Attapulgite-bentonite vertical antifouling barrier as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of civil and environmental engineering, and discloses an attapulgite-bentonite vertical antifouling barrier as well as a preparation method and application thereof. The high-strength concrete comprises concave expansion composite soil slurry and ardealite-cement-soil slurry in a mass ratio of 1: 1, the concave and expanded composite soil slurry comprises attapulgite, bentonite and a solution, wherein the mass ratio of the attapulgite to the bentonite is 1: 1. The vertical antifouling barrier disclosed by the invention has the characteristics of high salt stability, low permeability, high-strength synergy, high pollutant adsorption capacity, excellent ecological adaptability and high field adaptability.

Description

Technical Field

[0001] This invention relates to the field of civil and environmental engineering technology, and in particular to an attapulgite-bentonite vertical antifouling barrier, its preparation method, and its application. Background Technology

[0002] With the rapid development of industrial contaminated site remediation, landfill containment, water source protection, and coastal saline land remediation projects, underground pollution control places higher demands on the performance of vertical pollution barriers. Vertical pollution barriers, by constructing continuous, low-permeability vertical barriers underground, block the horizontal migration of pollutants in groundwater and are one of the most widely used underground pollution control technologies in current environmental geotechnical engineering. For existing typical vertical pollution barrier technologies, the most widely used material systems currently include the following three: (1) Cement-bentonite seepage barrier wall: Bentonite suspension is used as the skeleton, and an appropriate amount of cement is added to adjust the strength and hardening performance. After the wall is formed in situ, a low-permeability solidified body is formed. However, the cement production process involves a large amount of CO2 gas emission and excessive raw material loss; the overall deformation capacity of the material is weak, and drying shrinkage cracking or uneven settlement can easily lead to wall leakage; the adsorption capacity for heavy metals and organic pollutants is weak, and it only plays a physical barrier role, making it difficult to fix and retain pollutants; the preparation, injection, stirring and curing process of the slurry is highly sensitive to the site conditions, and quality problems such as stratification, segregation and wall discontinuity are prone to occur.

[0003] (2) Plastic concrete anti-seepage wall: It is a mixture of bentonite, cement, fly ash, crushed stone and other aggregates, which has both anti-seepage and certain bearing capacity. However, bentonite, especially high-quality sodium bentonite, is a national strategic resource and should not be over-reliant on; cement hydration products are easily eroded in saline groundwater, and their performance deteriorates over a long period of time; the material is dense and rigid, which is not conducive to the growth of plant roots and the survival of microorganisms, and is not suitable for ecological restoration collaborative projects; it is necessary to strictly control the aggregate gradation, water-cement ratio and plasticizer dosage, and the construction process requirements are high and the on-site curing period is long.

[0004] (3) Geomembrane + clay composite wall: High-density polyethylene membrane (HDPE) or geoclay geomembrane (GCL) is embedded in a vertical wall to form a composite multi-functional anti-fouling structure. However, the connection between the geomembrane and the clay layer depends on compaction or bonding. It is prone to slippage, delamination or interface peeling due to stress disturbance or temperature and humidity changes. Polymer materials such as HDPE membrane have high tensile strength but weak puncture resistance. Underground debris or stress concentration points can easily damage its integrity. Geomembrane is prone to aging and becoming brittle in long-term ultraviolet, oxidation, acid and alkali environments, forming hidden cracks and weakening the anti-seepage function. Membrane welding and interface sealing have high requirements for construction technology and it is difficult to guarantee the overall sealing effect of large-area continuous operation.

[0005] In addition, existing vertical antifouling barrier materials still have significant shortcomings in terms of stability in high-salt environments, adsorption-closure synergy, ecological compatibility, and durability, as summarized in Table 1.

[0006]

[0007] In response to the challenges posed by traditional vertical barrier walls in contaminated site conditions, such as poor erosion resistance and durability, excessive reliance on cement and bentonite (a national strategic resource) that generate CO2 during production, the potential for secondary pollution, and complex construction processes, there is an urgent need to develop a new type of composite barrier material and construction method that can resist ion exchange interference, possess low permeability and pollutant adsorption capacity, be green and eco-friendly, be compatible with underground micro-ecosystems, and achieve efficient wall formation through on-site controllable processes. Summary of the Invention

[0008] The purpose of this invention is to provide an attapulgite-bentonite vertical antifouling barrier, its preparation method, and its application, thereby solving the aforementioned problems existing in the prior art.

[0009] To achieve the above-mentioned objectives, the present invention provides the following technical solution: This invention provides a vertical antifouling barrier made of attapulgite-bentonite, comprising an attapulgite-bentonite composite slurry and a phosphogypsum-cement-soil slurry with a mass ratio of 1:1. The attapulgite-bentonite composite soil slurry includes attapulgite, bentonite, and a solution.

[0010] Preferably, the mass ratio of attapulgite to bentonite is 1:1.

[0011] Preferably, the total mass fraction of attapulgite and bentonite in the attapulgite-bentonite composite soil slurry is 5-15%.

[0012] Preferably, the phosphogypsum-cement-soil slurry includes phosphogypsum, cement, in-situ soil, and water.

[0013] Preferably, the water content in the phosphogypsum-cement-soil slurry accounts for 10-20% of the total mass of phosphogypsum, cement, and in-situ soil.

[0014] Preferably, the mass ratio of phosphogypsum, cement, and in-situ soil is 12~20:8:75~80.

[0015] This invention also provides a method for preparing an attapulgite-bentonite vertical antifouling barrier, comprising the following steps: The composite slurry is obtained by mixing the octoporoidal-soil slurry and the phosphogypsum-cement-soil slurry. The composite slurry is molded and then cured according to standard conditions to obtain an attapulgite-bentonite vertical antifouling barrier.

[0016] Preferably, the standard curing conditions are: temperature of 20~24℃, humidity of 93~97%, and curing time of 90 days.

[0017] The present invention also provides an application of attapulgite-bentonite vertical antifouling barrier in the vertical isolation of contaminated sites.

[0018] In this invention, a schematic diagram of the operation of the attapulgite-bentonite vertical antifouling barrier is shown below. Figure 1 As shown, this vertical barrier, through the synergistic effect of multiple mechanisms—attapulgite rod-shaped crystal rapid complexation / adsorption (linear) + montmorillonite sheet complexation / surface adsorption / interlayer cation exchange (surface) + composite framework for reduced permeability and increased tortuosity—significantly slows flow hydraulically and chemically fixes pollutants with high selectivity and capacity, forming a stable reaction-transport coupled barrier. This extends the breakthrough time and reduces the risk of leakage. Specifically, upstream, the attapulgite "linear network" rapidly captures highly active / easily complexed pollutants. Unfixed dissolved pollutants continue to enter the montmorillonite "surface" structure, where surface complexation and interlayer exchange provide a large-capacity "buffer pool." The negatively charged montmorillonite surface preferentially attracts divalent / trivalent cations (such as Pb). 2+ Cd 2+ Cu 2+ (etc.); the outer surface and edge sites of attapulgite also exhibit a net negative charge or possess coordinating hydroxyl groups (Si-OH, Al-OH, Mg-OH) under neutral to slightly alkaline conditions, attracting / complexing metal cations and polar organic compounds. Here, "lines" mainly refer to the complexation and adsorption of attapulgite rod-shaped crystals: M-OH + Me 2+ MO-Me + +H + (M represents the hydroxyl sites surrounding Al / Mg / Si, Me) 2+ (For metal ions). Stable surface complexes are formed through internal coordination complexation, preferentially consuming high-affinity metals. It provides hydrogen bonding and hydrophobic-hydrophilic balance adsorption for polar organic compounds (dyes, phenols, nitrogen-containing heterocycles, etc.); the rod-shaped channels and grooves have a "geometric matching" effect on linear / plate-like molecules. In the presence of localized pH increases or carbonates, the attapulgite surface can serve as a nucleation site for metal hydroxides / carbonates, promoting secondary precipitation and "locking in" pollutants. The "surface" mainly refers to the complexation, surface adsorption, and cation exchange of montmorillonite sheets: edge sites (≡Al-OH, ≡Si-OH) form internal / external coordination complexes with heavy metals; electrostatic adsorption occurs on the outer surface of the sheet. 2≡X-Na +Me 2+ ≡X2-Me + 2Na +(≡X represents interlayer exchange sites). Montmorillonite's high CEC provides a "reversible ion pool," preferentially exchanging high-valence, highly affinity metal cations and quaternary ammonium organic cations. This exchange is accompanied by adjustments to the interlayer hydration structure, further reducing effective porosity and diffusion coefficient. Interlayer water absorption and swelling further compress pores and inhibit convection at the microscopic level, driving the transport mechanism to shift from convection-dominated to diffusion / surface reaction-dominated.

[0019] In this invention, a vertical antifouling barrier composed of attapulgite and bentonite is formed by utilizing the physical cross-linking effect of the one-dimensional rod-shaped crystal structure of attapulgite and the two-dimensional layered crystal structure of montmorillonite. In terms of resource utilization, this reduces dependence on bentonite, a national strategic resource, while effectively utilizing the abundant attapulgite. In engineering applications, the natural three-dimensional network structure formed by attapulgite and bentonite reduces crack formation and propagation in bentonite barriers under wet-dry cycles or corrosive environments, enhancing the toughness of the barrier material. Furthermore, it reduces the penetration of moisture and pollutants, improving the overall sealing and chemical stability of the barrier, thereby extending its service life. The vertical barrier formed by this invention comprehensively improves the impermeability and adsorption performance of the barrier material without generating secondary pollution (such as the polymer gel in polymer-modified barriers), reducing environmental burden and economic costs.

[0020] As can be seen from the above technical solution, compared with the prior art, the present invention has the following beneficial effects: (1) High salt stability: The stable rod-shaped crystal structure of attapulgite can prevent the structural collapse of bentonite in a salt environment, which significantly improves the stability of seepage prevention performance; (2) Synergistic effect of low permeability and high strength: The composite grout has both low permeability and excellent consolidation strength, which can meet the dual requirements of antifouling and structural integrity. (3) Strong adsorption capacity for pollutants: The high specific surface area and active surface groups of attapulgite enable it to adsorb heavy metals and organic matter well; (4) Excellent ecological adaptability: It can be used in conjunction with subsequent ecological technologies such as phytoremediation and microbial remediation, and the materials are natural and environmentally friendly. (5) Strong on-site adaptability: In-situ mixing and grouting construction does not require large-scale excavation and is suitable for complex geological and urban polluted sites. Attached Figure Description

[0021] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below.

[0022] Figure 1 This is a schematic diagram of the working process of the attapulgite-bentonite vertical antifouling barrier of the present invention; Figure 2This is a mineral composition diagram of attapulgite and bentonite in this invention; Figure 3 The fluidity of the phosphogypsum-cement-soil slurry in Example 1; Figure 4 This is a visual representation of the attapulgite-bentonite vertical antifouling barrier of Example 1. Figure 5 The unconfined compressive strength curve of the attapulgite-bentonite vertical antifouling barrier in Example 1 is shown. Figure 6 The permeability coefficient of the attapulgite-bentonite vertical antifouling barrier in Example 1; Figure 7 The construction flowchart of the vertical antifouling barrier made of attapulgite-bentonite in Example 2 using the in-situ deep mixing method is shown below. Figure 8 The construction flowchart of the vertical antifouling barrier based on the excavation and backfilling method for attapulgite-bentonite in Example 3 is shown. Detailed Implementation

[0023] This invention provides a vertical antifouling barrier made of attapulgite-bentonite, comprising an attapulgite-bentonite composite slurry and a phosphogypsum-cement-soil slurry with a mass ratio of 1:1.

[0024] In this invention, the attapulgite-bentonite composite slurry preferably includes attapulgite, bentonite, and a solution.

[0025] In this invention, the preferred mass ratio of attapulgite to bentonite is 1:1.

[0026] In this invention, the total mass fraction of attapulgite and bentonite in the attapulgite-bentonite composite soil slurry is preferably 5-15%, more preferably 7-12%, and even more preferably 10%.

[0027] In this invention, the solution is preferably water or a salt solution, more preferably water; the salt solution is preferably a NaCl solution or a CaCl2 solution.

[0028] In this invention, the mineral composition of the attapulgite and bentonite is as follows: Figure 2 As shown.

[0029] In this invention, the phosphogypsum-cement-soil slurry preferably includes phosphogypsum, cement, in-situ soil, and water.

[0030] In this invention, the water content in the phosphogypsum-cement-soil slurry is preferably 10-20% of the total mass of phosphogypsum, cement, and in-situ soil, more preferably 12-18%, and even more preferably 15%.

[0031] In this invention, the mass ratio of phosphogypsum, cement, and in-situ soil is preferably 12~20:8:75~80, more preferably 15~18:8:75~78, and even more preferably 17:8:75.

[0032] In this invention, the cement is preferably PO42.5 cement.

[0033] In this invention, the in-situ soil was taken from Funing County, Yancheng City, Jiangsu Province; the basic physical properties of the in-situ soil are shown in Table 2.

[0034]

[0035] In this invention, the main components of the phosphogypsum are shown in Table 3.

[0036]

[0037] This invention also provides a method for preparing an attapulgite-bentonite vertical antifouling barrier, comprising the following steps: The composite slurry is obtained by mixing the octoporoidal-soil slurry and the phosphogypsum-cement-soil slurry. The composite slurry is molded and then cured according to standard conditions to obtain an attapulgite-bentonite vertical antifouling barrier.

[0038] In this invention, the preferred method for preparing the attapulgite-bentonite composite slurry is as follows: attapulgite and bentonite are crushed separately and passed through a 100-mesh sieve, then dried at 105°C for 24 hours, and then the two are mixed to obtain attapulgite-bentonite composite soil; the attapulgite-bentonite composite soil is stirred and mixed with a solution and left to stand for 24 hours to obtain attapulgite-bentonite composite slurry.

[0039] In this invention, the preferred method for preparing the phosphogypsum-cement-soil slurry is to mix phosphogypsum, cement, in-situ soil, and water to obtain the phosphogypsum-cement-soil slurry.

[0040] In this invention, the standard maintenance conditions are as follows: the temperature is preferably 20~24℃, more preferably 21~23℃, and even more preferably 22℃; the humidity is preferably 93~97%, more preferably 94~96%, and even more preferably 95%; and the maintenance time is preferably 90 days.

[0041] The present invention also provides an application of attapulgite-bentonite vertical antifouling barrier in the vertical isolation of contaminated sites.

[0042] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0043] Example 1

[0044] This embodiment provides a method for preparing an attapulgite-bentonite vertical antifouling barrier, including the following steps: After crushing attapulgite and bentonite separately and passing them through a 100-mesh sieve, they were dried at 105℃ for 24 hours. Then, the two were mixed at a mass ratio of 1:1 to obtain attapulgite-bentonite composite soil. The attapulgite-bentonite composite soil was stirred and mixed with water so that the total mass of attapulgite and bentonite in the water was 10% by mass. After standing for 24 hours, the attapulgite-bentonite composite soil slurry (viscosity of 770 cP at room temperature) was obtained. Phosphogypsum, cement, and in-situ soil were mixed with water in a mass ratio of 17:8:75, so that water accounted for 15% of the total mass of phosphogypsum, cement, and in-situ soil, resulting in a phosphogypsum-cement-soil slurry (viscosity 574 cP at room temperature). Its fluidity is as follows: Figure 3 As shown, it is 22.7cm; The composite slurry of octopus-swellable soil and phosphogypsum-cement-soil slurry were mixed at a mass ratio of 1:1 to obtain a composite slurry (viscosity of 692 cP at room temperature). The composite slurry was molded and then cured for 90 days under standard conditions of 22℃ and 95% humidity to obtain an attapulgite-bentonite vertical antifouling barrier, the appearance of which is shown in the figure below. Figure 4 As shown.

[0045] The unconfined compressive strength curves of the above-mentioned attapulgite-bentonite vertical antifouling barrier are as follows: Figure 5 As shown. By Figure 5 It can be seen that the peak value of the unconfined compressive strength can reach 92 kPa.

[0046] The permeability coefficient of the above-mentioned attapulgite-bentonite vertical antifouling barrier is as follows: Figure 6 As shown. By Figure 6 It is known that the permeability coefficient increases with increasing salt solution concentration, and the increase in permeability coefficient by divalent cations is much stronger than that by monovalent cations, indicating a sensitivity to the "ion valence state and ionic strength effect." However, the attapulgite-bentonite vertical antifouling barrier remains effective in environments with medium to high monovalent cations (NaCl) and medium divalent cations (CaCl2) (k≤10). -9 (m / s), which significantly improves the effect compared to traditional isolation walls.

[0047] The above-mentioned attapulgite-bentonite vertical antifouling barrier was subjected to batch isothermal adsorption experiments using Zn(NO3)2 solution, with pH controlled at 7 and an initial concentration of 100 mg / L. The adsorption of Zn was measured. 2+The adsorption capacity can reach 49.6 mg / g (based on the Langmuir model), which is greater than that of traditional bentonite-based barrier walls (at typical groundwater concentrations (0.1~1 mg / L), the equivalent adsorption capacity of traditional barrier wall materials for heavy metals is mostly only in the range of μg / g to 0.1 mg / g).

[0048] Example 2

[0049] The construction process of the attapulgite-bentonite vertical antifouling barrier on-site using the in-situ deep mixing method is as follows: Figure 7 As shown, it includes the following steps: Taking a remediation project of an abandoned power plant in Jiangsu as a pilot project, a continuous pollution barrier with low permeability and high adsorption capacity was constructed at the site boundary to prevent underground pollutants from migrating laterally to the surrounding farmland and groundwater.

[0050] Attapulgite and bentonite were mixed with water. Attapulgite and bentonite were crushed separately and passed through a 100-mesh sieve, then dried at 105℃ for 24 hours to obtain the attapulgite-bentonite composite soil. At the site, water was added to make the total mass fraction of attapulgite and bentonite in water 10%. The mixture was stirred in a vertical mixer for 30 minutes and then allowed to stand for 24 hours to form a viscous, gel-like attapulgite-bentonite composite slurry. A mixture of 80 kg of in-situ soil, 12 kg of phosphogypsum, 8 kg of cement, and 15% water was prepared and stirred until the fluidity reached 220 mm, yielding a phosphogypsum-cement-in-situ soil slurry. The attapulgite-bentonite composite slurry and the phosphogypsum-cement-in-situ soil slurry were then uniformly mixed at a mass ratio of 1:1 to form the main composite slurry for construction.

[0051] A vertical anti-pollution wall, 10m long, 0.6m thick, and 5m deep, was constructed along the eastern boundary of the contaminated site, according to the design. A twin-shaft deep mixing system was used, with each pile diameter of 0.6m, a shaft spacing of 0.5m, and a 25% overlap between adjacent piles. The mixing speed was 30rpm, and the lifting rate was 1.5m / min. After drilling to the designed depth, the composite grout was injected while mixing along the lifting direction to ensure thorough mixing with the in-situ soil. The grouting volume per hole was 1.2m³. 3 During construction, the grouting pressure was controlled at 0.5 MPa. After the wall was completed, a simple covering shed was erected on site, and regular misting was used to maintain moisture. The curing period was no less than 90 days. During this period, three core sampling points were set up in the east-west direction of the wall for later strength and permeability testing.

[0052] Table 4 summarizes the performance evaluation of the formed vertical wall structure after 90 days.

[0053]

[0054] Example 3

[0055] The construction process of attapulgite-bentonite vertical pollution barrier based on the excavation and backfill method is as follows: Figure 8 As shown, it includes the following steps: Use a grab bucket to excavate construction trenches, with a depth of 3-15m and a width of 0.5-1.0m; At the construction site or centralized mixing plant, attapulgite and bentonite are mixed evenly at a design ratio of 1:1 to obtain attapulgite-bentonite composite dry material; water is added to the site to make the total mass of attapulgite and bentonite in water 10% to form attapulgite-bentonite slurry. Mix 80 kg of in-situ soil, 12 kg of phosphogypsum, 8 kg of cement, and 15% water until the fluidity is 220 mm to obtain in-situ soil slurry. Mix the wall protection liquid, dent-bearing mud, and in-situ soil mud in a mass ratio of 1:1:1 to form the main slurry for construction. Mechanical layered backfilling was adopted, with moderate compaction to control the degree of compaction; After completion, cover the top with soil or restore vegetation to prevent rainwater infiltration.

[0056] The wall protection liquid of the attapulgite mud consists of 5% by mass of attapulgite mud (a mixture of attapulgite and bentonite composite dry material in a mass ratio of 1:1 and water), sodium carbonate, and PAC polymer. The mass of sodium carbonate is 2% of the attapulgite composite dry material, and the mass of PAC polymer is 0.2% of the attapulgite composite dry material.

[0057] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A vertical antifouling barrier made of attapulgite and bentonite, characterized in that, Including octoporoidal-swellable composite soil slurry with a mass ratio of 1:1, and phosphogypsum-cement-soil slurry; The attapulgite-bentonite composite soil slurry includes attapulgite, bentonite, and a solution.

2. The attapulgite-bentonite vertical antifouling barrier according to claim 1, characterized in that, The mass ratio of attapulgite to bentonite is 1:

1.

3. The attapulgite-bentonite vertical antifouling barrier according to claim 2, characterized in that, The total mass fraction of attapulgite and bentonite in the attapulgite-bentonite composite soil slurry is 5-15%.

4. The attapulgite-bentonite vertical antifouling barrier according to claim 1, characterized in that, The phosphogypsum-cement-soil slurry includes phosphogypsum, cement, in-situ soil, and water.

5. The attapulgite-bentonite vertical antifouling barrier according to claim 4, characterized in that, The water content in the phosphogypsum-cement-soil slurry accounts for 10-20% of the total mass of phosphogypsum, cement, and in-situ soil.

6. The attapulgite-bentonite vertical antifouling barrier according to claim 4, characterized in that, The mass ratio of phosphogypsum, cement, and in-situ soil is 12~20:8:75~80.

7. A method for preparing an attapulgite-bentonite vertical antifouling barrier according to any one of claims 1 to 6, characterized in that, Includes the following steps: The composite slurry is obtained by mixing the octoporoidal-soil slurry and the phosphogypsum-cement-soil slurry. The composite slurry is molded and then cured according to standard conditions to obtain an attapulgite-bentonite vertical antifouling barrier.

8. The method for preparing an attapulgite-bentonite vertical antifouling barrier according to claim 7, characterized in that, The standard curing conditions are: temperature 20~24℃, humidity 93~97%, and curing time 90 days.

9. The application of the attapulgite-bentonite vertical antifouling barrier according to any one of claims 1 to 6 in the vertical isolation of contaminated sites.

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