A saline-alkali soil conditioner and a preparation method thereof

Abstract

The application discloses a saline-alkali soil improver and a preparation method thereof, relates to the technical field of soil improvement, and belongs to the patent classification number C09K17 / 00. The method takes corn stalks as raw materials, carries out pretreatment of alkalization and phosphatization, and then grafts and copolymerizes with 2-acrylamido-2-methyl propane sulfonic acid to form an organic inner core. Subsequently, a magnesium-aluminum precursor is loaded and a hydrothermal reaction is carried out, so that a layered double hydroxide shell layer is in-situ grown on the surface of the inner core, and a core-shell structure is formed. Finally, surface cross-linking coating is carried out by using potassium humate and calcium chloride, and spray granulation is carried out to obtain the improver. The product has a core-shell structure, can efficiently adsorb salt, and has a good soil improvement effect.

Description

Technical Field

[0001] This invention relates to the field of soil improvement technology, belonging to patent classification number C09K17 / 00, specifically to a soil conditioner for saline-alkali land and its preparation method. Background Technology

[0002] Saline-alkali land, as an important type of low-yield soil, is widely distributed in many regions around the world. Its high salt content damages soil structure, inhibits crop root development, and severely restricts agricultural production efficiency and ecological environment quality. Therefore, the improvement of saline-alkali land has always been a key issue that urgently needs to be addressed in the field of agricultural science and technology. Currently, most commercially available saline-alkali land amendments use cation exchange as their core mechanism of action. Although they can remove harmful cations such as sodium ions from the soil to a certain extent through ion replacement and alleviate local saline-alkali stress, they have significant functional shortcomings: in addition to cations, the soil solution also contains a large number of harmful anions such as chloride ions. These amendments generally lack specific fixation and capture mechanisms for these anions, and cannot effectively retain and remove them. As a result, it is difficult to achieve a significant reduction in the total salt content of the soil, and the improvement effect is only at the surface level, failing to fundamentally improve the core problem of soil salinization.

[0003] Furthermore, traditional saline-alkali land conditioners (including organic and inorganic types) bind to salt ions in the soil primarily through physical adsorption or weak chemical bonding, resulting in generally weak binding forces and extremely poor stability. During agricultural production, under conventional water leaching conditions such as irrigation or natural rainfall, the salt ions that were originally displaced or adsorbed easily detach from the conditioner, migrate with the water flow, and accumulate in the topsoil, forming a significant "salt return" phenomenon. This salt return not only negates the benefits of previous improvements but may also exacerbate soil salinization due to secondary salt accumulation, increasing the difficulty and cost of subsequent improvements. Simultaneously, frequent salt return subjectes crops to repeated salt stress, further reducing crop yield and quality. This makes it difficult to sustain the effectiveness of existing improvement technologies, failing to meet the needs of large-scale, long-term saline-alkali land improvement, and severely hindering the efficient development and sustainable utilization of saline-alkali land resources. Summary of the Invention

[0004] The purpose of this invention is to provide a soil conditioner for saline-alkali land and its preparation method, so as to solve the technical problems mentioned in the background art.

[0005] To achieve the above objectives, the present invention provides the following technical solution: A method for preparing a soil conditioner for saline-alkali land includes the following steps: S1. Corn stalk powder is added to sodium hydroxide solution for pressurized alkalization pretreatment, followed by centrifugation, washing and drying to obtain pretreated corn stalk powder; S2. The pretreated corn stalk powder is mixed evenly with sodium tripolyphosphate and urea, and the reaction is carried out in a tube furnace under nitrogen protection. After washing with hot water and drying, the phosphorylated product is obtained. S3. The phosphorylation product was added to water to prepare a suspension. Under nitrogen protection, 2-acrylamido-2-methylpropanesulfonic acid monomer was added, and ammonium persulfate initiator was added dropwise to carry out free radical graft copolymerization. After ethanol precipitation, filtration and drying, the organic core material was obtained. S4. The organic core material is mixed with a mixed aqueous solution of magnesium nitrate and aluminum nitrate, and then subjected to mechanical stirring and ultrasonic treatment to obtain an impregnation system loaded with metal precursors. S5. Add a mixed solution of sodium hydroxide and sodium carbonate to the impregnation system to adjust the pH value, transfer it to a high-pressure reactor for hydrothermal reaction, and grow a layered bimetallic hydroxide shell in situ on the surface of the organic core material. After washing, the core-shell structure material is obtained. S6. The core-shell structure material is added to potassium humate solution to prepare a suspension, and then calcium chloride solution is added as a crosslinking agent for surface coating. The desalination-type saline-alkali land conditioner is obtained by spray granulation.

[0006] This invention overcomes the limitation of traditional soil conditioners, which can only treat single ions, by constructing a heterogeneous core-shell structure with a negatively charged organic core and a positively charged inorganic shell, utilizing a charge field spatial synergistic mechanism. On one hand, by grafting phosphate and sulfonic acid groups onto the biomass framework, a chemically active core with extremely high cation exchange capacity is constructed. The phosphate groups form stable chelate rings with divalent metal ions in the soil through multidentate coordination, which helps improve soil aggregate structure; while the strongly acidic sulfonic acid groups actively remove free Na+ ions from the soil solution using their strong electrostatic attraction. + It adsorbs and displaces into the interstices of the modified cellulose molecular chains. Through this dual action of chemical bonding and electrostatic binding, the concentration of cations in the soil solution is effectively reduced, mitigating the risk of alkalization caused by excessive sodium ions at its source. On the other hand, the magnesium-aluminum layered bimetallic hydroxide grown in situ on the surface of the organic core utilizes its unique positively charged lamellar structure to specifically target and remove anions from the soil. The magnesium-aluminum layered bimetallic hydroxide exhibits significant interlayer anion exchangeability, enabling it to remove harmful anions (such as Cl-) from the soil solution. - SO4 2- It is absorbed into its nanoscale interlayer confinement space through ion exchange and firmly locked in by the strong electrostatic field between the layers. This physical isolation and chemical fixation of anions directly makes up for the shortcomings of traditional soil conditioners in synergistically reducing anion content, thus achieving a comprehensive reduction in total salt content in the soil.

[0007] This invention utilizes the physical steric hindrance and electrostatic repulsion coupling of the core-shell structure to construct a robust salt-fixing nanocage on the surface of the biomass framework, significantly improving the durability of the modification effect. Layers of in-situ generated layered double hydroxide (LDH) nanosheets stack together to form a dense physical barrier, greatly extending the efflux migration path of captured ions. The positively charged LDH shell exerts a strong electrostatic repulsion on the sodium ions captured by the core, forming a chemical locking barrier, thus ensuring that the locked salts are difficult to desorb and release even under irrigation leaching or strong evaporation conditions. Furthermore, through the intercalation activation and interfacial cross-linking of humic acid, a bioactive flexible protective film is formed on the outermost layer of the modifier, achieving a two-way salt control effect. On the one hand, this barrier further strengthens the stability of the captured salt ions, preventing their desorption and loss under conditions of heavy irrigation or rainfall; on the other hand, the humic acid layer effectively blocks the continuity of soil capillaries, inhibiting the migration of deep salts to the surface driven by water evaporation, thereby forming a durable low-salt protection zone in the root zone. Through the aforementioned synergistic effect, the salt return phenomenon of soil conditioners can be effectively prevented.

[0008] Preferably, in step S1, the concentration of the sodium hydroxide solution is 5–10 wt%. Preferably, in step S2, the mass ratio of pretreated corn stalk powder, sodium tripolyphosphate, and urea is 10:(12-15):(40-60).

[0009] Preferably, in step S3, the amount of ammonium persulfate added is 3 to 5 wt% of the mass of 2-acrylamido-2-methylpropanesulfonic acid monomer.

[0010] Preferably, in step S4, the organic core material undergoes pretreatment, including the following steps: The organic core product was dispersed in a mixed solution of ethanol and water, and silane coupling agent KH-560 and polyethylene glycol (PEG-400) were added. The pH was adjusted to acidic, and the reaction was heated to obtain a pretreated organic core material slurry.

[0011] In-depth research revealed that the organic core (phosphorylated / sulfonated biomass) of soil conditioners is essentially a high-molecular-weight polyelectrolyte with strong hydrophilic swelling properties; while the inorganic LDH shell has a rigid crystalline structure. When the conditioner is applied to moist soil, the core absorbs water and swells, but the rigid shell cannot expand synchronously, leading to shell cracking and detachment (interfacial peeling). Simultaneously, an excessively dense LDH shell can form a physical barrier, hindering the absorption of Na+ from the soil. +The exchange sites that penetrate the shell to reach the core prevent the core's cation exchange capacity from being fully utilized, resulting in a "empty shell" effect. To further address this technical problem, this invention introduces the silane coupling agent KH-560 as a molecular bridge, improving the relationship between the organic core and inorganic shell from physical stacking to C-Si-OM covalent bonding. This effectively solves the problem of interfacial peeling and shell detachment caused by differences in expansion coefficients under alternating wet and dry soil conditions. Simultaneously, utilizing the "occupation-diffusion" mechanism of PEG-400, nanoscale "ion-dedicated channels" are artificially constructed within the originally dense LDH shell, completely eliminating the shielding effect of the shell on the core and ensuring that sodium ions in the soil can rapidly penetrate through the microporous channels and be captured by the core. Furthermore, these improvements enhance wettability, inducing uniform growth of Mg-Al LDH on the framework surface and fully exposing anion exchange sites, achieving efficient and synergistic improvement of the total salt content in saline-alkali land.

[0012] Preferably, the mass ratio of the organic core product to the silane coupling agent KH-560 is 5:(0.5~1.0).

[0013] Preferably, the mass ratio of the organic core product to polyethylene glycol is 5:(1-2).

[0014] Preferably, in step S4, the molar ratio of magnesium nitrate to aluminum nitrate is 4:(1-3).

[0015] Preferably, in step S6, the concentration of the potassium humate solution is 5-8 wt%.

[0016] A soil conditioner for saline-alkali land is prepared by the method described above.

[0017] Compared with the prior art, the beneficial effects of the present invention are: By constructing a heterogeneous core-shell structure with a negatively charged organic core and a positively charged inorganic shell, and utilizing the charge field spatial synergy mechanism, cations and anions in the soil are captured and locked simultaneously. This addresses the technical shortcoming of traditional soil conditioners in their inability to synergistically manage anions, and achieves a comprehensive reduction in total salt content.

[0018] By utilizing the physical steric hindrance and repulsive force of like charges in the core-shell structure to construct a solid salt nanocage, and combining it with the surface cross-linking of the humic acid flexible protective layer, the durability of salt retention is significantly enhanced, effectively preventing salt return.

[0019] By introducing the silane coupling agent KH-560 to construct covalent bridges, the problem of peeling and detachment of the organic / inorganic layer due to uneven swelling was solved; at the same time, PEG-400 was used to construct nanoscale ion-specific channels, eliminating the shielding effect of the outer shell on the core, and ensuring that soil salt ions can quickly penetrate and fully react with the internal active sites. Attached Figure Description

[0020] Figure 1 The image shows a SEM image of the saline-alkali soil conditioner prepared in Example 1 of this invention after a water soaking, drying, and cyclic testing.

[0021] Figure 2 This is a SEM image of the saline-alkali soil conditioner prepared in Comparative Example 3 of the present invention after water soaking, drying and cyclic testing. Detailed Implementation

[0022] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0023] Example 1 A method for preparing a soil conditioner for saline-alkali land includes the following steps: Step 1: Weigh 100g of corn stalk powder pulverized to 120 mesh and place it in a reaction vessel. Add 800mL of sodium hydroxide solution with a mass percentage concentration of 9wt%. Under a pressure of 0.15MPa and a constant temperature of 90℃, mechanically stir the mixture for 3h. After the reaction is completed, centrifuge the suspension, collect the solid product, and wash it repeatedly with deionized water until the pH of the washing solution is neutral. Then, place the solid in a vacuum drying oven at 65℃ and dry it to constant weight to obtain pretreated corn stalk powder.

[0024] Step 2: Weigh 100g of pretreated corn stalk powder, 140g of sodium tripolyphosphate, and 550g of urea, and mix them thoroughly in a ball mill. Then transfer the mixture to a tube furnace and heat it to 160℃ at a heating rate of 5℃ / min under nitrogen protection, and react at a constant temperature for 4 hours. After the reaction is completed, wait for the system to cool to room temperature, and wash the product repeatedly with hot water at 80℃ to remove unreacted inorganic salts until no phosphate ions are detected in the washing liquid. Finally, dry it in a vacuum drying oven at 60℃ to obtain the phosphorylated product.

[0025] Step 3: Add 50g of phosphorylated product to 500mL of deionized water to prepare a suspension. Under nitrogen protection, add 60g of 2-acrylamido-2-methylpropanesulfonic acid monomer (AMPS) and stir for 30min to allow the monomer to fully penetrate. Then, add ammonium persulfate at 4.5wt% of the monomer mass to prepare a solution, and slowly add it dropwise to the suspension. Stir the reaction at a constant temperature of 70℃ for 6h. After the reaction is completed, add anhydrous ethanol to the system to precipitate the solid. Collect the solid by suction filtration, wash it three times with anhydrous ethanol, and dry it under vacuum at 50℃ to obtain the organic core material.

[0026] Step 4: Disperse 50g of organic core material in 500mL of ethanol-water mixed solution with a volume ratio of 1:1, add 9g of silane coupling agent KH-560 and 18g of polyethylene glycol (PEG-400), adjust the pH of the system to 5.0, and heat and stir at 60℃ for 3h to obtain a pretreated organic core material slurry; then, dissolve 0.4mol of magnesium nitrate and 0.25mol of aluminum nitrate in 200mL of deionized water to prepare a metal salt solution, and slowly add it dropwise to the above slurry under stirring; after the dropwise addition is completed, continue mechanical stirring at room temperature for 12h and assist in ultrasonic treatment for 40min to obtain an impregnation system loaded with metal precursor.

[0027] Step 5: Under vigorous stirring, a mixed solution of 2.0 mol / L NaOH and 0.6 mol / L Na2CO3 is slowly added dropwise to the impregnation system of the loaded metal precursor to adjust the pH value of the system to 10.5; after adjustment, the resulting slurry is transferred to a high-pressure reactor and subjected to hydrothermal crystallization reaction at 120℃ for 15 h; after the reaction is completed and naturally cooled, the solid product is collected by filtration and washed with deionized water until neutral to obtain the modified material with a core-shell structure.

[0028] Step 6: The above core-shell structure material is added to 500 mL of potassium humate solution with a mass percentage concentration of 7 wt% to prepare a suspension. The suspension is slowly stirred at 55°C for 4 h to achieve intercalation and surface adsorption of humic acid. Then, 15 mL of calcium chloride solution with a mass fraction of 5 wt% is added dropwise to the system as a crosslinking agent, and the reaction is continued to be stirred for 40 min to form a crosslinking protective layer on the surface. Finally, the obtained composite slurry is granulated by a spray granulator with the inlet air temperature set at 180°C. The dried particles are collected to obtain the desalination-type saline-alkali land conditioner.

[0029] Example 2 A method for preparing a soil conditioner for saline-alkali land includes the following steps: Step 1: Weigh 100g of corn stalk powder pulverized to 120 mesh and place it in a reaction vessel. Add 800mL of sodium hydroxide solution with a mass percentage concentration of 6wt%. Under a pressure of 0.15MPa and a constant temperature of 90℃, mechanically stir the mixture for 3h. After the reaction is completed, centrifuge the suspension, collect the solid product, and wash it repeatedly with deionized water until the pH of the washing solution is neutral. Then, place the solid in a vacuum drying oven at 65℃ and dry it to constant weight to obtain pretreated corn stalk powder.

[0030] Step 2: Weigh 100g of pretreated corn stalk powder, 130g of sodium tripolyphosphate, and 450g of urea, and mix them thoroughly in a ball mill. Then transfer the mixture to a tube furnace and heat it to 160℃ at a heating rate of 5℃ / min under nitrogen protection, and react at a constant temperature for 4 hours. After the reaction is completed, wait for the system to cool to room temperature, and wash the product repeatedly with hot water at 80℃ to remove unreacted inorganic salts until no phosphate ions are detected in the washing liquid. Finally, dry it in a vacuum drying oven at 60℃ to obtain the phosphorylated product.

[0031] Step 3: Add 50g of phosphorylated product to 500mL of deionized water to prepare a suspension. Under nitrogen protection, add 60g of 2-acrylamido-2-methylpropanesulfonic acid monomer (AMPS) and stir for 30min to allow the monomer to fully penetrate. Then, add ammonium persulfate at 3.5wt% of the monomer mass to prepare a solution, and slowly add it dropwise to the suspension. Stir the reaction at a constant temperature of 70℃ for 6h. After the reaction is completed, add anhydrous ethanol to the system to precipitate the solid. Collect the solid by suction filtration, wash it three times with anhydrous ethanol, and dry it under vacuum at 50℃ to obtain the organic core material.

[0032] Step 4: Disperse 50g of organic core material in 500mL of ethanol-water mixture with a volume ratio of 1:1, add 6g of silane coupling agent KH-560 and 12g of polyethylene glycol (PEG-400), adjust the pH of the system to 5.0, and heat and stir at 60℃ for 3h to obtain a pretreated organic core material slurry; then, dissolve 0.4mol of magnesium nitrate and 0.15mol of aluminum nitrate in 200mL of deionized water to prepare a metal salt solution, and slowly add it dropwise to the above slurry under stirring; after the dropwise addition is completed, continue mechanical stirring at room temperature for 12h and assist in ultrasonic treatment for 40min to obtain an impregnation system loaded with metal precursor.

[0033] Step 5: Under vigorous stirring, a mixed solution of 2.0 mol / L NaOH and 0.6 mol / L Na2CO3 is slowly added dropwise to the impregnation system of the loaded metal precursor to adjust the pH value of the system to 10.5; after adjustment, the resulting slurry is transferred to a high-pressure reactor and subjected to hydrothermal crystallization reaction at 120℃ for 15 h; after the reaction is completed and naturally cooled, the solid product is collected by filtration and washed with deionized water until neutral to obtain the modified material with a core-shell structure.

[0034] Step 6: The above core-shell structure material is added to 500 mL of potassium humate solution with a mass percentage concentration of 6 wt% to prepare a suspension. The suspension is slowly stirred at 55°C for 4 h to achieve intercalation and surface adsorption of humic acid. Then, 15 mL of calcium chloride solution with a mass fraction of 5 wt% is added dropwise to the system as a crosslinking agent, and the reaction is continued to be stirred for 40 min to form a crosslinking protective layer on the surface. Finally, the obtained composite slurry is granulated by a spray granulator with the inlet air temperature set at 180°C. The dried particles are collected to obtain the desalination-type saline-alkali land conditioner.

[0035] Example 3 A method for preparing a soil conditioner for saline-alkali land includes the following steps: Step 1: Weigh 100g of corn stalk powder pulverized to 120 mesh and place it in a reaction vessel. Add 800mL of sodium hydroxide solution with a mass percentage concentration of 7wt%. Under a pressure of 0.15MPa and a constant temperature of 90℃, mechanically stir the mixture for 3h. After the reaction is completed, centrifuge the suspension, collect the solid product, and wash it repeatedly with deionized water until the pH of the washing solution is neutral. Then, place the solid in a vacuum drying oven at 65℃ and dry it to constant weight to obtain pretreated corn stalk powder.

[0036] Step 2: Weigh 100g of pretreated corn stalk powder, 135g of sodium tripolyphosphate, and 500g of urea, and mix them thoroughly in a ball mill. Then transfer the mixture to a tube furnace and heat it to 160℃ at a heating rate of 5℃ / min under nitrogen protection, and react at a constant temperature for 4 hours. After the reaction is completed, wait for the system to cool to room temperature, and wash the product repeatedly with hot water at 80℃ to remove unreacted inorganic salts until no phosphate ions are detected in the washing liquid. Finally, dry it in a vacuum drying oven at 60℃ to obtain the phosphorylated product.

[0037] Step 3: Add 50g of phosphorylated product to 500mL of deionized water to prepare a suspension. Under nitrogen protection, add 60g of 2-acrylamido-2-methylpropanesulfonic acid monomer (AMPS) and stir for 30min to allow the monomer to fully penetrate. Then, add ammonium persulfate at 4wt% of the monomer mass to prepare a solution, and slowly add it dropwise to the suspension. Stir the reaction at a constant temperature of 70℃ for 6h. After the reaction is completed, add anhydrous ethanol to the system to precipitate the solid. Collect the solid by suction filtration, wash it three times with anhydrous ethanol, and dry it under vacuum at 50℃ to obtain the organic core material.

[0038] Step 4: Disperse 50g of organic core material in 500mL of ethanol-water mixture with a volume ratio of 1:1, add 7g of silane coupling agent KH-560 and 15g of polyethylene glycol (PEG-400), adjust the pH of the system to 5.0, and heat and stir at 60℃ for 3h to obtain a pretreated organic core material slurry; then, dissolve 0.4mol of magnesium nitrate and 0.2mol of aluminum nitrate in 200mL of deionized water to prepare a metal salt solution, and slowly add it dropwise to the above slurry under stirring; after the dropwise addition is completed, continue mechanical stirring at room temperature for 12h and assist in ultrasonic treatment for 40min to obtain an impregnation system loaded with metal precursor.

[0039] Step 5: Under vigorous stirring, a mixed solution of 2.0 mol / L NaOH and 0.6 mol / L Na2CO3 is slowly added dropwise to the impregnation system of the loaded metal precursor to adjust the pH value of the system to 10.5; after adjustment, the resulting slurry is transferred to a high-pressure reactor and subjected to hydrothermal crystallization reaction at 120℃ for 15 h; after the reaction is completed and naturally cooled, the solid product is collected by filtration and washed with deionized water until neutral to obtain the modified material with a core-shell structure.

[0040] Step 6: The above core-shell structure material is added to 500 mL of potassium humate solution with a mass percentage concentration of 6.5 wt% to prepare a suspension. The suspension is slowly stirred at 55°C for 4 h to achieve intercalation and surface adsorption of humic acid. Then, 15 mL of calcium chloride solution with a mass fraction of 5 wt% is added dropwise to the system as a crosslinking agent, and the reaction is continued to be stirred for 40 min to form a crosslinking protective layer on the surface. Finally, the obtained composite slurry is granulated by a spray granulator with the inlet air temperature set at 180°C. The dried particles are collected to obtain the desalination-type saline-alkali land conditioner.

[0041] Example 4 A method for preparing a soil conditioner for saline-alkali land includes the following steps: Step 1: Weigh 100g of corn stalk powder pulverized to 120 mesh and place it in a reaction vessel. Add 800mL of sodium hydroxide solution with a mass percentage concentration of 10wt%. Under a pressure of 0.15MPa and a constant temperature of 90℃, mechanically stir the mixture for 3h. After the reaction is completed, centrifuge the suspension, collect the solid product, and wash it repeatedly with deionized water until the pH of the washing solution is neutral. Then, place the solid in a vacuum drying oven at 65℃ and dry it to constant weight to obtain pretreated corn stalk powder.

[0042] Step 2: Weigh 100g of pretreated corn stalk powder, 150g of sodium tripolyphosphate, and 600g of urea, and mix them thoroughly in a ball mill. Then transfer the mixture to a tube furnace and heat it to 160℃ at a heating rate of 5℃ / min under nitrogen protection, and react at a constant temperature for 4 hours. After the reaction is completed, wait for the system to cool to room temperature, and wash the product repeatedly with hot water at 80℃ to remove unreacted inorganic salts until no phosphate ions are detected in the washing liquid. Finally, dry it in a vacuum drying oven at 60℃ to obtain the phosphorylated product.

[0043] Step 3: Add 50g of phosphorylated product to 500mL of deionized water to prepare a suspension. Under nitrogen protection, add 60g of 2-acrylamido-2-methylpropanesulfonic acid monomer (AMPS) and stir for 30min to allow the monomer to fully penetrate. Then, add ammonium persulfate at 5wt% of the monomer mass to prepare a solution, and slowly add it dropwise to the suspension. Stir the reaction at a constant temperature of 70℃ for 6h. After the reaction is completed, add anhydrous ethanol to the system to precipitate the solid. Collect the solid by suction filtration, wash it three times with anhydrous ethanol, and dry it under vacuum at 50℃ to obtain the organic core material.

[0044] Step 4: Disperse 50g of organic core material in 500mL of ethanol-water mixed solution with a volume ratio of 1:1, add 10g of silane coupling agent KH-560 and 20g of polyethylene glycol (PEG-400), adjust the pH of the system to 5.0, and heat and stir at 60℃ for 3h to obtain a pretreated organic core material slurry; then, dissolve 0.4mol of magnesium nitrate and 0.3mol of aluminum nitrate in 200mL of deionized water to prepare a metal salt solution, and slowly add it dropwise to the above slurry under stirring; after the dropwise addition is completed, continue mechanical stirring at room temperature for 12h and assist in ultrasonic treatment for 40min to obtain an impregnation system loaded with metal precursor.

[0045] Step 5: Under vigorous stirring, a mixed solution of 2.0 mol / L NaOH and 0.6 mol / L Na2CO3 is slowly added dropwise to the impregnation system of the loaded metal precursor to adjust the pH value of the system to 10.5; after adjustment, the resulting slurry is transferred to a high-pressure reactor and subjected to hydrothermal crystallization reaction at 120℃ for 15 h; after the reaction is completed and naturally cooled, the solid product is collected by filtration and washed with deionized water until neutral to obtain the modified material with a core-shell structure.

[0046] Step 6: The above core-shell structure material is added to 500 mL of potassium humate solution with a mass percentage concentration of 8 wt% to prepare a suspension. The suspension is slowly stirred at 55°C for 4 h to achieve intercalation and surface adsorption of humic acid. Then, 15 mL of calcium chloride solution with a mass fraction of 5 wt% is added dropwise to the system as a crosslinking agent, and the reaction is continued to be stirred for 40 min to form a crosslinking protective layer on the surface. Finally, the obtained composite slurry is granulated by a spray granulator with the inlet air temperature set at 180°C. The dried particles are collected to obtain the desalination-type saline-alkali land conditioner.

[0047] Example 5 A method for preparing a soil conditioner for saline-alkali land includes the following steps: Step 1: Weigh 100g of corn stalk powder pulverized to 120 mesh and place it in a reaction vessel. Add 800mL of sodium hydroxide solution with a mass percentage concentration of 5wt%. Under a pressure of 0.15MPa and a constant temperature of 90℃, mechanically stir the mixture for 3h. After the reaction is completed, centrifuge the suspension, collect the solid product, and wash it repeatedly with deionized water until the pH of the washing solution is neutral. Then, place the solid in a vacuum drying oven at 65℃ and dry it to constant weight to obtain pretreated corn stalk powder.

[0048] Step 2: Weigh 100g of pretreated corn stalk powder, 120g of sodium tripolyphosphate, and 400g of urea, and mix them thoroughly in a ball mill. Then transfer the mixture to a tube furnace and heat it to 160℃ at a heating rate of 5℃ / min under nitrogen protection, and react at a constant temperature for 4 hours. After the reaction is completed, wait for the system to cool to room temperature, and wash the product repeatedly with hot water at 80℃ to remove unreacted inorganic salts until no phosphate ions are detected in the washing liquid. Finally, dry it in a vacuum drying oven at 60℃ to obtain the phosphorylated product.

[0049] Step 3: Add 50g of phosphorylated product to 500mL of deionized water to prepare a suspension. Under nitrogen protection, add 60g of 2-acrylamido-2-methylpropanesulfonic acid monomer (AMPS) and stir for 30min to allow the monomer to fully penetrate. Then, add ammonium persulfate at 3wt% of the monomer mass to prepare a solution, and slowly add it dropwise to the suspension. Stir the reaction at a constant temperature of 70℃ for 6h. After the reaction is completed, add anhydrous ethanol to the system to precipitate the solid. Collect the solid by suction filtration, wash it three times with anhydrous ethanol, and dry it under vacuum at 50℃ to obtain the organic core material.

[0050] Step 4: Disperse 50g of organic core material in 500mL of ethanol-water mixed solution with a volume ratio of 1:1, add 5g of silane coupling agent KH-560 and 10g of polyethylene glycol (PEG-400), adjust the pH of the system to 5.0, and heat and stir at 60℃ for 3h to obtain a pretreated organic core material slurry; then, dissolve 0.4mol of magnesium nitrate and 0.1mol of aluminum nitrate in 200mL of deionized water to prepare a metal salt solution, and slowly add it dropwise to the above slurry under stirring; after the dropwise addition is completed, continue mechanical stirring at room temperature for 12h and assist in ultrasonic treatment for 40min to obtain an impregnation system loaded with metal precursor.

[0051] Step 5: Under vigorous stirring, a mixed solution of 2.0 mol / L NaOH and 0.6 mol / L Na2CO3 is slowly added dropwise to the impregnation system of the loaded metal precursor to adjust the pH value of the system to 10.5; after adjustment, the resulting slurry is transferred to a high-pressure reactor and subjected to hydrothermal crystallization reaction at 120℃ for 15 h; after the reaction is completed and naturally cooled, the solid product is collected by filtration and washed with deionized water until neutral to obtain the modified material with a core-shell structure.

[0052] Step 6: The above-mentioned core-shell structure material is added to 500 mL of potassium humate solution with a mass percentage concentration of 5 wt% to prepare a suspension. The suspension is slowly stirred at 55°C for 4 h to achieve intercalation and surface adsorption of humic acid. Then, 15 mL of calcium chloride solution with a mass fraction of 5 wt% is added dropwise to the system as a crosslinking agent, and the reaction is continued to be stirred for 40 min to form a crosslinking protective layer on the surface. Finally, the obtained composite slurry is granulated by a spray granulator with the inlet air temperature set at 180°C. The dried particles are collected to obtain the desalination-type saline-alkali land conditioner.

[0053] Comparative Example 1: The difference between Comparative Example 1 and Example 1 is that steps 2-3 are omitted in the soil conditioner preparation process, and the organic core material in step 4 is replaced with an equal mass of pretreated corn stalk powder.

[0054] Comparative Example 2: The difference between Comparative Example 2 and Example 1 is that steps 4-6 are omitted in the soil conditioner preparation process. Comparative Example 3: The difference between Comparative Example 3 and Example 1 is that in step 4 of the soil conditioner preparation process, the organic core material is not pretreated.

[0055] Performance testing 1. Soil total salt removal rate test: Typical severely saline-alkali soil from northern China was used. The soil conditioner prepared in each example and comparative example was added at a mass ratio of 2%, and the mixture was thoroughly mixed and then placed into soil cylinders. Under constant temperature (25℃), deionized water was added periodically at 60% of field capacity, and the soil was cultured for 15 days. After the culture period, soil samples were taken to prepare an extract at a soil-to-water ratio of 1:5. The EC value was measured using a conductivity meter, and the total salt removal rate was calculated using the formula: Removal rate = (Initial EC value - EC value after culture) / Initial EC value × 100%. The test results are shown in Table 1.

[0056] 2. Anion and cation capture rate test: The Na content in the above soil extract was determined using ion chromatography (IC) and inductively coupled plasma atomic emission spectrometry (ICP). + (Representing harmful cations) and Cl - The mass concentration of (representing harmful anions) was used to evaluate the ability of the modifier's "organic core" to capture cations and its "inorganic shell" to capture anions by comparing the decrease in specific ions before and after treatment. The test results are shown in Table 1.

[0057] 3. Determination of Salt Reversion Stability: The soil column after equilibrium culture was subjected to simulated leaching treatment (adding twice the amount of deionized water with saturation water holding capacity), and the filtrate from the middle and lower layers was collected. The soil column was then placed in an oven and subjected to simulated strong light evaporation at 40℃ for 48 hours to induce salt migration upwards via capillary water. After the experiment, the salt content of the top 0-5 cm soil was measured. The salt reversion resistance was evaluated by comparing the ratio of the salt content of the treated surface layer to the initial salt content. The lower the salt reversion rate, the better the salt fixation stability of the humic acid cross-linked layer and the core-shell structure. The test results are shown in Table 1.

[0058] 4. Soil aggregate structure (>0.25mm) increase rate test: The content of water-stable macroaggregates (particle size >0.25mm) in the improved soil was determined using the wet sieving method. 50g of naturally air-dried soil sample was placed on a standard sieve and shaken uniformly in water for 30 minutes. Soil samples from each sieve were collected, dried, and weighed. The mass percentage of aggregates with a particle size >0.25mm was calculated. A higher proportion of aggregates with a particle size >0.25mm indicates a better effect on soil physical remediation. The test results are shown in Table 1.

[0059] 5. Take the modifier particles from each embodiment and comparative example and soak them in deionized water for 24 hours to reach a balanced swelling state. Then, transfer them to a vacuum drying oven at 65°C and dry them to constant weight. Repeat the above "immersion-drying" process 5 times to simulate the damage of the stress interface caused by the swelling of the core under alternating wet and dry soil conditions. After the cycle is completed, place the material in deionized water and use an ultrasonic crusher (set power 300W) to assist in the treatment for 30 minutes. Observe the surface morphology of the material using a scanning electron microscope (SEM).

[0060] Table 1:

[0061] Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a soil conditioner for saline-alkali land, characterized in that, Includes the following steps: S1. Corn stalk powder is added to sodium hydroxide solution for pressurized alkalization pretreatment, followed by centrifugation, washing and drying to obtain pretreated corn stalk powder; S2. The pretreated corn stalk powder is mixed evenly with sodium tripolyphosphate and urea, and the reaction is carried out in a tube furnace under nitrogen protection. After washing with hot water and drying, the phosphorylated product is obtained. S3. The phosphorylation product was added to water to prepare a suspension. Under nitrogen protection, 2-acrylamido-2-methylpropanesulfonic acid monomer was added, and ammonium persulfate initiator was added dropwise to carry out free radical graft copolymerization. After ethanol precipitation, filtration and drying, the organic core material was obtained. S4. The organic core material is mixed with a mixed aqueous solution of magnesium nitrate and aluminum nitrate, and then subjected to mechanical stirring and ultrasonic treatment to obtain an impregnation system loaded with metal precursors. The organic core material undergoes pretreatment, including the following steps: The organic core product was dispersed in a mixed solution of ethanol and water, and silane coupling agent KH-560 and polyethylene glycol were added. The pH was adjusted to acidic, and the reaction was carried out by heating to obtain a pretreated organic core material slurry. The mass ratio of the organic core product to polyethylene glycol was 5:(1-2); the mass ratio of the organic core product to silane coupling agent KH-560 was 5:(0.5-1.0). S5. Add a mixed solution of sodium hydroxide and sodium carbonate to the impregnation system to adjust the pH value, transfer it to a high-pressure reactor for hydrothermal reaction, and grow a layered bimetallic hydroxide shell in situ on the surface of the organic core material. After washing, the core-shell structure material is obtained. S6. The core-shell structure material is added to potassium humate solution to prepare a suspension, and then calcium chloride solution is added as a crosslinking agent for surface coating. The desalination-type saline-alkali land conditioner is obtained by spray granulation.

2. The method for preparing a saline-alkali soil conditioner according to claim 1, characterized in that, In step S1, the concentration of the sodium hydroxide solution is 5-10 wt%.

3. The method for preparing a saline-alkali soil conditioner according to claim 1, characterized in that, In step S2, the mass ratio of pretreated corn stalk powder, sodium tripolyphosphate, and urea is 10:(12-15):(40-60).

4. The method for preparing a saline-alkali soil conditioner according to claim 1, characterized in that, In step S3, the amount of ammonium persulfate added is 3 to 5 wt% of the mass of 2-acrylamido-2-methylpropanesulfonic acid monomer.

5. The method for preparing a saline-alkali soil conditioner according to claim 1, characterized in that, In step S4, the molar ratio of magnesium nitrate to aluminum nitrate is 4:(1-3).

6. The method for preparing a soil conditioner for saline-alkali land according to claim 1, characterized in that, In step S6, the concentration of the potassium humate solution is 5-8 wt%.

7. A soil conditioner for saline-alkali land, characterized in that, It is prepared by the method described in any one of claims 1 to 6 above.

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