A method for detecting the content of non-aqueous phase pollutants in low-permeability soil in different occurrence states

Abstract

The present invention discloses a method for jointly measuring the content of non-aqueous phase pollutants in different occurrence states in low-permeability soil, and belongs to the technical field of soil pollutant improvement. The present invention includes extraction of free non-aqueous phase organic pollutants, extraction of adsorbed non-aqueous phase organic pollutants, extraction of dissolved non-aqueous phase organic pollutants and determination of pollutant content. The present invention adopts a pre-treatment method of graded extraction by oil-absorbing cotton adsorption, liquid-liquid extraction and Soxhlet extraction, combined with gas chromatography instrument detection and analysis technology, to detect the content of organic pollutants in three different occurrence forms of free, dissolved and adsorbed in the soil. This method can accurately and quantitatively analyze the content of three different occurrence forms of organic pollutants in the soil, and will have great application value in soil pollution risk assessment, pollution control and remediation.

Description

Technical Field

[0001] The present invention relates to the technical field of soil pollutant improvement, and in particular to a method for detecting the content of non-aqueous phase pollutants in different occurrence states in low-permeability soil. Background Art

[0002] In soil and groundwater, the pollutants generated by leakage of underground storage tanks and pipeline leakage are mostly volatile organic compounds (VOCs). These volatile organic pollutants are mainly petroleum hydrocarbons and organochlorine solvents, which are industrial raw materials commonly used in modern industrialized countries. Since petroleum hydrocarbons and organochlorine solvents exist in liquid form and are difficult to dissolve in water, they are often called non-aqueous phase liquids (NAPLs). According to the density difference of NAPLs, they can be divided into two categories: those with a density less than water are called light non-aqueous phase liquids (LNAPLs); those with a density greater than water are called dense non-aqueous phase liquids (DNAPLs). Generally speaking, petroleum hydrocarbons, including gasoline, diesel, kerosene, etc., belong to LNAPLs; while organochlorine solvents, such as trichloroethylene and tetrachloroethylene, belong to DNAPLs. The distribution of LNAPLs and DNAPLs in the ground is also significantly different.

[0003] After leaking, organic pollutants seep downward from the surface, enter the aeration zone, saturate the soil, and then migrate vertically to the water table under the action of gravity. During the downward migration, part of it is retained in the pores of the soil, which also pollutes the soil. When organic pollutants migrate through the aeration zone, they are prone to lateral diffusion in low-permeability strata, while in strata with higher permeability, they will migrate vertically downward to the top of the capillary zone under the action of gravity. The pollutants that reach the capillary zone migrate laterally and vertically under the action of capillary force and gravity, forming a pollution interface in the capillary zone. Some organic pollutants enter the aeration zone and pollute the groundwater, while some organic pollutants are retained near the capillary zone. With the leaching effect of rainfall, organic pollutants retained in the aeration zone and capillary zone will further enter the groundwater, causing groundwater pollution.

[0004] In this process, the part of organic pollutants that can move freely under the action of gravity after leakage is called free organic pollutants. Since most of the organic pollutants found so far are volatile organic compounds; once they leak, they will continue to evaporate and enter the surrounding soil gas, and further diffuse due to the concentration gradient. This part is called volatile organic pollutants; and the organic pollutants in the strata will continue to dissolve into the groundwater due to rainfall, irrigation and direct contact with groundwater, migrate and diffuse with the groundwater, forming a contaminated groundwater plume. This part is called dissolved organic pollutants; in the process of soil infiltration, the organic pollutants that remain in the porous medium due to adsorption or capillary action, although they also exist in liquid form, cannot move freely under the action of gravity. This part is called adsorbed organic pollutants.

[0005] The four different states of existence of organic pollutants in the soil, namely free state, volatile state, dissolved state and adsorbed state, determine its migration and transformation process in the soil and its ecological risk. Moreover, the existence form of pollutants in the soil is affected by many factors such as the physical and chemical characteristics of pollutants (such as polarity, molecular structure), physical and chemical properties of soil (such as pH value, organic matter content), environmental conditions (such as temperature, acid rain), etc. The four different existence forms can be transformed as the above factors change. Therefore, it is very necessary to detect and analyze the content of different existence forms of organic pollutants in the soil, which plays an important role in understanding their environmental behavior and their ecological risks. Summary of the invention

[0006] In view of the problems that the total concentration of organic pollutants is commonly used to evaluate the pollution degree of low-permeability soil at home and abroad, and that no targeted detection method is proposed for non-aqueous phase organic pollutants, which is not scientific enough, the present invention adopts a pre-treatment method of oil-absorbing cotton adsorption-liquid-liquid extraction-Soxhlet extraction for graded extraction, combined with gas chromatography detection, to establish an analytical method for the content of three different occurrence forms of non-aqueous phase organic pollutants in low-permeability soil.

[0007] The object of the present invention is achieved in this way. The present invention provides a method for detecting the content of non-aqueous phase pollutants in different occurrence states in low-permeability soil, and the steps are as follows:

[0008] Step 1: Extraction of free non-aqueous organic pollutants

[0009] Weigh 40-50 g of the contaminated soil sample into a 250 mL stoppered conical flask, add 1 mL of 1000 mg / L HgCl2 solution and 100-150 mL of deionized water to prepare contaminated solution 1;

[0010] Put the contaminated solution 1 into a low-temperature shaking box, shake it at a low temperature of 4°C-10°C for 2 hours-3 hours, and quickly use oil-absorbing cotton to absorb the surface solution of the contaminated solution 1 after the shaking is completed, and then seal the oil-absorbing cotton into a headspace bottle. The pollutants extracted from the oil-absorbing cotton are free non-aqueous phase organic pollutants;

[0011] Step 2: Extraction of dissolved non-aqueous organic pollutants

[0012] The contaminated solution 1 after oscillation and absorption of the surface solution in step 1 is recorded as contaminated solution 2, the contaminated solution 2 is filtered using a Buchner funnel to obtain a contaminated filtrate, and the soil obtained after filtration is recorded as a filtered soil sample;

[0013] Place the contaminated filtrate in a 250 mL stoppered Erlenmeyer flask, add 100 L to 150 mL of dichloromethane, and then shake in a shaker for 6 to 7 hours;

[0014] After the shaking is completed, a separatory funnel is used to separate and concentrate the dichloromethane that has dissolved the pollutants. Specifically, the temperature of the electric heating mantle of the separatory funnel is controlled at 40° C.-45° C., and the mixture is concentrated to 10 mL to obtain a concentrated mixed solution of dichloromethane and dissolved non-aqueous organic pollutants;

[0015] Step 3: Extraction of adsorbed non-aqueous organic pollutants

[0016] Add 80g-100g of anhydrous sodium sulfate to the filtered soil sample obtained in step 2, mix thoroughly and grind to make dry soil;

[0017] Place the dry soil in a filter paper bucket, place the filter paper bucket in a Soxhlet extractor, add 300 mL of dichloromethane, and heat the Soxhlet extractor with an electric heating jacket for extraction. The heating temperature is 40°C-45°C, the extraction time is 8 hours-12 hours, and the reflux rate of the Soxhlet extractor is 5-6 times per hour;

[0018] After the extraction is completed, dichloromethane in which the pollutants are dissolved is obtained; the dichloromethane in which the pollutants are dissolved is concentrated using a separatory funnel, specifically, the temperature of the electric heating jacket of the separatory funnel is controlled at 40° C.-45° C., and concentrated to 10 mL, to obtain a concentrated mixed solution of dichloromethane-adsorbed non-aqueous phase organic pollutants;

[0019] Step 4, determination of pollutant content

[0020] Gas chromatography equipment is used to quantitatively determine the content of non-aqueous organic pollutants in the free non-aqueous organic pollutants obtained in step 1, the concentrated mixed solution of dichloromethane-dissolved non-aqueous organic pollutants obtained in step 2, and the concentrated mixed solution of dichloromethane-adsorbed non-aqueous organic pollutants obtained in step 3.

[0021] The present invention adopts a pre-treatment method of oil-absorbing cotton adsorption-dichloromethane organic solvent extraction-Soxhlet extraction and then separates and concentrates the dichloromethane through a constant pressure funnel for graded extraction, and combines gas chromatography analysis technology to detect the content of non-aqueous organic pollutants in three different occurrence forms of free, dissolved and adsorbed in the soil. This method can accurately and quantitatively analyze the different occurrence forms of non-aqueous organic pollutants in the soil, effectively solves the problem of detecting different occurrence phases of non-aqueous organic pollution in low-permeability soil, and provides an effective judgment basis for the evaluation of the risk of non-aqueous organic pollution sites, the judgment of the migration of non-aqueous organic pollutants, and the selection of contaminated site remediation technology. It can select more suitable remediation technology according to the occurrence state of non-aqueous organic pollutants on site, effectively reduce the remediation cost, greatly improve the remediation effect, and optimize the design of remediation plans. DETAILED DESCRIPTION

[0022] The present invention is further described below with reference to the embodiments.

[0023] Example 1, a method for detecting the content of non-aqueous phase pollutants in low-permeability soil in different occurrence states, the steps are as follows:

[0024] Step 1, extraction of free non-aqueous phase organic pollutants: Weigh 40-50 g of contaminated soil sample and put it into a 250 mL stoppered conical flask, add 1 mL of 1000 mg / L HgCl2 solution and 100-150 mL of deionized water to prepare contaminated solution 1;

[0025] The contaminated solution 1 is placed in a low-temperature shaking box and shaken at 4°C-10°C for 2-3 hours. After the shaking, the surface solution of the contaminated solution 1 is quickly absorbed using oil-absorbing cotton, and then the oil-absorbing cotton is sealed in a headspace bottle. The pollutants extracted from the oil-absorbing cotton are free non-aqueous organic pollutants.

[0026] Step 2: Extraction of dissolved non-aqueous organic pollutants

[0027] The contaminated solution 1 after oscillation and absorption of the surface solution in step 1 is recorded as contaminated solution 2, the contaminated solution 2 is filtered using a Buchner funnel to obtain a contaminated filtrate, and the soil obtained after filtration is recorded as a filtered soil sample;

[0028] Place the contaminated filtrate in a 250 mL stoppered Erlenmeyer flask, add 100 L to 150 mL of dichloromethane, and then shake in a shaker for 6 to 7 hours;

[0029] After the shaking is completed, a separatory funnel is used to separate and concentrate the dichloromethane that has dissolved the pollutants. Specifically, the temperature of the electric heating mantle of the separatory funnel is controlled at 40° C.-45° C. and concentrated to 10 mL to obtain a concentrated mixed solution of dichloromethane-dissolved non-aqueous phase organic pollutants.

[0030] Step 3: Extraction of adsorbed non-aqueous organic pollutants

[0031] Add 80g-100g of anhydrous sodium sulfate to the filtered soil sample obtained in step 2, mix thoroughly and grind to make dry soil;

[0032] Place the dry soil in a filter paper bucket, place the filter paper bucket in a Soxhlet extractor, add 300 mL of dichloromethane, and heat the Soxhlet extractor with an electric heating jacket for extraction. The heating temperature is 40°C-45°C, the extraction time is 8 hours-12 hours, and the reflux rate of the Soxhlet extractor is 5-6 times per hour;

[0033] After the extraction is completed, dichloromethane with dissolved pollutants is obtained;

[0034] The dichloromethane in which the pollutants are dissolved is concentrated using a separatory funnel. Specifically, the temperature of the electric heating mantle of the separatory funnel is controlled at 40° C.-45° C. and concentrated to 10 mL to obtain a concentrated mixed solution of dichloromethane-adsorbed non-aqueous organic pollutants.

[0035] Step 4, determination of pollutant content

[0036] Gas chromatography equipment is used to quantitatively determine the content of non-aqueous organic pollutants in the free non-aqueous organic pollutants obtained in step 1, the concentrated mixed solution of dichloromethane-dissolved non-aqueous organic pollutants obtained in step 2, and the concentrated mixed solution of dichloromethane-adsorbed non-aqueous organic pollutants obtained in step 3.

[0037] Example 2: Detection of the content of free, dissolved and adsorbed methyl tert-butyl ether (MTBE) in contaminated soil at a treatment site of a chemical plant.

[0038] Step 1, Free MTBE Extraction

[0039] Weigh 50 g of the contaminated soil sample into a 250 mL stoppered conical flask, add 1 mL of 1000 mg / L HgCl2 solution and 150 mL of deionized water to prepare contaminated solution 1;

[0040] Put the contaminated solution 1 into a low-temperature shaking box and shake it at 6°C for 2 hours. After the shaking, quickly use oil-absorbing cotton to absorb the surface solution of the contaminated solution 1, and then seal the oil-absorbing cotton into a headspace bottle. The pollutant extracted from the oil-absorbing cotton is the free MTBE pollutant;

[0041] Step 2, Dissolved MTBE Extraction

[0042] The contaminated solution 1 after oscillation and absorption of the surface solution in step 1 is recorded as contaminated solution 2, the contaminated solution 2 is filtered using a Buchner funnel to obtain a contaminated filtrate, and the soil obtained after filtration is recorded as a filtered soil sample;

[0043] Place the contaminated filtrate in a 250 mL stoppered Erlenmeyer flask, add 150 mL of dichloromethane, and then shake in a shaker for 7 hours;

[0044] After the shaking is completed, a separatory funnel is used to separate and concentrate the dichloromethane in which the pollutants are dissolved. Specifically, the temperature of the electric heating mantle of the separatory funnel is controlled at 42° C. and concentrated to 10 mL to obtain a concentrated mixed solution of dichloromethane-dissolved MTBE pollutants;

[0045] Step 3, Extraction of Adsorbed MTBE

[0046] Add 100 g of anhydrous sodium sulfate to the filtered soil sample obtained in step 2, mix thoroughly, and then grind to make dry soil;

[0047] Place the dry soil in a filter paper bucket, place the filter paper bucket in a Soxhlet extractor, add 300 mL of dichloromethane, and heat the Soxhlet extractor with an electric heating jacket for extraction. The heating temperature is 45°C, the extraction time is 10 hours, and the reflux rate of the Soxhlet extractor is 5 times per hour.

[0048] After the extraction is completed, dichloromethane with dissolved pollutants is obtained;

[0049] Use a separatory funnel to concentrate the dichloromethane that has dissolved the pollutants. Specifically, control the temperature of the electric heating mantle of the separatory funnel at 43° C. and concentrate to 10 mL to obtain a concentrated mixed solution of dichloromethane-adsorbed MTBE pollutants;

[0050] Step 4, MTBE content determination

[0051] Gas chromatography equipment was used to quantitatively determine the MTBE content in free MTBE pollutants, concentrated mixed solutions of dichloromethane-dissolved MTBE pollutants, and concentrated mixed solutions of dichloromethane-adsorbed MTBE pollutants.

[0052] In this embodiment, the data when the MTBE content is determined by a gas chromatograph are as follows: the specifications of the chromatographic column are a HP-INNOWAX polyethylene glycol capillary column 30m×0.25mm×0.25um; the column box temperature: maintained at 45°C for 0.5min, and increased to 80°C at 30°C / min; the column flow rate: 0.5m / min; the injection mode: split injection, the split ratio is 10:1; the temperature of the FID detector: 250°C, the hydrogen flow rate: 40mL / min, the air flow rate: 300mL / min, the headspace bottle heating temperature: 70°C; the injection needle temperature: 75°C; the transmission line temperature: 110°C; the headspace bottle heating time: 5min; the carrier gas pressure: 52.7psi; the injection volume: 1000uL.

[0053] Measurement results: The free MTBE content in the contaminated soil was 0.2 mg / L, the dissolved MTBE content was 2.25 mg / L, and the adsorbed MTBE content was 2.41 mg / L.

[0054] Example 3: Detection of free, dissolved and adsorbed tetrachloroethylene content in soil at a contaminated soil treatment site

[0055] Step 1: Extraction of free tetrachloroethylene

[0056] Weigh 50 g of the contaminated soil sample into a 250 mL stoppered conical flask, add 1 mL of 1000 mg / L HgCl2 solution and 150 mL of deionized water to prepare contaminated solution 1;

[0057] Put the contaminated solution 1 into a low-temperature shaking box and shake it at 5°C for 2 hours. After the shaking, quickly use oil-absorbing cotton to absorb the surface solution of the contaminated solution 1, and then seal the oil-absorbing cotton in a headspace bottle. The pollutant extracted from the oil-absorbing cotton is the free tetrachloroethylene pollutant.

[0058] Step 2: Extraction of dissolved tetrachloroethylene

[0059] The contaminated solution 1 after oscillation and absorption of the surface solution in step 1 is recorded as contaminated solution 2, the contaminated solution 2 is filtered using a Buchner funnel to obtain a contaminated filtrate, and the soil obtained after filtration is recorded as a filtered soil sample;

[0060] Place the contaminated filtrate in a 250 mL stoppered Erlenmeyer flask, add 150 mL of dichloromethane, and then shake in a shaker for 7 hours;

[0061] After the shaking is completed, a separatory funnel is used to separate and concentrate the dichloromethane that has dissolved the pollutants. Specifically, the temperature of the electric heating mantle of the separatory funnel is controlled at 42° C. and concentrated to 10 mL to obtain a concentrated mixed solution of dichloromethane and dissolved tetrachloroethylene pollutants.

[0062] Step 3: Extraction of adsorbed tetrachloroethylene

[0063] Add 100 g of anhydrous sodium sulfate to the filtered soil sample obtained in step 2, mix thoroughly, and then grind to make dry soil;

[0064] Place the dry soil in a filter paper bucket, place the filter paper bucket in a Soxhlet extractor, add 300 mL of dichloromethane, and heat the Soxhlet extractor with an electric heating jacket for extraction. The heating temperature is 45°C, the extraction time is 10 hours, and the reflux rate of the Soxhlet extractor is 5 times per hour.

[0065] After the extraction is completed, dichloromethane with dissolved pollutants is obtained;

[0066] The dichloromethane in which the pollutants are dissolved is concentrated using a separatory funnel. Specifically, the temperature of the electric heating mantle of the separatory funnel is controlled at 43° C. and concentrated to 10 mL to obtain a concentrated mixed solution of dichloromethane and adsorbed tetrachloroethylene pollutants.

[0067] Step 4, determination of tetrachloroethylene content

[0068] Gas chromatography equipment was used to quantitatively determine the tetrachloroethylene content in free tetrachloroethylene pollutants, concentrated mixed solutions of dichloromethane-dissolved tetrachloroethylene pollutants, and concentrated mixed solutions of dichloromethane-adsorbed tetrachloroethylene pollutants.

[0069] In this embodiment, the data when the content of tetrachloroethylene is measured by gas chromatography is:

[0070] The specifications of the chromatographic column are CD-1301 chromatographic column (60m×0.25mm×1.0μm); gas chromatograph inlet temperature: 200℃; ECD detector temperature: 250℃; column temperature: initial temperature 40℃ maintained for 1min, heated to 100℃ at a rate of 20℃, maintained for 2min; carrier gas is high-purity nitrogen with a flow rate of 1.0mL / min and tail gas flow rate of 40mL / min; non-split injection method is adopted, and the injection volume is 1μL.

[0071] Measurement results: The content of free tetrachloroethylene in the soil of a contaminated soil treatment point was 1.5 mg / L, the content of dissolved tetrachloroethylene was 1.21 mg / L, and the content of adsorbed tetrachloroethylene was 6.22 mg / L.

Claims

1. A method for detecting the content of non-aqueous phase pollutants in different occurrence states in low-permeability soil, characterized in that: Here are the steps: Step 1: Extraction of free non-aqueous organic pollutants Weigh 40-50 g of the contaminated soil sample into a 250 mL stoppered conical flask, add 1 mL of 1000 mg / L HgCl2 solution and 100-150 mL of deionized water to prepare contaminated solution 1; Put the contaminated solution 1 into a low-temperature shaking box, shake it at a low temperature of 4°C-10°C for 2 hours-3 hours, and quickly use oil-absorbing cotton to absorb the surface solution of the contaminated solution 1 after the shaking is completed, and then seal the oil-absorbing cotton into a headspace bottle. The pollutants extracted from the oil-absorbing cotton are free non-aqueous phase organic pollutants; Step 2: Extraction of dissolved non-aqueous organic pollutants The contaminated solution 1 after oscillation and absorption of the surface solution in step 1 is recorded as contaminated solution 2, the contaminated solution 2 is filtered using a Buchner funnel to obtain a contaminated filtrate, and the soil obtained after filtration is recorded as a filtered soil sample; Place the contaminated filtrate in a 250 mL stoppered Erlenmeyer flask, add 100 L to 150 mL of dichloromethane, and then shake in a shaker for 6 to 7 hours; After the shaking is completed, a separatory funnel is used to separate and concentrate the dichloromethane that has dissolved the pollutants. Specifically, the temperature of the electric heating mantle of the separatory funnel is controlled at 40° C.-45° C., and the mixture is concentrated to 10 mL to obtain a concentrated mixed solution of dichloromethane and dissolved non-aqueous organic pollutants; Step 3: Extraction of adsorbed non-aqueous organic pollutants Add 80g-100g of anhydrous sodium sulfate to the filtered soil sample obtained in step 2, mix thoroughly and grind to make dry soil; Place the dry soil in a filter paper bucket, place the filter paper bucket in a Soxhlet extractor, add 300 mL of dichloromethane, and heat the Soxhlet extractor with an electric heating jacket for extraction. The heating temperature is 40°C-45°C, the extraction time is 8 hours-12 hours, and the reflux rate of the Soxhlet extractor is 5-6 times per hour; After the extraction is completed, dichloromethane with dissolved pollutants is obtained; Use a separatory funnel to concentrate the dichloromethane that has dissolved the pollutants. Specifically, control the temperature of the electric heating mantle of the separatory funnel at 40° C.-45° C. and concentrate to 10 mL to obtain a concentrated mixed solution of dichloromethane-adsorbed non-aqueous phase organic pollutants; Step 4, determination of pollutant content The non-aqueous phase organic pollutant content in the free non-aqueous phase organic pollutant obtained in step 1, the concentrated mixed solution of dichloromethane-dissolved non-aqueous phase organic pollutant obtained in step 2, and the concentrated mixed solution of dichloromethane-adsorbed non-aqueous phase organic pollutant obtained in step 3 are quantitatively determined by gas chromatography equipment; The data when the content of non-aqueous organic pollutants was determined by gas chromatography: the specifications of the chromatographic column were HP-INNOWAX polyethylene glycol capillary column 30m×0.25mm×0.25um; the temperature of the column box was maintained at 45℃ for 0.5min, and the temperature was increased to 80℃ at 30℃ / min; the column flow rate was 0.5m / min; the injection method was split injection, and the split ratio was 10:1; the temperature of the FID detector was 250℃, the hydrogen flow rate was 40mL / min, the air flow rate was 300mL / min, the headspace bottle heating temperature was 70℃; the injection needle temperature was 75℃; the transmission line temperature was 110℃; Headspace bottle heating time: 5min; carrier gas pressure: 52.7psi; injection volume: 1000uL; The non-aqueous phase organic pollutant is methyl tert-butyl ether.