Humic-like substance intercalation modified attapulgite as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of environmental heavy metal pollution treatment. The invention discloses humic-like substance intercalation modified attapulgite as well as a preparation method and application thereof. According to the method, a humus-like substance organic precursor is introduced into an attapulgite interlayer domain in a wet immersion and in-situ polycondensation combined mode, a humus-like substance is generated in situ through a polyphenol-Maillard reaction, and successful loading of the humus-like substance on the outer surface and the interlayer domain of attapulgite is achieved. Compared with a traditional method, the problems of insufficient organic matter loading capacity and poor stability are solved, and the adsorption performance of the material on heavy metal ions (such as Cd (II)) is remarkably improved. The prepared modified material has the characteristics of excellent adsorption performance, structural stability and environmental protection, is suitable for treating cadmium ion pollution in water and stabilizing cadmium ions in soil, and provides a new thought for development of a novel environmental remediation material.

Description

Technical Field

[0001] The present invention relates to the technical field of environmental heavy metal pollution control, and particularly relates to a humic-like substance intercalated and modified attapulgite and its preparation method and application. Background Art

[0002] In the processes of smelting operations, the use of pesticides and chemical fertilizers, and mine drainage, excessive cadmium emissions can lead to excessive Cd(II) content in soil and water, thereby threatening the balance of the ecosystem and causing serious harm to human health. Therefore, it is of great practical significance to develop adsorption materials with strong practicability and high economic benefits to improve the remediation efficiency of cadmium-polluted soil and water bodies.

[0003] Attapulgite is a natural clay mineral. Due to its large specific surface area, moderate cation exchange capacity, and surface active hydroxyl groups, it can be used as a natural adsorbent and fixative for heavy metals in soil. However, its adsorption efficiency for Cd(II) is relatively limited and it is difficult to meet the high-efficiency requirements for cadmium pollution remediation in practical applications. To further improve the adsorption capacity of attapulgite, modification is an effective way.

[0004] Traditional methods for modifying attapulgite usually involve mechanically mixing organic matter with attapulgite, so that the organic matter is physically adsorbed on the mineral surface through electrostatic interaction. However, this method has obvious deficiencies: on the one hand, the binding strength between the organic matter and the mineral is weak, relying only on weak electrostatic interactions, and it is easy to fall off under acidic or slightly high-temperature conditions, resulting in poor material stability, poor adsorption effect, and short service life; on the other hand, due to the large hydrodynamic radius of the organic matter and the small interlayer spacing of the mineral, the organic matter is difficult to enter the interlayer domain of the mineral and can only be loaded on its outer surface, with a limited loading amount and difficult to improve the adsorption performance. Summary of the Invention

[0005] To solve the problems existing in the traditional attapulgite modification methods in the prior art, the present invention proposes an innovative method combining "wet impregnation + in-situ polycondensation" for preparing humic-like substance intercalated and modified attapulgite. Through in-situ polycondensation, the humic-like substance can achieve chemical bonding on the surface and in the interlayer domain of attapulgite, forming a firm intercalated structure. Compared with the traditional modification method, the present invention not only significantly improves the loading strength of the organic matter, but also effectively solves the problem of easy shedding of the loaded substances caused by physical adsorption, greatly enhancing the adsorption performance of attapulgite for Cd(II) ions and providing a more reliable method for the efficient remediation of cadmium pollution.

[0006] The preparation process of the present invention is based on the polyphenol-Maillard reaction mechanism. By introducing organic precursors of humic-like substances (such as reducing sugars, amino acids, polyphenolic compounds) into the interlayer domain of attapulgite, humic-like substances are in-situ generated through the polyphenol-Maillard reaction. In this process, reducing sugars provide reducing ability, amino acids provide amino and carboxyl groups, and polyphenolic compounds provide phenolic hydroxyl groups. The three act synergistically to generate complex polycondensation products. These products undergo further polymerization and crosslinking to finally form humic-like substances, which are firmly bonded to the surface and interlayer domain of attapulgite. During the adsorption process, the aromatic structures and functional groups (such as hydroxyl groups, carboxyl groups, etc.) in the humic-like substances undergo complexation reactions with Cd(II) ions to form stable chemical bonds. At the same time, the ion exchange characteristics and surface coordination of attapulgite further enhance the adsorption ability for Cd(II) ions.

[0007] The present invention also studies the adsorption effect of the humic-like substance intercalated and modified attapulgite on Cd(II) in water, aiming to apply it to the field of efficient treatment of Cd(II)-polluted wastewater.

[0008] Another object of the present invention is to provide a humic-like substance intercalated and modified attapulgite prepared by the above preparation method.

[0009] Another object of the present invention is to provide the application of the humic-like substance intercalated and modified attapulgite.

[0010] The present invention is achieved through the following technical solutions: A preparation method of a humic-like substance intercalated and modified attapulgite, comprising the following steps: (1) Add reducing sugars, amino acids and polyphenolic compounds to water, stir until completely dissolved to obtain a mixed solution; (2) Add attapulgite to the mixed solution obtained in step (1), perform ultrasonic treatment, and react at a constant temperature to obtain a suspension; (3) Perform solid-liquid separation on the suspension obtained in step (2), and dry the solid phase to obtain the product.

[0011] Preferably, the reducing sugars include but are not limited to glucose, fructose, maltose, etc.; the amino acids include but are not limited to glycine, alanine, lysine, arginine, etc.; the polyphenolic compounds include but are not limited to catechol, hydroquinone, gallic acid, protocatechuic acid, etc.

[0012] Since the principle of synthesizing humic-like substances is the polyphenol-Maillard theory, and this reaction mechanism is based on polyphenols, amino acids and reducing sugars as organic precursors of humic-like substances, and humic-like substances are in-situ generated through the polyphenol-Maillard reaction. Therefore, the above modifiers are selected as reducing sugars, amino acids and polyphenolic compounds, and none of them can be missing.

[0013] Preferably, glucose, glycine, and catechol are selected as precursors, and the specific reasons are as follows: As a simple reducing sugar, glucose contains multiple hydroxyl groups (-OH), which can participate in condensation reactions to form complex polymers. In the synthesis of humic-like substances, the hydroxyl groups of glucose can undergo dehydration condensation with other compounds to form a stable carbon skeleton.

[0014] As the simplest amino acid, glycine contains an amino group (-NH 2 ) and a carboxyl group (-COOH). These functional groups can participate in condensation reactions to form peptide bonds or crosslink with other organic substances, thereby increasing the complexity and stability of the synthesized products.

[0015] Catechol is an aromatic compound containing phenolic hydroxyl groups (-OH). Its aromatic ring structure and phenolic hydroxyl groups endow it with high reactivity. The phenolic hydroxyl groups of catechol can participate in oxidation reactions to form quinone intermediates, which can then undergo condensation reactions with other organic substances to form humic-like substances with aromatic structures.

[0016] Preferably, in the mixed solution of step (1), the concentration of reducing sugars is 0.025 - 0.1 mol / L, preferably 0.05 mol / L; as a carbon source, the dosage of reducing sugars directly affects the synthesis reaction of humic-like substances. The range of 0.025 - 0.1 mol / L can ensure that there is sufficient carbon source in the reaction system to participate in the condensation reaction and form a stable humic-like substance structure. 0.05 mol / L is considered the optimal dosage because it can not only ensure a high yield of humic-like substances but also avoid side reactions caused by excessive reducing sugars.

[0017] Preferably, in step (1), the concentration of amino acids is 0.025 - 0.3 mol / L, preferably 0.15 mol / L; the concentration of polyphenolic compounds is 0.025 - 0.3 mol / L, preferably 0.15 mol / L; the molar ratio of amino acids to polyphenolic compounds is preferably 5:1 (0.25 mol / L:0.05 mol / L), 3:1 (0.15 mol / L:0.05 mol / L), 1:1 (0.05 mol / L:0.05 mol / L), 1:3 (0.05 mol / L:0.15 mol / L), and 1:5 (0.05 mol / L:0.25 mol / L), and the molar ratio of 3:1 (0.15 mol / L:0.05 mol / L) is further preferred.

[0018] This is because amino acids provide amino groups and carboxyl groups, while polyphenolic compounds provide phenolic hydroxyl groups. A molar ratio of 3:1 can enable these functional groups to achieve better complementarity in the reaction and promote the condensation reaction. When it is too high (such as 1:5): When the proportion of polyphenolic compounds is too high, the oxidation reaction of phenolic hydroxyl groups may be too intense, resulting in an excessive amount of quinone intermediates generated, which instead inhibits the condensation reaction with amino acids. This will result in a lower molecular weight of the synthesized humic-like substances and a decrease in adsorption performance. When it is too low (such as 5:1): When the proportion of amino acids is too high, the reaction activities of amino groups and carboxyl groups may not be fully utilized, resulting in insufficient aromaticity of the humic-like substances and a reduction in adsorption sites. In addition, too high an amino acid proportion may also increase the synthesis cost. Preferably, in step (1), the water is deionized water; the amount of deionized water added is 200 mL; Preferably, in step (2), the ultrasonic treatment conditions are as follows: the time is 5 - 20 min, preferably 8 - 12 min, for example 10 min; the ultrasonic power is 200 - 300 W, preferably 230 - 250 W, for example 240 W. Research shows that an ultrasonic time of 5 - 20 minutes can not only ensure sufficient contact and dispersion between the organic matter and attapulgite, for example, 10 minutes of ultrasonic treatment can avoid energy waste caused by too long a time and possible damage to the molecular structure of the organic matter, but also ensure sufficient contact and dispersion between the organic matter and attapulgite. A power range of 200 - 300 W can provide sufficient energy to promote the intercalation reaction between the organic matter and attapulgite, while avoiding local overheating or damage to the organic matter structure caused by too high a power. For example, 240 W can improve the energy utilization efficiency while ensuring the reaction efficiency, making it easier for organic matter molecules to enter the interlayer of attapulgite and form a stable intercalated structure.

[0019] Preferably, in step (2), the constant-temperature reaction is carried out in a constant-temperature shaker, and the constant-temperature reaction conditions are as follows: 40 - 50 °C, reacting for 8 - 12 days, preferably maintaining the temperature at 45 °C and reacting for 10 days; this is because during the composting process, 40 - 50 °C is considered the optimal temperature range for humus formation, and the temperature conditions are set with reference to this. A reaction time of 8 - 12 days can ensure that the synthesis reaction of the humic-like substances proceeds fully.

[0020] Preferably, in step (3), the drying is carried out by vacuum freeze-drying, and the freeze-drying time is 72 ± 5 h.

[0021] The humic-like substance intercalated and modified attapulgite modified material prepared by the above preparation method.

[0022] The application of the above humic-like substance intercalated and modified attapulgite in treating Cd(II) pollution in the environment.

[0023] Preferably, the environment includes industrial wastewater, industrial solid waste, and polluted soil contaminated with Cd(II).

[0024] In addition, the present invention also provides a method for treating Cd(II)-polluted wastewater with humic substance-like intercalated modified attapulgite, which comprises the following steps: Add the humic substance-like intercalated modified attapulgite into the Cd(II)-polluted wastewater, and fully contact and react to remove Cd(II) in the water body.

[0025] Preferably, in order to make Cd(II) and the adsorbent fully contact, stirring or oscillation can be carried out.

[0026] Preferably, based on the comprehensive consideration of adsorption efficiency, economy and environmental impact, the dosage of the humic substance-like intercalated modified attapulgite is 0.5 - 2.5 g / L; in order to effectively improve the adsorption performance of Cd(II) ions and avoid the cost increase and environmental risks brought by excessive use, it is further preferably 2.0 g / L; Preferably, since the adsorption equilibrium time of the attapulgite material is short, the adsorption time for full contact reaction is 10 - 120 min; based on the comprehensive consideration of adsorption efficiency and economy, the adsorption equilibrium has been reached at 60 min, and it is further preferably 60 min.

[0027] The beneficial effects of the present invention are as follows: (1) Aiming at the problems of poor stability and short service life in the existing organic modification methods of attapulgite, the present invention prepares humic substance-like intercalated modified attapulgite through an innovative method combining "wet impregnation + in-situ polycondensation". The humic substance-like substances can be chemically adsorbed on the surface and interlayers of attapulgite, and a stable intercalated structure is formed through strong chemical bonding. This structure not only significantly enhances the adsorption ability of attapulgite for Cd(II) ions, improves the adsorption efficiency, but also can maintain good stability under acidic or slightly high temperature conditions, extends the service life of the material, effectively solves the problem of insufficient organic matter loading in traditional methods, and significantly improves the adsorption performance of the material; The core innovation of the present invention lies in the application of in-situ intercalation technology. Compared with traditional physical adsorption methods, in-situ intercalation fixes humic substance-like substances in the interlayers of attapulgite through chemical bonding, forming a stable intercalated structure, significantly improving the loading strength and avoiding the problem of easy shedding of the loaded substances. In addition, by optimizing the reaction conditions (such as temperature, pH value and the use of catalysts), the present invention realizes the efficient synthesis of humic substance-like substances, further improving the adsorption performance of the modified attapulgite. This technology not only improves the loading strength, but also enhances the adsorption ability for Cd(II) ions through the humic substance-like substances fixed by chemical bonding, and at the same time conforms to the development concept of green chemistry; (2) The treatment process of the present invention is to add the modified material to the sewage, which does not require special equipment or complex operations, and the operation is simple; (3) The raw materials used in the method of the present invention are widely sourced, low-cost, and environmentally friendly, in line with the concept of green chemistry, without secondary pollution, and have significant economic and environmental benefits. (4) By optimizing the preparation process and adsorption conditions, the modified attapulgite not only applies to treating industrial wastewater polluted by Cd(II), but also can be used to control polluted soil and industrial solid waste, providing new ideas for the development and application of new environmental materials and showing broad application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] To more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. The drawings in the following description are merely exemplary, and for those of ordinary skill in the art, other implementation drawings can be obtained by extension based on the provided drawings without creative efforts.

[0029] Figure 1 It is the influence of the modified material in Example 1 on the adsorption effect of Cd(II) under different dosing ratios of glycine and catechol. Figure 2 It is the influence of the modified material in Example 2 on the adsorption effect of Cd(II) under different dosages. Figure 3 It is the influence of the modified material in Example 3 on the adsorption effect of Cd(II) at different adsorption times. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0030] To more clearly elaborate the purpose, technical solutions, and advantages of the present invention, the following will be described in detail with reference to the drawings and specific embodiments. The embodiments shown in the drawings are only exemplary embodiments of the present invention and do not limit the implementation manner thereof. The present invention can be implemented in various forms, and its design concept and core technology are not limited by the embodiments shown in the drawings. The purpose of providing these embodiments is to make it easier for technicians to understand the principles, structures, and functions of the present invention, so as to better master and apply its technical solutions. The terms used in this specification are only for describing specific embodiments and do not constitute a limitation to the present invention.

[0031] Example 1: Preparation of the modified material Prepare humic-like substance intercalated modified attapulgite, and the specific steps are as follows: (1) Add a certain amount of glucose, glycine, and catechol in a certain proportion into a wide-mouth conical flask, add a certain amount of deionized water, and stir until completely dissolved to form a mixed solution. (2) Add 4 g of attapulgite to the solution obtained in step (1), after ultrasonic treatment for 10 min, place the mixture in a constant-temperature shaker and keep the temperature at 45°C for reaction for 10 days. (3) Intercalation modification of attapulgite with the humic substance-like material obtained in step (2). The suspension is subjected to solid-liquid separation, and the obtained solid phase is vacuum freeze-dried for 72 h to obtain the modified material, which is stored in a vacuum desiccator.

[0032] Among them, the preferred experiment on the dosing ratio of glycine and catechol: The material preparation process is basically the same as above. The difference is that in step (1), the dosing amount of glucose is 0.1 mol, and the molar ratios of glycine to catechol are 5:1 (0.05 mol:0.01 mol), 3:1 (0.03 mol:0.01 mol), 1:1 (0.01 mol:0.01 mol), 1:3 (0.01 mol:0.03 mol), and 1:5 (0.01 mol:0.05 mol), respectively. The preferred molar ratio is 3:1 (0.03 mol:0.01 mol).

[0033] In addition, a comparative experiment was also set up, which was attapulgite without modification in step (1), and the others were the same as steps (2) and (3) above.

[0034] The following application tests were carried out on the prepared materials: Prepare a solution with an initial cadmium concentration of 200 mg / L, adjust the initial pH = 7, and add 0.03 g of the different modified materials prepared above to 20 mL of Cd(II) solution respectively. Oscillatory reduction adsorption is carried out at 25 °C and 200 r / min for 1440 min. After filtration through a 0.22 μm filter membrane, the cadmium concentration in the filtrate is detected by "Determination of Copper, Zinc, Lead, and Cadmium in Water - Atomic Absorption Spectrophotometry" (GB 7475-87), and the Cd(II) reduction adsorption capacity of different modified materials is calculated.

[0035] The results are as Figure 1 shown. Among them, the modified material with a dosing ratio of glycine to catechol of 3:1 has the best adsorption effect, and the maximum reduction adsorption capacity is 54.47 mg / g. While the maximum adsorption capacities of the modified materials with dosing ratios of glycine to catechol of 5:1, 1:1, 1:3, 1:5, and unmodified attapulgite are 51.5, 47.52, 33.74, 26.85, and 1.54 mg / g respectively. The adsorption capacity of the modified material is much greater than that of unmodified attapulgite.

[0036] This example shows that the modified material has a better adsorption effect on Cd(II) in water, providing a basis for its practical application in treating Cd(II)-polluted wastewater.

[0037] Example 2: Influence of different dosing amounts on the adsorption effect Select the modified material with a glycine to catechol dosing ratio of 3:1 in Example 1. Accurately weigh different masses (0.01, 0.02, 0.03, 0.04, 0.05 g) and add them to 20 mL of a Cd(II) solution with a concentration of 200 mg / L at pH = 7, such that the dosing amounts of the modified material are 0.5, 1.0, 1.5, 2.0, 2.5 g / L respectively. The remaining operation procedures and detection methods are the same as those in the application test method of Example 1.

[0038] The adsorption capacities of the modified material under different dosing amounts are as Figure 2 shown. The experimental results show that when the dosing amounts of the modified material are 0.5, 1.0, 1.5, 2.0, 2.5 g / L respectively, the adsorption capacity data are 13.82, 20.19, 43.85, 54.47, 45.52 mg / g respectively. That is, when the dosing amount of the modified material is 2.0 g / L, the maximum adsorption capacity at this time is 54.47 mg / g.

[0039] This example shows that the addition of the modified material provides a basis for the rapid and efficient treatment of Cd(II)-containing wastewater.

[0040] Example 3: Influence of different reaction times on the adsorption effect Select the modified material with a glycine to catechol dosing ratio of 3:1 in Example 1. Accurately weigh the modified material and add it to 20 mL of a Cd(II) solution with a concentration of 200 mg / L at pH = 7. The experiment is carried out at room temperature. Take the supernatant at different time intervals (5, 10, 15, 30, 45, 60, 90, 120 min) to measure the Cd(II) concentration. The operation procedures and detection methods are the same as those in the application test method of Example 1.

[0041] It can be seen from Figure 3 that at different time intervals: 5, 10, 15, 30, 45, 60, 90, 120 min, the adsorption capacity data are: 34.62, 41.51, 47.72, 50.82, 52.34, 53.56, 54.01, 54.30 mg / g respectively. It can be seen that when the adsorption time reaches 60 min, the adsorption has reached equilibrium.

[0042] This example shows that the modified material has good treatment effects when repairing Cd(II)-containing wastewater with different concentrations, providing a technical guarantee for its rapid and efficient treatment of heavy metal pollution in water bodies.

[0043] Example 4: Comparison of different modified materials Using the same application test method as in Example 1, attapulgite modified by different modification methods was measured, and the maximum adsorption capacities are shown in the following table: Table 1. Comparison of the maximum adsorption capacities of different attapulgite modified materials

[0044] Literature 1: Cadmium adsorption onto aluminum hydroxide - modified attapulgite prepared with basic aluminum acetate. Zhang Q, Chu R, Wei Y, et al. Scientific Reports, 14: 31428, 2024. Literature 2: Removal of Cd(II) and Pb(II) from aqueous solution by modified attapulgite clay. Huang R, Lin Q, Zhong Q, et al. Arabian Journal of Chemistry, 13: 4994 - 5008, 2020. Literature 3: Study of adsorption property and mechanism of lead(II) and cadmium(II) onto sulfhydryl modified attapulgite. Fu C, Zhu X, Dong X, et al. Arabian Journal of Chemistry, 14: 102960, 2021. It can be seen from the above comparative experiments that, compared with methods such as aluminum hydroxide modification, sulfhydryl modification, high - temperature calcination, and hydrothermal loading of MgO, the present invention significantly enhances the adsorption capacity of attapulgite for Cd(II) ions and improves the adsorption efficiency by intercalating and modifying attapulgite with humic - like substances.

[0045] Finally, we need to emphasize that the examples provided here are only a part of the examples of the present invention, not all of them. All other examples obtained by those skilled in the art based on the present invention without creative efforts shall fall within the scope of protection of the present invention.

Claims

1. A method for preparing attapulgite modified by intercalation of humus-like substances, characterized in that: The following steps are involved: (1) Add reducing sugars, amino acids and polyphenol compounds to water and stir until they are completely dissolved to obtain a mixed solution; (2) adding attapulgite to the mixed solution obtained in step (1), subjecting the mixture to ultrasonic treatment and reacting the mixture at a constant temperature to obtain a suspension; (3) performing solid-liquid separation on the suspension obtained in step (2), and drying the solid phase to obtain; Among them, the reducing sugars include but are not limited to glucose, fructose, maltose, preferably glucose; the amino acids include but are not limited to glycine, alanine, lysine, arginine, preferably glycine; the polyphenol compounds include but are not limited to catechol, hydroquinone, gallic acid, protocatechuic acid, preferably catechol.

2. The preparation method according to claim 1, characterized in that: In the mixed solution of step (1), the concentration of reducing sugars is 0.025-0.1 mol / L, preferably 0.05 mol / L; the concentration of amino acids is 0.025-0.3 mol / L, preferably 0.15 mol / L; the concentration of polyphenols is 0.025-0.3 mol / L, preferably 0.15 mol / L; wherein the molar ratio of amino acids to polyphenols is preferably 5:1 (0.25 mol / L: 0.05 mol / L), 3:1 (0.15 mol / L: 0.05 mol / L), 1:1 (0.05 mol / L: The preferred molar ratio is 1:0 (0.05 mol / L: 0.05 mol / L), 1:3 (0.05 mol / L: 0.15 mol / L) and 1:5 (0.05 mol / L: 0.25 mol / L), and the more preferred molar ratio is 3:1 (0.15 mol / L: 0.05 mol / L).

3. The preparation method according to claim 1, characterized in that: In step (2), the ultrasonic treatment conditions are as follows: ultrasonic time is 5-20 min, preferably 8-12 min, for example 10 min; ultrasonic power is 200-300 W, preferably 230-250 W, for example 240 W.

4. The preparation method according to claim 1, characterized in that: In step (2), the isothermal reaction is carried out in a constant temperature shaker, and the constant temperature reaction conditions are: 40-50°C, and the reaction time is 8-12 days, preferably the temperature is kept at 45°C, and the reaction time is 10 days.

5. The preparation method according to claim 1, characterized in that: In step (3), drying is performed by vacuum freeze drying, and the freeze drying time is 72±5h.

6. Humus-like substance intercalation modified attapulgite prepared by the preparation method according to any one of claims 1 to 5.

7. The use of humus-like substance intercalation modified attapulgite according to claim 6, characterized in that: The invention is applied in treating Cd(II) pollution in the environment; the environment includes industrial wastewater, industrial solid waste and contaminated soil polluted by Cd(II).

8. The use according to claim 7, characterized in that: The method for treating wastewater contaminated with Cd(II) is as follows: adding humus-like intercalation-modified attapulgite into the wastewater contaminated with Cd(II) to allow for sufficient contact reaction.

9. The use according to claim 8, characterized in that: The dosage of humus-like substance intercalated modified attapulgite is 0.5-2.5 g / L, preferably 2.0 g / L.

10. The use according to claim 8, characterized in that: The time for sufficient contact reaction is 10-120 min, preferably 60 min.

Images