Preparation method of multifunctional zero-valent iron activator composite material and application of multifunctional zero-valent iron activator composite material in remediation of underground water in organic pollution site

Abstract

The invention belongs to the technical field of remediation of organic polluted groundwater, and discloses a preparation method of a multifunctional zero-valent iron activator composite material and application of the multifunctional zero-valent iron activator composite material in remediation of groundwater in an organic polluted site. The composite material is a multifunctional zero-valent iron activator composite material which has efficient dispersion performance, long-acting activation performance and pollution aging relieving performance and is formed by coupling micron zero-valent iron, activated carbon, sodium carboxymethyl cellulose, polyethylene glycol and sodium hydrosulfite, and the composite material is used for efficiently activating persulfate to repair underground water polluted by organic pollutants. The repairing material has good capability of activating, oxidizing and degrading organic pollutants and migration performance. The method has the advantages of simplicity and convenience in operation, low cost, reliable effect and the like, and shows wide application prospects and practical application values.

Description

Technical Field

[0001] The present invention belongs to the technical field of organically contaminated groundwater remediation, and relates to a multifunctional zero-valent iron activator composite material and its application in remediating groundwater in organically contaminated sites. Background Art

[0002] Organic pollutants in groundwater at organically contaminated sites are numerous and diverse, including petroleum hydrocarbons, benzene series, polycyclic aromatic hydrocarbons, chlorinated hydrocarbons, and pesticides. These pollutants are highly toxic, difficult to degrade, and highly mobile, posing a serious threat to groundwater resources and the ecological environment. There is an urgent need to develop efficient and low-cost in-situ remediation technologies for organically contaminated groundwater at these sites.

[0003] Compared to other remediation technologies, chemical oxidation remediation technology is widely used in the remediation of organically contaminated sites due to its rapid degradation of organic pollutants and wide applicability. Persulfate, with its high oxidative activity, stability, and water solubility, is a common oxidative remediation material for organically contaminated sites. Persulfate oxidants can be activated through various methods (such as heat, alkali, and zero-valent iron) to produce highly active oxidizing species such as sulfate and hydroxyl radicals, effectively degrading organic pollutants.

[0004] Alkali-activated materials, such as caustic soda flakes and quicklime, are remediation materials that are highly active in an alkaline environment. Their activation mechanism primarily relies on enhanced production of highly active free radical species during persulfate activation under alkaline conditions, effectively degrading organic pollutants in soil and water in a short period of time. Patent CN106753386A utilizes sodium hydroxide solution to activate persulfate, achieving removal rates of 100% for BCP-4-bromo-2-chlorophenol and 78.3% for CP-chlorpyrifos over three days. However, alkali-activated materials have a rapid release rate and poor long-term effectiveness. Their active components are easily consumed or inactivated during the reaction, resulting in a significant decrease in remediation effectiveness over time.

[0005] Zero-valent iron (ZVI) activators are highly efficient, economical, and environmentally friendly. Zero-valent iron (ZVI) enhances the generation of strong oxidizing free radicals during persulfate activation through its reduction reaction, effectively degrading organic pollutants. Among them, nano-ZVI (nZVI) is a highly effective remediation material with excellent persulfate activation capabilities. However, nZVI has significant limitations in practical applications, such as poor dispersibility, easy agglomeration, and susceptibility to oxidation or passivation in complex underground environments, resulting in insufficient long-term effectiveness. To address these issues, researchers have developed nano-iron-carbon materials and surface-modified ZVI materials that improve the dispersibility of nano-ZVI. Biochar-coated nano-ZVI synthesized in patent CN113943030A activated persulfate and removed 98.7% of chlorobenzene from water within 4 hours. Modified biochar-loaded nano-ZVI activated sodium persulfate in 60 minutes, removing 96.1% of naphthalene. However, the preparation of nano-iron-carbon materials and surface-modified zero-valent iron materials is complex, involving multiple steps such as nanoparticle synthesis, surface modification, or carbon-based composites, resulting in high production costs. Furthermore, the large-scale production and practical application of these materials still face technical bottlenecks, including issues such as reaction condition control, long-term stability, and environmental safety.

[0006] Persulfate activation with zero-valent iron composites is also a highly effective method for remediating organically contaminated soil. Patent CN115254938A describes a DTN-ZVI / PS system, consisting of a coupling of persulfate (PS), zero-valent iron (ZVI), and sodium dithionite (DTN). This system achieved removal rates of 61% and 82% for naphthalene and acenaphthene, respectively, in soil within five days. The patent emphasizes its high efficiency and rapid response, making it suitable for soil remediation. However, in actual groundwater, iron-sulfur materials may face challenges such as uneven dispersion, agglomeration, and decreased activity, which can affect their long-term effectiveness and remediation efficacy. However, no reports have been published on their effectiveness in remediating groundwater contamination.

[0007] In summary, traditional activator remediation materials have poor dispersion and diffusion properties in aquifers, and their activity is often difficult to fully exert, resulting in unsatisfactory remediation effects. In addition, to ensure the effective degradation of pollutants, it is usually necessary to use excessive amounts of remediation materials, which increases the cost of remediation and may also cause secondary pollution to the groundwater environment. At the same time, organic pollutants are easily adsorbed on soil particles or form non-aqueous phase liquids (NAPLs) in aging sites, significantly reducing the mass transfer and degradation performance of pollutants. They can also be slowly released over a long period of time, often leading to pollution tailing and rebound phenomena during the oxidation remediation process, resulting in poor long-term remediation and difficulty in meeting standards. At present, organic contaminated groundwater remediation technologies often focus on the activity of remediation materials, but have no effect on the mass transfer restriction problem of pollutant NAPLs, and the dispersion, migration and long-term effectiveness of the materials are insufficient.

[0008] This invention proposes a multifunctional zero-valent iron activator composite material that combines efficient dispersion, long-lasting activation, and pollution- and aging-mitigation properties. The composite material is composed of a coupling of micronized zero-valent iron (mZVI), activated carbon, sodium carboxymethyl cellulose (CMC), polyethylene glycol (PEG), and sodium dithionite (DTN). Compared to nano-zero-valent iron, micronized zero-valent iron is more affordable and readily available, and under the activation of DTN, it promotes the conversion of Fe in the system. 2+ / Fe 3+ The cyclical reaction delays passivation and significantly improves persulfate activation efficiency. The activated carbon coupled with micronized zero-valent iron, dispersed in CMC, forms a stable suspension system, enhancing the material's dispersibility, fluidity, and stability, improving its migration properties and long-term effectiveness. Polyethylene glycol (PEG) effectively improves the dispersibility and stability of the remediation material while also increasing the solubility of aged organic pollutants, alleviating their mass transfer limitations. This multifunctional zero-valent iron activator composite, composed of micronized zero-valent iron, DTN, activated carbon, CMC, and PEG, exhibits excellent dispersibility, catalytic oxidation activity, and aging mitigation capabilities, effectively activating persulfate to remediate groundwater contaminated by organic pollutants. Summary of the Invention

[0009] The present invention addresses the issues of organic pollutant groundwater pollution, such as the mass transfer and release limitations of pollutant NAPLs in aging sites, the dispersion migration and long-term effectiveness of remediation materials, and proposes a multifunctional zero-valent iron activator composite material composed of micron zero-valent iron, activated carbon, sodium carboxymethyl cellulose (CMC), polyethylene glycol (PEG), and sodium dithionite (DTN) coupled together, which has high-efficiency dispersion performance, long-term activation performance, and pollution aging mitigation performance. The composite material is used to efficiently activate persulfate and effectively remediate groundwater contaminated by organic pollutants.

[0010] The technical solution of the present invention:

[0011] A method for preparing a multifunctional zero-valent iron activator composite material comprises the following steps:

[0012] Micronized zero-valent iron (mZVI), activated carbon, and sodium dithionite (DTN) are added to water in sequence and stirred evenly; polyethylene glycol (PEG) is then added and stirred evenly to allow PEG to fully adhere to the surface of the material, thereby pre-dispersing the material; sodium carboxymethyl cellulose (CMC) is then added and stirred evenly to obtain a multifunctional zero-valent iron activator composite material coupled with activated carbon, CMC, and PEG-modified DTN.

[0013] The addition amount of the micron zero-valent iron in the multifunctional zero-valent iron activator composite material is 2% to 10%.

[0014] The added amount of the activated carbon in the multifunctional zero-valent iron activator composite material is 2% to 10%.

[0015] The CMC is sodium carboxymethyl cellulose, and its addition amount in the multifunctional zero-valent iron activator composite material is 1% to 4%.

[0016] The polyethylene glycol is PEG2000, and its addition amount in the multifunctional zero-valent iron activator composite material is 1% to 4%.

[0017] The DTN is sodium dithionite, and its addition amount in the multifunctional zero-valent iron activator composite material is 0.1% to 0.4%.

[0018] The persulfate is any one of sodium persulfate, potassium persulfate, ammonium persulfate and magnesium persulfate, preferably sodium persulfate, and its addition amount in groundwater is 0.1% to 2%.

[0019] Persulfate is injected into the multifunctional zero-valent iron activator composite material to initiate the activation oxidation reaction, thereby achieving effective removal of organic pollutants in groundwater.

[0020] Beneficial effects of the present invention: The advantages of the activated persulfate of the present invention in remediating groundwater contaminated by organic pollutants mainly include:

[0021] Compared to conventional zero-valent iron activator materials, the multifunctional zero-valent iron activator composite material synthesized in this invention exhibits enhanced activation and oxidation performance, dispersion properties, and the ability to degrade aged pollutants. The activated carbon, DTN, and micronized zero-valent iron in this composite material not only enhance the material's adsorption capacity through the activated carbon, but also enhance the micronized zero-valent iron's ability to activate and oxidize persulfates. This coupled adsorption and activation-oxidation effect significantly improves the material's degradation of organic pollutants. Furthermore, the activated carbon and micronized zero-valent iron, when dispersed in polyethylene glycol (PEG) and sodium carboxymethyl cellulose (CMC), form a stable suspension system, addressing the aggregation and sedimentation issues of conventional zero-valent iron materials and improving mobility in groundwater environments. PEG also enhances the material's ability to degrade aged pollutants, thereby alleviating the mass transfer and release limitations of NAPLs from aged sites, a problem that poses a significant challenge to groundwater pollution. CMC increases the system's viscosity, slowing the material's sedimentation rate, while also forming an adsorption layer on the material's surface, preventing aggregation and sedimentation. This multifunctional zero-valent iron activator composite material has good activation, oxidation and degradation capabilities of organic pollutants and migration performance, and has the advantages of simple operation, low cost and reliable effect, showing broad application prospects and practical application value. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1This is the degradation effect diagram of the DTN-mZVI / PS system with repeated addition of chlorobenzene every 12 hours.

[0023] Figure 2 This is a diagram of the dispersion and suspension effect of sodium carboxymethyl cellulose (CMC) on micron zero-valent iron, activated carbon, and micron zero-valent iron activated carbon coupling system in water at the same dosage ratio in the water sample.

[0024] Figure 3 This is a diagram of the dispersion and suspension effect of composite materials with different usage ratios of CMC in the composite material slurry.

[0025] Figure 4 This is a diagram showing the effect of two multifunctional zero-valent iron activator composite materials with different ratios on activating persulfate to degrade low-concentration chlorobenzene in five types of groundwater.

[0026] Figure 5 The effect of multifunctional zero-valent iron activator composite material on activating persulfate to degrade high-concentration chlorobenzene in five groundwaters. DETAILED DESCRIPTION

[0027] The specific implementation method of the present invention is further described below in conjunction with the accompanying drawings and technical solutions.

[0028] Example 1 Study on the performance of the DTN-mZVI / PS system in releasing chlorobenzene in a simulated aquifer.

[0029] Among them, according to the actual chlorobenzene pollution situation, the reaction solution was set to 30 mL, containing 224 mg / L chlorobenzene solution, and the usage of micron zero-valent iron (mZVI) and sodium dithionite (DTN) in the chlorobenzene solution accounted for 0.25% and 0.01% respectively; the remediation effect of the DTN-mZVI / PS system on chlorobenzene-contaminated groundwater was investigated. All the reaction glass bottles were shaken in a constant temperature shaker at 180 r / min at 25±0.2°C. After the reaction, the concentration of chlorobenzene was determined by high performance liquid chromatography. At the same time, in order to simulate the process of continuous release of chlorobenzene into the water by aquifers in the groundwater environment, the system was subjected to repeated addition of chlorobenzene at intervals of 12 hours ( Figure 1 Experimental results showed that at sodium persulfate (PS) mass fractions of 0.1%, 0.2%, and 0.5%, respectively, the system achieved degradation rates of 96.8%, 98.6%, and 99.7% for chlorobenzene in groundwater. Even after three repeated additions of chlorobenzene, the degradation rate remained above 90%. With the fifth, sixth, and seventh repeated additions, the degradation rates reached 51.8%, 39.3%, and 30.1%, respectively.

[0030] Example 2 Multifunctional zero-valent iron activator composite material activates persulfate to repair medium- and high-concentration chlorobenzene-contaminated water.

[0031] Chlorobenzene concentrations were set at 224 mg / L and 22.4 mg / L, respectively. The proportions of micronized zero-valent iron (mZVI), activated carbon, sodium carboxymethyl cellulose (CMC), polyethylene glycol (PEG), sodium dithionite (DTN), and sodium persulfate (PS) in the chlorobenzene solution were 0.25%, 0.25%, 0.1%, 0.1%, 0.01%, and 0.1%, respectively. The reaction glass bottles were shaken in a thermostatic shaker at 180 rpm and 25 ± 0.2°C. After 6 hours of reaction, the removal efficiency of chlorobenzene at both high and medium concentrations reached over 99%, demonstrating that this multifunctional zero-valent iron activator composite has excellent ability to activate persulfate to remediate groundwater contaminated by sites with varying concentrations of organic pollutants.

[0032] Example 3 Suspension and dispersion effect of CMC activated carbon micron zero-valent iron coupling system.

[0033] Set the suspension system to 50 mL, such as Figure 2 As shown in the figure, from left to right, the micronized zero-valent iron (mZVI) content in the water sample was 0.25%, 0.25%, and 0%, respectively; the activated carbon content was 0.25%, 0%, and 0.25%, respectively; and the sodium carboxymethyl cellulose (CMC) content was 0.1%. After 4 hours of stabilization, the activated carbon-mZVI coupled system exhibited improved dispersion and stability compared to the system containing either mZVI or activated carbon alone, with no significant sedimentation. This improves its transport properties in groundwater environments.

[0034] Example 4 Suspension and dispersion effect of the multifunctional zero-valent iron activator composite material.

[0035] The composite material slurry system was set to 60mL, with the mass fractions of micronized zero-valent iron (mZVI), activated carbon, polyethylene glycol (PEG), and sodium dithionite (DTN) in the composite material slurry being 5%, 5%, 2%, and 0.4%, respectively. Sodium carboxymethyl cellulose (CMC) was then added to each beaker, with the mass fractions of CMC in the composite material slurry being 0, 1%, 2%, and 4%, respectively. The mixture was stirred evenly and allowed to stand for 1 hour and 4 hours before observing the suspension and dispersion effect of the multifunctional zero-valent iron activator composite material. Figure 3As shown in the figure, after 1 hour of stabilization, the system without CMC had almost completely settled, while the systems with 1%, 2%, and 4% CMC content showed no significant change after 4 hours of stabilization. This indicates that CMC effectively prevents particle aggregation and sedimentation, enhancing the material's stability and fluidity, which effectively improves its mobility in groundwater. The system with a 1% CMC content exhibits a fluid liquid state, while the system with a 4% CMC content exhibits a poorly fluid paste state. The system with a 2% CMC content exhibits a highly fluid paste state, making it suitable for underground in-situ injection.

[0036] Example 5: Different types of multifunctional zero-valent iron activator composite materials activate persulfate to degrade low-concentration chlorobenzene in five types of groundwater.

[0037] The chemical compositions of the five simulated groundwater species are typical groundwater chemical compositions, mainly including: HCO3 − +Cl − (SGW1), NO3 − (SGW2), HCO3 − (SGW3), HCO3 − +NO3 − (SGW4) and HCO3 − +SO4 2− (SGW5).

[0038] The concentration of chlorobenzene is 22.4 mg / L, and two ratios are set for the activation materials. Ratio 1: the proportions of micron zero-valent iron (mZVI), activated carbon, sodium carboxymethyl cellulose (CMC), polyethylene glycol (PEG), sodium dithionite (DTN), and sodium persulfate (PS) in simulated groundwater are: 0.25%, 0.25%, 0.1%, 0.1%, 0.01%, and 0.1%, respectively; Ratio 2: the proportions of micron zero-valent iron (mZVI), activated carbon, sodium carboxymethyl cellulose (CMC), polyethylene glycol, sodium dithionite, and sodium persulfate in simulated groundwater are: 0.5%, 0.5%, 0.15%, 0.15%, 0.01%, and 0.2%, respectively. The reaction glass bottles were shaken in a constant temperature shaker at 180 r / min at 25±0.2°C, and the reaction time was 6h. The experimental results are as follows. Figure 4 As shown in the figure, the treatment effect of the two systems on the five types of groundwater contaminated with chlorobenzene reached more than 98%, and the residual concentration was less than 0.6 mg / L, which met the national standards and showed universality in different simulated groundwater components.

[0039] Example 6 Multifunctional zero-valent iron activator composite material activates persulfate to degrade high concentrations of chlorobenzene in five types of groundwater.

[0040] The chemical compositions of the five simulated groundwater species are typical groundwater chemical compositions, mainly including: HCO3 − +Cl − (SGW1), NO3 − (SGW2), HCO3 − (SGW3), HCO3 − +NO3 −（ SGW4) and HCO3 − +SO4 2− (SGW5).

[0041] The concentration of chlorobenzene was 224 mg / L. The proportions of micronized zero-valent iron (mZVI), activated carbon, sodium carboxymethyl cellulose (CMC), polyethylene glycol (PEG), sodium dithionite (DTN), and sodium persulfate (PS) in the simulated groundwater were 0.75%, 0.75%, 0.2%, 0.2%, 0.02%, and 0.3%, respectively. The reaction glass bottles were shaken in a thermostatic shaker at 180 rpm and 25 ± 0.2°C for 6 hours. The experimental results are shown in Figure 2. Figure 5 As shown, the system achieved treatment efficiencies of 99%, 99.4%, 98.9%, 99.6%, and 99.8%, respectively, for five types of groundwater contaminated with high concentrations of chlorobenzene. These experimental results demonstrate that the multifunctional zero-valent iron activator composite material, activated by oxidized persulfate, has excellent remediation capabilities for groundwater contaminated with high concentrations of organic pollutants.

[0042] Example 7 Multifunctional zero-valent iron activator composite material activates persulfate to degrade benzene series in groundwater of a certain chemical plant.

[0043] Chlorobenzene and benzene contaminated groundwater were collected from a site in East China. Chlorobenzene concentrations were monitored at 17 mg / L, and benzene concentrations were 12.9 mg / L. Micronized zero-valent iron (mZVI) and sodium dithionite (DTN) were added to the groundwater at 0.7% and 0.02%, respectively. Sodium persulfate (PS) was added at 1% and 2%, respectively. The reaction volume was 750 mL, and the reaction times were 5 and 26 days, respectively. The experimental results showed that after five days of dosing, the DTN-mZVI / PS system, with 1% and 2% sodium persulfate (PS) additions, achieved treatment efficiencies of 99.3% and 98.7% for chlorobenzene and 98.3% and 99.6% for benzene, respectively, in the contaminated groundwater. After 26 days of dosing, the DTN-mZVI / PS system with 1% and 2% sodium persulfate (PS) additions achieved 94.2% and 100% treatment effects on chlorobenzene in contaminated groundwater, and 100% treatment effects on benzene.

Claims

1. A method for preparing a multifunctional zero-valent iron activator composite material, characterized in that: Here are the steps: The first stage: add micron zero-valent iron, activated carbon, and sodium dithionite to water in sequence and stir evenly; then add polyethylene glycol and stir evenly to allow the polyethylene glycol to fully adhere to the surface of the material, thereby pre-dispersing the material; the second stage: then add sodium carboxymethyl cellulose and stir evenly to obtain a multifunctional zero-valent iron activator composite material coupled with activated carbon, sodium carboxymethyl cellulose, and polyethylene glycol-modified sodium dithionite.

2. The method for preparing the multifunctional zero-valent iron activator composite material according to claim 1, wherein: The addition amount of the micron zero-valent iron in the multifunctional zero-valent iron activator composite material is 2% to 10%.

3. The method for preparing the multifunctional zero-valent iron activator composite material according to claim 1, wherein: The added amount of the activated carbon in the multifunctional zero-valent iron activator composite material is 2% to 10%.

4. The method for preparing the multifunctional zero-valent iron activator composite material according to claim 1, wherein: The addition amount of the sodium carboxymethyl cellulose in the multifunctional zero-valent iron activator composite material is 1% to 4%.

5. The method for preparing the multifunctional zero-valent iron activator composite material according to claim 1, wherein: The polyethylene glycol is PEG2000, and its addition amount in the multifunctional zero-valent iron activator composite material is 1% to 4%.

6. The method for preparing the multifunctional zero-valent iron activator composite material according to claim 1, wherein: The addition amount of the sodium dithionite in the multifunctional zero-valent iron activator composite material is 0.1% to 0.4%.

7. The method for preparing the multifunctional zero-valent iron activator composite material according to claim 1, wherein: The persulfate is any one of sodium persulfate, potassium persulfate, ammonium persulfate and magnesium persulfate, and its addition amount in groundwater is 0.1% to 2%.

8. The method for preparing the multifunctional zero-valent iron activator composite material according to claim 1, wherein: The stirring speed in the first stage is 200-300 rpm.

9. The method for preparing the multifunctional zero-valent iron activator composite material according to claim 1, wherein: The stirring speed in the second stage is 300-400 rpm.

10. Use of the multifunctional zero-valent iron activator composite material obtained by the preparation method according to any one of claims 1 to 9 in remediating groundwater in organically contaminated sites, characterized in that: Persulfate is injected into the multifunctional zero-valent iron activator composite material to initiate the activation oxidation reaction, thereby achieving effective removal of organic pollutants in groundwater.

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