Slow release-repair gel beads based on lignin carbon-fulvic acid composite material, and preparation method therefor and use thereof

Abstract

The present invention relates to the technical field of the preparation of composite gel beads, and particularly relates to slow release-repair gel beads based on a lignin carbon-fulvic acid composite material, and a preparation method therefor and the use thereof. The preparation method comprises: dispersing a sodium lignin sulfonate carbon powder in a fulvic acid solution, and drying same to obtain a lignin biochar @ fulvic acid composite material; and by taking sodium alginate as a carrier, mixing the lignin biochar @ fulvic acid composite material, ammonium bicarbonate and the carrier, adding the resulting mixture dropwise into a calcium ion-containing solution, crosslinking same to form gel beads, and sequentially filtering, washing and freeze-drying same, so as to obtain slow release-repair gel beads based on a lignin carbon-fulvic acid composite material. The slow release-repair gel beads based on a lignin carbon-fulvic acid composite material can significantly improve the adsorption and fixation efficiency of heavy metals, has the advantages of pH-response intelligent slow release and an improvement in the physical and chemical properties of soil, is stable in structure, environmentally friendly, and high in adaptability, is a versatile material with multiple effects, and has a low cost and a high benefit.

Description

Sustained-release and repair gel beads based on lignin charcoal-fulvic acid composite materials, their preparation methods and applications Technical Field

[0001] This invention relates to the field of composite gel bead preparation technology, specifically to sustained-release-repair gel beads based on lignin-carbon-fulvic acid composite materials, their preparation methods, and applications. Background Technology

[0002] Currently, the main technologies used for soil heavy metal pollution remediation and nutrient slow release include biochar adsorption, mineral fixation, chemical modification, pH adjustment, and polymer hydrogel slow release methods. These methods are effective for Pb... 2+ Cu 2+ Pollutants can be adsorbed or immobilized and slowly release some nutrients, but they generally suffer from problems such as limited functionality, low application efficiency, poor stability, and weak environmental adaptability. For example, traditional biochar is mostly a powdered material, which easily migrates to non-target areas with water after being applied to the soil, resulting in a short action time and decreased adsorption efficiency. At the same time, its dense structure and limited specific surface area lead to insufficient loading capacity and adsorption activity for heavy metals. Although polymer-based slow-release materials have some advantages in nutrient regulation, their remediation effect on heavy metals is limited, and their release behavior is unstable in acidic environments, which can cause new negative impacts on the soil.

[0003] In addition, most existing multifunctional composite materials are designed based on polymer synthesis or composite encapsulation mechanisms, which are complex and costly to prepare, making them difficult to adapt to large-scale agricultural applications. Some adsorbent materials have good selectivity for single metal ions, but in actual soil environments, there are unfavorable conditions such as complex types of metal ions, large fluctuations in acidity and alkalinity, and a lot of organic matter interference, which leads to unstable adsorption efficiency and uncontrollable slow-release behavior. Furthermore, the material residues themselves can also bring microplastic pollution or secondary treatment burdens. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides a slow-release-repair gel bead based on a lignin-charcoal-fulvic acid composite material, its preparation method, and its applications. This invention uses sodium lignin sulfonate powder, fulvic acid, ammonium bicarbonate, and sodium alginate as main raw materials. The sodium lignin sulfonate powder is dispersed in a fulvic acid solution to achieve stable dispersion and surface activity modification. Then, it is mixed with ammonium bicarbonate and sodium alginate and added dropwise to a calcium ion-containing solution for gelation treatment. Finally, after filtration, washing, and freeze-drying, the slow-release-repair gel bead based on the lignin-charcoal-fulvic acid composite material is obtained. The slow-release-repair gel bead based on the lignin-charcoal-fulvic acid composite material prepared by this invention has the advantages of significantly improving heavy metal adsorption and fixation efficiency, possessing pH-responsive intelligent slow-release capability, improving soil physicochemical properties, structural stability and environmental friendliness, strong adaptability, multiple benefits from a single material, and low cost and high efficiency, overcoming the technical defects of existing technologies.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0006] The first objective of this invention is to provide a method for preparing sustained-release and repair gel beads based on lignin-charcoal-fulvic acid composite materials, comprising the following steps:

[0007] S1. Sodium lignosulfonate char powder is dispersed in a fulvic acid solution. Through interfacial adsorption and functional group complexation, stable dispersion and surface activity modification of the sodium lignosulfonate char powder are achieved, forming a composite material. After centrifugation and 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, providing a uniform precursor system for the construction of a sustained-release-repair gel bead network based on the lignin biochar-fulvic acid composite material, and enhancing its adsorption performance and structural stability.

[0008] S2. Using sodium alginate as a carrier, lignin biochar@fulvic acid composite material, ammonium bicarbonate and carrier are mixed to obtain a suspension.

[0009] S3. The suspension is 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 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 fulvic acid molecule 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. The release of CO2 forms a bubble template effect inside the gel beads, which helps to build a microporous structure, thereby effectively increasing the specific surface area and adsorption capacity of the gel beads. NH3 is absorbed by water in the soil to generate ammonium ions, which are one of the forms of nitrogen that plants can absorb, i.e., a source of nitrogen fertilizer.

[0010] S4. The gel beads are sequentially filtered, washed and freeze-dried to obtain sustained-release-repair gel beads based on lignin-carbon-fulvic acid composite material.

[0011] Preferably, 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; fulvic acid, as a natural humic acid extract, is usually dissolved in deionized water for use.

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

[0013] Preferably, the dispersion conditions are: ultrasonication at 0°C for 30-60 minutes in a dark environment; fulvic acid and sodium lignosulfonate carbon powder are usually adsorbed by low-temperature stirring.

[0014] Preferably, the crosslinking reaction is carried out under the following conditions: standing at 4°C for 4 to 12 hours.

[0015] Preferably, the suspension concentration is 2%–5%, and the calcium ion solution contains Ca... 2+ The mass concentration is 2% to 3%.

[0016] The second objective of this invention is to provide a slow-release, repair gel bead based on a lignin-charcoal-fulvic acid composite material, which is prepared by the above-described method.

[0017] Preferably, 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 4 mm.

[0018] A third objective of this invention is to provide the application of the above-mentioned slow-release-remediation gel beads based on lignin-charcoal-fulvic acid composite materials in the preparation of slow-release nutrient remediation agents for heavy metal contaminated soil.

[0019] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0020] 1. This invention provides a method for preparing sustained-release repair gel beads based on lignin-charcoal-fulvic acid composite materials. Sodium lignin sulfonate powder is dispersed in a fulvic acid solution. The sodium lignin sulfonate powder and fulvic acid form a composite through interfacial adsorption and functional group complexation. After drying, a lignin-charcoal@fulvic acid composite material is obtained. Using sodium alginate as a carrier, the lignin-charcoal@fulvic acid composite material, ammonium bicarbonate, and the carrier are mixed to obtain a suspension. The suspension is dropwise added to a calcium ion-containing solution to carry out a cross-linking reaction. During the cross-linking reaction, Ca... 2+ The lignin-based biochar@fulvic acid composite material undergoes coordination crosslinking with the carboxyl groups in the sodium alginate molecular chain, acting on the guluronic acid G segment to form a three-dimensional ionic crosslinking network with an "egg-box" structure. Simultaneously, hydrogen bonds or electrostatic interactions exist between the carboxyl and hydroxyl functional groups in the fulvic acid molecule and the sodium alginate molecular chain, thus forming structurally stable gel beads. During this process, ammonium bicarbonate decomposes and releases CO2. The release of CO2 creates a bubble template effect inside the gel beads, constructing a microporous structure to increase specific surface area and adsorption capacity, resulting in gel beads. The gel beads are then sequentially filtered, washed, and freeze-dried to obtain slow-release-repair gel beads based on the lignin-based biochar-fulvic acid composite material. The slow-release-repair gel beads based on the lignin-based biochar-fulvic acid composite material prepared in this invention have the advantages of significantly improving heavy metal adsorption and fixation efficiency, possessing pH-responsive intelligent slow-release capability, improving soil physicochemical properties, structural stability, environmental friendliness, strong adaptability, multi-functionality, and low cost and high efficiency, overcoming the technical defects of existing technologies.

[0021] Among them, lignin charcoal provides a porous framework and adsorption active sites, fulvic acid is a soil conditioner, and sodium alginate facilitates adsorption through Ca2+. 2+ Cross-linking forms a stable gel network. Ammonium bicarbonate is not only a source of nitrogen fertilizer for the soil, but also guides the formation of a porous structure. The decomposition of ammonium bicarbonate not only helps to build a porous structure to 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, which assists in the precipitation and fixation of heavy metals. This significantly improves the structural strength and adsorption capacity of the slow-release-repair gel beads based on lignin carbon-fulvic acid composite materials, achieving efficient removal of heavy metal ions and typical pollutants such as dyes.

[0022] 2. The ammonium bicarbonate used in this invention has the dual functions of a slow-release nitrogen source and an alkaline inducer in the slow-release-repair gel beads based on lignin carbon-fulvic acid composite material. It can provide nitrogen nutrition for plants and induce the formation of metal carbonate precipitation in the soil, effectively realizing the immobilization of heavy metals.

[0023] 3. The slow-release-repair gel beads based on lignin charcoal-fulvic acid composite material of the present invention can be used to repair Pb-damaged materials. 2+ Cu 2+ Farmland soils contaminated with heavy metals are particularly suitable for complex contaminated soil environments that are acidic, low in organic matter, nutrient-poor, and rich in migratable heavy metals.

[0024] 4. The slow-release and repair gel beads based on lignin charcoal-fulvic acid composite material of the present invention can significantly improve the adsorption and fixation efficiency of heavy metals, and the specific surface area of ​​the prepared sodium lignin sulfonate charcoal powder is as high as 1574 m². 2 / g, with abundant pore structure, forming a multi-site adsorption complex system after being loaded with fulvic acid; for Pb 2+ and Cu 2+ Heavy metal ions exhibit highly selective adsorption and stabilization capabilities, reducing heavy metal leaching rate by approximately 60% in soil column experiments; fulvic acid forms stable complex structures with metal ions, while ammonium bicarbonate decomposes to release CO3. 2- It induces metal precipitation, forming multiple fixation mechanisms.

[0025] 5. The slow-release and repair gel beads based on lignin charcoal-fulvic acid composite materials of this invention possess pH-responsive intelligent slow-release capabilities, further improving nutrient utilization. Especially in acidic environments, they regulate fulvic acid and NH4+. + Release rate: The slow decomposition of NH4HCO3 releases nitrogen nutrients, matching the crop's growth stage and effectively avoiding the problem of "early waste and later deficiency" of traditional fertilizers.

[0026] 6. The slow-release-repair gel beads based on lignin-charcoal-fulvic acid composite material of the present invention can improve the physical and chemical properties of soil and enhance plant physiological activity, including the content of organic matter, total nitrogen and pH value in soil, and improve soil aggregate structure and buffering capacity. When the slow-release-repair gel beads based on lignin-charcoal-fulvic acid composite material are applied to rice pot experiments in contaminated soil, the chlorophyll content of rice can be increased by 89.5%, the root activity can be increased by 55.6%, and the plant height can be increased by 31.2%. It helps to build a "safe growth environment" under heavy metal pollution and enhance plant stress resistance and yield potential.

[0027] 7. The slow-release and repair gel beads based on lignin charcoal-fulvic acid composite material of the present invention have a stable structure, are environmentally friendly, and have strong adaptability. They are not easily disintegrated or migrated in the soil, avoiding the problem of easy loss of powdered biochar in the soil in the prior art. In addition, the raw materials are environmentally friendly, biodegradable, non-toxic and pollution-free, 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 easy to apply mechanically or manually, making it highly applicable to farmland.

[0028] 8. The slow-release and repair gel beads based on lignin charcoal-fulvic acid composite material of the present invention have the advantages of multiple effects with one material, 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; the raw materials such as sodium lignosulfonate, 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 economic and sustainable characteristics. Attached Figure Description

[0029] Figure 1 shows the release curves of SA / LBC@FA / NH4HCO3 in Examples 1, 3-4 and the composite gel beads in Comparative Example 1. In Figure 1, a is the release curve under xenon lamp irradiation and b is the release curve of SA / LBC@FA / NH4HCO3 in water at different pH values ​​in Example 3.

[0030] Figure 2 shows the adsorption of Pb by SA / LBC@FA / NH4HCO3 in Example 3 at different pH values. 2+ Cu 2+ The effect diagram.

[0031] Figure 3 shows the adsorption of Pb by SA / LBC@FA / NH4HCO3 in Example 3 at different initial mass concentrations. 2+ Cu 2+ The effect diagram shows the impact of Pb. 2+ b is Cu 2+ .

[0032] Figure 4 shows the effect of different SA / LBC@FA / NH4HCO3 dosages on Pb adsorption in Example 3. 2+ Cu 2+ The effect diagram.

[0033] Figure 5 shows the Pb concentrations of the upper, middle, and lower parts of the soil column after 30 days under different treatments. 2+ and Cu 2+ The content effect diagram shows that (a) represents lead and (b) represents copper.

[0034] Figure 6 shows the effects of different treatment methods on the leaching of lead and copper in the soil column, where (a) represents lead and (b) represents copper.

[0035] Figure 7 shows the results of rice planting experiments using soils treated with different methods. (a) is a comparison of average plant height after 30 days of application, (b) is a comparison of average root length after 30 days of application, (c) and (d) are actual photos of rice planted in uncontaminated soil, and (e) and (f) are comparison photos of rice planted in Pb and Cu contaminated soil.

[0036] Figure 8 shows the changes in total phosphorus and total potassium content in soil under pollution-free and Pb and Cu pollution conditions. (a) shows the total phosphorus content, and (b) shows the total potassium content.

[0037] Figure 9 shows the changes in organic matter content and total nitrogen content in soil under pollution-free and Pb and Cu pollution conditions. (a) shows the organic matter content, and (b) shows the total nitrogen content.

[0038] Figure 10 shows the physical images of sodium alginate and SA / LBC@FA / NH4HCO3 from Example 3 of this invention. Detailed Implementation

[0039] The technical solution of the present invention will be clearly and completely described below with reference to the data in the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

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

[0041] In existing technologies, biochar adsorbents used for soil remediation are prone to migration and loss, polymer slow-release materials are unstable in acidic environments, and existing composite materials generally suffer from single function, complex preparation, poor environmental adaptability, and residual pollution risks.

[0042] To address the problems existing in the prior art, this invention provides a method for preparing sustained-release and repairing gel beads based on lignin biochar-fulvic acid composite materials, comprising the following steps: dispersing sodium lignin sulfonate carbon powder in a fulvic acid solution; the sodium lignin sulfonate carbon powder and fulvic acid form a composite through interfacial adsorption and functional group complexation; drying the composite material to obtain lignin biochar@fulvic acid composite material; mixing the lignin biochar@fulvic acid composite material, ammonium bicarbonate, and sodium alginate as a carrier to obtain a suspension; and adding the suspension dropwise to a calcium ion-containing solution to carry out a crosslinking reaction, wherein during the crosslinking reaction, Ca... 2+The lignin-based biochar@fulvic acid composite material undergoes coordination crosslinking with the carboxyl groups in the sodium alginate molecular chain, acting on the guluronic acid G segment to form a three-dimensional ionic crosslinking network with an "egg box" structure. Simultaneously, hydrogen bonds or electrostatic interactions exist between the carboxyl and hydroxyl functional groups in the fulvic acid molecule and the sodium alginate molecular chain, thus forming structurally stable gel beads. During this process, ammonium bicarbonate decomposes and releases CO2. The release of CO2 creates a bubble template effect inside the gel beads, constructing a microporous structure. The gel beads are then sequentially filtered, washed, and freeze-dried to obtain sustained-release and repair gel beads based on the lignin-based biochar-fulvic acid composite material.

[0043] To address the issues of functional fragmentation, failure in acidic environments, and secondary pollution risks in existing technologies, this invention overcomes these problems through a triple synergistic mechanism: a porous lignin-charcoal adsorption framework, pH-responsive slow release of fulvic acid, and ammonium bicarbonate pore-forming-alkaline precipitation.

[0044] To enable those skilled in the art to more clearly understand the technical solutions of this disclosure, the technical solutions of the present invention will be described in detail below with reference to specific embodiments:

[0045] Example 1

[0046] A method for preparing sustained-release and repair gel beads based on lignin-charcoal-fulvic acid composite materials includes the following steps:

[0047] S1. Disperse 50 mg of sodium lignosulfonate (LBC) powder in 50 mL of fulvic acid (FA) solution with a mass concentration of 1 g / L, sonicate at 0 °C for 30 min in the dark, then centrifuge and dry at 60 °C to obtain lignin biochar@fulvic acid composite material, denoted as LBC@FA.

[0048] S2. Mix LBC@FA, sodium alginate (SA) and ammonium bicarbonate (NH4HCO3) in a mass ratio of 1:2:4, and sonicate at 0°C in the dark for 30 minutes to obtain a uniform suspension.

[0049] S3. The suspension was added dropwise to a solution containing 3% (w / v) calcium chloride and allowed to stand at 4°C for 12 hours. The resulting gel beads were filtered out using a filter screen and rinsed multiple times with deionized water to remove residual impurities. After washing, the gel beads were freeze-dried to obtain composite gel beads based on lignin carbon-fulvic acid composite material, denoted as SA / LBC@FA / NH4HCO3.

[0050] Example 2

[0051] A method for preparing sustained-release and repairing gel beads based on lignin-charcoal-fulvic acid composite material is the same as the preparation steps in 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, and includes the following steps:

[0052] S1. Disperse 50 mg of LBC powder in 50 mL of FA solution with a mass concentration of 1 g / L, sonicate at 0 °C for 30 min in the dark, then centrifuge and dry at 60 °C to obtain lignin biochar@fulvic acid composite material, abbreviated as LBC@FA.

[0053] S2. Mix LBC@FA, SA and NH4HCO3 in a mass ratio of 2:2:4 and sonicate at 0℃ in the dark for 30 minutes to obtain a uniform suspension.

[0054] S3. The suspension was added dropwise to a solution containing 3% (w / v) calcium chloride and allowed to stand at 4°C for 12 hours. The resulting gel beads were filtered out using a filter screen and rinsed multiple times with deionized water to remove residual impurities. After washing, the gel beads were freeze-dried to obtain a slow-release-repair gel bead based on lignin carbon-fulvic acid composite material, denoted as SA / LBC@FA / NH4HCO3.

[0055] Example 3

[0056] A method for preparing sustained-release and repair gel beads based on lignin-charcoal-fulvic acid composite material is the same as the preparation steps in 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, and includes the following steps:

[0057] S1. Disperse 50 mg of LBC powder in 50 mL of FA solution with a mass concentration of 1 g / L, sonicate at 0 °C for 30 min in the dark, then centrifuge and dry at 60 °C to obtain lignin biochar@fulvic acid composite material, abbreviated as LBC@FA.

[0058] S2. Mix LBC@FA, SA and NH4HCO3 in a mass ratio of 3:2:4 and sonicate at 0℃ in the dark for 30 minutes to obtain a uniform suspension.

[0059] S3. The suspension was added dropwise to a solution containing 3% (w / v) calcium chloride and allowed to stand at 4°C for 12 hours. The resulting gel beads were filtered out using a filter screen and rinsed multiple times with deionized water to remove residual impurities. After washing, the gel beads were freeze-dried to obtain a slow-release-repair gel bead based on lignin-charcoal-fulvic acid composite material, denoted as SA / LBC@FA / NH4HCO3. Its physical image is shown in Figure 10.

[0060] Example 4

[0061] A method for preparing sustained-release and repairing gel beads based on lignin-charcoal-fulvic acid composite material is the same as the preparation steps in 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, and includes the following steps:

[0062] S1. Disperse 50 mg of LBC powder in 50 mL of FA solution with a mass concentration of 1 g / L, sonicate at 0 °C for 30 min in the dark, then centrifuge and dry at 60 °C to obtain lignin biochar@fulvic acid composite material, abbreviated as LBC@FA.

[0063] S2. Mix LBC@FA, SA and NH4HCO3 in a mass ratio of 4:2:4 and sonicate at 0℃ in the dark for 30 minutes to obtain a uniform suspension.

[0064] S3. The suspension was added dropwise to a solution containing 3% (w / v) calcium chloride and allowed to stand at 4°C for 12 hours. The resulting gel beads were filtered out using a filter screen and rinsed multiple times with deionized water to remove residual impurities. After washing, the gel beads were freeze-dried to obtain a slow-release-repair gel bead based on lignin carbon-fulvic acid composite material, denoted as SA / LBC@FA / NH4HCO3.

[0065] Example 5

[0066] A method for preparing sustained-release and repair gel beads based on lignin-charcoal-fulvic acid composite materials includes the following steps:

[0067] S1. Disperse 50 mg of LBC powder in 50 mL of FA solution with a mass concentration of 1 g / L, sonicate at 0 °C for 60 min in the dark, then centrifuge and dry at 60 °C to obtain lignin biochar@fulvic acid composite material, abbreviated as LBC@FA.

[0068] S2. Mix LBC@FA, SA and NH4HCO3 in a mass ratio of 3:2:4 and sonicate at 0℃ in the dark for 30 minutes to obtain a uniform suspension.

[0069] S3. The suspension was added dropwise to a solution containing 3% (w / v) calcium chloride and allowed to stand at 4°C for 4 hours. The resulting gel beads were filtered out using a filter screen and rinsed multiple times with deionized water to remove residual impurities. After washing, the gel beads were freeze-dried to obtain a slow-release-repair gel bead based on lignin carbon-fulvic acid composite material, denoted as SA / LBC@FA / NH4HCO3.

[0070] Comparative Example 1

[0071] A method for preparing composite gel beads includes the following steps:

[0072] S1. Sodium alginate and ammonium bicarbonate are 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.

[0073] S2. The suspension was added dropwise to a solution containing 3% (w / v) calcium chloride and allowed to stand at 4°C for 4 hours. The resulting gel beads were filtered out using a filter screen and rinsed multiple times with deionized water to remove residual impurities. After washing, the composite gel beads were obtained by freeze-drying and denoted as SA / NH4HCO3.

[0074] application:

[0075] a. Soil amendment (slow-release properties):

[0076] Weigh 0.5g of SA / LBC@FA / NH4HCO3 from Examples 1, 3 to 4 respectively. Place SA / LBC@FA / NH4HCO3 and 50mL of deionized water in a beaker. Under a xenon lamp, periodically (10min, 30min, 1h, 3h, 5h, 7h, 9h, 12h, 20h, 24h, 30h, 36h), extract 3mL of the supernatant to determine its concentration and replenish it with an equal amount of deionized water. Meanwhile, 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 samples were 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 absorbance, and the samples were immediately replaced with an equal volume of fresh solution. The FA concentration was measured at 274 nm, and the cumulative release rate of FA was calculated using the formula:

[0077] In the formula, C t V represents the concentration (μg / mL) of FA in the test solution taken at time t; total Vt is the total volume of the test solution (mL); Vt is the sample volume (3mL); m0 is the total drug loading in the test sample (μg).

[0078] Observing Figure 1a, we can see that when the mass ratio W LBC@FA :W SA :W NH4HCO3When the ratio of SA / LBC@FA / NH4HCO3 to FA was 3:2:4, the release rate of SA / LBC@FA / NH4HCO3 in Example 3 was optimal, at 51.87%, approximately twice that of the composite gel beads in Comparative Example 1. Observing Figure 1b, it can be seen 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 within 36 hours, at 85.11%; while within the pH range of 7–11, the release rate gradually increases over the same time period, reaching its highest point at pH = 9, at 96.35%.

[0079] b. Immobilized heavy metal ions:

[0080] (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 to 500mg / L. After constant temperature shaking until adsorption equilibrium is reached, centrifuge and collect the supernatant. Filter the supernatant 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.

[0081] Experimental parameters of the heavy metal ion solution were adjusted one by one based on SA / LBC@FA / NH4HCO3:

[0082] ① The effect of initial pH of the solution:

[0083] Observing Figure 2, it can be seen that SA / LBC@FA / NH4HCO3 in Example 3 has a positive effect on 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 is achieved at a pH value between 4 and 5, for Pb.2+ The removal rate was highest at pH 5.

[0084] ② The effect of initial mass concentration of heavy metal ions:

[0085] As shown in Figure 3, when the initial concentration increased from 20 mg / L to 200 mg / L, Pb 2+ The removal rate increased rapidly, reaching a maximum of 98.99%; however, it gradually decreased with increasing initial solution concentration. When the initial concentration increased from 40 mg / L to 120 mg / L, Cu... 2+ The removal rate rose rapidly to 99.42%, then declined slightly, but still remained above 96%.

[0086] ③The effect of SA / LBC@FA / NH4HCO3 dosage:

[0087] Figure 4 shows that when the dosage of SA / LBC@FA / NH4HCO3 increases from 0.01g to 0.02g, Pb 2+ The removal rate showed a rapid upward trend; however, with further increases in dosage, the removal rate only slightly improved. At a dosage of 0.02 g, Pb... 2+ The removal rate reached a maximum of 99.15%. For Cu 2+ As for the removal rate, it increased from 96.22% to 98.76% when the dosage increased from 0.01g to 0.02g; the removal rate decreased slightly to 97.62% when the dosage was 0.03g; and the removal rate rebounded to 97.89% when the dosage increased to 0.04g.

[0088] (2) Fixation of heavy metal ions in soil columns:

[0089] 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.

[0090] As shown in Figure 5, the initial heavy metal contents of lead-contaminated soil and copper-contaminated soil in the CK group 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, 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.

[0091] For copper-contaminated soil, the Cu content in the CK group also increased from top to bottom: 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 the L1 group, the Cu content distribution was similar to the CK group (240.06 mg / kg in the lower part), indicating that the L1 group had weak Cu adsorption capacity, similar to Pb. The copper content in the L2 group was significantly higher (upper part: 450 mg / kg). In summary, SA / LBC@FA / NH4HCO3 was more effective than pure LBC-KOH in immobilizing lead and copper. It significantly altered the distribution pattern of heavy metals in the soil column through Pb immobilization dominated by chemical complexation and Cu enrichment driven by alkaline precipitation.

[0092] Regarding the effect of heavy metal fixation, in simulating Pb 2+ and Cu 2+ In contaminated soil, the addition of 3% SA / LBC@FA / NH4HCO3 reduced heavy metal leaching by 58% (Pb) and 60% (Cu) compared to the control group (CK group), as shown in Figure 6. Heavy metals were mainly concentrated in the soil surface layer, with significantly inhibited vertical migration, effectively immobilizing the pollutants.

[0093] In terms of sustained-release performance and environmental responsiveness, the FA loading reached a maximum of 94.42 μg / mg, exhibiting good release control under different pH and light conditions. The FA release process of the sustained-release-repair gel beads based on lignin-charcoal-fulvic acid composite material conforms to a non-Fickian diffusion mechanism (Ritger–Peppas model n≈0.5~0.8), and is jointly controlled by diffusion and matrix expansion. The sustained-release-repair gel beads based on lignin-charcoal-fulvic acid composite material maintain good and stable release behavior within the pH range of 5–8, as shown in Figure 1.

[0094] Experimental Procedure: Pb and Cu contaminated soil control group (CK2), Pb and Cu contaminated soil + FA group (F2), and Pb and Cu contaminated soil + 3% SA / LBC-KOH@FA / NH4HCO3 group (L3). Each treatment was replicated three times, with a total of 700g of soil and either FA or SA / LBC-KOH@FA / NH4HCO3 in all treatments. All experimental groups were placed in a well-ventilated room at a temperature maintained between 25℃ and 27℃ and a relative humidity of 60% to 80%. Potted plants were randomly placed and rotated periodically to ensure consistent conditions. Rice seeds were sown evenly in the pots to a depth of approximately 2cm. After 7 days of germination, several healthy plants were retained from each pot, and harvested after 30 days to measure plant height and root length.

[0095] (1) Chlorophyll content:

[0096] Rice leaves were randomly picked, the veins were removed, the leaves were cut and ground, and 0.5 g of the sample was added to a 5 mL centrifuge tube. 25 mL of ethanol-acetone mixture (volume ratio 1:2) was added, and the mixture was extracted in the dark at room temperature for 8 h. The supernatant was then obtained by centrifugation.

[0097] The absorbance was measured at wavelengths of 645 nm and 663 nm using a UV-Vis spectrophotometer. The relevant calculation formulas are expressed as follows:

[0098] Chlorophyll a concentration: Ca = (12.7A663 - 2.69A645) (Equation 1)

[0099] Chlorophyll b concentration: Cb=(22.9A645-4.68A663)×0.05 Equation 2

[0100] Total chlorophyll concentration: Ca + b = (Ca + Cb) Equation 3

[0101] (2) Root vitality:

[0102] Rice root activity was determined using the TTC (2,3,5-triphenyltetrazolium chloride) method. Roots were first washed with distilled water, cut into 1-2 cm segments, placed in centrifuge tubes, and weighed. A 0.5% (w / v) TTC solution was prepared, added to the root samples, and reacted at 30°C in the dark for 3-6 hours. After the reaction, an equal volume of ethanol-acetone (1:1, v / v) was added to terminate the reaction. The mixture was shaken well, allowed to stand for 10 minutes, and then centrifuged. The absorbance of the supernatant was measured at 485 nm using a spectrophotometer, and the content was calculated based on the standard curve.

[0103] Tetrazolium reducing strength per unit mass of fresh root = C / (W·t) Equation 4

[0104] Where C represents the TTC reduction amount (mg) obtained from the standard curve; W is the sample mass (g); and t is the reaction time (h).

[0105] In terms of improving crop growth indicators and mitigating Pb and Cu contaminated soil environments, in a rice pot experiment: the total chlorophyll content of rice in group L2 reached 3.08 mg / g, an increase of 80.1% compared to the contaminated control group (CK2), recovering to 89.5% of the level in the uncontaminated group; root activity increased by 55.6%, and the accumulation of Pb and Cu in roots decreased by 72% and 65%, respectively, significantly alleviating phytotoxicity. Simultaneously, tests showed that after adding the gel, the pH of the contaminated soil increased from 3.8 to 4.8, alleviating the acidic environment and creating a more suitable microenvironment for plant growth, as shown in Figure 7.

[0106] (1) Organic matter content:

[0107] Determination Procedure: Accurately weigh approximately 0.5 g of soil sample into a 250 mL Erlenmeyer flask, add 25 mL of 0.1667 mol / L potassium dichromate solution and 10 mL of 1 mol / L sulfuric acid solution, and shake well; place the Erlenmeyer flask in a 180℃ oil bath for digestion for 30 min, during which organic matter is oxidized and potassium dichromate is reduced to Cr. 3+ After digestion, the solution was cooled to room temperature and diluted to 100 mL. The pH was then measured. Subsequently, a potentiometric titration was performed with 0.1 mol / L ferrous ammonium sulfate solution. The potential change was recorded, and the soil organic matter content (g / kg) was calculated according to Equation 5.

[0108] Organic matter content = 0.003·(V0-V1)·C / m (Equation 5)

[0109] Where V0 is the amount of ferrous ammonium sulfate consumed in the blank titration (mL); V1 is the amount of ferrous ammonium sulfate consumed in the sample titration (mL); C represents the concentration of ferrous ammonium sulfate solution (mol / L); and m is the mass of the soil sample (g).

[0110] (2) Total nitrogen content:

[0111] Determination Procedure: Weigh 0.5g of soil sample into a Kjeldahl flask, add 10mL of concentrated sulfuric acid, 10g of potassium sulfate, and a small amount of catalyst, and shake well. Place in a digestion apparatus, first carbonize at low temperature, then heat to approximately 420℃ and digest until the solution is blue-green and transparent. After cooling, transfer to a 100mL volumetric flask and dilute to volume with deionized water. Take 10mL of this solution into the reaction chamber of the Kjeldahl nitrogen analyzer, add 10mL of 2% boric acid solution and a few drops of mixed indicator, and distill to 50mL. Titrate with 0.1mol / L hydrochloric acid standard solution until the solution changes from blue to gray, record the volume consumed, and calculate the total nitrogen content of the soil (mg / kg) according to Equation 6.

[0112] Total nitrogen content = 0.014(Vb-Va)·C / m (Equation 6)

[0113] Where Vb represents the volume (mL) of hydrochloric acid standard solution consumed in the blank titration; Va is the volume (mL) of hydrochloric acid standard solution consumed in the sample titration; C is the concentration of hydrochloric acid standard solution (mol / L); and m is the mass (g) of the soil sample.

[0114] (3) Total phosphorus and total potassium content:

[0115] Determination Procedure: Weigh 0.2g of soil sample into a digestion tube, add 8mL of nitric acid and 2mL of hydrogen peroxide, shake well, and then place in a microwave digester for digestion. After digestion, cool to room temperature, transfer the solution to a 50mL volumetric flask, make up to volume, and shake well. If suspended matter is present, centrifuge and collect the supernatant. Prepare a series of phosphorus and potassium standard solutions, measure and record the signal intensity using ICP-OES, 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.

[0116] Total phosphorus / potassium content = 1000·C·V / m (Equation 7)

[0117] Where 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), and m is the mass of the soil sample (g).

[0118] Regarding the improvement of soil nutrient content, the contents of total phosphorus, total potassium, total nitrogen and organic matter in the soil were all increased after the gel was applied, showing good soil improvement ability and conducive to restoring the soil ecosystem structure, as shown in Figures 8 and 9.

[0119] It should be noted that when numerical ranges are involved in this invention, it should be understood that both endpoints of each numerical range, as well as any value between the two endpoints, can be selected. Since the steps and methods used are the same as in the embodiments, preferred embodiments are described here to avoid redundancy. Although preferred embodiments of the invention have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments as well as all changes and modifications falling within the scope of this invention.

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 to 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% to 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 materials 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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