CN113930245A - Environment-friendly Cr (VI) polluted soil remediation agent and preparation method thereof - Google Patents

Abstract

The invention provides an environment-friendly Cr (VI) polluted soil repairing agent and a preparation method thereof, wherein the method comprises the following steps: dissolving chitosan in a mixed solvent formed by glacial acetic acid and methanol, and then sequentially adding pyrrole monomer and oxidant FeCl₃The pyrrole monomer forms polypyrrole to coat on the surface of the chitosan, and the prepared chitosan/polypyrrole mixed solution is put in a refrigerator for overnight and refrigerated storage; adding the chitosan/polypyrrole mixed solution into a precipitator prepared from absolute ethyl alcohol and ethyl acetate until a black flocculent substance is separated out, centrifugally washing the black flocculent substance, and freeze-drying to obtain the repairing agent. The repairing agent is convenient for repairing Cr (VI) polluted soil, has spongy microscopic morphology and developed porosity, and can adsorb Cr⁶⁺Meanwhile, the fertilizer can play a role in reduction, cannot influence the soil recyclability after the soil is repaired, and even can increase the soil fertility so as to promote the growth of plantsLong.

Description

Environment-friendly Cr (VI) polluted soil remediation agent and preparation method thereof

Technical Field

The invention belongs to the technical field of heavy metal pollution remediation, and particularly relates to an environment-friendly Cr (VI) polluted soil remediation agent and a preparation method thereof.

Background

According to the national contaminated soil bulletin, the total standard exceeding rate of heavy metals in the Chinese soil is 16.1%, and the standard exceeding rate of chromium reaches 1.1%. Over 300 chromium contaminated sites have been identified worldwide, with about 1600 million people at risk of chromium exposure. The enterprise for producing chromium salt in China has about 25 families, and the annual output is about 3.29 multiplied by 10⁵The annual chromium slag yield exceeds 4.0 multiplied by 10⁵And piling up more than 4 hundred million tons of chromium slag without treatment. The average chromium concentration in the soil in China is 67.37mg/kg, which is higher than the average level in the world of 42.00 mg/kg.

Chromium may exist in nine valence states in nature (i.e., -2 to +6), but in soil, cr (vi) and cr (iii) are the predominant forms. Cr (VI) has strong oxidizing property, carcinogenicity, and toxicity 100 times higher than that of Cr (III), and Cr (VI) is not easy to degrade and easy to accumulate in organisms and human bodies, causing long-term harm. The conventional restoration method reduces hexavalent chromium with high toxicity into trivalent chromium with low toxicity, and solidifies and stabilizes the trivalent chromium in soil. The existing repairing material usually takes chemical reducing agents such as ferrite and the like as basic agents to reduce Cr (VI), and has good effect, but the problems of soil fertility reduction, secondary pollutant introduction, no biological degradation, influence on subsequent use of soil and the like exist in the fixing and stabilizing process. Therefore, the development of the environment-friendly Cr (VI) polluted soil repairing material has practical significance.

Disclosure of Invention

In view of this, the present invention provides an environment-friendly cr (vi) contaminated soil remediation agent, which can effectively reduce cr (vi) in soil and is an ecological and environment-friendly green remediation agent.

In order to achieve the purpose, the technical scheme of the invention is realized as follows:

a preparation method of an environment-friendly Cr (VI) polluted soil remediation agent comprises the following steps:

1) mixing glacial acetic acid and methanol in proportion to form a mixed solvent, dissolving chitosan in the mixed solvent and stirring until the chitosan is completely dissolved, and then sequentially adding pyrrole monomer and oxidant FeCl₃The pyrrole monomer forms polypyrrole to coat on the surface of the chitosan, and the prepared black chitosan/polypyrrole mixed solution is put in a refrigerator for overnight and refrigerated storage;

2) preparing a precipitator by using absolute ethyl alcohol and ethyl acetate, adding the chitosan/polypyrrole mixed solution into the precipitator, fully stirring until a black flocculent substance is separated out, centrifuging the black flocculent substance, washing the black flocculent substance by using distilled water and ethanol until the filtrate is neutral, and finally freeze-drying to obtain the repairing agent.

Further, the solid-liquid ratio of the chitosan to the mixed solvent is 1:150-1:200, and the unit of the solid-liquid ratio is g/ml.

Further, the mass concentration of the glacial acetic acid in the mixed solvent is 2%, and the volume ratio of the methanol to the glacial acetic acid is 1:4-1: 7.

Further, FeCl₃The concentration of (2) is 0.5 mol/L.

Further, pyrrole monomer and FeCl₃The molar ratio is 1:2 to 1: 3.

Further, the liquid-solid ratio of the pyrrole monomer to the chitosan is 1:2-1:3, and the unit of the liquid-solid ratio is ml/g.

Further, the black chitosan/polypyrrole mixed solution obtained in the step 1) is placed in a refrigerator for refrigeration and stabilization for 7-12 hours.

Further, the volume ratio of the absolute ethyl alcohol of the precipitator to the ethyl acetate is 3:1-5: 1.

Further, the conditions of freeze-drying in step 2) were-50 ℃ and 20 Pa.

The invention also provides an environment-friendly Cr (VI) polluted soil repairing agent prepared by any one of the preparation methods.

Compared with the prior art, the environment-friendly Cr (VI) polluted soil remediation agent has the following advantages:

the environment-friendly Cr (VI) polluted soil repairing agent prepared by the invention has a porous structure, has a large specific surface area, can adsorb and complex Cr (VI) in soil, and simultaneously, the surface of the repairing agent contains organic functional groups such as hydroxyl, amino and the like, so that the reduction of Cr (VI) in soil can be realized, and the toxicity and the biological effectiveness of hexavalent chromium are further reduced. Meanwhile, the organic matter of the repairing material can be biodegraded with low toxicity, the repairing material has small disturbance to the soil environment when being applied to soil, does not cause secondary pollution, is beneficial to the improvement of soil fertility and the reutilization of the repaired soil, and is an ecological environment-friendly green repairing agent.

Drawings

The accompanying drawings, which are incorporated in and constitute a part of this specification, are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the principles of the invention and not to limit the invention in any way. In the drawings:

FIG. 1 is a scanning electron micrograph of a restorative prepared according to examples 1-4;

FIG. 2 is a graph comparing the adsorption capacities of the remediation agents prepared in examples 1-4;

FIG. 3 is a chart of the infrared spectrum of the inner leaf of the repairing agent obtained in example 1;

FIG. 4 is an XPS plot of the repair agent obtained in example 1;

FIG. 5 is a graph comparing the adsorption effects of example 1 and comparative examples 1-2;

FIG. 6 is a scanning electron micrograph of the healant at different pyrrole additions: (a) PPy-0.2; (b) PPy-0.6(c) PPy-1.0; (d) PPy-1.5;

FIG. 7 is a graph comparing the effect of adsorption capacity of example 1 with comparative examples 9-10;

FIG. 8 is a scanning electron micrograph of example 1 and comparative examples 11 to 12; (a) the volume ratio of the absolute ethyl alcohol to the ethyl acetate is 6: 1; (b) the volume ratio of the absolute ethyl alcohol to the ethyl acetate is 4: 1; (c) the volume ratio of the absolute ethyl alcohol to the ethyl acetate is 1: 1;

FIG. 9 is a graph comparing the effect of adsorption capacity of example 1 with comparative examples 11-12;

FIG. 10 is a scanning electron micrograph of example 1 and comparative example 13; (a) example 1; (b) comparison 13;

FIG. 11 is a graph comparing the effect of adsorption capacity of example 1 with that of comparative example 13;

FIG. 12 is a scanning electron micrograph of example 1 and comparative example 14; (a) example 1; (b) comparison 14;

FIG. 13 is a graph comparing the effect of adsorption capacity of example 1 with that of comparative example 14;

FIG. 14 is a scanning electron micrograph of example 1 and comparative example 15; (a) example 1; (b) comparative example 15;

FIG. 15 is a graph comparing the adsorption capacity effects of example 1 and comparative example 15.

Detailed Description

It should be noted that the embodiments and features of the embodiments of the present invention may be combined with each other without conflict.

At present, Cr (VI) polluted soil remediation agents mostly focus on passivation effect and reduction efficiency, but secondary pollution caused by the ecological environment is rarely evaluated. Based on the environment-friendly Cr (VI) polluted soil remediation agent, two biodegradable substances, namely chitosan and polypyrrole are used as synthetic materials, the soil remediation agent is applied to soil, the soil environment is slightly disturbed, secondary pollution is avoided, the soil fertility is improved, and the soil is reused after remediation.

The present invention will be described in detail below with reference to the embodiments with reference to the attached drawings.

The following examples are for the preparation of the repair agent and for Cr⁶⁺The operation is illustrated by taking as an example the measurement of the adsorption capacity of a 50mg/L solution:

example 1

The preparation method of the environment-friendly Cr (VI) polluted soil remediation agent comprises the following steps:

(1)350mL of glacial acetic acid with a mass concentration of 2% and 50mL of methanol (V)_Methanol：V_{Glacial acetic acid}1: 7) mixing to form a mixed solvent, dissolving 2.5g of chitosan in the mixed solvent (solid-liquid ratio is 1:160), and stirring at room temperature for 30min to obtain uniformly dissolved chitosan hydrogel;

(2) adding 1.0ml of pyrrole monomer into the chitosan hydrogel in the step (1) under the stirring state (m)_Chitosan：v_{Azole compounds}2.5:1) and stirring for 3 hours to obtain chitosan/pyrrole mixed sol;

(3) 72.2 ml of FeCl₃Adding the chitosan/pyrrole mixed sol obtained in the step (2) as an oxidant, stirring for 30min, oxidizing pyrrole monomers to form polypyrrole, and coating the polypyrrole on the surface of chitosan to form black chitosan/polypyrrole mixed sol;

(4) placing the black chitosan/polypyrrole mixed sol obtained in the step (3) in a refrigerator at 4 ℃ for stabilization for 10 hours;

(5) preparing a precipitator by using absolute ethyl alcohol and ethyl acetate with the volume ratio of 4:1, adding the chitosan/polypyrrole mixed sol which is refrigerated and stabilized in the step (4) into the precipitator, and continuously stirring until black floccules are separated out;

(6) centrifuging the black floccule obtained in the step (5), keeping the centrifugal force at 3000g, centrifuging for 10min, and repeatedly washing with a precipitator until the filtrate is neutral to obtain black chitosan/polypyrrole precipitate;

(7) and (4) placing the black chitosan/polypyrrole precipitate obtained in the step (6) into a vacuum freeze dryer, and carrying out freeze drying at-50 ℃ and 20Pa to obtain the chitosan/polypyrrole repairing agent.

The repair agent obtained in example 1 was subjected to fourier infrared spectroscopy, as shown in fig. 3, and it can be seen that the chitosan/polypyrrole repair agent was successfully prepared.

When the repair agent obtained in example 1 was subjected to XPS, Cr (VI) was observed to be adsorbed, as shown in FIG. 4.

Example 2

The preparation method of the environment-friendly Cr (VI) polluted soil remediation agent comprises the following steps:

(1) 167mL of glacial acetic acid having a mass concentration of 2% was mixed with 33mL of methanol to form a mixed solvent (V)_Methanol：V_{Glacial acetic acid}1:5), dissolving 1.0g of chitosan in the mixed solvent (the solid-to-liquid ratio of the chitosan to the mixed solvent is 1:200), and stirring at room temperature to obtain chitosan hydrogel;

(2) under the stirring state, pyrrole monomer exists in a liquid form at the normal temperature, the density is 0.9691mg/L, 0.5ml of pyrrole monomer is added into the chitosan hydrogel in the step (1) (m_Chitosan：v_{Azole compounds}2:1) and stirring for 3 hours to obtain chitosan/pyrrole mixed sol;

(3) 40 ml of 0.5mol/L FeCl₃Adding the chitosan/pyrrole mixed sol (n) in the step (2) as an oxidizing agent_PPyAnd n_FeCl31:2.8), stirring for 30min, oxidizing pyrrole monomer to form polypyrrole, coating the polypyrrole on the surface of chitosan, and forming black chitosan/polypyrrole mixed sol;

(4) placing the black chitosan/polypyrrole mixed sol obtained in the step (3) in a refrigerator at 4 ℃ for stabilization for 8 hours;

(5) preparing a precipitator by using ethyl acetate and absolute ethyl alcohol in a volume ratio of 1:3, adding the chitosan/polypyrrole mixed sol which is refrigerated and stabilized in the step (4) into the precipitator, and continuously stirring until black floccules are separated out;

(6) centrifuging the black floccule obtained in the step (5) for 3000g for 10min, and repeatedly washing the floccule with a precipitator until the filtrate is neutral to obtain black chitosan/polypyrrole precipitate;

(7) and (4) placing the black chitosan/polypyrrole precipitate obtained in the step (6) into a vacuum freeze dryer, and carrying out freeze drying at-50 ℃ and 20Pa to obtain the chitosan/polypyrrole repairing agent.

Example 3

The preparation method of the environment-friendly Cr (VI) polluted soil remediation agent comprises the following steps:

(1) 324mL of glacial acetic acid with a mass concentration of 2% and 81mL of methanol were mixed to form a mixed solvent (V)_Methanol：V_{Glacial acetic acid}2.7g of chitosan is dissolved in the mixed solvent (the solid-to-liquid ratio of the chitosan to the mixed solvent is 1:150), and the mixture is stirred at room temperature to obtain chitosan hydrogel;

(2) adding 0.9ml of pyrrole monomer into the chitosan hydrogel in the step (1) under the stirring state (m)_Chitosan：V_{Azole compounds}1) stirring for 3 hours to obtain chitosan/pyrrole mixed sol;

(3) 52 ml of 0.5mol/L FeCl₃Adding the chitosan/pyrrole mixed sol (n) in the step (2) as an oxidizing agent_PPyAnd n_FeCl31:2), stirring for 30min, oxidizing pyrrole monomer to form polypyrrole, coating the polypyrrole on the surface of chitosan, and forming black chitosan/polypyrrole mixed sol;

(4) placing the black chitosan/polypyrrole mixed sol obtained in the step (3) in a refrigerator at 4 ℃ for stabilization for 10 hours;

(5) preparing a precipitator by using absolute ethyl alcohol and ethyl acetate with the volume ratio of 5:1, adding the chitosan/polypyrrole mixed sol which is refrigerated and stabilized in the step (4) into the precipitator, and continuously stirring until black floccules are separated out;

(6) centrifuging the black floccule obtained in the step (5) for 3000g for 10min, and repeatedly washing the floccule with a precipitator until the filtrate is neutral to obtain black chitosan/polypyrrole precipitate;

(7) and (4) placing the black chitosan/polypyrrole precipitate obtained in the step (6) into a vacuum freeze dryer, and carrying out freeze drying at-50 ℃ and 20Pa to obtain the chitosan/polypyrrole repairing agent.

Example 4

The preparation method of the environment-friendly Cr (VI) polluted soil remediation agent comprises the following steps:

(1) 300mL of glacial acetic acid with a mass concentration of 2% was mixed with 50mL of methanol to form a mixed solvent (V)_Methanol：V_{Glacial acetic acid}1:6), dissolving 2.0g of chitosan in the mixed solvent (the solid-to-liquid ratio of the chitosan to the mixed solvent is 1:175), and stirring at room temperature to obtain chitosan hydrogel;

(2) adding 0.8mL of pyrrole monomer into the chitosan hydrogel in the step (1) under the stirring state (m)_{Shell polymerCandy}：V_{Azole compounds}2.5:1) and stirring for 3 hours to obtain chitosan/pyrrole mixed sol;

(3) 46.2 ml of 0.5mol/L FeCl₃Adding the chitosan/pyrrole mixed sol (n) in the step (2) as an oxidizing agent_PPyAnd n_FeCl31:2), stirring for 30min, oxidizing pyrrole monomer to form polypyrrole, coating the polypyrrole on the surface of chitosan, and forming black chitosan/polypyrrole mixed sol;

(4) placing the black chitosan/polypyrrole mixed sol obtained in the step (3) in a refrigerator at 4 ℃ for stabilization for 9 hours;

(5) preparing a precipitator by using absolute ethyl alcohol and ethyl acetate in a volume ratio of 5:1, adding the chitosan/polypyrrole mixed sol which is refrigerated and stabilized in the step (4) into the precipitator, and continuously stirring until black floccules are separated out;

(6) centrifuging the black floccule obtained in the step (5) for 3000g for 10min, and repeatedly washing the floccule with a precipitator until the filtrate is neutral to obtain black chitosan/polypyrrole precipitate;

(7) and (4) placing the black chitosan/polypyrrole precipitate obtained in the step (6) into a vacuum freeze dryer, and carrying out freeze drying at-50 ℃ and 20Pa to obtain the chitosan/polypyrrole repairing agent.

FIG. 1 is a scanning electron microscope image of the repairing agents prepared in examples 1-4, FIG. 2 is a comparison image of the adsorption capacity of the repairing agents prepared in examples 1-4, and it can be seen from the scanning electron microscope image of FIG. 1 that the porosity of the prepared materials in a specified range is developed and uniform, and the materials are fluffy like sponges. The differences between examples 1 to 4 are also small in comparison with the adsorption capacity, indicating that the repairing agent prepared in the prescribed range satisfies the requirements.

Comparative example 1

This example provides a Cr (VI) repairing agent prepared in the same manner as in example 1, except that the amount of chitosan added in step 1) was 1.0g (solid-to-liquid ratio: 1: 400).

Comparative example 2

This example provides a Cr (VI) repairing agent prepared in the same manner as in example 1, except that the amount of chitosan added in step 1) was 5.0g (solid-to-liquid ratio: 1: 80).

Comparative example 3

This example provides a cr (vi) repair agent prepared in the same manner as in example 1, except that the ratio of glacial acetic acid to methanol in step 1) was changed to 1:0, i.e., no methanol was added.

Comparative example 4

This example provides a cr (vi) repair agent prepared in the same manner as in example 1 except that the ratio of methanol to glacial acetic acid added in step 1) was changed to 1: 3.

Comparative example 5

This example provides a cr (vi) repair agent prepared in the same manner as in example 1, except that the ratio of glacial acetic acid to methanol added in step 1) was changed to 0:1, i.e., no glacial acetic acid was added.

Comparative example 6

This example provides a cr (vi) repairing agent prepared in the same manner as in example 1, except that in step 2), the content of pyrrole is 0.2mL, and the liquid-solid ratio of pyrrole to chitosan is 1: 12.5.

Comparative example 7

This example provides a cr (vi) repairing agent prepared in the same manner as in example 1, except that in step 2), the content of pyrrole is 0.6mL, and the liquid-solid ratio of pyrrole to chitosan is 1: 4.17.

Comparative example 8

This example provides a cr (vi) repairing agent prepared in the same manner as in example 1, except that in step 2), the content of pyrrole is 1.5mL, and the liquid-solid ratio of pyrrole to chitosan is 1: 1.67.

Comparative example 9

This example provides a Cr (VI) repairing agent, which is prepared in the same manner as in example 1, except that FeCl is used in step 3)₃The molar ratio to pyrrole was 1:1.

Comparative example 10

This example provides a Cr (VI) repairing agent, which is prepared in the same manner as in example 1, except that FeCl is used in step 3)₃The molar ratio to pyrrole was 1: 5.

Comparative example 11

This example provides a cr (vi) repair agent prepared in the same manner as in example 1, except that the ratio of absolute ethanol to ethyl acetate used in step 5) was 6: 1.

Comparative example 12

This example provides a cr (vi) repair agent prepared in the same manner as in example 1, except that the ratio of absolute ethanol to ethyl acetate used in step 5) was 1:1.

Comparative example 13

This comparative example provides a cr (vi) repair agent prepared in the same manner as in example 1 except that the operation of step 5) was changed to the operation of adjusting the pH of the chitosan/polypyrrole gel solution to be alkaline with 0.1mol/L of sodium hydroxide until a large amount of flocs were precipitated, without using a precipitant prepared from absolute ethyl alcohol and ethyl acetate.

Comparative example 14

This example provides a cr (vi) repair agent prepared in the same manner as in example 1, except that bacterial fiber was used as a carrier for polypyrrole instead of chitosan.

The preparation method of the bacterial cellulose comprises the following steps:

and (2) putting the cleaned coconut into 2mo/L sodium hydroxide solution, boiling for 3h in a constant-temperature water bath kettle at 80 ℃, repeatedly cleaning the coconut from milk white to brown by using deionized water, soaking the coconut in the deionized water until the cleaning solution is neutral to obtain a required white BC gel block, and crushing the BC gel block by using a juicer to prepare the BC hydrogel.

Comparative example 15

This example provides a Cr (VI) repair agent prepared in the same manner as in example 1 except that the oxidizing agent in step 3) was replaced with 0.5mol/L potassium persulfate (K)₂S₂O₈). Test results and analysis:

1. effect of solid-to-liquid ratio of Chitosan to Mixed solvent (comparative example 1 and comparative example 2)

To determine the optimal adding ratio of chitosan to solvent, FIG. 5 shows the ratio of the repairing agent prepared in example 1 and comparative examples 1 and 2 to Cr in the aqueous solution⁶⁺And (4) removing.

The experimental conditions are as follows: the concentration of Cr (VI) is 50mg/L, the liquid volume is 100mL, the adding dosage of the repairing agent is 25mg under the conditions that the pH is 7, the temperature is 30 ℃, and the vibration is carried out at the level of 180r/min, the absorption amount (Qe) of Cr (VI) in the solution is respectively measured by sampling at 10 th, 20 th, 40 th, 60 th, 80 th, 100 th and 120 th min, and the determination of Cr (VI) adopts a dibenzoyl dihydrazide spectrophotometry, as shown in figure 5.

The adsorption capacity is (C0-Ce) V/m; c0 initial concentration; ce: concentration after reaction; v: a reaction volume; m is the mass of the adsorbent.

As shown in fig. 5, too much or too little chitosan may affect the adsorptive property of the repairing agent, and when the chitosan is added in a large amount, the chitosan may be insufficiently dissolved, and large bubbles may be generated, so that polypyrrole may not be coated on the surface of chitosan. When the chitosan is added too little, chitosan gel can not be formed, and a chitosan mixed solution is formed, so that the attachment of pyrrole monomers is not facilitated, and the small adsorption capacity is further influenced. When the solid-liquid ratio of the chitosan to the mixed solvent is 1:160, the obtained repairing agent pair Cr⁶⁺The best adsorption effect.

2. Effect of solvent mixture (comparative examples 3 to 5)

In order to find the optimal mixture ratio of the mixed solvent, the experimental example respectively compares the effects of the example 1 and the comparative examples 3-5, and the effect difference is obvious after the mixed solvents with different ratios dissolve chitosan for 30 min.

Comparative example 3 only glacial acetic acid (the volume ratio of glacial acetic acid to methanol is 1: 0) can cause insufficient dissolution of chitosan to form small particles floating on the surface, when methanol is added, hydrogen bonds among chitosan molecules can be destroyed, the solubility of chitosan is increased, when the chitosan is properly matched with chitosan, uniform chitosan gel can be formed, and then the subsequent crosslinking reaction with polypyrrole is more sufficient. In contrast, in comparative example 5, only methanol is used as a solvent (the volume ratio of glacial acetic acid to methanol is 0:1), the chitosan gel state is destroyed, a chitosan solution is formed, polypyrrole is not conveniently loaded, the adsorption capacity of the chitosan/polypyrrole repairing agent is greatly reduced, and the repairing effect is reduced.

When the volume ratio of the methanol and glacial acetic acid mixed solvent is 3:1, the viscosity of the dissolved chitosan gel is slightly lower than 7:1, so that the content of subsequent loaded pyrrole is low, and in consideration of economic factors, the optimal ratio of glacial acetic acid to methanol is finally determined to be 7: 1.

3. Effect of the amount of Chitosan added to the amount of pyrrole monomer (comparative examples 6 to 8)

To determine the optimal molar ratio of chitosan to pyrrole monomers, example 1 was compared to comparative examples 6-8 and the CS/PPy composites prepared separately were subjected to scanning electron microscopy, as shown in fig. 6.

As can be seen from FIG. 6, the optimum amount of pyrrole monomer is 1.0mL under the condition that the amount of chitosan is 2.5g, i.e. the ratio of the solid-liquid addition of chitosan to pyrrole monomer is: 2.5: 1; when the addition amount of the pyrrole monomer is too small, the formed composite material is compact and has insufficient void degree, so that the adsorption performance is influenced as shown in fig. 6(a) and (b); when the adding amount of the pyrrole monomer is too much, the condition shown in fig. 6(d) can be caused, the polypyrrole can not be supported by chitosan, and the polypyrrole can be broken into a sheet shape, and the formed gap is not uniform. When the adding amount of the pyrrole monomer is 1mL, the optimal adding amount is obtained, and the prepared chitosan polypyrrole composite material has uniform gaps, is in a loose sponge shape and has better adsorption performance.

4. Effect of amount of addition of pyrrole monomer and oxidizing agent (comparative examples 9 to 10)

The repairing agents prepared in example 1 and comparative examples 9-10 were used for Cr in aqueous solution⁶⁺The experimental conditions were the same as in experimental example 1, and the obtained effects are shown in fig. 7.

From FIG. 7 we can see that when FeCl is used₃At a molar ratio of 1:1 with pyrrole, due to FeCl₃Pyrrole monomers cannot be completely oxidized, so that the prepared repair material has small adsorption capacity of only 24.6 mg/g. When FeCl is added₃The molar ratio of the chitosan to the pyrrole PPy is gradually increased, and the adsorption capacity of the prepared chitosan/polypyrrole composite material is also gradually improved. When PPy and FeCl₃The molar ratio is 1: FeCl 5 time₃The excessive amount results in slightly reduced adsorption capacity of the prepared chitosan/polypyrrole composite material compared with the molar ratio of 1: 2.5. Description of FeCl₃The more the amount of (A) is added, the better, but there is a peak.

5. Comparison of the precipitants (comparative examples 11 to 12)

In order to prepare the chitosan/polypyrrole repairing agent as powder and be convenient to use as a soil repairing agent, the chitosan is poor in solubility in ethyl acetate and methanol solutions and the chitosan is insoluble in alkaline solutions, the powder repairing agents prepared in examples 1 and comparative examples 11-12 are respectively carried out, a scanning electron microscope is carried out on example 1 and comparative examples 11-12, and the adsorption capacity in an aqueous solution is tested, so that the repairing agent with higher adsorption capacity and better Cr (VI) reduction capacity is expected to be prepared, and the specific experimental operation is the same as that of experiment 1. The effect of the obtained repairing agent is shown in FIG. 8.

As can be seen from fig. 8, the bulk porosity of the surface of the prepared composite restorative agent is uniform and developed when the volume ratio of absolute ethyl alcohol to ethyl acetate is 4:1, as shown in fig. 8 (b); the highest adsorption capacity is shown in fig. 9. Absolute ethanol is used as a poor solvent for chitosan, but has a strong precipitation effect unlike aprotic solvents such as ethyl acetate, so that the prepared composite material is extremely compact. In comparative example 11 when the volume ratio of ethyl acetate is decreased (V)_{Anhydrous ethanol}：V_{Ethyl acetate}6:1), the prepared material has high water content, and the freeze-drying causes excessive voids and cracks on the surface of the material, as shown in fig. 8 (a). In comparative example 12, when the proportion of ethyl acetate is high (V)_{Anhydrous ethanol}：V_{Ethyl acetate}1:1), the prepared material has a compact surface and small pores as shown in fig. 8 (c). Therefore, when absolute ethyl alcohol and ethyl acetate are mixed according to a proper proportion, the chitosan/polypyrrole composite repairing agent with proper crystallinity and entanglement, loose surface and developed porosity can be obtained.

6. Effect of precipitation mode (comparative example 13)

In order to prepare a powdery restoration agent, acetic acid B and wastewater ethanol precipitant were prepared in example 1, and alkaline was prepared by adjusting pH with sodium hydroxide in comparative example 13, both of which were able to prepare a powdery chitosan/polypyrrole adsorbent, but the adsorption capacity was 13.4 greater than that of comparative example 13 by the method in example 1, as shown in FIG. 11. In addition, a large difference can be seen from the scanning electron microscope of fig. 10, and the material prepared by using the sodium hydroxide precipitant is spongy, fluffy but not as developed in porosity as in example 1.

6. Effect of different carriers (comparative example 14)

Comparative example 14 the BC hydrogel was used as a carrier instead of chitosan, and the morphology of the two was greatly different from the scanning electron microscope, and the material prepared from chitosan as a carrier was spongy as shown in fig. 12(a), while the material prepared from Bacterial Cellulose (BC) was filamentous as shown in fig. 12 (b). And the material prepared by BC is flocculent and has very light density, so the adsorption capacity in water is about 4 times of that of the chitosan/polypyrrole adsorption material, as shown in figure 13. But it is inconvenient to use as a soil remediation agent because it is flocculent.

7. Effect of different oxidants (comparative example 15)

Comparative example 15 Potassium persulfate (K) was used in comparison with example 1₂S₂O₈) And ferric trichloride (FeCl)₃) The performance of the prepared repair agent is different when the repair agent is used as an oxidizing agent. Comparative example 15 (K) can be obtained by comparing FIGS. 14 and 15₂S₂O₈) The repair agent prepared for the oxidant was not as effective as example 1 (fig. 14a), and the repair agent prepared for comparative example 15 (fig. 14b) apparently lacked uniform voids, resulting in slightly less adsorption capacity than example 1, as shown in fig. 15. This is also possible because of FeCl₃Not only acting as an oxidizing agent, but also Cl^-Also has ion exchange effect, and Cr is in aqueous solution⁶⁺With Cr₂O₇ ^2-Or CrO₄ ^2-Form and Cl^-Ion exchange is carried out, and then the chromium ions are adsorbed to the surface of the repairing agent and reduced, thereby achieving the purpose of Cr⁶⁺And (4) removing. And with K₂S₂O₈The repair material prepared for the oxidizing agent does not have the function of ion exchange. Thus, comparative example 15 had a less good adsorption capacity than example 1.

8. Cr (VI) contaminated soil remediation test (comparative examples 13 to 15)

The previous experiments are based on the evaluation of the physicochemical property of the material by the adsorption capacity in water, but the influence of the acting environment on the material is large, and the biological toxicity of different preparation methods and preparation materials to the environment is also greatly different. In order to evaluate the effects of the three remediation agents of comparative examples 13-15 and the soil reusability and biotoxicity of the chitosan/polypyrrole remediation agent of example 1 after remediation, a simulated chromium-contaminated soil remediation experiment and a post-remediation soil plant potting experiment were designed.

(1) Preparation of Cr (VI) contaminated soil:

the experimental soil was collected from soil of a certain farmland in south-yang city of Henan province, removed of stone grains and other impurities, and ground through a sieve of two 2 mm. The Cr (VI) polluted soil is prepared by artificially adding a potassium dichromate solution, and the prepared Cr (VI) polluted soil is aged for 3 months under natural conditions, so that the Cr form tends to be stable, and the simulated Cr (VI) polluted soil is obtained. The total chromium content in the soil is 200mg/kg through flame atomic absorption spectrophotometry, and the content of Cr (VI) is 163.2mg/kg through adopting an alkali solution extraction-flame atomic absorption spectrophotometry for determining the soil and the deposit hexavalent chromium of HJ 1082-2019.

(2) Cr (VI) contaminated soil remediation:

preparing aged Cr (VI) polluted soil with the same quality, wherein the first group is used as a blank control group (CK) without adding any repairing agent; the second group added 0.5% of the remediation agent (G1) prepared in example 1 by weight of Cr-contaminated soil used in the experiment; the third group was added with the repairing agent (G2) prepared in comparative example 14 in an amount of 0.5% by weight of Cr-contaminated soil used in the experiment; the fourth group added the repairing agent (G3) prepared in comparative example 15 added in an amount of 0.5% by weight of the Cr-contaminated soil used in the experiment; group 5 was added with the repairing agent (G4) prepared in comparative example 13 in an amount of 0.5% by weight of the Cr-contaminated soil used in the experiment, and the water content of the soil was adjusted to 30% to uniformly mix the repairing agent with the contaminated soil.

After 15 days of remediation, the content of Cr (VI) is determined by adopting an alkali solution extraction-flame atomic absorption spectrophotometry method for determining the soil and the deposit hexavalent chromium of HJ1082-2019, and the existing form and proportion of Cr in the soil are determined by adopting a BCR extraction method. The BCR extraction method can better reflect the fluidity and biological effectiveness of heavy metals in soil, the fluidity of weak acid state is best, the heavy metals are most easily absorbed by organisms, the biological toxicity is also the largest, the reduction state is the second, the residue state is the most stable, and the biological toxicity is the smallest. The repairing effect of example 1 and each comparative example is shown in table 1.

From the above table, the G1 group corresponding to example 1 has the least percentage of the extractable state of the contaminated acid after 15 days of remediation, the highest percentage of the oxidizable state and the residue state, and the removal rate of cr (vi) in the soil can reach 98%. The repairing agents prepared in other comparative examples have certain repairing effect on Cr (VI) polluted soil, the acid extractable state in the soil is obviously reduced in a certain proportion after the repairing agents are applied, the residue state is obviously improved, but the effect is not as good as that of the G1 group corresponding to the example 1.

(3) Soil recyclability and toxic action of the soil after restoration on plants (comparative examples 13 to 15)

In order to evaluate the restoration effect and soil recycling property of the restoration agent on Cr (VI) contaminated soil in example 1 and comparative example, and the toxic effect of the restored soil on plants, a post-restoration ryegrass potting experiment was performed. And (3) taking out the soil after 15 days of restoration, naturally drying the soil until the water content is about 10%, setting a chromium-free polluted soil YT group, uniformly stirring the soil, planting ryegrass, watering the soil regularly every day, harvesting the soil after 25 days, comparing the restoration effects of the example 1 and different control groups, and showing in table 2.

TABLE 2 plant growth characteristics

Experiments show that the growth condition of the ryegrass is related to the residual condition of Cr (VI) in the soil and the ratio of chromium in a residue state in the soil, the higher the concentration of the residual Cr (VI) in the soil is, the more obvious the inhibition effect on the ryegrass is, and the higher the ratio of the chromium in the residue state in the soil is, the more obvious the inhibition effect on the growth of the ryegrass is. The ryegrass of the G1 group corresponding to example 1 grows best, has thick and strong rootstocks and even has a tendency to exceed that of ryegrass of the YT group, which indicates that the chitosan/polypyrrole repairing agent prepared by example 1 not only can repair Cr (VI) polluted soil, but also can improve the fertility of the soil and promote the growth of plants. Rye grass in the CK group was the worst and very weak. The repairing agents prepared by other comparative examples also play a certain role in repairing Cr (VI) polluted soil, but the effect is not as good as that of example 1, and the growth effects are G4, G2 and G3 in sequence from good to poor.

The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents, improvements and the like that fall within the spirit and principle of the present invention are intended to be included therein.

Claims (10)

1. A preparation method of an environment-friendly Cr (VI) polluted soil remediation agent is characterized by comprising the following steps: the method comprises the following steps:

1) mixing glacial acetic acid and methanol in proportion to form a mixed solvent, dissolving chitosan in the mixed solvent and stirring until the chitosan is completely dissolved, and then sequentially adding pyrrole monomer and oxidant FeCl₃The pyrrole monomer forms polypyrrole to coat on the surface of the chitosan, and the prepared black chitosan/polypyrrole mixed solution is put in a refrigerator for overnight and refrigerated storage;

2) preparing a precipitator by using absolute ethyl alcohol and ethyl acetate, adding the chitosan/polypyrrole mixed solution into the precipitator, fully stirring until a black flocculent substance is separated out, centrifuging the black flocculent substance, washing the black flocculent substance by using distilled water and ethyl alcohol until the filtrate is neutral, and finally freeze-drying to obtain the repairing agent.

2. The method of claim 1 for preparing an environmentally friendly Cr (VI) contaminated soil remediation agent, wherein: the solid-liquid ratio of the chitosan to the mixed solvent is 1:150-1:200, and the unit of the solid-liquid ratio is g/ml.

3. The method of claim 1 for preparing an environmentally friendly Cr (VI) contaminated soil remediation agent, wherein: the mass concentration of the glacial acetic acid in the mixed solvent is 2%, and the volume ratio of the methanol to the glacial acetic acid is 1:4-1: 7.

4. The method of claim 1 for preparing an environmentally friendly Cr (VI) contaminated soil remediation agent, wherein: FeCl₃The concentration of (2) is 0.5 mol/L.

5. The method of claim 4 for preparing an environmentally friendly Cr (VI) contaminated soil remediation agent, wherein: pyrrole monomer and FeCl₃The molar ratio is 1:2 to 1: 3.

6. The method of claim 1 for preparing an environmentally friendly Cr (VI) contaminated soil remediation agent, wherein: the liquid-solid ratio of the pyrrole monomer to the chitosan is 1:2-1:3, and the unit of the liquid-solid ratio is ml/g.

7. The method of claim 1 for preparing an environmentally friendly Cr (VI) contaminated soil remediation agent, wherein: and (2) refrigerating the black chitosan/polypyrrole mixed solution obtained in the step 1) in a refrigerator, and stabilizing for 7-12 hours.

8. The method of claim 1 for preparing an environmentally friendly Cr (VI) contaminated soil remediation agent, wherein: the volume ratio of the absolute ethyl alcohol to the ethyl acetate serving as the precipitant is 3:1-5: 1.

9. The method of claim 1 for preparing an environmentally friendly Cr (VI) contaminated soil remediation agent, wherein: the conditions of freeze drying in the step 2) are-50 ℃ and 20 Pa.

10. An environmentally friendly Cr (VI) contaminated soil remediation agent prepared by the method of any one of claims 1-9.

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