Polymer / nano-clay composite material for repairing heavy metals in farmland soil and preparation method of polymer / nano-clay composite material

Abstract

The invention discloses a polymer / nano-clay composite material for repairing farmland soil heavy metals and a preparation method thereof.The polymer / nano-clay repairing material is prepared from a polymer and nano-clay, the nano-clay is modified through sulfydryl, and the polymer / nano-clay repairing material is obtained, the nano clay is prepared from bentonite, sepiolite and attapulgite, and the mercapto modifier is prepared from at least one of the following raw materials: 3-mercaptopropyltrimethoxysilane, 11-mercaptoundecyltrimethoxysilane or 2-amino-1, 4-butanedithiol hydrochloride. The polymer comprises at least one of polylactic acid, polyhydroxybutyrate, polyvinyl alcohol, a carbon dioxide copolymer, polycaprolactone, poly (butylene succinate) and a copolymer thereof. The polymer / nano-clay repairing material has the characteristics of good farmland soil composite heavy metal removal effect and good adsorption stability.

Description

Technical Field

[0001] The invention relates to the technical field of farmland soil heavy metal restoration, and in particular to a method for passivating and restoring farmland soil heavy metals by using a polymer / nanoclay composite material. Background Art

[0002] Heavy metal pollution in farmland soil poses a huge threat to food safety and human health, and has always been a hot topic in the global environmental field. Heavy metal in-situ passivation remediation technology is a promising treatment technology. This technology mainly adds exogenous remediation materials to the contaminated soil, undergoes a series of reactions such as adsorption, ion exchange, precipitation, oxidation-reduction, etc. with heavy metal ions, converts heavy metals into a more stable form, and fixes them in the soil, thereby preventing the migration of heavy metals from plant roots to the aboveground part, so as to achieve the purpose of soil remediation. In the passivation remediation technology, the most critical is the exogenous remediation material. In recent years, clay minerals including common minerals such as sepiolite, bentonite, zeolite, vermiculite, montmorillonite and attapulgite are relatively common remediation materials, mainly through mineral surface adsorption and co-precipitation to achieve the fixation of heavy metals. Although they are cheap and valuable, the use of clay minerals as exogenous remediation materials is limited due to low surface area, regeneration and recovery limits, etc. However, clay minerals can be used to enhance the performance of polymer materials. The combination of clay minerals and polymers produces clay-polymer nanocomposites with advanced properties, which can be used for efficient passivation of heavy metals and have attracted much attention.

[0003] Zhou Zhen et al. [Passivation remediation of cadmium and zinc co-contaminated soil by biochar and sepiolite composites [J]. Journal of Huazhong Agricultural University, 2023, 42(02): 158-166.] disclosed a method of passivating Cd and Zn in contaminated soil using two materials, biochar and sepiolite. However, the effectiveness of the passivation effect was poor.

[0004] Shenglan Ye et al. [Study of solidification and stabilization of heavy metals by passivators in heavy metal contaminated soil, Open Chemistry 2022, 20: 1–9] disclosed the study of solidification and stabilization of heavy metals by passivators in heavy metal contaminated soil. The results showed that Cu, Zn, cadmium (Cd) and Pb treated with zeolite had the best effect, followed by sepiolite and palygorskite, but the stability of passivation needs to be further improved. Therefore, the passivation effect of natural clay materials or composite materials with biochar on heavy metal pollutants is not ideal. Summary of the invention

[0005] The present invention aims to solve at least one of the technical problems existing in the above-mentioned prior art. To this end, the present invention proposes a polymer / nanoclay repair material, which has the characteristics of good simultaneous removal of composite heavy metals in farmland soil.

[0006] The invention also provides a method for preparing the polymer / nanoclay repair material.

[0007] The present invention also proposes the application of the polymer / nanoclay repair material.

[0008] In the first aspect of the present invention, a polymer / nanoclay repair material is proposed, wherein the raw materials for preparing the material include bentonite and an iron-based modifier, wherein the bentonite is modified by the iron-based modifier to obtain the nanoclay, which includes bentonite, sepiolite and attapulgite, and the raw materials of the mercapto modifier include at least one of 3-mercaptopropyltrimethoxysilane, 11-mercaptoundecyltrimethoxysilane or 2-amino-1,4-butanedithiol hydrochloride. The polymer includes at least one of polylactic acid, polyhydroxybutyrate, polyvinyl alcohol, carbon dioxide copolymer, polycaprolactone, polybutylene succinate and copolymers thereof.

[0009] The polymer / nanoclay repair material according to the embodiment of the present invention has at least the following beneficial effects:

[0010] The polymer / nanoclay repair material in the present invention overcomes the disadvantages of agglomeration and small surface area compared to single nanoclay, and overcomes the disadvantage of large usage compared to single polymer. The polymer / nanoclay repair material has stronger adsorption and stability, and the raw materials are self-degradable and not easy to cause secondary pollution, and can efficiently remove complex heavy metals in a shorter time.

[0011] The polymer / nanoclay repair material of the present invention is a material with large adsorption capacity, strong stability and good removal effect of composite heavy metals. The polymer / nanoclay repair material of the present invention can enhance the simultaneous fixation of composite heavy metals and enable plants to grow well in soil contaminated by composite heavy metals.

[0012] In some embodiments of the present invention, the polymer / nanoclay repair material is characterized in that the mass ratio of the polymer to the nanoclay is (5-20):100.

[0013] In some embodiments of the present invention, the polymer / nanoclay repair material is characterized in that the nanoclay includes bentonite, sepiolite and attapulgite.

[0014] In some embodiments of the present invention, the polymer / nanoclay repair material is characterized in that the preparation raw materials also include a mercapto modifier; preferably, at least one of 3-mercaptopropyltrimethoxysilane, 11-mercaptoundecyltrimethoxysilane or 2-amino-1,4-butanedithiol hydrochloride.

[0015] In some embodiments of the present invention, the polymer / nanoclay repair material is characterized in that the polymer / nanoclay repair material is used for passivation of Pb-Cd in farmland soil.

[0016] In some embodiments of the present invention, the polymer / nanoclay repair material is characterized in that the polymer / nanoclay repair material has a 2+ The leaching concentration reached the lowest value of 25.06 mg / L.

[0017] In some embodiments of the present invention, the method for preparing any one of the polymer / nanoclay repair materials is characterized by comprising the following steps: taking nanoclay and modifying it with a thiol modifier to obtain the polymer / nanoclay repair material.

[0018] In some embodiments of the present invention, the preparation method of the polymer / nanoclay repair material is characterized in that the preparation method comprises the following steps: taking nanoclay, washing and acidifying it, using a thiol modifier to modify it, and then compounding it with a polymer dispersion to obtain the polymer / nanoclay repair material.

[0019] In some embodiments of the present invention, the preparation method of the polymer / nanoclay repair material is characterized in that the preparation method also includes preparing a polymer dispersion, and the preparation step of the polymer dispersion includes the following operations: mixing a polymer with ethanol / water and heating to obtain the polymer dispersion.

[0020] In some embodiments of the present invention, any one of the polymer / nanoclay remediation materials is used in the remediation of multi-metal contamination in farmland soil. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The present invention will be further described below with reference to the accompanying drawings and embodiments, wherein:

[0022] Figure 1 This is a microscopic result diagram of the polycaprolactone / thiol-modified attapulgite of Example 1 of the present invention;

[0023] Figure 2 The polycaprolactone / thiol-modified attapulgite of Example 1 of the present invention is used to passivate Cd in heavy metal Pb-Cd contaminated soil 2+ The result graph of

[0024] Figure 3 The polycaprolactone / thiol-modified attapulgite of Example 1 of the present invention is used to passivate Pb in heavy metal Pb-Cd contaminated soil. 2+ The result graph of

[0025] Figure 4 These are photos of Chinese cabbage planted in heavy metal Pb-Cd contaminated soil treated with polymer / nanoclay repair materials in Example 1 of the present invention and Comparative Examples 1-5, and Chinese cabbage in the control group;

[0026] Figure 5 The plant heights of Chinese cabbage planted in Example 1 of the present invention and Comparative Examples 1-6;

[0027] Figure 6 The root length of Chinese cabbage planted in Example 1 of the present invention and Comparative Examples 1-6;

[0028] Figure 7 The dry weight of the Chinese cabbage planted in Example 1 of the present invention and Comparative Examples 1-6;

[0029] Figure 8 The total chlorophyll content of the pakchoi grown in Example 1 of the present invention and Comparative Examples 1-6;

[0030] Fig. 9 The soluble protein content of the Chinese cabbage planted in Example 1 of the present invention and Comparative Examples 1-6 is shown. DETAILED DESCRIPTION

[0031] The following will be combined with the embodiments to clearly and completely describe the concept of the present invention and the technical effects produced, so as to fully understand the purpose, characteristics and effects of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, other embodiments obtained by those skilled in the art without creative work are all within the scope of protection of the present invention.

[0032] The experimental methods without specific conditions in the following examples and comparative examples are generally based on conventional conditions in the art or conditions recommended by the manufacturers; the raw materials, reagents, etc. used, unless otherwise specified, are all raw materials and reagents that can be obtained from commercial channels such as conventional markets.

[0033] The experiment was conducted in a constant temperature incubator. Cd(NO3)2 and Pb(NO3)2 solutions were added to the experimental soil to make Cd 2+ The concentration reached 2.5mg / kg, Pb 2+To reach 446.7mg / kg, add water to reach 40% water content, and spray with a certain amount of pure water every day for 7 days to keep it moist. Prepare 2 groups of grid pots (24 grids), add 100g of soil to each grid, add 1g, 3g, and 5g of polycaprolactone (j) and polylactic acid (x) respectively, and use Pb 2+ and Cd 2+ The treated soil was the control group (CK), and the experiment was repeated three times in each group, and Chinese cabbage was planted. 2g of fertilizer was applied to the soil. The fertilizer and polymer / nanoclay repair materials of each treatment were fully mixed with the soil, and pure water was added to make the soil moisture content reach 60% of the field water holding capacity. Five Chinese cabbage seeds were evenly sown in each grid, and a certain amount of water was sprayed daily. The growth was recorded every 3 days. Soil and plant samples were collected after 10 and 20 days of growth. The collected soil was air-dried and ground through a 2mm sieve for later use.

[0034] Table 1 Experimental treatments

[0035]

[0036] Figure 1 This is the microscopic result of polycaprolactone / thiol-modified attapulgite. Figure 1 It can be seen that after the polycaprolactone / thiol-modified attapulgite is composited, there is still a certain amount of pore structure, which provides contact sites for the efficient passivation of Pb-Cd.

[0037] Figure 2 It can be seen that the corresponding soil Cd concentrations of Comparative Example 2, Example 1 and Comparative Examples 3-6 after implementation for 10 days were 2.2 mg / kg, 1.72 mg / kg, 1.27 mg / kg, 1.51 mg / kg, 1.07 mg / kg and 1.27 mg / kg, respectively, which were reduced by 23.08%, 39.86%, 55.59%, 47.2%, 62.59% and 55.59% respectively compared with Comparative Example 1CK.

[0038] Figure 3 It can be seen that the corresponding soil Cd concentrations of Comparative Example 2, Example 1 and Comparative Examples 3-6 are 409 mg / kg, 395 mg / kg, 375 mg / kg, 357 mg / kg, 320 mg / kg and 335 mg / kg, respectively, which are reduced by 8.5%, 11.63%, 16.11%, 20.13%, 28.41% and 25.1% respectively compared with Comparative Example 1CK.

[0039] Figure 4 and Figure 5 The photos and plant height measurement results of Chinese cabbage planted in heavy metal Pb-Cd contaminated soil treated with polymer / nanoclay repair materials in Example 1 of the present invention and Comparative Examples 1-5 and Chinese cabbage in the control group. Figure 4 and Figure 5It can be seen that the plant height of the Chinese cabbage group treated with polycaprolactone / thiol-modified attapulgite first increased and then decreased with the increase of polycaprolactone addition, but the 5g treatment group was still higher than the 1g treatment group. The tallest plant appeared when the polycaprolactone addition amount was 3g, which was 3.83cm, an increase of 59.58% compared with CK. The polylactic acid group first decreased and then increased with the increase of addition amount. The tallest plant appeared at 5g addition amount, which was 3.7cm, an increase of 54.2% compared with CK.

[0040] Figure 6 , Figure 7 , Figure 8 and Fig. 9 It can be seen that the root length, dry weight, total chlorophyll content and soluble protein of Chinese cabbage after treatment with polycaprolactone / thiol-modified attapulgite are as follows: the maximum root length is in Comparative Example 3, which is 2.21 times higher than that of the control group; the dry weight of Chinese cabbage reaches the maximum value in Example 1, which is 3.08 times higher than that of the control; the soluble protein content of Chinese cabbage growth index is 59.12% higher in Example 1 than in Comparative Example 1, and the influence of chlorophyll content of Chinese cabbage is not affected by various treatments.

Claims

1. A polymer / nanoclay composite material for repairing heavy metals in farmland soil and a preparation method thereof, characterized in that: The raw materials for preparing the polymer / nanoclay repair material include polymer and nanoclay, and the nanoclay is modified by mercapto groups to obtain the polymer / nanoclay repair material, wherein the nanoclay includes bentonite, sepiolite and attapulgite, and the raw materials of the mercapto modifier include at least one of 3-mercaptopropyltrimethoxysilane, 11-mercaptoundecyltrimethoxysilane or 2-amino-1,4-butanedithiol hydrochloride. The polymer includes at least one of polylactic acid, polyhydroxybutyrate, polyvinyl alcohol, carbon dioxide copolymer, polycaprolactone, polybutylene succinate and copolymers thereof.

2. The polymer / nanoclay repair material according to claim 1, characterized in that: The mass ratio of the polymer to the nanoclay is (5-20):

100.

3. The polymer / nanoclay repair material according to claim 1, characterized in that: The nano clay includes bentonite, sepiolite and attapulgite.

4. The polymer / nanoclay repair material according to claim 1, characterized in that: The preparation raw materials also include a mercapto modifier; preferably, at least one of 3-mercaptopropyltrimethoxysilane, 11-mercaptoundecyltrimethoxysilane or 2-amino-1,4-butanedithiol hydrochloride.

5. The polymer / nanoclay repair material according to claim 1, characterized in that: The polymer / nanoclay repair material is used for passivation of Pb-Cd in farmland soil.

6. The polymer / nanoclay repair material according to claim 1, characterized in that: The polymer / nanoclay repair material has an excellent effect on Pb 2+ The leaching concentration reached the lowest value of 25.06 mg / L.

7. A method for preparing a polymer / nanoclay repair material according to any one of claims 1 to 6, characterized in that: The method comprises the following steps: taking nano clay, modifying it with a mercapto modifier, and obtaining the polymer / nanoclay repair material.

8. The method for preparing the polymer / nanoclay repair material according to claim 7, characterized in that: The preparation method comprises the following steps: taking nano clay, washing and acidifying it, modifying it with thiol using a thiol modifier, and then compounding it with a polymer dispersion to obtain the polymer / nanoclay repair material.

9. The method for preparing the polymer / nanoclay repair material according to claim 7, characterized in that: The preparation method further comprises preparing a polymer dispersion, and the preparation step of the polymer dispersion comprises the following operations: mixing a polymer with ethanol / water, and heating to obtain the polymer dispersion.

10. Use of the polymer / nanoclay repair material according to any one of claims 1 to 6 in the repair of polymetallic contamination in farmland soil.

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