Soil conditioner for improving saline-alkali soil and preparation method thereof

Abstract

The invention discloses a soil conditioner for improving saline-alkali soil and a preparation method of the soil conditioner, and belongs to the technical field of saline-alkali soil improvement. A light / biological dual-degradation foaming carrier is used as a matrix and is filled with microcapsules with core-shell structures, and the microcapsules are filled with organic matter fulvic acid and humic acid; a layer of microgel film covers the surface of the light / biological dual-degradation foaming carrier, and the structure has a good slow release effect on organic matters; a hydroxyl group of a bio-based polyurethane monomer castor oil polyether polyol is bonded with a silicon hydroxyl group of modified nano titanium dioxide obtained by gamma-aminopropyltriethoxysilane treatment, so that the nano titanium dioxide is loaded in the bio-based polyurethane foam material; the light / biological dual-degradation foaming carrier can promote decomposition through light degradation and biological degradation, and chitosan and potassium alginate in the shell of the microcapsule are natural materials and have good degradability when applied to soil as a soil conditioner.

Description

Technical Field

[0001] The present invention belongs to the technical field of saline-alkali land improvement, and particularly relates to a soil conditioner for saline-alkali soil improvement and a preparation method thereof. Background Art

[0002] Saline-alkali land has characteristics such as high salt content, easy hardening, poor structure, low organic matter content, and weak water storage and fertilizer retention capacity. These characteristics determine that it is extremely difficult to utilize agriculturally during the initial stage of reclamation until the desalination to normal soil. At the same time, improper agricultural utilization methods make the soil salinization repetitive. Currently, saline-alkali land is a widespread form of land degradation globally, especially more common in arid and semi-arid regions. The formation of saline-alkali land is mainly due to the accumulation of salts in the soil, which will seriously affect the soil structure, reduce soil fertility, limit crop growth, and ultimately lead to a decrease in agricultural yields. The treatment of saline-alkali land is a complex and extremely challenging task, involving the improvement of soil physical properties, the reduction of salt content, and the enhancement of soil biological activity.

[0003] Currently, the biological method is considered the most effective and safe method among the saline-alkali land improvement techniques. By introducing salt-tolerant plants or microorganisms, it promotes the accumulation of soil organic matter and microbial diversity. This method is environmentally friendly and sustainable. However, the existing biological conditioners have a slow action speed, the effects are not obvious, and they are greatly restricted by environmental conditions.

[0004] Chinese Patent with Publication No. CN105001876B discloses a saline-alkali soil conditioner and its special microcapsule-type organic acid slow-release preparation. A slow-release preparation in the form of microcapsules is prepared with an acrylic polymer as the capsule wall and an organic acid as the capsule core. However, in this scheme, acrylic polymers are usually synthetic polymer materials, and their degradation speed in the natural environment is relatively slow. Due to the stability of their molecular structure and the lack of microbial enzymes that can effectively degrade in the natural environment, they are likely to remain in the soil for a long time, resulting in changes in the soil structure and having potential negative impacts on the soil ecosystem. Summary of the Invention

[0005] The object of the present invention is to provide a soil conditioner for saline-alkali soil improvement and a preparation method thereof. Using a photo / biodegradable foaming carrier as the matrix, microcapsules with a core-shell structure are filled inside. The microcapsules are filled with organic matters such as fulvic acid and humic acid, and a microgel film is covered on the surface of the photo / biodegradable foaming carrier. This structure has a good slow-release effect on organic matters; the modified nano-titanium dioxide treated with γ-aminopropyltriethoxysilane contains silanol groups, which are bonded to the hydroxyl groups of the biobased polyurethane monomer castor oil polyether polyol, so that the nano-titanium dioxide is loaded in the biobased polyurethane foaming material; the photo / biodegradable foaming carrier can be decomposed by photo-degradation and biodegradation. The chitosan and potassium alginate of the microcapsule shell are natural materials, and have good degradability when used as a soil conditioner in the soil.

[0006] The object of the present invention can be achieved by the following technical solutions: A preparation method of a soil conditioner for saline-alkali soil improvement, comprising the following steps:

[0007] Step 1: Add the microcapsule complex, the photo / biodegradable foaming carrier and deionized water into a reaction kettle, ultrasonically disperse for 40 - 60 min, stir at 20 - 25 °C and 400 - 500 r / min for 2 - 3 h, then add potassium alginate and a glutaraldehyde solution with a mass fraction of 1 - 2%, continue to stir and crosslink for 20 - 30 min, filter, wash the filter cake with deionized water and absolute ethanol respectively for 2 - 3 times, and vacuum dry at 60 - 80 °C for 1 - 2 h to obtain a double-assembled microcapsule carrier complex.

[0008] Step 2: Add N-isopropylacrylamide and N,N'-methylenebisacrylamide into a reaction kettle, stir at 20 - 25 °C and 400 - 500 r / min for 20 - 30 min, then add sodium dodecyl sulfate and deionized water, heat to 40 - 50 °C, continue to stir for 20 - 30 min, introduce ammonia gas at a flow rate of 10 - 12 min / L for 30 - 40 min, heat to 70 - 80 °C, add ammonium persulfate, continue to stir and react in a nitrogen atmosphere for 6 - 7 h, then add the double-assembled microcapsule carrier complex into the reaction kettle, continue to stir for 20 - 30 min, filter, wash the filter cake with petroleum ether and deionized water respectively for 2 - 3 times, and vacuum dry at 60 - 80 °C for 1 - 2 h to obtain a soil conditioner for saline-alkali soil improvement.

[0009] Further, in Step 1, the dosage ratio of the microcapsule complex, the photo / biodegradable foaming carrier, deionized water, potassium alginate and the glutaraldehyde solution is 2 - 2.5 kg : 2 - 3 kg : 3 - 4 L : 2 - 2.5 kg : 0.4 - 0.5 L.

[0010] Further, the dosage ratios of N-isopropylacrylamide, N,N'-methylenebisacrylamide, sodium dodecyl sulfate, deionized water, ammonium persulfate, and the double-assembled microcapsule carrier complex in step two are 3 - 4 kg : 1.2 - 1.5 kg : 0.1 - 0.2 kg : 3 - 4 L : 0.4 - 0.5 L : 2 - 3 kg.

[0011] Further, the microcapsule complex in step one is prepared through the following steps:

[0012] Add magnetically modified zeolite powder, fulvic acid, humic acid, and deionized water into a reaction kettle, ultrasonically disperse for 40 - 60 min, perform vacuum impregnation at 20 - 25 °C and 400 - 500 r / min for 20 - 30 min, then add a chitosan solution into the reaction kettle, ultrasonically disperse at 40 - 45 °C for 40 - 60 min, add a potassium chloride solution with a concentration of 0.5 - 0.6 mol / L to adjust the pH value to 5.5 - 6, and centrifuge at 1000 - 1200 r / min for 5 - 6 min to obtain the microcapsule complex with the first assembly coating.

[0013] Further, the chitosan solution is obtained by stirring and mixing chitosan and an ice acetic acid solution with a mass fraction of 1 - 2% according to a dosage ratio of 4 - 5 kg : 7.5 - 8.5 L.

[0014] Further, the dosage ratios of magnetically modified zeolite powder, fulvic acid, humic acid, deionized water, chitosan solution, and potassium chloride solution are 3 - 4 kg : 0.5 - 0.7 kg : 0.3 - 0.5 kg : 3 - 4 L : 8 - 9 L : 0.5 - 0.6 L.

[0015] Further, the magnetically modified zeolite powder is prepared through the following steps:

[0016] Add zeolite powder, citric acid, and deionized water into a reaction kettle, stir at 50 - 55 °C and 400 - 500 r / min for 20 - 30 min, then add nano-ferroferric oxide particles, perform vacuum impregnation at 50 - 55 °C and 400 - 500 r / min for 2 - 3 h, filter, wash the filter cake with deionized water until the last washing liquid is neutral to obtain the magnetically modified zeolite powder.

[0017] Further, the dosage ratios of zeolite powder, citric acid, deionized water, and nano-ferroferric oxide particles are 4 - 5 kg : 1 - 2 kg : 8 - 9 L : 0.8 - 1 kg.

[0018] Further, the light / biodegradable foaming carrier in step one is prepared through the following steps:

[0019] Castor oil polyether polyol, modified nano-titanium dioxide, and deionized water are added to a reaction kettle, stirred for 40 - 60 minutes under the conditions of 20 - 25 °C and 400 - 500 r / min, then triethylenediamine, dibutyltin dilaurate, 1,4-butanediol as a chain extender, and isocyanate are added, and stirring is continued for 40 - 60 minutes. Then it is injected into a mold, heated to 120 - 130 °C and stirred at 80 - 90 r / min for 10 - 12 minutes, cured, demolded, naturally cooled to room temperature, vacuum dried at 60 - 80 °C for 1 - 2 hours, and pulverized to obtain a light / biodegradable foaming carrier with a particle size of 0.5 - 0.7 mm.

[0020] Furthermore, the dosage ratio of castor oil polyether polyol, modified nano-titanium dioxide, deionized water, triethylenediamine, dibutyltin dilaurate, 1,4-butanediol, and isocyanate is 14 - 15 L : 5 - 6 kg : 20 - 25 L : 0.1 - 0.2 kg : 0.2 - 0.3 L : 0.1 - 0.2 L : 0.3 - 0.4 L.

[0021] Furthermore, the modified nano-titanium dioxide powder is prepared by the following steps:

[0022] Nano-titanium dioxide powder with a particle size of 40 - 50 nm and absolute ethanol are added to a reaction kettle, ultrasonically dispersed for 10 - 20 minutes, stirred for 1 - 2 hours under the conditions of 80 - 85 °C and 400 - 500 r / min, γ-aminopropyltriethoxysilane is added, and stirring is continued for 1 - 2 hours. Then it is filtered, and the filter cake is washed 2 - 3 times with deionized water and absolute ethanol respectively, and vacuum dried at 60 - 80 °C for 1 - 2 hours to obtain the modified nano-titanium dioxide powder treated with silane coupling agent.

[0023] Furthermore, the dosage ratio of nano-titanium dioxide powder, absolute ethanol, and γ-aminopropyltriethoxysilane is 3 - 4 kg : 8 - 9 L : 800 - 900 mL.

[0024] The beneficial effects of the present invention:

[0025] 1. The soil conditioner for saline-alkali soil improvement prepared by the present invention uses a light / biodegradable foaming carrier as the matrix, and is internally filled with double-assembled microcapsules with a core-shell structure. The double-assembled microcapsules are filled with organic matter humic acid and fulvic acid, and a microgel film is covered on the surface of the light / biodegradable foaming carrier. This structure has a good slow-release effect on organic matter and has good water retention ability. The foaming carrier and the microgel film show water absorption and swelling, and after water absorption and swelling, a porous structure is formed in the soil, reducing the pH, air permeability, and water permeability of the soil, alleviating the hardening phenomenon. This porous structure can provide a good parasitic environment for soil microorganisms, and the porous structure has abundant pores and a large specific surface area, which can provide more adsorption sites, thereby improving the adsorption ability of nano-ferroferric oxide to heavy metals.

[0026] 2. The double-assembled microcapsule carrier complex of the present invention is prepared by subjecting magnetically modified zeolite powder to citric acid etching treatment, resulting in a rough and porous surface with negatively charged carboxyl groups. It cross-links and assembles with the positively charged amino groups in the chitosan molecular chain. After the first assembly is completed, the microcapsule complex is dispersed in an aqueous potassium alginate solution and undergoes a second cross-linking assembly with the carboxyl groups in the potassium alginate molecular chain, forming a core-shell microcapsule with a polyelectrolyte membrane on the surface of the modified zeolite. The shell is potassium alginate, which has a large number of carboxyl groups. The light / biodegradable foaming carrier is loaded with modified nano-titanium dioxide treated with a silane coupling agent, and the amino groups on the surface of the nano-titanium dioxide can be used to fix the microcapsules, realizing the stable and long-term release of organic matter.

[0027] 3. For the microcapsule complex of the present invention, nano-ferroferric oxide particles are filled into the internal pores of zeolite. The nano-ferroferric oxide particles carry a positive charge under acidic conditions. The magnetically modified zeolite powder, fulvic acid, and humic acid are dispersed in deionized water, and the positive charge characteristics of the nano-ferroferric oxide particles are used to specifically adsorb the negative charges of fulvic acid and humic acid, thereby fixing fulvic acid and humic acid in the internal voids. Then, it cross-links and assembles with the positively charged amino groups in the chitosan molecular chain, and the porous property can improve the adsorption of nano-ferroferric oxide on soil heavy metals.

[0028] 4. For the light / biodegradable foaming carrier of the present invention, castor oil polyether polyol, nano-titanium dioxide, and deionized water are mixed to form a prepolymer, which polymerizes and foams under the action of an initiator, a catalyst, and a chain extender to obtain the light / biodegradable foaming carrier. The hydroxyl groups of the bio-based polyurethane monomer castor oil polyether polyol are bonded to the silanol groups of the modified nano-titanium dioxide treated with γ-aminopropyltriethoxysilane, enabling the nano-titanium dioxide to be loaded in the bio-based polyurethane foaming material. The light / biodegradable foaming carrier can be decomposed by photo-degradation and biodegradation, and has good degradability when used as a soil conditioner in soil. Detailed implementation mode

[0029] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the 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.

[0030] Example 1: A preparation method of a soil conditioner for saline-alkali soil improvement includes the following steps:

[0031] S1: Add 3 kg of nano-titanium dioxide powder with a particle size of 40 - 50 nm and 8 L of absolute ethanol into a reaction kettle, ultrasonically disperse for 10 min, stir for 1 h under the conditions of 80 °C and 400 r / min, add 800 mL of γ-aminopropyltriethoxysilane, continue to stir for 1 h, filter, wash the filter cake twice with deionized water and absolute ethanol respectively, and vacuum dry at 60 °C for 1 h to obtain modified nano-titanium dioxide powder treated with silane coupling agent.

[0032] S2: Add 14 L of castor oil polyether polyol, 5 kg of modified nano-titanium dioxide and 20 L of deionized water into a reaction kettle, stir at 20 °C and 400 r / min for 40 min, then add 0.1 kg of triethylenediamine, 0.2 L of dibutyltin dilaurate, 0.1 L of 1,4-butanediol as a chain extender and 0.3 L of isocyanate, continue to stir for 40 min, inject into a mold, heat to 120 °C and stir at 80 r / min for 10 min, cure, demold, naturally cool to room temperature, vacuum dry at 60 °C for 1 h, and pulverize to obtain a photo / biodegradable foaming carrier with a particle size of 0.5 - 0.7 mm.

[0033] Castor oil polyether polyol, nano-titanium dioxide and deionized water are mixed to form a prepolymer, which polymerizes and foams under the action of an initiator, a catalyst and a chain extender with isocyanate to obtain a photo / biodegradable foaming carrier; the hydroxyl group of the bio-based polyurethane monomer castor oil polyether polyol is bonded to the silanol group of the modified nano-titanium dioxide obtained by treatment with γ-aminopropyltriethoxysilane, so that nano-titanium dioxide is loaded in the bio-based polyurethane foaming material; the photo / biodegradable foaming carrier can promote decomposition through photo-degradation and biodegradation, and has good degradability when applied in soil as a soil conditioner.

[0034] S3: Add 4 kg of zeolite powder, 1 kg of citric acid and 8 L of deionized water into a reaction kettle, stir at 50 °C and 400 r / min for 20 min, then add 0.8 kg of nano-ferroferric oxide particles, vacuum impregnate at 50 °C and 400 r / min for 2 h, filter, wash the filter cake with deionized water until the last washing liquid is neutral to obtain magnetically modified zeolite powder.

[0035] Disperse zeolite powder and nano-ferroferric oxide particles in deionized water for impregnation, and fill nano-ferroferric oxide particles into the internal pores of zeolite through physical adsorption.

[0036] S4: Add 3 kg of modified zeolite powder, 0.5 kg of fulvic acid, 0.3 kg of humic acid and 3 L of deionized water into a reaction kettle, ultrasonically disperse for 40 min, vacuum impregnate for 20 min under the conditions of 20 °C and 400 r / min, then add 8 L of chitosan solution into the reaction kettle, ultrasonically disperse at 40 °C for 40 min, add 0.5 L of potassium chloride solution with a concentration of 0.5 mol / L to adjust the pH value to 5.5, and centrifuge for 5 min under the condition of 1000 r / min to obtain the microcapsule complex with the first assembly coating.

[0037] S5: Add 2 kg of microcapsule complex, 2 kg of photo / biodegradable foaming carrier and 3 L of deionized water into a reaction kettle, ultrasonically disperse for 40 min, stir for 2 h under the conditions of 20 °C and 400 r / min, then add 2 kg of potassium alginate and 0.4 L of glutaraldehyde solution with a mass fraction of 1%, continue to stir and crosslink for 20 min, filter, wash the filter cake twice with deionized water and absolute ethanol respectively, and vacuum dry at 60 °C for 1 h to obtain the double-assembled microcapsule carrier complex.

[0038] After the magnetically modified zeolite powder is treated by citric acid etching, the surface is rough and porous and carries negatively charged carboxyl groups, which crosslink and assemble with the positively charged amino groups in the chitosan molecular chain. After the first assembly is completed, it is dispersed in the aqueous solution of potassium alginate and completes the second crosslinking assembly with the carboxyl groups in the potassium alginate molecular chain to form a core-shell microcapsule with a polyelectrolyte membrane on the surface of the modified zeolite.

[0039] During the assembly process, negatively charged fulvic acid and humic acid will bind to the positively charged amino groups in the chitosan molecular chain, which is not conducive to the formation of the core-shell structure. By filling nano-ferroferric oxide particles into the internal pores of the zeolite, the nano-ferroferric oxide particles carry positive charges under acidic conditions. Disperse the magnetically modified zeolite powder, fulvic acid and humic acid in deionized water, and use the positively charged characteristics of the nano-ferroferric oxide particles to specifically adsorb the negative charges of fulvic acid and humic acid, so as to fix fulvic acid and humic acid in the internal voids, avoid affecting the formation of the core-shell structure, and avoid the shedding of fulvic acid and humic acid due to only physical adsorption.

[0040] The shell of the double-assembled microcapsule carrier complex is potassium alginate, which has a large number of carboxyl groups. The surface of the photo / biodegradable foaming carrier is loaded with modified nano-titanium dioxide treated by a silane coupling agent, and the amino groups on the surface of the nano-titanium dioxide can be used to fix the microcapsules.

[0041] S6: Add 3 kg of N-isopropylacrylamide and 1.2 kg of N,N'-methylenebisacrylamide into the reaction kettle, stir for 20 min under the conditions of 20 °C and 400 r / min, then add 0.1 kg of sodium dodecyl sulfate and 3 L of deionized water, heat to 40 °C, continue to stir for 20 min, introduce ammonia gas for 30 min at a flow rate of 10 min / L, heat to 70 °C, add 0.4 L of ammonium persulfate, and continue to stir and react for 6 h under a nitrogen atmosphere. Then add 2 kg of the double-assembled microcapsule carrier complex into the reaction kettle, continue to stir for 20 min, filter, wash the filter cake twice with petroleum ether and ionized water respectively, and dry it in vacuum at 60 °C for 1 h to obtain a soil conditioner for saline-alkali soil improvement.

[0042] Prepare a mixture of poly(N-isopropylacrylamide) microgel and hydrogel by emulsion polymerization using N-isopropylacrylamide to obtain a microgel film.

[0043] A soil conditioner for saline-alkali soil improvement uses a photo / biodegradable foaming carrier as the matrix, internally filled with microcapsules having a core-shell structure. The microcapsules are filled with organic matter humic acid and fulvic acid, and a microgel film is covered on the surface of the photo / biodegradable foaming carrier. This structure has good water retention capacity. The foaming carrier and the microgel film show water absorption and swelling, and after water absorption and swelling, a porous structure is formed in the soil, increasing soil aeration and water permeability, alleviating the hardening phenomenon. When the porous structure is combined with microbial agents, it can provide a good parasitic environment for soil microorganisms, and the porous structure can improve the adsorption capacity of nano-ferroferric oxide for heavy metals.

[0044] Example 2: A preparation method of a soil conditioner for saline-alkali soil improvement, comprising the following steps:

[0045] S1: Add 3.5 kg of nano-titanium dioxide powder with a particle size of 40 - 50 nm and 8.5 L of absolute ethanol into the reaction kettle, ultrasonically disperse for 15 min, stir for 1.5 h under the conditions of 82.5 °C and 450 r / min, add 850 mL of γ-aminopropyltriethoxysilane, continue to stir for 1.5 h, filter, wash the filter cake twice with ionized water and absolute ethanol respectively, and dry it in vacuum at 70 °C for 1.5 h to obtain the modified nano-titanium dioxide powder treated with a silane coupling agent.

[0046] S2: Add 14.5 L of castor oil polyether polyol, 5.5 kg of modified nano-titanium dioxide, and 22.5 L of deionized water into a reaction kettle, stir for 50 min under the conditions of 22.5 °C and 450 r / min, then add 0.15 kg of triethylenediamine, 0.25 L of dibutyltin dilaurate, 0.15 L of 1,4-butanediol as a chain extender, and 0.35 L of isocyanate, continue to stir for 50 min, inject into a mold, heat to 125 °C and stir at 85 r / min for 11 min, cure, demold, naturally cool to room temperature, vacuum dry at 70 °C for 1.5 h, and pulverize to obtain a light / biodegradable foaming carrier with a particle size of 0.5 - 0.7 mm.

[0047] S3: Add 4.5 kg of zeolite powder, 1.5 kg of citric acid, and 8.5 L of deionized water into a reaction kettle, stir for 25 min under the conditions of 52.5 °C and 450 r / min, then add 0.9 kg of nano-ferroferric oxide particles, vacuum impregnate for 2.5 h under the conditions of 52.5 °C and 450 r / min, filter, wash the filter cake with deionized water until the last washing liquid is neutral to obtain magnetically modified zeolite powder.

[0048] S4: Add 3.5 kg of magnetically modified zeolite powder, 0.6 kg of fulvic acid, 0.4 kg of humic acid, and 3.5 L of deionized water into a reaction kettle, ultrasonically disperse for 50 min, vacuum impregnate for 25 min under the conditions of 22.5 °C and 450 r / min, then add 8.5 L of chitosan solution into the reaction kettle, ultrasonically disperse at 42.5 °C for 50 min, then add 0.55 L of potassium chloride solution with a concentration of 0.55 mol / L to adjust the pH value to 5.75, and centrifuge at 1100 r / min for 5.5 min to obtain a microcapsule composite with the first assembly coating.

[0049] S5: Add 2.25 kg of microcapsule composite, 2.5 kg of light / biodegradable foaming carrier, and 3.5 L of deionized water into a reaction kettle, ultrasonically disperse for 50 min, stir for 2.5 h under the conditions of 22.5 °C and 450 r / min, then add 2.25 kg of potassium alginate and 0.45 L of glutaraldehyde solution with a mass fraction of 1.5%, continue to stir and crosslink for 25 min, filter, wash the filter cake twice with ionized water and absolute ethanol respectively, vacuum dry at 70 °C for 1.5 h to obtain a double-assembled microcapsule carrier composite.

[0050] S6: Add 3.5 kg of N-isopropylacrylamide and 1.35 kg of N,N'-methylenebisacrylamide into the reaction kettle, stir for 25 min under the conditions of 22.5 °C and 450 r / min, then add 0.15 kg of sodium dodecyl sulfate and 3.5 L of deionized water, heat to 45 °C, continue to stir for 25 min, introduce ammonia gas at a flow rate of 11 min / L for 35 min, heat to 75 °C, add 0.45 L of ammonium persulfate, and continue to stir and react for 6.5 h under a nitrogen atmosphere. Then add 2.5 kg of double-assembled microcapsule carrier complex into the reaction kettle, continue to stir for 25 min, filter, wash the filter cake twice with petroleum ether and ionized water respectively, and dry it in vacuum at 70 °C for 1.5 h to obtain a soil conditioner for improving saline-alkali soil.

[0051] Example 3: A preparation method of a soil conditioner for improving saline-alkali soil, comprising the following steps:

[0052] S1: Add 4 kg of nano-titanium dioxide powder with a particle size of 40 - 50 nm and 9 L of absolute ethanol into the reaction kettle, ultrasonically disperse for 20 min, stir for 2 h under the conditions of 85 °C and 500 r / min, add 900 mL of γ-aminopropyltriethoxysilane, continue to stir for 2 h, filter, wash the filter cake three times with ionized water and absolute ethanol respectively, and dry it in vacuum at 80 °C for 2 h to obtain modified nano-titanium dioxide powder treated with silane coupling agent.

[0053] S2: Add 15 L of castor oil polyether polyol, 6 kg of modified nano-titanium dioxide and 25 L of deionized water into the reaction kettle, stir for 60 min under the conditions of 25 °C and 500 r / min, then add 0.2 kg of triethylenediamine, 0.3 L of dibutyltin dilaurate, 0.2 L of 1,4-butanediol as a chain extender and 0.4 L of isocyanate, continue to stir for 60 min, inject into the mold, heat to 130 °C and stir at 90 r / min for 12 min, cure, demold, naturally cool to room temperature, dry it in vacuum at 80 °C for 2 h, and pulverize to obtain a light / biodegradable foaming carrier with a particle size of 0.5 - 0.7 mm.

[0054] S3: Add 5 kg of zeolite powder, 2 kg of citric acid and 9 L of deionized water into the reaction kettle, stir for 30 min under the conditions of 55 °C and 500 r / min, then add 1 kg of nano-ferroferric oxide particles, and carry out vacuum impregnation at 55 °C and 500 r / min for 3 h, filter, wash the filter cake with deionized water until the last washing liquid is neutral to obtain magnetically modified zeolite powder.

[0055] S4: Add 4 kg of magnetized modified zeolite powder, 0.7 kg of fulvic acid, 0.5 kg of humic acid, and 4 L of deionized water into the reaction kettle, ultrasonically disperse for 60 min, and perform vacuum impregnation for 30 min at 25 °C and 500 r / min. Then add 9 L of chitosan solution into the reaction kettle, ultrasonically disperse at 45 °C for 60 min, add 0.6 L of potassium chloride solution with a concentration of 0.6 mol / L to adjust the pH value to 6, and centrifuge for 6 min at 1200 r / min to obtain the microcapsule composite with the first assembly coating.

[0056] S5: Add 2.5 kg of microcapsule composite, 3 kg of photo / biodegradable foaming carrier, and 4 L of deionized water into the reaction kettle, ultrasonically disperse for 60 min, stir at 25 °C and 500 r / min for 3 h, then add 2.5 kg of potassium alginate and 0.5 L of glutaraldehyde solution with a mass fraction of 2%, continue to stir and crosslink for 30 min, filter, wash the filter cake with deionized water and absolute ethanol three times respectively, and vacuum dry at 80 °C for 2 h to obtain the double-assembled microcapsule carrier composite.

[0057] S6: Add 4 kg of N-isopropylacrylamide and 1.5 kg of N,N'-methylenebisacrylamide into the reaction kettle, stir at 25 °C and 500 r / min for 30 min, then add 0.2 kg of sodium dodecyl sulfate and 4 L of deionized water, heat to 50 °C, continue to stir for 30 min, introduce ammonia gas at a flow rate of 12 min / L for 40 min, heat to 80 °C, add 0.5 L of ammonium persulfate, and continue to stir and react for 7 h under a nitrogen atmosphere. Then add 3 kg of the double-assembled microcapsule carrier composite into the reaction kettle, continue to stir for 30 min, filter, wash the filter cake with petroleum ether and deionized water three times respectively, and vacuum dry at 80 °C for 2 h to obtain the soil conditioner for saline-alkali soil improvement.

[0058] Comparative Example 1: On the basis of Example 3, replace the modified nano-titanium dioxide in step S2 with nano-titanium dioxide powder with a particle size of 40 - 50 nm in step S1 with the same mass, and keep the rest of the steps unchanged to prepare a soil conditioner for saline-alkali soil improvement.

[0059] Comparative Example 2: On the basis of Example 3, do not add the photo / biodegradable foaming carrier in step S5, and keep the rest of the steps unchanged to prepare a soil conditioner for saline-alkali soil improvement.

[0060] Comparative Example 3: On the basis of Example 3, replace the magnetized modified zeolite powder in step S4 with the zeolite powder in step S3 with the same mass, and keep the rest of the steps unchanged to prepare a soil conditioner for saline-alkali soil improvement.

[0061] Comparative Example 4: On the basis of Example 3, the double-assembled microcapsule carrier complex in step S5 was directly used as a soil conditioner for saline-alkali soil improvement.

[0062] Performance tests were carried out on a soil conditioner for saline-alkali soil improvement prepared in Examples 1 - 3 and Comparative Examples 1 - 4. The test site was a saline-alkali area in the northeast of Suzhou City, Anhui Province. Two weeks before sowing corn, a subsoiling machine was used to subsoil the surface soil of the planting area. The depth of the subsoiled surface soil was 23 cm, and this was repeated 3 times. The soil conditioner was applied at a rate of 2 kg / mu. After application, reclamation was carried out once, and the reclamation depth was 30 cm. The physical and chemical properties of the soil were measured before planting corn and at the time of corn harvest. 20 samples were taken from each test field, and the average values of each physical and chemical property were calculated, and the content of heavy metal (cadmium) in the soil was measured. The results are shown in Table 1:

[0063] Table 1 Performance test table of soil conditioner for saline-alkali soil improvement

[0064]

[0065]

[0066] As can be seen from Table 1, for the soil conditioners prepared in Examples 1 - 3, after being applied to the soil, the organic matter, soil porosity, and water absorption were significantly better than those of the comparative examples, while the water-soluble total salt, soil pH, and cadmium content were significantly lower than those of the comparative examples. This shows that the soil conditioner prepared by the present invention has a good slow-release effect on organic matter, has excellent water absorption, can increase the soil pH and soil porosity, and can remove heavy metals from the soil.

[0067] In Comparative Example 1, the modified nano-titanium dioxide was replaced with nano-titanium dioxide powder. The nano-titanium dioxide was treated with a silane coupling agent, and the nano-titanium dioxide could be loaded on the photo / biodegradable foaming carrier. The nano-titanium dioxide could promote the degradation of the photo / biodegradable foaming carrier, and a large number of amino groups were carried on the surface of the modified nano-titanium dioxide, which bonded with the carboxyl groups on the surface of the microcapsules, thus realizing the fixation of the microcapsules and achieving the effect of long-term slow release.

[0068] In Comparative Example 2, the photo / biodegradable foaming carrier was not added. The photo / biodegradable foaming carrier has excellent water absorption capacity, large pores, can load more microcapsules, and uses amino groups to bond with the carboxyl groups on the surface of the microcapsules to realize the fixation of the microcapsules and achieve the effect of long-term slow release.

[0069] In Comparative Example 3, the magnetized modified zeolite powder was replaced with zeolite powder. After the magnetized modified zeolite powder was etched with citric acid, its surface was rough and porous and carried negatively charged carboxyl groups. By filling nano-ferroferric oxide particles into the internal pores of the zeolite, the nano-ferroferric oxide particles carried positive charges under acidic conditions. The magnetized modified zeolite powder, fulvic acid and humic acid were dispersed in deionized water, and the positive charge characteristics of the nano-ferroferric oxide particles were used to specifically adsorb the negative charges of fulvic acid and humic acid, so as to fix fulvic acid and humic acid in the internal voids and avoid affecting the formation of the core-shell structure.

[0070] In Comparative Example 4, the double-assembled microcapsule carrier complex was directly used as a soil conditioner for saline-alkali soil improvement. Using N-isopropylacrylamide, a mixture of poly-N-isopropylacrylamide microgel and hydrogel was prepared by emulsion polymerization to obtain a microgel film. The microgel film covered the surface of the light / biodegradable foaming carrier. The pores of the microgel film were smaller than those of the foaming carrier, forming a barrier to further improve the slow release of organic matter and the absorption of moisture.

[0071] It should be noted that in this article, relational terms such as first and second are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the terms "comprising", "including" or any other variant thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device comprising a series of elements not only includes those elements, but also includes other elements not expressly listed, or also includes elements inherent to such process, method, article or device.

[0072] Although the embodiments of the present invention 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 principles and spirit of the present invention. The scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a soil conditioner for improving saline-alkali soil, characterized in that: The steps include: Step 1: Add the microcapsule complex, the light / biological dual-degradable foaming carrier and deionized water into a reaction kettle, perform ultrasonic dispersion for 40-60 minutes, stir at 20-25° C. and 400-500 r / min for 2-3 hours, then add potassium alginate and 1-2wt% glutaraldehyde solution, continue stirring and cross-linking for 20-30 minutes, filter, wash the filter cake with deionized water and anhydrous ethanol for 2-3 times respectively, and vacuum dry to obtain a dual-assembly microcapsule carrier complex; Step 2: Add N-isopropylacrylamide and N,N'-methylenebispropylamide into a reaction kettle, stir at 20-25°C and 400-500r / min for 20-30min, then add sodium dodecyl sulfate and deionized water, heat to 40-50°C, continue stirring for 20-30min, introduce ammonia gas at a flow rate of 10-12min / L for 30-40min, heat to 70-80°C, add ammonium persulfate, continue stirring and reacting for 6-7h under a nitrogen atmosphere, then add the double-assembled microcapsule carrier complex into the reaction kettle, continue stirring for 20-30min, filter, wash the filter cake with petroleum ether and ionized water for 2-3 times respectively, and vacuum dry to obtain a soil conditioner for improving saline-alkali soil.

2. The method for preparing a soil conditioner for improving saline-alkali soil according to claim 1, characterized in that: In step 1, the usage ratio of the microcapsule composite, the light / biological dual-degradable foaming carrier, the deionized water, the potassium alginate and the glutaraldehyde solution is 2-2.5kg: 2-3kg: 3-4L: 2-2.5kg: 0.4-0.5L.

3. The method for preparing a soil conditioner for improving saline-alkali soil according to claim 1, characterized in that: The dosage ratio of N-isopropylacrylamide, N,N'-methylenebispropylamide, sodium lauryl sulfate, deionized water, ammonium persulfate and the double-assembled microcapsule carrier complex in step 2 is 3-4 kg: 1.2-1.5kg: 0.1-0.2kg: 3-4L: 0.4-0.5L: 2-3kg.

4. The method for preparing a soil conditioner for improving saline-alkali soil according to claim 1, characterized in that: The microcapsule composite in step 1 is prepared by the following steps: Adding magnetized modified zeolite powder, fulvic acid, humic acid and deionized water into a reactor, ultrasonically dispersing for 40-60 minutes, vacuum impregnating for 20-30 minutes at 20-25°C and 400-500r / min, then adding chitosan solution into the reactor, ultrasonically dispersing for 40-60 minutes at 40-45°C, then adding 0.5-0.6mol / L potassium chloride solution to adjust the pH value to 5.5-6, centrifuging at 1000-1200r / min for 5-6 minutes, and obtaining a first assembled and coated microcapsule complex; The chitosan solution is obtained by stirring and mixing chitosan and 1-2wt% glacial acetic acid solution in a dosage ratio of 4-5kg:7.5-8.5L.

5. The method for preparing a soil conditioner for improving saline-alkali soil according to claim 4, characterized in that: The usage ratio of the magnetized modified zeolite powder, fulvic acid, humic acid, deionized water, chitosan solution and potassium chloride solution is 3-4kg: 0.5-0.7kg: 0.3-0.5kg: 3-4L: 8-9L: 0.5-0.6L.

6. The method for preparing a soil conditioner for improving saline-alkali soil according to claim 4, characterized in that: The magnetized modified zeolite powder is prepared by the following steps: Add zeolite powder, citric acid and deionized water into a reaction kettle, stir at 50-55°C and 400-500 r / min for 20-30 min, then add nano-iron tetroxide particles, vacuum impregnate for 2-3 h, filter, wash the filter cake with deionized water until the last washing liquid is neutral, and obtain magnetized modified zeolite powder; The usage ratio of the zeolite powder, citric acid, deionized water and nano-iron tetroxide particles is 4-5kg: 1-2kg: 8-9L: 0.8-1kg.

7. The method for preparing a soil conditioner for improving saline-alkali soil according to claim 1, characterized in that: The light / biological dual-degradable foaming carrier in step 1 is prepared by the following steps: Castor oil polyether polyol, modified nano titanium dioxide and deionized water are added into a reaction kettle, stirred at 20-25°C and 400-500r / min for 40-60min, then triethylenediamine, dibutyltin dilaurate, 1,4-butanediol and isocyanate are added, stirred for 40-60min, injected into a mold, heated to 120-130°C and stirred at 80-90r / min for 10-12min, aged, demolded, naturally cooled to room temperature, vacuum dried, and crushed to obtain a light / biological dual-degradable foaming carrier with a particle size of 0.5-0.7mm.

8. The method for preparing a soil conditioner for improving saline-alkali soil according to claim 7, characterized in that: The usage ratio of castor oil polyether polyol, modified nano titanium dioxide, deionized water, triethylenediamine, dibutyltin dilaurate, 1,4-butanediol and isocyanate is 14-15L: 5-6kg: 20-25L: 0.1-0.2kg: 0.2-0.3L: 0.1-0.2L: 0.3-0.4L.

9. The method for preparing a soil conditioner for improving saline-alkali soil according to claim 7, characterized in that: The modified nano titanium dioxide powder is prepared by the following steps: Add nano titanium dioxide powder with a particle size of 40-50 nm and anhydrous ethanol into a reaction kettle, perform ultrasonic dispersion for 10-20 minutes, stir at 80-85° C. and 400-500 r / min for 1-2 hours, add γ-aminopropyltriethoxysilane, continue stirring for 1-2 hours, filter, wash the filter cake with deionized water and anhydrous ethanol for 2-3 times respectively, and vacuum dry to obtain modified nano titanium dioxide powder treated with a silane coupling agent; The dosage ratio of the nano titanium dioxide powder, anhydrous ethanol and gamma-aminopropyltriethoxysilane is 3-4kg: 8-9L: 800-900mL.

10. A soil conditioner for improving saline-alkali soil, characterized in that: Prepared by the preparation method described in any one of claims 1 to 9.

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