A method for removing aminohydroxyurea from nitric acid solutions

Abstract

The application discloses a method for removing amino hydroxy urea in nitric acid solution, and relates to the technical field of spent fuel reprocessing, and comprises the following steps: S1, heating a to-be-processed nitric acid-containing solution to a set temperature; and S2, adding a noble metal catalyst into the to-be-processed solution to perform a catalytic oxidation reaction, so that the amino hydroxy urea in the nitric acid solution is decomposed. The method provided by the application can efficiently, safely, economically and environmentally remove the amino hydroxy urea in the nitric acid solution.

Description

Technical Field

[0001] This invention belongs to the field of spent fuel reprocessing technology, specifically relating to a method for removing aminohydroxyurea from nitric acid solution. Background Technology

[0002] In the PUREX process, uranium and plutonium separation and uranium purification are mainly achieved through reduction complexation separation. Aminohydroxyurea, as a reducing complexing agent, has attracted the attention of scientists and is gradually being applied to uranium and plutonium separation and uranium product purification.

[0003] In the uranium purification cycle, to remove plutonium and neptunium from uranium, an excess of reducing complexing agent is typically used in the 2D process stage to achieve plutonium complexation reduction and back-extraction, thereby purifying the uranium product. Therefore, 2DW waste liquid contains an excess of aminohydroxyurea. The thermal decomposition of aminohydroxyurea produces hydroxylamine, the presence of which poses a safety risk to the subsequent evaporative denitrification process of the 2DW waste liquid.

[0004] Currently, reprocessing plants in various countries mainly destroy residual reducing agents by introducing nitrogen oxides into the waste liquid. The nitrogen oxide oxidation decomposition method has at least the following disadvantages: 1. It consumes a large amount of chemical reagents due to the use of excessive nitrogen oxides; 2. Excess nitrogen oxides and a large amount of air used for degassing enter the radioactive waste gas purification system, increasing the waste gas treatment load and cost; 3. It increases the equipment required for gas generators, oxidation, and air degassing systems. Summary of the Invention

[0005] In view of the deficiencies in the existing technology, the purpose of this invention is to provide a method for removing aminohydroxyurea from nitric acid solution. This method can remove aminohydroxyurea from nitric acid solution efficiently, safely, economically, and environmentally.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] A method for removing aminohydroxyurea from nitric acid solution includes the following steps:

[0008] S1. Heat the nitric acid-containing liquid to be treated to the set temperature;

[0009] S2. A precious metal catalyst is added to the liquid to be treated to carry out a catalytic oxidation reaction, and the aminohydroxyurea in the nitric acid solution is decomposed.

[0010] Furthermore, the method for removing aminohydroxyurea from nitric acid solution as described above employs a suspended slurry bed intermittent reaction mode, with a reaction temperature of 30–90°C, the amount of the noble metal catalyst being 1.0%–5% of the mass of the liquid to be treated, and a reaction time of 10–60 min.

[0011] Furthermore, in the method for removing aminohydroxyurea from nitric acid solution as described above, the nitric acid-containing solution to be treated comprises 1.0–2.5 mol / L nitric acid, 0.01–0.5 mol / L aminohydroxyurea, and 10 -2 ~10 -7 g / L Pu, 10 -2 ~10 -7 g / LU, 10 -2 ~10 -7 g / L Np, 0.1wt% TBP.

[0012] Furthermore, in the method for removing aminohydroxyurea from nitric acid solution as described above, the noble metal catalyst comprises a support and an active component dispersed on the surface of the support. The support is a silicon-based support or a carbon-based support, and the active component is one or a combination of two of the following metals: ruthenium, iridium, rhodium, palladium, and platinum.

[0013] Furthermore, in the method for removing aminohydroxyurea from nitric acid solution as described above, the active component in the noble metal catalyst has a mass fraction of 1.5% to 10%, and the metal nanoparticles dispersed on the surface of the support have a particle size of no more than 50 nm.

[0014] Furthermore, in the method for removing aminohydroxyurea from nitric acid solution as described above, the noble metal catalyst is resistant to nitric acid, radiation, and organic phases.

[0015] Furthermore, in the method for removing aminohydroxyurea from nitric acid solution as described above, the silicon-based support and the carbon-based support have a density of not less than 500 μm. 2 Specific surface area per g.

[0016] Furthermore, in the method for removing aminohydroxyurea from nitric acid solution as described above, the silicon-based carrier is silica, ZSM-5, or a reshaped spherical or cylindrical silicon-based carrier; the carbon-based carrier is coconut shell activated carbon, fruit shell activated carbon, or a reshaped spherical or cylindrical carbon-based carrier.

[0017] Furthermore, in the method for removing aminohydroxyurea from nitric acid solution as described above, the support of the noble metal catalyst is pretreated before use to remove acid-soluble impurities from the support.

[0018] Furthermore, in the method for removing aminohydroxyurea from nitric acid solution as described above, the pretreatment specifically involves immersing the carrier in an acidic solution with a concentration of not less than 1 mol / L.

[0019] Compared with the prior art, the method for removing aminohydroxyurea from nitric acid solution provided by the present invention has the following beneficial effects:

[0020] 1. This method avoids excessive nitrogen oxides and the use of large amounts of air for degassing, reduces radioactive waste gas, and lowers the waste gas treatment load and cost;

[0021] 2. Avoiding the use of excessive amounts of nitrogen oxides reduces the equipment required for the preparation, transportation, and storage of nitrogen oxides, and greatly reduces the use of chemical reagents;

[0022] 3. This invention uses a catalytic method to remove aminohydroxyurea from plutonium-containing nitric acid solution. Compared with the traditional method of adding nitrogen oxides, it is cleaner, more environmentally friendly, and has no safety hazards. Attached Figure Description

[0023] Figure 1 This is a flowchart of a method for removing aminohydroxyurea from nitric acid solution according to an embodiment of the present invention. Detailed Implementation

[0024] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0025] This invention provides a method for removing aminohydroxyurea from nitric acid solution, mainly through noble metal catalyst catalytic oxidation technology to decompose aminohydroxyurea in the nitric acid-containing solution. Figure 1 As shown, the method includes the following:

[0026] S1. Heat the nitric acid-containing liquid to be treated to the set temperature;

[0027] S2. A precious metal catalyst is added to the liquid to be treated to carry out a catalytic oxidation reaction, and the aminohydroxyurea in the nitric acid solution is decomposed.

[0028] The nitric acid-containing feed solution described in this invention contains nitric acid, aminohydroxyurea, trace amounts of uranium, neptunium, plutonium, fragmented elements, and a small amount of organic matter. In one specific embodiment, the feed solution includes 1.0–2.5 mol / L nitric acid, 0.01–0.5 mol / L aminohydroxyurea, and 10 -2 ~10 -7 g / L Pu, 10 -2 ~10 -7 g / LU, 10 -2 ~10 -7 g / L Np, 0.1wt% TBP.

[0029] The noble metal catalyst used comprises a support and an active component dispersed on the surface of the support. Preferably, the support is a silicon-based support or a carbon-based support, and the active component is one or a combination of two of the following metals: ruthenium, iridium, rhodium, palladium, and platinum. The mass fraction of the active component in the catalyst is 1.5% to 10%, and the particle size of the metal nanoparticles dispersed on the surface of the support is no greater than 50 nm. This noble metal catalyst is resistant to nitric acid, radiation, and organic phases.

[0030] Preferably, the silicon-based carrier is silicon dioxide, ZSM-5, or a reshaped spherical or cylindrical silicon-based carrier; the carbon-based carrier is coconut shell activated carbon, fruit shell activated carbon, or a reshaped spherical or cylindrical carbon-based carrier. The silicon-based and carbon-based carriers have a thickness of not less than 500 μm. 2 Specific surface area per g.

[0031] Preferably, the support for the noble metal catalyst needs to be pretreated before use to remove acid-soluble impurities. The pretreatment method specifically involves immersing the support in an acidic solution of not less than 1 mol / L, such as nitric acid, sulfuric acid, or hydrochloric acid, to remove acid-soluble impurities.

[0032] Preferably, when removing aminohydroxyurea from the liquid to be treated, a suspended slurry bed intermittent reaction method is adopted, with a reaction temperature of 30-90℃, a catalyst dosage of 1.0%-5% of the mass of the liquid to be treated, and a reaction time of 10-60 min.

[0033] Example 1

[0034] A round-bottom flask containing 10 mL of the solution to be treated was heated to 80°C. 0.1 g (dry weight) of 5% Ru / ZSM-5 (spherical) catalyst was added. The solution to be treated contained 1.5 mol / L nitric acid, 0.1 mol / L aminohydroxyurea, and 0.1 wt% TBP. After the reaction was complete, a sample was taken to test the aminohydroxyurea content in the solution. The reducing agent content in the treated solution was less than 10%. -4 mol / L.

[0035] Example 2

[0036] A round-bottom flask containing 10 mL of the solution to be treated was heated to 80°C. 0.5 g (dry weight) of 3% Ru / ZSM-5 (spherical) catalyst was added. The solution to be treated contained 1.5 mol / L nitric acid, 0.1 mol / L aminohydroxyurea, and 0.1 wt% TBP. After the reaction was complete, a sample was taken to test the aminohydroxyurea content in the solution. The reducing agent content in the treated solution was less than 10%. -4 mol / L.

[0037] Example 3

[0038] A round-bottom flask containing 10 mL of the solution to be treated was heated to 80°C. 0.1 g (dry weight) of 5% Rh / ZSM-5 (spherical) catalyst was added. The solution to be treated contained 2.5 mol / L nitric acid, 0.5 mol / L aminohydroxyurea, and 0.1 wt% TBP. After the reaction was complete, a sample was taken to test the aminohydroxyurea content in the solution. The reducing agent content in the treated solution was less than 10%. -4 mol / L.

[0039] Example 4

[0040] A round-bottom flask containing 10 mL of the solution to be treated was heated to 80°C. 0.1 g (dry weight) of 5% Ru / ZSM-5 (spherical) catalyst was added. The solution to be treated contained 1.5 mol / L nitric acid, 0.2 mol / L aminohydroxyurea, and 0.1 wt% TBP. After the reaction was complete, a sample was taken to test the aminohydroxyurea content in the solution. The reducing agent content in the treated solution was less than 10%. -4 mol / L.

[0041] Example 5

[0042] A round-bottom flask containing 10 mL of the solution to be treated was heated to 60°C. 0.5 g (dry weight) of 5% Ru / C (tablet) catalyst was added. The solution to be treated contained 1.0 mol / L nitric acid, 0.1 mol / L aminohydroxyurea, and 0.1 wt% TBP. After the reaction was complete, a sample was taken to test the aminohydroxyurea content in the solution. The reducing agent content in the treated solution was less than 10%. -4 mol / L.

[0043] Example 6

[0044] A round-bottom flask containing 10 mL of the solution to be treated was heated to 90°C. 0.1 g (dry weight) of 3% Rh / C (tablet) catalyst was added. The solution to be treated contained 1.5 mol / L nitric acid, 0.1 mol / L aminohydroxyurea, and 0.1 wt% TBP. After the reaction was complete, a sample was taken to test the aminohydroxyurea content in the solution. The reducing agent content in the treated solution was less than 10%. -4 mol / L.

[0045] Example 7

[0046] A round-bottom flask containing 10 mL of the solution to be treated was heated to 80°C. 0.2 g (dry weight) of 5% Ru-1% Pt / C (column-shaped) catalyst was added. The solution to be treated contained 1.5 mol / L nitric acid, 0.1 mol / L aminohydroxyurea, and 0.1 wt% TBP. After the reaction was complete, a sample was taken to test the aminohydroxyurea content in the solution. The reducing agent content in the treated solution was less than 10%. -4 mol / L.

[0047] Example 8

[0048] A round-bottom flask containing 10 mL of the solution to be treated was heated to 80°C. 0.2 g (dry weight) of 5% Rh-1% Ru / C (column-shaped) catalyst was added. The solution to be treated contained 1.5 mol / L nitric acid, 0.1 mol / L aminohydroxyurea, and 0.1 wt% TBP. After the reaction was complete, a sample was taken to test the aminohydroxyurea content in the solution. The reducing agent content in the treated solution was less than 10%. -4 mol / L.

[0049] Example 9

[0050] A round-bottom flask containing 10 mL of the solution to be treated was heated to 80°C. 0.2 g (dry weight) of 5% Ru-1% Ir / C (column-shaped) catalyst was added. The solution to be treated contained 1.5 mol / L nitric acid, 0.1 mol / L aminohydroxyurea, and 10... -4 g / L Pu, 10 -3 g / LU, 10 -4 After the reaction was completed (g / L Np, 0.1wt% TBP), the aminohydroxyurea content in the feed solution was measured. The reducing agent content in the treated feed solution was less than 10 g / L Np, 0.1wt% TBP. -4 mol / L.

[0051] Example 10

[0052] A round-bottom flask containing 10 mL of the solution to be treated was heated to 80°C. 0.2 g (dry weight) of 5% Ru-1% Ir / C (column-shaped) catalyst was added. The solution to be treated contained 1.5 mol / L nitric acid, 0.1 mol / L aminohydroxyurea, and 10... -3 g / L Pu, 10 -2 g / LU, 10 -3 After the reaction was completed (g / L Np, 0.1wt% TBP), the aminohydroxyurea content in the feed solution was measured. The reducing agent content in the treated feed solution was less than 10 g / L Np, 0.1wt% TBP. -4 mol / L.

[0053] The method for removing aminohydroxyurea from nitric acid solution provided by this invention decomposes aminohydroxyurea in the nitric acid-containing solution through precious metal catalyst catalytic oxidation technology. This method avoids excessive nitrogen oxides and the use of large amounts of air for degassing, reduces radioactive waste gas, and lowers the waste gas treatment load and cost; it also reduces the equipment for nitrogen oxide preparation, transportation and storage, and greatly reduces the use of chemical reagents; compared with the traditional method of adding nitrogen oxides, this method is cleaner, more environmentally friendly and has no safety hazards.

[0054] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention is also intended to include these modifications and variations.

Claims

1. A method for removing aminohydroxyurea from a nitric acid solution, wherein the nitric acid solution is spent fuel reprocessing 2DW wastewater; the method comprises the following steps: S1. Heat the nitric acid-containing solution to be treated to 30~90℃, wherein the nitric acid-containing solution comprises 1.0~2.5 mol / L nitric acid, 0.01~0.5 mol / L aminohydroxyurea, and 10 -2 ~ 10 -7 g / L Pu, 10 -2 ~10 -7 g / LU, 10 -2 ~10 -7 g / L Np, 0.1wt% TBP; S2. A noble metal catalyst is added to the solution to be treated to carry out a catalytic oxidation reaction, in which the aminohydroxyurea in the nitric acid solution is decomposed. The noble metal catalyst includes a support and an active component dispersed on the surface of the support. The support is a silicon-based support or a carbon-based support. The active component is one or a combination of two of the following: ruthenium, iridium, rhodium, palladium, and platinum. The amount of the noble metal catalyst is 1.0% to 5% of the mass of the solution to be treated, the reaction time is 10 to 60 min, and the aminohydroxyurea content of the treated solution is less than 10%. -4 mol / L.

2. The method for removing aminohydroxyurea from nitric acid solution according to claim 1, characterized in that, A suspended slurry bed intermittent reaction method is adopted.

3. The method for removing aminohydroxyurea from nitric acid solution according to claim 2, characterized in that, The active component in the noble metal catalyst has a mass fraction of 1.5% to 10%, and the metal nanoparticles dispersed on the surface of the support have a particle size of no more than 50 nm.

4. The method for removing aminohydroxyurea from nitric acid solution according to any one of claims 1-3, characterized in that, The noble metal catalyst is resistant to nitric acid, radiation, and organic phases.

5. The method for removing aminohydroxyurea from nitric acid solution according to claim 4, characterized in that, The silicon-based and carbon-based supports have a minimum thickness of 500 μm. 2 Specific surface area per g.

6. The method for removing aminohydroxyurea from nitric acid solution according to claim 5, characterized in that, The silicon-based carrier is silicon dioxide, ZSM-5, or a reshaped spherical or cylindrical silicon-based carrier; the carbon-based carrier is coconut shell activated carbon, fruit shell activated carbon, or a reshaped spherical or cylindrical carbon-based carrier.

7. The method for removing aminohydroxyurea from nitric acid solution according to claim 5 or 6, characterized in that, Before use, the support of the noble metal catalyst is pretreated to remove impurities that are easily soluble in acid.

8. The method for removing aminohydroxyurea from nitric acid solution according to claim 7, characterized in that, The pretreatment specifically involves immersing the carrier in an acidic solution with a concentration of not less than 1 mol / L.

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