A chemical oxidation method for remediation of svocs in soil

Abstract

The application discloses a chemical oxidation method for repairing SVOCs in soil, sodium persulfate and sodium percarbonate are used as oxidants, transition metals Fe 2+ and Cu 2+ are used as activators, and ascorbic acid is used as a conditioner. First, the activator and the conditioner are injected into the SVOCs contaminated soil in a certain proportion, mixed uniformly, and then the oxidant is added, and the reaction is fully oscillated under the condition of heating and ultrasonic, to form a ternary activated homogeneous reaction system of transition metal ion activation, thermal activation and ultrasonic activation, effectively promote the contact of SVOCs and the repair reagent, improve the circulation of metal ions in the reaction process, and stimulate the generation of more free radicals, thereby improving the removal efficiency of SVOCs in soil. The application patent establishes a high-efficiency field soil pollution repair system, and realizes the purpose of repairing SVOCs contaminated soil efficiently.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of soil environmental pollution remediation, in particular, to a chemical oxidation method for remediation of SVOCs in soil. BACKGROUND

[0002] Among numerous pollutants, semi-volatile pollutants seriously threaten the health of surrounding residents due to their numerous types, long existence time, difficulty in degradation, strong hydrophobicity and other characteristics. Therefore, in order to protect human health, it is urgent to develop efficient remediation technology for semi-volatile organic contaminated soil to realize the reuse of land resources.

[0003] For the remediation and removal of semi-volatile organic pollutants in soil, the remediation methods usually include physical, chemical, biological and their combined means. In recent years, advanced oxidation processes (AOPs) have stood out among numerous remediation technologies. As a kind of chemical remediation method, compared with physical remediation and biological remediation, AOPs can degrade pollutants into less toxic compounds, and the application of AOPs is more environmentally friendly and efficient, overcoming the problems existing in ordinary chemical remediation methods, and receiving more and more attention. AOPs are based on in-situ generation of strong oxidizing active oxygen species (for example: ·OH, SO4 •- 、 1 O2 and O2 •- ) to oxidize and degrade organic pollutants, among which the oxidation technology based on sulfate radicals (SO4 •- , E 0 =2.5~3.1 V) and hydroxyl radicals (·OH, E 0 =2.8 V) has stronger oxidation ability to pollutants. With the continuous development of AOPs process, the research on the activation of active radicals of oxidizing agents such as persulfate and hydrogen peroxide has developed from traditional light, electric auxiliary, Fenton activation to transition metal / oxide nanomaterials, semiconductor materials, ultrafine particle materials and other activation methods, but solid activation materials have problems such as easy agglomeration, poor mass transfer, high cost and other problems in practical application, which are not suitable for the remediation of actual site soil. Therefore, suitable activation remediation materials and activation methods are the key to efficient remediation of SVOCs in site soil by AOPs process, and liquid transition metal ions can also be used as activators of oxidizing agents at room temperature. Commonly used transition metal ions generally include Fe 2+ , Ag + , Mn 2+ , Cu 2+ , Co 2+Etc., these metal ions can be obtained by electron transfer and other ways of strong oxidative active oxygen free radicals, in addition, the introduction of small molecule organic acid as conditioner, can effectively control the competition of excessive metal ions on free radicals in oxidation process, adjust the cycle between different valence metal ions, promote the efficient degradation of organic pollutants in soil. The development and application of high mass transfer AOPs activation material, optimization of high efficient activation conditions can improve the contact of pollutants and remediation agent, stimulate more active free radicals, which has important theoretical significance and technical guidance for AOPs technology to remove SVOCs in the soil of site. SUMMARY

[0004] In order to make up for the above, the present application provides a kind of for repairing SVOCs in soil chemical oxidation method, which can promote the contact of oxidant and organic pollutants, stimulate more active oxygen free radicals in reaction system, improve the removal efficiency of SVOCs, realize the efficient degradation of organic pollutants.

[0005] The present application is realized as follows: first, a certain amount of oxidant is dissolved in water to prepare an oxidant solution, wherein the oxidant solution is a double oxidation system solution; then a certain amount of transition metal salt is dissolved in water to prepare an activator solution; then a certain amount of small molecule acid is dissolved in water to prepare a conditioner solution; finally, the activator and conditioner are injected into the SVOCs contaminated soil according to a certain proportion, and then the oxidant is injected and stirred uniformly, the mixture of reagent and soil is oscillated at 50 DEG C temperature condition, and ultrasonic activation treatment is carried out, and the reaction is closed.

[0006] The small molecule acid added by the conditioner is ascorbic acid, and the molar ratio of metal ion to conditioner is 10:1.

[0007] In a preferred technical scheme of the present application, the oxidant solution is formed by mixing two reagents selected from sodium persulfate (PS), sodium percarbonate (SPC) and hydrogen peroxide (H2O2) to form a double oxidation system.

[0008] In a preferred technical scheme of the present application, the oxidant solution is a double oxidant mixed system, and the molar ratio of the two oxidants in the mixed system is 10:0~0:10.

[0009] In a preferred technical scheme of the present application, the activator solution is formed by mixing two reagents selected from ferrous sulfate (FeSO4‧7H2O), copper chloride (CuCl2) and cobalt chloride (CoCl2‧6H2O) to form a double metal activation system.

[0010] In a preferred technical scheme of the present application, the activator solution is a mixed system of two metal ions, and the molar ratio of the two metal ions in the mixed system is 10:0~0:10.

[0011] The beneficial effects of the present application are: through the transition metal ion activated coupling of thermal activation, ultrasonic activation ternary activation mode catalyzes sodium persulfate / sodium carbonate double oxidation system, realizes the efficient degradation removal of SVOCs in soil. The technology is simple, green and environmentally friendly, and has low cost, and has wide practical application prospect in the field of soil remediation. BRIEF DESCRIPTION OF DRAWINGS

[0012] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings needed in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present application, and therefore should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can also be obtained without creative labor on the basis of these drawings.

[0013] Figure 1 Effect of four different dosages of conditioning agents on removal of BaP in contaminated soil by ternary catalytic oxidation system ([BaP]0=18.6 mg / kg; [PS]=4.8 mmol; [SPC]=1.2 mmol; [Cu 2+ ]=0.06 mmol; [Fe 2+ ]=0.54 mmol; [water-soil ratio]=2 / 1; 50℃, 180rpm; 50Hz, daily ultrasonic time 2h, reaction time: 72h);

[0014] Figure 2 Kinetic curves of removal of BaP in contaminated soil by five different oxidation systems ([BaP]0=18.6 mg / kg; [PS]=4.8 mmol; [SPC]=1.2 mmol; [Cu 2+ ]=0.06 mmol; [Fe 2+ ]=0.54 mmol; [ascorbic acid]=0.06 mmol; [water-soil ratio]=2 / 1; 50℃, 180rpm; 50Hz, daily ultrasonic time 2h, reaction time: 72h);

[0015] Figure 3 a Effect of ascorbic acid on removal of BaP in three different oxidation systems;

[0016] Figure 3 b Effect of ascorbic acid on Fe 2+ content in different oxidation systems ([BaP]0=18.6 mg / kg; [PS]=4.8 mmol; [SPC]=1.2 mmol; [Cu 2+ ]=0.06 mmol; [Fe2+ = 0.54 mmol; [ascorbic acid] = 0.06 mmol; [water / soil ratio] = 2 / 1; 25 °C, 180 rpm.

[0017] Figure 4 Radical quenching experiment results of multi-catalytic oxidation system for removing BaP in soil ([BaP]0= 18.6 mg / kg; [PS] = 4.8 mmol; [SPC] = 1.2 mmol; [Cu 2+ ] = 0.06 mmol; [Fe 2+ ] = 0.54 mmol; [ascorbic acid] = 0.06 mmol; [water / soil ratio] = 2 / 1; 25 °C, 180 rpm, 50 Hz, daily ultrasonic time 2 hours, reaction time: 72 hours.

[0018] Figure 5 Effect of oxidation time on multi-catalytic oxidation system for removing SVOCs in organic contaminated soil ([PS] = 8 mmol; [SPC] = 2 mmol; [Cu 2+ ] = 0.1 mmol; [Fe 2+ ] = 0.9 mmol; [ascorbic acid] = 0.1 mmol; [water / soil ratio] = 2 / 1; 25 °C, 180 rpm, 50 Hz, daily ultrasonic time 2 hours. DETAILED DESCRIPTION

[0019] In order to make the objects, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are some but not all of the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by a person of ordinary skill in the art without creative work fall within the protection scope of the present application.

[0020] Example 1

[0021] (I) Preparation of BaP contaminated soil: The background soil of the contaminated soil was collected from uncontaminated surface farmland soil. After natural air-drying, the soil was sieved through a 2 mm sieve to remove stones, leaves and other impurities and was ready for use. The contamination process was carried out in a fume hood. 20 mg of benzo[a]pyrene standard was dissolved in a certain volume of acetone and added to 1 kg of air-dried soil sample and mixed well. A glass rod was used to stir constantly during the process until the volatilization was complete. After aging for 1 month, a benzo[a]pyrene contaminated soil with a concentration of 18.6 mg / kg was obtained.

[0022] (II) Different small molecule acids promote the repair of BaP contaminated soil by multi-catalytic oxidation system: First, 10 g of prepared BaP contaminated soil was weighed into a brown glass bottle, and 0.6 mmol of metal ion solution was added to the glass bottle, wherein the metal salt used was a mixed solution prepared from ferrous sulfate heptahydrate and anhydrous copper chloride, and the molar ratio of Fe 2+ and Cu 2+ was 9:1; second, oxalic acid, citric acid, ascorbic acid and EDTA were added to the bottle respectively, and several addition amounts of 0.03, 0.06, 0.3, 0.6, 1.2 mmol were set; finally, 6 mmol of oxidant solution was added to the glass bottle, wherein the oxidant used was a mixed solution prepared from sodium persulfate (PS) and sodium percarbonate (SPC), and the molar ratio of PS to SPC was 8:2. The water-soil ratio of the reaction system was ensured to be 2:1, and the ultrasonic treatment was carried out under the condition of 50 Hz ultrasonic for not less than 2 hours every day, and the oscillation was carried out at 180 rpm and 50°C for 3 days. After the reaction was completed, the BaP in the soil was analyzed according to “Determination of Polycyclic Aromatic Hydrocarbons in Soil and Sediment-Gas Chromatography-Mass Spectrometry” (HJ 805-2016).

[0023] The experimental results are shown in Figure 1 , and the results show that when 0.06 mmol of ascorbic acid is added (i.e. the molar ratio of metal ions to conditioner is 10:1), the removal rate of BaP in the contaminated soil is the highest, reaching 72.2%. In the repair of BaP in soil by multi-catalytic oxidation system, the conditioning effect of ascorbic acid is better than that of citric acid, EDTA and oxalic acid.

[0024] (III) Synergistic effect of multi-catalytic oxidation system in repairing BaP contaminated soil: This example proves that the ternary activation oxidation system of transition metal, heat and ultrasonic has a synergistic effect on the removal of pollutants by comparing the kinetics experiments of 5 different oxidation systems for the removal of BaP in soil. First, 10 g of prepared BaP contaminated soil was weighed into a brown glass bottle, and the water-soil ratio of the reaction system was ensured to be 2:1. (1) 6 mmol of double oxidant solution (PS:SPC molar ratio=8:2) was added to the glass bottle, and the oscillation was carried out at 180 rpm for 72 hours at room temperature, which was recorded as the simple oxidant addition group (PS / SPC); (2) 0.6 mmol of double metal ion solution (Fe 2+ : Cu 2+ molar ratio=9:1) was added to the glass bottle on the basis of (1), which was recorded as the transition metal activated oxidation group (Fe 2+ / Cu 2 + -PS / SPC); (3) 0.06 mmol of ascorbic acid was added to the glass bottle on the basis of (2), which was recorded as the small molecule acid conditioning transition metal activated group (AA-Fe 2+ / Cu 2+ -PS / SPC); (4) based on (3), the reactor was placed in a constant temperature oscillator at 50 ℃, denoted as heat-AA-Fe 2+ / Cu 2+ -PS / SPC); (5) based on (4), ultrasonic treatment was carried out at a frequency of 50 Hz for 2 hours every day, and the temperature of the reaction system was maintained at 50 ℃ during the ultrasonic process, denoted as us-heat-AA-Fe 2+ / Cu 2+ -PS / SPC).

[0025] The experimental results are shown in Figure 2 , and the removal rates of BaP in the soil by the five different oxidation systems from high to low are us-heat-AA-Fe 2+ / Cu 2+ -PS / SPC group (72.5%) > heat-AA-Fe 2+ / Cu 2+ -PS / SPC group (63.4%) > AA-Fe 2+ / Cu 2+ -PS / SPC group (49.1%) > Fe 2+ / Cu 2+ -PS / SPC group (38.2%) > PS / SPC group (16.5%), and the removal rate of BaP by the ternary catalytic oxidation system is the highest, indicating that the transition metal activation, heat activation and ultrasonic activation play a synergistic promoting role on the PS / SPC system.

[0026] (Four) Mechanism of ascorbic acid in the oxidation system: on the one hand, ascorbic acid can activate persulfate to produce active free radicals, and on the other hand, ascorbic acid can reduce Fe 3+ generated in the oxidation process to Fe 2+ , promoting the continuous activation of Fe 2+ . In this embodiment, by comparing whether the addition of ascorbic acid in the oxidation process affects the removal rate of BaP in the contaminated soil, the activation effect of ascorbic acid on the oxidant is verified. At the same time, by determining the change of Fe 2+ concentration in the oxidation process by the o-phenanthroline method, it is proved that the addition of ascorbic acid promotes the circulation between Fe 2+ / Fe 3+ .

[0027] The results are shown in Figure 3 , Figure 3The study compared the removal rates of BaP in contaminated soil under conditions without heating and ultrasound: treatments involving the addition of oxidant (PS / SPC), the addition of ascorbic acid (AA), and the addition of both ascorbic acid and oxidant (AA+PS / SPC). At the reaction endpoint, the BaP removal rates were AA+PS / SPC (26.8%) > PS / SPC (19.0%) > AA (3.1%), verifying that ascorbic acid itself has a certain activating effect on oxidants. Figure 3 b compared the effects of Fe alone under normal temperature and non-ultrasonic conditions. 2+ Activated oxidation system (Fe) 2+ -PS / SPC), Cu 2+ Coupled Fe 2+ Activated oxidation system (Cu) 2+ / Fe 2+ -PS / SPC) and ascorbic acid conditioning Cu 2+ Coupled Fe 2+ Activated oxidation system (AA-Cu) 2+ / Fe 2+ Fe in three oxidation processes (PS / SPC) 2+ The concentration changes during the oxidation process, AA-Cu 2+ / Fe 2+ Fe in the PS / SPC system 2+ The concentration decreased most slowly, followed by Cu. 2+ / Fe 2+ -PS / SPC system, Fe 2+ Fe in the PS / SPC system 2+ The fastest rate of concentration decrease indicates that Cu 2+ The addition of ascorbic acid effectively regulated Fe 2+ / Fe 3+ The cycle makes Fe 2+ It can continuously activate oxidants to remove BaP from the soil.

[0028] (v) Free radicals generated during the oxidation of BaP by multiple catalysts: In this example, tert-butanol and methanol were used as quenchers to conduct free radical quenching experiments, which proved that free radicals play a major role in the degradation of pollutants in the oxidation reaction.

[0029] To determine the effect of free radicals on BaP removal from soil in a multi-component catalytic oxidation system, tert-butanol and methanol were selected as quenchers to investigate SO42-. •- The role of HO· in oxidation systems Figure 4It is shown that the addition of methanol and tert-butyl alcohol both inhibit the removal of BaP in the system, and the addition of 60 mmol of methanol has the greatest inhibitory effect on the removal of BaP, reducing the removal rate of BaP in the multi-catalytic oxidation system from 72.5% to 26.7%. The results show that SO4 •- and HO· play a major role in the removal of BaP during the oxidation process.

[0030] Example Two

[0031] 10 g of actual contaminated soil from a pesticide site was weighed and placed in a brown glass bottle with a lid. The experimental soil used was divided into two categories, the first category was polycyclic aromatic hydrocarbons (PAHs): benzo(a)pyrene 1.5 mg / kg, benzo(b)fluoranthene 9.1 mg / kg, dibenzo(a,h) anthracene 0.6 mg / kg, naphthalene 1979.5 mg / kg; the second category was organic pesticides (OPs): hexachlorobenzene 1.4 mg / kg, terbufos 62.7 mg / kg, 1,4 dichlorobenzene 10.0 mg / kg, ethion 356.0 mg / kg, parathion 19102.1 mg / kg, cypermethrin 15900.0 mg / kg, phorate 696.5 mg / kg. 0.1 mmol ascorbic acid, 1 mmol bimetallic ion solution (Fe 2+ : Cu 2+ molar ratio = 9:1) and 10 mmol of oxidant solution (PS: SPC molar ratio = 8:2) were added to the contaminated soil in turn, ensuring that the water-soil ratio in the reaction system was 2 / 1. The reaction system was oscillated at 50°C and 180 rpm, and was simultaneously treated with ultrasound at a frequency of 50 kHz for 2 hours per day. The reaction was closed for 30 days, after which the sample was removed and freeze-dried at -50°C. The concentration of each pollutant in the soil was then detected, and the removal rate of SVOCs was calculated.

[0032] The experimental results are as follows Figure 5 This example compares the removal of SVOCs in actual soil from a pesticide contaminated site by the ternary activation method developed in the developed persulfate / percarbonate dual oxidation system. The multi-catalytic oxidation system was used to remediate the soil of an organic contaminated site. The removal rate of SVOCs in the soil increased with the extension of the oxidation time. When the dosage of oxidant was 10 mmol, after 30 days of oxidation, the removal rate of total PAHs in the soil was 67.1%, and the removal rate of total OPs in the soil was 81.0%, among which the removal efficiency of organophosphorus pesticides in the soil all reached more than 85%, achieving efficient removal of SVOCs in the soil of the site.

[0033] Working principle:

[0034] (1) The application develops a high mass transfer liquid catalytic oxidation remediation agent, which can efficiently contact with SVOCs in the soil to form a homogeneous reaction system, overcome the problems of easy agglomeration and passivation of solid agents in the soil, and promote the full contact of oxidants and organic pollutants

[0035] (2) In the high-efficiency catalytic oxidation remediation agent developed by the application, Cu 2+ and ascorbic acid are added to effectively regulate the conversion between Fe 2+ and Fe 3+ , so that the activation of Fe 2+ continues, and ascorbic acid can also act as an effective activator of sodium persulfate to promote the generation of SO4 ·- and ·OH in the oxidation process, and improve the removal effect of organic pollutants.

[0036] (3) The high-efficiency catalytic oxidation remediation agent developed by the application is reacted under the condition of heating at 50 DEG C coupled with ultrasonic, to form a ternary catalytic oxidation system, when used for removing benzo[a]pyrene (BaP) contaminated soil, the removal rate of BaP in the soil is more than 70% within 3 days, and when used for removing SVOCs in contaminated site soil, the total removal rate of organic pesticides in the soil is 80.0% within 30 days, and the total removal rate of polycyclic aromatic hydrocarbons in the soil is 64.1%.

[0037] The above only describes the preferred embodiments of the application and is not used to limit the application, and the application can have various changes and variations for those skilled in the art. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the application shall be included in the protection scope of the application.

Claims

1. A chemical oxidation method for remediating SVOCs in soil, characterized in that, Includes the following steps: 1) Weigh a certain amount of oxidant and dissolve it in water to prepare an oxidant solution, wherein the oxidant solution is a two-oxidation system solution; 2) Weigh a certain amount of transition metal salt and dissolve it in water to prepare an activator solution; 3) Weigh a certain amount of small molecule acid and dissolve it in water to prepare a conditioning solution; 4) Inject the activator and conditioner into the SVOCs-contaminated soil in a certain proportion, then inject the oxidant and stir evenly. Shake the mixture of agent and soil at 50°C and simultaneously perform ultrasonic activation treatment to seal the reaction. The small molecule acid added to the conditioner is ascorbic acid, and the molar ratio of metal ions to conditioner is 10:

1.

2. The chemical oxidation method for remediating SVOCs in soil as described in claim 1, characterized in that: The oxidant solution is formed by mixing two reagents from sodium persulfate, sodium percarbonate, and hydrogen peroxide to form a dual oxidation system.

3. The chemical oxidation method for remediating SVOCs in soil as described in any one of claims 1-2, characterized in that: The oxidant solution is a mixed system of two oxidants.

4. The chemical oxidation method for remediating SVOCs in soil as described in claim 1, characterized in that: The activator solution is a bimetallic activation system formed by mixing two reagents from ferrous sulfate, copper chloride, and cobalt chloride.

5. The chemical oxidation method for remediating SVOCs in soil as described in claim 1 or 4, characterized in that: The activator solution is a mixture of two metal ions.

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