Slow release-repair gel bead based on lignin carbon-fulvic acid composite material and preparation method and application thereof

Abstract

The invention relates to the technical field of preparation of composite gel beads, in particular to slow-release-repair gel beads based on a lignin carbon-fulvic acid composite material as well as a preparation method and application of the slow-release-repair gel beads. Comprising the following steps: dispersing sodium lignin sulfonate carbon powder in a fulvic acid solution, and drying to obtain a lignin biochar-fulvic acid composite material; the preparation method comprises the following steps: by taking sodium alginate as a carrier, mixing the lignin charcoal-fulvic acid composite material, ammonium bicarbonate and the carrier, dropwise adding into a calcium ion-containing solution, crosslinking to form gel beads, and sequentially filtering, washing and freeze-drying to obtain the slow-release-repair gel beads based on the lignin charcoal-fulvic acid composite material. The slow-release-remediation gel bead based on the lignin carbon-fulvic acid composite material can remarkably improve the heavy metal adsorption and fixation efficiency, has the advantages of intelligent slow release in pH response and improvement of physical and chemical properties of soil, is stable in structure, environmentally friendly, high in adaptability, multiple in effect, low in cost and high in benefit, and overcomes the defects in 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] In order to achieve the above object, the technical solution adopted by the present invention is: The first object of the present invention is to provide a method for preparing slow-release-repair gel beads based on lignin charcoal-fulvic acid composite materials, comprising the following steps: S1. Disperse sodium lignin sulfonate carbon powder in a fulvic acid solution. Through interfacial adsorption and functional group complexation, the sodium lignin sulfonate carbon powder is stably dispersed and surface active modified to form a composite. After centrifugal drying, a lignin biochar@fulvic acid composite material is obtained. This increases the active sites on the surface of the lignin biochar@fulvic acid composite material, provides a uniform precursor system for the construction of a slow-release-repair gel bead network based on the lignin carbon-fulvic acid composite material, and enhances its adsorption performance and structural stability.

[0006] S2. Using sodium alginate as a carrier, the lignin biochar@fulvic acid composite material and ammonium bicarbonate are mixed with the carrier to obtain a suspension.

[0007] S3, adding the suspension dropwise to a solution containing calcium ions to carry out a cross-linking reaction. During the cross-linking reaction, Ca 2+ It undergoes coordination cross-linking with the carboxylate groups in the sodium alginate molecular chain and acts on the guluronic acid G segment to form a three-dimensional ion-crosslinked network with an "egg-box" structure. The lignin biochar@fulvic acid composite material is uniformly embedded in the three-dimensional ion-crosslinked network as a functional filler. At the same time, the carboxyl and hydroxyl functional groups in the fulvic acid molecules form hydrogen bonds or electrostatic interactions with the sodium alginate molecular chains, further enhancing the stability of the gel structure and functional synergy. Ammonium bicarbonate decomposes and releases NH3 and CO2. The release of CO2 forms a bubble template effect inside the gel beads, which helps to construct a microporous structure, thereby effectively improving the specific surface area and adsorption capacity of the gel beads. NH3 is absorbed by water in the soil to generate ammonium ions. Ammonium ions are one of the forms of nitrogen that can be absorbed by plants, that is, the source of nitrogen fertilizer.

[0008] S4. The gel beads are filtered, washed and freeze-dried in sequence to obtain slow-release-repair gel beads based on lignin charcoal-fulvic acid composite materials.

[0009] Preferably, the mass volume ratio of sodium lignin sulfonate carbon powder to fulvic acid solution is 0.05g:50mL, and the mass concentration of fulvic acid is 0.2g / L~1.5g / L; fulvic acid, as a natural humic acid extract, is usually dissolved in deionized water for use.

[0010] Preferably, the mass ratio of the lignin biochar@fulvic acid composite material, ammonium bicarbonate and sodium alginate is 1-4:2:4.

[0011] Preferably, the dispersion condition is: ultrasonic treatment for 30min~60min at 0℃ in dark environment; and the humic acid and the lignin sulfonate carbon powder are usually adsorbed by low-temperature stirring.

[0012] Preferably, the cross-linking reaction condition is: standing for 4h~12h at 4℃.

[0013] Preferably, the mass concentration of the suspension is 2%~5%, and the mass concentration of Ca 2+ in the calcium ion-containing solution is 2%~3%.

[0014] The second object of the present application is a lignin carbon-humic acid composite-based slow-release-repair gel bead prepared by the above preparation method.

[0015] Preferably, the lignin carbon-humic acid composite-based slow-release-repair gel bead is in a spherical structure, and the particle size is 3mm~4mm.

[0016] The third object of the present application is to provide the application of the above lignin carbon-humic acid composite-based slow-release-repair gel bead in the preparation of a heavy metal contaminated soil repair-nutrient slow-release agent.

[0017] Compared with the prior art, the present application has the following beneficial effects: 1、The present application provides a preparation method of a lignin carbon-humic acid composite-based slow-release-repair gel bead, wherein lignin sulfonate carbon powder is dispersed in a humic acid solution, the lignin sulfonate carbon powder and the humic acid form a complex through interfacial adsorption and functional group complexation, and the complex is dried to obtain a lignin biochar@humic acid composite material; the lignin biochar@humic acid composite material and ammonium bicarbonate are mixed with a carrier to obtain a suspension, and the suspension is added dropwise into a calcium ion-containing solution to perform cross-linking reaction, during which Ca 2+The ammonium bicarbonate reacts with the carboxylate groups in the sodium alginate molecular chain to form a coordinated crosslinking network, acting on the guluronic acid G segment to form a three-dimensional ion-crosslinked network with an "egg-box" structure. The lignin biochar@fulvic acid composite material is embedded in the three-dimensional ion-crosslinked network. At the same time, the carboxyl and hydroxyl functional groups in the fulvic acid molecules form hydrogen bonds or electrostatic interactions with the sodium alginate molecular chains, thereby forming structurally stable gel beads. During 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 increase the specific surface area and adsorption capacity, thereby obtaining gel beads. The gel beads are filtered, washed, and freeze-dried in sequence to obtain slow-release-repair gel beads based on the lignin charcoal-fulvic acid composite material. The slow-release-repair gel beads based on the lignin charcoal-fulvic acid composite material prepared by the present invention have the advantages of significantly improving the adsorption and fixation efficiency of heavy metals, having a pH-responsive intelligent slow-release ability, being able to improve the physical and chemical properties of soil, being structurally stable and environmentally friendly, having strong adaptability, being a single material with multiple effects, and being cost-effective and highly efficient, thus overcoming the technical defects of the prior art.

[0018] Among them, lignin charcoal provides porous skeleton and adsorption active sites, fulvic acid is a soil improver, and sodium alginate is a soil conditioner through Ca 2+ Cross-linking forms a stable gel network. Ammonium bicarbonate is not only a source of nitrogen fertilizer for the soil, but also can guide the formation of a porous structure. The decomposition of ammonium bicarbonate not only helps to build a porous structure and promote the controlled release of fulvic acid, but the decomposition products can also serve as a slow-release nitrogen fertilizer. At the same time, it can decompose in the soil to produce an alkaline environment, assisting in the precipitation and fixation of heavy metals, thereby significantly improving the structural strength and adsorption capacity of the slow-release-repair gel beads based on lignin carbon-fulvic acid composite materials, and achieving efficient removal of heavy metal ions and typical dye pollutants.

[0019] 2. The ammonium bicarbonate used in the present invention has the dual functions of a slow-release nitrogen source and an alkaline inducer in the slow-release-repair gel beads based on the lignin charcoal-fulvic acid composite material. It can not only provide nitrogen nutrition for plants, but also induce the formation of metal carbonate precipitation in the soil, effectively realizing the immobilization of heavy metals.

[0020] 3. The slow-release repair gel beads based on the lignin charcoal-fulvic acid composite material of the present invention can be used to repair Pb-damaged 2+ 、Cu 2+ Heavy metal contaminated farmland soil is particularly suitable for complex polluted soil environments that are acidic, low in organic matter, poor in nutrients and rich in mobile heavy metals.

[0021] 4. The slow-release-repair gel beads based on the lignin charcoal-fulvic acid composite material of the present invention can significantly improve the adsorption and fixation efficiency of heavy metals. The prepared sodium lignin sulfonate carbon powder has a specific surface area of ​​up to 1574m 2 / g, rich pore structure, combined with fulvic acid loading to form a multi-site adsorption composite system; 2+ and Cu 2+ Heavy metal ions exhibit highly selective adsorption and stabilization capabilities, and in soil column experiments, the leaching rate of heavy metals can be reduced by about 60%. Fulvic acid forms a stable complex structure with metal ions, while ammonium bicarbonate decomposes to release CO3. 2- Induce metal precipitation and form multiple fixation mechanisms.

[0022] 5. The slow-release and repairing gel beads based on the lignin charcoal-fulvic acid composite material of the present invention have the ability of pH-responsive intelligent slow-release, which further improves the nutrient utilization rate. In particular, it regulates the formamidinium ion and NH4 in an acidic environment. + Release speed: NH4HCO3 decomposes and releases nitrogen nutrients slowly, matching the growth stage of crops, effectively avoiding the problem of "early waste and late scarcity" of traditional fertilizers.

[0023] 6. The slow-release-repairing gel beads based on the lignin charcoal-fulvic acid composite material of the present invention can improve the physical and chemical properties of the soil and enhance the physiological activity of plants, including the organic matter content, total nitrogen content and pH value in the soil, and improve the soil aggregate structure and buffering performance. The slow-release-repairing gel beads based on the lignin charcoal-fulvic acid composite material were applied to rice pot experiments in contaminated soil, which could increase the chlorophyll content of rice by 89.5%, the root activity by 55.6%, and the plant height by 31.2%. It helps to build a "safe growth environment" under heavy metal pollution and enhance plant stress resistance and yield potential.

[0024] 7. The slow-release-repairing gel beads based on the lignin charcoal-fulvic acid composite material of the present invention have a stable structure, are environmentally friendly, have strong adaptability, are not easy to disintegrate or migrate in the soil, and avoid the problem of easy loss of powdered biochar in the soil in the prior art; in addition, the raw material source is environmentally friendly, degradable, non-toxic and pollution-free, suitable for large-scale farmland application, and does 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 applicability in farmland promotion.

[0025] 8. The slow-release-repair gel beads based on the lignin charcoal-fulvic acid composite material of the present invention have the advantages of one material with multiple effects, low cost and high efficiency. The present invention combines heavy metal remediation, nutrient slow-release and soil improvement functions into one, and can replace multiple materials with one application; raw materials such as sodium lignin sulfonate, sodium alginate, and ammonium bicarbonate are all low-cost raw materials or by-products, and the preparation process is low-consumption and environmentally friendly; it can significantly reduce the frequency of fertilization and pollution control costs, improve agricultural production efficiency, and has good economy and sustainability. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1Release curve diagram of SA / LBC@FA / NH4HCO3 of embodiment 1, embodiment 3 to embodiment 4 and composite gel beads of 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.

[0027] Figure 2 Effect diagram of SA / LBC@FA / NH4HCO3 of embodiment 3 on adsorption of Pb 2+ , Cu 2+ under different pH values.

[0028] 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+ .

[0029] Figure 4 Effect diagram of SA / LBC@FA / NH4HCO3 of embodiment 3 on adsorption of Pb 2+ , Cu 2+ under different dosages.

[0030] 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.

[0031] 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.

[0032] Figure 7 Results diagram of 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 photos of rice planted in uncontaminated soil, e and f diagrams are the actual photos of rice planted in Pb and Cu contaminated soil.

[0033] Figure 8 Change diagram of total phosphorus content and total potassium content in soil under uncontaminated and Pb and Cu contaminated conditions, wherein (a) is the total phosphorus content diagram, (b) is the total potassium content diagram.

[0034] 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.

[0035] Figure 10 Figure for sodium alginate and SA / LBC@FA / NH4HCO3 of Example 3 of the present application. DETAILED DESCRIPTION

[0036] 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.

[0037] 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.

[0038] 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.

[0039] 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+It undergoes coordination cross-linking with the carboxylate groups in the sodium alginate molecular chain, acts on the guluronic acid G segment, and forms a three-dimensional ion-crosslinked network with an "egg-box" structure. The lignin biochar@fulvic acid composite material is embedded in the three-dimensional ion-crosslinked network. At the same time, there are hydrogen bonds or electrostatic interactions between the carboxyl and hydroxyl functional groups in the fulvic acid molecules and the sodium alginate molecular chains, thereby forming structurally stable gel beads. During 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 are filtered, washed, and freeze-dried in sequence to obtain slow-release-repair gel beads based on the lignin charcoal-fulvic acid composite material.

[0040] In response to the problems of functional separation, failure in acidic environments and secondary pollution risks in existing technologies, the present invention overcomes these problems through a triple synergistic mechanism, namely, a porous adsorption skeleton of lignin carbon, pH-responsive sustained release of fulvic acid, and pore-forming and alkaline precipitation of ammonium bicarbonate.

[0041] In order to enable those skilled in the art to more clearly understand the technical solution of the present disclosure, the technical solution of the present disclosure will be described in detail below with reference to specific embodiments: Example 1 A method for preparing slow-release-repair gel beads based on lignin charcoal-fulvic acid composite materials comprises the following steps: S1. Disperse 50 mg of sodium lignin sulfonate carbon (LBC) powder in 50 mL of 1 g / L fulvic acid (FA) solution, ultrasonicate at 0°C in the dark for 30 min, then centrifuge and dry at 60°C to obtain a lignin biochar@fulvic acid composite material, denoted as LBC@FA.

[0042] S2. LBC@FA, sodium alginate (SA) and ammonium bicarbonate (NH4HCO3) were mixed in a mass ratio of 1:2:4 and ultrasonicated at 0°C for 30 min in the dark to obtain a uniform suspension.

[0043] S3. The suspension was added dropwise into a 3% (W / V) calcium chloride solution, allowed to stand at 4°C for 12 h, the formed gel beads were filtered out using a filter, and rinsed multiple times with deionized water to remove residual impurities; after washing, the suspension was freeze-dried to obtain composite gel beads based on lignin charcoal-fulvic acid composite material, which was recorded as SA / LBC@FA / NH4HCO3.

[0044] Example 2 A method for preparing slow-release and repair gel beads based on lignin charcoal-fulvic acid composite materials is the same as the preparation steps of Example 1, except that the mass ratio of LBC@FA, sodium alginate, and ammonium bicarbonate in S2 is replaced from 1:2:4 to 2:2:4, comprising the following steps: S1. Disperse 50 mg of LBC powder in 50 mL of 1 g / L FA solution, ultrasonicate at 0°C in the dark for 30 min, centrifuge, and dry at 60°C to obtain a lignin biochar@fulvic acid composite material, abbreviated as LBC@FA.

[0045] S2. LBC@FA, SA and NH4HCO3 were mixed in a mass ratio of 2:2:4 and ultrasonicated at 0°C for 30 min in the dark to obtain a uniform suspension.

[0046] S3. The suspension was added dropwise into a 3% (W / V) calcium chloride solution, allowed to stand at 4°C for 12 h, the formed gel beads were filtered out using a filter, and rinsed multiple times with deionized water to remove residual impurities; after washing, the suspension was freeze-dried to obtain slow-release-repair gel beads based on lignin charcoal-fulvic acid composite materials, which were recorded as SA / LBC@FA / NH4HCO3.

[0047] Example 3 A method for preparing slow-release and repair gel beads based on lignin charcoal-fulvic acid composite materials is the same as the preparation steps of Example 1, except that the mass ratio of LBC@FA, sodium alginate, and ammonium bicarbonate in S2 is replaced from 1:2:4 to 3:2:4, comprising the following steps: S1. Disperse 50 mg of LBC powder in 50 mL of 1 g / L FA solution, ultrasonicate at 0°C in the dark for 30 min, centrifuge, and dry at 60°C to obtain a lignin biochar@fulvic acid composite material, abbreviated as LBC@FA.

[0048] S2. LBC@FA, SA and NH4HCO3 were mixed in a mass ratio of 3:2:4 and ultrasonicated at 0°C for 30 min in the dark to obtain a uniform suspension.

[0049] S3. The suspension was added dropwise into a 3% (W / V) calcium chloride solution and allowed to stand at 4°C for 12 h. The formed gel beads were filtered out using a filter and rinsed multiple times with deionized water to remove residual impurities. After washing, the suspension was freeze-dried to obtain slow-release-repair gel beads based on lignin charcoal-fulvic acid composite materials, denoted as SA / LBC@FA / NH4HCO3. The physical figure is shown in the figure below. Figure 10 shown.

[0050] Example 4 A method for preparing slow-release and repair gel beads based on lignin charcoal-fulvic acid composite materials is the same as the preparation steps of Example 1, except that the mass ratio of LBC@FA, sodium alginate, and ammonium bicarbonate in S2 is replaced from 1:2:4 to 4:2:4, comprising the following steps: S1. Disperse 50 mg of LBC powder in 50 mL of 1 g / L FA solution, ultrasonicate at 0°C in the dark for 30 min, centrifuge, and dry at 60°C to obtain a lignin biochar@fulvic acid composite material, abbreviated as LBC@FA.

[0051] S2. LBC@FA, SA and NH4HCO3 were mixed in a mass ratio of 4:2:4 and ultrasonicated at 0°C for 30 min in the dark to obtain a uniform suspension.

[0052] S3. The suspension was added dropwise into a 3% (W / V) calcium chloride solution, allowed to stand at 4°C for 12 h, the formed gel beads were filtered out using a filter, and rinsed multiple times with deionized water to remove residual impurities; after washing, the suspension was freeze-dried to obtain slow-release-repair gel beads based on lignin charcoal-fulvic acid composite materials, which were recorded as SA / LBC@FA / NH4HCO3.

[0053] Example 5 A method for preparing slow-release-repair gel beads based on lignin charcoal-fulvic acid composite materials comprises the following steps: S1. Disperse 50 mg of LBC powder in 50 mL of 1 g / L FA solution, ultrasonicate at 0°C in the dark for 60 min, centrifuge, and dry at 60°C to obtain a lignin biochar@fulvic acid composite material, abbreviated as LBC@FA.

[0054] S2. LBC@FA, SA and NH4HCO3 were mixed in a mass ratio of 3:2:4 and ultrasonicated at 0°C for 30 min in the dark to obtain a uniform suspension.

[0055] S3. The suspension was added dropwise into a 3% (W / V) calcium chloride solution, allowed to stand at 4°C for 4 h, the formed gel beads were filtered out using a filter, and rinsed multiple times with deionized water to remove residual impurities; after washing, the suspension was freeze-dried to obtain slow-release-repair gel beads based on lignin charcoal-fulvic acid composite materials, which were recorded as SA / LBC@FA / NH4HCO3.

[0056] Comparative Example 1 A method for preparing composite gel beads comprises the following steps: S1. Sodium alginate and ammonium bicarbonate were mixed in a mass ratio of 2:4, and stirred at 30° C. and 180 rpm / min for 30 min to obtain a uniform suspension.

[0057] S2. The suspension was added dropwise into a 3% (W / V) calcium chloride solution. After immobilization for 30 minutes, the formed gel beads were filtered out using a filter and rinsed with deionized water several times to remove residual impurities. After washing, the composite gel beads were obtained by freeze-drying, which was recorded as SA / NH4HCO3.

[0058] application: a. Soil improvement (slow-release performance): 0.5 g of SA / LBC@FA / NH4HCO3 from Examples 1 and 3 to 4 was weighed respectively, and SA / LBC@FA / NH4HCO3 and 50 mL of deionized water were placed in a beaker. 3 mL of supernatant was extracted regularly (10 min, 30 min, 1 h, 3 h, 5 h, 7 h, 9 h, 12 h, 20 h, 24 h, 30 h, and 36 h) under a xenon lamp to determine its concentration and replenish with 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 immersed in solutions of different pH values. 3 mL of samples were taken regularly (10 min, 30 min, 1 h, 3 h, 5 h, 7 h, 9 h, 12 h, 20 h, 24 h, 30 h, and 36 h) to measure their absorbance and immediately replace them with an equal amount of fresh solution. The FA concentration was measured at a wavelength of 274 nm, and the cumulative release rate of FA was calculated using the formula:

[0059] Where C t represents the concentration of FA in the test solution taken out at time t (µg / mL); V total is the total volume of the test solution (mL); Vt is the sample volume (3 mL); m0 is the total drug loading in the test sample (µg).

[0060] observe Figure 1 Figure a shows that when the mass ratio W LBC@FA :W SA :W NH4HCO3 =3:2:4, that is, the release rate of SA / LBC@FA / NH4HCO3 in Example 3 is the best, which is 51.87%, about twice the release rate of the composite gel beads in Comparative Example 1. Figure 1Figure b shows that FA release from SA / LBC@FA / NH4HCO3 is significantly pH-dependent. Within the pH range of 3-11, the FA release rate increases with increasing pH. In an acidic environment (pH < 5), the release rate is lowest within 36 hours, reaching 85.11%. Within the pH range of 7-11, the release rate increases over the same time period, reaching a maximum of 96.35% at pH 9.

[0061] b. Immobilized heavy metal ions: (1) Static adsorption: at 25 °C and a stirring rate of 130 rpm, the adsorption of different pH values ​​(Pb 2+ :2~5.5,Cu 2+ :2~6)、different initial heavy metal concentrations(Pb 2+ :20mg / L~700mg / L, Cu 2+ To 10 mL of a solution containing 40 mg / L to 500 mg / L of SA / LBC@FA / NH4HCO3 (Example 3) was added an equal amount of SA / LBC@FA / NH4HCO3 and different amounts (0.01 g to 0.04 g) of SA / LBC@FA / NH4HCO3 of Example 3. The mixture was shaken at a constant temperature until adsorption equilibrium was reached. The supernatant was centrifuged and filtered through a 0.45 μm filter membrane. The Pb content in the filtrate was determined by flame atomic emission spectrometry. 2+ and Cu 2+ concentration to determine the optimal pH, initial concentration and dosage of SA / LBC@FA / NH4HCO3 in Example 3.

[0062] Based on SA / LBC@FA / NH4HCO3, the experimental parameters of heavy metal ion solution were adjusted one by one: ①Influence of initial pH of solution: observe Figure 2 It is concluded that the SA / LBC@FA / NH4HCO3 of Example 3 has a significant effect on Pb 2+ 、Cu 2+ The adsorption amount of Pb increases first and then decreases with the increase of pH. 2+ The removal rate of Cu increases between pH 2 and 5, reaching nearly 100%, and decreases to 90.92% between pH 5 and 6. 2+ The removal rate of Pb gradually increased from 96.56% to nearly 99.87% when the pH value was between 2 and 5, and decreased to 98.54% with the increase of pH value. 2+ The best removal effect is between pH 4 and 5. 2+ The removal rate was highest at a pH of 5.

[0063] ②Influence of initial mass concentration of heavy metal ions: from Figure 3As can be seen from the figure, when the initial mass concentration increases from 20 mg / L to 200 mg / L, Pb 2+ The removal rate of Cu increased rapidly, reaching a maximum of 98.99%; with the increase of the initial mass concentration of the solution, 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+ The removal rate quickly rose to 99.42%, then dropped slightly, but still remained above 96%.

[0064] ③The influence of SA / LBC@FA / NH4HCO3 dosage: from Figure 4 It is found that when the dosage of SA / LBC@FA / NH4HCO3 increases from 0.01g to 0.02g, Pb 2+ The removal rate of Pb showed a rapid upward trend; with the further increase of the dosage, the removal rate only increased slightly. When the dosage was 0.02g, the removal rate of Pb 2+ The removal rate reaches a maximum of 99.15%. 2+ For example, when the dosage increased from 0.01g to 0.02g, the removal rate increased from 96.22% to 98.76%; when the dosage was 0.03g, the removal rate slightly decreased to 97.62%; when the dosage increased to 0.04g, the removal rate returned to 97.89%.

[0065] (2) Fixation of heavy metal ions in soil columns: A layer of high-temperature sterilized pebbles was laid at the bottom of the soil column, and then glass beads were filled to fill small gaps. This operation was repeated until the filling height reached 80 mm. After the filler was flattened and compacted, it was covered with several layers of 100-mesh nylon filter screen. Based on the dry bulk density and moisture content of air-dried farmland soil, the disturbed soil dry pile method was used to load three simulated contaminated soils, namely, no soil amendment (denoted as CK group), 3% LBC-KOH (denoted as L1 group) and 3% SA / LBC@FA / NH4HCO3 (denoted as L2 group), into the soil column in batches. 2.57 kg of soil sample was evenly divided into 1 1 portion, each time filling 250g soil sample, each layer height 2cm, during the filling process, compaction operation is performed to make it reach the predetermined height, ensure that the dry bulk density is close to that of natural farmland soil, and the soil particles are evenly distributed; after the soil sample is filled, cover the top of the soil column with multiple layers of nylon filter mesh, and fill it with pebbles and glass beads, leaving about 5cm of space at the top of the soil column to prevent water accumulation, thus completing the filling of the loess soil column; after the experiment starts, start the spray device and adjust the flow rate to 400mL / d to make the water flow evenly through the soil column from bottom to top; collect the leachate every 24h, and use flame atomic emission spectrometry to determine the Pb content in it 2+ 、Cu 2+After the experiment, 30g of soil samples were collected from the 8cm, 18cm, and 28cm heights of the soil column (labeled as lower, middle, and upper, 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 using flame atomic emission spectrometry.

[0066] Depend on Figure 5 The results showed that in the CK group, the initial heavy metal contents of lead-contaminated soil and copper-contaminated soil were 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, 464.58 mg / kg in the middle, and 476.19 mg / kg in the lower part. This was because Pb migrated downward with the leachate and accumulated in the lower soil. The Pb content in the L1 group was more evenly distributed, that is, 419.32 mg / kg in the upper part, 384.12 mg / kg in the middle, and 357.74 mg / kg in the lower part. This was because the adsorption of LBC-KOH slowed down the Pb 2+ However, the adsorption capacity of LBC-KOH is limited and cannot completely block the migration. The Pb content in group L2 is slightly higher than that in the other two groups, and the Pb content in the upper part is the highest, reaching 476 mg / kg. This is because the slow-release-repair gel beads based on the lignin carbon-fulvic acid composite material can trap Pb through complexation and pore retention. 2+ Fixed to the upper layer, inhibiting downward migration.

[0067] In the copper-contaminated soil, the Cu content in the CK group also increased from the top layer to the bottom layer, reaching 284.60 mg / kg in the top layer, 352.73 mg / kg in the middle layer, and 333.95 mg / kg in the bottom layer, similar to that of Pb, but with a faster migration rate. The Cu content distribution in the L1 group was similar to that in the CK group (240.06 mg / kg in the bottom layer), indicating that the L1 group had a weak Cu adsorption capacity, similar to that of Pb. The copper content in the L2 group was significantly increased (450 mg / kg in the top layer). In summary, SA / LBC@FA / NH4HCO3 was more effective in fixing lead and copper than pure LBC-KOH. It significantly altered the distribution pattern of heavy metals in the soil column through Pb fixation driven by chemical complexation and Cu enrichment driven by alkaline precipitation.

[0068] In terms of heavy metal fixation effect, in simulating Pb 2+ and Cu 2+ In the contaminated soil, after adding 3% SA / LBC@FA / NH4HCO3, the leaching amount of heavy metals decreased by 58% (Pb) and 60% (Cu) compared with the CK group. Figure 6 Heavy metals are mainly enriched in the soil surface, and vertical migration is significantly inhibited, effectively fixing the pollutants.

[0069] In terms of sustained-release performance and environmental responsiveness, the FA loading capacity reached up to 94.42 μg / mg, and it showed good release control ability under different pH and light conditions. The FA release process of the sustained-release-repairing gel beads based on the lignin charcoal-fulvic acid composite material conforms to the non-Fickian diffusion mechanism (Ritger–Peppas model n≈0.5~0.8), which is controlled by diffusion and matrix expansion. The sustained-release-repairing gel beads based on the lignin charcoal-fulvic acid composite material maintain good and stable release behavior within the pH range of 5~8, such as Figure 1 shown.

[0070] Experimental procedures: A control group (CK2) of Pb and Cu-contaminated soil, a group (F2) of Pb and Cu-contaminated soil plus FA, and a group (L3) of Pb and Cu-contaminated soil plus 3% SA / LBC-KOH@FA / NH4HCO3. Each experimental treatment was replicated three times, and all treatments contained a total of 700 g of soil and either FA or SA / LBC-KOH@FA / NH4HCO3. Each experimental group was placed in a ventilated room maintained at a temperature of 25°C to 27°C and a relative humidity of 60% to 80%. Pots were randomly placed and rotated regularly to ensure consistent conditions. Rice seeds were evenly sown in the pots at a depth of approximately 2 cm. After 7 days of germination, a number of healthy plants were retained from each pot. Plants were harvested at 30 days, and plant height and root length were measured.

[0071] (1) Chlorophyll content: Rice leaves were picked randomly, the veins were removed, and the leaves were cut into pieces and ground. 0.5 g of sample was added to a 5 mL centrifuge tube, and 25 mL of ethanol-acetone mixture (volume ratio 1:2) was added. The leaves were extracted in the dark at room temperature for 8 h and then centrifuged to obtain the supernatant.

[0072] The absorbance was measured at 645 nm and 663 nm using a UV-visible spectrophotometer. The relevant calculation formula is as follows: Chlorophyll a concentration: Ca=(12.7A663-2.69A645) Formula 1 Chlorophyll b concentration: Cb = (22.9A645-4.68A663) × 0.05 Formula 2 Total chlorophyll concentration: Ca+b=(Ca+Cb) Formula 3 (2) Root activity: The TTC (2,3,5-triphenyltetrazolium chloride) method was used to determine rice root activity. First, the roots were washed with distilled water, cut into 1cm-2cm small segments, placed in centrifuge tubes, and weighed and recorded. A 0.5% (w / v) TTC solution was prepared and added to the root sample. The solution was reacted at 30°C in the dark for 3h-6h. After the reaction, an equal volume of ethanol-acetone (1:1, v / v) was added to terminate the reaction. The solution was shaken and centrifuged for 10min. The absorbance of the supernatant was measured at 485nm using a spectrophotometer, and the content was calculated based on the standard curve.

[0073] Tetrazolium reducing strength per unit mass of fresh root = C / (W∙t) Formula 4 wherein, C represents TTC reduction amount (mg) obtained from standard curve; W is sample mass (g); t is reaction time (h) In terms of improving crop growth indicators and improving the environment of Pb and Cu contaminated soil, in the rice pot experiment: the total chlorophyll content of L2 group rice reached 3.08 mg / g, which was 80.1% higher than the pollution control group (CK2) and 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 alleviated the acidic environment and created a more suitable microenvironment for plant growth, such as Figure 7 .

[0074] (1) Organic matter content: Measurement steps: accurately weigh about 0.5 g of soil sample into a 250 mL conical flask, add 25 mL of 0.1667 mol / L potassium dichromate solution and 10 mL of 1 mol / L sulfuric acid solution, shake well; place the conical flask in a 180°C oil bath for 30 min, during which the organic matter is oxidized and the potassium dichromate is reduced to Cr 3+ ; after cooling to room temperature, dilute to 100 mL, measure the pH; then perform potential titration with 0.1 mol / L ferrous ammonium sulfate solution, record the potential change, and calculate the soil organic matter content according to formula 5, g / kg.

[0075] Organic matter content = 0.003∙(V0-V1)∙C / m Formula 5 wherein, V0 is the amount of ferrous ammonium sulfate consumed by blank titration (mL); V1 is the amount of ferrous ammonium sulfate consumed by sample titration (mL); C represents the concentration of ferrous ammonium sulfate solution (mol / L); m is the mass of the soil sample (g).

[0076] (2) Total nitrogen content: Measurement steps: weigh 0.5 g of soil sample into a Kjeldahl flask, add 10 mL of concentrated sulfuric acid, 10 g of potassium sulfate and a small amount of catalyst, shake well. Place in a digestion device, first carbonize at low temperature, then heat to about 420°C for digestion until the solution is blue-green transparent. After cooling, transfer to a 100 mL volumetric flask and dilute with deionized water. Take 10 mL of the solution to the Kjeldahl nitrogen determination instrument reaction chamber, add 10 mL of 2% boric acid solution and a few drops of mixed indicator, distill to 50 mL. Titrate with 0.1 mol / 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.

[0077] Total nitrogen content = 0.014 (Vb-Va)∙C / m Formula 6 in, Vb Represents the volume of hydrochloric acid standard solution consumed in blank titration (mL); Va is the volume of hydrochloric acid standard solution consumed in sample titration (mL); C is the concentration of hydrochloric acid standard solution (mol / L); m is the mass of soil sample (g).

[0078] (3) Total phosphorus and total potassium content: Determination steps: Weigh 0.2g of soil sample into a digestion tube, add 8mL of nitric acid and 2mL of hydrogen peroxide, shake well, and digest in a microwave digester. After digestion, cool to room temperature, transfer the solution to a 50mL volumetric flask, and shake well. If there is any suspended matter, centrifuge and collect the supernatant. Prepare a series of phosphorus and potassium standard solutions, measure by ICP-OES, record the signal intensity, and plot a calibration curve. Based on the calibration curve, convert the sample signal intensity to concentration and calculate the total phosphorus and total potassium content in the soil in mg / kg.

[0079] Total phosphorus / potassium content = 1000∙C∙V / m Formula 7 in, 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) In terms of improving soil nutrient content, the total phosphorus, total potassium, total nitrogen and organic matter content in the soil increased after applying the gel group, showing good soil improvement ability and being beneficial to restoring the soil ecosystem structure, such as Figure 8 and Figure 9 shown.

[0080] It should be noted that when the present invention involves numerical ranges, it should be understood that both endpoints of each numerical range and any value between the two endpoints can be selected. Since the steps and methods used are the same as those in the embodiments, in order to avoid redundancy, the present invention describes preferred embodiments. Although preferred embodiments of the present invention have been described, those skilled in the art will be able to make additional changes and modifications to these embodiments once they understand the basic inventive concepts. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications that fall within the scope of the present invention.

Claims

1. A method for preparing slow-release-repair gel beads based on lignin charcoal-fulvic acid composite material, characterized in that: The following steps are involved: Sodium lignin sulfonate carbon powder is dispersed in a fulvic acid solution. The sodium lignin sulfonate carbon powder and fulvic acid form a composite through interfacial adsorption and functional group complexation. After drying, a lignin biochar@fulvic acid composite material is obtained. Using sodium alginate as a carrier, the lignin biochar@fulvic acid composite material and ammonium bicarbonate were mixed with the carrier to obtain a suspension; The suspension is added dropwise to a solution containing calcium ions to carry out a cross-linking reaction. During the cross-linking reaction, Ca 2+ The ammonium bicarbonate reacts with the carboxylate groups in the sodium alginate molecular chain to form a coordinated crosslinking reaction, acting on the guluronic acid G segment to form a three-dimensional ion-crosslinked network with an "egg-box" structure. The lignin biochar@fulvic acid composite material is embedded in the three-dimensional ion-crosslinked network. At the same time, hydrogen bonds or electrostatic interactions exist between the carboxyl and hydroxyl functional groups in the fulvic acid molecules and the sodium alginate molecular chains, forming structurally stable gel beads. During this process, ammonium bicarbonate decomposes and releases CO2, which forms a bubble template effect inside the gel beads, constructing a microporous structure and obtaining the gel beads. The gel beads are filtered, washed and freeze-dried in sequence to obtain slow-release-repair gel beads based on lignin charcoal-fulvic acid composite materials.

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

3. The method for preparing a slow-release-repairing gel bead based on a 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 a slow-release-repairing gel bead based on a lignin charcoal-fulvic acid composite material according to claim 1, characterized in that: The dispersion conditions of sodium lignin sulfonate carbon powder in fulvic acid solution are: ultrasonication for 30 min to 60 min at 0 ° C in a dark environment.

5. The method for preparing a slow-release-repairing gel bead based on a lignin charcoal-fulvic acid composite material according to claim 1, characterized in that: The conditions for the cross-linking reaction are: standing at 4°C for 4h~12h.

6. The method for preparing a slow-release-repairing gel bead based on a lignin charcoal-fulvic acid composite material according to claim 1, characterized in that: The mass concentration of the suspension is 2%~5%, and the Ca in the calcium ion solution is 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: 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 carbon-fulvic acid composite materials have a spherical structure and a particle size of 3mm~5mm.

9. Use of the slow-release-repair gel beads based on the lignin charcoal-fulvic acid composite material according to claim 7 in the preparation of a heavy metal contaminated soil remediation-nutrient slow-release agent.

10. The use 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%~40% of the mass of contaminated soil.

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