A method for constructing a barrier for a contaminated site
By mixing and in situ soil with activated materials and injection of carbon dioxide, an efficient barrier barrier for contaminated sites is formed, which solves the energy consumption and carbon dioxide emission problems of traditional cement materials, and improves barrier performance and environmental protection.
Patent Information
- Application Number
- CN202411396920.X
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- Filing Date
- 2024-10-09
- Publication Date
- 2024-12-20
- Estimated Expiration
- 2044-10-09
AI Technical Summary
The traditional vertical barrier uses cement and other materials, which leads to energy consumption and carbon dioxide emissions, which violates the green and low-carbon restoration strategy of polluted sites, and has insufficient barrier performance.
Using activated materials composed of steel slag powder, calcium carbide slag powder and red mud powder, the activated bentonite slurry is prepared by dry mixing and hydration reaction, stirring with in situ soil and injecting air and carbon dioxide, and forcibly carbonized to form an efficient barrier. barrier.
It significantly improves the barrier performance of the barrier barrier, reduces the permeability coefficient, achieves low permeability and efficient pollutant barriers, and meets the requirements of green and low-carbon repair.
Smart Images
Figure CN118906180B_ABST
Abstract
Description
Technical Field
[0001] The invention belongs to the field of building structures in contaminated sites, and in particular, relates to a method for building a barrier for contaminated sites. Background Art
[0002] Isolation barriers can effectively control the migration of pollutants or block the exposure pathways of pollutants, and are the most effective technology for risk management of contaminated sites.
[0003] Traditional vertical barriers are mainly made of cement soil, cement-bentonite and other materials. However, the production process of cement consumes a lot of energy and produces a lot of carbon dioxide, which is not in line with the green and low-carbon remediation strategy of contaminated sites. Therefore, it is necessary to develop new barrier construction technologies. Summary of the invention
[0004] The technical problem to be solved by the present invention is to provide a method for constructing a barrier for a contaminated site in view of the shortcomings of the prior art, so as to meet the risk management needs of the contaminated site and improve the barrier performance.
[0005] In order to solve the above technical problems, the present invention adopts a method for constructing a barrier for a contaminated site, comprising the following steps:
[0006] Step 10, preparing a barrier bentonite slurry;
[0007] Step 20, mixing the barrier bentonite slurry prepared in step 10 with the in-situ soil of the designed volume to form a first-stage barrier;
[0008] Step 30, injecting air into the first-stage barrier and continuing to stir until the barrier bentonite slurry and the in-situ soil are evenly mixed to form a second-stage barrier;
[0009] Step 40, injecting carbon dioxide into the second-stage barrier, and continuing to stir and force carbonize to form a barrier;
[0010] The step 10 comprises:
[0011] Step 101, mixing the activated material consisting of steel slag powder, carbide slag powder and red mud powder uniformly by dry method;
[0012] Step 102, mixing the activation material and bentonite uniformly to prepare activated bentonite;
[0013] Step 103, uniformly mixing the activated bentonite with water to obtain a barrier bentonite slurry.
[0014] As a preferred example, in step 101, in the activated material, according to the percentage by mass, steel slag powder accounts for 45% to 70%, carbide slag powder accounts for 10% to 30%, and red mud powder accounts for 10% to 30%; in step 102, the activated material accounts for 45% to 65% of the dry weight of bentonite; in step 103, the amount of water accounts for 115% to 175% of the dry weight of the activated bentonite.
[0015] As a preferred example, in step 20, a mixing tool is used to mix the barrier bentonite slurry with the in-situ soil to achieve continuous construction of barrier barriers of equal thickness.
[0016] As a preferred example, in step 20, the volume of the barrier bentonite slurry is 0.5 to 1.2 times the designed volume of the barrier; during the stirring process, the stirring tool is kept vertical on the longitudinal section of the barrier.
[0017] As a preferred example, in step 30, the air is compressed air; during the stirring process, the stirring tool is kept inclined on the longitudinal section of the barrier, and the inclination angle is 15° to 25°.
[0018] As a preferred example, in step 40, the mass concentration of carbon dioxide is above 99%; during the forced carbonization process, the stirring tool is kept inclined on the longitudinal section of the barrier, with an inclination angle of 20° to 40°.
[0019] As a preferred example, the barrier is constructed in units of sheets, and step 20 includes: starting to spray slurry at the beginning of the Nth barrier until the stirring tool moves to the end of the barrier, then stopping the spraying, and moving the stirring tool to the beginning of the barrier; N=1+m, m represents the number of times step 40 returns to step 20, and the initial value of m is 0;
[0020] The step 30 includes: opening an air injection nozzle, the air injection nozzle being connected to a stirring tool; moving the stirring tool from the beginning of the barrier to the end of the barrier; then closing the air injection nozzle, and moving the stirring tool from the end to the beginning of the barrier;
[0021] The step 40 includes: opening the carbon dioxide injection nozzle, which is connected to the stirring tool; moving the stirring tool from the beginning of the barrier to the end of the barrier; and returning to step 20 until all barrier barriers are constructed.
[0022] As a preferred example, the length of each of the barrier barriers is 5 to 10 m, and the overlapping length between two adjacent barrier barriers is greater than or equal to 1.0 m.
[0023] As a preferred example, the method further includes: step 50, covering the top of the barrier with soil.
[0024] As a preferred example, in step 50, the thickness of the covering soil is greater than or equal to 1.0 m.
[0025] Compared with the prior art, the present invention provides a method for constructing a barrier for a contaminated site, which can meet the risk control requirements of the contaminated site and improve the barrier performance. The construction method includes: step 10 to prepare a barrier bentonite slurry; step 20 to mix the barrier bentonite slurry prepared in step 10 with the in-situ soil of the designed volume to form a first-stage barrier barrier; step 30 to inject air into the first-stage barrier barrier, and continue to stir until the barrier bentonite slurry and the in-situ soil are evenly mixed to form a second-stage barrier barrier; step 40 to inject carbon dioxide into the second-stage barrier barrier, and continue to stir, forcibly carbonize, and form a barrier barrier. The method injects carbon dioxide to force carbonization of the activated bentonite, reduces the porosity of the barrier structure, and thus improves the barrier performance of the barrier. In addition, in the present invention, an activated material composed of steel slag powder, carbide slag powder, and red mud powder is used for the activation treatment of bentonite, which significantly improves the barrier performance of the barrier. BRIEF DESCRIPTION OF THE DRAWINGS
[0026] Figure 1 is a flow chart of an embodiment of the present invention;
[0027] Figure 2 is a graph of sample permeability coefficients of the barrier constructed in Example 1, Comparative Example 1 and Comparative Example 2 of the present invention;
[0028] Figure 3 Graphs of sample permeability coefficients of the barrier constructed in Examples 1 to 4 of the present invention. DETAILED DESCRIPTION
[0029] The technical solution of the present invention is described in detail below. The experimental methods described in the following examples are conventional methods unless otherwise specified; the reagents and materials described are commercially available unless otherwise specified.
[0030] An embodiment of the present invention provides a method for constructing a barrier for a contaminated site, such as Figure 1 As shown, the following steps are included:
[0031] Step 10, preparing a barrier bentonite slurry;
[0032] Step 20, mixing the barrier bentonite slurry prepared in step 10 with the in-situ soil of the designed volume to form a first-stage barrier;
[0033] Step 30, injecting air into the first-stage barrier and continuing to stir until the barrier bentonite slurry and the in-situ soil are evenly mixed to form a second-stage barrier;
[0034] Step 40, injecting carbon dioxide into the second-stage barrier, and continuing to stir and force carbonize to form the barrier.
[0035] The step 10 comprises:
[0036] Step 101, mixing the activated material consisting of steel slag powder, carbide slag powder and red mud powder uniformly by dry method;
[0037] Step 102, mixing the activation material and bentonite uniformly to prepare activated bentonite;
[0038] Step 103, uniformly mixing the activated bentonite with water to obtain a barrier bentonite slurry.
[0039] In the above-mentioned construction method step 101, in order to achieve the best activation efficiency of the activated material on bentonite, dry ball milling is used before it is mixed with bentonite. During the ball milling process, the surface energy of each component material of the activated material increases, but due to the large difference in hardness of the three component materials, the softer calcium carbide slag powder and red mud powder can obtain a larger surface energy than the harder steel slag powder during the ball milling process. In addition, after ball milling, the calcium carbide slag powder and red mud powder are evenly attached to the surface of the steel slag powder particles to form a high-energy difference core-shell structure. This method effectively overcomes the drawbacks of agglomeration and significant reduction of activity of the activated materials after wet mixing, and is a prerequisite for the subsequent activation material to fully react with the bentonite material.
[0040] In step 102, the activated material and bentonite are mixed by dry method to achieve uniform dispersion of the activated material in the bentonite. Due to the high energy difference between the surface and the core of the microscopic particles of the activated material, after the activated material and the bentonite are mixed, the bentonite is adsorbed to the surface of the activated material under the bridging effect of the high surface energy components distributed on the surface of the activated material, which greatly promotes the uniform distribution of the activated material and the bentonite, and provides a basis for the later efficient hydration reaction of the activated bentonite.
[0041] In step 103, after the activated bentonite is mixed with water, it is highly dispersed to form a network structure. Under the action of the electrostatic attraction of the activated material, polar water molecules gather at the contact surface of the activated material and the bentonite, converting a large amount of free water into bound water in the network structure. At the same time, the activated material with high energy difference core-shell structure characteristics undergoes a hydration reaction, and the hydroxide ions dissolved from the carbide slag and red mud increase the pH value of the slurry, increase the thickness of the bentonite double layer, and promote the hydration reaction of the silicate in the steel slag; the aluminate colloid dissolved from the red mud is wrapped on the surface of the bentonite double layer, effectively controlling the compression of the double layer after the calcium ions enter the bentonite double layer, thereby ensuring the efficient activation of the silicate in the steel slag, and avoiding significant changes in the bentonite network structure morphology. Compared with non-activated bentonite, the dispersibility and water retention of the activated bentonite slurry are significantly improved.
[0042] In step 20, the barrier bentonite slurry is mixed with the in-situ soil to form a first-stage barrier. After being injected into the bottom of the barrier, the activated bentonite slurry is converted from a colloid to a suspension during the cutting action of the stirring blades. During the mixing of the activated bentonite suspension with the in-situ soil, the fully hydrated bentonite is first adsorbed onto the surface of the sand and silt particles of the in-situ soil, bonding the soil particles into aggregates.
[0043] Step 30, inject air into the first-stage barrier and continue stirring. After the air is injected, the redox potential of the clay component of the in-situ soil increases under the cutting action of the stirring blades, and the particles gradually disperse, fully contact with the activated bentonite suspension, and deposit on the surface of the particles of the clay component. Steps 20 and 30 achieve efficient contact between the surfaces of the in-situ soil components of different particle sizes and the activated bentonite by stirring in stages, ensuring sufficient mixing of the activated bentonite suspension and the in-situ soil.
[0044] Step 40, injecting carbon dioxide into the second-stage barrier, and continuing to stir, forcing carbonization, and forming a barrier. The calcium ions dissolved from carbide slag and steel slag compress the double layer of the clay particles in the in-situ soil, increasing the bonding strength between the in-situ soil and the activated bentonite. However, in terms of the long-term stability of the system, the high concentration of calcium ions compresses and diffuses the double layer of bentonite, which will also compress the thickness of the double layer of bentonite and reduce the long-term service performance of the barrier. In order to avoid the above phenomenon, the calcium ions in the pore water of the barrier are carbonized into calcium carbonate by injecting carbon dioxide, thereby reducing the porosity of the barrier and further reducing the permeability coefficient of the barrier.
[0045] The barrier constructed by the above method has low permeability and can effectively prevent the outward diffusion of pollutants.
[0046] Preferably, in step 101, in the activated material, according to the mass percentage, steel slag powder accounts for 45% to 70%, carbide slag powder accounts for 10% to 30%, and red mud powder accounts for 10% to 30%. The selection of materials in this range of percentages provides an adaptive hydration environment for the steel slag powder with low hydration reaction activity through the rapid dissolution of carbide slag powder and red mud powder that are easy to be hydrated in water, thereby inducing the hydration of silicates in the steel slag powder and the formation of hydrated calcium silicate; at the same time, this component can ensure that the dissolved calcium ions and aluminum ions produce calcium aluminate, promoting the improvement of the barrier strength. In addition, the above ratio can ensure that a stable high-energy difference core-shell structure is formed after the activated material is prepared.
[0047] In step 102, the activated material accounts for 45% to 65% of the dry weight of the bentonite. Selecting this ratio can promote the thickness of the bentonite double layer after hydration to be at an appropriate thickness, avoid the compression of the double layer by calcium ions after entering the bentonite double layer, thereby ensuring the efficient activation of silicates in steel slag, and significantly improving the dispersibility and water retention of the activated bentonite slurry.
[0048] In step 103, the amount of water accounts for 115% to 175% of the dry weight of the activated bentonite. This proportion range is selected to achieve full reaction between the activated material and the bentonite in the activated bentonite to form a stable network colloidal structure; and to promote the bonding strength between the activated bentonite and the surface of the clay minerals in the in-situ soil. In addition, the water ensures that the barrier material has good fluidity, promotes the homogeneity of the barrier and the carbon dioxide capture efficiency of the subsequent carbonization process.
[0049] Preferably, in step 20, a stirring tool is used to stir the barrier bentonite slurry with the in-situ soil to achieve continuous construction of barrier barriers of equal thickness. The stirring tool is inserted into the in-situ soil, and the barrier bentonite slurry flows into the in-situ soil through a pipeline. The outlet end of the pipeline is connected to the stirring tool. In this way, the outlet end of the pipeline moves with the stirring tool in the in-situ soil to achieve continuous construction of barrier barriers of equal thickness.
[0050] Preferably, in step 20, the volume of the barrier bentonite slurry is 0.5 to 1.2 times the design volume of the barrier, which can ensure that the barrier bentonite slurry is fully mixed with the in-situ soil, and the active sites of the in-situ soil clay minerals are fully combined with the modified bentonite minerals, thereby minimizing the permeability coefficient of the barrier and enhancing the barrier effect. Due to the high-pressure jetting, the barrier bentonite slurry quickly gathers at the bottom of the barrier, and in order to reduce the upward slurry of the barrier bentonite slurry, the stirring tool is kept vertical on the longitudinal section of the barrier during the stirring process. This can effectively reduce the area of the stirring operation area, reduce the in-situ soil disturbance area, and thus achieve efficient utilization of the barrier bentonite slurry.
[0051] Preferably, in step 30, the air is compressed air. During the stirring process, the stirring tool maintains an inclined state on the longitudinal section of the barrier. By adjusting the inclination angle of the stirring tool, the mixing of barrier materials in spaces of different depths and lengths can be achieved, thereby improving the mixing efficiency. However, the greater the inclination angle of the stirring tool, the longer the tool is required, thereby increasing the equipment cost and affecting the mobility of the equipment. Preferably, the inclination angle of the stirring tool on the longitudinal section of the barrier is 15° to 25°.
[0052] Preferably, in step 40, the mass concentration of carbon dioxide is above 99%; in the forced carbonization process, in order to prolong the residence time of carbon dioxide bubbles in the barrier so that they can fully react with free calcium ions in the barrier to precipitate, the stirring tool is kept inclined on the longitudinal section of the barrier. Preferably, the inclination angle of the stirring tool on the longitudinal section of the barrier is 20° to 40°.
[0053] Preferably, the barrier is constructed in units of sheets. The entire barrier is composed of a plurality of barrier sheets. There is an overlap surface between two adjacent vertical barrier sheets, that is, there is an overlapping surface between two adjacent vertical barrier sheets.
[0054] When the barrier is constructed in units of sheets, step 20 includes: starting to spray slurry at the beginning of the Nth barrier sheet until the stirring tool moves to the end of the barrier sheet, then stopping the spraying and moving the stirring tool to the beginning of the barrier sheet; N=1+m, m represents the number of times step 40 returns to step 20, and the initial value of m is 0. Stopping the spraying and moving the stirring tool to the beginning of the barrier sheet is to prepare for step 30. Step 30 starts working from the beginning of the barrier sheet.
[0055] The step 30 includes: opening an air injection nozzle, the air injection nozzle is connected to a stirring tool; moving the stirring tool from the beginning of the barrier to the end of the barrier; then closing the air injection nozzle, and moving the stirring tool from the end to the beginning of the barrier. Closing the air injection nozzle and moving the stirring tool from the end to the beginning of the barrier is a preparation for step 40. Step 40 starts working from the beginning of the barrier.
[0056] The step 40 includes: opening the carbon dioxide injection nozzle, which is connected to the stirring tool; moving the stirring tool from the beginning of the barrier to the end of the barrier; returning to step 20 until all the barrier barriers are built. When returning to step 20, the stirring tool is located at the beginning of the next barrier. The beginning of the next barrier is located at the end of the previous barrier, so that an overlap surface is formed between the next barrier and the previous barrier.
[0057] In order to ensure the construction efficiency and service effect of the barrier, it is necessary to perform performance tests on the barrier according to a certain length as a unit. Because after the activated bentonite is cut by the stirring tool, that is, after stirring, it gradually transforms from a suspension into a network colloid. Therefore, it is necessary to perform sampling and testing after it is transformed into a colloid. Taking full account of factors such as the length of the stirring tool and the moving speed of the stirring tool, the barrier is constructed in sections to facilitate sampling and testing. In addition, the joints of the two adjacent barrier barriers are the weak points of the barrier, that is, the points most prone to leakage, so the joints of the two adjacent barrier barriers are overlapped. Through the two stirrings and injection of barrier bentonite slurry at the end of the Nth barrier and the beginning of the N+1th barrier in step 20, the construction defects of the barrier are effectively reduced.
[0058] Preferably, each of the barrier barriers is 5 to 10 m long, and the overlapping length between two adjacent barrier barriers is greater than or equal to 1.0 m.
[0059] Preferably, the method further includes: step 50, covering the top of the barrier with soil. After the construction of the barrier is completed, the top of the barrier is in contact with the atmospheric environment, which may cause insufficient maintenance of the top of the barrier due to evaporation and water loss. Covering the top of the barrier with soil can effectively reduce water evaporation, thereby providing a moist environment for the oxidation of bentonite at the top of the structure. In addition, the covering soil provides a gravity load for the top of the barrier, which can effectively inhibit cracking damage during the maintenance of the barrier. Preferably, the thickness of the covering soil is greater than or equal to 1.0 m.
[0060] Specific examples and comparative examples are provided below.
[0061] Referring to the preliminary site investigation data and the site risk control plan, it is necessary to build a barrier at the boundary of the contaminated land. The barrier is 180m long, 10m deep and 0.6m wide. With a length of 10m as one piece, the entire barrier can be divided into 18 pieces for construction. The following Example 1 builds 8 barrier barriers, and Example 2, Example 3, Example 4, Comparative Example 1 and Comparative Example 2 each build 2 barrier barriers, for a total of 18.
[0062] Example 1
[0063] The length of the mixing blade is 15m, and the rotation speed is 10~30m / min. The width of the mixing blade is 0.6m. The spacing between adjacent mixing blades is 3.0m. The mixing blade bracket is equipped with a barrier bentonite slurry through a gas-liquid common conduit and a carbon dioxide conduit.
[0064] Activated materials are prepared, with steel slag powder accounting for 60%, carbide slag powder accounting for 25%, and red mud powder accounting for 15%. They are evenly mixed by a dry mixing method to obtain a barrier material.
[0065] Activated bentonite was prepared, and the activated material was 60% of the dry weight of the bentonite.
[0066] The moisture content of the barrier slurry is determined by the physical and chemical characteristics of the barrier material and the moisture content of the site soil. In this embodiment, the moisture content of the barrier bentonite slurry is determined to be 125% through fluidity test.
[0067] According to the construction parameters (length, depth, thickness) of the barrier determined in the construction plan, calculate the amount of barrier materials. Transport the barrier materials to the site, prepare the barrier bentonite slurry according to the construction progress, and use it as soon as it is prepared. The prepared barrier bentonite slurry is placed in the slurry temporary storage tank for no more than 1 hour. The barrier bentonite slurry is introduced from the slurry temporary storage tank to the barrier through the gas-liquid common conduit.
[0068] The barrier is 10m long. A small test is carried out to determine the amount of bentonite slurry for the barrier. The volume of the bentonite slurry for the barrier is 0.7 times the design volume of the barrier, i.e. 42m 3 / width, which can ensure that the barrier bentonite slurry will not return to the ground.
[0069] Compressed air and carbon dioxide are stored in compression tanks for standby use, with a carbon dioxide concentration of 99.9%. Compressed air is introduced into the barrier from the compressed air storage tank through a gas-liquid common conduit, and carbon dioxide is introduced into the barrier from the carbon dioxide storage tank through a carbon dioxide conduit.
[0070] The steps for constructing the first barrier are:
[0071] The first step is to position the mixing tool at the beginning of the first barrier, turn on the mixing tool, and insert the mixing tool into the designed depth (10m) in the stratum; then, turn on the barrier bentonite slurry pumping switch to move the mixing tool along the design direction of the barrier until the mixing tool moves to the end of the first barrier. Subsequently, turn off the barrier bentonite slurry pumping switch and control the mixing tool to move from the end of the first barrier to the beginning of the first barrier along the design direction of the barrier. During this process, the angle between the mixing tool and the vertical direction on the longitudinal section of the barrier is 0°. The moving speed along the design direction of the barrier is 0.5m / min.
[0072] The second step is to adjust the angle between the stirring tool and the vertical direction on the longitudinal section of the barrier to 20°, turn on the air injection switch, and move the stirring tool from the beginning of the barrier to the end of the barrier. During this process, the moving speed of the stirring tool along the design direction of the barrier is 0.5m / min. Then turn off the air injection switch, and move the stirring tool from the end of the barrier to the beginning of the barrier. During this process, the moving speed of the stirring tool along the design direction of the barrier is 1.0m / min.
[0073] The third step is to adjust the angle between the stirring tool and the vertical direction on the longitudinal section of the barrier to 30°, turn on the carbon dioxide injection switch, and move the stirring tool from the beginning of the barrier to the end of the barrier. During this process, the moving speed of the stirring tool along the design direction of the barrier is 0.25m / min. Then turn off the carbon dioxide injection switch, and move the stirring tool from the end of the barrier to the beginning of the next barrier. During this process, the moving speed of the stirring tool along the design direction of the barrier is 1.0m / min.
[0074] At this point, the construction of the first barrier was completed.
[0075] The second barrier needs to be overlapped with the first barrier when it is constructed, and the overlap length is 1.0m. Therefore, the construction steps of the second barrier are as follows:
[0076] The first step is to position the mixing tool 1.0m in front of the end of the first barrier, turn on the mixing tool, and insert the mixing tool to the designed depth (10m) in the stratum; then, turn on the barrier bentonite slurry pumping switch; control the mixing tool to move along the design direction of the barrier until the mixing tool moves to the end of the second barrier. Then, turn off the barrier bentonite slurry pumping switch, and control the mixing tool to move from the end of the second barrier to the beginning of the second barrier (i.e., 1.0m in front of the end of the first barrier) along the design direction of the barrier. During this process, the angle between the mixing tool and the vertical direction on the longitudinal section of the barrier is 0°, and the moving speed along the design direction of the barrier is 0.5m / min.
[0077] Then, refer to the steps for building the first barrier to complete the remaining construction of the second barrier.
[0078] Referring to the construction steps of the first and second barrier barriers, the remaining 6 barrier barriers are constructed, so a total of 80 m of barrier barriers are constructed in this embodiment. The top of the barrier barrier is covered with 1.0 m thick clay soil and then compacted.
[0079] Example 2
[0080] A method for constructing a barrier for a contaminated site is the same as that in Example 1, except that:
[0081] Prepare activated materials, steel slag powder accounts for 70%, carbide slag powder accounts for 10%, and red mud powder accounts for 20%; prepare activated bentonite, the activated material accounts for 65% of the dry weight of bentonite; the amount of water accounts for 115% of the dry weight of activated bentonite. Example 2 Construct 2 barrier barriers with a length of 20m.
[0082] Example 3
[0083] A method for constructing a barrier for a contaminated site is the same as that in Example 1, except that:
[0084] Prepare activated materials, steel slag powder accounts for 45%, carbide slag powder accounts for 25%, and red mud powder accounts for 30%; prepare activated bentonite, the activated material accounts for 45% of the dry weight of bentonite; the amount of water accounts for 175% of the dry weight of activated bentonite. Example 3 Construct 2 barrier barriers with a length of 20m.
[0085] Example 4
[0086] A method for constructing a barrier for a contaminated site is the same as that in Example 1, except that:
[0087] Prepare the activated material, steel slag powder accounts for 60%, carbide slag powder accounts for 30%, and red mud powder accounts for 10%; prepare activated bentonite, the activated material accounts for 55% of the dry weight of bentonite; the amount of water accounts for 155% of the dry weight of activated bentonite. Example 4 Construct 2 barrier barriers with a length of 20m.
[0088] Comparative Example 1
[0089] In order to compare the difference between the activated material used in the present invention and the traditional bentonite activated material, a barrier barrier of a 20m site was selected for construction.
[0090] The comparative example uses conventional silicate cement as the bentonite activation material, and the silicate cement is 60% of the dry weight of the bentonite. The other construction methods are the same as those in Example 1. Comparative Example 1 constructs 2 barrier barriers with a length of 20 m.
[0091] Comparative Example 2
[0092] In order to compare the effect of injecting carbon dioxide for forced carbonization in step 40 of the present invention on the performance of the barrier, a barrier of 20 m in size was selected for construction.
[0093] The method of Comparative Example 2 is the same as that of Example 1, except that when constructing each barrier, the third step, that is, the step of injecting carbon dioxide for forced carbonization, is omitted.
[0094] Comparative Example 2: Two barrier barriers were constructed with a length of 20 m.
[0095] In order to evaluate the service performance of the barrier, samples were taken after the barrier was built and cured for 28 days, and the permeability coefficient of the soil samples was tested. The permeability coefficient was tested according to the procedures of standard ASTM D5084.
[0096] Usually, the overlap of the barrier construction is a weak point of the structure, so sampling is performed at the overlap between two barrier barriers. Sampling is performed at the overlap between the 3rd and 4th barrier barriers constructed in Example 1, the overlap between the 1st and 2nd barrier barriers constructed in Comparative Example 1, and the overlap between the 1st and 2nd barrier barriers constructed in Comparative Example 2. Each point is sampled from shallow to deep in depth, at depths of 2.0 m, 5.0 m, and 9.0 m, respectively.
[0097] The permeability coefficient of the barrier sample was tested and the results were as follows: Figure 2 As shown. Figure 2 It can be seen that the permeability coefficient of the barrier sample in Example 1 is significantly lower than that in Comparative Example 1 and Comparative Example 2. The average permeability coefficient of the samples at different depths in Example 1, Comparative Example 1 and Comparative Example 2 is 2.14×10 -9 cm / s、1.79×10 -6 cm / s、2.17×10 -7 cm / s.
[0098] Therefore, it can be seen from the test results of Example 1 and Comparative Example 1 that, compared with the traditional cement-activated bentonite barrier, the activated material composed of steel slag powder, carbide slag powder, and red mud powder in the present invention has a better activation effect on bentonite, and the corresponding barrier permeability coefficient is reduced by about 2 orders of magnitude, and the barrier performance is significantly improved. It can be seen from the test results of Example 1 and Comparative Example 2 that for the activated bentonite material composed of steel slag powder, carbide slag powder, and red mud powder in the present invention, after forced carbonization, the barrier permeability coefficient is reduced by about 1 order of magnitude, and the barrier performance is significantly improved.
[0099] Samples were collected at the joints between the first and second barrier barriers constructed in Examples 2 to 4. Samples were collected at depths of 2.0 m, 5.0 m, and 9.0 m from shallow to deep. The permeability coefficients of the barrier samples were tested and the results were as follows: Figure 3 As shown. Figure 3It can be seen that the permeability coefficients of Examples 2, 3, and 4 at different depths do not change much. This shows that changing the ratio of the activated material components, the mass ratio of the activated material to bentonite, and the water content of the barrier slurry within the scope of the present invention will not bring significant heterogeneity to the barrier. In addition, the average permeability coefficients of the samples at three depths in Examples 2, 3, and 4 are 2.33×10 -9 cm / s、2.07×10 -9 cm / s、2.15×10 - 9 cm / s, which is very close to that of Example 1. Therefore, the ratio of the components of the activated material, the mass ratio of the activated material to bentonite, and the water content of the barrier slurry used in the present invention can ensure the excellent barrier performance of the barrier.
[0100] The basic principles, main features and advantages of the present invention are shown and described above. Those skilled in the art should understand that the present invention is not limited to the above specific embodiments, and the descriptions in the above specific embodiments and the specification are only for further illustrating the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention may have various changes and improvements, and these changes and improvements all fall within the scope of the present invention claimed for protection.
Claims
1. A method for constructing a barrier for a contaminated site, characterized in that: The following steps are involved: Step 10, preparing a barrier bentonite slurry; Step 20, mixing the barrier bentonite slurry prepared in step 10 with the in-situ soil of the designed volume to form a first-stage barrier; Step 30, injecting air into the first-stage barrier and continuing to stir until the barrier bentonite slurry and the in-situ soil are evenly mixed to form a second-stage barrier; Step 40, injecting carbon dioxide into the second-stage barrier, and continuing to stir and force carbonize to form a barrier; The step 10 comprises: Step 101, mixing the activated material consisting of steel slag powder, carbide slag powder and red mud powder uniformly by dry method; Among the activated materials, by mass percentage, steel slag powder accounts for 45% to 70%, carbide slag powder accounts for 10% to 30%, and red mud powder accounts for 10% to 30%; Step 102, uniformly mixing the activation material with bentonite, wherein the activation material accounts for 45% to 65% of the dry weight of the bentonite, to prepare activated bentonite; Step 103, uniformly mixing the activated bentonite with water, wherein the amount of water accounts for 115% to 175% of the dry weight of the activated bentonite, to obtain a barrier bentonite slurry.
2. The method according to claim 1, characterized in that In step 20, the barrier bentonite slurry is mixed with the in-situ soil using a mixing tool to achieve continuous construction of barrier barriers of equal thickness.
3. The method according to claim 1, characterized in that: In step 20, the volume of the barrier bentonite slurry is 0.5 to 1.2 times the designed volume of the barrier; during the stirring process, the stirring tool is kept vertical on the longitudinal section of the barrier.
4. The method according to claim 1, characterized in that In step 30, the air is compressed air; during the stirring process, the stirring tool is kept in an inclined state on the longitudinal section of the barrier, and the inclination angle is 15° to 25°.
5. The method according to claim 1, characterized in that In the step 40, the mass concentration of carbon dioxide is above 99%; during the forced carbonization process, the stirring tool is kept inclined on the longitudinal section of the barrier, with an inclination angle of 20° to 40°.
6. The method according to claim 1, characterized in that The barrier is constructed in units of panels. The step 20 includes: starting to spray slurry at the beginning of the Nth barrier barrier until the stirring tool moves to the end of the barrier barrier, then stopping the spraying, and moving the stirring tool to the beginning of the barrier barrier; N=1+m, m represents the number of times step 40 returns to step 20, and the initial value of m is 0; The step 30 includes: opening an air injection nozzle, the air injection nozzle being connected to a stirring tool; moving the stirring tool from the beginning of the barrier to the end of the barrier; then closing the air injection nozzle, and moving the stirring tool from the end to the beginning of the barrier; The step 40 includes: opening the carbon dioxide injection nozzle, which is connected to the stirring tool; moving the stirring tool from the beginning of the barrier to the end of the barrier; and returning to step 20 until all barrier barriers are constructed.
7. The method according to claim 6, characterized in that The length of each barrier is 5 to 10 m, and the overlapping length between two adjacent barrier barriers is greater than or equal to 1.0 m.
8. The method according to claim 1, characterized in that Also includes: Step 50, covering the top of the barrier with soil.
9. The method according to claim 8, characterized in that In step 50, the thickness of the covering soil is greater than or equal to 1.0 m.