Aem cell for the reduction of uranyl, ee-er system for the recovery of uranium from off-shore spent fuel wastewater and recovery method

Abstract

The application provides an AEM electrolytic cell for reducing uranyl, an EE-ER system and method for recovering uranium in offshore spent fuel wastewater. The EE-ER system for recovering uranium in offshore spent fuel wastewater comprises an AEM electrolytic cell, an overflow distribution tank, an acid tank, an ammonia tank, a filter press and a high-temperature calcining furnace connected in sequence, wherein the cathode of the AEM electrolytic cell is ZrN / CF, the overflow outlet of the overflow distribution tank is connected with a water treatment system, and the sludge outlet of the overflow distribution tank is connected with the acid tank. The AEM electrolytic cell of the application selects ZrN / CF as the cathode, provides high active sites to promote the electrochemical deposition of uranium in spent fuel, and can achieve 100% degradation of uranium ions within two hours. Moreover, the whole EE-ER system realizes online and continuous treatment at the pollution source, avoids the use of organic solvents, and the purity of the recovered uranium dioxide can exceed 98%, which can be directly reused as nuclear reactor fuel.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of spent fuel reprocessing, 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

[0002] With the global energy system accelerating the transition 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, plays an important role in the energy structure, and uranium, as the core element of nuclear fuel, plays a key role in the process of nuclear energy utilization. The back-end processing stage of nuclear fuel cycle usually involves high-concentration uranium-containing wastewater, which not only has recycling value, but also can cause serious environmental pollution if not properly treated. Since most of the world's nuclear power plants are located in coastal areas, the discharge of uranium-containing wastewater into the marine environment has attracted much attention. If such wastewater is directly discharged into the sea, not only will it waste uranium resources, but it will also pollute the sea, which will pose a major threat to the ecosystem and human health. Therefore, it is crucial to efficiently extract and recover uranium from spent fuel wastewater or contaminated sea areas for energy recycling and environmental remediation.

[0003] Traditionally, PEREX (tributyl phosphate-uranium extraction) process is used for uranium separation and recovery from spent fuel. In the PEREX process, tributyl phosphate has high selectivity for uranium extraction, however, the PEREX process relies heavily on organic solvents, which will generate a large amount of radioactive organic waste liquid in 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 the nuclide, and traditional batch processing modes such as centrifugation, washing, etc. are difficult to adapt to high-throughput, long-period continuous industrial applications. Therefore, in order to improve the economy and operability, the back-end processing of uranium should be as much as possible to realize online and continuous processing at the source of pollution, rather than relying on intermittent batch processing.

[0004] Therefore, there is an urgent need for a continuous and scalable uranium recovery process to realize large-scale application and provide a new technical approach for eco-friendly nuclear fuel recycling. SUMMARY

[0005] (1) Technical problems solved

[0006] In view of the deficiencies of the prior art, the present application provides an AEM electrolytic cell for reducing uranyl, an EE-ER system for recovering uranium from offshore spent fuel wastewater and a recovery method. Under the action of an electric field, ions are driven to migrate and separate, and at the cathode region of the AEM electrolytic cell, electrochemical reduction is carried out to form insoluble precipitates, which are then purified to realize efficient recovery of uranium, solving the problems raised in the above background.

[0007] (II) Technical Solution

[0008] To achieve the above object, the present application is implemented by the following technical solution:

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

[0010] S1, urea is added to anhydrous ethanol containing zirconium chloride, and stirred uniformly to obtain a zirconium-containing gel;

[0011] S2, the foamed copper is sequentially subjected to ultrasonic treatment in a hydrochloric acid solution, deionized water and anhydrous ethanol to obtain clean foamed copper;

[0012] S3, after the zirconium-containing gel is coated on the surface of the clean foamed copper, the ZrN / CF cathode is obtained by nitriding treatment in a tube furnace under a nitrogen atmosphere.

[0013] The present application prepares an AEM electrolytic cell for reducing uranyl, uses ZrN / CF as a cathode, ZrN has excellent corrosion resistance to chlorides, can effectively resist degradation in seawater environment, and at the same time provides high active sites to promote the electrochemical deposition of uranium, CF is a high specific surface, flexible conductive substrate, which significantly improves the catalytic activity and durability of the motor, thereby reducing energy consumption and improving the recovery efficiency of uranium.

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

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

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

[0017] Preferably, in step S3, the parameters of the nitriding treatment are: heating at a heating rate of 2-5℃ / min to 900-1000℃, and holding for 1-5h.

[0018] According to a second aspect of the present application, there is provided an EE-ER system for uranium recovery in offshore spent fuel wastewater, comprising AEM electrolytic cells, overflow distribution tanks, acid tanks, ammonia tanks, filter presses and high-temperature calcining furnaces connected in sequence, wherein the AEM electrolytic cells are AEM electrolytic cells with ZrN / CF cathodes, the overflow water outlet of the overflow distribution tank is connected with a water treatment system, and the sludge outlet of the overflow distribution tank is connected with the acid tank.

[0019] The AEM electrolytic cell in the application adopts ZrN / CF as the cathode, can realize selective transmission of anions, ensure effective migration of uranyl ions to the cathode region, and prevent hypophosphite and other oxidizing substances generated by the anode from diffusing to the cathode, thereby avoiding re-oxidation of uranium species and improving the recovery efficiency. In addition, the AEM electrolytic cell can also effectively limit the migration of metal ions such as Ca 2+ and Mg 2+ ions to the cathode side, thereby reducing side reactions such as hydroxide precipitation and avoiding deposition of the electrode surface, thereby ensuring long-term stable operation of the EE-ER system for uranium recovery in offshore spent fuel wastewater.

[0020] According to a third aspect of the application, a method for uranium recovery in offshore spent fuel wastewater is provided, which uses the EE-ER system for uranium recovery in offshore spent fuel wastewater described above, and comprises the following steps:

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

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

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

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

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

[0026] Preferably, in step 1, the current density for reducing the uranyl ions at the cathode is 45-55 mA / cm 2 .

[0027] Preferably, in step 2, the acid washing 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℃, and the calcination time is 3-6h.

[0030] (Three) beneficial effects

[0031] The application provides an AEM electrolytic cell for reducing uranyl, an EE-ER system for recovering uranium in offshore spent fuel wastewater and a recovery method.

[0032] (1) The EE-ER system for recovering uranium in offshore spent fuel wastewater provided by the scheme adopts ZrN / CF as the cathode of the AEM electrolytic cell, provides high active sites to promote the electrochemical deposition of uranium, prevents the diffusion of hypophosphite and other oxidizing substances generated by the anode to the cathode, prevents the reoxidation of uranium elements, improves the recovery efficiency, and further effectively limits the AEM electrolytic cell.

[0033] (2) The EE-ER system for recovering uranium in offshore spent fuel wastewater provided by the scheme can realize 100% degradation of uranium ions within two hours even in a complex seawater environment, and 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 to long-period continuous industrial application.

[0034] (3) The EE-ER system for recovering uranium in offshore spent fuel wastewater provided by the scheme can avoid the use of organic solvents, reduce the generation of radioactive organic waste from the source, realize efficient separation and purification of uranium through electrochemical deposition, significantly reduce environmental pollution, and recover uranium dioxide with a purity of more than 98%, which can be directly reused as nuclear reactor fuel.

[0035] (4) The EE-ER system for recovering uranium in offshore spent fuel wastewater provided by the scheme can realize continuous treatment at the pollution source, and is more suitable for high-throughput and long-period continuous industrial application. BRIEF DESCRIPTION OF DRAWINGS

[0036] Figure 1 The characterization diagram of the ZrN / CF cathode prepared for the embodiment 1 of the application, 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 The flowchart of the EE-ER system for recovering uranium in offshore spent fuel wastewater provided by the embodiment 2 of the application;

[0038] Figure 3 The XRD diagram of the uranium dioxide recovered by the EE-ER method for recovering uranium in offshore spent fuel wastewater adopted by the embodiment 2 of the application;

[0039] Figure 4Figure of uranium extraction performance of AEM electrolytic cell in EE-ER system for uranium recovery in offshore spent fuel wastewater provided in embodiment 2 of the present application. DETAILED DESCRIPTION

[0040] In order to better illustrate the content of the present application, the following will be described in conjunction with specific embodiments.

[0041] Embodiment 1

[0042] A AEM electrolytic cell for reducing uranyl, comprising a bipolar plate and a membrane electrode assembly, the bipolar plate is a titanium plate, the membrane electrode assembly comprises an AEM anion exchange membrane, a ZrN / CF cathode and an anode, wherein the preparation method of the ZrN / CF cathode is as follows:

[0043] 1g of ZrCl4 powder is dispersed in 2mL of anhydrous ethanol to obtain a transparent solution, then 6g of urea is added and stirred until completely dissolved to obtain a transparent zirconium-containing gel;

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

[0045] The prepared transparent zirconium-containing gel is coated on the surface of the clean foam copper, and the whole is placed in a tube furnace and heated to 900℃ at a heating rate of 2℃ / min under a nitrogen atmosphere, and kept for 1h to obtain a ZrN / CF cathode.

[0046] The characterization graph of the ZrN / CF cathode prepared in this embodiment is shown in Figure 1 , which proves that the ZrN / CF cathode is successfully prepared in this embodiment.

[0047] Embodiment 2

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

[0049] The uranium recovery method based on the EE-ER system for recovering uranium from offshore spent fuel wastewater is as follows:

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

[0051] Step 2, the primary precipitation product is introduced into the overflow tank 2 for natural sedimentation, the supernatant is discharged through the overflow outlet into the water treatment system 7 for treatment and reuse, and the precipitate is discharged through the sludge outlet into the acid tank 3 for pickling 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 introduced 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, the soluble uranyl salt is introduced into the ammonia tank 4 with a pH of 10, and the soluble uranyl salt reacts with ammonia water to form an insoluble ammonium diuranate precipitate;

[0053] Step 4, the insoluble ammonium diuranate precipitate is transported to the filter press 5 by the air pump for solid-liquid separation, and the filter cake is collected;

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

[0055] The obtained uranium dioxide is detected, as shown in Figure 3 , the uranium in the spent fuel can be recovered, and the recovered uranium dioxide can be used as a reserve of the spent fuel.

[0056] According to Figure 4 , the AEM electrolytic cell 2h in the EE-ER system for recovering uranium from offshore spent fuel wastewater can achieve a degradation rate of 100%.

[0057] Although embodiments of the present application have been shown and described, it will be understood by those of ordinary skill in the art that various changes, modifications, substitutions and alterations can be made thereto without departing from the principles and spirit of the present application, the scope of which is defined by the appended claims and their equivalents.

Claims

1. An AEM electrolyzer for the reduction of uranyl characterized in that: The application relates to a kind of EE-ER systems for recovering uranium from offshore spent fuel wastewater, comprising bipolar plate and membrane electrode assembly, the bipolar plate is titanium plate, the membrane electrode assembly comprises AEM anion exchange membrane, ZrN / CF cathode and anode, wherein the preparation method of the ZrN / CF cathode is: S1, adding urea into zirconium chloride-containing anhydrous ethanol, stirring uniformly to obtain zirconium-containing gel; S2, cleaning foam copper is obtained by sequentially treating foam copper in hydrochloric acid solution, deionized water and anhydrous ethanol under ultrasonic; S3, after coating the zirconium-containing gel on the surface of the cleaning foam copper, nitrogenizing treatment is carried out in a tube furnace under nitrogen atmosphere to obtain the ZrN / CF cathode.

2. An AEM electrolyzer for the reduction of 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 of zirconium chloride to the volume of anhydrous ethanol is 1g:2mL.

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

4. The AEM electrolyzer for the reduction of uranyl according to claim 1, characterized in that: In step S3, the parameters of the nitrogenizing treatment are as follows: heating to 900-1000℃ at a heating rate of 2-5℃ / min, and keeping temperature for 1-5h.

5. An EE-ER system for uranium recovery from spent fuel wastewater in offshore nuclear power plants, characterized by: The application relates to a kind of EE-ER systems for recovering uranium from offshore spent fuel wastewater, comprising bipolar plate and membrane electrode assembly, the bipolar plate is titanium plate, the membrane electrode assembly comprises AEM anion exchange membrane, ZrN / CF cathode and anode, wherein the preparation method of the ZrN / CF cathode is:

6. A process for the recovery of uranium from spent nuclear fuel waste water in an offshore environment, characterised in that: The EE-ER system for recovering uranium from offshore spent fuel wastewater in claim 5 comprises the following steps: Step 1, passing spent fuel and seawater into the AEM electrolytic cell (1) to reduce uranyl ions at the cathode to obtain primary precipitation product; Step 2, passing the primary precipitation product into the overflow adjustment tank (2) to naturally settle, the supernatant is treated in the water treatment system (7) through the overflow outlet, and the precipitate flows into the acid tank (3) through the sludge outlet to obtain soluble uranyl salt after acid washing; Step 3, passing the soluble uranyl salt into the ammonia tank (4) to generate insoluble ammonium diuranate precipitate in an alkaline environment; Step 4, the insoluble ammonium diuranate precipitate generated in the ammonia tank (4) is delivered to the filter press (5) by a pneumatic pump to separate solid and liquid, and filter cake is collected; Step 5, placing the filter cake in the high-temperature calcining furnace (6) to roast to obtain uranium dioxide.

7. A process for the recovery of uranium from spent nuclear fuel waste water for offshore use according to claim 6, characterized in that: In step 1, the current density for the cathodic reduction of uranyl ions was 45-55 mA / cm 2 .

8. A process for the recovery of uranium from spent nuclear fuel waste water for offshore use as claimed in claim 6, wherein: In step 2, the acid washing solution is selected from at least one of nitric acid, hydrochloric acid and sulfuric acid.

9. A process for the recovery of uranium from spent nuclear fuel waste water for offshore use as claimed in claim 6, wherein: In step 3, the pH of the alkaline environment is 9-11.

10. A process for the recovery of uranium from spent nuclear fuel waste water for offshore use as claimed in claim 6, wherein: In step 5, the roasting temperature is 500-600℃, and the roasting time is 3-6h.

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