Preparation method of self-corrosion permeable pollutant blocking material for underground water treatment

Abstract

The invention provides a self-corrosion permeable pollutant blocking material for underground water treatment and a preparation method of the self-corrosion permeable pollutant blocking material, and belongs to the technical field of underground water remediation. The self-corrosion permeable pollutant blocking material for underground water treatment is prepared from the following components in percentage by mass: 25 to 35 percent of cement, 12 to 18 percent of 2CaSO4. H2O, 8 to 15 percent of fly ash, 25 to 30 percent of grading pore-forming aggregate, 14 to 18 percent of nano pore-forming aggregate, 1 to 1.5 percent of viscosity modifier, 0.5 to 1 percent of early strength agent and 3 to 4.5 percent of modified biomass fiber, a pore matrix is jointly built through grading pore-forming aggregate, nano pore-forming aggregate and modified biomass fibers, the grading pore-forming aggregate and the nano pore-forming aggregate have self-corrosion shells, the pore-forming aggregate is an inactive substance and does not participate in the reaction of silicate cement from the stage before grouting to the hardening stage, and after the material is completely hardened, the pore-forming aggregate is a self-corrosion shell. And the graded aggregate and the nano pore-forming aggregate are converted into permeable pores containing active substances. The material has the advantages of being good in connectivity, high in supporting performance, wide in pollutant treatment capacity, high in pollutant treatment efficiency, long in continuous treatment time and the like, has anti-blocking capacity and can be pumped.

Description

[0001] This invention relates to a method for preparing a self-dissolving, permeable, porous grouting material for groundwater treatment, belonging to the field of water pollution remediation technology. Background Technology

[0002] Cities are experiencing multi-layered and structurally complex mining subsidence areas, with numerous abandoned mine shafts and tunnels leaving behind pollutants. Preventing the spread of pollutants within these areas and protecting deep groundwater from contamination is a crucial issue that urgently needs to be addressed, both now and in the future.

[0003] Permeable reactive barriers (PRBs), a common in-situ remediation technology for water pollution control, primarily involve pre-screening or preparing materials that adsorb and degrade pollutant components in water bodies, constructing a wall-like pollutant adsorption barrier that allows pollutant plumes to permeate through the reaction medium under the natural hydraulic gradient. In recent years, water pollution has shown a trend towards increasing complexity and diversity. Addressing various complex types of pollutants has become a key focus. Consequently, continuous and sustainable reactive barrier materials have become the main development trend in in-situ remediation technologies.

[0004] Patent CN116639851A discloses a multi-stage permeable reactive barrier. The first stage is filled with activated carbon for primary adsorption and oxidation of pollutants. The second stage is filled with O3, KMnO4, and sodium persulfate for oxidation of pollutants. The third stage is filled with lactic acid and Pseudomonas B50D, utilizing microorganisms to treat pollutants. This three-stage treatment has a good removal effect on various pollutants in groundwater, but it also suffers from short service life and high cost. Furthermore, since most three-stage reactive barriers are open-type, their ability to treat deep-seated pollutants in groundwater is limited.

[0005] Patent CN113480284A discloses a cement-based pollutant blocking grouting material. It utilizes the delayed gas generation effect of modified aluminum-based gas-generating particles within the cement material, enabling the material to be injected into deep groundwater pollution plumes, forming porous materials and purifying the water. It is evident that this cement-based pollutant blocking grouting material is a post-gas-generating pore-forming material. The pore size, morphology, and permeability are affected by the pressure, temperature, and type of pollutants in deep groundwater, making it difficult to guarantee the desired pore size and morphology. Consequently, permeability is compromised, leading to low pollutant treatment efficiency. Furthermore, reactive wall blocking materials based on post-gas-generating porous cement-based frameworks inherently suffer from low material strength, failing to provide adequate support for pollution plume mine tunnels and increasing the risk of mine collapse.

[0006] While the aforementioned pollutant treatment materials have proven effective in purifying polluted water in experiments, their capabilities are insufficient for addressing real-world challenges such as deep-seated goaf areas, complex and easily collapsing tunnels, and the accumulation of multiple pollutants. To solve these problems, a new type of grouting blocking material is urgently needed. This material should possess excellent permeability, strong support, broad pollutant treatment capacity, high pollutant treatment efficiency, long continuous treatment time, a certain degree of anti-clogging capability, and pumpability, thereby enabling it to suppress the spread of deep-seated pollution sources at their source. Summary of the Invention

[0007] To address the shortcomings of the aforementioned materials and in light of practical engineering needs, this invention provides a self-dissolving, permeable pollutant-blocking material for groundwater treatment. The material is injected into the pollutant flow through the waterway using concrete grouting or injection techniques. Upon reaching the designated sealing point, the material rapidly hardens and strengthens, reducing the risk of erosion and effectively sealing and supporting the entire pollutant plume and its fissures. Over time, the material's strength increases, and continuous erosion causes the surface of the pore-forming particles to dissolve, exposing the pores and forming interconnected, graded pores of varying sizes. Furthermore, the presence of active substances within these pores purifies the wastewater.

[0008] To achieve the above technical objectives, the present invention adopts the following technical solution:

[0009] In a first aspect, the present invention provides a self-dissolving permeable pollutant blocking material for groundwater treatment, comprising the following mass percentages: 25-35% cement, 12-18% 2CaSO4·H2O, 8-15% fly ash, 25-30% graded porous aggregate, 14-18% nano-porous aggregate, 1-1.5% viscosity modifier, 0.5-1% early strength agent, and 3-4.5% modified biomass fiber.

[0010] To address the aforementioned problems, this invention provides a self-dissolving, permeable contaminant blocking material for groundwater treatment. The technical principle of this material is as follows:

[0011] This invention employs a graded aggregate grouting method, making the pore-forming particles part of the grouting material. Before and after grouting, during the hardening stage, the graded aggregate is an inactive substance and does not participate in the reaction of silicate cement. After the material is fully hardened, the graded aggregate completes its function and transforms into pore-forming aggregate. Because the aggregate is a non-gas-generating material, it reduces the damage to the concrete structure caused by the internal expansion force generated during the reaction of silicate adhesives. Furthermore, the pore-forming aggregate used in this invention is graded aggregate, which becomes part of the internal pores in the early stages of grout mixing, thus not changing the pore morphology, gradation, connectivity, or other characteristics in the later stages of molding. Modified biomass fiber materials provide bridging for the graded pores, further ensuring the continuity of the pores.

[0012] The self-dissolving pore-forming aggregate used in this invention is composed of ZVI and nZVI. ZVI is coated with a starch-based substance, while nZVI is coated with pectin. ZVI consists of relatively large particles in the graded aggregate, acting as early-stage support material for the framework, with a 100-500 nm shell. The passivation effect of the shell provides sufficient support strength for the early reaction. Once the framework stabilizes, the shell is completely dissolved, allowing the exposed ZVI particles to "move" within the pores remaining after the framework hardens. Because the graded aggregate has a high proportion of components, the resulting pores form a porous structure resembling natural zeolite, achieving interconnected large and small pores, thus enabling the flowing polluted water to fully react with the ZVI. Because ZVI particles can "rotate" inside the pores, any precipitates can be discharged in time, ensuring the overall continuity of the structure. Secondly, nZVI materials have the disadvantages of being prone to agglomeration and having poor stability. Adding a shell coating can effectively ensure its stability. In addition, its nano-particle size structure allows for a more reasonable distribution of the entire framework, resulting in higher repair efficiency.

[0013] This invention utilizes multiple modified biomass fibers as bridges to connect pores, ensuring the overall permeability of the material. The internal fibers allow pollutants to preferentially penetrate the matrix material, transforming self-dissolving graded porous aggregates and nanoporous aggregates into porous materials. Simultaneously, biomass materials can serve as carriers for other catalysts, thereby broadening the application of permeable reactive barrier materials in pollution control.

[0014] In a second aspect, the present invention provides a method for preparing a self-dissolving permeable pollutant blocking material for groundwater treatment, comprising the following steps:

[0015] (1) Material preparation: cement, 2CaSO 4· H2O, fly ash, viscosity modifier, early strength agent;

[0016] (2) Preparation of graded porous aggregate;

[0017] (3) Preparation of nanoporous aggregate;

[0018] (4) Preparation of modified biomass fiber materials;

[0019] (5) Weigh cement, 2CaSO4·H2O, fly ash, viscosity modifier, early strength agent, graded pore-forming aggregate, and nano-pore-forming aggregate, add 0.32 to 0.35% water by total mass, stir evenly to prepare a slurry, then add modified biomass fiber material to the slurry, stir at 150 r / min until the slurry is uniform, and then pour into a mold to obtain a self-dissolving and permeable pollutant blocking material for groundwater treatment.

[0020] Furthermore, in step (1), the cement is one or more of PO52.5R type silicate cement, PC52.5R silicate cement, and SAC725R sulfoaluminate cement;

[0021] Preferably, in step (1), 2CaSO4·H2O is β-type hemihydrate gypsum calcined at 200℃ with a mesh size of 300.

[0022] Preferably, the fly ash in step (1) is Class C fly ash with a mesh size of 300.

[0023] Preferably, the viscosity modifier in step (1) is one or more of ethylene ethyl acetate copolymer, sodium silicate, and polycarboxylate water-reducing agent mixed in any proportion;

[0024] Preferably, the early strength agent in step (1) is one or more of lithium carbonate, calcium hydroxide, calcium formate, calcium chloride, and aluminum chloride mixed in any proportion;

[0025] Preferably, in step (2), the method for preparing graded porous aggregate is as follows: weigh an appropriate amount of starch compound, add it to polyethylene glycol 400 solution and stir evenly, add zero-valent iron particles (particle size 100-1500 micrometers), stir it thoroughly under vacuum negative pressure for 30-50 minutes, filter out the granular material, and then freeze-dry the particles under nitrogen atmosphere at -40℃ to obtain graded porous aggregate.

[0026] More preferably, the starch compounds used in the preparation of the graded porous aggregate in step (2) are 21% G50 amylose, 17% G70 amylose, 30% G80 amylose, 31% glycerol, and 1% sodium chloride.

[0027] Preferably, in step (3), the preparation method of nanoporous aggregate is as follows: weigh an appropriate amount of pectin powder into distilled water and adjust the viscosity to 5500 mPa.s. Then, introduce nitrogen gas and dissolve it in a 35°C water bath for 20 min. Add nZVI particles and stir for 30 min. Filter out the granular material and freeze-dry the particles in a -40°C nitrogen atmosphere to obtain nanoporous aggregate.

[0028] Preferably, in step (4), the modified biomass fiber material is prepared as follows: one or more of the following are added to hot water to soften the fiber for 8-24 hours: loofah fiber, corn stalk fiber, horned melon fiber, and coconut shell fiber. The softened fiber is then removed, washed, and dried for later use. The fiber is then added to a 2-5% (mass percentage) sodium hydroxide solution and soaked for 3-4 hours. The fiber is then removed and washed with anhydrous ethanol and distilled water 3-5 times in sequence. After drying, the fiber skeleton is obtained.

[0029] The fiber skeleton is transferred into a tube furnace, protected by nitrogen, and the furnace temperature is raised to 500-650°C at a rate of 5-8°C / min. This temperature is maintained for 2 hours for high-temperature calcination. After cooling to room temperature and crushing, the modified biomass fiber material is obtained. This invention has the following advantages compared to existing technologies:

[0030] (1) The self-dissolving and permeable pollutant blocking material for groundwater treatment prepared in this invention uses a soluble and corrosive active material. While ensuring the material's activity, it is injected underground via grouting. After solidification, the material retains its integrity. This eliminates the defect of reduced material strength caused by internal stress generated after the injection of grouting foam materials. The viscosity of foamed materials needs to be adjusted appropriately during grouting, resulting in a prolonged initial setting time and increasing the risk of material erosion. The integral molding and grouting process of this invention ensures material strength while increasing its erosion resistance. The initial setting time is 10–25 minutes, the strength can reach 18 MPa in 1 hour, and the final strength can reach 75.3 MPa after 28 days of underwater curing.

[0031] (2) The self-dissolving permeable pollutant blocking material for groundwater treatment prepared in this invention uses soluble graded porous aggregate. The material has a slow-release shell, the thickness of which is increased or decreased according to the concentration and type of pollutants in the water. The core active material can be changed or replaced according to the concentration and type of pollutants. At the same time, the gradation can be changed to enhance the treatment efficiency. The self-dissolving pore structure is mainly based on the overall gradation of the material. The more reasonable the gradation, the better the pore distribution can improve the sewage treatment efficiency. Due to the shell self-dissolving effect of the self-dissolving aggregate, after the main material is formed, the pores are gradually exposed due to the erosion of water flow and the directional guiding effect of water pressure. As the water flow gradually penetrates, the pore structure gradually improves. The ingenuity of this invention lies in the fact that the active material inside the pores is confined within the graded pores, which can effectively increase the contact area between the active material and the pollutants, thereby improving the pollutant treatment efficiency.

[0032] (3) The self-dissolving permeable pollutant blocking material for groundwater treatment prepared in this invention uses modified biomass fiber materials and nanoporous aggregates. The nanoporous aggregates compensate for the particle isolation phenomenon between graded aggregates and increase the overall material connectivity. Due to the high activity and poor dispersibility of nZVI, the aggregates are coated with self-dissolving pectin, which is more difficult to dissolve, to increase connectivity while ensuring efficient filtration. Similarly, the modified biomass fibers also provide skeletal connectivity. By carrying capillary bridges, the pore connectivity is further improved. Before the self-dissolving aggregates have fully reacted, the bio-fiber bridges have become an important channel for water flow. At the same time, they can be loaded with high-level surfactants to expand the purification field of the material.

[0033] (4) This invention, employing grouting or injection methods, greatly expands the application range of reactive walls. Due to the difficulty in controlling the diffusion of deep-seated pollution plumes, and the inherent drawbacks of reactive walls primarily using surface treatment methods, there are very few methods for in-situ treatment of deep-seated pollution plumes. By injecting a self-dissolving, permeable pollutant-blocking material downstream of the pollution plume, the plume is cut off. Purification is achieved through a "layer-by-layer filtration" process. Once the reaction is complete, the material matrix becomes a completely permeable material with low resistance. At this point, the chemical filtration function fails, and the material can act as a support. After the water quality test is passed, the pollution plume is completely treated. Detailed Implementation

[0034] The present invention will be further described below with reference to specific embodiments. The advantages and features of the present invention will become clearer with further description. However, the embodiments are merely exemplary and do not constitute any limitation on the scope of the present invention. Those skilled in the art should understand that modifications or substitutions can be made to the details and form of the technical solutions of the present invention without departing from the spirit and scope of the present invention, but all such modifications and substitutions fall within the protection scope of the present invention.

[0035] Example 1:

[0036] (1) Overall material proportions: 30% cement (25% PO52.5R, 15% PC52.5R, 60% SAC725R), 15% 2CaSO4·H2O, 9% fly ash, 25% graded pore-forming aggregate, 15% nano-pore-forming aggregate, 1.5% viscosity modifier (15% ethylene acetate copolymer, 50% sodium silicate, 35% polycarboxylate water-reducing agent), 1% early strength agent (30% lithium carbonate, 20% calcium hydroxide, 15% calcium formate, 15% calcium chloride, 20% aluminum chloride), 3.5% modified biomass fiber (10% loofah fiber, 25% corn stalk fiber, 25% horned melon fiber, 40% coconut shell fiber);

[0037] (2) Preparation of modified biomass fibers: Loofah fiber, corn stalk fiber, horned melon fiber, and coconut shell fiber were soaked in hot water for 24 hours to soften them. After being removed, washed, and dried, they were soaked in a 5% (mass percentage) sodium hydroxide solution for 3 hours. Then, they were washed five times with anhydrous ethanol and distilled water, and dried. The dried fibers were then transferred into a tube furnace under nitrogen protection. The furnace temperature was raised to 650℃ at a rate of 5℃ / min and held at that temperature for 2 hours for high-temperature calcination. After cooling and crushing, the modified biomass fiber material was obtained.

[0038] (3) Weigh the cement, 2CaSO4·H2O, fly ash, viscosity modifier, early strength agent, graded pore-forming aggregate, and nano pore-forming aggregate, add 0.33% water of the total mass, stir evenly to prepare a slurry, and then add the modified biomass fiber material to the slurry. Stir at 150r / min until the slurry is uniform and then pour it into the mold.

[0039] Example 2:

[0040] (1) Overall material proportions: cement 25% (PO52.5R 25%, PC52.5R 15%, SAC725R 60%), 2CaSO4·H2O 17%, fly ash 8%, graded pore-forming aggregate 28%, nano-pore-forming aggregate 15%, viscosity modifier 1.5% (ethylene ethyl acetate copolymer 15%, sodium silicate 50%, polycarboxylate water-reducing agent 35%), early strength agent 1% (lithium carbonate 30%, calcium hydroxide 20%, calcium formate 15%, calcium chloride 15%, aluminum chloride 20%), modified biomass fiber 4.5% (loofah fiber 10%, corn stalk fiber 25%, horned melon fiber 25%, coconut shell fiber 40%);

[0041] (2) Preparation of modified biomass fibers: Loofah fiber, corn stalk fiber, horned melon fiber, and coconut shell fiber were soaked in hot water for 24 hours to soften them. After being removed, washed, and dried, they were soaked in a 5% (mass percentage) sodium hydroxide solution for 3 hours. Then, they were washed five times with anhydrous ethanol and distilled water, and dried. The dried fibers were then transferred into a tube furnace under nitrogen protection. The furnace temperature was raised to 650℃ at a rate of 5℃ / min and held at that temperature for 2 hours for high-temperature calcination. After cooling and crushing, the modified biomass fiber material was obtained.

[0042] (3) Weigh the cement, 2CaSO4·H2O, fly ash, viscosity modifier, early strength agent, graded pore-forming aggregate, and nano pore-forming aggregate, add 0.33% water of the total mass, stir evenly to prepare a slurry, and then add the modified biomass fiber material to the slurry. Stir at 150r / min until the slurry is uniform and then pour it into the mold.

[0043] Example 3:

[0044] (1) Overall material proportions: cement 25% (PO52.5R 25%, PC52.5R 15%, SAC725R 60%), 2CaSO4·H2O 17%, fly ash 8%, graded pore-forming aggregate 28%, nano-pore-forming aggregate 15%, viscosity modifier 1.5% (ethylene ethyl acetate copolymer 15%, sodium silicate 50%, polycarboxylate water-reducing agent 35%), early strength agent 1% (lithium carbonate 30%, calcium hydroxide 20%, calcium formate 15%, calcium chloride 15%, aluminum chloride 20%), modified biomass fiber 4.5% (loofah fiber 10%, corn stalk fiber 25%, horned melon fiber 25%, coconut shell fiber 40%);

[0045] (2) Preparation of modified biomass fibers: Loofah fiber, corn stalk fiber, horned melon fiber, and coconut shell fiber were soaked in hot water for 10 hours to soften them. After being removed, washed, and dried, they were soaked in a 3% (mass percentage) sodium hydroxide solution for 4 hours. After that, they were washed five times with anhydrous ethanol and distilled water, and then dried. The dried fibers were transferred into a tube furnace, protected with nitrogen, and the temperature inside the furnace was raised to 550℃ at a heating rate of 8℃ / min. The temperature was held for 2 hours for high-temperature calcination. After cooling and crushing, the modified biomass fiber material was obtained.

[0046] (3) Weigh the cement, 2CaSO4·H2O, fly ash, viscosity modifier, early strength agent, graded pore-forming aggregate, and nano pore-forming aggregate, add 0.34% water of the total mass, stir evenly to prepare a slurry, and then add the modified biomass fiber material to the slurry. Stir at 150r / min until the slurry is uniform and then pour it into the mold.

[0047] Table 1. Material structure and adsorption properties of the examples

[0048]

[0049] Cr 6+ Removal rate refers to the removal rate of 1g of material sample in a Cr concentration of 20mg / L. 6+ The removal rate of the solution over 6 hours was determined under the following conditions: 25 ± 0.5℃ and stirring at 150 r / min.

[0050] Cr 2+ Removal rate refers to the removal rate of 1g of material sample in a Cr concentration of 20mg / L. 6+ The removal rate of the solution over 6 hours was determined under the following conditions: 25 ± 0.5 °C and stirring at 150 r / min.

Claims

1. A self-dissolving, permeable pollutant-blocking material for groundwater treatment, characterized in that, The product is composed of the following raw materials by mass percentage: cement 25-35%, 2CaSO4·H2O 12-18%, fly ash 8-15%, graded porous aggregate 25-30%, nano porous aggregate 14-18%, viscosity modifier 1-1.5%, early strength agent 0.5-1%, modified biomass fiber 3-4.5%, and the sum of the contents of the above raw materials is 100%. The graded porous aggregate consists of zero-valent iron particles coated with starch-based compounds, and the particle size of the zero-valent iron particles is 100-1500 micrometers. The nanoporous aggregate is pectin-coated nZVI particles; The modified biomass fiber is obtained by softening, washing, drying, soaking in sodium hydroxide solution, washing and drying again, and then calcining at high temperature of 500-650°C under inert gas protection and then crushing. The modified biomass fiber is a mixture of one or more of the following: loofah fiber, corn stalk fiber, horned melon fiber, and coconut shell fiber, in any proportion.

2. The self-dissolving and permeable pollutant blocking material for groundwater treatment according to claim 1, characterized in that, The starch compounds consist of 21% G50 amylose, 17% G70 amylose, 30% G80 amylose, 31% glycerol, and 1% sodium chloride.

3. The self-dissolving and permeable pollutant blocking material for groundwater treatment according to claim 1, characterized in that, The cement is one or more of PO52.5R type silicate cement, PC52.5R silicate cement, and SAC725R sulfoaluminate cement, mixed in any proportion.

4. The self-dissolving and permeable pollutant blocking material for groundwater treatment according to claim 1, characterized in that, The 2CaSO4·H2O mentioned is β-type hemihydrate gypsum calcined at 200℃ with a mesh size of 300.

5. A self-dissolving, permeable pollutant blocking material for groundwater treatment according to claim 1, characterized in that, The fly ash mentioned is Class C fly ash with a mesh size of 300 mesh.

6. A self-dissolving permeable pollutant blocking material for groundwater treatment according to claim 1, characterized in that, The viscosity modifier is one or more of ethylene ethyl acetate copolymer, sodium silicate, and polycarboxylate water-reducing agent, mixed in any proportion.

7. A self-dissolving permeable pollutant blocking material for groundwater treatment according to claim 1, characterized in that, The early strength agent is one or more of lithium carbonate, calcium hydroxide, calcium formate, calcium chloride, and aluminum chloride, mixed in any proportion.

8. A method for preparing a self-dissolving, permeable pollutant blocking material for groundwater treatment according to claims 1-6, characterized in that, It includes the following steps: (1) Material preparation: cement, 2CaSO4·H2O, fly ash, viscosity modifier, early strength agent; (2) Preparation of graded porous aggregate: The graded porous aggregate is a starch-based compound coated with zero-valent iron particles with a particle size of 100-1500 micrometers. The particles are prepared under vacuum negative pressure and then freeze-dried in a nitrogen atmosphere at -40℃ to obtain the graded porous aggregate. (3) Preparation of nanoporous aggregate: pectin-coated nZVI particles are prepared by water bath under nitrogen protection to obtain granules, and then the particles are freeze-dried in nitrogen atmosphere at -40℃ to obtain nanoporous aggregate. (4) Preparation of modified biomass fiber materials: The modified biomass fiber materials are made from one or more of the following: loofah fiber, corn stalk fiber, horned melon fiber, and coconut shell fiber. After softening for 8-24 hours, washing and drying, soaking in sodium hydroxide solution for 3-4 hours, washing with anhydrous ethanol and distilled water 3-5 times, the materials are then transferred into a tube furnace, protected by nitrogen gas, and the furnace temperature is raised to 500-650℃ at a heating rate of 5-8℃ / min. The temperature is held for 2 hours for high-temperature calcination. After cooling to room temperature and crushing, the modified biomass fiber materials can be obtained. (5) Weigh cement, 2CaSO4·H2O, fly ash, viscosity modifier, early strength agent, graded porous aggregate, and nano porous aggregate, then add 0.32–0.35% water by weight of the total mass and stir to prepare a slurry. Add modified biomass fibers to the slurry, stir evenly, and then cast into a mold to obtain a self-dissolving, permeable pollutant blocking material for groundwater treatment.

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