1. An in-situ polymerization preparation method of polymer network modified bentonite is characterized by comprising the following steps:

(1) dissolving a monomer and a cross-linking agent in water, adding bentonite, fully and uniformly mixing, and adding an initiator to obtain a mixed system; the monomer contains a carbon-carbon double bond and a hydrophilic functional group; the cross-linking agent is a water-soluble molecule containing more than two carbon-carbon double bonds;

(2) heating the mixed system obtained in the step (1), so that an initiator generates free radicals, the free radicals are transferred to carbon-carbon double bonds on the monomers to initiate addition polymerization reaction of the carbon-carbon double bonds, the carbon-carbon double bonds are converted into single bonds, the monomers are polymerized under the action of a cross-linking agent to obtain a polymer network, and the polymer network is intercalated between the sheet layers of the bentonite in situ.

2. The method of claim 1, wherein the monomer is at least one of acrylic acid, acrylamide, acrylic sulfonic acid, 2-acrylamido-2-methylpropanesulfonic acid, acrylonitrile, N-dimethylacrylamide, maleic anhydride, itaconic acid, sodium p-styrenesulfonate, dimethyldiallylammonium chloride, diethyldiallylammonium chloride, and allyltrimethylammonium chloride;

the cross-linking agent is N, N' -vinyl bisacrylamide, ethylene glycol diacrylate, divinylbenzene or diacetone acrylamide.

3. The method for preparing polymer network modified bentonite according to claim 1 or 2, wherein the initiator is potassium persulfate or ammonium persulfate;

the bentonite is at least one of calcium bentonite, sodium bentonite and sodium calcium bentonite.

4. The method for preparing polymer network modified bentonite according to claim 1 or 2, wherein the mass ratio of the monomer to the cross-linking agent is (50-500): 1.

5. The method for preparing polymer network modified bentonite according to claim 1 or 3, wherein the mass ratio of the monomer to the bentonite is (1-30): 100; the mass ratio of the initiator to the monomer is (0.5-5): 100.

6. The method for preparing polymer network modified bentonite according to claim 1, wherein the mass ratio of the bentonite to the solvent water is (30-500): 60.

7. The method for preparing polymer network modified bentonite according to claim 1, wherein the heating temperature in the step (2) is 50-80 ℃.

8. The method of claim 1, further comprising the step of adding a base solution to enhance the hydrophilicity of the polymer network prior to adding the cross-linking agent.

9. A polymer network modified bentonite prepared by the method of any one of claims 1 to 8.

10. Use of a polymer network modified bentonite clay according to claim 9 as a barrier material for acid, base or salt solutions;

preferably, the pH value of the acid solution is less than or equal to 3, the pH value of the alkali solution is greater than or equal to 12, and the concentration of the salt solution is greater than or equal to 3 wt%.

Background

The main component of bentonite is montmorillonite, which is a 2:1 type crystal structure consisting of two silicon-oxygen tetrahedrons sandwiching a layer of aluminum-oxygen octahedron. The layered crystal surface of montmorillonite has negative charge and certain hydrophilicity, and can form an electric double layer in water. The gaps among the bentonite particles are main channels for water transfer, when the bentonite absorbs water and expands, the gaps among the clay particles can be blocked, the path for water transfer becomes narrow and tortuous, and the permeability coefficient of water is reduced. Natural bentonite is divided into two types, sodium-based and calcium-based. The sodium bentonite has strong expansibility and strong barrier property to water, and is a common barrier material in geotechnical work; calcium bentonite is far less hydrophilic than sodium bentonite, is difficult to absorb water and swell, and is considered unsuitable for use as a barrier material.

Sodium bentonite also has serious use defects, when the sodium bentonite is contacted with salt, strong acid and strong alkali solution, the generated electric double layer is obviously thinned, the water absorption swelling property of bentonite particles is deteriorated, gaps among the particles are difficult to be effectively sealed, and the barrier property is lost. However, bentonite-based barrier facilities often need to be faced with a wide variety of harsh environments. For example, in the vertical separation of a refuse landfill, landfill materials often generate a large amount of strong-acid or alkaline salt solution under the fermentation effect, the existing natural bentonite waterproof blanket is difficult to effectively separate, waste liquid leakage is often caused, and the life health and the sustainable development of economy of people are endangered. Therefore, the research and preparation of modified bentonite resistant to salt, acid and alkali are imminent.

For example, in CN111409318A, sodium dodecylbenzene sulfonate is used to intercalate montmorillonite, so that the layered montmorillonite is peeled into single pieces, and a larger specific surface area is given to the single pieces. And then, carrying out ion exchange on the bentonite by utilizing a silver nitrate solution so as to replace silver ions with large radius and low electricity price to the surface of the montmorillonite crystal. Finally, the montmorillonite is subjected to gradient roasting treatment, and a larger specific surface area is obtained. The modified bentonite has stronger adsorption effect, and meanwhile, the anti-permeability performance of the product can be maintained for a long time due to the antibacterial effect of silver ions. According to the scheme, under a severe modification condition, the antibacterial and adsorption properties of the bentonite are effectively improved through three steps of reactions, however, the blocking condition of the modified bentonite on strong acid, alkali and salt solution is not explored.

Among organic pollutants, the permeability coefficient of conventional bentonite is significantly increased. In the patent with publication No. CN105199288A, cationic polyacrylamide and bentonite are blended under hydrothermal and stirring conditions to realize intercalation of montmorillonite crystals by polymer, and obtain the macromolecular bentonite nanocomposite. The polyacrylamide effectively blocks gaps among the bentonite particles, and improves the barrier property of the bentonite to organic pollutant aqueous solution. In addition, the cationic groups on the polymer can generate electric neutralization with organic matters, so that colloidal particles are promoted to aggregate and precipitate, and conditions are created for removing organic pollutants. The protocol also involves two tedious steps of polymer (polyacrylamide) synthesis and purification, as viewed from the overall social cost, while the modified bentonite samples also did not exhibit barrier properties against strong acid, base and salt solutions.

In conclusion, a simple low-cost modification scheme for preparing the salt-resistant, acid-resistant and alkali-resistant high-seepage-proofing modified bentonite is still lacked.

Disclosure of Invention

Aiming at the technical problem that the bentonite in the prior art has poor barrier property to acid, alkali and salt solutions, the invention provides a simple scheme of modified bentonite by in-situ polymerization, which can realize the polymerization of monomers and the modification of the bentonite by one step to obtain the salt-resistant, acid-resistant and alkali-resistant modified bentonite material.

According to a first aspect of the present invention, there is provided a method for preparing polymer network modified bentonite by in-situ polymerization, comprising the steps of:

(1) dissolving a monomer and a cross-linking agent in water, adding bentonite, fully and uniformly mixing, and adding an initiator to obtain a mixed system; the monomer contains a carbon-carbon double bond and a hydrophilic functional group; the cross-linking agent is a water-soluble molecule containing more than two carbon-carbon double bonds;

(2) heating the mixed system obtained in the step (1), so that an initiator generates free radicals, the free radicals are transferred to carbon-carbon double bonds on the monomers to initiate addition polymerization reaction of the carbon-carbon double bonds, the carbon-carbon double bonds are converted into single bonds, the monomers are polymerized under the action of a cross-linking agent to obtain a polymer network, and the polymer network is intercalated between the sheet layers of the bentonite in situ.

Preferably, the monomer is at least one of acrylic acid, acrylamide, acrylic sulfonic acid, 2-acrylamide-2-methylpropanesulfonic acid, acrylonitrile, N-dimethylacrylamide, maleic anhydride, itaconic acid, sodium p-styrenesulfonate, dimethyldiallylammonium chloride, diethyldiallylammonium chloride and allyltrimethylammonium chloride;

the cross-linking agent is N, N' -vinyl bisacrylamide, ethylene glycol diacrylate, divinylbenzene or diacetone acrylamide.

Preferably, the initiator is potassium persulfate or ammonium persulfate;

the bentonite is at least one of calcium bentonite, sodium bentonite and sodium calcium bentonite.

Preferably, the mass ratio of the monomer to the crosslinking agent is (50-500): 1.

Preferably, the mass ratio of the monomer to the bentonite is (1-30): 100; the mass ratio of the initiator to the monomer is (0.5-5): 100.

Preferably, the mass ratio of the bentonite to the solvent water is (30-500): 60.

Preferably, the temperature of the heating in the step (2) is 50-80 ℃.

Preferably, a step of adding a lye is further included prior to adding the cross-linking agent to enhance the hydrophilicity of the polymer network.

According to another aspect of the present invention there is provided a polymer network modified bentonite obtainable by any of the methods described herein.

According to another aspect of the present invention, there is provided the use of said polymer network modified bentonite clay as a barrier material for acid, base or salt solutions;

preferably, the pH value of the acid solution is less than or equal to 3, the pH value of the alkali solution is greater than or equal to 12, and the concentration of the salt solution is greater than or equal to 3 wt%.

Generally, compared with the prior art, the above technical solution conceived by the present invention mainly has the following technical advantages:

(1) according to the preparation scheme of the polymer modified bentonite, the modified monomer and the bentonite are subjected to one-step in-situ polymerization reaction to obtain the product, and the preparation method is simple and rapid. The polymer modified bentonite prepared by the invention overcomes the defect of poor barrier property of the original bentonite to acid, alkali and salt solutions, and greatly expands the application scene of bentonite barrier facilities. Compared with a modification method of synthesizing the polymer and then blending the polymer with the bentonite, the in-situ polymerization method omits the steps of synthesizing and purifying the polymer, and the modification step is simpler and has wider application prospect.

(2) According to the preparation scheme of the polymer modified bentonite, the used solvent is water, the reaction raw materials (monomers) are easy to obtain, the reaction is safe, the cost is low, and the preparation method has a good application prospect.

(3) Tests show that the polymer modified bentonite with salt resistance, acid resistance and alkali resistance prepared by the invention shows extremely low permeability coefficient (10) in acid (pH is 3), alkali (pH is 12) and 3 wt% salt solution^-12m/s). The reason is that gaps among the bentonite particles are the main path of water transfer, compared with the original bentonite, the expansibility of the modified bentonite in acid, alkali and salt solution is obviously improved, the particles are extruded with each other after expansion, the gaps among the particles are blocked, and the barrier property is improved.

(4) The invention adds alkali liquor to neutralize acrylic acid monomer. Not only prevents reaction implosion and ensures the safety of the experiment; but also increases the hydrophilicity of the polymerization product and enhances the modification effect.

(5) In the present invention, acrylic acid and 2-acrylamido-2-methylpropanesulfonic acid are preferably used as monomers. Acrylic acid is an ionic monomer, and has good water absorption expansibility; the 2-acrylamide-2-methylpropanesulfonic acid is an amphoteric monomer, has good salt resistance and strong interaction with bentonite. The modified bentonite and the modified bentonite are matched with each other, so that the modified bentonite has good barrier property.

(6) The invention preferably takes calcium bentonite as the modifying material. Compared with sodium bentonite, calcium bentonite has poorer hydrophilicity and higher modification difficulty. However, the calcium bentonite has richer reserves and is low in price. The successful modification of the calcium bentonite reduces the production cost of the bentonite barrier material.

(7) According to the invention, the mass ratio of the bentonite to the solvent water is preferably (30-500): 60. Too little solvent, too high system viscosity and difficult stirring; the solvent is excessive, the monomer concentration is too dilute, the molecular weight of a polymerization product is influenced, and the modification effect is reduced.

Drawings

FIG. 1 is a schematic diagram showing the process for preparing modified bentonite in example 2 of the present invention.

FIG. 2 is an infrared spectrum of bentonite before and after modification in example 2 of the present invention.

FIG. 3 is a result of a test of free swelling property in water of bentonite before and after modification in example 2 of the present invention.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention. In addition, the technical features involved in the embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.

Example 1

The in-situ polymerization method of the high-barrier modified bentonite comprises the following steps:

(1) 18.8mL of acrylic acid and 38.8mL of 0.2g/mL of sodium hydroxide were added to 111mL of water, neutralized with an acid or a base, added with 0.1g N, N' -vinylbisacrylamide, and stirred until completely dissolved.

(2) 60g of calcium bentonite is added, and the solution and the bentonite are mixed evenly by vigorous stirring.

(3) Adding 0.36g of ammonium persulfate, heating to 70 ℃, and reacting for 3h to obtain a product. And drying the water in the product to obtain the polymer modified bentonite (the polymer content is 25 wt%).

Example 2

The in-situ polymerization method of the high-barrier modified bentonite in the invention, as shown in figure 1, comprises the following steps:

(1) 14.1mL of acrylic acid and 29.1mL of sodium hydroxide (0.2 g/mL) are added to 121mL of water, and after neutralization with an acid and base, 5g of 2-acrylamido-2-methylpropanesulfonic acid and 0.1g N, N' -vinylbisacrylamide are added and stirred until completely dissolved.

(2) 60g of calcium bentonite is added, and the solution and the bentonite are mixed evenly by vigorous stirring.

(3) Adding 0.36g of potassium persulfate, heating to 50 ℃, and reacting for 4 hours to obtain a product. And drying the water in the product to obtain the polymer modified bentonite (the polymer content is 25 wt%).

Example 3

The in-situ polymerization method of the high-barrier modified bentonite comprises the following steps:

(1) 17.9mL of acrylic acid and 36.86mL of sodium hydroxide (0.2 g/mL) were added to 111mL of water, and after neutralization with an acid or a base, 1g of 2-acrylamido-2-methylpropanesulfonic acid and 0.1g N, N' -vinylbisacrylamide were added and stirred until completely dissolved.

(2) 60g of calcium bentonite is added, and the solution and the bentonite are mixed evenly by vigorous stirring.

(3) Adding 0.36g of potassium persulfate, heating to 70 ℃, and reacting for 3 hours to obtain a product. And drying the water in the product to obtain the polymer modified bentonite (the polymer content is 25 wt%).

Example 4

The in-situ polymerization method of the high-barrier modified bentonite comprises the following steps:

(1) 30mL of acrylic acid and 61.4mL of sodium hydroxide (0.2 g/mL) were added to 163.6mL of water, neutralized with an acid or a base, and then added with 1.665g of 2-acrylamido-2-methylpropanesulfonic acid and 0.06g N, N' -vinylbisacrylamide, and stirred until completely dissolved.

(2) Adding 300g of calcium bentonite, and stirring vigorously to uniformly mix the solution and the bentonite.

(3) Adding 0.6g of potassium persulfate, heating to 60 ℃, and reacting for 3 hours to obtain a product. And drying the water in the product to obtain the polymer modified bentonite (the polymer content is 10 wt%).

Example 5

The in-situ polymerization method of the high-barrier modified bentonite comprises the following steps:

(1) 5.7mL of acrylic acid and 11.63mL of sodium hydroxide (0.2 g/mL) were added to 78.37mL of water, neutralized with an acid or a base, added with 0.316g of 2-acrylamido-2-methylpropanesulfonic acid and 0.01g N, N' -vinylbisacrylamide, and stirred until completely dissolved.

(2) 120g of calcium bentonite is added, and the mixture is stirred vigorously to ensure that the solution and the bentonite are mixed evenly.

(3) Adding 0.11g of ammonium persulfate, heating to 70 ℃, and reacting for 3 hours to obtain a product. And drying the water in the product to obtain the polymer modified bentonite (the polymer content is 5 wt%).

Example 6

The in-situ polymerization method of the high-barrier modified bentonite comprises the following steps:

(1) 9.4mL of acrylic acid and 19.4mL of 0.2g/mL of sodium hydroxide were added to 150mL of water, neutralized with an acid and base, and then added with 5g of 2-acrylamido-2-methylpropanesulfonic acid, 5g of acrylamide and 0.1g of N, N' -vinylbisacrylamide, and stirred until completely dissolved.

(2) 60g of calcium bentonite is added, and the solution and the bentonite are mixed evenly by vigorous stirring.

(3) Adding 0.36g of ammonium persulfate, heating to 70 ℃, and reacting for 3h to obtain a product. And drying the water in the product to obtain the polymer modified bentonite (the polymer content is 25 wt%).

Example 7

The sample from example 2 was infrared characterized (fig. 2) and compared to the ir spectrum of the original calcium bentonite. At 2950cm^-1An infrared absorption peak of C-H stretching vibration in a methylene (forming a high molecular main chain) functional group appears, and the polymerization reaction of the fed monomer is proved to be carried out at room temperature. In addition, 1160cm^-1The sulfonic acid radical absorption peak and 1730cm^-1The absorption peaks of the carbonyl stretching vibration are respectively from N, N-diethyl on the main chain of the polymerAcrylamide and sodium acrylate. In conclusion, the monomers undergo in-situ polymerization in the modification reaction, and the molecular structure of the generated polymer conforms to the experimental design.

Example 8

The free expansion coefficient test of the bentonite is carried out by referring to an expansion index experiment in national standard GB/T20973-2007 of the people's republic of China. The test solutions used were pure water, nitric acid solution (pH 3), sodium hydroxide solution (pH 12), sodium chloride solution (600mM) and calcium chloride solution (50mM), respectively.

As shown in FIG. 3, the hydrophilicity of the polymer-modified calcium bentonite (example 2) was greatly improved compared to the original calcium bentonite (comparative example), and the free expansion coefficient in water was increased from 4.3mL/2g to 241.5mL/2 g. Due to the improvement of hydrophilicity, the expansibility of the modified bentonite in acid, alkali and salt solutions is also remarkably improved (table 1).

TABLE 1 coefficient of free expansion in acid, base, salt solutions of examples and comparative examples

Example 9

The permeability coefficient test is carried out by using a variable head permeability experiment in JTG E40-2007 in the industrial standard of the people's republic of China. The test solutions were purified water, nitric acid solution (pH 3), sodium hydroxide solution (pH 12), sodium chloride solution (600mM) and calcium chloride solution (50mM), respectively, and the modified bentonite was tested for its barrier properties against acid, alkali and salt solutions and compared with the original calcium bentonite. The permeability coefficient test results are shown in table 2. It can be seen that the permeability coefficient of the modified bentonite in acid, alkali and salt solutions is far lower than that of the original calcium bentonite. When the high-molecular-weight doping amount reaches 10 wt% (example 4), the permeability coefficient of the modified calcium bentonite in the three solutions reaches 10^-12m/s is far lower than the national limit of the landfill seepage-proofing facility (10)^-9m/s)。

TABLE 2 Barrier Properties of the examples and comparative examples against acid, base, and salt solutions

It will be understood by those skilled in the art that the foregoing is only a preferred embodiment of the present invention, and is not intended to limit the invention, and that any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the scope of the present invention.