Method for identifying and detecting trace pollutants in shield muck

Abstract

The invention relates to the technical field of shield muck detection, in particular to a method for identifying and detecting trace pollutants in shield muck, which comprises the following steps: S1, pretreating shield muck, and extracting an anionic surfactant; s2, avoiding interference components; s3, detecting an anionic surfactant; and S4, calculating the content of the anionic surfactant. According to the method, the fresh shield muck is directly adopted for extraction, the phenomenon that in a traditional method, an anionic surfactant is decomposed due to high-temperature drying is avoided, the accuracy of a detection result is remarkably improved, 10-20 samples can be treated in batches at a time through a laboratory oscillator, the operation steps are simplified, meanwhile, the reagent consumption is reduced, and the cost is reduced. The problem that the separating funnel is easy to leak air is effectively avoided, the operation efficiency and the safety of experimenters are improved, the extraction of the anionic surfactant in the soil can be quickly and efficiently completed, and the device has a wide application prospect.

Description

Technical Field

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

[0002] Shield soil is formed when the shield machine excavates in the stratum and then is cut by the rotating cutter head. There is usually a large amount of chemical additives injected into the stratum to assist in engineering excavation. At the construction site, the shield soil will be screened and divided into sand and gravel and silty mud cake. For the silty mud cake that needs to be transported to the landfill, its particle size is smaller than that of normal farmland soil, and it is mixed with many chemical additives such as foaming agents remaining during engineering excavation. It has special physical properties and complex chemical composition. When conducting chemical detection of specific pollutants in shield slag, its treatment method and detection will be different from those of traditional soil chemical detection.

[0003] At present, there is no standard method for the determination of various types of trace anionic surfactants in shield slag. The identification and detection of trace pollutants in shield soil mainly include the extraction of pollutants in shield slag and the detection of pollutants. The main component of the foaming agent of the main pollutant in shield slag is anionic surfactant, mainly including polyoxyethylene dodecyl ether sulfate sodium AES, sodium dodecyl sulfate SDS, sodium dodecyl ether sulfate sulfonic acid SLES and other substances. There is no clear method for the extraction of anionic surfactants in shield slag. Methylene blue is commonly used for the detection of anionic surfactants. Spectrophotometry, the traditional national standard method is complicated to operate, has 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 soil anionic surfactant methylene blue method in "Environmental Science and Technology", but the fresh soil needs to be dried at 105°C. The high temperature treatment will cause the surfactant in the soil to decompose, resulting in a smaller test result. In addition, the consumption of single detection reagents in the existing technology is also very large, and the separatory funnel is prone to leakage when manual shaking is used in the extraction process, and it is difficult to avoid the volatilization of some reagents and the harm to the experimenters.

[0004] Therefore, based on the above-mentioned related technologies, it is urgent to develop a method for identifying and detecting trace pollutants in shield slag. 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 slag, aiming to provide a method that can detect the content of anionic surfactants in shield slag 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 tunneling muck.

[0007] A method for identifying and detecting trace pollutants in shield slag, comprising the following steps: Step S1. Pretreatment of shield slag, extraction with anionic surfactant; Step S2. Avoidance of interfering components; Step S3. anionic surfactant detection; Step S4. Calculating the content of anionic surfactant; The process of shield slag pretreatment in step S1 is as follows: the fresh soil of the shield 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 the soil sample is passed through a 10-mesh sieve and mixed to obtain a shield slag soil sample. Fresh soil is directly used for extraction operation, thereby avoiding the problem of inaccurate test results caused by high-temperature treatment.

[0008] The process of extracting the anionic surfactant in step S1 is as follows: The shield slag soil sample was placed in a centrifuge tube, the extract was added, and then oscillated in a horizontal oscillator. After the oscillation was completed, the obtained mixed solution was filtered through a 5 μm needle filter and then distilled in a water bath to obtain the test solution; Preferably, the usage ratio of the shield slag soil and the extract is 1g:20mL.

[0009] Preferably, the extract is any one of pure water and 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.

[0010] Preferably, the oscillation frequency of the horizontal oscillator is 660-700 r / min, and the oscillation time is 8-10 min.

[0011] Preferably, the operation of avoiding interfering components in step S2 is to remove carboxylates, phenols, thiocyanates, cyanates, nitrates and chlorides in the test solution.

[0012] Preferably, the detection process in step S3 is as follows: Step S31. Take a standard solution of anionic surfactant 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 1; Step S32. Add methylene blue solution to the mixed solution 1, fix it on a horizontal oscillator for oscillation, and obtain a mixed solution 2; Step S33. Add dichloromethane to the mixed solution 2, fix it on a vertical oscillator for oscillation, and let it stand for stratification after oscillation; Step S34. 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 S35. 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 S36. Add methylene blue solution to the mixed solution 3, fix it on a horizontal oscillator for oscillation, and obtain a mixed solution 4; Step S37. Add dichloromethane to the mixed solution 4, fix it on a vertical oscillator for oscillation, and let it stand for stratification after oscillation; Step S38. 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.

[0013] Preferably, the amount of the anionic surfactant used in step S31 is 5 mL, and the specification of the centrifuge tube is 15 mL.

[0014] Preferably, the amount of the methylene blue solution in step S32 is 2 mL.

[0015] Preferably, the frequency of the horizontal oscillator in step S32 is 660-700 r / min, and the oscillation time is 8-10 min.

[0016] Preferably, the amount of dichloromethane used in step S33 is 5 mL.

[0017] Preferably, the oscillation frequency of the vertical oscillator in step S33 is 660-700 r / min, and the oscillation time is 3 min.

[0018] Preferably, the amount of the test solution in step S35 is 5 mL, and the specification of the centrifuge tube is 15 mL.

[0019] Preferably, the amount of the methylene blue solution in step S36 is 2 mL.

[0020] Preferably, the frequency of the horizontal oscillator in step S36 is 660-700 r / min, and the oscillation time is 8-10 min.

[0021] Preferably, the amount of dichloromethane used in step S37 is 5 mL.

[0022] Preferably, the oscillation frequency of the vertical oscillator in step S37 is 660-700 r / min, and the oscillation time is 3 min.

[0023] The process of calculating the content of anionic surfactant in step S4 is as follows: Step S41. 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, wherein x is the anionic surfactant content and y is the absorbance; Step S42: Substitute the absorbance value measured for the test liquid into the standard curve regression equation to calculate the mass concentration of the anionic surfactant in the test liquid.

[0024] Preferably, the anionic surfactant is any one of sodium polyoxyethylene lauryl ether sulfate AES, sodium lauryl sulfate SDS, sodium lauryl ether sulfate sulfonic acid SLES, sodium α-olefin sulfonate AOS, and sodium linear alkylbenzene sulfonate LAS.

[0025] Beneficial effects of the present invention: 1. Improve detection accuracy: By directly using fresh shield slag for extraction, the decomposition of anionic surfactants caused by high-temperature drying in traditional methods is avoided, thereby significantly improving the accuracy of the detection results; 2. Optimize the selection of extraction liquid: Using pure water as the extraction liquid avoids the influence of ethanol on the accuracy of dichloromethane extraction and the absorbance interference of ethanol itself, further improving the accuracy of the test results; 3. Reduce the standing time: By using a 5μm needle filter to immediately filter the extract, the standing time is effectively reduced, avoiding the re-adsorption of anionic surfactants by fine particles of slag, ensuring the purity of the supernatant and the accuracy of subsequent testing; 4. Improve operational efficiency and safety: Use 15mL capped centrifuge tubes combined with vertical oscillators for vertical oscillation extraction, which not only simplifies the operating steps, but also uses laboratory oscillators to process 10-20 samples in batches at a time, reducing reagent consumption, and avoiding the problem of leakage in the separatory funnel, thereby improving operational efficiency and the safety of experimenters. It can quickly and efficiently complete the extraction of anionic surfactants in soil, and the recovery rate can reach 96.3%-104.5%. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In order to more clearly illustrate the technical solutions in the present invention or the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings in the following description are only for the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0027] Figure 1 It is a flow chart of the method for identifying and detecting trace pollutants in shield slag of the present invention; Figure 2 It is the absorbance mean and range quality control chart of 20 groups of blank tests in the present invention; Figure 3 It is the standard curve measured by the sodium dodecyl sulfate standard solution in the present invention; Figure 4 It is the standard curve measured by the fatty alcohol polyoxyethylene ether sodium sulfate standard solution in the present invention; Figure 5 is the standard curve determined by the sodium α-olefin sulfonate standard solution in the present invention; Figure 6 It is the standard curve determined by the linear alkylbenzene sulfonate sodium standard solution in the present invention. DETAILED DESCRIPTION

[0028] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with specific embodiments.

[0029] Example 1: Figure 1 As shown, a method for identifying and detecting trace pollutants in shield slag includes the following steps: S1. Shield slag pretreatment, anionic surfactant extraction: the fresh soil of the shield slag to be tested is naturally air-dried in a soil bellows for 24 hours, the moisture content is controlled at 10%, and the soil is sieved through a 10-mesh sieve and mixed to obtain a shield slag soil sample. Fresh soil is directly used for extraction operation to avoid the problem of inaccurate test results caused by high-temperature treatment. In order to make the soil sample more homogeneous and to more fully extract the test object later, the existing pretreatment method generally uses a 10-mesh sieve and mixing method to prepare the soil sample to be tested for the fresh soil. However, due to the differences in physical and chemical properties between shield slag and general farmland soil, shield slag has a finer particle size, a higher moisture content, and a higher viscosity than general soil. It is difficult to use the method of treating general soil for screening and subdivision in a fresh state. In order to solve the problem that the moisture content of shield slag from different sources is large and it is difficult to uniformly screen using general treatment methods, the present invention uniformly optimizes the pretreatment method of shield slag from different sources, and uses a uniform method to optimize the pretreatment method of the shield slag to be tested. First, air dry it naturally for 24-48 hours to control its moisture content at 10%-20% for easy preparation. The main purpose of air drying is to reduce the high moisture content of shield slag to below 20%, reduce soil adhesion, and facilitate the subsequent large pieces of shield slag to pass through a 10-mesh sieve to reduce the blockage and adhesion of large pieces of slag during the screening process. After the shield slag is naturally air-dried in the soil air-drying box for 24 hours, the anionic surfactant in it 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. The soil air-drying box usually simulates natural ventilation conditions, and the temperature is much lower than 105°C. Under such conditions, the stability of anionic surfactants is relatively high and it is not easy to thermally decompose. Anionic surfactants will only decompose under specific high temperature conditions. For example, during the high-temperature drying process at 105°C, the molecular structure of the surfactant may change due to the rapid increase in temperature, resulting in decomposition; Accurately weigh 1g of the prepared soil sample and place it in a 50mL centrifuge tube, add 20mL of the extract to the beaker. The centrifuge tube is a centrifuge tube with a lid, place the centrifuge tube in a horizontal vibrator, and vibrate at a speed of 700r / min for 10min. After the vibration is completed, immediately pass the extract through a 5μm needle filter to obtain 5mL of the test solution. Different shield foaming agents contain different anionic surfactant components, and their solubility in different extracts is also different. It is necessary to select the corresponding pretreatment extract according to the main components of the anionic surfactant in the actual shield slag. The extract includes pure water and ethanol aqueous solution: for shield slag mainly composed of polyoxyethylene dodecyl ether sodium sulfate AES and α-olefin sulfonate sodium AOS, it has better solubility in pure water, and pure water can be directly used as the extract;For shield slag mainly composed of sodium dodecyl sulfate (SDS), it has stronger solubility in ethanol-water solution. A 60% ethanol-water solution was selected as the extracting solution. Ethanol and water have a good extraction effect on anionic surfactants at this ratio. However, experiments have shown that it is feasible to use ethanol-water solution as the extracting solution for pre-treatment extraction of shield slag. However, if the test solution containing ethanol is directly used for methylene blue method detection, the absorbance of the blank group will be higher than that of the blank group using pure water extract. Ethanol and dichloromethane are miscible, and ethanol also has absorbance at 652nm, which affects the detection of anionic surfactants. Interference will result in inaccurate detection. Therefore, in order to solve the problem of inaccurate results caused by ethanol in the extract, the present invention adopts pure water as the extract or distills the ethanol aqueous solution to be tested at 80°C to remove ethanol to avoid this problem. The sample spike recovery rate 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. Ethanol is evaporated by heating to achieve 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 be decomposed or lost due to high temperature. During the distillation process, ethanol will evaporate first due to its lower boiling point, while dodecane Sodium dodecyl sulfate (SDS) remains in the solution due to its higher boiling point. The distillation conditions ensure the effective removal of ethanol and minimize the loss of sodium dodecyl sulfate (SDS). Experimental data also show that the recovery rate of sodium dodecyl sulfate (SDS) is very high after distillation, and its component content has not changed significantly. Usually, after adding the extracting solution and oscillating the soil, the method for obtaining the clear solution to be tested is to let it stand for a certain period of time to obtain the supernatant. However, the sample spike concentration measured in this way is much lower than the actual value in the experiment. The experiment was conducted by setting the standing time to 0, 10, and 20 minutes. The results showed that the anionic surfactant in the supernatant The detection concentration decreases as the standing time becomes longer. This may be due to the adsorption of anionic surfactants by fine soil particles, which causes the anionic surfactants dissolved in water to be re-adsorbed onto the soil particles, resulting in a reduction in the content in the final extract. In order to obtain the clear liquid to be tested immediately after the soil oscillation extraction, the present invention adopts a needle filter filtration method. After the oscillation extraction is completed, the extract is immediately filtered to obtain a clear liquid, and a 5μm needle filter with higher filtration effect and efficiency is selected from 0.22, 0.45, and 5μm pore size needle filters to solve this problem. Finally, the sample spike recovery rate measured by the present invention is the highest. S2. Avoidance of interfering components: The chemical composition of shield slag is complex, which may contain other organic sulfates, sulfonates, carboxylates, phenols, and inorganic thiocyanates, cyanates, nitrates, and chlorides in addition to the main test substances. These substances will react with methylene blue to form a blue complex soluble in dichloromethane or chloroform, resulting in a high measurement result. Therefore, it is necessary to remove these substances in the test solution, as follows: Avoidance of carboxylates, phenols, and inorganic thiocyanates, cyanates, nitrates, and chlorides: These positive interferences (organic sulfates, sulfonates, phenols, inorganic thiocyanates, cyanates, nitrates, and chlorides) can be eliminated by backwashing with aqueous solution. , sulfonates are excluded), among which the interference of chloride and nitrate is mostly removed. The backwash of aqueous solution mainly uses the reverse flow of water to wash away the impurities and pollutants attached to the filter medium or other surfaces. The specific operation is to place the liquid to be tested in the reverse osmosis membrane pressure vessel, and rinse the liquid to be tested inside the container 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 direction; control the water flow rate: adjust the water flow rate of the backwash water according to the specific situation and needs of the equipment. It is usually recommended that the water flow rate be moderate, not too fast or too slow; S3. Anionic surfactant detection: Take 5mL of anionic surfactant standard solution in a 15mL 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 mixed solution 1, add 2mL of methylene blue solution to mixed solution 1, fix it on a horizontal oscillator for oscillation, the frequency of the horizontal oscillator is 700r / min, the oscillation time is 10min, to obtain mixed solution 2, add 5mL of dichloromethane to mixed solution 2, fix it on a vertical oscillator for oscillation, the oscillation frequency of the vertical oscillator is 700r / min, the oscillation time is 3min, and let it stand for separation after oscillation. layer; the dichloromethane phase is sucked with a rubber-tipped dropper and injected into a cuvette, and the absorbance of the system at a wavelength of 652 nm is measured. In order to solve the problem that the upper and lower layers of methylene blue solution cannot be fully mixed in the prior art, the present invention uses a 15 mL centrifuge tube with a cover to replace the test tube, and uses a vertical oscillator to perform vertical oscillation extraction on 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 present invention adjusts the amount of each reagent in the national standard method, and uses a 15 mL centrifuge tube with a cover as an extraction container, which can ensure the effectiveness of the detection while avoiding the leakage of toxic gases during the oscillation extraction process, and protect the safety of the experimenter; Take 5 mL of the test solution in a 15 mL 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, and obtain mixed solution 3. Add 2 mL of methylene blue solution to mixed solution 3, fix it on a horizontal oscillator for oscillation, the oscillation frequency of the horizontal oscillator is 700 r / min, and the oscillation time is 10 min to obtain mixed solution 4. Add 5 mL of dichloromethane to mixed solution 4, fix it on a vertical oscillator for oscillation, the oscillation frequency of the vertical oscillator is 700 r / min, and the oscillation time is 3 min. After oscillation, let it stand for stratification, 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; S4. Calculation of anionic surfactant content: dilute the anionic surfactant standard solution with water, shake well, and prepare a plurality of anionic surfactant standard solutions of different mass concentrations, determine the absorbance values ​​corresponding to the anionic surfactant standard solutions at different mass concentrations, use the mass concentration of the anionic surfactant as the horizontal coordinate, and use the measured absorbance value minus the absorbance difference of the zero mass concentration anionic surfactant standard solution as the vertical coordinate to draw a standard curve, fit the standard curve regression equation: y=ax+b, wherein x is the anionic surfactant content, y is the absorbance, substitute the measured absorbance value of the test liquid into the standard curve regression equation, and calculate the mass concentration of the anionic surfactant in the test liquid. Since the foaming agent products used in shield construction are compounded with multiple anionic surfactants, for the detection of anionic surfactants in shield slag, the standard curve is calculated according to the anionic surfactants that are the main components in the actual foaming agent; The mass concentration of anionic surfactant detected by the present invention meets the quality control requirements, such as Figure 2 In the mean quality control chart, the absorbance of the 20 blank tests is 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. Figure 2 In the range quality control chart, the absorbance ranges of the 20 blank tests were all within UCL R and LCL R Between, LCL R It is a horizontal line with a vertical coordinate of 0, and there are no 7 consecutive points located on CL R On the same side, there are no 7 consecutive points increasing or decreasing, indicating that the system error is within the control range and meets the quality control requirements; Standard curve and detection limit: Take an appropriate amount of sodium dodecyl sulfate standard solution, dilute it step by step with water, shake it well, and prepare a series of standard solutions with mass concentrations of sodium dodecyl sulfate of 0, 0.4, 0.8, 1.2, 1.6, and 2.0 mg / L, respectively. Determine it according to the test method, and draw a standard curve with the mass concentration of sodium dodecyl sulfate as the abscissa and the measured absorbance value minus the absorbance value of 0 mg / L sodium dodecyl sulfate standard solution as the ordinate, as shown in the following figure: Figure 3 The results showed that the linear range of the sodium dodecyl sulfate standard curve was within 2.0 mg / L, the linear regression equation was y=0.3827x-0.0197, and the correlation coefficient was 0.9979. According to the provisions of the International Union of Pure and Applied Chemistry (IUPAC), the detection limit (3s / k) was calculated as the ratio of 3 times the standard deviation (s) to the slope of the linear regression equation (k), and the result was 0.1947 mg / L.

[0030] Precision and recovery test: According to the test method of the present invention, standard solutions of sodium dodecylbenzene sulfonate with mass concentrations of 0.2, 0.6 and 1.2 mg / L were measured 6 times respectively. The results showed that the relative standard deviations (RSD) of the measured values ​​were 1.150%, 1.219% and 1.102%, respectively, which met the requirement of precision (in-laboratory RSD of samples) not exceeding 20% ​​specified in the Quality Assurance Manual for Environmental Water Quality Monitoring (Second Edition), indicating that the improved method has higher precision.

[0031] Take samples with a concentration of 0.4 mg / L, and 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 concentrations are 0.2, 0.7, and 1.0 mg / L. The recoveries are 100.9%, 99.8%, and 103.3%, respectively, which meet the requirement of 95%-105% for the in-laboratory spiked recovery rate stipulated in the Quality Assurance Manual for Environmental Water Quality Monitoring (Second Edition), indicating that the improved method has a higher accuracy.

[0032] Detection process of different types of anionic surfactants: prepare standard solutions of sodium polyoxyethylene lauryl ether sulfate AES, sodium α-olefin sulfonate AOS, and sodium linear alkylbenzene sulfonate LAS with concentrations 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, and prepare two parallel samples in each group; like Figure 4 The results showed that the linear range of the polyoxyethylene dodecyl sodium sulfate AES standard curve was within 2.0 mg / L, the linear regression equation was y=0.2856x-0.0054, and the correlation coefficient was 0.9986; like 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. The present invention fits the standard curve with a ratio of 4:4:2 of sodium polyoxyethylene ether sulfate AES, sodium α-olefin sulfonate AOS and sodium dodecyl sulfate SDS in the shield construction site foaming agent, and 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 is fitted to y=0.3244x-0.008; like Figure 6 The results showed that the linear range of the standard curve of sodium linear alkylbenzene sulfonate was within 2.0 mg / L, the linear regression equation was y=0.334x-0.0041, and the correlation coefficient was 0.9998.

[0033] Table 1 Differences in physical and chemical properties between shield soil and general soil

[0034] Those skilled in the art should understand that the discussion of any of the above embodiments is merely illustrative 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 may be combined, the steps may be implemented in any order, and there are many other variations of the different aspects of the present invention as described above, which are not provided in detail for the sake of simplicity.

[0035] The present 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 the present invention should be included in the scope of protection 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. Pretreatment of shield slag, extraction with anionic surfactant; Step S2. Avoidance of interfering components; Step S3. anionic surfactant detection; Step S4. Calculation of anionic surfactant content.

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 bellows 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 anionic surfactant extraction process in step S1 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 5μm needle filter and then distilled in a water bath to obtain a test solution.

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

5. The method for identifying and detecting trace pollutants in shield slag according to claim 1 is characterized in that: The operation of avoiding interfering components in step S2 is to remove carboxylates, phenols, thiocyanates, cyanates, nitrates and chlorides in the test solution.

6. The method for identifying and detecting trace pollutants in shield slag according to claim 1 is characterized in that: The detection process in step S3 is as follows: Step S31. 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 S32. Add methylene blue solution to the mixed solution 1, fix it on a horizontal oscillator for oscillation, and obtain a mixed solution 2; Step S33. Add dichloromethane to the mixed solution 2, fix it on a vertical oscillator for oscillation, and let it stand for stratification after oscillation; Step S34. 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 S35. 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 S36. Add methylene blue solution to the mixed solution 3, fix it on a horizontal oscillator for oscillation, and obtain a mixed solution 4; Step S37. Add dichloromethane to the mixed solution 4, fix it on a vertical oscillator for oscillation, and let it stand for stratification after oscillation; Step S38. 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.

7. The method for identifying and detecting trace pollutants in shield slag according to claim 6 is characterized in that: The amount of the anionic surfactant used in step S31 is 5 mL, and the specification of the centrifuge tube is 15 mL.

8. The method for identifying and detecting trace pollutants in shield slag according to claim 6 is characterized in that: The amount of the methylene blue solution in step S32 is 2 mL; In step S32, the frequency of the horizontal oscillator is 700 r / min, and the oscillation time is 10 min; The amount of dichloromethane used in step S33 is 5 mL; In step S33, the oscillation frequency of the vertical oscillator is 700 r / min, and the oscillation time is 3 min.

9. The method for identifying and detecting trace pollutants in shield slag according to claim 6, characterized in that: In step S35, 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 S36 is 2 mL; The frequency of the horizontal oscillator in step S36 is 660-700 r / min, and the oscillation time is 10 min; The amount of dichloromethane used in step S37 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.

10. 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 S4 is as follows: Step S41. 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, wherein x is the anionic surfactant content and y is the absorbance; Step S42. 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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