Biochar-based slow-release fertilizer and method for preparing the same

Abstract

The application discloses a slow-release fertilizer based on biochar, which comprises a slow-release material and an agricultural fertilizer in a weight ratio of 2:8; wherein the slow-release material comprises equal weights of attapulgite and biochar, the attapulgite comprises first attapulgite subjected to heat modification pretreatment, second attapulgite subjected to acid modification pretreatment and third attapulgite subjected to heat modification and acid modification pretreatment in sequence; and the biochar comprises first biochar subjected to acid modification pretreatment, second biochar subjected to phosphorus modification pretreatment and third biochar subjected to acid modification and phosphorus modification pretreatment in sequence. The slow-release fertilizer based on biochar has good slow-release performance and high loading capacity, and can improve the utilization rate of the fertilizer, improve soil nutrients, and thus shorten the growth and development period of crops and improve the yield of crops.

Description

Technical Field

[0001] This invention relates to the field of agricultural fertilizer technology. More specifically, this invention relates to a biochar-based slow-release fertilizer and its preparation method. Background Technology

[0002] Biochar, with its stable carbon skeleton, well-developed pore structure, and large specific surface area, can be used as a soil carbon sink and amendment, thus attracting widespread attention from the academic community. Existing studies have found that biochar can improve acidic red soil environments and promote crop growth. Returning biochar to the field can also increase soil organic carbon content and improve soil compaction. Using biochar as a carrier for chemical fertilizers to prepare carbon-based compound fertilizers provides a more effective way to return biochar to the field, and at the same time provides a new perspective for the research of slow-release fertilizers.

[0003] However, while biochar-based fertilizers are widely used, they also present some problems. Most biochar fertilizers on the market are based on biochar produced from traditional pyrolysis biomass, which has low nutrient loading and irregular structure, greatly limiting its large-scale application in agriculture. Therefore, developing low-cost, green, slow-release, water-retaining, and biodegradable environmentally friendly biochar-based slow-release fertilizers, and exploring new energy-saving and efficient preparation methods, is an important direction for the future sustainable development of agriculture in Northwest China and even the whole country. Summary of the Invention

[0004] One object of the present invention is to solve at least the above-mentioned problems and to provide at least the advantages that will be described later.

[0005] Another objective of this invention is to provide a biochar-based slow-release fertilizer to address the technical problems that the low nutrient loading and irregular structure of existing biochar-based slow-release fertilizers greatly limit the large-scale promotion and application of biochar fertilizers in the agricultural field.

[0006] Another objective of this invention is to provide a method for preparing a biochar-based slow-release fertilizer. This method involves thermally modifying attapulgite and acidically modifying biochar, then combining the attapulgite and biochar to obtain an attapulgite-biochar composite. Subsequently, the attapulgite-biochar composite is compounded with agricultural fertilizer to obtain a novel biochar-based slow-release fertilizer with good slow-release performance and high loading capacity. This improves fertilizer utilization, significantly removes coating material residues, increases degradation rate, improves soil compaction, and enhances soil nutrients. The preparation method of this invention is simple and highly feasible.

[0007] In order to achieve these objectives and other advantages according to the present invention, a biochar-based slow-release fertilizer is provided, comprising slow-release materials and agricultural fertilizer in a weight ratio of 2:8;

[0008] The slow-release material is an attapulgite-biochar composite, which includes equal weights of attapulgite and biochar. The attapulgite includes equal amounts of thermally modified pretreated first attapulgite, acid-modified pretreated second attapulgite, and third attapulgite that has undergone thermal modification and acid modification pretreatment sequentially. The biochar includes equal amounts of acid-modified pretreated first biochar, phosphorus-modified pretreated second biochar, and third biochar that has undergone acid modification and phosphorus modification pretreatment sequentially.

[0009] Preferably, the preparation method of the biochar-based slow-release fertilizer, the first attapulgite is prepared by: calcining the attapulgite at 200-500℃ for 3 hours, cooling it to room temperature, and grinding it through a 0.15 mm sieve to obtain the product;

[0010] The preparation method of the second attapulgite is as follows: attapulgite is dispersed in a 9 mol / L phosphoric acid aqueous solution, heated in a boiling water bath for 2 hours, filtered, the filter cake is collected, washed with distilled water 2 to 5 times, dried at 103 to 107℃, and ground through a 0.15 mm sieve to obtain the product.

[0011] The preparation method of the third attapulgite is as follows: the first attapulgite is dispersed in a 9 mol / L phosphoric acid aqueous solution, heated in a boiling water bath for 2 hours, filtered, the filter cake is collected, washed with distilled water 2 to 5 times, dried at 103 to 107℃, and ground through a 0.15 mm sieve to obtain the final product.

[0012] Preferably, the method for preparing the biochar-based slow-release fertilizer involves crushing a mixture of waste branches and leaves to 6 cm and placing it in a muffle furnace, heating it to 200-500°C, and performing high-temperature pyrolysis at 200-500°C for 2 hours to obtain carbonized material. The carbonized material is then ground through a 0.15 mm sieve to obtain biochar.

[0013] The preparation method of the first biochar is as follows: biochar is mixed with hydrochloric acid aqueous solution with a concentration of 1 mol / L, and stirred continuously at room temperature for 8 hours. After filtration, the filter residue is collected, washed with deionized water until pH=7, and then placed in a vacuum drying oven at 105 ℃ for 48 hours. After grinding and passing through a 0.15 mm sieve, the biochar is obtained.

[0014] The second method for preparing biochar is as follows: Biochar and red phosphorus are mixed in a weight ratio of 10:4 and placed in an agate ball mill jar containing agate beads. The mixture is then milled for 30 minutes.

[0015] The preparation method of the third biochar is as follows: the first biochar and red phosphorus are mixed in a weight ratio of 10:4 and placed in an agate ball milling jar containing agate beads, and milled for 30 minutes.

[0016] Preferably, the preparation method of the biochar-based slow-release fertilizer, specifically the preparation method of the attapulgite-biochar composite, is as follows:

[0017] S1: Mix the first attapulgite soil, the second attapulgite soil, and the third attapulgite soil in a weight ratio of 1:1:1 to obtain an attapulgite soil mixture.

[0018] S2. Mix the first biochar, the second biochar, and the third biochar in a weight ratio of 1:1:1 to obtain a biochar mixture.

[0019] S3. Mix the attapulgite mixture and the biochar mixture in a weight ratio of 1:1, place them in a supercritical CO2 fluid at a temperature of 40~50℃, a stirring speed of 100~200r / min, and a pressure of 10~30MPa, and allow them to swell and permeate for 0.5~1h. Then, quickly depressurize to atmospheric pressure, cool to room temperature, and grind through a 0.15mm sieve to obtain the final product.

[0020] Preferably, in the preparation method of the biochar-based slow-release fertilizer, in step S3, the attapulgite mixture undergoes pretreatment before being mixed with the biochar mixture. Specifically, the attapulgite mixture is uniformly dispersed in ultrapure water to obtain an attapulgite aqueous solution. Polyacrylamide is added to the attapulgite aqueous solution, and after thorough stirring, it is treated under ultrasound for 20-30 minutes to obtain an attapulgite suspension. Tetraethyl orthosilicate, aluminum chloride, boric acid, and ultrapure water are mixed in a molar ratio of 1:2:5:50 and stirred thoroughly to obtain a sol. The sol is added dropwise to the attapulgite suspension under high-speed stirring, and after thorough stirring, it is treated under ultrasound for 20-30 minutes to obtain a dispersion. The dispersion is degassed (degassed in a vacuum chamber), frozen (dry ice, acetone cold bath), and calcined to obtain an attapulgite aerogel. The attapulgite aerogel is then ground and passed through a 0.15 mm sieve. The mass ratio of the attapulgite mixture, polyacrylamide, and sol is 5:1:20.

[0021] Preferably, in the method for preparing the biochar-based slow-release fertilizer, the agricultural fertilizer includes urea, superphosphate, and potassium sulfate.

[0022] The present invention also provides a method for preparing the above-mentioned biochar-based slow-release fertilizer, wherein agricultural fertilizer and slow-release material are mixed in a weight ratio of 8:2, and then ground evenly in a grinder. Sodium borate is added during the grinding process, and the mixture is passed through a 0.15mm sieve to obtain the slow-release fertilizer.

[0023] The present invention has at least the following beneficial effects:

[0024] 1. Attapulgite is a hydrous magnesium aluminum silicate clay mineral with a chain-like layered structure. It is porous and has ion exchange properties. It contains a variety of mineral nutrients and trace elements. Attapulgite can be used as fertilizer or soil conditioner to improve soil structure and properties, increase soil fertility, and can also combine with organic matter in the soil through certain forces to form organic matter-mineral complexes (i.e., soil aggregates). This helps to control and fix nutrients in the soil and has the ability to retain fertilizer, water, and slow release nutrients. Attapulgite can prevent soil nutrient loss and depletion. As an adsorbent mineral, attapulgite can enhance the soil's fertilizer retention capacity. Combining attapulgite with biochar to obtain a complex, and then compounding it with agricultural fertilizers to make slow-release fertilizers, can increase the nutrient loading of biochar-based slow-release fertilizers, thereby improving fertilizer utilization and slow-release effects, shortening the crop growth and development period, and increasing crop yield.

[0025] 2. Thermal modification treatment: Thermal modification of attapulgite alters the original structural composition of biochar, resulting in SiO2, MgFe4(SO4)6(OH)2(H2O). 20 The increased CaMg(CO3)2 content enhanced the intensity of the SiO2 and CaMg0.77Fe0.23(CO3)2 diffraction peaks in attapulgite. Acid modification dissolved the CaMg(CO3)2 content in attapulgite, altering the pore structure of the composite and improving the adsorption effect of the composite adsorbent. The interaction between carbon and mineral materials was also strengthened. High temperature resulted in a high degree of graphitization of the branch biochar, but it contained a large amount of ash. Acid modification caused the CaCO3 diffraction peak in the biochar to disappear, reducing the ash content. The modification of attapulgite resulted in a broken and circular collapsed structure with numerous gaps and cracks. Acid modification gave the biochar a larger semi-permeable to permeable circular pore size, which facilitated better storage and release of nutrients. The third biochar obtained by phosphorus modification of acidified biochar could lower soil pH, improve the available phosphorus content in the soil, and increase crop yield.

[0026] 3. After the modified biochar is combined with the modified attapulgite, the loading of the attapulgite particles makes the biochar structure loose and porous. The loaded attapulgite can provide many attachment sites for the biochar, with a high specific surface area and deep pore size, which can provide more opportunities for nutrient molecules to interact with the complex, greatly increasing the nutrient loading. At the same time, it can effectively prevent the agglomeration of biochar, making the fertilizer particles loose and uniform.

[0027] 4. This invention mixes three types of attapulgite that have undergone different pretreatments, and modifies biochar using three different pretreatment methods before mixing. This greatly reduces agglomeration during the mixing process, which leads to uneven loading of attapulgite and biochar, reducing the adsorption performance of the attapulgite-biochar composite. Furthermore, the different modified attapulgite / biochar properties complement each other, further improving the nutrient loading capacity of the attapulgite-biochar composite and enhancing the slow-release performance of the fertilizer.

[0028] Other advantages, objectives and features of the present invention will become apparent in part from the following description, and in part from those skilled in the art through study and practice of the invention. Detailed Implementation

[0029] The present invention will be further described in detail below with reference to embodiments, so that those skilled in the art can implement it based on the description.

[0030] It should be understood that terms such as “having,” “comprising,” and “including” as used herein do not exclude the presence or addition of one or more other elements or combinations thereof.

[0031] It should be noted that, unless otherwise specified, the experimental methods described in the following implementation plan are all conventional methods, and the reagents and materials described are all commercially available unless otherwise specified.

[0032] In the description of this invention, the terms "lateral", "longitudinal", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", and "outer" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0033] <Example 1>

[0034] This invention provides a biochar-based slow-release fertilizer, comprising a slow-release material and agricultural fertilizer in a weight ratio of 2:8. The slow-release material is an attapulgite-biochar composite, comprising equal weights of attapulgite and biochar. The attapulgite includes equal amounts of thermally modified pretreated first attapulgite, acid-modified pretreated second attapulgite, and third attapulgite that has undergone sequential thermal and acid-modified pretreatments. The biochar includes equal amounts of acid-modified pretreated first biochar, phosphorus-modified pretreated second biochar, and third biochar that has undergone sequential acid and phosphorus-modified pretreatments. The agricultural fertilizer includes urea, superphosphate, potassium sulfate, and water.

[0035] The preparation method of the first attapulgite is as follows: attapulgite is calcined at 200℃ for 3 hours, cooled to room temperature, and ground through a 0.15 mm sieve to obtain the product.

[0036] The preparation method of the second attapulgite is as follows: attapulgite is dispersed in a 9 mol / L phosphoric acid aqueous solution, heated in a boiling water bath for 2 hours, filtered, the filter cake is collected, washed twice with distilled water, dried at 103℃, and ground through a 0.15 mm sieve to obtain the product.

[0037] The preparation method of the third attapulgite is as follows: the first attapulgite is dispersed in a 9 mol / L phosphoric acid aqueous solution, heated in a boiling water bath for 2 hours, filtered, the filter cake is collected, washed twice with distilled water, dried at 103℃, and ground through a 0.15 mm sieve to obtain the final product.

[0038] The mixture of waste branches and leaves was crushed to 6 cm and placed in a muffle furnace. The temperature was raised to 200°C and pyrolyzed at 200°C for 2 hours to obtain carbonized material. The carbonized material was then ground through a 0.15 mm sieve to obtain biochar.

[0039] The preparation method of the first biochar is as follows: biochar is mixed with a 1 mol / L hydrochloric acid aqueous solution, and stirred continuously at room temperature for 8 hours. After filtration, the filter residue is collected, washed with deionized water until pH=7, and then placed in a vacuum drying oven at 105℃ for 48 hours. After grinding and passing through a 0.15 mm sieve, the biochar is obtained.

[0040] The second method for preparing biochar is as follows: Biochar and red phosphorus are mixed in a weight ratio of 10:4 and placed in an agate ball mill jar containing agate beads. The mixture is then milled for 30 minutes.

[0041] The preparation method of the third biochar is as follows: the first biochar and red phosphorus are mixed in a weight ratio of 10:4 and placed in an agate ball milling jar containing agate beads, and milled for 30 minutes.

[0042] The preparation method of attapulgite-biochar composite is as follows:

[0043] S1: Mix the first attapulgite soil, the second attapulgite soil, and the third attapulgite soil in a weight ratio of 1:1:1 to obtain an attapulgite soil mixture.

[0044] S2. Mix the first biochar, the second biochar, and the third biochar in a weight ratio of 1:1:1 to obtain a biochar mixture.

[0045] S3. Mix the attapulgite mixture and the biochar mixture in a weight ratio of 1:1, place them in a supercritical CO2 fluid at a temperature of 40℃, a stirring speed of 100r / min, and a pressure of 10MPa, and allow them to swell and permeate for 0.5h. Then, quickly depressurize to atmospheric pressure, cool to room temperature, and grind through a 0.15mm sieve to obtain the final product.

[0046] In step S3, the attapulgite mixture underwent pretreatment before being mixed with the biochar mixture. Specifically, the attapulgite mixture was uniformly dispersed in ultrapure water to obtain an attapulgite aqueous solution. Polyacrylamide was added to the attapulgite aqueous solution, and after thorough stirring, it was subjected to ultrasonic treatment for 20 minutes to obtain an attapulgite suspension. Tetraethyl orthosilicate, aluminum chloride, boric acid, and ultrapure water were mixed in a molar ratio of 1:2:5:50 and stirred thoroughly to obtain a sol solution. The sol solution was added dropwise to the attapulgite suspension under high-speed stirring, and after thorough stirring, it was subjected to ultrasonic treatment for 20 minutes to obtain a dispersion. The dispersion was placed in a vacuum chamber for degassing, and then calcined by freezing in a dry ice and acetone cold bath to obtain an attapulgite aerogel. The attapulgite aerogel was ground and passed through a 0.15 mm sieve to obtain the final product. The mass ratio of the attapulgite mixture, polyacrylamide, and sol was 5:1:20.

[0047] The present invention also provides a method for preparing a biochar-based slow-release fertilizer, wherein agricultural fertilizer and slow-release material are mixed in a weight ratio of 8:2, and then ground evenly in a grinder. Sodium borate is added during the grinding process, and the mixture is passed through a 0.15mm sieve to obtain the slow-release fertilizer.

[0048] <Example 2>

[0049] This invention provides a biochar-based slow-release fertilizer, comprising a slow-release material and agricultural fertilizer in a weight ratio of 2:8. The slow-release material is an attapulgite-biochar composite, comprising equal weights of attapulgite and biochar. The attapulgite includes equal amounts of thermally modified pretreated first attapulgite, acid-modified pretreated second attapulgite, and third attapulgite that has undergone sequential thermal and acid-modified pretreatments. The biochar includes equal amounts of acid-modified pretreated first biochar, phosphorus-modified pretreated second biochar, and third biochar that has undergone sequential acid and phosphorus-modified pretreatments. The agricultural fertilizer includes urea, superphosphate, potassium sulfate, and water.

[0050] The preparation method of the first attapulgite is as follows: attapulgite is calcined at 500℃ for 3 hours, cooled to room temperature, and ground through a 0.15 mm sieve to obtain the product.

[0051] The preparation method of the second attapulgite is as follows: attapulgite is dispersed in a 9 mol / L phosphoric acid aqueous solution, heated in a boiling water bath for 2 hours, filtered, the filter cake is collected, washed with distilled water 5 times, dried at 107℃, and ground through a 0.15 mm sieve to obtain the product.

[0052] The preparation method of the third attapulgite is as follows: the first attapulgite is dispersed in a 9 mol / L phosphoric acid aqueous solution, heated in a boiling water bath for 2 hours, filtered, the filter cake is collected, washed with distilled water 5 times, dried at 107℃, and ground through a 0.15 mm sieve to obtain the final product.

[0053] The mixture of waste branches and leaves was crushed to 6 cm and placed in a muffle furnace. The temperature was raised to 500℃ and pyrolyzed at 500℃ for 2 hours to obtain carbonized material. The carbonized material was then ground through a 0.15 mm sieve to obtain biochar.

[0054] The preparation method of the first biochar is as follows: biochar is mixed with a 1 mol / L hydrochloric acid aqueous solution, and stirred continuously at room temperature for 8 hours. After filtration, the filter residue is collected, washed with deionized water until pH=7, and then placed in a vacuum drying oven at 105℃ for 48 hours. After grinding and passing through a 0.15 mm sieve, the biochar is obtained.

[0055] The second method for preparing biochar is as follows: Biochar and red phosphorus are mixed in a weight ratio of 10:4 and placed in an agate ball mill jar containing agate beads. The mixture is then milled for 30 minutes.

[0056] The preparation method of the third biochar is as follows: the first biochar and red phosphorus are mixed in a weight ratio of 10:4 and placed in an agate ball milling jar containing agate beads, and milled for 30 minutes.

[0057] The preparation method of attapulgite-biochar composite is as follows:

[0058] S1: Mix the first attapulgite soil, the second attapulgite soil, and the third attapulgite soil in a weight ratio of 1:1:1 to obtain an attapulgite soil mixture.

[0059] S2. Mix the first biochar, the second biochar, and the third biochar in a weight ratio of 1:1:1 to obtain a biochar mixture.

[0060] S3. Mix the attapulgite mixture and the biochar mixture in a weight ratio of 1:1, place them in a supercritical CO2 fluid at a temperature of 50℃, a stirring speed of 200r / min, and a pressure of 30MPa, and allow them to swell and permeate for 1 hour. Then, quickly depressurize to atmospheric pressure, cool to room temperature, and grind through a 0.15mm sieve to obtain the final product.

[0061] In step S3, the attapulgite mixture underwent pretreatment before being mixed with the biochar mixture. Specifically, the attapulgite mixture was uniformly dispersed in ultrapure water to obtain an attapulgite aqueous solution. Polyacrylamide was added to the attapulgite aqueous solution, and after thorough stirring, it was subjected to ultrasonic treatment for 30 minutes to obtain an attapulgite suspension. Tetraethyl orthosilicate, aluminum chloride, boric acid, and ultrapure water were mixed in a molar ratio of 1:2:5:50 and stirred thoroughly to obtain a sol solution. The sol solution was added dropwise to the attapulgite suspension under high-speed stirring, and after thorough stirring, it was subjected to ultrasonic treatment for 30 minutes to obtain a dispersion. The dispersion was placed in a vacuum chamber for degassing, and then calcined by freezing in a dry ice and acetone cold bath to obtain an attapulgite aerogel. The attapulgite aerogel was ground and passed through a 0.15 mm sieve to obtain the final product. The mass ratio of the attapulgite mixture, polyacrylamide, and sol was 5:1:20.

[0062] The present invention also provides a method for preparing a biochar-based slow-release fertilizer, wherein agricultural fertilizer and slow-release material are mixed in a weight ratio of 8:2, and then ground evenly in a grinder. Sodium borate is added during the grinding process, and the mixture is passed through a 0.15mm sieve to obtain the slow-release fertilizer.

[0063] <Example 3>

[0064] This invention provides a biochar-based slow-release fertilizer, comprising a slow-release material and agricultural fertilizer in a weight ratio of 2:8. The slow-release material is an attapulgite-biochar composite, comprising equal weights of attapulgite and biochar. The attapulgite includes equal amounts of thermally modified pretreated first attapulgite, acid-modified pretreated second attapulgite, and third attapulgite that has undergone sequential thermal and acid-modified pretreatments. The biochar includes equal amounts of acid-modified pretreated first biochar, phosphorus-modified pretreated second biochar, and third biochar that has undergone sequential acid and phosphorus-modified pretreatments. The agricultural fertilizer includes urea, superphosphate, potassium sulfate, and water.

[0065] The preparation method of the first attapulgite is as follows: attapulgite is calcined at 300℃ for 3 hours, cooled to room temperature, and ground through a 0.15 mm sieve to obtain the product.

[0066] The preparation method of the second attapulgite is as follows: attapulgite is dispersed in a 9 mol / L phosphoric acid aqueous solution, heated in a boiling water bath for 2 hours, filtered, the filter cake is collected, washed with distilled water 3 times, dried at 105℃, and ground through a 0.15 mm sieve to obtain the product.

[0067] The preparation method of the third attapulgite is as follows: the first attapulgite is dispersed in a 9 mol / L phosphoric acid aqueous solution, heated in a boiling water bath for 2 hours, filtered, the filter cake is collected, washed with distilled water 3 times, dried at 105℃, and ground through a 0.15 mm sieve to obtain the final product.

[0068] The mixture of waste branches and leaves was crushed to 6 cm and placed in a muffle furnace. The temperature was raised to 300℃ and pyrolyzed at 300℃ for 2 hours to obtain carbonized material. The carbonized material was then ground through a 0.15 mm sieve to obtain biochar.

[0069] The preparation method of the first biochar is as follows: biochar is mixed with hydrochloric acid aqueous solution with a concentration of 1 mol / L, and stirred continuously at room temperature for 8 hours. After filtration, the filter residue is collected, washed with deionized water until pH=7, and then placed in a vacuum drying oven at 105 ℃ for 48 hours. After grinding and passing through a 0.15 mm sieve, the biochar is obtained.

[0070] The second method for preparing biochar is as follows: Biochar and red phosphorus are mixed in a weight ratio of 10:4 and placed in an agate ball mill jar containing agate beads. The mixture is then milled for 30 minutes.

[0071] The preparation method of the third biochar is as follows: the first biochar and red phosphorus are mixed in a weight ratio of 10:4 and placed in an agate ball milling jar containing agate beads, and milled for 30 minutes.

[0072] The preparation method of attapulgite-biochar composite is as follows:

[0073] S1: Mix the first attapulgite soil, the second attapulgite soil, and the third attapulgite soil in a weight ratio of 1:1:1 to obtain an attapulgite soil mixture.

[0074] S2. Mix the first biochar, the second biochar, and the third biochar in a weight ratio of 1:1:1 to obtain a biochar mixture.

[0075] S3. Mix the attapulgite mixture and the biochar mixture in a weight ratio of 1:1, place them in a supercritical CO2 fluid at a temperature of 45℃, a stirring speed of 150r / min, and a pressure of 10~30MPa, and allow them to swell and permeate for 1 hour. Then, quickly depressurize to atmospheric pressure, cool to room temperature, and grind through a 0.15mm sieve to obtain the final product.

[0076] In step S3, the attapulgite mixture underwent pretreatment before being mixed with the biochar mixture. Specifically, the attapulgite mixture was uniformly dispersed in ultrapure water to obtain an attapulgite aqueous solution. Polyacrylamide was added to the attapulgite aqueous solution, and after thorough stirring, it was subjected to ultrasonic treatment for 25 minutes to obtain an attapulgite suspension. Tetraethyl orthosilicate, aluminum chloride, boric acid, and ultrapure water were mixed in a molar ratio of 1:2:5:50 and stirred thoroughly to obtain a sol solution. The sol solution was added dropwise to the attapulgite suspension under high-speed stirring, and after thorough stirring, it was subjected to ultrasonic treatment for 25 minutes to obtain a dispersion. The dispersion was placed in a vacuum chamber for degassing, and then calcined by freezing in a dry ice and acetone cold bath to obtain an attapulgite aerogel. The attapulgite aerogel was ground and passed through a 0.15 mm sieve to obtain the final product. The mass ratio of the attapulgite mixture, polyacrylamide, and sol was 5:1:20.

[0077] The present invention also provides a method for preparing a biochar-based slow-release fertilizer, wherein agricultural fertilizer and slow-release material are mixed in a weight ratio of 8:2, and then ground evenly in a grinder. Sodium borate is added during the grinding process, and the mixture is passed through a 0.15mm sieve to obtain the slow-release fertilizer.

[0078] <Example 4>

[0079] This invention provides a biochar-based slow-release fertilizer, which differs from Example 3 in that the slow-release material is biochar, while the other conditions and parameters are the same as in Example 3. The biochar has not undergone any pretreatment.

[0080] This invention provides a method for preparing a biochar-based slow-release fertilizer, which is consistent with Example 3.

[0081] <Example 5>

[0082] This invention provides a biochar-based slow-release fertilizer, which differs from Example 3 in that the slow-release material is a mixture of biochar, while the other conditions and parameters are the same as in Example 3. The biochar is a mixture of equal amounts of the first biochar, the second biochar, and the third biochar described in Example 3.

[0083] This invention provides a method for preparing a biochar-based slow-release fertilizer, which is consistent with Example 3.

[0084] <Example 6>

[0085] This invention provides a biochar-based slow-release fertilizer. The difference from Example 3 is that the attapulgite-biochar composite comprises equal amounts of attapulgite and biochar, neither of which has undergone pretreatment. All other conditions and parameters are the same as in Example 3. The attapulgite-biochar composite has undergone the pretreatment in step S3.

[0086] This invention provides a method for preparing a biochar-based slow-release fertilizer, which is consistent with Example 3.

[0087] <Example 7>

[0088] This invention provides a biochar-based slow-release fertilizer. The difference from Example 3 is that the attapulgite-biochar composite includes equal amounts of attapulgite and biochar. The attapulgite mixture has not been pretreated. The other conditions and parameters are the same as in Example 3.

[0089] This invention provides a method for preparing a biochar-based slow-release fertilizer, which is consistent with Example 3.

[0090] <Example 8>

[0091] This invention provides a biochar-based slow-release fertilizer, which differs from Example 3 in that the attapulgite-biochar composite includes equal amounts of attapulgite and biochar, excludes step S3, and the remaining conditions and parameters are the same as in Example 3.

[0092] This invention provides a method for preparing a biochar-based slow-release fertilizer, which is consistent with Example 3.

[0093] <Example 9>

[0094] This invention provides a biochar-based slow-release fertilizer. The difference from Example 3 is that the attapulgite used in the attapulgite-biochar composite only includes the first attapulgite, while the other conditions and parameters are the same as in Example 3.

[0095] This invention provides a method for preparing a biochar-based slow-release fertilizer, which is consistent with Example 3.

[0096] <Example 10>

[0097] This invention provides a biochar-based slow-release fertilizer. The difference from Example 3 is that the attapulgite used in the attapulgite-biochar composite only includes the second type of attapulgite, while the other conditions and parameters are the same as in Example 3.

[0098] This invention provides a method for preparing a biochar-based slow-release fertilizer, which is consistent with Example 3.

[0099] <Example 11>

[0100] This invention provides a biochar-based slow-release fertilizer. The difference from Example 3 is that the attapulgite used in the attapulgite-biochar composite only includes the third type of attapulgite, while the other conditions and parameters are the same as in Example 3.

[0101] This invention provides a method for preparing a biochar-based slow-release fertilizer, which is consistent with Example 3.

[0102] <Example 12>

[0103] This invention provides a biochar-based slow-release fertilizer. The difference from Example 3 is that the attapulgite used in the attapulgite-biochar composite includes equal amounts of first attapulgite and second attapulgite, while the other conditions and parameters are the same as in Example 3.

[0104] This invention provides a method for preparing a biochar-based slow-release fertilizer, which is consistent with Example 3.

[0105] <Example 13>

[0106] This invention provides a biochar-based slow-release fertilizer. The difference from Example 3 is that the biochar used in the attapulgite-biochar composite only includes the first biochar, while the other conditions and parameters are the same as in Example 3.

[0107] This invention provides a method for preparing a biochar-based slow-release fertilizer, which is consistent with Example 3.

[0108] <Example 14>

[0109] This invention provides a biochar-based slow-release fertilizer. The difference from Example 3 is that the biochar used in the attapulgite-biochar composite only includes the second biochar, while the other conditions and parameters are the same as in Example 3.

[0110] This invention provides a method for preparing a biochar-based slow-release fertilizer, which is consistent with Example 3.

[0111] <Example 15>

[0112] This invention provides a biochar-based slow-release fertilizer. The difference from Example 3 is that the biochar used in the attapulgite-biochar composite only includes third biochar, while the other conditions and parameters are the same as in Example 3.

[0113] This invention provides a method for preparing a biochar-based slow-release fertilizer, which is consistent with Example 3.

[0114] <Example 16>

[0115] This invention provides a biochar-based slow-release fertilizer, which differs from Example 3 in that the biochar used in the attapulgite-biochar composite includes equal amounts of first biochar and second biochar, while the other conditions and parameters are the same as in Example 3.

[0116] This invention provides a method for preparing a biochar-based slow-release fertilizer, which is consistent with Example 3.

[0117] <Example 17>

[0118] This invention provides a biochar-based slow-release fertilizer, which differs from Example 3 in that the slow-release material is attapulgite clay (without any pretreatment), while the other conditions and parameters are the same as in Example 3.

[0119] This invention provides a method for preparing a biochar-based slow-release fertilizer, which is consistent with Example 3.

[0120] <Example 18>

[0121] This invention provides a biochar-based slow-release fertilizer, which differs from Example 3 in that the slow-release material is an attapulgite mixture, while the other conditions and parameters are the same as in Example 3. The attapulgite mixture comprises equal amounts of first attapulgite, second attapulgite, and third attapulgite.

[0122] This invention provides a method for preparing a biochar-based slow-release fertilizer, which is consistent with Example 3.

[0123] <Experimental Example 1>

[0124] The adsorption capacity of nitrogen, phosphorus, and potassium elements of different slow-release materials corresponding to Examples 3-16 and the original attapulgite soil was tested.

[0125] Test method:

[0126] (1) Adsorption of nitrogen by different materials (ammonium nitrogen-sodium reagent colorimetric method)

[0127] Weigh 2.5g of the sustained-release material sample into a 250mL Erlenmeyer flask, add 50mL of 50mg / L NH4-N / L solution (NH4Cl solution), and place at 25°C for 2 hours with constant shaking. After shaking, filter and test.

[0128] (2) Adsorption of phosphorus by different materials (vanadium molybdenum yellow colorimetric method)

[0129] Weigh 2.5g of sample into a 250mL Erlenmeyer flask, add 50mL of 50mg / L KH2PO4 solution, and place at 25°C for 2 hours with constant shaking. After shaking, filter the sample into a beaker using double filter paper for testing.

[0130] (3) Adsorption of potassium by different materials (flame spectrophotometry)

[0131] Weigh 2.5g of sample into a 250mL Erlenmeyer flask, add 50mL of 50mg / L KCl solution, and place at 25°C for 2 hours with constant shaking. After shaking, filter and test.

[0132] (4) The calculation formulas for the relevant indicators are as follows:

[0133] Q1 = (C0 - C) / M × V;

[0134] R1 = (C0 - C) / C0 × 100%;

[0135] Q2 = C / M × V;

[0136] R2 = Q2 / Q1 × 100%.

[0137] In the above formula: Q1 is the adsorption amount (mg / g); R1 is the removal rate (%); Q2 is the desorption amount (mg / g); R2 is the desorption rate (%); C0 is the initial mass concentration of the solute (mg / L); C is the final mass concentration of the solute (mg / L); V is the volume of the solution (L); M is the amount of adsorption matrix added (g).

[0138] The test results are shown in Table 1.

[0139] Table 1. Results of adsorption tests on nitrogen, phosphorus, and potassium elements by different sustained-release materials.

[0140]

[0141]

[0142] As shown in Table 1, the slow-release material prepared in Example 3 of this invention has a better adsorption effect on nitrogen, phosphorus and potassium compared with the slow-release materials in Examples 4 to 18. This indicates that the present invention combines biochar and attapulgite, performs different pretreatments on biochar and attapulgite, mixes different grades of biochar and attapulgite, further modifies the attapulgite, and mixes the biochar mixture and attapulgite mixture in a supercritical carbon dioxide environment, which can significantly improve the absorption of effective nutrients by the slow-release material.

[0143] <Experimental Example 2>

[0144] Crop planting test experiment:

[0145] 2.1 Test Materials

[0146] (1) Test location: Huangjiachuan Base, Xiji County, Guyuan City.

[0147] (2) Experimental materials: The attapulgite soil used in the experiment was purchased from Ningxia Attapulgite Soil Material Factory, and the earthworm castings used in the experiment were the products of earthworms decomposing cow manure in the Eisenia fetus 'Daping No. 2' biological treatment bed.

[0148] (3) Test substrate: sandy loam.

[0149] (4) Test crop: Cabbage variety “Zhonggan 15”, purchased from Ningxia Wangji Agricultural Development Co., Ltd.

[0150] 2.2 Test Methods

[0151] The field trial of cabbage began on May 14, 2022, at the Huangjiachuan base in Xiji County, Guyuan City, Ningxia. The test material was the cabbage variety "Zhonggan 15," an early-maturing spring cabbage variety, with a growth period of 50-55 days from transplanting to harvest. The experimental soil was sandy loam (total nitrogen 0.22 g / kg, total phosphorus 0.21 g / kg, available nitrogen 6.12 mg / kg, available phosphorus 21.41 mg / kg, available potassium 97.69 mg / kg, organic matter 7.38 g / kg, pH 8.17, EC 1.85 mS / cm). A total of 18 experimental groups were set up, as shown in Table 1, and slow-release fertilizers recommended by experts, recommended by the Ministry of Agriculture and Rural Affairs (see Table 3), and those corresponding to Examples 3-18 were used respectively. The experiment employed a single-factor split-plot design, with each experimental group occupying 0.5 mu (approximately 0.03 hectares). Each experimental group was planted with three unit plots, each unit plot consisting of three rows, each 1 m wide and 0.7 m apart, with four rows planted per ridge and a plant spacing of 30 cm. Organic fertilizer, compound fertilizer, and slow-release fertilizer were applied as a single basal application, followed by two top-dressing applications of chemical fertilizer. Specific fertilization details are shown in Table 4. The cabbage was planted on June 1, 2022. Seedling raising, transplanting, water and fertilizer management, and pesticide application were all managed uniformly using a field management model, and field management practices were consistent with local farming customs.

[0152] Table 2 Experimental group design

[0153]

[0154] Table 3. Nutritional Recommendations for Cabbage

[0155]

[0156] Table 4 Specific Fertilizer Application

[0157]

[0158] Note: Nutrients for each treatment were applied according to the recommendations of the Ministry of Agriculture and Rural Affairs, using compound fertilizer with an NPK ratio of 18-18-18; except for the nitrogen, phosphorus and potassium fertilizers listed in the table, each treatment was also treated with 600 kg / mu of organic fertilizer (earthworm castings).

[0159] 2.3 Physiological growth indicators of cabbage plants and cabbage yield determination

[0160] Fourteen days after cabbage transplanting, ten representative plants were randomly selected from the three unit areas of each experimental group. The plant height was measured with a measuring tape at the seedling stage (14 days), rosette stage (28 days), and early heading stage (42 days). Starting from the early heading stage (42 days), the size of the bulb was measured with a measuring tape every 8 days (the bulb was measured at the beginning of the heading stage). The measurement results are shown in Table 5.

[0161] Yield: After the cabbage matures, select 3 rows from each unit in each experimental group, and randomly select cabbages of the same size with an area of ​​1 square meter. Use an electronic scale to measure the weight of a single cabbage plant and the total weight per square meter, and convert the yield of the plot area into the yield per mu (unit of land area).

[0162] Table 5. Physiological growth indicators and yield of cabbage plants

[0163]

[0164] As shown in Table 5, the slow-release fertilizer prepared in Example 3 of this invention promotes faster plant height and bulb growth in cabbage, shortens the growth cycle, and significantly increases yield per acre compared to other experimental groups. This indicates that the present invention combines biochar and attapulgite, subjecting both to different pretreatments, then mixing different grades of biochar and attapulgite, further modifying the attapulgite, and finally mixing the biochar mixture and attapulgite mixture in a supercritical carbon dioxide environment. Introducing this slow-release material into the slow-release fertilizer can shorten the crop growth cycle and increase crop yield.

[0165] The number of devices and processing scale described herein are for the purpose of simplifying the description of the invention. Applications, modifications, and variations of the invention will be readily apparent to those skilled in the art.

[0166] Although the embodiments of the present invention have been disclosed above, they are not limited to the applications listed in the specification and embodiments. They can be applied to various fields suitable for the present invention. For those skilled in the art, other modifications can be easily made. Therefore, without departing from the general concept defined by the claims and their equivalents, the present invention is not limited to the specific details.

Claims

1. A slow release fertilizer based on biochar, characterized in that, The slow-release material, the agricultural fertilizer, and the slow-release material and the agricultural fertilizer are in a weight ratio of 2:

8. The slow-release material is a palygorskite-biochar compound, which comprises equal weights of palygorskite and biochar, the palygorskite comprises equal amounts of a first palygorskite subjected to heat modification pretreatment, a second palygorskite subjected to acid modification pretreatment, and a third palygorskite subjected to heat modification and acid modification pretreatment in sequence; and the biochar comprises equal amounts of a first biochar subjected to acid modification pretreatment, a second biochar subjected to phosphorus modification pretreatment, and a third biochar subjected to acid modification and phosphorus modification pretreatment in sequence. The first palygorskite is prepared by calcining palygorskite at 200-500°C for 3h, cooling to room temperature, and grinding through a 0.15mm sieve. The second palygorskite is prepared by dispersing palygorskite in a 9mol / L phosphoric acid aqueous solution, heating in a boiling water bath for 2h, filtering, washing the filter cake with distilled water for 2-5 times, and then drying at 103-107°C, and grinding through a 0.15mm sieve. The third palygorskite is prepared by dispersing the first palygorskite in a 9mol / L phosphoric acid aqueous solution, heating in a boiling water bath for 2h, filtering, washing the filter cake with distilled water for 2-5 times, and then drying at 103-107°C, and grinding through a 0.15mm sieve. The mixed raw materials of waste branches and leaves are crushed to 6cm, placed in a muffle furnace, heated to 200-500°C, and subjected to high-temperature pyrolysis at 200-500°C for 2h to obtain carbonized material, which is ground through a 0.15mm sieve to obtain biochar. The first biochar is prepared by mixing biochar with a 1mol / L hydrochloric acid aqueous solution, continuously stirring at room temperature for 8h, filtering, washing the filter residue with deionized water until pH=7, and then drying in a 105°C vacuum drying oven for 48h, and grinding through a 0.15mm sieve. The second biochar is prepared by mixing biochar with red phosphorus in a weight ratio of 10:4, and placing in a maroon ball mill jar containing maroon beads, and ball milling for 30min. The third biochar is prepared by mixing the first biochar with red phosphorus in a weight ratio of 10:4, and placing in a maroon ball mill jar containing maroon beads, and ball milling for 30min. The preparation method of the palygorskite-biochar compound is as follows: S1: mixing the first palygorskite, the second palygorskite, and the third palygorskite in a weight ratio of 1:1:1 to obtain a palygorskite mixture; S2: mixing the first biochar, the second biochar, and the third biochar in a weight ratio of 1:1:1 to obtain a biochar mixture; and S3: mixing the palygorskite mixture and the biochar mixture in a weight ratio of 2:8 to obtain the palygorskite-biochar compound. S3. Mix the attapulgite mixture and the biochar mixture in a weight ratio of 1:1 until homogeneous. Place the mixture in a supercritical CO2 fluid at a temperature of 40-50℃, a stirring speed of 100-200 r / min, and a pressure of 10-30 MPa for swelling and permeation for 0.5-1 h. Then, quickly depressurize to atmospheric pressure and cool to room temperature. Grind the mixture through a 0.15 mm sieve to obtain the final product. In step S3, the attapulgite mixture underwent pretreatment before being mixed with the biochar mixture. Specifically, the attapulgite mixture was uniformly dispersed in ultrapure water to obtain an attapulgite aqueous solution. Polyacrylamide was added to the attapulgite aqueous solution, and after thorough stirring, it was subjected to ultrasonic treatment for 20-30 minutes to obtain an attapulgite suspension. Tetraethyl orthosilicate, aluminum chloride, boric acid, and ultrapure water were mixed in a molar ratio of 1:2:5:50 and stirred thoroughly to obtain a sol solution. The sol solution was added dropwise to the attapulgite suspension under high-speed stirring, and after thorough stirring, it was subjected to ultrasonic treatment for 20-30 minutes to obtain a dispersion. The dispersion was degassed, frozen, and calcined to obtain an attapulgite aerogel. The attapulgite aerogel was then ground and passed through a 0.15 mm sieve. The mass ratio of the attapulgite mixture, polyacrylamide, and sol was 5:1:

20. Agricultural fertilizers include urea, superphosphate, potassium sulfate, and water; Agricultural fertilizer and slow-release material are mixed in a weight ratio of 8:2, then ground evenly in a grinder. Sodium borate is added during the grinding process, and the mixture is passed through a 0.15mm sieve to obtain slow-release fertilizer.

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