Method for modifying humic acid and modified humic acid

Abstract

The invention discloses a modification method of humic acid and modified humic acid, and relates to the technical field of humic acid modification. The modification method comprises the following steps: activating mineral source humic acid to obtain activated humic acid; adding activated humic acid, a grafting agent and a propenyl monomer into the cross-linking system, stirring, standing, and then heating for reaction; after the reaction is finished, adjusting the pH value to be alkaline, keeping heating and stirring, and then drying to obtain modified humic acid; wherein the grafting agent comprises the following raw materials: sodium sulfite and pyruvic acid. More hydrophilic groups are introduced into the grafted and modified humic acid, water molecules can be adsorbed to form hydrogen bonds, meanwhile, the hydrophilic groups can be adsorbed to the surfaces of soil particles, the solubility of the humic acid molecules is improved, and the water retention capacity of the humic acid molecules in soil is improved; therefore, the application range and adaptability of the humic acid water-soluble fertilizer are also increased in actual agricultural application.

Description

Technical Field

[0001] The present application relates to the technical field of humic acid modification, and in particular to a humic acid modification method and modified humic acid. Background Art

[0002] Humic acid is a type of organic matter accumulated from the remains of plants and animals through a series of processes such as microbial decomposition and transformation as well as geochemistry. Since humic acid is rich in a large number of active functional groups (such as hydroxyl, phenolic hydroxyl, carboxyl, carbonyl, quinone, methoxy, etc.) and has certain physical, chemical and biological activities, it can be used as a cheap, efficient and pollution-free fertilizer enhancer to improve soil water, fertilizer, air and heat, promote crop nutrient absorption and utilization, and increase crop yields. Humic acid itself is part of the soil organism and does not pollute the environment, so it is known as "green and environmentally friendly fertilizer". At the same time, humic acid also has certain weak acidity, surface activity, ion exchange and chelation properties. Therefore, humic acid usually forms humates with potassium, sodium, calcium, magnesium and other ions to prepare humic acid water-soluble fertilizer. However, humic acid also has some structural defects. Humic acid has a large number of aromatic rings in its molecular structure and its molecular polarity is weak, making it difficult to dissolve in water systems and having poor water retention in soil, which in turn leads to poor fertilizer efficiency in soil when humic acid is used as a water-soluble fertilizer. Based on this, the present application proposes a modification method of humic acid and modified humic acid. Summary of the invention

[0003] The main purpose of the present application is to provide a modification method of humic acid and modified humic acid, aiming to solve the technical problems of poor solubility of humic acid in water and poor water retention in soil.

[0004] To achieve the above purpose, the present application proposes a method for modifying humic acid, comprising the following steps:

[0005] Activating the mineral-source humic acid to obtain activated humic acid;

[0006] Adding the activated humic acid, grafting agent and acrylic monomer into the cross-linking system, stirring, standing, and then heating to react;

[0007] After the reaction is completed, the pH is adjusted to alkaline, the mixture is heated and stirred, and then dried to obtain modified humic acid;

[0008] Wherein, the raw materials of the grafting agent include sodium sulfite and pyruvic acid.

[0009] Optionally, the step of activating the mineral-source humic acid to obtain activated humic acid comprises:

[0010] Adding mineral humic acid into hydrogen peroxide solution, performing ultrasonic reaction, and then standing for 20-28 hours, taking the supernatant and drying it to obtain activated humic acid;

[0011] The mass concentration of the hydrogen peroxide solution is 10-15%; the mass ratio of the mineral humic acid to the hydrogen peroxide solution is 1:(5-10); the temperature of the ultrasonic reaction is 50-60°C, the time of the ultrasonic reaction is 3-5h, and the ultrasonic power is 250-350W.

[0012] Optionally, the mineral source humic acid includes one or more of weathered coal humic acid, peat humic acid and lignite humic acid.

[0013] Optionally, the preparation step of the cross-linking system comprises:

[0014] After heating water to 55-65° C., adding cellulose ether and starch ether, stirring for 0.8-1.2 hours until dissolved, to obtain the cross-linking system;

[0015] Wherein, the mass ratio of the cellulose ether to the starch ether is (1-1.5):1.

[0016] Optionally, the preparation step of the grafting agent comprises:

[0017] Sodium sulfite is added into water and stirred until dissolved, then pyruvic acid is added dropwise, heated to 50-60°C and kept warm, reacted for 1.5-2.5 hours, then heated to 60-70°C and kept warm, and formaldehyde solution is added dropwise at the same time, after the formaldehyde solution is added dropwise, heated to 85-95°C and kept warm, reacted for 4.5-5.5 hours, extracted with ethanol, separated, and dried to obtain the grafting agent.

[0018] Optionally, the mass ratio of the sodium sulfite to the pyruvic acid is 1:(1-2).

[0019] Optionally, the step of adding the activated humic acid, the grafting agent and the acrylic monomer into the cross-linking system, stirring, standing, and then heating to react comprises:

[0020] Add the activated humic acid, grafting agent and acrylic monomer to the crosslinking system and stir for 3-8 minutes, then stand for 1.5-2.5 hours, and then heat to 55-65° C. to react for 1.5-2.5 hours;

[0021] Wherein, the mass ratio of the activated humic acid, the grafting agent and the acrylic monomer is (1-5):10:(3-8).

[0022] Optionally, the acrylic monomer includes at least two of acrylamide, acrylic acid, methacrylic acid, hydroxypropyl methacrylate and N,N-dimethylacrylamide.

[0023] Optionally, the step of adjusting the pH to alkaline, maintaining heating and stirring, and then drying to obtain modified humic acid comprises:

[0024] Sodium hydroxide is used to adjust the pH to 9-12, the temperature is maintained at 40-50° C. and stirred for 10-14 hours, and then dried at 65-75° C. for 3-7 hours to obtain modified humic acid.

[0025] The present application also proposes a modified humic acid, which is obtained by the above-mentioned modification method of humic acid.

[0026] This application includes at least the following beneficial effects:

[0027] The present application modifies humic acid molecules based on their basic structure. Humic acid mainly includes three substances: fulvic acid small molecules, palmitic acid macromolecules and black humic acid macromolecules. These are aromatic heterocyclic compounds formed by several structural units with similar structures and different molecular sizes due to different degrees of polymerization. The aromatic rings are connected by bridge bonds, and there are also various active groups on the aromatic rings, such as phenolic hydroxyl, hydroxyl, quinone, carboxyl, carbonyl, alcoholic hydroxyl, methoxy, etc. The present application firstly increases the content of soluble humic acid and the content of active groups through activation treatment, and then forms a cross-linking system based on polymer materials. The cross-linking system contains hydrophilic groups, which can interact with water molecules and attract water into the structure of the cross-linking system, and then undergoes graft copolymerization reaction with activated humic acid, grafting agent and acryl monomer to form a long-chain polymer. The present application uses sodium sulfite and pyruvic acid in combination to form a grafting agent, which can react with the active groups in humic acid to introduce more hydrophilic groups, such as hydroxyl and carbonyl groups, and the introduction of acryl monomers can introduce short side chains into the molecular structure of humic acid, thereby introducing groups such as hydroxyl, carboxyl, ester, and amide, further improving the water solubility of humic acid. At the same time, the acryl monomers of the present application can also be used as water retaining agents to improve soil water retention. The grafted modified humic acid in the present application can not only adsorb water molecules to form hydrogen bonds, but also has a good bridging effect with soil particles. When it is applied to the soil, its action mechanism mainly includes water retention, association and bridging. The modified humic acid will interact with water molecules and will also be adsorbed on the surface of soil particles to form a bridging structure of water-modified humic acid-soil particles, which not only increases the solubility of humic acid molecules, but also improves its water retention capacity in the soil, thereby increasing the scope of application and adaptability of humic acid water-soluble fertilizers in actual agricultural applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. It is obvious that the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on the structures shown in these drawings without paying any creative work.

[0029] Figure 1 This is a process flow chart of the humic acid modification method described in the examples of this application.

[0030] The realization of the purpose, functional features and advantages of this application will be further explained in conjunction with embodiments and with reference to the accompanying drawings. DETAILED DESCRIPTION

[0031] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0032] In view of the technical problems existing in the prior art, the embodiments of the present application provide a method for modifying humic acid, such as Figure 1 As shown, the following steps are included:

[0033] S1. Activate the mineral-source humic acid to obtain activated humic acid.

[0034] In the specific implementation process, the mineral humic acid is added to the hydrogen peroxide solution, ultrasonic reaction is carried out, and then after standing for 20-28 hours, the supernatant is taken and dried to obtain the activated humic acid;

[0035] The mass concentration of the hydrogen peroxide solution is 10-15%; the mass ratio of the mineral humic acid to the hydrogen peroxide solution is 1:(5-10); the temperature of the ultrasonic reaction is 50-60°C, the time of the ultrasonic reaction is 3-5h, and the ultrasonic power is 250-350W.

[0036] The present application performs activation treatment on mineral-derived humic acid by adding hydrogen peroxide, so that the macromolecular chains in the mineral-derived humic acid are broken into small molecular chains under the oxidation action of hydrogen peroxide, and after the hydrogen peroxide activation treatment, the total acidic group and active group content of the humic acid can be increased, which is beneficial to the subsequent grafting reaction. The present application uses ultrasound for activation treatment, and the aqueous solution will induce a cavitation effect under the action of ultrasound, and "internal collapse" will occur in the compression phase of the sound field, thereby generating a large number of oxygen free radicals such as ·OH and ·HO to oxidize and degrade the humic acid, thereby increasing the oxygen-carbon ratio (O / C) and hydrogen-carbon ratio (H / C) of the humic acid, obtaining more free humic acid, and then increasing the content of soluble humic acid, which is beneficial to the subsequent modification of the molecular structure of the humic acid to increase the solubility of the humic acid in water.

[0037] Specifically, the mineral source humic acid used in the present application includes one or more of weathered coal humic acid, peat humic acid and lignite humic acid.

[0038] S2, adding the activated humic acid, grafting agent and acrylic monomer to the crosslinking system and stirring for 3-8 minutes, standing for 1.5-2.5 hours, and then heating to 55-65° C. to react for 1.5-2.5 hours;

[0039] Wherein, the mass ratio of the activated humic acid, the grafting agent and the acrylic monomer is (1-5):10:(3-8).

[0040] In the specific implementation process, the cross-linking system used in the present application is a spatial network colloid formed by cellulose ether and starch ether. The preparation steps of the cross-linking system include:

[0041] After heating water to 55-65° C., adding cellulose ether and starch ether, stirring for 0.8-1.2 hours until dissolved, to obtain the cross-linking system;

[0042] Wherein, the mass ratio of the cellulose ether to the starch ether is (1-1.5):1.

[0043] Cellulose ether has good water solubility and water swelling property, and starch ether is a compound formed by the combination of starch molecules and ether groups, which can absorb water and swell in water to form a gel or viscous solution. The combined action of cellulose ether and starch ether can provide better system stability, but due to the difference in chemical properties and molecular structures between the two, their compatibility may also be affected. The cross-linking system of the present application is based on a mass ratio of cellulose ether and starch ether (1-1.5):1. After the cross-linking of these two polymer materials, a colloid with a stable spatial network structure can be formed. The cross-linking system still contains hydrophilic hydroxyl groups (-OH) and other hydrophilic groups that can react with water. These groups can interact with water molecules, attract water into the structure of the cross-linking system, and then undergo graft copolymerization with activated humic acid, grafting agent and acrylic monomer to form long-chain polymers, which can not only adsorb water molecules to form hydrogen bonds, but also have a good bridging effect with soil particles. When applied to the soil, its mechanism of action mainly includes water retention, association and bridging. The modified humic acid will interact with water molecules and will also be adsorbed on the surface of soil particles to form a bridging structure of water-modified humic acid-soil particles, thereby increasing the solubility of humic acid molecules and their water retention capacity in the soil.

[0044] Specifically, the cellulose ether may be hydroxyethyl cellulose or methyl cellulose; the starch ether may be hydroxypropyl starch or ethyl starch.

[0045] In the specific implementation process, the preparation steps of the grafting agent used in the present application include:

[0046] Sodium sulfite is added into water and stirred until dissolved, then pyruvic acid is added dropwise, heated to 50-60°C and kept warm, reacted for 1.5-2.5 hours, then heated to 60-70°C and kept warm, and formaldehyde solution is added dropwise at the same time, after the formaldehyde solution is added dropwise, heated to 85-95°C and kept warm, reacted for 4.5-5.5 hours, extracted with ethanol, separated, and dried to obtain a grafting agent.

[0047] Specifically, the mass ratio of the sodium sulfite to the pyruvic acid is 1:(1-2).

[0048] The present application uses a grafting agent formed by combining sodium sulfite and pyruvic acid to graft-modify humic acid. Pyruvic acid contains ketone groups and carboxyl groups, which enable it to react with active groups in humic acid (such as phenolic hydroxyl groups, carboxyl groups, etc.). Sodium sulfite can reduce certain functional groups in humic acid, such as reducing carboxyl groups to alcohol groups, thereby increasing its hydrophilicity. At the same time, sulfite can also form sulfides with humic acid, further increasing the hydrophilicity of humic acid and obtaining more adsorption sites, thereby improving its adsorption capacity for heavy metal ions. The humic acid grafted with the grafting agent of the present application introduces more hydrophilic groups, such as hydroxyl groups and carbonyl groups. Since the lone pair of electrons of the oxygen atoms in the hydroxyl groups and carbonyl groups interact with the hydrogen in the water molecules to form hydrogen bonds, the solubility of humic acid in water is greatly improved, and its adsorption capacity for heavy metal ions in the soil can also be improved.

[0049] In a specific implementation process, the acrylic monomers include at least two of acrylamide, acrylic acid, methacrylic acid, hydroxypropyl methacrylate and N,N-dimethylacrylamide.

[0050] Acrylamide, acrylic acid, methacrylic acid, hydroxypropyl methacrylate and N, N-dimethylacrylamide all have similar functional groups and similar molecular structures, and their molecular structures contain groups such as hydroxyl, carboxyl, ester, and amide. The oxygen atom in the hydroxyl group can associate with hydrogen in water molecules to form hydrogen bonds, thereby increasing the solubility of humic acid in water, while the carboxyl group can adsorb soil particles, and the ester group and amide group can produce an association bridging effect with soil mud to form a stable spatial network structure, thereby increasing the water retention capacity of humic acid in the soil. By introducing acryl monomers for graft copolymerization, short side chains can be introduced into the molecular structure of humic acid, thereby introducing groups such as hydroxyl, carboxyl, ester, and amide, further increasing the water solubility of humic acid. At the same time, the acryl monomers used in this application can also be used as water retaining agents. When they are applied to the soil as topdressing, they can reduce the fixation of inorganic phosphorus, activate soil fixed phosphorus, and increase the content of soil available phosphorus, thereby improving the long-term stability of water-soluble fertilizers and water retention in the soil.

[0051] S3. Use sodium hydroxide to adjust the pH to 9-12, maintain 40-50° C. and stir for 10-14 hours, and then dry at 65-75° C. for 3-7 hours to obtain modified humic acid.

[0052] The embodiments of the present application also provide a modified humic acid obtained by the above-mentioned modification method of humic acid.

[0053] The present application modifies humic acid molecules based on their basic structure. Humic acid contains the main elements C, H, O, N, P, and S, and mainly includes three substances: fulvic acid small molecules, palmitic acid macromolecules, and black humic acid macromolecules. These are aromatic heterocyclic compounds formed by several structural units with similar structures and different molecular sizes (such as condensed rings, benzene rings, and some heterocyclic rings such as furan and indole) due to different polymerization degrees; the aromatic rings are connected by bridge bonds, and there are also various active groups on the aromatic rings, such as phenolic hydroxyl, hydroxyl, quinone, carboxyl, carbonyl, alcoholic hydroxyl, methoxy, etc., among which O is the main element constituting the functional group of humic acid. The present application firstly increases the content of soluble humic acid and the content of active groups through activation treatment, and then forms a cross-linking system based on polymer materials. The cross-linking system contains hydrophilic groups, which can interact with water molecules and attract water into the structure of the cross-linking system, and then undergoes graft copolymerization reaction with activated humic acid, grafting agent and acryl monomer to form a long-chain polymer. The present application uses sodium sulfite and pyruvic acid in combination to form a grafting agent, which can react with the active groups in humic acid to introduce more hydrophilic groups, such as hydroxyl and carbonyl groups, and the introduction of acryl monomers can introduce short side chains into the molecular structure of humic acid, thereby introducing groups such as hydroxyl, carboxyl, ester, and amide, further improving the water solubility of humic acid. At the same time, the acryl monomers of the present application can also be used as water retaining agents to improve soil water retention. The grafted modified humic acid in the present application can not only adsorb water molecules to form hydrogen bonds, but also has a good bridging effect with soil particles. When it is applied to the soil, its action mechanism mainly includes water retention, association and bridging. The modified humic acid will interact with water molecules and will also be adsorbed on the surface of soil particles to form a bridging structure of water-modified humic acid-soil particles, which not only increases the solubility of humic acid molecules, but also improves its water retention capacity in the soil, thereby increasing the scope of application and adaptability of humic acid water-soluble fertilizers in actual agricultural applications.

[0054] The above technical solution of the present application is described in detail below in conjunction with specific embodiments.

[0055] Example 1

[0056] A method for modifying humic acid comprises the following steps:

[0057] 1 kg of weathered coal humic acid was added to 7 kg of hydrogen peroxide solution with a mass concentration of 12%, and ultrasonic reaction was carried out at 55°C for 4 hours with an ultrasonic power of 300 W. After standing for 24 hours, the supernatant was taken and dried to obtain activated humic acid.

[0058] After heating 10 kg of deionized water to 60°C, add 0.72 kg of cellulose ether and 0.6 kg of starch ether, and stir for 1.0 h until dissolved to obtain a crosslinking system;

[0059] At room temperature, add 0.1 kg of sodium sulfite to 1.2 kg of water and stir until dissolved, then slowly drop 0.15 kg of pyruvic acid, heat to 55°C and keep warm, react for 2.0 hours, continue to heat to 65°C and keep warm, and slowly drop formaldehyde solution, wherein the mass ratio of formaldehyde to sodium sulfite is 1:1.2, after the formaldehyde solution is added, continue to heat to 90°C and keep warm, react for 5.0 hours, extract with ethanol, separate the liquid, and dry to obtain a grafting agent;

[0060] Add 0.6 kg of activated humic acid, 2 kg of grafting agent, 0.5 kg of acrylamide and 0.5 kg of acrylic acid into the crosslinking system and stir for 5 minutes, then let stand for 2.0 hours, and then heat to 60°C to react for 2.0 hours;

[0061] After the reaction was completed, the pH was adjusted to 10 with sodium hydroxide, the temperature was maintained at 45° C. and stirred for 12 h, and then dried at 70° C. for 4 h to obtain modified humic acid.

[0062] Example 2

[0063] A method for modifying humic acid comprises the following steps:

[0064] 1 kg of peat humic acid was added to 5 kg of hydrogen peroxide solution with a mass concentration of 10%, and ultrasonic reaction was carried out at 50°C for 5 hours with an ultrasonic power of 250 W. After standing for 24 hours, the supernatant was taken and dried to obtain activated humic acid.

[0065] After heating 10 kg of deionized water to 55°C, add 0.6 kg of cellulose ether and 0.6 kg of starch ether, and stir for 1.2 hours until dissolved to obtain a crosslinking system;

[0066] At room temperature, 0.1 kg of sodium sulfite was added to 1.2 kg of water and stirred until dissolved, and then 0.1 kg of pyruvic acid was slowly added dropwise, and the mixture was heated to 50°C and kept warm. After reacting for 2.5 hours, the mixture was further heated to 60°C and kept warm, and a formaldehyde solution was added dropwise at a mass ratio of formaldehyde to sodium sulfite of 1:1.1. After the addition of the formaldehyde solution was completed, the mixture was further heated to 85°C and kept warm. After reacting for 5.5 hours, the mixture was extracted with ethanol, and then the mixture was separated and dried to obtain a grafting agent.

[0067] Add 0.2 kg of activated humic acid, 2 kg of grafting agent, and 0.6 kg of methacrylic acid to the crosslinking system and stir for 3 minutes, then let stand for 2.5 hours, and then heat to 55°C to react for 2.5 hours;

[0068] After the reaction was completed, the pH was adjusted to 9 with sodium hydroxide, the temperature was maintained at 40° C. and stirred for 14 h, and then dried at 65° C. for 7 h to obtain modified humic acid.

[0069] Example 3

[0070] A method for modifying humic acid comprises the following steps:

[0071] 1 kg of lignite humic acid was added to 10 kg of hydrogen peroxide solution with a mass concentration of 15%, and ultrasonic reaction was carried out at 60°C for 3 hours with an ultrasonic power of 350 W. After standing for 24 hours, the supernatant was taken and dried to obtain activated humic acid.

[0072] After heating 10 kg of deionized water to 65°C, add 0.9 kg of cellulose ether and 0.6 kg of starch ether, and stir for 0.8 h until dissolved to obtain a cross-linking system;

[0073] At room temperature, add 0.1 kg of sodium sulfite to 1.2 kg of water and stir until dissolved, then slowly drop 0.2 kg of pyruvic acid, heat to 60°C and keep warm, react for 1.5 hours, continue to heat to 70°C and keep warm, and simultaneously drop formaldehyde solution, wherein the mass ratio of formaldehyde to sodium sulfite is 1:1.1, after the formaldehyde solution is added dropwise, continue to heat to 95°C and keep warm, react for 4.5 hours, extract with ethanol, separate the liquid, and dry to obtain the grafting agent;

[0074] 1 kg of activated humic acid, 2 kg of grafting agent, 0.8 kg of methacrylic acid and 0.8 kg of N,N-dimethylacrylamide were added to the cross-linking system and stirred for 8 minutes, then allowed to stand for 1.5 hours, and then heated to 65°C for reaction for 1.5 hours;

[0075] After the reaction was completed, the pH was adjusted to 12 with sodium hydroxide, the temperature was maintained at 50° C. and stirred for 10 h, and then dried at 75° C. for 3 h to obtain modified humic acid.

[0076] Example 4

[0077] A method for modifying humic acid comprises the following steps:

[0078] 1 kg of peat humic acid was added to 8 kg of hydrogen peroxide solution with a mass concentration of 11%, and the mass ratio of peat humic acid to hydrogen peroxide solution was 1:8. Ultrasonic reaction was carried out at 58°C for 4 hours with an ultrasonic power of 280 W. After standing for 22 hours, the supernatant was taken and dried to obtain activated humic acid.

[0079] After heating 10 kg of deionized water to 62°C, add 0.8 kg of cellulose ether and 0.6 kg of starch ether, and stir for 0.9 h until dissolved to obtain a crosslinking system;

[0080] At room temperature, add 0.1 kg of sodium sulfite to 1.2 kg of water and stir until dissolved, then slowly drop 0.18 kg of pyruvic acid, heat to 52°C and keep warm, react for 2.2 hours, continue to heat to 62°C and keep warm, and simultaneously drop formaldehyde solution, wherein the mass ratio of formaldehyde to sodium sulfite is 1:1.3, after the formaldehyde solution is added dropwise, continue to heat to 88°C and keep warm, react for 4.8 hours, extract with ethanol, separate the liquid, and dry to obtain a grafting agent;

[0081] 0.4 kg of activated humic acid, 2 kg of grafting agent, 0.7 kg of acrylamide and 0.7 kg of N,N-dimethylacrylamide were added to the cross-linking system and stirred for 7 minutes, then allowed to stand for 2.2 hours, and then heated to 59°C for reaction for 1.8 hours;

[0082] After the reaction was completed, the pH was adjusted to 10 with sodium hydroxide, the temperature was maintained at 42° C. and stirred for 11 h, and then dried at 68° C. for 4 h to obtain modified humic acid.

[0083] Comparative Example 1

[0084] Compared with Example 1, after the mineral humic acid is activated, it is modified by the existing sulfonic acid modification process, that is, the activated humic acid is added to deionized water, stirred to dissolve, and then 1,3-propyl sultone and triethylamine are added to carry out sulfonation reaction. After the reaction is completed, the deionized water is evaporated under reduced pressure to obtain sulfonated modified humic acid.

[0085] Comparative Example 2

[0086] Compared with Example 2, during the grafting reaction, no acrylic monomer was added for reaction, and the remaining steps were the same.

[0087] Experimental example

[0088] The solubility of the modified humic acid in Examples 1-4 and Comparative Examples 1-2 of the present application in water was tested. Specifically, 5 g and 5 g of each test sample were taken, placed in 100 mL of water, and their solubility was observed. The dissolution time required for the aqueous solution to be turbid and whether there were insoluble substances were recorded. Three experiments were performed respectively, and the average value was taken. The experimental results are shown in Table 1 below.

[0089] Table 1

[0090]

[0091] As can be seen from Table 1, compared with the method of increasing the water solubility of humic acid by sulfonation modification in Comparative Example 1, the modified humic acid obtained in the embodiment of the present application has a faster dissolution rate in water, and can still be completely dissolved after increasing the sample amount, without the presence of insoluble matter, and has better water solubility; in Comparative Example 2, no acryl monomer is added for grafting reaction, and the acryl monomer contains groups such as hydroxyl, carboxyl, ester, and amide, and these groups can interact with water molecules to improve the solubility of the modified humic acid in water, so the solubility of the modified humic acid in Comparative Example 2 is reduced.

[0092] The above description is only an optional embodiment of the present application, and does not limit the patent scope of the present application. All equivalent structural transformations made by using the contents of the present application specification and drawings under the inventive concept of the present application, or directly / indirectly applied in other related technical fields are included in the patent protection scope of the present application.

Claims

1. A method for modifying humic acid, characterized in that: The following steps are involved: Activating the mineral-source humic acid to obtain activated humic acid; Adding the activated humic acid, grafting agent and acrylic monomer into the cross-linking system, stirring, standing, and then heating to react; After the reaction is completed, the pH is adjusted to alkaline, the mixture is heated and stirred, and then dried to obtain modified humic acid; Wherein, the raw materials of the grafting agent include sodium sulfite and pyruvic acid.

2. The method for modifying humic acid according to claim 1, characterized in that: The step of activating the mineral-source humic acid to obtain activated humic acid comprises: Adding mineral humic acid into hydrogen peroxide solution, performing ultrasonic reaction, and then standing for 20-28 hours, taking the supernatant and drying it to obtain activated humic acid; The mass concentration of the hydrogen peroxide solution is 10-15%; the mass ratio of the mineral humic acid to the hydrogen peroxide solution is 1:(5-10); the temperature of the ultrasonic reaction is 50-60°C, the time of the ultrasonic reaction is 3-5h, and the ultrasonic power is 250-350W.

3. The method for modifying humic acid according to claim 2, characterized in that: The mineral source humic acid includes one or more of weathered coal humic acid, peat humic acid and lignite humic acid.

4. The method for modifying humic acid according to claim 1, characterized in that: The preparation steps of the cross-linking system include: After heating water to 55-65° C., adding cellulose ether and starch ether, stirring for 0.8-1.2 hours until dissolved, to obtain the cross-linking system; Wherein, the mass ratio of the cellulose ether to the starch ether is (1-1.5):

1.

5. The method for modifying humic acid according to claim 1, characterized in that: The preparation steps of the grafting agent include: Sodium sulfite is added into water and stirred until dissolved, then pyruvic acid is added dropwise, heated to 50-60°C and kept warm, reacted for 1.5-2.5 hours, then heated to 60-70°C and kept warm, and formaldehyde solution is added dropwise at the same time, after the formaldehyde solution is added dropwise, heated to 85-95°C and kept warm, reacted for 4.5-5.5 hours, extracted with ethanol, separated, and dried to obtain the grafting agent.

6. The method for modifying humic acid according to claim 5, characterized in that: The mass ratio of the sodium sulfite to the pyruvic acid is 1:(1-2).

7. The method for modifying humic acid according to claim 1, characterized in that: The step of adding the activated humic acid, the grafting agent and the acrylic monomer into the cross-linking system, stirring, standing, and then heating to react comprises: Add the activated humic acid, grafting agent and acrylic monomer to the crosslinking system and stir for 3-8 minutes, then stand for 1.5-2.5 hours, and then heat to 55-65° C. to react for 1.5-2.5 hours; Wherein, the mass ratio of the activated humic acid, the grafting agent and the acrylic monomer is (1-5):10:(3-8).

8. The method for modifying humic acid according to claim 1, characterized in that: The acrylic monomers include at least two of acrylamide, acrylic acid, methacrylic acid, hydroxypropyl methacrylate and N,N-dimethylacrylamide.

9. The method for modifying humic acid according to claim 1, characterized in that: The step of adjusting the pH to alkaline, maintaining heating and stirring, and then drying to obtain modified humic acid comprises: Sodium hydroxide is used to adjust the pH to 9-12, the temperature is maintained at 40-50° C. and stirred for 10-14 hours, and then dried at 65-75° C. for 3-7 hours to obtain modified humic acid.

10. A modified humic acid, characterized in that: Obtained by the modification method of humic acid as described in any one of claims 1 to 9.

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