Preparation method of uranium dioxide
阅读说明：本技术 一种二氧化铀的制备方法 (Preparation method of uranium dioxide ) 是由 廖俊生 杜云峰 唐浩 高瑞 杨振亮 李冰清 邵浪 姜交来 于 2021-09-06 设计创作，主要内容包括：本发明属于核化工技术领域,尤其涉及一种二氧化铀的制备方法。本发明提供的制备方法,包括以下步骤：采用三电极体系,以熔融态碱金属卤化物为电解液,以U-(3)O-(8)为工作电极进行电解还原,得到所述二氧化铀。本发明提供的制备方法以U-(3)O-(8)为工作电极进行电解还原,在熔融态碱金属卤化物中,通过电子扩散、电子迁移和电子对流的作用在辅助电极完成放电,最终制备得到二氧化铀。本发明提供的制备方法采用电解还原U-(3)O-(8)制备二氧化铀,不仅能够制备得到化学计量比稳定的二氧化铀,且制备方法简单、系统安全性高、工艺流程短。(The invention belongs to the technical field of nuclear chemical industry, and particularly relates to a preparation method of uranium dioxide. The preparation method provided by the invention comprises the following steps: adopts a three-electrode system, takes molten alkali metal halide as electrolyte and U as electrolyte 3 O 8 And carrying out electrolytic reduction on the working electrode to obtain the uranium dioxide. The preparation method provided by the invention uses U 3 O 8 And performing electrolytic reduction on the working electrode, and completing discharge on the auxiliary electrode under the action of electron diffusion, electron migration and electron convection in molten alkali metal halide to finally prepare the uranium dioxide. The present invention providesThe preparation method adopts electrolytic reduction of U 3 O 8 The uranium dioxide is prepared, the uranium dioxide with stable stoichiometric ratio can be prepared, and the preparation method is simple, high in system safety and short in process flow.)
1. The preparation method of uranium dioxide is characterized by comprising the following steps:
adopts a three-electrode system, takes molten alkali metal halide as electrolyte and U as electrolyte3O8And carrying out electrolytic reduction on the working electrode to obtain the uranium dioxide.
2. The preparation method according to claim 1, wherein the reference electrode in the three-electrode system is Ag/AgCl, and the voltage of the working electrode is-1.5 to-2.1V.
3. The method of claim 1, wherein the molten alkali metal halide is LiCl molten salt, and Li is in the LiCl molten salt2The mass percent of O is less than or equal to 1 percent.
4. The method according to claim 3, wherein the LiCl molten salt has a temperature of 620 to 700 ℃.
5. The method according to claim 1, wherein the U is3O8Is U3O8Block body of U3O8The density of the block body is 59-90%.
6. The method according to claim 5, wherein the U is3O8The preparation method of the block comprises the following steps:
will U3O8Tabletting the powder to obtain U3O8A shaped body;
will be the U3O8Sintering the formed body to obtain the U3O8A block body;
the sintering temperature is 800-1200 ℃.
7. The method according to claim 6, wherein the pressure of the compressed tablet is 30 to 300MPa, and the dwell time is 1 to 10 seconds.
8. The preparation method according to claim 6, wherein the sintering is carried out for 3-24 h at a temperature rising rate of 2-10 ℃/min from room temperature to the sintering temperature.
9. The method according to claim 6, wherein the U is3O8The particle size of the powder is 0.1 to 1 μm.
10. The method according to claim 5, wherein the U is3O8The block body is cylindrical, the U3O8The diameter of the block body is 5-20 mm, U3O8The height of the block body is 3-15 mm.
Technical Field
The invention belongs to the technical field of nuclear chemical industry, and particularly relates to a preparation method of uranium dioxide.
Background
Mixed Oxide (MOX) fuels have important application prospects in the nuclear power field, particularly in fast neutron breeder reactors (FBRs). Uranium dioxide is an important component of uranium dioxide, and the O/U ratio of uranium dioxide has an important influence on the physicochemical properties of fuel. Even at room temperature, spontaneous oxidation of uranium dioxide occurs when exposed to air, and the O/U ratio is highly susceptible to shift.
The industrial preparation of uranium dioxide generally employs an Ammonium Diuranate (ADU) process, namely: using UF6 as raw material, hydrolyzing and precipitating to obtain Ammonium Diuranate (ADU), and subjecting to H2Decomposing and reducing the uranium dioxide into uranium dioxide powder under the atmosphere. In order to obtain a product with uniform properties, the process generally requires further stabilization of the product in cold air. The process has the advantages of long production period and complex working procedures, and the obtained uranium dioxide powder has unstable O/U ratio and is not suitable for scenes with strict requirements on the O/U ratio.
Another commonly used method for obtaining near-stoichiometric uranium dioxide is to subject the partially oxidized uranium dioxide to a reduction in H2And carrying out high-temperature reduction for a long time under the atmosphere. Although the O/U ratio of the obtained uranium dioxide powder is relatively stable, the process is a gas-solid reaction process at high temperature, so that the potential safety hazard is great.
Disclosure of Invention
In view of the above, the invention provides a preparation method of uranium dioxide, and the uranium dioxide prepared by the preparation method provided by the invention has stable stoichiometric ratio and high system safety.
The invention provides a preparation method of uranium dioxide, which comprises the following steps:
adopts a three-electrode system, takes molten alkali metal halide as electrolyte and U as electrolyte3O8And carrying out electrolytic reduction on the working electrode to obtain the uranium dioxide.
Preferably, the reference electrode in the three-electrode system is Ag/AgCl, and the voltage of the working electrode is-1.5 to-2.1V.
Preferably, the molten alkali metal halide is a LiCl molten salt in which Li is present2The mass percent of O is less than or equal to 1 percent.
Preferably, the temperature of the LiCl molten salt is 620-700 ℃.
Preferably, said U is3O8Is U3O8Block body of U3O8The density of the block body is 59-90%.
Preferably, said U is3O8The preparation method of the block comprises the following steps:
will U3O8Sequentially tabletting the powder to obtain U3O8A shaped body;
will be the U3O8Sintering the formed body to obtain the U3O8A block body;
the sintering temperature is 800-1200 ℃.
Preferably, the pressure of the tabletting is 30-300 MPa, and the pressure maintaining time is 1-10 s.
Preferably, the heat preservation time of the sintering is 3-24 h, and the heating rate of the temperature from room temperature to the sintering temperature is 2-10 ℃/min.
Preferably, said U is3O8The particle size of the powder is 0.1 to 1 μm.
Preferably, said U is3O8The block body is cylindrical, the U3O8The diameter of the block body is 5-20 mm, U3O8The height of the block body is 3-15 mm.
The invention provides a dioxygenThe preparation method of uranium oxide comprises the following steps: adopts a three-electrode system, takes molten alkali metal halide as electrolyte and U as electrolyte3O8And carrying out electrolytic reduction on the working electrode to obtain the uranium dioxide. The preparation method provided by the invention uses U3O8Electrolytic reduction for the working electrode, U3O8Has semiconductor properties in molten alkali metal halide and has an electrical conductivity of 138.4 (omega cm)-1Under the action of an electric field, U3O8Oxygen ions in the uranium dioxide enter and are dissolved in molten alkali metal halide, and discharge is completed on an auxiliary electrode in a three-electrode system under the action of electron diffusion, electron migration and electron convection, so that the uranium dioxide is finally prepared. The following electrode reactions occur during this process: u shape3O8+4e-＝3UO2+2O2-，2O2-+C＝CO2+4e-，O2-+C＝CO+2e-，2O2-＝O2+4e-. The preparation method provided by the invention adopts electrolytic reduction of U3O8The uranium dioxide is prepared, the uranium dioxide with stable stoichiometric ratio can be prepared, and the system safety is high.
Drawings
FIG. 1 shows a U-shaped section of the present invention3O8Cyclic voltammetric electrochemical curves in LiCl molten salt;
FIG. 2 shows example 1U of the present invention3O8Physical appearance images and electron microscope images before and after sintering at 1000 ℃;
FIG. 3 is a UO prepared in example 1 of the present invention2.000SEM topography of the powder;
FIG. 4 is a UO prepared in example 1 of the present invention2.000XRD pattern of the powder;
FIG. 5 is a UO prepared in example 1 of the present invention2.000TG/DSC profile of the powder.
Detailed Description
The invention provides a preparation method of uranium dioxide, which comprises the following steps:
adopts a three-electrode system, takes molten alkali metal halide as electrolyte and U as electrolyte3O8And carrying out electrolytic reduction on the working electrode to obtain the uranium dioxide.
In the present invention, the starting materials used are all commercially available products well known to those skilled in the art, unless otherwise specified.
The preparation method provided by the invention adopts a three-electrode system, and the three-electrode system comprises a working electrode, a reference electrode and an auxiliary electrode.
In the present invention, the electrolyte is a molten alkali metal halide, which preferably comprises LiCl molten salt and/or KCl molten salt.
In the present invention, the electrolyte is preferably a LiCl molten salt in which Li is present2The mass percentage of O is preferably not more than 1%, more preferably not more than 0.5%.
In the present invention, when the electrolyte is preferably a LiCl molten salt, the temperature of the LiCl molten salt is preferably 620 to 700 ℃, more preferably 630 to 680 ℃, and most preferably 640 to 660 ℃.
In the present invention, the reference electrode is preferably an Ag/AgCl electrode.
In the present invention, the working electrode (cathode) is U3O8。
In the present invention, the Ag/AgCl electrode is used as a reference electrode, and the voltage of the working electrode is preferably-1.5 to-2.1V, and more preferably-1.8 to-2V.
In the present invention, said U is3O8Preferably U3O8Block body of U3O8The process for the preparation of the block preferably comprises the following steps:
will U3O8Tabletting the powder to obtain U3O8A shaped body;
will be the U3O8Sintering the formed body to obtain the U3O8A block body;
the sintering temperature is 800-1200 ℃.
The invention connects U with3O8Tabletting the powder to obtain U3O8A shaped body. In the present invention, said U is3O8The particle size of the powder is preferably 0.1 to 1 μm, more preferably 0.2 to 0.8. mu.m.
In the present invention, said U is3O8The water content of the powder is preferably 0.1% or less.
The invention preferably selects the U3O8The powder is pretreated, the pretreatment preferably comprises drying, and the drying temperature is preferably 100-550 ℃, and more preferably 110-250 ℃. The invention has no special requirement on the drying time, and the U is3O8Drying the powder to constant weight. In the present invention, the drying is preferably performed in a muffle furnace.
In the present invention, the pressure of the tablet is preferably 30 to 300MPa, more preferably 50 to 250MPa, and most preferably 100 to 200 MPa. In the invention, the dwell time is preferably 1 to 10s, more preferably 1.5 to 8s, and most preferably 5 to 7 s. In the present invention, the tableting is preferably performed in a tablet press, and the die of the tableting is preferably cylindrical.
To obtain U3O8After forming the body, the present invention provides the U3O8Sintering the formed body to obtain the U3O8And (3) a block body. In the invention, the sintering temperature is preferably 800-1200 ℃, more preferably 850-1100 ℃, and most preferably 900-1000 ℃. In the invention, the heat preservation time of the sintering is preferably 3-24 h, more preferably 3.5-20 h, and most preferably 10-15 h. In the invention, the heating rate of the temperature from room temperature to the sintering temperature is preferably 2-10 ℃/min, and more preferably 3-8 ℃/min. In the present invention, the sintering atmosphere is preferably air or an inert gas, and the inert gas is argon, and in a specific embodiment of the present invention, the sintering atmosphere is argon. In the present invention, the sintering is preferably carried out in a tube furnace.
In the present invention, said U is3O8The density of the block body is preferably 59-90%, and more preferably 62-89%.
In the invention, the density is U3O8Ratio of actual density to theoretical density of block. The invention characterizes the U by the compactness3O8Porosity of the block.
In the present invention, said U is3O8The blocks being formed by U's bridging each other but not being fully dense3O8Powder particle composition of U3O8The block acquires both structural strength and porosity.
The invention uses the U3O8The density of the block is preferably 59-90%, and the U can be further improved3O8The contact area of the block and the electrolyte is further increased3O8The degree of integral full electrolytic reduction of the block realizes U3O8The block is completely electrolytically reduced to uranium dioxide.
In a specific embodiment of the present invention, the U is3O8The block is preferably cylindrical, said U3O8The diameter of the block body is preferably 5-20 mm, and more preferably 6-18 mm. The U is3O8The height of the block body is preferably 3-15 mm, and more preferably 3.5-12 mm.
In a specific embodiment of the present invention, the U is3O8The block is preferably used as a working electrode in the form of a bundle of inert wires. In the present invention, the inert metal wire preferably includes a molybdenum wire, a tungsten wire, or a nickel wire. In a particular embodiment of the invention, the inert metal wire is preferably a nickel wire, the diameter of which is preferably 1 mm.
In a specific embodiment of the present invention, the U is3O8The block is preferably wrapped in an inert metal mesh as the working electrode. In the present invention, the inert metal mesh preferably includes a molybdenum mesh, a tungsten mesh or a nickel mesh.
In the present invention, the auxiliary electrode (anode) is preferably graphite, glassy carbon or platinum, and more preferably glassy carbon.
In the present invention, the electrolytic reduction is preferably constant-voltage electrolytic reduction.
In the present invention, the time of the electrolytic reduction and the U3O8The mass ratio of the block is preferably (0.5-1.5) h:1gIn the present invention, in the specific embodiment, the time of the electrolytic reduction and the U are3O8The mass ratio of the blocks is preferably 2h:3 g.
After the electrolytic reduction, the present invention preferably performs a post-treatment on the working electrode, and in the present invention, the post-treatment preferably includes: ultrasonic dispersion, solid-liquid separation and drying are sequentially carried out. The working electrode after electrolytic reduction is preferably placed in water for ultrasonic dispersion, the water is preferably deionized water, the specific implementation process of the ultrasonic treatment method has no special requirement, and the working electrode after electrolytic reduction is completely dispersed. The dispersion liquid obtained by ultrasonic dispersion is preferably subjected to solid-liquid separation, the solid-liquid separation is preferably suction filtration, the solid product obtained by the solid-liquid separation is preferably dried, the drying is preferably vacuum drying, and the temperature of the vacuum drying is preferably 80-90 ℃.
The preparation method provided by the invention carries out electrolytic reduction in the molten alkali metal halide, and the molten alkali metal halide hardly has free oxygen and water, so that UO can be effectively avoided2Reoxidation of (a); and the alkali metal halide dissolves O in the molten state2-Strong ionic capacity and can rapidly dissolve UO2+xAnd the residual oxygen is reduced and transported to the anode. The invention adopts electrolytic reduction, has strong reducibility of electrons, and can easily reduce UO2+xReduction to UO2(ii) a The invention adopts U for electrolytic reduction3O8Reduction to UO2Potential of (-0.48V) and UO2The potentials for reduction to U (-2.40V) are far apart, and the potential shift will not be for UO2The product has a great influence. Therefore, the preparation method provided by the invention can be used for preparing uranium dioxide with stable stoichiometric ratio.
Preparation process provided by the invention, and H2Compared with a reduction method, the method has the advantages of simple equipment, high system safety, high process efficiency, stable stoichiometric ratio and low cost, is a novel method for preparing the uranium dioxide with the stoichiometric ratio, and has potential application in the aspect of preparing standard substances.
The technical solution of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. It is to be understood that the described embodiments are merely exemplary of the invention, and not restrictive of the full scope of the invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
Example 1
3g of U3O8Drying the powder (particle diameter of 1 μm) in muffle furnace at 110 deg.C to constant weight, cooling, tabletting with cylindrical mold with diameter of 10mm under 100Mpa in tabletting machine, and maintaining pressure for 6s to obtain U3O8Pre-blocking. Finally, the U is put3O8Heating the pre-block body to 1000 ℃ at the heating rate of 5 ℃/min in a tubular furnace, sintering for 6 hours in the atmosphere of argon to obtain U3O8Block (porous structure, density 79%).
Firstly LiCl (Li)2O is less than or equal to 1 percent by mass percent) is heated to 650 ℃ in a well type furnace, glassy carbon with the diameter of 6 millimeters is used as an anode (an auxiliary electrode), and U is put into the furnace3O8Binding metal nickel wires with the diameter of 1mm as a cathode (working electrode) and Ag/AgCl as a reference electrode in a block body, performing constant-voltage electrolytic reduction in LiCl molten salt for 2 hours by a three-electrode system at the voltage of-1.8V, and then carrying out electrolytic reduction on the U3O8Putting the block body into water, performing ultrasonic dispersion to obtain dispersion, performing suction filtration to obtain a filter cake, putting the filter cake into a vacuum drying oven, and performing vacuum drying at 80 ℃ to constant weight to obtain UO2.000And (3) powder.
FIG. 2 shows the embodiment U3O8The physical and electronic appearance images before and after sintering at 1000 ℃ can be obtained from FIG. 2, and the invention makes U by sintering3O8Powder fusion, U3O8The particles are bridged but not fully dense, so that U is formed3O8The block obtains both sufficient structural strength and porosity. Sintered U3O8The porosity of a block is characterized by the ratio of the density of the block to the theoretical density (relative density), this factThe example obtained a density of 79% when sintered at 1000 ℃.
FIG. 3 shows the UO prepared in this example2.000SEM morphology of powder, FIG. 4 is UO prepared in this example2.000XRD pattern of the powder; by applying to the electrolysis product UO2.000SEM and XRD analysis of the micro-morphology and crystal structure of the powder respectively show that the UO prepared in this example2.000The phase composition of the powder product is a single uranium dioxide phase.
According to the invention, through thermogravimetry/differential thermal (TG/DSC) analysis, the O/U ratio of the obtained product can be calculated by adopting a formula shown in a formula I:
r-17.54167/(1 + Δ W) -14.8751 formula I.
Wherein R is the O/U ratio of uranium dioxide, and Δ W is the percent weight gain of the sample in the TG/DSC test.
FIG. 5 is a UO prepared in example 1 of the present invention2.000TG/DSC profile of the powder by comparison with UO2.000The powder product was analyzed by TG/DSC, and the weight change curve showed that the weight gain W was 3.951%, indicating that the O/U ratio of the product was 2.000. + -. 0.001.
Example 2
3g of U3O8Drying the powder (particle diameter of 1 μm) in muffle furnace at 250 deg.C to constant weight, cooling, tabletting with cylindrical mold with diameter of 10mm under 100Mpa in tabletting machine, and maintaining pressure for 6s to obtain U3O8Pre-blocking. Finally, the U is put3O8Heating the pre-block to 1200 ℃ at the heating rate of 5 ℃/min in a tubular furnace, and sintering for 6 hours in the presence of argon to obtain U3O8Bulk (porous structure, density).
Firstly LiCl (Li)2O is less than or equal to 1 percent by mass percent) is heated to 650 ℃ in a well type furnace, glassy carbon with the diameter of 6 millimeters is used as an anode (an auxiliary electrode), and U is put into the furnace3O8Binding metal nickel wires with the diameter of 1mm as a cathode (working electrode) and Ag/AgCl as a reference electrode in a block body, performing constant-voltage electrolytic reduction in LiCl molten salt for 2 hours by a three-electrode system at the voltage of-1.5V, and then carrying out electrolytic reduction on the U3O8Block bodyPlacing into water, performing ultrasonic dispersion to obtain dispersion, performing suction filtration to obtain filter cake, placing the filter cake into a vacuum drying oven, and vacuum drying at 80 deg.C to constant weight to obtain UO2.000And (3) powder.
Example 3
3g of U3O8Drying the powder (particle diameter of 1 μm) in muffle furnace at 450 deg.C to constant weight, cooling, tabletting with 10mm cylindrical mold under 200Mpa for 10s, and maintaining the pressure to obtain U3O8Pre-blocking. Finally, the U is put3O8Heating the pre-block body to 1000 ℃ at the heating rate of 5 ℃/min in a tubular furnace, sintering for 6 hours in the atmosphere of argon to obtain U3O8Block (porous structure, density 79%).
Firstly LiCl (Li)2O is less than or equal to 1 percent by mass percent) is heated to 650 ℃ in a well type furnace, glassy carbon with the diameter of 6 millimeters is used as an anode (an auxiliary electrode), and U is put into the furnace3O8Binding metal nickel wires with the diameter of 1mm as a cathode (working electrode) and Ag/AgCl as a reference electrode in a block body, performing constant-voltage electrolytic reduction in LiCl molten salt for 2 hours by a three-electrode system at the voltage of-2.1V, and then carrying out electrolytic reduction on the U3O8Putting the block body into water, performing ultrasonic dispersion to obtain dispersion, performing suction filtration to obtain a filter cake, putting the filter cake into a vacuum drying oven, and performing vacuum drying at 80 ℃ to constant weight to obtain UO2.000And (3) powder.
The foregoing is only a preferred embodiment of the present invention, and it should be noted that, for those skilled in the art, various modifications and decorations can be made without departing from the principle of the present invention, and these modifications and decorations should also be regarded as the protection scope of the present invention.
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