Modified humic acid as well as preparation method and application thereof

Abstract

The invention discloses modified humic acid as well as a preparation method and application thereof, and relates to the technical field of humic acid modification. The preparation method comprises the following steps: activating mineral source humic acid, and adding a manganese-based activator to obtain activated humic acid; adding activated humic acid, a grafting agent and a silane monomer into a 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 acetylacetone. The modified humic acid still has high water solubility in hard water, and flocculent precipitate formed by the humic acid and metal ions can be avoided.

Description

Technical Field

[0001] The present application relates to the technical field of humic acid modification, and particularly relates to a modified humic acid, a preparation method thereof, and an application thereof. Background Art

[0002] Humic acid is a class of organic substances accumulated through a series of processes of decomposition, transformation by microorganisms, and geochemistry of animal and plant remains. Since humic acid is rich in a large number of active functional groups (such as hydroxyl groups, phenolic hydroxyl groups, carboxyl groups, carbonyl groups, quinone groups, methoxy groups, etc.) and has certain physical, chemical, and biological activities, it can be used as a cheap, efficient, and pollution-free fertilizer synergist to play a unique role in improving soil water, fertilizer, gas, and heat, promoting the absorption and utilization of crop nutrients, and increasing crop yields. Moreover, humic acid itself is a part of soil organisms and is pollution-free to the environment, so it is known as the "green environmental protection fertilizer". However, in actual applications, humic acid often has a very small solubility in hard water and poor hard water resistance. This is mainly because humic acid has weak acidity and is prone to combine with metal ions such as calcium, magnesium, iron, and aluminum in water to form insoluble salts, resulting in flocculation precipitation. Once the flocculation phenomenon occurs, it will affect the use effect of humic acid products because only the nutrients dissolved in water can be utilized by crops. Therefore, it is urgent to modify the molecular structure of humic acid to improve its hard water resistance. Summary of the Invention

[0003] The main purpose of the present application is to provide a modified humic acid, a preparation method thereof, and an application thereof, aiming to solve the technical problem of poor hard water resistance of humic acid.

[0004] To achieve the above purpose, the present application provides a preparation method of a modified humic acid, including the following steps:

[0005] Activating the mineral source humic acid and adding a manganese-based activator to obtain activated humic acid;

[0006] Adding the activated humic acid, a grafting agent, and a silane monomer into a cross-linking system for stirring, and after standing, heating for reaction;

[0007] After the reaction is completed, adjusting the pH to alkaline, maintaining heating and stirring, and then drying to obtain the modified humic acid;

[0008] Among them, the raw materials of the grafting agent include sodium sulfite and acetylacetone.

[0009] Optionally, the manganese-based activator is obtained by doping Cu into δ-MnO 2 ;

[0010] The preparation steps of the manganese-based activator include:

[0011] Adding KMnO 4The powder and Cu(NO 3 ) 2 After the powder and Cu(NO 3 ) 2 powder are mixed at a mass ratio of (6 - 8):1, they are heated to 900°C - 1100°C in an air atmosphere for calcination for 4h - 6h. After natural cooling, they are washed, filtered, and the solid substance is collected. Then, it is dried at 50°C - 60°C for 3h - 6h to obtain the manganese-based activator.

[0012] Optionally, the step of activating the mineral source humic acid and adding the manganese-based activator to obtain the activated humic acid includes:

[0013] The mineral source humic acid is crushed and added to the hydrogen peroxide solution, and the manganese-based activator is added. Then, ultrasonic reaction is carried out. After standing for 10h - 15h, the supernatant is taken and dried to obtain the activated humic acid;

[0014] Among them, the mass fraction of the hydrogen peroxide solution is 10% - 15%; the mass ratio of the mineral source humic acid to the hydrogen peroxide solution is 1:(5 - 10); the temperature of the ultrasonic reaction is 50°C - 60°C, the time of the ultrasonic reaction is 2h - 4h, and the ultrasonic power is 250W - 350W.

[0015] Optionally, the preparation step of the cross-linking system includes:

[0016] Water is heated to 55°C - 65°C, and then cellulose ether and starch ether are added. After stirring for 0.8h - 1.2h until dissolved, the cross-linking system is obtained;

[0017] Among them, the mass ratio of the cellulose ether to the starch ether is (1 - 1.5):1.

[0018] Optionally, the preparation step of the grafting agent includes:

[0019] Sodium sulfite is added to water and stirred until dissolved, then acetylacetone is added dropwise. It is heated to 45°C - 55°C and kept warm for 0.8h - 1.2h. Then, it is continuously heated to 60°C - 70°C and kept warm, and at the same time, formaldehyde solution is added dropwise. After the formaldehyde solution is added dropwise, it is continuously heated to 85°C - 95°C and kept warm. After reacting for 4.5h - 5.5h, a reddish-brown solution is obtained, and then it is extracted with ethanol. After liquid separation, it is dried to obtain the grafting agent;

[0020] Among them, the mass ratio of the sodium sulfite to the acetylacetone is 5:(5 - 9).

[0021] Optionally, the step of adding the activated humic acid, grafting agent, and silane monomer to the cross-linking system, stirring, standing, and then heating for reaction includes:

[0022] After adding the activated humic acid, grafting agent and silane monomer into the cross-linking system and stirring for 3 min - 8 min, let it stand for 2.5 h - 3.5 h, and then heat to 60°C - 70°C for reaction for 4 h - 6 h;

[0023] Among them, the mass ratio of the activated humic acid, the grafting agent to the silane monomer is (1 - 5):10:(1 - 3).

[0024] Optionally, the silane monomer includes at least one of methyltriethoxysilane, trichlorovinylsilane and triethoxysilane.

[0025] Optionally, the step of adjusting the pH to alkaline, maintaining heating and stirring, and then obtaining the modified humic acid after drying includes:

[0026] Adjust the pH to 9 - 12 with sodium hydroxide, maintain at 50°C - 60°C and stir for 6 h - 10 h, and then dry at 60°C - 70°C for 1 h - 4 h to obtain the modified humic acid.

[0027] This application also provides a modified humic acid obtained by the above preparation method of the modified humic acid.

[0028] This application also provides an application of the modified humic acid, using the modified humic acid as a soil conditioner or a crop fertilizer.

[0029] This application has at least the following beneficial effects:

[0030] This application modifies humic acid based on its basic structure. Humic acid mainly includes three substances: fulvic acid (small molecule), brown humic acid (macromolecule), and black humic acid (macromolecule). 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 groups, hydroxyl groups, quinone groups, carboxyl groups, carbonyl groups, alcohol hydroxyl groups, methoxy groups, etc. This application first conducts an activation treatment to increase the content of soluble humic acid. A manganese-based activator is used to provide an oxidation potential to promote the breakage of the complex macromolecular structure in humic acid, decomposing high-molecular-weight humic acid into smaller fulvic acid. The decomposition of humic acid is often accompanied by an oxidation reaction, and the oxidation will cause the breakage of some complex chemical bonds in its molecules, especially the oxidative degradation of the aromatic ring structure. In this process, high-molecular-weight brown and black humic acids are broken, generating more low-molecular-weight and higher-water-soluble fulvic acid. Then, crosslinking modification is carried out based on the crosslinking system formed by polymer materials. The crosslinking system contains hydrophilic groups that can interact with water molecules, attracting water into the structure of the crosslinking system, and then reacting with activated humic acid, grafting agent, and silane monomer. A grafting agent formed by the combination of sodium sulfite and acetylacetone reacts with carboxyl groups (-COOH), phenolic hydroxyl groups (-OH), etc. in humic acid. Since a large number of negatively charged groups (such as carboxyl groups and phenolic hydroxyl groups) contained in humic acid itself will interact with calcium and magnesium ions in hard water, resulting in the precipitation of humic acid, the introduction of the grafting agent can change the charge characteristics of humic acid through electrostatic or coordination effects, thereby improving its stability in hard water. At the same time, a crosslinking reaction occurs between the silane monomer and humic acid to form a stable silicon-oxygen bond crosslinking structure. This crosslinking structure can effectively prevent the reaction between calcium, magnesium, and other hard water ions in water and humic acid, reducing the formation of precipitation. The modified humic acid in this application still has high water solubility in hard water, and can avoid the formation of flocculation precipitation between humic acid and metal ions. Brief Description of the Drawings

[0031] In order to more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the following drawings are only some embodiments of this application. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on the structures shown in these drawings.

[0032] Figure 1 It is a flow chart of the preparation method of the modified humic acid described in the embodiments of this application.

[0033] The realization of the purpose of this application, functional features, and advantages will be further described in combination with the embodiments with reference to the drawings. Detailed Embodiments

[0034] The following will clearly and completely describe the technical solutions in the embodiments of the present application with reference to the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments in the present application without making creative efforts belong to the scope of protection of the present application.

[0035] In view of the technical problems existing in the prior art, an embodiment of the present application provides a preparation method of modified humic acid, as Figure 1 shown, including the following steps:

[0036] S1. Activate the mineral source humic acid and add a manganese-based activator to obtain activated humic acid.

[0037] In a specific implementation process, the mineral source humic acid is pulverized and added to a hydrogen peroxide solution, and a manganese-based activator is added, followed by ultrasonic reaction. After standing for 10 h - 15 h, the supernatant is taken and dried to obtain activated humic acid;

[0038] wherein, the mass fraction of the hydrogen peroxide solution is 10% - 15%; the mass ratio of the mineral source humic acid to the hydrogen peroxide solution is 1:(5 - 10); the temperature of the ultrasonic reaction is 50°C - 60°C, the time of the ultrasonic reaction is 2 h - 4 h, and the ultrasonic power is 250 W - 350 W.

[0039] 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.

[0040] The manganese-based activator is obtained after Cu doping of δ-MnO 2 ; the preparation steps of the manganese-based activator include:

[0041] Mix the KMnO 4 powder and Cu(NO 3 ) 2 powder in a mass ratio of (6 - 8):1, heat it to 900°C - 1100°C in an air atmosphere for calcination for 4 h - 6 h, cool it naturally, then wash, filter, collect the solid substance, and dry it at 50°C - 60°C for 3 h - 6 h to obtain the manganese-based activator.

[0042] During the activation process of mineral source humic acid, the present application oxidizes the mineral source humic acid by adding hydrogen peroxide, converting the large molecular weight brown-black humic acid into small molecular weight fulvic acid, so as to improve the solubility and dispersibility of humic acid in water, enhance its adaptability to hard water, and after the activation treatment with hydrogen peroxide, the content of total acidic groups and active groups of humic acid can be increased, which is beneficial to the subsequent grafting reaction. And the present application uses ultrasonic waves for activation treatment. Under the action of ultrasonic waves, cavitation effect will be triggered in the aqueous solution, and "internal collapse" will occur in the compression phase of the sound field, and then a large number of oxygen free radicals such as ·OH and ·HO will oxidize and degrade humic acid, thereby increasing the oxygen-carbon ratio (O / C) and hydrogen-carbon ratio (H / C) of humic acid, obtaining more soluble humic acid, and by enhancing the water solubility of humic acid, the chance of precipitation reaction with metal ions in hard water can be reduced.

[0043] Meanwhile, the present application also uses Cu-doped δ-MnO 2 as an activator. δ-MnO 2 As an oxide with a high specific surface area, it has excellent adsorption characteristics and redox activity. When combined with humic acid, through its surface adsorption and redox action, it can enhance the exposure of hydrophilic groups on the surface of humic acid molecules, improving the solubility and dispersibility of humic acid in water, thereby improving its stability and hard water resistance in water. At the same time, the redox reaction of δ-MnO 2 will change the electronic state of some groups in the humic acid molecule. For example, some phenolic hydroxyl groups or carboxyl groups in humic acid may be oxidized or reduced, thus changing the chemical properties of humic acid. This redox action may enhance the reactivity of humic acid and affect its coordination ability with metal ions, avoiding the formation of flocculent precipitation of humic acid and metal ions; and Cu, as a transition metal, can affect the active sites of the catalytic reaction through the change of its surface electronic structure, making the Cu / δ-MnO 2 activator of the present application can provide more reactive sites, thereby enhancing its performance of catalyzing the cleavage of humic acid and generating more fulvic acid with lower molecular weight and higher water solubility.

[0044] S2. After adding the activated humic acid, grafting agent and silane monomer into the cross-linking system and stirring for 3 min - 8 min, let it stand for 2.5 h - 3.5 h, and then heat to 60°C - 70°C for reaction for 4 h - 6 h;

[0045] Among them, the mass ratio of the activated humic acid, the grafting agent to the silane monomer is (1 - 5):10:(1 - 3).

[0046] In the specific implementation process, the cross-linking system adopted by the present application is a three-dimensional network colloid formed by cellulose ether and starch ether. The preparation steps of the cross-linking system include:

[0047] After heating water to 55°C - 65°C, add cellulose ether and starch ether, and stir for 0.8 h - 1.2 h until dissolved to obtain the cross-linked system.

[0048] Among them, the mass ratio of the cellulose ether to the starch ether is (1 - 1.5):1.

[0049] Cellulose ether has good water solubility and water swelling properties. 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. Through the combined action of cellulose ether and starch ether, better system stability can be provided. However, due to the differences in their chemical properties and molecular structures, their compatibility may also be affected. The cross-linked system of this application is based on the mass ratio of cellulose ether and starch ether of (1 - 1.5):1. After cross-linking these two polymer materials, a stable three-dimensional network structure colloid can be formed. The cross-linked system still contains hydrophilic hydroxyl groups (-OH) and other groups that can form hydrogen bonds with water molecules. These groups can interact with water molecules, attract water into the structure of the cross-linked system, and then carry out cross-linking reactions with activated humic acid, grafting agent, and silane monomer. It 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. Modified humic acid will interact with water molecules and also adsorb on the surface of soil particles to form a bridging structure of water-modified humic acid-soil particles, thereby increasing the water solubility of humic acid molecules and avoiding the formation of flocculation precipitation of humic acid with metal ions.

[0050] Specifically, the cellulose ether can be hydroxyethyl cellulose or methyl cellulose; the starch ether can be hydroxypropyl starch or ethyl starch.

[0051] In the specific implementation process, the preparation steps of the grafting agent include:

[0052] Add sodium sulfite to water and stir until dissolved, then dropwise add acetylacetone, heat to 45°C - 55°C and keep warm, react for 0.8 h - 1.2 h, then continue to heat to 60°C - 70°C and keep warm, while dropwise adding formaldehyde solution. After the formaldehyde solution is added dropwise, continue to heat to 85°C - 95°C and keep warm, react for 4.5 h - 5.5 h to obtain a reddish-brown solution, then extract with ethanol, separate by liquid separation, and dry to obtain the grafting agent.

[0053] Among them, the mass ratio of the sodium sulfite to the acetylacetone is 5:(5 - 9).

[0054] In this application, a grafting agent formed by the combined use of sodium sulfite and acetylacetone is used to graft-modify humic acid. Sodium sulfite can reduce some functional groups in humic acid, such as reducing carboxyl groups to alcohol groups, increasing its hydrophilicity. At the same time, sulfite ions can also form sulfides with humic acid, further increasing the hydrophilicity of humic acid. Acetylacetone contains functional groups such as carbonyl (C=O) and ether group (C-O-C), and can react with carboxyl groups (-COOH), phenolic hydroxyl groups (-OH), etc. in humic acid. Since humic acid itself contains a large number of negatively charged groups (such as carboxyl groups, phenolic hydroxyl groups), these negative charges will interact with calcium and magnesium ions in hard water, resulting in the precipitation of humic acid. The carbonyl and ether groups introduced by acetylacetone can change the charge characteristics of humic acid through electrostatic or coordination effects, thereby improving its stability in hard water. After graft-modification with the grafting agent of this application, the hydrophilicity and solubility of humic acid can be greatly improved.

[0055] In the specific implementation process, the silane monomer includes at least one of methyltriethoxysilane, trichlorovinylsilane, and triethoxysilane.

[0056] This application introduces a silane monomer to carry out a cross-linking reaction with humic acid. The organic groups of the silane (such as amino groups, vinyl groups, etc.) react with functional groups such as carboxyl groups and hydroxyl groups in humic acid, and a stable silicon-oxygen bond cross-linked structure can be formed. This silicon-oxygen bond cross-linked structure can enhance the hydrophilicity of humic acid molecules, reduce the direct influence of hard water ions on humic acid molecules, and thus improve its ability to resist hard water precipitation. Moreover, a three-dimensional network structure is formed through the cross-linking reaction, which can increase the intermolecular interaction of humic acid, improve the stability of humic acid, and prevent it from precipitating in hard water. In addition, the cross-linked structure generated by the silicon-oxygen bond can form a protective film on the surface of humic acid, thereby reducing the competition between metal ions (such as calcium, magnesium, etc.) in hard water and humic acid, maintaining the solubility and stability of humic acid, and further improving the hard water resistance of humic acid.

[0057] S3. Adjust the pH to 9 - 12 with sodium hydroxide, maintain at 50°C - 60°C and stir for 6 h - 10 h, and then dry at 60°C - 70°C for 1 h - 4 h to obtain modified humic acid.

[0058] The embodiment of this application also provides a modified humic acid, which is obtained by using the above preparation method of modified humic acid.

[0059] The embodiment of this application also provides an application of the modified humic acid, and the modified humic acid is used as a soil conditioner or a crop fertilizer.

[0060] This application modifies humic acid based on its basic structure. The main elements contained in humic acid are C, H, O, N, P, and S. It mainly includes three substances: small molecule fulvic acid, macromolecule brown humic acid, and macromolecule black humic acid. 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 heterocycles such as furan and indole) 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 groups, hydroxyl groups, quinone groups, carboxyl groups, carbonyl groups, alcohol hydroxyl groups, methoxy groups, etc. Among them, O is the main element constituting the functional groups of humic acid. This application first conducts activation treatment to increase the content of soluble humic acid. A manganese-based activator is used to provide an oxidation potential to promote the breaking of the complex macromolecular structure in humic acid, decomposing high-molecular-weight humic acid into smaller fulvic acid. The decomposition of humic acid is often accompanied by an oxidation reaction, and the oxidation will cause some complex chemical bonds in its molecules to break, especially the oxidative degradation of the aromatic ring structure. In this process, high-molecular-weight brown and black humic acids are broken, generating more low-molecular-weight and higher-water-soluble fulvic acids. Then, crosslinking modification is carried out based on the crosslinking system formed by polymer materials. The crosslinking system contains hydrophilic groups, and these groups can interact with water molecules, attracting water into the structure of the crosslinking system, and then reacting with activated humic acid, grafting agent, and silane monomer. A grafting agent formed by the combination of sodium sulfite and acetylacetone reacts with carboxyl groups (-COOH), phenolic hydroxyl groups (-OH), etc. in humic acid. Since a large number of negatively charged groups (such as carboxyl groups and phenolic hydroxyl groups) contained in humic acid itself will interact with calcium and magnesium ions in hard water, resulting in the precipitation of humic acid, the introduction of the grafting agent can change the charge characteristics of humic acid through electrostatic or coordination effects, thereby improving its stability in hard water. At the same time, a crosslinking reaction occurs between the silane monomer and humic acid to form a stable silicon-oxygen bond crosslinking structure. This crosslinking structure can effectively prevent the reaction between calcium, magnesium, and other hard water ions in water and humic acid, reducing the formation of precipitation. The modified humic acid in this application still has high water solubility in hard water, and can avoid the formation of flocculation precipitation between humic acid and metal ions.

[0061] The above technical solutions of this application will be described in detail below with specific examples.

[0062] Example 1

[0063] A preparation method of modified humic acid, comprising the following steps:

[0064] Mix KMnO 4 powder with Cu(NO 3 ) 2After the powders are mixed at a mass ratio of 7:1, they are heated to 1000 °C in an air atmosphere for calcination for 5 h. After natural cooling, they are washed, filtered, and after collecting the solid matter, they are dried at 55 °C for 4.5 h to obtain a manganese-based activator;

[0065] 1 kg of weathered coal humic acid is pulverized and added to 7 kg of a hydrogen peroxide solution with a mass fraction of 12%, and 0.01 kg of a manganese-based activator is added. An ultrasonic reaction is carried out at 55 °C for 3 h, and after standing for 12 h, the supernatant is taken and dried to obtain activated humic acid;

[0066] 10 kg of deionized water is heated to 60 °C, 0.72 kg of cellulose ether and 0.6 kg of starch ether are added, and after stirring for 1.0 h until dissolved, a cross-linked system is obtained;

[0067] At room temperature, 0.5 kg of sodium sulfite is added to 1.2 kg of water and stirred until dissolved, 0.7 kg of acetylacetone is slowly added dropwise, heated to 50 °C and kept warm, after reacting for 1.0 h, it is continuously heated to 65 °C and kept warm, and at the same time, a formaldehyde solution is slowly added dropwise, where the mass ratio of formaldehyde to sodium sulfite is 1:1.2. After the formaldehyde solution is added dropwise, it is continuously heated to 90 °C and kept warm. After reacting for 5.0 h, a reddish-brown solution is obtained, and then it is extracted with ethanol. After liquid separation, it is dried to obtain a grafting agent;

[0068] 30 g of activated humic acid, 100 g of grafting agent, and 20 g of methyltriethoxysilane are added to the cross-linked system and stirred for 5 min, then left standing for 3.0 h, and then heated to 65 °C for reaction for 5 h;

[0069] After the reaction is completed, the pH is adjusted to 11 with sodium hydroxide, kept at 45 °C and stirred for 12 h, and then dried at 65 °C for 2 h to obtain modified humic acid.

[0070] Example 2

[0071] A preparation method of modified humic acid, comprising the following steps:

[0072] Mix the KMnO 4 powder with the Cu(NO 3 ) 2 powder at a mass ratio of 6:1, heat it to 900 °C in an air atmosphere for calcination for 6 h, after natural cooling, wash, filter, and after collecting the solid matter, dry it at 50 °C for 6 h to obtain a manganese-based activator;

[0073] 1 kg of peat humic acid is pulverized and added to 5 kg of a hydrogen peroxide solution with a mass fraction of 10%, and 0.03 kg of a manganese-based activator is added. An ultrasonic reaction is carried out at 50 °C for 4 h, and after standing for 10 h, the supernatant is taken and dried to obtain activated humic acid;

[0074] After heating 10 kg of deionized water to 55 °C, 0.6 kg of cellulose ether and 0.6 kg of starch ether were added, and after stirring for 1.2 h until dissolved, a crosslinked system was obtained;

[0075] At room temperature, 0.5 kg of sodium sulfite was added to 1.2 kg of water and stirred until dissolved, then 0.5 kg of acetylacetone was slowly added dropwise, heated to 45 °C and kept warm, after reacting for 1.2 h, it was continuously heated to 60 °C and kept warm, while slowly adding a formaldehyde solution, where the mass ratio of formaldehyde to sodium sulfite was 1:1.2. After the formaldehyde solution was added dropwise, it was continuously heated to 85 °C and kept warm, after reacting for 5.5 h, a reddish-brown solution was obtained, then extracted with ethanol, and after liquid separation, it was dried to obtain a grafting agent;

[0076] 10 g of activated humic acid, 100 g of grafting agent and 10 g of trichlorovinylsilane were added to the crosslinked system and stirred for 3 min, then left standing for 2.5 h, and then heated to 60 °C for reaction for 6 h;

[0077] After the reaction ended, the pH was adjusted to 9 with sodium hydroxide, kept at 50 °C and stirred for 10 h, and then dried at 60 °C for 4 h to obtain modified humic acid.

[0078] Example 3

[0079] A preparation method of modified humic acid, comprising the following steps:

[0080] KMnO 4 powder and Cu(NO 3 ) 2 powder were mixed in a mass ratio of 8:1, then heated to 1100 °C in an air atmosphere for calcination for 4 h, after natural cooling, washed, filtered, and after collecting the solid substance, dried at 60 °C for 3 h to obtain a manganese-based activator;

[0081] 1 kg of lignite humic acid was crushed and added to 10 kg of a hydrogen peroxide solution with a mass fraction of 15%, and 0.05 kg of manganese-based activator was added, and ultrasonic reaction was carried out at 60 °C for 2 h, then left standing for 10 h, and then the supernatant was taken and dried to obtain activated humic acid;

[0082] After heating 10 kg of deionized water to 65 °C, 0.9 kg of cellulose ether and 0.6 kg of starch ether were added, and after stirring for 0.8 h until dissolved, a crosslinked system was obtained;

[0083] At room temperature, add 0.5 kg of sodium sulfite to 1.2 kg of water and stir until dissolved. Then, slowly add 0.9 kg of acetylacetone dropwise. Heat the mixture to 55 °C and keep it warm for 0.8 h. After that, continue to heat it to 70 °C and keep it warm while slowly adding a formaldehyde solution, where the mass ratio of formaldehyde to sodium sulfite is 1:1.2. After the formaldehyde solution is added dropwise, continue to heat it to 95 °C and keep it warm. After reacting for 4.5 h, a reddish-brown solution is obtained. Then, extract it with ethanol, separate the layers by liquid separation, and dry it to obtain a grafting agent.

[0084] Add 50 g of activated humic acid, 100 g of grafting agent, 20 g of methyltriethoxysilane, and 10 g of trichlorovinylsilane to the crosslinking system and stir for 3 min - 8 min. Then, let it stand for 2.5 h - 3.5 h, and then heat it to 60 °C - 70 °C and react for 4 h - 6 h.

[0085] After the reaction is completed, adjust the pH to 12 with sodium hydroxide, keep it at 60 °C and stir for 6 h, and then dry it at 70 °C for 1 h to obtain modified humic acid.

[0086] Example 4

[0087] A preparation method of modified humic acid, comprising the following steps:

[0088] Mix KMnO 4 powder and Cu(NO 3 ) 2 powder in a mass ratio of 7:1, heat it to 1050 °C in an air atmosphere and calcine for 5 h. After natural cooling, wash, filter, collect the solid substance, and dry it at 52 °C for 4 h to obtain a manganese-based activator.

[0089] Crush 1 kg of weathered coal humic acid and add it to 8 kg of hydrogen peroxide solution with a mass fraction of 14%. Add 0.02 kg of manganese-based activator, carry out ultrasonic reaction at 52 °C for 3 h, then let it stand for 14 h, take the supernatant and dry it to obtain activated humic acid.

[0090] Heat 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.

[0091] At room temperature, add 0.5 kg of sodium sulfite to 1.2 kg of water and stir until dissolved. Then, slowly add 0.7 kg of acetylacetone dropwise. Heat the mixture to 48 °C and keep it warm for 0.9 h. After that, continue to heat it to 68 °C and keep it warm while slowly adding a formaldehyde solution, where the mass ratio of formaldehyde to sodium sulfite is 1:1.2. After the formaldehyde solution is added dropwise, continue to heat it to 88 °C and keep it warm. After reacting for 5.2 h, a reddish-brown solution is obtained. Then, extract it with ethanol, separate the layers by liquid separation, and dry it to obtain a grafting agent.

[0092] Add 20 g of activated humic acid, 100 g of grafting agent, 10 g of trichlorovinylsilane, and 10 g of triethoxysilane to the crosslinking system, stir for 6 min, let stand for 2.5 h, and then heat to 68 °C for reaction for 5 h;

[0093] After the reaction is completed, adjust the pH to 10 with sodium hydroxide, maintain at 53 °C and stir for 7 h, and then dry at 65 °C for 2 h to obtain modified humic acid.

[0094] Comparative Example 1

[0095] Compared with Example 1, when activating the mineral source humic acid, the manganese-based activator was not added, and the remaining steps were the same.

[0096] Comparative Example 2

[0097] Compared with Example 1, when preparing the manganese-based activator, Cu(NO 3 ) 2 powder was not incorporated, and the remaining steps were the same.

[0098] Comparative Example 3

[0099] Compared with Example 1, during the modification process, the silane monomer was not added for reaction, and the remaining steps were the same.

[0100] Experimental Example

[0101] Measure the flocculation limit values of the modified humic acids prepared in the examples and comparative examples of the present application respectively. The measurement steps are as follows:

[0102] Weigh 0.1 g of the modified humic acid sample to be tested, dissolve it in sodium bicarbonate with a concentration of 0.05 mol / L, adjust the pH to 8, and make up the volume to 500 mL with sodium bicarbonate to obtain the humic acid solution to be tested;

[0103] Add 2.5 mL of CaCl 2 solutions with different concentrations and 5 mL of the humic acid solution to be tested with a concentration of 0.02 wt% into test tubes respectively. After covering the bottle caps and shaking well, let stand for about 1 h, and observe whether turbidity or precipitation appears in each test tube;

[0104] Find two test tubes with flocculation and without flocculation, and continue to prepare CaCl 2 solutions with different concentrations. The volume difference of the original CaCl 2 solution added to adjacent test tubes does not exceed 0.02 mL. Add 5 mL of the humic acid solution to be tested with a concentration of 0.02 wt% respectively, shake well, let stand for 1 h, and find the test tube where flocculation starts.

[0105] The calculation formula for the flocculation limit value is as follows:

[0106]

[0107] In the formula, Cmax represents the flocculation value of the modified humic acid, mmol / mL; M is the concentration of CaCl in the solution 2 ; V is the volume of CaCl used in the flocculation process, mL. 2

[0108] The test results are shown in Table 1 below.

[0109] Table 1

[0110] Group Flocculation limit value (mmol / mL) Example 1 13.6 Example 2 12.3 Example 3 12.5 Example 4 13.4 Comparative Example 1 11.2 Comparative Example 2 11.9 Comparative Example 3 10.3

[0111] As can be seen from Table 1, the larger the flocculation value, the more it indicates that the humic acid can maintain an active state in a higher concentration of calcium ions, has a stronger resistance to hard water, and will not undergo a complexation reaction with calcium ions and flocculate and inactivate. The modified humic acid prepared in the embodiments of the present application has a higher flocculation value compared to Comparative Examples 1-3, indicating that it has a stronger resistance to hard water.

[0112] The above are only optional embodiments of the present application, and do not limit the patent scope of the present application. Any equivalent structural transformation made using the content of the specification and drawings of the present application under the inventive concept of the present application, or direct / indirect application in other related technical fields, is included in the patent protection scope of the present application.​

Claims

1. A method for preparing modified humic acid, characterized in that: The following steps are involved: The mineral-source humic acid is activated and a manganese-based activator is added to obtain activated humic acid; Adding the activated humic acid, grafting agent and silane 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 acetylacetone.

2. The method for preparing modified humic acid according to claim 1, characterized in that: The manganese-based activator is obtained by doping δ-MnO2 with Cu; The preparation steps of the manganese-based activator include: KMnO4 powder and Cu(NO3)2 powder are mixed in a mass ratio of (6-8):1, and then heated to 900℃-1100℃ in an air atmosphere for calcination for 4h-6h. After natural cooling, the mixture is washed and filtered, and the solid matter is collected and dried at 50℃-60℃ for 3h-6h to obtain the manganese-based activator.

3. The method for preparing modified humic acid according to claim 1, characterized in that: The step of activating the mineral-source humic acid and adding a manganese-based activator to obtain activated humic acid comprises: The mineral humic acid is crushed and added to a hydrogen peroxide solution, and a manganese-based activator is added to perform an ultrasonic reaction. After standing for 10 hours to 15 hours, the supernatant is taken and dried to obtain activated humic acid. The mass fraction 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°C-60°C, the time of the ultrasonic reaction is 2h-4h, and the ultrasonic power is 250W-350W.

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

1.

5. The method for preparing modified 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 acetylacetone is added dropwise, heated to 45-55°C and kept warm, reacted for 0.8h-1.2h, then continued to heat to 60-70°C and kept warm, and formaldehyde solution is added dropwise at the same time, after the formaldehyde solution is added dropwise, continued to heat to 85-95°C and kept warm, reacted for 4.5h-5.5h, a reddish brown solution is obtained, then extracted with ethanol, separated, and dried to obtain the grafting agent; Wherein, the mass ratio of the sodium sulfite to the acetylacetone is 5:(5-9).

6. The method for preparing modified humic acid according to claim 1, characterized in that: The step of adding the activated humic acid, the grafting agent and the silane monomer into the cross-linking system, stirring, standing, and then heating to react comprises: Add the activated humic acid, grafting agent and silane monomer to the crosslinking system and stir for 3-8 minutes, then stand for 2.5-3.5 hours, and then heat to 60-70° C. to react for 4-6 hours; Wherein, the mass ratio of the activated humic acid, the grafting agent and the silane monomer is (1-5):10:(1-3).

7. The method for preparing modified humic acid according to claim 1, characterized in that: The silane monomer includes at least one of methyltriethoxysilane, trichlorovinylsilane and triethoxysilane.

8. The method for preparing modified 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: The pH value is adjusted to 9-12 with sodium hydroxide, the temperature is maintained at 50-60° C. and stirred for 6 h-10 h, and then dried at 60-70° C. for 1 h-4 h to obtain modified humic acid.

9. A modified humic acid, characterized in that: Obtained by the preparation method of humic acid according to any one of claims 1 to 8.

10. A use of the modified humic acid as claimed in claim 9, characterized in that: The modified humic acid is used as a soil conditioner or a crop fertilizer.

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