A semi-rigid vertical barrier reinforced by synergizing microorganism mineralization and carbide slag and a preparation method thereof

Abstract

This invention relates to a semi-rigid vertical barrier reinforced by synergistic microbial mineralization and carbide slag, and its preparation method. The raw materials include calcium-based bentonite, in-situ soil, urease-inducing bacteria activator, and carbide slag. The dry weight of the calcium-based bentonite accounts for 15.0%–25.0% of the dry weight of the in-situ soil, the total dry weight of all components in the urease-inducing bacteria activator accounts for 2.0%–4.0% of the dry weight of the in-situ soil, and the dry weight of the carbide slag accounts for 3.0%–6.0% of the dry weight of the in-situ soil. This invention addresses the shortcomings of microbial mineralization technology in improving and reinforcing fine-grained soil, significantly improving the strength and impermeability of calcium-based bentonite-based barrier materials. Simultaneously, it utilizes ammonium ions, a byproduct of the microbial mineralization process, reducing the cost and carbon emissions of the barrier material.

Description

Technical Field

[0001] This invention belongs to the field of pollution barrier technology, and relates to a semi-rigid vertical barrier enhanced by microbial mineralization and carbide slag synergistically, and its preparation method. Background Technology

[0002] In the research and application of pollutant containment at contaminated sites, in-situ vertical barrier technology can intercept the migration of pollutants in groundwater and soil, thereby achieving risk management of contaminated sites. Currently, the most common vertical barrier technology is the bentonite-based flexible vertical barrier, which is widely researched and applied due to its advantages of good barrier performance and low material cost. It is suitable for large-scale contaminated sites where there are no requirements for barrier strength and deformation control. For the containment of pollutants under existing buildings in operating chemical or pharmaceutical industrial parks, the applied vertical barrier must have a certain degree of mechanical stability to prevent external loads such as nearby cargo stacking and heavy machinery transportation from affecting the integrity of the vertical barrier.

[0003] Currently, traditional water-stopping curtain structures such as cement-mixed piles, plastic concrete, and diaphragm walls are still the main water-stopping measures in China. However, the hydration of cement-based materials under pollutant stress is severely inhibited, easily creating dominant seepage channels. Consequently, their seepage prevention and anti-pollution performance usually cannot meet the seepage prevention requirements of vertical barriers (<10). - 8 (m / s). Furthermore, silicate cement is a high-energy-consuming and high-carbon-emission material, failing to meet energy conservation and environmental protection requirements. Therefore, developing semi-rigid vertical barriers with excellent barrier properties and low carbon emissions is a current development trend.

[0004] In recent years, environmentally friendly microbial mineralization technology has gradually become a research hotspot in geotechnical and environmental engineering. This technology mainly utilizes the metabolic products and biochemical reaction products of microorganisms to form cementing substances on the soil surface and between particles, thereby improving the strength and impermeability of the soil and rock. These characteristics mean that it is feasible to develop semi-rigid vertical barriers based on microbial mineralization technology. Introducing microbial mineralization technology into commonly used bentonite-in-situ soil vertical barrier materials can further reduce their permeability coefficient and significantly improve the strength of the barrier material. However, the improvement and reinforcement effect of microbial mineralization technology on fine-grained soils such as bentonite-in-situ soil barrier materials is not ideal. Conventional treatment methods such as bacterial solutions, calcium chloride, and urea are insufficient to meet the strength and impermeability requirements of semi-rigid vertical barrier materials for contaminated sites. In addition, the ammonium ions produced during the microbial mineralization process can affect the quality of water and soil environment, and the materials using calcium sources such as calcium chloride are costly. Therefore, the application of microbial mineralization technology in bentonite-in-situ soil barrier materials needs to address key issues such as the optimization methods for treating fine-grained soil, the treatment of ammonium byproducts, and low-cost calcium sources.

[0005] On the other hand, the bentonite used in bentonite-based vertical barrier materials is usually sodium-based bentonite or sodium-modified calcium-based bentonite. Calcium-based bentonite, which has more abundant mineral resources and lower material costs, is less commonly used due to its poor impermeability and expansion properties. Therefore, when developing semi-rigid vertical barrier materials based on microbial mineralization, it is necessary to consider not only improving the strength and impermeability of the barrier material, but also how to fully utilize calcium-based bentonite and improve its expansion properties. Summary of the Invention

[0006] The purpose of this invention is to provide a semi-rigid vertical barrier reinforced by microbial mineralization and carbide slag synergistically, and its preparation method, in order to solve the defect of poor effect of microbial mineralization technology in improving and reinforcing fine-grained soil, and to significantly improve the strength and seepage prevention performance of barrier materials based on calcium-based bentonite. At the same time, by utilizing ammonium ions, a byproduct of the microbial mineralization process, the cost and carbon emissions of the barrier material are reduced.

[0007] The objective of this invention can be achieved through the following technical solutions:

[0008] One of the technical solutions of the present invention provides a semi-rigid vertical barrier synergistically reinforced by microbial mineralization and carbide slag. Its raw material components include calcium-based bentonite, in-situ soil, urease-inducing bacteria activator and carbide slag. The dry weight of the calcium-based bentonite accounts for 15.0% to 25.0% of the dry weight of the in-situ soil, the total dry weight of each component in the urease-inducing bacteria activator accounts for 2.0% to 4.0% of the dry weight of the in-situ soil, and the dry weight of the carbide slag accounts for 3.0% to 6.0% of the dry weight of the in-situ soil.

[0009] Furthermore, the calcium-based bentonite has a montmorillonite content of more than 60%.

[0010] Furthermore, the urease-inducing agent comprises nutrient broth, urea, and ammonium chloride, wherein the nutrient broth accounts for 0.7% to 1.3% of the dry mass of the in-situ soil, the urea accounts for 0.8% to 1.5% of the dry mass of the in-situ soil, and the ammonium chloride accounts for 0.5% to 1.2% of the dry mass of the in-situ soil.

[0011] Furthermore, the calcium content of the carbide slag is greater than 65%, and the pH value is between 11.5 and 12.8.

[0012] The second technical solution of the present invention provides a method for preparing a semi-rigid vertical barrier synergistically reinforced by microbial mineralization and carbide slag, comprising the following steps:

[0013] (1) Weigh calcium-based bentonite, urease activator and carbide slag according to the proportion, mix them and add water to stir to prepare bentonite slurry.

[0014] (2) After mixing the bentonite slurry with the in-situ soil, it is placed in a standard curing room for curing, thus obtaining a semi-rigid vertical barrier that is synergistically enhanced by microbial mineralization and carbide slag.

[0015] Furthermore, in step (1), the stirring time is 10 min.

[0016] Furthermore, in step (1), the fluidity of the bentonite slurry is adjusted by setting the water-cement ratio to 180mm-220mm to meet the fluidity requirements of the construction method (ultra-deep equal-thickness cement-soil continuous mixing wall method (TRD method)). Even further, the water-cement ratio is 2.3 to 2.5.

[0017] Furthermore, in step (2), the maintenance period is 7 to 28 days.

[0018] Compared with the prior art, the present invention has the following advantages:

[0019] (1) This invention proposes a semi-rigid vertical barrier and its preparation method that is synergistically reinforced by microbial mineralization and carbide slag, comprehensively considering the environmental and low-carbon benefits of the barrier material. Microbial mineralization technology is an environmentally friendly low-carbon technology. The bacteria used in the mineralization process, such as urease bacteria, are widely present in nature and are harmless to human health. The urease bacteria activators used are all non-toxic and harmless substances. The industrial solid waste carbide slag contains a small amount of cationic heavy metals, which can react with carbonate ions produced by microbial mineralization to form carbonate precipitates, thereby stabilizing the heavy metals. In addition, the resource utilization of carbide slag can greatly reduce carbon emissions compared with cement-based materials.

[0020] (2) In this invention, carbide slag is used as the main solidification material for the semi-rigid barrier material, providing the calcium source required for microbial mineralization technology and inducing a pozzolanic reaction under alkaline activation. First, the calcium chloride generated by the reaction of calcium hydroxide, the main component of carbide slag, with ammonium chloride in the urease activator in solution can serve as the calcium source required for the microbial mineralization process. This calcium chloride then combines with carbonate ions generated from urea hydrolysis to form calcium carbonate crystals. These calcium carbonate crystals fill soil pores and cement soil particles, thereby significantly improving the strength of the barrier material and reducing its permeability coefficient. Second, the high pH value of carbide slag significantly increases the alkalinity of the soil liquid phase, which can break the Si-O and Al-O bonds in clay minerals to form free unsaturated active bonds. These bonds readily react with calcium hydroxide to form hydrated calcium silicate and hydrated calcium aluminate, further improving the strength and impermeability of the barrier material.

[0021] (3) In this invention, the ammonium ions produced by the microbial mineralization process can undergo cation exchange with the interlayer calcium ions of calcium-based bentonite, which significantly increases the double-layer thickness of calcium-based bentonite, thereby improving its swelling and chemical compatibility under pollutant stress. By drawing on the principle of sodium modification of calcium-based bentonite, this invention directly uses ammonium ions with the same valence as sodium ions to complete the modification of calcium-based bentonite, realizing the full utilization of the ammonium ions, a byproduct of microbial mineralization technology.

[0022] (4) The presence of carbide slag in the raw materials will result in a high alkalinity of the barrier material. In this invention, an in-situ activated microbial mineralization method is adopted to achieve the microbial mineralization process by in-situ enrichment of indigenous urease-producing bacteria. This method can screen for dominant bacterial strains with strong environmental adaptability in a highly alkaline environment. Compared with conventional bio-enhanced microbial mineralization methods, although the high-urease-producing bacteria used have certain environmental adaptability, the urease activity and mineralization efficiency will be significantly affected under highly alkaline conditions. In addition, the in-situ activation method eliminates the processes of bacterial isolation, purification, and selective cultivation compared to the bio-enhanced method, making the construction process simpler and more suitable for practical engineering applications.

[0023] (5) The resource utilization of carbide slag, the application of calcium-based bentonite in barrier materials, and the full utilization of ammonium ions, a byproduct of microbial mineralization, proposed in this invention can all reduce the cost of barrier materials. First, carbide slag provides a calcium source for the microbial mineralization process, eliminating the need to purchase more expensive chemical products. Second, the market price of calcium-based bentonite is about 50% to 80% of that of sodium-based bentonite, greatly reducing material costs. Finally, the byproduct ammonium ions significantly improve the expansibility and chemical compatibility of calcium-based bentonite through cation exchange, eliminating the need for additional modification measures to improve the anti-seepage and anti-fouling performance of barrier materials. Attached Figure Description

[0024] Figure 1 This is a flowchart of the preparation process of Example 1 of the present invention;

[0025] Figure 2 A schematic diagram illustrating the working principle of a semi-rigid vertical barrier synergistically enhanced by microbial mineralization and carbide slag.

[0026] Figure 3 A comparison diagram of the strength of the calcium-based bentonite barrier material prepared by microbial mineralization technology and this invention;

[0027] Figure 4 This is a comparison diagram of the permeability of the calcium-based bentonite barrier material prepared by microbial mineralization technology and the present invention. Detailed Implementation

[0028] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. These embodiments are based on the technical solution of the present invention and provide detailed implementation methods and specific operating procedures. However, the scope of protection of the present invention is not limited to the following embodiments.

[0029] In the following embodiments, the in-situ soil used was from a site of pollution to be controlled; the calcium-based bentonite was purchased from Shijiazhuang Chenran Mineral Products (i.e., Lingshou County Chenran Mineral Products Co., Ltd.); the nutrient broth was purchased from Ron Reagent, and its main components include 10 g / L peptone, 3 g / L beef extract powder and 5 g / L sodium chloride; and the carbide slag was purchased from Lingshou County Taiyue Mineral Products Processing Plant.

[0030] Unless otherwise specified, all other raw materials or processing techniques are commercially available materials or conventional processing techniques in the field.

[0031] Example 1

[0032] (1) This embodiment provides a semi-rigid vertical barrier that is synergistically reinforced by microbial mineralization and carbide slag, the raw materials of which include: calcium-based bentonite, in-situ soil, urease activator and carbide slag.

[0033] (2) First, the montmorillonite content of the calcium-based bentonite is tested by X-ray diffraction analysis. The montmorillonite content is greater than 60%, which can ensure that the calcium-based bentonite has a certain degree of expansion under pollutant stress.

[0034] (3) Urease-inducing agents were used to in situ enrich indigenous urease-inducing bacteria in calcium-based bentonite and in situ soil, and to screen for dominant strains with strong environmental adaptability in a highly alkaline environment. The mass ratio of nutrient broth, urea, and ammonium chloride in the urease-inducing agents was selected as 7:8:5.

[0035] (4) The calcium carbide slag is the main solidification material of the semi-rigid barrier material. The calcium content of the calcium carbide slag was tested by X-ray fluorescence spectrometry. A calcium content greater than 65% can ensure that sufficient calcium source is provided for the microbial mineralization process and the pozzolanic reaction. The pH value of the calcium carbide slag was tested to be between 11.5 and 12.8, so that the high alkalinity can break the Si-O and Al-O bonds in the clay minerals, and then react with calcium hydroxide, the main component of the calcium carbide slag, to undergo a pozzolanic reaction.

[0036] (5) Select the appropriate calcium-based bentonite, enzyme activator and carbide slag as described above. Prepare the raw materials for the semi-rigid vertical barrier according to the dry mass ratio of calcium-based bentonite, in-situ soil, urease activator and carbide slag of 10:50:1:2, and then start the preparation of a semi-rigid vertical barrier with synergistic reinforcement of microbial mineralization and carbide slag.

[0037] (6) Add water to the mixture of calcium-based bentonite, urease activator, and carbide slag and stir manually for 1 minute. Then, place it in an electric mixer and stir thoroughly for 10 minutes to make bentonite slurry. The TRD method is used as a construction method for semi-rigid vertical barriers. The water-cement ratio of the bentonite slurry is selected to be 2.3, that is, the mass of water added is 2.3 times the dry mass of the mixture of calcium-based bentonite, urease activator, and carbide slag.

[0038] (7) The fluidity of bentonite slurry shall be tested in accordance with the test method for the fluidity of cement paste (GB / T8077-2012). Taking the TRD method as an example, the fluidity of bentonite slurry should be between 180mm and 220mm.

[0039] (8) After the prepared mud is fully mixed with the in-situ soil, it is placed in a standard curing room with a temperature of (20±2)℃ and a relative humidity of over 95% for 28 days to obtain a semi-rigid vertical barrier that is synergistically enhanced by microbial mineralization and carbide slag.

[0040] Figure 1 The present invention provides a process flow diagram of a method for preparing a semi-rigid vertical barrier with synergistic enhancement of microbial mineralization and carbide slag, as well as the preparation conditions that need to be met in each process.

[0041] like Figure 2 As shown, in this embodiment, an in-situ activation method is used to stimulate the growth and reproduction of indigenous urease bacteria in calcium-based bentonite and in-situ soil. After screening out dominant bacterial species that can adapt to the highly alkaline environment, a calcium carbonate mineralization reaction is induced. The calcium ions required for the reaction are calcium chloride, a product of carbide slag and ammonium chloride (if ammonium chloride is replaced with sodium chloride, it cannot react with calcium hydroxide in carbide slag to generate calcium ions). The calcium carbonate crystals generated by microbial mineralization will fill the soil pores and cement the soil particles, thereby significantly improving the strength of the barrier and reducing its permeability coefficient. Meanwhile, the high alkalinity of carbide slag can break the Si-O and Al-O bonds in calcium-based bentonite and in-situ soil. The resulting unsaturated active bonds readily react with calcium hydroxide, the main component of carbide slag, in a pozzolanic reaction to generate cementitious substances such as hydrated calcium silicate and hydrated calcium aluminate, thereby further improving the strength and impermeability of the barrier. It should be noted that if the pH is below 11.5, an effective pozzolanic reaction cannot occur, and the technical effect of improving the strength and impermeability of the barrier as described in this invention cannot be achieved. In addition, ammonium ions, a byproduct of microbial mineralization, can undergo cation exchange with interlayer calcium ions in calcium-based bentonite, significantly increasing the double-layer thickness of the calcium-based bentonite, thereby improving the expansibility and chemical compatibility of the barrier under pollutant stress.

[0042] Figure 3 and Figure 4The figures compare the strength and permeability of the calcium-based bentonite barrier materials prepared by microbial mineralization technology and this invention. As can be seen from the figures, the unconfined compressive strength of both technologies increases with curing age. However, due to the small pore size of the calcium-based bentonite barrier material, microbial mineralization technology cannot form effective calcium carbonate cementation, and the strength after 28 days of curing only reaches a maximum of about 50 kPa, which cannot meet the requirement of a semi-rigid vertical barrier strength greater than 100 kPa for industrial contaminated sites. In contrast, the barrier material prepared by this invention can achieve a strength of over 250 kPa after 28 days of curing. Regarding the permeability comparison of the two methods, the calcium carbonate precipitate generated in the microbial mineralization technology can fill soil pores, but the filling efficiency is low, and the permeability coefficient after 28 days of curing is slightly below 10. -8 m / s. The permeability coefficient of this invention reached 1.14 × 10⁻⁶ m / s on day 28 of curing. -9 The flow rate is m / s, which improves the seepage resistance by about 10 times.

[0043] Example 2:

[0044] Compared with Example 1, most of them are the same, except that in this example, the nutrient broth accounts for 0.7% of the dry mass of the in-situ soil, urea accounts for 0.8% of the dry mass of the in-situ soil, and ammonium chloride accounts for 0.5% of the dry mass of the in-situ soil in each raw material component of the urease activator.

[0045] Example 3:

[0046] Compared with Example 1, most of them are the same, except that in this example, the nutrient broth accounts for 1.3% of the dry mass of the in-situ soil, urea accounts for 1.5% of the dry mass of the in-situ soil, and ammonium chloride accounts for 1.2% of the dry mass of the in-situ soil in each raw material component of the urease activator.

[0047] Example 4:

[0048] Compared with Example 1, most of them are the same, except that in this example, the dry weight of calcium-based bentonite accounts for 15.0% of the dry weight of the in-situ soil, the total dry weight of each component in the urease activator accounts for 2.0% of the dry weight of the in-situ soil, and the dry weight of carbide slag accounts for 3.0% of the dry weight of the in-situ soil.

[0049] Example 5:

[0050] Compared with Example 1, most of them are the same, except that in this example, the dry weight of calcium-based bentonite accounts for 25.0% of the dry weight of the in-situ soil, the total dry weight of each component in the urease activator accounts for 4.0% of the dry weight of the in-situ soil, and the dry weight of carbide slag accounts for 6.0% of the dry weight of the in-situ soil.

[0051] The above description of the embodiments is provided to enable those skilled in the art to understand and use the invention. It will be apparent to those skilled in the art that various modifications can be made to these embodiments, and the general principles described herein can be applied to other embodiments without inventive effort. Therefore, the present invention is not limited to the above embodiments, and any improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the invention should be within the protection scope of the present invention.

Claims

1. A semi-rigid vertical barrier synergistically reinforced by microbial mineralization and carbide slag, characterized in that, Its raw material components include calcium-based bentonite, in-situ soil, urease-inducing bacteria activator, and carbide slag. The dry weight of the calcium-based bentonite accounts for 15.0% to 25.0% of the dry weight of the in-situ soil, the total dry weight of all components in the urease-inducing bacteria activator accounts for 2.0% to 4.0% of the dry weight of the in-situ soil, and the dry weight of the carbide slag accounts for 3.0% to 6.0% of the dry weight of the in-situ soil. The urease-inducing agent comprises nutrient broth, urea, and ammonium chloride, wherein the nutrient broth accounts for 0.7% to 1.3% of the dry mass of the in-situ soil, the urea accounts for 0.8% to 1.5% of the dry mass of the in-situ soil, and the ammonium chloride accounts for 0.5% to 1.2% of the dry mass of the in-situ soil. The calcium content of the carbide slag is greater than 65%, and the pH value is between 11.5 and 12.

8.

2. The semi-rigid vertical barrier synergistically reinforced by microbial mineralization and carbide slag as described in claim 1, characterized in that, The calcium-based bentonite has a montmorillonite content of more than 60%.

3. The method for preparing a semi-rigid vertical barrier synergistically reinforced by microbial mineralization and carbide slag as described in claim 1 or 2, characterized in that, Includes the following steps: (1) Weigh calcium-based bentonite, urease activator and carbide slag according to the ratio, mix them and add water to stir to prepare bentonite slurry; (2) After mixing the bentonite slurry with the in-situ soil, it is placed in a standard curing room for curing, thus obtaining a semi-rigid vertical barrier that is synergistically enhanced by microbial mineralization and carbide slag.

4. The method for preparing a semi-rigid vertical barrier synergistically reinforced by microbial mineralization and carbide slag according to claim 3, characterized in that, In step (1), the stirring time is 10 minutes.

5. The method for preparing a semi-rigid vertical barrier synergistically reinforced by microbial mineralization and carbide slag according to claim 3, characterized in that, In step (1), the fluidity of the bentonite slurry is adjusted by changing the water-cement ratio to 180 mm-220 mm.

6. The method for preparing a semi-rigid vertical barrier synergistically reinforced by microbial mineralization and carbide slag according to claim 5, characterized in that, The water-cement ratio is 2.3~2.

5.

7. The method for preparing a semi-rigid vertical barrier synergistically reinforced by microbial mineralization and carbide slag according to claim 3, characterized in that, In step (2), the maintenance period is 7 to 28 days.

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