Heavy metal contaminated soil remediation device based on freeze-thaw cycle

Abstract

The invention belongs to the technical field of geotechnical engineering testing, and particularly relates to a heavy metal contaminated soil remediation device based on freeze-thaw cycle, which is composed of a temperature control system, a data acquisition system, a test generation device, a rainfall and snowfall simulation system and a heavy metal adsorption device. The temperature control system comprises a constant-temperature water bath box and a refrigerator; the test generating device is arranged in the refrigerator; the data acquisition device is connected with the experiment generation device and is used for acquiring data generated by the experiment generation device; the heavy metal adsorption device is arranged in the experiment generation device; the rainfall and snowfall simulation system is arranged at two ends of the test generation device, is connected with the constant-temperature water bath box through a hose and is used for simulating an external environment; according to the device for precisely repairing the heavy metal contaminated soil, migration of heavy metal in the soil under various natural environment conditions is simulated, and the heavy metal is quantitatively eliminated at a fixed point.

Description

Technical Field

[0001] The present invention belongs to the technical field of geotechnical engineering testing, and in particular relates to a heavy metal contaminated soil remediation device based on freeze-thaw cycles. Background Art

[0002] Soil is a complex, multi-phase, dynamic, open system consisting primarily of solid, liquid, gaseous, and biological phases. It constantly exchanges substances with the outside world. During this process, many pollutants enter the soil and settle there, severely damaging the soil ecosystem. It is estimated that the area of ​​soil contaminated by pesticides, heavy metals, and other pollutants reaches tens of millions of hectares, of which 2 million hectares are contaminated in mining areas. 2 , about 5 million hm2 of oil-contaminated soil 2 , solid waste dumping polluted soil of about 50,000 hm 2 , which has posed a serious threat to ecological environment quality, food safety and sustainable social and economic development.

[0003] With the construction of infrastructure and the continuous advancement of industrialization, environmental pollution problems are becoming increasingly serious, among which soil pollution is the most prominent. There are many types of pollutants in the soil, among which soluble pollutants dissolve in water and migrate with the migration of free water. Freeze-thaw cycles can exacerbate the migration of water in the soil, increase the scope of pollution, and affect the ecological environment. Therefore, it is particularly important to study the migration of pollutants with water under the action of freeze-thaw cycles. There are many research results on the hazards of soil pollution at home and abroad, but there are fewer studies on the migration of soluble pollutants in soil. This is mainly because the composition of soil is complex and diverse, so there are many factors that affect the migration of soluble pollutants. Freeze-thaw cycles are the driving force for the migration of soluble pollutants in soil. Therefore, studying the interaction between freeze-thaw cycles and the migration of soluble pollutants is crucial for the control of soil pollution.

[0004] Currently, methods for remediating heavy metal contamination in soil can be roughly divided into physical remediation, chemical remediation, and bioremediation. The simplest physical remediation method, and one that is very effective for regional heavy metal contamination in soil, is soil replacement. This involves covering the cultivated layer with uncontaminated soil to dilute the concentration of heavy metals in the soil. However, this method does not fundamentally address the problem of heavy metal contamination in soil. Currently, the most widely used method is chemical leaching, which utilizes the migration of eluents in the soil to chemically react with heavy metals, converting them into more stable forms. Experiments have shown that composite eluents are more effective than single eluents, but the cost is higher. Bioremediation involves fixing heavy metals through biological metabolism. However, excessively high concentrations of heavy metals can damage the bioremediation system and require a long remediation cycle. Other remediation methods use porous media to adsorb heavy metals in soil. However, these methods involve uniformly mixing the porous media with the heavy metal-contaminated soil, which can easily result in incomplete adsorption of areas with high heavy metal content and waste of the porous media in areas with low heavy metal content. Summary of the Invention

[0005] In order to solve the problems existing in the above-mentioned prior art, the present invention proposes a heavy metal contaminated soil remediation device based on freeze-thaw cycle, which consists of five major parts: a temperature control system, a data acquisition system, a test generation device, a simulated rainfall and snowfall system, and a heavy metal adsorption device; the temperature control system includes a constant temperature water bath and a refrigerator; the test generation device is arranged inside the refrigerator; the data acquisition device is connected to the test generation device for collecting data generated by the test generation device; the heavy metal adsorption device is arranged inside the test generation device; the simulated rainfall and snowfall systems are arranged at both ends of the test generation device and are connected to the constant temperature water bath through a hose for simulating the external environment.

[0006] Beneficial effects of the present invention:

[0007] The present invention simulates the migration of heavy metals in soil under various natural environmental conditions and eliminates heavy metals at specific locations and in specific quantities, thereby improving the precision of heavy metal contaminated soil remediation. The present invention promotes heavy metal migration through freeze-thaw cycles and simulated rainfall and snowfall systems, thereby revealing the patterns of heavy metal migration and providing a basis for precise soil remediation. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Figure 1 This is a diagram of the overall freeze-thaw cycle device of the present invention;

[0009] Figure 2 This is a diagram of a double-layer soil column of the present invention;

[0010] Figure 3 This is a structural diagram of the temperature conducting plate of the present invention;

[0011] Figure 4 This is a structural diagram of the atomizing disk of the present invention;

[0012] Figure 5 This is a structural diagram of the rainfall simulation system of the present invention;

[0013] Figure 6 This is a structural diagram of the implant tube of the present invention;

[0014] Figure 7 This is a schematic diagram of heavy metal monitoring according to the present invention;

[0015] 1. Constant temperature water bath, 2. Hose, 3. Refrigerator, 4. Temperature guide plate, 5. Soil column, 6. Data acquisition system. DETAILED DESCRIPTION

[0016] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0017] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0018] A heavy metal contaminated soil remediation device based on freeze-thaw cycles, such as Figure 1 The device consists of five parts: a temperature control system, a data acquisition system, a test generation device, a simulated rainfall and snowfall system, and a heavy metal adsorption device; the temperature control system includes a constant temperature water bath and a refrigerator; the test generation device is arranged inside the refrigerator; the data acquisition device is connected to the test generation device and is used to collect data generated by the test generation device; the heavy metal adsorption device is arranged inside the test generation device; the simulated rainfall and snowfall systems are arranged at both ends of the test generation device and are connected to the constant temperature water bath through a hose to simulate the external environment.

[0019] In this embodiment, the temperature control system includes a constant temperature water bath and a refrigerator. The constant temperature water bath controls the temperature of the temperature conducting plate through a refrigerant, thereby controlling the temperature at both ends of the soil column. The interior of the refrigerator is a closed space system, in which the test device is placed, and the ambient temperature is controlled by controlling the temperature inside the refrigerator. The data acquisition system includes a data acquisition instrument and a three-in-one probe for temperature, moisture, and conductivity, which can record the temperature, moisture, and conductivity at different depths inside the soil column in real time. This simulated rainfall and snowfall system includes a thimble nozzle, a micro water pump, a flow meter, and a centrifugal atomization disk. The micro water pump transports water to the flow meter. The thimble nozzle is connected to the flow meter through a conduit. The thimble nozzle is suspended above the soil column. This device can simulate different rainfall types and rainfall amounts. The motor drives the centrifugal disk to rotate at high speed, and water flows into the edge of the centrifugal disk through the central conduit and is atomized. By replacing atomizing disks with different apertures (0.1mm / 0.5mm / 1mm), different snow qualities (powder snow, wet snow) can be simulated; the heavy metal adsorption system consists of an implantation tube and modified zeolite. The implantation tube can implant the zeolite into any depth of the soil column through a double-layer cylinder test generator. The amount of zeolite used is determined by the heavy metal content monitored at different depths. The main advantages of the invention are: the ambient temperature is provided by a refrigerator, and the soil column is frozen in one direction using a temperature conducting disk to simulate the permafrost formation process in cold regions to the greatest extent possible. The integrated data acquisition system can monitor the temperature, moisture, and electrical conductivity at different depths inside the soil column in real time. The change in electrical conductivity at different depths can reflect the migration pattern of heavy metals, providing a basis for the precise remediation of heavy metal-contaminated soil; the simulated rainfall and snowfall system can simulate various types of rainfall and snowfall in nature to the greatest extent possible. The acrylic soil column container can clearly observe the changes in soil samples during freeze-thaw cycles and before and after remediation.

[0020] The precise remediation device for heavy metal contaminated soil is composed of multiple parts, including a temperature control system, a data acquisition system, a test device, a simulated rainfall and snowfall system, and a heavy metal adsorption device.

[0021] The temperature control device is composed of a low-temperature constant temperature bath device and a refrigerator. The low-temperature constant temperature device includes a constant temperature water bath, a hose and a temperature guide plate. The constant temperature water bath has a power of 1500W and a temperature control range of -30℃ to 30℃. It can accommodate 16L of freezing liquid inside. The freezing liquid is controlled at the target temperature and transported to the inside of the temperature guide plate through the hose. The hose is made of silicone. In order to ensure that the freezing liquid maintains a constant temperature in the hose, the hose is wrapped with thermal insulation cotton. The temperature guide plate is made of aluminum alloy to ensure that it will not rust under the action of the freezing liquid. There are grooves inside to guide the freezing liquid, and the overall temperature of the temperature guide plate remains constant. There are spiral holes around the temperature guide plate, which is fixed to the bottom and top ends of the soil column by threaded steel bars. There is a circular groove with a diameter of 150mm and a width of 5mm on one side of the temperature guide plate, which can match the soil column tube. The structure of the temperature guide plate is as follows Figure 3 shown.

[0022] The data acquisition part is composed of a data acquisition instrument and a temperature probe, and is connected to an external computer to read real-time data.

[0023] The test apparatus consists of a soil column and a soil column. The soil column is made of acrylic and consists of two layers. The inner layer has a 1.5cm wide gap perpendicular to the bottom of the column, while the outer layer has an arc-shaped gap on the side from the bottom to the top. The inner and outer layers fit tightly together, and lubricant is injected between the gaps to facilitate rotation. Rotation allows the double-layered cylinder to have an implantation hole at any height for zeolite implantation. The soil column inside the soil column is 450mm high, with the upper 150mm containing contaminated soil and the lower 300mm containing uncontaminated soil.

[0024] The simulated rainfall and snowfall system consists of a water storage bucket, a bracket, a micro water pump, a flow meter, a thimble nozzle freezing plate and a silica gel catheter.

[0025] The heavy metal adsorption device consists of an implantation tube and modified zeolite. The zeolite can be implanted into a predetermined position in the soil through a reserved hole on the soil column. The type and amount of zeolite are determined according to actual conditions.

[0026] The functions of the heavy metal migration monitoring and soil improvement system in soil columns include the following:

[0027] Freezing function: Add enough freezing liquid to the constant temperature water bath, let the freezing liquid enter the temperature guide plate through the silicone hose, place the temperature guide plate in the refrigerator, power on the refrigerator, set the target ambient temperature, and close the refrigerator lid.

[0028] Soil column internal temperature, moisture, and conductivity monitoring function: When loading soil samples into the soil column, whenever the soil sample surface is flush with the reserved small hole in the soil column, place the three-in-one probe through the reserved small hole on the soil sample surface, then immediately fill the next layer of soil, and so on. After the soil column is completed, it is placed in the refrigerator, with the upper and lower surfaces anchored to the temperature conducting plate.

[0029] Data acquisition function: Connect the other end of the three-in-one probe buried in the soil column to the data acquisition instrument, record the number and location of each probe, and then connect the data acquisition instrument to the notebook to monitor the temperature, moisture and conductivity changes at each temperature probe in real time.

[0030] Melting function: Turn off the power of the refrigerator, open the refrigerator lid, and let the ambient temperature inside the refrigerator rise to room temperature. At the same time, set the control temperature of the constant temperature water bath to positive temperature, so that the antifreeze liquid rises to a certain temperature and then inputs it into the temperature conduction disk through a hose, and transmits the positive temperature to both ends of the soil column through the temperature conduction disk.

[0031] Rainfall and snowfall simulation: When conducting heavy metal migration tests in the test device, to simulate the effects of rainfall on heavy metal migration, a thimble nozzle can be positioned above the soil column using a bracket. A water pump delivers water to the nozzle to simulate rainfall, and a flow meter controls the type and amount of rainfall. When simulating the freeze-thaw cycle of soil in cold regions, directly adding room-temperature liquid water would affect the experimental results. Therefore, snowfall is simulated during water addition. Mechanical centrifugal force atomizes the water into micron-sized droplets, which instantly freeze into snowflake-like ice crystals in a low-temperature environment. This simulates the process of melting snow replenishing soil water.

[0032] Soil remediation function: When heavy metals migrate in the soil column, the three-in-one probe buried at different depths can detect changes in temperature, moisture, and conductivity at the corresponding positions. The migration depth and relative amount of heavy metals can be determined based on the changes in conductivity. Zeolite is then implanted into the soil at different depths through reserved holes. Where the conductivity is high, the amount of zeolite used is relatively high, and where the conductivity is low, the amount of zeolite used is relatively low, thus avoiding zeolite waste and enabling targeted adsorption of heavy metals.

[0033] The present invention is a frozen soil environmental engineering research platform. The temperature at the bottom and top of the soil column is controlled by a temperature-conducting plate connected to a constant-temperature water bath. At the same time, a refrigerator is used to control the ambient temperature. When freezing, the refrigerator lid is closed and the temperature is set to negative temperature. At the same time, the control temperature of the constant-temperature water bath is also set to negative temperature, forming a closed low-temperature environment. Test soil can be loaded into the soil column, and the compaction degree is controlled according to the water content. At the same time, the soil column tube is made of acrylic material, and the water movement inside the soil column can be observed through the tube wall. There is a temperature probe jack on the side wall of the soil column tube. During the freeze-thaw cycle, the temperature changes inside the soil column can be monitored in real time by the temperature probe. The collected temperature information is transmitted to the data acquisition instrument, and then the data in the data acquisition instrument is collected by a laptop computer.

[0034] like Figure 1 As shown, the heavy metal migration monitoring and soil improvement system in the soil column of the present invention mainly includes a temperature control device consisting of a constant temperature water bath 1, a temperature conducting plate 4 and a refrigerator 3, a connecting device consisting of a hose 2, a data acquisition device consisting of a temperature and moisture probe and a data acquisition instrument 6, and an experimental device consisting of a soil column tube 5.

[0035] The constant temperature water bath 1 can hold 16 liters of freezing liquid, with a temperature control range of -30℃ to 30℃, a power of 1500W, and a 24V voltage. The freezing liquid at a certain temperature can be transported to the temperature conducting plate through a connecting pipe to control the temperature of the temperature conducting plate. The hose 2 is made of silicone with an inner diameter of 10mm. The temperature conducting plate 3 in the figure is 170mm long and 40mm thick, with a built-in circulation groove to allow the freezing liquid to flow in it. There are threaded holes in the four corners, and threaded steel bars can pass through them to fix the temperature conducting plate. There is a circular groove on one side that can match the cylindrical tube.

[0036] Figure 2 The soil column used in the test is made of acrylic material. The height of the soil column is 450mm, the inner diameter is 150mm, and the thickness is 5mm. There are temperature probe holes on the four sides. The temperature probe holes are circular holes with a diameter of 10mm. The uppermost temperature probe hole is 15mm away from the top and is 120mm apart. There are a total of 8 temperature probe holes.

[0037] When promoting the migration of heavy metals in the soil under the action of freeze-thaw cycles, pour the prepared freezing liquid into the interior of a constant temperature water bath with a volume of about 16L; turn on the constant temperature water bath, set the temperature to a certain value, and put the constant temperature water bath into operation; turn on the freezing liquid circulation switch and the reflux switch to allow the freezing liquid to enter the interior of the temperature conduction plate through the hose 2 to control the temperature of the temperature conduction plate; the temperature conduction plate is fixed to both ends of the soil column by nuts and threaded steel bars to control the temperature at both ends of the soil column; load the loess into the soil column according to a certain degree of compaction, and insert the three-in-one probe into the soil, turn on the data acquisition instrument, and collect the temperature, moisture, and conductivity change data in the soil column; close the refrigerator lid to form a closed space, turn on the refrigerator switch, and control the ambient temperature. Observe the changes in temperature, moisture, and conductivity inside the soil column during the freeze-thaw cycle. During the freeze-thaw cycle, if the soil needs to be replenished with water, Figure 4 Place the freezing tray in the refrigerator where the soil column is located, add the required amount of water, and freeze it together with the soil column. When the soil column is melted, take out the ice in the freezing tray of the soil column, place it on the top of the soil column, and melt it together with the soil column to replenish water.

[0038] When simulating the impact of rainfall in non-cold regions on the migration of heavy metals in soil, the Figure 5 The simulated rainfall device shown in the figure fixes the top needle nozzle above the soil column, the flow meter controls the precipitation type and rainfall amount, and the water pump provides water delivery power.

[0039] When improving soil, the conductivity data obtained by the data acquisition instrument is used to determine the depth and relative amount of heavy metal migration. Figure 2 The implant hole in the Figure 6 The implantation tube shown implants the modified zeolite into the soil at different depths to adsorb heavy metals. The amount of zeolite is determined by the heavy metal content at different depths, and the type of zeolite is determined by the type of heavy metal.

[0040] The data logger can set the data collection time and has a certain storage function to store the collected data internally.

[0041] The purpose of this invention is to provide a precise remediation device for heavy metal-contaminated soil. This device can control the top and bottom temperatures of a soil column, as well as the ambient temperature within the column, simulating the temperature and moisture conditions of a natural environment. It can also obtain information on the temperature, moisture, and electrical conductivity of the soil column, monitor the migration of heavy metals in the soil, calculate the heavy metal content at any depth, and remove heavy metals at a specific point and in a specific quantity. The specific implementation process is as follows:

[0042] like Figure 7 As shown in the middle left figure, the total height of the soil column is 450mm. From top to bottom, 0-150mm is heavy metal contaminated soil, and 150mm-450mm is contaminated soil. Taking the upper surface of the soil column as the reference plane, the first three-in-one probe is arranged at a depth of 20mm, numbered 1. Then, a three-in-one probe is arranged every 50mm in the vertical direction of the ground, numbered 2, 3, 4...9 from top to bottom. Figure 7 As shown in the figure on the right, probes 1 to 3 are located in the heavy metal contaminated soil area, while probes 4 to 9 are located in the uncontaminated soil area. The heavy metal concentration in the contaminated area is uniform, so the conductivity readings of probes 1 to 3 will not change initially. The heavy metal concentrations at the depths where probes 3 and 4 are located differ greatly, and the heavy metals migrate downward. When the conductivity reading detected by probe 4 suddenly increases, it indicates that the heavy metals have migrated to h = 170 mm. The same applies to the other probes. This solves the problem of monitoring the migration depth of heavy metals in the soil. To calculate the amount of heavy metal migration, the conductivity σ is first used to convert the dissolved heavy metal concentration C at that location. dis :

[0043] C dis =kσ+d

[0044] Under freeze-thaw conditions, the unfrozen water content in the soil is constantly changing. The working principle of the conductivity probe is that the probe applies an alternating electric field between electrodes, measures the current formed by ion migration, and calculates the conductivity. Where L is the electrode spacing, A is the electrode cross-sectional area, and G is the measured conductivity. When the temperature is below 0°C, the unfrozen water content decreases continuously, the heavy metal concentration increases sharply, and the detected conductivity reading also increases. The conductivity in frozen soil is determined by the unfrozen water content θ u and its ion concentration C dis As the number of freeze-thaw cycles increases, the soil's ability to adsorb heavy metals decreases. Therefore, it is also necessary to consider that as the number of freeze-thaw cycles increases, under the condition of the same total heavy metal content, the proportion of dissolved metals increases and the proportion of adsorbed metals decreases. If the formula for calculating the conductivity and dissolved heavy metal concentration at room temperature is used, the result will deviate greatly. Therefore, a correction formula based on temperature T and freeze-thaw number n under freeze-thaw conditions is given:

[0045]

[0046] where θ u =a·|T| -b (Empirical formula, a, b are soil type parameters, clay: a≈0.3, b≈0.5; sand: a≈0.1, b≈0.2), λ is the freeze-thaw attenuation coefficient.

[0047] Because the probe only detects ionic conductivity in unfrozen water, data is unreliable when the water is completely frozen (σ < 10 μS / cm).

[0048] Then use C dis Calculate the adsorbed heavy metal concentration C ads :

[0049] C ads =ρ b ·K d ·C dis

[0050] where ρ b is the soil bulk density, K d is the adsorption distribution coefficient of heavy metals. Using the time series as monitoring data, the heavy metal content at that location can be calculated.

[0051] The dissolved state accumulation is:

[0052] M dis =θ·A·∫0 t C dis (z,t)dt

[0053] Where θ is the volumetric water content, A is the cross-sectional area of ​​the soil column;

[0054] The adsorption accumulation is: M ads =A·Δz·C ads , Δz is the soil thickness at the target depth.

[0055] Total heavy metal content: M total =A·(θ∫C dis dt+Δz·ρ b K d C dis ).

[0056] Then you can choose an adsorbent (such as zeolite) and implant it into the soil column at a fixed point and in a fixed quantity to repair the contaminated soil.

[0057] The following is a further description of the device of the present invention through specific embodiments and in conjunction with the accompanying drawings. The examples described are only part of the examples of the present invention, not all of them.

[0058] When promoting the migration of heavy metals in the soil under the action of freeze-thaw cycles, pour the prepared freezing liquid into the interior of a constant temperature water bath with a volume of about 16L; turn on the constant temperature water bath, set the temperature to a certain value, and put the constant temperature water bath into operation; turn on the freezing liquid circulation switch and the reflux switch to allow the freezing liquid to enter the interior of the temperature conduction plate through the hose 2 to control the temperature of the temperature conduction plate; the temperature conduction plate is fixed to both ends of the soil column by nuts and threaded steel bars to control the temperature at both ends of the soil column; load the loess into the soil column according to a certain degree of compaction, and insert the three-in-one probe into the soil, turn on the data acquisition instrument, and collect the temperature, moisture, and conductivity change data in the soil column; close the refrigerator lid to form a closed space, turn on the refrigerator switch, and control the ambient temperature. Observe the changes in temperature, moisture, and conductivity inside the soil column during the freeze-thaw cycle. During the freeze-thaw cycle, if the soil needs to be replenished with water, Figure 4 Place the freezing tray in the refrigerator where the soil column is located, add the required amount of water, and freeze it together with the soil column. When the soil column is melted, take out the ice in the freezing tray of the soil column, place it on the top of the soil column, and melt it together with the soil column to replenish water.

[0059] When simulating the impact of rainfall in non-cold regions on the migration of heavy metals in soil, the Figure 5 The simulated rainfall device shown in the figure fixes the top needle nozzle above the soil column, the flow meter controls the precipitation type and rainfall amount, and the water pump provides water delivery power.

[0060] When improving soil, the conductivity data obtained by the data acquisition instrument is used to determine the depth and relative amount of heavy metal migration. Figure 2 The implant hole in the Figure 6 The implantation tube shown implants the modified zeolite into the soil at different depths to adsorb heavy metals. The amount of zeolite is determined by the heavy metal content at different depths, and the type of zeolite is determined by the type of heavy metal.

[0061] The data logger can set the data collection time and has a certain storage function to store the collected data internally.

[0062] C dis Calibrate k and d in σ = kσ + d: Prepare solutions of a heavy metal (e.g., PbCl) with varying concentration gradients. Measure the conductivity of the solutions three times for each concentration and take the average. Randomly select three concentration points (e.g., 10, 50, and 100 mg / L) and determine the actual concentrations using ICP-MS / AAS. Calculate the recovery. (Required 95% to 105%). If the temperature is not constant, make corrections according to the formula:

[0063]

[0064] It is necessary to verify the linear range by increasing the concentration gradient to avoid nonlinear effects at high concentrations.

[0065] C ads =ρ b ·K d ·C dis Middle K d Calibration: Determined by batch adsorption experiment, the steps are as follows: a known mass of soil is mixed with heavy metal solutions of different concentrations; oscillation is carried out at a constant temperature until adsorption equilibrium (usually 24-48 hours); the solid and liquid phases are separated by centrifugation, and the heavy metal concentration C in the liquid phase is determined. dis .

[0066]

[0067] Where C0 is the initial concentration of the solution, V is the volume of the solution, and m is the mass of the soil.

[0068] Calibration of the parameter λ; Comparison of the conductivity changes of solutions with the same concentration before and after freezing and thawing n times

[0069] The above embodiments further illustrate the purpose, technical solutions and advantages of the present invention in detail. It should be understood that the above embodiments are only preferred implementation plans of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made to the present invention within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A heavy metal contaminated soil remediation device based on freeze-thaw cycles, characterized in that: The device consists of five parts: a temperature control system, a data acquisition system, a test device, a simulated rainfall and snowfall system, and a heavy metal adsorption device; the temperature control system includes a constant temperature water bath and a refrigerator; the test device is arranged inside the refrigerator; the data acquisition device is connected to the test device to collect data generated by the test device; the heavy metal adsorption device is arranged inside the test device; the simulated rainfall and snowfall systems are arranged at both ends of the test device and connected to the constant temperature water bath through a hose to simulate the external environment.

2. The heavy metal contaminated soil remediation device based on freeze-thaw cycles according to claim 1 is characterized in that: The constant temperature water bath of the temperature control device has a power of 1500W and contains 16L of freezing liquid.

3. The heavy metal contaminated soil remediation device based on freeze-thaw cycles according to claim 1 is characterized in that: The refrigerator power of the temperature control device is 2000W, and the temperature of the refrigerator is controlled between 0°C and 20°C.

4. The heavy metal contaminated soil remediation device based on freeze-thaw cycles according to claim 1, characterized in that: The data acquisition system includes a data acquisition instrument and a three-in-one probe of temperature, moisture and conductivity; the temperature, moisture and conductivity of the soil are collected through the probe.

5. The heavy metal contaminated soil remediation device based on freeze-thaw cycles according to claim 4 is characterized in that: The data acquisition instrument calculates the dissolved concentration of heavy metals based on the collected data. The formula is: C ads =ρ d ·K d ·C dis i u =a·|T| -b Among them, C ads is the dissolved concentration of heavy metals, ρ b is the soil bulk density, K d is the adsorption distribution coefficient of heavy metals, C dis is the correction parameter based on temperature T and freeze-thaw number n under freeze-thaw conditions, σ is the conductivity, k is the correction parameter, L is the electrode spacing, A is the electrode cross-sectional area, and G is the measured conductivity; a and b are soil type parameters, and λ is the freeze-thaw attenuation coefficient.

6. The heavy metal contaminated soil remediation device based on freeze-thaw cycles according to claim 1, characterized in that: The test device is a soil column tube, which is made of acrylic material, cylindrical in shape, with a diameter of 10mm, a wall thickness of 5mm, and a height of 450mm. It consists of two layers. A 1.5cm wide gap perpendicular to the bottom of the tube is reserved on one side of the inner tube, and an arc-shaped gap from the bottom to the top of the tube is left on the side of the outer tube. The inner and outer layers of the tube fit tightly, and lubricant is poured between the gaps to facilitate rotation. By rotating, the double-layer tube can have implantation holes at any height.

7. The heavy metal contaminated soil remediation device based on freeze-thaw cycles according to claim 1 is characterized in that: The simulated rainfall and snowfall system includes a thimble nozzle, a micro water pump, a flow meter and a centrifugal atomizing disk.

8. The heavy metal contaminated soil remediation device based on freeze-thaw cycles according to claim 1 is characterized in that: The heavy metal adsorption device is an implant tube. The head of the implant tube is in the shape of a bird's beak that can be controlled to open and close. The head is closed during the insertion into the soil column. After reaching the predetermined position, the head is controlled to open at the tail, and modified zeolite is placed at the tail. The zeolite is delivered to the predetermined soil through the smooth inside of the implant tube.

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