A working electrode for electrochemical extraction of uranium from wastewater and a preparation method thereof

Abstract

The present invention relates to a working electrode for electrochemical extraction of uranium from wastewater and a preparation method thereof, belonging to the technical field of electrochemical wastewater treatment. The working electrode has amidoxime groups, or amidoxime groups and glutarimidedioxime groups as functional groups, a hydrophilic carbon material as a conductive medium, and a melamine sponge as an electrode skeleton; the working electrode is a three-dimensional porous structure material with ultra-large pores, mesopores and / or macropores secondary continuous pore structures; the functional groups are distributed on the polyamidooxime molecular chains in the working electrode; the conductive medium is distributed in the three-dimensional pore wall, and a composite of polymer and conductive medium is filled in the electrode skeleton; the hydrophilic carbon material is a hydroxylated carbon nanotube or a carboxylated carbon nanotube; the working electrode is prepared by a freeze casting method. The working electrode is a three-dimensional porous working electrode with characteristics such as high electrochemical properties, good hydrophilicity and antibacterial properties.

Description

Technical Field

[0001] The present invention relates to a working electrode for electrochemical extraction of uranium from wastewater and a preparation method thereof, specifically to a three-dimensional porous working electrode having a continuous secondary pore structure of ultra-large pores, mesopores and / or macropores, and having uranium coordination functional groups, high electrochemical performance, good hydrophilicity and antibacterial properties. The electrode is prepared by a freeze casting method, and belongs to the technical field of electrochemical wastewater treatment. Background Art

[0002] Nuclear power generation, with its significant advantages of high efficiency and low cost, has been vigorously developed in my country. Uranium, the most important raw material for nuclear power generation, is mined from large and small uranium mines. This mining, smelting, and processing generate large amounts of uranium-containing wastewater, posing a serious threat to ecosystems and human health. However, this uranium-containing wastewater still contains significant uranium resources, which hold significant economic value. Therefore, effectively extracting uranium from this wastewater offers a strategy that can both remediate the environment and recycle resources.

[0003] Currently, various techniques, such as solvent extraction, co-precipitation, microbial enrichment, adsorption, photocatalysis, and electrochemical extraction, have been applied to uranium extraction. Among them, electrochemical extraction is highly efficient, environmentally friendly, and energy-efficient, making it a promising uranium extraction technology. Its principle is to induce the directional migration of uranyl ions through an electric field, causing them to accumulate on the surface of the working electrode to form an electrical double layer (EDL), where they are adsorbed by functional groups on the electrode, while simultaneously inducing the reduction of the uranyl ions. Compared to other methods, this technology is not only more efficient but also can recover uranium through a simple reverse current elution process, showing great potential for application.

[0004] For electrochemical extraction technology, designing a working electrode with uranium-coordinating functional groups, high electrochemical performance, and a well-hydrophilic pore structure is paramount. These factors can all enhance the electrochemical extraction performance of uranium. Amidoxime groups are currently the most efficient functional groups for uranium adsorption and selectivity. In addition, glutarimidodioxime groups, which are converted from amidoxime groups, also effectively complex uranium, and even exhibit stronger binding capacity. However, due to the lack of free electrons, materials containing these groups are often limited to static adsorption. Some technologies construct conductive composite materials by adding conductive media such as carbon black or graphene. However, the naturally low surface energy of these carbon-based materials makes them highly hydrophobic, hindering the mass transfer of uranyl ions in the aqueous phase. Furthermore, the antibacterial properties of these materials need to be improved for their practical application, as long-term uranium extraction efficiency decreases due to bacterial accumulation in the wastewater, which clogs the electrode pores.

[0005] Designing a three-dimensional porous electrode with a continuous ultra-large pore structure (5μm to 10μm) can greatly improve the mass transfer efficiency and thus enhance the mass transfer performance. In addition, materials rich in mesopores (2nm to 50nm) and / or macropores (50nm to 200nm) not only enhance the diffusion of uranium through the formation of EDLs, providing sufficient space for uranium storage, but also avoid the EDL overlap that may be caused by micropores (<2nm), which is detrimental to electrochemical extraction. However, mesoporous materials (such as covalent organic framework compounds and metal-organic framework compounds) are usually in the form of powders or granules, and their practical application is hindered due to the difficulty of collection. There are very few technologies that use ultra-large pore, mesoporous and / or macroporous secondary continuous pore structure materials (i.e., materials with continuous and through-going primary ultra-large pore structures and secondary mesopores and / or macropores at their pore walls) for physical and chemical adsorption of uranium (L. Yang, et al. Bioinspired hierarchical porous membrane for efficient uranium extraction from seawater, Nat. Sustain. 5 (2022) 71-80); however, the materials used in this technology do not have electrical conductivity and antibacterial properties, and therefore cannot be used for efficient electrochemical extraction.

[0006] Freeze-drying is a widely used pore-forming method, creating porous materials through the melting of frozen ice crystals. However, conventional freeze-drying can only produce ultra-large pore structures. For example, patent CN108659256B describes a method for preparing a thin interfacial porous membrane using freeze-drying technology, but this method cannot produce materials with secondary continuous pore structures. Summary of the Invention

[0007] To overcome the shortcomings of the prior art, the present invention aims to provide a working electrode for the electrochemical extraction of uranium from wastewater and a method for preparing the same. The electrode is a three-dimensional porous working electrode with a continuous secondary pore structure of ultra-macropores, mesopores, and / or macropores. It possesses uranium-coordinating functional groups, high electrochemical performance, and excellent hydrophilicity and antibacterial properties.

[0008] To achieve the purpose of the present invention, the following technical solutions are provided.

[0009] A working electrode for electrochemical extraction of uranium from wastewater, the working electrode having amidoxime groups as functional groups, or amidoxime groups and glutarimidedioxime groups as functional groups, a hydrophilic carbon material as a conductive medium, and a melamine sponge as an electrode skeleton; preferably, the functional groups are amidoxime groups and glutarimidedioxime groups;

[0010] The working electrode is a three-dimensional porous structure material having a secondary continuous pore structure of ultra-large pores, mesopores and / or macropores. The secondary continuous pore structure is a pore with a continuous primary ultra-large pore structure, and the pore wall position has a secondary mesopore and / or macropore structure;

[0011] The functional groups are distributed on the polyamidooxime molecular chains in the working electrode; the conductive medium is distributed in the three-dimensional pore walls to form a continuous conductive path; the composite of the polymer and the conductive medium is evenly filled in the electrode skeleton; preferably, the functional groups are evenly distributed on the polyamidooxime molecular chains in the working electrode; and the conductive medium is evenly distributed in the three-dimensional pore walls.

[0012] The hydrophilic carbon material is a hydroxylated carbon nanotube or a carboxylated carbon nanotube, such as a hydroxylated single-walled carbon nanotube, a carboxylated single-walled carbon nanotube, a hydroxylated multi-walled carbon nanotube or a carboxylated multi-walled carbon nanotube.

[0013] The wastewater is wastewater containing metal ions including but not limited to uranyl ions.

[0014] A method for preparing a working electrode for electrochemical extraction of uranium from wastewater according to the present invention comprises the following steps:

[0015] (1) Dissolve hydroxylamine hydrochloride in dimethyl sulfoxide, then add sodium carbonate and sodium hydroxide, heat and stir to allow the three to react fully; after the reaction is completed, add polyacrylonitrile to the reaction system, and after the polyacrylonitrile is completely dissolved, raise the reaction temperature to 60°C to 75°C and react for more than 24 hours; after the reaction is completed, let it stand, cool, centrifuge, and separate the supernatant to obtain a uniform polyamidooxime-dimethyl sulfoxide solution.

[0016] In step (1):

[0017] Preferably, the molar ratio of hydroxylamine hydrochloride, dimethyl sulfoxide, sodium carbonate, sodium hydroxide and polyacrylonitrile is 20:211:9:6:20, which can fully carry out the reaction.

[0018] The reaction temperature is preferably raised to 65° C. and the reaction is carried out for more than 24 hours to avoid slow reaction speed due to too low a temperature or generation of by-products due to too high a temperature.

[0019] Preferably, dimethyl sulfoxide is heated to 40° C. to 50° C. before adding hydroxylamine hydrochloride for dissolution, which has a better dissolution effect.

[0020] (2) The polyamidooxime-dimethyl sulfoxide solution obtained in step (1) is mixed evenly with the hydrophilic carbon material, and ultrasonically degassed to obtain an electrode preparation precursor solution.

[0021] In step (2):

[0022] Preferably, when the molar ratio of hydroxylamine hydrochloride, dimethyl sulfoxide, sodium carbonate, sodium hydroxide, and polyacrylonitrile is 20:211:9:6:20, the mass ratio of the prepared polyamidoxime-dimethyl sulfoxide solution to the hydrophilic carbon material is 5:1. The electrode prepared at this ratio has a sufficient mass fraction of the conductive medium to obtain good electrical properties and contains a large number of uranium coordination groups.

[0023] (3) The clean and dry melamine sponge is completely immersed in the electrode preparation precursor solution obtained in step (2), and is taken out after the precursor solution has fully penetrated into the sponge; the sponge is placed in a freezing treatment below -20°C for more than 2 hours. Since the melting point of dimethyl sulfoxide is 18.4°C, dimethyl sulfoxide is rapidly frozen and crystallized to form tiny ice crystals; the sponge is further placed in anhydrous ethanol at -20°C to -114°C and continues to be frozen for more than 10 hours to allow the dimethyl sulfoxide ice crystals to fully dissolve in the anhydrous ethanol. At this time, the super-large pores formed by the dimethyl sulfoxide ice crystals still exist. At the same time, since polyamidooxime is insoluble in ethanol, the polyamidooxime molecular chains constituting the super-large pore walls precipitate and undergo self-physical cross-linking to form a secondary continuous mesoporous and / or macroporous structure; the sponge is then taken out and dried, and the residual dimethyl sulfoxide and ethanol are washed and removed, and dried to obtain a working electrode for electrochemical extraction of uranium from wastewater, wherein the functional group is an amidoxime group;

[0024] When the functional groups are amidoxime and glutarimidedioxime, the working electrode needs to be further placed in an alkaline solution and heated to 55° C. to 65° C. for 0.5 h to 1.5 h, then washed and dried to obtain a working electrode for electrochemical extraction of uranium from wastewater.

[0025] In step (3):

[0026] The melamine sponge is a commercially available porous melamine sponge, preferably the Basotect G+ product of BASF, Germany.

[0027] Clean and dry melamine sponge can be obtained by the following method:

[0028] The melamine sponge was ultrasonically washed in anhydrous ethanol to remove oil stains and then dried to constant weight.

[0029] The melamine sponge can be cut into corresponding shapes and sizes, such as sheets, according to the shape and size requirements of the working electrode in this field.

[0030] It is preferably placed in a -20°C freezer for more than 2 hours. This temperature can allow dimethyl sulfoxide to crystallize rapidly, and commonly used commercial freezing equipment can reach this temperature.

[0031] It is preferred to use water with a purity higher than deionized water for washing to remove residual dimethyl sulfoxide and ethanol.

[0032] The alkaline solution is a sodium hydroxide solution or a potassium hydroxide solution.

[0033] Preferably, the concentration of the alkaline solution is 0.1 mol / L to 0.5 mol / L. In this concentration range, amidoxime groups are partially converted into glutarimidedioxime groups. Too low a concentration results in poor conversion, while too high a concentration results in complete conversion and damage to the polymer structure.

[0034] Preferably, when the functional group is amidoxime group and glutarimidedioxime group, the working electrode needs to be further placed in an alkaline solution and heated to 50° C. to 60° C. for 0.5 h to 1.5 h to maintain the stability of the material structure.

[0035] Beneficial effects

[0036] 1. The present invention provides a working electrode for electrochemical extraction of uranium from wastewater. The working electrode is a three-dimensional electrode having a super-macroporous-mesoporous / macroporous secondary continuous pore structure. The super-macroporous-mesoporous / macroporous secondary continuous pore structure can significantly reduce the migration resistance of uranyl ions during electrochemical extraction, improve mass transfer capacity, and facilitate the formation of a double electrical layer. The functional groups in the electrode are amidoxime groups, or amidoxime groups and glutarimidodioxime groups, which can effectively complex uranyl ions, resulting in the electrode having good electrochemical extraction capacity and extraction selectivity for uranyl ions. The electrode uses a hydrophilic carbon material as a conductive medium, which is uniformly distributed within the three-dimensional pore walls to form a continuous conductive path, giving the electrode excellent electrical properties. The hydrophilic carbon material is hydroxylated or carboxylated nanotubes. The carbon nanotubes can pierce bacterial cell walls, causing cell membrane damage, thereby having good antibacterial effects and effectively preventing electrode pore blockage caused by bacterial aggregation during actual wastewater treatment.

[0037] 2. The present invention provides a method for preparing a working electrode for electrochemical extraction of uranium from wastewater, wherein the method adopts a modified freeze-casting method to obtain the ultra-large pore-mesopore / macroporous secondary continuous pore structure of the electrode. The method is different from the traditional freeze-drying pore-forming method and can achieve the simultaneous acquisition of a continuous and orderly secondary pore structure and reliable macromolecular cross-linking in step (3) of the method, so that the structure is reliable and stable in electrochemical extraction; the working electrode prepared by the method has micron-scale ultra-large pores (5μm to 10μm) formed by freeze-casting, and secondary nano-large pores and mesopores (20nm to 200nm) formed by the precipitation of polyamidooxime molecular chains.

[0038] 3. The present invention provides a method for preparing a working electrode for electrochemical extraction of uranium from wastewater. The method can obtain an electrode having amidoxime and glutarimidodioxime functional groups and further improved performance through alkali treatment. After alkali treatment, the terminal hydrogen of the oxime group on the amidoxime group is deprived, making the electrode material negatively charged and enhancing its complexing ability for uranyl ions. The alkali treatment also causes micropores in the electrode material to swell and converts a small number of amidoxime groups into carboxyl groups, thereby increasing the hydrophilicity of the electrode material and facilitating the mass transfer of uranyl ions. During the alkali treatment, some amidoxime groups react with adjacent amidoxime groups to convert into glutarimidodioxime groups. The imine in the glutarimidodioxime group is a strong electron-donating group with a stronger coordination ability with uranyl ions, and may also form a more stable tri-coordinated complex.

[0039] 4. The present invention provides a method for preparing a working electrode for electrochemical extraction of uranium from wastewater. In step (1) of the method, preferably, in the reaction system, the molar ratio of hydroxylamine hydrochloride, dimethyl sulfoxide, sodium carbonate, sodium hydroxide, and polyacrylonitrile is 20:211:9:6:20, so that the reaction can proceed fully.

[0040] 5. The present invention provides a method for preparing a working electrode for electrochemical extraction of uranium from wastewater. In step (1) of the method, dimethyl sulfoxide is preferably heated to 40°C to 50°C and then hydroxylamine hydrochloride is added for dissolution, which has a better dissolution effect.

[0041] 6. The present invention provides a method for preparing a working electrode for electrochemical extraction of uranium from wastewater. In step (1) of the method, the reaction temperature is preferably 65°C to avoid slow reaction speed due to too low temperature or generation of by-products due to too high temperature.

[0042] 7. The present invention provides a method for preparing a working electrode for electrochemical extraction of uranium from wastewater. In step (2) of the method, preferably when the molar ratio of hydroxylamine hydrochloride, dimethyl sulfoxide, sodium carbonate, sodium hydroxide, and polyacrylonitrile is 20:211:9:6:20, the mass ratio of the prepared polyamidooxime-dimethyl sulfoxide solution to the hydrophilic carbon material is 5:1. The electrode prepared at this ratio has a sufficient mass fraction of a conductive medium to obtain good electrical properties and contains a large number of uranium coordination groups.

[0043] 8. The present invention provides a method for preparing a working electrode for electrochemical extraction of uranium from wastewater. In step (3) of the method, the preferred freezing treatment temperature is -20°C, which can allow dimethyl sulfoxide to crystallize rapidly and can be reached by commonly used commercial freezing equipment.

[0044] 9. The present invention provides a method for preparing a working electrode for electrochemical extraction of uranium from wastewater. In step (3) of the method, the concentration of the alkaline solution is preferably 0.1 mol / L to 0.5 mol / L. Within this concentration range, the amidoxime groups are partially converted into glutarimidedioxime groups. If the concentration is too low, the conversion effect will be poor, while if the concentration is too high, complete conversion will result in damage to the polymer structure. The heating temperature is preferably 50°C to 60°C to maintain the stability of the material structure. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 The microscopic morphology of a working electrode for electrochemical extraction of uranium from wastewater prepared in Example 1 is shown in FIG. 1 , wherein FIG. (1) is a scanning electron microscope (SEM) image of the working electrode surface; and FIG. (2) is a locally enlarged SEM image of the pore wall of the working electrode in the area of FIG. (1).

[0046] Figure 2 This is a Fourier transform infrared spectrum (FT-IR) diagram of a working electrode for electrochemical extraction of uranium from wastewater prepared in Example 1. DETAILED DESCRIPTION

[0047] The present invention will be described in detail below with reference to specific embodiments. The following embodiments will help those skilled in the art to further understand the present invention, but are not intended to limit the present invention in any form. It should be noted that, for those skilled in the art, several variations and improvements can be made without departing from the scope of the present invention. These all fall within the scope of protection of the present invention.

[0048] In the following embodiments:

[0049] The hydroxylamine hydrochloride, dimethyl sulfoxide, sodium carbonate, sodium hydroxide, and polyacrylonitrile are all commercially available analytically pure drugs.

[0050] The melamine sponge is a product of BASF of Germany, model number is Basotect G+.

[0051] The hydroxylated multi-walled carbon nanotubes, carboxylated multi-walled carbon nanotubes and hydroxylated single-walled carbon nanotubes are all commercially available drugs.

[0052] The polyacrylonitrile has an average molecular weight of 150,000 and a purity of 99%.

[0053] The wastewater is a self-made multi-metal ion simulated wastewater solution, wherein the uranyl ion concentration is 50 mg / L, the ion concentrations of copper, manganese, zirconium, iron, sodium, zinc, calcium, magnesium, strontium, cesium, nickel and lead are 20 mg / L, and the solvent is deionized water.

[0054] The electrochemical extraction device consists of a conventional electrosorption cell and a power supply. The working electrode is a working electrode for electrochemical extraction of uranium from wastewater, as described in the examples. It is connected to the negative terminal of the power supply via a wire, providing chemical adsorption sites for uranyl ions in the wastewater under electric field conditions, adsorbing metal ions in the wastewater onto the working electrode. The counter electrode is a commercially available platinum sheet electrode, connected to the positive terminal of the power supply via a wire. The power supply is capable of providing a voltage of 1.5V.

[0055] The extraction amount is the mass of uranium that can be extracted by the working electrode per unit mass, and the unit is mg / g.

[0056] Example 1

[0057] A method for preparing a working electrode for electrochemical extraction of uranium from wastewater, the method comprising the following steps:

[0058] (1) 4.17 g (60 mmol) of hydroxylamine hydrochloride was dissolved in 45 mL (633 mmol) of dimethyl sulfoxide which had been preheated to 45°C, and then 2.87 g (27 mmol) of sodium carbonate and 0.72 g (18 mmol) of sodium hydroxide were added. The mixture was stirred under magnetic stirring at 45°C for 3 hours. The reaction was carried out in a round-bottom flask and the reaction temperature was kept constant at 45°C. After the reaction was fully completed, 3.18 g (60 mmol) of polyacrylonitrile was added to the reaction system. After the polyacrylonitrile was completely dissolved, the reaction temperature was raised to 65°C and the mixture was reacted for 24 hours. The mixture was allowed to stand and the solution was cooled to room temperature before centrifugation to remove insoluble matter. The resulting supernatant was separated to obtain a uniform polyamidooxime-dimethyl sulfoxide solution.

[0059] (2) Weigh 10 g of the polyamidoximine-dimethyl sulfoxide solution obtained in step (1) into a beaker, add 2 g of hydroxylated multi-walled carbon nanotubes, stir magnetically for 2 h to mix evenly, and degas by ultrasonication at a frequency of 450 kHz for 30 min to obtain an electrode preparation precursor solution.

[0060] (3) Cut the melamine sponge into thin slices with a length of 1 cm, a width of 1 cm and a height of 0.1 cm, place it in anhydrous ethanol and ultrasonically wash it at a frequency of 450 kHz for 30 minutes to remove oil stains, and then dry it to constant weight to obtain a clean and dry melamine sponge slice; completely immerse the clean and dry melamine sponge slice in the electrode preparation precursor solution prepared in step (2), take it out after the precursor solution has fully penetrated into the sponge, and then place it in a -20°C freezer for 2 hours; further place it in anhydrous ethanol at -20°C and continue freezing for 10 hours to allow the dimethyl sulfoxide ice crystals to fully dissolve in the anhydrous ethanol; then take it out and place it in a temperature of 25°C to dry to constant weight, wash the residual dimethyl sulfoxide and ethanol with deionized water 3 times, and dry it; further place it in a sodium hydroxide solution with a sodium hydroxide concentration of 0.5 mol / L and heat it to 60°C for 1 hour, take it out and wash it with deionized water and dry it, repeating 3 times to prepare a working electrode for electrochemical extraction of uranium from wastewater.

[0061] The working electrode for electrochemical extraction of uranium from wastewater prepared in this example was observed and tested as follows:

[0062] (1) Microscopic morphology observation

[0063] The working electrode was observed by scanning electron microscope. Figure 1 As shown, Figure 1

[0064] (1) shows that the electrode has a large pore structure. Figure 1 (2) shows that after the ultra-large pore wall area is magnified, there are secondary pore structures of mesopores and / or macropores. Therefore, it can be seen that the working electrode is a three-dimensional porous structure material with ultra-large pores, mesopores and / or macropores. The secondary continuous pore structure is a pore with a continuous primary ultra-large pore structure, and at the same time, its pore wall position has a secondary mesopore and / or macropore structure;

[0065] According to SEM test, the results are as follows Figure 1 As shown, it can be seen that the working electrode has amidoxime and glutarimidedioxime as functional groups, a hydrophilic carbon material as a conductive medium, and a melamine sponge as an electrode skeleton;

[0066] According to FT-IR test, the results are as follows Figure 2 As shown in the figure, four characteristic peaks representing the uniform distribution of amidoxime groups and glutarimidedioxime groups are marked. It can be seen that the functional groups are uniformly distributed on the polyamidoxime molecular chains in the working electrode; the conductive medium is uniformly distributed in the three-dimensional pore wall to form a continuous conductive path; and the composite of the polymer and the conductive medium is uniformly filled in the electrode skeleton.

[0067] (2) Test of electrochemical extraction capacity of uranium from wastewater

[0068] Using the working electrode described in this example, the power supply voltage was set to 1.5 V. 50 ml of wastewater was added to the electrochemical extraction device. After 3 h, the residual uranyl ion concentration in the wastewater was measured by microwave plasma emission spectrometry (MP-AES, Agilent). The calculated extraction yield of uranyl ions was 74.35 mg / g.

[0069] Example 2

[0070] A method for preparing a working electrode for electrochemical extraction of uranium from wastewater, the method comprising the following steps:

[0071] (1) 5.56 g (80 mmol) of hydroxylamine hydrochloride was dissolved in 60 mL (844 mmol) of dimethyl sulfoxide which had been preheated to 40°C, and then 3.83 g (36 mmol) of sodium carbonate and 0.96 g (24 mmol) of sodium hydroxide were added. The mixture was stirred under magnetic stirring at 40°C for 4 hours. The reaction was carried out in a round-bottom flask and the reaction temperature was kept constant at 40°C. After the reaction was fully completed, 4.24 g (80 mmol) of polyacrylonitrile was added to the reaction system. After the polyacrylonitrile was completely dissolved, the reaction temperature was raised to 60°C and the mixture was reacted for 24 hours. The mixture was allowed to stand and the solution was cooled to room temperature before centrifugation to remove insoluble matter. The supernatant was separated to obtain a uniform polyamidooxime-dimethyl sulfoxide solution.

[0072] (2) Weigh 10 g of polyamidoximine-dimethyl sulfoxide solution into a beaker, add 2 g of carboxylated multi-walled carbon nanotubes, stir magnetically for 2 h to mix evenly, and degas by ultrasonication at a frequency of 450 kHz for 30 min to obtain an electrode preparation precursor solution.

[0073] (3) Cut the melamine sponge into thin slices with a length of 1 cm, a width of 1 cm and a height of 0.1 cm, place it in anhydrous ethanol and ultrasonically wash it at a frequency of 450 kHz for 30 minutes to remove oil stains, and then dry it to constant weight to obtain a clean and dry melamine sponge slice; completely immerse the clean and dry melamine sponge slice in the electrode preparation precursor solution prepared in step (2), take it out after the precursor solution has fully penetrated into the sponge, and then place it in a -20°C freezer for 2 hours; further place it in anhydrous ethanol at -20°C and continue freezing for 10 hours to allow the dimethyl sulfoxide ice crystals to fully dissolve in the anhydrous ethanol; then take it out and place it in a temperature of 25°C to dry to constant weight, wash the residual dimethyl sulfoxide and ethanol with deionized water 3 times, and dry it; further place it in a sodium hydroxide solution with a sodium hydroxide concentration of 0.44 mol / L and heat it to 55°C for 1.5 hours, take it out and wash it with deionized water and dry it, repeating 3 times to prepare a working electrode for electrochemical extraction of uranium from wastewater.

[0074] The working electrode for electrochemical extraction of uranium from wastewater prepared in this example was observed and tested as follows:

[0075] (1) Microscopic morphology observation

[0076] The working electrode was observed by scanning electron microscope. Figure 1 Similarly, it is shown that the working electrode has an ultra-large pore structure, and after the ultra-large pore wall area is magnified, a secondary pore structure of mesopores and / or macropores is present. Therefore, it can be known that the working electrode is a three-dimensional porous structure material with a secondary continuous pore structure of ultra-large pores, mesopores and / or macropores. The secondary continuous pore structure is a pore with a continuous and through primary ultra-large pore structure, and at the same time, its pore wall position has a secondary mesopore and / or macropore structure;

[0077] According to the SEM test results, it can be seen that the working electrode has amidoxime and glutarimidedioxime as functional groups, a hydrophilic carbon material as a conductive medium, and a melamine sponge as an electrode skeleton;

[0078] According to the FT-IR test results, four characteristic peaks representing the uniform distribution of amidoxime groups and glutarimidedioxime groups were displayed, indicating that the functional groups were uniformly distributed on the polyamidooxime molecular chains in the working electrode; the conductive medium was uniformly distributed in the three-dimensional pore walls, forming a continuous conductive path; and the composite of the polymer and the conductive medium was uniformly filled in the electrode skeleton.

[0079] (2) Test of electrochemical extraction capacity of uranium from wastewater

[0080] Using the working electrode described in this example, the power supply voltage was set to 1.5 V. 100 ml of wastewater was added to the electrochemical extraction device. After 3 h, the residual uranyl ion concentration in the wastewater was measured by microwave plasma emission spectrometry (MP-AES, Agilent). The calculated extraction yield of uranyl ions was 93.56 mg / g.

[0081] Example 3

[0082] A method for preparing a working electrode for electrochemical extraction of uranium from wastewater, the method comprising the following steps:

[0083] (1) 4.17 g (60 mmol) of hydroxylamine hydrochloride was dissolved in 45 mL (633 mmol) of dimethyl sulfoxide which had been preheated to 45°C, and then 2.87 g (27 mmol) of sodium carbonate and 0.72 g (18 mmol) of sodium hydroxide were added. The mixture was stirred under magnetic stirring at 45°C for 3 hours. The reaction was carried out in a round-bottom flask and the reaction temperature was kept constant at 45°C. After the reaction was fully completed, 3.18 g (60 mmol) of polyacrylonitrile was added to the reaction system. After the polyacrylonitrile was completely dissolved, the reaction temperature was raised to 75°C and the mixture was reacted for 24 hours. The mixture was allowed to stand and the solution was cooled to room temperature before centrifugation to remove insoluble matter. The supernatant was separated to obtain a uniform polyamidooxime-dimethyl sulfoxide solution.

[0084] (2) Weigh 10 g of polyamidoximine-dimethyl sulfoxide solution into a beaker, add 2 g of hydroxylated single-walled carbon nanotubes, stir magnetically for 2 h to mix evenly, and degas by ultrasonication at a frequency of 450 kHz for 30 min to obtain an electrode preparation precursor solution.

[0085] (3) Cut the melamine sponge into thin slices with a length of 1 cm, a width of 1 cm and a height of 0.1 cm, place it in anhydrous ethanol and ultrasonically wash it at a frequency of 450 kHz for 30 minutes to remove oil stains, and then dry it to constant weight to obtain a clean and dry melamine sponge slice; completely immerse the clean and dry melamine sponge slice in the electrode preparation precursor solution prepared in step (2), take it out after the precursor solution has fully penetrated into the sponge, and then place it in a -20°C freezer for 2 hours; further place it in anhydrous ethanol at -20°C and continue freezing for 10 hours to allow the dimethyl sulfoxide ice crystals to fully dissolve in the anhydrous ethanol; then take it out and place it in a temperature of 25°C to dry to constant weight, wash the residual dimethyl sulfoxide and ethanol with deionized water 3 times, and dry it; further place it in a potassium hydroxide solution with a potassium hydroxide concentration of 0.5 mol / L and heat it to 65°C for 0.5 hours, take it out and wash it with deionized water and dry it, repeat 3 times to prepare a working electrode for electrochemical extraction of uranium from wastewater.

[0086] The working electrode for electrochemical extraction of uranium from wastewater prepared in this example was observed and tested as follows:

[0087] (1) Microscopic morphology observation

[0088] The working electrode was observed by scanning electron microscope. Figure 1 Similarly, it is shown that the working electrode has an ultra-large pore structure, and after the ultra-large pore wall area is magnified, a secondary pore structure of mesopores and / or macropores is present. Therefore, it can be known that the working electrode is a three-dimensional porous structure material with a secondary continuous pore structure of ultra-large pores, mesopores and / or macropores. The secondary continuous pore structure is a pore with a continuous and through primary ultra-large pore structure, and at the same time, its pore wall position has a secondary mesopore and / or macropore structure;

[0089] According to the SEM test results, it can be seen that the working electrode has amidoxime and glutarimidedioxime as functional groups, a hydrophilic carbon material as a conductive medium, and a melamine sponge as an electrode skeleton;

[0090] According to the FT-IR test results, four characteristic peaks representing the uniform distribution of amidoxime groups and glutarimidedioxime groups were displayed, indicating that the functional groups were uniformly distributed on the polyamidooxime molecular chains in the working electrode; the conductive medium was uniformly distributed in the three-dimensional pore walls, forming a continuous conductive path; and the composite of the polymer and the conductive medium was uniformly filled in the electrode skeleton.

[0091] (2) Test of electrochemical extraction capacity of uranium from wastewater

[0092] Using the electrodes described in this example, the power supply voltage was set to 1.5 V. 50 ml of wastewater was added to the electrochemical extraction device. After 3 h, the residual uranyl ion concentration in the wastewater was measured by microwave plasma emission spectrometry (MP-AES, Agilent). The calculated extraction yield of uranyl ions was 93.56 mg / g.

[0093] Example 4

[0094] A method for preparing a working electrode for electrochemical extraction of uranium from wastewater, the method comprising the following steps:

[0095] (1) 4.17 g (60 mmol) of hydroxylamine hydrochloride was dissolved in 45 mL (633 mmol) of dimethyl sulfoxide which had been preheated to 45°C, and then 2.87 g (27 mmol) of sodium carbonate and 0.72 g (18 mmol) of sodium hydroxide were added. The mixture was stirred under magnetic stirring at 45°C for 3 hours. The reaction was carried out in a round-bottom flask and the reaction temperature was kept constant at 45°C. After the reaction was fully completed, 3.18 g (60 mmol) of polyacrylonitrile was added to the reaction system. After the polyacrylonitrile was completely dissolved, the reaction temperature was raised to 65°C and the mixture was reacted for 24 hours. The mixture was allowed to stand and the solution was cooled to room temperature before centrifugation to remove insoluble matter. The resulting supernatant was separated to obtain a uniform polyamidooxime-dimethyl sulfoxide solution.

[0096] (2) Weigh 10 g of the polyamidoximine-dimethyl sulfoxide solution obtained in step (1) into a beaker, add 2 g of hydroxylated multi-walled carbon nanotubes, stir magnetically for 2 h to mix evenly, and degas by ultrasonication at a frequency of 450 kHz for 30 min to obtain an electrode preparation precursor solution.

[0097] (3) Cut the melamine sponge into thin slices with a length of 1 cm, a width of 1 cm and a height of 0.1 cm, place it in anhydrous ethanol and ultrasonically wash it at a frequency of 450 kHz for 30 minutes to remove oil stains, and then dry it to constant weight to obtain a clean and dry melamine sponge slice; completely immerse the clean and dry melamine sponge slice in the electrode preparation precursor solution prepared in step (2), take it out after the precursor solution has fully penetrated into the sponge, and then place it in a -20°C freezer for 2 hours; further place it in anhydrous ethanol at -20°C and continue to freeze it for 10 hours to allow the dimethyl sulfoxide ice crystals to fully dissolve in the anhydrous ethanol; then take it out and place it at 25°C to dry to constant weight, wash the residual dimethyl sulfoxide and ethanol with deionized water 3 times, and dry it to prepare a working electrode for electrochemical extraction of uranium from wastewater.

[0098] The working electrode for electrochemical extraction of uranium from wastewater prepared in this example was observed and tested as follows:

[0099] (1) Microscopic morphology observation

[0100] The working electrode was observed by scanning electron microscope. Figure 1 Similarly, it is shown that the working electrode has an ultra-large pore structure, and after the ultra-large pore wall area is magnified, a secondary pore structure of mesopores and / or macropores is present. Therefore, it can be known that the working electrode is a three-dimensional porous structure material with a secondary continuous pore structure of ultra-large pores, mesopores and / or macropores. The secondary continuous pore structure is a pore with a continuous and through primary ultra-large pore structure, and at the same time, its pore wall position has a secondary mesopore and / or macropore structure;

[0101] According to the SEM test results, it can be seen that the working electrode has amidoxime groups as functional groups, hydrophilic carbon materials as conductive media, and melamine sponge as electrode skeleton;

[0102] According to the FT-IR test results, characteristic peaks representing the uniform distribution of amidoxime groups are displayed, indicating that the functional groups are uniformly distributed on the polyamidoxime molecular chains in the working electrode; the conductive medium is uniformly distributed in the three-dimensional pore walls, forming a continuous conductive path; and the composite of the polymer and the conductive medium is uniformly filled in the electrode skeleton.

[0103] (2) Test of electrochemical extraction capacity of uranium from wastewater

[0104] Using the electrodes described in this example, the power supply voltage was set to 1.5 V. 50 ml of wastewater was added to the electrochemical extraction device. After 3 h, the residual uranyl ion concentration in the wastewater was measured by microwave plasma emission spectrometry (MP-AES, Agilent). The calculated extraction yield of uranyl ions was 58.02 mg / g.

Claims

1. A working electrode for electrochemical extraction of uranium from wastewater, characterized by: The working electrode has amidoxime groups as functional groups, or amidoxime groups and glutarimidedioxime groups as functional groups, a hydrophilic carbon material as a conductive medium, and a melamine sponge as an electrode skeleton; The working electrode is a three-dimensional porous material having a secondary continuous pore structure of ultra-large pores, mesopores and / or macropores. The secondary continuous pore structure is a pore with a continuous primary ultra-large pore structure, and the pore wall position has a secondary mesopore and / or macropore structure. The functional groups are distributed on the polyamidooxime molecular chains in the working electrode, the conductive medium is distributed in the three-dimensional pore walls, and the composite of the polymer and the conductive medium is filled in the electrode skeleton; The hydrophilic carbon material is hydroxylated carbon nanotubes or carboxylated carbon nanotubes.

2. A working electrode for electrochemical extraction of uranium from wastewater according to claim 1, characterized in that: The functional groups are amidoxime and glutarimidedioxime.

3. A working electrode for electrochemical extraction of uranium from wastewater according to claim 1 or 2, characterized in that: The functional groups are evenly distributed on the polyamidoxime molecular chains in the working electrode, the conductive medium is evenly distributed in the three-dimensional pore walls, and the composite of the polymer and the conductive medium is evenly filled in the electrode skeleton.

4. A method for preparing a working electrode for electrochemical extraction of uranium from wastewater according to any one of claims 1 to 3, characterized in that: The method steps are as follows: (1) Dissolve hydroxylamine hydrochloride in dimethyl sulfoxide, then add sodium carbonate and sodium hydroxide, heat and stir to allow the three to react fully; after the reaction is completed, add polyacrylonitrile to the reaction system, and after the polyacrylonitrile is completely dissolved, raise the reaction temperature to 60°C to 75°C and react for more than 24 hours; after the reaction is completed, let it stand, cool, centrifuge, and separate the supernatant to obtain a uniform polyamidooxime-dimethyl sulfoxide solution; (2) uniformly mixing the polyamidooxime-dimethyl sulfoxide solution and the hydrophilic carbon material, and ultrasonically degassing the mixture to obtain an electrode preparation precursor solution; (3) completely immersing a clean and dry melamine sponge in an electrode preparation precursor solution, taking it out after the precursor solution has fully penetrated the sponge, freezing it below -20°C for more than 2 hours, then freezing it in anhydrous ethanol at -20°C to -114°C for more than 10 hours, drying it, washing it, and drying it again to obtain a working electrode for electrochemical extraction of uranium from wastewater, wherein the functional group is an amidoxime group; When the functional groups are amidoxime and glutarimidedioxime, the working electrode is placed in an alkaline solution, heated to 55° C. to 65° C. for 0.5 h to 1.5 h, washed and dried to obtain a working electrode for electrochemical extraction of uranium from wastewater, wherein the alkaline solution is a sodium hydroxide solution or a potassium hydroxide solution.

5. The method for preparing a working electrode for electrochemical extraction of uranium from wastewater according to claim 4, characterized in that: In step (1), the molar ratio of hydroxylamine hydrochloride, dimethyl sulfoxide, sodium carbonate, sodium hydroxide and polyacrylonitrile is 20:211:9:6:20; in step (2), the mass ratio of polyamidooxime-dimethyl sulfoxide solution to hydrophilic carbon material is 5:1; in step (3), the concentration of the alkaline solution is 0.1 mol / L to 0.5 mol / L.

6. The method for preparing a working electrode for electrochemical extraction of uranium from wastewater according to claim 4, characterized in that: In step (1), the reaction temperature is raised to 65°C and the reaction is carried out for more than 24 hours. In step (3), the working electrode is frozen at -20°C for more than 2 hours. When the functional group is an amidoxime group and a glutarimidedioxime group, the working electrode is placed in an alkaline solution and heated to 50°C to 60°C for 0.5h to 1.5h.

7. The method for preparing a working electrode for electrochemical extraction of uranium from wastewater according to claim 4, characterized in that: In step (3), the melamine sponge is Basotect G+ product of BASF, Germany.

8. The method for preparing a working electrode for electrochemical extraction of uranium from wastewater according to claim 4, characterized in that: In step (3), water with a purity higher than that of deionized water is used for washing.

9. The method for preparing a working electrode for electrochemical extraction of uranium from wastewater according to claim 4, characterized in that: In step (1), the molar ratio of hydroxylamine hydrochloride, dimethyl sulfoxide, sodium carbonate, sodium hydroxide and polyacrylonitrile is 20:211:9:6:20, the reaction temperature is raised to 65° C., and the reaction is carried out for more than 24 hours; In step (2), the mass ratio of the polyamidooxime-dimethyl sulfoxide solution to the hydrophilic carbon material is 5:1; In step (3), the electrode is frozen at -20°C for more than 2 hours. When the functional group is an amidoxime group or a glutarimidedioxime group, the concentration of the alkaline solution is 0.1 mol / L to 0.5 mol / L. The working electrode is placed in the alkaline solution and heated to 50°C to 60°C for 0.5 to 1.5 hours. The melamine sponge is a Basotect G+ product of BASF, Germany. Water with a purity higher than deionized water is used for washing.

10. The method for preparing a working electrode for electrochemical extraction of uranium from wastewater according to any one of claims 4 to 9, characterized in that: In step (1), dimethyl sulfoxide is heated to 40° C. to 50° C. and then hydroxylamine hydrochloride is added to dissolve it; a clean and dry melamine sponge is obtained by the following method: the melamine sponge is ultrasonically washed in anhydrous ethanol to remove oil stains, and then dried to constant weight.

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