A heavy metal in situ characterization system coupled with high-resolution technology to simulate changes in soil micro-region redox conditions

Abstract

The invention discloses a heavy metal in-situ characterization system coupled with a high-resolution technology for simulating soil micro-region redox changes, comprising a soil box ventilation system, an optode membrane working system and an adsorption membrane processing and analysis system, wherein the soil box ventilation system comprises an oxygen pump, a soil box device and a ventilation hose, the optode membrane working system comprises an oxygen optode membrane, and the adsorption membrane processing and analysis system comprises a DGT adsorption membrane; the soil box device comprises a breathable hose, a rear cover plate and a two-dimensional plane exposed after the rear cover plate is disassembled for sequential attachment of the DGT adsorption membrane and the oxygen optode membrane, the breathable hose is used to form an aerobic / anoxic micro-interface inside the soil; the optode membrane working system is used to analyze the oxygen concentration of the two-dimensional plane on the oxygen optode membrane, and the adsorption membrane processing and analysis system is used to analyze the two-dimensional distribution of the effective state concentration of the metal on the DGT adsorption membrane.

Description

Technical Field

[0001] The present invention belongs to the field of heavy metal migration and transformation assessment in contaminated soil, and more specifically, relates to a heavy metal in-situ characterization system coupled with a high-resolution technology capable of simulating soil micro-region redox changes. Background Art

[0002] With the rapid development of science and technology, heavy metals are found in air, soil, water, and even food. In particular, sudden heavy metal pollution has become a global environmental problem, posing a serious threat to the ecological environment and food safety. After heavy metals enter the soil, due to the significant spatial heterogeneity of the soil, various environmental processes such as rainfall runoff and microbial activity will cause the migration and transformation of heavy metals in the soil environment, posing a serious threat to the health of animals, plants and humans. Various environmental factors such as pH, Eh, organic matter, and iron and manganese oxides in the soil environment will affect the migration and transformation of heavy metals. Among them, Eh, as an important physical and chemical property of soil, will change during periodic river water impact plains, groundwater level fluctuations, or flooding irrigation, changing the redox environment of the soil, affecting the redox, adsorption-desorption, and precipitation and dissolution processes of heavy metals in the soil, thereby affecting the effective concentration of heavy metals.

[0003] At present, the research on the migration and transformation of heavy metals in soil caused by changes in redox conditions is mainly carried out by ex situ research methods, that is, after collecting soil from the contaminated area, it is stored and transported to the laboratory, and the soil after the experiment is graded and extracted by flooded soil column experiment or anaerobic culture batch experiment. However, the above research methods have certain defects. First, during the sample collection, transportation, storage and pretreatment process, the redox conditions are very easy to change, and the form and bioavailability of heavy metals change, causing deviations in the experimental results; secondly, when exploring the migration and transformation mechanism of heavy metals, the multi-step analysis process of different heavy metals and soil physical and chemical properties causes high experimental and time costs; finally, the experimental results of most current studies are limited to the migration and transformation process of heavy metals at the centimeter level on a one-dimensional scale, ignoring the difference in effective concentration of heavy metals caused by changes in Eh in the microscale, and lacking higher resolution result analysis on a two-dimensional plane.

[0004] Thin film gradient diffusion technology (DGT) is an in-situ passive sampling technology used to determine the effectiveness of solutes. The adsorption of DGT can establish a concentration gradient in the local environment around it, promote dissociation in the solid phase, and the measured diffusion flux can better reflect the dynamic equilibrium process of heavy metals in the soil. Planar optode membrane technology (PO) is an in-situ high-resolution technology based on the principle of fluorescence sensing. The sensing membrane is made of fluorescent dyes. After being installed and placed in the environment, it can be excited by a specific light source to collect the fluorescence image of the sensing membrane in situ. After processing, a two-dimensional quantitative distribution image of the object to be tested can be obtained. At present, PO technology can be used to detect pH, O2, pCO2, NH4, etc. in soil or sediment, among which O2 is the most widely used. In recent years, with the development of DGT and PO technology, the combination of the two in-situ high-resolution technologies has gradually been used. Coupling high-resolution DGT (HR-DGT) and planar optode to establish a new two-dimensional high-resolution (millimeter-submillimeter level) sensing technology can achieve in-situ analysis of the concentration and effectiveness of elements with different valence states, and explore the influence mechanism of environmental factors on their two-dimensional plane and micro-area in soil.

[0005] In summary, building an in situ characterization system for heavy metals coupled with high-resolution technology for complex soil environments is not only an effective means to explore in situ the effective state distribution law and migration and transformation mechanism of heavy metals during the dynamic changes of redox conditions in micro-areas, but also a research focus in the field of heavy metal migration and transformation assessment in contaminated soils. Summary of the invention

[0006] 1. Problem to be solved

[0007] In the prior art, most studies on the effects of redox changes on the migration and transformation of heavy metals are conducted through traditional ex situ methods such as batch experiments with continuous saline / intermittent flooding or graded extraction of soil column sampling on site. The experimental operations are cumbersome and highly destructive to the actual soil redox environment. The form and effectiveness of heavy metals are prone to change, which affects the accuracy of the experiment. Therefore, it is impossible to monitor and capture the redox conditions of the soil dynamic equilibrium process in a two-dimensional plane and in soil micro-areas as well as the effective concentration of heavy metals in real time.

[0008] The present invention aims to provide a high-resolution in-situ characterization system which is simple to operate, highly accurate, and capable of real-time monitoring and capturing of effective state concentrations of heavy metals.

[0009] 2. Technical solution

[0010] In order to solve the above problems, the technical solution adopted by the present invention is as follows:

[0011] The present invention provides a heavy metal in-situ characterization system coupled with a high-resolution technology for simulating soil micro-region redox changes, comprising a soil box ventilation system, an optode membrane working system and an adsorption membrane processing and analysis system, wherein the soil box ventilation system comprises an oxygen pump, a soil box device and a ventilation hose for passing oxygen into the soil box device, the adsorption membrane processing and analysis system comprises a DGT adsorption membrane and corresponding analysis equipment, and the optode membrane working system comprises an oxygen optode membrane and corresponding analysis equipment; the soil box device comprises a breathable hose, a rear cover plate and a two-dimensional plane exposed after the rear cover plate is disassembled for sequential attachment of the DGT adsorption membrane and the oxygen optode membrane, the breathable hose is used to form an aerobic / anoxic micro-interface inside the soil; the optode membrane working system is used to analyze the oxygen concentration of the two-dimensional plane on the oxygen optode membrane, and the adsorption membrane processing and analysis system is used to analyze the two-dimensional distribution of the effective state concentration of the metal on the DGT adsorption membrane.

[0012] The heavy metal micro-area characterization system of the present invention can simulate redox micro-interfaces with different oxygen contents, does not destroy the overall solid-liquid environment of the soil during dynamic changes, applies the oxygen photoelectrode membrane and the adsorption membrane in situ on the two-dimensional plane of the soil box, and simultaneously obtains the oxygen concentration and heavy metal effective state concentration information at the aerobic / anoxic micro-interface of the soil. It is easy to operate and provides an important basis for explaining the migration and transformation of pollutants in the soil.

[0013] As a further improvement, the optode membrane working system of the present invention utilizes an optode membrane fluorescence sensor, which can directly record high-resolution two-dimensional measurement of O2 in the environment through a camera under the excitation of an LED light source. The adsorption membrane processing and analysis system realizes high-resolution (μm level) two-dimensional distribution of effective state concentrations of heavy metals or non-metals in soil by combining DGT adsorption membrane with laser ablation-inductively coupled plasma mass spectrometry technology.

[0014] The DGT adsorption membrane includes various adsorption membranes for different elements known in the prior art, such as S 2- The AgI adsorption film with diffusion flux, the DGT adsorption film is produced by DGT Research Co., Ltd. in the UK. The oxygen photoelectrode film is prepared by mixing oxygen quencher phenylporphyrin platinum, antenna dye MY, polystyrene and dichloromethane in a certain proportion to form a thin film. The film has a fast response time, uniform dye distribution, and can present different fluorescence responses to different oxygen concentrations. The oxygen photoelectrode film can also be a purchased photoelectrode film.

[0015] As a further improvement of the present invention, the soil box device includes a plexiglass box, a breathable hose, a track-etched membrane, a cover plate with a mold, a sealing side plate, and a rear cover plate. The cover plate with a mold and the sealing side plate are used to seal the device before the soil sample is loaded. The cover plate with a mold is also used to produce a groove in the soil sample that matches the shape of the breathable hose. The track-etched membrane is tightly attached to the two-dimensional plane of the soil containing the breathable hose. The rear cover plate is used to seal the soil box device after the breathable hose and the track-etched membrane are loaded; after the rear cover plate is removed, the two-dimensional plane is exposed for sequential attachment of the DGT adsorption membrane and the oxygen photoelectrode membrane.

[0016] As a further improvement of the present invention, the soil box device can simultaneously fill soil at different depths of the site to achieve synchronous experiments on multiple soils. The rear cover plate and the cover plate with mold can be used and replaced at different stages. The cover plate with mold is used when filling the soil box to form a groove in the soil that is conducive to the embedding of the breathable hose. The rear cover plate is used during the ventilation experiment. After the rear cover plate is removed, a two-dimensional plane can be exposed, which is convenient for the attachment of the oxygen photoelectrode membrane and the adsorption membrane to the detection application, and at the same time, it can ensure that the stability of the redox conditions during the ventilation process is not changed.

[0017] As a further improvement of the present invention, the cover plate with mold is a cover plate with U-shaped mold; the intermediate specifications of the soil box device are 10×1.5×18.5cm, the air permeable hose is U-shaped expanded polytetrafluoroethylene, which has the properties of air permeability and water-tightness, the inner diameter×outer diameter of the hose is 2×3mm, the pore size on the hose is between 0.2-0.5μm, the air permeability is 60%-80%, and after the gas is introduced, it can diffuse from the hose to the soil on both sides to form an aerobic / anoxic micro-interface.

[0018] As a further improvement of the present invention, the soil box ventilation system also includes an airflow control board. The gas generated by the oxygen pump can be pumped into the airflow control board through a ventilation hose. The airflow control board contains multiple gas flow meters. The gas flow meters are equipped with regulating valves. The gas flow rate of each ventilation pipeline can be adjusted separately through the regulating valves to transmit airflows of different sizes to the soil box device.

[0019] As a further improvement of the present invention, the adsorption film processing and analysis system includes a DGT adsorption film, a dry gel analyzer, laser ablation and an inductively coupled plasma mass spectrometer; the photoelectrode membrane system includes an oxygen photoelectrode membrane, an LED light source, a camera and a computer.

[0020] As a further improvement of the present invention, the track-etched membrane has a pore size of 0.2 μm and a thickness of about 10 μm.

[0021] As a further improvement of the present invention, the present invention provides a method for in-situ characterization of heavy metals by coupling high-resolution technology to simulate soil micro-region redox changes, comprising the following steps:

[0022] 1) Seal the soil box device, load the soil samples into the soil box device layer by layer, and compact them;

[0023] 2) Remove the cover of the soil box device, bury the air-permeable hose, attach the track-etched membrane, make full contact with the soil layer, and seal the device;

[0024] 3) Continue to introduce oxygen, and after the soil ventilation is stable, remove the rear cover to expose the two-dimensional plane, and place the DGT adsorption film tightly on the two-dimensional plane of the soil box device, accurately record the contact time between the adsorption film and the soil, and remove the adsorption film and use the corresponding analysis equipment to in-situ analyze the two-dimensional distribution of the metal effective state concentration obtained on the DGT adsorption film;

[0025] 4) The oxygen photoelectrode membrane is closely attached to the DGT adsorption membrane, and after being in contact with the soil to equilibrium, the oxygen concentration distribution in the two-dimensional plane on the oxygen photoelectrode membrane is analyzed in situ using corresponding analysis equipment.

[0026] As a further improvement of the present invention, the cover plate is a cover plate with a U-shaped mold, the air-permeable hose is a U-shaped expanded polytetrafluoroethylene hose, and the detachable rear cover plate in step 2) is disassembled to expose a U-shaped groove, and the U-shaped expanded polytetrafluoroethylene hose is embedded and installed in the U-shaped groove.

[0027] As a further improvement of the present invention, in step 4), the DGT adsorption film is tightly attached to the two-dimensional plane of the soil box device, and the contact time between the adsorption film and the soil is accurately recorded. The adsorption film is removed and spread on the polyethersulfone filter membrane, and covered with a layer of flat and clean plastic film. After light pressing at room temperature for 8 hours, it is dried using a dry glue instrument for 2 hours, and quantitative analysis is performed using laser ablation and inductively coupled plasma mass spectrometry to obtain the metal effective state concentration in the two-dimensional plane.

[0028] As a further improvement of the present invention, in step 4), after the oxygen photoelectrode membrane is in contact with the soil to reach equilibrium, the LED light source is turned on to emit excitation light of corresponding wavelength to evenly irradiate the oxygen photoelectrode membrane, and the oxygen photoelectrode membrane is excited to produce fluorescence of specific wavelength. The camera captures the fluorescence image of the entire soil box device. The whole process is controlled by a computer. The fluorescence image can be saved in the computer and data processing is performed according to the response curve of the oxygen photoelectrode membrane to oxygen to obtain the monitoring result.

[0029] 3. Beneficial effects

[0030] Compared with the prior art, the present invention has the following beneficial effects:

[0031] (1) The heavy metal in situ characterization system provided by the present invention is coupled with a high-resolution technology that simulates the redox changes in soil micro-regions. The designed aerated soil box system can simulate different ventilation conditions to form an aerobic / anoxic micro-interface inside the soil of the soil box. Coupled with the oxygen photoelectrode membrane-DGT technology, it can simultaneously obtain in situ a two-dimensional high-resolution distribution image of the soil oxygen content and the effective state concentration of heavy metals in the dynamic equilibrium process of the soil after ventilation without destroying the redox environment of the soil, and more comprehensively explain the migration and transformation mechanism of heavy metals in the soil micro-region during the dynamic equilibrium process promoted by redox.

[0032] (2) The heavy metal in-situ characterization system coupled with high-resolution technology for simulating soil micro-region redox changes provided by the present invention can not only form an aerobic / anoxic micro-interface in the soil micro-region during soil aeration, but also be easily disassembled; and a two-dimensional photoelectrode membrane and a high-resolution DGT adsorption membrane are simultaneously assembled, so that the physical and chemical properties of the soil and the two-dimensional distribution high-resolution image acquisition of the effective state of heavy metals in the soil can be obtained simultaneously during the redox dynamic change process without destroying the soil redox environment, and quantitative analysis can be performed on them, so as to more accurately and effectively assess the environmental risks of heavy metals in the soil environment and explore the migration and transformation mechanism of heavy metals. However, most of the traditional studies on the migration and transformation of heavy metals by redox have ignored the changes in soil redox conditions in the micro-region, and can only realize the monitoring of Eh and heavy metal concentration at a point within the centimeter scale. If high-resolution two-dimensional data is to be obtained, a large number of electrode supports or a large number of experiments are required, which undoubtedly greatly increases the cost and complicates the measurement process. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 is an overall schematic diagram of the in-situ characterization system of the present invention;

[0034] Figure 2 A three-dimensional perspective view of the soil box device of the present invention;

[0035] Figure 3 is the standard curve of the oxygen photoelectrode membrane analysis system in Example 2;

[0036] Figure 4 The standard curve of the target element Cr(VI) of the DGT adsorption membrane analysis system in Example 2;

[0037] Figure 5 The two-dimensional image of the oxygen photoanode film after (A) air and (B) oxygen are introduced into the soil box in Example 3;

[0038] Figure 6 This is a distribution diagram of dissolved oxygen percentage in the soil around the oxygen photoanode membrane of the hose before and after oxygen is passed through in Example 3;

[0039] Figure 7The S around the hose obtained by the adsorption glue before and after ventilation in Example 3 2- Diffusion flux distribution trend;

[0040] In the figure: 1. oxygen pump; 2. ventilation hose; 3. air flow control board; 4. gas flow meter; 5. soil box device; 6. track etching mold; 7. DGT adsorption membrane; 8. oxygen photoelectrode membrane; 9. LED light source; 10. camera; 11. computer; 12. polyethersulfone filter membrane; 13. dry glue instrument; 14. laser ablation; 15. inductively coupled plasma mass spectrometer; 16. expanded polytetrafluoroethylene hose; 17. plexiglass box; 18. rear cover; 19. sealing side panel; 20. fastening screws. DETAILED DESCRIPTION

[0041] The present invention is further described in detail below in conjunction with the embodiments and drawings. The following description is only a preferred embodiment of the present invention and does not limit the present invention in other forms. Any technician familiar with the profession may use the technical content disclosed below to change it into an equivalent embodiment with equivalent changes. Any simple modification or equivalent change made to the following embodiments based on the technical essence of the present invention without departing from the content of the present invention is within the protection scope of the present invention.

[0042] Example 1

[0043] This embodiment provides a heavy metal in-situ characterization system coupled with a high-resolution technology that simulates soil micro-area redox changes, which consists of a soil box ventilation system, a photoelectrode membrane working system, and an adsorption membrane processing and analysis system.

[0044] The soil box ventilation system is composed of an oxygen pump 1, an air flow control board 3, a ventilation hose 2 and a soil box device 5. The gas generated by the oxygen pump can be pumped into the air flow control board 3 through the ventilation hose 2. The air flow control board contains multiple gas flow meters. The gas flow meters are equipped with regulating valves, which can adjust the gas flow of each ventilation pipeline separately to transmit airflows of different sizes to the soil box device 5.

[0045] The soil box device 5 includes an organic glass box, a U-shaped expanded polytetrafluoroethylene hose 16, a track etching membrane 6, a U-shaped mold cover, a rear cover 18, a sealing side plate 19 and a fastening screw 20. The U-shaped mold cover and the sealing side plate 19 are used to seal the device before the soil sample is loaded. The U-shaped mold cover is also used to produce a U-shaped groove in the soil sample that matches the shape of the U-shaped expanded polytetrafluoroethylene hose 16, that is: remove the U-shaped mold cover, leave the U-shaped groove, bury the U-shaped expanded polytetrafluoroethylene hose 16, attach a track etching membrane 6 with a pore size of 0.2μm and a thickness of about 10μm, fully contact with the soil layer, install the detachable organic glass plate and the sealing side plate 19, screw on the fastening screws 20, and seal the device. The track-etched membrane 6 is in close contact with the two-dimensional soil plane containing the air-permeable hose, and the rear cover 18 is used to seal the soil box device 5 after the air-permeable hose and the track-etched membrane 6 are loaded; after the rear cover 18 is removed, the two-dimensional plane is exposed for the DGT adsorption membrane 7 and the oxygen photoelectrode membrane 8 to be attached in sequence.

[0046] The middle specification of the soil box device 5 is 10×1.5×18.5cm. The air permeable hose is U-shaped expanded polytetrafluoroethylene, which has the properties of air permeability and water-tightness. The inner diameter×outer diameter of the hose is 2×3mm. The pore size on the hose is between 0.2-0.5μm, and the air permeability is 60%-80%. After the gas is introduced, it can diffuse from the hose to the soil on both sides to form an aerobic / anoxic micro-interface.

[0047] Adsorption film processing and analysis system: The adsorption film processing and analysis system includes a DGT adsorption film 7, a dry glue instrument 13, a laser ablation 14, and an inductively coupled plasma mass spectrometer 15. In the adsorption film processing and analysis system, the DGT adsorption film 7 is tightly attached to the two-dimensional plane of the soil box, and the contact time between the DGT adsorption film 7 and the soil is accurately recorded. The DGT adsorption film 7 is removed and laid flat on the polyethersulfone filter membrane 12, and a layer of flat clean plastic film is covered on it. After light pressing for 8 hours at room temperature, it is dried for 2 hours using a dry glue instrument 13, and quantitative analysis is performed using a combination of laser ablation 14 and inductively coupled plasma mass spectrometer 15 to obtain the metal effective state concentration on the two-dimensional plane of the soil box.

[0048] Photoanode membrane working system: The photoanode membrane working system includes an oxygen photoanode membrane 8, an LED light source 9, a camera 10, and a computer 11; in the photoanode membrane working system, the oxygen photoanode membrane 8 is tightly attached to the two-dimensional plane of the soil box, and after contacting with the soil until the gas flow is balanced, the 455nm LED light source 9 is turned on to emit the corresponding wavelength excitation light uniformly to illuminate the oxygen photoanode membrane 8, and the oxygen photoanode membrane 8 is excited to produce fluorescence, and the camera 10 captures the fluorescence image of the entire soil box. The whole process is controlled by the computer 10, and the fluorescence image can be saved in the computer to perform data processing according to the response curve of the oxygen photoanode membrane 8 to the oxygen concentration to obtain the monitoring result.

[0049] Example 2

[0050] This example is a stability verification of the oxygen photoelectrode membrane system and the DGT adsorption membrane analysis system.

[0051] 1) Calibration of oxygen photoelectrode membrane: The photoelectrode membrane needs to be calibrated before use, that is, a strip of membrane of appropriate size is cut out and attached to the inside of a quartz glass box of a size close to that of the soil box. Fill the water with tap water saturated with oxygen. A nitrogen / oxygen mixture or the addition of Na2SO3 can be used to adjust the dissolved oxygen content in the water. After the oxygen concentration stabilizes, take pictures under the excitation of 455nm LEDs. The fluorescence intensity value of the photoelectrode membrane at each oxygen content is compared with the intensity value at the anaerobic concentration as the vertical coordinate, and the oxygen content value is used as the horizontal coordinate for nonlinear fitting. It can be seen that R 2 =0.991, such as Figure 3 As shown, this confirms the stability of the O2 photoelectrode film and the reliability of the data in subsequent research. Therefore, in the subsequent use of the photoelectrode film, the obtained fluorescence intensity ratio is substituted into the standard curve to obtain the corresponding oxygen concentration value.

[0052] 2) Quantification of DGT adsorption film in adsorption gel analysis system: Before using the adsorption film analysis system to obtain the effective concentration of heavy metals on the adsorption film, prepare DGT adsorption gel with standard concentration in advance for debugging instrument parameters and final quantitative analysis. Prepare a sufficient number of ordinary disc-type DGTs, put them into a solution containing a certain concentration of the target element, stir them under constant temperature conditions, and take out 6 DGTs from the solution at different times. Three of them are used to elute the adsorption gel according to the conventional DGT method, and the concentration of the target element is determined by ICP-MS, and the mass and density of the target element on the adsorption film are calculated. The other three are dried according to the operating methods in the reference adsorption film analysis system for LA analysis. Based on the above data, a linear relationship between the signal value of the LA test sample and the amount of the target element on the adsorption film is established, and the data fitting can obtain R 2 =0.998, such as Figure 4 In subsequent analysis, the signal value of the sample adsorption film can be substituted into the above linear relationship for calculation, thus realizing the in-situ quantitative calculation of the element flux of the adsorption film.

[0053] Example 3

[0054] The device of Example 1 was used to study the influence of the change of redox conditions on the change of soil oxygen content and element migration and transformation at the aerobic / anoxic micro-interface of the soil.

[0055] The steps are as follows: fill the lower half of the soil box device 5 with soil at a depth of 3m at a site in Shanghai, and fill the upper half with soil at a depth of 1m at a site in Shanghai, and keep the density uniform as much as possible during the filling process. Then remove the cover of the soil box with a U-shaped mold, install the U-shaped expanded polytetrafluoroethylene hose 16 without damaging the soil, attach a track etching membrane 6 with a pore size of 0.2 μm and a thickness of about 10 μm, and make it fully contact with the soil layer, seal it with waterproof tape, and then install the rear cover 18 back, and then use a slow gravity water flow tool to slowly wet the soil block at a uniform speed until the saturated water content is reached. The outer periphery of the filled soil box is wrapped with aluminum foil and placed in a dark place. Let it stabilize for two weeks while maintaining a moist state, and then oxygen / air is passed into the hose of the soil box. During the ventilation process, regularly observe and take fluorescence photos of the oxygen photoelectrode membrane. After the aerobic / anoxic microinterface of the soil is basically stable, the photoelectrode membrane and adsorption gel are used to perform two-dimensional in situ characterization of the oxygen content changes O2 and the effective state concentration of elements at the aerobic / anoxic microinterface (around the hose) in the soil.

[0056] Figure 5 A and B are two-dimensional images of dissolved oxygen captured by oxygen photoelectrode membrane on the two-dimensional plane of the soil box after air and oxygen were introduced, respectively. It can be seen that for soils from different depths, continuous introduction of air makes the oxygen content around the hose diffuse significantly different. In the soil from 1m depth (upper part of the soil box), it can be observed that the oxygen content around the hose increases significantly, forming an obvious aerobic / anoxic micro-interface, but the oxygen content in the soil from 3m depth (lower part of the soil box) does not change significantly. Compare the changes in the percentage of dissolved oxygen in the soil around the hose before and after oxygen is introduced ( Figure 6 ) It can be seen that there is an obvious oxygen content gradient extending from the hose to the surrounding soil, and the oxygen content increases significantly after the oxygen is introduced. Before the oxygen is introduced, the dissolved oxygen saturation percentage of the soil far from the hose is less than 25%, and the dissolved oxygen saturation percentage of the soil near the hose is as high as about 111%. However, after the oxygen is introduced, the dissolved oxygen saturation percentage rises to 265%. This shows that the O2 photoelectrode membrane can accurately capture the distribution and migration of oxygen content at the aerobic / anoxic micro-interface on both sides of the hose in situ.

[0057] like Figure 7 As shown in A, select any point in the vertical direction of the soil at two depths to calculate S 2- Diffusion flux, when air is introduced, S from the soil at a depth of 1m and from the soil at a depth of 3m can be clearly seen. 2- The diffusion flux difference of S in the soil at 1m depth 2- Diffusion flux at 27 μmol cm -2 h -1 to 39 μmol cm -2 h -1In the soil at a depth of 3 m, the concentration of -2 h -1 At the same time, it can be seen that as air is input, S 2- The flux changes significantly from the hose to the soil on both sides. Figure 7 In B, after the air is introduced, the hose is at S 2- The lowest value was 17 μmol cm -2 h -1 , soil S on both sides of the hose 2- Up to 40 μmol cm -2 h -1 However, in the oxygen group, due to the higher net oxygen flow, the S 2- Most of it may be oxidized, and the S 2- The gradient change of S is weak. 2- The diffusion flux was lower than 20 μmol cm in soil at both depths. -2 h -1 , horizontally S 2- The diffusion flux from the center of the hose to the soil on both sides did not change significantly. The above results show that the system can be used to control the S 2- The diffusion flux can be used to characterize the aerobic / anoxic micro-interface in different soil properties.

Claims

1. A heavy metal in-situ characterization system coupled with high-resolution technology simulating soil micro-area redox changes, characterized by: It comprises a soil box ventilation system, a photoelectrode membrane working system and an adsorption membrane processing and analysis system, wherein the soil box ventilation system comprises an oxygen pump (1), a soil box device (5) and a ventilation hose (2) for passing oxygen into the soil box device (5), the adsorption membrane processing and analysis system comprises a DGT adsorption membrane (7), and the photoelectrode membrane working system comprises an oxygen photoelectrode membrane (8); The soil box device (5) comprises a permeable hose, a rear cover plate (18), and a two-dimensional plane exposed after the rear cover plate (18) is disassembled to which a DGT adsorption film (7) and an oxygen photoelectrode film (8) are sequentially attached, wherein the permeable hose is used to form an aerobic / anoxic micro-interface inside the soil; the photoelectrode film working system is used to analyze the oxygen concentration of the two-dimensional plane on the oxygen photoelectrode film (8), and the adsorption film processing analysis system is used to analyze the two-dimensional distribution of the metal effective state concentration on the DGT adsorption film (7); The soil box device (5) also includes an organic glass box body (17), a breathable hose, a track-etched membrane (6), a cover plate with a mold, a sealing side plate (19), and a rear cover plate (18). The cover plate with a mold and the sealing side plate (19) are used to seal the device before the soil sample is loaded. The cover plate with a mold is also used to generate a groove in the soil sample that matches the shape of the breathable hose. The track-etched membrane (6) is tightly attached to the two-dimensional soil plane containing the breathable hose (2). The rear cover plate (18) is used to seal the soil box device (5) after the breathable hose and the track-etched membrane (6) are loaded. After the rear cover plate (18) is disassembled, the two-dimensional plane is exposed, which is used for sequentially attaching the DGT adsorption membrane (7) and the oxygen photoelectrode membrane (8).

2. The heavy metal in-situ characterization system coupled with high-resolution technology for simulating soil micro-area redox changes according to claim 1, characterized in that: The permeable hose is an expanded polytetrafluoroethylene hose (16), the pore size of the hose is between 0.2 and 0.5 μm, and the air permeability is between 60% and 80%. After the gas is introduced, it can diffuse from the expanded polytetrafluoroethylene hose (16) to the soil on both sides, forming an aerobic / anoxic micro-interface.

3. The heavy metal in-situ characterization system coupled with high-resolution technology for simulating soil micro-area redox changes according to claim 2, characterized in that: The cover plate with a mold is a cover plate with a U-shaped mold, and the expanded polytetrafluoroethylene hose (16) is U-shaped.

4. The heavy metal in-situ characterization system coupled with high-resolution technology for simulating soil micro-area redox changes according to claim 1, characterized in that: The soil box ventilation system also includes an airflow control plate (3). The gas generated by the oxygen pump (1) can be pumped into the airflow control plate (3) through a ventilation hose (2). The airflow control plate (3) includes a plurality of gas flow meters (4). The gas flow meters (4) are provided with regulating valves. The gas flow rate of each ventilation pipeline can be adjusted through the regulating valves to transmit airflows of different sizes to the soil box device (5).

5. The heavy metal in-situ characterization system coupled with high-resolution technology for simulating soil micro-area redox changes according to claim 1, characterized in that: The adsorption film processing and analysis system comprises a DGT adsorption film (7), a dry gel analyzer (13), laser ablation (14) and an inductively coupled plasma mass spectrometer (15); the photoelectrode film working system comprises an oxygen photoelectrode film (8), an LED light source (9), a camera (10) and a computer (11).

6. A method for in-situ characterization of heavy metals by coupling high-resolution technology to simulate soil micro-area redox changes using the system of claim 1, characterized in that: The following steps are involved: 1) The soil box device (5) is sealed, and the soil samples are loaded into the soil box device (5) layer by layer and compacted; 2) Remove the cover of the soil box device, bury the air-permeable hose, attach the track-etched membrane (6), make it fully contact with the soil layer, and seal the device; 3) Continue to introduce oxygen, and after the soil ventilation is stable, remove the rear cover (18) to expose the two-dimensional plane, and place the DGT adsorption film (7) closely on the two-dimensional plane of the soil box device (5), accurately record the contact time between the adsorption film and the soil, remove the adsorption film, and use the corresponding analysis equipment to in-situ analyze the two-dimensional distribution of the metal effective state concentration obtained on the DGT adsorption film (7); 4) The oxygen photoelectrode membrane (8) is closely attached to the DGT adsorption membrane (7), and after being in contact with the soil until equilibrium is reached, the oxygen concentration distribution on the two-dimensional plane of the oxygen photoelectrode membrane (8) is analyzed in situ using corresponding analysis equipment.

7. The in-situ characterization method for heavy metals coupled with high-resolution technology for simulating soil micro-area redox changes according to claim 6, characterized in that: The cover plate is a cover plate with a U-shaped mold, and the air-permeable hose is a U-shaped expanded polytetrafluoroethylene hose (16). In step 2), the detachable rear cover plate is disassembled to expose a U-shaped groove, and the U-shaped expanded polytetrafluoroethylene hose (16) is embedded and installed in the U-shaped groove.

8. The in-situ characterization method for heavy metals coupled with high-resolution technology simulating soil micro-area redox changes according to claim 6, characterized in that: In step 4), the DGT adsorption film (7) is tightly attached to the two-dimensional plane of the soil box device (5), and the contact time between the adsorption film and the soil is accurately recorded. The adsorption film is removed and spread flat on the polyethersulfone filter membrane, and then covered with a layer of flat clean plastic film. After light pressing for a period of time at room temperature, it is dried using a dry glue instrument (13), and quantitative analysis is performed using laser ablation (14) and inductively coupled plasma mass spectrometry (15) to obtain the metal effective state concentration in the two-dimensional plane.

9. The heavy metal in-situ characterization method coupled with high-resolution technology for simulating soil micro-area redox changes according to claim 6, characterized in that: In step 5), after the oxygen photoelectrode membrane (8) contacts the soil to a balance, the LED light source (9) is turned on to emit excitation light of a corresponding wavelength to evenly illuminate the oxygen photoelectrode membrane (8), and the oxygen photoelectrode membrane (8) is excited to produce fluorescence of a specific wavelength. The camera (10) captures the entire fluorescence image of the soil box device (5). The entire process is controlled by a computer, and the fluorescence image can be saved in the computer to perform data processing based on the response curve of the oxygen photoelectrode membrane (8) to oxygen to obtain the monitoring result.

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