Preparation method and application of humic acid base saline soil conditioner

Abstract

This invention discloses a method for preparing and applying a fulvic acid-based saline-alkali soil conditioner, relating to superabsorbent polymer technology and the field of saline-alkali soil remediation. The saline-alkali soil conditioner is prepared by a method comprising the following steps: first, dispersing fulvic acid in water; then adding neutralized acrylic acid and the anionic monomer potassium 3-sulfonate propylmethylpropylacrylate; and finally, sequentially adding a crosslinking agent and an initiator to carry out a graft polymerization reaction to obtain the saline-alkali soil conditioner. In this invention, the fulvic acid contains active groups with strong ion exchange and complexing capabilities, enabling it to react with Na+ in saline-alkali soil. + K + This process facilitates water exchange, adjusts soil pH, and enhances the water absorption and salt tolerance of saline-alkali soils. Experiments have demonstrated that the saline-alkali soil conditioner prepared in this invention can absorb more than 120 times its own weight in 0.9% sodium chloride, more than 130 times its own weight in 0.9% potassium chloride, more than 300 times its own weight in tap water, and nearly 2300 times its own weight in deionized water. Therefore, it can improve the water-holding capacity of saline-alkali soils and reduce soil salinity.

Description

Technical Field

[0001] This invention relates to the field of soil remediation technology, and in particular to a method for preparing and applying a fulvic acid-based saline-alkali soil conditioner. Background Technology

[0002] Soil salinization is a serious global ecological problem that severely impacts the effective use of land resources and sustainable agricultural development. According to statistics, over 1 billion hectares of land worldwide are threatened by salinization, which not only renders vast amounts of land unusable for agricultural production but also exacerbates food shortages and ecological degradation.

[0003] With the continuous growth of the population and the acceleration of urbanization, the demand for land resources is increasing. How to effectively manage and improve saline-alkali soil and increase its productivity has become an urgent scientific problem and a practical need.

[0004] In recent years, superabsorbent polymers (SAPPs) have shown promise as a novel functional material in soil improvement. SAPPs possess exceptional water absorption and retention capabilities, effectively improving soil physical properties and enhancing its water retention capacity and drought resistance. However, most commercially available SAPPs suffer from poor salt tolerance and biodegradability, limiting their widespread application in saline-alkali soil improvement.

[0005] Fulvic acid is an important component of humic substances. It has a low molecular weight and contains numerous active functional groups, including carboxyl (-COOH), phenolic hydroxyl (-OH), carbonyl (-C=O), and methoxy (-OCH3). These active functional groups endow fulvic acid with strong ion exchange and chelating capabilities, enabling it to chelate with metal ions in the soil, promoting the migration of mineral elements and the formation of soil aggregates, thereby improving soil aeration and water and fertilizer retention capacity. Furthermore, fulvic acid exhibits good biocompatibility and environmental friendliness, making it an ideal soil amendment material. However, there are currently no reports of using fulvic acid directly as a raw material to prepare superabsorbent polymers for the treatment of desertification and saline-alkali soils.

[0006] Potassium 3-sulfonopropyl methacrylate (SPMA) is an anionic monomer with numerous sulfonic acid groups on its surface, exhibiting good hydrophilicity and cation selectivity. Its high charge density and the coordination of metal ions with functional groups can enhance the conductivity of the hydrogel, while the sulfonate metal coordination compounds also possess a certain toughening effect. These properties make SPMA a potential candidate for preparing high-performance, superabsorbent polymers. However, currently, there are no known applications of this monomer in the preparation of superabsorbent polymers, especially in the field of saline-alkali soil improvement.

[0007] Therefore, developing a highly absorbent polymer based on fulvic acid and combined with monomers such as SPMA for improving saline-alkali soils is not only of significant theoretical importance but also has substantial practical application value. This novel saline-alkali soil conditioner is expected to overcome the shortcomings of traditional methods, achieving efficient and stable improvement of saline-alkali soils, and providing a new technological approach for saline-alkali land management in my country and globally. Summary of the Invention

[0008] The purpose of this invention is to provide a method for preparing a fulvic acid-based saline-alkali soil conditioner. By compounding fulvic acid with potassium 3-sulfonopropyl methacrylate, a highly efficient, stable, and salt-tolerant saline-alkali soil conditioner is prepared, thereby solving the problems existing in the prior art.

[0009] To achieve the above objectives, the present invention provides the following technical solution:

[0010] A method for preparing a fulvic acid-based saline-alkali soil conditioner includes the following steps: first, dispersing the raw material fulvic acid in water; then, adding an acrylic acid solution reacted with a neutralizing agent and potassium 3-sulfonopropyl methacrylate to the fulvic acid solution; and after uniform dispersion, sequentially adding a crosslinking agent solution and an initiator solution to carry out a graft polymerization reaction to obtain the saline-alkali soil conditioner.

[0011] Preferably, the mass ratio of the total mass of acrylic acid and potassium 3-sulfonopropyl methacrylate to fulvic acid, crosslinking agent, and initiator is 100:(0.1~1):(0.01~0.12):(0.1~0.8); the mass ratio of potassium 3-sulfonopropyl methacrylate to acrylic acid is 1:3~10.

[0012] Preferably, the specific conditions for the graft polymerization reaction are as follows: the reaction is carried out in a nitrogen atmosphere, the polymerization temperature is 60~80℃, the graft polymerization time is 60~120min, and the graft polymerization reaction is carried out under stirring conditions, with a stirring speed of 200~300r / min.

[0013] Preferably, after the graft polymerization reaction, the reaction product is soaked in anhydrous ethanol, then cut, dried, pulverized, and sieved to obtain a saline-alkali soil conditioner.

[0014] Preferably, the degree of neutralization of acrylic acid in the acrylic acid solution after the neutralizing agent reaction is 45% to 85%; the neutralizing agent is sodium hydroxide or potassium hydroxide. The term "degree of neutralization" refers to the extent to which the neutralization reaction proceeds, and is usually expressed as the molar ratio of the reaction products.

[0015] Preferably, the crosslinking agent is one or more of N,N-methylenebisacrylamide, glutaraldehyde, and ethylene glycol; and the initiator is one or two of ammonium sulfate and potassium persulfate.

[0016] More preferably, the crosslinking agent is N,N-methylenebisacrylamide, and the initiator is ammonium persulfate.

[0017] More preferably, the mass ratio of the total mass of acrylic acid and potassium 3-sulfonopropyl methacrylate to fulvic acid, crosslinking agent, and initiator is 100:(0.1~0.5):(0.02~0.04):(0.1~0.3); the mass ratio of potassium 3-sulfonopropyl methacrylate to acrylic acid is 1:5~6.

[0018] Further preferably, the mass ratio of the total mass of acrylic acid and potassium 3-sulfonopropyl methacrylate to fulvic acid, crosslinking agent, and initiator is 100:0.2:0.03:0.2; and the mass ratio of potassium 3-sulfonopropyl methacrylate to acrylic acid is 1:6.

[0019] More preferably, the degree of neutralization of acrylic acid in the acrylic acid solution after the neutralizing agent reaction is 55%~75%.

[0020] More preferably, the degree of neutralization of acrylic acid in the acrylic acid solution after the neutralizing agent reaction is 60%.

[0021] An application of a fulvic acid-based saline-alkali soil conditioner, characterized in that the fulvic acid-based saline-alkali soil conditioner is used for desertification control and soil structure improvement, soil salinity reduction and plant growth promotion.

[0022] The present invention discloses the following technical effects:

[0023] (1) This invention uses fulvic acid, acrylic acid, and potassium 3-sulfopropyl methacrylate graft polymerization to produce a polymer with high water absorption properties, which can be used as a soil conditioner for saline-alkali soils. The raw material, fulvic acid, has active groups with strong ion exchange and complexing capabilities. The carboxyl group (-COOH) in fulvic acid can react with Na+. + K + When monovalent metal ions undergo complexation, sodium fulvic acid and potassium fulvic acid are formed, thus creating a buffer system for the interconversion of fulvic acid and fulvic acid salts. This system regulates soil pH and alleviates saline-alkali stress. Furthermore, fulvic acid polymerizes with acrylic acid and potassium 3-sulfonopropyl methacrylate, introducing hydrophilic groups such as sulfonic acid groups (-SO3H) and carboxyl groups (-COOH) into the polymer. These two groups can also adsorb Na+ and K+ through ion exchange, effectively improving the water retention and saline-alkali resistance of the soil conditioner.

[0024] (2) The superabsorbent polymer prepared by the present invention can interact with soil particles through electrostatic interaction and hydrogen bonding, promote the aggregation of soil particles, thereby improving soil structure and avoiding soil desertification.

[0025] (3) The superabsorbent polymer of the present invention, as a soil conditioner, contains nitrogen and potassium elements to provide nutrients for plant growth. Attached Figure Description

[0026] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0027] Figure 1 A flowchart illustrating the preparation process of fulvic acid-based saline-alkali soil conditioner;

[0028] Figure 2 FTIR and XRD patterns of the fulvic acid-based saline-alkali soil conditioner prepared in Example 2;

[0029] Figure 3 This is a scanning electron microscope image of fulvic acid.

[0030] Figure 4 Scanning electron microscope image of the saline-alkali soil conditioner prepared in Example 2;

[0031] Figure 5 The images show fulvic acid, the superabsorbent polymer obtained in Example 2, the superabsorbent polymer after absorbing tap water, absorbing 0.9% sodium chloride solution, absorbing 0.9% potassium chloride solution, and swelling after absorbing deionized water. Detailed Implementation

[0032] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0033] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention.

[0034] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0035] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be readily apparent to those skilled in the art. This specification and embodiments are merely exemplary.

[0036] This invention provides a method for preparing a fulvic acid-based saline-alkali soil conditioner, comprising the following steps: first, dispersing fulvic acid in water; then adding an acrylic acid solution reacted with a neutralizing agent and potassium 3-sulfonopropyl methacrylate to the fulvic acid solution; after uniform dispersion, sequentially adding a crosslinking agent solution and an initiator solution to carry out a graft polymerization reaction; finally, soaking the reaction product in anhydrous ethanol, cutting, drying, pulverizing, and sieving to obtain the saline-alkali soil conditioner.

[0037] In some embodiments of the present invention, the mass ratio of the total mass of acrylic acid and potassium 3-sulfonopropyl methacrylate to fulvic acid, crosslinking agent, and initiator is 100:0.2:0.03:0.2; the mass ratio of potassium 3-sulfonopropyl methacrylate to acrylic acid is 1:6.

[0038] In some embodiments of the present invention, the specific conditions for the graft polymerization reaction are as follows: the reaction is carried out in a nitrogen atmosphere, the temperature of the polymerization reaction is 60~80℃, the graft polymerization reaction time is 60~120 min, and the graft polymerization reaction is carried out under stirring conditions, wherein the stirring speed is 200~300 r / min.

[0039] In some embodiments of the present invention, the graft polymerization reaction temperature is 75°C.

[0040] Excessively high reaction temperatures lead to excessively high free radical activity, making it easy for chain transfer to occur with solvents or monomers, and excessive consumption of crosslinking agents, resulting in uneven crosslinking and reduced water absorption performance. When the temperature is too low, the initiator decomposes slowly, resulting in insufficient free radical concentration and incomplete polymerization (more residual monomers), thus affecting performance. Too short a reaction time leads to low monomer conversion and insufficient crosslinking density. Too long a reaction time leads to an overly dense network structure or side reactions. The shear force generated by high-speed stirring may cut off the formed polymer chains, destroy the network structure, and reduce the molecular weight, affecting gel strength. Low-speed stirring cannot fully mix the system, resulting in excessively high local monomer concentrations or initiator enrichment.

[0041] In some embodiments of the present invention, the degree of neutralization of acrylic acid in the acrylic acid solution after the neutralizing agent reaction is 60%; the neutralizing agent is potassium hydroxide.

[0042] In some embodiments of the present invention, the crosslinking agent is one or more of N,N-methylenebisacrylamide, glutaraldehyde, and ethylene glycol; the initiator is one or two of ammonium sulfate and potassium persulfate.

[0043] This invention utilizes graft polymerization of fulvic acid, acrylic acid, and potassium 3-sulfopropyl methacrylate to prepare a polymer with high water absorption properties, which can be used as a soil conditioner for saline-alkali soils. The raw material, fulvic acid, possesses active groups with strong ion exchange and complexing capabilities. A scanning electron microscope image of fulvic acid is shown below. Figure 3 As shown. The carboxyl group (-COOH) in fulvic acid can react with Na. + K + When monovalent metal ions undergo complexation, sodium and potassium fulvic acid salts are formed, creating a buffer system for the interconversion of fulvic acid and fulvic acid salts. This system regulates soil pH and alleviates saline-alkali stress. Furthermore, fulvic acid polymerizes with acrylic acid and potassium 3-sulfonopropyl methacrylate, introducing hydrophilic groups such as sulfonic acid groups (-SO3H) and carboxyl groups (-COOH) into the polymer. These two groups can also adsorb sodium sulfonate through ion exchange. + K + It effectively improves the water retention and salt-alkali resistance of soil conditioners.

[0044] In the following embodiments and comparative examples of the present invention, the raw materials used were all obtained through conventional commercial channels.

[0045] It should be noted that the technical means not described in detail in the following embodiments and comparative examples of the present invention are all conventional technical means in the art.

[0046] Example 1

[0047] like Figure 1 As shown, a method for preparing a fulvic acid-based saline-alkali soil conditioner includes the following steps:

[0048] Add 0.0139g of fulvic acid to 10 mL of deionized water and stir on a magnetic stirrer for 20 min to disperse the fulvic acid evenly. Set aside.

[0049] Dissolve 1.9797 g of sodium hydroxide in 10 mL of deionized water to obtain a sodium hydroxide solution;

[0050] Mix 5.945 g of acrylic acid with sodium hydroxide solution to obtain a neutralized acrylic acid solution (neutralization degree 60%), and set aside for later use;

[0051] Add 0.0014 g of N,N-methylenebisacrylamide (MBA) to 2 ml of deionized water, and sonicate until completely dissolved to obtain a crosslinking agent solution for later use.

[0052] Dissolve 0.069 g of ammonium persulfate (APS) in 2 ml of deionized water and sonicate to obtain an initiator solution for later use;

[0053] Aqueous solution polymerization was employed. The mixture was stirred at 300 r / min in a 75°C water bath. Neutralized acrylic acid solution and 0.9898 g of potassium 3-sulfonate propyl methacrylate (SPMA) were added sequentially to the fulvic acid dispersion. After reacting for 10 min, a crosslinking agent solution was added, followed by an initiator solution after 15 min. Graft copolymerization was carried out under a nitrogen atmosphere for 70 min. The mixture was then removed from the water bath to obtain the copolymer. The product was washed with anhydrous ethanol, dried at 60°C for 24 h, and pulverized to 20-40 mesh to obtain highly absorbent polymer particles, which were used as a soil conditioner for saline-alkali soils.

[0054] Example 2

[0055] A method for preparing a fulvic acid-based saline-alkali soil conditioner, wherein the remaining steps are the same as in Example 1, except that the amount of N,N-methylenebisacrylamide added is adjusted to 0.0021 g and the amount of ammonium persulfate added is adjusted to 0.0139 g.

[0056] The FTIR and XRD patterns of the prepared soil conditioner are shown below. Figure 2 As shown, Figure 2 'a' is the FTIR spectrum of the material, containing the infrared spectra of four components: (a), (b), (c), and (d). Among these, the spectrum at 3421 cm⁻¹ is shown in (d). -1 2931 cm -1 1720 cm -1 3415 cm -1 The peaks at these points correspond to the stretching vibrations of OH, -CH2-, C=O, and -CH2- of PAA, respectively. Compared to (d), the FTIR spectrum of P(AA-co-SPMA) in (c) shows a higher peak at 1203 cm⁻¹. -1 1061cm -1 The peak at 3415 cm⁻¹ exhibits both S=O symmetric and S=O asymmetric stretching vibrations, indicating that the two monomers SPMA and AA underwent a polymerization reaction. (a) is the FTIR spectrum of FA at 3415 cm⁻¹. -1 The peak value is attributed to the tensile vibration of OH in the FA structural unit, 2927 cm. -1 The peak value is attributed to the asymmetric stretching vibration of -CH2-, 1602 cm⁻¹. -1 The peak value is attributed to the C=C stretching vibration on the benzene ring skeleton, 1411 cm. -1 The peak value is attributed to the asymmetric stretching vibration of the -CH2- group in the benzene ring skeleton, 661 cm⁻¹. -1The peak value is attributed to the out-of-plane bending vibration of -CH2- on the benzene ring. Compared with (a) and (c), the FTIR spectrum of (b) FA-gP(AA-co-SPMA) at 1602 cm⁻¹... -1 and 661 cm -1 The presence of stretching vibrations of C=C and out-of-plane bending vibrations of -CH2- on the benzene ring skeleton indicates that FA participates in the reaction during this polymerization process.

[0057] Figure 2 b shows the XRD patterns of three components: FA, P(AA-co-SPMA), and FA-gP(AA-co-SPMA). FA exhibits two distinct diffraction peaks at 2θ = 27.7° and 39.8°, indicating an ordered crystalline structure. No new diffraction peaks were observed in the XRD pattern of P(AA-co-SPMA), but the intensity of its diffraction peaks decreased significantly. Compared to P(AA-co-SPMA), the addition of FA reduces the crystallinity of the polymer. This is because the long-range order of the internal crystal structure decreases after the graft copolymerization reaction between the natural component FA and the polymer P(AA-co-SPMA), indicating that the existing intramolecular and intermolecular hydrogen bonds in the material interact significantly with other ions. Simultaneously, the reduced crystallinity suggests a tendency towards an amorphous crystal structure, a characteristic that enhances the copolymer's water absorption and retention capacity, facilitating better water absorption and release.

[0058] Scanning electron micrograph of the prepared soil conditioner is shown below. Figure 4 As shown, the soil conditioner has uniform and dense pores, which have a strong adsorption effect on water.

[0059] The swelling of the prepared soil conditioner is shown in the following figure. Figure 5 As shown, the swelling effect is as follows: distilled water > tap water > 0.9% KCl > 0.9% NaCl. In distilled water, the hydrophilic groups in the superabsorbent polymer, such as carboxyl and sulfonic acid groups, are completely ionized, resulting in the greatest electrostatic repulsion, sufficient network diffusion, and the highest swelling rate. In tap water, there may be some divalent groups, such as Ca2+... 2+ Na⁺ and K⁺ undergo ionic cross-linking with -COO⁻, further inhibiting swelling. The swelling rate is between that of distilled water and brine. In salt solutions, Na⁺ / K⁺ shields the negative charge of -COO⁻, weakening electrostatic repulsion and causing network contraction, resulting in a significant decrease in the swelling rate. Na⁺ has a smaller hydration radius than K⁺, making it easier to approach -COO⁻ and providing stronger charge shielding. Therefore, the swelling rate in 0.9% NaCl is slightly lower than that in 0.9% KCl.

[0060] Example 3

[0061] A method for preparing a fulvic acid-based saline-alkali soil conditioner, the remaining steps are the same as in Example 1, except that the amount of N,N-methylenebisacrylamide added is adjusted to 0.0028g.

[0062] Example 4

[0063] Add 0.0346g of fulvic acid to 10mL of deionized water and stir on a magnetic stirrer for 20min to disperse the fulvic acid evenly.

[0064] Dissolve 1.9797 g of sodium hydroxide in 10 mL of deionized water to obtain a sodium hydroxide solution.

[0065] Mix 5.945g of acrylic acid with sodium hydroxide solution to obtain a neutralized acrylic acid solution for later use.

[0066] Add 0.0021g of N,N-methylenebisacrylamide (MBA) to 2 ml of deionized water and sonicate until completely dissolved to obtain a crosslinking agent solution for later use.

[0067] Dissolve 0.0139 g of ammonium persulfate (APS) in 2 ml of deionized water and sonicate to obtain an initiator solution for later use.

[0068] Aqueous solution polymerization was employed. The mixture was stirred at 300 rpm in a 75°C water bath. Neutralized acrylic acid solution and 0.9898 g of potassium 3-sulfonate propyl methacrylate (SPMA) were added sequentially to the fulvic acid dispersion. After reacting for 10 min, a crosslinking agent solution was added, followed by an initiator solution after 15 min. Graft copolymerization was carried out under a nitrogen atmosphere for 70 min. The mixture was then removed from the water bath to obtain the copolymer. The product was washed with anhydrous ethanol, dried at 60°C for 24 h, and pulverized to 20-40 mesh to obtain highly absorbent polymer particles, which were used as a soil conditioner for saline-alkali soils.

[0069] Example 5

[0070] Add 0.0139g of fulvic acid to 10mL of deionized water and stir on a magnetic stirrer for 20min to disperse the fulvic acid evenly.

[0071] Dissolve 1.9797 g of sodium hydroxide in 10 mL of deionized water to obtain a sodium hydroxide solution.

[0072] Mix 3.77g of acrylic acid with sodium hydroxide solution to obtain a neutralized acrylic acid solution for later use.

[0073] Add 0.0021g of N,N-methylenebisacrylamide (MBA) to 2ml of deionized water and sonicate until completely dissolved to obtain a crosslinking agent solution for later use.

[0074] Dissolve 0.0139 g of ammonium persulfate (APS) in 2 ml of deionized water and sonicate to obtain an initiator solution for later use.

[0075] Aqueous solution polymerization was employed. In a water bath at 75°C, the mixture was stirred at 300 rpm. Neutralized acrylic acid solution and 0.9898 g of potassium 3-sulfopropyl methacrylate (SPMA) were added sequentially to the fulvic acid dispersion. After reacting for 10 min, a crosslinking agent solution was added, followed by an initiator solution after 15 min. Graft copolymerization was carried out under a nitrogen atmosphere for 70 min. The mixture was then removed from the water bath to obtain the copolymer. The product was washed with anhydrous ethanol, dried at 60°C for 24 h, and pulverized to 20-40 mesh to obtain highly absorbent polymer particles, which were used as a soil conditioner for saline-alkali soils.

[0076] Example 6

[0077] Add 0.0139g of fulvic acid to 10mL of deionized water and stir on a magnetic stirrer for 20min to disperse the fulvic acid evenly.

[0078] Dissolve 1.9797 g of sodium hydroxide in 10 mL of deionized water to obtain a sodium hydroxide solution.

[0079] Mix 6.93g of acrylic acid with sodium hydroxide solution to obtain a neutralized acrylic acid solution for later use.

[0080] Add 0.0021g of N,N-methylenebisacrylamide (MBA) to 2ml of deionized water and sonicate until completely dissolved to obtain a crosslinking agent solution for later use.

[0081] Dissolve 0.0139 g of ammonium persulfate (APS) in 2 ml of deionized water and sonicate to obtain an initiator solution for later use.

[0082] Aqueous solution polymerization was employed. In a water bath at 75°C, the mixture was stirred at 300 rpm. Neutralized acrylic acid solution and 0.9898 g of potassium 3-sulfopropyl methacrylate (SPMA) were added sequentially to the fulvic acid dispersion. After reacting for 10 min, a crosslinking agent solution was added, followed by an initiator solution after 15 min. Graft copolymerization was carried out under a nitrogen atmosphere for 70 min. The mixture was then removed from the water bath to obtain the copolymer. The product was washed with anhydrous ethanol, dried at 60°C for 24 h, and pulverized to 20-40 mesh to obtain highly absorbent polymer particles, which were used as a soil conditioner for saline-alkali soils.

[0083] Example 7

[0084] Add 0.0277g of fulvic acid to 10mL of deionized water and stir on a magnetic stirrer for 20 minutes to disperse the fulvic acid evenly.

[0085] Dissolve 1.9797 g of sodium hydroxide in 10 mL of deionized water to obtain a sodium hydroxide solution.

[0086] Mix 6.93g of acrylic acid with sodium hydroxide solution to obtain a neutralized acrylic acid solution for later use.

[0087] Add 0.0021g of N,N-methylenebisacrylamide (MBA) to 2ml of deionized water and sonicate until completely dissolved to obtain a crosslinking agent solution for later use.

[0088] Dissolve 0.0139 g of ammonium persulfate (APS) in 2 ml of deionized water and sonicate to obtain an initiator solution for later use.

[0089] An aqueous solution polymerization method was adopted. In a water bath at 75°C, the mixture was stirred at 300 r / min. Acrylic acid solution and 0.9898 g of potassium 3-sulfonate propyl methacrylate (SPMA) were added sequentially to the fulvic acid dispersion. After reacting for 10 min, a crosslinking agent solution was added, followed by an initiator solution after 15 min, to carry out the graft copolymerization reaction under a nitrogen atmosphere for 70 min. The mixture was then removed from the water bath to obtain the copolymer product. The obtained product was washed with anhydrous ethanol, dried at 60°C for 24 h, and pulverized to 20-40 mesh to obtain superabsorbent polymer particles, which were used as a soil conditioner for saline-alkali soil.

[0090] Comparative Example 1

[0091] The preparation method is basically the same as in Example 1, except that fulvic acid is not added.

[0092] Comparative Example 2

[0093] The preparation method is basically the same as in Example 1, except that the raw material potassium 3-sulfonate propyl methacrylate is not added.

[0094] Table 1. Water absorption capacity of the water-absorbing polymer particles prepared in Examples 1-7 and Comparative Examples 1-2

[0095]

[0096] As shown in the table above, as in Example 2, when the mass ratio of acrylic acid to SPMA is 6:1, and the mass ratio of total mass of acrylic acid and potassium 3-sulfonopropyl methacrylate to fulvic acid, crosslinking agent, and initiator is 100:0.2:0.03:0.2, the saline-alkali soil conditioner exhibits the best salt tolerance and water absorption. As shown in Example 1, excessive initiator leads to a relatively low content of SPMA participating in graft polymerization, limiting its strong hydrophilic function and ultimately causing the saline-alkali soil conditioner to absorb salt. The effect was reduced; as shown in Examples 4 and 7, excessive addition of fulvic acid reduced the salt absorption effect of the saline-alkali soil conditioner. Similarly, as shown in Examples 5 and 6, excessive addition of acrylic acid reduced the salt absorption effect. Furthermore, as shown in Comparative Examples 1 and 2, the water absorption and salt tolerance of the saline-alkali soil conditioner without the addition of fulvic acid or potassium 3-sulfonopropyl methacrylate were significantly reduced, indicating that the synergistic effect of fulvic acid and potassium 3-sulfonopropyl methacrylate significantly improved the salt tolerance and water absorption of the saline-alkali soil conditioner. The saline-alkali soil conditioner prepared by this invention has good salt tolerance and water absorption, and shows promising application prospects in desertification control, saline-alkali soil improvement, and plant growth promotion.

[0097] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A method for preparing a fulvic acid-based saline-alkali soil conditioner, characterized in that, It is prepared by graft polymerization reaction using fulvic acid, acrylic acid and potassium 3-sulfopropyl methacrylate as monomer raw materials; The process includes the following steps: First, the raw material fulvic acid is dispersed in water. Then, the acrylic acid solution reacted with the neutralizing agent and potassium 3-sulfonopropyl methacrylate are added to the fulvic acid solution. After uniform dispersion, the crosslinking agent solution and the initiator solution are added in sequence to carry out the grafting polymerization reaction to obtain the saline-alkali soil conditioner. The mass ratio of the total mass of acrylic acid and potassium 3-sulfonopropyl methacrylate to fulvic acid, crosslinking agent, and initiator is 100:(0.1-1):(0.01-0.12):(0.1-0.8). The mass ratio of potassium 3-sulfonopropyl methacrylate to acrylic acid is 1:(3-10); The specific conditions for the graft polymerization reaction are as follows: the reaction is carried out in a nitrogen atmosphere, the polymerization temperature is 60-80℃, the graft polymerization time is 60-120 min, and the graft polymerization reaction is carried out under stirring conditions, with a stirring speed of 200-300 r / min.

2. The method for preparing the fulvic acid-based saline-alkali soil conditioner according to claim 1, characterized in that, After the graft polymerization reaction, the reaction product was washed with anhydrous ethanol, then cut, dried, pulverized and sieved to obtain a saline-alkali soil conditioner.

3. The method for preparing the fulvic acid-based saline-alkali soil conditioner according to claim 1, characterized in that: The degree of neutralization of acrylic acid in the acrylic acid solution after the reaction with the neutralizing agent is 45% to 85%; the neutralizing agent is sodium hydroxide or potassium hydroxide.

4. The method for preparing the fulvic acid-based saline-alkali soil conditioner according to claim 1, characterized in that, The crosslinking agent is one or more of N,N-methylenebisacrylamide, glutaraldehyde, and ethylene glycol; and / or the initiator is one or two of ammonium persulfate and potassium persulfate.

5. The method for preparing the fulvic acid-based saline-alkali soil conditioner according to claim 1, characterized in that, The mass ratio of the total mass of acrylic acid and potassium 3-sulfonopropyl methacrylate to fulvic acid, crosslinking agent, and initiator is 100:(0.1-0.5):(0.02-0.04):(0.1-0.3); and / or, the mass ratio of potassium 3-sulfonopropyl methacrylate to acrylic acid is 1:5-6.

6. The method for preparing the fulvic acid-based saline-alkali soil conditioner according to claim 2, characterized in that, The mass ratio of the total mass of acrylic acid and potassium 3-sulfonopropyl methacrylate to fulvic acid, crosslinking agent, and initiator is 100:0.2:0.03:0.2; and / or, the mass ratio of potassium 3-sulfonopropyl methacrylate to acrylic acid is 1:

6.

7. The application of a fulvic acid-based saline-alkali soil conditioner, characterized in that, The fulvic acid-based saline-alkali soil conditioner is used for desertification control and soil structure improvement, soil salinity reduction and plant growth promotion. The fulvic acid-based saline-alkali soil conditioner is prepared by the preparation method described in any one of claims 1-6.

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