Apparatus and method for studying stability of micp mineralized products under dry-wet-freeze-thaw cycles

Abstract

The application discloses a kind of equipment for studying the stability of MICP mineralization product under dry-wet-freeze-thaw cycle, comprising: soil column test unit, refrigeration cycle system, heating cycle system, temperature monitoring system and water injection unit;Soil column test unit includes temperature guide plate, soil column sample cylinder, heat preservation layer and water permeable plate;Refrigeration cycle system includes refrigeration device, cooling liquid inlet pipe and cooling liquid outlet pipe;Heating cycle system includes heating device, hot liquid inlet pipe and hot liquid outlet pipe;Temperature monitoring system includes temperature sensor and data acquisition equipment;Water injection unit includes water storage tank and peristaltic pump;Soil column sample cylinder is also provided with water outlet for discharging water in soil column sample cylinder.The equipment can simulate the dry-wet and freeze-thaw cycle environment of soil column sample, obtain the stability parameters of soil column sample under the action of dry-wet cycle and freeze-thaw cycle alone or coupling, and evaluate the stability effect of MICP technology in repairing heavy metal pollution, providing theoretical and practical basis.

Description

Technical Field

[0001] This invention belongs to the field of geotechnical engineering technology, specifically relating to equipment and methods for studying the stability of MICP mineralization products under wet-dry-freeze-thaw cycles. Background Technology

[0002] Microbial induced carbonate (MICP) remediation experiments for heavy metal pollution in soil utilize microorganisms to generate urease to decompose urea, producing carbonate ions that combine with heavy metal ions to form carbonate precipitates. This process converts heavy metals from an exchangeable state into a stable carbonate state, thereby achieving the goal of immobilizing heavy metal ions.

[0003] Freeze-thaw cycles refer to the continuous thawing and freezing process in the soil surface and at certain depths under low-temperature conditions. Because freeze-thaw cycles cause the decomposition of soil aggregates, they affect the physical and chemical properties of the soil. The stability of carbonate precipitation from heavy metals in MIP-mineralized soil is affected to varying degrees by wet-dry cycles and freeze-thaw cycles, and is also a key external factor in the re-dissolution of heavy metal ions from their carbonate state to their exchangeable state. Currently, most studies on the application of MIP technology to remediate heavy metal-contaminated soil only focus on the short-term solidification effect of MIP mineralization, neglecting the weakening effect of wet-dry cycles and freeze-thaw cycles on the remediation effect and stability. The carbonate-bound state in the soil may be difficult to maintain long-term stability. To investigate the effect of MIP technology on the fixation of heavy metals in soil after wet-dry cycles and freeze-thaw cycles, an equipment and method for studying the stability of MIP mineralization of heavy metal contaminated soil under wet-dry-freeze-thaw cycles were adopted. Through in-depth analysis of the results of heavy metal leaching rate and Tessier five-step extraction method, the stability of microbial mineralization (MICP) technology under the action of single freeze-thaw cycle and wet-dry cycle and the coupling effect of wet-dry-freeze-thaw cycle was evaluated. Summary of the Invention

[0004] The technical problem to be solved by this invention is to address the shortcomings of the prior art by providing an apparatus and method for studying the stability of MIP mineralization products under wet-dry and freeze-thaw cycles. This apparatus simulates the wet-dry and freeze-thaw environments of soil column samples through a soil column test unit, a refrigeration cycle system, a heating cycle system, a temperature monitoring system, and a water injection unit, and obtains the stability parameters of the soil column samples under the individual or coupled effects of wet-dry and freeze-thaw cycles, providing a theoretical and practical basis for evaluating the effectiveness of MIP technology in remediating the stability of heavy metal pollution.

[0005] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is: a device for studying the stability of MICP mineralization products under wet-dry-freeze-thaw cycles, characterized in that it includes: a soil column test unit, a refrigeration cycle system, a heating cycle system, a temperature monitoring system, and a water injection unit;

[0006] The soil column test unit includes a temperature-conducting plate and a soil column sample tube for holding soil column samples. The temperature-conducting plate is detachably covered on the soil column sample. The soil column sample tube is provided with a heat insulation layer and a water-permeable plate. The water-permeable plate is located inside the heat insulation layer and below the soil column sample.

[0007] The refrigeration cycle system includes a refrigeration device, a coolant inlet pipe, and a coolant outlet pipe. One end of the coolant inlet pipe and one end of the coolant outlet pipe are both connected to the refrigeration device, and the other end of the coolant inlet pipe and the other end of the coolant outlet pipe are both connected to a temperature guide plate.

[0008] The heating cycle system includes a heating device, a hot liquid inlet pipe and a hot liquid outlet pipe. One end of the hot liquid inlet pipe and one end of the hot liquid outlet pipe are both connected to the heating device, and the other end of the hot liquid inlet pipe and the other end of the hot liquid outlet pipe are both connected to a temperature guide plate.

[0009] The temperature monitoring system includes temperature sensors and data acquisition equipment. There are multiple temperature sensors, which are evenly installed from top to bottom on the side of the soil column sample tube. The part of the temperature sensor that penetrates into the soil column sample tube passes through the insulation layer and extends into the soil column sample.

[0010] The water injection unit includes a water storage tank and a peristaltic pump. The water storage tank is connected to the lower side of the soil column sample tube. The peristaltic pump is located between the water storage tank and the soil column sample tube. The lower side of the soil column sample tube has an inlet that connects to the water storage tank.

[0011] The soil column sample tube is also provided with an outlet for draining the water inside the soil column sample tube.

[0012] The aforementioned apparatus for studying the stability of MIP mineralization products under wet-dry-freeze-thaw cycles is characterized in that the coolant is industrial alcohol and the hydrothermal fluid is deionized water.

[0013] The aforementioned device for studying the stability of MIP mineralization products under wet-dry-freeze-thaw cycles is characterized in that the outlet and the inlet are positioned opposite each other and both are located below the permeable plate.

[0014] Furthermore, this invention also provides a method for studying the stability of MIP mineralized heavy metal contaminated soil using the aforementioned equipment for studying the stability of MIP mineralization products under wet-dry-freeze-thaw cycles, characterized by comprising:

[0015] Step 1: The soil that has been repaired using MICP technology is placed into a soil column sample tube to obtain a soil column sample.

[0016] Step 2: Perform one wet-dry freeze-thaw cycle, which includes:

[0017] Step 201: Turn on the peristaltic pump, inject water into the soil column sample, turn off the peristaltic pump, and let it stand.

[0018] Step 202: Start the heating device. The hot liquid is injected into the temperature conducting plate through the hot liquid inlet pipe and then enters the heating device through the hot liquid outlet pipe to form a heating cycle. When the temperature of the soil column sample is 60℃, open the drain outlet. The heating cycle continues to heat and dry the soil column sample.

[0019] Step 203: Turn on the peristaltic pump, inject water into the soil column sample, and then turn off the peristaltic pump;

[0020] Step 204: Start the refrigeration device. The coolant is injected into the temperature guide plate through the coolant inlet pipe and then enters the refrigeration device through the coolant outlet pipe to form a refrigeration cycle. The soil column temperature is -20℃. The refrigeration cycle continues to freeze the soil column sample.

[0021] Step 205: After freezing is complete, turn off the refrigeration device and turn on the heating device. The hot liquid is injected into the temperature conducting plate through the hot liquid inlet pipe and then enters the heating device through the hot liquid outlet pipe to form a thermal cycle. When the temperature of the soil column sample is 25℃, open the drain outlet and continue the heating cycle to melt the soil column sample, completing one dry-wet-freeze-thaw cycle.

[0022] Step 3: Repeat Step 2 according to the preset number of cycles to complete multiple dry-wet-freeze-thaw cycles;

[0023] Step 4: Conduct soil heavy metal toxicity leaching tests on soil column samples after one wet-dry-freeze-thaw cycle and soil column samples after multiple wet-dry-freeze-thaw cycles, and determine the concentration of heavy metals in the leachate of the soil column samples.

[0024] The method described above is characterized in that, in step 201, the water content of the soil column sample after water injection is 22 wt%, and the settling time is 4 h.

[0025] The method described above is characterized in that, in step 202, the heating cycle duration after opening the drain outlet is 12 hours.

[0026] The method described above is characterized in that, in step 203, the water content of the soil column sample after water injection is 100 wt%.

[0027] The method described above is characterized in that, in step 204, the duration of the refrigeration cycle after the soil column temperature is -20℃ is 12h.

[0028] The method described above is characterized in that, in step 205, the heating cycle duration after opening the drain outlet is 12 hours.

[0029] The method described above is characterized in that, in step three, the preset number of cycle periods is 3, 7, or 14.

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

[0031] 1. This invention relates to an apparatus for studying the stability of MIP mineralization products under wet-dry and freeze-thaw cycles. It simulates the wet-dry and freeze-thaw environments of soil column samples through a soil column test unit, a refrigeration cycle system, a heating cycle system, a temperature monitoring system, and a water injection unit. This allows for the acquisition of stability parameters of the soil column samples under the individual or coupled effects of wet-dry and freeze-thaw cycles, providing theoretical and practical basis for evaluating the stability of mineralization products in the remediation of heavy metal pollution using MIP technology.

[0032] 2. The equipment used in this invention to study the stability of MIP mineralization products under wet-dry-freeze-thaw cycles is simple to operate and can be flexibly assembled for different environmental conditions. In particular, it can switch between the wet state and the state after wetting and drying of soil column samples, thereby simulating wet-dry cycle conditions and obtaining response patterns that are more consistent with actual conditions.

[0033] 3. The equipment for studying the stability of MIP mineralization products under wet-dry-freeze-thaw cycles can realize multiple wet-dry-freeze-thaw cycles, with long continuous operation time and high simulation stability.

[0034] 4. The device for studying the stability of MIP mineralization products under wet-dry-freeze-thaw cycles in this invention includes a temperature-conducting plate placed on the soil column sample, which can simulate one-dimensional conduction at temperatures ranging from -40℃ to 100℃ under natural conditions, making it easier to obtain the response law of the soil column sample under extreme climatic conditions.

[0035] 5. The method of the present invention is easy to operate and has high research significance and application value.

[0036] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0037] Instruction manual illustrations

[0038] Figure 1 This is a schematic diagram of the equipment used in Example 1 to study the stability of MIP mineralization products under wet-dry-freeze-thaw cycles.

[0039] Explanation of reference numerals in the attached figures

[0040] 1—Soil column sample; 11—Soil column sample cylinder; 12—Insulation layer;

[0041] 13—Permeable plate; 2—Temperature guide plate; 3—Refrigeration device;

[0042] 31—Coolant inlet pipe; 32—Coolant outlet pipe; 4—Heating device;

[0043] 41—Hydrothermal inlet pipe; 42—Hydrothermal outlet pipe; 5—Temperature sensor;

[0044] 51—Data acquisition equipment; 6—Water storage tank; 61—Peristaltic pump;

[0045] 14—Outlet. Detailed Implementation

[0046] Example 1

[0047] This embodiment provides an apparatus for studying the stability of MICP mineralization products under wet-dry-freeze-thaw cycles, such as... Figure 1 As shown, it includes: a soil column test unit, a refrigeration cycle system, a heating cycle system, a temperature monitoring system, and a water injection unit;

[0048] The soil column test unit includes a temperature-conducting plate 2 and a soil column sample cylinder 11 for holding the soil column sample 1. The temperature-conducting plate 2 is detachably placed on the soil column sample 1. The soil column sample cylinder 11 is provided with an insulation layer 12 and a permeable plate 13. The insulation layer 12 is a cylindrical shape with an open top. The permeable plate 13 is placed inside the insulation layer 12 and located below the soil column sample 1. The soil column sample 1 is loaded in the cylindrical inner cavity of the insulation layer. The soil column sample 1 is a soil column sample after heavy metal pollution has been remediated using MIP technology. The insulation layer 12 is made of rubber and plastic insulation material, which reduces the heat exchange between the soil column sample and the outside environment and can simulate one-dimensional conduction of soil temperature more closely in actual natural environments.

[0049] The refrigeration cycle system includes a refrigeration device 3, a coolant inlet pipe 31, and a coolant outlet pipe 32. One end of the coolant inlet pipe 31 and one end of the coolant outlet pipe 32 are both connected to the refrigeration device 3, and the other ends of the coolant inlet pipe 31 and the coolant outlet pipe 32 are both connected to the temperature guide plate 2. The refrigeration device 3 is a DLSB-5L low-temperature coolant circulator. The coolant inlet pipe 31 and the coolant outlet pipe 32 transmit coolant, which conducts temperature to the soil column sample 1 through the temperature guide plate 2, thereby freezing the soil column sample 1 in a low-temperature environment. The coolant is industrial alcohol, which has a freezing point of -117.3℃ and will not freeze during the refrigeration cycle. The temperature guide plate 2 has a passage connecting the coolant inlet pipe 31 and the coolant outlet pipe 32.

[0050] The heating circulation system includes a heating device 4, a hot liquid inlet pipe 41, and a hot liquid outlet pipe 42. One end of the hot liquid inlet pipe 41 and one end of the hot liquid outlet pipe 42 are connected to the heating device 4, and the other ends of the hot liquid inlet pipe 41 and the hot liquid outlet pipe 42 are connected to the temperature guide plate 2. The heating device 4 is a GSC-5L high-temperature circulating water bath. The hot liquid inlet pipe 41 and the hot liquid outlet pipe 42 are made of polypropylene, which has high temperature resistance, enabling the soil column sample 1 to melt at ambient temperature. The hot liquid is deionized water. The temperature guide plate 2 has a channel connecting the hot liquid inlet pipe 41 and the hot liquid outlet pipe 42.

[0051] The temperature monitoring system includes temperature sensors 5 and a data acquisition device 51. Multiple temperature sensors 5 are evenly distributed from top to bottom along the side of the soil column sample cylinder 11. The portion of each temperature sensor 5 penetrating the soil column sample cylinder 11 passes through the insulation layer 11 and extends into the soil column sample 1. The temperature sensor 5 is model WZP-035, with a measurement range of -50℃ to 100℃. After controlling the temperature of the soil column sample 1 through a cooling and heating device, the system monitors the temperature changes inside the soil column sample 1 at different depths in real time. The temperature monitoring sensors 5 are connected to the data acquisition device 51 via leads.

[0052] The water injection unit includes a water storage tank 6 and a peristaltic pump 61. The water storage tank 6 is connected to the lower side of the soil column sample tube 11, and the peristaltic pump 61 is located between the water storage tank 6 and the soil column sample tube 11. The water in the water storage tank 6 seeps into the soil column sample 1 through the permeable plate 13, so that the soil column sample 1 reaches a moist or saturated moisture content state.

[0053] The soil column sample tube 11 has an inlet connected to the water storage tank 6 at the lower side. The soil column sample tube 11 also has an outlet 14 for discharging water from the soil column sample tube 11. The outlet 14 and the inlet are directly opposite each other and both are located below the permeable plate 13.

[0054] Example 2

[0055] This embodiment provides a method for studying the stability of MIP mineralized heavy metal contaminated soil using the equipment from Example 1 for studying the stability of MIP mineralization products under wet-dry-freeze-thaw cycles, including:

[0056] Step 1: The soil remediated by MICP technology is placed into a soil column sample cylinder 11 to obtain soil column sample 1; the lead concentration of soil column sample 1 is 3000 mg / kg; the method for obtaining soil remediated by MICP technology includes:

[0057] Step 101: Mix 10g of deionized water containing Pb(NO3)2 with 6.3kg of soil, stir thoroughly, and air dry naturally to obtain lead-contaminated soil with a concentration of 3000mg / kg.

[0058] Step 102: Obtain the remediated soil using a step-by-step grouting method. Specifically, this includes dividing 150 mL of bacterial solution and 350 mL of a mixed solution containing urea and calcium chloride into three portions, and injecting them sequentially into the lead-contaminated soil in the following order: the first portion of bacterial solution, the first portion of the mixed solution containing urea and calcium chloride, the second portion of bacterial solution, the second portion of the mixed solution containing urea and calcium chloride, and the third portion of bacterial solution and the third portion of the mixed solution containing urea and calcium chloride, to obtain the remediated soil. The bacterial solution is obtained by culturing urease-producing bacteria to OD600 = 2.0. The mixed solution containing urea and calcium chloride is a mixture of a 0.5 mol / L urea solution and a 0.5 mol / L calcium chloride solution, with a volume ratio of 1:1.

[0059] Step 103: Cur the repaired soil for 48 hours and dry it to obtain the soil repaired by MICP technology;

[0060] Step 2: Perform one wet-dry freeze-thaw cycle, which includes:

[0061] Step 201: Turn on the peristaltic pump 61 to allow water in the water storage tank 6 to seep into the soil column sample 1 through the permeable plate 13 until the water content is 22wt%. Turn off the peristaltic pump 61 and let it stand for 4 hours.

[0062] Step 202: Start the heating device 4, open the valve of the hot liquid inlet pipe 41 and the valve of the hot liquid outlet pipe 42. The hot liquid is injected into the temperature guide plate 2 through the hot liquid inlet pipe 41 and then enters the heating device 4 through the hot liquid outlet pipe 42 to form a heating cycle. The temperature of the hot liquid is adjusted by the temperature monitoring system. When the temperature of the soil column sample 1 is 60℃, the drain outlet 14 is opened. The heating cycle continues for 12 hours to heat and dry the soil column sample 1 for 12 hours.

[0063] Step 203: Turn on the peristaltic pump 61 to allow the water in the water storage tank 6 to seep into the soil column sample 1 through the permeable plate 13 until the water content is 100wt%, that is, it is completely saturated, and then turn off the peristaltic pump 61.

[0064] Step 204: Start the refrigeration device 3, open the valve of the coolant inlet pipe 31 and the valve of the coolant outlet pipe 32. The coolant is injected into the temperature guide plate 2 through the coolant inlet pipe 31 and then enters the refrigeration device 3 through the coolant outlet pipe 32 to form a refrigeration cycle. The temperature of the coolant is adjusted by the temperature monitoring system to make the temperature of the soil column -20℃. The refrigeration cycle continues for 12 hours to freeze the soil column sample 1 for 12 hours.

[0065] Step 205: After freezing is complete, turn off the refrigeration device and turn on the heating device 4. Open the valves of the hot liquid inlet pipe 41 and the hot liquid outlet pipe 42. The hot liquid is injected into the temperature conducting plate 2 through the hot liquid inlet pipe 41 and then enters the heating device 4 through the hot liquid outlet pipe 42 to form a heat cycle. Adjust the hot liquid temperature through the temperature monitoring system. When the temperature of the soil column sample 1 is 25℃, open the drain outlet 14. The heating cycle continues for 12 hours to melt the soil column sample 1 for 12 hours, completing one dry-wet-freeze-thaw cycle.

[0066] Step 3: Repeat Step 2 according to the preset number of cycles to complete multiple dry-wet-freeze-thaw cycles; the preset number of cycles is 3, 7 or 14.

[0067] Step 4: Conduct soil heavy metal toxicity leaching tests on soil column sample 1 after one wet-dry-freeze-thaw cycle and soil column sample 1 after multiple wet-dry-freeze-thaw cycles. Specifically, this includes determining the concentration of heavy metals in the leachate of soil column sample 1 using atomic flame absorption spectrometry, and calculating the heavy metal leaching rate according to the following formula:

[0068]

[0069] Wherein, M is the heavy metal concentration in the leachate of soil column sample 1 after wet-dry-freeze-thaw cycles, in mg / g; M0 is the heavy metal concentration in the leachate of soil column sample 1 in step one, in mg / g; the determination of the heavy metal concentration in the leachate of soil column sample 1 specifically includes: taking dried soil sample, crushing it through a 0.5mm sieve, adding it to the leachate, placing it in a shaking box and shaking at 180r / min for 24h, then letting it stand, filtering the mixture with a 0.22um pinhole filter, and determining the heavy metal concentration in the filtered mixture using an atomic flame absorption spectrometer; the mass ratio of soil sample to leachate is 1:20, and the leachate is diethyl ether. The diethylenetriaminepentaacetic acid (DTA) extract is prepared by dissolving 1.967 g of DTA in a system containing 14.92 g of triethanolamine and a small amount of water to obtain a DTA system. The DTA system and a calcium chloride solution containing 1.47 g of CaCl2 are then transferred to a 1000 mL volumetric flask. Water is added to approximately 950 mL, and the pH is adjusted to 7.30 with a 6 mol / L HCl solution. Finally, the volume is reduced to 1000 mL with water to obtain the DTA extract.

[0070] In this embodiment, the heavy metal leaching rates after 3, 7, and 14 wet-dry freeze-thaw cycles were 14%, 22%, and 31%, respectively, indicating that the leaching rate of Pb increases with the number of wet-dry freeze-thaw cycles. 2+ The leaching rate is increased;

[0071] Step 5: Using the Tessier five-step extraction method, the morphological changes of heavy metals in soil after MIP treatment under single or coupled effects of wet-dry and freeze-thaw cycles were obtained, further verifying the long-term stability of MIP technology.

[0072] Comparative Example 1

[0073] This comparative example is the same as Example 2, except that in step one, the soil is unrepaired.

[0074] Wet-dry cycle and freeze-thaw cycle promote the migration of heavy metals such as lead ions in soil samples. Compared with the comparative example, the Pb concentration in the soil sample after wet-dry cycle and freeze-thaw cycle in Example 2 was significantly lower. 2+ The leaching rates decreased by 60%, 45%, and 20% respectively, indicating that the leaching of heavy metals in the soil samples after MIP (microbial induced carbonate precipitation) solidification was slower. MIP technology can effectively achieve the mineralization and fixation of heavy metals in soil samples. This may be based on the fact that, under wet-dry-freeze-thaw cycles, compared to free heavy metals in unrestored soil, the carbonate precipitates containing heavy metals in the soil after MIP mineralization are more stable and less prone to migration and leaching. The equipment and method for stabilizing MIP mineralization products under wet-dry-freeze-thaw cycles of this invention provide a data-driven and intuitive understanding of the stability performance of carbonate precipitates in soil after MIP remediation, providing theoretical support and practical basis for its application in actual working conditions and even extreme environmental conditions.

[0075] The above description is merely a preferred embodiment of the present invention and does not constitute any limitation on the present invention. Any simple modifications, alterations, or equivalent structural changes made to the above embodiments based on the technical essence of the invention shall still fall within the protection scope of the present invention.

Claims

1. An apparatus for studying the stability of MIP mineralization products under wet-dry-freeze-thaw cycles, characterized in that, include: Soil column test unit, refrigeration cycle system, heating cycle system, temperature monitoring system, and water injection unit; The soil column test unit includes a temperature-conducting plate (2) and a soil column sample tube (11) for holding the soil column sample (1). The temperature-conducting plate (2) is detachably covered on the soil column sample (1). The soil column sample tube (11) is provided with a heat insulation layer (12) and a water-permeable plate (13). The water-permeable plate (13) is located inside the heat insulation layer (12) and below the soil column sample (1). The refrigeration cycle system includes a refrigeration device (3), a coolant inlet pipe (31) and a coolant outlet pipe (32). One end of the coolant inlet pipe (31) and one end of the coolant outlet pipe (32) are both connected to the refrigeration device (3). The other end of the coolant inlet pipe (31) and the other end of the coolant outlet pipe (32) are both connected to the temperature guide plate (2). The heating cycle system includes a heating device (4), a hot liquid inlet pipe (41) and a hot liquid outlet pipe (42). One end of the hot liquid inlet pipe (41) and one end of the hot liquid outlet pipe (42) are both connected to the heating device (4), and the other end of the hot liquid inlet pipe (41) and the other end of the hot liquid outlet pipe (42) are both connected to the temperature guide plate (2). The temperature monitoring system includes a temperature sensor (5) and a data acquisition device (51). There are multiple temperature sensors (5), which are evenly installed from top to bottom on the side of the soil column sample tube (11). The part of the temperature sensor (5) that penetrates into the soil column sample tube (11) passes through the insulation layer (11) and extends into the soil column sample (1). The water injection unit includes a water storage tank (6) and a peristaltic pump (61). The water storage tank (6) is connected to the lower side of the soil column sample tube (11). The peristaltic pump (61) is located between the water storage tank (6) and the soil column sample tube (11). The lower side of the soil column sample tube (11) has an inlet that connects to the water storage tank (6). The soil column sample tube (11) is also provided with an outlet (14) for discharging water from inside the soil column sample tube (11).

2. The apparatus for studying the stability of MICP mineralization products under wet-dry-freeze-thaw cycles according to claim 1, characterized in that, The coolant is industrial alcohol; the hot liquid is deionized water.

3. The apparatus for studying the stability of MICP mineralization products under wet-dry-freeze-thaw cycles according to claim 1, characterized in that, The outlet (14) and the inlet are positioned opposite each other and both are located below the permeable plate (13).

4. A method for studying the stability of MIP mineralized heavy metal contaminated soil using the equipment described in claim 1 for studying the stability of MIP mineralization products under wet-dry-freeze-thaw cycles, characterized in that, include: Step 1: The soil that has been repaired by MICP technology is put into the soil column sample tube (11) to obtain the soil column sample (1). Step 2: Perform one wet-dry freeze-thaw cycle, which includes: Step 201: Turn on the peristaltic pump (61) to inject water into the soil column sample (1), turn off the peristaltic pump (61), and let it stand. Step 202: Start the heating device (4). The hot liquid is injected into the temperature conducting plate (2) through the hot liquid inlet pipe (41) and then enters the heating device (4) through the hot liquid outlet pipe (42) to form a heating cycle. When the temperature of the soil column sample (1) is 60℃, open the drain outlet (14) and continue the heating cycle to heat and dry the soil column sample (1). Step 203: Turn on the peristaltic pump (61) to inject water into the soil column sample (1), and turn off the peristaltic pump (61); Step 204: Start the refrigeration device (3). The coolant is injected into the temperature guide plate (2) through the coolant inlet pipe (31) and then enters the refrigeration device (3) through the coolant outlet pipe (32) to form a refrigeration cycle. The soil column temperature is -20℃. The refrigeration cycle continues to freeze the soil column sample (1). Step 205: After freezing is completed, turn off the refrigeration device and turn on the heating device (4). The hot liquid is injected into the temperature conducting plate (2) through the hot liquid inlet pipe (41) and then enters the heating device (4) through the hot liquid outlet pipe (42) to form a heat cycle. When the temperature of the soil column sample (1) is 25℃, open the drain outlet (14) and continue the heating cycle to melt the soil column sample (1) and complete one dry-wet-freeze-thaw cycle. Step 3: Repeat Step 2 according to the preset number of cycles to complete multiple dry-wet-freeze-thaw cycles; Step 4: Conduct soil heavy metal toxicity leaching tests on soil column sample (1) after one dry-wet-freeze-thaw cycle and soil column sample (1) after multiple dry-wet-freeze-thaw cycles, and determine the concentration of heavy metals in the leachate of soil column sample (1).

5. The method according to claim 4, characterized in that, In step 201, the water content of the soil column sample (1) after water injection is 22wt%, and the static time is 4h.

6. The method according to claim 4, characterized in that, In step 202, the heating cycle lasts for 12 hours after the drain outlet is opened.

7. The method according to claim 4, characterized in that, In step 203, the water content of the soil column sample (1) after water injection is 100 wt%.

8. The method according to claim 4, characterized in that, In step 204, the refrigeration cycle lasts for 12 hours after the soil column temperature is -20℃.

9. The method according to claim 4, characterized in that, In step 205, the heating cycle lasts for 12 hours after the drain outlet (14) is opened.

10. The method according to claim 4, characterized in that, In step three, the preset number of cycle periods is 3, 7, or 14.

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