the magnetic biochar. In the present invention, plant residues are added to farmland sludge as raw materials, so that the obtained biochar has more abundant oxygen-containing functional groups on the surface, a more developed pore structure and a larger specific surface area, significantly improving the adsorption performance. The prepared magnetic biochar mainly adsorbs BPA and inorganic substances such as phosphate, nitrate nitrogen, and fluorine in fertilizers through pore filling, hydrogen bonding, hydrophobic interaction and electrostatic interaction. When the pH value is small, the Fe-OH + ₂ sites on the surface can also electrostatically adsorb NO₃ - and F - . Moreover, the magnetic biochar has strong magnetism, enabling it to be separated from the compost product by means of an external magnetic device after adsorbing harmful substances such as BPA, avoiding adverse effects on the soil and the environment. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the embodiments. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0030] Figure 1 Schematic flow chart of the application of the magnetic biochar obtained in Examples 1 to 3 to the return of organic fertilizers to the field;

[0031] Figure 2 Test data graph of the adsorption capacity of the magnetic biochar obtained in Example 2 for bisphenol A. Detailed implementation manners

[0032] The present invention provides a method for preparing magnetic biochar, comprising the following steps:

[0033] Mix farmland sludge and plant residues, and perform carbonization to obtain sludge biochar;

[0034] Mix the sludge biochar, an activator and water, and perform soaking to obtain an activated biochar system;

[0035] Mix an iron salt, an alkaline reagent and water, and successively perform a precipitation reaction and dehydration to obtain magnetic particles;

[0036] Mix the magnetic particles, a surfactant and water, and perform modification in an alkaline environment to obtain modified magnetic particles;

[0037] Mix the modified magnetic particles, a complexing agent and water to obtain a magnetizing agent;

[0038] Mix the activated biochar system and the magnetizing agent, and perform magnetization to obtain the magnetic biochar.

[0039] In the present invention, unless otherwise specified, all raw material components are commercially available products well-known to those skilled in the art, and all raw materials are of analytical purity.

[0040] The present invention mixes farmland sludge and plant residues, and performs carbonization to obtain sludge biochar.

[0041] In the present invention, the farmland sludge is the farmland sludge of fruit and vegetable plants; the farmland sludge of fruit and vegetable plants is the farmland sludge of vine fruit and vegetable plants, the water content of the farmland sludge can be 60-80%, and can also be 65-75%; the plant residues are the residues of fruit and vegetable plants, and in specific embodiments, can be watermelon vines, tomato vines, eggplant seedlings or bean seedlings; the mass ratio of the farmland sludge to the plant residues is 1-6:1-8, and in specific embodiments, can be 1:1 or 2:1.

[0042] In the present invention, before carbonization, it further includes drying, grinding, and sieving the mixture of farmland sludge and plant residues in sequence; the drying includes natural drying and drying in sequence; the time of natural drying is 32 - 48 h, and in a specific embodiment, it can be 40 h; the temperature of drying is 60 - 80 °C, and in a specific embodiment, it can be 60 °C, 65 °C, 70 °C, 75 °C, or 80 °C; the time is 12 - 20 h, and in a specific embodiment, it can be 12 h, 15 h, 16 h, 18 h, or 20 h; the present invention has no special limitation on the grinding process, and it can be carried out in a manner well-known to those skilled in the art; the mesh number of the sieve for sieving is 100 - 120 meshes; the temperature of carbonization is 300 - 600 °C, and in a specific embodiment, it can be 400 °C or 500 °C; the time is 2 - 8 h, and in a specific embodiment, it can be 4 h or 6 h; after carbonization, it further includes grinding and sieving the carbonized product in sequence; the present invention has no special limitation on the grinding process, and it can be carried out in a manner well-known to those skilled in the art; the mesh number of the sieve for sieving is 100 - 120 meshes.

[0043] In the present invention, farmland sludge and plant residues are rich in organic matter, cellulose, lignin, and various nutrient elements, and these components can be converted into biochar with a high specific surface area and a rich pore structure during the pyrolysis process. The sources of farmland sludge and plant residues are extensive and the cost is low. Utilizing them to prepare biochar can achieve the resource utilization of waste and reduce environmental pollution.

[0044] After obtaining the sludge biochar, in the present invention, the sludge biochar, an activator, and water are mixed and soaked to obtain an activated biochar system.

[0045] In the present invention, the mixing may include the following steps:

[0046] Dissolve the activator in water to obtain an activator solution;

[0047] Mix the sludge biochar and the activator solution for the first time.

[0048] In the present invention, the activator is 5,5 - dimethyl - 1 - pyrroline - N - oxide; the mass ratio of the sludge biochar to the activator is 10 - 50:1, and in a specific embodiment, it can be 20 - 30:1; the mass ratio of the sludge biochar to water is 1 - 1.5:10, and in a specific embodiment, it can be 1:7. The present invention has no special limitation on the molar concentration of the activator solution, as long as the dosage ratio of the sludge biochar, the activator, and water is satisfied.

[0049] In the present invention, the soaking time is 2 - 3 h. In the present invention, under the action of the activator, the surface active sites of the sludge biochar increase, and these active sites can undergo redox reactions with BPA, further improving its catalytic performance and promoting the degradation process of BPA.

[0050] In the present invention, after the soaking, it further includes adjusting the pH value of the system to 6 - 8. In specific embodiments, it can be 6, 6.5, 7, 7.2, 7.5 or 8. The present invention has no special requirements for the method of adjusting the pH value of the system, as long as the required pH value can be achieved.

[0051] The present invention mixes iron salts, alkaline reagents and water, and successively carries out precipitation reaction and dehydration to obtain magnetic particles.

[0052] In the present invention, the iron salts include divalent iron salts and trivalent iron salts; the divalent iron salts include one or more of ferrous sulfate, ferrous nitrate and ferrous chloride. In specific embodiments, it can be ferrous sulfate heptahydrate; the trivalent iron salts include ferric chloride and / or polyferric chloride. In specific embodiments, it can be ferric chloride hexahydrate; the mass ratio of the iron salts to the volume of water is 6 - 10.8 g:10 mL. In specific embodiments, it can be 7 - 9 g:10 mL, or can also be 8 g:10 mL; the mass ratio of the divalent iron salts to the trivalent iron salts is 2 - 4:3 - 5. In specific embodiments, it can be 3:4; the alkaline reagents include one or more of ammonia water, calcium hydroxide and sodium carbonate; the mass percentage content of ammonia in the ammonia water is 50 - 60%. In specific embodiments, it can be 56%; the volume ratio of the alkaline reagents to water is 1:1 - 3. In specific embodiments, it can be 1:2. In the present invention, the iron salts mainly participate in the oxidation reaction of catalyzing BPA to promote its degradation. The divalent iron salts mainly participate in the reduction reaction and precipitation reaction, while the trivalent iron salts participate in the oxidation reaction and hydrolysis reaction; under the combined action of the divalent iron salts and the trivalent iron salts, magnetic iron tetroxide is generated.

[0053] In the present invention, the time of the precipitation reaction is 1 - 6 h. In specific embodiments, it can be 2 h; after the precipitation reaction, it further includes solid-liquid separation; the dehydration is heating dehydration; the temperature of the heating dehydration is 60 - 80 °C. In specific embodiments, it can be 70 °C; the time is 20 - 40 min. In specific embodiments, it can be 30 min; after the dehydration, it further includes collection and washing; the collection is by magnet collection. In the present invention, the function of the washing is to wash away the remaining iron salts.

[0054] After obtaining the magnetic particles, the present invention mixes the magnetic particles, surfactant and water, and carries out modification under an alkaline environment to obtain modified magnetic particles.

[0055] In the present invention, the surfactant includes an anionic surfactant and / or a cationic surfactant; the anionic surfactant includes sodium dodecyl sulfate and / or sodium dodecylbenzenesulfonate; the cationic surfactant includes cetyltrimethylammonium bromide; in a specific embodiment, the surfactant may be sodium dodecyl sulfate; the mass ratio of the magnetic particles to the surfactant is 150:0.1 to 0.8, and in a specific embodiment, it may be 150:0.1, 150:0.2, 150:0.3, 150:0.4, 150:0.5, 150:0.6, 150:0.7 or 150:0.8. In the present invention, the surfactant plays the role of a surfactant during the degradation process of BPA, promoting the dispersion and dissolution of biochar. The mass ratio of the magnetic particles to water is 14 to 16:1, and in a specific embodiment, it may be 15:1.

[0056] In the present invention, the pH value of the alkaline environment is 7 to 8; the reagent providing the alkaline environment is a sodium hydroxide solution; the modification temperature is 90 to 100 °C, and the time is 40 to 50 min; after the modification, it further includes adjusting the pH value and collecting; the pH value for adjusting the pH is 6.5 to 7.5, and in a specific embodiment, it may be 7; the collection is by magnet. In the present invention, during the modification process, the surfactant is fully adsorbed on the surface of the above magnetic particles.

[0057] After obtaining the modified magnetic particles, the present invention mixes the modified magnetic particles, a complexing agent and water to obtain a magnetizing agent.

[0058] In the present invention, the complexing agent includes one or more of sodium tripolyphosphate, ethylenediaminetetraacetic acid, citric acid and tartaric acid, and in a specific embodiment, it may be sodium tripolyphosphate; the mass ratio of the modified magnetic particles to the complexing agent may be 100:0.5 to 1, and in a specific embodiment, it may be 100:0.5, 100:0.75 or 100:1. In the present invention, the role of the complexing agent is to participate in the degradation reaction of BPA. The mass ratio of the modified magnetic particles to water is 9 to 11:1, and in a specific embodiment, it may be 10:1.

[0059] In the present invention, before the mixing, it further includes washing the modified magnetic particles; the washing is by water washing; the number of washing times is 3 to 5 times; the mixing includes stirring and ultrasonic treatment in sequence; the ultrasonic treatment time is 10 to 20 min, and in a specific embodiment, it may be 15 min.

[0060] After obtaining the activated biochar system and the magnetizing agent, the present invention mixes the activated biochar system and the magnetizing agent and performs magnetization to obtain the magnetic biochar.

[0061] In the present invention, the mass ratio of the sludge biochar to the modified magnetic particles in the magnetic agent in the activated biochar system is 5 to 10:1. In specific embodiments, it can be 5:1, 6:1, 7:1, 8:1, 9:1, or 10:1.

[0062] In the present invention, the magnetization temperature is 80 to 90 °C, and the time is 2 to 3 h; the magnetization is carried out under stirring conditions; after magnetization, solid-liquid separation, washing, and drying are also included. In the present invention, the function of the washing is to wash away the remaining activator and magnetic agent on the magnetic biochar. The drying is drying by baking; the temperature of the baking is 90 to 105 °C.

[0063] In the present invention, plant residues are added to the farmland sludge as raw materials, so that the obtained biochar has richer oxygen-containing functional groups on the surface, a more developed pore structure, and a larger specific surface area, significantly improving the adsorption performance. The obtained magnetic biochar mainly adsorbs BPA, as well as inorganic substances such as phosphate, nitrate nitrogen, and fluorine in fertilizers through pore filling, hydrogen bonding, hydrophobic interaction, and electrostatic interaction. When the pH value is small, the Fe-O + H2 sites can also electrostatically adsorb NO3 - and F - . Moreover, the magnetic biochar has strong magnetism, enabling it to be separated from the compost product by means of an external magnetic device after adsorbing harmful substances such as BPA, avoiding adverse effects on the soil and the environment.

[0064] The present invention also provides the magnetic biochar obtained by the preparation method described in the above technical solution. The average particle size of the magnetic biochar is 74 to 150 μm, and it can be 96 to 130 μm; the specific surface area of the magnetic biochar is 215.25 to 305.1 m 2 ·g - −1, and it can be 260 to 280 m 2 ·g - −1.

[0065] The magnetic biochar provided by the present invention has strong adsorption ability for bisphenol A due to the rich functional groups and pore structure on its surface, but is not limited to adsorbing bisphenol A, and can also adsorb common organic pollutants and inorganic pollutants, such as phenol, heavy metal ions, nitrogen oxides, and phosphates.

[0066] The present invention also provides the application of the magnetic biochar described in the above technical solution in the preparation of fertilizers. As a specific embodiment of the present invention, the magnetic biochar can be used as an adsorption material in the process of fertilizer preparation to adsorb endocrine disruptors and degrade them, thereby improving the safety of compost; the fertilizer can be an organic fertilizer, and the organic fertilizer can be organic compost.

[0067] The present invention also provides a method for preparing an organic fertilizer, comprising the following steps:

[0068] Mix the compost raw materials and magnetic biochar, and perform composting to obtain the organic fertilizer; the magnetic biochar is the magnetic biochar described in the above technical solution.

[0069] In the present invention, the mass ratio of the magnetic biochar to the compost raw materials is 3-9:100, and can also be 5-8.5:100.

[0070] In the present invention, the composting includes a heating period, a high-temperature period, and a cooling period in sequence; the temperature of the heating period is 20-50 °C, and the time is 2-4 d; the temperature of the high-temperature period is 50-70 °C, and the time is 7-8 d; the temperature of the cooling period is 20-50 °C, and the time is 10-12 d; the composting process also includes photocatalysis. In the present invention, the complexation between BPA and magnetic biochar is affected by temperature, pressure, and solvent. The higher the temperature, the higher the efficiency of magnetic biochar in degrading BPA. Photocatalysis can be used to promote the degradation of BPA by magnetic biochar. Through photocatalysis, using the photosensitive active substances on the surface of magnetic biochar, reactive oxygen species are generated under the condition of light irradiation, thereby degrading BPA. After the composting, it also includes oxidation treatment and / or photocatalytic degradation. In the present invention, the role of oxidation treatment and photocatalytic degradation is to convert substances such as phenol, phenolic aldehyde, and phenolic acid into harmless products.

[0071] The present invention applies magnetic biochar to the organic fertilizer, achieving the effect of effectively adsorbing bisphenol A and other impurities, which is beneficial to screening out bisphenol A, antibiotics, heavy metals and other substances from the compost sample, improving the quality of the fertilizer. And it is also beneficial to the recycling of waste. Adding magnetic biochar to the compost will increase the porosity of the added material, and the activities of catalase, dehydrogenase, pH value, and organic matter in the material will all increase. It can be seen that magnetic biochar can also regulate the composting process, reduce nitrogen loss, increase the carbon content of the compost product, and enrich the role of biochar in the composting process.

[0072] Specifically, magnetic biochar has a rich pore structure. BPA molecules can enter the pores through physical adsorption and interact with the pore walls. The hydroxyl groups on the surface of magnetic biochar can serve as active sites to promote the process of electron transfer and can form hydrogen bonds with the hydroxyl groups in BPA to form hydrogen-bonded compounds. This hydrogen-bonding interaction can enhance the interaction force between magnetic biochar and BPA, which is beneficial to the adsorption process. The surface of magnetic biochar is usually rich in hydrophobic groups, and BPA is a hydrophobic substance. The hydrophobic interaction makes BPA molecules more likely to be adsorbed on the surface of magnetic biochar, thus achieving effective adsorption. The hydroxyl and carboxyl groups on the surface of magnetic biochar carry positive and negative charges, and electrostatic interactions occur with the corresponding groups in BPA during the adsorption process, which can help enhance the adsorption effect on BPA.

[0073] The hydroxyl and carboxyl groups on the surface of magnetic biochar can form hydrogen bonds or electrostatic interactions with phosphate ions, thereby adsorbing phosphates. The pore structure of magnetic biochar is also conducive to the adsorption of phosphates. Through physical adsorption, phosphates are fixed on the surface of biochar. The nitrogen-containing functional groups on the surface of magnetic biochar can form hydrogen bonds with nitrate nitrogen to achieve the adsorption of nitrate nitrogen. The fluorine-containing functional groups on the surface of magnetic carbon can form hydrogen bonds or electrostatic interactions with fluorides to achieve the adsorption of fluorine. The pore structure and large surface area of magnetic biochar are also conducive to the adsorption of fluoride ions, improving the adsorption efficiency.

[0074] To further illustrate the present invention, the following will describe in detail a magnetic biochar and its preparation method and application, and the preparation method of organic fertilizer provided by the present invention with reference to the accompanying drawings and embodiments, but they should not be construed as limiting the protection scope of the present invention.

[0075] Example 1

[0076] Take 300 g of sludge from the watermelon planting land in the Shunyi base of Beijing (including 200 g of farmland sludge with a water content of 70% and 100 g of watermelon vines). After naturally air-drying the sludge for 48 h, dry it in a drying oven at 60 °C for 12 h. Grind the dried sludge into fine powder, sieve the fine powder of sludge through a 100-mesh sieve, and then put the sieved fine powder of sludge into a box-type resistance furnace and pyrolytically carbonize the fine powder of sludge at 300 °C for 2 h. After cooling the crude product of carbonized sludge biochar to room temperature, grind it and sieve it through a 100-mesh sieve to obtain sludge biochar (SBC), and store it in a sample bottle for later use.

[0077] Dissolve 3.6 g of FeSO4·7H2O and 4.8 g of FeCl3·6H2O in 10 mL of water, then add 5 mL of 56% ammonia water solution, and stir rapidly for 2 h to produce precipitation. After separating the generated precipitate from water, heat it to 80 °C for 20 min, collect the magnetic particles by wrapping a nylon cloth around a magnet, and then rinse off the remaining salts with running water to obtain magnetic particles.

[0078] Mix 150 g of the obtained magnetic particles with 10 mL of water, add 0.6 g of sodium dodecyl sulfate and 5 drops of sodium hydroxide solution to make the pH value 7.5, heat to 90 °C and react for 50 min to allow sodium dodecyl sulfate to be fully adsorbed on the surface of the magnetic particles. After the reaction is completed, add hydrochloric acid, and the pH value of the mixed solution drops from 7.5 to 7.0. Then use a magnet wrapped with a nylon cloth to collect the modified magnetic particles, and discard the remaining liquid.

[0079] Wash the collected modified magnetic particles 4 times with water. Take 100 g and put it into a container, add 0.75 g of isobutyl tripolyphosphate and 9.25 g of distilled water, stir and mix, and perform ultrasonic treatment for 10 min to prepare a magnetizer.

[0080] Soak 50 g of sludge biochar in 200 mL of a 5,5-dimethyl-1-pyrroline-N-oxide solution with a molar concentration of 0.1 mol / L for 2 h, and adjust the pH value to 7.2 to obtain an activated biochar system;

[0081] Add 10 g of the magnetizer to the activated biochar system, then heat up to 85 °C and stir for 2.5 h, and then separate the crude magnetic biochar. Rinse the remaining 5,5-dimethyl-1-pyrroline-N-oxide and magnetizer on the crude magnetic biochar with running water, and then put it into a drying oven at 100 °C to dry to obtain the finished magnetic biochar.

[0082] In the present invention, the average particle size of the finally obtained magnetic biochar is 96 μm, and the specific surface area is 265.25 m² / g. These parameters indicate that through the modification treatment, the specific surface area of the biochar has increased significantly, which helps to improve its adsorption performance.

[0083] Example 2

[0084] Prepare magnetic biochar according to the technical solution described in Example 1, with the only difference being that the dosage of FeSO4·7H2O is 2.4 g and the dosage of FeCl3·6H2O is 3.6 g.

[0085] Example 3

[0086] Prepare magnetic biochar according to the technical solution described in Example 1, except that the dosage of FeSO4·7H2O is 4.8 g and the dosage of FeCl3·6H2O is 6 g.

[0087] Application Example 1

[0088] Figure 1 It is a schematic flow chart of applying the magnetic biochar obtained in Examples 1 to 3 to the return of organic fertilizers to the field. The specific process includes: using compost materials as the test raw materials, incorporating magnetic biochar (the mass ratio of compost materials to magnetic biochar is 100:3 - 7). BPA molecules are first adsorbed on the surface of magnetic biochar through physical adsorption, and BPA temporarily stays on the surface of magnetic biochar. Then, it undergoes a chemical reaction with the active sites on the surface of magnetic biochar to form chemical bonds. Chemical adsorption involves interactions such as hydrogen bonding and π-π stacking. On the basis of chemical adsorption, BPA molecules undergo a complexation reaction with the functional groups on the surface of magnetic activated carbon, in which chemical bonds are formed between some structures of BPA and the functional groups on the surface of activated carbon. After magnetic biochar degrades BPA through chemical adsorption, organic substances such as phenol, phenolic compounds, and phenolic acids are produced. First, use analytical methods such as gas chromatography-mass spectrometry to identify and quantitatively analyze the degradation products, determine the types and concentrations of the main degradation products, use oxidation treatment to convert organic oxides such as phenol into harmless products, use photocatalytic degradation to degrade organic substances such as phenolic acids under light conditions and convert them into harmless substances. After the treatment is completed, use an external magnetic field to separate the magnetic biochar from it, and use an analytical instrument to monitor the state of the treated materials to ensure that the degraded materials are effectively treated and meet the agricultural fertilizer standards, ensuring the safe application of fertilizers.

[0089] Use a gas chromatography-mass spectrometer to detect the concentrations of BPA before and after degradation by the magnetic biochar obtained in Examples 1 to 3 (the mass ratio of compost materials to magnetic biochar is 100:8.5). The experiment was carried out in a 50 mL beaker, and the conditions of the magnetic stirrer were set at a constant temperature of 25 °C and a stirring speed of 700 r / min. In a constant temperature and constant speed device, the prepared sludge-based magnetic biochar was mixed and reacted with a bisphenol A solution (10 mg / L), and the reaction time was 12 min. Samples were taken at regular intervals, and a high-performance liquid chromatograph was used to detect the pollutant concentration. The content of BPA in the materials is shown in Table 1.

[0090] Table 1 Concentration data of BPA before and after degradation by the magnetic biochar obtained in Examples 1 to 3

[0091]

[0092] As can be seen from Table 1, the dosages of FeSO4·7H2O and FeCl3·6H2O are 3.6 g and 4.8 g respectively, and the adsorption capacity is 6.54 mg / g; the dosages of FeSO4·7H2O and FeCl3·6H2O are 2.4 g and 3.6 g respectively, and the adsorption capacity is 4.43 mg / g; the dosages of FeSO4·7H2O and FeCl3·6H2O are 4.8 g and 6 g respectively, and the adsorption capacity is 5.26 mg / g. It can be seen that increasing the dosages of FeSO4·7H2O and FeCl3·6H2O can first increase the adsorption capacity and then decrease it, and the adsorption capacity of Example 1 is the highest. Regarding the change in the BPA concentration before and after adsorption, the BPA concentration before adsorption is 1.42 mg / L, and the BPA concentration after adsorption is 0.28 mg / L; the BPA concentration before adsorption is 1.53 mg / L, and the BPA concentration after adsorption is 0.73 mg / L; the BPA concentration before adsorption is 1.45 mg / L, and the BPA concentration after adsorption is 0.54 mg / L. From these data, we can see that the BPA concentration after adsorption has decreased, indicating that the magnetic particles have a certain adsorption effect on BPA. The adsorption effect of Example 1 is the best, probably because the higher dosages of FeSO4·7H2O and FeCl3·6H2O lead to the generation of more magnetic particles, thus increasing the adsorption capacity and adsorption rate.

[0093] Application Example 2

[0094] Using a sequencing batch aerobic fermentation device, 20 kg of watermelon vines and sludge from its land are taken as compost raw materials (including 10 kg of farmland sludge with a water content of 70% and 10 kg of watermelon vines), and the magnetic biochar obtained in Example 2 is used in dosages of 0.6 kg, 1 kg, and 1.4 kg respectively. After mixing evenly, the materials are put into the fermentation chamber. After 15 days of fermentation, the materials are taken out, fully mixed with the raw materials, and the obtained compost products are subjected to the determination of bisphenol A (BPA) content and other index analyses. The test results are shown in Figure 2 and Table 2.

[0095] Table 2 Concentration data of BPA before and after degradation with different dosages of the magnetic biochar obtained in Example 2

[0096]

[0097] As Figure 2 can be seen, under the condition that the application amount of biochar is 5% (the dosage of magnetic biochar is 1 kg), the quality of the compost product is the highest and the utilization rate of biochar is the highest.

[0098] As can be seen from Table 2, the magnetic biochar provided by the present invention has good adsorption and separation effects on endocrine disruptors in compost. With the increase in the dosage of magnetic biochar, the concentration of heavy metals in compost generally decreases, indicating that magnetic biochar has good adsorption effects on heavy metals. In particular, when the dosage of magnetic biochar is 1.4 kg, the adsorption effects on Cu, Pb, Zn, Cr, and Cd are the most significant. This provides strong data support for the application of magnetic biochar in compost.

[0099] Although the above embodiments have described the present invention in detail, they are only a part of the embodiments of the present invention, rather than all embodiments. Other embodiments can also be obtained based on these embodiments without creative efforts, and these embodiments all fall within the protection scope of the present invention.

Claims

1. An application of magnetic biochar in fertilizer preparation, characterized in that: The following steps are involved: The compost raw material and the magnetic biochar are mixed and composted to obtain an organic fertilizer; The method for preparing magnetic biochar comprises the following steps: Mixing farmland sludge and plant residues, carbonizing, and obtaining sludge biochar; the mass ratio of the farmland sludge to the plant residues is 1-6:2-8; the farmland sludge is farmland sludge of fruit and vegetable plants, and the plant residues are fruit and vegetable plant residues; the carbonization temperature is 300-600° C., and the time is 2-8 hours; The sludge biochar, an activator and water are mixed and soaked to obtain an activated biochar system; the mass ratio of the sludge biochar to the activator is 10-50:1; the activator is 5,5-dimethyl-1-pyrroline-N-oxide; The iron salt, alkaline reagent and water are mixed, and precipitation reaction and dehydration are carried out in sequence to obtain magnetic particles; The magnetic particles, a surfactant and water are mixed and modified in an alkaline environment to obtain modified magnetic particles; the mass ratio of the magnetic particles to the surfactant is 150:0.1-0.8; The modified magnetic particles, a complexing agent and water are mixed to obtain a magnetizing agent; the mass ratio of the modified magnetic particles to the complexing agent is 100:0.5-1; The activated biochar system and a magnetizing agent are mixed and magnetized to obtain the magnetic biochar.

2. The use according to claim 1, characterized in that The water content of the farmland sludge is 60-80%.

3. The use according to claim 1, characterized in that: The soaking time is 2 to 3 hours.

4. The use according to claim 1, characterized in that: The iron salt includes a divalent iron salt and a trivalent iron salt; the divalent iron salt includes one or more of ferrous sulfate, ferrous nitrate and ferrous chloride; the trivalent iron salt includes ferric chloride and / or polyferric chloride; the alkaline agent includes one or more of ammonia water, calcium hydroxide and sodium carbonate; The precipitation reaction time is 1-6 hours; the dehydration method is heating dehydration; the heating dehydration temperature is 60-80° C. and the time is 20-40 minutes.

5. The use according to claim 1, characterized in that: The surfactant includes anionic surfactant and / or cationic surfactant; The pH value of the alkaline environment is 7-8, excluding the endpoint value 7; the temperature of the modification is 90-100° C., and the time is 40-50 minutes.

6. The use according to claim 1, characterized in that: The complexing agent includes one or more of sodium isobutyl tripolyphosphate, ethylenediaminetetraacetic acid, citric acid and tartaric acid.

7. The use according to claim 1, characterized in that: The mass ratio of the sludge biochar in the activated biochar system to the modified magnetic particles in the magnetizer is 5-10:1; The magnetization temperature is 80-90° C. and the time is 2-3 hours.

8. The use according to any one of claims 1 to 7, characterized in that: The particle size of the magnetic biochar is 74-150 μm, and the specific surface area is 215.25-305.1 m 2 ·g -1 .

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