A permeable reactive barrier process and its application for simultaneously removing hexavalent uranium and sulfate from groundwater

Abstract

This invention provides a permeable reactive wall process and its application for simultaneously removing hexavalent uranium and sulfate from groundwater. The permeable reactive wall process consists of a first treatment unit and a second treatment unit arranged sequentially along the water flow direction. The first treatment unit is filled with a first reaction medium, including zero-valent iron, sulfur-modified coconut shell charcoal, and sulfate-reducing bacteria. The second treatment unit is filled with a second reaction medium, including zero-valent iron, ferric oxide, sulfur-modified coconut shell charcoal, and *Priestia* sp., a non-pathogenic and environmentally friendly bacterium that can simultaneously remove uranium from water through adsorption and reduction. The composite permeable reactive wall process provided by this invention has strong resistance to interference from other substances in the water. When used to simultaneously remove sulfate and hexavalent uranium from groundwater at 15–35°C, the removal rates of both sulfate and uranium in the groundwater are greater than or equal to 90%.

Description

Technical Field

[0001] This invention relates to the field of environmental engineering technology, and in particular to a permeable reactive barrier process and its application for simultaneously removing hexavalent uranium and sulfate from groundwater. Background Technology

[0002] Permeable reactive barriers (PRBs) are a typical low-disturbance in-situ remediation and risk management technology for groundwater. PRBs offer advantages such as low cost, the ability to treat multiple contaminants (even simultaneously), no impact on surface land use, and avoidance of significant groundwater loss due to extraction. Therefore, PRB technology is considered one of the most promising groundwater remediation and risk management technologies. Currently, many types of reaction media are used in PRBs, such as zero-valent iron (ZVI), activated carbon, zeolite, peat blocks, sawdust, and oxygen-releasing compounds, with ZVI being the most common. ZVI, as a common active reaction material in PRBs, has received widespread attention both domestically and internationally. However, some problems still exist in the practical application of ZVI. Zero-valent iron is the most widely used reaction media in permeable reactive barrier processes. Studies have shown that the permeation reactive wall process using zero-valent iron (ZVFe) as the reaction medium can effectively remove halogenated hydrocarbons and heavy metals from groundwater. However, during use, the iron oxides formed on the surface of ZVFe can passivate it, eventually causing it to lose its reactivity as the reaction proceeds. How to slow down the passivation of ZVFe and the resulting decrease in activity or deactivation is the key to the effective application of permeation reactive wall technology using ZVFe as the reaction medium.

[0003] Furthermore, when PRB technology is used for groundwater remediation in uranium tailings pond areas, residual uranium in the uranium mine will leach out as seepage water at the downstream end of the tailings pond under the action of rainwater, polluting both surface water and groundwater. The use of sulfuric acid as a uranium leaching agent in acid leaching of uranium leads to excessive sulfate levels in groundwater. Therefore, there is a problem of simultaneous excesses of uranium and sulfate in the groundwater of tailings pond areas. In the application of ZVI as the reaction medium for permeable reactive barriers in the remediation of groundwater with simultaneous excesses of uranium and sulfate, zero-valent iron can reduce sulfate ions, but its ability to remove sulfate ions is weak due to the influence of groundwater composition in actual water bodies. Moreover, when uranium and sulfate ions are present in the water, they will compete for the same reaction, resulting in neither uranium nor sulfate ion removal reaching the ideal level.

[0004] Currently, there is no effective groundwater remediation solution that can simultaneously remove hexavalent uranium and sulfate ions. Summary of the Invention

[0005] To address the aforementioned problems in existing technologies, this invention provides a permeable reactive wall process and its application that can simultaneously remove hexavalent uranium and sulfate from groundwater. This permeable reactive wall process exhibits strong resistance to interference from other components in the water quality and shows promising application prospects in the treatment of uranium-containing water bodies with high sulfate content.

[0006] The specific details of the invention are as follows:

[0007] In a first aspect, the present invention provides a permeable reactive wall process for simultaneously removing hexavalent uranium and sulfate from groundwater, the permeable reactive wall process comprising a first processing unit and a second processing unit arranged sequentially along the water flow direction;

[0008] The first processing unit is filled with a first reaction medium, comprising: zero-valent iron, sulfur-modified coconut shell charcoal, and sulfate-reducing bacteria; wherein the volume ratio of zero-valent iron to modified coconut shell charcoal is 0.1-2; and the inoculum amount of sulfate-reducing bacteria in the first reaction medium is 0.01-0.1 wt.‰.

[0009] The second processing unit is filled with a second reaction medium, including: zero-valent iron, ferric oxide, sulfur-modified coconut shell charcoal, and Priestia sp.; wherein the volume ratio of zero-valent iron, ferric oxide, and sulfur-modified coconut shell charcoal is 1:1:1, the inoculum amount of Priestia sp. in the second reaction medium is 0.01-0.1 wt.‰, the classification name of Priestia sp. is Priestia sp., the depositary institution is China General Microbiological Culture Collection Center, the deposit date is September 22, 2022, and the deposit number is CGMCC No. 25638.

[0010] Optionally, the sulfate-reducing bacteria are native sulfate-reducing bacteria from the area to be repaired.

[0011] Optionally, the inoculum amount of sulfate-reducing bacteria in the first reaction medium is 0.05 wt.‰.

[0012] Optionally, the inoculum amount of Priestella in the second reaction medium is 0.05 wt.‰.

[0013] Optionally, the sulfur-modified coconut shell charcoal has a particle size of 60-100 mesh;

[0014] The zero-valent iron has a particle size of 60-100 mesh;

[0015] The particle size of the iron oxide is 100-200 mesh.

[0016] Optionally, the sulfate-reducing bacteria, after being expanded and cultured to prepare a sulfate-reducing bacterial agent, are used in the construction of the first treatment unit. The expansion culture and preparation of the sulfate-reducing bacterial agent includes: adding the sulfate-reducing bacteria to a solution containing LB medium and trace elements, culturing under anaerobic or facultative anaerobic conditions at 15–35°C for 24 h, then centrifuging the solution obtained from the expansion culture at 8000–10000 rpm for 10 min, and filtering to obtain the sulfate-reducing bacterial agent.

[0017] Optionally, the *Pristevella* strain, after being expanded and cultured to prepare a *Pristevella* agent, is used in the construction of the second treatment unit. The expansion and preparation of the *Pristevella* agent includes: adding the *Pristevella* strain to a solution containing LB medium and trace elements, culturing it at 15–35°C for 24 h, then centrifuging the solution obtained from the expansion culture at 8000–10000 rpm for 10 min, and filtering it to obtain the *Pristevella* agent.

[0018] Optionally, the chemical composition of the trace elements is: FeCl2·4H2O 1.5 g / L, CoC l2 ·6H2O0.19g / L, MnSO4 7H2O 0.1g / L, ZnCl2 0.07g / L, NiCl2·4H2O 0.024g / L, Na2MoO4·2H2O 0.024g / L, MnCl2·4H2O 0.006g / L, CuCl2·2H2O 0.002g / L.

[0019] In a second aspect, the present invention provides an application of the permeable reactive wall process described in the first aspect above in groundwater remediation projects, wherein the permeable reactive wall process is used to simultaneously remove sulfate and hexavalent uranium from groundwater.

[0020] Optionally, the permeable reactive wall process achieves a sulfate removal rate of greater than or equal to 90% in groundwater at 15–35°C.

[0021] The described permeation reactive wall process achieves a removal rate of hexavalent uranium in groundwater of greater than or equal to 90% at 15–35°C.

[0022] Compared with the prior art, the present invention has the following advantages:

[0023] This invention provides a permeable reactive wall process for simultaneously removing hexavalent uranium and sulfate from groundwater. The permeable reactive wall process consists of a first treatment unit and a second treatment unit arranged sequentially along the water flow direction. The first treatment unit is filled with a first reaction medium, including zero-valent iron, sulfur-modified coconut shell charcoal, and sulfate-reducing bacteria. The second treatment unit is filled with a second reaction medium, including zero-valent iron, ferric oxide, sulfur-modified coconut shell charcoal, and Priestia sp. Priestia sp. is classified as Priestia sp., deposited at the China General Microbiological Culture Collection Center (CGMCC) on September 22, 2022, with accession number CGMCC No. 25638. Priestia sp. is a non-pathogenic and environmentally friendly bacterium that can simultaneously remove uranium from water through adsorption and reduction. The permeable reactive wall process provided by this invention, when used in groundwater remediation projects, allows the groundwater to be remediated to flow through the first treatment unit. The zero-valent iron in the first reaction medium initially consumes dissolved oxygen in the water, creating anaerobic conditions for sulfate-reducing bacteria, thus enabling them to fully utilize their sulfate-reducing properties. Simultaneously, due to the consumption of dissolved oxygen, the oxidation of zero-valent iron in the second reaction medium is effectively slowed down when the water flows through the second treatment unit. This allows the zero-valent iron in the second reaction medium to undergo a reduction reaction with U(VI) (hexavalent uranium) in the groundwater to be remediated, forming Fe(II). U(VI) is then converted into solid or precipitated U(IV) (tetravalent uranium). The newly formed Fe(II) can continue to react with U(VI) in the groundwater to be remediated, forming Fe(III). Fe(III) further reacts with zero-valent iron to produce Fe(II), realizing the conversion of Fe(III) to Fe(II). In the above series of reactions, iron(III) oxide acts as an electron shuttle, promoting electron transfer between biochar, zero-valent iron and Priestella, thereby promoting the reduction of Fe(III) to Fe(II) and enhancing the overall uranium removal performance of the second reaction medium.

[0024] Furthermore, sulfur-modified coconut shell charcoal not only provides a carrier for microorganisms but also enhances their resistance to interference from other substances in groundwater. Some of the charcoal can also provide a carbon source for microorganisms, thereby enhancing their activity. Further, sulfur modification alters the charge distribution on the surface of the coconut shell charcoal, creating electron-rich regions. This directly enhances the adsorption and reduction capacity of U(VI) by the charcoal and also promotes the conversion of Fe(III) to Fe(II). Moreover, sulfur modification increases the number of pores on the surface of the coconut shell charcoal, thereby increasing the number of microorganisms loaded on the surface and enhancing the continuous removal of uranium. The permeable reactive barrier process provided by this invention exhibits strong resistance to interference from other substances in the water. When used to simultaneously remove sulfate and hexavalent uranium from groundwater, the removal rates of both sulfate and uranium in the groundwater are greater than or equal to 90%. Attached Figure Description

[0025] 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. 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.

[0026] Figure 1 A schematic diagram of the permeation reactive wall process provided in an embodiment of the present invention is shown. Detailed Implementation

[0027] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The following description of at least one exemplary embodiment is merely illustrative and is in no way intended to limit the present invention or its application or use. Based on the embodiments of the present invention, any product that is the same as or similar to the present invention, derived by any person under the guidance of the present invention or by combining the features of the present invention with other prior art, falls within the protection scope of the present invention. Furthermore, all other embodiments obtained by those skilled in the art without inventive effort are within the protection scope of the present invention.

[0028] Specific experimental steps or conditions are not specified in the embodiments; they can be performed according to the conventional experimental steps or conditions described in the prior art. Reagents and other instruments used, unless otherwise specified, are all commercially available conventional reagent products. Furthermore, the accompanying drawings are merely illustrative diagrams of the embodiments of the present invention and are not necessarily drawn to scale. The same reference numerals in the drawings denote the same or similar parts, and therefore, repeated descriptions of them will be omitted. Some block diagrams shown in the drawings are functional entities and do not necessarily correspond to physically or logically independent entities.

[0029] Techniques, methods, and devices known to those skilled in the art may not be discussed in detail, but where appropriate, such techniques, methods, and devices should be considered part of this specification.

[0030] In the description of this invention, it should be understood that the use of terms such as "first" and "second" to define components is merely for the purpose of distinguishing the corresponding components. Unless otherwise stated, the above terms have no special meaning and therefore should not be construed as limiting the scope of protection of this invention.

[0031] Furthermore, the technical features involved in the different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0032] Currently, the main methods for removing sulfate from water include: flocculation and sedimentation, ion exchange, membrane treatment, adsorption, and bioremediation. Flocculation and sedimentation is simple to operate, but is greatly affected by practical factors, and the precipitate usually requires secondary treatment. Ion exchange is highly dependent on water quality, and ion exchange resins are prone to aging and are costly. Membrane treatment offers good treatment results, but is also expensive. Adsorption relies on the physicochemical properties of materials to remove sulfate from water, offering simple operation and good treatment results, but its application in actual water bodies is subject to many interfering factors and has poor selectivity. Bioremediation offers high efficiency, low cost, no secondary pollutants, and easy separation. Currently, the main microorganisms reported to remove sulfate include sulfate-reducing bacteria. Sulfate-reducing bacteria can remove not only sulfate but also U(VI) through bioreduction, but their effectiveness is significantly affected by water quality. Nitrate in water significantly inhibits the U(VI) removal performance of sulfate-reducing bacteria.

[0033] Therefore, this invention aims to improve the existing permeable reactive wall process by combining bioremediation technology with the permeable reactive wall process, in order to effectively slow down the passivation of zero-valent iron and simultaneously remove hexavalent uranium and sulfate from uranium-containing water bodies with high sulfate content. The specific implementation details are as follows:

[0034] In a first aspect, the present invention provides a permeable reactive barrier process for simultaneously removing hexavalent uranium and sulfate from groundwater. Figure 1 A schematic diagram of the permeation reactive wall process provided in an embodiment of the present invention is shown, as follows: Figure 1 As shown, the permeation reactive wall process consists of a first treatment unit 1 and a second treatment unit 2 arranged sequentially along the water flow direction;

[0035] The first processing unit 1 is filled with a first reaction medium, including: zero-valent iron, sulfur-modified coconut shell charcoal, and sulfate-reducing bacteria; wherein the volume ratio of zero-valent iron to modified coconut shell charcoal is 0.1-2; the inoculum amount of sulfate-reducing bacteria in the first reaction medium is 0.01-0.1 wt.‰, preferably 0.05 wt.‰; the second processing unit 2 is filled with a second reaction medium, including: zero-valent iron, ferric oxide, sulfur-modified coconut shell charcoal, and Priestia sp.; wherein the volume ratio of zero-valent iron, ferric oxide, and sulfur-modified coconut shell charcoal is 1:1:1; the inoculum amount of Priestia sp. in the second reaction medium is 0.01-0.1 wt.‰, preferably 0.05 wt.‰; the classification name of Priestia sp. is CGMCC No. 25638.

[0036] In practice, in the first reaction medium, zero-valent iron consumes dissolved oxygen in the water to be remediated, creating anaerobic conditions for sulfate-reducing bacteria and allowing them to fully utilize their sulfate-removing capabilities. Sulfur modification increases the number of pores on the surface of coconut shell charcoal, thereby increasing the number of microorganisms (sulfate-reducing bacteria) loaded on the surface and enhancing the ability to continuously remove sulfate. Furthermore, sulfur-modified coconut shell charcoal provides a carrier for microorganisms while improving their resistance to interference from other substances in groundwater. Some coconut shell charcoal can also provide a carbon source for microorganisms, further enhancing their activity.

[0037] In specific implementation, the second treatment unit 2 is set after the first treatment unit 1. After the water body to be repaired is treated by the first treatment unit 1, the dissolved oxygen in the water is consumed by the zero-valent iron in the first treatment unit 1. Therefore, when flowing through the second treatment unit 2, the dissolved oxygen content in the water to be remediated is extremely low. This effectively avoids the oxidation of zero-valent iron in the second reaction medium, allowing the zero-valent iron in the second reaction medium to fully participate in the reaction with U(VI) (zero-valent iron reacts with U(VI) (hexavalent uranium) in the underground to be remediated to form Fe(II). U(VI) is converted into solid or precipitated U(IV) (tetravalent uranium). The newly formed Fe(II) can continue to react with U(VI) in the underground to be remediated to form Fe(III). Fe(III) further reacts with zero-valent iron to produce Fe(II), realizing the conversion of Fe(III) to Fe(II)). Furthermore, during the reduction of U(VI) by zero-valent iron, iron(III) oxide acts as an electron shuttle, promoting electron transfer between coconut shell carbon, zero-valent iron, and Priestella, thus promoting the reduction of Fe(III) to Fe(II).

[0038] In specific implementation, this embodiment of the invention also fills the second treatment unit 2 with the uranium-removing microorganism Priestia sp., which was isolated for the first time, for biological uranium removal. This microorganism possesses both bioadsorption and bioreduction characteristics. Combined with the electron transport capabilities of sulfur-modified coconut shell carbon and iron tetroxide, Priestia sp. exhibits a sustained and efficient removal capacity for uranium in groundwater. Simultaneously, Priestia sp. shows strong resistance to interference from other components in the water, demonstrating promising application prospects in the treatment of uranium-contaminated groundwater.

[0039] In specific implementation, this embodiment of the invention requires large-scale culture of sulfate-reducing bacteria and *Priestiasp.* before inoculation to obtain a sufficient quantity of microorganisms. The large-scale culture conditions are simple. The large-scale culture of sulfate-reducing bacteria includes: adding the sulfate-reducing bacteria to a solution containing LB medium and trace elements, and culturing under anaerobic or facultative anaerobic conditions at 15–35°C for 24 hours; the large-scale culture of *Priestiasp.* includes: adding *Priestiasp.* to a solution containing LB medium and trace elements, and culturing at 15–35°C for 24 hours; wherein the chemical composition of the trace elements is: FeCl2·4H2O 1.5 g / L, CoC l2 ·6H2O 0.19g / L, MnSO47H2O 0.1g / L, ZnCl20.07g / L, NiCl2·4H2O 0.024g / L, Na2MoO4·2H2O 0.024g / L, MnCl2·4H2O 0.006g / L, CuCl2·2H2O 0.002g / L.

[0040] In practical applications, this invention constructs a first treatment unit 1 and a second treatment unit 2 along the direction of groundwater flow. The sulfur-modified coconut shell carbon and zero-valent iron have a particle size of 60-100 mesh, while the iron oxide (Fe3O4) has a particle size of 100-200 mesh. This results in a composite system with abundant pores, allowing groundwater to pass through smoothly. The high-sulfate uranium-containing groundwater to be remediated begins remediation work after passing through the treatment unit at 15-35°C via a permeable reactive barrier. After treatment, the uranium removal rate and sulfate removal rate in the water are both greater than or equal to 90%. This method offers advantages such as good treatment effect, low treatment cost, and long treatment time.

[0041] To enable those skilled in the art to more clearly understand the present invention, the following embodiments are provided to illustrate in detail the permeable reactive barrier process and application for the simultaneous removal of hexavalent uranium and sulfate from groundwater.

[0042] The following examples all use Figure 1 The structural diagram shown illustrates the construction of a permeable reactive wall process.

[0043] Example 1

[0044] Removal of U(VI) from water bodies at different initial concentrations

[0045] In the first treatment unit 1, sulfur-modified coconut shell charcoal and zero-valent iron were added in a volume ratio of 3:7, with a length of 0.6 m and a width of 1 m. In the second treatment unit 2, sulfur-modified coconut shell charcoal, zero-valent iron, and iron(III) oxide were added in a volume ratio of 1:1:1, with a length and width of 1 m each. Sulfate-reducing bacteria and Priestia sp. were cultured separately in LB medium and trace element solutions. After 24 h of culture, the solution was centrifuged at 8000 rpm for 10 min, and filtered to obtain sulfate-reducing bacteria and Priestia sp. inoculum. The sulfate-reducing bacteria inoculum was added to the first treatment unit 1, and the Priestia sp. inoculum was added to the second treatment unit 2, with an inoculum size of 0.05 wt.‰ for both.

[0046] When the initial concentrations of U(VI) in the water were 5 mg / L, 10 mg / L, 20 mg / L and 50 mg / L, respectively, and the flow rate was 1 m / d, the uranium removal rates in the water after treatment were 99.0%, 100%, 100% and 100%, respectively.

[0047] Example 2

[0048] Removal effect of U(VI) at different temperatures

[0049] In Unit 1, sulfur-modified coconut shell charcoal and zero-valent iron were added in a volume ratio of 3:7, with a length of 0.6 m and a width of 1 m. In Unit 2, sulfur-modified coconut shell charcoal, zero-valent iron, and iron(III) oxide were added in a volume ratio of 1:1:1, with a length and width of 1 m each. Sulfate-reducing bacteria and Priestia sp. were cultured separately in LB medium and trace element solutions. After 24 h of culture, the solution was centrifuged at 8000 rpm for 10 min, and filtered to obtain sulfate-reducing bacteria and Priestia sp. inoculum. The sulfate-reducing bacteria inoculum was added to Unit 1, and the Priestia sp. inoculum was added to Unit 2, with an inoculum size of 0.05 wt.‰ for both.

[0050] With an initial uranium concentration of 10 mg / L in groundwater and a flow rate of 1 m / d, the removal rates of U(VI) in the treated water were 99.4%, 100%, and 100% at water temperatures of 15℃, 25℃, and 35℃, respectively. This demonstrates that the process can effectively remove U(VI) from water at temperatures between 15℃ and 35℃.

[0051] Example 3

[0052] Simultaneously remove sulfate and uranium from the water.

[0053] In Unit 1, sulfur-modified coconut shell charcoal and zero-valent iron were added in a volume ratio of 3:7, with a length of 0.6 m and a width of 1 m. In Unit 2, sulfur-modified coconut shell charcoal, zero-valent iron, and iron(III) oxide were added in a volume ratio of 1:1:1, with a length and width of 1 m each. Sulfate-reducing bacteria and Priestia sp. were cultured separately in LB medium and trace element solutions. After 24 h of culture, the solution was centrifuged at 8000 rpm for 10 min, and filtered to obtain sulfate-reducing bacteria and Priestia sp. inoculum. The sulfate-reducing bacteria inoculum was added to Unit 1, and the Priestia sp. inoculum was added to Unit 2, with an inoculum size of 0.05 wt.‰ for both.

[0054] The initial concentration of uranium in the water was 10 mg / L, 0.4 m / d, and the concentration of sulfate ions was 5000 mg / L. After treatment, the removal rate of uranium in the water was 99.4%, and the removal rate of sulfate ions was 97.4%. This shows that the process can effectively remove U(VI) and sulfate ions from the water at the same time.

[0055] Example 4

[0056] Removal efficiency of U(VI) and sulfate ions in actual water bodies

[0057] In Unit 1, sulfur-modified coconut shell charcoal and zero-valent iron were added in a volume ratio of 3:7, with a length of 0.6 m and a width of 1 m. In Unit 2, sulfur-modified coconut shell charcoal, zero-valent iron, and iron(III) oxide were added in a volume ratio of 1:1:1, with a length and width of 1 m each. Sulfate-reducing bacteria and Priestia sp. were cultured separately in LB medium and trace element solutions. After 24 h of culture, the solution was centrifuged at 8000 rpm for 10 min, and filtered to obtain sulfate-reducing bacteria and Priestia sp. inoculum. The sulfate-reducing bacteria inoculum was added to Unit 1, and the Priestia sp. inoculum was added to Unit 2, with an inoculum size of 0.05 wt.‰ for both.

[0058] The composition of actual groundwater is quite complex, containing not only U(VI) but also iron ions, manganese ions, sulfate ions, and dissolved organic matter. The initial concentration of U(VI) was 1.7 mg / L, and the initial concentration of sulfate ions was 4.7 g / L. The simulated groundwater flow velocity in the mining area was 0.2 m / d. After treatment, the removal rate of uranium in the water was 97.2%, and the removal rate of sulfate ions was 98.7%. This indicates that the process can effectively remove sulfate and U(VI) from actual groundwater, achieving the goal of water purification.

[0059] Example 5

[0060] The effect of continuous operation of the process on the removal of U(VI) and sulfate ions from actual water bodies

[0061] In Unit 1, sulfur-modified coconut shell charcoal and zero-valent iron were added in a volume ratio of 3:7, with a length of 0.6 m and a width of 1 m. In Unit 2, sulfur-modified coconut shell charcoal, zero-valent iron, and iron(III) oxide were added in a volume ratio of 1:1:1, with a length and width of 1 m each. Sulfate-reducing bacteria and Priestia sp. were cultured separately in LB medium and trace element solutions. After 24 h of culture, the solution was centrifuged at 8000 rpm for 10 min, and filtered to obtain sulfate-reducing bacteria and Priestia sp. inoculum. The sulfate-reducing bacteria inoculum was added to Unit 1, and the Priestia sp. inoculum was added to Unit 2, with an inoculum size of 0.05 wt.‰ for both.

[0062] Using simulated groundwater as the treatment target, with an initial concentration of U(VI) of 1.7 mg / L and an initial concentration of sulfate ions of 4.7 g / L, and a simulated groundwater flow velocity of 0.2 m / d, after six months of continuous operation, the removal rate of uranium in the treated water still reached 94.7%, and the removal rate of sulfate ions was 95.6%. This indicates that the process has a long service life.

[0063] In summary, this permeation reactive wall process has the advantages of good treatment effect, less impact from water quality, low cost and long service life. It can remove uranium and sulfate from uranium-containing wastewater with high sulfate content at the same time, and can play a very good purification role for uranium-containing high sulfate groundwater.

[0064] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. In addition, those skilled in the art can combine and integrate the different embodiments or examples described in this specification.

[0065] For the sake of simplicity, the method embodiments are described as a series of actions. However, those skilled in the art should understand that the present invention is not limited to the described order of actions, as some steps can be performed in other orders or simultaneously according to the present invention. Furthermore, those skilled in the art should also understand that the embodiments described in the specification are preferred embodiments, and the actions and components involved are not necessarily essential to the present invention.

[0066] The above provides a detailed description of the permeable reactive barrier process and its application for simultaneously removing hexavalent uranium and sulfate from groundwater. Specific examples have been used to illustrate the principles and implementation methods of the invention. The descriptions of the above embodiments are only for the purpose of helping to understand the method and core ideas of the invention. At the same time, those skilled in the art will recognize that, based on the ideas of the invention, there will be changes in the specific implementation methods and application scope. Therefore, the content of this specification should not be construed as a limitation of the invention.

Claims

1. A permeable reactive barrier process for simultaneously removing hexavalent uranium and sulfate from groundwater, characterized in that, The permeable reactive wall process consists of a first treatment unit and a second treatment unit arranged sequentially along the water flow direction; The first processing unit is filled with a first reaction medium, comprising: zero-valent iron, sulfur-modified coconut shell charcoal, and sulfate-reducing bacteria; wherein the volume ratio of zero-valent iron to sulfur-modified coconut shell charcoal is 0.1-2; and the inoculum amount of sulfate-reducing bacteria in the first reaction medium is 0.01-0.1 wt.‰. The second processing unit is filled with a second reaction medium, including: zero-valent iron, ferric oxide, sulfur-modified coconut shell charcoal, and Priestia sp.; wherein the volume ratio of zero-valent iron, ferric oxide, and sulfur-modified coconut shell charcoal is 1:1:1, the inoculum amount of Priestia sp. in the second reaction medium is 0.01-0.1 wt.‰, the classification name of Priestia sp. is Priestia sp., the depositary institution is China General Microbiological Culture Collection Center, the deposit date is September 22, 2022, and the deposit number is CGMCC No. 25638; The sulfur-modified coconut shell charcoal has a particle size of 60-100 mesh. The zero-valent iron has a particle size of 60-100 mesh; The particle size of the iron oxide is 100-200 mesh.

2. The permeable reactive wall process according to claim 1, characterized in that, The sulfate-reducing bacteria are native sulfate-reducing bacteria from the area to be remediated.

3. The permeable reactive wall process according to claim 1, characterized in that, The inoculum amount of sulfate-reducing bacteria in the first reaction medium is 0.05 wt.‰.

4. The permeable reactive wall process according to claim 1, characterized in that, The inoculum amount of *Priestella* in the second reaction medium is 0.05 wt.‰.

5. The permeable reactive wall process according to claim 1, characterized in that, The sulfate-reducing bacteria, after being expanded and cultured to prepare a sulfate-reducing bacterial agent, are used in the construction of the first treatment unit. The expanded culture includes adding the sulfate-reducing bacteria to a solution containing LB medium and trace elements, and incubating at 15-35 °C. o The culture was carried out for 24 h under anaerobic or facultative anaerobic conditions within the range of C. Then, the solution obtained from the expanded culture was centrifuged at 8000-10000 rpm for 10 min and filtered to obtain the sulfate-reducing bacterial agent.

6. The permeable reactive wall process according to claim 1, characterized in that, After being expanded and cultured to prepare a Priestera agent, the Priestera bacteria are used in the construction of the second treatment unit. The expansion and preparation of the Priestera agent includes: adding the Priestera bacteria to a solution containing LB medium and trace elements, and incubating at 15-35 °C. o The culture was carried out in a C range for 24 h, and then the solution obtained from the expanded culture was centrifuged at 8000-10000 rpm for 10 min and filtered to obtain the Priestella agent.

7. The permeable reactive wall process according to claim 5 or 6, characterized in that, The chemical composition of the trace elements is: FeCl2·4H2O 1.5 g / L, CoC l2 ·6H2O 0.19 g / L, MnSO4 7H2O 0.1 g / L, ZnCl20.07 g / L, NiCl2·4H2O 0.024 g / L, Na2MoO4·2H2O 0.024 g / L, MnCl2·4H2O 0.006 g / L, CuCl2·2H2O0.002 g / L.

8. The application of the permeable reactive wall technology according to any one of claims 1-7 in groundwater remediation projects, characterized in that, The permeable reactive wall process is used to simultaneously remove sulfates and hexavalent uranium from groundwater.

9. The application according to claim 8, characterized in that, The permeable reactive wall process is at 15~35 o At temperature C, the removal rate of sulfate in groundwater is greater than or equal to 90%. The permeable reactive wall process is at 15~35 o At temperature C, the removal rate of hexavalent uranium in groundwater is greater than or equal to 90%.

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