A method for identifying and detecting trace pollutants in shield muck

Abstract

The present invention relates to the technical field of shield muck detection, and particularly relates to a method for identifying and detecting trace pollutants in shield muck, which comprises the following steps: Step S1. Pretreatment of shield muck, extraction with an anionic surfactant; Step S2. Avoidance of interfering components; Step S3. Detection of an anionic surfactant; Step S4. Calculation of the content of an anionic surfactant. The present invention directly uses fresh shield muck for extraction, avoiding the decomposition of anionic surfactants caused by high-temperature drying in traditional methods, significantly improving the accuracy of detection results. Moreover, by using a laboratory oscillator, 10-20 samples can be processed in batches at one time, simplifying the operation steps, reducing the consumption of reagents at the same time, effectively avoiding the problem of easy air leakage of separating funnels, improving the operation efficiency and the safety of experimental personnel, and can quickly and efficiently complete the extraction of anionic surfactants in soil, having broad application prospects.

Description

Technical Field

[0001] The present invention relates to the technical field of shield muck detection, and particularly to a method for identifying and detecting trace pollutants in shield muck. Background Art

[0002] Shield soil is formed by the shield machine tunneling in the stratum and then being cut by the rotation of the cutter head. It usually remains a large amount of chemical additives injected into the stratum to assist the engineering tunneling. At the construction site, the shield soil will be screened into sand and gravel and silty mud cakes. For the silty mud cakes that need to be transported to the landfill, compared with normal farmland soil, they have smaller particle sizes and are mixed with many chemical additives such as foaming agents remaining during engineering excavation. Their physical properties are special and their chemical compositions are complex. When conducting chemical detection on specific pollution components in shield muck, the treatment methods and detections are different from those of traditional soil chemical detections.

[0003] Currently, there is no standard method for determining various trace anionic surfactants in shield muck. The identification and detection of trace pollutants in shield soil mainly include two parts: the extraction of pollutants in shield muck and the detection of pollutants. The main pollutant in shield muck, the foaming agent, mainly contains anionic surfactants, mainly including substances such as sodium polyoxyethylene dodecyl ether sulfate AES, sodium dodecyl sulfate SDS, and sodium dodecyl ether sulfate sulfonate SLES. There is currently no clear method for the extraction of anionic surfactants in shield muck. The commonly used method for the detection of anionic surfactants is methylene blue spectrophotometry. The traditional national standard method has complex operations, low analysis efficiency, and is easily affected by various coexisting substances. For example, Wan Hanxing et al. published a study on the total amount of anionic surfactants in soil by the methylene blue method in "Environmental Science and Technology". However, the fresh soil therein needs to be dried at 105 °C. Due to the decomposition of surfactants in the soil during high-temperature treatment, the detection results are on the small side. Moreover, the consumption of detection reagents is very large in the existing technology, and when the extraction process uses manual shaking, the separatory funnel is prone to air leakage, making it difficult to avoid the poisoning of experimental personnel caused by the volatilization of some reagents.

[0004] Therefore, according to the above related technologies, it is urgent to develop a method for identifying and detecting trace pollutants in shield muck. Summary of the Invention

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

[0006] Based on the above purpose, the present invention provides a method for identifying and detecting trace pollutants in shield muck.

[0007] A method for identifying and detecting trace pollutants in shield muck, comprising the following steps:

[0008] Step S1. Pretreatment of shield muck, extraction with anionic surfactant;

[0009] Step S2. Avoidance of interfering components;

[0010] Step S3. Detection of anionic surfactant;

[0011] Step S4. Calculation of the content of anionic surfactant;

[0012] The process of the shield muck pretreatment in Step S1 is as follows: The fresh soil of the shield muck to be tested is naturally air-dried in a soil bellows for 24 - 48 h, the moisture content is controlled at 10% - 20%, and it is passed through a 10-mesh sieve and mixed evenly to obtain a shield muck soil sample. The extraction operation is directly carried out with fresh soil, avoiding the problem of inaccurate test results caused by high-temperature treatment.

[0013] The process of the anionic surfactant extraction in Step S1 is as follows:

[0014] The shield muck soil sample is placed in a centrifuge tube, the extraction solution is added, and then it is oscillated in a horizontal shaker. After the oscillation is completed, the obtained mixed solution is passed through a 5-μm needle filter, and then through water bath distillation to obtain a test solution;

[0015] Preferably, the dosage ratio of the shield muck soil to the extraction solution is 1 g:20 mL.

[0016] Preferably, the extraction solution is any one of pure water and an ethanol aqueous solution. The volume ratio of ethanol to water in the ethanol aqueous solution is 60 - 80:40 - 50, and ethanol is removed during the water bath distillation process.

[0017] Preferably, the oscillation frequency of the horizontal shaker is 660 - 700 r / min, and the oscillation time is 8 - 10 min.

[0018] Preferably, the operation of avoiding interfering components in Step S2 is to remove carboxylates, phenols, and thiocyanates, cyanates, nitrates, and chlorides in the test solution.

[0019] Preferably, the process of the detection in Step S3 is as follows:

[0020] Step S31. Take the anionic surfactant standard solution in a centrifuge tube, use phenolphthalein as an indicator, dropwise add sodium hydroxide solution until the solution turns pink, and then dropwise add sulfuric acid until the pink color just disappears to obtain a mixed solution 1;

[0021] Step S32. Add methylene blue solution to the mixed solution 1, fix it on a horizontal shaker and oscillate to obtain a mixed solution 2;

[0022] Step S33. Add dichloromethane to the mixture 2, fix it on a vertical shaker for shaking, and let it stand for layering after shaking.

[0023] Step S34. Use a dropper to suck the dichloromethane phase and inject it into a cuvette, and measure the absorbance of the system at a wavelength of 652 nm.

[0024] Step S35. Take the test solution in a centrifuge tube, use phenolphthalein as an indicator, add sodium hydroxide solution drop by drop until the solution turns pink, and then add sulfuric acid drop by drop until the pink color just disappears to obtain the mixture 3.

[0025] Step S36. Add methylene blue solution to the mixture 3, fix it on a horizontal shaker for shaking to obtain the mixture 4.

[0026] Step S37. Add dichloromethane to the mixture 4, fix it on a vertical shaker for shaking, and let it stand for layering after shaking.

[0027] Step S38. Use a dropper to suck the dichloromethane phase and inject it into a cuvette, and measure the absorbance of the system at a wavelength of 652 nm.

[0028] Preferably, the dosage of the anionic surfactant in step S31 is 5 mL, and the specification of the centrifuge tube is 15 mL.

[0029] Preferably, the dosage of the methylene blue solution in step S32 is 2 mL.

[0030] Preferably, the frequency of the horizontal shaker in step S32 is 660 - 700 r / min, and the shaking time is 8 - 10 min.

[0031] Preferably, the dosage of the dichloromethane in step S33 is 5 mL.

[0032] Preferably, the oscillation frequency of the vertical shaker in step S33 is 660 - 700 r / min, and the oscillation time is 3 min.

[0033] Preferably, the dosage of the test solution in step S35 is 5 mL, and the specification of the centrifuge tube is 15 mL.

[0034] Preferably, the dosage of the methylene blue solution in step S36 is 2 mL.

[0035] Preferably, the frequency of the horizontal shaker in step S36 is 660 - 700 r / min, and the shaking time is 8 - 10 min.

[0036] Preferably, the dosage of the dichloromethane in step S37 is 5 mL.

[0037] Preferably, the oscillation frequency of the vertical oscillator described in step S37 is 660 - 700 r / min, and the oscillation time is 3 min.

[0038] The process of calculating the content of the anionic surfactant described in step S4 is as follows:

[0039] Step S41. Dilute the anionic surfactant standard solution with water, shake well, and prepare anionic surfactant standard solutions with multiple different mass concentrations. Measure the absorbance values corresponding to the anionic surfactant standard solutions at different mass concentrations. Take the anionic surfactant mass concentration as the abscissa and the difference between the measured absorbance value and the absorbance of the anionic surfactant standard solution with zero mass concentration as the ordinate to plot a standard curve, and fit the standard curve regression equation: y = ax + b, where x is the content of the anionic surfactant and y is the absorbance;

[0040] Step S42. Substitute the measured 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.

[0041] Preferably, the anionic surfactant is any one of polyoxyethylene lauryl ether sulfate AES, sodium dodecyl sulfate SDS, sodium dodecyl ether sulfate sulfonic acid SLES, α - olefin sulfonate AOS, and linear alkylbenzene sulfonate LAS.

[0042] Advantages of the present invention:

[0043] 1. Improve detection accuracy: By directly using fresh shield muck for extraction, the decomposition phenomenon of anionic surfactants caused by high - temperature drying in the traditional method is avoided, thus significantly improving the accuracy of the detection results;

[0044] 2. Optimize the selection of extraction liquid: Using pure water as the extraction liquid avoids the influence of ethanol on the extraction accuracy of dichloromethane and the absorbance interference of ethanol itself, further improving the accuracy of the detection results;

[0045] 3. Reduce the standing time: By immediately filtering the extraction liquid with a 5 - μm needle - type filter, the standing time is effectively reduced, avoiding the re - adsorption phenomenon of fine muck particles on anionic surfactants, ensuring the purity of the supernatant and the accuracy of subsequent detections;

[0046] 4. Improve operation efficiency and safety: Use a 15 mL capped centrifuge tube in combination with a vertical oscillator for vertical oscillation extraction. This not only simplifies the operation steps, but also enables batch processing of 10 - 20 samples at a time using a laboratory oscillator, reducing reagent consumption. It also avoids the problem of air leakage in separatory funnels, improving operation efficiency and the safety of laboratory personnel. It can quickly and efficiently complete the extraction of anionic surfactants in soil, with a recovery rate ranging from 96.3% to 104.5%. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] In order to more clearly illustrate the technical solutions in the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the drawings in the following description are only those of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0048] Figure 1 is a flowchart of the method for identifying and detecting trace pollutants in shield muck of the present invention;

[0049] Figure 2 is a quality control chart of the average absorbance and range of 20 groups of blank tests in the present invention;

[0050] Figure 3 is a standard curve for the determination of sodium dodecyl sulfate standard solution in the present invention;

[0051] Figure 4 is a standard curve for the determination of sodium laureth sulfate standard solution in the present invention;

[0052] Figure 5 is a standard curve for the determination of alpha - olefin sulfonate standard solution in the present invention;

[0053] Figure 6 is a standard curve for the determination of linear alkylbenzene sulfonate standard solution in the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0054] To make the objectives, technical solutions, and advantages of the present invention clearer and more understandable, the following further elaborates on the present invention in detail with reference to specific embodiments.

[0055] Example 1: As Figure 1 shown, a method for identifying and detecting trace pollutants in shield muck includes the following steps:

[0056] S1. Pretreatment of shield muck and extraction with anionic surfactant: The fresh soil of the shield muck to be tested is naturally air-dried in a soil wind box for 24 h, with the moisture content controlled at 10%. It is sieved through a 10-mesh sieve and mixed evenly to obtain the shield muck soil sample. The extraction operation is directly carried out using the fresh soil, avoiding the problem of inaccurate test results caused by high-temperature treatment. To make the soil sample more homogeneous and enable more complete extraction of the analyte to be measured in the follow-up, the existing pretreatment method generally prepares the soil sample to be tested by sieving and mixing the fresh soil through a 10-mesh sieve. However, due to the differences in physical and chemical properties between shield muck and general farmland soil, the particle size of shield muck is finer and the moisture content is higher, and its viscosity is also higher than that of general soil. It is difficult to carry out sieving and subdivision treatment using the method for treating general soil in the fresh state. To solve the problem of large differences in moisture content of shield muck from different sources and the difficulty in unified sieving using general treatment methods, the present invention uniformly optimizes the pretreatment method for shield muck from different sources. The soil sample to be tested is first air-dried naturally for 24 - 48 h, and its moisture content is controlled at 10% - 20%, which is convenient for preparation. The main purpose of air-drying is to reduce the high moisture content of the shield muck to below 20%, reduce the soil adhesiveness, and facilitate passing the large pieces of shield muck through a 10-mesh sieve in the follow-up, reducing the blockage and adhesion phenomena of large pieces of muck during the sieving process. After the shield muck is naturally air-dried in the soil wind box for 24 h, the anionic surfactant therein will not decompose because the natural air-drying conditions are mild and will not affect the thermal stability of the surfactant. Natural air-drying is carried out at room temperature, and the soil wind box usually simulates natural ventilation conditions, with the temperature much lower than 105°C. Under such conditions, the stability of the anionic surfactant is relatively high and it is not prone to thermal decomposition. The anionic surfactant will decompose only under specific high-temperature conditions. For example, during the high-temperature drying process at 105°C, due to the sharp increase in temperature, the molecular structure of the surfactant may change, resulting in decomposition;

[0057] Accurately weigh 1 g of the prepared soil sample and place it in a 50 mL centrifuge tube. Add 20 mL of the extraction solution to the beaker. The centrifuge tube is a capped centrifuge tube. Place the centrifuge tube in a horizontal shaker and shake it at a speed of 700 r / min for 10 min. Immediately after the shaking is completed, filter the extraction solution through a 5 μm needle filter to obtain 5 mL of the test solution. Different shield foam agents contain different anionic surfactant components, and their solubilities in different extraction solutions also vary. It is necessary to select the corresponding pretreatment extraction solution according to the main components of the anionic surfactants in the actual shield muck. The extraction solutions include pure water and ethanol aqueous solution: For shield muck mainly composed of sodium dodecyl polyoxyethylene ether sulfate AES and α-olefin sulfonate AOS, it has better solubility in pure water, and pure water can be directly used as the extraction solution;For shield muck mainly composed of sodium dodecyl sulfate (SDS), it has stronger solubility in an ethanol aqueous solution. An aqueous solution with an ethanol content of 60% is selected as the extraction solution. Ethanol and water have a good extraction effect on anionic surfactants at this ratio. However, through experiments, it is found that using an ethanol aqueous solution as the extraction solution for pre-treatment of shield muck for extraction is feasible. But if the test solution containing ethanol is directly used for methylene blue method detection subsequently, the absorbance of the blank group will be higher than that of the blank group using pure water as the extraction solution. Ethanol and dichloromethane are miscible, and ethanol also has absorbance at 652 nm, which causes interference in the detection of anionic surfactants, resulting in inaccurate detection. Therefore, to solve the problem of inaccurate results caused by the presence of ethanol in the extraction solution, the present invention uses pure water as the extraction solution or distills the ethanol aqueous test solution at 80 °C to remove ethanol to avoid this problem. The recovery rate of the spiked sample measured by this method is closest to the spiked amount. This method is based on the principle that the boiling point of ethanol is lower than that of water. By heating, ethanol evaporates, thereby achieving the purpose of removing ethanol. During the distillation process, the distillation temperature (80 °C) and time are strictly controlled to ensure that sodium dodecyl sulfate (SDS) will not decompose or be lost due to high temperature. During the distillation process, ethanol will evaporate preferentially due to its lower boiling point, while sodium dodecyl sulfate (SDS) remains in the solution due to its higher boiling point. These distillation conditions ensure the effective removal of ethanol while minimizing the loss of sodium dodecyl sulfate (SDS) to the greatest extent. Experimental data also show that the recovery rate of sodium dodecyl sulfate (SDS) after distillation is very high, and its component content has not changed significantly. Usually, after adding the extraction solution to the muck and oscillating for extraction, the method to obtain the test clear solution is to let it stand for a certain time to obtain the supernatant. However, in the experiment, the spiked concentration of the sample measured by this method is much smaller than the actual value. The experiment was carried out by setting the standing times of 0, 10, and 20 minutes. The results show that the detected concentration of anionic surfactants in the supernatant decreases as the standing time becomes longer. This may be due to the adsorption of anionic surfactants by fine muck particles, causing the anionic surfactants dissolved in water to be re-adsorbed onto the muck particles, resulting in a decrease in the content in the final extraction solution. To be able to obtain the test clear solution immediately after soil oscillation extraction, the present invention uses a needle filter for filtration. After completing the oscillation extraction, the extraction solution is immediately filtered to obtain the clear solution, and a 5-μm needle filter with higher filtration effect and efficiency is selected from 0.22-μm, 0.45-μm, and 5-μm pore size needle filters to solve this problem. Finally, the recovery rate of the spiked sample measured by the present invention is the highest;

[0058] S2. Avoidance of interfering components: The chemical composition of shield muck is complex, which may contain other organic sulfates, sulfonates, carboxylates, phenols, and inorganic thiocyanates, cyanates, nitrates, and chlorides other than the main analytes. These substances will react with methylene blue to form blue complexes soluble in dichloromethane or chloroform, resulting in higher measurement results. Therefore, these substances in the test solution need to be removed, as follows: Methods for avoiding carboxylates, phenols, and inorganic thiocyanates, cyanates, nitrates, and chlorides: These positive interferences (except for organic sulfates and sulfonates) can be eliminated by backwashing with an aqueous solution. Most of the interferences of chlorides and nitrates are removed. Backwashing with an aqueous solution mainly flushes away impurities and pollutants attached to the filter medium or other surfaces through the reverse-flowing water. The specific operation is to place the test solution in a reverse osmosis membrane pressure vessel and rinse the test solution inside the vessel with clean water, and then open the backwash valve: Open the backwash valve of the equipment so that the backwash water can flow reversely into the equipment from the water outlet; Control the water flow rate: Adjust the water flow rate of the backwash water according to the specific situation and requirements of the equipment. Usually, it is recommended that the water flow rate be moderate, neither too fast nor too slow;

[0059] S3. Detection of anionic surfactants: Take 5 mL of anionic surfactant standard solution into a 15 mL centrifuge tube. Using phenolphthalein as an indicator, gradually add sodium hydroxide solution drop by drop until the solution turns pink, and then gradually add sulfuric acid drop by drop until the pink color just disappears to obtain mixture 1. Add 2 mL of methylene blue solution to mixture 1, fix it on a horizontal shaker and shake. The frequency of the horizontal shaker is 700 r / min, and the shaking time is 10 min to obtain mixture 2. Add 5 mL of dichloromethane to mixture 2, fix it on a vertical shaker and shake. The oscillation frequency of the vertical shaker is 700 r / min, and the shaking time is 3 min. After shaking, let it stand for stratification; Use a dropper to suck the dichloromethane phase and inject it into a cuvette, and measure the absorbance of the system at a wavelength of 652 nm. To solve the problem in the prior art that the methylene blue solution in the upper and lower layers cannot be fully mixed evenly, the present invention uses a 15 mL centrifuge tube with a lid to replace the test tube, and uses a vertical shaker to perform vertical shaking extraction on the solution to be extracted in the centrifuge tube, which can achieve more complete extraction, the highest detection value of the test solution with the same concentration, and a smaller variance of the detection value. In addition, in the present invention, the dosages of various reagents in the national standard method are adjusted, and a 15 mL centrifuge tube with a lid is used as the extraction container, which can ensure the detection effectiveness and avoid the leakage of toxic gases during the shaking extraction process, protecting the safety of experimental personnel;

[0060] Take 5 mL of the test solution in a 15 mL centrifuge tube. Using phenolphthalein as an indicator, gradually add sodium hydroxide solution drop by drop until the solution turns pink. Then, gradually add sulfuric acid drop by drop until the pink color just disappears to obtain mixture 3. Add 2 mL of methylene blue solution to mixture 3, fix it on a horizontal shaker and shake. The shaking frequency of the horizontal shaker is 700 r / min, and the shaking time is 10 min to obtain mixture 4. Add 5 mL of dichloromethane to mixture 4, fix it on a vertical shaker and shake. The shaking frequency of the vertical shaker is 700 r / min, and the shaking time is 3 min. After shaking, let it stand for layering. Use a dropper to suck the dichloromethane phase and inject it into a cuvette, and measure the absorbance of the system at a wavelength of 652 nm.

[0061] S4. Calculation of anionic surfactant content: Dilute the anionic surfactant standard solution with water, shake well, and prepare anionic surfactant standard solutions with multiple different mass concentrations. Measure the absorbance values corresponding to the anionic surfactant standard solutions at different mass concentrations. Use the anionic surfactant mass concentration as the abscissa and the difference between the measured absorbance value and the absorbance of the anionic surfactant standard solution with zero mass concentration as the ordinate to plot a standard curve, and fit the standard curve regression equation: 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 standard curve regression equation to calculate the mass concentration of the anionic surfactant in the test solution. Since the foam agent products used in shield construction are composed of multiple anionic surfactants, for the detection of anionic surfactants in shield muck, calculate the standard curve according to the main component anionic surfactant in the actual foam agent.

[0062] The mass concentration of the anionic surfactant detected by the present invention meets the quality control requirements. For example, Figure 2 in the mean value quality control chart, the absorbances of 20 groups of blank tests are all between UCLx and LCLx, and there are no 7 consecutive points on the same side of CLx, nor are there 7 consecutive points increasing or decreasing, indicating that the system blank is stable and meets the quality control requirements. For example, Figure 2 in the range quality control chart, the ranges of the absorbances of 20 groups of blank tests are all between UCL R and LCL R . LCL R is a horizontal line with a vertical coordinate of 0, and there are no 7 consecutive points on the same side of CL R , nor are there 7 consecutive points increasing or decreasing, indicating that the systematic error is within the control range and meets the quality control requirements.

[0063] Standard curve and detection limit:

[0064] Take an appropriate amount of sodium dodecyl sulfate standard solution, dilute it step by step 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 respectively. Measure according to the test method. Use the sodium dodecyl sulfate mass concentration as the abscissa and the measured absorbance value minus the absorbance value of the 0 mg / L sodium dodecyl sulfate standard solution as the ordinate to draw a standard curve. As 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 regulations of the International Union of Pure and Applied Chemistry (IUPAC), calculate the detection limit (3s / k) by the ratio of 3 times the standard deviation (s) to the slope (k) of the linear regression equation. The result is 0.1947 mg / L.

[0065] Precision and recovery tests: Measure the sodium dodecyl benzene sulfonate standard solutions with mass concentrations of 0.2, 0.6, and 1.2 mg / L six times respectively according to the test method of the present invention. The results show that the relative standard deviations (RSD) of the measured values are 1.150%, 1.219%, and 1.102% in sequence, meeting the requirement that the precision (RSD in the laboratory for samples) specified in the "Environmental Water Quality Monitoring Quality Assurance Manual" (Second Edition) is not greater than 20%, indicating that the precision of the improved method is relatively high.

[0066] Take a sample with a concentration of 0.4 mg / L, add 0.5, 1.75, and 2.5 mL of 2.0 mg / L SDS standard solution to each group respectively, so that the spiked concentration is 0.2, 0.7, and 1.0 mg / L. The recovery rates are 100.9%, 99.8%, and 103.3% in sequence, meeting the requirement that the spiked recovery rate in the laboratory specified in the "Environmental Water Quality Monitoring Quality Assurance Manual" (Second Edition) is 95% - 105%, indicating that the accuracy of the improved method is relatively high.

[0067] Detection process of different anionic surfactant types: Prepare standard solutions with concentrations of polyoxyethylene lauryl ether sulfate AES, α-olefin sulfonate AOS, and linear alkylbenzene sulfonate LAS of 0, 0.4, 1.2, and 2.0 mg / L respectively according to the process of steps S1 to S3 of the present invention. Each group has two parallel samples;

[0068] As Figure 4 The results show that the linear range of the polyoxyethylene lauryl sulfate AES standard curve is within 2.0 mg / L. The linear regression equation is y = 0.2856x - 0.0054, and the correlation coefficient is 0.9986;

[0069] As Figure 5The results show that the linear range of the standard curve of sodium α-olefin sulfonate AOS is within 2.0 mg / L, the linear regression equation is y = 0.3277x - 0.0012, and the correlation coefficient is 0.9993. In this invention, the standard curve is fitted with the ratio of sodium polyoxyethylene ether sulfate AES, sodium α-olefin sulfonate AOS, and sodium dodecyl sulfate SDS in the shield construction site foam agent being 4:4:2. The linear regression equation of sodium polyoxyethylene ether sulfate AES is y = 0.2856x - 0.0054, the linear regression equation of sodium α-olefin sulfonate AOS is y = 0.334x - 0.0041, and the linear regression equation of sodium dodecyl sulfate SDS is y = 0.3827x - 0.0197, which are fitted into y = 0.3244x - 0.008;

[0070] As Figure 6 The results show that the linear range of the standard curve of linear alkylbenzene sulfonate is within 2.0 mg / L, the linear regression equation is y = 0.334x - 0.0041, and the correlation coefficient is 0.9998.

[0071] Table 1 Differences in physical and chemical properties between shield soil and general soil

[0072]

[0073] Those of ordinary skill in the art should understand that the discussion of any of the above embodiments is only exemplary and is not intended to imply that the scope of the present invention is limited to these examples; under the concept of the present invention, the technical features in the above embodiments or different embodiments can also be combined, the steps can be implemented in any order, and there are many other variations in different aspects of the present invention as described above, which are not provided in detail for the sake of brevity.

[0074] The present invention aims 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 principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for identifying and detecting trace pollutants in shield slag, characterized in that: The following steps are involved: Step S1. Pre-treatment of shield slag; Step S2. Anionic surfactant extraction; Step S3. removing interfering components; Step S4. Detection of anionic surfactant: measuring absorbance by methylene blue method; Step S5. Calculating the content of anionic surfactant; The anionic surfactant extraction process in step S2 is as follows: placing the shield slag soil sample in a centrifuge tube, adding the extract, and then oscillating in a horizontal oscillator. After the oscillation is completed, the obtained mixed solution is filtered through a 5 μm needle filter, and then distilled in a water bath to remove ethanol to obtain a test solution; The extract is an ethanol aqueous solution.

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

3. The method for identifying and detecting trace pollutants in shield slag according to claim 1 is characterized in that: The usage ratio of the shield slag soil and the extract is 1g:20mL; the volume ratio of ethanol and 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 slag according to claim 1 is characterized in that: The operation of removing interfering components in step S3 is to remove carboxylates, phenols, thiocyanates, cyanates, nitrates and chlorides in the test solution.

5. The method for identifying and detecting trace pollutants in shield slag according to claim 1 is characterized in that: The detection process in step S4 is as follows: Step S41. Place a standard solution of anionic surfactant in a centrifuge tube, add sodium hydroxide solution dropwise with phenolphthalein as an indicator until the solution turns pink, and then add sulfuric acid dropwise until the pink color just disappears, to obtain a mixed solution 1; Step S42. Add methylene blue solution to the mixed solution 1, fix it on a horizontal oscillator for oscillation, and obtain a mixed solution 2; Step S43. Add dichloromethane to the mixed solution 2, fix it on a vertical oscillator for oscillation, and let it stand for stratification after oscillation; Step S44. Use a rubber-tipped dropper to absorb the dichloromethane phase, inject it into a cuvette, and measure the absorbance of the system at a wavelength of 652 nm; Step S45. Take the test solution in a centrifuge tube, use phenolphthalein as an indicator, add sodium hydroxide solution dropwise until the solution turns pink, and then add sulfuric acid dropwise until the pink color just disappears to obtain a mixed solution 3; Step S46. Add methylene blue solution to the mixed solution 3, fix it on a horizontal oscillator for oscillation, and obtain a mixed solution 4; Step S47. Add dichloromethane to the mixed solution 4, fix it on a vertical oscillator for oscillation, and let it stand for stratification after oscillation; Step S48. Use a rubber-tipped dropper to absorb the dichloromethane phase, inject it into a cuvette, and measure the absorbance of the system at a wavelength of 652 nm.

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

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

8. The method for identifying and detecting trace pollutants in shield slag according to claim 5 is characterized in that: In step S45, the amount of the test solution is 5 mL, and the specification of the centrifuge tube is 15 mL; The amount of the methylene blue solution 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, the oscillation frequency of the vertical oscillator in step S47 is 660-700 r / min, and the oscillation time is 3 min.

9. According to the method for identifying and detecting trace pollutants in shield slag according to claim 1, the process of calculating the content of the anionic surfactant in step S5 is as follows: Step S51. dilute the anionic surfactant standard solution with water, shake well, and prepare a plurality of anionic surfactant standard solutions with different mass concentrations, measure the absorbance values ​​corresponding to the anionic surfactant standard solutions at different mass concentrations, and draw a standard curve with the mass concentration of the anionic surfactant as the horizontal axis and the difference between the measured absorbance value and the absorbance of the zero mass concentration anionic surfactant standard solution as the vertical axis, and fit the standard curve regression equation: y=ax+b, where x is the anionic surfactant content and y is the absorbance; Step S52. Substituting the absorbance value measured by the test liquid into the standard curve regression equation to calculate the mass concentration of the anionic surfactant in the test liquid; The anionic surfactant is any one of polyoxyethylene sodium lauryl ether sulfate AES, sodium lauryl sulfate SDS, sodium lauryl ether sulfate sulfonic acid SLES, sodium α-olefin sulfonate AOS and linear alkylbenzene sulfonate LAS.

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