Method for identifying and measuring trace contaminant in shield tunneling waste

Abstract

The present invention relates to the technical field of shield tunneling waste measurement, and in particular to a method for identifying and measuring a trace contaminant in shield tunneling waste, comprising the following steps: step S1. pretreating shield tunneling waste; step S2. extracting an anionic surfactant; step S3. removing interfering components; S4. measuring the anionic surfactant; and step S5. calculating the content of the anionic surfactant. In the present invention, fresh shield tunneling waste is directly used for extraction, avoiding anionic surfactant degradation caused by high temperature drying in conventional methods and significantly improving the accuracy of measurement results; in addition, by means of a laboratory shaker, 10-20 samples can be batch-processed at one time, simplifying operation steps, reducing the consumption of a reagent, further effectively avoiding the problem that a separatory funnel is prone to air leakage, improving the operation efficiency and laboratory personnel's safety, and rapidly and efficiently completing extraction of an anionic surfactant in soil. The present invention has wide prospects for application.

Description

A method for identifying and detecting trace pollutants in tunnel boring machine excavation soil Technical Field

[0001] This invention relates to the field of shield tunneling spoil detection technology, and in particular to a method for identifying and detecting trace pollutants in shield tunneling spoil. Background Technology

[0002] Shield tunneling soil is formed by the tunnel boring machine excavating through the strata and then cutting it with the rotating cutterhead. It usually contains a large amount of chemical additives that were injected into the strata during the excavation process to assist in the project. At the construction site, the shield tunneling soil is screened into sand and gravel and silty mud cake. For the silty mud cake that needs to be transported to landfills, its particle size is smaller than that of normal farmland soil, and it contains many chemical additives such as foaming agents left over from the excavation. Its physical properties are special and its chemical composition is complex. Therefore, when conducting chemical testing on specific pollutants in shield tunneling soil, the treatment methods and testing will be different from those for chemical testing of traditional soil.

[0003] Currently, there are no standard methods for determining various trace anionic surfactants in tunnel boring machine (TBM) slag. The identification and detection of trace pollutants in TBM slag mainly includes two parts: extraction and detection of pollutants. The main pollutant in TBM slag, foaming agent, is primarily composed of anionic surfactants, including sodium polyoxyethylene dodecyl ether sulfate (AES), sodium dodecyl sulfate (SDS), and sodium dodecyl ether sulfate sulfonic acid (SLES). There is currently no clear method for extracting anionic surfactants from TBM slag. Methylene blue is commonly used for the detection of anionic surfactants. Traditional spectrophotometric methods, according to national standards, are complex to operate, have low analytical efficiency, and are easily affected by various coexisting substances. For example, Wan Hanxing et al. published a study on the total amount of anionic surfactants in soil using the methylene blue method in "Environmental Science and Technology." However, the fresh soil in this study needs to be dried at 105°C. Since high-temperature treatment can decompose the surfactants in the soil, the detection results will be too low. In addition, the amount of reagent consumed per test in the existing technology is also very large. Moreover, when the extraction process is carried out by manual shaking, the separatory funnel is prone to air leakage, and it is difficult to avoid the toxicity of some reagents to the experimental personnel caused by volatilization.

[0004] Therefore, based on the relevant technologies mentioned above, there is an urgent need to develop a method for identifying and detecting trace pollutants in tunnel boring machine (TBM) slag. Summary of the Invention

[0005] In view of this, the purpose of this invention is to propose a method for identifying and detecting trace pollutants in shield tunnel slag, aiming to provide a method that can detect the content of anionic surfactants in shield tunnel slag in large quantities, quickly and accurately.

[0006] To achieve the above objectives, the present invention provides a method for identifying and detecting trace pollutants in tunnel boring machine slag.

[0007] A method for identifying and detecting trace pollutants in tunnel boring machine excavation soil includes the following steps:

[0008] Step S1. Pre-treatment of tunnel boring machine excavation;

[0009] Step S2. Extraction of anionic surfactants;

[0010] Step S3. Remove interfering components;

[0011] Step S4. Detection of anionic surfactants;

[0012] Step S5. Calculation of anionic surfactant content;

[0013] The pretreatment process of shield tunneling slag in step S1 is as follows: the fresh soil of the shield tunneling slag to be tested is naturally air-dried in a soil bellows for 24-48 hours, the moisture content is controlled at 10%-20%, and it is passed through a 10-mesh sieve and mixed evenly to obtain the shield tunneling slag soil sample. The extraction operation is carried out directly using fresh soil, which avoids the problem of inaccurate test results caused by high temperature treatment.

[0014] The extraction process of the anionic surfactant in step S2 is as follows:

[0015] The soil sample of the tunnel boring machine was placed in a centrifuge tube, the extract was added, and then the mixture was shaken in a horizontal shaker. After shaking, the resulting mixture was filtered through a 5μm needle filter and then distilled in a water bath to obtain the test solution.

[0016] Preferably, the ratio of the shield tunneling slag soil to the extract is 1g:20mL.

[0017] Preferably, the extract is either pure water or an aqueous ethanol solution, wherein the volume ratio of ethanol to water in the aqueous ethanol solution is 60-80:40-50, and ethanol is removed during the water bath distillation process.

[0018] Preferably, the horizontal oscillator has an oscillation frequency of 660-700 r / min and an oscillation time of 8-10 min.

[0019] Preferably, the specific operation for removing interfering components in step S3 is to remove carboxylates, phenols, thiocyanates, cyanates, nitrates, and chlorides from the test solution.

[0020] Preferably, the detection process in step S4 is as follows:

[0021] Step S41. Take the standard solution of anionic surfactant into a centrifuge tube, use phenolphthalein as an indicator, add sodium hydroxide solution dropwise until the solution turns pink, then add sulfuric acid dropwise until the pink color just disappears, to obtain mixture 1;

[0022] Step S42. Add methylene blue solution to mixture 1, fix it on a horizontal shaker and shake to obtain mixture 2;

[0023] Step S43. Add dichloromethane to mixture 2, fix it on a vertical shaker and shake, then let it stand to separate into layers;

[0024] Step S44. Use a dropper to pick up the dichloromethane phase and inject it into a cuvette. Measure the absorbance of the system at a wavelength of 652 nm.

[0025] Step S45. Take the test solution into a centrifuge tube, use phenolphthalein as an indicator, add sodium hydroxide solution dropwise until the solution turns pink, then add sulfuric acid dropwise until the pink color just disappears, to obtain mixture 3;

[0026] Step S46. Add methylene blue solution to mixture 3, fix it on a horizontal shaker and shake to obtain mixture 4;

[0027] Step S47. Add dichloromethane to mixture 4, fix it on a vertical shaker and shake, then let it stand to separate into layers;

[0028] Step S48. Use a dropper to pick up the dichloromethane phase and inject it into a cuvette. Measure the absorbance of the system at a wavelength of 652 nm.

[0029] Preferably, the amount of anionic surfactant used in step S41 is 5 mL, and the centrifuge tube has a specification of 15 mL.

[0030] Preferably, the amount of methylene blue solution used in step S42 is 2 mL.

[0031] Preferably, the frequency of the horizontal oscillator in step S42 is 660-700 r / min, and the oscillation time is 8-10 min.

[0032] Preferably, the amount of dichloromethane used in step S43 is 5 mL.

[0033] Preferably, the oscillation frequency of the vertical oscillator in step S43 is 660-700 r / min, and the oscillation time is 3 min.

[0034] Preferably, the volume of the test solution used in step S45 is 5 mL, and the centrifuge tube has a specification of 15 mL.

[0035] Preferably, the amount of methylene blue solution used in step S46 is 2 mL.

[0036] Preferably, the frequency of the horizontal oscillator in step S46 is 660-700 r / min, and the oscillation time is 8-10 min.

[0037] Preferably, the amount of dichloromethane used in step S47 is 5 mL.

[0038] Preferably, the oscillation frequency of the vertical oscillator in step S47 is 660-700 r / min, and the oscillation time is 3 min.

[0039] The calculation process for the anionic surfactant content in step S5 is as follows:

[0040] Step S51. Dilute the anionic surfactant standard solution with water, shake well, and prepare multiple anionic surfactant standard solutions with different mass concentrations. Measure the absorbance values ​​corresponding to the anionic surfactant standard solutions at different mass concentrations. Plot a standard curve with the anionic surfactant mass concentration as the abscissa and the difference between the measured absorbance value and the absorbance of the zero-mass-concentration anionic surfactant standard solution as the ordinate. Fit the regression equation of the standard curve: y = ax + b, where x is the anionic surfactant content and y is the absorbance.

[0041] Step S52. Substitute the absorbance value of the test solution into the standard curve regression equation to calculate the mass concentration of the anionic surfactant in the test solution.

[0042] Preferably, the anionic surfactant includes sodium polyoxyethylene dodecyl ether sulfate (AES), sodium dodecyl sulfate (SDS), sodium dodecyl ether sulfate sulfonic acid (SLES), sodium α-alkenyl sulfonate (AOS), and sodium linear alkylbenzene sulfonate (LAS).

[0043] The beneficial effects of this invention are:

[0044] 1. Improved detection accuracy: Extraction is performed directly using fresh tunnel boring machine (TBM) slag. This avoids the decomposition of anionic surfactants caused by high-temperature drying in traditional methods, thus significantly improving the accuracy of the detection results.

[0045] 2. Optimized extraction solution selection: Using pure water as the extraction solution avoids the impact of ethanol on the accuracy of dichloromethane extraction and the interference of ethanol's absorbance, further improving the accuracy of the detection results;

[0046] 3. Reduced settling time: By using a 5μm needle filter to immediately filter the extract, the settling time is effectively reduced, avoiding the re-adsorption of anionic surfactants by fine soil particles, and ensuring the purity of the supernatant and the accuracy of subsequent testing.

[0047] 4. Improved operational efficiency and safety: Using 15mL capped centrifuge tubes combined with a vertical shaker for vertical extraction not only simplifies the operation steps, but also allows for batch processing of 10-20 samples at a time using a laboratory shaker, reducing reagent consumption. It also avoids the problem of air leakage from separatory funnels, improving operational efficiency and the safety of laboratory personnel. This method enables rapid and efficient extraction of anionic surfactants from soil, with a recovery rate of 96.3%-104.5%. Attached Figure Description

[0048] To more clearly illustrate the technical solutions in this invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only for this invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0049] Figure 1 is a flowchart of the method for identifying and detecting trace pollutants in tunnel boring machine slag according to the present invention;

[0050] Figure 2 shows the mean and range quality control charts of absorbance for 20 blank experiments in this invention;

[0051] Figure 3 is the standard curve determined by the sodium dodecyl sulfate standard solution in this invention;

[0052] Figure 4 is the standard curve for the determination of sodium fatty alcohol polyoxyethylene ether sulfate standard solution in this invention;

[0053] Figure 5 is the standard curve determined by the sodium α-alkenylsulfonate standard solution in this invention;

[0054] Figure 6 is the standard curve determined by the sodium linear alkylbenzene sulfonate standard solution in this invention. Detailed Implementation

[0055] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments.

[0056] Example 1: A method for identifying and detecting trace pollutants in tunnel boring machine (TBM) slag, comprising the following steps:

[0057] S1. Pretreatment of Shield Tunneling Excavated Soil: Fresh soil from the shield tunneling excavated soil to be tested is naturally air-dried in a soil bellows for 24 hours, controlling the moisture content to 10%. It is then passed through a 10-mesh sieve and mixed thoroughly to obtain the shield tunneling excavated soil sample. Directly using fresh soil for extraction avoids the inaccurate test results caused by high-temperature treatment. To ensure a more homogeneous soil sample and more complete extraction of the analyte, existing pretreatment methods generally involve passing the fresh soil through a 10-mesh sieve and mixing it thoroughly. However, due to the differences in physicochemical properties between shield tunneling excavated soil and general farmland soil—shield tunneling excavated soil has a finer particle size, higher moisture content, and higher viscosity—it is difficult to perform the same sieving and fine-graining methods used for general soil when fresh. To address the problem of large differences in moisture content among shield tunneling excavated soil from different sources, making it difficult to standardize sieving using general methods, this invention optimizes the pretreatment method for shield tunneling excavated soil from different sources. The soil sample to be tested is first subjected to 24 hours of air drying. -48h natural air drying, controlling its moisture content to 10%-20%, facilitates preparation. The main purpose of air drying is to reduce the high moisture content of the shield tunneling soil to below 20%, reducing soil adhesion and making it easier to pass large pieces of shield tunneling soil through a 10-mesh sieve, reducing clogging and adhesion during the screening process. After the shield tunneling soil is naturally air-dried in the soil drying chamber for 24 hours, the anionic surfactants in it will not decompose because the natural air drying conditions are mild and will not affect the thermal stability of the surfactants. Natural air drying is carried out at room temperature. The soil drying chamber usually simulates natural ventilation conditions, with a temperature far below 105℃. Under these conditions, the anionic surfactants have high stability and are not prone to thermal decomposition. Anionic surfactants will only decompose under specific high-temperature conditions. For example, during the high-temperature drying process at 105℃, the molecular structure of the surfactant may change due to the rapid increase in temperature, leading to decomposition.

[0058] S2. Anionic surfactant extraction: Accurately weigh 1g of the prepared soil sample and place it in a 50mL centrifuge tube. Add 20mL of extraction solution to the beaker. The centrifuge tube is a capped centrifuge tube. Place the centrifuge tube in a horizontal shaker and shake at 700r / min for 10min. After shaking, immediately pass the extraction solution through a 5μm needle filter to obtain 5mL of test solution. Different shield foam agents contain different anionic surfactant components, and their solubility in different extraction solutions also varies. It is necessary to select the corresponding pretreatment extraction solution according to the main components of anionic surfactants in the actual shield slag. The extraction solutions include pure water and ethanol aqueous solution. For shield slag mainly composed of sodium polyoxyethylene dodecyl ether sulfate (AES) and sodium α-alkenyl sulfonate (AOS), it has better solubility in pure water and can be used directly as the extraction solution.For shield tunneling slag primarily composed of sodium dodecyl sulfate (SDS), its solubility in ethanol-water solutions is stronger. A 60% ethanol solution was chosen as the extraction solvent, as this ratio of ethanol to water showed good extraction efficiency for anionic surfactants. However, experiments revealed that while using an ethanol-water solution for pretreatment extraction of shield tunneling slag is feasible, subsequent methylene blue assays using the ethanol-containing solution resulted in higher absorbance in the blank group compared to the blank group using the pure water extract. Ethanol and dichloromethane exhibit miscibility, and ethanol also shows absorbance at 652 nm, which negatively impacts the detection of anionic surfactants. Ethanol in the extract can cause interference and lead to inaccurate detection. Therefore, to address the problem of inaccurate results due to ethanol in the extract, this invention uses pure water as the extract or removes ethanol from the ethanol-water solution by distillation at 80°C. This method yields a sample spike recovery rate closest to the spiked amount. This method is based on the principle that ethanol has a lower boiling point than water. By heating, ethanol is evaporated, thus removing it. During distillation, the distillation temperature (80°C) and time are strictly controlled to ensure that sodium dodecyl sulfate (SDS) does not decompose or fail due to high temperatures. During distillation, ethanol evaporates preferentially due to its lower boiling point, while dodecyl sulfate... Sodium dodecyl sulfate (SDS) remained in the solution due to its high boiling point. These distillation conditions ensured effective removal of ethanol while minimizing SDS loss. Experimental data showed a very high recovery rate of SDS after distillation, with no significant change in its composition. Typically, after adding the extractant and shaking to the slag, the supernatant is obtained by allowing it to stand for a certain time. However, in this experiment, the spiked concentration obtained using this method was much lower than the actual value. Experiments were conducted with standing times of 0, 10, and 20 minutes. The results showed that the supernatant contained anionic surfactants. The concentration of the sample decreased with the increase of the settling time. This may be due to the adsorption of anionic surfactants by the fine particles of the soil, which causes the anionic surfactants dissolved in the water to be re-adsorbed onto the soil particles, resulting in a decrease in the content in the final extract. In order to obtain the test liquid immediately after soil shaking extraction, this invention uses a needle filter to filter the extract immediately after shaking extraction to obtain the clear liquid. Among the 0.22, 0.45 and 5 μm pore size needle filters, the 5 μm needle filter with high filtration effect and efficiency was selected to solve this problem. Finally, the sample spiked recovery rate measured by this invention is the highest.

[0059] S3. Removal of Interfering Components: The chemical composition of tunnel boring machine (TBM) slag is complex, potentially containing organic sulfates, sulfonates, carboxylates, phenols, and inorganic thiocyanates, cyanates, nitrates, and chlorides, in addition to the main analytes. These substances can react with methylene blue to form blue complexes soluble in dichloromethane or chloroform, leading to falsely high test results. Therefore, it is necessary to remove these substances from the test solution. Specifically: Methods to avoid carboxylates, phenols, and inorganic thiocyanates, cyanates, nitrates, and chlorides: Backwashing with aqueous solution can eliminate these positive interferences (organic sulfates, sulfonates, cyanates, nitrates, and chlorides). Except for sulfonates), most of the interference from chlorides and nitrates is removed. Aqueous backwashing mainly uses countercurrent water flow to flush away impurities and contaminants attached to the filter media or other surfaces. The specific operation is as follows: place the test solution in the reverse osmosis membrane pressure vessel, rinse the test solution inside the vessel with clean water, open the backwash valve: open the backwash valve of the equipment so that the backwash water can flow into the equipment from the outlet in reverse; control the water flow rate: adjust the backwash water flow rate according to the specific conditions and needs of the equipment. It is generally recommended that the water flow rate be moderate, neither too fast nor too slow.

[0060] S4. Detection of Anionic Surfactants: Take 5 mL of anionic surfactant standard solution into a 15 mL centrifuge tube. Using phenolphthalein as an indicator, add sodium hydroxide solution dropwise until the solution turns pink. Then add sulfuric acid dropwise until the pink color just disappears, obtaining mixture 1. Add 2 mL of methylene blue solution to mixture 1, fix the tube on a horizontal shaker, and shake at a frequency of 700 rpm for 10 min, obtaining mixture 2. Add 5 mL of dichloromethane to mixture 2, fix the tube on a vertical shaker, and shake at a frequency of 700 rpm for 3 min. After shaking, let it stand for a period of time. The dichloromethane phase is drawn up using a dropper and injected into a cuvette. The absorbance of the system at a wavelength of 652 nm is measured. To solve the problem that the upper and lower methylene blue solutions cannot be fully mixed in the existing technology, this invention uses a 15 mL capped centrifuge tube instead of a test tube. A vertical shaker is used to vertically shake and extract the solution to be extracted in the centrifuge tube, which can extract more completely, and the detection value of the same concentration of the test solution is the highest, and the variance of the detection value is smaller. In addition, the amount of each reagent in the national standard method is adjusted in this invention, and a 15 mL capped centrifuge tube is used as the extraction container, which can ensure the effectiveness of the detection while avoiding the leakage of toxic gases during the shaking extraction process and protecting the safety of the experimental personnel.

[0061] S5. Take 5 mL of the test solution into a 15 mL centrifuge tube. Using phenolphthalein as an indicator, add sodium hydroxide solution dropwise until the solution turns pink. Then add sulfuric acid dropwise until the pink color just disappears, resulting in mixture 3. Add 2 mL of methylene blue solution to mixture 3, fix it on a horizontal shaker and shake it at a frequency of 700 r / min for 10 min, resulting in mixture 4. Add 5 mL of dichloromethane to mixture 4, fix it on a vertical shaker and shake it at a frequency of 700 r / min for 3 min. After shaking, let it stand to separate into layers. Use a dropper to pick up the dichloromethane phase and inject it into a cuvette. Measure the absorbance of the system at a wavelength of 652 nm.

[0062] S6. Calculation of Anionic Surfactant Content: Dilute the anionic surfactant standard solution with water, shake well, and prepare multiple anionic surfactant standard solutions with different mass concentrations. Measure the absorbance values ​​corresponding to the anionic surfactant standard solutions at different mass concentrations. Plot a standard curve with the anionic surfactant mass concentration as the abscissa and the difference between the measured absorbance value and the absorbance of the zero-mass-concentration anionic surfactant standard solution as the ordinate. Fit the regression equation of the standard curve: y = ax + b, where x is the anionic surfactant content and y is the absorbance. Substitute the measured absorbance value of the test solution into the regression equation of the standard curve to calculate the mass concentration of the anionic surfactant in the test solution. Since the foaming agent products used in shield tunneling are composed of multiple anionic surfactants, the standard curve for the detection of anionic surfactants in shield tunnel slag should be calculated based on the anionic surfactants that are the main components of the actual foaming agent.

[0063] The anionic surfactant concentration detected by this invention meets the quality control requirements. As shown in the mean control chart in Figure 2, the absorbance of all 20 blank tests is between UCLx and LCLx, and there are no seven consecutive points on the same side of CLx, nor are there seven consecutive points increasing or decreasing, indicating that the system blank is stable and meets the quality control requirements. As shown in the range control chart in Figure 2, the absorbance range of all 20 blank tests is within UCLx. R and LCL R Between, LCL R The horizontal line has a vertical coordinate of 0, and no seven consecutive points lie within CL. R On the same side, there are no seven consecutive points of increase or decrease, indicating that the system error is within the control range and meets the quality control requirements.

[0064] Standard curve and limit of detection:

[0065] Take an appropriate amount of sodium dodecyl sulfate standard solution, dilute it stepwise with water, shake well, and prepare a series of standard solutions with sodium dodecyl sulfate mass concentrations of 0, 0.4, 0.8, 1.2, 1.6, and 2.0 mg / L. Determine the concentration of sodium dodecyl sulfate on the x-axis and subtract the absorbance of the 0 mg / L sodium dodecyl sulfate standard solution from the measured absorbance value on the y-axis, as shown in Figure 3. The results show that the linear range of the sodium dodecyl sulfate standard curve is within 2.0 mg / L, the linear regression equation is y = 0.3827x - 0.0197, and the correlation coefficient is 0.9979. According to the International Union of Pure and Applied Chemistry (IUPAC) standards, the limit of detection (3s / k) is calculated as the ratio of three times the standard deviation (s) to the slope (k) of the linear regression equation, and the result is 0.1947 mg / L.

[0066] Precision and recovery tests: Sodium dodecylbenzenesulfonate standard solutions with mass concentrations of 0.2, 0.6, and 1.2 mg / L were measured six times according to the test method of this invention. The results showed that the relative standard deviations (RSDs) of the measured values ​​were 1.150%, 1.219%, and 1.102%, respectively, which met the requirement of precision (laboratory RSD of the sample) not exceeding 20% ​​as specified in the "Environmental Water Quality Monitoring Quality Assurance Manual" (Second Edition), indicating that the improved method has high precision.

[0067] Samples with a concentration of 0.4 mg / L were taken, and 0.5, 1.75, and 2.5 mL of 2.0 mg / L SDS standard solution were added to each group, respectively, to make the spiked concentrations 0.2, 0.7, and 1.0 mg / L. The recovery rates were 100.9%, 99.8%, and 103.3%, respectively, which meet the requirements of 95%-105% for laboratory spiked recovery rate specified in the "Environmental Water Quality Monitoring Quality Assurance Manual" (Second Edition), indicating that the improved method has high accuracy.

[0068] Detection process for different types of anionic surfactants: Prepare standard solutions of sodium polyoxyethylene dodecyl ether sulfate (AES), sodium α-alkenyl sulfonate (AOS), and sodium linear alkylbenzene sulfonate (LAS) with concentrations of 0, 0.4, 1.2, and 2.0 mg / L, respectively, according to steps S1 to S3 of this invention, with two parallel samples for each group;

[0069] As shown in Figure 4, the linear range of the AES standard curve for polyoxyethylene dodecyl sulfate sodium sulfate is within 2.0 mg / L, the linear regression equation is y = 0.2856x - 0.0054, and the correlation coefficient is 0.9986.

[0070] As shown in Figure 5, the linear range of the standard curve for sodium α-alkenyl sulfonate (AOS) is within 2.0 mg / L, with a linear regression equation of y = 0.334x - 0.0012 and a correlation coefficient of 0.9993. This invention uses a 4:4:2 ratio of sodium polyoxyethylene ether sulfate (AES), sodium α-alkenyl sulfonate (AOS), and sodium dodecyl sulfate (SDS) in the foaming agent for tunnel boring machines to fit the standard curve. The linear regression equations for sodium polyoxyethylene ether sulfate (AES) (y = 0.2856x - 0.0054), sodium α-alkenyl sulfonate (AOS) (y = 0.334x - 0.0041), and sodium dodecyl sulfate (SDS) (y = 0.3827x - 0.0197) are fitted to y = 0.3244x - 0.008.

[0071] Table 1. Differences in physicochemical properties between shield tunnel soil and ordinary soil

[0072] Those skilled in the art should understand that the discussion of any of the above embodiments is merely exemplary and is not intended to imply that the scope of the invention is limited to these examples; within the framework of the invention, the technical features of the above embodiments or different embodiments can also be combined, the steps can be implemented in any order, and there are many other variations of the different aspects of the invention as described above, which are not provided in detail for the sake of brevity.

[0073] This invention is intended to cover all such substitutions, modifications, and variations that fall within the broad scope of the appended claims. Therefore, any omissions, modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this invention should be included within the scope of protection of this invention.

Claims

1. A method for identifying and detecting trace pollutants in tunnel boring machine (TBM) slag, characterized in that, Includes the following steps: Step S1. Pre-treatment of tunnel boring machine excavation; Step S2. Extraction of anionic surfactants; Step S3. Remove interfering components; Step S4. Detection of anionic surfactants: The absorbance was determined using the methylene blue method; Step S5. Calculation of anionic surfactant content; The anionic surfactant extraction process described in step S2 is as follows: Place the shield tunnel slag soil sample in a centrifuge tube, add the extraction solution, and then shake in a horizontal shaker. After shaking, pass the resulting mixture through a 5μm needle filter, and then distill it in a water bath to remove ethanol and obtain the test solution. The extract is an aqueous solution of ethanol.

2. The method for identifying and detecting trace pollutants in shield tunnel slag as described in claim 1, characterized in that, The pretreatment process of shield tunneling slag in step S1 is as follows: the fresh soil of the shield tunneling slag to be tested is naturally air-dried in a soil bellows for 24-48 hours, the moisture content is controlled at 10%-20%, and it is passed through a 10-mesh sieve and mixed evenly to obtain the shield tunneling slag soil sample.

3. The method for identifying and detecting trace pollutants in tunnel boring machine excavation soil according to claim 1, characterized in that, The ratio of the shield tunnel slag soil to the extract is 1g:20mL; the volume ratio of ethanol to water in the ethanol-water solution is 60-80:40-50; the oscillation frequency of the horizontal oscillator is 660-700r / min; and the oscillation time is 8-10min.

4. The method for identifying and detecting trace pollutants in shield tunneling slag as described in claim 1, characterized in that, The operation of removing interfering components in step S3 is to remove carboxylates, phenols, thiocyanates, cyanates, nitrates and chlorides from the test solution.

5. The method for identifying and detecting trace pollutants in tunnel boring machine excavation soil according to claim 1, characterized in that, The detection process described in step S4 is as follows: Step S41. Place the standard solution of anionic surfactant in a centrifuge tube, use phenolphthalein as an indicator, add sodium hydroxide solution dropwise until the solution turns pink, then add sulfuric acid dropwise until the pink color just disappears, to obtain mixture 1; Step S42. Add methylene blue solution to mixture 1, fix it on a horizontal shaker and shake to obtain mixture 2; Step S43. Add dichloromethane to mixture 2, fix it on a vertical shaker and shake, then let it stand to separate into layers; Step S44. Use a dropper to pick up the dichloromethane phase and inject it into a cuvette. Measure the absorbance of the system at a wavelength of 652 nm. Step S45. Take the test solution into a centrifuge tube, use phenolphthalein as an indicator, add sodium hydroxide solution dropwise until the solution turns pink, then add sulfuric acid dropwise until the pink color just disappears, to obtain mixture 3; Step S46. Add methylene blue solution to mixture 3, fix it on a horizontal shaker and shake to obtain mixture 4; Step S47. Add dichloromethane to mixture 4, fix it on a vertical shaker and shake, then let it stand to separate into layers; Step S48. Use a dropper to pick up the dichloromethane phase and inject it into a cuvette. Measure the absorbance of the system at a wavelength of 652 nm.

6. The method for identifying and detecting trace pollutants in tunnel boring machine slag according to claim 5, characterized in that, The amount of anionic surfactant used in step S41 is 5 mL, and the centrifuge tube has a specification of 15 mL.

7. The method for identifying and detecting trace pollutants in tunnel boring machine slag according to claim 5, characterized in that, The amount of methylene blue solution used in step S42 is 2 mL; The frequency of the horizontal oscillator in step S42 is 700 r / min, and the oscillation time is 10 min; The amount of dichloromethane used in step S43 is 5 mL; The vertical oscillator described in step S43 has an oscillation frequency of 700 r / min and an oscillation time of 3 min.

8. The method for identifying and detecting trace pollutants in tunnel boring machine slag according to claim 5, characterized in that, The volume of the test solution used in step S45 is 5 mL, and the centrifuge tube has a specification of 15 mL. The amount of methylene blue solution used in step S46 is 2 mL; The frequency of the horizontal oscillator in step S46 is 660-700 r / min, and the oscillation time is 10 min; The amount of dichloromethane used in step S47 is 5 mL, and the oscillation frequency of the vertical oscillator in step S47 is 660-700 r / min, and the oscillation time is 3 min.

9. The method for identifying and detecting trace pollutants in tunnel boring machine slag according to claim 1, wherein the calculation process for the anionic surfactant content in step S5 is as follows: Step S51. Dilute the anionic surfactant standard solution with water, shake well, and prepare multiple anionic surfactant standard solutions with different mass concentrations. Measure the absorbance values ​​corresponding to the anionic surfactant standard solutions at different mass concentrations. Plot a standard curve with the anionic surfactant mass concentration as the abscissa and the difference between the measured absorbance value and the absorbance of the zero-mass-concentration anionic surfactant standard solution as the ordinate. Fit the regression equation of the standard curve: y = ax + b, where x is the anionic surfactant content and y is the absorbance. Step S52. Substitute the absorbance value of the test solution into the standard curve regression equation to calculate the mass concentration of the anionic surfactant in the test solution; The anionic surfactant is any one of sodium polyoxyethylene dodecyl ether sulfate (AES), sodium dodecyl sulfate (SDS), sodium dodecyl ether sulfate sulfonic acid (SLES), sodium α-alkenyl sulfonate (AOS), and sodium linear alkylbenzene sulfonate (LAS).

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