Attapulgite-based hydrogel, its preparation method and application in repairing saline-alkali soil

Abstract

This invention discloses a method for preparing attapulgite-based hydrogel. The method includes: (1) mixing ethylene carbonate, ethylene glycol, phosphoric acid, and straw powder and heating to react, obtaining liquid biomass; (2) mixing acid-modified attapulgite, acrylic acid, acrylamide, and liquid biomass in water, then adding a crosslinking agent to react and obtain the attapulgite-based hydrogel. Compared with the prior art, the attapulgite-based hydrogel of this invention not only reduces the salinity of saline-alkali soils but also significantly increases the soil's cation exchange capacity and the levels of key N and K nutrients.

Description

Technical Field

[0001] This invention belongs to the field of saline-alkali soil remediation, and specifically relates to an attapulgite-based hydrogel for remediating saline-alkali soil. Background Technology

[0002] Saline-alkali land is a significant abiotic stress factor that restricts the improvement of agricultural production quality and efficiency, and has a serious adverse impact on the normal operation of agricultural production. Excessive salinity and alkalinity in this type of soil hinders normal crop growth and development, affects root uptake of water and nutrients, and interferes with crop physiological metabolism and morphogenesis, leading to substantial yield reductions or even complete crop failure, resulting in significant economic losses to agricultural production. Summary of the Invention

[0003] The purpose of this invention is to provide an attapulgite-based hydrogel that not only reduces the salinity of saline-alkali soils, but also significantly increases the soil's cation exchange capacity and the levels of key N and K nutrients.

[0004] To achieve the above objectives, the present invention adopts the following technical solution:

[0005] A method for preparing an attapulgite-based hydrogel, comprising:

[0006] (1) Mix ethylene carbonate, ethylene glycol, phosphoric acid and straw powder and heat to react to obtain liquid biomass;

[0007] (2) After mixing acid-modified attapulgite, acrylic acid, acrylamide and liquid biomass in water, a crosslinking agent is added to react and the attapulgite-based hydrogel is obtained.

[0008] Preferably, in step (1), the mass ratio of ethylene carbonate, ethylene glycol, phosphoric acid and straw powder is 5~6:0.7~0.8:0.2~0.3:1.

[0009] Preferably, in step (1), the heating reaction temperature is 160~200℃ and the time is 0.5~1 hour.

[0010] Preferably, in step (2), the mass ratio of acrylic acid to acrylamide is 2~4:1, the mass ratio of acid-modified attapulgite to liquid biomass is 1:1~3, and the amount of acid-modified attapulgite is 1~8% of the total mass of acrylic acid and acrylamide.

[0011] Preferably, in step (2), the degree of neutralization of acrylic acid is 60-80%.

[0012] Preferably, in step (2), the crosslinking agent is N,N-methylenebisacrylamide.

[0013] More preferably, the amount of N,N-methylenebisacrylamide used is 0.1 to 0.2% of the total mass of acrylic acid and acrylamide.

[0014] Preferably, the acid-modified attapulgite is obtained by mixing attapulgite with acid for a certain period of time.

[0015] More preferably, the acid solution is a phosphoric acid solution or nitric acid solution with a concentration of 2-10 wt%, the amount of acid solution used is 50-80 wt% of the mass of attapulgite, and the reaction time is 1-2 hours.

[0016] An attapulgite-based hydrogel prepared according to the above method.

[0017] The application of the above-mentioned attapulgite-based hydrogel in the remediation of saline-alkali soil.

[0018] A method for remediating saline-alkali soil includes:

[0019] (1) The above-mentioned attapulgite-based hydrogel is brought into full contact with urea solution and then dried;

[0020] (2) Add 0.5~1.5wt% of attapulgite-based hydrogel treated in step (1) and 2~4wt% of acid-modified attapulgite to the saline-alkali soil.

[0021] Preferably, after the treatment in step (1), the urea content in the attapulgite-based hydrogel is 2-5 wt%.

[0022] More preferably, the urea content in the attapulgite-based hydrogel is 2-3 wt%. Attached Figure Description

[0023] Figure 1 Scanning electron micrograph (a) and elemental distribution map (b) of LBH-ATP prepared for Example 1.

[0024] Figure 2 The changes in pH, electrical conductivity (EC), cation exchange capacity (CEC), and soil organic matter (SOM) before and after saline-alkali soil remediation were studied.

[0025] Figure 3 The changes in available potassium (AK), available nitrogen (AN), and available phosphorus (AP) before and after saline-alkali soil remediation. Detailed Implementation

[0026] The technical solution of the present invention will be further described in detail below with reference to the embodiments.

[0027] Attapulgite (ATP) was purchased from Linze County Fenjun Mining Co., Ltd.

[0028] The saline-alkali soil sample was collected in Jingyuan County, Baiyin City, Gansu Province. The pH reached 8.91, and the electrical conductivity was 2580 µS·cm. -1 It far exceeds the suitable range for arable soil and exhibits obvious characteristics of saline-alkali stress.

[0029] Preparation of acid-modified attapulgite (A-ATP): Phosphoric acid was diluted to a concentration of 10 wt%, and then the phosphoric acid solution was thoroughly mixed with attapulgite and reacted for 1 hour. The amount of phosphoric acid solution used was 60 wt% of the mass of attapulgite. After the reaction was completed, the mixture was sieved, aged at room temperature for 12 h, and then dried at 30 ℃ for 24 h for later use.

[0030] Example 1

[0031] The corn stalks were crushed and passed through an 80-mesh sieve and set aside.

[0032] Preparation of liquid biomass: Add 176 mL of ethylene carbonate (C3H4O3, a strong polar cyclic solvent that strongly dissolves lignin, cellulose, and hemicellulose), 28.6 mL of ethylene glycol (C2H6O2, which is compounded with ethylene carbonate to reduce the viscosity of the system, enhance fluidity, and facilitate mass transfer and stirring reaction) and 6 mL of phosphoric acid (H3PO4, a strong catalyst) to a flask. After mixing, heat to 180℃, and then add 42 g of corn straw while stirring (750 rpm). After the addition is complete, continue stirring and reacting for 50 min to obtain liquid biomass (LCS). Allow it to cool naturally for later use.

[0033] Neutralizing acrylic acid: Add 15.85 mL of acrylic acid (AA) to a beaker, followed by dilution with 30 mL of deionized water. Place the beaker in an ice-water bath and, with magnetic stirring, gradually add a 1 mol·L⁻¹ solution. -1 Add NaOH solution until the acrylic acid reaches the specified degree of neutralization.

[0034] Preparation of attapulgite-based hydrogel: Add 2g of A-ATP and 30mL of deionized water to a beaker, stir well, then add 5g of acrylamide (AM), the above-mentioned neutralized acrylic acid solution, and liquid biomass to the beaker according to the ratio (see Table 1), stir well, then add 0.1wt% (based on the total amount of monomers AA+AM) of N,N-methylenebisacrylamide (MBA), heat the temperature to 30℃ and stir for 15 min to obtain attapulgite-based hydrogel (denoted as LCS-ATP).

[0035] A 12wt% urea solution was uniformly sprayed onto the surface of attapulgite-based hydrogel (87.32g). The amount of urea solution used in a single spray was 7.00g. The surface was then air-dried at 30℃ for 2 hours. The spraying was repeated three times, and finally the surface was air-dried at 30℃ for 12 hours to obtain attapulgite-based hydrogel that had absorbed urea (denoted as LBH-ATP).

[0036] The experiment was designed using Design-Expert software, with the following variables: A, degree of neutralization; B, AA:AM (mass ratio); and C, LCS:A-ATP (mass ratio).

[0037] Table 1 LBH-ATP Preparation Experiment

[0038]

[0039] The mass swelling ratio (Y) of LBH-ATP prepared in each experimental group in NaCl solution (30%wt) was used as the indicator for fitting a multiple quadratic regression equation and analysis of variance. The results are as follows:

[0040] The multiple quadratic regression equation is:

[0041] Y=245.31+10.63A+9.01B+6.96C-6.25AB-5.84AC-12.75BC-29.50A 2 -19.40B 2 -19.82C 2

[0042] Table 2. Analysis of variance of each term in the regression equation

[0043]

[0044] Note: * P<0.05, significant difference; ** P<0.01, highly significant difference.

[0045] The optimal solution of the model is: when the degree of neutralization is 70.84%, the ratio of AA to AM is 3.17:1, and the ratio of LCS to A-ATP is 2.12:1, the predicted swelling rate of LBH-ATP in NaCl solution is 247.11%.

[0046] Verification experiments were conducted with a neutralization degree of 70%, an AA:AM ratio of 3:1, and an LCS:A-ATP ratio of 2:1. The measured swelling rate of the prepared LBH-ATP in NaCl solution was 245.56%, with a relative error of only 0.63% compared to the predicted value, indicating that the actual result is very close to the predicted value. Leaching experiments were then conducted on saline-alkali soils using LBH-ATP prepared under these conditions.

[0047] Figure 1The images show scanning electron microscopy (SEM) images and elemental distribution diagrams of the prepared LBH-ATP. It can be seen that the material exhibits an inter-linked folded structure, with abundant three-dimensional pores between the layers, and a tightly stacked and coherent porous layered structure internally.

[0048] Soil leaching test of saline-alkali soil:

[0049] The remediation agent was mixed with 2 kg of sieved saline-alkali soil according to the specified ratio (see Table 3), and then packed into an acrylic glass column (inner diameter 115 mm, column height 300 mm) and compacted. Based on the local average annual rainfall of 300 mm, leaching was performed every three days for a total of 33 days, with 10 leaching cycles to simulate the annual rainfall infiltration. After leaching, the sample was removed from the soil column, air-dried in a cool place, ground, sieved, and analyzed.

[0050] Table 3 Dosage of Repair Agent

[0051]

[0052] Note: n=3.

[0053] Figure 2 The changes in pH, electrical conductivity (EC), cation exchange capacity (CEC), and soil organic matter (SOM) before and after saline-alkali soil remediation were studied.

[0054] Figure 3 The changes in available potassium (AK), available nitrogen (AN), and available phosphorus (AP) before and after saline-alkali soil remediation.

[0055] from Figure 2-3 It can be seen that after the saline-alkali soil was repaired by the LBH-ATP method of this invention, the conductivity decreased from 2580 μs·cm. -1 Reduced to 335 μs·cm -1 The salinity has approached the desalination level, and the cation exchange capacity, available potassium and alkaline nitrogen have also been significantly improved, indicating that the LBH-ATP of the present invention can not only reduce soil salinity, but also improve the soil's fertilizer retention and potassium fixation performance.

[0056] from Figure 3 It can be seen that the combination of LBH-ATP and A-ATP can significantly improve the supply level of available phosphorus in the soil.

[0057] Finally, it should be noted that the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing an attapulgite-based hydrogel, comprising: (1) Mix ethylene carbonate, ethylene glycol, phosphoric acid and straw powder and heat to react to obtain liquid biomass; (2) After mixing acid-modified attapulgite, acrylic acid, acrylamide and liquid biomass in water, a crosslinking agent is added to react and the attapulgite-based hydrogel is obtained.

2. The preparation method according to claim 1, characterized in that: In step (1), the mass ratio of ethylene carbonate, ethylene glycol, phosphoric acid and straw powder is 5~6:0.7~0.8:0.2~0.3:

1.

3. The preparation method according to claim 1, characterized in that: In step (1), the temperature of the heating reaction is 160~200℃ and the time is 0.5~1 hour.

4. The preparation method according to claim 1, characterized in that: In step (2), the mass ratio of acrylic acid to acrylamide is 2-4:1, the mass ratio of acid-modified attapulgite to liquid biomass is 1:1-3, and the amount of acid-modified attapulgite used is 1-8% of the total mass of acrylic acid and acrylamide.

5. The preparation method according to claim 1, characterized in that: In step (2), the degree of neutralization of acrylic acid is 60-80%.

6. The preparation method according to claim 1, characterized in that: In step (2), the crosslinking agent is N,N-methylenebisacrylamide. Preferably, the amount of N,N-methylenebisacrylamide used is 0.1 to 0.2% of the total mass of acrylic acid and acrylamide.

7. The preparation method according to claim 1, characterized in that: The acid-modified attapulgite is obtained by mixing attapulgite with an acid solution and reacting for a certain period of time. Preferably, the acid solution is a phosphoric acid solution or nitric acid solution with a concentration of 2-10 wt%, the amount of acid solution is 50-80 wt% of the mass of attapulgite, and the reaction time is 1-2 hours.

8. An attapulgite-based hydrogel prepared according to the method of any one of claims 1-7.

9. The application of the attapulgite-based hydrogel according to claim 8 in the remediation of saline-alkali soil.

10. A method for remediating saline-alkali soil, comprising: (1) The attapulgite-based hydrogel of claim 8 is brought into full contact with a urea solution and then dried; (2) Add 0.5~1.5wt% of attapulgite-based hydrogel treated in step (1) and 2~4wt% of acid-modified attapulgite to saline-alkali soil; Preferably, after the treatment in step (1), the urea content in the attapulgite-based hydrogel is 2-5 wt%, more preferably 2-3 wt%.

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