A composite gel material, its preparation method and use

Abstract

The application discloses a kind of composite gel materials and preparation method and application thereof, it is related to gel material technical field.The preparation raw material of composite gel material of the application includes chitosan, modified iron oxyhydroxide and crosslinking agent;The modified iron oxyhydroxide is aluminum ion doped iron oxyhydroxide.The composite gel material provided by the application can be used as soil remediation material, used in heavy metal contaminated soil remediation, can effectively adsorb heavy metal ions, promote the oxidation of arsenic, enhance the treatment effect of arsenic, and the fixing effect of heavy metal is good, it is favorable to prevent the migration and pollution of heavy metal, simultaneously also significantly improve the water retention and fertilizer retention of soil, solve the problem that existing soil remediation material cannot simultaneously satisfy soil remediation and soil nutrition protection, it is the effective measure of soil pollution treatment and heavy metal remediation.

Description

Technical Field

[0001] This invention relates to the field of gel materials technology, and in particular to a composite gel material, its preparation method, and its application. Background Technology

[0002] Heavy metal pollution in soil is a long-term and complex problem, and its remediation process needs to consider multiple factors such as remediation efficiency, soil health, and the sustainability of agricultural production. Traditional soil remediation methods (such as chemical precipitation and elution) may lead to the loss of beneficial nutrients in the soil, affecting soil fertility and structural stability, and failing to achieve the dual goals of heavy metal pollution remediation and soil nutrient protection. For example, some conventional remediation processes require large amounts of water or chemical reagents, causing elution and loss of nutrients in the soil (such as nitrogen, phosphorus, and potassium), thereby affecting crop growth and soil sustainability.

[0003] Existing technologies disclose a carbon-bacterial coupled heavy metal soil remediation material, using goethite-modified biochar and Burkholderia as the main functional components. While the resulting material can remove heavy metal cations, its removal effect on heavy metal anions is minimal due to the large number of negative charges on its surface as an organic material. Existing iron-based materials (such as iron ore powder and iron oxides) can adsorb and passivate certain heavy metals when remediating soil heavy metal pollution, but their effectiveness is often unstable. This is because iron-based materials may undergo polymerization, precipitation, or redox reactions, affecting their adsorption capacity and long-term effectiveness for heavy metals. Furthermore, most current soil remediation methods fail to effectively prevent the secondary release of heavy metals during removal or immobilization, especially in environments containing reducing microorganisms. Heavy metals often return to the soil solution due to reduction reactions, causing secondary pollution. For example, iron-based materials may interact with reducing bacteria in the soil, leading to the reduction and dissolution of iron minerals, thereby releasing the adsorbed heavy metals and reducing the remediation effect. Therefore, most current heavy metal soil remediation materials or methods have different limitations, such as being unable to remove both anions and cations, having poor long-term adsorption effects, or being unable to simultaneously meet the requirements of soil remediation and soil nutrient protection. Summary of the Invention

[0004] The present invention aims to at least solve one of the aforementioned technical problems existing in the prior art. Therefore, the objective of the present invention is to provide a composite gel material, using chitosan, modified ferric hydroxide, and a crosslinking agent as the main raw materials, which can effectively adsorb heavy metal ions, while simultaneously achieving water retention, fertilizer retention, and mitigation of acidification effects. Furthermore, the heavy metal passivation effect is stable, avoiding the problem of secondary pollution.

[0005] A second aspect of the present invention is to provide a method for preparing a composite gel material.

[0006] A third aspect of the present invention is to provide a soil remediation material.

[0007] A fourth aspect of the present invention is to provide a soil remediation method.

[0008] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0009] The first aspect of the present invention provides a composite gel material, the raw materials for which include chitosan, modified ferric hydroxide and a crosslinking agent; wherein the modified ferric hydroxide is aluminum ion-doped ferric hydroxide.

[0010] In the composite gel material of this invention, chitosan, as a natural organic substance, can enhance the water and fertilizer retention capacity of soil. The network structure of chitosan is strengthened using a cross-linking agent, resulting in a gel that helps reduce nutrient loss and protects soil fertility. Simultaneously, the composite gel material contains modified ferric hydroxide, which is aluminum-doped ferric hydroxide. The transition metal aluminum ions undergo isomorphic substitution with the iron atoms on the ferric hydroxide, leading to disordered lattice arrangement of the ferric hydroxide, forming numerous structural defects and highly reactive oxygen vacancies. This provides a large number of adsorption sites, and the enhanced surface defects improve the adsorption and passivation effects on heavy metals. Its arsenic oxidation ability also helps inhibit arsenic migration, making it difficult for already adsorbed and fixed heavy metal ions to be released secondary. Furthermore, because the modified ferric hydroxide is present in the gel, the gel network structure effectively isolates the ferric hydroxide from contact with reducing bacteria in an environment containing reducing microorganisms, avoiding the reduction and dissolution of ferric hydroxide caused by reduction reactions, thereby reducing secondary pollution from heavy metals. Heavy metal ions are individual atoms or molecules, much smaller than reducing bacteria. Therefore, the gel effectively isolates reducing bacteria without hindering the adsorption of heavy metal ions. Furthermore, the gel's network structure not only maintains the stability of ferric hydroxide but also prevents the aggregation and precipitation of modified ferric hydroxide, enhancing its dispersibility and stability in the soil. This achieves a synergistic effect in promoting soil remediation and heavy metal passivation.

[0011] Therefore, the composite gel material provided by this invention can solve multiple problems in the remediation of soil heavy metal pollution, such as heavy metal removal and soil nutrient protection, and has important practical application significance, especially in the fields of agricultural pollution control, soil health restoration and environmental protection.

[0012] It should be noted that chitosan ultimately exists in the composite gel material in the form of chitosan hydrochloride.

[0013] In some embodiments of the present invention, the mass concentration of the crosslinking agent in the composite gel material is 0.4-1.2%.

[0014] In some embodiments of the present invention, the mass concentration of the crosslinking agent in the composite gel material is 0.5% to 1%.

[0015] The concentration of crosslinking agent affects the gel network structure of composite gel materials, thus affecting their water retention and fertilizer retention effects.

[0016] In some embodiments of the present invention, the crosslinking agent includes at least one of glutaraldehyde and sucralose.

[0017] In some embodiments of the present invention, the specific surface area of ​​the composite gel material is 700–1000 m². 2 / g.

[0018] In some embodiments of the present invention, the specific surface area of ​​the composite gel material is 750–960 m². 2 / g.

[0019] A second aspect of the present invention provides a method for preparing the composite gel material described in the first aspect of the present invention, comprising the following steps:

[0020] Modified ferric hydroxide was mixed with chitosan solution, and a crosslinking agent was added to carry out a crosslinking reaction to obtain the composite gel material.

[0021] In the preparation process of this invention, the modified ferric hydroxide is thoroughly mixed with the chitosan solution to ensure that the modified ferric hydroxide is completely dispersed in the chitosan solution, and to avoid the formation of undissolved particles.

[0022] After adding a crosslinking agent, the mixture of modified ferric hydroxide and chitosan solution gradually becomes viscous, forming a gel. This is because the crosslinking agent reacts chemically with the amino and aldehyde groups of chitosan molecules, forming a stable crosslinked network structure and enhancing the chemical stability of the gel.

[0023] In some embodiments of the present invention, the chitosan solution has a chitosan mass concentration of 1-3%.

[0024] In some embodiments of the present invention, the solvent of the chitosan solution includes an acetic acid solution; the pH of the acetic acid solution is 4 to 6.

[0025] In some embodiments of the present invention, the precipitant comprises sodium hydroxide; the concentration of the sodium hydroxide is 4 to 6 mol / L.

[0026] In some embodiments of the present invention, the crosslinking reaction takes 1.5 to 2.5 hours.

[0027] In some embodiments of the present invention, the preparation method of the modified ferric hydroxide includes the following steps:

[0028] A solution of ferric salt and an aluminum salt were mixed, and a precipitant was added to carry out a precipitation reaction to obtain a precipitate. The precipitate was then purified to obtain the modified ferric hydroxide.

[0029] In some embodiments of the present invention, the trivalent iron salt includes ferric chloride; the aluminum salt includes aluminum chloride; and the molar ratio of ferric chloride to aluminum chloride is 1:(0.2-0.7).

[0030] In some embodiments of the present invention, the molar ratio of ferric chloride to aluminum chloride is 1:(0.3 to 0.5).

[0031] Specifically, the molar ratio of ferric chloride to aluminum chloride can be 1:0.3, 1:0.4, 1:0.5, or 1:0.7.

[0032] In some embodiments of the present invention, the endpoint pH of the precipitation reaction is 7.0 to 7.5.

[0033] In some embodiments of the present invention, the purification method includes dialysis.

[0034] In some embodiments of the present invention, the dialysis step includes dispersing the precipitate in water and performing dialysis using a dialysis bag with a molecular weight cutoff of 95-105 kDa; the dialysis time is 70-75 h.

[0035] In some embodiments of the present invention, the purification process further includes an aging step.

[0036] In some embodiments of the present invention, the aging temperature is 65-75°C; and the aging time is 55-65 hours.

[0037] A third aspect of the present invention provides a soil remediation material, comprising the composite gel material described in the first aspect of the present invention, or the composite gel material prepared by the preparation method described in the second aspect of the present invention.

[0038] To address soil heavy metal pollution and soil conservation, soil remediation materials generally need to improve the soil's physicochemical properties, particularly enhancing its water and fertilizer retention capacity, while simultaneously remediating heavy metals. This reduces nutrient loss during remediation and ensures soil fertility and optimal plant growth conditions. The composite gel material of this invention forms a gel network structure through chitosan and a cross-linking agent, while simultaneously loading modified iron hydroxide, exhibiting excellent water and fertilizer retention properties and enhancing the soil's water and fertilizer retention capacity.

[0039] Furthermore, the composite gel material of the present invention has a long-term fixation and passivation effect on heavy metal ions. The gel network structure combined with modified iron hydroxide avoids the aggregation, precipitation and reduction dissolution of iron hydroxide, and can maintain or enhance its adsorption capacity while avoiding the secondary release of heavy metals.

[0040] A fourth aspect of the present invention provides a soil remediation method, which utilizes the composite gel material described in the first aspect of the present invention or the soil remediation material described in the third aspect of the present invention for soil remediation.

[0041] Compared with the prior art, the present invention has at least the following beneficial technical effects:

[0042] The composite gel material of this invention uses chitosan, modified ferric hydroxide, and a crosslinking agent as raw materials. The modified ferric hydroxide has abundant adsorption sites, while the gel formed by chitosan and the crosslinking agent has chemical stability and good water and fertilizer retention for soil. The resulting composite gel material has high adsorption capacity and high adsorption efficiency for heavy metal ions and can be used as a soil remediation material. It can solve the problem of soil nutrient loss while remediating heavy metal pollution, ensuring soil fertility and plant growth conditions, and reducing the risk of secondary pollution. Detailed Implementation

[0043] The present invention will be further described in detail below through specific embodiments. Unless otherwise specified, the raw materials, reagents, or apparatus used in the embodiments and comparative examples are all available from conventional commercial sources or can be obtained by existing technical methods. Unless otherwise specified, the test or experimental methods are conventional methods in the art.

[0044] The following detailed description is provided in conjunction with specific examples, embodiments, and comparative examples.

[0045] Example 1

[0046] A composite gel material is prepared from chitosan, modified ferric hydroxide, and glutaraldehyde as a crosslinking agent; wherein the modified ferric hydroxide is aluminum ion-doped ferric hydroxide; and the mass concentration of glutaraldehyde in the composite gel material is 1%.

[0047] The preparation method of this composite gel material includes the following steps:

[0048] S1. Preparation of modified ferric hydroxide:

[0049] A ferric chloride and aluminum chloride solution (molar ratio 1:0.5, chloride ion concentration 4.5 mol / L) was thoroughly mixed, and then sodium hydroxide (5 mol / L) precipitant was added dropwise while maintaining a magnetic stirring speed of 150 rpm. When co-precipitation of the ferric chloride and aluminum chloride mixture began to occur, the temperature of the mixture was maintained at 25°C until the pH of the mixture rose to 8.0. At this point, the addition of precipitant was stopped, and the mixture was then magnetically stirred at 150 rpm for 3 hours.

[0050] After the mixture was stirred, the precipitate was obtained by centrifugation. The precipitate was dispersed in deionized water and placed in a dialysis bag with a molecular weight cutoff of 100 KD. The dialysis bag was used for purification to remove residual solvent, unreacted ions and other impurities from the precipitate suspension. The dialysis time was 72 hours.

[0051] The purified precipitate suspension was placed in an oven and aged at 70°C for 60 hours to obtain modified iron hydroxide with abundant surface defects.

[0052] S2. A mixture of modified ferric hydroxide and chitosan:

[0053] 15g of chitosan was dissolved in acetic acid solution (pH=5) and stirred until completely dissolved, avoiding the formation of undissolved particles, to form a transparent chitosan solution (mass concentration of 3%). Then, the chitosan solution was thoroughly mixed with 1g of modified ferric hydroxide to ensure complete dispersion of the modified ferric hydroxide in the chitosan solution. The mass ratio of chitosan to modified ferric hydroxide was 15:1. The specific surface area of ​​the modified ferric hydroxide was 367 m². 2 / g;

[0054] S3. Crosslinking agent reaction forms gel:

[0055] The crosslinking agent glutaraldehyde was dissolved in deionized water and then added to the chitosan solution containing modified ferric hydroxide obtained in step S2 to form a precursor solution. The solution was stirred until homogeneous to ensure sufficient distribution of the crosslinking agent. The mass concentration of the crosslinking agent in the precursor solution was 1%, and the mass ratio of chitosan to modified ferric hydroxide was 15:1. The precursor solution was allowed to stand for 2 hours to allow the crosslinking reaction to proceed fully, resulting in a composite gel material. The specific surface area of ​​this composite gel material was 959 m². 2 / g.

[0056] Example 2

[0057] A composite gel material and its preparation method differ from Example 1 in that: the mass concentration of the crosslinking agent in the composite gel material is 0.5%; and the mass concentration of the crosslinking agent in the precursor solution in its preparation method is 0.5%.

[0058] Example 3

[0059] A composite gel material and its preparation method are disclosed. The raw materials are the same as in Example 1, except that the molar ratio of ferric chloride to aluminum chloride is 1:0.3 in the preparation of the modified ferric hydroxide; the specific surface area of ​​the obtained modified ferric hydroxide is 253 m². 2 / g, the specific surface area of ​​the composite gel material is 753m². 2 / g.

[0060] Comparative Example 1

[0061] A chitosan gel, the preparation method of which differs from that of Example 1, is provided in that modified ferric hydroxide is not added; the specific surface area of ​​this chitosan gel is 561 m². 2 / g.

[0062] Comparative Example 2

[0063] A chitosan gel, the preparation method of which differs from that of Example 2, is that no modified iron hydroxide is added.

[0064] Comparative Example 3

[0065] A type of ferric hydroxide, the preparation method of which differs from step S1 of Example 1 in that aluminum chloride is not added; otherwise, the steps are the same as in step S1 of Example 1; the specific surface area of ​​this ferric hydroxide is 116 m². 2 / g.

[0066] Test case

[0067] The gel materials obtained in the examples and comparative examples were used as soil remediation materials. Soil samples were taken from the top 0–20 cm soil layer in Yingtan City, Jiangxi Province (28°8′39″N, 116°47′21″E). The collected soil samples were air-dried and sieved through a 2 mm sieve for subsequent soil experiments. Their physicochemical properties are shown in Table 1. Control groups were set up by replacing the gel materials with the raw materials used in the examples and comparative examples. The materials used in different control groups are shown in Table 2.

[0068] Table 1. Physicochemical properties of the soil used in the experiment.

[0069]

[0070]

[0071] Table 2. Raw materials used to replace gel materials in different control groups.

[0072]

[0073] Meanwhile, a blank control group was set up containing only the same soil without the addition of any gel material or its raw materials.

[0074] The specific testing method is as follows:

[0075] 1. Take equal amounts of materials from the example, comparative example, and each control group, and add them to the same soil to conduct soil nutrient protection tests:

[0076] Water retention test: By simulating drought conditions (temperature 40℃, humidity 35%), the changes in soil moisture content of different groups were recorded, and the soil moisture evaporation rate was measured within 48 hours to obtain the water retention rate.

[0077] Fertilizer retention test: A standard fertilizer (NPK compound fertilizer with a total nutrient content of 35%, a NPK ratio of 1:3:2, and an application rate of 5g) was applied. The fertilizer release rate was recorded after fertilization, and the residual amount of fertilizer was analyzed 48 hours after fertilization using soil extraction methods to obtain the fertilizer retention rate. Fertilizer retention rate = residual amount of fertilizer at 48 hours / application amount of fertilizer × 100%.

[0078] Soil organic matter content: Dry the soil sample and take an appropriate amount (2g); place the sample in a high-temperature furnace and heat at 550℃ for more than 4 hours; calculate the organic matter content by the reduction in sample mass. Organic matter content (%) = (Initial soil mass - Soil mass after incineration) / (Initial soil mass)

[0079] 2. Heavy metal ion removal test:

[0080] Adding heavy metal ions (Pb) to the soil 2+ Cu 2+ Cd 2+ The solution of As (arsenite) was mixed thoroughly. After 1 hour of adsorption in the soil, the materials from the examples, comparative examples, and control groups were added to the soil. After another 1 hour of reaction, the changes in heavy metal ion concentration were analyzed and calculated. During the adsorption process, the pH ranged from 6.0 to 7.4, and Eh ranged from 251 to 260 mV. The adsorption capacity was calculated based on the adsorption rate equation of the adsorption isotherm.

[0081] 3. Oxidizing power test for trivalent arsenic:

[0082] The soil was subjected to an adsorption test using the same method as in "2. Heavy Metal Ion Removal Test". Then, arsenic present in the soil was extracted using hydrochloric acid. Subsequently, the valence state of arsenic was tested using liquid chromatography-atomic fluorescence spectrometry (LC-AFS) to obtain the concentrations of trivalent and pentavalent arsenic. The oxidation rate of trivalent arsenic = (trivalent arsenic concentration / (trivalent arsenic concentration + pentavalent arsenic concentration)) × 100%.

[0083] The test results are shown in Tables 3 to 6.

[0084] Table 3 Results of Soil Nutrient Protection Tests

[0085]

[0086] As shown in Table 3, the composite gel material obtained in the embodiments of the present invention, when used as a soil remediation material, can effectively ensure soil nutrition, has good water and fertilizer retention effects, and can significantly improve the soil's water retention capacity and soil organic matter content. Compared with the blank control group that did not use any soil remediation material, its water retention rate and fertilizer retention rate increased by at least 20%, and as the mass concentration of the crosslinking agent increased from 0.5% to 1%, the soil water retention rate increased from 65% to 72% after use. In contrast, Comparative Examples 1 and 2, which did not add modified ferric hydroxide and only used chitosan gel, had lower water and fertilizer retention rates than the embodiments, and the soil organic matter content was also lower. Control groups 1 and 2, which used chitosan or modified ferric hydroxide alone, had worse effects than Examples 1-2 and Comparative Examples 1-2. This indicates that the combination of modified ferric hydroxide and chitosan gel helps to slowly release and stabilize soil organic matter after fertilization and can improve the soil's water retention effect.

[0087] Table 4 Results of heavy metal ion adsorption capacity test

[0088]

[0089]

[0090] Table 5 Results of heavy metal ion adsorption efficiency test

[0091]

[0092] As can be seen from Tables 4 and 5, using the composite gel material of this invention as a soil remediation material significantly improves both the adsorption capacity and adsorption efficiency for heavy metal ions. The adsorption capacity for arsenic is no less than 60%, and the adsorption efficiency is no less than 90%, while the adsorption capacity for Pb is also significantly improved. 2+ Cu 2+ Cd 2+ The adsorption efficiencies all reached over 70%, significantly higher than the comparative and control groups. Furthermore, comparing Examples 1 and 3 shows that as the molar ratio of ferric chloride to aluminum chloride decreases, the adsorption efficiency of the resulting composite gel material for heavy metal ions in the soil increases. It should be noted that the adsorption efficiency of the blank control group represents the adsorption efficiency of the soil itself after the heavy metal ions are added to the soil.

[0093] Furthermore, the addition of cross-linking agents gives the resulting chitosan gel an amorphous structure with a larger adsorption surface, while the modified iron hydroxide also has more adsorption sites, thus enabling it to adsorb more heavy metal ions and achieve better anchoring, preventing the adsorbed heavy metal ions from rapidly desorbing. At the same time, the gel's protection of the modified iron hydroxide also prevents the desorption caused by reducing bacteria in the soil environment acting on the modified iron hydroxide, thus avoiding secondary pollution.

[0094] Table 6. Results of Arsenic Oxidation Capacity Test

[0095]

[0096]

[0097] As shown in Table 6, the composite gel material of this invention, when used as a soil remediation material, exhibits excellent arsenic oxidation capability. For example, Examples 1 and 3 in Table 6 demonstrate significant advantages in arsenic oxidation, effectively oxidizing As(III) to As(V) with an arsenic oxidation rate of not less than 70%. Furthermore, the arsenic oxidation rate increases with increasing aluminum doping content. This is because the active oxygen vacancies on the surface of the aluminum-doped iron hydroxide allow it to catalyze the arsenic oxidation reaction, while the chitosan gel provides a stable environment, contributing to improved oxidation efficiency. In contrast, the blank soil group without any remediation material achieved only 20% arsenic oxidation.

[0098] In summary, the composite gel material provided by this invention can be used as a soil remediation material for the remediation of soils contaminated with heavy metals. It can effectively adsorb heavy metal ions, promote the oxidation of arsenic, enhance the remediation effect of arsenic, and has a good fixation effect on heavy metals, which helps prevent the migration and pollution of heavy metals. At the same time, it significantly improves the water retention and fertilizer retention of the soil, solving the problem that existing soil remediation materials cannot simultaneously meet the requirements of soil remediation and soil nutrient protection. It is an effective measure for soil pollution control and heavy metal remediation.

[0099] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A composite gel material, characterized by, The raw materials for preparation include chitosan, modified ferric hydroxide, and a crosslinking agent; the modified ferric hydroxide is aluminum ion-doped ferric hydroxide. The crosslinking agent is glutaraldehyde; The preparation method of the composite gel material includes the following steps: Modified ferric hydroxide was mixed with chitosan solution, and a crosslinking agent was added to carry out a crosslinking reaction to obtain the composite gel material.

2. The composite gel material of claim 1, wherein, In the composite gel material, the mass concentration of the crosslinking agent is 0.4~1.2%.

3. A method of preparing the composite gel material of claim 1 or 2, characterized in that, Includes the following steps: Modified ferric hydroxide was mixed with chitosan solution, and a crosslinking agent was added to carry out a crosslinking reaction to obtain the composite gel material.

4. The production method according to claim 3, characterized by, The preparation method of the modified ferric hydroxide includes the following steps: A solution of ferric salt and an aluminum salt were mixed, and a precipitant was added to carry out a precipitation reaction to obtain a precipitate. The precipitate was then purified to obtain the modified ferric hydroxide.

5. The production method according to claim 4, characterized by, The ferric salt includes ferric chloride; the aluminum salt includes aluminum chloride; the molar ratio of ferric chloride to aluminum chloride is 1:(0.2~0.7).

6. The preparation method according to claim 3, characterized in that, The chitosan solution contains 1-3% chitosan by mass.

7. The preparation method according to claim 4, characterized in that, The endpoint pH of the precipitation reaction is 8.

8. The preparation method according to claim 4, characterized in that, The purification method includes dialysis; And / or, the purification process may further include an aging step.

9. A soil remediation material, characterized by, Includes the composite gel material according to any one of claims 1 to 2, or the composite gel material prepared by the preparation method according to any one of claims 3 to 8.

10. A soil remediation method, characterized in that, Soil remediation is carried out using the composite gel material according to any one of claims 1 to 2 or the soil remediation material according to claim 9.

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