Groundwater permeable reaction wall and groundwater repair method

Abstract

The present invention discloses a groundwater permeable reaction wall and a groundwater remediation method, which belong to the technical field of groundwater pollution remediation. The groundwater permeable reaction wall includes a reaction wall and two water-blocking walls, the two water-blocking walls are symmetrically arranged on both sides of the reaction wall, and the pollution plume is located between the two water-blocking walls; perpendicular to the flow direction of groundwater, the reaction wall extends from the upper end of the underground aquifer to the lower end of the underground aquifer; the reaction wall includes a quartz sand layer, an iron powder layer, a hydroxyapatite layer and a biochar layer, and the quartz sand layer, the iron powder layer, the hydroxyapatite layer and the biochar layer are arranged in sequence along the flow direction of groundwater. The reaction wall of the specific structure of the present invention can play a good role in filtering, precipitation and adsorption, has a good interception effect on uranium, comprehensively considers environmental friendliness and remediation sustainability, can effectively prevent the reaction wall from being blocked, improves the reaction wall remediation efficiency, and reduces the remediation cost.

Description

Technical Field

[0001] The present invention relates to the technical field of groundwater remediation, and in particular to a groundwater permeable reaction wall and a groundwater remediation method. Background Art

[0002] Uranium is an extremely important energy source and a raw material for nuclear weapons and nuclear medicine. It is used in the production of nuclear fuel, nuclear weapons, and radiotherapy and diagnostics. However, uranium mining, transportation, storage, and processing can lead to leakage, as well as the direct discharge of uranium-containing wastewater and residue, which can lead to groundwater contamination. Because uranium is extremely radioactive, excessive radiation can cause damage to the human body's hematopoietic organs, nervous system, reproductive system, and digestive system, raising concerns about uranium contamination of groundwater. Furthermore, when uranium enters the human body through the food chain, it is absorbed and deposited in the kidneys and bones, causing irreversible damage to these areas. This damage can reduce the body's absorption of protein. Therefore, cost-effective remediation of uranium-contaminated groundwater is crucial for protecting human health and improving the ecological environment.

[0003] Currently, some scholars have used permeable reactive wall technology to remediate groundwater contamination. For example, biochar and iron powder are used as filling materials for permeable reactive walls to remediate trichloroethylene-contaminated groundwater. This material mainly utilizes the reducing effect of iron powder and the adsorption effect of biochar. In the laboratory, this material can remove trichloroethylene at a rate of up to 98.2%. Compared with groundwater extraction and treatment technology, permeable reactive walls have the advantages of less interference with the groundwater flow field, less risk of secondary pollution, easy construction, and simple structure. In addition, studies have shown that permeable reactive wall technology has a good removal rate for lead and cadmium. However, the geological conditions of the actual contaminated area, engineering design, and filling materials of the permeable reactive wall will have a significant impact on the removal efficiency of the permeable reactive wall remediation technology.

[0004] Therefore, developing a groundwater permeable reaction wall that can effectively repair uranium-contaminated groundwater is a technical problem that needs to be solved urgently. Summary of the Invention

[0005] Based on the defects of the existing technology, the purpose of the present invention is to provide a groundwater permeable reaction wall and a groundwater repair method.

[0006] In order to achieve the above object, the technical solution adopted by the present invention is:

[0007] In the first aspect, the present invention provides a groundwater permeable reaction wall comprising a reaction wall and two water-retaining walls, wherein the two water-retaining walls are symmetrically arranged on both sides of the reaction wall, and the pollution plume is located between the two water-retaining walls; the reaction wall extends from the upper end of the underground aquifer to the lower end of the underground aquifer perpendicular to the flow direction of the groundwater; the reaction wall comprises a quartz sand layer, an iron powder layer, a hydroxyapatite layer and a biochar layer, and the quartz sand layer, the iron powder layer, the hydroxyapatite layer and the biochar layer are arranged in sequence along the flow direction of the groundwater.

[0008] As a preferred embodiment of the present invention, the length of the reaction wall is not less than 3 m, and the length of the reaction wall is the dimension of the reaction wall perpendicular to the direction of groundwater flow.

[0009] As a preferred embodiment of the present invention, the width of the reaction wall is not less than 1.6 m, and the width of the reaction wall is the dimension of the reaction wall parallel to the direction of groundwater flow.

[0010] Furthermore, in extremely slightly permeable strata, the width of the reaction wall is not less than 1.6 m; in slightly permeable strata, the width of the reaction wall is not less than 2 m; in weakly permeable strata, the width of the reaction wall is not less than 2.4 m.

[0011] In the present invention, the extremely micro-permeable stratum has a permeability coefficient K < 10 -6 cm / s underground aquifer; the micro-permeable stratum has a permeability coefficient K that satisfies 10 -6 cm / s≤K<10 -5 cm / s underground aquifer; the weakly permeable stratum is a stratum with a permeability coefficient K satisfying 10 -5 cm / s≤K<10 -4 cm / s underground aquifer.

[0012] As a preferred embodiment of the present invention, the size of the quartz sand layer parallel to the direction of groundwater flow is 0.1-0.5m, the size of the iron powder layer parallel to the direction of groundwater flow is 0.3-1.0m, the size of the hydroxyapatite layer parallel to the direction of groundwater flow is 0.3-1.0m, and the size of the biochar layer parallel to the direction of groundwater flow is 0.5-1.5m.

[0013] As a preferred embodiment of the present invention, monitoring holes are provided on the reaction wall.

[0014] In a second aspect, the present invention provides a method for remediating uranium-contaminated groundwater, comprising the following steps:

[0015] S1. Conduct geological exploration in the contaminated area to determine the geological structure and test the permeability of the underground aquifer; collect multiple groundwater samples for uranium concentration testing to determine the contamination plume;

[0016] The geological structure includes geological structure information and groundwater flow direction;

[0017] S2. constructing a groundwater permeable reactive wall as described in the first aspect downstream of the pollution plume;

[0018] S3. The first monitoring well 4, the second monitoring well, and the third monitoring well are arranged in sequence in the direction of groundwater flow. The first monitoring well and the third monitoring well are located on both sides of the reaction wall, and the second monitoring well is inserted in the reaction wall.

[0019] As a preferred embodiment of the present invention, step S1 employs geological radar for geological exploration. Compared to traditional geological exploration methods, geological radar can detect the geological structure of underground objects without damaging or altering the structure of the contaminated area. Furthermore, geological radar is low-cost and can obtain detection results in a short period of time.

[0020] As a preferred embodiment of the present invention, in step S1, the permeability coefficient of the underground aquifer is measured by a simple water injection test with a decreasing head or a simple water injection test with a constant head;

[0021] The calculation formula of the permeability coefficient K1 in the simple water head reduction water injection test is as follows:

[0022]

[0023] Where, Q is the injection flow rate (in L / min); l is the length of the test section (in cm); H is the water head height (in cm); r is the radius of the test section borehole (in cm);

[0024] The calculation formula of the permeability coefficient K2 in the simple constant head water injection test is as follows:

[0025]

[0026] Wherein, H1 is the corresponding test head height at time t1 (in cm), H2 is the corresponding test head height at time t2 (in cm), and t1 and t2 are the test times at a certain moment of the water injection test (in min).

[0027] Furthermore, the permeability coefficient of the underground aquifer is the average value of K1 and K2, that is, (K1+K2) / 2.

[0028] As a preferred embodiment of the present invention, step S2 further includes: arranging monitoring holes on the reaction wall.

[0029] As a preferred embodiment of the present invention, the distance between the first monitoring well and the reaction wall is 0.5-2m, and the distance between the third monitoring well and the reaction wall is 0.5-2m.

[0030] As a preferred embodiment of the present invention, the diameter of the first monitoring well is 100-200 mm, the diameter of the second monitoring well is 100-200 mm, and the diameter of the third monitoring well is 100-200 mm.

[0031] As a preferred embodiment of the present invention, the first monitoring well, the second monitoring well and the third monitoring well are all inserted with hollow polyethylene pipes, and a plurality of through holes are distributed on the pipe wall of the polyethylene pipe; the bottom of the first monitoring well, the bottom of the second monitoring well and the bottom of the third monitoring well are all on the same horizontal plane as the bottom of the reaction wall.

[0032] Compared with the prior art, the present invention has the following beneficial effects:

[0033] The present invention sequentially arranges a quartz sand layer, an iron powder layer, a hydroxyapatite layer, and a biochar layer along the flow direction of groundwater to form a reaction wall. The quartz sand layer can effectively filter out the sediment in the groundwater to prevent the sediment from clogging the pores of other layers, and can also perform preliminary adsorption on heavy metals; the iron powder is used to reduce hexavalent uranium ions to tetravalent uranium ions; the phosphate released by the hydroxyapatite and the tetravalent uranium ions form a stable uranium phosphate precipitate, and the phosphate-fixed uranium has high selectivity; finally, the biochar is used to adsorb the residual unprecipitated uranium ions, and the iron ions and phosphate ions released by the filling material can also be adsorbed to prevent secondary pollution of the groundwater. The reaction wall of the specific structure of the present invention can play a good role in filtering, precipitation, and adsorption, has a good interception effect on uranium, comprehensively considers environmental friendliness and repair sustainability, can effectively prevent the reaction wall from being blocked, improves the reaction wall repair efficiency, and reduces the repair cost.

[0034] The present invention designs different reaction wall widths for different permeability coefficients, taking into account both hydraulic retention time and economic practicality. This allows uranium in the groundwater to fully react with the filling material, effectively reducing uranium in the groundwater while preserving the filling material of the reaction wall. This ensures the stable operation of the permeable reaction wall. Furthermore, monitoring wells are located in front, middle, and back of the reaction wall. These wells can monitor the water entering and exiting the reaction wall, allowing for real-time observation of the permeable reaction wall's uranium removal rate and its impact on groundwater quality. A monitoring hole is provided at the top of the reaction wall to allow for the removal of filling material, allowing staff to assess the material's operating status, identify problems, and replace them promptly. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 A schematic structural diagram of the groundwater permeable reaction wall provided by the present invention;

[0036] Figure 2 The geological radar spectrum provided by the present invention;

[0037] Figure 3 This is a statistical diagram of the repair structure provided by the present invention.

[0038] In the figure, 1-reaction wall, 11-quartz sand layer, 12-iron powder layer, 13-hydroxyapatite layer, 14-biochar layer, 2-water-retaining wall, 3-pollution plume, 4-first monitoring well, 5-second monitoring well, 6-third monitoring well. DETAILED DESCRIPTION

[0039] In order to better illustrate the purpose, technical solutions and advantages of the present invention, the present invention will be further described below with reference to specific embodiments and comparative examples. The purpose is to provide a detailed understanding of the content of the present invention, but not to limit the present invention. All other embodiments obtained by those of ordinary skill in the art without creative work are within the scope of protection of the present invention.

[0040] The present invention provides a groundwater permeable reaction wall and a groundwater repair method, wherein the groundwater permeable reaction wall is Figure 1 As shown, the groundwater remediation method includes the following steps:

[0041] S1. Conduct geological exploration in the contaminated area to determine the geological structure and permeability coefficient of the underground aquifer; take multiple groundwater samples, test the uranium concentration, and determine the contamination plume;

[0042] The geological structure includes geological structure information and groundwater flow direction;

[0043] S2. A groundwater permeable reaction wall is arranged downstream of the pollution plume 3; the groundwater permeable reaction wall includes a reaction wall 1 and two water-retaining walls 2, the two water-retaining walls 2 are symmetrically arranged on both sides of the reaction wall 1, and the pollution plume 3 is located between the two water-retaining walls 2; the reaction wall 1 extends from the upper end of the underground aquifer to the lower end of the underground aquifer in the direction perpendicular to the flow of groundwater; the reaction wall 1 includes a quartz sand layer 11, an iron powder layer 12, a hydroxyapatite layer 13 and a biochar layer 14, and the quartz sand layer 11, the iron powder layer 12, the hydroxyapatite layer 13 and the biochar layer 14 are arranged in sequence along the flow direction of groundwater.

[0044] S3. The first monitoring well 4, the second monitoring well 5, and the third monitoring well 6 are arranged in sequence in the direction of groundwater flow. The first monitoring well 4 and the third monitoring well 6 are located on both sides of the reaction wall 1, and the second monitoring well 5 is inserted in the reaction wall 1.

[0045] The present invention sequentially arranges a quartz sand layer 11, an iron powder layer 12, a hydroxyapatite layer 13, and a biochar layer 14 along the flow direction of groundwater to form a reaction wall 1. The quartz sand layer 11 can effectively filter out the sediment in the groundwater to prevent the sediment from clogging the pores of other layers, and can also perform preliminary adsorption of heavy metals; the iron powder is used to reduce hexavalent uranium ions to tetravalent uranium ions; the phosphate released by the hydroxyapatite forms a stable uranium phosphate precipitate with the tetravalent uranium ions, and the phosphate fixation of uranium has high selectivity; finally, the biochar is used to adsorb the remaining unprecipitated uranium ions, and can also adsorb the iron ions and phosphate ions in the iron powder layer 12 to prevent secondary pollution of the groundwater. The reaction wall of the specific structure of the present invention can play a good role in filtering, precipitating, and adsorbing, has a good interception effect on uranium, comprehensively considers environmental friendliness and repair sustainability, can effectively prevent the reaction wall from clogging, improves the reaction wall repair efficiency, and reduces the repair cost.

[0046] In one embodiment, step S1 employs geological radar for geological exploration. Compared to traditional geological exploration methods, geological radar can detect the geological structure of underground objects without damaging or altering the structure of the contaminated area. Furthermore, geological radar is low-cost and can obtain detection results in a short period of time.

[0047] In one embodiment, in step S1, the permeability coefficient of the underground aquifer is measured using a simple water injection test with a decreasing head or a simple water injection test with a constant head;

[0048] In the present invention, the calculation formula of the permeability coefficient K1 in the simple precipitation head water injection test is as follows:

[0049]

[0050] Where, Q is the injection flow rate (in L / min); l is the length of the test section (in cm); H is the water head height (in cm); r is the radius of the test section borehole (in cm);

[0051] In the present invention, the calculation formula of the permeability coefficient K2 in the simple constant head water injection test is as follows:

[0052]

[0053] Wherein, H1 is the corresponding test head height at time t1 (in cm), H2 is the corresponding test head height at time t2 (in cm), and t1 and t2 are the test times at a certain moment of the water injection test (in min).

[0054] Specifically, the permeability coefficient of the underground aquifer is the average value of K1 and K2, that is, (K1+K2) / 2.

[0055] In the present invention, the underground aquifer refers to a rock layer below the groundwater level that has water permeability and water supply capabilities.

[0056] In one embodiment, the length of the reaction wall 1 is not less than 3 m, and the length of the reaction wall 1 is the dimension of the reaction wall 1 perpendicular to the direction of groundwater flow.

[0057] In one embodiment, the width of the reaction wall 1 is not less than 1.6m, and the width of the reaction wall 1 is the dimension of the reaction wall 1 parallel to the direction of groundwater flow; specifically, in extremely slightly permeable formations, the width of the reaction wall 1 is not less than 1.6m; in slightly permeable formations, the width of the reaction wall 1 is not less than 2m; in weakly permeable formations, the width of the reaction wall 1 is not less than 2.4m.

[0058] In one embodiment, the depth of the reaction wall 1 is not less than the height of the underground aquifer.

[0059] In the present invention, the permeability coefficient K of the extremely micro-permeable formation satisfies: K<10 -6 cm / s; the permeability coefficient K of the micro-permeable formation satisfies: 10 -6 cm / s≤K<10 -5 cm / s; the permeability coefficient K of the weakly permeable formation satisfies: 10 -5 cm / s≤K<10 -4 cm / s.

[0060] In one embodiment, the width of the quartz sand layer 11 is 0.2-0.5 m, the width of the iron powder layer 12 is 0.5-1.0 m, the width of the hydroxyapatite layer 13 is 0.5-1.0 m, and the width of the biochar layer 14 is 0.7-1.5 m. The sum of the widths of the quartz sand layer 11, the iron powder layer 12, the hydroxyapatite layer 13, and the biochar layer 14 is equal to the width of the reaction wall 1.

[0061] In one embodiment, the width ratio of the quartz sand layer 11 , the iron powder layer 12 , the hydroxyapatite layer 13 , and the biochar layer 14 is 1:(1-2):(1-3):(1-4).

[0062] Furthermore, the width ratio of the quartz sand layer 11 , the iron powder layer 12 , the hydroxyapatite layer 13 and the biochar layer 14 is 1:2:(1.5-2):(3-3.5).

[0063] In one embodiment, the angle between the length direction of the water-blocking wall 2 and the length direction of the reaction wall 1 is 30-75°.

[0064] In one embodiment, the depth of the water-blocking wall 2 is not less than 10 m.

[0065] In one embodiment, step S2 further includes: providing a monitoring hole on the water-blocking wall 2 .

[0066] In one embodiment, the distance between the first monitoring well 4 and the reaction wall 1 is 0.5-2 m, and the distance between the third monitoring well 6 and the reaction wall 1 is 0.5-2 m.

[0067] In one embodiment, the diameter of the first monitoring well 4 is 100-200 mm, the diameter of the second monitoring well 5 is 100-200 mm, and the diameter of the third monitoring well 6 is 100-200 mm.

[0068] In one embodiment, the first monitoring well 4 , the second monitoring well 5 and the third monitoring well 6 are all hollow polyethylene tubes with a plurality of through holes distributed on the tube wall; the bottom of the polyethylene tube is on the same horizontal plane as the bottom of the reaction wall 1 .

[0069] The following examples are provided to facilitate understanding of the present invention. These examples are not provided to limit the scope of the claims.

[0070] The biochar used in the following examples and comparative examples was prepared by carbonizing coconut shells.

[0071] The following examples and comparative examples are used to remediate uranium-contaminated groundwater in different contaminated areas of the same mining area.

[0072] The groundwater in the mining area can be roughly divided into Quaternary pore water, Tertiary sandstone interlayer fissure water, bedrock weathering fissure water, and bedrock structural fissure water from top to bottom. It has weak permeability and few wells and springs. The water quality in the mining area is poor, mostly alkaline water, with high hardness and a mineralization of about 2g / L. In most gullies, the groundwater gradually deepens from the gully mouth upward, with the shallow water level buried at a depth of about 1m and the deep water level reaching tens of meters or more. The groundwater depth within the mining area is greater than 50m.

[0073] The contaminated groundwater in the mining area is primarily Quaternary pore water, distributed in the alluvial and diluvial gravel and pebble layers at the bottom of larger valleys, and in the alluvial and diluvial fans and sloping plains on the north and south flanks of the piedmont. The water level is 0.30-16.50 m deep, with a maximum depth of 60 m. The spring flow rate is 0.033-1.140 L / s, with a maximum of 15.20 L / s. The water chemistry is primarily SO4.Cl (SO4·Cl·HCO3)-Na (Na·Ca, Na·Mg), followed by Cl·SO4-Na. The mineralization is 0.36-5.90 g / L, the pH ranges from 7.20-9.30, and the uranium base number is 1.34×10 -6 g / L, radon base number 5.6Ba / L; unit water inflow 0.0033m 3 / d;

[0074] The Quaternary pore water can obtain relatively abundant atmospheric precipitation and surface water recharge during heavy rain and snowmelt periods, but the distance between the aquifer that produces the Quaternary pore water and the bedrock is too large, so the bedrock and surface water can be considered to have no direct hydraulic connection.

[0075] Example 1

[0076] The embodiment of the groundwater permeable reaction wall and the uranium contaminated groundwater remediation method of the present invention, the result of the groundwater permeable reaction wall is as follows Figure 1 As shown, the uranium contaminated groundwater remediation method includes the following steps:

[0077] S1. Using three equally spaced sections in the contaminated area (denoted as A'-A, B'-B and C'-C, each section is perpendicular to the flow direction of groundwater) as exploration targets, geological exploration was carried out using geological radar. The results are as follows: Figure 2 As shown in the figure, radar test results show that the geological strata in the contaminated area are unevenly distributed. The surface layer is compacted topsoil or simple road surface, and the lower layer is mainly Quaternary sediments (referring to materials deposited by geological processes during the Quaternary period) composed of rock fragments, medium / fine sand, kaolin clay, etc., and is locally interspersed with gravel and bedrock fragments and blocks.

[0078] A simple water injection test with a reduced head was used to measure the permeability of the aquifer producing Quaternary pore water, with the measured permeability coefficient recorded as K1. A simple water injection test with a constant head was used to measure the permeability of the aquifer producing Quaternary pore water, with the measured permeability coefficient recorded as K2. The average of K1 and K2 was taken as (K1 + K2) / 2. The results showed that the permeability coefficient of the aquifer producing Quaternary pore water was 0.083m / d, which is a weakly permeable stratum.

[0079] S2. Deploy a groundwater permeable reaction wall downstream of the pollution plume 3. The groundwater permeable reaction wall includes a reaction wall 1 and two water-blocking walls 2, which are symmetrically arranged on either side of the reaction wall 1, with the pollution plume 3 located between the two water-blocking walls 2. The reaction wall 1 extends from the upper end of the underground aquifer to the lower end of the underground aquifer, perpendicular to the direction of groundwater flow. The reaction wall 1 includes a quartz sand layer 11, an iron powder layer 12, a hydroxyapatite layer 13, and a biochar layer 14, which are arranged in sequence along the direction of groundwater flow, with the upper end of the water-blocking wall 2 extending to the mountain ridge.

[0080] The reaction wall 1 has a length of 4 m, a width of 2.49 m, and a height of 3 m. The width of the quartz sand layer 11 is 0.31 m, and the particle size of the quartz sand in the quartz sand layer 11 is 20 mesh. The width of the iron powder layer 12 is 0.63 m, and the particle size of the iron powder in the iron powder layer 12 is 50 mesh. The width of the hydroxyapatite layer 13 is 0.63 m, and the particle size of the hydroxyapatite in the hydroxyapatite layer 13 is 30 mesh. The width of the biochar layer 14 is 0.93 m, and the particle size of the biochar in the biochar layer 14 is 20 mesh.

[0081] The length of the water barrier wall 2 is 10 m. The angle between the length direction of the water barrier wall 2 and the length direction of the reaction wall 1 is 60°, which is not less than the width of the pollution plume 3 (the width of the pollution plume 3 refers to the dimension parallel to the direction of groundwater flow);

[0082] S3. Arrange the first monitoring well 4, the second monitoring well 5, and the third monitoring well 6 1 m in front of the permeable reaction wall. The depth of each well is 10 m, and PVC pipes are buried in each monitoring well. Punch holes in the PVC pipes within the depth range of 7-10 m (i.e., the range 7-10 m from the top of the monitoring well) to allow water to flow freely through the PVC pipes.

[0083] The contaminated area was remediated for 60 days. Every two days, water from monitoring well 1 (PRB outflow) and monitoring well 3 (PRB inflow) was collected for uranium concentration monitoring. The monitoring results are as follows: Figure 3 It can be seen that the uranium concentration of the contaminated site is between 4.6-3.4 mg / L, which is seriously contaminated by uranium. After the permeable reactive wall (PRB), the uranium concentration is reduced to between 0.84-0.22 mg / L, which shows that the permeable reactive wall technology has a good remediation effect, and the uranium removal rate can reach up to 93.4%. In addition, Figure 3 It can be seen that the uranium concentration in the PRB effluent gradually decreased within 60 days, indicating that the permeable reactive wall technology has good stability and is suitable for remediation of uranium-contaminated groundwater in a groundwater environment.

[0084] Example 2

[0085] In an embodiment of the uranium-contaminated groundwater remediation method of the present invention, the contaminated area of this embodiment belongs to a micro-permeable stratum. The difference between this embodiment and Example 1 is that in step S2 of this embodiment, the width of the reaction wall 1 is 2m, the width of the quartz sand layer 11 is 0.25m, the width of the iron powder layer 12 is 0.5m, the width of the hydroxyapatite layer 13 is 0.5m, and the width of the biochar layer 14 is 0.75m.

[0086] After the contaminated area was repaired for 60 days using the method of this embodiment, the uranium removal rate was 72.6%.

[0087] Example 3

[0088] In an embodiment of the uranium-contaminated groundwater remediation method of the present invention, the contaminated area of this embodiment belongs to a micro-permeable stratum. The difference between this embodiment and Example 1 is that in step S2 of this embodiment, the width of the reaction wall 1 is 4m, the width of the quartz sand layer 11 is 0.5m, the width of the iron powder layer 12 is 1.0m, the width of the hydroxyapatite layer 13 is 1.0m, and the width of the biochar layer 14 is 1.5m.

[0089] After the contaminated area was repaired for 60 days using the method of this embodiment, the uranium removal rate was 94.8%.

[0090] Example 4

[0091] In an embodiment of the uranium-contaminated groundwater remediation method of the present invention, the contaminated area of this embodiment belongs to a micro-permeable stratum. The difference between this embodiment and Example 1 is that in step S2 of this embodiment, the width of the reaction wall 1 is 3.2m, the width of the quartz sand layer 11 is 0.4m, the width of the iron powder layer 12 is 0.8m, the width of the hydroxyapatite layer 13 is 0.8m, and the width of the biochar layer 14 is 1.2m.

[0092] After the contaminated area was repaired for 60 days using the method of this embodiment, the uranium removal rate was 94.6%.

[0093] Example 5

[0094] In an embodiment of the uranium-contaminated groundwater remediation method of the present invention, the contaminated area of this embodiment belongs to a micro-permeable stratum. The difference between this embodiment and Example 1 is that in step S2 of this embodiment, the width of the reaction wall 1 is 3.2m, the width of the quartz sand layer 11 is 0.8m, the width of the iron powder layer 12 is 0.8m, the width of the hydroxyapatite layer 13 is 0.8m, and the width of the biochar layer 14 is 0.8m.

[0095] After the contaminated area was repaired for 60 days using the method of this embodiment, the uranium removal rate was 92.1%.

[0096] Example 6

[0097] In an embodiment of the uranium-contaminated groundwater remediation method of the present invention, the contaminated area of this embodiment belongs to a micro-permeable stratum. The difference between this embodiment and Example 1 is that in step S2 of this embodiment, the width of the reaction wall 1 is 3.2m, the width of the quartz sand layer 11 is 0.4m, the width of the iron powder layer 12 is 0.8m, the width of the hydroxyapatite layer 13 is 0.6m, and the width of the biochar layer 14 is 1.4m.

[0098] After the contaminated area was repaired for 60 days using the method of this embodiment, the uranium removal rate was 94.4%.

[0099] Example 7

[0100] In an embodiment of the uranium-contaminated groundwater remediation method of the present invention, the contaminated area of this embodiment belongs to a micro-permeable stratum. The difference between this embodiment and Example 1 is that in step S2 of this embodiment, the width of the reaction wall 1 is 3.2m, the width of the quartz sand layer 11 is 0.32m, the width of the iron powder layer 12 is 0.64m, the width of the hydroxyapatite layer 13 is 0.96m, and the width of the biochar layer 14 is 1.28m.

[0101] After the contaminated area was repaired for 60 days using the method of this embodiment, the uranium removal rate was 91.8%.

[0102] Comparative Example 1

[0103] This comparative example differs from Example 1 in that, in step S2, quartz sand, iron powder, hydroxyapatite, and biochar are mixed and used to construct the reaction wall. After 60 days of remediation of the contaminated area using the method of this comparative example, the uranium removal rate was 77.5%.

[0104] The contaminated areas of Examples 1-4 belong to micro-permeable formations. The width of the reaction wall in Example 1 is 2.49m. Compared with Example 1, the width of the reaction wall in Example 2 is 2m, and its remediation effect on contaminated water is significantly worse than that of Example 1. The width of the reaction wall in Example 3 is 4m, and its uranium removal rate is slightly higher. The width of the reaction wall in Example 4 is 3.2m, and its removal rate is not much different from that of Example 3. This shows that increasing the reaction wall from 3.2m to 4m will not significantly improve the remediation effect of contaminated water, but will significantly increase the construction cost of the reaction wall. Therefore, for micro-permeable formations, the width of the reaction wall 1 is suitable to be no less than 2.4m, and more preferably 2.4-3.2m.

[0105] It can be seen from Examples 4-7 and Comparative Example 1 that the width ratio of the quartz sand layer 11, the iron powder layer 12, the hydroxyapatite layer 13 and the biochar layer 14 in the reaction wall is suitable for being controlled at 1:(1-2):(1-3):(1-4), and is further preferably 1:2:(1.5-2):(3-3.5). When contaminated water passes through the hydroxyapatite layer 13, the hydroxyapatite layer 13 can release sufficient phosphate to react with the uranium ions carried in the water and intercept and precipitate, and leave enough space for biochar to adsorb residual uranium ions.

[0106] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A method for remediating uranium-contaminated groundwater, characterized in that: The steps include: S1. Conduct geological exploration in the contaminated area to determine the geological structure and test the permeability of the underground aquifer; take multiple groundwater samples, test the uranium concentration, and determine the contamination plume; The geological structure includes geological structure information and groundwater flow direction; S2. Construct a groundwater permeable reactive wall downstream of the contamination plume; S3. Arrange a first monitoring well, a second monitoring well, and a third monitoring well in sequence in the direction of groundwater flow, wherein the first monitoring well and the third monitoring well are located on both sides of the reaction wall, and the second monitoring well is inserted into the reaction wall; The groundwater permeable reaction wall includes a reaction wall and two water-retaining walls, the two water-retaining walls are symmetrically arranged on both sides of the reaction wall, and the pollution plume is located between the two water-retaining walls; the reaction wall extends from the upper end of the underground aquifer to the lower end of the underground aquifer in a direction perpendicular to the flow of groundwater; the reaction wall includes a quartz sand layer, an iron powder layer, a hydroxyapatite layer and a biochar layer, the quartz sand layer, the iron powder layer, the hydroxyapatite layer and the biochar layer are arranged in sequence along the flow direction of groundwater, the width of the reaction wall is not less than 1.6m, the width of the reaction wall is the dimension of the reaction wall in the direction parallel to the flow direction of groundwater, and the width ratio of the quartz sand layer, the iron powder layer, the hydroxyapatite layer and the biochar layer is 1:2:(1.5-2):(3-3.5); In the extremely slightly permeable stratum, the width of the reaction wall is not less than 1.6m; in the slightly permeable stratum, the width of the reaction wall is not less than 2m; in the weakly permeable stratum, the width of the reaction wall is not less than 2.4m; the permeability coefficient K of the extremely slightly permeable stratum satisfies: K<10 -6 cm / s; the permeability coefficient K of the micro-permeable formation satisfies 10 -6 cm / s≤K<10 -5 cm / s; the permeability coefficient K of the weakly permeable formation satisfies: 10 -5 cm / s≤K<10 -4 cm / s.

2. The method for remediating uranium-contaminated groundwater according to claim 1, wherein: The length of the reaction wall is not less than 3m, and the length of the reaction wall is the dimension of the reaction wall perpendicular to the direction of groundwater flow.

3. The method for remediating uranium-contaminated groundwater according to claim 1, wherein: Step S2 also includes: arranging monitoring holes on the reaction wall.

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