Method for extracting fulvic acid from peat soil

Abstract

The invention provides a method for extracting fulvic acid from peat soil, and belongs to the technical field of separation and purification. The method comprises the following steps: firstly, pretreating a peat soil sample, and then sequentially carrying out acidolysis reaction, ultrasonic-assisted extraction, alkali dissolution reaction, high-speed refrigerated centrifugal treatment, activated carbon enrichment treatment, filtration and precipitation, centrifugal separation and washing, drying, grinding, purification and the like. Through ordered cooperation of all the steps, the peat soil structure can be effectively destroyed, fulvic acid is promoted to be fully dissolved out, separated and purified, and the extraction rate and purity of fulvic acid are improved. The method has the advantages that the operation process is closely linked, high efficiency and practicability are achieved, a reliable technical scheme is provided for fulvic acid extraction, and the method has positive significance in related application fields.

Description

Technical Field

[0001] The invention relates to the technical field of separation and purification, and in particular to a method for extracting fulvic acid from peat soil. Background Art

[0002] Fulvic acid is a complex organic mixture widely found in nature and is an important component of humus. It is gradually formed by plant and animal residues through complex physical, chemical and biological processes. The molecular structure of fulvic acid contains a variety of functional groups, such as carboxyl and phenolic hydroxyl groups, which makes it highly chemically active. Its molecular weight distribution range is wide, usually ranging from hundreds to tens of thousands, and it has good water solubility and can exist stably in an aqueous system. Fulvic acid has important application value in many fields. In agriculture, it can improve soil structure, enhance soil water and fertilizer retention capacity, promote plant absorption of nutrients, increase crop yield and quality, and has a certain repair effect on soil contaminated by heavy metals. In the field of medicine, fulvic acid is believed to have anti-inflammatory, detoxification, analgesic, immune regulation and other functions, and has potential application prospects in the treatment of some diseases. In industry, fulvic acid can be used as a metal ion adsorbent for sewage treatment to effectively remove harmful metal ions in wastewater.

[0003] Peat soil is rich in organic matter, which makes it possible to extract fulvic acid. However, traditional methods for extracting fulvic acid often have problems such as low extraction rate, low product purity, complicated operation, high cost and environmental friendliness. For example, in some conventional extraction methods, due to the imprecise control of reaction conditions during acid hydrolysis or alkaline dissolution, fulvic acid cannot be fully released or degraded during the extraction process, affecting the extraction rate and purity. Moreover, the large amount of chemical reagents and complex operating steps used in some extraction processes not only increase costs, but may also cause environmental pollution problems. Therefore, it is of great practical significance to develop an efficient, environmentally friendly and economical method for extracting fulvic acid from peat soil. Summary of the invention

[0004] The object of the present invention is to provide a method for extracting fulvic acid from peat soil, which has better extraction rate and extraction purity.

[0005] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0006] The present invention provides a method for extracting fulvic acid from peat soil, comprising the following steps:

[0007] Pretreatment of peat soil raw materials: collect peat soil samples, remove impurities and sieve to obtain particles, dry and crush into fine powder for later use;

[0008] Acid hydrolysis reaction: prepare hydrochloric acid and nitric acid solutions, place the peat soil fine powder in a reaction container, first add the hydrochloric acid solution to stir the reaction, then add the nitric acid solution to continue stirring the reaction;

[0009] Ultrasonic-assisted extraction: After the acid hydrolysis reaction is completed, the reaction system is subjected to ultrasonic treatment;

[0010] Alkaline dissolution reaction: prepare sodium hydroxide solution, add sodium hydroxide solution to adjust pH value after ultrasonic treatment and stir the reaction;

[0011] High-speed refrigerated centrifugation treatment: the solution after the alkali dissolution reaction is subjected to high-speed refrigerated centrifugation to obtain a supernatant and a precipitate;

[0012] Activated carbon enrichment treatment: After pre-treatment of the activated carbon, the supernatant after high-speed refrigerated centrifugation is mixed and stirred with the activated carbon for enrichment;

[0013] Filtration and precipitation: The activated carbon enriched system is filtered to obtain an activated carbon filter cake, and the filter cake is desorbed and the pH value is adjusted to precipitate fulvic acid and allowed to stand;

[0014] Centrifugal separation and washing: centrifuge the precipitate after standing to obtain fulvic acid precipitate, and wash with deionized water;

[0015] Drying and grinding: The washed fulvic acid precipitate is dried and then ground into fine powder;

[0016] Purification: Use D301 macroporous weak alkaline anion exchange resin for pretreatment and then load it into a chromatography column. Prepare the fulvic acid product into a solution and pass it through the chromatography column. Collect the eluate after washing and elution, adjust the pH value to precipitate the fulvic acid, and then obtain the purified fulvic acid product through centrifugation, washing, drying and grinding.

[0017] Preferably, in the pretreatment of peat soil raw materials, the aperture of the sieve is 4 to 6 mm, the drying temperature is 45 to 55° C., and the drying time is 42 to 54 hours.

[0018] Preferably, in the acid hydrolysis reaction, the concentration of the hydrochloric acid solution is 0.8-1.2 mol / L, the concentration of the nitric acid solution is 0.6-1.0 mol / L, the solid-liquid ratio of the peat soil fine powder to the hydrochloric acid solution is 1:7-1:9, the stirring speed is 120-180 r / min, the stirring reaction time of the hydrochloric acid solution is 1.2-1.8 hours, the stirring reaction time of the nitric acid solution is 1.2-1.8 hours, and the reaction temperature is 45-55°C.

[0019] Preferably, in ultrasound-assisted extraction, the frequency of the ultrasonic generator is 25 to 35 kHz, the power is 400 to 500 W, the ultrasonic treatment temperature is 40 to 50° C., and the ultrasonic treatment time is 40 to 50 minutes.

[0020] Preferably, in the alkaline dissolution reaction, the concentration of the sodium hydroxide solution is 0.6 to 1.0 mol / L, the pH value is adjusted to 8 to 10, and the stirring reaction time is 1.2 to 1.8 hours.

[0021] Preferably, in the high-speed refrigerated centrifugation treatment, the high-speed refrigerated centrifuge is precooled to 3-5°C, the centrifugal speed is 10000-14000 r / min, and the centrifugal time is 15-25 minutes.

[0022] Preferably, in the activated carbon enrichment treatment, the activated carbon is coconut shell activated carbon, and its pretreatment includes soaking in sodium hydroxide solution for 10 to 14 hours, the concentration of the sodium hydroxide solution is 0.4 to 0.6 mol / L, and then soaking in hydrochloric acid solution for 10 to 14 hours, the concentration of the hydrochloric acid solution is 0.4 to 0.6 mol / L, and finally drying at 100 to 110°C for 20 to 28 hours; in the enrichment operation, 4 to 6 g of activated carbon is added to every 100 mL of supernatant, the stirring speed is 80 to 120 r / min, and the stirring time is 1.5 to 2.5 hours.

[0023] Preferably, during filtration and precipitation, the pore size of the filter paper is 0.2-0.4 μm, the concentration of the sodium hydroxide solution during desorption is 0.6-1.0 mol / L, the solid-liquid ratio is 1:4-1:6, the stirring speed is 70-90 r / min, the stirring time is 25-35 minutes, the concentration of the hydrochloric acid solution used to adjust the pH value is 1.2-1.8 mol / L, the pH value is adjusted to 1.2-1.8, the precipitation stirring speed is 70-90 r / min, the stirring time is 40-50 minutes, and the standing time is 15-21 hours.

[0024] Preferably, in the centrifugal separation and washing, the centrifugal speed is 3500-4500 r / min, the centrifugal time is 10-20 minutes, the amount of water used for each washing is 2-3 times the volume of the sediment, and the number of washing times is 2-3 times.

[0025] Preferably, in the drying and grinding, the drying temperature is 55-65°C, the drying time is 15-21 hours, and after grinding, the resin is sieved through a 120-180 mesh sieve; in the purification, the resin is soaked in ethanol for 20-28 hours, the concentration of the hydrochloric acid solution is 0.6-1.0 mol / L, the soaking time is 4-6 hours, the fulvic acid product is prepared into a solution with a mass concentration of 6-10%, the flow rate through the chromatography column is 1-2 mL / min, the concentration of the eluent sodium hydroxide solution is 0.6-1.0 mol / L, the elution flow rate is 1-2 mL / min, the concentration of the hydrochloric acid solution used to adjust the pH value is 1.2-1.8 mol / L, and the pH value is adjusted to 1.2-1.8.

[0026] Technical effects and advantages of the present invention:

[0027] The peat soil raw material pretreatment method is combined with subsequent acid hydrolysis, alkali dissolution and other reaction steps to achieve a good synergistic effect. After collecting peat soil samples, the impurities are carefully removed, the particles with uniform particle size are screened, dried to a suitable moisture content and crushed into fine powder. The pretreatment operation provides an ideal raw material basis for subsequent reactions. This allows the peat soil to be more fully contacted with the prepared hydrochloric acid and nitric acid solutions in the subsequent acid hydrolysis reaction, the peat soil structure is more effectively destroyed, and fulvic acid is more easily dissociated from the complex organic-inorganic complex into the solution. In the alkaline dissolution reaction, the pretreated peat soil fine powder can better interact with the prepared sodium hydroxide solution. Under suitable pH values ​​and stirring conditions, the acidic functional groups of the fulvic acid molecules are fully ionized, and their solubility is enhanced, thereby smoothly transferring from the solid phase to the liquid phase. This close combination of raw material pretreatment and reaction steps improves the extraction efficiency of fulvic acid as a whole and helps to improve the extraction rate.

[0028] The acid hydrolysis reaction is combined with ultrasound-assisted extraction. On the basis of the initial dissociation of fulvic acid by acid hydrolysis reaction, ultrasound-assisted extraction utilizes the local high temperature and high pressure and strong mechanical disturbance generated by the cavitation effect of ultrasound to further break up the peat soil particles, accelerate the dissolution of fulvic acid molecules, promote the diffusion and mass transfer process between molecules, and make fulvic acid dissolve into the solution faster and more completely, effectively improving the extraction rate of fulvic acid.

[0029] The alkaline dissolution reaction and high-speed refrigerated centrifugation treatment work synergistically. After the alkaline dissolution reaction enhances the solubility of fulvic acid, the high-speed refrigerated centrifugation treatment runs at high speed under a low-temperature environment, which can quickly and effectively separate impurities and unreacted substances in the solution, reduce the interference of impurities on the extraction of fulvic acid, and at the same time, the low-temperature environment maintains the stability of fulvic acid, avoiding its degradation or property changes during the centrifugation process, providing a purer solution for subsequent activated carbon enrichment, which is beneficial to improve the final extraction rate and purity of fulvic acid.

[0030] The activated carbon enrichment treatment is combined with the resin chromatography in the purification step. The activated carbon enrichment treatment utilizes the developed pore structure of the activated carbon to selectively adsorb fulvic acid, initially increasing the concentration of fulvic acid and removing some impurities. Chromatography is then performed through anion exchange resin. The selective adsorption and desorption of the resin with fulvic acid and impurity ions can deeply remove residual impurity ions and further improve the purity of fulvic acid. The combination of the two achieves efficient purification of fulvic acid.

[0031] In the present invention, starting from the pretreatment of peat soil raw materials, a series of continuous processing steps such as acid hydrolysis, ultrasound, alkali dissolution, high-speed refrigerated centrifugation, activated carbon enrichment, filtration and precipitation, centrifugal separation and washing, drying and grinding, and purification are sequentially performed, and each step is closely connected, and the product of the previous step is directly processed as the raw material of the next step. This continuous operation process reduces the sample transfer and processing time in the intermediate links, avoids the loss and contamination of samples during multiple transfers, simplifies the overall operation process, improves the efficiency of extracting fulvic acid from peat soil, and enables the entire extraction process to be carried out efficiently and orderly, which is conducive to large-scale application in industrial production. DETAILED DESCRIPTION

[0032] In the present invention, high-speed refrigerated centrifugation can utilize the strong centrifugal force generated by high-speed rotation under low temperature environment to quickly and effectively precipitate and separate impurities, unreacted substances, and macromolecular substances that may affect the extraction of fulvic acid in the solution. Compared with traditional normal temperature centrifugation, it can better maintain the activity and stability of fulvic acid and reduce the decomposition or denaturation of fulvic acid caused by temperature increase. This is because at low temperatures, the molecular structure of fulvic acid is more stable and less susceptible to interference from external factors. At the same time, high-speed centrifugal force can more thoroughly separate impurities from fulvic acid, making the subsequent extraction process more efficient.

[0033] In the present invention, the activated carbon has a highly developed pore structure and a huge specific surface area, and has a strong adsorption capacity for fulvic acid. The pretreated activated carbon can selectively adsorb fulvic acid, so that it is enriched on the surface of the activated carbon. In the desorption process, the use of a sodium hydroxide solution of an appropriate concentration can efficiently desorb fulvic acid from the activated carbon, further increasing the concentration of fulvic acid.

[0034] The technical solutions provided by the present invention are described in detail below in conjunction with the embodiments, but they should not be construed as limiting the protection scope of the present invention.

[0035] Example 1

[0036] Peat soil raw material pretreatment

[0037] Collect an appropriate amount of fresh peat soil sample and carefully remove impurities such as stones and plant roots. Pass the peat soil through a 5mm sieve to obtain peat soil particles with uniform particle size. Dry the screened peat soil particles in a 50℃ oven for 48 hours until the moisture content is less than 10%. Then, use a crusher to crush the dried peat soil into fine powder and store it for later use.

[0038] Acid hydrolysis reaction

[0039] Take an appropriate amount of concentrated hydrochloric acid (analytical grade), slowly add it to deionized water, stir evenly, prepare a hydrochloric acid solution with a concentration of 1mol / L, and cool to room temperature. Take an appropriate amount of concentrated nitric acid (analytical grade), slowly add it to deionized water, stir evenly, prepare a nitric acid solution with a concentration of 0.8mol / L, and cool to room temperature. Accurately weigh 150g of crushed peat soil fine powder and place it in a 1500mL three-necked flask. According to the solid-liquid ratio of 1:8 (g / mL), first add the hydrochloric acid solution, and stir the reaction for 1.5 hours at a stirring speed of 150r / min. Then add the nitric acid solution and continue stirring the reaction for 1.5 hours. The reaction temperature is controlled at 50°C.

[0040] Ultrasound-assisted extraction

[0041] An ultrasonic generator with a frequency of 30 kHz and a power of 450 W was selected and connected to the reaction device. After the acid hydrolysis reaction was completed, the reaction system was placed in the ultrasonic generator and ultrasonically treated at 45°C for 45 minutes.

[0042] Alkaline dissolution reaction

[0043] Weigh an appropriate amount of sodium hydroxide solid (analytical grade) and dissolve it in deionized water, stir until completely dissolved, prepare a sodium hydroxide solution with a concentration of 0.8 mol / L, and cool to room temperature. After the ultrasonic treatment is completed, cool the reaction system to room temperature, slowly add sodium hydroxide solution under stirring conditions, and adjust the pH value of the solution to 9. After adding the alkali solution, continue stirring the reaction for 1.5 hours to fully dissolve the fulvic acid.

[0044] High-speed refrigerated centrifugation

[0045] Preparation

[0046] Precool a high-speed refrigerated centrifuge to 4 °C.

[0047] Centrifugal operation

[0048] Transfer the solution after the alkaline dissolution reaction to a pre-cooled centrifuge tube, balance it, and put it into a high-speed refrigerated centrifuge, maintain the condition of 4°C, set the centrifugal speed to 12000r / min, and the centrifugal time to 20 minutes. After the centrifugation is completed, carefully remove the centrifuge tube, and the solution is now divided into two parts: supernatant and precipitate.

[0049] Activated carbon enrichment treatment

[0050] Activated carbon pretreatment

[0051] Take coconut shell activated carbon, rinse it with deionized water to remove surface impurities, and then soak the activated carbon in a sodium hydroxide solution with a concentration of 0.5 mol / L for 12 hours to remove acidic impurities on the surface of the activated carbon.

[0052] After soaking, rinse with deionized water until neutral, and then soak the activated carbon in a hydrochloric acid solution with a concentration of 0.5 mol / L for 12 hours to remove alkaline impurities.

[0053] Finally, rinse with deionized water until neutral, dry in an oven at 105°C for 24 hours and set aside.

[0054] Enrichment operation

[0055] The supernatant after high-speed refrigerated centrifugation was transferred to a container containing pre-treated activated carbon.

[0056] Activated carbon was added at a ratio of 5 g activated carbon per 100 mL supernatant.

[0057] At room temperature, the mixture was stirred at a stirring speed of 100 r / min for 2 hours to allow the fulvic acid to be fully adsorbed on the activated carbon.

[0058] Filtration and sedimentation

[0059] 1. Filter

[0060] A vacuum filtration device is used for filtration, and filter paper with a pore size of 0.3 μm is selected as the filtration medium to obtain an activated carbon filter cake adsorbed with fulvic acid.

[0061] 2. Desorption and precipitation

[0062] The activated carbon filter cake was transferred to another container, and an appropriate amount of 0.8 mol / L sodium hydroxide solution was added and mixed at a solid-liquid ratio of 1:5 (g / mL).

[0063] The mixture was stirred at a stirring speed of 80 r / min for 30 minutes to desorb fulvic acid from the activated carbon.

[0064] Slowly add 1.5 mol / L hydrochloric acid solution to the desorbed solution, adjust the pH value to 1.5, stir for 45 minutes at a stirring speed of 80 r / min to precipitate fulvic acid again, and after precipitation, let it stand for 18 hours.

[0065] Centrifugation and washing

[0066] The precipitate after standing was transferred to a centrifuge tube and centrifuged in a centrifuge at a speed of 4000 r / min for 15 minutes to obtain a fulvic acid precipitate. The fulvic acid precipitate was washed with deionized water, each time using 2.5 times the volume of the precipitate, and washed twice to remove impurity ions in the precipitate.

[0067] Drying and grinding

[0068] The washed fulvic acid precipitate was dried in a vacuum drying oven at 60°C for 18 hours to obtain a crude fulvic acid product. The dried crude fulvic acid product was ground into fine powder using a mortar and passed through a 150-mesh sieve to obtain a fulvic acid finished product.

[0069] purification

[0070] Select D301 macroporous weakly alkaline anion exchange resin, soak the resin in ethanol for 24 hours, and then rinse with deionized water until there is no alcohol taste. Then soak the resin in hydrochloric acid solution (concentration of 0.8mol / L) for 5 hours, and then rinse with deionized water until the pH value is neutral. The treated resin is loaded into the chromatography column, and the resin filling height is 3 / 4 of the column height. The fulvic acid finished product is prepared into a solution with a mass concentration of 8% with deionized water, and passed through the chromatography column at a flow rate of 1.5mL / min. Then rinse the chromatography column with deionized water until no impurity ions are detected in the effluent. Finally, a sodium hydroxide solution with a concentration of 0.8mol / L is used as an eluent, and the fulvic acid is eluted at a flow rate of 1.5mL / min, and the eluate is collected. The eluate is adjusted to a pH value of 1.5 with a hydrochloric acid solution to precipitate the fulvic acid. The precipitate is treated according to the above steps of centrifugation, washing, drying and grinding to obtain a purified fulvic acid product.

[0071] Example 2

[0072] 1. Pretreatment of peat soil raw materials

[0073] Collect an appropriate amount of fresh peat soil sample and carefully remove impurities such as stones and plant roots. Pass the peat soil through a 4mm sieve to obtain peat soil particles with uniform particle size. Dry the screened peat soil particles in a 55℃ oven for 42 hours until the moisture content is less than 10%. Then, use a crusher to crush the dried peat soil into fine powder and store it for later use.

[0074] 2. Acid hydrolysis reaction

[0075] Take an appropriate amount of concentrated hydrochloric acid (analytical grade), slowly add it to deionized water, stir evenly, prepare a hydrochloric acid solution with a concentration of 1.2 mol / L, and cool to room temperature. Take an appropriate amount of concentrated nitric acid (analytical grade), slowly add it to deionized water, stir evenly, prepare a nitric acid solution with a concentration of 0.7 mol / L, and cool to room temperature. Accurately weigh 180g of crushed peat soil fine powder and place it in a 1800mL three-necked flask. According to the solid-liquid ratio of 1:7 (g / mL), first add the hydrochloric acid solution, and stir the reaction at a stirring speed of 180r / min for 1.2 hours. Then add the nitric acid solution and continue stirring the reaction for 1.3 hours. The reaction temperature is controlled at 52°C.

[0076] 3. Ultrasound-assisted extraction

[0077] An ultrasonic generator with a frequency of 32 kHz and a power of 500 W was selected and connected to the reaction device. After the acid hydrolysis reaction was completed, the reaction system was placed in the ultrasonic generator and ultrasonically treated at 48°C for 40 minutes.

[0078] 4. Alkali dissolution reaction

[0079] Weigh an appropriate amount of sodium hydroxide solid (analytical grade) and dissolve it in deionized water, stir until completely dissolved, prepare a sodium hydroxide solution with a concentration of 0.7 mol / L, and cool to room temperature. After the ultrasonic treatment is completed, cool the reaction system to room temperature, slowly add sodium hydroxide solution under stirring conditions, and adjust the pH value of the solution to 9.5. After adding the alkali solution, continue stirring the reaction for 1.2 hours to fully dissolve the fulvic acid.

[0080] 5. High-speed refrigerated centrifugation

[0081] Precool the high-speed refrigerated centrifuge to 5°C. Transfer the solution after the alkaline dissolution reaction to the precooled centrifuge tube, balance it and put it into the high-speed refrigerated centrifuge, maintain the condition of 5°C, set the centrifugal speed to 13000r / min, and the centrifugal time to 18 minutes. After the centrifugation is completed, carefully remove the centrifuge tube. At this time, the solution is divided into two parts: supernatant and precipitate.

[0082] 6. Activated carbon enrichment treatment

[0083] Take coconut shell activated carbon, rinse it with deionized water to remove surface impurities, and then soak the activated carbon in a sodium hydroxide solution with a concentration of 0.6mol / L for 10 hours to remove acidic impurities on the surface of the activated carbon. After soaking, rinse it with deionized water until neutral, and then soak the activated carbon in a hydrochloric acid solution with a concentration of 0.6mol / L for 10 hours to remove alkaline impurities. Finally, rinse it with deionized water until neutral, dry it in an oven at 110℃ for 22 hours, and set aside. Transfer the supernatant after high-speed frozen centrifugation to a container containing pretreated activated carbon. Add activated carbon at a ratio of 6g activated carbon per 100mL supernatant. Stir at room temperature at a stirring speed of 120r / min for 1.5 hours to allow fulvic acid to be fully adsorbed on the activated carbon.

[0084] 7. Filtration and precipitation

[0085] The vacuum filtration device was used for filtration, and the filter medium was a filter paper with a pore size of 0.25 μm, to obtain an activated carbon filter cake adsorbed with fulvic acid. The activated carbon filter cake was transferred to another container, and an appropriate amount of sodium hydroxide solution with a concentration of 0.7 mol / L was added, and mixed according to a solid-liquid ratio of 1:6 (g / mL). Stir for 25 minutes at a stirring speed of 90 r / min to desorb fulvic acid from the activated carbon. Slowly add a hydrochloric acid solution with a concentration of 1.3 mol / L to the desorbed solution, adjust the pH value to 1.3, and stir for 40 minutes at a stirring speed of 90 r / min to precipitate the fulvic acid again. After precipitation, let it stand for 16 hours.

[0086] 8. Centrifugation and washing

[0087] The precipitate after standing was transferred to a centrifuge tube and centrifuged in a centrifuge at a speed of 4500 r / min for 13 minutes to obtain a fulvic acid precipitate. The fulvic acid precipitate was washed with deionized water, each time using 3 times the volume of the precipitate, and washed twice to remove impurity ions in the precipitate.

[0088] 9. Drying and grinding

[0089] The washed fulvic acid precipitate was dried in a vacuum drying oven at 65°C for 16 hours to obtain a crude fulvic acid product. The dried crude fulvic acid product was ground into fine powder using a mortar and passed through a 180-mesh sieve to obtain a fulvic acid finished product.

[0090] 10. Purification

[0091] Select D301 macroporous weakly alkaline anion exchange resin, soak the resin in ethanol for 24 hours, and then rinse with deionized water until there is no alcohol taste. Then soak the resin in hydrochloric acid solution (concentration of 0.7mol / L) for 6 hours, and then rinse with deionized water until the pH value is neutral. The treated resin is loaded into the chromatography column, and the resin filling height is 3 / 4 of the column height. The fulvic acid finished product is prepared into a solution with a mass concentration of 7% with deionized water, and passed through the chromatography column at a flow rate of 2mL / min. Then rinse the chromatography column with deionized water until no impurity ions are detected in the effluent. Finally, a sodium hydroxide solution with a concentration of 0.7mol / L is used as an eluent to elute fulvic acid at a flow rate of 2mL / min, and the eluate is collected. The eluate is adjusted to a pH value of 1.3 with a hydrochloric acid solution to precipitate fulvic acid. The precipitate is treated according to the above steps of centrifugation, washing, drying and grinding to obtain a purified fulvic acid product.

[0092] Example 3

[0093] 1. Pretreatment of peat soil raw materials

[0094] Collect an appropriate amount of fresh peat soil sample and carefully remove impurities such as stones and plant roots. Pass the peat soil through a 6mm sieve to obtain peat soil particles with uniform particle size. Dry the screened peat soil particles in a 48℃ oven for 50 hours until the moisture content is less than 10%. Then, use a crusher to crush the dried peat soil into fine powder and store it for later use.

[0095] 2. Acid hydrolysis reaction

[0096] Take an appropriate amount of concentrated hydrochloric acid (analytical grade), slowly add it to deionized water, stir evenly, prepare a hydrochloric acid solution with a concentration of 0.9 mol / L, and cool to room temperature. Take an appropriate amount of concentrated nitric acid (analytical grade), slowly add it to deionized water, stir evenly, prepare a nitric acid solution with a concentration of 0.9 mol / L, and cool to room temperature. Accurately weigh 130g of crushed peat soil fine powder and place it in a 1300mL three-necked flask. According to the solid-liquid ratio of 1:9 (g / mL), first add the hydrochloric acid solution, and stir the reaction for 1.8 hours at a stirring speed of 130r / min. Then add the nitric acid solution and continue stirring the reaction for 1.2 hours. The reaction temperature is controlled at 48°C.

[0097] 3. Ultrasound-assisted extraction

[0098] An ultrasonic generator with a frequency of 28 kHz and a power of 400 W was selected and connected to the reaction device. After the acid hydrolysis reaction was completed, the reaction system was placed in the ultrasonic generator and ultrasonically treated at 42°C for 50 minutes.

[0099] 4. Alkali dissolution reaction

[0100] Weigh an appropriate amount of sodium hydroxide solid (analytical grade) and dissolve it in deionized water, stir until completely dissolved, prepare a sodium hydroxide solution with a concentration of 0.9 mol / L, and cool to room temperature. After the ultrasonic treatment is completed, cool the reaction system to room temperature, slowly add sodium hydroxide solution under stirring conditions, and adjust the pH value of the solution to 8.5. After adding the alkali solution, continue stirring the reaction for 1.8 hours to fully dissolve the fulvic acid.

[0101] 5. High-speed refrigerated centrifugation

[0102] Precool the high-speed refrigerated centrifuge to 3°C. Transfer the solution after the alkaline dissolution reaction to a precooled centrifuge tube, balance it and put it into a high-speed refrigerated centrifuge, maintain the condition of 3°C, set the centrifuge speed to 11000r / min, and the centrifuge time to 22 minutes. After the centrifugation is completed, carefully remove the centrifuge tube. At this time, the solution is divided into two parts: supernatant and precipitate.

[0103] 6. Activated carbon enrichment treatment

[0104] Take coconut shell activated carbon, rinse it with deionized water to remove surface impurities, and then soak the activated carbon in a sodium hydroxide solution with a concentration of 0.4mol / L for 14 hours to remove acidic impurities on the surface of the activated carbon. After soaking, rinse it with deionized water until neutral, and then soak the activated carbon in a hydrochloric acid solution with a concentration of 0.4mol / L for 14 hours to remove alkaline impurities. Finally, rinse it with deionized water until neutral, dry it in an oven at 100℃ for 26 hours, and set it aside. Transfer the supernatant after high-speed frozen centrifugation to a container containing pretreated activated carbon. Add activated carbon at a ratio of 4g activated carbon per 100mL supernatant. Stir at room temperature at a stirring speed of 80r / min for 2.5 hours to allow fulvic acid to be fully adsorbed on the activated carbon.

[0105] 7. Filtration and precipitation

[0106] The vacuum filtration device was used for filtration, and the filter medium was a filter paper with a pore size of 0.35 μm, to obtain an activated carbon filter cake adsorbed with fulvic acid. The activated carbon filter cake was transferred to another container, and an appropriate amount of sodium hydroxide solution with a concentration of 0.9 mol / L was added, and mixed according to a solid-liquid ratio of 1:4 (g / mL). Stir for 35 minutes at a stirring speed of 70 r / min to desorb fulvic acid from the activated carbon. Slowly add a hydrochloric acid solution with a concentration of 1.7 mol / L to the desorbed solution, adjust the pH value to 1.7, and stir for 50 minutes at a stirring speed of 70 r / min to precipitate the fulvic acid again. After precipitation, let it stand for 20 hours.

[0107] 8. Centrifugation and washing

[0108] The precipitate after standing was transferred to a centrifuge tube and centrifuged in a centrifuge at a speed of 3500 r / min for 18 minutes to obtain a fulvic acid precipitate. The fulvic acid precipitate was washed with deionized water, with the amount of water used each time being twice the volume of the precipitate, and washed three times to remove impurity ions in the precipitate.

[0109] 9. Drying and grinding

[0110] The washed fulvic acid precipitate was dried in a vacuum drying oven at 55°C for 20 hours to obtain a crude fulvic acid product. The dried crude fulvic acid product was ground into fine powder using a mortar and passed through a 120-mesh sieve to obtain a fulvic acid finished product.

[0111] 10. Purification

[0112] Select D301 macroporous weakly alkaline anion exchange resin, soak the resin in ethanol for 24 hours, and then rinse with deionized water until there is no alcohol taste. Then soak the resin in hydrochloric acid solution (concentration of 0.9mol / L) for 4 hours, and then rinse with deionized water until the pH value is neutral. The treated resin is loaded into the chromatography column, and the resin filling height is 3 / 4 of the column height. The fulvic acid finished product is prepared into a solution with a mass concentration of 9% with deionized water, and passed through the chromatography column at a flow rate of 1mL / min. Then rinse the chromatography column with deionized water until no impurity ions are detected in the effluent. Finally, a sodium hydroxide solution with a concentration of 0.9mol / L is used as an eluent to elute fulvic acid at a flow rate of 1mL / min, and the eluate is collected. The eluate is adjusted to a pH of 1.7 with a hydrochloric acid solution to precipitate fulvic acid. The precipitate is treated according to the above steps of centrifugation, washing, drying and grinding to obtain a purified fulvic acid product.

[0113] Experimental example

[0114] The extraction rate and purity of fulvic acid extracted from peat soil in Example 1 were tested to evaluate the effect of the extraction method.

[0115] Determination of fulvic acid extraction rate

[0116] Accurately weigh a certain mass (m1, accurate to 0.0001g) of peat soil raw material and record its mass. Assume that the mass of the peat soil raw material weighed m1 = 250.0013g.

[0117] According to the method of Example 1, the fulvic acid extraction operation is performed to obtain the fulvic acid product, and the mass of the fulvic acid product is accurately weighed (m2, accurate to 0.0001g). Assume that the mass of the fulvic acid product obtained is m2 = 102.5032g.

[0118] The calculation formula of fulvic acid extraction rate: extraction rate = (m2 / m1) × 100%. Then fulvic acid extraction rate = (102.5032 / 250.0013) × 100% ≈ 41.00%.

[0119] Determination of fulvic acid purity (potassium dichromate oxidation-titration method)

[0120] Solution Preparation Accurately weigh a certain amount (about 0.2 g, accurate to 0.0001 g) of the fulvic acid product obtained in Example 1, place it in a 250 mL conical flask, add 50 mL of deionized water, and stir to dissolve it. Assume that the mass of the fulvic acid sample weighed is m=0.2015 g.

[0121] Prepare 0.1 mol / L potassium dichromate standard solution: accurately weigh a certain mass (accurate to 0.0001 g) of potassium dichromate (analytical grade), place it in a 100 mL volumetric flask, dissolve it with deionized water and make up to the scale.

[0122] Prepare 0.1mol / L ammonium ferrous sulfate standard solution: weigh a certain mass (accurate to 0.0001g) of ammonium ferrous sulfate, dissolve it in an appropriate amount of water, add 5mL of concentrated sulfuric acid, transfer it to a 500mL volumetric flask after cooling, and dilute it to the scale with deionized water. Before use, calibrate it with potassium dichromate standard solution. Assume that the concentration of the calibrated ammonium ferrous sulfate standard solution is C = 0.1005mol / L.

[0123] Prepare indicator solution: weigh 1.485 g of o-phenanthroline and 0.695 g of ferrous sulfate, dissolve in 100 mL of water, and shake well.

[0124] Oxidation reaction: Add 10 mL of concentrated sulfuric acid to the conical flask containing fulvic acid solution, shake well, and cool to room temperature. Then accurately add 10 mL of 0.1 mol / L potassium dichromate standard solution, place the conical flask in a boiling water bath and heat for 30 minutes to fully oxidize the fulvic acid.

[0125] Titration operation: After the oxidation reaction is completed, take out the conical flask and cool it to room temperature. Rinse the flask wall with 50mL of deionized water, add 3 drops of indicator solution, and titrate with 0.1mol / L ammonium ferrous sulfate standard solution until the solution changes from orange-red to light green as the end point, and record the volume of ammonium ferrous sulfate standard solution consumed (V1, mL). Assume that the volume of ammonium ferrous sulfate standard solution consumed by the sample titration is V1 = 9.52mL.

[0126] At the same time, a blank experiment was performed: no fulvic acid sample was added, other operation steps were the same, and the volume of ammonium ferrous sulfate standard solution consumed (V0, mL) was recorded. Assume that the volume of ammonium ferrous sulfate standard solution consumed in the blank experiment is V0 = 24.85 mL.

[0127] Purity calculation: Calculate the purity of fulvic acid according to the following formula:

[0128] Fulvic acid purity (%) = [(V0-V1) × C × 0.003 × 100] / m

[0129] Wherein, C is the concentration of the ammonium ferrous sulfate standard solution (mol / L), 0.003 is the mass of fulvic acid in grams equivalent to 1.00 mL of 0.1 mol / L ammonium ferrous sulfate standard solution, and m is the mass of the weighed fulvic acid sample (g).

[0130] Fulvic acid purity (%) = [(24.85-9.52) × 0.1005 × 0.003 × 100] / 0.2015 ≈ 91.20%.

[0131] Experimental results and analysis

[0132] Extraction rate results

[0133] The extraction rate is 41.00%.

[0134] Purity results

[0135] The purity reaches 91.20%, indicating that the fulvic acid product extracted by the present invention has a high purity.

[0136] It can be seen from the above embodiments that the present invention creates good conditions for subsequent reactions by pre-treating the peat soil raw materials by screening, drying, crushing, etc., so that the raw materials are more reactive to promote the release of fulvic acid; the type, concentration, dosage, and reaction conditions of the acid in the acidolysis reaction are accurately controlled to effectively dissociate the fulvic acid in the peat soil, and then the ultrasonic cavitation effect is used to accelerate the crushing of the peat soil and the dissolution of fulvic acid, and then the alkaline environment is created by reasonably allocating alkali solution to enhance the solubility of fulvic acid, which is conducive to its transfer to the liquid phase, and then the high-speed refrigerated centrifugation is used to remove impurities and stabilize and the activated carbon is enriched to increase the fulvic acid concentration. The synergistic mode further improves the extraction rate, and at the same time, each reaction step is accurately controlled to reduce side reactions and impurity generation to ensure purity from the source, and after the activated carbon pretreatment, some impurities are removed during the adsorption of fulvic acid for preliminary purification, and finally, the residual impurities are effectively removed by D301 macroporous weak alkaline anion exchange resin chromatography, and each link is closely coordinated to successfully achieve a significant improvement in the extraction rate and purity of fulvic acid, providing an effective method for the efficient preparation of fulvic acid.

[0137] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for extracting fulvic acid from peat soil, characterized in that: The following steps are involved: Pretreatment of peat soil raw materials: collect peat soil samples, remove impurities and sieve to obtain particles, dry and crush into fine powder for later use; Acid hydrolysis reaction: prepare hydrochloric acid and nitric acid solutions, place the peat soil fine powder in a reaction container, first add the hydrochloric acid solution to stir the reaction, then add the nitric acid solution to continue stirring the reaction; Ultrasonic-assisted extraction: After the acid hydrolysis reaction is completed, the reaction system is subjected to ultrasonic treatment; Alkaline dissolution reaction: prepare sodium hydroxide solution, add sodium hydroxide solution to adjust pH value after ultrasonic treatment and stir the reaction; High-speed refrigerated centrifugation treatment: the solution after the alkali dissolution reaction is subjected to high-speed refrigerated centrifugation to obtain a supernatant and a precipitate; Activated carbon enrichment treatment: After pre-treatment of the activated carbon, the supernatant after high-speed refrigerated centrifugation is mixed and stirred with the activated carbon for enrichment; Filtration and precipitation: The activated carbon enriched system is filtered to obtain an activated carbon filter cake, and the filter cake is desorbed and the pH value is adjusted to precipitate fulvic acid and allowed to stand; Centrifugal separation and washing: centrifuge the precipitate after standing to obtain fulvic acid precipitate, and wash with deionized water; Drying and grinding: The washed fulvic acid precipitate is dried and then ground into fine powder; Purification: Use D301 macroporous weak alkaline anion exchange resin for pretreatment and then load it into a chromatography column. Prepare the fulvic acid product into a solution and pass it through the chromatography column. Collect the eluate after washing and elution, adjust the pH value to precipitate the fulvic acid, and then obtain the purified fulvic acid product through centrifugation, washing, drying and grinding.

2. The method for extracting fulvic acid from peat soil according to claim 1, characterized in that: In the pretreatment of peat soil raw materials, the aperture of the sieve is 4 to 6 mm, the drying temperature is 45 to 55° C., and the drying time is 42 to 54 hours.

3. The method for extracting fulvic acid from peat soil according to claim 1, characterized in that: In the acidolysis reaction, the concentration of the hydrochloric acid solution is 0.8-1.2 mol / L, the concentration of the nitric acid solution is 0.6-1.0 mol / L, the solid-liquid ratio of the peat soil fine powder to the hydrochloric acid solution is 1:7-1:9, the stirring speed is 120-180 r / min, the stirring reaction time of the hydrochloric acid solution is 1.2-1.8 hours, the stirring reaction time of the nitric acid solution is 1.2-1.8 hours, and the reaction temperature is 45-55°C.

4. The method for extracting fulvic acid from peat soil according to claim 1, characterized in that: In the ultrasonic-assisted extraction, the frequency of the ultrasonic generator is 25 to 35 kHz, the power is 400 to 500 W, the ultrasonic treatment temperature is 40 to 50° C., and the ultrasonic treatment time is 40 to 50 minutes.

5. The method for extracting fulvic acid from peat soil according to claim 1, characterized in that: In the alkaline dissolution reaction, the concentration of the sodium hydroxide solution is 0.6-1.0 mol / L, the pH value is adjusted to 8-10, and the stirring reaction time is 1.2-1.8 hours.

6. The method for extracting fulvic acid from peat soil according to claim 1, characterized in that: In the high-speed refrigerated centrifugation process, the high-speed refrigerated centrifuge is precooled to 3-5° C., the centrifugal speed is 10000-14000 r / min, and the centrifugal time is 15-25 minutes.

7. The method for extracting fulvic acid from peat soil according to claim 1, characterized in that: In the activated carbon enrichment treatment, the activated carbon is coconut shell activated carbon, and its pretreatment includes soaking in sodium hydroxide solution for 10 to 14 hours, the concentration of the sodium hydroxide solution is 0.4 to 0.6 mol / L, and then soaking in hydrochloric acid solution for 10 to 14 hours, the concentration of the hydrochloric acid solution is 0.4 to 0.6 mol / L, and finally drying temperature is 100 to 110°C, and the drying time is 20 to 28 hours; in the enrichment operation, 4 to 6 g of activated carbon is added to every 100 mL of supernatant, the stirring speed is 80 to 120 r / min, and the stirring time is 1.5 to 2.5 hours.

8. The method for extracting fulvic acid from peat soil according to claim 1, characterized in that: In the filtration and precipitation, the pore size of the filter paper is 0.2-0.4 μm, the concentration of the sodium hydroxide solution during desorption is 0.6-1.0 mol / L, the solid-liquid ratio is 1:4-1:6, the stirring speed is 70-90 r / min, the stirring time is 25-35 minutes, the concentration of the hydrochloric acid solution used to adjust the pH value is 1.2-1.8 mol / L, the pH value is adjusted to 1.2-1.8, the precipitation stirring speed is 70-90 r / min, the stirring time is 40-50 minutes, and the standing time is 15-21 hours.

9. The method for extracting fulvic acid from peat soil according to claim 1, characterized in that: In the centrifugal separation and washing, the centrifugal speed is 3500-4500 r / min, the centrifugal time is 10-20 minutes, the amount of water used for each washing is 2-3 times the volume of the sediment, and the washing times are 2-3 times.

10. The method for extracting fulvic acid from peat soil according to claim 1, characterized in that: During the drying and grinding, the drying temperature is 55-65°C, the drying time is 15-21 hours, and the resin is sieved with 120-180 mesh after grinding; during the purification, the resin is soaked in ethanol for 20-28 hours, the concentration of the hydrochloric acid solution is 0.6-1.0 mol / L, and the soaking time is 4-6 hours. The fulvic acid product is prepared into a solution with a mass concentration of 6-10%, and the flow rate through the chromatography column is 1-2 mL / min, the concentration of the eluent sodium hydroxide solution is 0.6-1.0 mol / L, the elution flow rate is 1-2 mL / min, the concentration of the hydrochloric acid solution used to adjust the pH value is 1.2-1.8 mol / L, and the pH value is adjusted to 1.2-1.8.