A material for removing sodium ions from saline-alkali soil and its preparation method

Abstract

The present invention provides a material and a preparation method for removing sodium ions from saline-alkali land, which relates to the field of sodium ion adsorbents and comprises the following steps: (1) modifying lignin: dissolving sulfate lignin in a mixed solution of analytically pure acetic acid and 30% hydrogen peroxide under water bath conditions, adding ferric chloride, reacting for 1.5-2.5 hours, diluting 7-8 times with distilled water, centrifuging, washing, and drying to obtain oxidized lignin; (2) synthesizing hydrogel: mixing oxidized lignin with analytically pure acrylic acid, adding a crosslinking agent and an initiator, and reacting in an oven at 65-75°C for 1.5-2.5 hours to form a sodium ion adsorption material with a porous interpenetrating network structure; the present invention can improve the performance of lignin in applications such as adsorbing ions and preparing hydrogels by modifying lignin, especially introducing more hydroxyl and carboxyl groups.

Description

Technical Field

[0001] The present invention relates to the field of sodium ion adsorbents, in particular to a material for removing sodium ions from saline-alkali soils and a preparation method thereof. Background Art

[0002] Saline-alkali land refers to land containing excessive amounts of soluble salts (such as sodium, chloride, and sulfate ions), which deteriorate the soil's physical and chemical properties and affect plant growth. Sodium ions are one of the most potent ions in saline-alkali land. High concentrations of sodium ions can damage soil structure, reduce permeability, and decrease nutrient availability, leading to stunted plant growth, reduced yields, and even plant death. Therefore, effectively removing or reducing sodium ion levels in saline-alkali land is a key issue in soil improvement.

[0003] Chinese patent publication number CN118369155A discloses a sodium ion adsorbent, a preparation method thereof, and a sodium ion removal method. The sodium ion adsorbent for removing sodium ions may include a compound represented by the following chemical formula 1. Chemical formula 1: H x M 1-x AlSi2O6, in the chemical formula 1, M is one or more elements selected from Na, K, Cs and Rb, and 0 <x≤1。

[0004] This adsorbent is based on a specific aluminosilicate compound and shows certain effectiveness in removing sodium ions, but it still has some limitations, which restricts its widespread application in saline-alkali soil improvement.

[0005] First, the sodium ion adsorbent disclosed in this invention is primarily based on inorganic compounds. Its preparation process may involve high-temperature calcination and complex synthesis steps, resulting in high energy consumption and relatively high production costs. This may increase the economic burden for large-scale application in saline-alkali soil improvement, limiting its widespread use.

[0006] Secondly, inorganic adsorbents are often sensitive to environmental conditions (such as pH, temperature, and ionic strength), and their adsorption performance can vary significantly under different environmental conditions. The complex and variable environment of saline-alkali lands, with significant fluctuations in factors such as pH and ionic strength, can lead to unstable adsorption performance of these inorganic adsorbents in practical applications, making it difficult to consistently and effectively remove sodium ions.

[0007] Furthermore, the adsorbent disclosed in this invention primarily removes sodium ions from water. However, sodium ions in saline-alkali soils not only exist in the soil solution but are also tightly bound to soil particles, forming a complex soil salinity system. Therefore, relying solely on sodium ion removal technology from water is unlikely to fully address the sodium ion problem in saline-alkali soils. Summary of the Invention

[0008] To address the above technical issues, the present invention proposes a high-molecular sodium ion adsorption material synthesized from organic matter. This material not only has the advantages of low cost, readily available raw materials, and a simple synthesis method, but also has good water absorption and water retention, and can effectively adsorb sodium ions in saline-alkali land and improve soil structure. Compared with traditional materials, the adsorption material of the present invention has significant advantages in terms of environmental friendliness, resource conservation, and ease of operation. It can also adsorb sodium ions under relatively low conditions, greatly reducing production and application costs, and promoting the popularization and application of saline-alkali land soil improvement technology. The details are as follows:

[0009] A method for preparing a material for removing sodium ions from saline-alkali soil comprises the following steps:

[0010] (1) Modified lignin: Dissolve the kraft lignin in a mixed solution of analytical grade acetic acid and 30% hydrogen peroxide at 75-90°C in a water bath, then add ferric chloride. After reacting for 1.5-2.5 hours, dilute it 7-8 times with distilled water, centrifuge it, wash it with anhydrous ethanol, and dry it to obtain oxidized lignin.

[0011] (2) Hydrogel synthesis: Mix oxidized lignin and analytically pure acrylic acid and stir for 10-20 minutes, add a crosslinker and an initiator, stir for 10-20 minutes, and then react in an oven at 65-75°C for 1.5-2.5 hours to form a sodium ion adsorption material with a porous interpenetrating network structure.

[0012] Furthermore, a method for preparing a material for removing sodium ions from saline-alkali soil comprises the following steps:

[0013] (1) Modified lignin: Dissolve the sulfated lignin in a mixed solution of analytical grade acetic acid and 30% hydrogen peroxide at 80°C in a water bath, then add ferric chloride. After reacting for 2 hours at 80°C in a water bath, dilute the solution 7.5 times with distilled water, centrifuge, wash with anhydrous ethanol, and dry to obtain oxidized lignin.

[0014] (2) Hydrogel synthesis: Oxidized lignin was mixed with analytically pure acrylic acid and stirred for 15 minutes, a cross-linking agent and an initiator were added, and the mixture was stirred for 15 minutes and then reacted in an oven at 70°C for 2 hours to form a sodium ion adsorption material with a porous interpenetrating network structure.

[0015] Moreover, in step (1), the volume ratio of the analytically pure acetic acid to 30% hydrogen peroxide is 3.5-4.5:1; the material-liquid ratio of the mixed solution of the kraft lignin: pure acetic acid and 30% hydrogen peroxide is 1:4-6 (g / ml);

[0016] The material-liquid ratio of the ferric chloride to 30% hydrogen peroxide is 0.01-0.02:1 (g / ml).

[0017] Furthermore, in step (1), centrifugation is performed at 4800 rpm for 25-35 minutes.

[0018] Moreover, in step (2), the mass ratio of oxidized lignin to cross-linking agent + initiator is 1:2.5-3.5.

[0019] Moreover, in step (2), the mass ratio of the oxidized lignin to analytically pure acrylic acid is 1:19-23.

[0020] Moreover, in step (2), the cross-linking agent is N,N-methylenebisacrylamide, and the initiator is potassium persulfate.

[0021] Moreover, in step (2), the mass ratio of the cross-linking agent MBA to the initiator KPS is 1.8-2.2:1.

[0022] In a second aspect, the present invention discloses an adsorption material for removing sodium ions from saline-alkali land obtained by a preparation method.

[0023] In a third aspect, the present invention discloses an application of an adsorption material for removing sodium ions from saline-alkali land, which is used for improving saline-alkali land soil.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] The present invention modifies lignin to add hydroxyl and carboxyl groups to the lignin. Lignin is an important component of plant cell walls and has a porous structure and natural aromatic chemical properties. Since its main function in wood is to provide structural support and antioxidant properties, the natural structure and function of lignin are not ideal in some applications, especially in scenarios where improved adsorption performance is required. The present invention improves the performance of lignin in applications such as ion adsorption and hydrogel preparation by modifying lignin, especially introducing more hydroxyl and carboxyl groups. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 The SEM micromorphologies of various gels are as follows: 1(a) Example 1, 1(b) Comparative Example 1, 1(c) Comparative Example 2, 1(d) Comparative Example 3, 1(e) Comparative Example 4;

[0027] Figure 2 The water absorption images of various gels;

[0028] Figure 3 is the result of sodium ion adsorption. DETAILED DESCRIPTION

[0029] Example 1

[0030] A method for preparing a material for removing sodium ions from saline-alkali soil comprises the following steps:

[0031] Step 1: Add 16.0 ml of analytical grade acetic acid and 4.0 ml of 30% hydrogen peroxide to a 200 ml beaker to prepare a solution. Place the prepared solution in an 80°C water bath.

[0032] Step 2: Add 4.0 g of sulfate lignin to the prepared solution, react in a water bath at 80° C. for 15 minutes, then add 0.04 g of ferric chloride, and react in a water bath at 80° C. for 2 hours; dilute the reacted solution 7.5 times with distilled water, centrifuge at 4800 rpm for 30 minutes, wash with anhydrous ethanol, and finally dry to obtain oxidized lignin.

[0033] Step 3: At room temperature, 0.2 g of oxidized lignin and 4.0 ml of analytical grade acrylic acid were mixed and stirred for 15 minutes. Then, 0.4 g of cross-linking agent N,N-methylenebisacrylamide and 0.2 g of initiator potassium persulfate were added and stirred for 15 minutes. The mixture was then placed in a 70°C oven for reaction for 2 hours.

[0034] Example 2

[0035] A method for preparing a material for removing sodium ions from saline-alkali soil comprises the following steps:

[0036] Step 1: Add 18.0 ml of analytical grade acetic acid and 4.0 ml of 30% hydrogen peroxide to a 200 ml beaker to prepare a solution. Place the prepared solution in an 85°C water bath.

[0037] Step 2: Add 4.0 g of sulfate lignin to the prepared solution, react in a water bath at 85° C. for 25 minutes, then add 0.04 g of ferric chloride, and react in a water bath at 85° C. for 2.5 hours; dilute the reacted solution 8-fold with distilled water, centrifuge at 4800 rpm for 35 minutes, wash with anhydrous ethanol, and finally dry to obtain oxidized lignin.

[0038] Step 3: At room temperature, 0.2 g of oxidized lignin and 4.4 ml of analytical grade acrylic acid were mixed and stirred for 25 minutes. Then, 0.44 g of cross-linking agent N,N-methylenebisacrylamide and 0.2 g of initiator potassium persulfate were added and stirred for 25 minutes. The mixture was then placed in a 75°C oven for reaction for 2.5 hours.

[0039] Example 3

[0040] A method for preparing a material for removing sodium ions from saline-alkali soil comprises the following steps:

[0041] Step 1. Add 14.0 ml of analytical grade acetic acid and 4.0 ml of 30% hydrogen peroxide to a 200 ml beaker to prepare a solution. Place the prepared solution in a 75°C water bath.

[0042] Step 2: Add 4.0 g of sulfate lignin to the prepared solution, react in a water bath at 75° C. for 10 minutes, then add 0.04 g of ferric chloride, and react in a water bath at 75° C. for 1.5 hours; dilute the reacted solution 7-fold with distilled water, centrifuge at 4800 rpm for 25 minutes, wash with anhydrous ethanol, and finally dry to obtain oxidized lignin.

[0043] Step 3: At room temperature, 0.2 g of oxidized lignin and 3.6 ml of analytical grade acrylic acid were mixed and stirred for 10 minutes. Then, 0.36 g of cross-linking agent N,N-methylenebisacrylamide and 0.2 g of initiator potassium persulfate were added and stirred for 10 minutes. The mixture was then placed in a 65°C oven for reaction for 1.5 hours.

[0044] Comparative Example 1

[0045] The main difference between this comparative example and Example 1 is that in step 2, the amounts of oxidized lignin, cross-linking agent N,N-methylenebisacrylamide and initiator potassium persulfate are different, as follows:

[0046] A method for preparing a material for removing sodium ions from saline-alkali soil comprises the following steps:

[0047] Step 1. Add 16.0 ml of analytical grade acetic acid and 4.0 ml of 30% hydrogen peroxide to a 200 ml beaker to prepare a solution. Place the prepared solution in an 80°C water bath.

[0048] Step 2: Add 4.0 g of sulfate lignin to the prepared solution, react in a water bath at 80° C. for 15 minutes, then add 0.04 g of ferric chloride, and react in a water bath at 80° C. for 2 hours; dilute the reacted solution 7.5 times with distilled water, centrifuge at 4800 rpm for 30 minutes, wash with anhydrous ethanol, and finally dry to obtain oxidized lignin.

[0049] Step 3: At room temperature, 0.4 g of oxidized lignin and 4.0 ml of analytical grade acrylic acid were mixed and stirred for 15 minutes. Then, 0.8 g of cross-linking agent N,N-methylenebisacrylamide and 0.4 g of initiator potassium persulfate were added and stirred for 15 minutes. The mixture was then placed in a 70°C oven for reaction for 2 hours.

[0050] Comparative Example 2

[0051] The main difference between this comparative example and Example 1 is that in step 2, ferric chloride is not added, as follows:

[0052] A method for preparing a material for removing sodium ions from saline-alkali soil comprises the following steps:

[0053] Step 1: Add 16.0 ml of analytical grade acetic acid and 4.0 ml of 30% hydrogen peroxide to a 200 ml beaker to prepare a solution. Place the prepared solution in an 80°C water bath.

[0054] Step 2: Add 4.0 g of sulfate lignin to the prepared solution and react in a water bath at 80° C. for 2 hours; dilute the reaction solution 7.5 times with distilled water, centrifuge at 4800 rpm for 30 minutes, wash with anhydrous ethanol, and finally dry to obtain oxidized lignin.

[0055] Step 3: At room temperature, 0.2 g of oxidized lignin and 4.0 g of analytically pure acrylic acid were mixed and stirred for 15 minutes. Then, 0.4 g of cross-linking agent N,N-methylenebisacrylamide and 0.2 g of initiator potassium persulfate were added and stirred for 15 minutes. The mixture was then placed in a 70°C oven for reaction for 2 hours.

[0056] Comparative Example 3

[0057] The main difference between this comparative example and Example 1 is that in step 2, acetic acid is not added, as follows:

[0058] A method for preparing a material for removing sodium ions from saline-alkali soil comprises the following steps:

[0059] Step 1. Add 16.0 ml of distilled water and 4.0 ml of 30% hydrogen peroxide to a 200 ml beaker to prepare a solution. Place the prepared solution in an 80°C water bath.

[0060] Step 2: Add 4.0 g of kraft lignin to the prepared solution, react in an 80°C water bath for 15 minutes, then add 0.04 g of ferric chloride, and react in an 80°C water bath for 2 hours. The resulting solution is diluted 7.5 times with distilled water, centrifuged at 4800 rpm for 30 minutes, washed with anhydrous ethanol, and finally dried to obtain oxidized lignin.

[0061] Step 3: At room temperature, 0.2 g of oxidized lignin and 4.0 ml of analytical grade acrylic acid were mixed and stirred for 15 minutes. Then, 0.4 g of cross-linking agent N,N-methylenebisacrylamide and 0.2 g of initiator potassium persulfate were added and stirred for 15 minutes. The mixture was then placed in a 70°C oven for reaction for 2 hours.

[0062] Comparative Example 4

[0063] The main difference between this comparative example and Example 1 is that in step 2, no hydrogen peroxide is added, as follows:

[0064] A method for preparing a material for removing sodium ions from saline-alkali soil comprises the following steps:

[0065] Step 1. Add 16.0 g of analytical grade acetic acid and 4.0 ml of distilled water to a 200 ml beaker to prepare a solution. Place the prepared solution in an 80°C water bath.

[0066] Step 2: 4.0 g of sulfate lignin was added to the prepared solution, and the mixture was reacted in a water bath at 80° C. for 15 minutes. 0.04 g of ferric chloride was then added, and the mixture was reacted in a water bath at 80° C. for 2 hours. The reacted solution was diluted 7.5 times with distilled water, centrifuged at 4800 rpm for 30 minutes, washed with anhydrous ethanol, and finally dried to obtain oxidized lignin.

[0067] Step 3: At room temperature, 0.2 g of oxidized lignin and 4.0 ml of analytical grade acrylic acid were mixed and stirred for 15 minutes. Then, 0.4 g of cross-linking agent N,N-methylenebisacrylamide and 0.2 g of initiator potassium persulfate were added and stirred for 15 minutes. The mixture was then placed in a 70°C oven for reaction for 2 hours.

[0068] 1. Analyze the microstructure

[0069] The microstructure of the gels prepared in Example 1 and Comparative Examples 1-4 was analyzed by SEM images. Figure 1 , Figure 1 The microscopic morphologies of the gels are as follows: (a) Example 1, (b) Comparative Example 1, (c) Comparative Example 2, (d) Comparative Example 3, and (e) Comparative Example 4.

[0070] It can be clearly seen from the figure that Figure 1 In (a), many salt crystalline particles are attached to the gel wall, and the microstructural characteristics of the oxidized lignin hydrogel can be observed; the gel wall in the figure shows an obvious network structure, which may be due to the cross-linking characteristics of the hydrogel; in detail, the gel wall is covered with some small particles or sediments, which are adsorbed sodium ions or the products of the interaction between sodium ions and the hydrogel.

[0071] As can be seen from Figures 1(b) and 1(c), the hydrogel has a distinct pore structure, showing a relatively regular grid-like pattern of pores, which contributes to improved adsorption capacity. The size and shape of the gel's pore structure may affect the adsorption efficiency of sodium ions, as larger pores provide more adsorption surface area, while smaller pores may contribute to higher surface energy, further promoting ion adsorption.

[0072] The surface features in images 1(d) and 1(e) reveal a relatively fine microstructure on the gel wall, likely representing the site of sodium ion adsorption. These features suggest that the oxidized lignin hydrogel exhibits surface affinity and adsorption capacity during sodium ion adsorption, albeit at a lower level than in Example 1.

[0073] In general, Figure 1 The figure provides an intuitive demonstration of the sodium ion adsorption process of the oxidized lignin hydrogel. The network structure and micropore characteristics of the gel may have an important influence on the ion adsorption efficiency. It can be seen from the figure that Example 1 has the best adsorption performance.

[0074] 2. Water absorption performance analysis

[0075] The seven gels prepared in Examples 1-3 and Comparative Examples 1-4 were weighed after absorbing water for 2, 4, 8, 16, 24, 48, 72, 96, and 120 hours, and the water absorption of the gels was measured. The water absorption curve of the gels over time ( Figure 2 ) shows that the water absorption rate of each gel is above 120g / g. The effect of the embodiment is significantly improved compared with the comparative example. The best effect is embodiment 1, which has a water absorption rate of 139.364g / g. The high water absorption rate of the gel indicates that there are many internal adsorption points. Figure 1 The same conclusion can be obtained, indicating that the adsorption effect of Example 1 is the most significant.

[0076] 3. Analysis of sodium ion adsorption performance

[0077] To evaluate the sodium ion adsorption performance of the materials, 1 g of each of the seven hydrogel samples (Examples 1-3 and Comparative Examples 1-4) was placed in a solution with a sodium ion concentration of 1.5 g / L. Adsorption experiments were carried out at 25°C, pH = 9, and an oscillation frequency of 120 rpm / min. The adsorption amount was measured by atomic absorption spectrometry, with samples taken every 2 hours for 24 hours.

[0078] The results showed that ( Figure 3 ), the adsorption performance of all examples was significantly superior to that of the comparative example, with Example 1 demonstrating the highest adsorption capacity, reaching a maximum adsorption capacity of 220 μg / g. This result confirms that the material prepared in this invention possesses excellent sodium ion adsorption capabilities. In contrast, the lack of any of the components in the comparative example, including ferric chloride, hydrogen peroxide, or acetic acid, resulted in insufficient lignin oxidation and a significant decrease in adsorption capacity. This experiment further demonstrates the crucial role of ferric chloride, hydrogen peroxide, and acetic acid in this invention; any of these components are essential; otherwise, the oxidation of the oxidized lignin would be compromised, thereby reducing the adsorption performance of the final material.

Claims

1. A method for preparing an adsorption material for removing sodium ions from saline-alkali soil, characterized in that: The steps include: (1) Modified lignin: Dissolve the kraft lignin in a mixed solution of analytical grade acetic acid and 30% hydrogen peroxide at 75-90°C in a water bath, then add ferric chloride. After reacting for 1.5-2.5 hours, dilute it 7-8 times with distilled water, centrifuge it, wash it with anhydrous ethanol, and dry it to obtain oxidized lignin. The volume ratio of the analytically pure acetic acid to 30% hydrogen peroxide is 3.5-4.5:1; The material-liquid ratio of the kraft lignin: a mixed solution of analytically pure acetic acid and 30% hydrogen peroxide is 1:4-6 (g / ml); The material-liquid ratio of the ferric chloride to 30% hydrogen peroxide is 0.01-0.02:1 (g / ml); (2) Hydrogel synthesis: oxidized lignin and analytically pure acrylic acid were mixed and stirred for 10-20 minutes, a crosslinker and an initiator were added, and the mixture was stirred for 10-20 minutes and then reacted in an oven at 65-75°C for 1.5-2.5 hours to form a porous interpenetrating network structure of sodium ion adsorption material; The mass ratio of the oxidized lignin to analytically pure acrylic acid is 1:19-23.

2. The method for preparing an adsorption material for removing sodium ions from saline-alkali soil according to claim 1, wherein: In step (1), centrifuge at 4800 rpm for 25-35 minutes.

3. The method for preparing an adsorption material for removing sodium ions from saline-alkali soil according to claim 1, wherein: In step (2), the mass ratio of oxidized lignin to cross-linking agent + initiator is 1:2.5-3.

5.

4. The method for preparing an adsorption material for removing sodium ions from saline-alkali soil according to claim 1, wherein: In step (2), the cross-linking agent is N,N-methylenebisacrylamide, and the initiator is potassium persulfate.

5. The method for preparing an adsorption material for removing sodium ions from saline-alkali soil according to claim 1, wherein: In step (2), the mass ratio of the cross-linking agent to the initiator is 1.8-2.2:

1.

6. An adsorption material for removing sodium ions from saline-alkali land, characterized in that: The adsorption material is obtained by the preparation method according to any one of claims 1 to 5.

7. The use of an adsorption material for removing sodium ions from saline-alkali soil according to claim 6, characterized in that: Used for saline-alkali soil improvement.

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