Saline-alkali soil conditioner based on complex adsorption reaction and preparation method of saline-alkali soil conditioner

Abstract

The invention relates to the technical field of soil conditioners, in particular to a saline-alkali soil conditioner based on complex adsorption reaction and a preparation method of the saline-alkali soil conditioner. The improver is prepared from the following components in parts by weight: 5 to 15 parts of PAAC copolymer, 20 to 40 parts of phosphogypsum, 10 to 20 parts of bentonite, 5 to 15 parts of weathered coal, 5 to 15 parts of straw charcoal, 100 to 200 parts of water, 1.0 to 1.5 parts of dispersing agent and 0.1 to 0.15 part of preservative. The PAAC copolymer is formed by cross-linking after acrylic acid, acrylamide and betaine acrylate react. The prepared saline-alkali soil conditioner has excellent complexing adsorption capacity, strong ion exchange efficiency and good stability under different saline-alkali degrees, the raw materials are green and environment-friendly, the soil pollution risk is remarkably reduced, and the saline-alkali soil conditioner is suitable for repairing and treating various saline-alkali soil, can effectively improve the quality of cultivated land and the yield of crops, and is applied along with water during use.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of saline-alkali soil improver, and particularly relates to a saline-alkali soil improver based on complexation adsorption reaction and a preparation method thereof. BACKGROUND

[0002] As an important land resource, the salinization of saline-alkali soil seriously restricts the development of agricultural production and also has an adverse impact on the ecological environment. These saline-alkali soils contain excessive salt and alkaline substances in the soil, which leads to poor soil structure, poor aeration and water permeability, low fertility, and difficulty for crops to grow normally, greatly limiting the land use efficiency. Traditional improvers can reduce the soil alkalinity by ion exchange, but the improvement effect is relatively slow, and a large amount of application is required, which increases the improvement cost. Industrial by-products such as desulfurized gypsum as improvers have complex components and may bring some harmful impurities, which may pose potential risks to the soil and crops. Chemical improvers such as potassium dihydrogen phosphate can adjust the soil pH in a short period of time, but the duration is short, which can easily lead to soil compaction and damage the natural structure of the soil. Although organic fertilizer improvers can improve soil fertility, the improvement effect on severe saline-alkali soil is limited, and the effect is slow, which is difficult to meet the demand for rapid improvement.

[0003] Therefore, it is of great significance to develop a saline-alkali soil improver which can rapidly reduce salt and alkali, improve soil structure, retain water and fertilizer, and has no secondary pollution, so as to improve the productivity of saline-alkali soil, ensure food security, and improve the ecological environment. SUMMARY

[0004] In view of the above, the present application aims to provide a saline-alkali soil improver based on complexation adsorption reaction and a preparation method thereof, so as to solve the problems of traditional saline-alkali soil improvers, such as poor improvement effect, damage to soil micro-ecology, and secondary pollution to soil structure.

[0005] In order to achieve the above purpose, the present application provides a saline-alkali soil improver based on complexation adsorption reaction, which is characterized by comprising the following raw materials in parts by weight: PAAC copolymer 5-15 parts, phosphogypsum 20-40 parts, bentonite 10-20 parts, weathered coal 5-15 parts, straw biochar 5-15 parts, water 100-200 parts, dispersant 1.0-1.5 parts, and preservative 0.1-0.15 parts.

[0006] Preferably, the phosphogypsum (Guizhou Phosphate Green Environmental Protection Industry Co., Ltd.) needs to undergo impurity removal treatment, wherein the calcium sulfate dihydrate content is ≥85%, and the content of heavy metals such as lead and cadmium meets the standards; the bentonite is sodium-based bentonite (Shandong Sishui Shengfeng Bentonite Co., Ltd.), with a montmorillonite content of ≥70%; the weathered coal (Zhaotong Kaiye Humic Acid Co., Ltd.) has a humic acid content of ≥50% and a pH value of 6-8; the straw biochar (Henan Zhongxin Lantian Environmental Protection Equipment Co., Ltd.) needs to be carbonized at a high temperature of 600-800℃, with an ash content of ≤10% and a specific surface area of ​​≥200m². 2 / g, pH 8.0-9.5. Calcium sulfate dihydrate is the core component of phosphogypsum for reducing alkali, and it works through Ca... 2+ Replace Na in soil colloids + High content ensures efficient alkali reduction; meeting heavy metal content standards avoids the introduction of new soil pollutants, reducing ecological risks. Montmorillonite is a key component of bentonite in adsorbing water and nutrients; high content enhances soil water and fertilizer retention capacity, forming a synergistic effect with polymers. Polymers fix salt and alkali ions, while bentonite maintains soil moisture. Humic acid increases soil organic matter content, improves the soil micro-ecological environment, and promotes microbial activity; a neutral pH avoids interference with soil pH regulation caused by the acidity or alkalinity of weathered coal itself, forming a dual effect of "salt reduction and fertilizer enhancement" with polymers and phosphogypsum. High-temperature carbonization allows straw biochar to form a richer porous structure, enhancing its physical adsorption capacity for salt and alkali ions; low ash content reduces the secondary salinization of soil caused by ineffective impurities such as potassium and sodium oxides; a slightly alkaline pH of 8.0-9.5 buffers extreme soil pH, forming an acid-base balance with the acidity of phosphogypsum, avoiding drastic fluctuations in soil pH.

[0007] Preferably, the PAAC copolymer, phosphogypsum, bentonite, weathered coal, and straw biochar all require pretreatment, including crushing and passing through a 200-mesh sieve. This ensures the fineness and uniformity of the particles, enabling them to remain stably suspended in the liquid system, preventing precipitation and agglomeration, and increasing the reaction surface area, thereby enhancing the improvement effect.

[0008] Furthermore, the present invention also provides a method for preparing the above-mentioned saline-alkali soil conditioner based on complexation adsorption reaction, specifically including the following steps: S1. Preparation of PAAC copolymer (1) Weigh acrylamide (AM) and betaine acrylate (CBMA), add deionized water and stir until completely dissolved; add acrylic acid (AA) to another device placed in an ice-water bath, and slowly add 20% NaOH solution dropwise with a dropper while stirring vigorously to neutralize it to a pH of about 5.5; mix the neutralized acrylic acid solution with the acrylic amine and betaine acrylate solution to obtain a monomer mixture; (2) Add deionized water to the four-necked flask as the bottom water, turn on the stirrer, and start continuously purging nitrogen gas into the water at a flow rate that allows for the observation of continuous bubbles; continue purging nitrogen for 20-30 minutes to completely remove oxygen from the reaction system; heat the bottom water to 75°C and keep it stable, maintaining a nitrogen atmosphere; once the temperature stabilizes at 75°C, simultaneously and slowly add the monomer mixture and initiator solution into the deionized water bottom water; during the reaction, control the temperature of the reaction solution to be maintained between 75-80°C. Control the monomer solution to be added dropwise at a uniform rate within 60-90 minutes, and the initiator solution should be added dropwise before or simultaneously with the completion of the monomer addition; (3) Prepare the crosslinking agent. When the solution has been added dropwise, add the crosslinking agent solution to the reaction flask. Continue to keep the reaction at 75-80℃ for 1.5-2 hours to ensure the reaction is complete and the monomer is fully converted. (4) After the reaction is complete, a transparent or translucent elastic gel is obtained. The large gel is cut into small pieces of 1-2 cm3 and placed in an 80°C forced-air oven to dry for 12-24 hours until the gel blocks become hard and brittle solids, thus obtaining the PAAC copolymer.

[0009] S2. Add water to the preparation tank, start stirring, add dispersant and preservative in sequence, and stir until completely dissolved; S3. Under high-speed stirring, the pretreated PAAC copolymer, weathered coal, biochar, phosphogypsum, and bentonite are gradually and slowly added to the aqueous phase according to the designed ratio; after the addition is completed, high-speed shearing is continued for 20-30 minutes to form a preliminary viscous suspension without obvious particles. S4. Transfer the suspension to a high-pressure homogenizer and circulate it 2-3 times under a pressure of 20-30MPa; the finished product is then packaged and sealed in drums.

[0010] Preferably, the acrylamide AA (Jinan Century Tongda Chemical Co., Ltd.) and betaine acrylate (CBAM, Hubei Zhonglong Kangcheng Fine Chemical Co., Ltd.) must be industrial-grade pure products with a purity ≥95%; the sodium hydroxide must be analytical grade, with a solution concentration of 20% and must be freshly prepared; the acrylic acid AM (Jinan Century Tongda Chemical Co., Ltd.) must be colorless and transparent, and free of polymerization inhibitors. The acrylamide and betaine acrylate must have a purity ≥95%. Excessive impurities can interfere with the monomer polymerization reaction, leading to uneven polymer molecular weight distribution and a reduction in complexation sites. High purity ensures uniform cross-linking of the monomers and guarantees stable adsorption capacity of the polymer for salt and alkali ions. Analytical grade sodium hydroxide avoids impurities affecting the neutralization accuracy and ensures that the pH of the acrylic acid remains stable at 5.5, at which the monomer double bond activity is highest. The sodium hydroxide concentration is the optimal concentration for the neutralization reaction; too high a concentration can easily lead to localized overheating and damage to the double bonds, while too low a concentration results in low reaction efficiency. Freshly prepared solutions prevent sodium hydroxide from absorbing CO2 from the air to form sodium carbonate, which would reduce the neutralization capacity. Colored impurities in acrylic acid can reduce the reactivity of monomers, while polymerization inhibitors can directly suppress the polymerization reaction, preventing the polymer from forming an effective network structure.

[0011] Preferably, the acrylate, acrylic acid, and betaine acrylate are present in a weight ratio of 1:1.70-2.21:0.25-0.41. Acrylamide provides amide groups to enhance water solubility, and neutralized acrylic acid provides a negative charge to adsorb cations such as Na+. This ratio ensures that the polymer has sufficient water solubility to facilitate diffusion in the soil, as well as sufficient charge sites to enhance the complexation with salt and alkali ions. Betaine acrylate contains zwitterionic groups, which can improve the polymer's salt tolerance in high-salt environments, prevent polymer failure due to salting out, and enhance its binding ability with soil colloids, thus extending the duration of the improvement effect.

[0012] Preferably, the initiator needs to be freshly prepared and used at a concentration of 1-5%. It is a solution obtained by dissolving ammonium persulfate (APS, Shanghai Shijian Industrial Co., Ltd.) in deionized water, with the amount of ammonium persulfate added being 0.4%-0.8% of the total monomer mass. Ammonium persulfate is easily affected by moisture and decomposes, losing its initiation activity. Freshly prepared initiation ensures its free radical generation efficiency. A concentration of 1-5% is the optimal concentration for initiation. If the concentration is too low, initiation will be insufficient, resulting in low monomer conversion. If the concentration is too high, there will be an excess of free radicals, leading to an excessively small polymer molecular weight. An addition amount of 0.4%-0.8% allows for precise control of the polymerization rate, avoiding excessively vigorous reactions that could lead to localized overheating and damage to the molecular chains, or excessively slow reactions that could result in excessive monomer residue. Ultimately, this ensures that the polymer forms a stable three-dimensional network structure.

[0013] Preferably, neutralizing acrylic acid to pH 5.5 in an ice-water bath avoids double bond oxidation, and nitrogen protection matches the reaction temperature of 75-80℃ to the peak activity of the initiator ammonium persulfate, ensuring uniform polymerization of monomers and enhancing the complexation ability of molecular chains.

[0014] Preferably, the concentration range of the crosslinking agent is 0.5%-1%, which is a solution obtained by dissolving N,N'-methylenebisacrylamide MBA (Shanghai Bosen Biotechnology Co., Ltd.) in deionized water. The amount of N,N'-methylenebisacrylamide added is 0.03%-0.10% of the total mass of the monomers. If the amount is too low, the network structure is loose, the polymer has weak water and fertilizer retention capacity, and it is easily washed away by water flow in the soil. If the amount is too high, excessive crosslinking will lead to excessive rigidity of the polymer and reduced water solubility, which will prevent it from effectively diffusing into the soil pores. This range can form a "loose and stable" network structure, which takes into account that the network pores can accommodate more salt and alkali ions and avoid breakage during soil cultivation.

[0015] The beneficial effects of this invention are: 1. The saline-alkali soil conditioner of this invention achieves a synergistic effect of "chemical improvement - physical improvement - biological improvement" through the synergistic action of its components. The polymer and humic acid in weathered coal fix and lock excess salt ions in the soil solution through complexation and adsorption; phosphogypsum provides calcium ions for efficient ion exchange, fundamentally replacing sodium ions on soil colloids; simultaneously, bentonite and biochar, through their binding and porosity, break up compaction and improve aggregate structure. This multi-mechanism synergistic action achieves a three-dimensional and fundamental improvement of saline-alkali land.

[0016] 2. The saline-alkali soil conditioner of this invention achieves efficient salt regulation by constructing a triple complex adsorption system. The specially formulated terpolymer, with its carboxyl and amide groups, actively captures and fixes sodium ions in the soil like miniature magnets, rapidly reducing salt concentration and alleviating crop stress. Natural humic acid from weathered coal provides a powerful and long-lasting ion exchange and complexation capacity with its abundant functional groups, acting as an ion buffer. Straw biochar and bentonite serve as porous carriers, physically adsorbing and enriching ions and dispersing functional molecules, greatly improving overall adsorption efficiency and persistence. This synergistic system achieves immediate passivation and long-term control of harmful salts.

[0017] 3. The saline-alkali soil conditioner of this invention possesses both excellent salt and alkali resistance and water and fertilizer retention properties, effectively alleviating crop stress. The amphoteric polymer and humic acid, both containing numerous hydrophilic functional groups, maintain excellent water retention capacity even in highly saline-alkali environments, forming a "micro-reservoir" around the crop roots, significantly alleviating osmotic stress and physiological drought caused by salinity. Simultaneously, the large specific surface area of ​​bentonite and biochar gives them strong fertilizer retention capacity, effectively reducing the loss of nutrients such as nitrogen and potassium, providing continuous nutrient support for crop seedlings to grow under adverse conditions.

[0018] 4. The soil conditioner for saline-alkali land of this invention uses environmentally friendly and inexpensive raw materials. The main components, phosphogypsum, weathered coal, and straw biochar, are all industrial and agricultural by-products or natural minerals, achieving efficient resource utilization of waste. This not only significantly reduces raw material costs, making it economically feasible for large-scale promotion, but also reduces potential environmental pollution risks, meeting the requirements of green agriculture development.

[0019] 5. The saline-alkali soil conditioner of this invention has long-lasting and stable function, and does not cause secondary pollution to the soil. The biochar used has extremely high chemical stability and resistance to microbial decomposition, and can remain in the soil for hundreds of years. Its porous structure provides a permanent habitat for beneficial microorganisms, ensuring the long-term and stable improvement effect. The degradation products of the polymer and weathered coal are water and carbon dioxide, which are harmless and can be further utilized by microorganisms. All raw materials have undergone strict screening, and phosphogypsum has been tested for heavy metals, eliminating the risk of heavy metal and radioactive pollution at the source, ensuring high environmental safety. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments.

[0021] Example 1: A specific preparation method for a saline-alkali soil conditioner based on complexation adsorption reaction, comprising the following steps: Weigh 100g of acrylamide AM and 25g of betaine acrylate CBMA, add deionized water, and stir until completely dissolved; in another apparatus placed in an ice-water bath, add 170g of acrylic acid AA, and under vigorous stirring, slowly add 20% NaOH solution dropwise to neutralize it to a pH of approximately 5.5; mix the neutralized acrylic acid solution with the acrylic amide and betaine acrylate solution to obtain a monomer mixture;

[0022] (2) Add deionized water to the four-necked flask as the bottom water, start stirring, and begin to continuously purge nitrogen into the water at a flow rate that allows for the observation of continuous bubbles; continue purging nitrogen for 20-30 minutes to completely remove oxygen from the reaction system; heat the bottom water to 75°C and keep it stable, maintaining a nitrogen atmosphere; once the temperature stabilizes at 75°C, simultaneously begin to slowly add the monomer mixture and 0.4g of initiator solution into the deionized water bottom water; during the reaction, control the temperature of the reaction solution to be maintained between 75-80°C. Control the monomer solution to be added dropwise at a uniform rate over 60-90 minutes, and the initiator solution should be added dropwise before or simultaneously with the completion of the monomer addition; (3) Prepare the crosslinking agent. When the solution is completely added, add 0.03g of the crosslinking agent solution to the reaction flask; continue to keep the reaction at 75-80℃ for 1.5-2 hours to ensure the reaction is complete and the monomer is fully converted. (4) After the reaction is complete, a transparent or translucent elastic gel is obtained. Cut the large piece of gel into 1-2 cm pieces. 3 Small pieces are placed in an 80°C forced-air oven and dried for 12-24 hours until the gel blocks become hard and brittle solids, thus obtaining PAAC copolymer; (5) Add 1500g of water to the preparation tank, start stirring, add 19.5g of dispersant and 1.95g of preservative in sequence, and stir until completely dissolved; (6) Under high-speed stirring, 50g of pretreated PAAC copolymer, 50g of weathered coal, 50g of biochar, 200g of phosphogypsum and 100g of bentonite are gradually and slowly added to the aqueous phase; after the addition is completed, high-speed shearing is continued for 20-30 minutes to form a preliminary viscous suspension without obvious particles. (7) Transfer the suspension to a high-pressure homogenizer and circulate it 2-3 times under a pressure of 20-30 MPa to obtain the finished product, which is then sealed in a barrel.

[0023] Example 2: A specific preparation method for a saline-alkali soil conditioner based on complexation adsorption reaction, comprising the following steps: (1) Weigh 100g of acrylamide and 30g of betaine acrylate, add deionized water and stir until completely dissolved; add 200g of acrylic acid to another device placed in an ice-water bath, and slowly add 20% NaOH solution dropwise with a dropper while stirring vigorously to neutralize it to a pH of about 5.5; mix the neutralized acrylic acid solution with the acrylic amide and betaine acrylate solution to obtain a monomer mixture; (2) Add deionized water to the four-necked flask as the bottom water, start stirring, and begin to continuously purge nitrogen into the water at a flow rate that allows for the observation of continuous bubbles; continue purging nitrogen for 20-30 minutes to completely remove oxygen from the reaction system; heat the bottom water to 75°C and maintain a stable temperature while keeping the nitrogen atmosphere; once the temperature stabilizes at 75°C, simultaneously begin to slowly add the monomer mixture and 0.6g of initiator solution into the deionized water bottom water; during the reaction, maintain the temperature of the reaction solution between 75-80°C. Control the monomer solution to be added dropwise at a uniform rate over 60-90 minutes, and the initiator solution should be added before or simultaneously with the completion of the monomer addition; (3) Prepare the crosslinking agent. When the solution is completely added, add 0.06g of the crosslinking agent solution to the reaction flask; continue to keep the reaction at 75-80℃ for 1.5-2 hours to ensure the reaction is complete and the monomer is fully converted. (4) After the reaction is complete, a transparent or translucent elastic gel is obtained. Cut the large piece of gel into 1-2 cm pieces. 3 Small pieces are placed in an 80°C forced-air oven and dried for 12-24 hours until the gel blocks become hard and brittle solids, thus obtaining PAAC copolymer.

[0024] (5) Add 2250g of water to the preparation tank, start stirring, add 37.5g of dispersant and 3.75g of preservative in sequence, and stir until completely dissolved; (6) Under high-speed stirring, 100g of pretreated PAAC copolymer, 100g of weathered coal, 100g of biochar, 300g of phosphogypsum and 150g of bentonite are gradually and slowly added to the aqueous phase; after the addition is completed, the mixture is continuously sheared at high speed for 20-30 minutes to form a preliminary viscous suspension without obvious particles. (7) Transfer the suspension to a high-pressure homogenizer and circulate it 2-3 times under a pressure of 20-30 MPa; the finished product is obtained and sealed in a barrel.

[0025] Example 3: A specific preparation method for a saline-alkali soil conditioner based on complexation adsorption reaction, comprising the following steps: (1) Weigh 100g of acrylamide and 41g of betaine acrylate, add deionized water and stir until completely dissolved; add 221g of acrylic acid to another device placed in an ice-water bath, and slowly add 20% NaOH solution dropwise with a dropper while stirring vigorously to neutralize it to a pH of about 5.5; mix the neutralized acrylic acid solution with the acrylic amide and betaine acrylate solution to obtain a monomer mixture; (2) Add deionized water to the four-necked flask as the bottom water, start stirring, and begin to continuously purge nitrogen into the water at a flow rate that allows for the observation of continuous bubbles; continue purging nitrogen for 20-30 minutes to completely remove oxygen from the reaction system; heat the bottom water to 75°C and maintain a stable temperature while keeping the nitrogen atmosphere; once the temperature stabilizes at 75°C, simultaneously begin to slowly add the monomer mixture and 0.8g of initiator solution into the deionized water bottom water; during the reaction, maintain the temperature of the reaction solution between 75-80°C. Control the monomer solution to be added dropwise at a uniform rate over 60-90 minutes, and the initiator solution should be added before or simultaneously with the completion of the monomer addition; (3) Prepare the crosslinking agent. When the solution is completely added, add 0.1g of the crosslinking agent solution to the reaction flask; continue to keep the reaction at 75-80℃ for 1.5-2 hours to ensure the reaction is complete and the monomer is fully converted. (4) After the reaction is complete, a transparent or translucent elastic gel is obtained. Cut the large piece of gel into 1-2 cm pieces. 3 Small pieces are placed in an 80°C forced-air oven and dried for 12-24 hours until the gel blocks become hard and brittle solids, thus obtaining PAAC copolymer.

[0026] (5) Add 3000g of water to the preparation tank, start stirring, and add 60.75g of dispersant and 6.08g of preservative in sequence, stirring until completely dissolved; (6) Under high-speed stirring, 150g of pretreated PAAC copolymer, 150g of weathered coal, 150g of biochar, 400g of phosphogypsum and 200g of bentonite are gradually and slowly added to the aqueous phase; after the addition is completed, high-speed shearing is continued for 20-30 minutes to form a preliminary viscous suspension without obvious particles. (7) Transfer the suspension to a high-pressure homogenizer and circulate it 2-3 times under a pressure of 20-30 MPa; the finished product is obtained and sealed in a barrel.

[0027] Comparative Example 1: The difference between Comparative Example 1 and Example 2 is that ordinary polyacrylamide is used instead of the PAAC copolymer of the present invention. The specific process is as follows: The specific preparation method of the saline-alkali soil conditioner based on complexation adsorption reaction includes the following process: (1) Add 2250g of water to the preparation tank, start stirring, add 37.5g of dispersant and 3.75g of preservative in sequence, and stir until completely dissolved; (2) Commercially available industrial-grade polyacrylamide (Henan Senwo Environmental Protection Technology Co., Ltd.) non-ionic type with a molecular weight of 8 million and a purity of ≥90% was selected. It was directly crushed and passed through a 200-mesh sieve. Under high-speed stirring, 100g of polyacrylamide, 100g of weathered coal, 100g of biochar, 300g of phosphogypsum, and 150g of bentonite were gradually and slowly added to the aqueous phase. After the addition was completed, the mixture was continuously sheared at high speed for 20-30 minutes to form a preliminary viscous suspension without obvious particles. (3) Transfer the suspension to a high-pressure homogenizer and circulate it 2-3 times under a pressure of 20-30MPa to obtain the finished product, which is then sealed in a barrel.

[0028] Comparative Example 2: The difference between Comparative Example 2 and Example 2 is that undiluted phosphogypsum (Zaozhuang Liyuan Gypsum Co., Ltd.) was used.

[0029] Comparative Example 3: The difference between Comparative Example 3 and Example 2 is that calcium-based bentonite (Lingshou County Hongkai Mineral Products Processing Plant) is used instead of sodium-based bentonite.

[0030] Comparative Example 4: The difference between Comparative Example 4 and Example 2 is that 30% low-humic acid weathered coal is used instead of high-humic acid weathered coal.

[0031] Comparative Example 5: The difference between Comparative Example 5 and Example 2 is that 300℃ low-temperature carbonized straw biochar (Zigong Kaili Trading Co., Ltd.) was used instead of high-temperature carbonized biochar.

[0032] Comparative Example 6: The difference between Comparative Example 6 and Example 2 is that the straw biochar component is omitted.

[0033] Performance testing: 1. Soil pH Test: Three replicates were taken from the 0-20cm topsoil layer of soil treated with the amendments from Examples 1-3 and Comparative Examples 1-6. Each replicate was passed through a 2mm sieve to remove impurities. 10.0g of soil sample was placed in a 50mL centrifuge tube, and 50mL of deionized water was added at a water-to-soil ratio of 1:5. The sample was shaken at 200r / min for 30min, allowed to stand for 30min, and then the supernatant was collected. A pH meter was inserted into the supernatant, and the pH value was recorded after the reading stabilized. The soil pH was measured before amendment and at 1 month, 3 months, and 6 months after amendment, and the average of the three replicates was taken. The experimental results are shown in Table 1.

[0034] 2. Soil electrical conductivity: Take soil samples from the 0-20cm topsoil layer after treatment with the amendments from Examples 1-3 and Comparative Examples 1-6, with three replicates for each sample. Each sample was passed through a 2mm sieve to remove impurities. Using the supernatant from the pH test after shaking, insert the electrodes of the conductivity meter into the supernatant and record the EC value after the reading stabilizes.

[0035] EC values ​​were measured before improvement and at 1 month, 3 months, and 6 months after improvement, and the average value of three replicates was taken. The experimental results are shown in Table 1.

[0036] 3. Exchangeable Sodium Percentage: Take 5.0 g of air-dried soil samples treated with the amendments from Examples 1-3 and Comparative Examples 1-6 (passed through a 2 mm sieve) and place them in a 100 mL beaker. Add 50 mL of 1 mol / L ammonium acetate solution to a pH of 7.0. Stir magnetically for 30 min, then filter. Collect the filtrate and repeat the extraction three times. Combine the filtrates. Determine the sodium ion (Na) content in the filtrate using a flame photometer. + Concentration was calculated, and the exchangeable sodium content (cmol / kg) was determined. The soil cation exchange capacity (CEC) was also determined using the same method (cmol / kg). The percentage of exchangeable sodium (ESP%) was calculated as (exchangeable sodium content / CEC) × 100. The average of three replicates was taken, and the experimental results are shown in Table 1.

[0037] 4. Test on the proportion of aggregates larger than 0.25 mm: Take fresh soil samples treated with the amendments of Examples 1-3 and Comparative Examples 1-6, weigh 100.0 g of soil sample, place it on a sieve with the top layer being a 2 mm sieve and the bottom layer being a 0.25 mm sieve, and slowly immerse it in a container filled with deionized water, let it stand for 10 min; move the sieve up and down by 3 cm at a rate of 30 times per minute for 5 min; remove the residue on the 0.25 mm sieve, transfer it to an aluminum box, dry it at 105℃ to constant weight, and record the weight as m1. Record the total mass of the dried soil sample as m. The proportion of aggregates (%) = (m1 / m) × 100, and take the average of 3 replicates. The experimental results are shown in Table 1.

[0038] 5. Sodium ion adsorption rate test: Take the modifiers from Examples 1-3 and Comparative Examples 1-6, shake well, and measure the volume V = 0.5 / ρ, where ρ is the solid content of the liquid modifier in g / mL. Prepare a 500 mg / L sodium chloride solution to simulate the sodium ion environment of saline-alkali soil. Take a 250 mL Erlenmeyer flask, add the measured liquid modifier and 50 mL sodium chloride solution, seal it, and place it on a shaker at 25℃, shaking at 150 r / min for 24 h. After shaking, take the supernatant and filter it through a 0.45 μm filter membrane. Measure the remaining sodium ion concentration using a flame photometer and record it as C1. For the blank control group without modifier, measure the initial sodium ion concentration and record it as C0. Sodium ion adsorption rate (%) = [(C0-C1) / C0] × 100, and take the average of 3 replicates. The experimental results are shown in Table 1.

[0039] 6. Salt return rate test after 6 months of improvement: Field soils treated with the improvers of Examples 1-3 and Comparative Examples 1-6 for 6 months were collected, and the initial EC value of the top 0-5cm soil layer was measured and recorded as EC1; Simulated 50mm rainfall: Water was sprayed evenly on a 1m×1m plot using a sprayer to ensure that the water penetrated to the 10cm soil layer; The EC value of the top 0-5cm soil layer was measured again after 7 days and recorded as EC2; Salt return rate (%) = [(EC2-EC1) / EC1]×100, and the average value of 3 replicates was taken. The experimental results are shown in Table 1.

[0040] 7. Germination rate and biomass test: Alfalfa seeds were selected and soil treated with the amendments of Examples 1-3 and Comparative Examples 1-6 was used. 50 seeds were sown per pot, covered with 1 cm of soil, and the soil moisture content was maintained at 20%. The pots were placed in a light incubator at 25℃ for 12 hours of light. After 7 days, the number of germinated seeds was counted, and the germination rate was calculated. After 30 days of cultivation, the plants were harvested, and the plant height was measured, with the average of 10 plants being recorded. The fresh weight of the above-ground parts was also recorded as fresh weight. Results were calculated as follows: Germination rate (%) = (Number of germinated seeds / 50) × 100; Plant height (cm) and fresh weight (g / pot) were the average of three replicates. The experimental results are shown in Table 1.

[0041] Table 1: Sample Test Data

[0042] Data Analysis: As shown in Table 1, the soil conditioners for saline-alkali land prepared using the method of this invention in Examples 1-3 exhibit balanced performance across various aspects, demonstrating excellent salt-alkali reduction, soil structure improvement, fertility enhancement, and long-lasting resistance to salt return. Example 2 shows the best overall performance. This is attributed to the scientific ratio and synergistic effect of the raw materials: the terpolymer acrylamide-acrylic acid-betaine acrylate efficiently adsorbs sodium ions through complexation; refined phosphogypsum provides sufficient calcium ions for calcium-sodium exchange; sodium-based bentonite and high-temperature biochar synergistically improve soil aggregate structure; and high-humic acid weathered coal replenishes organic matter and regulates pH. The components form a synergistic system of "complexation adsorption-ion exchange-structure improvement-fertility enhancement," thus outperforming the comparative examples in all tests.

[0043] Regarding soil pH, the soil pH values ​​of Examples 1-3 remained stable at 7.7-8.2 for 1-6 months after improvement, with minimal fluctuations. This is because the carboxyl and betaine groups in the terpolymer can continuously complex OH groups in the soil. - The calcium-sodium exchange of phosphogypsum reduces the concentration of alkaline ions, while the humic acid buffer system of weathered coal inhibits pH rise. Comparative Example 1 (ordinary polyacrylamide) lacks functional groups and cannot continuously complex alkaline ions, resulting in a pH rise to 8.8 after 6 months. Comparative Example 2 (unremoved phosphogypsum) has a weaker alkalinity-reducing effect than the examples due to impurities such as calcium chloride interfering with calcium-sodium exchange. Comparative Example 4 (low-humic acid weathered coal) has poor pH stability due to insufficient buffering capacity.

[0044] Regarding the soil electrical conductivity (EC) value, the total salt content of the EC values ​​in Examples 1-3 was significantly lower than that in the comparative example, and the recovery rate after 6 months was small. The key reason is the sodium ion complexation of the terpolymer and the physical barrier effect of biochar: the carboxyl groups and betaine groups on the copolymer molecular chain form multi-point adsorption, reducing free salt; the porous structure of high-temperature biochar prevents salt from migrating to the surface.

[0045] Comparative Example 1: Ordinary polyacrylamide, due to its limited adsorption sites, could not effectively fix salts, and its EC value reached 5.0 dS / m after 6 months. Comparative Example 6: Without biochar, the salt content rebounded the fastest due to the lack of physical barriers. Comparative Example 3: Calcium-based bentonite, due to its poor expansibility, had a weaker salt adsorption capacity than sodium-based bentonite, resulting in poor EC value control.

[0046] Regarding the percentage of exchangeable sodium, the ESP values ​​of Examples 1-3 decreased to 10%-18% after one month of improvement and stabilized at 11%-19% after six months. This is because the refined phosphogypsum with ≥85% calcium sulfate dihydrate provides highly active calcium ions, which synergistically promote sodium ion exchange with the terpolymer: the copolymer complexes free sodium ions, reducing their re-adsorption, while the calcium ions from the phosphogypsum continuously replenish the exchange sites. In Comparative Example 2, the unremoved phosphogypsum contained impurities such as calcium chloride, which inhibited calcium ion activity, resulting in an ESP value that only decreased to 20%-23%. In Comparative Example 1, ordinary polyacrylamide could not complex sodium ions, and the exchanged sodium ions were easily re-adsorbed, leading to a significant increase in ESP. In Comparative Example 4, low-humic acid weathered coal lacked the charge-balancing effect of humic acid, resulting in low exchange efficiency.

[0047] Regarding the proportion of aggregates larger than 0.25 mm, Examples 1-3 showed an aggregate structure proportion of 30%-42%, which remained stable after 6 months. This is attributed to the synergistic effect of sodium-based bentonite and high-temperature biochar: the strong interlayer expansion of montmorillonite in sodium-based bentonite interweaves with the porous structure of biochar to form a stable three-dimensional network, encapsulating soil particles to form water-stable aggregates. In Comparative Example 3, calcium-based bentonite, due to the limitation of expansion by interlayer calcium ions, could not form a continuous network, with an aggregate structure proportion of only 20%-22%; the low-temperature biochar at 5300℃ in Comparative Example had an insufficiently developed porous structure with a specific surface area of ​​100 m². 2 / g, with weak interweaving ability with bentonite, resulting in poor aggregate stability; compared to Example 6, which lacks biochar support, the aggregate structure is easily destroyed.

[0048] Regarding sodium ion adsorption rates, Examples 1-3 achieved 40%-50%, significantly higher than the comparative examples. This is primarily due to the structural advantages of the terpolymer: the amide groups of acrylamide, the carboxyl groups of acrylic acid, and the quaternary ammonium groups of betaine form synergistic adsorption sites, resulting in a much stronger complexation ability for sodium ions compared to single functional groups. Comparative Example 1, with its ordinary polyacrylamide containing only amide groups, had fewer adsorption sites and an adsorption rate of only 20%; Comparative Example 4, with its low-humic acid weathered coal, had weak auxiliary adsorption capacity due to insufficient humic acid; and Comparative Example 2, with its unremoved phosphogypsum, had an adsorption rate reduced to 35% due to impurities competing for adsorption sites.

[0049] After 6 months of improvement, the salt return rate of Examples 1-3 was only 7%-10%. This is due to the synergistic anti-salt return mechanism of biochar and sodium-based bentonite: the porous structure of high-temperature biochar physically blocks salt migration, while the adsorption effect of sodium-based bentonite fixes the lower layer salts, and the two work together to inhibit surface salt return. Comparative Example 6, without biochar, had a salt return rate of 35% due to the lack of physical barriers; Comparative Example 1, with ordinary polyacrylamide, had a salt return rate of 25% because it could not fix salts for a long time; Comparative Example 2, with unremoved phosphogypsum, had a salt return rate of 28% after 6 months due to rapid calcium ion loss caused by impurities.

[0050] Regarding crop germination rate and biomass, the crops in Examples 1-3 achieved a germination rate of 85%-95%, a plant height of 35-50cm, and a fresh weight of 80-150g / pot. This reflects the comprehensive improvement effect: after reducing salinity and alkalinity, the soil pH and EC values ​​are suitable for crop growth; the granular structure improves aeration and water permeability; the high-humic acid weathered coal and biochar supplement nutrients; and the heavy metal content is low and meets the standards. Comparative Example 2, with its unremoved phosphogypsum, had a germination rate of only 65% ​​due to excessive heavy metals such as lead and cadmium; Comparative Example 5, with its low-temperature biochar, had a fresh weight of only 60g / pot due to its high 20% ash content inhibiting root development; and Comparative Example 1, with its ordinary polyacrylamide, had a plant height of only 25cm due to poor fertilizer retention and rapid nutrient loss.

[0051] Those skilled in the art should understand that the discussion of any of the above embodiments is merely exemplary and is not intended to imply that the scope of the invention is limited to these examples; within the framework of the invention, the technical features of the above embodiments or different embodiments can also be combined, the steps can be implemented in any order, and there are many other variations of the different aspects of the invention as described above, which are not provided in detail for the sake of brevity.

Claims

1. A soil conditioner for saline-alkali land based on complexation adsorption reaction, characterized in that, The raw materials include the following parts by weight: PAAC copolymer: 5-15 parts, phosphogypsum: 20-40 parts, bentonite: 10-20 parts, weathered coal: 5-15 parts, straw biochar: 5-15 parts, water: 100-200 parts, dispersant: 1.0-1.5 parts, and preservative: 0.1-0.15 parts.

2. The saline-alkali soil conditioner based on complexation adsorption reaction according to claim 1, characterized in that, The phosphogypsum must undergo impurity removal treatment, with a calcium sulfate dihydrate content ≥85%, and heavy metals such as lead and cadmium meeting agricultural standards; the bentonite is sodium-based bentonite with a montmorillonite content ≥70%; the weathered coal contains humic acid ≥50% and has a pH value between 6 and 8; the straw biochar needs to be carbonized at a high temperature of 600-800℃, with an ash content ≤10% and a specific surface area ≥200 m². 2 / g, pH 8.0-9.5; dispersant is sodium lignosulfonate; preservative is potassium sorbate; based on the total mass of the liquid soil conditioner: dispersant is 1.0%-1.5%, preservative is 0.1%-0.15%; water to solid mass ratio is 1-2:

1.

3. The saline-alkali soil conditioner based on complexation adsorption reaction according to claim 1, characterized in that, The PAAC copolymer, phosphogypsum, bentonite, weathered coal, and straw biochar all require pretreatment, including crushing and passing through a 200-mesh sieve.

4. The method for preparing the saline-alkali soil conditioner based on complexation adsorption reaction according to any one of claims 1-3, characterized in that, Includes the following steps: S1. Preparation of PAAC copolymer (1) Weigh acrylamide and betaine acrylate, add deionized water and stir until completely dissolved; add acrylic acid to another device placed in an ice-water bath, and slowly add 20% NaOH solution dropwise with a dropper while stirring vigorously to neutralize it to a pH of about 5.5; mix the neutralized acrylic acid solution with the acrylic amine and betaine acrylate solution to obtain a monomer mixture; (2) Add deionized water to the four-necked flask as the bottom water, turn on the stirrer, and start continuously purging nitrogen into the water at a flow rate that allows continuous bubbles to be observed; continue purging nitrogen for 20-30 minutes to completely remove oxygen from the reaction system; heat the bottom water to 75°C and keep it stable to maintain a nitrogen atmosphere; when the temperature stabilizes at 75°C, start slowly adding the monomer mixture and initiator solution into the deionized water bottom water; during the reaction, control the temperature of the reaction solution to be maintained between 75-80°C, control the monomer solution to be added at a uniform rate within 60-90 minutes, and the initiator solution should be added before or at the same time as the monomer addition is completed; (3) Prepare the crosslinking agent. When the solution has been added dropwise, add the crosslinking agent solution to the reaction flask. Continue to keep the reaction at 75-80℃ for 1.5-2 hours to ensure the reaction is complete and the monomer is fully converted. (4) After the reaction is complete, a transparent or semi-transparent elastic gel is obtained; the large gel is cut into small pieces of 1-2 cm3 and placed in an 80°C forced-air oven to dry for 12-24 hours until the gel block becomes a hard and brittle solid, thus obtaining the PAAC copolymer. S2. Add water to the preparation tank, start stirring, add dispersant and preservative in sequence, and stir until completely dissolved; S3. Under high-speed stirring, the pretreated PAAC copolymer, weathered coal, biochar, phosphogypsum, and bentonite are gradually and slowly added to the aqueous phase according to the designed ratio; after the addition is completed, high-speed shearing is continued for 20-30 minutes to form a preliminary viscous suspension without obvious particles. S4. Transfer the suspension to a high-pressure homogenizer and circulate it 2-3 times under a pressure of 20-30MPa; the finished product is then packaged and sealed in drums.

5. The saline-alkali soil conditioner based on complexation adsorption reaction according to claim 4, characterized in that, The acrylamide and betaine acrylate must be industrial grade pure products with a purity ≥95%; sodium hydroxide must be analytical grade, and the solution concentration must be 20% and must be freshly prepared; acrylic acid AA must be colorless and transparent and free of polymerization inhibitors.

6. The saline-alkali soil conditioner based on complexation adsorption reaction according to claim 4, characterized in that, The acrylate, acrylic acid, and betaine acrylate are present in a weight ratio of 1:1.70-2.21:0.25-0.

41.

7. The saline-alkali soil conditioner based on complexation adsorption reaction according to claim 4, characterized in that, The initiator needs to be prepared fresh and has a concentration range of 1-5%. It is a solution obtained by dissolving ammonium persulfate in deionized water, and the amount of ammonium persulfate added is 0.4%-0.8% of the total mass of the monomer.

8. The saline-alkali soil conditioner based on complexation adsorption reaction according to claim 4, characterized in that, The crosslinking agent concentration range is 0.5%-1%, and it is a solution obtained by dissolving N,N'-methylenebisacrylamide MBA in deionized water. The amount of N,N'-methylenebisacrylamide added is 0.03%-0.10% of the total monomer mass.

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