CN110665474A - Modified chitosan cross-linked zeolite porous adsorbent and application thereof - Google Patents

Abstract

The invention belongs to the technical field of materials, and particularly relates to a modified chitosan crosslinked zeolite porous adsorbent and application thereof. The invention has the advantages that: the structure of the zeolite is in a space grid structure, and the structure of the zeolite has a plurality of cavities and channels, so that the zeolite has a large specific surface area (300-600 m)²/g), the chitosan grafted acrylic polymer has a plurality of chemical groups capable of chelating metal ions, so the chitosan grafted acrylic polymer has high adsorption capacity and adsorption efficiency, and the chitosan and the zeolite have different working environments, so the zeolite is suitable for being used under acidic conditions, and the chitosan is suitable for being used under alkaline conditions, so the chitosan grafted acrylic polymer and the zeolite can be combined togetherWith good complementarity, the combination of chitosan and zeolite can be used over a wide pH range.

Description

Modified chitosan cross-linked zeolite porous adsorbent and its application

technical field

The invention belongs to the technical field of materials, and in particular relates to a modified chitosan cross-linked zeolite porous adsorbent and its application.

Background technique

The tailings dam is a dam body formed by the accumulation and rolling of tailings. Generally, a tailings dam is composed of an initial dam (foundation dam) and a later dam (tailings stack dam). The height of the dam body can reach tens of meters or even hundreds of meters. Meter. Mine dams play a very important role in the protection and management of the mine environment. They are mainly used to store tailings or other industrial wastes discharged from metal and non-metal mines after ore sorting. Geotextiles are made of polymer fibers. The raw material is a water-permeable geosynthetic material made by hot-pressing needle punching, cementing and weaving. The most common applications are polyester fibers and polypropylene fibers, followed by polyamide fibers and polyvinyl acetal fibers. Geotextiles have a variety of uses, and their main functions include filtration, drainage, isolation, reinforcement, protection, and anti-seepage. As a kind of seepage drainage and reverse filtration material, geotextile is very important in the seepage drainage system of tailings dam. Due to the existence of the geotextile, the dam body can prevent the tailings from leaking while the water level is reduced, and the geotextile will also be blocked. Substances (ocher) will accumulate in the voids of the geotextiles and adhere to the surface layer, resulting in poor permeability of the geotextiles and, in severe cases, the collapse of the tailings dam.

At present, domestic and foreign treatment methods for clogging are mainly divided into two types: physical methods and chemical methods. The physical methods are more complicated to implement, and the chemical methods are simple to implement.

Chitosan is a natural polymer material with reserves second only to cellulose. It is the only alkaline natural polysaccharide that exists in nature so far, and has good adsorption properties; zeolite is an inorganic porous adsorption material with selective adsorption, It has unique properties such as easy modification and is considered to be a promising new type of adsorption material.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide a modified chitosan cross-linked zeolite composite adsorbent that can adsorb metal ions that cause the geotextile to block the geotextile for the chemical blocking on the tailings dam, and the adsorption material is simple to prepare and convenient to construct. , The adsorption effect is good.

The technical scheme adopted by the present invention to solve the above technical problems is: modified chitosan cross-linked zeolite composite adsorbent, and its structural formula is:

where n is the degree of polymerization of chitosan.

The modified chitosan cross-linked zeolite composite adsorbent is used as a tailings dam anti-blocking adsorption material.

According to the above scheme, the modified chitosan cross-linked zeolite composite adsorbent is configured so that the solution is evenly covered on the geotextile.

According to the above scheme, the covering method is to cover the surface of the geotextile with the modified chitosan cross-linked zeolite composite adsorbent using the surface coating technology.

According to the above scheme, the surface coating technology is brush coating.

According to the above scheme, the steps of the brush coating method are: dissolving the modified chitosan cross-linked zeolite composite adsorbent in a solvent, heating while stirring, and concentrating the solution to a viscosity, then brushing the concentrated solution on the geotechnical site with a brush cloth surface.

According to the above scheme, the solvent is acetic acid solution, formic acid solution or oxalic acid solution.

According to the above scheme, the heating temperature is 70-110°C.

The reaction mechanism of chitosan grafting acrylic acid in the present invention is that Ce ⁴⁺ reacts before sugar residues C ₂ -NH ₂ and C ₃ -OH to form a complex. Then the chemical bond between the 2- and 3-position carbon atoms is opened to generate -CH=NH· and -CH(OH)· two free radicals, and then polymerized with acrylic double bond, chain initiation, chain growth, chain termination specific process As follows:

The chain throws:

M+Ce ⁴⁺ →M·+Ce ³⁺ +H ⁺

Chain Growth:

ChitosanM·+M→ChitosanM ₂ ·

...

ChitosanM _n-1 ·+M→ChitosanM _n ·

M _n-1 ·+M→M _n ·

Chain termination:

ChitosanMn · ₊ Ce ⁴⁺ →graft copolymer +Ce ³⁺ +H ⁺

_Mn · +Ce ⁴⁺ →Homopolymer +Ce ³⁺ +H ⁺

The combination with zeolite is physical cross-linking.

The advantages of the present invention are:

1. There are wide sources of raw materials, all of which have great reserves in nature. Chitosan ranks second in the world in reserves, and more than 400 natural zeolite deposits have been discovered in my country, with reserves of about 4 billion tons, so chitosan is and low price of zeolite;

2. The structure of zeolite is in the form of a space grid, and its structure has many holes and pores, which makes zeolite have a large specific surface area (300-600m ² /g), while the chitosan-grafted acrylic polymer has many chemical bases. The group can chelate metal ions, so the adsorption capacity and adsorption efficiency of this invention are high, and because the working environment of chitosan and zeolite is different, zeolite is suitable for use under acidic conditions, and chitosan is suitable for use under alkaline conditions, so the combination of the two Can be very complementary, the combination of chitosan and zeolite can be used in a wide pH range;

3. The metal ions adsorbed by the adsorbent can be recovered by the elution method, and the adsorbent can continue to be put into use, with good sustainable adsorption performance, and these materials are harmless to the environment.

Description of drawings

Fig. 1 is the infrared spectrogram of chitosan-grafted acrylic acid in Example 1 of the present invention;

Fig. 2 is the infrared spectrogram of chitosan-grafted acrylic acid in Example 2 of the present invention;

Fig. 3 is the adsorption capacity change curve of the modified chitosan cross-linked zeolite adsorbent with different adsorption times in Example 3 of the present invention;

FIG. 4 is a graph showing the variation curve of the adsorption capacity of the adsorption material for calcium ions with the amount of zeolite added in Example 4 of the present invention.

Detailed ways

The following examples further illustrate the technical solutions of the present invention, but are not intended to limit the protection scope of the present invention.

Modified chitosan cross-linked zeolite composite adsorbent, its structural formula is:

where n is the degree of polymerization of chitosan.

Comparative Example 1 (without zeolite)

The preparation of modified chitosan solution, its preparation steps are as follows

0.2 g of chitosan and 75 mL of acetic acid solution with a volume fraction of 2% were added to a 250 mL three-necked flask, and stirred to dissolve. 0.2 g of ceric ammonium nitrate was added to initiate 30 min, 3.5 mL of acrylic acid was added dropwise, and the graft copolymerization was carried out at 65 °C for 8 h in a _N2 environment. The pH of the reactant was adjusted to alkaline with NaOH solution, and the modified chitosan product was precipitated as flocculent. After precipitation using a high-speed centrifuge, soak in absolute ethanol for 2 hours to dehydrate, freeze-dry and pulverize.

The infrared spectrum of the acrylic acid grafted chitosan obtained in this example is shown in Figure 1 of the accompanying drawings.

Compared with the CS spectrum, the presence of intermolecular hydrogen bonds in the CS/AA spectrum leads to a red shift of the -OH stretching vibration, and the infrared absorption peak of CS/AA has -OH stretching vibration (3404cm ^-1 ), C=O Stretching vibration (1545cm ^-1 ), -OH in-plane (1309cm ^-1 ) and out-of-plane (989cm ^-1 ) bending vibration and -CO stretching vibration indicate that -COOH in acrylic acid was introduced into chitosan, that is, acrylic acid was successfully grafted on chitosan.

Comparative Example 2 (without zeolite)

0.2 g of chitosan and 75 mL of acetic acid solution with a volume fraction of 2% were added to a 250 mL three-necked flask, and stirred to dissolve. 0.2 g of ceric ammonium nitrate was added to initiate 30 min, 2.5 mL of acrylic acid was added dropwise, and the graft copolymerization was carried out in a _N2 environment at 65 °C for 8 h. The pH of the reactant was adjusted to alkaline with NaOH solution, and the modified chitosan product was precipitated as flocculent. After separation using a high-speed centrifuge, soak in absolute ethanol for 2 hours to dehydrate, freeze-dry and pulverize.

The infrared spectrum of the acrylic acid-grafted chitosan obtained in this example is shown in Figure 2 of the accompanying drawings.

Compared with the CS spectrum, the presence of intermolecular hydrogen bonds in the CS/AA spectrum leads to a red shift of the -OH stretching vibration, and the infrared absorption peak of CS/AA has -OH stretching vibration (3355cm ^-1 ), C=O Stretching vibration (1545cm ^-1 ), -OH in-plane (1280cm ^-1 ) and out-of-plane (989cm ^-1 ) bending vibration and -CO stretching vibration indicate that -COOH in acrylic acid was introduced into chitosan, that is, acrylic acid was successfully grafted on chitosan.

Example 3

The treatment method adopted by the activated zeolite of the present invention is to take a certain amount of clinoptilolite (100 mesh) and soak it in dilute hydrochloric acid, wash it with sodium carbonate solution to neutrality after 6-18 hours, dry it, and put it in a muffle furnace at 300° C. Firing activation for 2.5h.

0.2 g of chitosan and 75 mL of acetic acid solution with a volume fraction of 2% were added to a 250 mL three-necked flask, and stirred to dissolve. Add 0.2 g of ceric ammonium nitrate to initiate 30 min, add 3.5 mL of acrylic acid dropwise, graft copolymerization for 8 h under a water bath at 65 °C in a _N2 environment, and under stirring, adjust the pH of the reactant to alkaline with NaOH solution, and modify the chitosan product As flocculent precipitation, 2 g of activated zeolite was slowly added to the modified chitosan solution, stirred at room temperature for 2 hours, precipitated in a high-speed centrifuge, soaked in absolute ethanol for 2 hours for dehydration, freeze-dried and pulverized to obtain modified chitosan Cross-linked zeolite adsorbent.

The obtained adsorbent was placed in the calcium standard solution, adsorbed for 1 h, and 0.5 g of the adsorbent was weighed into 50 mL of 0.02mol/LCa ²⁺ standard solution and stirred. Add about 1mL of xylenol orange color developer, take a small amount of solution every 10min for centrifugation, and then perform UV analysis on the clear liquid obtained by centrifugation to characterize the calcium ion adsorption capacity of the modified chitosan cross-linked zeolite adsorbent with time. Changes.

The change curve of the adsorption capacity of the adsorbent for solutions with different adsorption times is shown in Figure 3 of the accompanying drawings. With the increase of adsorption time, the adsorption capacity first decreased and then increased, indicating that the adsorption of calcium ions by the cross-linked product varied with time, and the adsorption capacity reached the maximum at 20 min, indicating that the adsorption equilibrium was reached at this time, which proved that the modification The adsorption performance of chitosan cross-linked zeolite adsorbent has achieved the expected effect.

After characterizing the adsorption effect of the modified chitosan cross-linked zeolite composite adsorbent, it can be applied to the geotextile. The modified chitosan cross-linked zeolite composite adsorbent is dissolved in a 2% volume fraction of acetic acid solution while stirring. While heating at 90°C, the solution was concentrated to a viscosity, and the concentrated solution was brushed on the surface of the geotextile with a brush. After drying, it can be used in tailings dams.

Example 4

0.2 g of chitosan and 75 mL of acetic acid solution with a volume fraction of 2% were added to a 250 mL three-necked flask, and stirred to dissolve. Add 0.2 g of ceric ammonium nitrate to initiate 30 min, add 3.5 mL of acrylic acid dropwise, graft copolymerization for 8 h under a water bath at 65 °C in a _N2 environment, and under stirring, adjust the pH of the reactant to alkaline with NaOH solution, and modify the chitosan product As flocculent precipitation, slowly add activated zeolite of different quality to the modified chitosan solution, stir at room temperature for 2 hours, use a high-speed centrifuge for precipitation, soak in absolute ethanol for 2 hours to dehydrate, freeze-dry and pulverize to obtain modified shells Glycan cross-linked zeolite adsorbent.

Use EDTA titration method to carry out titration adsorption experiment at pH 6.5～7.8 (simulating tailings dam environment) to characterize the adsorption capacity of zeolite content to adsorbent, as shown in Figure 4 of the accompanying drawings. quantity change curve.

With the increase of zeolite, the adsorption performance of the adsorbent for calcium ions gradually improved, and the adsorption capacity reached a maximum value of 42 mg/g when the mass of zeolite was 2 g. When the amount of zeolite exceeded 2 g, the adsorption capacity of calcium ions decreased. This is because the adsorption capacity of calcium ions will increase after adding zeolite, but when it exceeds 2g, too much zeolite will fill the pores of the chitosan-grafted acrylic acid-grafted polymer, reducing the specific surface area of the entire material, thereby reducing the adsorption capacity. reduce.

After characterizing the adsorption effect of the modified chitosan cross-linked zeolite composite adsorbent, it can be applied to the geotextile. The modified chitosan cross-linked zeolite composite adsorbent is dissolved in a 2% volume fraction of acetic acid solution while stirring. While heating at 90°C, the solution was concentrated to a viscosity, and the concentrated solution was brushed on the surface of the geotextile with a brush. After drying, it can be used in tailings dams.

Claims (8)

1. Modified chitosan cross-linked zeolite composite adsorbent, its structural formula is: where n is the degree of polymerization of chitosan. 2. The application of the modified chitosan cross-linked zeolite composite adsorbent as claimed in claim 1 as a tailings dam anti-blocking adsorbent material. 3. The application according to claim 2, characterized in that the modified chitosan cross-linked zeolite composite adsorbent configuration solution is uniformly covered on the geotextile. 4. The application according to claim 3, characterized in that the covering method is to cover the surface of the geotextile with the modified chitosan cross-linked zeolite composite adsorbent using a surface coating technique. 5. The application according to claim 4, characterized in that the surface coating technique is brush coating. 6. application according to claim 5 is characterized in that described brushing method step is, dissolving modified chitosan cross-linked zeolite composite adsorbent in solvent, heating while stirring, make the solution concentrated to viscous Afterwards, brush the concentrated solution on the surface of the geotextile. 7. The application according to claim 6, wherein the solvent is an acetic acid solution, a formic acid solution or an oxalic acid solution. 8. The application according to claim 6, characterized in that the heating temperature is 70-110°C.

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