Slow-release-repair gel beads based on lignin charcoal-humic acid composite material and preparation method and application thereof

Abstract

The present application relates to the technical field of composite gel bead preparation, in particular to a slow-release-repair gel bead based on a lignin charcoal-humic acid composite material and a preparation method and application thereof, comprising: dispersing sodium lignosulfonate charcoal powder in a humic acid solution, drying to obtain a lignin biochar@humic acid composite material; using sodium alginate as a carrier, mixing the lignin biochar@humic acid composite material, ammonium bicarbonate and the carrier, then dropping into a calcium ion-containing solution, cross-linking to form gel beads, and sequentially filtering, washing and freeze-drying to obtain a slow-release-repair gel bead based on a lignin charcoal-humic acid composite material. The slow-release-repair gel bead based on the lignin charcoal-humic acid composite material can significantly improve the heavy metal adsorption and fixation efficiency, has the advantages of pH response intelligent slow release, improved soil physical and chemical properties, stable structure, environmental friendliness, adaptability, one material with multiple effects, low cost and high efficiency, and overcomes the defects of the prior art.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of composite gel bead preparation, in particular to a slow-release-repair gel bead based on a lignin charcoal-humic acid composite material and a preparation method and application thereof. BACKGROUND

[0002] Currently, the technical means for soil heavy metal pollution repair and nutrient slow release mainly include biochar adsorption, mineral fixation, chemical improvement, acid-base conditioning, and polymer hydrogel slow release method. These methods have adsorption or fixation effect on Pb 2+ , Cu 2+ pollutants, and can slowly release part of the nutrients, but generally face the problems of single function, low application efficiency, poor stability, and weak environmental adaptability. For example, traditional biochar is mostly in powder state, which is easy to migrate to non-target areas with water after being applied to soil, resulting in short action time and decreased adsorption efficiency. At the same time, the compact structure and limited specific surface area of biochar lead to insufficient loading capacity and adsorption activity for heavy metals. Although polymer slow-release materials have some advantages in nutrient regulation, their repair effect on heavy metals is limited, and their release behavior is unstable in acidic environment, which may cause new negative effects on soil.

[0003] In addition, the design of existing multifunctional composite materials is mostly based on high polymer synthesis or composite wrapping mechanism, and the preparation process is complex and costly, which is difficult to adapt to large-area agricultural application. Some adsorption materials have good selectivity for single metal ions, but in actual soil environment, there are unfavorable conditions such as complex metal ion types, large acid-base fluctuations, and many organic matter interferences, which lead to unstable adsorption efficiency and uncontrollable slow-release behavior. Moreover, the material residues themselves may cause microplastic pollution or secondary treatment burden. SUMMARY

[0004] In view of the deficiencies of the prior art, the present application provides a slow-release-repair gel bead based on a lignin charcoal-humic acid composite material and a preparation method and application thereof. The slow-release-repair gel bead based on a lignin charcoal-humic acid composite material is prepared by dispersing lignin sodium sulfonate charcoal powder in a humic acid solution to achieve stable dispersion and surface activity modification, then mixing with ammonium bicarbonate and sodium alginate, and then adding dropwise into a calcium ion-containing solution for gelation treatment, and finally filtering, washing, and freeze-drying. The slow-release-repair gel bead based on a lignin charcoal-humic acid composite material prepared by the present application has the advantages of significantly improving heavy metal adsorption and fixation efficiency, having intelligent slow-release ability in response to pH, being able to improve soil physical and chemical properties, being stable in structure and environmentally friendly, having strong adaptability, being one material with multiple effects, and being low in cost and high in efficiency, thereby overcoming the technical defects of the prior art.

[0005] To achieve the above object, the technical scheme adopted by the present application is:

[0006] The first object of the present application is to provide a preparation method of a slow-release-repair gel bead based on a lignin charcoal-humic acid composite material, comprising the following steps:

[0007] S1, dispersing lignin sodium sulfonate charcoal powder in a humic acid solution, realizing stable dispersion and surface activity modification of the lignin sodium sulfonate charcoal powder through interfacial adsorption and functional group complexation, forming a composite, and obtaining a lignin biochar@humic acid composite material through centrifugal drying treatment, increasing the active sites on the surface of the lignin biochar@humic acid composite material, providing a uniform precursor system for network construction of the slow-release-repair gel bead based on the lignin charcoal-humic acid composite material, and enhancing the adsorption performance and structural stability thereof,

[0008] S2, mixing the lignin biochar@humic acid composite material, ammonium bicarbonate and the carrier with sodium alginate as the carrier to obtain a suspension.

[0009] S3, adding the suspension dropwise into a calcium ion-containing solution to perform a crosslinking reaction, in which Ca 2+ forms a three-dimensional ionic crosslinking network with an "egg box" structure through coordination crosslinking with the carboxylate groups in the sodium alginate molecular chain, acting on the guluronate G segment, and the lignin biochar@humic acid composite material is uniformly embedded in the three-dimensional ionic crosslinking network as a functional filler; at the same time, the carboxyl and hydroxyl functional groups in the humic acid molecules form hydrogen bonds or electrostatic interactions with the sodium alginate molecular chain, further enhancing the stability and functional synergy of the gel structure; ammonium bicarbonate decomposes and releases NH3 and CO2, wherein the release of CO2 forms a bubble template effect inside the gel bead, which helps to construct a microporous structure, thereby effectively improving the specific surface area and adsorption capacity of the gel bead, and NH3 is absorbed by water in the soil to form ammonium ions, which is one of the nitrogen forms that plants can absorb, i.e., a source of nitrogen fertilizer.

[0010] S4, sequentially filtering, washing and freeze-drying the gel bead to obtain a slow-release-repair gel bead based on a lignin charcoal-humic acid composite material.

[0011] Preferably, the mass-volume ratio of the lignin sodium sulfonate charcoal powder to the humic acid solution is 0.05g:50mL, and the mass concentration of the humic acid is 0.2g / L-1.5g / L; the humic acid is usually dissolved in deionized water for use as a natural humic acid extract.

[0012] Preferably, the mass ratio of the lignin biochar@humic acid composite material, ammonium bicarbonate and sodium alginate is 1-4:2:4.

[0013] Preferably, the dispersion condition is that the lignin sulfonate carbon powder is dispersed in the fulvic acid solution under dark environment at 0 DEG C for 30 min to 60 min; and the fulvic acid and the lignin sulfonate carbon powder are usually adsorbed by low-temperature stirring.

[0014] Preferably, the cross-linking reaction condition is that the cross-linking reaction is carried out at 4 DEG C for 4 h to 12 h.

[0015] Preferably, the mass concentration of the suspension is 2% to 5%, and the mass concentration of Ca 2+ in the calcium ion-containing solution is 2% to 3%.

[0016] The second object of the present application is a lignin carbon-fulvic acid composite-based slow-release-repair gel bead prepared by the above preparation method.

[0017] Preferably, the lignin carbon-fulvic acid composite-based slow-release-repair gel bead has a spherical structure, and the particle size is 3 mm to 4 mm.

[0018] The third object of the present application is to provide the application of the above lignin carbon-fulvic acid composite-based slow-release-repair gel bead in the preparation of a heavy metal contaminated soil repair-nutrient slow-release agent.

[0019] Compared with the prior art, the present application has the following beneficial effects:

[0020] 1. The present application provides a preparation method of a lignin carbon-fulvic acid composite-based slow-release-repair gel bead. The lignin sulfonate carbon powder is dispersed in the fulvic acid solution, the lignin sulfonate carbon powder and the fulvic acid are combined by interfacial adsorption and functional group complexation to form a composite, the composite is dried to obtain a lignin biochar@fulvic acid composite material; the lignin biochar@fulvic acid composite material and ammonium bicarbonate are mixed with a carrier to obtain a suspension; the suspension is added dropwise into a calcium ion-containing solution to carry out a cross-linking reaction, and Ca 2+The carboxylate groups in the sodium alginate molecular chain are cross-linked to form a three-dimensional ion cross-linking network with a "egg box" structure, and the lignin biochar-humic acid composite material is embedded in the three-dimensional ion cross-linking network; meanwhile, there is a hydrogen bond or electrostatic interaction between the carboxyl and hydroxyl functional groups in the humic acid molecule and the sodium alginate molecular chain, and then a stable structure gel bead is formed; in this process, ammonium bicarbonate is decomposed and CO2 is released, and the release of CO2 forms a bubble template effect inside the gel bead, constructs a microporous structure to improve the specific surface area and adsorption capacity, and obtains the gel bead; the gel bead is sequentially filtered, washed and freeze-dried to obtain the slow-release-repair gel bead based on the lignin carbon-humic acid composite material. The slow-release-repair gel bead based on the lignin carbon-humic acid composite material prepared by the application has the advantages of significantly improving the heavy metal adsorption and fixing efficiency, having the intelligent slow-release ability of pH response, being able to improve the soil physical and chemical properties, being structure stable and environment-friendly, being strong in adaptability, being one material with multiple effects, and being low in cost and high in efficiency, and overcomes the technical defects existing in the prior art.

[0021] Among them, the lignin carbon provides a porous skeleton and an adsorption active site, the humic acid is a soil conditioner, the sodium alginate is cross-linked with Ca 2+ to form a stable gel network, ammonium bicarbonate not only provides a source of soil nitrogen fertilizer, but also can guide the formation of a porous structure, and the decomposition of ammonium bicarbonate not only helps to construct a porous structure to promote the controlled release of humic acid, but also can be used as a slow-release nitrogen fertilizer, and at the same time, can decompose to produce an alkaline environment in the soil to assist heavy metal precipitation and fixation, thereby significantly improving the structure strength and adsorption capacity of the slow-release-repair gel bead based on the lignin carbon-humic acid composite material, and realizing efficient removal of heavy metal ions and dye typical pollutants.

[0022] 2、The ammonium bicarbonate used in the application has dual functions of slow-release nitrogen source and alkaline inducer in the slow-release-repair gel bead based on the lignin carbon-humic acid composite material, which can not only provide nitrogen nutrition for plants, but also induce the formation of metal carbonate precipitates in the soil to effectively realize heavy metal immobilization.

[0023] 3、The slow-release-repair gel bead based on the lignin carbon-humic acid composite material of the application can be used to repair farmland soil contaminated by Pb 2+ , Cu 2+ heavy metals, and is especially suitable for use in acid, low-organic matter, nutrient-poor and composite pollution soil environments rich in migratory heavy metals.

[0024] 4、The slow-release-repair gel bead based on the lignin carbon-humic acid composite material of the application can significantly improve the adsorption and fixing efficiency of heavy metals, and the specific surface area of the prepared lignin sulfonate carbon powder is as high as 1574m 2 / g, the pore structure is rich, and a multi-site adsorption composite system is formed after being combined with fulvic acid; the adsorption capacity of Pb 2+ and Cu 2+ Heavy metal ions exhibit high selective adsorption and stabilization capacity, and in the soil column experiment, the heavy metal leaching rate can be reduced by about 60%; fulvic acid and metal ions form stable complex structures, and the decomposition of ammonium bicarbonate releases CO3 2- Induces metal precipitation, forming a multiple fixation mechanism.

[0025] 5. The lignin charcoal-fulvic acid composite material-based slow-release-repair gel beads of the present application have pH-responsive intelligent slow-release capacity, further improving nutrient utilization rate. Especially in the acidic environment, the release speed of formamidine ions and NH4 + is regulated; NH4HCO3 slowly releases nitrogen nutrients, which matches the growth stage of crops, effectively avoiding the problem of "early waste and late scarcity" of traditional fertilizers.

[0026] 6. The lignin charcoal-fulvic acid composite material-based slow-release-repair gel beads of the present application can improve soil physical and chemical properties and improve plant physiological activity, including soil organic matter content, total nitrogen content, and pH value, improve soil aggregate structure and buffer performance; the lignin charcoal-fulvic acid composite material-based slow-release-repair gel beads are applied to the rice pot experiment of contaminated soil, which can increase the chlorophyll content of rice by 89.5%, increase the root activity by 55.6%, and increase the plant height by 31.2%; it is helpful to build a "safe growth environment" under heavy metal pollution and improve plant stress resistance and yield potential.

[0027] 7. The lignin charcoal-fulvic acid composite material-based slow-release-repair gel beads of the present application are stable in structure, environmentally friendly, and have strong adaptability, and are not easy to disintegrate or migrate in soil, avoiding the problem that the powder-like biochar in the prior art is easy to lose in soil; in addition, the raw materials are environmentally friendly, biodegradable, non-toxic and non-polluting, suitable for large-scale farmland application, and do not cause secondary environmental burden; the preparation process is simple, the particle size is controllable, and it is convenient for mechanical application or manual sowing, and has strong application in farmland.

[0028] 8. The lignin charcoal-fulvic acid composite material-based slow-release-repair gel beads of the present application have the advantages of one material with multiple effects, low cost and high efficiency, heavy metal repair, nutrient slow release and soil improvement function three in one, which can replace multiple materials at one time; the raw materials such as lignin sulfonate sodium, sodium alginate and ammonium bicarbonate are low-cost raw materials or by-products, and the preparation process is low in consumption and environmentally friendly; the frequency of fertilization and pollution treatment cost can be significantly reduced, the agricultural production efficiency is improved, and good economic nature and sustainability are achieved. BRIEF DESCRIPTION OF DRAWINGS

[0029] Figure 1Release curve diagram of SA / LBC@FA / NH4HCO3 of embodiment 1, embodiment 3~embodiment 4 and comparative example 1, wherein a is the release curve diagram under xenon lamp irradiation, b is the release curve diagram of SA / LBC@FA / NH4HCO3 of embodiment 3 in water with different pH values.

[0030] Figure 2 Effect diagram of SA / LBC@FA / NH4HCO3 of embodiment 3 on adsorption of Pb 2+ , Cu 2+ under different pH values.

[0031] Figure 3 Effect diagram of SA / LBC@FA / NH4HCO3 of embodiment 3 on adsorption of Pb 2+ , Cu 2+ under different initial mass concentrations, wherein a is Pb 2+ , b is Cu 2+ .

[0032] Figure 4 Effect diagram of SA / LBC@FA / NH4HCO3 of embodiment 3 on adsorption of Pb 2+ , Cu 2+ under different dosages.

[0033] Figure 5 Effect diagram of different treatment methods on Pb 2+ and Cu 2+ contents in upper, middle and lower parts of the soil column after 30 days, wherein (a) is lead, (b) is copper.

[0034] Figure 6 Effect diagram of different treatment methods on Pb and Cu leaching amount changes in the soil column, wherein (a) is lead, (b) is copper.

[0035] Figure 7 Result diagram of the soil treated by different treatment methods for rice planting experiment, wherein (a) is the average plant height comparison diagram after 30 days of application, (b) is the average root length comparison diagram after 30 days of application, c and d diagrams are the actual pictures of rice planted in uncontaminated soil, e and f diagrams are the actual pictures of rice planted in Pb and Cu contaminated soil.

[0036] Figure 8 Change diagram of total phosphorus content and total potassium content in the soil under uncontaminated and Pb and Cu contaminated conditions, wherein (a) is the total phosphorus content diagram, (b) is the total potassium content diagram.

[0037] Figure 9Figures for changes in organic matter content and total nitrogen content in soil under non-pollution and Pb, Cu pollution, wherein (a) is the figure for organic matter content, and (b) is the figure for total nitrogen content.

[0038] Figure 10 Figures for sodium alginate and SA / LBC@FA / NH4HCO3 of Example 3 of the present application. DETAILED DESCRIPTION

[0039] The technical solutions of the present application will be described clearly and completely below in combination with data in the embodiments of the present application. Obviously, the described embodiments are only some of the embodiments of the present application, but not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0040] It should be noted that the professional terms used in the present application are only for the purpose of describing the specific embodiments, and are not intended to limit the scope of protection of the present application. Unless otherwise specified, the various raw materials, reagents, instruments and equipment used in the following embodiments of the present application can be purchased from the market or prepared by existing methods.

[0041] In the prior art, the biochar adsorbent used for soil remediation is prone to migration and loss, the polymer slow-release material is unstable in an acidic environment, and the existing composite materials generally have the problems of single function, complex preparation, poor environmental adaptability and residual pollution risk.

[0042] In view of the problems in the prior art, the present application provides a preparation method of slow-release-remediation gel beads based on lignin charcoal-humic acid composite material, which comprises the following steps: dispersing sodium lignosulfonate charcoal powder in a humic acid solution, the sodium lignosulfonate charcoal powder and the humic acid forming a composite through interfacial adsorption and functional group complexation, and then drying to obtain a lignin biochar@humic acid composite material; taking sodium alginate as a carrier, mixing the lignin biochar@humic acid composite material, ammonium bicarbonate and the carrier to obtain a suspension; adding the suspension dropwise into a calcium ion-containing solution to perform a crosslinking reaction, and in the crosslinking reaction process, Ca 2+The carboxylate groups in the sodium alginate molecular chain are coordinated and crosslinked, acting on the guluronic acid G segment to form a three-dimensional ionic crosslinking network of the "egg box" structure, and the lignin biochar-humic acid composite material is embedded in the three-dimensional ionic crosslinking network; meanwhile, there is a hydrogen bond or electrostatic interaction between the carboxyl and hydroxyl functional groups in the humic acid molecule and the sodium alginate molecular chain, and then a stable structure gel bead is formed; in this process, ammonium bicarbonate is decomposed and CO2 is released, and the CO2 release forms a bubble template effect inside the gel bead to construct a microporous structure, and the gel bead is obtained; the gel bead is sequentially filtered, washed and freeze-dried to obtain the slow-release-repair gel bead based on the lignin carbon-humic acid composite material.

[0043] In view of the problems of functional fragmentation, acidic environment failure and secondary pollution risk in the prior art, the present application overcomes the problems through a triple synergistic mechanism, i.e., a lignin carbon porous adsorption skeleton, a humic acid pH response slow release and ammonium bicarbonate pore forming-alkaline precipitation.

[0044] In order for those skilled in the art to more clearly understand the technical solutions of the present disclosure, the technical solutions of the present application will be described in detail below with specific examples:

[0045] Example 1

[0046] A preparation method of a slow-release-repair gel bead based on a lignin carbon-humic acid composite material, comprising the following steps:

[0047] S1, disperse 50mg of lignin sulfonate sodium carbon (LBC) powder in 50mL of a humic acid (FA) solution with a mass concentration of 1g / L, ultrasonic for 30min at 0℃ in the dark, then centrifugal treatment and drying at 60℃, to obtain a lignin biochar-humic acid composite material, denoted as LBC@FA.

[0048] S2, mix LBC@FA, sodium alginate (SA) and ammonium bicarbonate (NH4HCO3) according to a mass ratio of 1:2:4, ultrasonic for 30min at 0℃ in the dark, to obtain a uniform suspension.

[0049] S3, drop the suspension into a 3% (W / V) calcium chloride solution drop by drop, stand at 4℃ for 12h, filter the formed gel bead using a filter screen, and wash with deionized water for multiple times to remove residual impurities; after washing, freeze-drying treatment is performed to obtain a composite gel bead based on the lignin carbon-humic acid composite material, denoted as SA / LBC@FA / NH4HCO3.

[0050] Example 2

[0051] A preparation method of a slow-release-repair gel bead based on a lignin charcoal-humic acid composite material, which has the same preparation steps as those of Example 1, except that the mass ratio of LBC@FA, sodium alginate, and ammonium bicarbonate in S2 is replaced by 2:2:4, including the following steps:

[0052] S1, 50 mg of LBC powder is dispersed in 50 mL of FA solution with a mass concentration of 1 g / L, ultrasonic treatment is performed in the dark at 0°C for 30 min, followed by centrifugal treatment, and drying is performed at 60°C to obtain a lignin biochar@humic acid composite material, which is denoted as LBC@FA.

[0053] S2, LBC@FA, SA, and NH4HCO3 are mixed in a mass ratio of 2:2:4, a uniform suspension is obtained by ultrasonic treatment in the dark at 0°C for 30 min.

[0054] S3, the suspension is added dropwise into a 3% (W / V) calcium chloride solution, and the mixture is placed at 4°C for 12 h, the gel bead formed is filtered out using a filter screen, and deionized water is used for multiple washing to remove residual impurities; after washing is completed, freeze-drying treatment is performed to obtain a slow-release-repair gel bead based on a lignin charcoal-humic acid composite material, which is denoted as SA / LBC@FA / NH4HCO3.

[0055] Example 3

[0056] A preparation method of a slow-release-repair gel bead based on a lignin charcoal-humic acid composite material, which has the same preparation steps as those of Example 1, except that the mass ratio of LBC@FA, sodium alginate, and ammonium bicarbonate in S2 is replaced by 3:2:4, including the following steps:

[0057] S1, 50 mg of LBC powder is dispersed in 50 mL of FA solution with a mass concentration of 1 g / L, ultrasonic treatment is performed in the dark at 0°C for 30 min, followed by centrifugal treatment, and drying is performed at 60°C to obtain a lignin biochar@humic acid composite material, which is denoted as LBC@FA.

[0058] S2, LBC@FA, SA, and NH4HCO3 are mixed in a mass ratio of 3:2:4, a uniform suspension is obtained by ultrasonic treatment in the dark at 0°C for 30 min.

[0059] S3, the suspension is added dropwise into a 3% (W / V) calcium chloride solution, and the mixture is placed at 4°C for 12 h, the gel bead formed is filtered out using a filter screen, and deionized water is used for multiple washing to remove residual impurities; after washing is completed, freeze-drying treatment is performed to obtain a slow-release-repair gel bead based on a lignin charcoal-humic acid composite material, which is denoted as SA / LBC@FA / NH4HCO3, and a photograph of the actual object is as shown in Figure 10as shown.

[0060] Example 4

[0061] A preparation method of a slow-release-repair gel bead based on a lignin charcoal-humic acid composite material, which has the same preparation steps as those of Example 1, except that the mass ratio of LBC@FA, sodium alginate and ammonium bicarbonate in S2 is changed from 1:2:4 to 4:2:4, comprising the following steps:

[0062] S1, 50 mg of LBC powder is dispersed in 50 mL of FA solution with a mass concentration of 1 g / L, ultrasonic treatment is performed in the dark at 0°C for 30 min, followed by centrifugal treatment and drying at 60°C, to obtain a lignin biochar@humic acid composite material, abbreviated as LBC@FA.

[0063] S2, LBC@FA, SA and NH4HCO3 are mixed in a mass ratio of 4:2:4, and a uniform suspension is obtained by ultrasonic treatment in the dark at 0°C for 30 min.

[0064] S3, the suspension is added dropwise to a solution containing 3% (W / V) calcium chloride, and is placed at 4°C for 12 h, the gel beads formed are filtered out using a filter screen, and are washed with deionized water for multiple times to remove residual impurities; after washing is completed, freeze-drying treatment is performed, to obtain a slow-release-repair gel bead based on a lignin charcoal-humic acid composite material, denoted as SA / LBC@FA / NH4HCO3.

[0065] Example 5

[0066] A preparation method of a slow-release-repair gel bead based on a lignin charcoal-humic acid composite material, comprising the following steps:

[0067] S1, 50 mg of LBC powder is dispersed in 50 mL of FA solution with a mass concentration of 1 g / L, ultrasonic treatment is performed in the dark at 0°C for 60 min, followed by centrifugal treatment and drying at 60°C, to obtain a lignin biochar@humic acid composite material, abbreviated as LBC@FA.

[0068] S2, LBC@FA, SA and NH4HCO3 are mixed in a mass ratio of 3:2:4, and a uniform suspension is obtained by ultrasonic treatment in the dark at 0°C for 30 min.

[0069] S3, the suspension is added dropwise to a solution containing 3% (W / V) calcium chloride, and is placed at 4°C for 4 h, the gel beads formed are filtered out using a filter screen, and are washed with deionized water for multiple times to remove residual impurities; after washing is completed, freeze-drying treatment is performed, to obtain a slow-release-repair gel bead based on a lignin charcoal-humic acid composite material, denoted as SA / LBC@FA / NH4HCO3.

[0070] Comparative Example 1

[0071] A preparation method of a composite gel bead, comprising the following steps:

[0072] S1, sodium alginate and ammonium bicarbonate were mixed in a mass ratio of 2:4, and stirred at 30°C at a stirring rate of 180 rpm / min for 30 min to obtain a uniform suspension.

[0073] S2, the suspension was added dropwise to a solution containing 3% (W / V) calcium chloride, and after immobilization for 30 min, the formed gel beads were filtered out using a filter screen, and washed with deionized water for multiple times to remove residual impurities; after washing, freeze-drying treatment was performed to obtain a composite gel bead, denoted as SA / NH4HCO3.

[0074] Application:

[0075] a. Soil improvement (slow-release performance):

[0076] 0.5 g of SA / LBC@FA / NH4HCO3 of Example 1, Example 3 to Example 4 were respectively weighed, and SA / LBC@FA / NH4HCO3 was placed in a beaker with 50 mL of deionized water, and 3 mL of supernatant was periodically (10 min, 30 min, 1 h, 3 h, 5 h, 7 h, 9 h, 12 h, 20 h, 24 h, 30 h, 36 h) extracted under a xenon lamp to determine its concentration and supplement an equal amount of deionized water. At the same time, the release behavior of SA / LBC@FA / NH4HCO3 under different pH conditions was investigated, 0.05 g of SA / LBC@FA / NH4HCO3 was soaked in different pH solutions, and 3 mL of sample was taken periodically (10 min, 30 min, 1 h, 3 h, 5 h, 7 h, 9 h, 12 h, 20 h, 24 h, 30 h, 36 h) to measure its absorbance and immediately replace an equal amount of fresh solution, and the concentration of FA was determined at a wavelength of 274 nm, and the cumulative release rate of FA was calculated using the formula:

[0077]

[0078] In the formula, C t represents the concentration of FA (µg / mL) in the test solution taken at time t; V total is the total volume of the test solution (mL); Vt is the sampling amount (3 mL); m0 is the total drug loading in the test sample (µg).

[0079] From the a graph in Figure 1 , it can be seen that when the mass ratio W LBC@FA :W SA :W NH4HCO3When the ratio is 3:2:4, the release rate of SA / LBC@FA / NH4HCO3 in Example 3 is optimal, at 51.87%, which is approximately twice the release rate of the composite gel beads in Comparative Example 1. Observation Figure 1 Figure b shows that the FA release from SA / LBC@FA / NH4HCO3 exhibits a significant pH dependence. Within the pH range of 3–11, the FA release rate gradually increases with increasing pH. In an acidic environment (pH < 5), the release rate is lowest at 85.11% within 36 hours. However, within the pH range of 7–11, the release rate gradually increases over the same time period, reaching its highest point at pH = 9 (96.35%).

[0080] b. Immobilized heavy metal ions:

[0081] (1) Static adsorption: At 25℃, with a stirring rate of 130 rpm, adsorption was carried out on different pH values ​​(Pb). 2+ : 2~5.5, Cu 2+ :2~6), different initial heavy metal mass concentrations (Pb 2+ 20mg / L~700mg / L, Cu 2+ Add an equal mass of SA / LBC@FA / NH4HCO3 from Example 3 and different masses (0.01g~0.04g) of SA / LBC@FA / NH4HCO3 from Example 3 to 10mL of a solution with a concentration of 40mg / L~500mg / L. After constant temperature shaking until adsorption equilibrium is reached, centrifuge and collect the supernatant. Filter through a 0.45μm filter membrane, and determine the Pb content in the filtrate using flame atomic emission spectrometry. 2+ and Cu 2+ The concentration was determined to establish the optimal pH, initial concentration, and the dosage of SA / LBC@FA / NH4HCO3 in Example 3.

[0082] Experimental parameters of the heavy metal ion solution were adjusted one by one based on SA / LBC@FA / NH4HCO3:

[0083] ① The effect of initial pH of the solution:

[0084] observe Figure 2 It was found that SA / LBC@FA / NH4HCO3 in Example 3 was effective against Pb. 2+ Cu 2+ The adsorption capacity of Pb first increases and then decreases with increasing pH; 2+ The removal rate increases to nearly 100% between pH 2 and 5, and decreases to 90.92% between pH 5 and 6. Cu 2+ The removal rate gradually increased from 96.56% to nearly 99.87% between pH values ​​of 2 and 5, then decreased to 98.54% with further increases in pH. (Pb) 2+The best removal effect of Pb 2+ was between pH 4 and 5. The removal rate was the highest at pH 5.

[0085] ②The influence of the initial mass concentration of heavy metal ions:

[0086] From Figure 3 the above data, it can be seen that when the initial mass concentration increased from 20 mg / L to 200 mg / L, the removal rate of Pb 2+ rose rapidly and reached a maximum of 98.99%; as the initial mass concentration of the solution increased, the removal rate gradually decreased. When the initial mass concentration increased from 40 mg / L to 120 mg / L, the removal rate of Cu 2+ rose rapidly to 99.42%, then decreased slightly but remained above 96%.

[0087] ③The influence of the dosage of SA / LBC@FA / NH4HCO3:

[0088] From Figure 4 the above data, it can be seen that when the dosage of SA / LBC@FA / NH4HCO3 increased from 0.01 g to 0.02 g, the removal rate of Pb 2+ showed a rapid upward trend; as the dosage further increased, the removal rate only increased slightly. When the dosage was 0.02 g, the removal rate of Pb 2+ reached a maximum of 99.15%. For Cu 2+ , its removal rate increased from 96.22% to 98.76% when the dosage increased from 0.01 g to 0.02 g; when the dosage was 0.03 g, the removal rate decreased slightly to 97.62%; when the dosage increased to 0.04 g, the removal rate increased to 97.89%.

[0089] (2)The fixation of heavy metal ions in soil columns:

[0090] A layer of high-temperature sterilized pebbles was laid at the bottom of the soil column, followed by filling with glass beads to fill small gaps. This process was repeated until the filling height reached 80 mm. After leveling and compacting the filling material, several layers of 100-mesh nylon filter screen were covered. Based on the dry bulk density and moisture content of the air-dried farmland soil, the disturbed soil dry-pile method was used to fill the soil column with three simulated contaminated soils in batches: no soil conditioner added (CK group), added with 3% LBC-KOH (L1 group), and added with 3% SA / LBC@FA / NH4HCO3 (L2 group). 2.57 kg of soil sample was evenly divided into 1 One layer of soil sample was used, with 250g of soil added each time, each layer 2cm high. Compaction was performed during filling to achieve the predetermined height, ensuring the dry density was close to that of natural farmland soil and that the soil particles were evenly distributed. After filling, multiple layers of nylon mesh were placed on top of the soil column, along with pebbles and glass beads. Approximately 5cm of space was left at the top of the column to prevent water accumulation. This completed the filling of the loess column. At the start of the experiment, the spray system was activated and the flow rate adjusted to 400mL / d, allowing water to flow evenly from bottom to top across the soil column. The leachate was collected every 24 hours, and Pb was determined using flame atomic emission spectrometry. 2+ Cu 2+ The concentrations were determined. After the experiment, 30g soil samples were taken from the soil column at heights of 8cm, 18cm, and 28cm (marked as the lower, middle, and upper parts, respectively). The soil samples were air-dried, ground, and passed through a 100-mesh sieve. After digestion, the total amount of Pb and Cu in the soil was determined by flame atomic emission spectrometry.

[0091] Depend on Figure 5 The initial heavy metal contents of lead-contaminated soil and copper-contaminated soil in the control group (CK) were found to be 500 mg / kg and 400 mg / kg, respectively. The Pb content in the CK group showed an increasing trend from top to bottom: 381.76 mg / kg in the upper part, increasing to 464.58 mg / kg in the middle part, and reaching 476.19 mg / kg in the lower part. This is because Pb migrates downwards with the leachate and accumulates in the lower soil layers. The Pb content in the L1 group was more evenly distributed, with 419.32 mg / kg in the upper part, 384.12 mg / kg in the middle part, and 357.74 mg / kg in the lower part. This is because the adsorption of Pb by LBC-KOH slowed down the process. 2+ While migration can occur, the limited adsorption capacity of LBC-KOH prevents complete blocking. The Pb content in group L2 is slightly higher than the other two groups, with the highest Pb content at the top (476 mg / kg). This is because the sustained-release / repair gel beads based on lignin-charcoal-fulvic acid composites can trap Pb through complexation and pore retention. 2+ It is fixed to the upper layer, inhibiting downward migration.

[0092] For copper contaminated soil, the Cu content of CK group also increased from top to bottom, i.e. 284.60 mg / kg in the upper part, 352.73 mg / kg in the middle part, and 333.95 mg / kg in the lower part, similar to Pb, but with a faster migration rate. In L1 group, the Cu content distribution was similar to that of the CK group (240.06 mg / kg in the lower part), indicating that the adsorption capacity of L1 group for Cu was weak, similar to Pb; the copper content of L2 group was significantly increased (450 mg / kg in the upper part). In summary, the effect of SA / LBC@FA / NH4HCO3 on fixing lead and copper is better than that of pure LBC-KOH, which can significantly change the distribution pattern of heavy metals in the soil column through Pb fixation dominated by chemical complexation and Cu enrichment driven by alkaline precipitation.

[0093] In terms of heavy metal fixation effect, in the simulated Pb 2+ and Cu 2+ contaminated soil, after adding 3% of SA / LBC@FA / NH4HCO3, the leaching amount of heavy metals decreased by 58% (Pb) and 60% (Cu) compared with the CK group, as shown in Figure 6 Heavy metals are mainly enriched in the surface layer of the soil, and vertical migration is significantly inhibited, effectively fixing the pollutants.

[0094] In terms of slow-release performance and environmental responsiveness, the highest FA loading is up to 94.42 μg / mg, and it shows good release control ability under different pH and light conditions; the release process of FA based on lignin charcoal-humic acid composite slow-release-repair gel beads conforms to the non-Fickian diffusion mechanism (Ritger-Peppas model n≈0.5~0.8), which is jointly controlled by diffusion and matrix swelling; the slow-release-repair gel beads based on lignin charcoal-humic acid composite show good stable release behavior within a pH range of 5~8, as shown in Figure 1 .

[0095] Experimental operation method: Pb, Cu contaminated soil control group (CK2), Pb, Cu contaminated soil + FA group (F2), Pb, Cu contaminated soil + 3% of SA / LBC-KOH@FA / NH4HCO3 group (L3). Each experimental treatment was set up in triplicate, and all experimental treatments contained a total of 700 g of soil and FA or SA / LBC-KOH@FA / NH4HCO3. Each experimental group was placed in a ventilated room, and the temperature was maintained at 25°C~27°C, and the relative humidity was 60%~80%. The potted rice seeds were evenly sown in the pots, with a depth of about 2 cm. After germination for 7 days, several healthy plants were retained in each pot, and were harvested at 30 days for determination of plant height and root length.

[0096] (1) Chlorophyll content:

[0097] Randomly take rice leaves, remove the veins, cut and grind, take 0.5g sample into 5mL centrifuge tube, add 25mL ethanol-acetone mixture (volume ratio 1:2), extract at room temperature in the dark for 8h, then centrifugal separation to get supernatant.

[0098] Determine the absorbance at 645nm and 663nm wavelength by UV-visible spectrophotometer, and the related calculation formula is expressed as follows:

[0099] Chlorophyll a concentration: Ca = (12.7A663 - 2.69A645) Formula 1

[0100] Chlorophyll b concentration: Cb = (22.9A645 - 4.68A663) x 0.05 Formula 2

[0101] Total chlorophyll concentration: Ca+b = (Ca+Cb) Formula 3

[0102] (2) Root activity:

[0103] Determine the root activity of rice by TTC (2,3,5-triphenyl tetrazolium chloride) method, first wash the roots with distilled water, cut into 1cm~2cm small pieces and put into centrifuge tube, weigh and record; Prepare 0.5% (w / v) TTC solution, add root sample, react at 30°C in the dark for 3h~6h; After reaction, add equal volume of ethanol-acetone (1:1, v / v) to terminate, shake well, stand for 10min and centrifugal; Determine the absorbance of supernatant at 485nm by spectrophotometer, and calculate the content according to the standard curve.

[0104] Tetrazolium reduction intensity per unit mass of fresh root = C / (W*t) Formula 4

[0105] Wherein, C represents the TTC reduction amount (mg) obtained from the standard curve; W is the sample mass (g); t is the reaction time (h)

[0106] In terms of improving crop growth index and improving Pb, Cu contaminated soil environment, in the rice pot experiment: the total chlorophyll content of L2 group rice reached 3.08mg / g, which was 80.1% higher than that of the pollution control group (CK2), and recovered to 89.5% of the non-pollution group; The root activity was improved by 55.6%, and the Pb and Cu enrichment in the roots was reduced by 72% and 65% respectively, and the plant toxicity was greatly relieved. At the same time, the detection showed that after adding the gel, the pH of the contaminated soil increased from 3.8 to 4.8, which relieved the acidic environment and created a more suitable microenvironment for plant growth, as shown in Figure 7

[0107] (1) Organic matter content:

[0108] ​Determination steps: about 0.5g of soil sample was accurately weighed into a 250mL conical flask, 25mL of 0.1667mol / L potassium dichromate solution and 10mL of 1mol / L sulfuric acid solution were added and shaken well; the conical flask was placed in a 180℃ oil bath for 30min of digestion, during which the organic matter was oxidized and the potassium dichromate was reduced to Cr 3+ ; after cooling to room temperature, it was diluted to 100mL and the pH was measured; then potential titration was carried out with 0.1mol / L ferrous ammonium sulfate solution, the potential change was recorded, and the soil organic matter content was calculated according to formula 5, g / kg.

[0109] Organic matter content = 0.003*(V0-V1)*C / m Formula 5

[0110] Among them, V0 the ferrous ammonium sulfate content consumed by blank titration (mL); V1 the ferrous ammonium sulfate content consumed by sample titration (mL); C representing the concentration of ferrous ammonium sulfate solution (mol / L); m the mass of the soil sample (g).

[0111] (2) Total nitrogen content:

[0112] Determination steps: 0.5g of soil sample was weighed into a Kjeldahl flask, 10mL of concentrated sulfuric acid, 10g of potassium sulfate and a small amount of catalyst were added and shaken well. It was placed in a digestion device, first carbonized at low temperature and then heated to about 420℃ for digestion until the solution was blue-green transparent. After cooling, it was transferred to a 100mL volumetric flask and diluted with deionized water. 10mL of the solution was taken to the Kjeldahl nitrogen determination instrument reaction chamber, 10mL of 2% boric acid solution and a few drops of mixed indicator were added, and distilled to 50mL. Titrate with 0.1mol / L hydrochloric acid standard solution until the solution changes from blue to gray, record the consumption volume, and calculate the soil total nitrogen content according to formula 6, mg / kg.

[0113] Total nitrogen content = 0.014*(Vb-Va)*C / m Formula 6

[0114] Among them, Vb representing the volume of hydrochloric acid standard solution consumed by blank titration (mL); Va the volume of hydrochloric acid standard solution consumed by sample titration (mL); C the concentration of hydrochloric acid standard solution (mol / L); m the mass of the soil sample (g).

[0115] (3) Total phosphorus and total potassium content:

[0116] Determination step: 0.2 g of soil sample was weighed and placed in a digestion tube, 8 mL of nitric acid and 2 mL of hydrogen peroxide were added, and after shaking, it was placed in a microwave digestion instrument for digestion. After digestion, it was cooled to room temperature, and the solution was transferred to a 50 mL volumetric flask and diluted to volume, and then shaken. If there is suspended matter, centrifuge and take the supernatant. Prepare a series of phosphorus and potassium standard solution, determine and record the signal intensity by ICP-OES, and draw a calibration curve. According to the calibration curve, the signal intensity of the sample is converted into concentration, and the content of total phosphorus and total potassium in the soil is calculated, mg / kg.

[0117] Total phosphorus / potassium content = 1000*C*V / m Formula 7

[0118] wherein, V is the total volume of the sample solution (mL), C represents the concentration of phosphorus or potassium in the sample solution obtained from the calibration curve (mg / L), m is the mass of the soil sample (g)

[0119] In terms of improving the content of soil nutrients, the total phosphorus, total potassium, total nitrogen and organic matter content in the soil are increased after the application of the gel group, which shows good soil improvement capacity and is beneficial to the recovery of the soil ecosystem structure, such as Figure 8 and Figure 9 as shown.

[0120] It should be noted that when numerical ranges are involved in the present application, both endpoints of each numerical range and any number between the two endpoints can be selected. Since the same steps and examples are used, in order to prevent repetition, the preferred examples are described in the present application. Although the preferred embodiments of the present application have been described, those skilled in the art can make further changes and modifications to these embodiments once they understand the basic inventive concept. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications falling within the scope of the present application.

Claims

1. A method for preparing sustained-release and repair gel beads based on lignin-charcoal-fulvic acid composite materials, characterized in that, Includes the following steps: Sodium lignosulfonate char powder was dispersed in a fulvic acid solution. The sodium lignosulfonate char powder and fulvic acid formed a complex through interfacial adsorption and functional group complexation. After drying, the lignin biochar@fulvic acid composite material was obtained. Using sodium alginate as a carrier, lignin biochar@fulvic acid composite material, ammonium bicarbonate and carrier were mixed to obtain a suspension; The suspension was added dropwise to a calcium ion-containing solution to initiate a cross-linking reaction. During the cross-linking reaction, Ca... 2+ The lignin biochar@fulvic acid composite material undergoes coordination crosslinking with the carboxyl groups in the sodium alginate molecular chain, acting on the G segment of guluronic acid to form a three-dimensional ionic crosslinking network with an "egg box" structure. The lignin biochar@fulvic acid composite material is embedded in the three-dimensional ionic crosslinking network. At the same time, there are hydrogen bonds or electrostatic interactions between the carboxyl and hydroxyl functional groups in the fulvic acid molecule and the sodium alginate molecular chain, thereby forming structurally stable gel beads. In this process, ammonium bicarbonate decomposes and releases CO2. The release of CO2 forms a bubble template effect inside the gel beads, constructing a microporous structure to obtain gel beads. The gel beads were sequentially filtered, washed, and freeze-dried to obtain sustained-release and repair gel beads based on lignin-charcoal-fulvic acid composite materials.

2. The method for preparing sustained-release-repair gel beads based on lignin-charcoal-fulvic acid composite material according to claim 1, characterized in that, The mass-to-volume ratio of sodium lignosulfonate charcoal powder to fulvic acid solution is 0.05 g: 50 mL, and the mass concentration of fulvic acid is 0.2 g / L to 1.5 g / L.

3. The method for preparing sustained-release-repair gel beads based on lignin-charcoal-fulvic acid composite material according to claim 1, characterized in that, The mass ratio of lignin biochar@fulvic acid composite material, ammonium bicarbonate and sodium alginate is 1~4:2:

4.

4. The method for preparing sustained-release-repair gel beads based on lignin-charcoal-fulvic acid composite material according to claim 1, characterized in that, The dispersion conditions for sodium lignosulfonate charcoal powder in fulvic acid solution are: ultrasonication at 0℃ in a dark environment for 30-60 minutes.

5. The method for preparing sustained-release-repair gel beads based on lignin-charcoal-fulvic acid composite material according to claim 1, characterized in that, The conditions for the cross-linking reaction are: standing at 4℃ for 4h~12h.

6. The method for preparing sustained-release-repair gel beads based on lignin-charcoal-fulvic acid composite material according to claim 1, characterized in that, The suspension concentration is 2%~5%, and the calcium ion content in the solution is Ca 2+ The mass concentration is 2%~3%.

7. A sustained-release, repair gel bead based on lignin-charcoal-fulvic acid composite material, characterized in that, It is prepared by the preparation method according to any one of claims 1 to 6.

8. The sustained-release-repair gel beads based on lignin-charcoal-fulvic acid composite material according to claim 7, characterized in that, The slow-release-repair gel beads based on lignin-charcoal-fulvic acid composite material have a spherical structure and a particle size of 3 mm to 5 mm.

9. The application of the slow-release-remediation gel beads based on lignin charcoal-fulvic acid composite material as described in claim 7 in the preparation of a slow-release nutrient agent for the remediation of heavy metal contaminated soil.

10. The application according to claim 9, characterized in that, The addition amount of slow-release remediation gel beads based on lignin-charcoal-fulvic acid composite material is 10% to 40% of the quality of contaminated soil.

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