Separation method of actinide elements

Abstract

The invention discloses a separation method of actinide elements. The separation method comprises the following steps: reacting a mixture containing a molten salt phase, a metal phase and a reducing agent; the molten salt phase comprises actinide metal, fission products and molten salt; the actinide metal exists in the form of ions; the metal phase comprises a first metal; the first metal exists in a simple substance form; the reducing agent comprises a 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); the reaction temperature is not higher than 800 DEG C. According to the method, metal lithium in an alloy form is used as a reducing agent for carrying out reduction extraction reaction, and actinide elements and fission products in the molten salt are separated. The separation method can realize efficient separation of actinide elements and fission products in the molten salt, improves the separation coefficient, decontamination coefficient and recovery rate of the actinide elements, and meets the strict requirements of the nuclear industry on separation and purification of the actinide elements.

Description

TECHNICAL FIELD

[0001] The present application relates to a method for separating actinides. BACKGROUND

[0002] Actinides (such as uranium, thorium, plutonium, etc.) are key substances in the nuclear industry, and play an important role in the fields of nuclear power generation, nuclear fuel preparation, etc. However, in the process of nuclear reaction, actinides are mixed with a large amount of fission products (such as cesium, strontium, cerium, samarium, neodymium, lanthanum, europium, etc.) in the nuclear reactor molten salt; these fission products often have strong radioactivity and toxicity, and if not effectively separated and purified, not only will it affect the reuse of actinides, but also will cause serious threats to the environment and human health.

[0003] At present, the existing actinide separation and purification technologies mainly include solvent extraction method, precipitation method, etc. However, these technologies generally have some defects: in the solvent extraction method, the organic solvent is easily damaged by radiation when dealing with high radioactivity materials, resulting in a decrease in separation efficiency, and a large amount of radioactive organic waste liquid is generated; the separation selectivity of the precipitation method is poor, and the separation effect of actinides and fission products is not ideal, and the decontamination factor is usually difficult to reach 10 3 The above-mentioned actinide recovery rate is also low, which cannot meet the requirements of the nuclear industry for high-purity recovery of actinides.

[0004] Therefore, it is of great significance to develop an efficient and highly selective actinide separation method to realize the deep separation of actinides and fission products, and to improve the recovery rate and decontamination factor of actinides, for promoting the sustainable development of the nuclear industry and the safe disposal of radioactive waste. SUMMARY

[0005] In order to solve the problems of low separation efficiency, poor decontamination effect, and low recovery rate of actinides in the existing actinide separation method, the present application provides a method for separating actinides, which uses metal lithium in the form of alloy as a reducing agent for reduction extraction reaction to separate actinides and fission products in molten salt. The separation method can realize efficient separation of actinides and fission products in molten salt, improve the separation coefficient, decontamination factor and recovery rate of actinides, and meet the strict requirements of the nuclear industry for actinide separation and purification.

[0006] The present application solves the above technical problems by the following technical solutions:

[0007] The present application provides a method for separating actinides, which comprises the following steps: a mixture of a molten salt phase, a metal phase and a reducing agent is reacted; wherein,

[0008] The molten salt phase comprises actinide metals, fission products and molten salt; the actinide metals exist in the form of ions;

[0009] The metal phase comprises a first metal; the first metal exists in elemental form;

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

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

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

[0013] In the present application, based on the metal-based reduction extraction reaction, the actinide metals to be separated in the molten salt phase can be transferred to the metal phase, and the remaining fission products (such as alkali metals, alkaline earth metals, lanthanide metals, etc.) are left in the molten salt, thereby realizing the effective separation of the actinide metals in the molten salt phase; wherein the molten salt phase can be regarded as a conventional nuclear reactor molten salt containing actinide metals and their fission products, and the obtained separation product only contains a single metal phase and actinide metals, which is more conducive to the recycling of actinide metals to a certain extent compared with the molten salt.

[0014] In the present application, the meaning of "existing in elemental form" can refer to the first metal existing in the form of not containing alloy, but only in elemental form.

[0015] In the present application, the meaning of "existing in alloy form" can refer to the first metal and the second metal existing in the form of not containing elemental, but only in alloy form.

[0016] In the present application, the meaning that the metal phase and the reducing agent both comprise the first metal can refer to the types of the first metal in the metal phase and the reducing phase being consistent.

[0017] In the present application, the actinide metal can be conventional in the art, and preferably comprises one or more of uranium, thorium and plutonium, for example, uranium.

[0018] In the present application, the fission product can refer to the fission product existing in the conventional nuclear reactor molten salt in the art, which can generally comprise one or more of alkali metals, alkaline earth metals, noble metals, semi-noble metals and lanthanide metals; specifically, it can comprise one or more of cesium, strontium, cerium, samarium, praseodymium, dysprosium, erbium, thulium, neodymium, lanthanum and europium.

[0019] In the present application, the molten salt can comprise fluoride molten salt and / or chloride molten salt, and is preferably fluoride molten salt.

[0020] In the present application, the molten salt can be lithium-sodium-potassium-containing molten salt; preferably, it is lithium-sodium-potassium fluoride molten salt.

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

[0022] In the application, the first metal can comprise one or more of aluminum, copper, gallium, zinc, tin, bismuth and cadmium, and preferably bismuth.

[0023] In the application, the purity of the bismuth metal is preferably ≥ 99%.

[0024] In the application, the reducing agent can comprise one or more of an aluminum-lithium alloy, a copper-lithium alloy, a gallium-lithium alloy, a zinc-lithium alloy, a tin-lithium alloy, a bismuth-lithium alloy and a cadmium-lithium alloy, and is for example a bismuth-lithium alloy.

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

[0026] In the application, 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 the application, 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 the application, 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 the application, the molar ratio of the reducing agent to the molten salt phase, based on the total molar amount of actinides and fission products in the molten salt phase, can be 1:(1-10), and is preferably 1:(1-7), 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 the application, the temperature of the reaction can be 500-800℃, and is preferably 550-800℃, for example 550℃, 600℃, 700℃ or 800℃.

[0031] In the application, the time of the reaction can be 1-10h, and is preferably 3-10h, for example 3h, 4h, 5h, 6h, 8h or 10h.

[0032] In the present invention, the reaction can be carried out under stirring; 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] Among them, the shape of the stirring paddle in the stirring device is preferably spiral ribbon type and / or "field" type, such as "field" type.

[0035] Among them, 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 include the following steps:

[0037] S1. First, mix the molten salt phase and the metal phase and melt them to obtain a premix;

[0038] S2. Add the reducing agent to the premix to obtain the product.

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

[0040] Among them, the addition method of the reducing agent is preferably one-time addition or batch addition.

[0041] Among them, the batch addition is preferably carried out in 6 batches.

[0042] Among them, the batch addition is preferably carried out in equal amounts in batches.

[0043] Among them, the melting can be a conventional operation in the art, and the melting temperature can be 500 - 600 °C, such as 550 °C.

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

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

[0046] The positive and progressive effects of the present invention are as follows:

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

[0048] (1) Good separation effect: This technology can make the separation coefficient of actinides and fission products reach 10 2 or more; the decontamination coefficient of alkali metals reaches 10 4 or more; the decontamination coefficient of alkaline earth metals reaches 10 3 or more; the decontamination coefficient 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 of actinide and lanthanide (i.e. molten salt phase): melt 0.15% of uranium tetrafluoride and lanthanide fluoride (0.0075% cesium fluoride, 0.0065% strontium fluoride, 0.0060% lanthanum fluoride, 0.0080% samarium fluoride, 0.0080% neodymium fluoride) into fluoride molten salt at 650℃, cool for standby, and obtain the molten salt phase. The percentage refers to the mass percentage of the molten salt phase.

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

[0061] The graphite crucible 3 is placed in the corundum crucible 2, and the corundum crucible 2 is placed in the electric furnace 1, wherein the electric furnace 1 is filled with resistance wire 6. The stirrer 7 is placed above the electric furnace 1, and the molybdenum stirring paddle 4 is connected with the stirrer 7. The quartz sampling tube is placed on both sides of the stirrer 7, and the lower end is respectively placed in the graphite crucible 3.

[0062] In the following examples and comparative examples, the reagents and equipment information involved are 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 Reagent Co., Ltd. The purity was AR.

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

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

[0066] The prepared molten salt phase and metal phase were put into the stirring device as shown in Figure 1 at different proportions, melted at a certain temperature, and then a certain proportion of reducing agent was added after the molten salt phase and the metal phase were completely changed into liquid state. Different reducing agent addition methods, reaction temperatures, stirring speeds, and stirring times (i.e. reaction times) were set to carry out the reduction extraction reaction. The separation of actinide and fission product from the molten salt phase containing actinide and fission product was carried out according to the parameters shown 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 and fission product in the molten salt phase.

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

[0069]

[0070] Effect examples

[0071] For the separation methods of examples 1-14 and comparative examples 1-2, the corresponding inspection of separation effect was carried out, and the effect parameter test method and calculation method involved are as follows:

[0072] After the reaction was completed, the molten salt phase and the metal phase were sampled respectively, and then melted to prepare the analysis sample. The actinide elements and fission products in the sample were analyzed by ICP-OES and ICP-MS analysis equipment, and the results were calculated according to the analysis results, as shown in Table 2. The specific calculation method is as follows:

[0073] 1. Separation coefficient

[0074] The equation of the actinide metal reduction reaction is as follows:

[0075]

[0076] The calculation formula of the reaction equilibrium constant (K) is as follows:

[0077]

[0078] Wherein, N MF3 represents the molar percentage content of fluoride of actinide elements or fission products in the molten salt, N M represents the molar percentage content of actinide elements or fission products after reduction in bismuth metal, N Li represents the molar percentage content of lithium in bismuth metal, and N LiF represents the molar percentage content of lithium fluoride in the molten salt.

[0079] The distribution coefficient (D M ) represents the ratio of the molar percentage (N M ) of metal ions in bismuth after the reduction extraction reaction equilibrium to the molar percentage (N MF ) in the molten salt phase, and the calculation formula is as follows:

[0080]

[0081] The equilibrium constant (K * M ) represents the equilibrium constant of the reduction extraction reaction, and the logarithmic value can be represented by the logarithmic value of the ratio of the distribution coefficient (D M ) of metal ions to the nth power of the distribution coefficient (D Li ) of the reducing agent, and the calculation formula is as follows:

[0082]

[0083]

[0084] Separation coefficient β between lanthanide elements M1 / M2 The separation coefficient β between lanthanide elements represents the ratio of the distribution coefficients between lanthanide elements after the reduction extraction reaction reaches equilibrium, and the calculation formula is as follows:

[0085]

[0086] 2. Decontamination coefficient

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

[0088]

[0089] 3. Recovery rate

[0090] Material balance value (MB M ) represents the ratio of the sum of the masses of the metal in the molten salt and the bismuth phase after the reduction extraction reaction reaches equilibrium to the mass of the metal ion in the molten salt at the start of the reaction, usually expressed as a percentage, and the calculation formula is as follows:

[0091]

[0092] Recovery rate (E M ) represents the ratio of the mass of the metal transferred to the bismuth phase after the reduction extraction reaction reaches equilibrium to the mass of the metal ion in the molten salt at the start of the reaction, usually expressed as a percentage, and the calculation formula is as follows:

[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 recovery rate results 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 decontamination coefficient of the alkali metal reached 10 4 The decontamination coefficient of the alkaline earth metal reached 10 3 The decontamination coefficient of the lanthanide metal reached 10 2 The above, which demonstrates excellent separation and decontamination effects. The actinide recovery rate of Examples 1-14 can reach 88% or more, which is superior to Comparative Examples 1-2.

[0097] Although the specific embodiments of the present application have been described above, it is understood by those skilled in the art that the present application is only illustrated by way of example, and the scope of protection of the present application is defined by the appended claims. Those skilled in the art can make various changes or modifications to the embodiments without departing from the principles and essence of the present application, and such changes and modifications fall within the scope of protection of the present application.

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 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), for example 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:(5-25), 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; 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), preferably 1:(1-7), 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; And / or, the temperature of the reaction is 500°C-800°C, preferably 550°C-800°C, for example 550°C, 600°C, 700°C or 800°C.

3. The method for separating actinide elements as described in claim 1, characterized in that, The first metal includes one or more of aluminum, copper, gallium, zinc, tin, bismuth, and cadmium, preferably bismuth; Preferably, the purity of the bismuth is ≥99%.

4. The method for separating actinide elements as described in claim 1, characterized in that, The reducing agent includes 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; And / or, the molar ratio of the first metal and the second metal is (60-95):(5-40), preferably 70:30; Preferably, 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.

5. 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, for example, uranium; And / or, the fission products include one or more of alkali metals, alkaline earth metals, noble metals, semi-noble metals and lanthanides; preferably, they include one or more of cesium, strontium, cerium, samarium, praseodymium, dysprosium, erbium, thulium, neodymium, lanthanum and europium.

6. 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, preferably fluoride molten salt; And / or, the molten salt is a molten salt containing lithium, sodium, and potassium; Preferably, the molten salt is a sodium-potassium fluoride molten salt; 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.

7. The method for separating actinide elements as described in claim 1, characterized in that, The reaction time is 1 - 10 h, preferably 3 - 10 h, such as 3 h, 4 h, 5 h, 6 h, 8 h or 10 h; And / or, the reaction is carried out under stirring; the stirring speed is preferably 200 - 500 rpm, such as 200 rpm, 300 rpm, 400 rpm or 500 rpm.

8. The method for separating actinide elements as described in claim 1, characterized in that, The reaction is carried out in a stirring device; Among them, the shape of the stirring paddle in the stirring device is preferably spiral ribbon type and / or "field" type, such as "field" type; Among them, the material of the stirring paddle in the stirring device is preferably metal, more preferably molybdenum.

9. The method for separating actinide elements as described in claim 1, characterized in that, The preparation of the mixture may include the following steps: S1. First, mix the molten salt phase and the metal phase, and melt them to obtain a premix; S2. Add the reducing agent to the premix to obtain the product.

10. The method for separating actinide elements as described in claim 9, characterized in that, In step S1, the preparation of the molten salt phase includes: mixing an actinide metal source, a fission product source and a molten salt, and melting them to obtain the molten salt phase; And / or, in step S1, the melting temperature is 500 - 600 °C, such as 550 °C; And / or, in step S2, the adding method of the reducing agent is one-time addition or batch addition; Among them, the batch addition is preferably equal - amount batch addition.

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