CN113371810A - Preparation method and application of bentonite-loaded nano iron sulfide repairing agent - Google Patents

Abstract

The invention provides a preparation method and application of a bentonite-loaded nano iron sulfide repairing agent. The preparation method comprises the following steps: under the condition of no oxygen, adding bentonite and polyethylene glycol into ferrous salt solution, and then adding NaBH₄And alkaline solution of a vulcanizing agent, and preparing the bentonite loaded vulcanized nano-iron repairing agent (PSNZVI) by a one-step synthesis method. The PSNZVI provided by the invention has the advantages of reduced agglomeration, reduced biotoxicity, enhanced oxidation resistance and sedimentation property, greatly improved reaction activity, obviously improved trichloroethylene removal efficiency, new idea for groundwater chlorohydrocarbon pollution remediation and wide application prospect.

Description

Preparation method and application of bentonite-loaded nano iron sulfide repairing agent

Technical Field

The invention relates to the technical field of groundwater pollution remediation, in particular to a preparation method and application of a bentonite-loaded nano iron sulfide remediation agent.

Background

With the development of industrial society, chlorinated hydrocarbons are widely produced and used as common chemical raw materials, industrial solvents and cleaning agents. However, due to the reasons of irregular storage, transportation leakage and the like, the chlorinated hydrocarbons in soil, air and water bodies are often polluted. The chlorinated hydrocarbon has strong hydrophobicity, low solubility, easy volatilization, difficult degradation and can continuously and widely exist in the environment. While causing harm to the environment, the health of human beings is also seriously threatened. Trichloroethylene is one of the most widely chlorinated hydrocarbons present in the environment and is classified as a class 2A (probably carcinogenic) by the international agency for research on cancer (IARC).

In the past decades, groundwater pollution has begun to attract human attention, and various groundwater treatment techniques have been gradually developed. According to the principle of groundwater remediation technology, the technology can be roughly divided into three categories, namely physical remediation technology, chemical remediation technology and biological remediation technology. The reaction rate of the nanometer zero-valent iron in-situ chemical reduction of trichloroethylene is higher, the pollutant removal efficiency is higher, and the dechlorination can be completely eliminated through reduction, so that the method has a wide application prospect. Although Nano Zero Valent Iron (NZVI) has been used for remediation of various contaminants of groundwater due to its physicochemical properties, NZVI not only has high reactivity to contaminants, but also rapidly reacts with surrounding media (e.g., dissolved oxygen and water) and other non-target compounds in the subsurface environment, causing NZVI to be greatly reduced in reactivity. In addition, the strong magnetic interaction between the particles can cause agglomeration, thereby destroying the colloidal stability, reducing the reactive surface and influencing the migration and transportation of the NZVI in the aquifer. Simultaneously, NZVI produces Fe²⁺The oxidative stress of (A) may destroy the microorganismsA cell membrane of the substance. The application of NZVI in polluted sewage remediation is limited by the easiness of oxidation, volatility, poor mobility, biological toxicity and the like of the NZVI.

In view of this, the invention is particularly proposed.

Disclosure of Invention

The invention aims to overcome the defects of the prior art and provides a preparation method and application of a bentonite-loaded nano iron sulfide repairing agent.

In order to achieve the purpose, the invention adopts the following technical scheme:

a preparation method of a bentonite loaded nanometer iron sulfide repairing agent comprises the following steps: under the condition of no oxygen, adding bentonite and polyethylene glycol into ferrous salt solution, and then adding NaBH₄And alkaline solution of a vulcanizing agent, and preparing the bentonite loaded vulcanized nano-iron repairing agent (PSNZVI) by a one-step synthesis method.

According to the invention, the bentonite is adopted to load the ferric sulfide nanoparticles, meanwhile, the polyethylene glycol is added into the reaction system, the agglomeration effect of the repairing agent prepared by the one-step synthesis method is obviously reduced, the selectivity of the repairing agent on target pollutants is improved, the degradation rate is accelerated, the capability of reducing and degrading trichloroethylene by the nanoscale zero-valent iron is obviously enhanced, meanwhile, the biotoxicity is reduced, and the comprehensive performance of the repairing agent product is improved.

Further, the weight ratio of the iron element in the bentonite and the ferrous salt to the polyethylene glycol is (0.5-2): 1: (0.25-1).

Or, the ferrous salt, NaBH₄And a vulcanizing agent in a molar ratio of 1: (2-4): (0.012-0.1).

Further, the solvent of the ferrous salt solution is (3-7) by volume: (3-7) ethanol and deoxygenated deionized water, preferably 1: 2; the concentration of the ferrous salt solution is 0.1-0.2M;

further, the bentonite-loaded vulcanized nano-iron repairing agent has the Fe/S molar ratio of 10-40, preferably 12-28.

Further, the ferrous salt is ferrous chloride tetrahydrate or ferrous sulfate heptahydrate;

and/or the vulcanizing agent is Na₂S or Na₂S₂O₄Preferably Na₂S₂O₄。

Further, the bentonite is pretreated before use as follows: placing the bentonite in 1-3mol/L diluted hydrochloric acid, oscillating for 18-24h in a shaking table at the speed of 180-220r/min, then washing with deionized water, and drying at 50-80 ℃ for later use. Therefore, the pore canal of the bentonite is dredged, which is beneficial to the diffusion of adsorbate molecules.

Further, the pH value of the alkaline solution is 10-12;

or, the alkaline solution is added in a dropping mode at the speed of 4-10 ml/min;

or the dropping time of the alkaline solution is not more than 2 hours.

Further, the following operations were performed under anaerobic conditions:

1) dissolving ferrous salt in a mixed solution of ethanol and deoxidized deionized water, adding bentonite and polyethylene glycol, and uniformly stirring;

2) dissolving sodium borohydride and a vulcanizing agent in an aqueous solution of sodium hydroxide, wherein the pH value of the obtained mixed solution is 10-12;

3) and (3) dropwise adding the mixed solution obtained in the step 2) into the mixed solution obtained in the step 1), stirring at 220r/min for 180-.

The invention also provides application of the bentonite-loaded ferric sulfide restoration agent prepared by the method in underground water trichloroethylene pollution.

Further, adding the bentonite-loaded vulcanized nano-iron restoration agent into deoxidized deionized water containing trichloroethylene, oscillating at constant temperature, and periodically detecting the removal amount of the trichloroethylene by using GCMS;

and/or the initial concentration of the trichloroethylene in the deoxidized deionized water is 30-40ppm, the pH is 7-11, and preferably 9-11;

and/or the addition amount of the bentonite-loaded vulcanized nano-iron repairing agent is 1-5g/L, preferably 3 g/L;

and/or the constant temperature oscillation is carried out at the temperature of 20-25 ℃ for 3-24h at the rotating speed of 180-220 r/min.

The technical scheme provided by the invention has the following advantages:

the PSNZVI provided by the invention has the advantages of reduced agglomeration, enhanced oxidation resistance and sedimentation property, greatly improved reaction activity, obviously improved degradation efficiency on trichloroethylene, new idea for repairing underground water chlorinated hydrocarbon pollution and wide application prospect.

Drawings

FIG. 1 is a transmission electron micrograph of PSNZVI prepared in example 3;

FIG. 2 is a transmission electron microscope image of SNZVI prepared in comparative example 3;

FIG. 3 is a transmission electron microscope photograph of the NZVI prepared in comparative example 9;

FIG. 4 is a graph of the sedimentation curves for NZVI, SNZVI, PSNZVI;

FIG. 5 shows Na₂TCE removal effect plot of S-sulfurized SNZVI;

FIG. 6 shows Na₂S₂O₄TCE removal effect profile of sulfurized SNZVI;

FIG. 7 shows Na₂S₂O₄TCE removal effect plot of sulfurized PSNZVI;

FIG. 8 is a graph of TCE removal effect for different amounts of PSNZVI;

FIG. 9 is a graph of the effect of TCE removal of PSNZVI at various pH.

Detailed Description

The following detailed description of embodiments of the present invention is provided in connection with the accompanying drawings and examples.

The following examples are merely illustrative of the present invention and are not intended to limit the scope of the present invention.

The experimental procedures used in the following examples are conventional unless otherwise specified.

Materials, reagents and the like used in the following examples are commercially available unless otherwise specified.

In the following examples and comparative examples,

before use, the bentonite is pretreated as follows: placing bentonite in 2mol/L dilute hydrochloric acid, shaking in a shaking table at a speed of 200r/min for 24h, then washing with deionized water, and drying at 80 ℃ for later use.

Example 1

The embodiment provides a preparation method of a bentonite-loaded nano iron sulfide repairing agent (PSNZVI):

1) in a three-necked flask, 5.964g of FeCl under a nitrogen atmosphere₂·4H₂O, 2.52g of bentonite and 1g of polyethylene glycol are dissolved in a mixed solution of 100ml of ethanol and 200ml of deoxidized deionized water.

2) 4.855g of NaBH₄And 0.261g of Na₂S₂O₄Dissolving in 200ml of deoxygenated distilled water, adjusting the addition amount of sodium hydroxide, and controlling the pH of the obtained alkaline solution to be about 10.

3) Dropping the alkaline solution obtained in the step 2) into the mixed solution obtained in the step 1) through a constant pressure funnel at a speed of 5ml/min, stirring the solution at a speed of 200rpm by using an electric stirrer to enable the solution to react uniformly, controlling the dropping time of the alkaline solution not to exceed 2 hours, continuing stirring after the dropping is finished, and introducing nitrogen for 30 min. And (3) carrying out solid-liquid separation by using a vacuum suction filter, washing the black precipitate for 3 times by using deoxygenated ultrapure water and absolute ethyl alcohol respectively, and finally placing the black precipitate in a vacuum freeze dryer for drying for 24 hours to obtain PSNZVI with the Fe/S molar ratio of 10.

Examples 2 to 4

On the basis of example 1, a vulcanizing agent Na was adjusted₂S₂O₄The PSNZVI with different Fe/S molar ratios can be obtained by adding the above-mentioned components. When Na is present₂S₂O₄When the amounts of (A) and (B) were 0.174g, 0.104g and 0.065g, PSNZVI was obtained in which the Fe/S molar ratios were 15 (example 2), 25 (example 3) and 40 (example 4).

Examples 5 to 8

On the basis of example 1, a vulcanizing agent Na₂S₂O₄By substitution of Na₂And S, adjusting the addition amount of the S to obtain PSNZVI with different Fe/S molar ratios. When Na is present₂When the amounts of S added were 0.234g, 0.156g, 0.094g and 0.059g, respectively, Fe/S molar ratios of 10 (example 5) and 1 were obtained5 (example 6), 25 (example 7), and 40 (example 8).

Examples 9 to 11

On the basis of the embodiment 3, the PSNZVI with different bentonite loading amounts can be obtained by adjusting the addition amount of the bentonite. When the amounts of bentonite added were 0.84g, 1.68g and 3.36g, PSNZVI (Fe/S molar ratio was 25) was obtained for bentonite/Fe mass ratios of 0.5 (example 9), 1 (example 10) and 2 (example 11).

Comparative examples 1 to 4

The difference between the preparation method of the nano iron Sulfide (SNZVI) provided by the comparative example and the preparation method of the SNZVI in the example 1 is that no bentonite is added in the step 1), and the vulcanizing agent Na is adjusted at the same time₂S₂O₄When the amounts of (1) and (4) were 0.261g, 0.174g, 0.104g and 0.065g, SNZVI having Fe/S molar ratios of 10 (comparative example 1), 15 (comparative example 2), 25 (comparative example 3) and 40 (comparative example 4) were obtained.

Comparative examples 5 to 8

The difference between the preparation method of the nano iron Sulfide (SNZVI) provided by the comparative example and the preparation method of the SNZVI is that no bentonite is added in the step 1), and a vulcanizing agent Na is used₂S for Na₂S₂O₄Regulating Na₂When the S was added in an amount of 0.234g, 0.156g, 0.094g, 0.059g, SNZVI having Fe/S molar ratios of 10 (comparative example 5), 15 (comparative example 6), 25 (comparative example 7), and 40 (comparative example 8) were obtained.

Comparative example 9

The preparation method of nano-iron (NZVI) provided in the present comparative example differs from example 3 only in that bentonite is not added in step 1) and a vulcanizing agent is not added in step 2), i.e., NZVI is obtained.

Test example 1

FIGS. 1-3 are transmission electron microscope representations of the repair agents prepared in example 3, comparative example 3, and comparative example 9, respectively.

The results show that NZVI prepared in comparative example 9 exhibits micron-sized agglomerates (fig. 3), SNZVI prepared in comparative example 3 exhibits chain-shaped agglomerates (fig. 2), and PSNZVI prepared in example 3 is more uniformly supported on bentonite (fig. 1). It can be seen that the agglomeration of PSNZVI is reduced and the distribution is more uniform compared to NZVI and SNZVI.

Suspensions of NZVI (comparative example 9), SNZVI (comparative example 3), PSNZVI (example 3) with a particle concentration of 5g/L were prepared with a background solution of 10mM NaHCO₃The sample is ultrasonically dispersed for 5min, the sample is moved into a cuvette by a pipette, the cuvette is placed into an ultraviolet spectrophotometer UV-2550 sample pool, and the absorbance values of different materials are detected by a kinetic module to form a sedimentation curve, and the result is shown in figure 4, wherein the speed of decrease of the absorbance value of PSNZVI is slowest, namely, the sedimentation is slowest. It can be seen that the settling performance of PSNZVI is significantly improved compared to NZVI and SNZVI.

Test example 2

The TCE degradation effects of the restoratives prepared in comparative examples 1-4 and comparative examples 5-8 were tested.

Adding SNZVI with different Fe/S molar ratios into a trichloroethylene polluted system. The reaction system was a 50ml serum bottle containing 40ml of deoxygenated distilled water, the trichloroethylene concentration was 30ppm, and the amount of SNZVI added was 0.2 g. Placing the reaction system on a constant temperature shaking table in a dark place, wherein the rotating speed is 220r/min, the reaction time is 12h, the reaction pH is 7, and periodically detecting the content of the residual TCE by using GCMS. Specific results are shown in table 1.

TABLE 1 TCE removal efficiency of SNZVI at 12h with different sulfiding agents, different Fe/S molar ratios

As can be seen from Table 1, the SNZVI synthesized with different sulfurizing agents had TCE removal efficiencies of 37% to 69% and consisted of Na at the same Fe/S molar ratio₂S₂O₄The TCE removal efficiency of the prepared SNZVI is better than that of Na₂S。

Test example 3

The PSNZVI prepared in example 3, examples 9-11 was added to the trichloroethylene contaminated system. The reaction system was a 50ml serum bottle containing 40ml of deoxygenated distilled water, the trichloroethylene concentration was 30ppm, and the PSNZVI was added in an amount of 0.2 g. Placing the reaction system on a constant temperature shaking table in a dark place, wherein the rotating speed is 220r/min, the reaction time is 12h, and the pH value is 7. The residual TCE content was measured periodically by GCMS. Specific results are shown in table 2.

TABLE 2 TCE removal efficiency for PSNZVI at different iron loadings

As is clear from table 2, the removal rate of TCE was maximized at a bentonite/iron mass ratio of 1.5 (example 3). When the iron loading was low (example 11), it may result in a decrease in active sites reacting with TCE, thereby decreasing TCE removal rate. When the mass ratio of bentonite to iron is 1.5 (example 3), the bentonite effectively adsorbs TCE, and simultaneously the contact between TCE and SNZVI is increased, at this time, the removal rate of TCE reaches the maximum, and when the content of bentonite is further reduced (examples 9 and 10), the adsorption efficiency of bentonite is reduced and the removal rate of TCE is reduced compared with example 3.

Test example 4

PSNZVI prepared in examples 1-4 was added to the trichloroethylene contaminated system. The reaction system was a 50ml serum bottle containing 40ml of deoxygenated distilled water, the trichloroethylene concentration was 30ppm, and the amount of all materials added was 0.2 g. Placing the reaction system on a constant temperature shaking table in a dark place, wherein the rotating speed is 220r/min, the reaction time is 12h, and the pH value is 7. The residual TCE content was measured periodically by GCMS. Specific results are shown in table 3.

TABLE 3 TCE removal efficiency of PSNZVI at 12h at different Fe/S molar ratios

As can be seen from Table 3, the PSNZVI of examples 1-4 had TCE removal efficiencies of 62% to 84% at 12h, with the best efficiency of example 3.

Test example 5

The PSNZVI prepared in example 3 was added to the trichloroethylene contaminated system. The reaction system was a 50ml serum bottle containing 40ml of deoxygenated distilled water, the trichloroethylene concentration was 30ppm, and the PSNZVI was added in an amount of 0.04g, 0.08g, 0.12g, 0.16g, 0.2 g. Placing the reaction system on a constant temperature shaking table in a dark place, wherein the rotating speed is 220r/min, the reaction time is 12h, and the pH value is 7. The residual TCE content was measured periodically by GCMS. Specific results are shown in table 4.

TABLE 4 TCE removal efficiency at different PSNZVI dosing amounts

As can be seen from Table 4, the effect of removing TCE is enhanced as the addition amount of PSNZVI is increased, but when the addition amount exceeds 3g/L, the increase of the removal rate is small, and the optimal addition amount is selected to be 3g/L in consideration of economic factors.

Test example 6

The PSNZVI prepared in example 3 was added to the trichloroethylene contaminated system. The reaction system was a 50ml serum bottle containing 40ml of deoxygenated distilled water, the trichloroethylene concentration was 30ppm, and the PSNZVI was added in an amount of 0.12 g. And placing the reaction system on a constant temperature shaking table in a dark place, wherein the rotating speed is 220r/min, the reaction time is 12h, and the pH value is 5, 7, 9 and 11. The residual TCE content was measured periodically by GCMS. Specific results are shown in table 5.

TABLE 5 TCE removal efficiency at different pH

As can be seen from Table 5, as pH increased, the removal rate of TCE increased, and alkaline conditions were seen to favor the removal of TCE by PSNZVI.

Further, for a TCE concentration of 30ppm, the sulfidizing agent was Na₂S₂O₄In the reaction system with the Fe/S molar ratio of 25, the adding amount of SNZVI of 3g/L and the pH value of 11, the removal rate of TCE can reach 95% within 24h, and the PSNZVI is a potential TCE repairing agent.

Test example 7

Luminescent bacteria, vibrio fisheri, are selected as tested bacteria, NZVI, SNZVI (Fe/S molar ratio of 25) and PSNZVI (Fe/S molar ratio of 25, bentonite/Fe mass ratio of 1.5) with the concentration of 3g/L are respectively prepared, and are subjected to ultrasonic dispersion for 5min to serve as water samples to be tested. After the test water sample is contacted with the luminous bacteria for a period of time, the luminous intensity of the luminous bacteria and the toxicity of the water sample show a negative correlation relationship, and the toxicity of the test water sample is represented by the luminous quantity reduction percentage (namely the inhibition rate) of the luminous bacteria. The specific process is as follows: resuscitating a vial of photobacteria with 2.5ml NaCl dilution, pouring the resuscitated reagent into one cuvette and mixing 3-4 times with pipette aspiration, adding 1ml resuscitating reagent to each of the two cuvettes (a1, a2), waiting 15min, counting the control sample (a1) with the MicrotoxFX analyzer, taking out a1, and reading a 2. Immediately adding 20 mu L of water sample to be tested into A2, shaking and mixing, and reading A1 and A2 respectively after 15 min. The obtained NZVI has the light loss of 71%, the SNZVI has the light loss of 56% and the PSNZVI has the light loss of 44%, so that the PSNZVI prepared by the method effectively reduces the biological toxicity of the NZVI.

Finally, it should be noted that: the above examples are only intended to illustrate the technical solution of the present invention, but not to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some technical features may be equivalently replaced; and such modifications or substitutions do not depart from the spirit and scope of the corresponding technical solutions of the embodiments of the present invention.

Claims (10)

1. A preparation method of a bentonite-loaded nanometer iron sulfide repairing agent is characterized by comprising the following steps: under the condition of no oxygen, adding bentonite and polyethylene glycol into ferrous salt solution, and then adding NaBH₄And alkaline solution of a vulcanizing agent, and preparing the bentonite loaded vulcanized nano-iron repairing agent by a one-step synthesis method.

2. The preparation method of the bentonite-supported nano iron sulfide repairing agent according to claim 1, wherein the weight ratio of iron element and polyethylene glycol in the bentonite and ferrous salt is (0.5-2): 1: (0.25-1);

or, the ferrous salt, NaBH₄And a vulcanizing agent in a molar ratio of 1: (2-4): (0.012-0.1).

3. The preparation method of the bentonite-supported nano iron sulfide restoration agent according to claim 1 or 2, wherein the solvent of the ferrous salt solution is (3-7): (3-7) ethanol and deoxidized deionized water, wherein the concentration of the ferrous salt solution is 0.1-0.2M.

4. The method for preparing the bentonite-supported nano iron sulfide restoration agent according to any one of claims 1 to 3, wherein the molar ratio of Fe/S in the bentonite-supported nano iron sulfide restoration agent is 10 to 40, preferably 12 to 28.

5. The preparation method of the bentonite-supported nano iron sulfide restoration agent according to claim 1 or 4, wherein the ferrous salt is ferrous chloride tetrahydrate or ferrous sulfate heptahydrate;

and/or the vulcanizing agent is Na₂S or Na₂S₂O₄Preferably Na₂S₂O₄。

6. The preparation method of the bentonite-supported nano iron sulfide repairing agent according to any one of claims 1 to 5, wherein the bentonite is pretreated before use as follows: placing the bentonite in 1-3mol/L diluted hydrochloric acid, oscillating for 3-24h in a shaking table at the speed of 180-220r/min, then washing with deionized water, and drying at 50-80 ℃ for later use.

7. The preparation method of the bentonite-supported nano iron sulfide repairing agent as claimed in any one of claims 1 to 6, wherein the pH value of the alkaline solution is 10 to 12;

or, the alkaline solution is added in a dropping mode at the speed of 4-10 ml/min;

or the dropping time of the alkaline solution is not more than 2 hours.

8. The preparation method of the bentonite-supported nano iron sulfide repairing agent as claimed in any one of claims 1 to 7, wherein the following operations are carried out under oxygen-free conditions:

1) dissolving ferrous salt in a mixed solution of ethanol and deoxidized deionized water, adding bentonite and polyethylene glycol, and uniformly stirring;

2) dissolving sodium borohydride and a vulcanizing agent in an aqueous solution of sodium hydroxide, wherein the pH value of the obtained mixed solution is 10-12;

3) and (3) dropwise adding the mixed solution obtained in the step 2) into the mixed solution obtained in the step 1), stirring at 220r/min for 180-.

9. The application of the bentonite-loaded vulcanized nano-iron restoration agent prepared by the method of any one of claims 1 to 8 in underground water trichloroethylene pollution.

10. The application of the repairing agent as claimed in claim 9, wherein the bentonite-loaded vulcanized nano-iron repairing agent is added into deoxidized deionized water containing trichloroethylene, the repairing agent is vibrated at a constant temperature, and the removal amount of the trichloroethylene is periodically detected by GCMS;

and/or the initial concentration of the trichloroethylene in the deoxidized deionized water is 30-40ppm, the pH is 7-11, and preferably 9-11;

and/or the addition amount of the bentonite-loaded vulcanized nano-iron repairing agent is 1-5 g/L;

and/or the constant temperature oscillation is carried out at the temperature of 20-25 ℃ for 3-24h at the rotating speed of 180-220 r/min.

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