Method for repairing polycyclic aromatic hydrocarbon contaminated soil through small molecule acid reinforced nZVI / H2O2 system

Abstract

A method for repairing soil polluted by polycyclic aromatic hydrocarbons (PAHs) through a small molecule acid reinforced nZVI / H2O2 system comprises the steps that nZVI, OA and H2O2 are added into the soil polluted by PAHs, the water-soil ratio is fixed, full oscillation is conducted for 0.1-3 hours at the normal temperature, and then polluted soil repairing is completed. According to the method, nZVI, OA and H2O2 are combined to achieve a good degradation effect on soil polluted by PAHs, operation is easy, and the method is suitable for large-scale application and popularization. According to the method, the defect that nZVI is prone to passivation is overcome by adding OA, Fe (II) in the nZVI is dissolved out, circulation of Fe (II) / Fe (III) in a reaction system is promoted, the utilization rate of H2O2 is high, the generation amount of HO. Is remarkably increased, the reaction time is greatly shortened, and efficient removal and mineralization of PAHs in the contaminated soil are achieved while the agent dosage is reduced. The method can be quickly and efficiently carried out at normal temperature and normal pressure without adjusting the pH value of soil.

Description

Technical Field

[0001] The present invention belongs to the technical field of soil remediation, and relates to a method for remediating soil contaminated by polycyclic aromatic hydrocarbons, and specifically refers to a method for remediating soil contaminated by polycyclic aromatic hydrocarbons by using a small molecule acid-enhanced nZVI / H2O2 system. Background Art

[0002] Polycyclic aromatic hydrocarbons (PAHs) are a typical class of organic pollutants with high ecotoxicity, persistence, carcinogenicity, mutagenicity and teratogenicity. Due to the high hydrophobicity and low volatility of PAHs, more than 90% of PAHs will accumulate in the soil and exist for a long time. Polycyclic aromatic hydrocarbon pollution in Chinese soil is widespread throughout the country and the soil pollution concentration is as high as several thousand ppm. PAHs will pose a health risk to humans through the food chain and other pathways (Polycyclic aromatic hydrocarbons contamination in surface soil of China: A review. Pei Zhang et al. Science of The Total Environment, 2017, 605-606: 1011-1020.). At present, for soils contaminated with high concentrations of PAHs, the most commonly used remediation technologies are physical remediation and biological remediation, but they have the disadvantages of huge energy consumption, low efficiency and long remediation cycle. Therefore, it is urgent to develop a new remediation technology for high-concentration PAHs contaminated sites that is fast, efficient, safe and economical.

[0003] Advanced oxidation process (AOPs) has a significant effect on the treatment of toxic and difficult-to-degrade organic pollutants. It can decompose organic pollutants into more low-toxic and non-toxic small molecules, or even completely mineralize them. It is an economical, efficient and environmentally friendly remediation technology. The Fenton reaction based on Fe(Ⅱ) and hydrogen peroxide (H2O2) is one of the most popular AOPs. Compared with other AOPs, the Fenton method has the advantages of convenient operation, high treatment efficiency, fast treatment speed and wide application range. The hydroxyl radical (HO·) produced by it has a strong redox potential (E°=2.8V) and can instantly oxidize almost all organic pollutants in a non-selective manner (Formula 1). (Hydroxyl radicals based advanced oxidation processes (AOPs) for remediation of soils contaminated with organic compounds: A review. Min Cheng et al. Chemical Engineering Journal, 2016, 284: 582-598.)

[0004] However, traditional Fenton oxidation has many disadvantages. For example, the reaction is carried out at an acidic pH value. Maintaining such an acidic pH value in the soil will increase the treatment cost. A large amount of H2O2 needs to be added during the remediation process, which is costly and has certain risks due to its harsh transportation and storage conditions. During the reaction, Fe(III) is slowly converted to Fe(II), and the activation efficiency is poor. In order to solve the above shortcomings, heterogeneous Fenton oxidation using nanoscale zero-valent iron (nZVI) instead of Fe(II) has received widespread attention. nZVI has been widely used in water pollution remediation as an environmentally friendly, relatively non-toxic, and cost-effective H2O2 activator. nZVI can not only slowly release Fe 2+ , effectively preventing Fe 2+ Quench hydroxyl radicals and reduce Fe 3+Accelerate the activation process of H2O2 (Formulas 2, 3, 4 and 5). (Tailored design of three-dimensional rGOA-nZVIcatalyst as an activator of persulfate for degradation of organophosphoruspesticides.MYFan et al.Journal of Hazardous.2022,428:128254.)

[0005] Fe 3+ + H2O2→Fe 2+ + HO2·+ H + k2 ~ 2 × 10 -3 M -1 s -1 (Formula 1)

[0006] Fe 2+ + H2O2 → Fe 3+ + ·OH + OH - k1 = 63 M -1 s -1 (Formula 2)

[0007] Fe 3+ + H2O2 → Fe 2+ + HO2· + H + k2 = 2.7 × 10 -3 M -1 s -1 (Formula 3)

[0008] Fe 2+ + ·OH → Fe 3+ + OH - k1 = 3.2 × 10 8 M -1 s -1 (Formula 4)

[0009] Fe 0 + 2Fe 3+ → 3Fe 2+ (Formula 5)

[0010] However, in the actual soil remediation process, due to the high surface energy and activity of nZVI, a passivation layer composed of iron (hydroxide) oxides (FeOOH, Fe2O3, Fe3O4, etc.) is easily formed. This passivation layer will limit the transfer of external protons to the nZVI core, causing the rate of Fe(III) reduction and Fe(II) generation to decrease, affecting the efficiency of electron transfer, resulting in a significant reduction in catalytic efficiency, which restricts the application of nZVI / H2O2 in soil. (Increasing the electron selectivity of nanoscalezero-valent iron in environmental remediation:A review.Long Zhou etal.Journal of Hazardous Materials,2022 421:126709.)

[0011] Studies have shown that the addition of chelating agents (citric acid, ethylenediaminetetraacetic acid, etc.) can prevent precipitation on the surface of nZVI, thereby improving the removal efficiency of pollutants (Enhanced oxidative activity of zero-valent iron by citric acid complexation. Yake et al. Chemical Engineering Journal, 2019, 373: 891-901.). Among the many chelating agents, oxalic acid (OA) is the simplest dicarboxylic acid, which is widely present in soil and other environments. It is an economical and environmentally friendly metal chelator that can be safely used in soil remediation. Compared with other chelating agents such as citric acid and ethylenediaminetetraacetic acid, OA and its dissociated products react slowly with ·OH (k HO·,OA =1.4×10 6 M -1 s -1 ~1×10 7 M -1 s -1), consuming less hydroxyl groups, thus avoiding obvious competitive reactions with target pollutants. At the same time, OA can also reduce the standard redox potential of Fe(II) / Fe(III) coupling (Fe(II) / Fe(III)=0.77V, Fe(II) / Fe(III)-OA=0.002V), promoting Fe(II) / Fe(III) cycle. (Application of Chelating Agents to Enhance Fenton Process in Soil Remediation: A Review. Checa-Fernandez et al. Catalysts, 2021, 11: 722.) Therefore, it is reasonable to expect that OA can improve the effect of nZVI catalyzing H2O2. However, the effectiveness of OA in promoting nZVI / H2O2 has not yet been reported. Summary of the invention

[0012] In order to solve the above problems of nZVI, the present invention provides a method for promoting nZVI to activate H2O2 to degrade high-concentration polycyclic aromatic hydrocarbons in soil by using oxalic acid (OA). This method effectively overcomes the defect of nZVI being easily passivated, promotes the dissolution of Fe(II), and efficiently degrades PAHs in soil. It has the characteristics of simple operation, wide application range and low treatment cost.

[0013] The technical solution of the present invention:

[0014] A method for remediating polycyclic aromatic hydrocarbons contaminated soil by using a low molecular weight organic acid enhanced heterogeneous Fenton technique, the steps are as follows:

[0015] Add nZVI, OA and H2O2 to the PAHs contaminated soil in sequence, fix the water-soil ratio, and fully oscillate at room temperature for 0.1-3 hours (preferably 1 hour) to complete the remediation of the contaminated soil.

[0016] Furthermore, the PAHs is one or a combination of two or more of phenanthrene, benzopyrene, benzo(A)anthracene, pyrene, and indenyl(1,2,3-cd)pyrene.

[0017] Furthermore, the concentration of PAHs in soil is 90–110 mg / kg.

[0018] Furthermore, nZVI uses commercial nano zero-valent iron, and its dosage is 0.1-0.7 mmol / g soil, preferably 0.5 mmol / g soil.

[0019] Furthermore, the dosage of OA is 0.1-0.5 mmol / g soil, preferably 0.3 mmol / g soil.

[0020] Furthermore, the dosage of H2O2 is 0.1-0.7 mmol / g soil, preferably 0.5 mmol / g soil.

[0021] Furthermore, the ratio of the volume ml of water in the system to the mass g of soil in the system is 1:1-5:1, preferably 3:1.

[0022] Through the above-mentioned treatment method, the removal rate of most PAHs in the soil reaches more than 80% within 10 minutes, and preferably the removal rate reaches more than 95% within 1 hour.

[0023] Beneficial effects of the present invention:

[0024] (1) The method of degrading high-concentration PAHs in soil of the present invention only requires a simple combination of commercially available nZVI, OA and H2O2 to achieve good degradation effects on different types of soils contaminated by PAHs. The method is simple to operate and suitable for large-scale promotion and application.

[0025] (2) This method improves the shortcoming of nZVI's easy passivation by adding OA, causing the internal Fe(II) to dissolve, promoting the Fe(II) / Fe(III) cycle in the reaction system, and achieving high H2O2 utilization. The production of HO· is significantly increased, and the reaction time is greatly shortened. The efficient removal and mineralization of PAHs in contaminated soil can be achieved while reducing the dosage of reagents.

[0026] (3) The present invention does not require soil pH adjustment and can be carried out quickly and efficiently at normal temperature and pressure. In addition, the OA added in the present invention is low-cost, environmentally friendly, biodegradable, and has no secondary pollution, providing broad application prospects for the harmless remediation of PAHs-contaminated soil. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 The application effect and degradation mechanism of nZVI / H2O2 / OA system on PAHs in soil. (a) is the degradation effect of different systems on PAHs in soil; (b) is the determination of HO· in nZVI / H2O2 / OA and nZVI / H2O2 systems by electron paramagnetic resonance technology; (c) is the degradation effect of nZVI / H2O2 / OA system on different types of soils contaminated by various PAHs; (d) is the dissolution of iron in nZVI / H2O2 / OA and nZVI / H2O2 systems.

[0028] Figure 2 The degradation effect of different concentrations of H2O2 on PAHs in soil.

[0029] Figure 3 The degradation effect of different concentrations of nZVI on PAHs in soil.

[0030] Figure 4 The degradation effect of different concentrations of OA on PAHs in soil.

[0031] Figure 5 The degradation effect of PAHs in soil under different water-soil ratios. DETAILED DESCRIPTION

[0032] The specific implementation of the present invention is further described below in conjunction with the technical scheme and the accompanying drawings.

[0033] Example 1

[0034] Benz(a)anthracene (1,2-Benzanthracene, BaA) was selected as a typical PAHs in soil, with a concentration of 92 mg / kg. 1 g of contaminated soil containing BaA was weighed and placed in a 50 mL cylindrical glass vial, sealed with a Teflon cap, and wrapped with aluminum foil to avoid possible photomutagenic effects. The remediation effects of different systems on BaA contaminated soil were investigated. The experimental systems were divided into nZVI, OA, H2O2, nZVI / H2O2, and nZVI / H2O2 / OA. In the above five systems, the dosages of nZVI, OA, and H2O2 were the same. The degradation experiment was carried out in a constant temperature shaker at 25 °C and 220 rpm. The experiment adopted the sacrificial bottle method, and a set of parallel samples were taken out at 0, 2, 5, 10, 15, 20, 40, and 60 min of reaction. After sampling, 5 mL of methanol was immediately added and shaken for 1 min to completely quench the reaction. After treatment, the total residual BaA content was determined by liquid chromatography (the recovery rate of BaA extracted from the soil using the above steps was between 95% and 102%). Finally, the degradation rate of PAHs in the soil was obtained by calculation. The results are shown in the attached figure. Figure 1 As shown in (a), in the absence of an activator, the degradation of BaA is almost negligible. The degradation rates of BaA when nZVI, OA, and H2O2 are added alone are low. This indicates that the adsorption of BaA by nZVI and the oxidation of BaA by OA and H2O2 contribute little to its degradation. In the nZVI / H2O2 system, the activation effect of nZVI on H2O2 is poor, and the degradation rate of BaA is only 39%, which is only 12% higher than that of H2O2 alone. However, when nZVI / H2O2 / OA work together, nearly 80% of BaA can be degraded within 5 minutes. After 1 hour of reaction, the degradation rate increased to 95%, which is much higher than other combinations. At the same time, as shown in the attached Figure 1 As shown in (d), OA can improve the leaching of iron in the nZVI / H2O2 system, promote the cycle of Fe(II) / Fe(III) in the system, and activate H2O2 to generate more HO·. The HO· in the nZVI / H2O2 / OA and nZVI / H2O2 systems was further determined by electron paramagnetic resonance technology. Figure 1As shown in (b), the signal intensity of HO· in the nZVI / H2O2 / OA system is much higher than that of nZVI / H2O2. The degradation efficiency of the nZVI / H2O2 / OA system on different soils contaminated with different PAHs was investigated. Soil from Dalian University of Technology campus (loess), soil from Qiqihar, Heilongjiang (black soil), and red soil from Yunnan (red soil) were collected to prepare soils contaminated with different PAHs (phenanthrene, benzopyrene, benzo(a)anthracene, pyrene, indenyl(1,2,3-cd)pyrene) for artificial spike addition. Actual contaminated soil (a chemical plant in Tianjin) was also collected, as shown in the attached figure. Figure 1 As shown in (c), in different types of artificial spiked soils, the degradation rates of phenanthrene, benzopyrene, benzo(a)anthracene, pyrene, and indenyl(1,2,3-cd)pyrene can reach more than 90%, and can also be maintained above 80% in actual soils, indicating that the nZVI / H2O2 / OA system has a good degradation effect on different soils contaminated with different types of PAHs.

[0035] Example 2

[0036] Weigh 1g of contaminated soil containing BaA and place it in a 50mL cylindrical glass vial, seal it with a Teflon cap, and wrap it with aluminum foil to avoid possible photomutagenic effects. Add 0.5mmol / g soil of nZVI, 0.3mmol / g soil of OA, and then add 0.1, 0.2, 0.3, 0.5 and 0.7mmol / g soil of H2O2, respectively, with a water-soil ratio of 3:1. The degradation experiment was carried out in a constant temperature shaker at 25°C and 220rpm. The experiment used the sacrificial bottle method, and samples were taken at 0, 2, 5, 10, 15, 20, 40, and 60min of reaction. After sampling, 5mL of methanol was immediately added and shaken for 1min to completely quench the reaction. After treatment, the total residual BaA content was determined by liquid chromatography. The results are shown in the attached figure. Figure 2 As shown in the figure, as the amount of H2O2 increased from 0.1 to 0.5 mmol / g soil, the removal rate of BaA increased significantly from 38.26% to 95.17%. However, when the H2O2 concentration was further increased to 0.7 mmol / g soil, the removal of BaA was inhibited. This may be because excessive H2O2 would remove HO·. Therefore, the optimal addition amount of H2O2 was 0.5 mmol / g soil.

[0037] Example 3

[0038] Weigh 1g of BaA-containing contaminated soil and place it in a 50mL cylindrical glass vial, seal it with a Teflon cap, and wrap it with aluminum foil to avoid possible photomutagenic effects. Add 0.5mmol / g soil of H2O2, 0.3mmol / g soil of OA, and then add 0.1, 0.2, 0.3, 0.5 and 0.7mmol / g soil of nZVI, respectively, with a water-soil ratio of 3:1. The degradation experiment was carried out in a constant temperature shaker at 25°C and 220rpm. The experiment used the sacrificial bottle method, and samples were taken at 0, 2, 5, 10, 15, 20, 40, and 60min of reaction. After sampling, 5mL of methanol was immediately added and shaken for 1min to completely quench the reaction. After treatment, the total residual BaA content was determined by liquid chromatography. The results are shown in the attached figure. Figure 3 As shown in the figure, when the dosage of nZVI increased from 0.1 to 0.3 mmol / g soil, the degradation efficiency of BaA increased from 48.77% to 92%. When the dosage of nZVI was further increased to 0.5 mmol / g soil, the removal rate of BaA in the soil increased slightly to 96%. However, when the addition amount reached 0.7 mmol / g soil, the degradation rate of BaA decreased significantly. This may be because too much nZVI will release excessive Fe(II), and the released Fe(II) will compete with BaA for HO·. Therefore, the optimal addition amount of nZVI is 0.5 mmol / g soil.

[0039] Example 4

[0040] Weigh 1g of contaminated soil containing BaA and place it in a 50mL cylindrical glass vial, seal it with a Teflon cap, and wrap it with aluminum foil to avoid possible photomutagenic effects. Add 0.5mmol / g soil of H2O2, 0.5mmol / g soil of nZVI, and then add 0.1, 0.2, 0.3, 0.4 and 0.5mmol / g soil of OA, respectively, with a water-soil ratio of 3:1. The degradation experiment was carried out in a constant temperature shaker at 25°C and 220rpm. The experiment used the sacrificial bottle method, and samples were taken at 0, 2, 5, 10, 15, 20, 40, and 60min of reaction. After sampling, 5mL of methanol was immediately added and shaken for 1min to completely quench the reaction. After treatment, the total residual BaA content was determined by liquid chromatography. The results are shown in the attached figure. Figure 4 As shown in the figure, when the dosage of OA increases from 0.1 to 0.3 mmol / g soil, the degradation efficiency of BaA increases from 40.24% to 96.12%. However, when the dosage of OA continues to increase to 0.5 mmol / g soil, the degradation rate of BaA decreases significantly. This is mainly because too much OA will react with HO· to ​​quench it. Therefore, the optimal dosage of OA is 0.3 mmol / g soil.

[0041] Example 5

[0042] Weigh 1g of BaA-containing contaminated soil into a 50mL cylindrical glass vial, seal it with a Teflon cap, and wrap it with aluminum foil to avoid possible photomutagenic effects. Add 0.5mmol / g soil of H2O2, 0.3mmol / g soil of OA, and 0.5mmol / g soil of nZVI in sequence, and set the water-soil ratio in the glass bottle to 1:1, 2:1, 3:1, 4:1, and 5:1, respectively. The degradation experiment was carried out in a constant temperature shaker at 25°C and 220rpm. The experiment adopted the sacrificial bottle method, and samples were taken at 0, 2, 5, 10, 15, 20, 40, and 60min of reaction. After sampling, 5mL of methanol was immediately added and shaken for 1min to completely quench the reaction. After treatment, the total residual BaA content was determined by liquid chromatography. The results are shown in the attached figure. Figure 5 As shown in the figure, when the soil-water ratio increased from 1:1 to 3:1, the removal rate of BaA by the nZVI / H2O2 / OA system increased from 21.46% to 93.2%. However, when the soil-water ratio was further increased to 5:1, the removal of BaA was inhibited, mainly because the continued increase in the soil-water ratio would dilute the concentration of H2O2 and activator in the reaction system, resulting in a decrease in the H2O2 conversion rate. Therefore, the optimal soil-water ratio of the system should be 3:1.

Claims

1. A method for repairing polycyclic aromatic hydrocarbons contaminated soil by using a small molecule acid-enhanced nZVI / H2O2 system, characterized in that: The steps are as follows: Add nZVI, OA, and H2O2 to the PAHs-contaminated soil in sequence, fix the water-soil ratio, and fully oscillate at room temperature for 0.1 - 3 hours to complete the remediation of the contaminated soil.

2. The method according to claim 1, characterized in that: PAHs are one or a combination of two or more of phenanthrene, benzo[a]pyrene, benzo[a]anthracene, pyrene, and indeno[1,2,3-cd]pyrene.

3. The method according to claim 1, characterized in that The concentration of PAHs in the contaminated soil is 90 - 110 mg / kg.

4. The method according to claim 1, characterized in that: nZVI is nano zero-valent iron, and its dosage is 0.1 - 0.7 mmol / g soil.

5. The method according to claim 1, characterized in that: The dosage of OA is 0.1 - 0.5 mmol / g soil.

6. The method according to claim 1, characterized in that The dosage of H2O2 is 0.1 - 0.7 mmol / g soil0.

7. The method according to claim 1, characterized in that The ratio of the volume of water (ml) to the mass of soil (g) in the system is 1:1 - 5:1.

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