A bag reaction device and method for simulating nano-zero-valent iron to degrade chlorinated hydrocarbon-contaminated soil

Abstract

The present invention discloses a bag-type reaction device for simulating the degradation of chlorinated hydrocarbon-contaminated soil by zero-valent iron. The device comprises a Tedlar bag encased in an aluminum foil bag; the Tedlar bag has four sides, three of which are sealed and one of which has a sealing strip; a metal valve and a PV three-way valve are installed on the top of the aluminum foil bag; the metal valve is topped with a metal cap with an internal sealing gasket; the PV three-way valve is topped with a PV cap with an internal sealing gasket. The present invention simulates the degradation of CAHs-contaminated soil by nZVI using the bag-type reaction device. Headspace gas chromatography (HJ 741) is used to quantitatively identify nine degradation products from the sampled soil. This allows for the complete collection of small organic molecules produced during the degradation of CAHs-contaminated soil by nZVI, enabling evaluation of the effectiveness and impact of nZVI in remediating and degrading CAHs.

Description

Technical Field

[0001] The present invention belongs to the technical field of soil remediation and pollutant degradation, and specifically relates to a bag-type reaction device and method for simulating nano-zero-valent iron to degrade chlorinated hydrocarbon-contaminated soil. Background Art

[0002] Chlorinated hydrocarbons (CAHs) are excellent organic solvents and intermediates, widely used in various industrial fields. However, due to improper storage and disposal, they enter the soil environment through volatilization, leakage, and wastewater discharge, posing a threat to human health and the ecological environment. CAHs have a long history of use and are widely used. Such pollution is commonly found in soil and groundwater, and the concentrations detected are relatively high. CAHs pollutants on sites are complex in composition, highly polluting, and have high concentrations, making them a potential source of pollution. They also produce some more toxic intermediates in the environment. If they are not treated promptly over a long period of time, they will pollute the surrounding soil, surface water, and even groundwater. They can also enter the human body through drinking water or the soil-plant system, and through the food chain, endangering ecological safety and human health.

[0003] Common and typical soil remediation technologies mainly include ex situ remediation technology and in situ remediation technology. Ex situ remediation is mainly based on P&T (Pump and Treat) technology. P&T technology is the earliest soil and groundwater remediation technology. It is to extract groundwater from its original location, remediate it in a different location, and then inject it back into the underground location. However, due to the effect of capillary tension, the non-aqueous phase solution retained in the water layer is almost impossible to be pumped out from the pump, so it is not very suitable for CAHs pollutants. In situ remediation technology is mainly carried out inside the soil and groundwater. It has low remediation costs, good effects, a variety of remediation methods, very low disturbance to the remediation area, and a wide range of applications. Therefore, in the future soil and groundwater pollution remediation process, in situ remediation technology will be increasingly used in actual remediation processes, especially in CAHs-contaminated sites. In-situ remediation technology primarily relies on in-situ chemical techniques. Some nanomaterials exhibit strong adsorption and redox reactions with heavy metals and organic pollutants. Since its introduction in environmental remediation in 2001, nano-zero-valent iron (nZVI) boasts a large surface area, exceptional reactivity, and excellent catalytic activity, making it a reductant that effectively removes a wide range of pollutants from soil and groundwater. This plays a crucial role in the engineering application of in-situ remediation technology. According to incomplete statistics, 77 sites worldwide have been remediated using nano-zero-valent iron technology, and the number of sites using this technology is increasing annually. Numerous studies have demonstrated the strong reduction effect of nZVI on pollutants such as CAHs. However, its safety and effectiveness require further research and promotion. nZVI remediation technology involves injecting slurry into contaminated soil, converting pollutants into non-toxic or less toxic substances. When using nZVI remediation technology at contaminated sites, simulation studies are necessary to determine the treatment efficacy and impact of nZVI, and further pilot testing is required to determine or optimize design parameters.

[0004] Compared to field test devices, indoor pollution simulation devices offer advantages such as low cost, minimal pollution, simple construction, and significant effectiveness, making them particularly suitable for research related to contaminated site soils. Existing indoor simulation experimental devices for contaminated site soils include column and tank devices. For example, CN 112404115 A uses a column experiment to simulate chemical oxidation soil remediation processes; CN 115739969 A uses a column experiment to simulate the migration and transformation of antimony in soil under varying redox conditions; and CN 113219043 B uses a column experiment to simulate the monitoring of odorous substances during soil remediation. CN 214488284 U uses a tank experiment to simulate the reaction of thermal cremation and persulfate remediation of organically contaminated soil; CN 2183611296 U uses a transverse tank experiment to simulate the oxidation reaction process of organically contaminated soil; CN 114646661 A uses a tank reactor bed to simulate in-situ heat treatment coupled with microbial remediation of contaminated sites; and CN 114487350 A uses a reaction chamber to investigate the microbial degradation of organic contaminated soil. Existing devices primarily simulate one-dimensional pollutant distribution characteristics with column experiments, and three-dimensional pollutant distribution characteristics with trough experiments. These primarily study the degradation and removal efficiency of soil pollutants, but are unable to fully capture the degradation products, particularly small organic molecules. Existing indoor simulation devices are cumbersome to maintain and are not designed specifically for the characteristics of CAHs pollution. The devices also suffer from poor sealing, stability, anti-volatilization, and adsorption properties, resulting in significant discrepancies between simulation results and actual conditions. These devices are unable to meet the research needs of conducting simulation experiments on the degradation of chlorinated hydrocarbons by nZVI, making it difficult to fully understand the mechanisms of pollutant remediation. Summary of the Invention

[0005] The present invention aims to overcome the problems of the prior art by providing a bag-type reactor and method for simulating the degradation of chlorinated hydrocarbon-contaminated soil using nano-zero-valent iron. This invention utilizes a Tedlar and aluminum foil bag-type reactor to simulate the degradation of CAHs-contaminated soil using nZVI, resulting in minimal pollution, simple construction, and excellent airtightness.

[0006] The purpose of the present invention and the solution to the technical problem are achieved by adopting the following technical solutions.

[0007] A first aspect of the present invention provides a bag-type reaction device for simulating the degradation of chlorinated hydrocarbon-contaminated soil by nano-zero-valent iron, comprising a Tedlar bag, the Tedlar bag being covered with an aluminum foil bag; the Tedlar bag comprising four sides, three of which are sealed and one of which is provided with a sealing strip; a metal valve and a PV three-way valve are provided on the aluminum foil bag, the top cover of the metal valve is provided with a metal cap, the metal cap is provided with a built-in sealing gasket, and the top cover of the PV three-way valve is provided with a PV cap, the PV cap is provided with a built-in sealing gasket.

[0008] A second aspect of the present invention provides a method for simulating the degradation of chlorinated hydrocarbon-contaminated soil by nano-zero-valent iron according to the aforementioned device, comprising the following steps:

[0009] Preparation of CAHs-contaminated soil with uniform texture;

[0010] Prepare oxygen-free water;

[0011] The CAHs-contaminated soil was placed in a bag-type reactor and sealed, and the PV three-way valve was opened to remove air, and then the PV three-way valve was closed;

[0012] Nano-zero-valent iron is added into the reaction device through a metal valve, and then oxygen-free water is added. The reaction bag is gently squeezed to mix the soil in the bag into a slurry. The samples are mixed regularly and destructively sampled and tested using the metal valve.

[0013] In some preferred embodiments, the preparation process of the CAHs-contaminated soil is as follows:

[0014] The collected natural soil was air-dried, ground and sieved;

[0015] Weigh CAHs into a brown soil sample bottle, add the sieved soil to the sample bottle in batches in a gradient dilution manner, shake well and mix thoroughly after each addition of soil, finally cover the bottle cap and seal with sealing film, and shake and place it to achieve a uniform concentration of soil CAHs. The storage time is ≥ 9 days;

[0016] Three soil samples were taken for analysis. When the RSD of the CAHs concentrations in the three soil samples was ≤ 20%, the soil samples were considered to be evenly mixed and the preparation of CAHs-contaminated soil was completed.

[0017] In some preferred embodiments, the preparation process of the oxygen-free water is as follows: ultrapure water is blown under a nitrogen flow for 1 hour.

[0018] In some preferred embodiments, the nano zero-valent iron comprises nZVI CA20nm 、nZVI 20nm 、nZVI 40nm .

[0019] In some preferred embodiments, the chlorinated hydrocarbons include tetrachloroethylene, dichloroethane, hexachlorobutadiene, and chlorobenzene.

[0020] In some preferred embodiments, the volume of the muddy soil does not exceed two-thirds of the total volume of the reaction bag.

[0021] Through the above-mentioned technical solution, the present invention has at least the following advantages: It overcomes the shortcomings of the prior art by providing a bag-type simulation device and its application for indoor nZVI remediation and degradation of CAHs contaminants in field soil. The present invention utilizes a Tedlar and aluminum foil bag-type reaction device to simulate nZVI degradation of CAHs-contaminated soil, characterized by low pollution, simple construction, and good airtightness. The Tedlar and aluminum foil materials provide an adsorption-resistant, light-proof, and stable simulated experimental environment. The bag-type reaction device can fully collect the small organic molecules produced during nZVI degradation of CAHs-contaminated soil, enabling experimental research on the treatment effects and impacts of nZVI remediation and degradation of CAHs, further revealing the pollutant remediation mechanism. During the simulated nZVI degradation of PCE-contaminated soil, the reaction device employed headspace gas chromatography (HJ 741) to quantitatively identify nine degradation products, achieving comprehensive collection and identification of degradation products.

[0022] The above description is only an overview of the technical solution of the present invention. In order to more clearly understand the technical means of the present invention and implement it according to the contents of the specification, the following is a detailed description of the preferred embodiments of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is a schematic structural diagram of a bag-type reaction device for simulating nano-zero-valent iron to degrade chlorinated hydrocarbon-contaminated soil according to the present invention;

[0024] Figure 2 This is a characteristic analysis diagram of the degradation product components of tetrachloroethylene-contaminated soil after degradation by different nano-zero-valent iron;

[0025] Figure 3 Comparison of the degradation rates of tetrachloroethylene-contaminated soil by different nano-zero-valent iron. DETAILED DESCRIPTION

[0026] In order to make the technical means, creative features, objectives and effects achieved by the present invention easier to understand, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts shall fall within the scope of protection of the present invention. Example

[0027] like Figure 1As shown, the bag-type reaction device for simulating the degradation of chlorinated hydrocarbon-contaminated soil by nano-zero-valent iron of the present invention includes a Tedlar bag 1, and the Tedlar bag 1 is covered with an aluminum foil bag 2. The aluminum foil bag 2 provides a simulated experimental environment for CAHs that is anti-adsorption, light-proof, and has good stability. The Tedlar bag 2 includes four sides, three of which are sealed and one side is provided with a sealing strip 3. The soil is placed in through this opening and then sealed by the sealing strip 3. The aluminum foil bag 2 is provided with a metal valve 4 and a PV three-way valve 5. The top cover of the metal valve 4 is provided with a metal cap 6, and the metal cap 6 has a built-in sealing gasket 7. The top cover of the PV three-way valve 5 is provided with a PV cap 8, and the PV cap 8 has a built-in sealing gasket 9. This makes the airtightness controllable during the reaction process. Example

[0028] The bag-type reaction device of Example 1 is used to simulate the degradation of chlorinated hydrocarbon-contaminated soil by nano-zero-valent iron, which specifically includes the following steps:

[0029] Prepare uniform CAHs-contaminated soil: Air-dry the collected natural soil, grind it, and sieve it. Weigh CAHs into a brown soil sample bottle. Add the sieved soil to the sample bottle in batches using a gradient dilution method. Shake well after each addition of soil, and seal the bottle with a sealing film. Shake the bottle to achieve uniform CAHs concentration in the soil. The storage time should be ≥ 9 days. Take three soil samples for analysis. When the RSD of the CAHs concentration of the three soil samples is ≤ 20%, the soil samples are considered to be uniformly mixed and the CAHs-contaminated soil preparation is complete.

[0030] Prepare oxygen-free water: blow ultrapure water under nitrogen flow for 1 h;

[0031] The CAHs-contaminated soil was placed in a bag-type reactor and sealed, and the PV three-way valve was opened to remove air, and then the PV three-way valve was closed;

[0032] Add nano-zero-valent iron into the reaction device through a metal valve, then add oxygen-free water, gently squeeze the reaction bag to mix the soil in the bag into a slurry (the volume of the slurry in the reaction bag should not exceed two-thirds of the total volume of the reaction bag), and mix the samples regularly and then take destructive samples for testing through the metal port.

[0033] In some preferred embodiments, the nano zero-valent iron comprises nZVI CA20nm 、nZVI 20nm 、nZVI 40nm .

[0034] In some preferred embodiments, the chlorinated hydrocarbon comprises tetrachloroethylene. Example

[0035] The device of Example 1 and the method of Example 2 were used to simulate the degradation of chlorinated hydrocarbon-contaminated soil by nano-zero-valent iron, specifically:

[0036] The volume of the bag reaction device used in the experiment was 0.2L, the soil in the bag was 50g, the mass ratio of oxygen-free water to soil was 1:2.5, the amount of nZVI powder added was 5mg / g, and the PCE concentration of the PCE-contaminated soil prepared was 80mg / kg. The experiment was carried out at room temperature of 25℃, and samples were taken for testing at different times.

[0037] The three commercial nano zero-valent irons used in the experiment are nZVI CA20nm (Purchased from Shanghai Pantian Powder Material Co., Ltd.), nZVI 20nm (Purchased from Shanghai Pantian Powder Material Co., Ltd.), nZVI 40nm (purchased from Guangzhou Hongwu Material Technology Co., Ltd.); the chlorinated hydrocarbon used was tetrachloroethylene (purchased from Tianjin Kemiou Chemical Reagent Co., Ltd.).

[0038] The degradation components in the samples were analyzed and the degradation rates were calculated. Headspace gas chromatography (HJ 741) was used to quantify and identify the degradation products. Figure 2 、 Figure 3 shown.

[0039] like Figure 2 As shown, headspace gas chromatography can be used to screen and identify the types and content distribution of degradation products. By analyzing the changes in the content and types of degradation products, the optimal materials and reaction conditions can be effectively selected, which is of great significance for in-depth revelation of the degradation and remediation mechanism of pollutants. Figure 2 The results showed that the types and contents of degradation products produced by different types of nano-zero-valent iron at different times were different: among them, the types and contents of degradation product components in group a and group b samples did not change significantly with time, and were mainly composed of 1,2-dichloroethylene, dichloromethane and 1,1,1-trichloroethane; in group c, vinyl chloride and trichloroethylene were the main components, among which the content of vinyl chloride increased and trichloroethylene decreased at 41 hours; in group d, 1,2-dichloroethylene, dichloromethane, 1,1,1-trichloroethane and trichloroethylene were the main components at 25 hours, and trichloroethylene was the main component at other times.

[0040] like Figure 3 As shown in the figure, the degradation rate of tetrachloroethylene by different types of nano zero-valent iron showed obvious differences: nZVI 20nm The removal rate of PCE is the highest.

[0041] The above description is merely a preferred embodiment of the present invention and does not constitute any form of limitation to the present invention. Although the present invention has been disclosed as a preferred embodiment as above, it is not intended to limit the present invention. Any technician familiar with this profession can make slight changes or modifications to equivalent embodiments of the methods and technical contents disclosed above without departing from the scope of the technical solution of the present invention. However, any simple modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention are still within the scope of the technical solution of the present invention.

Claims

1. A method for degrading chlorinated hydrocarbon-contaminated soil by simulating nano-zero-valent iron using a bag reactor, characterized in that: The bag-type reaction device comprises a Tedlar bag, which is covered with an aluminum foil bag; the Tedlar bag has four sides, three of which are sealed and one side is provided with a sealing strip; a metal valve and a PV three-way valve are provided on the top of the aluminum foil bag; the top of the metal valve is provided with a metal cap, which is provided with a sealing gasket; the top of the PV three-way valve is provided with a PV cap, which is provided with a sealing gasket; the method comprises the following steps: Preparation of CAHs-contaminated soil with uniform texture; Prepare oxygen-free water; The CAHs-contaminated soil was placed in a bag-type reactor and sealed, and the PV three-way valve was opened to remove air, and then the PV three-way valve was closed; Nano-zero-valent iron is added into the reaction device through a metal valve, and then oxygen-free water is added. The reaction bag is gently squeezed to mix the soil in the bag into a slurry. The samples are mixed regularly and destructively sampled and tested through the metal valve.

2. The method according to claim 1, characterized in that The preparation process of the CAHs-contaminated soil is as follows: The collected natural soil was air-dried, ground and sieved; Weigh CAHs into a brown soil sample bottle, add the sieved soil to the sample bottle in batches in a gradient dilution manner, shake well and mix thoroughly after each addition of soil, finally cover the bottle cap and seal with sealing film, and shake and place it to achieve a uniform concentration of soil CAHs. The storage time is ≥ 9 days; Three soil samples were taken for analysis. When the RSD of the CAHs concentrations in the three soil samples was ≤ 20%, the soil samples were considered to be evenly mixed and the preparation of CAHs-contaminated soil was completed.

3. The method according to claim 1, characterized in that The preparation process of the oxygen-free water is as follows: ultrapure water is blown under a nitrogen flow for 1 h.

4. The method according to claim 1, wherein The nano zero-valent iron includes nZVI CA20nm 、nZVI 20nm 、nZVI 40nm .

5. The method according to claim 1, wherein The chlorinated hydrocarbons include tetrachloroethylene, dichloroethane, hexachlorobutadiene, and chlorobenzene.

6. The method according to claim 1, wherein The volume of the muddy soil does not exceed two-thirds of the total volume of the reaction bag.

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