A mineral source humic acid in-situ depolymerization modification composition and method

Abstract

This invention discloses an in-situ depolymerization modification composition of mineral-derived humic acid, its method, and its applications. The composition comprises a hydrogen bond acceptor and an acidic hydrogen bond donor, wherein the hydrogen bond acceptor is selected from one or more of choline compounds, betaine compounds, and quaternary ammonium salt compounds; and the acidic hydrogen bond donor is an aliphatic polycarboxylic acid or a hydroxycarboxylic acid. This method is simple, green, and efficient, yielding a product with low molecular weight, good water solubility, and strong resistance to hard water. It is suitable for various product forms such as solid fertilizers, liquid fertigation fertilizers, and soil conditioners, and has broad application prospects in modern agriculture and ecological restoration.

Description

Technical Field

[0001] This invention relates to the field of comprehensive utilization of agricultural resources and functional fertilizers, specifically to a composition and method for in-situ depolymerization and functionalization modification of mineral-derived humic acid using an acidic eutectic composition, and the use of the modified humic acid product prepared therefrom in agriculture, horticulture and ecological restoration. Background Technology

[0002] Mineral-derived humic acid is widely found in natural mineral resources such as weathered coal, lignite, and peat, and is an important organic substance that can improve soil structure and enhance nutrient utilization efficiency. However, natural humic acid usually has a large molecular weight, complex structure, and poor water solubility. In particular, it is prone to flocculation and precipitation in hard water systems with high calcium and magnesium ion content, which seriously restricts its application in modern integrated water and fertilizer technologies such as drip irrigation and fertigation.

[0003] Fulvic acid, also known as humic acid, has a relatively small molecular weight and is mainly composed of complex aromatic hydroxycarboxylic acids. Due to its small molecular weight, it is soluble in water or weakly acidic water, and it exhibits stronger biological activity compared to humic acids with larger molecular weights.

[0004] Currently, the main processing methods for mineral-derived humic acid include alkaline extraction and acid precipitation, oxidative degradation, and physical dispersion. These methods generally suffer from problems such as complex processes, high energy consumption, heavy pollution, and limited ability to regulate the molecular structure of humic acid. The resulting products have insufficient stability against hard water, making it difficult to meet the requirements for use as liquid fertilizers in high-hardness water.

[0005] Eutectic solvents, as a type of green solvent composition, are gradually gaining attention in the field of resource extraction. Existing technologies include patents related to the extraction of humic acid using alkaline eutectic solvents. Chinese patent document CN112812323A discloses a method for extracting humic acid from mineral sources, in which choline chloride or betaine is used as the hydrogen bond acceptor and urea as the hydrogen bond donor in the eutectic solvent. However, its mechanism of action is still limited to physical dissolution, failing to effectively break stable chemical bonds such as ether bonds in the humic acid molecule, and also failing to introduce active oxygen-containing functional groups, resulting in a still relatively high molecular weight of the product and limited improvement in calcium resistance.

[0006] Therefore, there is an urgent need to develop a green modified composition that can achieve efficient depolymerization and structural regulation of mineral-derived humic acid under mild conditions, and significantly improve its water solubility and hard water resistance. Summary of the Invention

[0007] This invention provides an in-situ depolymerization modification composition of mineral-derived humic acid, its preparation method, and its application, aiming to solve the aforementioned technical problems.

[0008] In a first aspect, the present invention provides a composition for in-situ depolymerization modification of mineral-derived humic acid, comprising a hydrogen bond acceptor and an acidic hydrogen bond donor, wherein the hydrogen bond acceptor is selected from one or more of choline compounds, betaine compounds, and quaternary ammonium compounds; and the acidic hydrogen bond donor is an aliphatic polycarboxylic acid or a hydroxycarboxylic acid.

[0009] Preferably, the acidic hydrogen bond donor is one or more of citric acid, oxalic acid, lactic acid, malic acid, tartaric acid, gluconic acid, and succinic acid.

[0010] Further, the composition, by weight, comprises 100-2000 parts of hydrogen bond acceptor and acidic hydrogen bond donor; and further comprises 100-1000 parts of aqueous medium and 10-100 parts of functionalizing agent; wherein the molar ratio of hydrogen bond acceptor to acidic hydrogen bond donor is 1:0.5-1:3.

[0011] Furthermore, the mineral-derived humic acid originates from weathered coal, lignite, peat, oil shale, lignite extraction residue, or biochemical humic acid.

[0012] Furthermore, the aqueous medium is selected from one or more of tap water, industrial water, deionized water, activated water, and plant extracts.

[0013] Furthermore, the functionalized adjuvant is selected from one or more of oxidants, phosphorus-containing compounds, plant-derived active substances, and trace element compounds, wherein the oxidant is hydrogen peroxide or persulfate; and the phosphorus-containing compound is phytic acid, phosphoric acid, or dihydrogen phosphate.

[0014] This application also provides a method for in-situ depolymerization modification of mineral-derived humic acid, comprising the following steps: S1: A composition is prepared by mixing a humic acid-containing raw material, a hydrogen bond acceptor, an acidic hydrogen bond donor, an aqueous medium, and optional functionalizing agents; wherein the hydrogen bond acceptor is selected from one or more of choline compounds, betaine compounds, and quaternary ammonium salt compounds; the acidic hydrogen bond donor is an aliphatic polycarboxylic acid or a hydroxycarboxylic acid, preferably one or more of citric acid, oxalic acid, lactic acid, malic acid, tartaric acid, gluconic acid, and succinic acid; S2: Under conditions of 65-130℃, the composition obtained in step S1 is reacted in dynamic stirring or static impregnation for 0.5-6 hours to allow the acidic eutectic composition to penetrate and act on the humic acid structure, thereby achieving in-situ depolymerization, oxidation and introduction of functional groups to obtain the reaction mixture. S3: Process the reaction mixture obtained in step S2 according to the form and application requirements of the target product, including: (a) Without solid-liquid separation, directly dilute with water and selectively add an alkaline regulator to adjust the pH to produce a suspension-type fertigation fertilizer; or (b) Without solid-liquid separation, the activated product is mixed with calcium source mineral powder, dried, and granulated to produce granular humic acid fertilizer or soil conditioner; or (c) Perform solid-liquid separation, the solid part is dried and granulated for use as solid fertilizer or soil conditioner, the liquid part is diluted and used as liquid fertilizer, or further separated and recovered as eutectic solvent to obtain fulvic acid product.

[0015] Furthermore, the method for preparing the composition may be as follows: (a) Pre-prepared solvent path: First, hydrogen bond acceptor and acidic hydrogen bond donor are made into acidic eutectic solvent, and then mixed with humic acid-containing raw materials. Aqueous medium is added as viscosity modifier in 0-1000 parts. (b) In-situ hydration pathway: Mix humic acid-containing raw materials, hydrogen bond acceptors and acidic hydrogen bond donors, and add an aqueous medium to form a slurry or paste. The aqueous medium is added in 50-1000 parts as a mass transfer carrier and reaction permeator.

[0016] Furthermore, the calcium source mineral powder in step S3 is desulfurized gypsum, phosphogypsum, or oyster shell powder.

[0017] Thirdly, the present invention also provides modified humic acid solid, suspension fertigation fertilizer, fulvic acid liquid fertilizer or fulvic acid products prepared by the above method.

[0018] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. By using an acidic eutectic composition, in-situ depolymerization of humic acid molecules and introduction of functional groups can be achieved under mild conditions, significantly reducing its molecular weight and improving its water solubility and bioactivity.

[0019] 2. The obtained liquid product can still maintain stable dispersion in water with high calcium ion concentration, and has outstanding resistance to hard water. It is suitable for drip irrigation, fertigation and other fertilization methods in areas with high water hardness.

[0020] 3. The process is flexible and can be implemented through two routes: pre-prepared solvent or in-situ hydration. The process is short, environmentally friendly, and does not generate large amounts of acid or alkaline wastewater.

[0021] 4. The composition and proportions of the composition are adjustable, and the product forms are diverse. It can be made into solid fertilizer, liquid fertilizer or soil conditioner as needed, and has a wide range of applications.

[0022] 5. The selected eutectic components are mostly small organic molecules with good biocompatibility. In addition to being used as solvents in the reaction system, their residual components can exist in the product as sources of carbon- and nitrogen-containing organic matter, which is beneficial to endow the obtained product with certain biological activity potential. Detailed Implementation

[0023] To make the technical problem to be solved, the technical solution, and the beneficial effects of the present invention clearer, the present invention will be further described in detail below with reference to specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention. The present invention will be specifically described below with reference to specific embodiments.

[0024] Unless otherwise specified, the experimental methods used in the following examples are conventional methods. Unless otherwise specified, the materials and reagents used in the following examples are commercially available, and techniques not described in detail were performed according to standard methods well known to those skilled in the art.

[0025] This invention provides an in-situ depolymerization modification technology for mineral-derived humic acid based on an acidic eutectic composition. The core of this technology lies in utilizing an acidic eutectic solvent or a hydrated eutectic composition composed of hydrogen bond acceptors and acidic hydrogen bond donors. Under mild heating conditions, this solvent directly acts on the mineral-derived humic acid raw material to achieve in-situ depolymerization, oxidative chain scission, and the introduction of oxygen-containing functional groups into its molecular structure. This significantly improves the water solubility, resistance to calcium and magnesium ion flocculation, and bioactivity of humic acid. The hydrogen bond acceptors used are selected from one or more of choline compounds, betaine compounds, and quaternary ammonium salt compounds; the acidic hydrogen bond donors are aliphatic polycarboxylic acids or hydroxycarboxylic acid derivatives, preferably one or more of citric acid, oxalic acid, lactic acid, malic acid, tartaric acid, gluconic acid, and succinic acid.

[0026] This application also provides a method for in-situ depolymerization modification of mineral-derived humic acid, including the following steps: S1: Mix the humic acid-containing raw material, the above-mentioned hydrogen bond acceptor, the above-mentioned acidic hydrogen bond donor, an aqueous medium, and optional functionalizing agents to prepare a composition; S2: The composition obtained in step S1 is reacted at 65-130℃ under dynamic stirring or static impregnation for 0.5-6 hours. This step allows the acidic eutectic composition to penetrate and act on the humic acid structure, achieving in-situ depolymerization, oxidation and introduction of functional groups, to obtain the reaction mixture. S3: Process the reaction mixture obtained in step S2 according to the form and application requirements of the target product, including: (a) Without solid-liquid separation, directly dilute with water and selectively add an alkaline regulator to adjust the pH to produce a suspension-type fertigation fertilizer; or (b) Without solid-liquid separation, the activated product is mixed with calcium source mineral powder, dried, and granulated to produce granular humic acid fertilizer or soil conditioner; or (c) Perform solid-liquid separation, the solid part is dried and granulated for use as solid fertilizer or soil conditioner, the liquid part is diluted and used as liquid fertilizer, or further separated and recovered as eutectic solvent to obtain fulvic acid product. The following description is based on specific embodiments. Unless otherwise specified, all parts used in the following embodiments are parts by weight: Example 1

[0027] Take 100 parts of weathered coal sample that has been air-dried, pulverized, and passed through a 100-mesh sieve, with a humic acid content of 60%. Place the weathered coal in a corrosion-resistant reactor equipped with a stirrer, add 1500 parts of a pre-prepared choline chloride-citric acid eutectic solvent, and add 100 parts of water as a viscosity modifier, wherein the molar ratio of choline chloride to citric acid is 1:1. The above composition is dynamically stirred and reacted at 100°C for 3 hours. After the reaction, 1000 parts of water are added to the composition to dilute it and reduce its viscosity. Solid-liquid separation is achieved by filtration to obtain modified humic acid solid and a filtrate rich in fulvic acid. The obtained filtrate was tested, and its pH value was approximately 1.3. The absorbance ratio (E4 / E6) of the obtained filtrate at wavelengths of 465 nm and 665 nm was calculated. The measured E4 / E6 value in the UV-Vis spectrum was approximately 15, and the apparent fulvic acid equivalent content was approximately 7-9 g / L. This indicates that the molecular weight of humic acid was significantly reduced after treatment by this method, and the low molecular weight fulvic acid component was significantly enriched. Example 2

[0028] The filtrate obtained in Example 1 was diluted 100 times to prepare a liquid fertilizer containing fulvic acid. CaCl2 aqueous solutions with calcium ion concentrations of 50 mmol / L, 100 mmol / L, and 200 mmol / L were prepared to simulate the calcium ion concentrations in tap water and high-hardness water sources. The above liquid fertilizer was added to these solutions for calcium resistance stability testing. After shaking, the solutions were allowed to stand for 24 hours for observation. The results showed that under all calcium ion concentrations, the composition remained uniformly clear without significant flocculation, indicating that the liquid fertilizer has good calcium resistance stability and is suitable for drip irrigation or fertigation in areas with high-hardness water sources. Example 3

[0029] Take 100 parts of weathered coal sample that has been air-dried, pulverized, and passed through a 100-mesh sieve, with a humic acid content of 60%. Place the weathered coal in a corrosion-resistant reactor equipped with a stirrer, and add 1500 parts of a pre-prepared choline chloride-lactic acidic eutectic solvent, wherein the molar ratio of choline chloride to lactic acid is 1:2. The above composition is dynamically stirred and reacted at 100°C for 3 hours. After the reaction, 1000 parts of water are added to the composition to dilute it and reduce its viscosity. Solid-liquid separation is achieved by filtration to obtain modified humic acid solid and a filtrate rich in fulvic acid. The obtained filtrate was analyzed by ultraviolet-visible spectroscopy, and the results showed that its pH value was approximately 1.1. The absorbance ratio (E4 / E6) of the obtained filtrate at wavelengths of 465 nm and 665 nm was calculated, and the measured E4 / E6 value of the ultraviolet-visible spectrum was approximately 15. The apparent fulvic acid equivalent content was approximately 7-9 g / L, indicating that the molecular weight of humic acid was significantly reduced after treatment by this method, and the low molecular weight fulvic acid component was significantly enriched. Example 4

[0030] Take 100 parts of weathered coal sample that has been air-dried, pulverized, and passed through a 100-mesh sieve, with a humic acid content of approximately 60%. Place the weathered coal in a mortar, add 300 parts of choline chloride-citric acid powder (molar ratio 1:1), and grind until homogeneous. Place the mixed powder in a reaction vessel and add 100 parts of distilled water. At this point, the system exhibits a moist, black mud-like quasi-solid phase. Perform a closed static impregnation reaction at 100°C for 2 hours. After the reaction, add 1000 parts of water to dilute the system to reduce its viscosity, and then separate the solid and liquid phases by filtration to obtain modified humic acid solid and a filtrate rich in fulvic acid. The obtained filtrate was analyzed by ultraviolet-visible spectroscopy, and the results showed that its pH value was approximately 1.8. The absorbance ratio (E4 / E6) of the obtained filtrate at wavelengths of 465 nm and 665 nm was calculated, and the measured ultraviolet-visible E4 / E6 value was approximately 14. The apparent fulvic acid equivalent content was approximately 6-8 g / L, indicating that the molecular weight of humic acid was significantly reduced after treatment by this method, and the low molecular weight fulvic acid component was significantly enriched. Example 5

[0031] The filtrate obtained in Example 4 was diluted 100 times to prepare a liquid fertilizer containing fulvic acid. CaCl2 aqueous solutions with calcium ion concentrations of 50 mmol / L, 100 mmol / L, and 200 mmol / L were prepared to simulate the calcium ion concentrations in commonly used tap water and high-hardness water sources. These solutions were then added to the liquid fertilizer for calcium resistance stability testing. After shaking, the mixture was allowed to stand for 24 hours for observation. The results showed that under all calcium ion concentrations, the composition remained uniformly clear without significant flocculation, indicating that the liquid fertilizer composition also exhibits good calcium resistance stability. Example 6

[0032] One hundred parts of air-dried, pulverized lignite sample passing through a 100-mesh sieve were taken, containing approximately 33% humic acid. The lignite was placed in a mortar, and 300 parts of betaine-oxalic acid powder (molar ratio 1:1) were added and ground until homogeneous. The mixed powder was placed in a reaction vessel, and 100 parts of distilled water were added. At this point, the composition exhibited a moist, black, mud-like quasi-solid phase. The composition was subjected to a closed static impregnation reaction at 80°C for 6 hours. After the reaction, 1000 parts of water were added to the composition to dilute it and reduce its viscosity. Solid-liquid separation was achieved by filtration, yielding modified humic acid solid and a filtrate rich in fulvic acid. The filtrate was analyzed by UV-Vis spectroscopy, and the results showed that its E4 / E6 value was approximately 11, indicating that the composition could also effectively depolymerize mineral-derived humic acid.

[0033] To more clearly illustrate the advantages of the present invention compared to traditional methods and related alternative compositions, several comparative examples are provided below, which respectively simulate the treatment effects of traditional alkali extraction and acid precipitation processes, alkaline eutectic compositions, and conditions lacking key components, and are compared and analyzed with the aforementioned examples. Comparative Example 1 One hundred samples of weathered coal, dried, pulverized, and passed through a 100-mesh sieve, containing 60% humic acid, were taken. 1000 parts of a 2% sodium hydroxide solution were added, and the mixture was extracted at 100℃ with stirring for 2 hours. After the reaction, the residue was removed by centrifugation. The supernatant was adjusted to pH 2.0 with hydrochloric acid, and the precipitated humic acid was collected by centrifugation. After washing with water, the precipitate was dissolved again with sodium hydroxide to adjust the pH to neutral and then spray-dried to obtain sodium humate powder. This process is time-consuming, generates a large amount of acidic wastewater, and does not chemically modify the molecular structure, resulting in a product with poor hard water resistance. UV-Vis spectroscopy analysis of the supernatant after precipitation showed that the apparent fulvic acid equivalent content was approximately 1-2 g / L, with a UV-Vis E4 / E6 value of approximately 7, and the product could not be effectively fractionated for utilization. Comparative Example 2 One hundred samples of weathered coal, dried, pulverized, and passed through a 100-mesh sieve, were taken, with a humic acid content of 60%. An alkaline eutectic solvent was prepared using choline chloride and urea at a 1:2 molar ratio, instead of the acidic composition of this invention. Other conditions were the same as in Example 1 of this invention. After reaction and solid-liquid separation, the pH of the supernatant was adjusted to 2.0 with hydrochloric acid. The supernatant after precipitation was subjected to UV-Vis spectroscopy. The results showed that the apparent fulvic acid equivalent content was approximately 1-2 g / L, and its UV-Vis E4 / E6 value was approximately 7, indicating that the composition only achieved physical dissolution, the humic acid structure did not undergo significant depolymerization, and the product could not be effectively fractionated for utilization. Comparative Example 3 The raw material ratio was exactly the same as in Example 3, but no aqueous medium was added. Observation revealed that the mixture remained a dry, hard, and lumpy mass with no flowability, indicating that the solvent failed to penetrate the coal matrix. Sampling analysis showed that the humic acid content was comparable to that of the raw materials and adhered to the bottom of the reaction vessel, indicating that the reaction could not proceed effectively in the absence of a mass transfer medium. Comparative Example 4 Weigh out the same amount of choline chloride-citric acid eutectic solvent as in Example 4, and heat and stir at 100°C for 3 hours without adding humic acid-containing raw materials. After the reaction, dilute with water in the same manner as in Example 1, and perform UV-Vis spectroscopy on the resulting solution. The results show that the solution has low absorbance in the 400-600 nm wavelength range and does not exhibit obvious E4 / E6 characteristic changes, indicating that the acidic eutectic solvent itself contributes very little to the E4 / E6 value, and the increase in E4 / E6 value in the examples mainly comes from the change in humic acid structure. Table 1 shows the experimental data of the above examples and comparative examples.

[0034] Table 1 Summary of Experimental Data

[0035] As shown in Comparative Example 4, the acidic eutectic solvent itself has little effect on the UV-Vis spectral characteristics. The changes in the E4 / E6 values ​​in the embodiments of this invention mainly originate from the depolymerization and reconstruction of the molecular structure of mineral-derived humic acid. The obtained modified humic acid solid still exhibits strong water solubility after water washing, indicating that the macromolecular humic acid and inert humin underwent effective in-situ depolymerization and carboxyl group introduction under the action of the acidic eutectic composition, successfully transforming into water-soluble modified humic acid. The apparent fulvic acid equivalent content was determined by using a UV absorbance-concentration standard curve established using commercially available fulvic acid standards.

[0036] The above examples and comparative examples fully demonstrate that the acidic eutectic composition provided by the present invention can achieve efficient depolymerization and stabilization modification of mineral-derived humic acid under different process routes, different raw materials and different functional additives. The resulting product has excellent hard water resistance and agricultural application potential.

[0037] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A mineral-derived humic acid in-situ depolymerization modified composition, characterized in that, The composition comprises a hydrogen bond acceptor and an acidic hydrogen bond donor, wherein the hydrogen bond acceptor is selected from one or more of choline compounds, betaine compounds, and quaternary ammonium compounds; and the acidic hydrogen bond donor is an aliphatic polycarboxylic acid or a hydroxycarboxylic acid.

2. The composition according to claim 1, characterized in that, The acidic hydrogen bond donor is one or more of citric acid, oxalic acid, lactic acid, malic acid, tartaric acid, gluconic acid, and succinic acid.

3. The composition according to claim 1, characterized in that, The composition, by weight, comprises 100-2000 parts of hydrogen bond acceptor and acidic hydrogen bond donor, and further comprises 100-1000 parts of aqueous medium and 10-100 parts of functionalizing agent; wherein the molar ratio of hydrogen bond acceptor to acidic hydrogen bond donor is 1:0.5-1:

3.

4. The composition according to claim 1, characterized in that, The mineral-derived humic acid comes from weathered coal, lignite, peat, oil shale, lignite extraction residue, or biochemical humic acid.

5. The composition according to claim 3, characterized in that, The aqueous medium is selected from one or more of tap water, industrial water, deionized water, activated water, and plant extracts.

6. The composition according to claim 3, characterized in that, The functionalized adjuvant is selected from one or more of oxidants, phosphorus-containing compounds, plant-derived active substances, and trace element compounds, wherein the oxidant is hydrogen peroxide or persulfate; and the phosphorus-containing compound is phytic acid, phosphoric acid, or dihydrogen phosphate.

7. A method for in-situ depolymerization and modification of mineral-derived humic acid, characterized in that, Includes the following steps: S1: A composition is prepared by mixing humic acid-containing raw materials, hydrogen bond acceptors, acidic hydrogen bond donors, an aqueous medium, and optional functionalizing agents, wherein the hydrogen bond acceptors are selected from one or more of choline compounds, betaine compounds, and quaternary ammonium salt compounds; and the acidic hydrogen bond donors are aliphatic polycarboxylic acids or hydroxycarboxylic acids. S2: The composition obtained in step S1 is reacted at 65-130℃ under dynamic stirring or static impregnation for 0.5-6 hours to obtain a reaction mixture; S3: Process the reaction mixture obtained in step S2 according to the form and application requirements of the target product, including: a: Without solid-liquid separation, water is added directly for dilution and an alkaline regulator is selectively added to adjust the pH, thus producing a suspension-type fertigation fertilizer; or b: Without solid-liquid separation, the activated product is mixed with calcium source mineral powder, dried, and granulated to produce granular humic acid fertilizer or soil conditioner; or c: Perform solid-liquid separation. The solid portion is dried and granulated for use as solid fertilizer or soil conditioner. The liquid portion is diluted and used as liquid fertilizer, or further separated and recovered as a eutectic solvent to obtain fulvic acid product.

8. The method as described in claim 7, characterized in that, In step S1, the method for preparing the composition is as follows: a. Pre-prepared solvent route: First, prepare an acidic eutectic solvent by combining hydrogen bond acceptors and acidic hydrogen bond donors, then mix it with humic acid-containing raw materials, adding 0-1000 parts of an aqueous medium as a viscosity modifier; or b. In-situ hydration pathway: The raw material containing humic acid, hydrogen bond acceptor and acidic hydrogen bond donor are directly mixed and then mixed with an aqueous medium to form a slurry or paste. The aqueous medium is added in 50-1000 parts as a mass transfer carrier and reaction permeator.

9. The method as described in claim 7, characterized in that, The calcium source mineral powder in step S3 is desulfurized gypsum, phosphogypsum, or oyster shell powder.

10. Modified humic acid solid, suspension fertigation fertilizer, fulvic acid liquid fertilizer or fulvic acid product prepared by the method according to claim 7.

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