AEM electrolytic cell for uranyl reduction, EE-ER system for uranium recovery in offshore spent fuel wastewater and recovery method

Abstract

The invention provides an AEM electrolytic cell for reducing uranyl, and an EE-ER system and method for recovering uranium from offshore spent fuel wastewater. The EE-ER system comprises an AEM electrolytic bath, an overflow blending tank, an acid pool, an ammonia tank, a filter press and a high-temperature calcining furnace which are sequentially connected, a cathode of the AEM electrolytic bath is ZrN / CF, an overflow water outlet of the overflow blending tank is connected with a water treatment system, and a sludge outlet of the overflow blending tank is connected with the acid pool. ZrN / CF is selected as a cathode of the AEM electrolytic cell, high-activity sites are provided to promote electrochemical deposition of uranium in the spent fuel, and 100% degradation of uranium ions can be achieved within two hours. Moreover, the whole EE-ER system realizes online and continuous treatment at a pollution source, the use of an organic solvent is avoided, the purity of the recycled uranium dioxide can exceed 98%, and the recycled uranium dioxide can be directly reused as a nuclear reactor fuel.

Description

Technical Field

[0001] The invention relates to the technical field of spent fuel post-processing, and in particular to an AEM electrolytic cell for reducing uranyl, an EE-ER system for recovering uranium from offshore spent fuel wastewater, and a recovery method. Background Art

[0002] As the global energy system accelerates its transformation from fossil fuels to sustainable energy, the demand for clean and efficient alternative energy is growing. Nuclear fission, as a reliable low-carbon energy technology, occupies an important position in the energy structure. Uranium, as the core element of nuclear fuel, plays a key role in the utilization of nuclear energy. The back-end processing stage of the nuclear fuel cycle usually involves wastewater with high concentrations of uranium nuclides. This type of wastewater not only has recycling value, but also may cause serious environmental pollution if improperly handled. Since most nuclear power plants in the world are located in coastal areas, the discharge of uranium-containing wastewater in the marine environment has attracted much attention. If such wastewater is discharged directly into the ocean, it will not only waste uranium resources, but also cause seawater pollution, which will pose a major threat to the ecosystem and human health. Therefore, the efficient extraction and recovery of uranium from spent fuel wastewater or contaminated sea areas is crucial for energy recycling and environmental remediation.

[0003] Traditionally, the PEREX (tributyl phosphate-uranium extraction) process is used to separate and recover uranium from spent fuel. In the PEREX process, tributyl phosphate has a high selectivity for uranium extraction. However, the PEREX process relies heavily on organic solvents, and a large amount of radioactive organic waste liquid is generated during the complex multi-stage liquid-liquid extraction and phase separation process. In addition, the recovery efficiency of the PEREX process depends largely on the selectivity of the organic extractant for nuclides, and traditional batch processing modes such as centrifugation and washing are difficult to adapt to high-throughput, long-cycle continuous industrial applications. Therefore, in order to improve economy and operability, the back-end treatment of uranium should be achieved as much as possible at the source of pollution, online and continuous, rather than relying on intermittent batch processing.

[0004] Therefore, there is an urgent need for a continuous and scalable uranium recovery process to achieve large-scale application and provide a new technical path for eco-friendly nuclear fuel recycling. Summary of the invention

[0005] 1. Technical issues to be solved

[0006] In view of the deficiencies in the prior art, the present invention provides an AEM electrolytic cell for reducing uranyl, an EE-ER system for recovering uranium from offshore spent fuel wastewater, and a recovery method, which drives out migration and separation of ions under the action of an electric field, electrochemically reduces them to insoluble precipitates in the cathode region of the AEM electrolytic cell, and then performs subsequent purification to achieve efficient recovery of uranium, thereby solving the problems raised in the above-mentioned background technology.

[0007] (II) Technical solution

[0008] To achieve the above objectives, the present invention is implemented through the following technical solutions:

[0009] According to a first aspect of the present invention, an AEM electrolytic cell for reducing uranyl is provided, comprising a bipolar plate and a membrane electrode assembly, wherein the bipolar plate is a titanium plate, and the membrane electrode assembly comprises an AEM anion exchange membrane, a ZrN / CF cathode and an anode, wherein the ZrN / CF cathode is prepared by:

[0010] S1. Add urea to anhydrous ethanol containing zirconium chloride and stir evenly to obtain a zirconium-containing gel;

[0011] S2, subjecting the copper foam to ultrasonic treatment in hydrochloric acid solution, deionized water and anhydrous ethanol in sequence to obtain clean copper foam;

[0012] S3. After coating the surface of the clean copper foam with zirconium-containing gel, the surface is placed in a tube furnace and subjected to nitridation treatment in a nitrogen atmosphere to obtain the ZrN / CF cathode.

[0013] The present invention prepares an AEM electrolytic cell for reducing uranyl, and adopts ZrN / CF as a cathode. ZrN has excellent chloride corrosion resistance and can effectively resist degradation in a seawater environment, while providing highly active sites to promote the electrochemical deposition of uranium. CF serves as a high specific surface area and flexible conductive substrate, which significantly improves the catalytic activity and durability of the motor, thereby reducing energy consumption and improving uranium recovery efficiency.

[0014] Preferably, in step S1, the mass ratio of zirconium chloride to urea is 1:2-9;

[0015] The mass ratio of the zirconium chloride to the volume of anhydrous ethanol is 1 g:2 mL.

[0016] Preferably, in step S2, the concentration of the hydrochloric acid solution is 1 to 3 mol / L.

[0017] Preferably, in step S3, the parameters of the nitriding treatment are: heating to 900-1000° C. at a heating rate of 2-5° C. / min, and keeping the temperature for 1-5 hours.

[0018] According to a second aspect of the present invention, there is provided an EE-ER system for uranium recovery in offshore spent fuel wastewater, comprising an AEM electrolytic cell, an overflow blending tank, an acid tank, an ammonia tank, a filter press and a high-temperature calcining furnace connected in sequence, wherein the AEM electrolytic cell adopts an AEM electrolytic cell with a cathode of ZrN / CF, the overflow outlet of the overflow blending tank is connected to a water treatment system, and the sludge outlet of the overflow blending tank is connected to the acid tank.

[0019] The AEM electrolytic cell of the present invention uses ZrN / CF as the cathode, which can achieve the selective transmission of anions, ensure the effective migration of uranyl ions to the cathode area, and prevent the diffusion of hypophosphite and other oxidizing substances generated by the anode to the cathode, thereby avoiding the reoxidation of uranium species and improving the recovery efficiency. In addition, the AEM electrolytic cell can also effectively limit the Ca 2+ and Mg 2+ The migration of metal ions such as hydroxide on the cathode side is reduced, thereby reducing side reactions such as hydroxide precipitation and avoiding deposition and clogging on the electrode surface, thereby ensuring the long-term stable operation of the EE-ER system for the recovery of offshore spent fuel wastewater.

[0020] According to a third aspect of the present invention, a method for recovering uranium from offshore spent fuel wastewater is provided, using the above-mentioned EE-ER system for recovering uranium from offshore spent fuel wastewater, comprising the following steps:

[0021] Step 1, introducing spent fuel and seawater into the AEM electrolytic cell, reducing uranyl ions at the cathode to obtain a primary precipitation product;

[0022] Step 2, passing the primary precipitation product into the overflow blending tank for natural sedimentation, the supernatant enters the water treatment system through the overflow outlet for treatment and reuse, and the precipitate flows into the acid tank through the sludge outlet for acid washing to obtain soluble uranyl salt;

[0023] Step 3, passing the soluble uranyl salt into the ammonia tank to generate insoluble ammonium diuranate precipitate under alkaline environment;

[0024] Step 4, the insoluble ammonium diuranate precipitate generated in the ammonia tank is transported to the filter press via a pneumatic pump for solid-liquid separation, and the filter cake is collected;

[0025] Step 5: placing the filter cake in the high-temperature calcining furnace for calcining to obtain uranium dioxide.

[0026] Preferably, in step 1, the current density of uranyl ion reduction at the cathode is 45-55 mA / cm 2 .

[0027] Preferably, in step 2, the pickling solution is selected from at least one of nitric acid, hydrochloric acid and sulfuric acid.

[0028] Preferably, in step 3, the pH of the alkaline environment is 9-11.

[0029] Preferably, in step 5, the calcination temperature is 500-600° C., and the calcination time is 3-6 hours.

[0030] (III) Beneficial effects

[0031] The present invention provides an AEM electrolytic cell for reducing uranyl, an EE-ER system for recovering uranium from offshore spent fuel wastewater, and a recovery method. The following beneficial effects are achieved:

[0032] (1) This scheme provides an EE-ER system for uranium recovery from offshore spent fuel wastewater, which uses ZrN / CF as the cathode of the AEM electrolyzer to provide highly active sites to promote the electrochemical deposition of uranium, while preventing hypophosphite and other oxidizing substances produced at the anode from diffusing to the cathode, preventing the reoxidation of uranium elements and improving the recovery efficiency. In addition, the AEM electrolyzer can also effectively limit the AEM electrolyzer.

[0033] (2) This scheme provides an EE-ER system for uranium recovery from offshore spent fuel wastewater. Even in a complex seawater environment, 100% degradation of uranium ions can be achieved within two hours. At the same time, the prepared ZrN / CF cathode has the performance of regenerating active sites, which not only overcomes the limitations of traditional adsorption methods, but also can be applied in long-term continuous industrial applications.

[0034] (3) This scheme provides an EE-ER system for uranium recovery from offshore spent fuel wastewater. Compared with the traditional PUREX process, it can avoid the use of organic solvents and reduce the generation of radioactive organic waste from the source. At the same time, it can achieve efficient separation and purification of uranium through electrochemical deposition, significantly reducing environmental pollution while recovering uranium dioxide with a purity of more than 98%, which can be directly reused as nuclear reactor fuel.

[0035] (4) This scheme provides an EE-ER system for uranium recovery from offshore spent fuel wastewater, which can achieve continuous treatment at the source of pollution and is more adaptable to high-throughput, long-cycle continuous industrial applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 Characterization diagram of the ZrN / CF cathode prepared in Example 1 of the present invention, wherein (A) is an XRD diagram of the ZrN / CF cathode material, and (B) is a transmission electron microscope diagram of the ZrN / CF cathode material;

[0037] Figure 2 A schematic diagram of the process of an EE-ER system for uranium recovery in offshore spent fuel wastewater provided in Example 2 of the present invention;

[0038] Figure 3 This is a schematic diagram of XRD of uranium dioxide recovered by the EE-ER method for uranium recovery from offshore spent fuel wastewater in Example 2 of the present invention;

[0039] Figure 4This is a diagram of the uranium extraction performance of the AEM electrolytic cell in the EE-ER system for uranium recovery in offshore spent fuel wastewater provided in Example 2 of the present invention. DETAILED DESCRIPTION

[0040] In order to better illustrate the content of the present invention, a detailed description is given below in conjunction with specific embodiments.

[0041] Example 1

[0042] An AEM electrolytic cell for reducing uranyl includes a bipolar plate and a membrane electrode assembly, wherein the bipolar plate is a titanium plate, and the membrane electrode assembly includes an AEM anion exchange membrane, a ZrN / CF cathode and an anode, wherein the ZrN / CF cathode is prepared as follows:

[0043] Disperse 1 g of ZrCl4 powder in 2 mL of anhydrous ethanol and stir to obtain a transparent solution. Then add 6 g of urea and stir until completely dissolved to obtain a transparent gel containing zirconium.

[0044] The copper foam is subjected to ultrasonic treatment in 1M hydrochloric acid, deionized water and anhydrous ethanol in sequence to remove the surface oxide layer and impurities and improve the adhesion of the precursor to obtain clean copper foam;

[0045] The prepared zirconium-containing transparent gel was coated on the surface of the clean foam copper and placed in a tube furnace. In a nitrogen atmosphere, it was heated to 900°C at a heating rate of 2°C / min and kept warm for 1 hour to obtain a ZrN / CF cathode.

[0046] The characterization diagram of the ZrN / CF cathode prepared in this example is shown in FIG. Figure 1 As shown, it is proved that the ZrN / CF cathode is successfully prepared in this example.

[0047] Example 2

[0048] An EE-ER system for uranium recovery from offshore spent fuel wastewater, such as Figure 2 As shown, it includes an AEM electrolytic cell 1, an overflow mixing tank 2, an acid tank 3, an ammonia tank 4, a filter press 5 and a high-temperature calcining furnace 6. The outlet of the AEM electrolytic cell 1 is connected to the inlet of the overflow mixing tank 2. The overflow mixing tank 2 is provided with an overflow outlet and a sludge outlet. The overflow outlet is connected to the inlet of the water treatment system 7, and the sludge outlet is connected to the inlet of the acid tank 3. A scraper is provided at the bottom of the overflow mixing tank 2. At the end of each cycle, the sludge at the bottom of the overflow mixing tank 2 is discharged through the scraper and transported to the acid tank 3 through a pipeline. The outlet of the acid tank 3 is connected to the inlet of the ammonia tank 4. The ammonia tank 4 is connected to the filter press 5 through a pneumatic pump, and the filter press 5 is connected to the high-temperature calcining furnace 6. The cathode in the AEM electrolytic cell 1 is 1×1 cm 2 Specifications of ZrN / CF cathode.

[0049] The uranium recovery method based on the above-mentioned EE-ER system for uranium recovery in offshore spent fuel wastewater comprises the following steps:

[0050] Step 1: Spent fuel and seawater are introduced into the AEM electrolyzer 1 at a current density of 50 mA / cm 2 , the flow rate of the electrolyte is 40 mL / min, so that the electrolyte reduces uranyl ions at the cathode to obtain a primary precipitation product;

[0051] Step 2, passing the primary precipitation product into the overflow blending tank 2 for natural sedimentation, the supernatant enters the water treatment system 7 through the outflow outlet for treatment and reuse, and the precipitate flows into the acid tank 3 through the sludge outlet for acid washing to obtain a soluble uranyl salt, wherein the solution in the acid tank 3 is a 5% nitric acid solution, and the primary precipitation product is passed into the acid tank for acid dissolution and stabilization reaction, so that the uranium oxide compound is converted into a soluble uranyl salt, and the alkaline earth metal and alkali metal impurities in the primary precipitation product can be removed at the same time;

[0052] Step 3, passing the soluble uranyl salt into an ammonia tank 4 with a pH of 10, and the soluble uranyl salt reacts with the ammonia water to form an insoluble ammonium diuranate precipitate;

[0053] Step 4, transporting the insoluble diuranylated salt precipitate to the filter press 5 through a pneumatic pump for solid-liquid separation, and collecting the filter cake;

[0054] Step 5: placing the collected filter cake in a high-temperature calcining furnace and calcining at 600° C. for 5 hours to obtain uranium dioxide with a purity of >98%.

[0055] The obtained uranium dioxide is tested, such as Figure 3 As shown, the uranium in the spent fuel can be recovered, and the recovered uranium dioxide can be stored as a reactive fuel for future use.

[0056] according to Figure 4 It can be seen that the AEM electrolytic cell in the EE-ER system for uranium recovery in offshore spent fuel wastewater in this embodiment can achieve a 100% degradation rate within 2 hours.

[0057] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. An AEM electrolytic cell for reducing uranyl, characterized in that: It includes a bipolar plate and a membrane electrode assembly, wherein the bipolar plate is a titanium plate, and the membrane electrode assembly includes an AEM anion exchange membrane, a ZrN / CF cathode and an anode, wherein the preparation method of the ZrN / CF cathode is: S1. Add urea to anhydrous ethanol containing zirconium chloride and stir evenly to obtain a zirconium-containing gel; S2, subjecting the copper foam to ultrasonic treatment in hydrochloric acid solution, deionized water and anhydrous ethanol in sequence to obtain clean copper foam; S3. After coating the surface of the clean copper foam with zirconium-containing gel, the surface is placed in a tube furnace and subjected to nitridation treatment in a nitrogen atmosphere to obtain the ZrN / CF cathode.

2. An AEM electrolytic cell for reducing uranyl according to claim 1, characterized in that: In step S1, the mass ratio of zirconium chloride to urea is 1:2-9; The mass ratio of the zirconium chloride to the volume of anhydrous ethanol is 1 g:2 mL.

3. An AEM electrolytic cell for reducing uranyl according to claim 1, characterized in that: In step S2, the concentration of the hydrochloric acid solution is 1-3 mol / L.

4. The AEM electrolytic cell for reducing uranyl according to claim 1, characterized in that: In step S3, the parameters of the nitriding treatment are: heating to 900-1000° C. at a heating rate of 2-5° C. / min, and keeping the temperature for 1-5 hours.

5. An EE-ER system for uranium recovery from offshore spent fuel wastewater, characterized in that: The invention comprises an AEM electrolytic cell (1), an overflow preparation tank (2), an acid tank (3), an ammonia tank (4), a filter press (5) and a high-temperature calcining furnace (6) which are connected in sequence, wherein the AEM electrolytic cell (1) is the AEM electrolytic cell for reducing uranyl according to any one of claims 1 to 4, the overflow outlet of the overflow preparation tank (2) is connected to a water treatment system (7), and the sludge outlet of the overflow preparation tank (2) is connected to the acid tank (3).

6. A method for recovering uranium from offshore spent fuel wastewater, characterized in that: The EE-ER system for uranium recovery from offshore spent fuel wastewater as claimed in claim 5 comprises the following steps: Step 1, introducing spent fuel and seawater into the AEM electrolytic cell (1), reducing uranyl ions at the cathode to obtain a primary precipitation product; Step 2, passing the primary precipitation product into the overflow blending tank (2) for natural sedimentation, the supernatant enters the water treatment system (7) through the overflow outlet for treatment and reuse, and the precipitate flows into the acid tank (3) through the sludge outlet for acid washing to obtain soluble uranyl salt; Step 3, passing the soluble uranyl salt into the ammonia tank (4) to generate insoluble ammonium diuranate precipitate under alkaline environment; Step 4, the insoluble ammonium diuranate precipitate generated in the ammonia tank (4) is transported to the filter press (5) via a pneumatic pump for solid-liquid separation, and the filter cake is collected; Step 5: placing the filter cake in the high-temperature calcining furnace (6) for calcination to obtain uranium dioxide.

7. A method for recovering uranium from offshore spent fuel wastewater according to claim 6, characterized in that: In step 1, the current density of uranyl ion reduction at the cathode is 45-55 mA / cm 2 .

8. A method for recovering uranium from offshore spent fuel wastewater according to claim 6, characterized in that: In step 2, the pickling solution is selected from at least one of nitric acid, hydrochloric acid and sulfuric acid.

9. A method for recovering uranium from offshore spent fuel wastewater according to claim 6, characterized in that: In step 3, the pH of the alkaline environment is 9-11.

10. A method for recovering uranium from offshore spent fuel wastewater according to claim 6, characterized in that: In step 5, the calcination temperature is 500-600° C., and the calcination time is 3-6 hours.

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