Method for repairing groundwater based on in-situ construction of reactive silicon-aluminum polymer reaction zone

Abstract

The application provides a method for repairing groundwater based on in-situ construction of a reaction zone by using active silicon-aluminum polymers, comprising the following steps: A, preparation of a silicon solution and an aluminum solution; B, injection of the silicon solution and the aluminum solution into the same storage tank at the same flow rate to form a silicon-aluminum mixed solution; C, setting a row of injection wells in the direction perpendicular to the groundwater flow direction in the groundwater pollution source area; D, intermittent injection of the silicon-aluminum mixed solution in the multiple injection wells at equal time intervals; the silicon-aluminum mixed solution migrates in the aquifer under the action of concentration difference and groundwater flow, and simultaneously generates an in-situ polymerization reaction to form active silicon-aluminum gel and construct a continuous reaction zone. The reaction zone has no obvious influence on the permeability coefficient of the aquifer, has good migration performance, and has a remarkable removal effect on heavy metals. The application innovatively uses silicon-aluminum materials for the construction of an in-situ reaction zone, has little influence on the groundwater acid-base environment, and can support the implementation of groundwater remediation engineering from raw materials to technology.

Description

Technical Field

[0001] This invention belongs to the field of groundwater pollution remediation technology, and relates to a method for in-situ construction of reaction zones to remediate polluted groundwater, specifically a method for in-situ construction of reaction zones based on active silica-alumina polymers to remediate groundwater. Background Technology

[0002] Groundwater, with its stable supply and good quality, is a vital water source for agricultural irrigation, industrial manufacturing, and urban domestic water use, making it an indispensable resource for human production and daily life. However, the complex geological structure beneath the Earth's surface and the slow flow of groundwater make remediation extremely difficult once polluted. Heavy metal pollution in groundwater is characterized by its cumulative, delayed, hidden, and irreversible nature. In-situ reactive remediation technology involves injecting reactive reagents to create a permeable contaminant treatment zone within the underground environment. Heavy metal pollutants migrating to this zone are intercepted, adsorbed, and immobilized, altering their form within the aquifer and reducing their mobility and bioavailability.

[0003] The existing patent for the preparation of related materials, CN115504712A, discloses a geopolymer material solidified with heavy metal ions and its preparation method. The effective component of the geopolymer is an inorganic polymer formed by the condensation of silicon-oxygen tetrahedra and aluminum-oxygen tetrahedra. Specifically, it uses red mud, Class I fly ash and quicklime powder as basic raw materials, adds 0.5-3.0% by mass of heavy metal salts, and prepares a solidified heavy metal geopolymer under the action of an alkaline activator. The concentrations of heavy metal ions copper, lead and cadmium in the leachate of the solidified body, as determined by different leaching methods, all meet the national standards. Existing patents related to the construction of in-situ reaction zones for groundwater include CN109290350A, which discloses a method for constructing nano-ferrous sulfide reaction zones in situ to remediate contaminated groundwater. This method involves drilling one or more injection wells near the pollution source along the groundwater flow direction, and intermittently injecting a solution of sodium sulfide, a mixed solution of ferrous sulfate and sodium dithionite into the wells. This oxidation-reduction reaction in the aquifer forms nano-ferrous sulfide reaction zones, thus remediating the contaminated groundwater. CN109013678A discloses a method for preparing porous silicon-coated zero-valent iron materials for in-situ remediation of groundwater pollution. While also using iron materials, this method modifies the zero-valent iron through a coating process. However, a common problem with iron materials is that the particles are prone to agglomeration and oxidation due to the groundwater environment, thus limiting the formation of reaction zones and the ability to remove heavy metals. Currently, there are no reports of using silicon-aluminum polymer materials for the construction of in-situ reaction zones for groundwater and the remediation of heavy metal-contaminated groundwater. Summary of the Invention

[0004] This invention addresses the problems of existing technologies by providing a method for constructing in-situ reaction zones using silicon-aluminum materials to remediate groundwater contaminated with heavy metals. This reaction zone is formed in a liquid-solid two-phase migration, polymerization-construction mode, effectively adsorbing and immobilizing heavy metals while exhibiting good acid-base stability and minimal susceptibility to the groundwater environment. This method, from raw materials to technology, can support the implementation of groundwater remediation projects and has promising application prospects.

[0005] The technical solution adopted in this invention is as follows:

[0006] A method for groundwater remediation based on in-situ construction of reactive zones using active silica-alumina polymers includes the following steps:

[0007] A. Preparation of silicon and aluminum solutions: By mass percentage, 0.1%-0.5% of the silicon source reagent is dissolved in 99.5%-99.9% deionized water to prepare a silicon solution; by mass percentage, 0.1%-0.5% of the aluminum source reagent is dissolved in 99.5%-99.9% deionized water to prepare an aluminum solution.

[0008] B. Inject the above silicon solution and aluminum solution into the same storage tank at the same flow rate, stirring while injecting, to form a silicon-aluminum mixed solution;

[0009] C. Within the groundwater pollution source area, a row of injection wells shall be set up in a direction perpendicular to the groundwater flow direction, with a spacing of 1-2m between the injection wells; at least one observation well shall be set up 3-5m downstream of the center of the injection well row. The injection wells and observation wells shall both reach the bottom of the aquifer, and the bottom surfaces and vadose zone sections of the injection wells and observation wells shall be sealed, with water permeable only in the aquifer section.

[0010] D. The silica-alumina mixed solution from step B is simultaneously injected intermittently at equal time intervals into multiple injection wells using a pulsed injection method. Under the influence of concentration difference and groundwater flow, the silica-alumina mixed solution migrates in the aquifer and simultaneously undergoes an in-situ polymerization reaction to form an active silica-alumina gel. The gel particles continue to migrate through pores under the influence of water flow, forming a continuous reaction zone. In the downstream observation wells of the groundwater flow direction, the formation of the reaction zone is monitored in real time by monitoring changes in silica-alumina content and pH until the reaction zone reaches the boundary of the pollution plume, at which point the injection is stopped. After the injection is stopped, the stability of the active silica-alumina polymer reaction zone is continuously monitored.

[0011] Furthermore, the silicon source reagent is sodium metasilicate nonahydrate, the aluminum source reagent is sodium aluminate, the mass ratio of silicon source reagent to aluminum source reagent is 3:2, and the silicon solution and aluminum solution must be prepared fresh for use.

[0012] Furthermore, an alkaline reagent is added to the silicon-aluminum mixed solution according to the different pH levels of the groundwater;

[0013] The mass ratio of alkaline reagent added to the silicon-aluminum mixed solution is as follows:

[0014] A-1, Strongly acidic groundwater, pH≤5.0, add 0.4%-0.5% alkaline reagent;

[0015] B-1, weakly acidic groundwater, 5.0 < pH ≤ 6.5, add 0.2%-0.4% alkaline reagent;

[0016] C-1, Neutral and weakly alkaline water, 6.5 < pH ≤ 9.0, no need to add alkali reagent.

[0017] Furthermore, the alkaline reagent is sodium hydroxide.

[0018] The beneficial effects obtained by this invention are as follows:

[0019] 1. When a silica-alumina solution is injected into groundwater, the solution diffuses and migrates within underground pores due to the concentration gradient and groundwater flow. Under the influence of mixing and dilution, polymerization occurs as the pH decreases, forming a silica-alumina polymer gel. The gel has a negative zeta potential, which facilitates its migration in the generally negatively charged aquifer medium and makes it less susceptible to adsorption. The gel particle size corresponds to the pore size, allowing it to continue migrating through the pores under the influence of water flow. This liquid-solid two-phase migration and simultaneous polymerization and construction ultimately forms an active silica-alumina polymer reaction zone. This method effectively solves the problems of agglomeration, blockage of injection wells and underground aquifer media, and poor migration of solid materials such as nanoparticles after in-situ injection. Experiments show that the silica-alumina polymer reaction zone constructed using this method did not significantly affect the permeability coefficient in aquifer media of different sizes, and its migration effect is superior to that of traditional solid materials.

[0020] 2. This gel has a geopolymer structure and exhibits excellent adsorption and fixation capabilities for multiple heavy metals coexisting in groundwater. Its mechanism of action includes ion exchange and precipitation, as well as physical encapsulation and ion bonding. Furthermore, this invention injects the raw materials as a mixed solution, which, compared to existing technologies that inject the raw material solutions separately into the aquifer for reaction, improves the efficiency of the reaction reagents.

[0021] 3. This invention is guided by the actual needs of groundwater remediation at the site, and breaks through the industrial processing and production bottlenecks that are commonly faced in material research and development. The raw materials selected have all achieved industrial-scale production, which supports the implementation of the method for in-situ construction of active silicon-aluminum polymer reaction zones. Attached Figure Description

[0022] Figure 1 This is a planar layout diagram of the in-situ active silicon-aluminum polymer reaction zone construction of the present invention;

[0023] Figure 2This is a schematic diagram of the simulated column structure in this invention;

[0024] Figure 3 This is a graph showing the change in silicon concentration in the simulated column of this invention.

[0025] Figure 4 This is a top view of the simulated groove of the present invention;

[0026] Figure 5 This is a side view of the simulated groove of the present invention;

[0027] Figure 1 In the diagram, 1 is the injection well, 2 is the observation well, 3 is the pollution source area, 4 is the pollution plume, and 5 is the groundwater flow direction. Detailed Implementation

[0028] To more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0029] In practice, the method for remediating groundwater based on in-situ construction of reaction zones using active silica-alumina polymers includes the following steps:

[0030] A. Preparation of silicon and aluminum solutions: By mass percentage, 0.1%-0.5% of the silicon source reagent is dissolved in 99.5%-99.9% deionized water to prepare a silicon solution; by mass percentage, 0.1%-0.5% of the aluminum source reagent is dissolved in 99.5%-99.9% deionized water to prepare an aluminum solution.

[0031] B. Inject the above silicon solution and aluminum solution into the same storage tank at the same flow rate, stirring while injecting, to form a silicon-aluminum mixed solution;

[0032] C. For example Figure 1 As shown, within the groundwater pollution source area 3, a row of injection wells is set in a direction perpendicular to the groundwater flow direction, with a spacing of 1-2m between injection wells 1; at least one observation well 2 is set 3-5m downstream of the center of the row of injection wells 1. Both injection wells 1 and observation wells 2 are deep enough to reach the bottom of the aquifer, and the bottom surface and vadose zone of injection wells 1 and observation wells 2 are sealed, with water permeating only in the aquifer zone.

[0033] D. The silica-alumina mixed solution from step B is simultaneously injected intermittently at equal time intervals into multiple injection wells 1 using a pulsed injection method. Under the influence of concentration difference and groundwater flow, the silica-alumina mixed solution migrates in the aquifer and simultaneously undergoes an in-situ polymerization reaction to form an active silica-alumina gel. The gel particles continue to migrate through pores under the influence of water flow, forming a continuous reaction zone. In the downstream observation well 2 of the groundwater flow direction 5, the formation of the reaction zone is monitored in real time by monitoring changes in silica-alumina content and pH until the reaction zone reaches the boundary of the pollution plume 4. After stopping the injection, the stability of the active silica-alumina polymer reaction zone is monitored.

[0034] The silicon source reagent is sodium metasilicate nonahydrate, and the aluminum source reagent is sodium aluminate. The mass ratio of silicon source reagent to aluminum source reagent is 3:2, and both silicon and aluminum solutions must be prepared fresh for use.

[0035] Depending on the pH of the groundwater, sodium hydroxide, an alkaline reagent, is added to the silica-alumina mixed solution. The mass ratio of the alkaline reagent added to the silica-alumina mixed solution is as follows:

[0036] A-1, Strongly acidic groundwater, pH≤5.0, add 0.4%-0.5% alkaline reagent;

[0037] B-1, weakly acidic groundwater, 5.0 < pH ≤ 6.5, add 0.2%-0.4% alkaline reagent;

[0038] C-1, Neutral and weakly alkaline water, 6.5 < pH ≤ 9.0, no need to add alkali reagent.

[0039] Example 1

[0040] In a simulated column filled with medium sand, such as Figure 2 As shown, a multi-metal composite pollutant solution was injected into the left side to saturate it, simulating an aquifer contaminated with heavy metals. The simulated column was 70 cm long and 5 cm in radius, with medium sand particles ranging from 0.25 to 0.55 mm in size. The water flow rate in the simulated column was 5 cm / d. The concentrations of cadmium, nickel, and zinc in the multi-metal composite pollutant solution exceeded the Class III groundwater quality standard by 20-30 times, and the pH was 4.5.

[0041] 100g of a silicon solution was prepared by dissolving 0.3% sodium metasilicate nonahydrate in 99.7% deionized water, and 100g of an aluminum solution was prepared by dissolving 0.2% sodium aluminate in 99.8% deionized water. The prepared silicon and aluminum solutions were mixed in the same beaker, and 0.8g of sodium hydroxide was added to form a silicon-aluminum mixed solution. Using well b as the injection well, the solution was injected with a syringe. Under the influence of concentration gradient and groundwater flow, the mixed solution migrated within the aquifer, simultaneously undergoing an in-situ polymerization reaction to form an active silicon-aluminum gel. The gel particles continued to migrate through the pores under the influence of the water flow, forming a continuous reaction zone. Samples were taken from wells a, b, c, d, and e to test the silicon-aluminum content. Figure 3 The silicon concentration in the mixed solution decreased continuously in the direction of groundwater flow, indicating the gradual formation of the reaction zone. The persistently low silicon concentration in the later stages suggests good stability of the reaction zone within the groundwater environment. After the injection of the silicon-aluminum mixed solution, the concentrations of cadmium, nickel, and zinc in the aquifer decreased from 138, 412, and 21500 μg / L at the inlet to 1.03, 3.64, and 129 μg / L at the outlet, respectively, all meeting the Class III groundwater quality standard and remaining stable for 70-80 hours.

[0042] Example 2

[0043] In a simulated tank filled with medium sand, such as Figure 4 and 5 As shown, the aquifer is filled with a multi-metal composite contaminated liquid. The groundwater flows from left to right. A row of injection wells is installed perpendicular to the groundwater flow direction. The simulated tank measures 80×40×40cm (length×width×height), with six injection holes in a row. Monitoring is conducted on the side of the simulated tank and downstream behind the aquifer. The injection wells reach the bottom of the aquifer and are sealed at the bottom. The medium sand particles are 0.25-0.55mm in size. The water flow velocity in the simulated tank is 5cm / d. The concentrations of cadmium, nickel, and zinc in the multi-metal composite contaminated liquid exceed the Class III groundwater quality standard by 20-30 times, and the pH is 6.0.

[0044] A silicon solution of 1740g was prepared by dissolving 0.36% sodium metasilicate nonahydrate in 99.64% deionized water, and an aluminum solution of 1740g was prepared by dissolving 0.24% sodium aluminate in 99.76% deionized water. The prepared silicon and aluminum solutions were mixed in the same plastic container, and 10.44g of sodium hydroxide was added to form a silicon-aluminum mixed solution.

[0045] Injection was carried out simultaneously at equal time intervals in six injection holes using a peristaltic pump, with an injection time of 1 hour. The mixed solution migrated within the aquifer under the influence of concentration gradient and groundwater flow, simultaneously undergoing in-situ polymerization to form active silica-alumina gel. The gel particles continued to migrate through pores under the influence of water flow, forming a continuous reaction zone. Samples were taken from the side of the simulated tank and downstream of the baffle plate to test changes in silica-alumina content and pH, and the formation and stability of the active silica-alumina polymer reaction zone were monitored in real time. The results showed that after the silica-alumina mixed solution was injected, the reaction zone gradually formed along the groundwater flow direction and exhibited good stability. The concentrations of cadmium, nickel, and zinc in the aquifer decreased from 143, 445, and 22630 μg / L at the inlet to 1.25, 3.14, and 112 μg / L at the outlet, respectively, all meeting the Class III groundwater quality standard.

[0046] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for remediating groundwater by in-situ construction of reaction zones based on active silica-alumina polymers, characterized in that: Includes the following steps: A. Preparation of silicon and aluminum solutions: By mass percentage, dissolve 0.1%-0.5% of the silicon source reagent in 99.5%-99.9% deionized water to prepare a silicon solution; by mass percentage, dissolve 0.1%-0.5% of the aluminum source reagent in 99.5%-99.9% deionized water to prepare an aluminum solution. B. Inject the above silicon solution and aluminum solution into the same storage tank at the same flow rate, stirring while injecting, to form a silicon-aluminum mixed solution; C. Within the groundwater pollution source area, a row of injection wells shall be set up in a direction perpendicular to the groundwater flow direction, with a spacing of 1-2m between the injection wells; at least one observation well shall be set up 3-5m downstream of the center of the injection well row. The injection wells and observation wells shall both reach the bottom of the aquifer, and the bottom surfaces and vadose zone sections of the injection wells and observation wells shall be sealed, with water permeable only in the aquifer section. D. The silica-alumina mixed solution from step B is simultaneously injected intermittently at equal time intervals into multiple injection wells using a pulsed injection method. Under the influence of concentration difference and groundwater flow, the silica-alumina mixed solution migrates in the aquifer and simultaneously undergoes an in-situ polymerization reaction to form an active silica-alumina gel. The gel particles continue to migrate through pores under the influence of water flow, forming a continuous reaction zone. In the downstream observation wells of the groundwater flow direction, the formation of the reaction zone is monitored in real time by monitoring changes in silica-alumina content and pH until the reaction zone reaches the boundary of the contamination plume. After stopping the injection, the stability of the active silica-alumina polymer reaction zone is continuously monitored. The silicon-aluminum mixed solution is supplemented with alkaline reagents according to the different pH levels of the groundwater; The mass ratio of alkaline reagent added to the silicon-aluminum mixed solution is as follows: A-1, Strongly acidic groundwater, pH≤5.0, add 0.4%-0.5% alkaline reagent; B-1, weakly acidic groundwater, 5.0 < pH ≤ 6.5, add 0.2%-0.4% alkaline reagent; C-1, Neutral and weakly alkaline water, 6.5 < pH ≤ 9.0, no need to add alkali reagent.

2. The method for remediating groundwater based on in-situ construction of reaction zones using active silica-alumina polymers according to claim 1, characterized in that: The silicon source reagent is sodium metasilicate nonahydrate, and the aluminum source reagent is sodium aluminate. The mass ratio of silicon source reagent to aluminum source reagent is 3:2, and the silicon solution and aluminum solution must be prepared fresh for use.

3. The method for remediating groundwater based on in-situ construction of reaction zones using active silica-alumina polymers according to claim 2, characterized in that: The alkaline reagent is sodium hydroxide.

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