Efficient fertilizer and preparation method thereof

Abstract

The invention discloses an efficient fertilizer and a preparation method thereof, and relates to the technical field of fertilizers. Phosphoric acid and bentonite are sequentially used for pretreating pecan shells, the compact biomass structure of the pecan shells is overcome, the adsorption capacity, the storage capacity and the release capacity of fertilizer elements are effectively improved, then low-temperature carbonization treatment and high-temperature carbonization treatment are conducted respectively, cellulose and lignin are converted into aromatic carbonaceous substances in the low-temperature state, and then the fertilizer elements are decomposed into the aromatic carbonaceous substances in the high-temperature state. According to the high-temperature carbonization treatment, a microwave method is utilized, so that the pore structure in biomass is enlarged, the effects of sealing, water retention and fertilizer conservation are achieved in the fertilizer, the long-term effect of the fertilizer is enhanced, and then iron and phosphorus are adsorbed and loaded on the surface of the biochar and in the gap structure, so that the effect of the fertilizer is improved; finally, a complex is formed with humic acid and is introduced into a water-absorbing polymer, so that the water retention and slow release effects of the fertilizer are further improved.

Description

Technical Field

[0001] The present invention relates to the technical field of fertilizers, and specifically to an efficient fertilizer and a preparation method thereof. Background Art

[0002] Chemical fertilizers are known as "the food of food" and play an important role in promoting the increase of food production, with a contribution rate to crop yield as high as 46.3%. The excessive application of chemical fertilizers has caused a series of environmental problems: (1) Soil degradation: The soil aggregate structure is damaged, resulting in soil compaction and infertility; (2) Soil salinization: The accumulation of soil salts reduces soil microbial diversity and crop nutrient imbalance, ultimately leading to a decrease in crop yield and quality; (3) Contamination of agricultural products: Chemical fertilizers are rich in nitrate, and a large amount of application will cause the accumulation of nitrates in agricultural products, endangering the health of consumers; (4) Water and soil pollution: Chemical fertilizers contain a large amount of readily soluble available nutrients, which cause eutrophication of groundwater and rivers as they are lost with water. The main reason for the low fertilizer utilization rate is that the dissolution rate of existing chemical fertilizers is too fast, and the fertilizer nutrient release characteristics do not match well with the plant nutrient absorption law. In addition, the long-term fertilization method of "emphasizing chemical fertilizers over organic fertilizers" has made it impossible to supplement humus in a timely manner, causing problems such as soil quality degradation and microecological damage, which have severely restricted the sustainable development of modern agriculture.

[0003] Therefore, in order to balance the comprehensive effects of crop yield, quality and environment, promote the "reduction and efficiency increase" of chemical fertilizers, improve the effective utilization rate of fertilizers, and improve soil environment problems; using slow-release fertilizers is an effective means to improve fertilizer utilization rate. Compared with ordinary chemical fertilizers, slow-release fertilizers have greater advantages in delaying fertilizer release, reducing environmental pollution and increasing crop yield. Traditional slow-release fertilizers mainly rely on coated slow-release fertilizers, and the preparation process of such slow-release fertilizers is complex and lacks an effective water absorption and storage mechanism. Therefore, developing a series of slow-release fertilizers with water absorption, water retention and slow-release functions is of great significance for improving water resource and fertilizer utilization rates.

[0004] At the same time, the Chinese hickory is an important economic forest tree species in China, mainly produced in the Tianmu Mountain area of Anhui and Zhejiang, as well as Jinzhai County, Anhui in the Dabie Mountain area. In addition, it is also distributed in Hunan, Guizhou, Guangxi and Northeast China. After most manufacturers extract seeds and oils, a large amount of hickory shells are discarded, which not only wastes resources but also pollutes the environment. Moreover, how to comprehensively utilize hickory resources and the utilization of the remaining hard shells after removing the kernels from hickory fruits is still blank. Summary of the Invention

[0005] The purpose of the present invention is to provide an efficient fertilizer and a preparation method thereof to solve the problems existing in the prior art.

[0006] To solve the above technical problems, the present invention provides the following technical solution: A preparation method of an efficient fertilizer, comprising the following steps:

[0007] (1) Heat the pecan shells at 65 - 85°C for 24 h, then grind and sieve them, and place them in a 20 wt% phosphoric acid solution. After impregnating for 6 - 12 h, take the solid, wash it with deionized water 4 - 8 times, then mix it with bentonite and deionized water, stir at 500 - 1000 rpm for 30 - 70 min, dry at 100°C for 10 - 15 h, grind and sieve to obtain a biochar precursor;

[0008] (2) Place the biochar precursor under a nitrogen atmosphere and perform low-temperature carbonization treatment to obtain low-temperature biochar;

[0009] (3) Place the biochar precursor under a vacuum environment and perform microwave carbonization treatment to obtain high-temperature biochar;

[0010] (4) Mix the low-temperature biochar and high-temperature biochar, grind and sieve through a 150 - 250 mesh sieve, add it to a 1 mol / L aqueous ferric chloride solution, stir at 500 - 1000 rpm for 1 h, let it stand for 15 - 20 h, filter, take the solid, then add it to a 2 wt% aqueous potassium dihydrogen phosphate solution, stir at 200 rpm for 20 h, centrifuge at 5000 rpm for 3 min, dry at 80°C for 10 h to obtain phosphorus-rich biochar;

[0011] (5) Under a nitrogen atmosphere, mix deionized water, ethanol, and phosphorus-rich biochar, stir at 120 rpm for 30 min, add a humic acid solution, continue stirring for 10 h, add a 5 wt% sodium borohydride aqueous solution at 0.5 mL / s, continue stirring for 1 h, let it stand for 4 h, then wash with ultrapure water 3 - 6 times, dry at 50 - 70°C for 12 h to obtain a complex;

[0012] (6) Mix acrylic acid and a 0.02 g / mL aqueous potassium hydroxide solution, stir at 100 rpm for 2 - 6 h, add nanocellulose and the complex, continue stirring for 3 h, then add potassium persulfate, N, N - methylenebisacrylamide. Under a nitrogen atmosphere, heat to 50 - 70°C, stir at 300 - 700 rpm for 2 - 5 h, then cool to room temperature, dry at 50 - 70°C for 12 - 20 h, grind and sieve through a 60 - 150 mesh sieve to obtain an efficient fertilizer.

[0013] Further, the mesh number of the sieving in step (1) is 40 - 80 mesh.

[0014] Further, the mass ratio of the pecan shells, 20 wt% phosphoric acid solution, bentonite, and deionized water in step (1) is 1:15 - 40:0.3 - 0.7:30 - 80.

[0015] Further, the process parameters of the low-temperature carbonization in step (2) are as follows: the heating rate is 2-6 °C / min, the temperature is 250-350 °C, and the heat preservation time is 2-6 h.

[0016] Further, the vacuum degree of the vacuum environment in step (3) is 0.08 MPa.

[0017] Further, the process parameters of the microwave carbonization in step (3) are as follows: the power is 600-1000 W, and the time is 12-30 min.

[0018] Further, the mass ratio of the low-temperature biochar, high-temperature biochar, 1 mol / L ferric chloride aqueous solution, and 2 wt% potassium dihydrogen phosphate aqueous solution in step (4) is 0.1-0.6:1:100:20.

[0019] Further, the preparation method of the humic acid solution in step (5) is as follows: mix humic acid and 2 wt% sodium hydroxide aqueous solution at a mass ratio of 1:500, and adjust the pH of the solution to 7 with hydrochloric acid to obtain it.

[0020] Further, the mass ratio of deionized water, ethanol, phosphorus-rich biochar, humic acid solution, and 5 wt% sodium borohydride aqueous solution in step (5) is 9:3-5:0.01-0.1:2.5:8.

[0021] Further, the mass ratio of acrylic acid, 0.02 g / mL potassium hydroxide aqueous solution, nanocellulose, complex, potassium persulfate, and N,N-methylenebisacrylamide in step (6) is 2:10:0.4:0.2:0.1:0.01.

[0022] Compared with the prior art, the beneficial effects achieved by the present invention are as follows:

[0023] The present invention sequentially uses phosphoric acid and bentonite to pretreat pecan shells, overcoming the dense biomass structure of walnut shells. First, the phosphoric acid solution infiltrates into the interior of the lignocellulose, reacting with cellulose, hemicellulose, lignin, etc. to undergo hydrolysis and dehydration reactions, thereby generating small-molecule substances, changing the structure and degree of polymerization of the biomass. Then, the alkaline earth metals in the bentonite form fixed precipitates with the phosphorus remaining in the biomass, which is beneficial to the formation of a porous structure of the biomass during pyrolysis, thereby effectively improving the adsorption capacity, preservation capacity, and release capacity of fertilizer elements. Next, low-temperature and high-temperature carbonization treatments are carried out respectively. In the low-temperature state, bentonite acts as a binder to promote the conversion of cellulose and lignin into aromatic carbonaceous substances and reduce the loss of volatile components of biochar during pyrolysis. At the same time, phosphoric acid can enhance the aromatization reaction of biochar, thereby increasing the content of organic matter in the soil. The high-temperature carbonization treatment uses the microwave method. Through the extremely strong penetration of microwave irradiation, the pore structure in the biomass is enlarged, playing a role in sealing, retaining water and fertilizer in the fertilizer, and enhancing the aromaticity and stability of biochar, delaying the degradation time of nutrients in the soil, thereby enhancing the long-term effectiveness of the fertilizer. Then, iron and phosphorus are adsorbed and loaded on the surface and pore structure of the biochar. The oxides and hydroxides generated by iron make the surface of the carbon body rougher, thereby increasing the adsorption sites on the biochar and improving the ion exchange capacity of the system. At the same time, iron elements can promote the growth of microorganisms in the soil, thereby improving the effect of the fertilizer. Phosphorus forms stable phosphates in the form of precipitates through magnesium and calcium in the bentonite again, and the oxides and hydroxides of iron can also improve the adsorption capacity for phosphorus. Finally, a complex is formed with humic acid and introduced into the water-absorbing polymer. Through the growth of polymer chains, a dense three-dimensional network structure is formed, increasing the swelling capacity of the matrix, thereby further improving the water retention and slow-release effects of the fertilizer. Detailed implementation mode

[0024] The following will combine the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts belong to the scope of protection of the present invention.

[0025] In order to more clearly illustrate the method provided by the present invention, the following examples are used for detailed description. The test methods for each index of the high-efficiency fertilizer prepared in the following examples are as follows:

[0026] Slow release: Take the same-sized examples and comparative examples and refer to GB / T23348 to detect the release rate of phosphorus.

[0027] Water retention: Take the examples and comparative examples of the same size, mix them thoroughly with dry soil, and slowly spray with tap water until water seeps out from the bottom of the container, then stop spraying. Test the water retention rate of the samples in the soil within 36 days.

[0028] Example 1

[0029] (1) The pecan shells were dried at 65 °C for 24 h, then ground through a 40-mesh sieve, placed in a 20 wt% phosphoric acid solution, impregnated for 6 h, and then the solid was taken, washed 4 times with deionized water, and then mixed with bentonite and deionized water, stirred at 500 rpm for 30 min, dried at 100 °C for 10 h, and ground through a 40-mesh sieve to obtain a biochar precursor; the mass ratio of the pecan shells, 20 wt% phosphoric acid solution, bentonite, and deionized water was 1:15:0.3:30;

[0030] (2) The biochar precursor was placed in a nitrogen atmosphere and subjected to low-temperature carbonization treatment. The process parameters were: heating rate 2 °C / min, temperature 250 °C, and holding time 2 h to obtain low-temperature biochar;

[0031] (3) The biochar precursor was placed in an environment with a vacuum degree of 0.08 MPa and subjected to microwave carbonization treatment. The process parameters were: power 600 W, time 12 min to obtain high-temperature biochar;

[0032] (4) The low-temperature biochar and high-temperature biochar were mixed, ground through a 150-mesh sieve, added to a 1 mol / L ferric chloride aqueous solution, stirred at 500 rpm for 1 h, allowed to stand for 15 h, filtered, and the solid was taken, then added to a 2 wt% potassium dihydrogen phosphate aqueous solution, stirred at 200 rpm for 20 h, centrifuged at 5000 rpm for 3 min, and dried at 80 °C for 10 h to obtain phosphorus-rich biochar; the mass ratio of the low-temperature biochar, high-temperature biochar, 1 mol / L ferric chloride aqueous solution, and 2 wt% potassium dihydrogen phosphate aqueous solution was 0.1:1:100:20;

[0033] (5) Humic acid and 2 wt% sodium hydroxide aqueous solution were mixed at a mass ratio of 1:500, and the pH of the solution was adjusted to 7 with hydrochloric acid to obtain a humic acid solution; in a nitrogen atmosphere, deionized water, ethanol, and phosphorus-rich biochar were mixed, stirred at 120 rpm for 30 min, the humic acid solution was added, and stirring was continued for 10 h. A 5 wt% sodium borohydride aqueous solution was added at 0.5 mL / s, and stirring was continued for 1 h, allowed to stand for 4 h, then washed 3 times with ultrapure water, and dried at 50 °C for 12 h to obtain a complex; the mass ratio of deionized water, ethanol, phosphorus-rich biochar, humic acid solution, and 5 wt% sodium borohydride aqueous solution was 9:3:0.01:2.5:8;

[0034] (6) Mix acrylic acid and 0.02 g / mL potassium hydroxide aqueous solution, stir at 100 rpm for 2 h, add nanocellulose and the complex, continue to stir for 3 h, then add potassium persulfate and N,N-methylenebisacrylamide. Under a nitrogen atmosphere, heat up to 50 °C and stir at 300 rpm for 2 h, then cool to room temperature, dry at 50 °C for 12 h, grind through a 60-mesh sieve to obtain a high-efficiency fertilizer; the mass ratio of acrylic acid, 0.02 g / mL potassium hydroxide aqueous solution, nanocellulose, the complex, potassium persulfate, and N,N-methylenebisacrylamide is 2:10:0.4:0.2:0.1:0.01.

[0035] Example 2

[0036] (1) Dry pecan shells at 75 °C for 24 h, then grind through a 60-mesh sieve, place them in a 20 wt% phosphoric acid solution, impregnate for 9 h, take the solid, wash it 6 times with deionized water, then mix it with bentonite and deionized water, stir at 800 rpm for 50 min, dry at 100 °C for 12 h, grind through a 60-mesh sieve to obtain a biochar precursor; the mass ratio of pecan shells, 20 wt% phosphoric acid solution, bentonite, and deionized water is 1:30:0.5:55;

[0037] (2) Place the biochar precursor under a nitrogen atmosphere and perform low-temperature carbonization treatment. The process parameters are: heating rate of 4 °C / min, temperature of 300 °C, and holding time of 4 h to obtain low-temperature biochar;

[0038] (3) Place the biochar precursor under an environment with a vacuum degree of 0.08 MPa and perform microwave carbonization treatment. The process parameters are: power of 800 W and time of 20 min to obtain high-temperature biochar;

[0039] (4) Mix the low-temperature biochar and high-temperature biochar, grind through a 200-mesh sieve, add it to a 1 mol / L ferric chloride aqueous solution, stir at 800 rpm for 1 h, let it stand for 17 h, filter, take the solid, then add it to a 2 wt% potassium dihydrogen phosphate aqueous solution, stir at 200 rpm for 20 h, centrifuge at 5000 rpm for 3 min, and dry at 80 °C for 10 h to obtain phosphorus-rich biochar; the mass ratio of low-temperature biochar, high-temperature biochar, 1 mol / L ferric chloride aqueous solution, and 2 wt% potassium dihydrogen phosphate aqueous solution is 0.3:1:100:20;

[0040] (5) Mix humic acid and 2 wt% sodium hydroxide aqueous solution at a mass ratio of 1:500, adjust the pH of the solution to 7 with hydrochloric acid to obtain a humic acid solution; under a nitrogen atmosphere, mix deionized water, ethanol, and phosphorus-rich biochar, stir at 120 rpm for 30 min, add the humic acid solution, continue to stir for 10 h, add 5 wt% sodium borohydride aqueous solution at a rate of 0.5 mL / s, continue to stir for 1 h, let stand for 4 h, then wash 5 times with ultrapure water and dry at 60 °C for 12 h to obtain a complex; the mass ratio of deionized water, ethanol, phosphorus-rich biochar, humic acid solution, and 5 wt% sodium borohydride aqueous solution is 9:4:0.06:2.5:8;

[0041] (6) Mix acrylic acid and 0.02 g / mL potassium hydroxide aqueous solution, stir at 100 rpm for 4 h, add nanocellulose and the complex, continue to stir for 3 h, then add potassium persulfate and N,N'-methylenebisacrylamide. Under a nitrogen atmosphere, heat to 60 °C and stir at 500 rpm for 3.5 h, then cool to room temperature, dry at 60 °C for 16 h, and grind through a 100-mesh sieve to obtain a high-efficiency fertilizer; the mass ratio of acrylic acid, 0.02 g / mL potassium hydroxide aqueous solution, nanocellulose, the complex, potassium persulfate, and N,N'-methylenebisacrylamide is 2:10:0.4:0.2:0.1:0.01.

[0042] Example 3

[0043] (1) Dry the pecan shells at 85 °C for 24 h, then grind through an 80-mesh sieve, place them in a 20 wt% phosphoric acid solution, after impregnating for 12 h, take the solid, wash 8 times with deionized water, then mix with bentonite and deionized water, stir at 1000 rpm for 70 min, dry at 100 °C for 15 h, and grind through an 80-mesh sieve to obtain a biochar precursor; the mass ratio of pecan shells, 20 wt% phosphoric acid solution, bentonite, and deionized water is 1:40:0.7:80;

[0044] (2) Place the biochar precursor under a nitrogen atmosphere and perform low-temperature carbonization treatment with the following process parameters: heating rate of 6 °C / min, temperature of 350 °C, and holding time of 6 h to obtain low-temperature biochar;

[0045] (3) Place the biochar precursor in an environment with a vacuum degree of 0.08 MPa and perform microwave carbonization treatment with the following process parameters: power of 1000 W and time of 30 min to obtain high-temperature biochar;

[0046] (4) Mix the low-temperature biochar and high-temperature biochar, grind them through a 250-mesh sieve, add them to a 1 mol / L aqueous solution of ferric chloride, stir at 1000 rpm for 1 h, let stand for 20 h, filter, take the solid, and then add it to a 2 wt% aqueous solution of potassium dihydrogen phosphate, stir at 200 rpm for 20 h, centrifuge at 5000 rpm for 3 min, and dry at 80 °C for 10 h to obtain phosphorus-rich biochar; the mass ratio of the low-temperature biochar, high-temperature biochar, 1 mol / L aqueous solution of ferric chloride, and 2 wt% aqueous solution of potassium dihydrogen phosphate is 0.6:1:100:20;

[0047] (5) Mix humic acid and a 2 wt% aqueous solution of sodium hydroxide in a mass ratio of 1:500, adjust the pH of the solution to 7 with hydrochloric acid to obtain a humic acid solution; under a nitrogen atmosphere, mix deionized water, ethanol, and phosphorus-rich biochar, stir at 120 rpm for 30 min, add the humic acid solution, continue to stir for 10 h, add a 5 wt% aqueous solution of sodium borohydride at 0.5 mL / s, continue to stir for 1 h, let stand for 4 h, and then wash 6 times with ultrapure water and dry at 70 °C for 12 h to obtain a complex; the mass ratio of deionized water, ethanol, phosphorus-rich biochar, humic acid solution, and 5 wt% aqueous solution of sodium borohydride is 9:5:0.1:2.5:8;

[0048] (6) Mix acrylic acid and a 0.02 g / mL aqueous solution of potassium hydroxide, stir at 100 rpm for 6 h, add nanocellulose and the complex, continue to stir for 3 h, then add potassium persulfate and N,N-methylenebisacrylamide, under a nitrogen atmosphere, heat up to 70 °C, stir at 700 rpm for 5 h, then cool to room temperature, dry at 70 °C for 20 h, and grind through a 150-mesh sieve to obtain a high-efficiency fertilizer; the mass ratio of acrylic acid, 0.02 g / mL aqueous solution of potassium hydroxide, nanocellulose, the complex, potassium persulfate, and N,N-methylenebisacrylamide is 2:10:0.4:0.2:0.1:0.01.

[0049] Comparative Example 1

[0050] The difference between Comparative Example 1 and Example 2 is that step (1) is different. Modify step (1) as follows: Dry the pecan shells at 75 °C for 24 h, and then grind through a 60-mesh sieve to obtain a biochar precursor; the remaining steps are the same as in Example 2.

[0051] Comparative Example 2

[0052] The difference between Comparative Example 2 and Example 2 lies in the absence of Step (2). Step (4) is modified as follows: Grind the high-temperature biochar through a 200-mesh sieve, add it to an aqueous solution of 1 mol / L ferric chloride, stir at 800 rpm for 1 h, let it stand for 17 h, filter, take the solid, and then add it to an aqueous solution of 2 wt% potassium dihydrogen phosphate, stir at 200 rpm for 20 h, centrifuge at 5000 rpm for 3 min, and dry at 80 °C for 10 h to obtain phosphorus-rich biochar; the mass ratio of the high-temperature biochar, the 1 mol / L ferric chloride aqueous solution, and the 2 wt% potassium dihydrogen phosphate aqueous solution is 1:100:20; the remaining steps are the same as those in Example 2.

[0053] Comparative Example 3

[0054] The difference between Comparative Example 3 and Example 2 lies in the absence of Step (3). Step (4) is modified as follows: Grind the low-temperature biochar through a 200-mesh sieve, add it to an aqueous solution of 1 mol / L ferric chloride, stir at 800 rpm for 1 h, let it stand for 17 h, filter, take the solid, and then add it to an aqueous solution of 2 wt% potassium dihydrogen phosphate, stir at 200 rpm for 20 h, centrifuge at 5000 rpm for 3 min, and dry at 80 °C for 10 h to obtain phosphorus-rich biochar; the mass ratio of the low-temperature biochar, the 1 mol / L ferric chloride aqueous solution, and the 2 wt% potassium dihydrogen phosphate aqueous solution is 0.3:100:20; the remaining steps are the same as those in Example 2.

[0055] Comparative Example 4

[0056] The difference between Comparative Example 4 and Example 2 lies in Step (4). Step (4) is modified as follows: Mix the low-temperature biochar and the high-temperature biochar, grind them through a 200-mesh sieve, add them to an aqueous solution of 2 wt% potassium dihydrogen phosphate, stir at 200 rpm for 20 h, centrifuge at 5000 rpm for 3 min, and dry at 80 °C for 10 h to obtain phosphorus-rich biochar; the mass ratio of the low-temperature biochar, the high-temperature biochar, and the 2 wt% potassium dihydrogen phosphate aqueous solution is 0.3:1:20; the remaining steps are the same as those in Example 2.

[0057] Comparative Example 5

[0058] The difference between Comparative Example 5 and Example 2 is that step (5) is absent, and step (6) is changed to: Mix acrylic acid and 0.02 g / mL potassium hydroxide aqueous solution, stir at 100 rpm for 4 h, add nanocellulose and phosphorus-rich biochar, continue stirring for 3 h, then add potassium persulfate and N,N'-methylenebisacrylamide. Under a nitrogen atmosphere, heat up to 60 °C and stir at 500 rpm for 3.5 h, then cool to room temperature, dry at 60 °C for 16 h, grind through a 100-mesh sieve to obtain a high-efficiency fertilizer; the mass ratio of acrylic acid, 0.02 g / mL potassium hydroxide aqueous solution, nanocellulose, phosphorus-rich biochar, potassium persulfate, and N,N'-methylenebisacrylamide is 2:10:0.4:0.2:0.1:0.01; the remaining steps are the same as those in Example 2.

[0059] Effect Example

[0060] The following Table 1 gives the performance analysis results of the high-efficiency fertilizers using Examples 1 to 3 and Comparative Examples 1 to 5 of the present invention.

[0061] Table 1

[0062]

[0063]

[0064] From the comparison of the experimental data of the examples and comparative examples in Table 1, it can be found that the present invention sequentially uses phosphoric acid and bentonite to pretreat pecan shells, overcoming the dense biomass structure of pecan shells. First, the phosphoric acid solution infiltrates into the interior of the lignocellulose and reacts with cellulose, hemicellulose, lignin, etc. to generate small-molecule substances, changing the structure and degree of polymerization of the biomass. Then, the alkaline earth metal in the bentonite forms a fixed precipitate with the phosphorus remaining in the biomass, which is beneficial to the formation of a porous structure of the biomass during pyrolysis, thereby effectively improving the adsorption capacity, preservation capacity, and release capacity of fertilizer elements. Next, low-temperature and high-temperature carbonization treatments are carried out respectively. At low temperature, bentonite acts as a binder to promote the conversion of cellulose and lignin into aromatic carbonaceous substances and reduce the loss of volatile components of biochar during pyrolysis. The high-temperature carbonization treatment uses the microwave method. Through the extremely strong penetration of microwave irradiation, the pore structure in the biomass is enlarged, which plays a role in sealing and retaining water and fertilizer in the fertilizer and enhances the aromaticity and stability of biochar, delaying the degradation time of nutrients in the soil. Then, iron and phosphorus are adsorbed and loaded on the surface and void structure of the biochar. The oxides and hydroxides generated by iron make the surface of the carbon body rougher, thereby increasing the adsorption sites on the biochar. At the same time, iron elements can promote the growth of microorganisms in the soil, thereby improving the effect of the fertilizer. Phosphorus forms stable phosphates in the form of precipitation through magnesium and calcium in the bentonite again, and the oxides and hydroxides of iron can also improve the adsorption capacity for phosphorus. Finally, a complex is formed with humic acid and introduced into the water-absorbing polymer. Through the growth of polymer chains, a dense three-dimensional network structure is formed, further improving the water retention and slow-release effects of the fertilizer.

[0065] For those skilled in the art, it is obvious that the present invention is not limited to the details of the above exemplary embodiments, and without departing from the spirit or basic characteristics of the present invention, the present invention can be implemented in other specific forms. Therefore, from any point of view, the embodiments should be regarded as exemplary and non-limiting. The scope of the present invention is defined by the appended claims rather than the above description. Therefore, all changes falling within the meaning and scope of the equivalent elements of the claims are intended to be included in the present invention. Any reference signs in the claims should not be construed as limiting the claimed rights.

Claims

1. A method for preparing a high-efficiency fertilizer, characterized in that: The following steps are involved: (1) The pecan shell is dried at 65-85°C for 24 hours, then ground and sieved, and placed in a 20wt% phosphoric acid solution. After immersion for 6-12 hours, the solid is taken out, washed with deionized water for 4-8 times, and then mixed with bentonite and deionized water, stirred at 500-1000 rpm for 30-70 minutes, dried at 100°C for 10-15 hours, ground and sieved to obtain a biochar precursor; (2) placing the biochar precursor under a nitrogen atmosphere for low-temperature carbonization treatment to obtain low-temperature biochar; (3) placing the biochar precursor in a vacuum environment and subjecting it to microwave carbonization treatment to obtain high-temperature biochar; (4) The low-temperature biochar and the high-temperature biochar were mixed, ground through a 150-250 mesh sieve, added to a 1 mol / L ferric chloride aqueous solution, stirred at 500-1000 rpm for 1 hour, allowed to stand for 15-20 hours, filtered, and the solid was taken. Then, the solid was added to a 2 wt% potassium dihydrogen phosphate aqueous solution, stirred at 200 rpm for 20 hours, centrifuged at 5000 rpm for 3 minutes, and dried at 80°C for 10 hours to obtain phosphorus-rich biochar; (5) Under a nitrogen atmosphere, deionized water, ethanol, and phosphorus-rich biochar were mixed, stirred at 120 rpm for 30 min, humic acid solution was added, stirring was continued for 10 h, 5 wt% sodium borohydride aqueous solution was added at 0.5 mL / s, stirring was continued for 1 h, and the mixture was allowed to stand for 4 h, and then washed with ultrapure water for 3 to 6 times, and dried at 50 to 70 ° C for 12 h to obtain a complex; (6) Acrylic acid and 0.02 g / mL potassium hydroxide aqueous solution are mixed, stirred at 100 rpm for 2 to 6 h, nanocellulose and complex are added, stirring is continued for 3 h, potassium persulfate and N,N-methylenebisacrylamide are added, and the temperature is raised to 50 to 70° C. under a nitrogen atmosphere, stirred at 300 to 700 rpm for 2 to 5 h, and then cooled to room temperature, dried at 50 to 70° C. for 12 to 20 h, and ground through a 60 to 150 mesh sieve to obtain a high-efficiency fertilizer.

2. The method for preparing a high-efficiency fertilizer according to claim 1, characterized in that: The mesh size of the sieving in step (1) is 40 to 80 meshes.

3. The method for preparing a high-efficiency fertilizer according to claim 1, characterized in that: The mass ratio of the pecan shell, 20wt% phosphoric acid solution, bentonite and deionized water in step (1) is 1:15-40:0.3-0.7:30-80.

4. The method for preparing a high-efficiency fertilizer according to claim 1, characterized in that: The process parameters of the low-temperature carbonization in step (2) are as follows: a heating rate of 2 to 6°C / min, a temperature of 250 to 350°C, and a holding time of 2 to 6h.

5. The method for preparing a high-efficiency fertilizer according to claim 1, characterized in that: The vacuum degree of the vacuum environment in step (3) is 0.08 MPa.

6. The method for preparing a high-efficiency fertilizer according to claim 1, characterized in that: The process parameters of the microwave carbonization in step (3) are: power of 600-1000W and time of 12-30min.

7. The method for preparing a high-efficiency fertilizer according to claim 1, characterized in that: In step (4), the mass ratio of the low-temperature biochar, the high-temperature biochar, the 1 mol / L ferric chloride aqueous solution, and the 2 wt% potassium dihydrogen phosphate aqueous solution is 0.1-0.6:1:100:

20.

8. The method for preparing a high-efficiency fertilizer according to claim 1, characterized in that: The preparation method of the humic acid solution in step (5) is as follows: humic acid and 2wt% sodium hydroxide aqueous solution are mixed in a mass ratio of 1:500, and the pH value of the solution is adjusted to 7 with hydrochloric acid to obtain the humic acid solution.

9. The method for preparing a high-efficiency fertilizer according to claim 1, characterized in that: The mass ratio of the deionized water, ethanol, phosphorus-rich biochar, humic acid solution, and 5wt% sodium borohydride aqueous solution in step (5) is 9:3-5:0.01-0.1:2.5:

8.

10. The method for preparing a high-efficiency fertilizer according to claim 1, characterized in that: The mass ratio of the acrylic acid, 0.02 g / mL potassium hydroxide aqueous solution, nanocellulose, complex, potassium persulfate, and N,N-methylenebisacrylamide in step (6) is 2: 10：0.4：0.2：0.1：0.01。

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