A method for separating actinides

Abstract

The application discloses an actinide separation method, which comprises the following steps: a mixture of a molten salt phase, a metal phase and a reducing agent is reacted; the molten salt phase comprises an actinide metal, a fission product and a molten salt; the actinide metal exists in an ionic form; the metal phase comprises a first metal; the first metal exists in a simple substance form; the reducing agent comprises the first metal and a second metal, and the second metal is lithium; the first metal and the second metal exist in an alloy form; the volume ratio of the molten salt phase to the metal phase is 1:(1-8); and the reaction temperature is not higher than 800 DEG C. The application separates the actinide from the fission product in the molten salt by using the metallic lithium in the alloy form as the reducing agent to perform a reduction extraction reaction. The separation method can realize efficient separation of the actinide from the fission product in the molten salt, improve the separation coefficient, the decontamination coefficient and the recovery rate of the actinide, and meet the strict requirements of the nuclear industry on the separation and purification of the actinide.

Description

Technical Field

[0001] This invention relates to a method for separating actinide elements. Background Technology

[0002] Actinide elements (such as uranium, thorium, and plutonium) are key materials in the nuclear industry, playing a vital role in nuclear power generation and nuclear fuel preparation. However, during nuclear reactions, actinide elements mix with a large number of fission products (such as cesium, strontium, cerium, samarium, neodymium, lanthanum, and europium) and exist in the molten salt of nuclear reactors. These fission products are often highly radioactive and toxic. If they are not effectively separated and purified, they will not only affect the reuse of actinide elements but also pose a serious threat to the environment and human health.

[0003] Currently, existing technologies for separating and purifying actinides mainly include solvent extraction and precipitation. However, these technologies generally have some drawbacks: in solvent extraction, the organic solvent is easily damaged by radiation when processing highly radioactive materials, leading to a decrease in separation efficiency and the generation of large amounts of radioactive organic waste liquid; precipitation methods have poor separation selectivity, the separation effect between actinides and fission products is not ideal, and the decontamination coefficient is usually difficult to reach 10. 3 In addition, the recovery rate of actinides is also low, which cannot meet the requirements of the nuclear industry for high-purity recovery of actinides.

[0004] Therefore, developing an efficient and highly selective method for separating actinides to achieve deep separation of actinides from fission products and improve the recovery rate and decontamination coefficient of actinides is of great significance for promoting the sustainable development of the nuclear industry and the safe disposal of radioactive waste. Summary of the Invention

[0005] This invention addresses the problems of low separation efficiency, poor decontamination effect, and low actinide recovery rate in existing actinide separation methods. It provides a method for separating actinides using alloyed lithium metal as a reducing agent in a reduction extraction reaction to separate actinides from fission products in molten salt. This method achieves highly efficient separation of actinides from fission products in molten salt, improving the separation coefficient, decontamination coefficient, and recovery rate of actinides, thus meeting the stringent requirements of the nuclear industry for the separation and purification of actinides.

[0006] The present invention solves the above-mentioned technical problems through the following technical solutions:

[0007] This invention provides a method for separating actinide elements, comprising the following steps: reacting a mixture containing a molten salt phase, a metallic phase, and a reducing agent; wherein,

[0008] The molten salt phase comprises actinides, fission products, and molten salt; the actinides exist in ionic form.

[0009] The metallic phase includes a first metal; the first metal exists in elemental form.

[0010] The reducing agent comprises a first metal and a second metal, wherein the second metal is lithium; the first metal and the second metal exist in an alloy form.

[0011] The volume ratio of the molten salt phase to the metal phase is 1:(1-8);

[0012] The reaction temperature is not higher than 800℃.

[0013] In this invention, based on the metal reduction extraction reaction, the actinide metals to be separated in the molten salt phase can be transferred to the metal phase, while the remaining fission products (such as alkali metals, alkaline earth metals, lanthanides, etc.) remain in the molten salt, thereby achieving effective separation of actinide metals in the molten salt phase. The molten salt phase can be regarded as the molten salt of a conventional nuclear reactor containing actinide metals and their fission products. The separated products obtained contain only a single metal phase and actinide metals, which is more conducive to the recycling of actinide metals to a certain extent compared with molten salt.

[0014] In this invention, the meaning of "existing in elemental form" can refer to the first metal existing in a form that is entirely elemental and contains no alloys.

[0015] In this invention, "existing in alloy form" means that the first metal and the second metal exist in an alloy form without any elemental components.

[0016] In this invention, the meaning of "both the metal phase and the reducing agent include a first metal" can refer to the fact that the first metal in the metal phase and the reduced phase are of the same type.

[0017] In this invention, the actinide metal can be conventional in the art, preferably including one or more of uranium, thorium and plutonium, such as uranium.

[0018] In this invention, the fission products may refer to the fission products present in the molten salt of conventional nuclear reactors in the art, and may generally include one or more of alkali metals, alkaline earth metals, noble metals, semi-noble metals and lanthanides; specifically, they may include one or more of cesium, strontium, cerium, samarium, praseodymium, dysprosium, erbium, thulium, neodymium, lanthanum and europium.

[0019] In this invention, the molten salt may include fluoride molten salt and / or chloride molten salt, preferably fluoride molten salt.

[0020] In this invention, the molten salt may be a molten salt containing lithium, sodium, and potassium; preferably, it is a molten salt containing fluorine, lithium, sodium, and potassium.

[0021] The fluorine-lithium sodium-potassium molten salt includes, for example, LiF, NaF and KF; the molar ratio of LiF, NaF and KF is preferably (45-50):(10-15):(40-45), more preferably 46.5:11.5:42.

[0022] In this invention, the first metal may include one or more of aluminum, copper, gallium, zinc, tin, bismuth and cadmium, preferably bismuth.

[0023] Preferably, the purity of the metallic bismuth is ≥99%.

[0024] In this invention, the reducing agent may include one or more of aluminum-lithium alloy, copper-lithium alloy, gallium-lithium alloy, zinc-lithium alloy, tin-lithium alloy, bismuth-lithium alloy, and cadmium-lithium alloy, for example, bismuth-lithium alloy.

[0025] The molar ratio of the first metal to the second metal can be (60-95):(5-40), preferably 70:30.

[0026] The reducing agent is a bismuth-lithium alloy, and the molar ratio of bismuth to lithium in the bismuth-lithium alloy is preferably 70:30.

[0027] In this invention, the mass ratio of the molten salt phase to the metal phase can be 1:(5-25), for example 1:5, 1:5.08, 1:5.11, 1:5.13, 1:5.17, 1:5.18, 1:5.24, 1:5.25, 1:5.32, 1:5.41, 1:10, 1:15, 1:20 or 1:25.

[0028] In this invention, the volume ratio of the molten salt phase to the metal phase is preferably 1:(1-5), for example 1:1, 1:2, 1:3, 1:4 or 1:5.

[0029] In this invention, the molar ratio of the reducing agent to the molten salt phase can be 1:(1-10), preferably 1:(1-7), based on the total molar amount of actinides and fission products in the molten salt phase, for example 1:2.72, 1:2.96, 1:3.02, 1:3.05, 1:3.07, 1:3.18, 1:3.64, 1:3.82, 1:3.85, 1:4.02 or 1:6.32.

[0030] In this invention, the reaction temperature can be 500℃-800℃, preferably 550℃-800℃, for example 550℃, 600℃, 700℃ or 800℃.

[0031] In this invention, the reaction time can be 1-10 hours, preferably 3-10 hours, for example 3 hours, 4 hours, 5 hours, 6 hours, 8 hours or 10 hours.

[0032] In the present invention, the reaction can be carried out under stirring conditions; the stirring speed is preferably 200-500 rpm, such as 200 rpm, 300 rpm, 400 rpm or 500 rpm.

[0033] In the present invention, the reaction can be carried out in a stirring device.

[0034] Wherein, the shape of the stirring paddle in the stirring device is preferably a helical ribbon type and / or a "field" shape, for example, a "field" shape.

[0035] Wherein, the material of the stirring paddle in the stirring device is preferably metal, more preferably molybdenum.

[0036] In the present invention, the preparation of the mixture may comprise the following steps:

[0037] S1, mixing the molten salt phase and the metal phase first, melting to obtain a premix;

[0038] S2, adding the reducing agent into the premix to prepare the mixture.

[0039] Wherein, the preparation of the molten salt phase preferably comprises: mixing an actinide metal source, a fission product source and a molten salt, and melting to obtain the molten salt phase.

[0040] Wherein, the adding mode of the reducing agent is preferably one-time addition or batch addition.

[0041] Wherein, the batch addition is preferably divided into 6 batches.

[0042] Wherein, the batch addition is preferably equal batch addition.

[0043] Wherein, the melting can be a conventional operation in the art, and the melting temperature can be 500-600°C, for example, 550°C.

[0044] On the basis of conforming to common general knowledge in the art, the above preferred conditions can be arbitrarily combined to obtain preferred embodiments of the present invention.

[0045] All the reagents and raw materials used in the present invention are commercially available.

[0046] The positive progressive effect of the present invention is:

[0047] The separation method of the present invention can simultaneously ensure:

[0048] (1) Good separation effect: the present technology enables the separation coefficient of actinides and fission products to reach 10 2 or more, the decontamination factor of alkali metals reaches 10 4 or more, the decontamination factor of alkaline earth metals reaches 10 3 or more, and the decontamination factor of lanthanide metals reaches 102 The above methods can effectively remove fission products from actinides and improve the purity of actinides.

[0049] (2) High recovery rate of actinides: The recovery rate of actinides can reach more than 88%, which reduces the loss of actinides and improves the utilization rate of resources.

[0050] (3) Wide range of applications: This technology can be widely used in the recovery and purification of actinides in the nuclear fuel cycle, as well as the treatment and disposal of radioactive waste, which is of great significance for promoting the sustainable development of the nuclear industry. Attached Figure Description

[0051] Figure 1 This is a schematic diagram of the apparatus used to separate actinide elements according to the present invention.

[0052] Explanation of reference numerals in the attached drawings: 1-Electric furnace; 2-Corundum crucible; 3-Graphite crucible; 4-Molybdenum stirring paddle; 5-Quartz sampling tube; 6-Resistance wire; 7-Stirrer. Detailed Implementation

[0053] 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.

[0054] The overall steps of the separation method involved in the following embodiments and comparative examples are as follows:

[0055] The prepared molten salt phase and metal phase are added in different proportions as follows: Figure 1 In the stirring device, the molten salt phase and the metal phase are melted at a certain temperature. After the molten salt phase and the metal phase have all become liquid, a certain proportion of reducing agent is added. Different methods of adding reducing agent, reaction temperature, stirring speed, and stirring time (i.e., reaction time) are set to carry out the reduction extraction reaction.

[0056] The reducing agent, bismuth-lithium alloy, was prepared according to the method reported in existing literature (M. Kurata, et al., J. Nucl. Mater., 1995, 227: 110-121), with a molar ratio of bismuth to lithium of 70:30.

[0057] The method for preparing the molten salt phase is as follows:

[0058] (1) First, prepare fluoride molten salt: Weigh a certain amount of anhydrous lithium fluoride, anhydrous sodium fluoride and anhydrous potassium fluoride (molar ratio of 46.5:11.5:42) into a corundum crucible, place it in a heating furnace, keep it at 250℃ for 3 hours, then raise the temperature to 600℃ and keep it at 6 hours, cool and store for later use.

[0059] (2) Then, prepare the fluoride eutectic salt (i.e., molten salt phase) of actinides and lanthanides: 0.15% of uranium tetrafluoride and lanthanide fluorides (0.0075% cesium fluoride, 0.0065% strontium fluoride, 0.0060% lanthanum fluoride, 0.0080% samarium fluoride, and 0.0080% neodymium fluoride) are melted into the fluoride molten salt at 650°C, cooled, and set aside to obtain the molten salt phase. % refers to the mass percentage of the molten salt phase.

[0060] The overall structure of the stirring device used is as follows:

[0061] A graphite crucible 3 is placed inside a corundum crucible 2, which is then placed inside an electric furnace 1, which is filled with resistance wire 6. A stirrer 7 is placed above the electric furnace 1, and a molybdenum stirring paddle 4 is connected to the stirrer 7. Quartz sampling tubes are placed on both sides of the stirrer 7, with their lower ends placed inside the graphite crucible 3.

[0062] The reagent and equipment information involved in the following examples and comparative examples is as follows:

[0063] Reagents: Anhydrous lithium fluoride, anhydrous potassium fluoride, anhydrous sodium fluoride, uranium tetrafluoride, lanthanum fluoride, cesium fluoride, strontium fluoride, samarium fluoride, neodymium fluoride, bismuth powder, and metallic lithium were purchased from Shanghai Sinopharm Chemical Reagent Co., Ltd., with a purity of AR.

[0064] Equipment: Corundum crucible (24*60 mm, Shanghai Guoyao Group Chemical Reagent Co., Ltd.; 50*150 mm, Tangshan Shengxing Chemical Porcelain Factory), stirring paddle (Shanghai Yuye Electric Furnace Co., Ltd., molybdenum material, 6*250 mm).

[0065] Examples 1-14 and Comparative Examples 1-2

[0066] The prepared molten salt phase and metal phase are added in different proportions as follows: Figure 1 In a stirring apparatus, the molten salt phase and the metal phase are melted at a certain temperature. Once both phases are completely liquid, a certain proportion of reducing agent is added. Different methods of adding the reducing agent, reaction temperatures, stirring speeds, and stirring times (i.e., reaction times) are set to carry out the reduction extraction reaction. Actinide metals and fission products are separated from the molten salt phase containing the metals and fission products, following the steps described in Table 1.

[0067] The molar ratio of reducing agent to molten salt phase refers to the ratio of the total molar amount of reducing agent to actinide elements and fission products in the molten salt phase.

[0068] Table 1. Main parameters involved in Examples 1-14 and Comparative Examples 1-2

[0069]

[0070] Effect Example

[0071] The separation effects of the separation methods in Examples 1-14 and Comparative Examples 1-2 were checked respectively. The specific test methods and calculation methods for the effect parameters involved are as follows:

[0072] After the reaction, samples of the molten salt phase and the metallic phase were taken separately, then melted to prepare analytical samples. ICP-OES and ICP-MS were used to analyze the actinide elements and fission products in the samples. Calculations were performed based on the analytical results, as shown in Table 2. The specific calculation method is as follows:

[0073] 1. Separation coefficient

[0074] The equations for the reduction reactions of actinide metals are shown below:

[0075]

[0076] The formula for calculating the equilibrium constant (K) of the reaction is shown below:

[0077]

[0078] Where, N MF3 N represents the molar percentage of fluorides, which are actinides or fission products, in molten salt. M N represents the molar percentage of reduced actinides or fission products in metallic bismuth. Li N represents the molar percentage of lithium in metallic bismuth. LiF This indicates the molar percentage of lithium fluoride in the molten salt.

[0079] Distribution coefficient (D) M The molar percentage (N) of metal ions in bismuth metal after the reduction-extraction reaction reaches equilibrium represents the percentage of metal ions in the bismuth metal. M ) and in the molten salt phase (N MF The ratio of mole percentages in () is calculated using the following formula:

[0080]

[0081] Equilibrium constant (K) * M The equilibrium constant for the reduction-extraction reaction is represented by , and its logarithm can be expressed using the partition coefficient of metal ions (D). M The partition coefficient of the reducing agent (D) Li The logarithmic representation of the ratio of powers of n is expressed by the following formula:

[0082]

[0083]

[0084] Separation coefficient β among lanthanides M1 / M2 The ratio of the partition coefficients among the lanthanides after the reduction-extraction reaction reaches equilibrium is expressed by the following formula:

[0085]

[0086] 2. Decontamination coefficient

[0087] The decontamination factor is the ratio of the molar percentage of fission products to the molar percentage of uranium in the molten salt, divided by the ratio of the molar percentage of fission products to the molar percentage of uranium in the metallic bismuth phase. The calculation formula is as follows:

[0088]

[0089] 3. Recovery rate

[0090] Material balance (MB) M The ratio () represents the sum of the masses of the metal in the molten salt and bismuth phases after the reduction-extraction reaction reaches equilibrium, to the mass of the metal ions in the molten salt at the start of the reaction. It is usually expressed as a percentage and is calculated using the following formula:

[0091]

[0092] Recovery rate (E) M The ratio () represents the mass of metal transferred to the bismuth phase after the reduction-extraction reaction reaches equilibrium, to the mass of metal ions in the molten salt at the start of the reaction. It is usually expressed as a percentage and is calculated using the following formula:

[0093]

[0094] Table 2 Separation coefficient, decontamination coefficient, and actinide recovery rate of Examples 1-14 and Comparative Examples 1-2

[0095]

[0096] The separation coefficient, decontamination coefficient, and actinide element recovery rates of Examples 1-14 and Comparative Examples 1-2 are shown in Table 1. The separation coefficient of Examples 1-14 reached 10. 2 The above shows that the detergency coefficient of alkali metals reaches 10. 4 The above shows that the decontamination coefficient of alkaline earth metals reaches 10. 3 The above shows that the decontamination coefficient of lanthanide metals reaches 10. 2 The above demonstrates excellent separation and decontamination effects. The recovery rate of actinides in Examples 1-14 can reach over 88%, which is superior to that in Comparative Examples 1-2.

[0097] While specific embodiments of the present invention have been described above, those skilled in the art should understand that these are merely illustrative examples, and the scope of protection of the present invention is defined by the appended claims. Those skilled in the art can make various changes or modifications to these embodiments without departing from the principles and essence of the present invention, but all such changes and modifications fall within the scope of protection of the present invention.

Claims

1. A method for separating actinide elements, characterized in that, It includes the following steps: A reaction involving a mixture of molten salt phase, metallic phase, and reducing agent; wherein, The molten salt phase comprises actinides, fission products, and molten salt; the actinides exist in ionic form. The metallic phase includes a first metal; the first metal exists in elemental form; the first metal is bismuth; The reducing agent comprises a first metal and a second metal, wherein the second metal is lithium; the first metal and the second metal exist in an alloy form; the volume ratio of the molten salt phase to the metal phase is 1:(1-8); The reaction temperature is no higher than 800℃.

2. The method for separating actinide elements as described in claim 1, characterized in that, The volume ratio of the molten salt phase to the metal phase is 1:(1-5); And / or, the mass ratio of the molten salt phase to the metal phase is 1:(5-25); And / or, based on the total molar amount of actinides and fission products in the molten salt phase, the molar ratio of the reducing agent to the molten salt phase is 1:(1-10); And / or, the temperature of the reaction is 500℃-800℃.

3. The method for separating actinide elements as described in claim 2, characterized in that, The volume ratio of the molten salt phase to the metal phase is 1:1, 1:2, 1:3, 1:4 or 1:5; And / or, the mass ratio of the molten salt phase to the metal phase is 1:5, 1:5.08, 1:5.11, 1:5.13, 1:5.17, 1:5.18, 1:5.24, 1:5.25, 1:5.32, 1:5.41, 1:10, 1:15, 1:20 or 1:25; And / or, the molar ratio of the reducing agent to the molten salt phase is 1:(1-7); And / or, the temperature of the reaction is 550℃-800℃.

4. The method for separating actinide elements as described in claim 3, characterized in that, The molar ratio of the reducing agent to the molten salt phase is 1:2.72, 1:2.96, 1:3.02, 1:3.05, 1:3.07, 1:3.18, 1:3.64, 1:3.82, 1:3.85, 1:4.02, or 1:6.32; And / or, the temperature of the reaction is 550°C, 600°C, 700°C or 800°C.

5. The method for separating actinide elements as described in claim 1, characterized in that, The purity of the bismuth is ≥99%.

6. The method for separating actinide elements as described in claim 1, characterized in that, The reducing agent is a bismuth-lithium alloy; And / or, in the reducing agent, the molar ratio of the first metal and the second metal is (60-95):(5-40).

7. The method for separating actinide elements as described in claim 6, characterized in that, In the reducing agent, the molar ratio of the first metal to the second metal is 70:

30.

8. The method for separating actinide elements as described in claim 1, characterized in that, The actinide metals include one or more of uranium, thorium, and plutonium; And / or, the fission products include one or more of alkali metals, alkaline earth metals, noble metals, semi-noble metals, and lanthanides.

9. The method for separating actinide elements as described in claim 8, characterized in that, The actinide metal is uranium; And / or, the fission products include one or more of cesium, strontium, cerium, samarium, praseodymium, dysprosium, erbium, thulium, neodymium, lanthanum, and europium.

10. The method for separating actinide elements as described in claim 1, characterized in that, The molten salt includes fluoride molten salt and / or chloride molten salt; And / or, the molten salt is a molten salt containing lithium, sodium, and potassium.

11. The method for separating actinide elements as described in claim 10, characterized in that, The molten salt is a fluoride molten salt; And / or, the molten salt is a sodium-potassium fluoride molten salt.

12. The method for separating actinide elements as described in claim 11, characterized in that, The fluorine-lithium sodium-potassium molten salt includes LiF, NaF, and KF.

13. The method for separating actinide elements as described in claim 12, characterized in that, The molar ratio of LiF, NaF, and KF is (45-50):(10-15):(40-45).

14. The method for separating actinide elements as described in claim 13, characterized in that, The molar ratio of LiF, NaF, and KF is 46.5:11.5:

42.

15. The method for separating actinide elements as described in claim 1, characterized in that, The reaction time is 1-10 hours; and / or, the reaction is carried out under stirring conditions.

16. The method for separating actinide elements as described in claim 15, characterized in that, the reaction time is 3-10 h; and / or, the stirring speed is 200-500 rpm.

17. The method for separating actinide elements as described in claim 16, characterized in that, the reaction time is 3h, 4h, 5h, 6h, 8h or 10h; and / or, the stirring speed is 200 rpm, 300 rpm, 400 rpm or 500 rpm.

18. The method for separating actinide elements as described in claim 1, characterized in that, the reaction is carried out in a stirring device.

19. The method for separating actinide elements as described in claim 18, characterized in that, the shape of the stirring blade in the stirring device is a helical ribbon type and / or a "field" type; and / or, the material of the stirring blade in the stirring device is metal.

20. The method for separating actinide elements as described in claim 19, characterized in that, the shape of the stirring blade in the stirring device is "field" type; and / or, the material of the stirring blade in the stirring device is molybdenum.

21. The method for separating actinide elements as described in claim 1, characterized in that, the preparation of the mixture comprises the following steps: S1, mixing the molten salt phase and the metal phase first, and melting to obtain a premix; S2, adding the reducing agent into the premix to obtain the product.

22. The method for separating actinide elements as described in claim 21, characterized in that, in step S1, the preparation of the molten salt phase comprises: mixing an actinide metal source, a fission product source and a molten salt, and melting to obtain the molten salt phase; and / or, in step S1, the melting temperature is 500-600°C; and / or, in step S2, the reducing agent is added in one portion or in portions.

23. The method for separating actinide elements as described in claim 22, characterized in that, in step S1, the melting temperature is 550°C; and / or, the adding in batches is equal adding in batches.

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