Preparation method of artificial humic acid

Abstract

The invention provides a preparation method of artificial humic acid, which comprises the following steps: by taking a humus precursor as a raw material, adding isomorphous substituted manganese goethite prepared by a coprecipitation method, reacting at room temperature, washing a reaction product with hydrochloric acid and deionized water, and drying to obtain the artificial humic acid, the preparation method is simple, low in energy consumption and easy to scale, complex and expensive instruments are not needed, the problems of high energy consumption and large equipment size limitation in preparation of artificial humic acid by a hydrothermal method are solved, the prepared humic acid has a remarkable plant growth promoting effect, the dye and heavy metal adsorption capacity of the humic acid is superior to that of commercial humic acid, and the humic acid has a wide application prospect. The method also has great application potential in the aspect of pollutant adsorption.

Description

Technical Field

[0001] The present invention belongs to the technical field of agricultural chemistry, and particularly relates to a preparation method of artificial humic acid and its application in promoting plant growth. Background Art

[0002] Humic acid, a widely occurring macromolecular organic polymer, plays a crucial role in agriculture. It is a key builder of soil aggregates and a central hub for fertilizer transport within the soil. Its molecular structure is rich in reactive functional groups such as carboxyl, hydroxyl, alcoholic hydroxyl, and carbonyl groups. These groups endow humic acid with numerous unique properties, enabling it to exchange, adsorb, complex, and chelate with metal ions, effectively improving soil structure and creating an optimal environment for crop growth. In dispersed systems, humic acid acts as a polyelectrolyte, possessing cohesive, peptizing, and dispersing properties. It can comprehensively improve soil physical and chemical properties, enhance fertilizer utilization efficiency, stimulate crop growth, enhance crop resistance, and improve the quality of agricultural products. It is a high-quality additive for fertilizers, pesticides, drought-resistant agents, and other products. Currently, humic acid used in various fields is primarily derived from peat, coal, or other natural raw materials, produced through bioengineering (microbiological) and chemical methods. However, mineral resources such as weathered coal, lignite, and peat are facing increasing depletion and have poor regeneration. Some researchers have used crop straw as raw material to prepare artificial humic acid through a hydrothermal method. Although the raw material sources are wide, there are still problems such as high energy consumption in the preparation process and limited size of the reaction equipment.

[0003] In this context, developing a new, low-carbon method for preparing artificial humic acid using renewable resources is of extremely important practical significance for meeting the demand for humic acid in agricultural production, alleviating resource pressure and promoting sustainable agricultural development. Summary of the Invention

[0004] The present invention provides a method for preparing artificial humic acid, which uses low-cost raw materials to prepare a material that can effectively promote a humification reaction, thereby quickly preparing a humification product with good performance.

[0005] The specific technical solutions of the present invention are as follows:

[0006] A method for preparing artificial humic acid, comprising the following steps:

[0007] (1) dissolving the precursor in alkaline phosphate buffer, adding a preservative and manganese-substituted goethite powder to the resulting mixture, and shaking the resulting mixture at a constant temperature of 25° C. at a speed of 150-160 rpm for more than 60 days;

[0008] (2) The product of step (1) is acidified with 6 mol / L concentrated hydrochloric acid to pH = 1, and after standing for 30-40 minutes, the precipitate and the supernatant are separated by centrifugation, and the precipitate is repeatedly washed with dilute hydrochloric acid until the washing liquid is colorless, and then dried to obtain humic acid.

[0009] The precursor of step (1) is obtained by mixing sugars, amino acids, and polyphenols in a substance ratio of 2:2:1, wherein the sugars are glucose, fructose, etc., the amino acids are glycine, alanine, etc., and the polyphenols are catechol, hydroquinone, catechol, etc.

[0010] The alkaline phosphate buffer in step (1) is a phosphate buffer with a pH value of 8-10 and a concentration of 0.2 mol / L.

[0011] In the mixed solution of step (1), the sugar concentration is 0.002-0.004 mol / L, the amino acid concentration is 0.002-0.004 mol / L, and the polyphenol concentration is 0.001-0.002 mol / L.

[0012] The preservative in step (1) is sodium thimerosal.

[0013] The mass volume percentage concentration of the preservative in the mixture of step (1) is 0.1-0.4% g / L, and the concentration of the manganese-substituted goethite powder is 1-3 g / L.

[0014] The preparation method of the manganese-substituted goethite powder in step (1) comprises the following steps:

[0015] A. Add the precursor iron-manganese solution to the potassium hydroxide solution and mix well. Pour the mixed solution into a polytetrafluoroethylene beaker, then add deionized water twice the volume of the mixed solution. Place the suspension in an oven at 40-80°C for aging for 5-30 days to obtain a mixture, stirring it for 2-15 minutes every day.

[0016] B. The mixture obtained in step A is centrifuged, and deionized water is added and the centrifugation operation is repeated until the supernatant is neutral. The bottom solid washed to neutrality is dried, and the dried solid is ground to obtain manganese-substituted goethite powder.

[0017] The precursor iron-manganese solution in step A is prepared by mixing 54 mL of Fe(NO3)3 with a concentration of 0.5-2 mol / L and 12 mL of Mn(NO3)2 with a concentration of 0.5-2 mol / L; the solvent of the potassium hydroxide solution is one or more of water, ethanol, ethylene glycol, n-propanol, and isopropanol, the concentration of the potassium hydroxide solution is 2-8 mol / L, and the amount added is 72 mL.

[0018] The manganese-substituted goethite of the present invention accelerates the non-biological humification process to prepare humic acid. The prepared artificial humic acid promotes plant growth and is used to adsorb dyes and heavy metal ions. The plants include but are not limited to soybeans; the dyes include but are not limited to direct blue 6, sodium fluorescein, 5-carboxyfluorescein, Congo red, etc.; the heavy metal system includes but is not limited to copper, zinc, cadmium, nickel, etc.

[0019] The invention uses low-cost raw materials and a low-toxicity preparation process, has low energy consumption, is environmentally friendly, and saves energy.

[0020] The present invention realizes isomorphous substitution of manganese for goethite during the aging reaction process, has simple operation and does not require secondary doping preparation.

[0021] The isomorphously substituted manganese-substituted goethite of the present invention has good oxidizability and abundant surface active sites, which is conducive to combining with the precursor in water and increasing the effective contact area between the material and the precursor substance.

[0022] The humic acid generated by the manganese-substituted goethite material of the present invention has better ability to remove dyes and heavy metals as an adsorbent than commercial humic substances.

[0023] The humic acid generated by the manganese-substituted goethite material of the present invention has an obvious promoting effect on plant growth. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is the surface photo of goethite and manganese-substituted goethite, where Goe is goethite and MnGoe is manganese-substituted goethite;

[0025] Figure 2 This is the XRD comparison diagram of goethite and manganese-substituted goethite;

[0026] Figure 3 This is a FTIR comparison chart of goethite and manganese-substituted goethite;

[0027] Figure 4 (a) is the XPS oxygen peak diagram of goethite, (b) is the XPS oxygen peak diagram of manganese-substituted goethite;

[0028] Figure 5 This is a kinetic comparison diagram of goethite and manganese-substituted goethite applied to abiotic humification reaction and left for 60 days respectively;

[0029] Figure 6 This is a comparison of Raman spectra of artificial humic acid and commercial humic acid;

[0030] Figure 7 (a) Comparison of the adsorption performance of artificial humic acid and commercial humic acid for different dyes, (b) Comparison of the adsorption performance of artificial humic acid and commercial humic acid for different heavy metal solutions;

[0031] Figure 8 Schematic diagram of soybean plants cultivated under different application rates of artificial humic acid;

[0032] Figure 9 This is a comparison chart of the fresh weight and dry weight of soybean plants cultured under different application rates of artificial humic acid;

[0033] Figure 10 This is a comparison chart of fresh K content and nitrate content in soybean plants cultured under different application rates of artificial humic acid. DETAILED DESCRIPTION

[0034] The following examples are used to illustrate the present invention but are not intended to limit the scope of the present invention.

[0035] Example 1

[0036] The preparation method of manganese-substituted goethite powder comprises the following specific steps:

[0037] A. In a polytetrafluoroethylene beaker, 54 mL of 1 mol / L Fe(NO3)3 and 12 mL of 0.5 mol / L Mn(NO3)2 were mixed to prepare a precursor iron-manganese solution, 72 mL of a 2 mol / L KOH aqueous solution was added, and then 600 mL of deionized water was added. The suspension was placed in an oven at 80°C for aging for 5 days to obtain a mixture, with appropriate stirring for 15 minutes every day;

[0038] B. The mixture obtained in step A is centrifuged, and deionized water is added and the centrifugation operation is repeated until the supernatant is neutral. The bottom solid washed to neutrality is dried, and the dried solid is ground to obtain manganese-substituted goethite powder MnGoe1.

[0039] Example 2

[0040] Preparation method of manganese-substituted goethite powder:

[0041] A. In a polytetrafluoroethylene beaker, 54 mL of 1 mol / L Fe(NO3)3 and 12 mL of 1 mol / L Mn(NO3)2 were mixed to prepare a precursor iron-manganese solution, 72 mL of 8 mol / L KOH ethanol solution was added, and then 600 mL of deionized water was added. The suspension was placed in an oven at 40°C for aging for 30 days to obtain a mixture, during which it was properly stirred for 2 minutes every day;

[0042] B. The mixture obtained in step A is centrifuged, and deionized water is added and the centrifugation operation is repeated until the supernatant is neutral. The bottom solid washed to neutrality is dried, and the dried solid is ground to obtain manganese-substituted goethite powder MnGoe2.

[0043] Example 3

[0044] Preparation method of manganese-substituted goethite powder:

[0045] A. In a polytetrafluoroethylene beaker, 54 mL of 1 mol / L Fe(NO3)3 and 12 mL of 2 mol / L Mn(NO3)2 were mixed to prepare a precursor iron-manganese solution, 72 mL of a 5 mol / L KOH aqueous solution was added, and then 600 mL of deionized water was added. The suspension was placed in an oven at 60°C for aging for 15 days to obtain a mixture, during which time it was properly stirred for 10 minutes every day;

[0046] B. The mixture obtained in step A is centrifuged, and deionized water is added and the centrifugation operation is repeated until the supernatant is neutral. The bottom solid washed to neutrality is dried, and the dried solid is ground to obtain manganese-substituted goethite powder MnGoe3.

[0047] Example 4

[0048] Preparation method of goethite Goe:

[0049] A. In a polytetrafluoroethylene beaker, 54 mL of 1 mol / L Fe(NO3)3 was added to 72 mL of a 5 mol / L KOH aqueous solution, followed by 600 mL of deionized water. The suspension was aged in an oven at 60°C for 15 days, with appropriate stirring for 10 minutes each day.

[0050] B. The mixture obtained in step A is centrifuged, and deionized water is added and the centrifugation operation is repeated until the supernatant is neutral. The bottom solid washed to neutrality is dried, and the dried solid is ground to obtain goethite powder Goe.

[0051] Example 5

[0052] The preparation method of artificial humic acid has the following specific steps:

[0053] (1) Glucose, glycine, and catechol were mixed to obtain a precursor, and the precursor was dissolved in a phosphate buffer solution having a pH of 9 and a concentration of 0.2 mol / L to obtain a mixed solution, wherein the concentration of glucose in the mixed solution was 0.003 mol / L, the concentration of glycine was 0.003 mol / L, and the concentration of catechol was 0.001 mol / L. A preservative, sodium thiomersal, and manganese-substituted goethite powder (prepared in Example 3) were then added to the mixed solution, wherein the mass volume percentage concentration of the preservative was 0.2% g / L, and the concentration of the manganese-substituted goethite powder was 2 g / L. The mixture was shaken at a speed of 150 rpm at a constant temperature of 25° C. for 60 days;

[0054] (2) The product of step (1) was acidified to pH = 1 with 6 mol / L concentrated hydrochloric acid. After standing for 35 minutes, the precipitate and the supernatant were separated by centrifugation. The precipitate was repeatedly washed with dilute hydrochloric acid (0.5 mol / L) until the washing solution was colorless and dried for later use.

[0055] Example 6

[0056] The preparation method of artificial humic acid has the following specific steps:

[0057] (1) Glucose, glycine, and catechol are mixed to obtain a precursor, and the precursor is dissolved in a phosphate buffer having a pH value of 8 and a concentration of 0.2 mol / L to obtain a mixed solution, wherein the concentration of glucose in the mixed solution is 0.002 mol / L, the concentration of glycine is 0.002 mol / L, and the concentration of catechol is 0.0015 mol / L. A preservative, sodium thimerosal, and manganese-substituted goethite powder (prepared in Example 3) are then added to the mixed solution, wherein the mass volume percentage concentration of the preservative is 0.1% g / L, and the concentration of the manganese-substituted goethite powder is 1 g / L. The mixture is shaken at a speed of 155 rpm at 25° C. for 60 days;

[0058] (2) The product of step (1) was acidified to pH = 1 with 6 mol / L concentrated hydrochloric acid. After standing for 30 minutes, the precipitate and the supernatant were separated by centrifugation. The precipitate was repeatedly washed with dilute hydrochloric acid (0.5 mol / L) until the washing solution was colorless and dried for later use.

[0059] Example 7

[0060] The preparation method of artificial humic acid has the following specific steps:

[0061] (1) Glucose, glycine, and catechol are mixed to obtain a precursor, and the precursor is dissolved in a phosphate buffer solution having a pH value of 10 and a concentration of 0.2 mol / L to obtain a mixed solution, wherein the concentration of glucose in the mixed solution is 0.004 mol / L, the concentration of glycine is 0.004 mol / L, and the concentration of catechol is 0.002 mol / L. A preservative, sodium thiomersal, and manganese-substituted goethite powder (prepared in Example 3) are then added to the mixed solution, wherein the mass volume percentage concentration of the preservative is 0.4% g / L, and the concentration of the manganese-substituted goethite powder is 3 g / L. The mixture is shaken at a speed of 160 rpm at a constant temperature of 25° C. for reaction for 80 days;

[0062] (2) The product of step (1) was acidified to pH = 1 with 6 mol / L concentrated hydrochloric acid. After standing for 40 minutes, the precipitate and the supernatant were separated by centrifugation. The precipitate was repeatedly washed with dilute hydrochloric acid (0.5 mol / L) until the washing solution was colorless and dried for later use.

[0063] The manganese-substituted goethite powder prepared in Example 3 in Example 7 was replaced with the manganese-substituted goethite powder prepared in Example 1 and Example 2, and the operations of Example 7 were carried out respectively to prepare different products for use.

[0064] Example 8

[0065] (1) Glucose, glycine, and catechol were mixed to obtain a precursor, and the precursor was dissolved in a phosphate buffer solution with a pH value of 9 and a concentration of 0.2 mol / L to obtain a mixed solution, wherein the concentration of glucose in the mixed solution was 0.004 mol / L, the concentration of glycine was 0.004 mol / L, and the concentration of catechol was 0.002 mol / L. A preservative, sodium thimerosal, and goethite powder (prepared in Example 4) were then added to the mixed solution, wherein the mass volume percentage concentration of the preservative was 0.4% g / L, and the concentration of the goethite powder was 3 g / L. The mixture was shaken at a speed of 160 rpm at a constant temperature of 25° C. for 80 days;

[0066] (2) The product of step (1) was acidified to pH = 1 with 6 mol / L concentrated hydrochloric acid. After standing for 40 minutes, the precipitate and the supernatant were separated by centrifugation. The precipitate was repeatedly washed with dilute hydrochloric acid (0.5 mol / L) until the washing solution was colorless and dried for later use.

[0067] Example 9

[0068] A certain amount of the product of Example 3 was taken and compared with commercial humic acid for dye and heavy metal adsorption performance. The test dyes included but were not limited to direct blue 6, sodium fluorescein, 5-carboxyfluorescein, Congo red, etc., and the test heavy metal system included but was not limited to copper, zinc, cadmium, nickel, etc.

[0069] Example 10

[0070] (1) Rinse the soybean seeds with distilled water, place them evenly in a flower pot with nutrient soil, and germinate them in an artificial climate box at 20-30°C. After the seeds germinate, transplant them into a hydroponic seedling sponge, placing 5-10 seeds in each sponge block. Then, place the hydroponic box in an artificial climate box for cultivation;

[0071] (2) A certain amount of the product of Example 3 was taken, and different amounts of components were added or no components were added for comparison. Five hydroponic samples were set up. After the soybean leaves matured, samples with good growth, regular leaves and representativeness were selected to conduct tests on their physiological and biochemical indicators.

[0072] Figure 1 、 Figure 2 and Figure 3The following are photos of samples prepared with and without manganese solution added in Examples 3 and 4, as well as XRD and FTIR comparison diagrams of the samples. It can be seen from the XRD diagram that the diffraction peaks of manganese-substituted iron ore have changed significantly compared with goethite, where the characteristic peaks at 29.6° and 42.4° correspond to the (111) crystal plane and (221) crystal plane of goethite, respectively. With the increase of the Mn ratio in the initial solution, the diffraction peaks of manganese-substituted iron ore show more obvious displacement, and the color of the mineral becomes darker. These results indicate that manganese has been successfully substituted into goethite. The results of infrared spectroscopy show that at 892.29 cm -1 and 795.55cm -1 The Fe-O(H) peak at 642.72 cm-1 shifts to a higher wavenumber, which is due to the expansion of the hydroxyl group. -1 The peak at 20° moves to a lower wave number because after manganese substitution, the Mn-O bond The bond length is longer than that of Fe-O bond In short, these results indicate that isomorphous substitution occurred during the synthesis of the samples.

[0073] Figure 4 The surface hydroxyl density of the products prepared with and without adding manganese solution in Examples 3 and 4 is compared. The XPS oxygen peak results show that the peak at 531.1 eV corresponding to the surface hydroxyl group is enhanced with the addition of manganese content, which shows that the surface hydroxyl density of the mineral increases.

[0074] Figure 5 The UV spectra of the products prepared by adding and not adding manganese solution in Examples 1, 2, 3, and 4 to catalyze the non-biological humification reaction, that is, the products of Example 7 and Example 8, were compared. Figure 5 It can be seen that manganese-substituted goethite has a better promoting effect than the components promoted by goethite, and the effect increases with the increase of manganese content.

[0075] Figure 6 The Raman spectra of the artificial humic acid and commercial humic acid (McLean Chemical Reagent Co., Ltd., AR) prepared in Example 7 are shown in the figure. The Raman spectra of the two humic acids are basically the same. -1 and 1250cm -1 The presence of miscellaneous peaks nearby may be due to the influence of the benzene ring structure in the sample.

[0076] Figure 7 This is a comparison chart of Example 7 and commercial humic acid in removing dyes and heavy metals in Example 9. Figure 7 It can be seen that the humification products of manganese-substituted goethite have a better degree of humification than those of the goethite-promoting component.

[0077] Figure 8-10This is a test chart of the fresh weight, dry weight, K content, and nitrate content of soybean plants after the hydroponic experiment in Example 10. Figure 8-10 It was shown that after 15 days, the soybean plant component with the most outstanding growth after adding humic acid had an average fresh weight of 1.33 times that of the blank group (without adding humic acid), and the K content and nitrate content were also significantly increased.

[0078] The specific embodiments of the present invention are described in detail above with reference to the accompanying drawings. However, the present invention is not limited to the above embodiments. Various changes can be made within the knowledge of ordinary technicians in this field without departing from the scope of the present invention.

Claims

1. A method for preparing artificial humic acid, characterized in that: The specific steps are as follows: (1) dissolving the precursor in alkaline phosphate buffer, adding a preservative and manganese-substituted goethite powder to the resulting mixture, and shaking the resulting mixture at a constant temperature of 25° C. at a speed of 150-160 rpm for more than 60 days; (2) The product of step (1) is acidified with concentrated hydrochloric acid to pH=1, allowed to stand for 30-40 minutes, and then centrifuged to separate the precipitate and the supernatant. The precipitate is repeatedly washed with dilute hydrochloric acid until the washing liquid is colorless, and then dried to obtain humic acid.

2. The method for preparing artificial humic acid according to claim 1, wherein: The precursor in step (1) is obtained by mixing sugars, amino acids, and polyphenols in a substance ratio of 2:2:1, wherein the sugars are glucose and fructose, the amino acids are glycine and alanine, and the polyphenols are catechol, hydroquinone, and pyrocatechol.

3. The method for preparing artificial humic acid according to claim 1, wherein: The alkaline phosphate buffer in step (1) is a phosphate buffer with a pH value of 8-10 and a concentration of 0.2 mol / L.

4. The method for preparing artificial humic acid according to claim 2, wherein: In the mixed solution of step (1), the sugar concentration is 0.002-0.004 mol / L, the amino acid concentration is 0.002-0.004 mol / L, and the polyphenol concentration is 0.001-0.002 mol / L.

5. The method for preparing artificial humic acid according to claim 1, characterized in that: The preservative in step (1) is sodium thimerosal.

6. The method for preparing artificial humic acid according to claim 1, characterized in that: The mass volume percentage concentration of the preservative in the mixture of step (1) is 0.1-0.4% g / L, and the concentration of the manganese-substituted goethite powder is 1-3 g / L.

7. The method for preparing artificial humic acid according to claim 1, characterized in that: The preparation method of the manganese-substituted goethite powder in step (1) comprises the following specific steps: A. Add the precursor iron-manganese solution to the potassium hydroxide solution and mix well. Add deionized water twice the volume of the mixed solution and age at 40-80°C for 5-30 days to obtain a mixture, stirring every day. B. The mixture obtained in step A is centrifuged, and deionized water is added and the centrifugation operation is repeated until the supernatant is neutral. The bottom solid washed to neutrality is dried, and the dried solid is ground to obtain manganese-substituted goethite powder.

8. The method for preparing artificial humic acid according to claim 7, characterized in that: The precursor iron-manganese solution in step A is prepared by mixing 54 mL of Fe(NO3)3 with a concentration of 0.5-2 mol / L and 12 mL of Mn(NO3)2 with a concentration of 0.5-2 mol / L.

9. The method for preparing artificial humic acid according to claim 8, characterized in that: The solvent of the potassium hydroxide solution in step A is one or more of water, ethanol, ethylene glycol, n-propanol, and isopropanol. The concentration of the potassium hydroxide solution is 2-8 mol / L, and the amount added is 72 mL.

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