Lignite humic acid activation method and application thereof

Abstract

The invention discloses a lignite humic acid activation method and application thereof, and the activation method comprises the following steps: adding a KOH solution into crushed and dried lignite, and carrying out ultrasonic treatment to obtain a humic acid solution; (2) adding HCl into the humic acid solution obtained in the step (1) to adjust the pH value, adding an H2O2 solution into the solution, reacting at 10-30 DEG C for 5-10 minutes, then adding Fe2SO4, and keeping the temperature to continuously react for 5-10 minutes to obtain a reaction product; and acidifying the reaction product with HCl, centrifuging to obtain a precipitate after acidification, and washing and drying to obtain the lignite humic acid. The lignite is used as a precursor, the lignite is pre-activated through ultrasonic waves, the lignite treated through the ultrasonic waves is activated through the Fenton reaction, the preparation process is simple and easy to operate, the reaction time is short, energy consumption is small, the method is green and free of pollution, the agricultural industry chain of the humic acid can be prolonged, and the obtained humic acid is higher in water-soluble humic acid content, smaller in molecular weight and higher in yield. The humic acid modifier has the characteristics of high water solubility and low molecular weight, and is easy to contact and react with soil, thereby being beneficial to popularization and application of the humic acid as the modifier.

Description

Technical Field

[0001] The invention relates to the technical field of humic acid, and in particular to an activation method of lignite humic acid and application thereof. Background Art

[0002] Humic acid is an active substance separated from mineral substances such as lignite, peat, river mud and weathered coal. Humic acid is a polyacid with at least two acidic groups (hydroxyl and carboxyl). Humic acid has the advantages of enhancing crop resistance, stimulating crop growth, improving soil environment, improving fruit quality and reducing heavy metal pollution due to its multiple active groups. In addition, the active functional groups in humic acid can react with chemical elements by chelation and complexation, slowing down the release of nutrients, promoting the absorption and utilization of nutrients by crops and further improving the utilization rate of fertilizers by crops. Humic acid has a wide source and low price, and is a green and environmentally friendly fertilizer for achieving sustainable development. However, humic acid easily reacts with metal ions such as calcium, magnesium, aluminum and iron to form insoluble metal ion-bound humic acid, which makes the water solubility of humic acid poor. Therefore, humic acid needs to be activated to make it more widely applicable.

[0003] During the production process, the molecular weight, acidic functional group content, water-soluble humic acid content and other chemical properties of humic acid determine its excellent quality. In particular, increasing the water-soluble humic acid content in humic acid is of great significance for enhancing its activity and expanding its application. Due to its good solubility and activity, water-soluble humic acid can be more widely used in soil remediation, agricultural production and pollution control. It can dissolve quickly in water, facilitate diffusion and absorption, and show stronger effects in promoting plant growth, improving soil structure and chelating heavy metals. In addition, increasing the content of water-soluble humic acid can enhance the environmental functionality of humic acid, improve its efficiency in wastewater treatment and environmental pollution remediation, while reducing the cost of use and making its application more flexible and diverse. In addition, the increase in the content of water-soluble humic acid is closely related to the activity of humic acid. By optimizing the molecular structure of humic acid and increasing its water solubility and acidic functional group content, its biological activity can be significantly improved, its fertilizer efficiency can be further enhanced, the growth environment of crops can be improved, and nutrient utilization can be promoted, ultimately achieving increased agricultural production and income. Therefore, increasing the content of water-soluble humic acid can not only enhance the fertilizer efficiency of humic acid and improve the growth environment of crops, but also broaden its application scope in agriculture, soil remediation and environmental management.

[0004] Patent CN102747381A discloses a method for preparing humic acid by electrochemical oxidation of lignite, wherein lignite is mixed with alkaline solution to form coal slurry, an electrochemical reactor is used for experiments, the prepared coal slurry is added to the anode area, and an alkaline solution of the same concentration is added to the cathode area, and an electrolysis experiment is performed using a three-electrode system. The upper layer solution obtained by centrifugal separation of the anode slurry is acidified and filtered to obtain a solid product, and then washed and dried to obtain humic acid. However, this method has a complex process and consumes a lot of energy. Patent CN106810703B discloses a method for preparing humic acid by catalytic oxidation of lignite, including drying, pickling, loading catalyst, catalyst morphology transformation and coal sample oxidation, alkali extraction, acid precipitation and drying to obtain humic acid. In the use of catalysts, this patent uses a loaded copper catalyst, which is relatively expensive, and humic acid is prepared after catalyst morphology transformation and coal sample oxidation, which has a complex process. Patent CN110183682A discloses a method for extracting humic acid from low-rank lignite by thermal oxidation. The method uses oxygen oxidation, oxidizes at a high temperature of 100-240°C for 5-10 days, and the oxidation product is alkali-extracted at 80-100°C for 1.5-2.5 hours. Humic acid is obtained by filtration, acid precipitation and drying. This method consumes a lot of energy and takes a long time, and there is no mention of the activation of humic acid. In summary, most traditional methods of extracting humic acid are complex, energy-intensive, and inefficient, and it is difficult to make humic acid meet the requirements of low molecular weight, high water solubility, and multiple acidic functional groups. Summary of the invention

[0005] In view of the above prior art, the object of the present invention is to provide a method for activating lignite humic acid and application thereof.

[0006] To achieve the above object, the present invention adopts the following technical solution:

[0007] The first aspect of the present invention provides a method for activating lignite humic acid, comprising the following steps:

[0008] (1) adding KOH solution to the crushed and dried lignite and performing ultrasonic treatment to obtain a humic acid solution;

[0009] (2) adding HCl to the humic acid solution obtained in step (1) to adjust the pH, adding H2O2 solution to the solution, reacting at 10-30°C for 5-10 minutes, then adding Fe2SO4, maintaining the temperature and continuing the reaction for 5-10 minutes to obtain a reaction product;

[0010] (3) The reaction product obtained in step (2) is acidified with HCl, and then centrifuged to obtain a precipitate, which is then washed and dried to obtain lignite humic acid.

[0011] By adopting the above technical scheme, lignite is used as a precursor, and the lignite is pre-activated by ultrasound. The lignite treated with ultrasound is then activated by Fenton reaction. The Fenton reaction is the reaction of hydrogen peroxide and divalent iron ions to form hydroxyl groups with strong oxidizing properties. Therefore, the role of ferrous sulfate is to react with hydrogen peroxide to form hydroxyl groups to oxidize the lignite.

[0012] The reasons for waiting a few minutes before adding: ① Adding hydrogen peroxide first can avoid its instantaneous reaction with a large amount of divalent iron, reducing the waste of hydrogen peroxide. ② Initiation of chain reaction: The essence of the Fenton reaction is the chain reaction between divalent iron ions and hydrogen peroxide to catalyze the generation of hydroxyl radicals. This chain reaction requires an initial reaction between divalent iron and hydrogen peroxide to generate intermediates, which then further react with hydrogen peroxide and divalent iron. If hydrogen peroxide and divalent iron are added at the same time at the beginning, the reaction may be too violent, making it difficult to control the reaction, affecting the progress of the chain reaction. ③ pH control: The Fenton reaction needs to be carried out at a lower pH value, usually between 2.5 and 5.0. If the pH value is lower than 2.5, ferric iron (Fe 3+ ) will become a stable state, which is not conducive to the progress of the Fenton reaction. Therefore, adding hydrogen peroxide first can ensure that the pH value is appropriate when adding divalent iron, maintain the activity of divalent iron, and effectively start and maintain the chain reaction. In summary, the order of adding hydrogen peroxide first and then adding divalent iron ions for a few minutes helps to improve the efficiency and effect of Fenton method for treating wastewater, while ensuring the controllability of the reaction and the smooth progress of the chain reaction.

[0013] Preferably, in step (1), the concentration of the KOH solution is 0.1 to 1 M, and the solid-liquid ratio of the lignite raw material to the KOH solution is 1 g: (5 to 20) ml.

[0014] Preferably, in step (1), the frequency of ultrasonic treatment is 20-40 kHz, the temperature is 30-60° C., and the time is 0.5-1 h.

[0015] Preferably, in step (2), the concentration of HCl is 0.1-1 M, the pH is adjusted to 2.5-5.0, and the concentration of H2O2 solution is 500-5000 mg / L.

[0016] Preferably, the ratio of the added amounts of lignite, H2O2 solution and Fe2SO4 is (3-7) g:(1-10) ml:(0.1-1) g.

[0017] Preferably, in step (3), the concentration of HCl is 0.1 to 1 M, and the pH is adjusted to 1 to 2.5 by acidification.

[0018] The second aspect of the present invention provides the use of the above activation method in improving the activity of lignite humic acid.

[0019] Preferably, the activation method improves the activity of lignite humic acid by at least one of the following (1)-(3):

[0020] (1) Increasing the water-soluble humic acid content in lignite humic acid;

[0021] (2) Reduce the molecular weight of lignite humic acid;

[0022] (3) Increase the acidic functional group content of lignite humic acid.

[0023] The third aspect of the present invention provides lignite humic acid prepared by the above method.

[0024] The fourth aspect of the present invention provides the use of the above-mentioned lignite humic acid in improving acidic soil.

[0025] Beneficial effects of the present invention:

[0026] (1) The present invention uses lignite as a precursor, pre-activates the lignite by ultrasound, and then activates the lignite treated by ultrasound by Fenton reaction. The preparation process is simple and easy to operate, with short reaction time, low energy consumption, green and pollution-free, and can extend the humic acid agricultural industry chain. The present invention uses the Fenton method to activate humic acid using lignite as a raw material, changes the content of humic acid acidic functional groups, and makes the obtained lignite humic acid have a higher content of water-soluble humic acid and a smaller molecular weight. It has the characteristics of high water solubility and low molecular weight, and is easy to react with soil in contact, which is conducive to the promotion and application of humic acid as an improver.

[0027] (2) The lignite of the present invention is processed after being ground, and the specific surface area of ​​the lignite reaction is increased, thereby accelerating the reaction; the ultrasonic treatment is simple and easy to operate, and the lignite is pre-activated before the Fenton reaction, so that the lignite activation is more complete; the purpose of adding KOH is to extract the activated humic acid, and the humic acid is extracted by using the alkali dissolution and acid precipitation method, and some impurities are removed while obtaining the humic acid to obtain pure humic acid.

[0028] (3) The activated humic acid prepared by the present invention is applied to the soil by broadcasting, which can effectively increase the pH of the acidic soil, promote the growth and development of rapeseed, and increase the yield of rapeseed. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 : Absorbance ratio change diagram of lignite humic acid prepared in Example 1 and commercial lignite at wavelengths of 465nm and 665nm;

[0030] Figure 2 : Surface morphology of lignite humic acid prepared in Example 1 and commercially available lignite;

[0031] Figure 3: Schematic diagram of infrared spectra of lignite humic acid prepared in Example 1 and commercially available lignite;

[0032] Figure 4 : Nitrogen content in rapeseed soil treated with lignite humic acid prepared in Example 1 and commercially available lignite. DETAILED DESCRIPTION

[0033] It should be noted that the following detailed descriptions are illustrative and are intended to provide further explanation of the present application. Unless otherwise specified, all technical and scientific terms used herein have the same meanings as those commonly understood by those skilled in the art to which the present application belongs.

[0034] In order to enable those skilled in the art to more clearly understand the technical solution of the present application, the technical solution of the present application will be described in detail below in conjunction with specific embodiments.

[0035] The test materials used in the examples of the present invention are all conventional test materials in the art and can be purchased through commercial channels.

[0036] The lignite used in the present invention is purchased from Shanghai Dongyiyang Chemical New Materials Co., Ltd.

[0037] Example 1: Preparation of lignite humic acid

[0038] (1) grind lignite, pass it through a 70-mesh sieve, and dry it in an oven to constant weight to obtain a lignite raw material. Weigh 5 g of the lignite raw material, add 25 ml of a 0.1 M KOH solution, and perform ultrasonic treatment at 50° C. for 0.5 h at a frequency of 30 kHz to obtain a humic acid solution.

[0039] (2) adding 0.1 M HCl to the humic acid solution obtained in step (1) to adjust the pH to 2.8, adding 10 ml of H2O2 solution (concentration of 500 mg / L) to the solution, reacting at 25° C. for 5 min, adding 0.5 g of Fe2SO4, and continuing to react at 25° C. for 5 min to obtain a reaction product;

[0040] (3) The pH of the reaction product obtained in step (2) was adjusted to 1.8 with 0.1 M HCl, and then the reaction product was centrifuged at 3000 r / min for 15 min to obtain a precipitate, the precipitate was washed three times with deionized water, and placed in an oven at 60° C. to dry to constant weight to obtain lignite humic acid.

[0041] Example 2: Preparation of lignite humic acid

[0042] 1) grind lignite, pass it through a 60-mesh sieve, and dry it in an oven to constant weight to obtain a lignite raw material; weigh 5 g of the lignite raw material, add 25 ml of a 0.3 M KOH solution, and perform ultrasonic treatment at 40° C. for 1 h at a frequency of 30 kHz to obtain a humic acid solution;

[0043] (2) adding 0.2 M HCl to the humic acid solution obtained in step (1) to adjust the pH to 3.2, adding 10 ml of H2O2 (concentration of 2500 mg / L) solution to the solution, reacting at 25° C. for 5 min, adding 0.2 g of Fe2SO4, and continuing to react at 25° C. for 5 min to obtain a reaction product;

[0044] (3) The pH of the reaction product obtained in step (2) was adjusted to 1.5 with 0.2 M HCl, and then the reaction product was centrifuged at 3000 r / min for 15 min to obtain a precipitate, the precipitate was washed three times with deionized water, and placed in an oven at 60° C. to dry to constant weight to obtain lignite humic acid.

[0045] Comparative Example 1:

[0046] (1) grind lignite, pass it through a 70-mesh sieve, and dry it in an oven to constant weight to obtain a lignite raw material. Weigh 5 g of the lignite raw material, add 25 ml of a 0.1 M KOH solution, and perform ultrasonic treatment at 50° C. for 0.5 h at a frequency of 30 kHz to obtain a humic acid solution.

[0047] (2) adding 0.1 M HCl to the humic acid solution obtained in step (1) to adjust the pH to 1.8, and then centrifuging the reaction product at 3000 r / min for 15 min to obtain a precipitate, washing the precipitate with deionized water three times, and drying it in an oven at 60° C. to constant weight to obtain lignite humic acid.

[0048] Comparative Example 2:

[0049] The lignite was ground, passed through a 70-mesh sieve, and dried in an oven to constant weight to obtain the lignite raw material. 5 g of the lignite raw material was weighed, 10 ml of H2O2 (concentration of 500 mg / L) solution was added, and the reaction was carried out at 25°C for 5 min, and then 0.5 g of Fe2SO4 was added, and the reaction was continued at 25°C for 5 min, and the lignite humic acid was obtained by drying.

[0050] Test Example 1: Study on the activation effect of lignite humic acid prepared by the present invention:

[0051] The lignite humic acid prepared in Example 1, the lignite humic acid prepared in Comparative Examples 1-2, and commercially available lignite were characterized, and the water-soluble humic acid content of the lignite humic acid prepared in Example 1, the lignite humic acid prepared in Comparative Examples 1-2, and commercially available lignite was detected; the molecular weight, surface morphology, and changes in the carboxyl groups of the acidic functional groups of the lignite humic acid prepared in Example 1 and commercially available lignite were determined.

[0052] 1. Test method:

[0053] 1.1 The water-soluble humic acid content was determined by hot water extraction-K2Cr2O7 volumetric method.

[0054] 1.2 The molecular weight of humic acid is expressed by the ratio of the absorbance at 465nm and the absorbance at 665nm of the UV spectrophotometer. The smaller the molecular weight of humic acid, the larger the E4 / E6.

[0055] 1.3 Use SEM to analyze the surface morphology of humic acid.

[0056] 1.4 Determination of humic acid acidic functional groups by Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) analyzer.

[0057] 2. Test results:

[0058] Table 1 Water-soluble humic acid content in lignite humic acid obtained by different treatments

[0059]

[0060]

[0061] As shown in Table 1, the water-soluble humic acid content in the lignite humic acid prepared in Example 1 of the present invention reached 56.09%, which was significantly increased by 55.24% compared with the commercially available lignite.

[0062] like Figure 1 As shown, the smaller the molecular weight of humic acid, the larger the E4 / E6. For E4 / E6, the value of lignite humic acid prepared in Example 1 of the present invention is 3.64, which is significantly greater than 2.61 of commercially available lignite, indicating that the molecular weight of lignite humic acid prepared by the activation method of the present invention is significantly reduced.

[0063] The surface morphology of humic acid Figure 2 As shown: the lignite humic acid prepared in Example 1 has a smoother surface, better size uniformity, and has aggregated spherical structures and non-uniform porous structures.

[0064] like Figure 3 Shown: at 3400cm -1 The peak at 1685 cm indicates the increase of phenolic or alcoholic -OH groups. -1The peak at indicates that there is C=N or C=O on the surface of the lignite humic acid prepared in Example 1.

[0065] In summary, the present invention significantly improves the activity of lignite humic acid by optimizing the activation method, including the increase of water-soluble humic acid content, the decrease of molecular weight, the optimization of surface morphology and the increase of acidic functional groups. Specifically, the water-soluble humic acid content is increased from 36.13% to 56.09%, the molecular weight is reduced, the E4 / E6 value is significantly increased to 3.64, the surface is smoother and a porous spherical structure is formed, and more acidic functional groups are introduced. These modifications improve the solubility, adsorption and chelating ability of humic acid, so that it shows more efficient and wider application value in agricultural efficiency improvement, soil remediation and environmental governance.

[0066] Test Example 2: Test on the effect of lignite humic acid prepared by the present invention on rapeseed in soil:

[0067] The lignite humic acid prepared in Example 1 and the commercially available lignite were mixed with acidic soil and then rapeseed was planted, as follows:

[0068] The experiment set up two treatments:

[0069] Treatment 1: 10 kg of acidic soil (pH 4.65) and 20 g of lignite humic acid prepared in Example 1 were weighed and mixed into a ceramic pot;

[0070] Control group: 10 kg of acidic soil (pH 4.65) and 20 g of commercially available lignite were weighed and mixed into a ceramic pot;

[0071] Each treatment was repeated three times.

[0072] The same amount of N-P2O5-K2O was applied to both the treatment group and the control group, and all fertilizers were mixed and applied as a single basal fertilizer. The treatment group and the control group maintained the same other planting management measures.

[0073] Test indicators: After harvest, the rapeseed yield and soil pH differences under different treatments were measured.

[0074] Soil pH was determined by the potentiometric method with a water-soil ratio of 5:1, and soil ammonium nitrogen and nitrate nitrogen were determined by ultraviolet spectrophotometry, referring to the "Determination of soil nitrate nitrogen by ultraviolet spectrophotometry" GB / T 32737-2016

[0075] Table 2 pH of acidic soil after application of different humic acids

[0076]

[0077] As shown in Table 2, the lignite humic acid prepared in Example 1 significantly increased the pH of the acidic soil after use, and the pH of the soil treated with commercial lignite was increased by 0.71 units.

[0078] Table 3 Rapeseed yield after application of different humic acids

[0079]

[0080] It can be seen from Table 3 that the plant height, root biomass per plant and biomass per plant of rapeseed in the control group were 23.7 cm, 6.8 g and 186.3 g respectively, while the plant height, root biomass per plant and biomass per plant of rapeseed in treatment group 1 were 24.9 cm, 8.2 g and 229.5 g respectively, which were increased by 5.1%, 20.5% and 23.2% respectively compared with the control group.

[0081] Depend on Figure 4 It can be seen that the ammonium nitrogen and nitrate nitrogen contents of the root soil of rapeseed treated with commercial lignite were 12.4 mg / kg and 26.8 mg / kg, respectively, and the ammonium nitrogen and nitrate nitrogen contents of the root soil of rapeseed treated with humic acid prepared in Example 1 were 19.1 mg / kg and 20.7 mg / kg, respectively, with the ammonium nitrogen content increasing by 54.4% and the nitrate nitrogen content decreasing by 22.7%. This indicates that the lignite humic acid prepared by the activation method of the present invention effectively reduces the conversion of ammonium nitrogen into nitrate nitrogen in the root soil of rapeseed, thereby reducing H + Release, raising the soil pH.

[0082] The above description is only the preferred embodiment of the present application and is not intended to limit the present application. For those skilled in the art, the present application may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A method for activating lignite humic acid, characterized in that: The steps include: (1) adding KOH solution to the crushed and dried lignite and performing ultrasonic treatment to obtain a humic acid solution; (2) adding HCl to the humic acid solution obtained in step (1) to adjust the pH, adding H2O2 solution to the solution, reacting at 10-30°C for 5-10 minutes, then adding Fe2SO4, maintaining the temperature and continuing the reaction for 5-10 minutes to obtain a reaction product; (3) The reaction product obtained in step (2) is acidified with HCl, and then centrifuged to obtain a precipitate, which is then washed and dried to obtain lignite humic acid.

2. The activation method according to claim 1, characterized in that In step (1), the concentration of the KOH solution is 0.1-1M, and the solid-liquid ratio of lignite to the KOH solution is 1g:(5-20)ml.

3. The activation method according to claim 1, characterized in that The frequency of ultrasonic treatment is 20-40 kHz, the temperature is 30-60°C, and the time is 0.5-1 h.

4. The activation method according to claim 1, characterized in that In step (2), the concentration of HCl is 0.1-1 M, the pH is adjusted to 2.5-5.0, and the concentration of H2O2 solution is 500-5000 mg / L.

5. The activation method according to claim 1, characterized in that The ratio of the added amounts of lignite, H2O2 solution and Fe2SO4 is (3-7) g:(1~10) ml:(0.1~1) g.

6. The activation method according to claim 1, characterized in that: In step (3), the concentration of HCl is 0.1 to 1 M, and the pH is adjusted to 1 to 2.5 by acidification.

7. Use of the activation method according to any one of claims 1 to 6 in improving the activity of lignite humic acid.

8. The use according to claim 7, characterized in that: The activation method improves the activity of lignite humic acid by at least one of the following (1)-(3): (1) Increasing the water-soluble humic acid content in lignite humic acid; (2) Reduce the molecular weight of lignite humic acid; (3) Increase the acidic functional group content of lignite humic acid.

9. Lignite humic acid prepared by the activation method according to any one of claims 1 to 6.

10. Use of the lignite humic acid according to claim 9 in improving acidic soil.

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