A method for preparing uranium dioxide by catalyzing sodium uranyl carbonate with a magnetic catalyst

Abstract

The present application relates to a kind of magnetic catalyst for the preparation of uranium dioxide of sodium uranyl carbonate, preparation method and its application, the catalyst is composed of two parts of carrier and active metal, wherein the carrier is the magnetic cobalt tetroxide, and active metal is the mixture of one or two elements of Ru, Rh, Pt and Pd.Active gold belongs to the mass percentage content of catalyst is 0.1-1wt%.The catalyst of the present application has good activity for the preparation of uranium dioxide by hydrogenation of sodium uranyl carbonate, and the catalyst has magnetism, can realize online separation of catalyst and reaction product solid uranium dioxide in the fluidized bed reactor of external magnetic field, the purity of uranium dioxide is improved to 99.5% or more, meet the industrial application requirements of sodium uranyl carbonate by catalytic reduction to prepare uranium dioxide.

Description

Technical Field

[0001] This invention relates to a magnetic catalyst for the preparation of uranium dioxide from sodium uranyl carbonate, its preparation method, and its application. The catalyst consists of a support and an active metal. The support is magnetic cobalt tetroxide, and the active metal is one or a mixture of two elements selected from Ru, Rh, Pt, and Pd. The catalyst of this invention exhibits excellent activity in the hydrogenation of sodium uranyl carbonate to uranium dioxide. Furthermore, the magnetic nature of the catalyst allows for online separation of the catalyst and the reaction product solid uranium dioxide in a fluidized bed reactor under an external magnetic field, increasing the purity of uranium dioxide to over 99.5%, thus meeting the requirements for the industrial application of uranyl carbonate to uranium dioxide via catalytic reduction. Background Technology

[0002] As human demand for energy increases daily, countries worldwide face increasingly severe environmental pollution and energy shortages. Against this backdrop, the advantages of nuclear energy as a clean energy source become particularly important. Currently, the international community considers uranium a low-carbon fuel resource that can help achieve sustainable development goals and climate commitments. Nuclear fuel is the fundamental material for nuclear energy utilization, and researching reactors with higher utilization rates is one method to fully utilize uranium resources.

[0003] Uranium dioxide, with its unique performance advantages, has become a widely used nuclear fuel in power reactors and is also an important raw material for the dry production of uranium tetrafluoride. The nuclear fuel production process begins with uranium mining, followed by in-situ leaching and heap leaching to extract sodium diuranate (yellowcake). After refining the uranium concentrate, it is dissolved, extracted, and purified with nitric acid to obtain pure uranyl nitrate, ammonium diuranate, or ammonium tricarbonate. This is then calcined and pyrolyzed to produce uranium oxides, or further processed into uranium fluorides. Currently, my country employs advanced CO2+O2 in-situ leaching technology in uranium mining. The extracted fluid is enriched by separation resin, then leached with a carbonate solution to form a uranyl carbonate solution. After precipitation with caustic soda, sodium diuranate is produced. To obtain high-purity fuel uranium and sodium diuranate, further nitric acid dissolution, extraction to separate sodium ions, and ammonia precipitation are required to obtain solid ammonium diuranate. Calcination yields fuel-grade uranium oxide. During the precipitation process, the supernatant of the reaction system needs to be managed as radioactive wastewater. The preparation process is complex and lengthy, and the production process generates a high level of radioactive wastewater containing uranium (roughly estimated at over 50 tons of wastewater per ton of uranium produced), resulting in high uranium fuel costs.

[0004] This application proposes for the first time a method for preparing high-purity uranium dioxide by catalytic hydrogenation reduction of sodium uranyl carbonate, which solves the problems of high discharge of uranium-containing radioactive wastewater, low uranium content of sodium diuranate products, and long and costly production processes in my country's uranium fuel production process.

[0005] The catalytic hydrogenation reduction process of sodium uranyl carbonate actually proceeds in two steps. The first step is the catalytic hydrogenation reduction of sodium uranyl carbonate to produce tetravalent uranium.

[0006] Na4[UO2(CO3)3]+H2=U(OH)2CO3+2Na2CO3(1)

[0007] In the second step, under high temperature (temperature > 90℃) and alkaline conditions, the uranium carbonate generated in the above process can undergo further hydrolysis to produce uranium oxide solid particles:

[0008] U(OH)₂CO₃+OH - =UO2 (precipitate) + HCO3 - +H2O(2)

[0009] Based on reaction equations (1) and (2), we can see that by controlling the reactor temperature, the two processes of catalytic hydrogenation reduction and hydrolysis to generate UO2 (precipitate) can be separated, thus avoiding the catalyst from being deactivated by being encapsulated by the generated uranium oxide solid.

[0010] This application employs a supported catalyst with magnetic cobalt tetroxide as a carrier, utilizing an external magnetic field to separate the catalyst and the reaction product solid uranium dioxide online in a fluidized bed reactor, thereby improving the purity of uranium dioxide. This meets the industrial application requirements for the preparation of uranium dioxide from sodium uranyl carbonate via catalytic reduction. Summary of the Invention

[0011] This invention relates to a magnetic catalyst for the preparation of uranium dioxide from sodium uranyl carbonate, a preparation method thereof, and its application.

[0012] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0013] A method for preparing uranium dioxide using sodium uranyl carbonate catalyzed by a magnetic catalyst, wherein the catalyst consists of a support and an active metal, wherein the support is magnetic cobalt tetroxide, and the active metal is one or a mixture of two elements selected from Ru, Rh, Pt and Pd, and the mass percentage of the active metal in the catalyst is 0.1 to 1 wt%.

[0014] The catalyst preparation method is as follows: first, a cobalt tetroxide sample is prepared by citric acid complexation; then, the active metal is precipitated onto the cobalt tetroxide support by urea deposition sedimentation method, and the target catalyst is obtained after calcination and reduction treatment.

[0015] The catalyst preparation method is as follows: First, a cobalt-containing precursor, citric acid, ethylene glycol, and water are prepared into an aqueous solution containing the cobalt precursor in a molar ratio of 4-5:5-6:0.8-1.2. After complexation at 60-80℃ for 8-12 hours, the solution is vacuum dried in an oven at 80-120℃ for 12-24 hours and calcined at 450℃ for 2-4 hours to obtain a cobalt tetroxide sample.

[0016] An active metal precursor and urea were prepared into an active metal precursor solution at a molar ratio of 1:60 to 1:25. The solution was then impregnated onto a cobalt tetroxide sample, allowed to stand at 80-90℃ for 2-4 hours, dried at 110-120℃ for 6-8 hours, calcined at 200-400℃ for 2-4 hours under Ar and / or N2 atmosphere, and reduced at 300-600℃ for 2-4 hours under hydrogen atmosphere to obtain the target catalyst.

[0017] The catalyst preparation method wherein the cobalt precursor is one or both of cobalt nitrate hexahydrate or cobalt nitrate tetrahydrate;

[0018] The active metal precursor is one or more of chloroplatinic acid, rhodium trichloride, palladium chloride, or ruthenium trichloride.

[0019] The application of the catalyst is carried out in a fluidized bed reactor with an external magnetic field; the fluidized bed reactor is set vertically, the catalyst is placed in the middle of the fluidized bed reactor, and an electromagnetic field is provided outside the fluidized bed reactor;

[0020] First, the catalyst is confined in a fluidized bed reactor with an external magnetic field strength of 10–20 mT. Then, hydrogen gas is introduced into the fluidized bed reactor from the bottom at a flow rate of 1000–2000 mL / min. The catalyst tumbles up and down in the middle of the reactor. Finally, sodium uranyl carbonate eluent, preheated to 25–30 °C, is added to the fluidized bed reactor from the bottom at a flow rate of 20–30 g / min using a liquid pump. Under the action of the catalyst, sodium uranyl carbonate is reduced to tetravalent uranium carbonate. After being reduced to tetravalent uranium carbonate, sodium uranyl carbonate undergoes hydrolysis at 120–150 °C, and the resulting solid uranium dioxide settles to the bottom of the container.

[0021] Compared with existing technologies, the essential features of this invention are:

[0022] (1) The catalyst support cobalt tetroxide prepared by the present invention is obtained by citric acid complexation, which has a large specific surface area and is conducive to the dispersion of active component particles. The active component is prepared by urea precipitation, which has small particles, uniform distribution, and high activity. The catalyst has good catalytic activity for the hydrogen reduction of sodium uranyl carbonate to produce uranium dioxide.

[0023] (2) The catalyst support cobalt tetroxide is magnetic. In a fluidized bed reactor with an external magnetic field, the catalyst and the reaction product solid uranium dioxide are separated online, which can increase the purity of uranium dioxide to more than 99.5%.

[0024] (3) Compared with the traditional process for preparing uranium oxide, the process of preparing uranium oxide by reducing sodium uranyl carbonate with magnetic catalyst is simple, has a short process, does not produce wastewater, has low cost, and produces high purity uranium dioxide. It has obvious technical advantages and is more suitable for industrial application. Attached Figure Description

[0025] Figure 1 The XRD pattern of the 0.5Pt / Co3O4 catalyst prepared in Example 1 is shown below. Detailed Implementation

[0026] The following examples are provided to illustrate the invention in more detail, but the invention is not limited thereto.

[0027] Example 1

[0028] Preparation of 0.5Pt / Co3O4 (Pt content 0.5wt%)

[0029] First, 29.1g of cobalt nitrate hexahydrate, 25.2g of citric acid and 1.24g of ethylene glycol were added to water to make 500g, stirred in an 80℃ water bath for 8h, vacuum dried in an oven at 80℃ for 24h, and calcined at 450℃ for 4h to obtain a cobalt tetroxide sample.

[0030] A 10g mixed solution containing 0.11g chloroplatinic acid and 0.64g urea was impregnated onto a cobalt tetroxide sample. After standing at 90℃ for 2h and drying at 120℃ for 8h, the sample was calcined at 400℃ for 4h under an Ar atmosphere and reduced at 300℃ for 4h under a hydrogen atmosphere to obtain the target catalyst 0.5Pt / Co3O4 (the number before the catalyst represents the mass percentage of the active metal in the catalyst, the same below). Figure 1 The XRD pattern of the 0.5Pt / Co3O4 catalyst is shown. Only Co3O4 diffraction peaks are detected, with no Pt species diffraction peaks observed, indicating that the Pt species are highly dispersed on Co3O4. The specific surface area of ​​the catalyst is shown in Table 1.

[0031] Example 2

[0032] Preparation of 0.5Rh / Co3O4 (Rh content 0.5wt%)

[0033] The difference from Example 1 is that 0.08 g of rhodium trichloride was added instead of chloroplatinic acid, while the amounts of other materials and operating conditions were the same as in Example 1, resulting in a 0.5Rh / Co3O4 catalyst. The XRD pattern of the 0.5Rh / Co3O4 catalyst showed only diffraction peaks for Co3O4, with no diffraction peaks detected for Pt species. This indicates that Pt species are highly dispersed on Co3O4. The specific surface area results of the catalyst are shown in Table 1.

[0034] Example 3

[0035] Preparation of 0.5Pd / Co3O4 (Pd content 0.5 wt%)

[0036] The difference from Example 1 is that 0.07 g of palladium dichloride was added instead of chloroplatinic acid, while the amounts of other materials and operating conditions were the same as in Example 1, resulting in a 0.5Pd / Co3O4 catalyst. The XRD pattern of 0.5Rh / Co3O4 showed only diffraction peaks for Co3O4, with no diffraction peaks detected for Pd species, indicating that Pd species were highly dispersed on Co3O4. The specific surface area of ​​the catalyst is shown in Table 1.

[0037] Example 4

[0038] Preparation of 0.5Ru / Co3O4 (Ru content 0.5 wt%)

[0039] The difference from Example 1 is that 0.10 g of Ru trichloride was added instead of chloroplatinic acid, while the amounts of other materials and operating conditions were the same as in Example 1, resulting in a 0.5Ru / Co3O4 catalyst. The XRD pattern of the 0.5Ru / Co3O4 catalyst showed only diffraction peaks for Co3O4 and no diffraction peaks for Pt species were detected, indicating that Pt species were highly dispersed on Co3O4. The specific surface area of ​​the catalyst is shown in Table 1.

[0040] Example 5

[0041] Preparation of 0.1Pt / Co3O4 (Pt content 0.1 wt%)

[0042] The difference from Example 1 is that the amount of chloroplatinic acid used was 0.02 g, the amount of urea used was 0.13 g, and the reduction was performed with hydrogen at 300°C for 4 h. The amounts of other materials and operating conditions were the same as in Example 1, resulting in a 0.1 Pt / Co3O4 catalyst. The XRD pattern of the 0.1 Pt / Co3O4 catalyst showed only diffraction peaks for Co3O4, with no diffraction peaks detected for Pt species, indicating that Pt species were highly dispersed on Co3O4. The specific surface area of ​​the catalyst is shown in Table 1.

[0043] Example 6

[0044] Preparation of 1Pt / Co3O4 (Pt mass content 1 wt%)

[0045] The difference from Example 1 is that the amount of chloroplatinic acid used was 0.22 g, and the amount of urea used was 1.28 g. The amounts of other materials and operating conditions were the same as in Example 1, resulting in a 1Pt / Co3O4 catalyst. The XRD pattern of the 1Pt / Co3O4 catalyst showed only diffraction peaks for Co3O4, with no diffraction peaks detected for Pt species, indicating that the Pt species were highly dispersed on Co3O4. The specific surface area of ​​the catalyst is shown in Table 1.

[0046] Example 7

[0047] Preparation of 0.5Pt-0.5Pd / Co3O4 (Pt and Pd content are 0.5 wt%)

[0048] The difference from Example 1 is that 0.11g of chloroplatinic acid and 0.07g of palladium dichloride were added instead of chloroplatinic acid, the amount of urea was 1.28g, and the reduction was carried out with hydrogen at 600℃ for 2h. The amounts of other materials and operating conditions were the same as in Example 1, resulting in a 0.5Pt-0.5Pd / Co3O4 catalyst. The XRD pattern of 0.5Pt-0.5Pd / Co3O4 showed only diffraction peaks for Co3O4, with no diffraction peaks detected for Pt species, indicating that Pt species are highly dispersed on Co3O4. The specific surface area of ​​the catalyst is shown in Table 1.

[0049] Example 8

[0050] Preparation of 0.5Pt / Co3O4 (Pt content 0.5 wt%)

[0051] Unlike Example 1, 24.9 g of cobalt nitrate tetrahydrate was added instead of cobalt nitrate hexahydrate. The amounts of other materials and other operating conditions remained the same as in Example 1, yielding a 0.5Pt / Co3O4 catalyst. The XRD pattern of the 0.5Pt / Co3O4 catalyst showed only diffraction peaks for Co3O4, with no diffraction peaks detected for Pt species, indicating that Pt species were highly dispersed on Co3O4. The specific surface area of ​​the catalyst is shown in Table 1.

[0052] Comparative Example 1

[0053] Preparation of 0.5Pt / Fe3O4 (Pt content 0.5 wt%)

[0054] The difference in Example 1 is that 0.5Pt / Fe3O4 was prepared using the traditional impregnation method, and the specific surface area of ​​the catalyst is shown in Table 1.

[0055] Comparative Example 2

[0056] Preparation of 0.5Pt / Co2O3 (Pt content 0.5 wt%)

[0057] The difference in Example 1 is that commercially available Co2O3 was used, and 0.5Pt / Co2O3 was prepared by the traditional impregnation method. The specific surface area of ​​the catalyst is shown in Table 1.

[0058] Table 1. Relevant information on the catalysts of Examples 1-9 and Comparative Examples 1-2.

[0059]

[0060] Example 9

[0061] The reaction is carried out in a fluidized bed reactor with an external magnetic field; the fluidized bed reactor is set vertically, a catalyst is installed in the middle of the fluidized bed reactor, and an electromagnetic field is provided outside the fluidized bed reactor (Power Engineering, 2008, 28(6):940-944).

[0062] First, 2g of the 0.5Pt / Co3O4 catalyst prepared in Example 1 was confined to a fluidized bed reactor with an external magnetic field (10mT). Then, hydrogen gas was introduced into the fluidized bed reactor at a flow rate of 1000mL / min, causing the catalyst to tumble up and down in the reactor. Finally, sodium uranyl carbonate eluent, preheated to 30°C, was added to the fluidized bed reactor at a flow rate of 20g / min using a liquid high-pressure pump. Under the action of the catalyst, sodium uranyl carbonate was reduced to tetravalent uranium carbonate, which then underwent hydrolysis at 120°C. The resulting solid uranium dioxide settled to the bottom of the container. After 30 minutes, the uranium dioxide was collected, and the purity of the uranium dioxide was determined to be 99.8%. The experimental results are shown in Table 2.

[0063] Example 10

[0064] The difference from Example 9 is that 2g of the 0.5Rh / Co3O4 catalyst prepared in Example 2 was loaded into a fluidized bed reactor with an external magnetic field, while the amounts of other materials and other operating conditions were the same as in Example 9. The purity of uranium dioxide was 99.6%, and the test results are shown in Table 2.

[0065] Example 11

[0066] The difference from Example 9 is that 2g of the 0.5Pd / Co3O4 catalyst prepared in Example 3 was loaded into a fluidized bed reactor with an external magnetic field, while the amounts of other materials and other operating conditions were the same as in Example 9. The purity of uranium dioxide was 99.6%, and the test results are shown in Table 2.

[0067] Example 12

[0068] The difference from Example 9 is that 2g of the 0.5Ru / Co3O4 catalyst prepared in Example 4 was loaded into a fluidized bed reactor with an external magnetic field, while the amounts of other materials and other operating conditions were the same as in Example 9. The purity of uranium dioxide was 99.7%, and the experimental results are shown in Table 2.

[0069] Example 13

[0070] The difference from Example 9 is that 2g of the 0.1Pt / Co3O4 catalyst prepared in Example 5 was loaded into a fluidized bed reactor with an external magnetic field, while the amounts of other materials and other operating conditions were the same as in Example 9. The purity of uranium dioxide was 99.5%, and the test results are shown in Table 2.

[0071] Example 14

[0072] The difference from Example 9 is that 2g of the 1Pt / Co3O4 catalyst prepared in Example 6 was loaded into a fluidized bed reactor equipped with an external magnetic field (20mT). Hydrogen gas was then introduced into the fluidized bed reactor at a flow rate of 2000mL / min. Finally, sodium uranyl carbonate eluent, preheated to 30°C, was added to the fluidized bed reactor at a flow rate of 30g / min using a high-pressure liquid pump. Other material quantities and operating conditions were the same as in Example 9. The purity of uranium dioxide was 99.8%, and the experimental results are shown in Table 2.

[0073] Example 15

[0074] The difference from Example 9 is that 2g of the 0.5Pt-0.5Pd / Co3O4 catalyst prepared in Example 7 was loaded into a fluidized bed reactor with an external magnetic field. Other material amounts and operating conditions were the same as in Example 9. The purity of uranium dioxide was 99.7%, and the experimental results are shown in Table 2.

[0075] Example 16

[0076] The difference from Example 9 is that 2g of the 0.5Pt / Co3O4 catalyst prepared in Example 8 was loaded into a fluidized bed reactor with an external magnetic field, while the amounts of other materials and other operating conditions were the same as in Example 9. The purity of uranium dioxide was 99.6%, and the test results are shown in Table 2.

[0077] Comparative Example 3

[0078] Unlike Example 9, 2g of the 0.5Pt / Fe3O4 catalyst prepared in Comparative Example 1 was loaded into a fluidized bed reactor with an external magnetic field. The amounts of other materials and other operating conditions were the same as in Example 9. The purity of uranium dioxide was 75.5%. The results are shown in Table 2.

[0079] Comparative Example 4

[0080] Unlike Example 9, 2g of the 0.5Pt / Co2O3 catalyst prepared in Comparative Example 2 was loaded into a fluidized bed reactor with an external magnetic field. The amounts of other materials and other operating conditions were the same as in Example 9, and the purity of uranium dioxide was 61.3%.

[0081] Comparative Example 5

[0082] The difference from Example 9 is that 2g of 0.5Pt / SiO2 catalyst was loaded into a fluidized bed reactor with an external magnetic field. The amounts of other materials and other operating conditions were the same as in Example 9. The uranium dioxide product contained most of the catalyst solid particles and the purity of uranium dioxide was less than 50%.

[0083] Table 2. Test results of Examples 9-16 and Comparative Examples 3-5

[0084]

[0085]

[0086] Comparative analysis of results: As can be seen from Table 2, the uranium dioxide prepared by the catalyst of the present invention (Examples 9-16) has a higher purity than that prepared by other catalysts (Comparative Examples 3-5), with the purity of uranium dioxide prepared by the catalyst of the present invention reaching over 99.5%.

Claims

1. A method for preparing uranium dioxide using sodium uranyl carbonate catalyzed by a magnetic catalyst, characterized in that: The catalyst consists of two parts: a support and an active metal. The support is magnetic cobalt tetroxide, and the active metal is one or a mixture of two elements selected from Ru, Rh, Pt, and Pd. The mass percentage of the active metal in the catalyst is 0.1-1 wt%. The reaction takes place in a fluidized bed reactor with an external magnetic field; the fluidized bed reactor is vertically arranged, with a catalyst installed in the middle of the fluidized bed reactor and an electromagnetic field installed outside the fluidized bed reactor; First, the catalyst is confined in a fluidized bed reactor with an external magnetic field strength of 10-20 mT. Then, hydrogen gas is introduced into the fluidized bed reactor from the bottom at a flow rate of 1000-2000 mL / min. The catalyst tumbles up and down in the middle of the reactor. Finally, sodium uranyl carbonate eluent, preheated to 25-30°C, is added to the fluidized bed reactor from the bottom at a flow rate of 20-30 g / min using a liquid pump. Under the action of the catalyst, sodium uranyl carbonate is reduced to tetravalent uranium carbonate. After being reduced to tetravalent uranium carbonate under the action of the catalyst, it undergoes hydrolysis at 120-150°C, and the resulting solid uranium dioxide settles to the bottom of the container.

2. The method according to claim 1, characterized in that, The catalyst preparation process is as follows: first, a cobalt tetroxide sample is prepared by citric acid complexation; then, the active metal is precipitated onto the cobalt tetroxide support by urea deposition sedimentation method, and the target catalyst is obtained after calcination and reduction treatment.

3. The method according to claim 1 or 2, characterized in that, The specific preparation process of the catalyst is as follows: First, a cobalt-containing precursor, citric acid, ethylene glycol and water are prepared into an aqueous solution containing cobalt precursor in a molar ratio of 4~5:5~6:0.8~1.

2. After complexing at 60-80℃ for 8~12h, the solution is vacuum dried in an oven at 80~120℃ for 12~24h and calcined at 450℃ for 2~4h to obtain a cobalt tetroxide sample. An active metal precursor and urea were prepared into a solution containing the active metal precursor at a molar ratio of 1:60 to 1:

25. The solution was then impregnated onto a cobalt tetroxide sample, allowed to stand at 80-90℃ for 2-4 hours, dried at 110-120℃ for 6-8 hours, calcined at 200-400℃ for 2-4 hours under Ar and / or N2 atmosphere, and reduced at 300-600℃ for 2-4 hours under hydrogen atmosphere to obtain the target catalyst.

4. The method according to claim 3, characterized in that, The cobalt precursor is one or both of cobalt nitrate hexahydrate or cobalt nitrate tetrahydrate. The active metal precursor is one or more of chloroplatinic acid, rhodium trichloride, palladium chloride, or ruthenium trichloride.

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