A composite soil conditioner for farmland and its preparation method

Abstract

The present invention discloses a composite soil conditioner for farmland, comprising the following raw materials: modified diatomite, humic acid, plant ash, red mud, polyglutamic acid-modified biochar, nano zero-valent iron, ferrous chloride, carboxymethyl chitosan derivative, aldehyde group-modified polyvinyl alcohol; the present invention also provides a preparation method of the composite soil conditioner. The composite soil conditioner provided by the present invention has a multi-layer slow-release structure, and each raw material cooperates with each other and synergistically enhances the effect. It can not only effectively remove heavy metals in the soil and improve the soil pH, but also improve the soil microenvironment, promote the utilization of fertilizers, increase the yield of crops, improve the soil permeability, enhance the soil water and fertilizer retention capacity, and improve the soil compaction situation.

Description

Technical Field

[0001] The present invention belongs to the technical field of soil repair agents, and particularly relates to a composite soil repair agent for farmland and a preparation method thereof. Background Art

[0002] Soil damage in agricultural production is manifested as soil compaction, acidification, secondary salinization, serious soil pollution represented by excessive heavy metal content, and serious stubble death and root rot of crops. Among these, any one phenomenon can cause harm to crops, leading to high incidence of various crop diseases and pests, low fertilizer utilization rate, poor crop quality and other problems.

[0003] The patent with the application number CN201910432800.3 provides a soil repair agent, which includes the following raw materials in parts by weight: 20-40 parts of nano-phosphate, 20-40 parts of modified silicon-containing minerals, 10-30 parts of industrial waste, 10-20 parts of magnesium compounds, and 5-10 parts of pH regulators. The raw materials in the soil repair agent provided by this invention cooperate with each other, so that after the soil repair agent is applied to the soil, it can achieve in-situ solidification of heavy metals through various methods such as adsorption, surface complexation, ion exchange, and coprecipitation. The solidification efficiency is high, and it can act stably on the soil and form stable substances with heavy metals, so that the stability of the soil repair agent is good. However, this soil repair agent is in powder form, with poor long-acting and slow-release effects, low utilization rate of active ingredients, and easy to cause waste of resources. The patent with the application number CN202010160897.X provides a preparation method of an acidic soil repair agent, which includes the following steps: first mix polyglutamic acid-modified biochar and attapulgite, sinter and crush them, granulate them, and then spray a chitosan acetate solution on the surface of the granules to obtain the product. The acidic soil repair agent provided by this invention has good environmental response ability through the synergistic effect of various raw materials and by wrapping a chitosan film on the surface of the granules, which can be selectively released according to the soil pH environment and is convenient to use. However, the chitosan film is brittle and has poor mechanical properties, and is easy to break during transportation and use, resulting in unstable product quality and further affecting the pH response performance of the soil repair agent. Summary of the Invention

[0004] Aiming at the deficiencies of the prior art, the purpose of the present invention is to provide a composite soil repair agent for farmland. This composite soil repair agent is prepared by compounding carboxymethyl chitosan derivatives, aldehyde-modified polyvinyl alcohol, modified diatomite, polyglutamic acid-modified biochar, etc. By adjusting the raw material ratio, each component synergistically enhances the effect, and has remarkable effects on soil heavy metal repair, soil pH adjustment, and crop yield increase. The present invention also provides a preparation method of this composite soil repair agent.

[0005] The technical solution adopted by the present invention to achieve the above purpose is as follows:

[0006] A composite soil conditioner for farmland, comprising the following raw materials in parts by weight: 20-30 parts of modified diatomite, 5-10 parts of humic acid, 10-20 parts of plant ash, 10-15 parts of red mud, 10-20 parts of polyglutamic acid-modified biochar, 1-3 parts of nano zero-valent iron, 0.5-2 parts of ferrous chloride, 10-15 parts of carboxymethyl chitosan derivative, 10-20 parts of aldehyde group-modified polyvinyl alcohol. The preparation method of the carboxymethyl chitosan derivative is as follows:

[0007] S1. Disperse 4-methylbenzylamine in 2-methyltetrahydrofuran, and successively add 5-bromopentanoic acid, benzyltriethylammonium chloride, and potassium hydroxide. Heat up to 60-70 °C, stir and react for 3-7 h, adjust the pH to 6-7, filter, take the filtrate, and obtain intermediate 1 through vacuum distillation and drying.

[0008] S2. Disperse the intermediate 1 obtained in step S1 in 2-methyltetrahydrofuran, and successively add butyl ethylene oxide and chromium acetate. Heat up to 65-75 °C, stir and react for 6-10 h, filter, take the filtrate, and obtain intermediate 2 through vacuum distillation, extraction, and drying.

[0009] S3. Disperse carboxymethyl chitosan in N,N-dimethylformamide, heat up to 65-80 °C, stir for 30-50 min, then successively add p-toluenesulfonic acid and the intermediate 2 obtained in step S2, continue to stir for 2-6 h, and obtain the carboxymethyl chitosan derivative through concentration, dialysis, and drying.

[0010] The synthesis route of the carboxymethyl chitosan derivative is as follows:

[0011]

[0012]

[0013] In the present invention, 4-methylbenzylamine and 5-bromopentanoic acid are used as starting materials, and under the action of benzyltriethylammonium chloride and potassium hydroxide, an N-alkylation reaction occurs to obtain intermediate 1; intermediate 1 and butyl ethylene oxide undergo a ring-opening reaction of epoxy alkane under the catalysis of chromium acetate to obtain intermediate 2; under the action of p-toluenesulfonic acid, intermediate 2 and carboxymethyl chitosan further undergo an esterification reaction to obtain the carboxymethyl chitosan derivative.

[0014] In order to obtain carboxymethyl chitosan derivatives and ensure product consistency, the molar ratio of 4-methylbenzylamine, 5-bromovaleric acid, benzyltriethylammonium chloride, and potassium hydroxide in step S1 is 1.2:0.8 - 1.2:0.04 - 0.06:0.7 - 1.1, and the addition amount of 4-methylbenzylamine in 2-methyltetrahydrofuran is 0.1 - 0.3 g / mL; the molar ratio of intermediate 1, butyl ethylene oxide, and chromium acetate in step S2 is 1:0.8 - 1.0:0.012 - 0.015, and the addition amount of intermediate 1 in 2-methyltetrahydrofuran is 0.17 - 0.26 g / mL; the mass ratio of carboxymethyl chitosan, intermediate 2, and p-toluenesulfonic acid in step S3 is 10:1 - 2:0.2 - 0.5, and the addition amount of carboxymethyl chitosan in N,N-dimethylformamide is 0.15 - 0.25 g / mL.

[0015] Preferably, the preparation method of the aldehyde-functionalized polyvinyl alcohol is as follows: Disperse polyvinyl alcohol in deionized water, add sodium periodate, and stir and react in the dark at 25 - 35 °C for 4 - 8 h, then add ethylene glycol and continue to stir for 40 - 60 min, and obtain the product after dialysis and drying. The mass ratio of polyvinyl alcohol, sodium periodate, and ethylene glycol is 1:0.6 - 0.9:0.5 - 0.8, and the addition amount of polyvinyl alcohol in deionized water is 10 - 30 mg / mL; the preparation method of the modified diatomite is as follows: Take an ethanol aqueous solution with a mass fraction of 85 - 95%, adjust the pH to 3 - 3.5, dropwise add 3-aminopropyltriethoxysilane under stirring conditions, stir for 30 - 50 min after dropping, then add diatomite and continue to stir for 20 - 40 min, filter, take the filter residue, and obtain the product after drying. The mass ratio of the ethanol aqueous solution, 3-aminopropyltriethoxysilane, and diatomite is 95 - 100:0.5 - 1.5:40; the preparation method of the polyglutamic acid-modified biochar is as follows: Dry and crush corn straw, pyrolyze at 400 - 600 °C for 2 - 3 h under nitrogen protection, wash, dry, and grind to obtain biochar. Disperse the biochar in deionized water, add polyglutamic acid, ultrasonically disperse for 5 - 15 min, adjust the pH to neutral, filter, dry, and grind to obtain the product. The mass ratio of biochar and polyglutamic acid is 1:1 - 2, and the addition amount of biochar in deionized water is 30 - 60 mg / mL.

[0016] The present invention also provides a preparation method of a composite soil conditioner for farmland, comprising the following steps:

[0017] (1) Mix the modified diatomite with an equal weight of water and grind for 30 - 50 min, then sequentially add a part of aldehyde-functionalized polyvinyl alcohol, humic acid, plant ash, red mud, polyglutamic acid-modified biochar, nano zero-valent iron, and ferrous chloride, mix evenly and granulate to obtain composite particles;

[0018] (2) Disperse the carboxymethyl chitosan derivative and the remaining aldehyde-functionalized polyvinyl alcohol in deionized water. After high-speed homogenization treatment, a mixed solution is obtained. Spray the mixed solution evenly on the surface of the composite particles obtained in step (1), and place it at a temperature of 30 - 50 °C and a humidity of 60 - 80% for 4 - 8 h, then dry to obtain the product.

[0019] In order to control the slow release of the active ingredients of the repair agent, improve the utilization efficiency of the repair agent, reduce the dosage of the repair agent, and reduce resource waste, the partially aldehyde-functionalized polyvinyl alcohol described in step (1) is 20 - 30% of the total mass of the aldehyde-functionalized polyvinyl alcohol; in step (2), the mass ratio of the carboxymethyl chitosan derivative to deionized water is 5 - 10:100. The high-speed homogenization treatment is carried out at 900 - 1200 r / min for 5 - 15 s, and the weight of the mixed solution sprayed on the surface of the composite particles accounts for 2 - 6% of the weight of the composite particles.

[0020] The present invention has the following beneficial effects:

[0021] (1) The present invention obtains the carboxymethyl chitosan derivative through N-alkylation reaction, epoxy compound ring-opening reaction and esterification reaction in sequence, introducing benzene ring structure, ester group and imino group into the long chain of carboxymethyl chitosan molecules; the ring structure and π-bond characteristics of the benzene ring enable π-π interactions to exist between polymer molecular chains, and at the same time increase the frictional force between molecular chains, increasing the intermolecular force, thereby improving the mechanical properties of carboxymethyl chitosan; the ester group and imino group can adsorb heavy metal ions through complexation or redox reactions, improving the adsorption performance of carboxymethyl chitosan for heavy metal ions; chitosan and its derivatives also have the function of regulating the soil microbial community structure and enhancing the activity of soil enzymes, thereby promoting the degradation and circulation of soil organic matter.

[0022] (2) The present invention uses modified diatomite as a carrier, aldehyde-functionalized polyvinyl alcohol as a binder and crosslinking agent, and is compounded with raw materials such as plant ash, red mud, polyglutamic acid-modified biochar, and nano-zero-valent iron to obtain composite particles; then a porous membrane material formed by crosslinking the carboxymethyl chitosan derivative and aldehyde-functionalized polyvinyl alcohol is coated on the outer surface of the composite particles to obtain a composite soil repair agent.

[0023] (3) The composite soil repair agent provided by the present invention has a multi-layer slow-release structure. Each raw material cooperates with each other, synergistically enhancing the effect, wrapping the active ingredients, improving their utilization rate, and achieving the purpose of long-term soil repair. The composite soil repair agent provided by the present invention can not only effectively remove heavy metals from the soil and improve the soil pH, but also improve the soil microenvironment, promote the utilization of fertilizers, increase the yield of crops, improve the soil permeability, increase the soil water and fertilizer retention capacity, and improve the soil compaction situation. Specific embodiments

[0024] Next, in combination with the embodiments of the present application, the technical solutions in the embodiments of the present application will be clearly and completely described. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present application. All raw materials used in the following embodiments are ordinary commercially available products.

[0025] Example 1

[0026] A preparation method of a carboxymethyl chitosan derivative, comprising the following steps:

[0027] S1. Disperse 4-methylbenzylamine in 2-methyltetrahydrofuran, and successively add 5-bromovaleric acid, benzyltriethylammonium chloride, and potassium hydroxide. Heat to 65 °C and stir for 5 h. Adjust the pH to 6-7 with sulfuric acid, filter, take the filtrate, and remove 2-methyltetrahydrofuran by vacuum distillation. After drying, Intermediate 1 is obtained, where the molar ratio of 4-methylbenzylamine, 5-bromovaleric acid, benzyltriethylammonium chloride, and potassium hydroxide is 1.2:0.9:0.05:0.9, and the addition amount of 4-methylbenzylamine in 2-methyltetrahydrofuran is 0.2 g / mL;

[0028] S2. Disperse Intermediate 1 obtained in step S1 in 2-methyltetrahydrofuran, and successively add butyl ethylene oxide and chromium acetate. Heat to 70 °C and stir for 8 h. Filter, take the filtrate, and remove 2-methyltetrahydrofuran by vacuum distillation. Add ethyl acetate and water for extraction, take the organic phase, concentrate and dry to obtain Intermediate 2, where the molar ratio of Intermediate 1, butyl ethylene oxide, and chromium acetate is 1:0.9:0.014, the addition amount of Intermediate 1 in 2-methyltetrahydrofuran is 0.22 g / mL, and the volume ratio of ethyl acetate to water is 1:1;

[0029] The NMR results of Intermediate 2 are as follows: 1 H NMR(300MHz, DMSO-d6)δ7.13-7.19(m, 4H), 5.37(s, 1H), 4.33-4.38(m, 1H), 4.09-4.15(m, 3H), 3.76(s, 2H), 2.53(t, 2H), 2.31(t, 2H), 2.18(s, 3H), 1.61-1.65(m, 2H), 1.20-1.25(m, 2H), 1.34-1.40(m, 6H), 0.88(t, 3H).

[0030] S3. Disperse carboxymethyl chitosan (particle size 80 - 100 mesh, purchased from Xi'an Longmao Biotechnology Co., Ltd.) in N,N - dimethylformamide, heat up to 70 °C, stir for 40 min, then successively add p - toluenesulfonic acid and the intermediate 2 obtained in step S2, continue stirring for 4 h, concentrate to remove part of N,N - dimethylformamide, dialyze with a dialysis bag with a molecular weight cut - off of 8000 - 14000 D for 72 h, change deionized water every 12 h, collect the solution in the dialysis bag and carry out vacuum freeze - drying to obtain the carboxymethyl chitosan derivative, where the mass ratio of carboxymethyl chitosan, intermediate 2, and p - toluenesulfonic acid is 10:1.2:0.3, and the addition amount of carboxymethyl chitosan in N,N - dimethylformamide is 0.2 g / mL.

[0031] The preparation method of aldehyde - modified polyvinyl alcohol is as follows: Disperse polyvinyl alcohol (content 93%, purchased from Nanchang Yizheng Chemical Industry Co., Ltd.) in deionized water, add sodium periodate, stir and react under dark conditions at 30 °C for 6 h, then add ethylene glycol and continue stirring for 50 min. Place the reaction mixture in a dialysis bag with a molecular weight cut - off of 8000 - 14000 D and dialyze for 72 h, change deionized water every 12 h, collect the solution in the dialysis bag and carry out vacuum freeze - drying to obtain it, where the mass ratio of polyvinyl alcohol, sodium periodate, and ethylene glycol is 1:0.7:0.6, and the addition amount of polyvinyl alcohol in deionized water is 20 mg / mL.

[0032] The preparation method of modified diatomite is as follows: Take an ethanol aqueous solution with a mass fraction of 90%, adjust the pH to 3 - 3.5 with acetic acid, dropwise add 3 - aminopropyltriethoxysilane under stirring conditions, stir for 40 min after dropping, then add diatomite (specific surface area 0.35 (m 2 / g, purchased from Guangdong Yuanlin New Materials Co., Ltd.), continue stirring for 30 min, filter, take the filter residue, vacuum - dry at 50 °C for 2 h, then dry at 120 °C under normal pressure for 1 h, and cool to room temperature to obtain it, where the mass ratio of the ethanol aqueous solution, 3 - aminopropyltriethoxysilane, and diatomite is 99:1:40.

[0033] The preparation method of polyglutamic acid - modified biochar is as follows: Dry and crush corn straw, pyrolyze at 500 °C for 2 h under nitrogen protection, wash with deionized water 2 - 3 times, dry at 60 °C, grind and pass through a 150 - mesh sieve to obtain biochar. Disperse the biochar in deionized water, add polyglutamic acid (particle size 80 - 100 mesh, purchased from Shandong Pingju Biotechnology Co., Ltd.), ultrasonically disperse for 10 min, adjust the pH to neutral, filter, take the filter residue, dry at 50 °C, grind and pass through a 150 - mesh sieve to obtain it, where the mass ratio of biochar and polyglutamic acid is 1:1.5, and the addition amount of biochar in deionized water is 50 mg / mL.

[0034] Example 2

[0035] A composite soil conditioner for farmland, comprising raw materials in the following parts by weight: 25 parts of the modified diatomite obtained in Example 1, 8 parts of humic acid, 15 parts of plant ash, 12 parts of red mud, 15 parts of the polyglutamic acid-modified biochar obtained in Example 1, 2 parts of nano zero-valent iron, 1 part of ferrous chloride, 12 parts of the carboxymethyl chitosan derivative obtained in Example 1, and 16 parts of the aldehyde-group modified polyvinyl alcohol obtained in Example 1.

[0036] A preparation method of a composite soil conditioner for farmland, comprising the following steps:

[0037] (1) Mix the modified diatomite with water in an equal number of parts by weight and grind for 40 min, then successively add part of the aldehyde-group modified polyvinyl alcohol (the part of the aldehyde-group modified polyvinyl alcohol is 25% of the total mass of the aldehyde-group modified polyvinyl alcohol), humic acid, plant ash, red mud, polyglutamic acid-modified biochar, nano zero-valent iron (grade 260, particle size 150 - 500 mesh, purchased from Shanghai Maoguo Nano Technology Co., Ltd.), and ferrous chloride, mix evenly and granulate to obtain composite particles;

[0038] (2) Disperse the carboxymethyl chitosan derivative and the remaining aldehyde-group modified polyvinyl alcohol in deionized water, and after high-speed homogenization treatment, obtain a mixed solution. Spray the mixed solution evenly on the surface of the composite particles obtained in step (1), place at a temperature of 40 °C and a humidity of 75% for 6 h, and dry to obtain the product. The mass ratio of the carboxymethyl chitosan derivative to deionized water is 7:100. The high-speed homogenization treatment is carried out at 1000 r / min for 10 s, and the weight of the mixed solution sprayed on the surface of the composite particles accounts for 4% of the weight of the composite particles.

[0039] Example 3

[0040] A composite soil conditioner for farmland, comprising raw materials in the following parts by weight: 25 parts of the modified diatomite obtained in Example 1, 8 parts of humic acid, 15 parts of plant ash, 12 parts of red mud, 15 parts of the polyglutamic acid-modified biochar obtained in Example 1, 2 parts of nano zero-valent iron, 1 part of ferrous chloride, 10 parts of the carboxymethyl chitosan derivative obtained in Example 1, and 16 parts of the aldehyde-group modified polyvinyl alcohol obtained in Example 1; The difference from Example 2 is that the weight part of the carboxymethyl chitosan derivative is changed.

[0041] Example 4

[0042] A composite soil conditioner for farmland, comprising the following raw materials in parts by weight: 25 parts of the modified diatomite obtained in Example 1, 8 parts of humic acid, 15 parts of plant ash, 12 parts of red mud, 15 parts of the polyglutamic acid-modified biochar obtained in Example 1, 2 parts of nano zero-valent iron, 1 part of ferrous chloride, 15 parts of the carboxymethyl chitosan derivative obtained in Example 1, 16 parts of the aldehyde group-modified polyvinyl alcohol obtained in Example 1; The difference from Example 2 is that the weight fraction of the carboxymethyl chitosan derivative is changed.

[0043] Example 5

[0044] A composite soil conditioner for farmland, comprising the following raw materials in parts by weight: 25 parts of the modified diatomite obtained in Example 1, 8 parts of humic acid, 15 parts of plant ash, 12 parts of red mud, 15 parts of the polyglutamic acid-modified biochar obtained in Example 1, 2 parts of nano zero-valent iron, 1 part of ferrous chloride, 12 parts of the carboxymethyl chitosan derivative obtained in Example 1, 12 parts of the aldehyde group-modified polyvinyl alcohol obtained in Example 1; The difference from Example 2 is that the weight fraction of the aldehyde group-modified polyvinyl alcohol is changed.

[0045] Comparative Example 1

[0046] A composite soil conditioner for farmland, comprising the following raw materials in parts by weight: 25 parts of the modified diatomite obtained in Example 1, 8 parts of humic acid, 15 parts of plant ash, 12 parts of red mud, 15 parts of the polyglutamic acid-modified biochar obtained in Example 1, 2 parts of nano zero-valent iron, 1 part of ferrous chloride, 5 parts of the carboxymethyl chitosan derivative obtained in Example 1, 16 parts of the aldehyde group-modified polyvinyl alcohol obtained in Example 1; The difference from Example 2 is that the weight fraction of the carboxymethyl chitosan derivative is changed.

[0047] Comparative Example 2

[0048] A composite soil conditioner for farmland, comprising the following raw materials in parts by weight: 25 parts of the modified diatomite obtained in Example 1, 8 parts of humic acid, 15 parts of plant ash, 12 parts of red mud, 15 parts of the polyglutamic acid-modified biochar obtained in Example 1, 2 parts of nano zero-valent iron, 1 part of ferrous chloride, 12 parts of the carboxymethyl chitosan derivative obtained in Example 1, 16 parts of polyvinyl alcohol; The difference from Example 2 is that the aldehyde group-modified polyvinyl alcohol is replaced by polyvinyl alcohol.

[0049] Comparative Example 3

[0050] A composite soil conditioner for farmland, comprising the following raw materials in parts by weight: 25 parts of the modified diatomite obtained in Example 1, 8 parts of humic acid, 15 parts of plant ash, 12 parts of red mud, 15 parts of the polyglutamic acid-modified biochar obtained in Example 1, 2 parts of nano zero-valent iron, 1 part of ferrous chloride, 12 parts of carboxymethyl chitosan, 16 parts of the aldehyde group-modified polyvinyl alcohol obtained in Example 1; The difference from Example 2 is that the carboxymethyl chitosan derivative is replaced by carboxymethyl chitosan.

[0051] The composite soil remediation agents for farmland described in Examples 3-5 and Comparative Examples 1-3 were all prepared according to the method described in Example 2.

[0052] The carboxymethyl chitosan derivative and the aldehyde-group modified polyvinyl alcohol were dispersed in deionized water, and after high-speed homogenization treatment, a mixed solution 1 was obtained, where the mass ratio of the carboxymethyl chitosan derivative, the aldehyde-group modified polyvinyl alcohol to deionized water was 7:7:100; the carboxymethyl chitosan derivative and polyvinyl alcohol were dispersed in deionized water, and after high-speed homogenization treatment, a mixed solution 2 was obtained, where the mass ratio of the carboxymethyl chitosan derivative, polyvinyl alcohol to deionized water was 7:7:100; the carboxymethyl chitosan and the aldehyde-group modified polyvinyl alcohol were dispersed in deionized water, and after high-speed homogenization treatment, a mixed solution 3 was obtained, where the mass ratio of the carboxymethyl chitosan, the aldehyde-group modified polyvinyl alcohol to deionized water was 7:7:100; 10 mL of the mixed solution 1, the mixed solution 2, and the mixed solution 3 were respectively taken and spread into films in a petri dish with a diameter of 9 cm, placed for 6 h at a temperature of 40 °C and a humidity of 75%, and then dried at room temperature for 24 h. The mechanical properties of the obtained film materials were tested, which were respectively the experimental group 1, the experimental group 2, and the experimental group 3. The mechanical property test was carried out in accordance with the provisions of GB13022-91 "Test Method for Tensile Properties of Plastic Films", using a universal mechanical testing machine. The test conditions were: the tensile speed was 5 mm / min, the temperature was 25 °C, and 3 samples were tested in each group and the average value was taken; the test results are shown in Table 1. It can be seen from the table that the tensile strength and elongation at break of the experimental group 1 were significantly better than those of the experimental group 2 and the experimental group 3; compared with the experimental group 2 and the experimental group 3 (using the mechanical blending method), in the experimental group 1, the carboxymethyl chitosan derivative and the aldehyde-group modified polyvinyl alcohol used a combination of chemical cross-linking and physical cross-linking, which significantly improved the mechanical properties of the film material.

[0053] Table 1 Test results of the mechanical properties of the film material

[0054] Test items Experiment Group 1 Experiment Group 2 Experiment Group 3 Tensile strength / MPa 61.5 47.7 52.0 Elongation at break / % 117 88 65

[0055] The composite soil remediation agents prepared in Examples 2-5 and Comparative Examples 1-3 were subjected to relevant tests. Take the surface 15 cm soil of a heavy metal contaminated farmland, air-dry it naturally, grind it repeatedly and sieve it, stir and mix it thoroughly, divide it into 8 equal parts by weight, and apply the composite soil remediation agents prepared in Examples 2-5 and Comparative Examples 1-3 to the heavy metal contaminated soil and stir evenly (1 kg per cubic meter). Sprinkle an appropriate amount of water every day to achieve the purpose of moistening, and cure for 8 days. The soil in the control group was not treated, and the heavy metal remediation effect test and pH test were carried out on the treated soil; for the heavy metal remediation effect test, the chromium content, lead content, mercury content, cadmium content, and arsenic content in the soil samples were determined; for the soil pH test, dissolve 5 g of soil samples in 25 mL of water, shake at 160 rpm for 12 h, let it stand for 3 h, and take the supernatant for measurement with a pH meter; for the field test, the tested crop: Zhengdan 958 corn, select land with consistent soil conditions, divide it into 8 plots after normal fertilization, and apply the composite soil remediation agents prepared in Examples 2-5 and Comparative Examples 1-3 respectively before sowing the crops, scatter them at 40 kg per mu along with fine tillage. After the scattering, cure for 1-2 days, then sow the seeds, and the planting density is 5000 plants per mu. Take the group without applying the composite soil remediation agent as the control group, and carry out unified field management. After the corn is harvested, count the yield per mu of corn; the above tests were repeated three times and the average value was taken. The test results are shown in Table 2. It can be seen from the table that the composite soil remediation agents provided in Examples 2-5 compound carboxymethyl chitosan derivatives, aldehyde-modified polyvinyl alcohol, modified diatomite, polyglutamic acid-modified biochar, etc. By adjusting the raw material ratio, each component synergistically enhances the effect, and has a significant effect on soil heavy metal remediation, soil pH adjustment, and crop yield increase. The heavy metal removal effect has reached the first-class standard of soil detection, which is significantly better than that of Comparative Examples 1-3; from the effect data of Examples 2-5 and Comparative Example 1, it can be seen that the weight parts of carboxymethyl chitosan derivatives and aldehyde-modified polyvinyl alcohol can affect the comprehensive performance of the composite soil remediation agent; from the effect data of soil pH, the composite soil remediation agents provided in Examples 2-5 and Comparative Example 1 compound carboxymethyl chitosan derivatives, aldehyde-modified polyvinyl alcohol, and modified diatomite, and form a multi-layer slow-release structure by using a combination of chemical cross-linking and physical cross-linking to effectively adjust the soil pH and keep the soil pH in a relatively stable environment. The composite soil remediation agents provided in Comparative Examples 2-3 compound each component raw material by mechanical blending. Although they can play a certain degree of repair role on the soil, their slow-release effect is poor. Once the soil acidity and alkalinity are adjusted after application, it will lead to over-repair, resulting in alkaline soil and affecting the normal growth of crops.

[0056] Table 2 Relevant Performance Test Results of Composite Soil Remediation Agents

[0057]

[0058]

[0059] The present invention uses modified diatomite as a carrier, aldehyde-group modified polyvinyl alcohol as a binder and crosslinking agent, and is compounded with raw materials such as plant ash, red mud, polyglutamic acid modified biochar, nano zero-valent iron, etc. to obtain composite particles; then a porous membrane material formed by crosslinking carboxymethyl chitosan derivative and aldehyde-group modified polyvinyl alcohol is coated on the outer surface of the composite particles to obtain a composite soil repair agent. The composite soil repair agent has a multi-layer slow-release structure, and the various raw materials cooperate with each other, synergistically enhancing the effect, wrapping the active ingredients, improving their utilization rate, and achieving the purpose of long-term soil repair. The composite soil repair agent provided by the present invention can not only effectively remove heavy metals in the soil and improve the soil pH, but also improve the soil microenvironment, promote the utilization of fertilizers, increase the yield of crops, improve the soil permeability, enhance the soil water and fertilizer retention capacity, and improve the soil compaction situation.

[0060] Although the embodiments of the present application have been shown and described, for those of ordinary skill in the art, it can be understood that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principle and spirit of the present application. The scope of the present application is defined by the appended claims and their equivalents.

Claims

1. A composite soil conditioner for farmland, characterized in that, It comprises raw materials in the following parts by weight: 20 - 30 parts of modified diatomite, 5 - 10 parts of humic acid, 10 - 20 parts of plant ash, 10 - 15 parts of red mud, 10 - 20 parts of polyglutamic acid modified biochar, 1 - 3 parts of nano zero-valent iron, 0.5 - 2 parts of ferrous chloride, 10 - 15 parts of carboxymethyl chitosan derivative, and 10 - 20 parts of aldehyde group modified polyvinyl alcohol. The preparation method of the carboxymethyl chitosan derivative is as follows: S1. Disperse 4-methylbenzylamine in 2-methyltetrahydrofuran, successively add 5-bromovaleric acid, benzyltriethylammonium chloride, and potassium hydroxide, heat up to 60 - 70 °C, stir and react for 3 - 7 h, adjust the pH to 6 - 7, filter, take the filtrate, and obtain Intermediate 1 through vacuum distillation and drying. The structural formula of Intermediate 1 is: ； S2. Disperse Intermediate 1 obtained in Step S1 in 2-methyltetrahydrofuran, successively add butyl epoxyethane and chromium acetate, heat up to 65 - 75 °C, stir and react for 6 - 10 h, filter, take the filtrate, and obtain Intermediate 2 through vacuum distillation, extraction, and drying. The structural formula of Intermediate 2 is: ； S3. Disperse carboxymethyl chitosan in N,N-dimethylformamide, heat up to 65 - 80 °C, stir for 30 - 50 min, then successively add p-toluenesulfonic acid and Intermediate 2 obtained in Step S2, continue to stir for 2 - 6 h, and obtain the carboxymethyl chitosan derivative through concentration, dialysis, and drying.

2. The composite soil conditioner for farmland according to claim 1, characterized in that, In Step S1, the molar ratio of 4-methylbenzylamine, 5-bromovaleric acid, benzyltriethylammonium chloride, and potassium hydroxide is 1.2:0.8 - 1.2:0.04 - 0.06:0.7 - 1.1, and the addition amount of 4-methylbenzylamine in 2-methyltetrahydrofuran is 0.1 - 0.3 g / mL.

3. The composite soil conditioner for farmland according to claim 1, characterized in that, In Step S2, the molar ratio of Intermediate 1, butyl epoxyethane, and chromium acetate is 1:0.8 - 1.0:0.012 - 0.015, and the addition amount of Intermediate 1 in 2-methyltetrahydrofuran is 0.17 - 0.26 g / mL.

4. The composite soil conditioner for farmland according to claim 1, characterized in that, In Step S3, the mass ratio of carboxymethyl chitosan, Intermediate 2, and p-toluenesulfonic acid is 10:1 - 2:0.2 - 0.5, and the addition amount of carboxymethyl chitosan in N,N-dimethylformamide is 0.15 - 0.25 g / mL.

5. The composite soil conditioner for farmland according to claim 1, characterized in that, The preparation method of the aldehyde group modified polyvinyl alcohol is: Disperse polyvinyl alcohol in deionized water, add sodium periodate, stir and react under light avoidance at 25 - 35 °C for 4 - 8 h, then add ethylene glycol and continue to stir for 40 - 60 min, and obtain it through dialysis and drying. The mass ratio of polyvinyl alcohol, sodium periodate, and ethylene glycol is 1:0.6 - 0.9:0.5 - 0.8, and the addition amount of polyvinyl alcohol in deionized water is 10 - 30 mg / mL.

6. The composite soil conditioner for farmland according to claim 1, characterized in that, The preparation method of the modified diatomite is as follows: Take an ethanol aqueous solution with a mass fraction of 85-95%, adjust the pH to 3-3.5, dropwise add 3-aminopropyltriethoxysilane under stirring conditions, stir for 30-50 min after the addition is completed, then add diatomite, continue to stir for 20-40 min, filter, take the filter residue, and dry it to obtain the product, where the mass ratio of the ethanol aqueous solution, 3-aminopropyltriethoxysilane to diatomite is 95-100:0.5-1.5:

40.

7. The composite soil conditioner for farmland according to claim 1, characterized in that, The preparation method of the polyglutamic acid-modified biochar is as follows: Dry and crush corn straw, pyrolyze it at 400-600 °C for 2-3 h under nitrogen protection, wash, dry and grind it to obtain biochar. Disperse the biochar in deionized water, add polyglutamic acid, ultrasonically disperse for 5-15 min, adjust the pH to neutral, filter, dry and grind it to obtain the product, where the mass ratio of biochar to polyglutamic acid is 1:1-2, and the addition amount of biochar in deionized water is 30-60 mg / mL.

8. A preparation method of the composite soil conditioner for farmland according to any one of claims 1 - 7, characterized in that, It includes the following steps: (1) Mix the modified diatomite with an equal weight portion of water and grind for 30-50 min, then sequentially add partial aldehyde-functionalized polyvinyl alcohol, humic acid, plant ash, red mud, polyglutamic acid-modified biochar, nano zero-valent iron, and ferrous chloride, mix evenly and granulate to obtain composite particles; (2) Disperse the carboxymethyl chitosan derivative and the remaining aldehyde-functionalized polyvinyl alcohol in deionized water, and obtain a mixed solution after high-speed homogenization treatment. Spray the mixed solution evenly on the surface of the composite particles obtained in step (1), place it at a temperature of 30-50 °C and a humidity of 60-80% for 4-8 h, and dry it to obtain the product.

9. The preparation method of the composite soil conditioner for farmland according to claim 8, characterized in that, In step (1), the partial aldehyde-functionalized polyvinyl alcohol is 20-30% of the total mass of the aldehyde-functionalized polyvinyl alcohol.

10. The preparation method of the composite soil conditioner for farmland according to claim 8, characterized in that, In step (2), the mass ratio of the carboxymethyl chitosan derivative to deionized water is 5-10:

100. The high-speed homogenization treatment is carried out at 900-1200 r / min for 5-15 s, and the weight of the mixed solution sprayed on the surface of the composite particles accounts for 2-6% of the weight of the composite particles.

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