Method for repairing polycyclic aromatic hydrocarbon contaminated soil by activated persulfate with sodium salt of cyclodextrin

Abstract

The application belongs to the technical field of organic contaminated soil remediation, and discloses a method for remediation of polycyclic aromatic hydrocarbon contaminated soil by sodium cyclodextrin activated persulfate. In view of the problems of poor mass transfer of reagents, low reagent utilization rate and poor remediation effect when the persulfate oxidation technology is used to remediate polycyclic aromatic hydrocarbon contaminated soil, a sodium cyclodextrin with the functions of catalytic activation and improvement of the availability of polycyclic aromatic hydrocarbons in contaminated soil is provided, and a method for remediation of polycyclic aromatic hydrocarbon contaminated soil by using the sodium cyclodextrin to activate persulfate is provided. Under the same conditions, the first-order degradation rate of HPCD sodium salt / PS to phenanthrene is 3.03 times, 3.62 times, 7.24 times and 11.71 times that of NaOH-HPCD / PS, NaOH / PS, HPCD / PS and PS system to phenanthrene, respectively. The method has the advantages of high reagent utilization rate, low remediation cost and low environmental risk, and has a wide application prospect in the remediation of polycyclic aromatic hydrocarbon contaminated soil.

Description

Technical Field

[0001] The invention belongs to the technical field of organic contaminated soil remediation, and particularly relates to a method for remediating polycyclic aromatic hydrocarbon-contaminated soil by activating persulfate with cyclodextrin sodium salt. Background Art

[0002] Polycyclic aromatic hydrocarbons (PAHs) are a general term for hydrocarbons containing two or more benzene rings and various compounds derived from them. PAHs have attracted public attention due to their "triglyceridity, toxicity, and toxicity" effects on organisms and their toxic impact on the ecosystem. The U.S. Environmental Protection Agency (EPA) announced 16 PAHs among the 129 priority monitoring pollutants in 1979. Studies have shown that PAHs in the environment primarily enter the human body through soil. PAHs are highly hydrophobic and easily adsorbed on the surfaces of soil particles or minerals / soil organic matter. PAHs in the soil accumulate continuously through adsorption and eventually enter the human body through the food chain, causing harm to human health. Faced with the severe problem of PAH soil contamination, remediation work is imperative.

[0003] Remediation technologies for PAH-contaminated soil include chemical remediation, bioremediation, and physical remediation. Compared with other remediation technologies, chemical oxidation remediation technology has the advantages of short remediation time, wide application range, and portable engineering implementation. Persulfate is easy to transport, relatively stable, and easily soluble in water, which meets the requirements for contaminated site remediation. Persulfate can be activated by heat, alkali, transition metal ions, ultrasound, and ultraviolet light to produce active species such as sulfate radicals, hydroxyl radicals, and superoxide radicals to degrade organic pollutants. Compared with other activation methods, alkali-activated persulfate can simultaneously generate sulfate radicals and hydroxyl radicals, and the latter is greater in number than the former. Alkali-activated persulfate has been widely used for in situ remediation of organically contaminated soil.

[0004] Patent (CN201611127304.X) discloses a method for treating soil contaminated with high concentrations of organophosphorus pesticides using alkaline-activated persulfate. This method involves adding a 0.21 mol / L persulfate solution and a 7 mol / L sodium hydroxide solution to the contaminated soil, mixing them and initiating a degradation reaction. The method achieves a 92.3% removal rate for high concentrations of organophosphorus pesticides in the soil. A study (Lominchar MA, et al., "Remediation of aged diesel contaminated soil by alkaline-activated persulfate," Science of the Total Environment 622-623 (2018): 41-48) reports on the degradation of diesel in aged soil using sodium hydroxide-activated sodium persulfate. The results showed that at a PS:NaOH ratio of 1:4 and a PS ratio of 420 mM, 5000 mg / kg of petroleum hydrocarbons in the soil were completely degraded within 56 days.

[0005] The literature (Yan Zhilou et al. "Experimental study on the remediation of TPH and PAH contaminated soil by alkali-activated sodium persulfate and thermal desorption technology." Chemical Engineering Management 12(2021):12) reported the use of sodium hydroxide-activated sodium persulfate and thermal desorption technology to remediate petroleum hydrocarbon and PAH contaminated soil. The experimental results showed that for low-concentration PAH contaminated soil, both technologies could meet the remediation requirements; for high-concentration PAH contaminated soil, the remediation effect of sodium hydroxide-activated sodium persulfate was much lower than that of thermal desorption technology, and failed to achieve the remediation target. This is mainly due to the poor mass transfer and low utilization rate of persulfate in PAH contaminated soil, which in turn leads to poor degradation effect of sodium hydroxide-activated sodium persulfate system on petroleum hydrocarbon and PAH contaminated soil. If the soil remediation target is met by increasing the dosage of sodium hydroxide and sodium persulfate, it will not only increase the remediation cost, but also cause changes in soil properties and bring about secondary pollution.

[0006] In order to solve the above problems, surfactants are usually used to strengthen persulfate and increase the solubility of hydrophobic pollutants in the aqueous phase. Surfactants are a class of amphiphilic organic substances that can improve the oxidative removal effect of persulfate on pollutants by forming micelles, reducing interfacial tension, and promoting the transfer of hydrophobic pollutants from the soil phase to the aqueous phase. The literature (Heidari M, et al. "Combination of nonionic surfactants with thermal-activated persulfate for simultaneous removal of phenanthrene and pyrene from alluvialsoil: A kinetic study." Soil & Sediment Contamination 2021: 41-48) reported that phenanthrene and pyrene contaminated soil with a concentration of 500 mg / kg was oxidatively repaired in the presence of TX 100 and sodium persulfate (0.5M), and a removal effect of about 90% was obtained within 1 hour. However, when the concentration of surfactant is high, its toxicity is relatively large. The large-scale addition of surfactants will cause a decrease in the microbial biomass and enzyme activity in the soil, destroy soil organic matter, and cause secondary pollution to the soil.

[0007] Cyclodextrin is a naturally non-toxic, harmless supramolecular host compound that slowly biodegrades in soil, converting into nutrients such as glucose, with a half-life ranging from several months to two years. Cyclodextrins possess a hydrophilic outer rim and a hydrophobic cavity, allowing them to form inclusion complexes with all or part of the functional groups of a host molecule, increasing the solubility of organic molecules in water. Compared to organic solvents and non-ionic surfactants, cyclodextrins exhibit low toxicity to soil microbial communities, are highly biodegradable, lack a critical micelle concentration, and do not form highly viscous micelles. This unique structure gives cyclodextrins excellent prospects for widespread application in environmental protection. The literature (Bardi L, et al. "Cyclodextrin-enhanced insitu bioremediation of polyaromatic hydrocarbons-contaminated soils and plantuptake." Journal of Inclusion Phenomena & Macrocyclic Chemistry 57 (2007): 439-434) reported a study on the removal rate of polycyclic aromatic hydrocarbons by β-cyclodextrin. It was found that β-cyclodextrin can increase the degradation rate of polycyclic aromatic hydrocarbons in soil, reduce the permeability of polycyclic aromatic hydrocarbons in soil, and slow down the diffusion of polycyclic aromatic hydrocarbons in soil. The literature (Hanna K, et al. "Coupling enhanced water solubilization with cyclodextrin to indirect electrochemical treatment for pentachlorophenol contaminated soil remediation." Water Research 39 (2005): 2763-2773) reported the use of cyclodextrin coupled electrochemical remediation technology to treat PCP-contaminated soil. The results showed that cyclodextrin promoted the removal of PCP. When the cyclodextrin concentration was 5 mmol / L, the soil PCP removal rate was 70%. The literature (Lv Zhengyong et al. "Effect of surfactants on the bioavailability of PAHs in aged soil." Soil 44 (2021): 436-443) reported a study on adding hydroxypropyl-β-cyclodextrin to PAHs contaminated soil and using Tenax resin to predict its bioavailability. The results showed that when the concentration of hydroxypropyl-β-cyclodextrin was 500 mg / L, the Tenax extractable amount of soil was as high as 462.24 μg / kg, which was much higher than the 290.71 μg / kg without addition. That is, the addition of hydroxypropyl-β-cyclodextrin greatly improved the bioavailability of PAHs.

[0008] Currently, there is limited research on the coupled degradation of organic pollutants using cyclodextrin and persulfate oxidation technology. Given the stability of cyclodextrin in alkaline media, the combination of cyclodextrin and the alkaline activation reagent sodium hydroxide to activate persulfate may have potential for the remediation of PAH-contaminated soils.

[0009] The present invention proposes a cyclodextrin sodium salt that has the functions of catalytic activation and improving the effectiveness of polycyclic aromatic hydrocarbons in contaminated soil, and a method for using the cyclodextrin sodium salt to activate persulfate to repair polycyclic aromatic hydrocarbons contaminated soil. On the one hand, the supramolecular cavity packaging effect of the cyclodextrin material is used to regulate the occurrence form of pollutants in polycyclic aromatic hydrocarbons contaminated soil, optimize the persulfate oxidation process, and improve the utilization rate of oxidants on pollutants and the oxidation repair effect. On the other hand, cyclodextrin sodium salt creates an alkaline environment for the reaction system, and persulfate is activated under alkaline conditions to produce a variety of highly reactive free radicals. The cyclodextrin sodium salt / PS system greatly improves the effectiveness of polycyclic aromatic hydrocarbon pollutants in the soil, and the pollutants can come into contact with the system more, which is beneficial to SO4 - The oxidative degradation of PAHs by · and ·OH achieves the dual purpose of efficiently repairing PAH-contaminated soil and reducing the amount of activated oxidants used. Summary of the Invention

[0010] The present invention addresses the problem of low pollutant effectiveness in polycyclic aromatic hydrocarbons (PAHs) contaminated soil, which leads to poor pollutant degradation. A cyclodextrin sodium salt material with both the ability to increase the effectiveness of PAHs in contaminated soil and the catalytic activation function is proposed, and a method for using the material to activate persulfate to repair PAHs contaminated soil is proposed. The cyclodextrin sodium salt is prepared from NaOH and Na + Replace the H on the alcoholic hydroxyl group on the outer surface of the cyclodextrin molecule + And a sodium alcohol is generated.

[0011] The technical solution of the present invention:

[0012] A method for remediating polycyclic aromatic hydrocarbon-contaminated soil by activating persulfate with sodium cyclodextrin, comprising the following steps:

[0013] (1) Dissolve cyclodextrin and sodium hydroxide in water, heat in a water bath at 35°C with stirring, and react for 1 hour until the solution becomes clear to obtain a cyclodextrin sodium salt solution; if used for ectopic repair, freeze-dry and grind the cyclodextrin sodium salt solution to obtain a cyclodextrin sodium salt solid material, and dissolve the cyclodextrin sodium salt solid material in water to obtain a cyclodextrin sodium salt solution again;

[0014] (2) Sodium cyclodextrin and persulfate solution were added to the PAH-contaminated soil at the same time to construct a sodium cyclodextrin-activated persulfate system to effectively remove PAHs from the soil.

[0015] The cyclodextrin used to prepare the cyclodextrin sodium salt is any one of α-CD, β-CD, γ-CD, and hydroxypropyl-β-cyclodextrin (HPCD), preferably HPCD.

[0016] The molar ratio of the cyclodextrin to the sodium hydroxide is 1:4-1:10.

[0017] The persulfate is any one of sodium persulfate, potassium persulfate, ammonium persulfate and magnesium persulfate, preferably sodium persulfate, and its addition amount in the soil is 0.5% to 2% of the soil mass.

[0018] The Na of the cyclodextrin sodium salt + The molar ratio of Na to persulfate is 1:1 to 3:1. + When the molar ratio of sodium hydroxide to persulfate is less than 2:1, the amount of sodium hydroxide added to prepare sodium cyclodextrin is too low, and too few hydroxyl radicals and sulfate radicals are generated in the system, resulting in poor soil remediation effect; when Na + When the molar ratio of cyclodextrin to persulfate is greater than 2:1, the higher pH value in the system will cause the soil properties to change, resulting in secondary pollution. + The molar ratio of chlorinated bisulfate to persulfate is 2:1.

[0019] Beneficial effects of the present invention: The mechanism of the present invention of cyclodextrin sodium salt activating persulfate to repair polycyclic aromatic hydrocarbons contaminated soil includes: cyclodextrin sodium salt activates persulfate to produce SO4 - The multi-radical system of · and ·OH degrades PAHs in soil; sodium cyclodextrin can also solubilize and elute PAHs in soil. This is due to the supramolecular recognition "hydrophobic cavity" of the cyclodextrin material, which can encapsulate PAHs in the soil. After encapsulation, a portion of the pollutants enters the aqueous phase and is degraded by the sodium cyclodextrin / PS system, while the remaining portion is directly removed by elution. This method is simple to operate, low-cost, and stable, with broad application prospects and practical significance. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is a picture of HPCD sodium salt material.

[0021] Figure 2 This is a diagram showing the degradation effect of persulfate activated by HPCD sodium salt on polycyclic aromatic hydrocarbons in soil.

[0022] Figure 3 This is a diagram showing the elution effect of different concentrations of HPCD sodium salt on polycyclic aromatic hydrocarbons in soil.

[0023] Figure 4 This is a diagram showing the degradation effect of the HPCD sodium salt / PS system on different types of polycyclic aromatic hydrocarbons contaminated soils. DETAILED DESCRIPTION

[0024] The specific implementation method of the present invention is further described below in conjunction with the accompanying drawings and technical solutions.

[0025] Example 1

[0026] A method for preparing a HPCD sodium salt material comprises the following steps:

[0027] (1) Prepare HPCD sodium salt solution:

[0028] Dissolve 20 g of HPCD and 2.8 g of sodium hydroxide in 25 mL of water, heat in a water bath at 35° C. with stirring, and react for 1 h until the solution becomes clear to obtain a sodium salt solution of HPCD.

[0029] (2) The HPCD sodium salt solution prepared above was divided into several portions and placed in a -80°C refrigerator for one day, and then placed in a freeze dryer for freeze drying. After one day, a solid sample was taken out and ground to obtain the HPCD sodium salt material.

[0030] Figure 1 This image shows HPCD sodium salt. Unlike its white powder form, HPCD sodium salt appears as pale yellow solid particles. Dissolving HPCD sodium salt in water yields an HPCD sodium salt solution. Solid HPCD sodium salt is more portable and suitable for site remediation than its solution.

[0031] Example 2

[0032] HPCD sodium salt activated persulfate to remediate polycyclic aromatic hydrocarbons contaminated soil

[0033] 50g of PAH-contaminated soil sample was collected. The typical PAH is phenanthrene, and its concentration is 75.42mg / kg. The remediation effect of HPCD sodium salt / PS system on PAH-contaminated soil was investigated. The control systems were PS, HPCD / PS, NaOH / PS, and NaOH-HPCD / PS. In the NaOH-HPCD / PS system, NaOH solution and HPCD solution were added separately in sequence. In the above five systems, the dosage of HPCD, NaOH, and PS were the same, which were 1.15%, 0.168%, and 2% of the soil mass, respectively. The reaction was allowed to stand at room temperature for 6 days. A certain amount of soil sample was collected and freeze-dried every day of reaction. 1.0g of homogenized soil sample was weighed for ultrasonic extraction, and the final PAH removal rate was calculated, as shown below: Figure 2As shown. After 6 days of reaction, the degradation rate of phenanthrene by HPCD sodium salt / PS can reach 83.11%, the degradation rate of phenanthrene by NaOH-HPCD / PS is 60.03%, and the degradation rates of phenanthrene by NaOH / PS, HPCD / PS and PS are 45.66%, 23.87% and 14.55% respectively. The primary degradation rate of phenanthrene by HPCD sodium salt / PS is 3.03 times, 3.62 times, 7.24 times and 11.71 times that of NaOH-HPCD / PS, NaOH / PS, HPCD / PS and PS systems respectively. Compared with the NaOH-HPCD / PS system, on the one hand, the cyclodextrin sodium salt / PS system has the functions of both inclusion and oxidation degradation of polycyclic aromatic hydrocarbons, so the pollutants can be in contact with the system more, which is beneficial to SO4 - · and ·OH for the oxidative degradation of polycyclic aromatic hydrocarbons pollutants; on the other hand, in the NaOH-HPCD / PS system to which NaOH and HPCD solutions were added respectively, SO4 - · and ·OH oxidize the hydroxyl groups on the cyclodextrin cavity skeleton, consuming the active species produced in the system, thereby reducing the degradation rate of the NaOH-HPCD / PS system.

[0034] Example 3

[0035] Elution effect of different concentrations of HPCD sodium salt on polycyclic aromatic hydrocarbons in soil

[0036] Soil samples contaminated with PAHs were collected. Typical PAHs were naphthalene, acenaphthene, and phenanthrene, with concentrations of 19.21 mg / kg, 33.20 mg / kg, and 75.42 mg / kg, respectively. One gram of PAH-contaminated soil containing naphthalene, acenaphthene, and phenanthrene was weighed and placed in a glass centrifuge tube. A sodium cyclodextrin solution was prepared with a molar ratio of HPCD to NaOH of 1:8. 10 mL of the HPCD sodium salt solution was added to the tube. The final concentrations of sodium cyclodextrin in the system were 100 mg / L, 500 mg / L, 1000 mg / L, 2000 mg / L, 4000 mg / L, 6000 mg / L, and 8000 mg / L, respectively. Elution experiments were performed in a thermostatic shaker at 25°C and 180 rpm. After 24 hours of oscillation, the centrifuge tube was removed and placed in a centrifuge for centrifugation. The centrifuge speed was set to 2500 r / min. After centrifugation for 10 minutes, the supernatant was taken out and the concentration of polycyclic aromatic hydrocarbons in the supernatant was measured. At the same time, the soil sample was freeze-dried, 1g of homogenized soil sample was weighed and ultrasonically extracted with dichloromethane and n-hexane, and the concentration of remaining polycyclic aromatic hydrocarbons in the soil was detected by liquid chromatography. Finally, the elution rate of polycyclic aromatic hydrocarbons in the soil was calculated. The results are shown in the attached figure. Figure 3As shown in the figure, the elution rates of naphthalene, acenaphthene, and phenanthrene gradually increase with increasing cyclodextrin sodium salt concentration. At a cyclodextrin sodium salt concentration of 8000 mg / L, the elution rates of naphthalene, acenaphthene, and phenanthrene in contaminated soil were 63.75%, 84.39%, and 87.83%, respectively, for a total elution rate of 83.46%. This indicates that cyclodextrin sodium salt has a good elution effect on PAHs in soil, and the higher the cyclodextrin sodium salt concentration, the better the elution effect.

[0037] Example 4

[0038] Degradation of different types of polycyclic aromatic hydrocarbons contaminated soils by HPCD sodium salt / PS system

[0039] Soil samples from Shihezi, Xinjiang (S1), Jiyuan, Henan (S2), Xinxiang, Henan (S3), and Dalian University of Technology campus (S4) were collected for the preparation of polycyclic aromatic hydrocarbon-contaminated soils. The organic matter content (SOM) of the four soils was 18.56 g / kg (S1), 15.43 g / kg (S2), 14.17 g / kg (S3), and 16.64 g / kg (S4), respectively. The designed PS dosage was 2%, the molar ratio of HPCD to NaOH for the preparation of sodium cyclodextrin salt was 1:8, and the NaOH dosage was 0.67%. 50 g of each of the four soils was weighed into a 100 mL beaker, and 10 mL of sodium cyclodextrin salt and 10 mL of sodium persulfate solution were added to the beaker. The beaker was then sealed and allowed to react at room temperature. After 7 days of degradation reaction, the soil contaminated with PAHs was sampled and freeze-dried. 1 g of homogenized soil was weighed and ultrasonically extracted with dichloromethane and n-hexane. The concentration of pollutants after the reaction was detected by liquid chromatography, and the removal rate of PAHs was calculated. Figure 4 As shown, the degradation rates of phenanthrene in soil types S1, S2, S3, and S4 were 49.67%, 59.12%, 61.23%, and 60.23%, respectively, indicating that soil organic matter participates in the oxidative degradation process, competitively inhibiting the degradation of PAHs by active species. The degradation rates of naphthalene and acenaphthene were approximately 65.00% and 97.00% in the four soil types, respectively, demonstrating that the HPCD sodium salt / PS system has a good degradation effect on different PAH-contaminated soil types.

Claims

1. A method for remediating polycyclic aromatic hydrocarbons-contaminated soil by activating persulfate with cyclodextrin sodium salt, characterized in that: Here are the steps: (1) Dissolving cyclodextrin and sodium hydroxide in water, stirring under heating at 35° C. in a water bath, and reacting for 1 hour until the solution becomes clear, thereby obtaining a cyclodextrin sodium salt solution; the molar ratio of the cyclodextrin to the sodium hydroxide is 1:4-1:10; and the cyclodextrin is hydroxypropyl-β-cyclodextrin; If used for ectopic repair, the cyclodextrin sodium salt solution is freeze-dried and ground to obtain a cyclodextrin sodium salt solid material, and the cyclodextrin sodium salt solid material is dissolved in water to obtain a cyclodextrin sodium salt solution again; (2) Cyclodextrin sodium salt and persulfate solution were added simultaneously to the PAH-contaminated soil to construct a cyclodextrin sodium salt activated persulfate system to effectively remove PAHs from the soil; The Na of the cyclodextrin sodium salt + The molar ratio of iodine to persulfate is 1:1 to 3:

1.

2. The method for remediating polycyclic aromatic hydrocarbons-contaminated soil by activating persulfate with cyclodextrin sodium salt according to claim 1, characterized in that: The persulfate is any one of sodium persulfate, potassium persulfate, ammonium persulfate and magnesium persulfate. The amount of sodium persulfate added to the soil is 0.5% to 2% of the soil mass.

3. The method for remediating polycyclic aromatic hydrocarbons-contaminated soil by activating persulfate with cyclodextrin sodium salt according to claim 1, characterized in that: The Na of the cyclodextrin sodium salt + The molar ratio of chlorinated bisulfate to persulfate is 2:1.

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