Compound as well as preparation method and application thereof

Abstract

The invention provides a compound as well as a preparation method and application thereof. The compound is represented by the following formula (I) wherein R is a C1 to C14 alkyl group. The compound can be used for efficiently extracting tetravalent plutonium in a spent fuel post-treatment process, and is wide in applicable nitric acid concentration and high in extraction efficiency.

Description

Technical Field

[0001] This application relates to the field of spent fuel reprocessing technology, and in particular to a compound, its preparation method, and its application. Background Technology

[0002] Nuclear energy, as a clean energy source, has become an indispensable part of the future energy system. The safe, reliable and efficient disposal of spent fuel generated from the operation of nuclear power plants is a key aspect of nuclear energy utilization. Its main purpose is to separate, purify and extract uranium and plutonium contained in spent fuel.

[0003] Plutonium, as a strategic material, plays a crucial role in nuclear power generation and isotope batteries. Extracting plutonium from spent fuel or irradiated targets is challenging because irradiated spent fuel contains not only large amounts of uranium and plutonium, but also significant amounts of fission products, radiolysis products, and minor actinides such as strontium, cesium, zirconium, iron, neptunium, americium, and lanthanides. Currently, commercially available neutral phosphate ester extractants, such as tributyl phosphate (TBP), have good extraction capabilities for both tetravalent and hexavalent actinides (U(VI), Pu(IV)), making it impossible to separate and purify tetravalent plutonium using only this type of extractant. Furthermore, since TBP is slightly soluble in water, it may form a third phase (red oil) during extraction when plutonium concentrations are high or when impurity ions such as zirconium are present, thus affecting extraction efficiency and posing significant safety hazards to the extraction process.

[0004] Therefore, for the reasons mentioned above, the development of efficient tetravalent plutonium extractants is of great practical significance for the efficient separation of plutonium and the utilization of nuclear energy. Summary of the Invention

[0005] In view of this, the purpose of this application is to provide a compound, its preparation method, and its application. This compound can efficiently extract tetravalent plutonium in spent fuel reprocessing processes, is applicable to a wide range of nitric acid concentrations, and exhibits high extraction efficiency.

[0006] The first aspect of this application provides a compound, which is represented by formula (I).

[0007]

[0008] Wherein, R is a C1 to C14 alkyl group.

[0009] In some embodiments, R is a C6 to C10 alkyl group.

[0010] In some embodiments, R is a straight-chain C8 alkyl group.

[0011] A second aspect of this application provides a method for preparing the compound described in the first aspect, the method comprising the following steps:

[0012] Step 1: In the presence of 4-dimethylaminopyridine and triethylamine, dialkylamine NH(R)2 is reacted with chloroacetyl chloride in a solvent to give the compound shown in formula (II), wherein R is as defined above;

[0013] ClCH2CON(R)2(II)

[0014] Step 2: Under an inert gas atmosphere and in the presence of sodium hydride, triethanolamine is reacted with the compound shown in formula (II) in a solvent to obtain the compound shown in formula (I).

[0015] In some embodiments, in step 1, the reaction temperature is 0–5°C, and / or the reaction time is 6–12 hours, and / or the solvent is selected from one or more of anhydrous dichloromethane, anhydrous tetrahydrofuran, anhydrous dimethylformamide, and anhydrous acetonitrile.

[0016] In some embodiments, in step 2, the reaction temperature is 10–60°C, and / or the reaction time is 6–24 hours, and / or the solvent is selected from one or more of anhydrous tetrahydrofuran, anhydrous dimethylformamide, anhydrous acetonitrile, and anhydrous dichloromethane.

[0017] A third aspect of this application provides the use of the compound of the first aspect in the extraction of tetravalent plutonium in a spent fuel reprocessing process, the use comprising the following steps:

[0018] Step 11: Dissolve the compound shown in formula (I) in an organic solvent to obtain an organic phase;

[0019] Step 12: Mix spent fuel with an aqueous nitric acid solution to obtain an aqueous phase;

[0020] Step 13: Mix the organic phase and the aqueous phase, and stir for 0.5–15 minutes; and

[0021] Step 14: After stirring, separate the organic phase and the aqueous phase to extract tetravalent plutonium partially or completely in the organic phase.

[0022] In some embodiments, in step 12, the concentration of nitric acid in the nitric acid aqueous solution is 1.0 to 8.0 mol / L.

[0023] In some embodiments, in step 12, the concentration of nitric acid in the nitric acid aqueous solution is 2.0 to 8.0 mol / L.

[0024] In some embodiments, in step 11, the organic solvent is selected from one or more of alkane and alcohol organic solvents.

[0025] In some embodiments, in step 11, the concentration of the compound represented by formula (I) in the organic phase is 0.01 to 0.2 mol / L.

[0026] The compound disclosed in this application can be used as an extractant for extracting tetravalent plutonium in spent fuel reprocessing. Compared to tributyl phosphate, a commonly used extractant in related technologies, the compound of this application does not contain non-combustible phosphorus, conforming to the carbon, nitrogen, oxygen, and hydrogen (CNOH) principles of green and sustainable development. The compound structure of this application includes a nitrogen-centered triangular structure, an amide group, and a flexible ether oxygen chain structure. Through the combined action of these structures, highly efficient extraction of tetravalent plutonium from acidic aqueous solutions of spent fuel can be achieved, with an extraction partition ratio as high as 76. This extractant is suitable for acidic aqueous solutions with nitric acid concentrations of 1.0–8.0 mol / L, covering a wide range of nitric acid concentrations and exhibiting high extraction efficiency. Attached Figure Description

[0027] Figure 1 The proton NMR spectrum of the compound of formula (I-1) prepared in Preparation Example 1 is shown.

[0028] Figure 2 The carbon NMR spectrum of the compound of formula (I-1) prepared in Preparation Example 1 is shown. Detailed Implementation

[0029] The technical solutions in the embodiments of this application will be clearly and completely described below in conjunction with the implementation methods of this application. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments in this application without inventive effort are within the scope of protection of this application.

[0030] Throughout this specification, unless otherwise specified, the terminology used herein should be understood as having the meaning commonly used in the art. Therefore, unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains. In the event of any conflict, this specification shall prevail.

[0031] It should be noted that, in this document, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a product or method that comprises a list of elements includes not only the elements expressly stated, but also other elements not expressly listed, or elements inherent to implementing the product, method, or apparatus. Unless otherwise specified, an element defined by the phrase "comprising one..." does not exclude the presence of other related elements in the product or method that includes that element.

[0032] In related technologies, tributyl phosphate is used as the extractant for extracting metal ions from spent fuel dissolution liquids. It has a good affinity for both uranium and plutonium. Therefore, to obtain plutonium products with high purity, a large number of chemical separation processes are required. At the same time, it is necessary to precisely adjust the valence state of plutonium to reduce its affinity for tributyl phosphate, thereby separating it from uranium.

[0033] Furthermore, tributyl phosphate contains phosphorus, making it impossible to completely incinerate, which contradicts the CNOH principle of green and sustainable development. Therefore, developing a novel, environmentally friendly extractant that complies with CNOH principles and exhibits high selectivity for tetravalent plutonium to obtain high-purity plutonium products through simple chemical separation would not only effectively reduce process complexity but also decrease the amount of toxic and harmful chemicals such as nitric acid and kerosene used in plutonium extraction. This has significant practical implications for the efficient, green, and sustainable development of nuclear energy.

[0034] In view of the above, the first aspect of this application provides a compound. The compound is represented by formula (I):

[0035]

[0036] Wherein, R is a C1 to C14 alkyl group.

[0037] The compound disclosed in this application can be used as an extractant for extracting tetravalent plutonium in spent fuel reprocessing. Compared to tributyl phosphate, a commonly used extractant in related technologies, the compound of this application does not contain non-combustible phosphorus, conforming to the carbon, nitrogen, oxygen, and hydrogen (CNOH) principles of green and sustainable development. The compound structure of this application includes a nitrogen-centered triangular structure, an amide group, and a flexible ether oxygen chain structure. Through the combined action of these structures, highly efficient extraction of tetravalent plutonium from acidic aqueous solutions of spent fuel can be achieved, with an extraction partition ratio as high as 76. This extractant is suitable for acidic aqueous solutions with nitric acid concentrations of 1.0–8.0 mol / L. It has a wide applicable nitric acid concentration range and high extraction efficiency.

[0038] The term "alkyl" refers to a branched, straight-chain, or cyclic saturated aliphatic hydrocarbon group, which can be represented as -C. n H 2n+1 Where n represents the number of carbon atoms. "C1 to C14 alkyl" refers to alkyl groups having 1 to 14 carbon atoms, such as C1, C2, C3, C4, C5, C6, C7, C8, C9, C10, C11, C12, C13, C14 alkyl groups, or any range of two of these values. Examples of alkyl groups include, but are not limited to: methyl, ethyl, n-propyl, isopropyl, n-butyl, tert-butyl, n-pentyl, n-hexyl, n-heptyl, n-octyl, n-nonyl, or n-decyl.

[0039] In some embodiments, R in formula (I) can be a C6 to C10 alkyl group, and optionally R can be a straight-chain C8 alkyl group. Thus, the alkyl chain on the nitrogen atom in the amide group has appropriate length and flexibility, which is beneficial for the complexation of the compound shown in formula (I) with tetravalent plutonium, thereby improving the extraction effect.

[0040] A second aspect of this application provides a method for preparing the compound described in the first aspect of this application. The method includes the following steps:

[0041] Step 1: In the presence of 4-dimethylaminopyridine and triethylamine, dialkylamine NH(R)2 is reacted with chloroacetyl chloride in a solvent to give the compound shown in formula (II), wherein R is as defined above;

[0042] ClCH2CON(R)2(II)

[0043] Step 2: Under an inert gas atmosphere and in the presence of sodium hydride, triethanolamine is reacted with the compound shown in formula (II) in a solvent to obtain the compound shown in formula (I).

[0044] The preparation method of this application is schematically illustrated by the following reaction formula.

[0045]

[0046] In some embodiments, the reaction temperature in step 1 can be 0–5°C, optionally 0°C, 1°C, 2°C, 3°C, 4°C, or 5°C. In some embodiments, the reaction time in step 1 can be 6–12 hours, optionally 8–12 hours, optionally 8 hours. In some embodiments, the solvent in step 1 can be selected from one or more of anhydrous dichloromethane, anhydrous tetrahydrofuran, anhydrous dimethylformamide, and anhydrous acetonitrile, optionally anhydrous dichloromethane. In step 1, triethylamine is mainly used to provide basicity, and 4-dimethylaminopyridine is used as a catalyst for the reaction of acyl chlorides with amine compounds to form amide compounds. The presence of these substances promotes the reaction towards the target reactant.

[0047] In some embodiments, the reaction temperature in step 2 can be 10–60°C, optionally 10°C, 20°C, 30°C, 40°C, 50°C, 55°C, or 60°C, but is not limited thereto. In some embodiments, the reaction time in step 2 can be 6–24 hours, optionally 8–20 hours, optionally 8–16 hours, optionally 12 hours, but is not limited thereto. In some embodiments, the solvent in step 2 can be selected from one or more of anhydrous tetrahydrofuran, anhydrous dichloromethane, anhydrous dimethylformamide, and anhydrous acetonitrile, optionally anhydrous tetrahydrofuran.

[0048] When the reaction needs to be carried out in an inert gas atmosphere, the inert gas can be selected from helium, nitrogen, argon, etc. Optionally, argon is selected as the inert gas. By carrying out the reaction in an inert gas atmosphere, interference from external gases such as oxygen and moisture can be prevented from affecting the reaction system.

[0049] A third aspect of this application provides the use of the compound described in the first aspect for extracting tetravalent plutonium in a spent fuel reprocessing process. The use includes the following steps:

[0050] Step 11: Dissolve the compound shown in formula (I) in an organic solvent to obtain an organic phase;

[0051] Step 12: Mix spent fuel with an aqueous nitric acid solution to obtain an aqueous phase;

[0052] Step 13: Mix the organic phase and the aqueous phase, and stir for 0.5–15 minutes; and

[0053] Step 14: After stirring, separate the organic phase and the aqueous phase to extract tetravalent plutonium partially or completely in the organic phase.

[0054] In some embodiments, in step 12, the concentration of nitric acid in the aqueous nitric acid solution can be 1.0–8.0 mol / L. Exemplarily, the concentration of nitric acid in the aqueous nitric acid solution can be 1.0 mol / L, 2.0 mol / L, 3.0 mol / L, 4.0 mol / L, 5.0 mol / L, 6.0 mol / L, 7.0 mol / L, 8.0 mol / L, or a range consisting of any two of these values, but is not limited thereto. The compound represented by formula (I) of this application exhibits high stability over a wide range of nitric acid concentrations, reducing the likelihood of decomposition and facilitating the efficient extraction of tetravalent plutonium.

[0055] In some embodiments, in step 13, the organic phase and the aqueous phase are mixed and stirred for 0.5 to 15 minutes. Exemplarily, the stirring time can be 0.5 minutes, 1 minute, 2 minutes, 3 minutes, 4 minutes, 5 minutes, 10 minutes, 15 minutes, or any range of two such values, but is not limited thereto. Stirring for the above-mentioned times facilitates the reaching of extraction equilibrium between the organic and aqueous phases.

[0056] In some embodiments, in step 11, the organic solvent is selected from one or more of alkanes, alcohols, 3-nitrotrifluorotoluene, and hydrogenated tetrapropylene. Alkanes may be selected from one or more of alkanes with 8 to 14 carbon atoms, optionally with 12 carbon atoms. Alcohols may be selected from one or more of n-octanol, n-decanol, isodecanol, and nonanol. Optionally, the organic solvent is selected from a mixture of n-dodecane and isodecanol. Optionally, the volume ratio of n-dodecane to isodecanol is 95:5. These solvents are immiscible with water and have low solubility in water. The density difference between these solvents and water facilitates phase separation from the aqueous phase, thereby improving extraction efficiency.

[0057] In some embodiments, in step 11, the concentration of the compound represented by formula (I) in the organic phase can be 0.01 to 0.2 mol / L. Exemplarily, the concentration of the compound represented by formula (I) in the organic phase can be 0.01 mol / L, 0.02 mol / L, 0.04 mol / L, 0.06 mol / L, 0.08 mol / L, 0.1 mol / L, 0.2 mol / L, or a value within a range of any two of these values, but is not limited thereto.

[0058] The present application will be described in further detail below with reference to specific embodiments. The purpose of this description is merely illustrative and not intended to limit the scope of this disclosure.

[0059] In the following embodiments, unless otherwise specified, all components used are commercially available products. Furthermore, all equipment and instruments involved are commercially available standardized products, and their operating conditions and parameter settings are in accordance with the standard instructions provided by the equipment manufacturer.

[0060] Preparation Example 1: Preparation of the compound shown in formula (I-1)

[0061] Prepare the compound shown in formula (I-1) according to the following reaction formula.

[0062]

[0063] 1. Preparation of compound ClCH2CON(n-C8H) 17 )2

[0064] (1) Under argon protection, 10.0 g of dioctylamine was dissolved in 50 mL of anhydrous dichloromethane;

[0065] (2) Add 0.1 g of 4-dimethylaminopyridine and 10 mL of triethylamine to the system in (1), and lower the temperature of the system to 0 °C;

[0066] (3) Slowly add 20 mL of anhydrous dichloromethane solution containing 10.0 g of chloroacetyl chloride to the system in (2) and stir. React for 12 hours.

[0067] (4) The solvent was evaporated to dryness to obtain the compound ClCH2CON(n-C8H). 17 )2.

[0068] 2. Preparation of the compound shown in formula (I-1)

[0069] (1) Under an argon protective atmosphere, 1.43 g of 60% sodium hydride (NaH) was added to 20 mL of anhydrous tetrahydrofuran;

[0070] (2) Lower the system temperature to 0℃;

[0071] (3) Dissolve 1g of triethanolamine in 5mL of anhydrous tetrahydrofuran;

[0072] (4) At 0℃, slowly add the solution from step (3) to the solution from step (1) and stir for 15 minutes;

[0073] (5) 10g of compound ClCH2CON(n-C8H) 17 )2 Dissolved in 20 mL of anhydrous tetrahydrofuran;

[0074] (6) Slowly add the solution from step (5) to the solution from step (4) while stirring slowly until the temperature reaches room temperature;

[0075] (7) Heat the liquid oil bath obtained in step (6) to 55°C and continuously stir and reflux for 12 hours;

[0076] (8) Slowly add 20 mL of saturated sodium bicarbonate aqueous solution to quench the reaction;

[0077] (9) Add 20 mL of ethyl acetate;

[0078] (10) Separate the organic phase and wash it three times with 30 mL of saturated sodium chloride solution;

[0079] (11) Separate the organic phase and dry it with anhydrous magnesium sulfate;

[0080] (12) Rotary evaporate the organic phase until it becomes thick;

[0081] (13) The compound shown in formula (I-1) was purified by column chromatography using silica gel as the stationary phase and ethyl acetate as the mobile phase, with a yield of 83%.

[0082] The compound represented by formula (I-1) was subjected to 1H and 1C NMR spectra (400 MHz). The solvent used in the tests was deuterated chloroform. The test results are shown in... Figure 1 and Figure 2 middle.

[0083] Example 1

[0084] 0.1 mol of the compound represented by formula (I-1) was used as the extractant and dissolved in 1 L of n-dodecane solution containing 5% isodecanol to prepare an organic phase of 0.1 mol / L. 1 mL of this organic phase was mixed with an equal volume of an aqueous phase containing 4.0 mol / L nitric acid and 1 mg / L tetravalent plutonium and stirred for 5 minutes. The organic and aqueous phases were then separated, and the concentrations of plutonium in both phases were measured and the partition ratio was calculated. The resulting partition ratio was 8.6.

[0085] The formula for calculating the distribution ratio is: Distribution ratio = Plutonium concentration in the organic phase ÷ Plutonium concentration in the aqueous phase.

[0086] The method for testing plutonium concentration in the aqueous and organic phases is as follows: After separating the aqueous and organic phases, the solvents are evaporated by heating them separately in an electric furnace at 300°C to obtain radioactive sources containing only metal elements. Then, the activity of the radioactive sources in the aqueous and organic phases is analyzed by an alpha spectrometer, and the concentration of plutonium in the original aqueous and organic phases is obtained by comparing with a standard source.

[0087] Example 2

[0088] 0.1 mol of the compound represented by formula (I-1) was used as the extractant and dissolved in 1 L of n-dodecane solution containing 5% isodecanol to prepare an organic phase of 0.1 mol / L. 1 mL of this organic phase was mixed with an equal volume of an aqueous phase containing 6.0 mol / L nitric acid and 1 mg / L tetravalent plutonium and stirred for 5 minutes. The organic and aqueous phases were then separated, and the concentrations of plutonium in both phases were measured and the partition ratio was calculated. The resulting partition ratio was 19.1.

[0089] Example 3

[0090] 0.1 mol of the compound represented by formula (I-1) was used as the extractant and dissolved in 1 L of n-dodecane solution containing 5% isodecanol to prepare an organic phase of 0.1 mol / L. 1 mL of this organic phase was mixed with an equal volume of an aqueous phase containing 2.0 mol / L nitric acid and 1 mg / L tetravalent plutonium and stirred for 5 minutes. The organic and aqueous phases were then separated, and the concentrations of plutonium in both phases were measured and the partition ratio was calculated. The resulting partition ratio was 4.3.

[0091] Example 4

[0092] 0.1 mol of the compound represented by formula (I-1) was used as the extractant and dissolved in 1 L of n-dodecane solution containing 5% isodecanol to prepare an organic phase of 0.1 mol / L. 1 mL of this organic phase was mixed with an equal volume of an aqueous phase containing 7.0 mol / L nitric acid and 1 mg / L tetravalent plutonium and stirred for 5 minutes. The organic and aqueous phases were then separated, and the concentrations of plutonium in both phases were measured and the partition ratio was calculated. The resulting partition ratio was 38.6.

[0093] Example 5

[0094] 0.1 mol of the compound represented by formula (I-1) was used as the extractant and dissolved in 1 L of n-dodecane solution containing 5% isodecanol to prepare an organic phase of 0.1 mol / L. 1 mL of this organic phase was mixed with an equal volume of an aqueous phase containing 8.0 mol / L nitric acid and 1 mg / L tetravalent plutonium and stirred for 5 minutes. The organic and aqueous phases were then separated, and the plutonium concentrations in both phases were measured and the partition ratio was calculated. The resulting partition ratio was 76.

[0095] Comparative Example 1

[0096] 0.1 mol of tributyl phosphate (TBP) was added to 1 L of a dodecane solution containing 5% isodecanol to prepare a 0.1 mol / L organic phase. 1 mL of this organic phase was mixed with an equal volume of an aqueous phase containing 4.0 mol / L nitric acid and 1 mg / L tetravalent plutonium, and stirred for 5 minutes. The organic and aqueous phases were then separated, and the plutonium concentrations in both phases were measured and the partition ratio was calculated. The resulting partition ratio was 0.9.

[0097] The types and concentrations of extractants used in Examples 1 to 5 and Comparative Example 1, the concentration of nitric acid in the nitric acid aqueous solution, the stirring time of the organic phase and the aqueous phase, and the distribution ratio of tetravalent plutonium in the organic phase and the aqueous phase are shown in Table 1 below.

[0098] Table 1

[0099]

[0100]

[0101] In Examples 1 to 5, aqueous solutions of tetravalent plutonium with nitric acid concentrations of 4.0, 6.0, 2.0, 7.0, and 8.0 mol / L were used, respectively, to test the extraction efficiency of the compound represented by formula (I-1) as an extractant for tetravalent plutonium. In Comparative Example 1, an aqueous solution of tetravalent plutonium with a nitric acid concentration of 4.0 mol / L was used to test the extraction efficiency of tributyl phosphate (TBP), a commonly used extractant in the art. As can be seen from Table 1, compared with Comparative Example 1, Examples 1 to 5 of this application all have significantly higher extraction partition ratios, especially Example 5, which has an extraction partition ratio as high as 76. This indicates that the compound of this application can efficiently extract tetravalent plutonium over a wide range of nitric acid concentrations. In particular, the extraction partition ratio increases with increasing nitric acid concentration. This indicates that the compound of this application has higher stability at higher nitric acid concentrations, reducing the possibility of decomposition reactions and facilitating the effective extraction of tetravalent plutonium.

[0102] The above description is only a preferred embodiment of this application and does not limit the patent scope of this application. All equivalent structural transformations made using the content of this application's specification under the inventive concept of this application, or direct / indirect applications in other related technical fields, are included within the patent protection scope of this application.

Claims

1. A compound, characterized in that, The compound is represented by formula (I): Wherein, R is a C1 to C14 alkyl group.

2. The compound according to claim 1, wherein, R is a C6 to C10 alkyl group.

3. The compound according to claim 1 or 2, wherein, R is a straight-chain C8 alkyl group.

4. A method for preparing the compound of claim 1, characterized in that, The method includes the following steps: Step 1: In the presence of 4-dimethylaminopyridine and triethylamine, dialkylamine NH(R)2 is reacted with chloroacetyl chloride in a solvent to give the compound shown in formula (II), wherein R is as defined in claim 1; ClCH2CON(R)2(II) Step 2: Under an inert gas atmosphere and in the presence of sodium hydride, triethanolamine is reacted with the compound shown in formula (II) in a solvent to obtain the compound shown in formula (I).

5. The method according to claim 4, wherein, In step 1, the reaction temperature is 0–5°C, and / or the reaction time is 6–12 hours, and / or the solvent is selected from one or more of anhydrous dichloromethane, anhydrous tetrahydrofuran, anhydrous dimethylformamide, and anhydrous acetonitrile.

6. The method according to claim 4 or 5, wherein, In step 2, the reaction temperature is 10–60°C, and / or the reaction time is 6–24 hours, and / or the solvent is selected from one or more of anhydrous tetrahydrofuran, anhydrous dimethylformamide, anhydrous acetonitrile, and anhydrous dichloromethane.

7. The application of the compound of claim 1 in the extraction of tetravalent plutonium in spent fuel reprocessing, characterized in that, The application includes the following steps: Step 11: Dissolve the compound shown in formula (I) in an organic solvent to obtain an organic phase; Step 12: Mix spent fuel with an aqueous nitric acid solution to obtain an aqueous phase; Step 13: Mix the organic phase and the aqueous phase, and stir for 0.5–15 minutes; and Step 14: After stirring, separate the organic phase and the aqueous phase to extract tetravalent plutonium partially or completely in the organic phase.

8. The application according to claim 7, wherein, In step 12, the concentration of nitric acid in the nitric acid aqueous solution is 1.0 to 8.0 mol / L.

9. The application according to claim 7 or 8, wherein, In step 11, the organic solvent is selected from one or more of alkane and alcohol organic solvents.

10. The application according to any one of claims 7 to 9, wherein, In step 11, the concentration of the compound represented by formula (I) in the organic phase is 0.01 to 0.2 mol / L.

Images