A method for separating rare earth fission products from a fluorolithium beryllium molten salt system

Abstract

The application discloses a method for separating rare earth fission products in a fluorine-lithium-beryllium molten salt system, which comprises the following steps: using Ni, Cu, Al, Au, Ru, Rh, Pd, Os, Ir, Pt or graphite as a working electrode; using graphite, glass carbon, Pt or Ni as an auxiliary electrode; using a beryllium electrode as a reference electrode, wherein the beryllium electrode comprises a beryllium metal rod and a LiF-BeF2 molten salt; performing constant potential electrolysis or pulse electrolysis on the fluorine-lithium-beryllium molten salt containing rare earth fission products, wherein the electrolysis condition of the constant potential electrolysis is that the constant electrolysis potential is 0.15-0.6 V; and the condition of the pulse electrolysis is that the negative pulse potential is-0.1-(-0.5) V, the positive pulse potential is 0.15-0.6 V, and the positive and negative pulses are alternately performed. The separation method can directly and effectively separate rare earth fission products from the fluorine-lithium-beryllium molten salt system, and can be used for online treatment of molten salt reactor fuel.

Description

Technical Field

[0001] This invention relates to a method for separating rare earth fission products in a fluorine-lithium-beryllium molten salt system. Background Technology

[0002] Molten lithium-beryllium salt (LiF) and BeF2 is a typical fuel carrier and heat transfer medium in molten salt reactor (MSR) systems. Nuclear fuel, in the form of fluorides (such as UF4 and ThF4), dissolves in the LiF-beryllium carrier salt and undergoes a fission reaction in the reactor core, releasing heat and generating various fission products. These include gaseous fission products with large neutron absorption cross-sections (such as Kr, Xe, and T) and rare earth fission products (mainly Pr, Nd, Sm, and Eu). The accumulation of fission products within the reactor consumes valuable neutron resources necessary to sustain the fuel chain reaction in the reactor core, significantly reducing the reactor's neutron economy. Therefore, periodic or online separation of these products is essential. The separation of fission products is one of the core issues in molten salt reactor fuel reprocessing.

[0003] Batch processing of fuel salts in molten salt reactors is a compromise or alternative approach. Given the significant challenges of online processing, researchers have adopted the concept of batch processing, drawing inspiration from traditional reactor fuel reprocessing methods. This approach can be understood as a fuel reconfiguration model, where valuable and easily separable components in the fuel salt are separated and recovered using various separation technologies, and then the fuel salt is resynthesized and returned to the molten salt reactor for reuse. Currently, the most researched technologies include fluorination volatilization (CN113881862A) or electrolytic recovery (J Radioanal Nucl Chem (2017) 311:1891–1897) for uranium recovery, vacuum distillation (J Radioanal Nucl Chem (2017) 311:36-42) and liquid metal reduction extraction (J Alloy Compd (2005) 389:29–33) for carrier salt recovery, and electrochemical separation (AIChE J (2016) 62:1236–1243) for thorium recovery. While fuel reconfiguration can theoretically support the successful operation of molten salt reactors, the high cost of fuel processing and failure to fully leverage the advantages of online fuel processing in molten salt reactors limit its application to a transitional approach. To fully realize the inherent advantages of molten salt reactors, it is essential to rely on online separation technologies for fission products, including rare earth elements.

[0004] Molten salt reactors are the only type of reactor that allows for in-situ processing of nuclear fuel. Developing in-situ fuel processing technology for molten salt reactors would significantly enhance their competitiveness. In-situ processing is a removal method, directly separating harmful fission products from the fuel salt. In-situ processing of molten salt reactor fuel is an ideal mode, highly efficient, but also the most technically challenging. Currently, relatively mature in-situ separation technologies include the online separation of gaseous fission products such as Kr, Xe, and T using bubbling degassing. However, for rare earth fission products that are readily soluble in molten salt and stable in nature, there is currently no mature in-situ separation technology.

[0005] In recent years, some scholars have begun to explore possible methods for the direct separation of rare earth elements in molten salt systems. For example, electrochemical separation studies of rare earth elements have been conducted in LiCl-KCl systems (Electrochim Acta (2010) 55:3022-3025, Ionics (2019) 25:1897-1909) or LiF-CaF2 systems (J Radioanal Nucl Chem (2014) 301:589-595, J Electroanal Chem (2010) 642:150-156). However, due to the influence of Be... 2+ The reduction potential is higher than that of rare earth element ions, making it easier to reduce and deposit on the electrode than rare earth elements. Since rare earth elements cannot be separated from beryllium in the lithium-fluorine-beryllium system by constant potential deposition, these methods for non-fluorine-beryllium systems are not suitable for the online separation of rare earth fission products in molten salt reactors. Straka et al. studied the reduction and recovery of Gd and Sm from lithium-fluorine-beryllium melt using a nickel electrode. They found that after constant potential deposition, a Gd-Ni alloy formed on the surface of the nickel electrode, and metallic beryllium was simultaneously deposited on the nickel electrode. They failed to successfully separate rare earth Gd from the lithium-fluorine-beryllium molten salt system (Procedia Chemistry (2012) 7:804-813).

[0006] There is an urgent need for an effective separation method to successfully separate rare earth fission products from a fluorine-lithium-beryllium molten salt system. Summary of the Invention

[0007] To overcome the technical deficiency in existing technologies where rare earth elements cannot be directly separated in fluorine-lithium-beryllium molten salt systems, this invention provides a method for separating rare earth fission products from fluorine-lithium-beryllium molten salt systems. This method can directly and effectively separate rare earth fission products from fluorine-lithium-beryllium molten salt systems and can be used for online processing of molten salt reactor fuel.

[0008] This invention provides a method for separating rare earth fission products in a fluorine-lithium-beryllium molten salt system, comprising the following steps:

[0009] Ni, Cu, Al, Au, Ru, Rh, Pd, Os, Ir, Pt or graphite are used as working electrodes;

[0010] Graphite, glassy carbon, Pt, or Ni are used as auxiliary electrodes;

[0011] A beryllium electrode is used as the reference electrode, and the beryllium electrode comprises a beryllium metal rod and LiF-BeF2 molten salt;

[0012] Constant potential electrolysis or pulse electrolysis was performed on fluorine-lithium-beryllium molten salt containing rare earth fission products.

[0013] The electrolysis conditions for the constant potential electrolysis are: a constant potential of 0.15 to 0.6V, where the constant potential is the potential value of the working electrode relative to the reference electrode;

[0014] The conditions for pulse electrolysis are: negative pulse potential of -0.1 to -0.5V and positive pulse potential of 0.15 to 0.6V; the positive pulse potential or the negative pulse potential is the potential value of the working electrode relative to the reference electrode.

[0015] In this invention, preferably, the method for separating rare earth fission products in the fluorine-lithium-beryllium molten salt system includes the following steps:

[0016] S1. The raw material of the lithium fluoride beryllium molten salt is heated and melted to obtain the lithium fluoride beryllium molten salt.

[0017] S2. Insert the working electrode, the auxiliary electrode, and the reference electrode into the fluorine-lithium-beryllium molten salt and connect them to an electrochemical workstation or a pulse power supply respectively. The reference electrode serves as the reference electrode for the working electrode and the auxiliary electrode. The working electrode and the auxiliary electrode form a conductive circuit to perform electrolysis under pulse potential.

[0018] S3. Under the negative pulse potential, the rare earth elements and Be are deposited on the working electrode, forming rare earth intermetallic compounds and Be intermetallic compounds. Then, under the positive pulse potential, metallic Be and Be-rich intermetallic compounds are oxidized and re-immersed in molten salt, while the rare earth-poor intermetallic compounds remain on the working electrode and precipitate out.

[0019] In this invention, preferably, the method for separating rare earth fission products in the fluorine-lithium-beryllium molten salt system includes the following steps:

[0020] S1. The raw material of the lithium fluoride beryllium molten salt is heated and melted to obtain the lithium fluoride beryllium molten salt.

[0021] S2. Using Ni, Cu, Al, Au, Ru, Rh, Pd, Os, Ir, Pt, or graphite as the working electrode, and graphite, glassy carbon, Pt, or Ni as the auxiliary electrode, and the beryllium electrode as the reference electrode, the working electrode, the auxiliary electrode, and the reference electrode are inserted into the lithium fluoride beryllium molten salt and connected to an electrochemical workstation or electrolysis power supply respectively. The reference electrode serves as the reference electrode for the working electrode and the auxiliary electrode. The working electrode and the auxiliary electrode form a conductive circuit for electrolysis.

[0022] S3. Under the constant potential, the rare earth elements and Be are deposited on the working electrode and form rare earth-depleted and Be-depleted intermetallic compounds, which are then precipitated.

[0023] In this invention, the negative pulse potential is preferably -0.2V to -0.4V, and the positive pulse potential is preferably 0.2V to 0.5V. The positive and negative pulse potentials are the potential values ​​of the working electrode relative to the reference electrode. The positive pulse potential is preferably 0.2V to 0.5V, for example, 0.2V, 0.35V, 0.40V, or 0.48V; the negative pulse potential is preferably -0.2V or -0.4V.

[0024] As is known to those skilled in the art in this invention, under pulse electrolysis, positive and negative pulses are delivered alternately.

[0025] In this invention, the constant potential is preferably 0.3V to 0.5V.

[0026] In this invention, the pulse frequency of the pulse electrolysis is preferably 0.1–1000 Hz, more preferably 10–500 Hz, for example, 50 Hz, 400 Hz, or 500 Hz. The duty cycle of the pulse electrolysis is preferably (0–0.5):1, more preferably (0.05–0.25):1. The duty cycle refers to the ratio of the negative pulse time to the positive pulse time.

[0027] In this invention, the pulse electrolysis time is preferably 1-3 hours, for example 2 hours.

[0028] In this invention, in the beryllium electrode, the molar ratio of LiF to BeF2 in the LiF-BeF2 molten salt is preferably 1:1 to 4:1, for example, 2:1.

[0029] In this invention, the diameter of the beryllium metal rod in the beryllium electrode is preferably 2-3 mm.

[0030] In this invention, as is known to those skilled in the art, the beryllium electrode uses a beryllium metal rod as the electrode material, and a portion of the beryllium metal rod is immersed in LiF-BeF2 molten salt.

[0031] In this invention, as those skilled in the art will know, the beryllium electrode generally also includes a sleeve. The ratio of the total volume of the lithium fluoride-beryllium molten salt to the volume of the sleeve is preferably 0.3 to 0.5. The wall thickness of the sleeve is preferably 1 to 5 mm. The sleeve material can be an inert material resistant to molten salt corrosion, preferably a ceramic material, such as hot-pressed boron nitride, alumina, magnesium oxide, or zirconium oxide. The inert material refers to a material with very stable chemical properties that does not easily react chemically with other substances. The thinnest part of the sleeve at its bottom is preferably 0.1 to 1.0 mm thick.

[0032] As is known to those skilled in the art in this invention, the fluorine-lithium-beryllium molten salt generally contains LiF and BeF2.

[0033] In this invention, the temperature of the fluorine-lithium-beryllium molten salt is preferably 500-800℃.

[0034] In this invention, the fluorine-lithium-beryllium molten salt preferably also includes one or more of UF4, ThF4, PmF3 and ZrF4.

[0035] In this invention, the rare earth elements in the rare earth fission products can be conventional in the art, preferably Pr, Nd, Gd, Ce, La, Sm or Eu.

[0036] In this invention, the rare earth fission products may include rare earth element fluorides, such as one or more of LaF3, CeF3, PrF3, NdF3, SmF3, EuF3 and GdF3.

[0037] In this invention, the purity of the material of the working electrode, the auxiliary electrode, or the reference electrode is preferably not less than 95%. For example, using Cu as the working electrode, the purity of Cu in the working electrode is not less than 95%.

[0038] In this invention, preferably, the atmosphere in which the fluorine-lithium-beryllium molten salt, the working electrode, the auxiliary electrode, or the reference electrode is located is an inert gas atmosphere, and the element of the inert gas is, for example, Ar or He, and the purity of the inert gas is preferably ≥99.999%.

[0039] In this invention, the electrolysis power supply used for pulse electrolysis can be a device commonly used in the art, such as a KOST electrochemical workstation, preferably a CS350M KOST electrochemical workstation.

[0040] In this invention, the lithium fluoride beryllium molten salt system is quite special, differing from other molten salt systems such as molten salt KCl and LiCl systems, because Be... 2+The reduction potential of rare earth elements is higher than that of rare earth ions, making them difficult to separate in electrolytic methods. This invention, by using a Be electrode as a reference electrode and through experiments combined with thermodynamic calculations, obtained the stable potentials of different rare earth metals and rare earth intermetallic compounds, laying a theoretical foundation for the electrolytic separation of rare earth elements in a lithium fluoride-beryllium molten salt system. This technique is not something that can be achieved by those skilled in the art using conventional electrolytic methods; currently, there are no reports of any successful separation of rare earth elements using a lithium fluoride-beryllium molten salt system.

[0041] Based on common knowledge in the field, the above-mentioned preferred conditions can be combined arbitrarily to obtain various preferred embodiments of the present invention.

[0042] The positive and progressive effects of this invention are as follows:

[0043] This invention achieves the extraction and separation of rare earth elements by pulse electrolysis of fluorine-lithium-beryllium molten salt containing rare earth fission products, depositing rare earth elements onto the working electrode while avoiding the deposition of large amounts of beryllium or other metal elements (such as U, Th, Zr) on the working electrode. Compared to fuel reconfiguration, this invention can directly remove rare earth fission products from molten salt reactor fuel salts, with low equipment requirements, simple operation, high efficiency, and low cost, which can greatly improve the processing efficiency of molten salt reactor fuels and the economics of the reactor. Attached Figure Description

[0044] Figure 1 This is a schematic diagram of the structure of a beryllium reference electrode.

[0045] Figure 2 This is a schematic diagram illustrating the principle of rare earth element separation in this invention. Detailed Implementation

[0046] The present invention is further illustrated below by way of embodiments, but the invention is not limited to the scope of the embodiments described herein. Experimental methods in the following embodiments that do not specify specific conditions were performed according to conventional methods and conditions, or as selected according to the product instructions.

[0047] In the following examples and comparative examples, the rare earth element content in the molten salt was detected using an ICP-AES analyzer, and the crystal form of the rare earth deposits was determined using an XRD analyzer. The pulse electrolysis was performed using a CS350M KOST electrochemical workstation.

[0048] Example 1

[0049] Electrolytic extraction separation of Eu in the LiF-BeF2-EuF3 molten salt system.

[0050] Weigh out 52g LiF, 47g BeF2, and 1g EuF3 respectively, mix them evenly, and place them in a glassy carbon crucible with an inner diameter of 40mm and a height of 60mm. Melt the crucible at 500℃ under an argon atmosphere for later use.

[0051] Using an Au metal sheet as the working electrode, a platinum metal sheet as the auxiliary electrode, and a beryllium electrode as the reference electrode, the working electrode and the auxiliary electrode form a conductive circuit, and pulse electrolysis is performed at constant potential under the control of an electrochemical workstation.

[0052] The Au electrode specifications are 7mm × 20mm × 1mm, and the platinum electrode specifications are 10mm × 30mm × 1mm. The beryllium reference electrode structure is as follows: Figure 1 As shown, the beryllium rod has a diameter of 2 mm, the hot-pressed boron nitride tube has a wall thickness of 1 mm, and the thinnest part at the bottom of the tube has a thickness of 0.1 mm. Part of the beryllium metal rod is immersed in LiF-BeF2 molten salt, and the total volume of the liquid LiF-BeF2 molten salt accounts for 0.3% of the volume of the boron nitride tube.

[0053] The conditions for pulse electrolysis are: negative pulse potential -0.2V, positive pulse potential 0.35V, pulse frequency 10Hz, and duty cycle 0.05:1. Both positive and negative pulse potentials are the potential values ​​of the working electrode relative to the reference electrode.

[0054] The principle of Example 1 can be derived from Figure 2 Provided. Figure 2 RE in this context represents rare earth elements, such as Eu in this embodiment. (The last part, "relative to Be," appears to be a typo and can be left as is.) 2+ / Be reference electrode at a negative pulse potential of -0.2V, Be 2+ With Eu 2+ Simultaneously, reduction precipitation occurs on the Au electrode surface, followed by intermetallic chemical reactions with the Au electrode. Subsequently, relative to Be... 2+ At a positive pulse potential of 0.35V, unreacted Be and Eu, or the beryllium-rich and europium-rich intermetallic compounds formed by their combination, are re-oxidized and dissolved back into the molten salt. Rare earth-rich gold intermetallic compounds such as Au4Eu and Cu4Eu remain on the electrode. As the pulse continues, Eu elements existing in the form of rare earth-rich gold intermetallic compounds continuously diffuse into the interior of the gold electrode, thereby achieving the purpose of electrochemical extraction and separation of Eu elements in the lithium fluoride-beryllium molten salt system.

[0055] Those skilled in the art know that Eu3Au, EuAu, etc. are europium-rich intermetallic compounds, while EuAu5, EuAu4, etc. are gold-rich compounds. Eu can form a variety of intermetallic compounds with Au. Eu-rich intermetallic compounds such as Eu3Au and EuAu have very low stable potentials, close to that of Be, and therefore cannot be retained on the electrode during pulse electrolysis. Instead, gold-rich compounds such as EuAu5 and EuAu4, which have higher stable potentials, can be retained.

[0056] After 2 hours of pulsed electrolytic deposition, the concentration of Eu in the molten salt decreased by 36.1% as measured by ICP-AES (meaning that 36.1% of the Eu content in 1g EuF3 was precipitated). XRD analysis showed that the Eu deposit on Au was mainly Au4Eu.

[0057] Example 2

[0058] Electrolytic extraction separation of Sm in the LiF-BeF2-SmF3 molten salt system.

[0059] 26g LiF, 47g BeF2, and 1g SmF3 were weighed out, mixed thoroughly, and placed in a glassy carbon crucible with an inner diameter of 40mm and a height of 60mm. The mixture was then melted at 600℃ under an argon atmosphere. A Ni metal sheet was used as the working electrode, glassy carbon as the auxiliary electrode, and a beryllium electrode as the reference electrode. Pulse electrolysis was performed under the control of an electrochemical workstation. The Ni electrode dimensions were 7mm × 20mm × 1mm, and the glassy carbon electrode dimensions were 10mm × 30mm × 3mm. The beryllium reference electrode structure was as follows. Figure 1 As shown, the beryllium rod has a diameter of 2 mm, the alumina sleeve has a wall thickness of 2 mm, the thinnest part at the bottom of the tube has a thickness of 0.5 mm, and the total volume of the liquid LiF-BeF2 molten salt accounts for 0.4% of the volume of the boron nitride tube.

[0060] The conditions for pulse electrolysis are: negative pulse potential -0.4V, positive pulse potential 0.2V, pulse frequency 100Hz, and duty cycle 0.25:1.

[0061] After 2 hours of electrolytic deposition, the Sm concentration in the molten salt decreased by 25.4%. XRD analysis showed that the Sm deposit on Ni was mainly Ni. 17 Sm2.

[0062] Example 3

[0063] Electrolytic extraction separation of Eu in the LiF-BeF2-UF4-EuF3 molten salt system.

[0064] Weigh out 78g LiF, 47g BeF2, 2g UF4 and 1g EuF3 respectively, mix them evenly and place them in a glassy carbon crucible with an inner diameter of 40mm and a height of 60mm. Melt the crucible at 600℃ under an argon atmosphere for later use.

[0065] Pt metal sheet was used as the working electrode, graphite as the auxiliary electrode, and beryllium electrode as the reference electrode. Pulse electrolysis was performed under the control of an electrochemical workstation. The Pt electrode dimensions were 7mm × 20mm × 1mm, and the graphite electrode dimensions were 10mm × 30mm × 3mm. The beryllium reference electrode structure was as follows. Figure 1As shown, the beryllium rod has a diameter of 2 mm, the magnesium oxide sleeve has a wall thickness of 3 mm, the thinnest part at the bottom of the tube has a thickness of 0.75 mm, and the total volume of the liquid LiF-BeF2 molten salt accounts for 0.5 of the volume of the boron nitride tube.

[0066] The pulse electrolysis conditions were: negative pulse potential -0.2V, positive pulse potential 0.48V, pulse frequency 1000Hz, and duty cycle 0.5:1. After 2 hours of electrolytic deposition, the Eu concentration in the molten salt decreased by 28.3%, and XRD analysis showed that the Eu deposit on Ni was mainly Pt5Eu.

[0067] Example 4

[0068] Electrolytic extraction separation of La in the LiF-BeF2-ThF4-LaF3 molten salt system.

[0069] Weigh out 52g LiF, 47g BeF2, 2g ThF4 and 1g LaF3 respectively, mix them evenly and place them in a glassy carbon crucible with an inner diameter of 40mm and a height of 60mm. Melt the crucible at 600℃ under an argon atmosphere for later use.

[0070] Using a Ni metal sheet as the working electrode, glassy carbon as the auxiliary electrode, and a beryllium electrode as the reference electrode, pulse electrolysis at a constant potential was performed under the control of an electrochemical workstation. The Ni electrode dimensions were 7mm × 20mm × 1mm, and the glassy carbon electrode dimensions were 10mm × 30mm × 3mm. The beryllium reference electrode structure was as follows. Figure 1 As shown, the beryllium rod has a diameter of 2 mm, the zirconia sleeve has a wall thickness of 4 mm, the thinnest part at the bottom of the tube has a thickness of 0.75 mm, and the total volume of the liquid LiF-BeF2 molten salt accounts for 0.4% of the volume of the boron nitride tube.

[0071] The pulse electrolysis conditions were: negative pulse potential -0.2V, positive pulse potential 0.40V, pulse frequency 500Hz, and duty cycle 0.25:1. After 2 hours of electrolytic deposition, the Pm concentration in the molten salt decreased by 29.5%. XRD analysis showed that the La deposits on Ni were mainly Ni. 17 La2.

[0072] Example 5

[0073] Electrolytic extraction separation of Nd in the LiF-BeF2-UF4-ThF4-NdF3 molten salt system.

[0074] Weigh out 104g LiF, 47g BeF2, 2g UF4, 2g ThF4 and 1g NdF3 respectively, mix them evenly and place them in a glassy carbon crucible with an inner diameter of 40mm and a height of 60mm. Melt the crucible at 700℃ under a helium atmosphere for later use.

[0075] Pt metal sheet was used as the working electrode, nickel metal sheet as the auxiliary electrode, and beryllium electrode as the reference electrode. Pulse electrolysis was performed under the control of an electrochemical workstation. The Pt electrode dimensions were 7mm × 20mm × 1mm, and the nickel auxiliary electrode dimensions were 10mm × 30mm × 3mm. The beryllium reference electrode structure was as follows. Figure 1 As shown, the beryllium rod has a diameter of 3 mm, the hot-pressed boron nitride tube has a wall thickness of 3 mm, the thinnest part at the bottom of the tube has a thickness of 1 mm, and the total volume of the liquid LiF-BeF2 molten salt accounts for 0.4% of the volume of the boron nitride tube.

[0076] The pulse electrolysis conditions were: negative pulse potential -0.5V, positive pulse potential 0.50V, pulse frequency 500Hz, and duty cycle 0.25:1. After 2 hours of electrolytic deposition, the Nd concentration in the molten salt decreased by 22.9%, and XRD analysis showed that the Pr deposit on Pt was mainly Pt5Nd.

[0077] Example 6

[0078] Electrolytic extraction separation of Nd in the LiF-BeF2-UF4-ThF4-ZrF4-NdF3 molten salt system.

[0079] 104g LiF, 47g BeF2, 2g UF4, 2g ThF4, 5g ZrF4, and 1g NdF3 were weighed out, mixed thoroughly, and placed in a glassy carbon crucible with an inner diameter of 40mm and a height of 60mm. The mixture was then melted at 800℃ under a helium atmosphere and set aside for later use. Pulse electrolysis was performed under the control of an electrochemical workstation, using an Ir metal sheet as the working electrode, a nickel metal sheet as the auxiliary electrode, and a beryllium electrode as the reference electrode.

[0080] The Ir electrode dimensions are 7mm × 20mm × 1mm, and the nickel auxiliary electrode dimensions are 10mm × 30mm × 3mm. The beryllium reference electrode structure is as follows: Figure 1 As shown, the beryllium rod has a diameter of 3 mm, the hot-pressed boron nitride tube has a wall thickness of 5 mm, the thinnest part at the bottom of the tube has a thickness of 1 mm, and the total volume of the liquid LiF-BeF2 molten salt accounts for 0.4% of the volume of the boron nitride tube.

[0081] The pulse electrolysis conditions were: negative pulse potential -0.5V, positive pulse potential 0.60V, pulse frequency 500Hz, and duty cycle 0.25:1. After 2 hours of electrolytic deposition, the Nd concentration in the molten salt decreased by 23.7%.

[0082] Example 7

[0083] Electrolytic extraction separation of Ce in the LiF-BeF2-CeF3 molten salt system.

[0084] 52g of LiF, 47g of BeF2, and 1g of CeF3 were weighed out, mixed thoroughly, and placed in a glassy carbon crucible with an inner diameter of 40mm and a height of 60mm. The mixture was then melted at 700℃ under an argon atmosphere. Pulse electrolysis was performed under the control of an electrochemical workstation, using a Ru metal sheet as the working electrode, graphite as the auxiliary electrode, and a beryllium electrode as the reference electrode.

[0085] The Ru electrode specifications are 7mm × 20mm × 1mm, and the graphite electrode specifications are 10mm × 30mm × 3mm. The beryllium reference electrode structure is as follows: Figure 1 As shown, the beryllium rod has a diameter of 2 mm, the hot-pressed boron nitride tube has a wall thickness of 2 mm, the thinnest part at the bottom of the tube has a thickness of 1 mm, and the total volume of the liquid LiF-BeF2 molten salt accounts for 0.4% of the volume of the boron nitride tube.

[0086] The pulse electrolysis conditions were: negative pulse potential -0.5V, positive pulse potential 0.5V, pulse frequency 500Hz, and duty cycle 0.25:1. After 2 hours of electrolytic deposition, the Ce concentration in the molten salt decreased by 28.5%.

[0087] Example 8

[0088] Electrolytic extraction separation of Gd in the LiF-BeF2-UF4-GdF3 molten salt system.

[0089] 78g LiF, 47g BeF2, 2g UF4, and 1g PrF3 were weighed out, mixed thoroughly, and placed in a glassy carbon crucible with an inner diameter of 40mm and a height of 60mm. The mixture was then melted at 650℃ under an argon atmosphere. Pulse electrolysis was performed using an Rh metal sheet as the working electrode, graphite as the auxiliary electrode, and a beryllium electrode as the reference electrode, under the control of an electrochemical workstation.

[0090] The Rh electrode specifications are 7mm × 20mm × 1mm, and the graphite electrode specifications are 10mm × 30mm × 3mm. The beryllium reference electrode structure is as follows. Figure 1 As shown, the beryllium rod has a diameter of 2 mm, the hot-pressed boron nitride tube has a wall thickness of 2 mm, the thinnest part at the bottom of the tube has a thickness of 0.8 mm, and the total volume of the liquid LiF-BeF2 molten salt accounts for 0.4% of the volume of the boron nitride tube.

[0091] The pulse electrolysis conditions were: negative pulse potential -0.5V, positive pulse potential 0.5V, pulse frequency 1000Hz, and duty cycle 0.5:1. After 2 hours of electrolytic deposition, the Gd concentration in the molten salt decreased by 28.3%.

[0092] Example 9

[0093] Electrolytic extraction separation of Nd in the LiF-BeF2-ThF4-NdF3 molten salt system.

[0094] 52g LiF, 47g BeF2, 2g ThF4, and 1g NdF3 were weighed out, mixed thoroughly, and placed in a glassy carbon crucible with an inner diameter of 40mm and a height of 60mm. The mixture was then melted at 600℃ under an argon atmosphere. Pulse electrolysis was performed under the control of an electrochemical workstation, using a Pd metal sheet as the working electrode, graphite as the auxiliary electrode, and a beryllium electrode as the reference electrode.

[0095] The Pd electrode has dimensions of 7mm × 20mm × 1mm, and the graphite electrode has dimensions of 10mm × 30mm × 3mm. The beryllium reference electrode structure is as follows. Figure 1 As shown, the beryllium rod has a diameter of 2 mm, the hot-pressed boron nitride tube has a wall thickness of 2 mm, the thinnest part at the bottom of the tube has a thickness of 1 mm, and the total volume of the liquid LiF-BeF2 molten salt accounts for 0.4% of the volume of the boron nitride tube.

[0096] The pulse electrolysis conditions were: negative pulse potential -0.5V, positive pulse potential 0.5V, pulse frequency 500Hz, and duty cycle 0.25:1. After 2 hours of electrolytic deposition, the Nd concentration in the molten salt decreased by 27.9%.

[0097] Example 10

[0098] Electrolytic extraction separation of Pr in the LiF-BeF2-ZrF4-PrF3 molten salt system.

[0099] 52g LiF, 47g BeF2, 2g ZrF4, and 1g PrF3 were weighed out, mixed thoroughly, and placed in a glassy carbon crucible with an inner diameter of 40mm and a height of 60mm. The mixture was then melted at 650℃ under an argon atmosphere. Pulse electrolysis was performed using an Os metal sheet as the working electrode, graphite as the auxiliary electrode, and a beryllium electrode as the reference electrode, under the control of an electrochemical workstation.

[0100] The Os electrode specifications are 7mm × 20mm × 1mm, and the graphite electrode specifications are 10mm × 30mm × 3mm. The beryllium reference electrode structure is as follows. Figure 1 As shown, the beryllium rod has a diameter of 2 mm, the hot-pressed boron nitride tube has a wall thickness of 2 mm, the thinnest part at the bottom of the tube has a thickness of 1 mm, and the total volume of the liquid LiF-BeF2 molten salt accounts for 0.4% of the volume of the boron nitride tube.

[0101] The pulse electrolysis conditions were: negative pulse potential -0.5V, positive pulse potential 0.5V, pulse frequency 500Hz, and duty cycle 0.25:1. After 2 hours of electrolytic deposition, the Pr concentration in the molten salt decreased by 30.2%.

[0102] Example 11

[0103] Electrolytic extraction separation of Sm in the LiF-BeF2-SmF3 molten salt system.

[0104] 52g of LiF, 47g of BeF2, and 1g of SmF3 were weighed out, mixed thoroughly, and placed in a glassy carbon crucible with an inner diameter of 40mm and a height of 60mm. The crucible was then melted at 500℃ under an argon atmosphere. A pulsed electrolysis was performed using an Au metal sheet as the working electrode, glassy carbon as the auxiliary electrode, and a beryllium electrode as the reference electrode, under the control of an electrochemical workstation.

[0105] The Au electrode dimensions are 7mm × 20mm × 1mm, and the glassy carbon electrode dimensions are 10mm × 30mm × 3mm. The beryllium reference electrode structure is as follows: Figure 1 As shown, the beryllium rod has a diameter of 2 mm, the hot-pressed boron nitride tube has a wall thickness of 1 mm, the thinnest part at the bottom of the tube has a thickness of 0.1 mm, and the total volume of the liquid LiF-BeF2 molten salt accounts for 0.4% of the volume of the boron nitride tube.

[0106] The pulse electrolysis conditions were: negative pulse potential -0.4V, positive pulse potential 0.3V, pulse frequency 400Hz, and duty cycle 0.25:1. After 2 hours of electrolytic deposition, the Sm concentration in the molten salt decreased by 27.4%.

[0107] Example 12

[0108] Electrolytic extraction separation of Sm in the LiF-BeF2-SmF3 molten salt system.

[0109] 26g LiF, 47g BeF2, and 1g SmF3 were weighed out, mixed thoroughly, and placed in a glassy carbon crucible with an inner diameter of 40mm and a height of 60mm. The mixture was then melted at 600℃ under an argon atmosphere. Pulse electrolysis was performed under the control of an electrochemical workstation, using a graphite sheet as the working electrode, nickel as the auxiliary electrode, and a beryllium electrode as the reference electrode.

[0110] The graphite working electrode measures 10mm × 30mm × 3mm, and the nickel electrode measures 10mm × 40mm × 2mm. The beryllium reference electrode structure is as follows. Figure 1 As shown, the beryllium rod has a diameter of 2 mm, the alumina sleeve has a wall thickness of 2 mm, the thinnest part at the bottom of the tube has a thickness of 0.5 mm, and the total volume of the liquid LiF-BeF2 molten salt accounts for 0.4% of the volume of the boron nitride tube.

[0111] The pulse electrolysis conditions were: negative pulse potential -0.4V, positive pulse potential 0.2V, pulse frequency 0.1Hz, and duty cycle 0.25:1. After 2 hours of electrolytic deposition, the Sm concentration in the molten salt decreased by 22.3%. XRD analysis showed that the Sm deposit on glassy carbon was mainly SmC6.

[0112] Example 13

[0113] Electrolytic extraction separation of Nd in the LiF-BeF2-ThF4-NdF3 molten salt system.

[0114] 52g LiF, 47g BeF2, 2g ThF4, and 1g NdF3 were weighed out, mixed thoroughly, and placed in a glassy carbon crucible with an inner diameter of 40mm and a height of 60mm. The mixture was then melted at 550℃ under an argon atmosphere. A constant potential electrolysis was performed using an Al metal sheet as the working electrode, graphite as the auxiliary electrode, and a beryllium electrode as the reference electrode, under the control of an electrochemical workstation.

[0115] The Al electrode specifications are 7mm × 20mm × 1mm, and the graphite electrode specifications are 10mm × 30mm × 3mm. The beryllium reference electrode structure is as follows. Figure 1 As shown, the beryllium rod has a diameter of 2 mm, the hot-pressed boron nitride tube has a wall thickness of 2 mm, the thinnest part at the bottom of the tube has a thickness of 1 mm, and the total volume of the liquid LiF-BeF2 molten salt accounts for 0.4% of the volume of the boron nitride tube.

[0116] The constant electrolysis conditions were: a constant electrolysis potential of 0.15V. After 2 hours of electrolytic deposition, the Nd concentration in the molten salt decreased by 28.3%.

[0117] Comparative Example 1

[0118] Electrolytic extraction separation of Eu in the LiF-BeF2-EuF3 molten salt system.

[0119] 26g LiF, 47g BeF2, and 1g EuF3 were weighed out, mixed thoroughly, and placed in a glassy carbon crucible with an inner diameter of 40mm and a height of 60mm. The mixture was then melted at 600℃ under an argon atmosphere. Using a Ni metal sheet as the working electrode, glassy carbon as the auxiliary electrode, and a beryllium electrode as the reference electrode, pulse electrolysis was performed at a constant potential under the control of an electrochemical workstation.

[0120] The Ni electrode has dimensions of 7mm × 20mm × 1mm, and the glassy carbon electrode has dimensions of 10mm × 30mm × 3mm. The beryllium reference electrode structure is as follows. Figure 1 As shown, the beryllium rod has a diameter of 2 mm, the alumina sleeve has a wall thickness of 2 mm, the thinnest part at the bottom of the tube has a thickness of 0.5 mm, and the total volume of the liquid LiF-BeF2 molten salt accounts for 0.4% of the volume of the boron nitride tube.

[0121] The conditions for pulse electrolysis are: negative pulse potential -0.6V, positive pulse potential 0.05V, pulse frequency 100Hz, and duty cycle 0.25:1.

[0122] After 2 hours of electrolytic deposition, the Eu concentration in the molten salt did not decrease significantly, and XRD analysis showed that the deposits on Ni were mainly NiBe. The main reason for the failure of Eu electrolytic extraction separation was that it was not operated at a reasonable pulse potential.

[0123] Comparative Example 2

[0124] Electrolytic extraction separation of Nd in the LiF-BeF2-UF4-ThF4-NdF3 molten salt system.

[0125] Weigh out 104g LiF, 47g BeF2, 2g UF4, 2g ThF4 and 1g NdF3 respectively, mix them evenly and place them in a glassy carbon crucible with an inner diameter of 40mm and a height of 60mm. Melt the crucible at 600℃ under a helium atmosphere for later use.

[0126] Using an Au metal sheet as the working electrode, a nickel metal sheet as the auxiliary electrode, and a beryllium electrode as the reference electrode, pulse electrolysis was performed under the control of an electrochemical workstation.

[0127] The Au electrode dimensions are 7mm × 20mm × 1mm, and the nickel auxiliary electrode dimensions are 10mm × 30mm × 3mm. The beryllium reference electrode structure is as follows: Figure 1 As shown, the beryllium rod has a diameter of 3 mm, the hot-pressed boron nitride tube has a wall thickness of 3 mm, the thinnest part at the bottom of the tube has a thickness of 1 mm, and the total volume of the liquid LiF-BeF2 molten salt accounts for 0.4% of the volume of the boron nitride tube.

[0128] The conditions for pulse electrolysis are: negative pulse potential -0.7V, positive pulse potential 0.08V, pulse frequency 500Hz, and duty cycle 0.25:1.

[0129] After 2 hours of electrolytic deposition, the Nd concentration in the molten salt did not decrease significantly, and there was a dissolution loss of metallic Au. The main reason for the failure of Nd electrolytic extraction separation was that it was not operated under a reasonable pulse potential, and the formation of low-melting-point beryllium-rich Au-Be intermetallic compounds on the Au electrode led to Au dissolution loss.

Claims

1. A method for separating rare earth fission products in a fluorine-lithium-beryllium molten salt system, characterized in that, It includes the following steps: Ni, Cu, Al, Au, Ru, Rh, Pd, Os, Ir, Pt or graphite are used as working electrodes; Graphite, glassy carbon, Pt, or Ni are used as auxiliary electrodes; A beryllium electrode is used as the reference electrode, and the beryllium electrode comprises a beryllium metal rod and LiF-BeF2 molten salt; Constant potential electrolysis or pulse electrolysis was performed on fluorine-lithium-beryllium molten salt containing rare earth fission products. The electrolysis conditions for the constant potential electrolysis are: a constant potential of 0.15~0.6V, where the constant potential is the potential value of the working electrode relative to the reference electrode; The conditions for pulse electrolysis are: negative pulse potential of -0.1 to -0.5V and positive pulse potential of 0.15 to 0.6V; the positive pulse potential and the negative pulse potential are the potential values ​​of the working electrode relative to the reference electrode.

2. The method for separating rare earth fission products in a fluorine-lithium-beryllium molten salt system as described in claim 1, characterized in that, The negative pulse potential is -0.2V to -0.4V; And / or, the constant potential is 0.3V~0.5V; And / or, the pulse frequency of the pulse electrolysis is 0.1~1000Hz; And / or, the duty cycle of the pulse electrolysis is (0~0.5):1; And / or, the pulse electrolysis time is 1-3 hours.

3. The method for separating rare earth fission products in a fluorine-lithium-beryllium molten salt system as described in claim 2, characterized in that, The negative pulse potential is -0.2V or -0.4V; And / or, the pulse frequency of the pulse electrolysis is 10~500Hz; And / or, the duty cycle of the pulse electrolysis is (0.05~0.25):1; And / or, the pulse electrolysis time is 2 hours.

4. The method for separating rare earth fission products in a fluorine-lithium-beryllium molten salt system as described in claim 3, characterized in that, The pulse frequency of the pulse electrolysis is 50Hz, 400Hz, or 500Hz.

5. The method for separating rare earth fission products in a fluorine-lithium-beryllium molten salt system as described in claim 1, characterized in that, The positive pulse potential is 0.2~0.5V.

6. The method for separating rare earth fission products in a fluorine-lithium-beryllium molten salt system as described in claim 5, characterized in that, The positive pulse potential is 0.2V, 0.35V, 0.40V, or 0.48V.

7. The method for separating rare earth fission products in a fluorine-lithium-beryllium molten salt system as described in claim 1, characterized in that, In the beryllium electrode, the molar ratio of LiF to BeF2 in the LiF-BeF2 molten salt is 1:1 to 4:

1. And / or, the diameter of the beryllium metal rod is 2~3mm; And / or, the beryllium electrode includes a sleeve.

8. The method for separating rare earth fission products in a fluorine-lithium-beryllium molten salt system as described in claim 7, characterized in that, In the beryllium electrode, the molar ratio of LiF to BeF2 in the LiF-BeF2 molten salt is 2:

1.

9. The method for separating rare earth fission products in a fluorine-lithium-beryllium molten salt system as described in claim 7, characterized in that, The total volume of the fluorine-lithium-beryllium molten salt accounts for 0.3 to 0.5 of the volume of the sleeve; And / or, the wall thickness of the sleeve is 1~5 mm; And / or, the sleeve is made of an inert material resistant to molten salt corrosion; And / or, the thickness of the thinnest part of the bottom of the sleeve is 0.1~1.0 mm.

10. The method for separating rare earth fission products in a fluorine-lithium-beryllium molten salt system as described in claim 9, characterized in that, The sleeve is made of ceramic material.

11. The method for separating rare earth fission products in a fluorine-lithium-beryllium molten salt system as described in claim 10, characterized in that, The sleeve is made of hot-pressed boron nitride, aluminum oxide, magnesium oxide, or zirconium oxide.

12. The method for separating rare earth fission products in a fluorine-lithium-beryllium molten salt system as described in claim 1, characterized in that, The fluorine-lithium-beryllium molten salt comprises LiF and BeF2; And / or, the temperature of the fluorine-lithium-beryllium molten salt is 500-800°C; And / or, the fluorine-lithium beryllium molten salt comprises one or more of UF4, ThF4, PmF3 and ZrF4.

13. The method for separating rare earth fission products in a fluorine-lithium-beryllium molten salt system as described in claim 1, characterized in that, The rare earth elements in the rare earth fission products are Pr, Nd, Gd, Ce, La, Sm or Eu; And / or, the rare earth fission products include rare earth element fluorides.

14. The method for separating rare earth fission products in the fluorine-lithium-beryllium molten salt system according to claim 13, characterized in that, The rare earth fission products are one or more of LaF3, CeF3, PrF3, NdF3, SmF3, EuF3 and GdF3.

15. The method for separating rare earth fission products in a fluorine-lithium-beryllium molten salt system as described in claim 1, characterized in that, The purity of the material of the working electrode, the auxiliary electrode, or the reference electrode is not less than 95%. And / or, the atmosphere in which the fluorine-lithium-beryllium molten salt, the working electrode, the auxiliary electrode, or the reference electrode is inert gas atmosphere.

16. The method for separating rare earth fission products in a fluorine-lithium-beryllium molten salt system as described in claim 15, characterized in that, The inert gas is of the element Ar or He.

17. The method for separating rare earth fission products in a fluorine-lithium-beryllium molten salt system as described in claim 1, characterized in that, It includes the following steps: S1. The raw material of the lithium fluoride beryllium molten salt is heated and melted to obtain the lithium fluoride beryllium molten salt. S2. Insert the working electrode, the auxiliary electrode, and the reference electrode into the fluorine-lithium-beryllium molten salt and connect them to an electrochemical workstation or a pulse power supply respectively. The reference electrode serves as the reference electrode for the working electrode and the auxiliary electrode. The working electrode and the auxiliary electrode form a conductive circuit for pulse electrolysis. S3. Under the negative pulse potential, rare earth elements and Be are deposited on the working electrode, and rare earth intermetallic compounds and Be intermetallic compounds are formed simultaneously. Under the positive pulse potential, metallic Be and Be-rich intermetallic compounds are oxidized and re-immersed in molten salt, while rare-earth-poor intermetallic compounds remain on the working electrode and precipitate out.

18. The method for separating rare earth fission products in a fluorine-lithium-beryllium molten salt system as described in claim 1, characterized in that, It includes the following steps: S1. The raw material of the lithium fluoride beryllium molten salt is heated and melted to obtain the lithium fluoride beryllium molten salt. S2. Using Ni, Cu, Al, Au, Ru, Rh, Pd, Os, Ir, Pt, or graphite as the working electrode, and graphite, glassy carbon, Pt, or Ni as the auxiliary electrode, and the beryllium electrode as the reference electrode, the working electrode, the auxiliary electrode, and the reference electrode are inserted into the lithium fluoride beryllium molten salt and connected to an electrochemical workstation or electrolysis power supply respectively. The reference electrode serves as the reference electrode for the working electrode and the auxiliary electrode. The working electrode and the auxiliary electrode form a conductive circuit for electrolysis. S3. Under the constant potential, rare earth elements and Be are deposited on the working electrode and rare earth-depleted and Be-depleted intermetallic compounds are precipitated.

19. The method for separating rare earth fission products in a fluorine-lithium-beryllium molten salt system as described in claim 1, characterized in that, The electrolysis power source used for the constant potential electrolysis or pulse electrolysis is the KOST electrochemical workstation.

20. The method for separating rare earth fission products in a fluorine-lithium-beryllium molten salt system as described in claim 19, characterized in that, The electrolysis power supply used for the constant potential electrolysis or pulse electrolysis is a CS350M Kosite electrochemical workstation.

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