WO2023088292A1 - Environment-friendly remediation agent for cr(vi)-contaminated soil, and preparation method therefor and use thereof - Google Patents

Abstract

Provided in the present invention are an environment-friendly remediation agent for Cr(VI)-contaminated soil and a preparation method therefor. The method comprises the following steps: dissolving chitosan in a mixed solvent formed by glacial acetic acid and methanol, then adding a pyrrole monomer and an oxidizing agent FeCl3 in sequence, enabling the pyrrole monomer to form polypyrrole that coats the surface of the chitosan, placing the prepared chitosan/polypyrrole mixed solution in a refrigerator for refrigeration overnight; and adding the chitosan/polypyrrole mixed solution to a precipitant prepared from absolute ethyl alcohol and ethyl acetate until a black flocculent substance is precipitated, and centrifugally washing and freeze-drying the black flocculent substance to obtain the remediation agent. The remediation agent can be conveniently used for the remediation of Cr(VI)-contaminated soil, has a spongy microstructure and developed porosity, can further play a role in reduction while adsorbing Cr(VI), does not affect the reusability of the soil after remediation is completed, and even can increase the fertility of the soil to promote the growth of plants.

Description

A kind of environment-friendly Cr (VI) contaminated soil remediation agent and its preparation method and application

This application requires the priority of the Chinese patent application submitted to the China Patent Office on November 16, 2021, with the application number CN202111354350.4, and the invention title "An environment-friendly Cr(VI) polluted soil remediation agent and its preparation method" rights, the entire contents of which are incorporated in this application by reference.

technical field

The invention relates to the technical field of remediation of heavy metal pollution, in particular to an environment-friendly Cr(VI) contaminated soil remediation agent and its preparation method and application.

Background technique

According to the National Polluted Soil Bulletin, the total excess rate of heavy metals in Chinese soil is 16.1%, and the excess rate of chromium has reached 1.1%. Worldwide, more than 300 chromium-contaminated sites have been identified, and about 16 million people are at risk of chromium exposure. There are about 25 enterprises producing chromium salts in China, with an annual output of about 3.29×10 ⁵ tons and an annual output of chromium slag exceeding 4.0×10 ⁵ tons. More than 400 million tons of chromium slag are piled up without treatment. The average concentration of chromium in soil in my country is 67.37mg/kg, which is higher than the world average level of 42.00mg/kg.

Chromium exists in nine valence states (ie -2 to +6) in nature, but in soil, Cr(VI) and Cr(III) are the main forms of existence. Cr(VI) is strong oxidizing and carcinogenic, and its toxicity is 100 times greater than that of Cr(III). Moreover, Cr(VI) is not easy to degrade, and it is easy to accumulate in organisms and human body, causing long-term harm. The existing common restoration methods reduce the highly toxic hexavalent chromium to the less toxic trivalent chromium and stabilize it in the soil. Existing repair materials usually use chemical reducing agents such as ferrous salts as the basic components, and the effect of reducing Cr(VI) is better, but the fixation and stabilization process reduces soil fertility and introduces secondary pollutants, which are not biodegradable and affect soil quality. Subsequent use and other issues. Therefore, it is of practical significance to develop environmentally friendly Cr(VI) contaminated soil remediation materials.

Contents of the invention

In view of this, the present invention aims to propose an environment-friendly Cr(VI) polluted soil remediation agent, which can effectively reduce Cr(VI) in the soil, and is also an eco-friendly green remediation agent.

In order to achieve the above object, technical solution of the present invention is achieved in that way:

A preparation method of an environment-friendly Cr (VI) contaminated soil remediation agent, the method comprising the steps of:

1) Mix glacial acetic acid and methanol in proportion to form a mixed solvent, dissolve chitosan in the mixed solvent and stir until completely dissolved, then add pyrrole monomer and oxidant FeCl ₃ sequentially, pyrrole monomer forms polypyrrole coated on chitosan On the sugar surface, the prepared black chitosan/polypyrrole mixed solution was overnight and refrigerated in the refrigerator;

2) Prepare a precipitant with absolute ethanol and ethyl acetate, add the chitosan/polypyrrole mixed solution into the precipitant, stir well until black flocculents are precipitated, centrifuge the black flocculents and wash with distilled water and ethanol until the filtrate is neutral, and finally freeze-dried to obtain a restoration agent.

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

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

Further, the concentration of FeCl ₃ is 0.5mol/L.

Further, the molar ratio of pyrrole monomer to _FeCl3 =1:2-1:3.

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 step 1) is placed in a refrigerator to be refrigerated and stable for 7-12 hours.

Further, the volume ratio of the precipitating agent absolute ethanol to ethyl acetate is 3:1-5:1.

Further, the freeze-drying conditions in step 2) are -50°C, 20Pa.

The present invention also provides an environment-friendly Cr(VI) polluted soil remediation agent prepared by the preparation method described in any one of the above.

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

The environment-friendly Cr(VI) contaminated soil remediation agent prepared by the present invention has a porous structure and a huge specific surface area, and can absorb Cr(VI) in the complexed soil; meanwhile, the surface of the remediation agent contains organic functional groups such as hydroxyl and amino groups, which can realize Reduction of Cr(VI) in soil, thereby reducing the toxicity and bioavailability of hexavalent chromium. At the same time, the repair agent itself has low organic matter toxicity and can be biodegraded. When applied to the soil, it will cause little disturbance to the soil environment, will not cause secondary pollution, and will help improve soil fertility and reuse after soil repair. An eco-friendly green restorative.

Description of drawings

The drawings constituting a part of the present invention are used to provide a further understanding of the present invention, and the schematic embodiments and descriptions of the present invention are used to explain the present invention, and do not constitute an improper limitation of the present invention. In the attached picture:

Fig. 1 is the scanning electron micrograph of the restoration agent prepared by embodiment 1-4;

Fig. 2 is the comparison chart of the adsorption capacity of the restoration agent prepared in embodiment 1-4;

Fig. 3 is the Fourier transform infrared spectrogram of the restorative agent gained in embodiment 1;

Fig. 4 is the XPS figure of the restorative agent gained in embodiment 1;

Fig. 5 is the comparative figure of the adsorption effect of embodiment 1 and comparative example 1-2;

Figure 6 is the scanning electron microscope images of the restorative agent under different pyrrole additions: (a) PPy-0.2; (b) PPy-0.6; (c) PPy-1.0; (d) PPy-1.5;

Fig. 7 is the comparative figure of adsorption capacity effect of embodiment 1 and comparative example 9-10;

Fig. 8 is scanning electron micrograph of embodiment 1 and comparative example 11-12; (a) dehydrated alcohol and ethyl acetate volume ratio 6:1; (b) dehydrated alcohol and ethyl acetate volume ratio 4:1; (c ) absolute ethanol and ethyl acetate volume ratio 1:1;

Fig. 9 is the comparative figure of adsorption capacity effect of embodiment 1 and comparative example 11-12;

Fig. 10 embodiment 1 and comparative example 13 scanning electron micrographs; (a) embodiment 1; (b) contrast 13

Fig. 11 is the comparative figure of adsorption capacity effect of embodiment 1 and comparative example 13;

Fig. 12 embodiment 1 and comparative example 14 scanning electron micrographs; (a) embodiment 1; (b) contrast 14

Fig. 13 is a comparison chart of adsorption capacity effects of Example 1 and Comparative Example 14;

Fig. 14 embodiment 1 and comparative example 15 scanning electron micrographs; (a) embodiment 1; (b) comparative example 15;

Fig. 15 is a comparison chart of the adsorption capacity effects of Example 1 and Comparative Example 15.

Detailed ways

It should be noted that, in the case of no conflict, the embodiments of the present invention and the features in the embodiments can be combined with each other.

At present, most Cr(VI) contaminated soil remediation agents focus on the passivation effect and reduction efficiency, but the secondary pollution caused by the ecological environment is rarely evaluated. Based on this, the present invention provides an environment-friendly Cr(VI) polluted soil remediation agent, with chitosan/polypyrrole two kinds of biodegradable substances as synthetic materials, applied in the soil to the soil environment disturbance is little, will not Cause secondary pollution, contribute to the improvement of soil fertility, and the reuse of soil after restoration.

The present invention will be described in detail below with reference to the accompanying drawings and examples.

The following examples take the preparation of the restorative agent and the measurement of its adsorption capacity in a solution with a Cr(VI) concentration of 50 mg/L as an example to illustrate the operation process:

Example 1

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

(1) 350mL mass concentration is 2% glacial acetic acid and 50mL methyl alcohol are mixed according to the volume ratio of methyl alcohol and glacial acetic acid as 1:7 to form mixed solvent, 2.5g chitosan is dissolved in mixed solvent (solid-liquid ratio is 1: 160), stirred at room temperature for 30min to obtain a homogeneously dissolved chitosan hydrogel;

(2) Under stirring, add 1.0 mL of pyrrole monomer into the chitosan hydrogel described in step (1) (m _chitosan :v _pyrrole =2.5:1), and stir for 3 hours to obtain shell Polysaccharide/pyrrole mixed sol;

(3) 72.2 milliliters of _FeCl3 are added in the chitosan/pyrrole mixed sol described in step (2) as oxidant, after stirring for 30min, the pyrrole monomer is oxidized to form polypyrrole and is coated on the chitosan surface, forms black shell Polysaccharide/polypyrrole mixed sol;

(4) Place the black chitosan/polypyrrole mixed sol described in step (3) in a refrigerator at 4° C. for 10 h;

(5) Prepare a precipitating agent with absolute ethanol and ethyl acetate with a volume ratio of 4:1, add the chitosan/polypyrrole mixed sol after step (4) refrigerated and stabilized in the precipitating agent, and keep stirring until black flocculation precipitation;

(6) The black floc described in step (5) is centrifuged, the centrifugal force is maintained at 3000g, centrifuged for 10min, and repeatedly washed with a precipitating agent until the filtrate is neutral to obtain a black chitosan/polypyrrole precipitation;

(7) Place the black chitosan/polypyrrole precipitate obtained in step (6) in a vacuum freeze dryer at -50° C. and 20 Pa to freeze-dry to obtain the chitosan/polypyrrole restoration agent.

The restoration agent obtained in Example 1 was subjected to Fourier transform infrared spectroscopy, as shown in Figure 3, it can be seen that the chitosan/polyrole restoration agent was successfully prepared.

The restorative agent obtained in Example 1 was subjected to XPS, as shown in Figure 4, it can be seen that Cr(VI) is adsorbed.

Example 2

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

(1) 167mL mass concentration is 2% glacial acetic acid and 33mL methyl alcohol are mixed according to the volume ratio of methyl alcohol and glacial acetic acid as 1:5 to form mixed solvent, 1.0g chitosan is dissolved in mixed solvent (chitosan and mixed Solvent solid-to-liquid ratio=1:200), stirred at room temperature to obtain chitosan hydrogel;

(2) under stirring state, pyrrole monomer exists in liquid form and density is 0.9691mg/L under normal temperature state, and the pyrrole monomer of 0.5ml is added in the chitosan hydrogel described in step (1) (m _{shell Polysaccharide} : v _pyrrole =2:1), stirred for 3 hours to obtain chitosan/pyrrole mixed sol;

(3) 40 milliliters of 0.5mol/L _FeCl3 is added in the chitosan/pyrrole mixed sol described in step (2) as oxidant (nPPy and _nFeCl3 =1:2.8), after stirring for 30min, pyrrole monomer oxidation Form polypyrrole and coat on the surface of chitosan to form a black chitosan/polypyrrole mixed sol;

(4) Place the black chitosan/polypyrrole mixed sol described in step (3) in a refrigerator at 4° C. for 8 hours;

(5) Prepare a precipitating agent with ethyl acetate and absolute ethanol with a volume ratio of 1:3, add the chitosan/polypyrrole mixed sol after step (4) refrigerated and stabilized in the precipitating agent, and keep stirring until black flocculation precipitation;

(6) The black floc described in step (5) is centrifuged for 3000g, 10min, and repeatedly washed with a deprecipitating agent until the filtrate is neutral to obtain a black chitosan/polypyrrole precipitation;

(7) Place the black chitosan/polypyrrole precipitate obtained in step (6) in a vacuum freeze dryer at -50° C. and 20 Pa to freeze-dry to obtain the chitosan/polypyrrole restoration agent.

Example 3

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

(1) 324mL mass concentration is 2% glacial acetic acid and 81mL methyl alcohol are mixed according to the volume ratio of methanol and glacial acetic acid as 1:4 to form a mixed solvent, 2.7g chitosan is dissolved in the mixed solvent (chitosan and mixed Solvent solid-to-liquid ratio=1:150), stirred at room temperature to obtain chitosan hydrogel;

(2) Under stirring, add 0.9 mL of pyrrole monomer into the chitosan hydrogel described in step (1) (m _chitosan : V _pyrrole = 3:1), stir for 3 hours to obtain shell Polysaccharide/pyrrole mixed sol;

(3) _FeCl3 of 52 milliliters of 0.5mol/L is added in the chitosan/pyrrole mixed sol described in step (2) as oxidant (nPPy and _nFeCl3 =1:2), after stirring for 30min, pyrrole monomer oxidation Form polypyrrole and coat on the surface of chitosan to form a black chitosan/polypyrrole mixed sol;

(4) Place the black chitosan/polypyrrole mixed sol described in step (3) in a refrigerator at 4° C. for 10 h;

(5) Prepare a precipitant with absolute ethanol and ethyl acetate with a volume ratio of 5:1, add the chitosan/polypyrrole mixed sol after step (4) refrigerated and stabilized in the precipitant, and stir continuously until black flocculation is present. precipitation;

(6) The black floc described in step (5) is centrifuged for 3000g, 10min, and repeatedly washed with a deprecipitating agent until the filtrate is neutral to obtain a black chitosan/polypyrrole precipitation;

(7) Place the black chitosan/polypyrrole precipitate obtained in step (6) in a vacuum freeze dryer at -50° C. and 20 Pa to freeze-dry to obtain the chitosan/polypyrrole restoration agent.

Example 4

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

(1) 300mL mass concentration is 2% glacial acetic acid and 50mL methyl alcohol are mixed according to the volume ratio of methyl alcohol and glacial acetic acid as 1:6 to form mixed solvent, 2.0g chitosan is dissolved in mixed solvent (chitosan and mixed Solvent solid-to-liquid ratio=1:175), stirred at room temperature to obtain chitosan hydrogel;

(2) Under stirring, add 0.8 mL of pyrrole monomer into the chitosan hydrogel described in step (1) (m _chitosan : V _pyrrole = 2.5:1), stir for 3 hours to obtain shell Polysaccharide/pyrrole mixed sol;

(3) 46.2 milliliters of 0.5mol/L _FeCl3 is added in the chitosan/pyrrole mixed sol described in step (2) as oxidant (nPPy and _nFeCl3 =1:2), after stirring for 30min, pyrrole monomer oxidation Form polypyrrole and coat on the surface of chitosan to form a black chitosan/polypyrrole mixed sol;

(4) Place the black chitosan/polypyrrole mixed sol described in step (3) in a refrigerator at 4° C. for 9 hours;

(5) Prepare a precipitant with absolute ethanol and ethyl acetate with a volume ratio of 5:1, add the chitosan/polypyrrole mixed sol after step (4) refrigerated and stabilized in the precipitant, and stir continuously until black flocculation is present. precipitation;

(6) The black floc described in step (5) is centrifuged for 3000g, 10min, and repeatedly washed with a deprecipitating agent until the filtrate is neutral to obtain a black chitosan/polypyrrole precipitation;

(7) Place the black chitosan/polypyrrole precipitate obtained in step (6) in a vacuum freeze dryer at -50° C. and 20 Pa to freeze-dry to obtain the chitosan/polypyrrole restoration agent.

Fig. 1 is the scanning electron micrograph of the restorative agent prepared in embodiment 1-4, and Fig. 2 is the comparison chart of the adsorption capacity of the repair agent prepared in embodiment 1-4, as can be seen from the scanning electron microscope of Fig. 1, within the specified range The porosity of the prepared materials is relatively developed and uniform, fluffy like a sponge. Comparing the adsorption capacity, the difference between Examples 1-4 is also very small, indicating that the repairing agent prepared within the specified range meets the requirements.

Comparative example 1

This comparative example provides a Cr(VI) restoration agent, the preparation method of which is the same as that of Example 1, the only difference being that the dosage of chitosan in step 1) is 1.0 g (solid-to-liquid ratio is 1:400).

Comparative example 2

This comparative example provides a Cr(VI) restoration agent, the preparation method of which is the same as that of Example 1, the only difference being that the dosage of chitosan in step 1) is 5.0 g (solid-to-liquid ratio is 1:80).

Comparative example 3

This comparative example provides a Cr(VI) restoration agent, the preparation method of which is the same as that of Example 1, the only difference being that the ratio of glacial acetic acid to methanol in step 1) is changed to 1:0, that is, methanol is not added.

Comparative example 4

This comparative example provides a Cr(VI) restoration agent, the preparation method of which is the same as that of Example 1, the only difference being that the dosage ratio of methanol and glacial acetic acid in step 1) is changed to 1:3.

Comparative example 5

This comparative example provides a Cr(VI) restoration agent, the preparation method of which is the same as that of Example 1, the only difference being that the ratio of glacial acetic acid to methanol in step 1) is changed to 0:1, that is, no glacial acetic acid is added.

Comparative example 6

This comparative example provides a kind of Cr (VI) restoration agent, and its preparation method is identical with embodiment 1, and difference only is, the content of pyrrole in step 2) is 0.2mL, and the liquid-solid ratio of pyrrole and chitosan is 1:12.5 .

Comparative example 7

This comparative example provides a kind of Cr (VI) restoration agent, and its preparation method is identical with embodiment 1, and difference only is, the content of pyrrole in step 2) is 0.6mL, and the liquid-solid ratio of pyrrole and chitosan is 1:4.17 .

Comparative example 8

This comparative example provides a kind of Cr (VI) restorative agent, and its preparation method is identical with embodiment 1, difference only is, the content of pyrrole in step 2) is 1.5mL, and the liquid-solid ratio of pyrrole and chitosan is 1:1.67 .

Comparative example 9

This comparative example provides a Cr(VI) restoration agent, the preparation method of which is the same as that of Example 1, the only difference being that the molar ratio of _FeCl3 to pyrrole in step 3) is 1:1.

Comparative example 10

This comparative example provides a Cr(VI) restoration agent, the preparation method of which is the same as that of Example 1, the only difference being that the molar ratio of _FeCl3 to pyrrole in step 3) is 1:5.

Comparative example 11

This comparative example provides a Cr(VI) restoration agent, the preparation method of which is the same as that of Example 1, the only difference being that the ratio of absolute ethanol to ethyl acetate in step 5) is 6:1.

Comparative example 12

This comparative example provides a Cr(VI) restoration agent, the preparation method of which is the same as that of Example 1, the only difference being that the ratio of absolute ethanol to ethyl acetate in step 5) is 1:1.

Comparative example 13

This comparative example provides a kind of Cr (VI) restoration agent, and its preparation method is the same as that of Example 1, the only difference is that the operation of step 5) is changed to use 0.1mol/L sodium hydroxide to regulate the coagulation of chitosan/polypyrrole The pH of the gel solution is alkaline until a large number of flocs are precipitated, and no precipitant prepared by absolute ethanol and ethyl acetate is used.

Comparative example 14

This comparative example provides a Cr(VI) restoration agent, the preparation method of which is the same as that of Example 1, the only difference being that bacterial fiber is used instead of chitosan as the carrier of polypyrrole.

The preparation method of bacterial cellulose is as follows:

Put the cleaned coconuts into 2mo/L sodium hydroxide solution, boil them in a constant temperature water bath at 80°C for 3 hours, the coconuts will turn from milky white to brown, wash them repeatedly with deionized water, and soak them in deionized water until The washing solution is neutral, and the desired white BC gel blocks are obtained, and the BC gel blocks are crushed with a juice extractor to prepare BC hydrogel.

Comparative example 15

This comparative example provides a Cr(VI) restoration agent, the preparation method of which is the same as that of Example 1, except that the oxidant in step 3) is replaced with 0.5 mol/L potassium persulfate (K ₂ S ₂ O ₈ ). Test results and analysis:

1, the influence of the solid-liquid ratio of chitosan and mixed solvent (comparative example 1 and comparative example 2)

In order to determine the optimal dosing ratio of chitosan and solvent, Figure 5 shows the removal of Cr(VI) in the aqueous solution by the restoration agent prepared in Example 1 and Comparative Example 1 and Comparative Example 2.

Experimental conditions: Cr(VI) concentration is 50mg/L, liquid volume is 100mL, pH is 7, temperature is 30°C, and 180r/min horizontal vibration conditions, the dosage of restorative agent is 25mg. Samples were taken at 20, 40, 60, 80, 100, and 120 minutes to measure the adsorption capacity (Qe) of Cr(VI) in the solution. The determination of Cr(VI) was carried out by diphenylcarbazide spectrophotometry, as shown in Figure 5.

Adsorption capacity=(C0-Ce)*V/m; initial concentration of CO; Ce: concentration after reaction; V: reaction volume; m: mass of adsorbent.

It can be seen from Figure 5 that too much or too little chitosan dosage will affect the adsorption performance of the repair agent. When the chitosan dosage is too large, the dissolution of chitosan will be insufficient, and large bubbles will be generated. As a result, polypyrrole cannot be well coated on the surface of chitosan. However, when chitosan is added too little, chitosan gel cannot be formed, but a chitosan mixed solution is formed, which is not conducive to the attachment of pyrrole monomers, thereby affecting the small adsorption capacity. When the solid-to-liquid ratio of chitosan and mixed solvent is 1:160, the restoration agent has the best adsorption effect on Cr(VI).

2, the influence of mixed solvent (comparative example 3-5)

In order to find the best mixed solvent ratio, this experimental example compares the effects of Example 1 and Comparative Examples 3-5, and the effects of different mixed solvents dissolving chitosan for 30 minutes are significantly different.

In comparative example 3, only glacial acetic acid (glacial acetic acid to methanol volume ratio = 1:0) will cause insufficient dissolution of chitosan and form small particles floating on the surface. When methanol is added, the hydrogen bond between chitosan molecules will be destroyed, increasing Due to the solubility of chitosan, a uniform chitosan gel will be formed when it is properly proportioned with chitosan, and then the subsequent cross-linking reaction with polypyrrole will be more sufficient. And comparative example 5 only can destroy chitosan gel state with methanol as solvent (glacial acetic acid and methanol volume ratio=0:1), forms chitosan solution, is not easy to load polypyrrole, greatly reduces the effect on chitosan The adsorption capacity of the sugar/polypyrrole repair agent reduces the repair effect.

When the volume ratio of methanol to glacial acetic acid mixed solvent is 3:1, the viscosity of the chitosan gel formed by dissolving is slightly worse than 7:1, which will cause less pyrrole content in subsequent loads. The optimum ratio of acetic acid to methanol is 7:1.

3, the influence of the addition amount of chitosan and pyrrole monomer (comparative example 6-8)

In order to determine the optimal molar ratio of chitosan to pyrrole monomer, Example 1 and Comparative Examples 6-8 were compared experimentally, and the CS/PPy composite materials prepared respectively were subjected to scanning electron microscopy, as shown in FIG. 6 .

As can be seen from Figure 6, under the condition that the dosage of chitosan is 2.5g, the optimal dosage of pyrrole monomer is 1.0mL, that is, the ratio of chitosan and pyrrole monomer to the solid solution is: 2.5: 1; When the dosage of pyrrole monomer is too small, as shown in Figure 6(a)(b), the formed composite material is relatively dense and the porosity is insufficient, which affects the adsorption performance; and when the dosage of pyrrole monomer is too much It will cause the situation shown in Figure 6(d), the chitosan cannot carry the polypyrrole and breaks into flakes, and the gaps formed are not uniform. When the dosage of pyrrole monomer is 1mL, it is the best dosage. At this time, the prepared chitosan-polypyrrole composite material has uniform voids, loose sponge shape, and good adsorption performance.

4, the influence of the addition amount of pyrrole monomer and oxidizing agent (comparative example 9-10)

The restoration agent prepared in Example 1 and Comparative Examples 9-10 was used to remove Cr(VI) in the aqueous solution, and the experimental conditions were kept the same as in Experimental Example 1. The obtained effect is shown in FIG. 7 .

From Figure 7, we can see that when the molar ratio of FeCl ₃ to pyrrole is 1:1, since FeCl ₃ cannot completely oxidize pyrrole monomer, the adsorption capacity of the prepared restoration material is small, only 24.6 mg/g. When the molar ratio of FeCl ₃ to pyrrole PPy gradually increased, the adsorption capacity of the prepared chitosan/polypyrrole composites also increased gradually. When the molar ratio of PPy to FeCl ₃ is 1:5, the excess of FeCl ₃ leads to a slight decrease in the adsorption capacity of the prepared chitosan/polypyrrole composite compared with the molar ratio of 1:2.5. It shows that the amount of FeCl ₃ added is not the more the better, but there is a peak.

5, the comparison of precipitation agent (comparative example 11-12)

In order to make the preparation of chitosan/polypyrrole remediation agent powdery, it is convenient to use as soil remediation agent, utilize chitosan poor solubility in ethyl acetate and methanol solution and the property of chitosan insoluble in alkaline solution, carry out respectively Example 1 and comparative examples 11-12 have made the powdered restorative agent, now embodiment 1 and comparative examples 11-12 are carried out scanning electron microscope and adsorption capacity test in aqueous solution, hope that the obtained adsorption capacity is higher, to Cr(VI ) Restorative agent with better reducing ability, the specific experimental operation is the same as that of Experimental Example 1. The effect of the obtained restorative agent is shown in Figure 8.

It can be seen from Figure 8 that the composite repair agent prepared when the volume ratio of absolute ethanol to ethyl acetate is 4:1 has a uniform and well-developed surface porosity, as shown in Figure 8(b); the highest adsorption capacity is shown in Figure 9 shown. Absolute ethanol is not a good solvent for chitosan, but unlike aprotic solvents such as ethyl acetate, it has a strong precipitation effect and makes the prepared composite materials extremely compact. In Comparative Example 11, when the volume ratio of ethyl acetate is reduced (V _{absolute ethanol} : V _{ethyl acetate} = 6:1), the moisture content of the prepared material is high, and the surface voids of the material will be too large and cracked after freeze-drying, as shown in Figure 8 (a) shown. In Comparative Example 12, when the proportion of ethyl acetate is high (V _{absolute ethanol} : V _{ethyl acetate} = 1:1), the prepared material has a compact surface and small pores, as shown in Figure 8(c). Therefore, when anhydrous ethanol and ethyl acetate are proportioned in an appropriate ratio, a chitosan/polypyrrole composite restoration agent with appropriate crystallinity and entanglement, loose surface, and well-developed porosity can be obtained.

6, the influence of precipitation mode (comparative example 13)

In order to make powdery restorative agent, prepare ethyl acetate and dehydrated alcohol precipitant in embodiment 1, comparative example 13 adopts sodium hydroxide to adjust pH to alkaline, these two kinds of methods can make powdery chitosan / polypyrrole adsorption material, but as shown in Figure 11 on the adsorption capacity, the method in Example 1 is adopted to be 13.4 larger than the adsorption capacity of Comparative Example 13. In addition, it can be seen from the scanning electron microscope in Figure 10 that there is a big difference. The structure of the material prepared by using the sodium hydroxide precipitant is also like a sponge, fluffy but the porosity is not as developed as in Example 1.

6. The influence of different carriers (comparative example 14)

Comparative example 14 replaces chitosan with bacterial cellulose (BC) hydrogel as carrier, the morphology of both has very big difference from scanning electron microscope, and the material that chitosan prepares as carrier is spongy as shown in Figure 12 ( As shown in a), the material prepared by BC is in the form of filaments as shown in Figure 12 (b). Moreover, the material prepared by BC is flocculent and has a very light density, so the adsorption capacity in water is about 4 times that of chitosan/polypyrrole adsorption material, as shown in Figure 13. However, it is not convenient to use as a soil remediation agent because of its flocculent shape.

7, the influence of different oxidants (comparative example 15)

Comparative Example 15 is used to compare with Example 1 the difference in performance of the restoration agent prepared when potassium persulfate (K ₂ S ₂ O ₈ ) and ferric chloride (FeCl ₃ ) are respectively used as oxidants. From the comparison of Figures 14 and 15, it can be seen that the restoration agent prepared in Comparative Example 15 (K ₂ S ₂ O ₈ ) is not as good as that of Example 1 (Fig. 14a), and the restoration agent prepared in Comparative Example 15 (Fig. 14b) is obviously lacking Uniform voids, resulting in a slightly smaller adsorption capacity than Example 1, as shown in Figure 15. This may also be because FeCl ₃ not only acts as an oxidant, but the Cl ^- in it also acts as an ion exchange. In aqueous solution, Cr ⁶⁺ is ionized with Cl ^- in the form of Cr ₂ O ₇ ^2- or CrO ₄ ^2- Exchange, and then adsorbed to the surface of the repair agent and reduced, so as to achieve the purpose of Cr ⁶⁺ removal. However, the restoration material prepared with K ₂ S ₂ O ₈ as oxidant has no ion exchange function. Therefore, the adsorption capacity of Comparative Example 15 is not as good as that of Example 1.

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

The previous experiments were all based on the water adsorption capacity test to evaluate the physical and chemical properties of the material, but the environment in which it is used also has a great impact on the material itself, and the biological toxicity of different preparation methods and materials to the environment also varies greatly. In order to evaluate the effect of the chitosan/polypyrrole repair agent in the soil and the evaluation of soil reutilization and biological toxicity after the three repair agents of comparative examples 13-15 and embodiment 1, a simulated chromium-contaminated soil repair was designed Experiments and soil plant pot experiments after restoration.

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

The experimental soil was collected from a farmland soil in Nanyang City, Henan Province, and impurities such as stone particles were removed, and ground through two 2mm sieves. The Cr(VI)-contaminated soil was prepared by artificially adding potassium dichromate solution, and the prepared Cr(VI)-contaminated soil was aged for 3 months under natural conditions to stabilize the Cr form and obtain a simulated Cr(VI)-contaminated soil . The total chromium content in the soil was measured by flame atomic absorption spectrophotometry to be 200mg/kg, and the HJ1082-2019 Determination of hexavalent chromium in soil and sediment was used for alkaline solution extraction-flame atomic absorption spectrophotometry to determine the Cr(VI) content to be 163.2mg /kg.

(2) Cr(VI) contaminated soil remediation:

Prepare the Cr(VI) polluted soil of the same quality, after aging, the first group does not add any restorative agent, as blank control group (CK); The second group adds the repair prepared by example 1 of Cr polluted soil weight 0.5% used in the experiment agent (G1); the third group added the restorative agent (G2) prepared by adding 0.5% of Cr-contaminated soil weight used in the experiment to the comparative example 14; the fourth group added the comparative example 15 prepared by adding 0.5% of Cr-contaminated soil weight used in the experiment The restorative agent (G3); the 5th group added the restorative agent (G4) prepared by the comparative example 13 that added 0.5% of the weight of Cr polluted soil used in the experiment (G4), and adjusted the soil moisture content to 30%, so that the restorative agent was mixed evenly with the contaminated soil.

After 15 days of restoration, the HJ1082-2019 Determination of Hexavalent Chromium in Soil and Sediments was used to determine the Cr(VI) content by alkaline solution extraction-flame atomic absorption spectrophotometry, and the BCR extraction method was used to measure the existing forms and proportions of Cr in the soil. The BCR extraction method can better reflect the mobility and bioavailability of heavy metals in the soil. The weak acid state has the best fluidity, is most easily absorbed by organisms, and causes the greatest biological toxicity, followed by the reduced state, and the most stable residue state. , with minimal biological toxicity. The repair effects of Example 1 and each comparative example are shown in Table 1.

Table 1 Embodiment 1 and each comparison ratio restoration effect

It can be seen from the above table that the G1 group corresponding to Example 1 has the least acid-extractable state after 15 days of restoration, the highest proportion of oxidizable state and residue state, and the removal rate of Cr(VI) in the soil can reach 98%. . The remediation agent prepared in other comparative examples has a certain remediation effect on Cr(VI) polluted soil. After application, the extractable state of weak acid in the soil is obviously decreased by a certain percentage, and the residue state is obviously improved, but its effect is not as good as that of Example 1. The G1 group.

(3) Soil reuse properties and the toxic effect of remediated soil on plants (comparative examples 13-15)

In order to evaluate the remediation effect and soil reuse properties of the remediation agent in Example 1 and Comparative Example on Cr(VI) contaminated soil, and the toxicity of the remediated soil to plants, a pot experiment of ryegrass after remediation was carried out. Take out the repaired soil after 15 days and let it air-dry naturally until the moisture content is about 10%. Set up the chromium-free soil YT group, stir evenly for planting ryegrass, water regularly every day, and harvest after 25 days. Compare Example 1 with different control groups The restoration effect is shown in Table 2.

Table 2 Plant growth characteristics of different treatment groups

Experiments have found that the growth of ryegrass is related to the remaining Cr(VI) in the soil and the proportion of residual chromium in the soil. The higher the concentration of remaining Cr(VI) in the soil, the more obvious the inhibitory effect on ryegrass. The higher the proportion of residual chromium in the soil, the more obvious the inhibitory effect on the growth of ryegrass. The corresponding G1 group ryegrass of embodiment 1 grows the best, and the rhizome is thick and strong, even has the trend that surpasses YT group ryegrass, illustrates that the chitosan/polypyrrole restoration agent prepared in embodiment 1 can not only treat Cr(VI) polluted soil It plays a repairing role, and can also improve soil fertility and promote plant growth. The ryegrass of the CK group grew the worst and was very weak. The remediation agents prepared in other comparative examples also play a certain role in the remediation of Cr(VI) contaminated soil, but the effect is not as good as that of Example 1, and the growth effects are G4, G2, and G3 in order from good to poor.

The above descriptions are only preferred embodiments of the present invention, and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included in the scope of the present invention. within the scope of protection.

Claims (12)

1. A preparation method of environment-friendly Cr (VI) polluted soil remediation agent, is characterized in that: the method comprises the steps:

   1) Mix glacial acetic acid and methanol in proportion to form a mixed solvent, dissolve chitosan in the mixed solvent and stir until completely dissolved, then add pyrrole monomer and oxidant FeCl ₃ sequentially, pyrrole monomer forms polypyrrole coating on On the chitosan surface, the prepared black chitosan/polypyrrole mixed solution was overnight and refrigerated in the refrigerator;

   2) Configure a precipitant with absolute ethanol and ethyl acetate, add the chitosan/polypyrrole mixed solution into the precipitant, stir fully until black flocculents are precipitated, centrifuge the black flocculents and use Wash with distilled water and ethanol until the filtrate is neutral, and finally freeze-dry to prepare the restoration agent.
2. The preparation method according to claim 1, characterized in that: the solid-to-liquid ratio of the chitosan to the mixed solvent is 1:150-1:200, and the unit of the solid-to-liquid ratio is g/ml.
3. The preparation method according to claim 1, characterized in that: the mass concentration of glacial acetic acid in the mixed solvent is 2%, and the volume ratio of methanol to glacial acetic acid is 1:4-1:7.
4. The preparation method according to claim 1, characterized in that: the concentration of the oxidizing agent _FeCl3 is 0.5mol/L.
5. The preparation method according to claim 4, characterized in that: the molar ratio of the pyrrole monomer to the oxidizing agent _FeCl3 is 1:2-1:3.
6. The preparation method according to claim 1, characterized in that: the liquid-solid ratio of the pyrrole monomer and chitosan added is 1:2-1:3, and the unit of the liquid-solid ratio is ml/g.
7. The preparation method according to claim 1, characterized in that: in the step 1), the time for refrigerating and stabilizing in the refrigerator is 7-12 hours.
8. The preparation method according to claim 1, characterized in that: the volume ratio of absolute ethanol to ethyl acetate in the precipitant is 3:1-5:1.
9. The preparation method according to claim 1, characterized in that: the freeze-drying conditions in the step 2) are -50°C and 20Pa.
10. An environment-friendly Cr(VI) contaminated soil remediation agent prepared by the preparation method described in any one of claims 1-9.
11. The application of the environment-friendly Cr(VI) polluted soil remediation agent described in claim 10 in remediation soil.
12. The application according to claim 11, wherein the method for remediating chromium-contaminated soil comprises the following steps:

    The environment-friendly Cr(VI) polluted soil restoration agent described in claim 10 is mixed with the soil to be repaired, and repaired;

    The moisture content of the chromium-contaminated soil is 30%.

    The repair time is 15 days.

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