CN115807161A - Novel method for extracting plutonium-238 and recycling neptunium-237 from irradiated neptunium target dissolving liquid - Google Patents

Abstract

The invention relates to a new method for extracting plutonium-238 from irradiated neptunium target dissolving liquid and recovering neptunium-237, which comprises the following steps: firstly, adjusting the valence and the acid of irradiated neptunium target solution, adjusting the valence of neptunium and plutonium to be tetravalent, and then adjusting the acidity of the irradiated neptunium target solution by nitric acid to prepare a circulating feed liquid; then in a cycle, respectively obtaining a crude product liquid of the plutonium-238 and a crude product liquid of the neptunium-237 through the cycle of the neptunium plutonium co-extraction, the plutonium reduction and back-extraction and the neptunium back-extraction; finally, the plutonium-238 product liquid meeting the product requirement is obtained by performing purification cycle on the crude product liquid of the plutonium-238, and the neptunium-237 product liquid meeting the product requirement is obtained by performing purification cycle on the crude product liquid of the neptunium-237. The method provided by the invention can simplify the process flow of extracting the plutonium-238 and recovering the neptunium-237 from the irradiated neptunium target dissolving liquid, reduce the construction cost, reduce the radiation and defense difficulty and improve the purification rate of extracting the plutonium from the irradiated neptunium target dissolving liquid by changing the feeding valence state of the neptunium plutonium in a circulating feeding material liquid into Np (IV) -Pu (IV).

Description

Novel method for extracting plutonium-238 from irradiated neptunium target dissolving liquid and recovering neptunium-237

Technical Field

The invention belongs to the technical field of nuclear material extraction, and particularly relates to a new method for extracting plutonium-238 from irradiated neptunium target dissolving liquid and recovering neptunium-237.

Background

The heat source and isotope battery made of plutonium-238 have the advantages of high power density, long half-life period, low toxicity, few harmful impurities (no generation of high-energy neutrons and high-energy gamma), simple protection, light shielding and the like. Therefore, heat sources and isotope batteries made therefrom have found wide use in many harsh environments, such as aerospace, extremely cold regions, and the like.

But do not ²³⁸ Pu does not exist in nature and can only be artificially produced by reactor irradiation ²³⁸ Pu. The common method is as follows: recovery from spent fuel reprocessing ²³⁷ Np, after recovery ²³⁷ Np is made into a neptunium-237 target (an aluminum matrix and a magnesium matrix), and then the neptunium-237 target is irradiated in a reactor, and the irradiated neptunium target is subjected to a series of chemical treatment to extract plutonium-238 and recycle neptunium-237.

Disclosure of Invention

In view of the defects in the prior art, the invention aims to provide a new method for extracting plutonium-238 and recovering neptunium-237 from an irradiated neptunium target dissolving solution, and simplify the processes of extracting the plutonium-238 and recovering the neptunium-237 from the irradiated neptunium target dissolving solution by changing the valence state of the neptunium plutonium feed so as to reduce the construction cost; the high-level areas are reduced to reduce the radiation protection difficulty; reducing the amount of radioactive solid waste by reducing the use of saline reagents; and the purification rate of plutonium extracted from the irradiated neptunium target dissolving liquid is improved by optimizing the process design.

In order to achieve the above purposes, the invention adopts the technical scheme that: a new process for extracting plutonium-238 from an irradiated neptunium target dissolution liquor and recovering neptunium-237, said process comprising the steps of:

s1, adjusting the valence and the acid of the irradiated neptunium target solution: the neptunium in the irradiated neptunium target dissolving liquid is reduced to be tetravalent, and the plutonium is reduced to be trivalent; then, adjusting the valence states of the neptunium and plutonium to be tetravalent by adopting a first oxidant, and adjusting the acidity of the irradiated neptunium target solution by using nitric acid to prepare a circulating feed liquid;

s2, circulating, comprising the following specific steps:

s21, performing neptunium plutonium co-extraction, and adopting a neptunium plutonium co-extraction agent to extract Np (IV) and Pu (IV) in the feed liquid in the first circulation together to enter a neptunium plutonium co-extraction organic phase;

s22, performing reduction and back extraction on plutonium, namely reducing Pu (IV) in the neptunium and plutonium co-extraction organic phase to Pu (III) by adopting a first plutonium reduction and back extraction agent, and back extracting the Pu (III) into a reduction and back extraction aqueous phase of the plutonium to obtain a crude product liquid of the plutonium-238;

s23, performing back extraction circulation of the neptunium, and performing back extraction on the neptunium in a reduction back extraction organic phase of the plutonium into a back extraction circulation water phase of the neptunium by adopting a first neptunium back extraction agent to obtain a crude product liquid of the neptunium-237;

s3, plutonium purification cycle: performing seasoning treatment on the crude plutonium-238 product liquid to obtain plutonium purification cycle process feed liquid; and the plutonium purification cycle process feed liquid is subjected to chemical separation to obtain plutonium-238 product liquid meeting the product requirements;

s4, neptunium purification cycle: performing seasoning treatment on the crude product liquid of the neptunium-237 to prepare feed liquid in the neptunium purification cycle process; and the feed liquid in the neptunium purification cycle process is chemically separated to obtain the neptunium-237 product liquid meeting the product requirement.

Further, in step S1, the first oxidant is nitrous gas or N ₂ O ₄ ；

The concentration of the nitric acid is 1-10mol/L;

and adjusting the acidity of the irradiated neptunium target solution to 2-5mol/L by using the nitric acid.

Further, in step S21, the neptunium plutonium co-extractant is an organic solvent containing bis (1-methylheptyl) methylphosphonate;

in the organic solvent containing the methyl phosphonic acid di (1-methylheptyl) ester, the volume percentage content of the methyl phosphonic acid di (1-methylheptyl) ester is 5-50%.

Further, in step S22, the first plutonium reduction stripping agent is a salt-free reducing agent in an acidic medium;

the salt-free reducing agent is one or a combination of more of hydroxylamine, dimethylhydroxylamine and hydrazine;

the acidic medium is nitric acid.

Further, in step S22, after the Pu (IV) in the organic phase from which the neptunium plutonium is co-extracted is reduced to Pu (III) with the first plutonium reduction stripping agent, and Pu (III) is stripped into the aqueous phase from which plutonium is reduced and stripped, the method further includes the following steps:

performing supplementary extraction on the neptunium in the reduction back extraction aqueous phase of the plutonium by adopting a first supplementary extraction agent;

the first extraction supplement agent is an organic solvent containing methylphosphonic acid di (1-methylheptyl) ester.

Further, in step S23, the first neptunium stripping agent is (0.2-0.3) mol/L HNO ₃ 。

Further, in step S3, the method of seasoning the crude product liquid of plutonium-238 includes:

and oxidizing the plutonium-238 in the crude plutonium-238 product liquid into a tetravalent plutonium by using a second oxidizing agent, and adjusting the concentration of nitric acid in the crude plutonium-238 product liquid to 2-5mol/L to prepare the feed liquid in the plutonium purification cycle process.

Further, in step S3, the method for chemically separating the feed liquid in the plutonium purification cycle process includes the following steps:

s31, plutonium is extracted, and plutonium and neptunium in feed liquid in the plutonium purification cycle process are extracted into an plutonium extraction organic phase by adopting a plutonium extraction agent;

and S32, a back-extraction cycle of the plutonium, namely adding a second plutonium reduction and back-extraction agent into the plutonium extraction organic phase to reduce the plutonium to Pu (III) and back-extract the Pu (III) into a back-extraction cycle aqueous phase of the plutonium, wherein the neptunium is remained in the back-extraction cycle organic phase of the plutonium.

Further, in step S4, the seasoning treatment method for the crude product liquid of neptunium-237 is as follows:

and reducing the neptunium in the crude product liquid of the neptunium-237 to the tetravalent state and the plutonium to the trivalent state by adopting a reducing agent, and adjusting the concentration of nitric acid in the crude product liquid of the neptunium-237 to 2-5mol/L to prepare the feed liquid in the neptunium purification cycle process.

Further, in step S4, the method for chemically separating the feed liquid of the neptunium purification cycle process includes the following steps:

s41, extracting the neptunium, and extracting the neptunium in the feed liquid in the neptunium purification circulating process into an extraction organic phase of the neptunium by adopting a neptunium extracting agent;

s42, a back extraction circulation of the neptunium, wherein a second neptunium back extraction agent is added into the extracted organic phase of the neptunium, so that the neptunium is back extracted from the extracted organic phase of the neptunium to a back extraction circulation water phase of the neptunium.

The invention has the beneficial effects that: the new method for extracting the plutonium-238 and recovering the neptunium-237 from the irradiated neptunium target dissolving liquid comprises the following steps: firstly, adjusting the valence and the acid of irradiated neptunium target solution, adjusting the valence of neptunium plutonium to quadrivalence, and adjusting the acidity of the irradiated neptunium target solution by nitric acid to prepare a circulating feed liquid; then in a cycle, respectively obtaining a crude product liquid of the plutonium-238 and a crude product liquid of the neptunium-237 through the cycle of the neptunium plutonium co-extraction, the plutonium reduction and back-extraction and the neptunium back-extraction; finally, the crude product liquid of the plutonium-238 is purified and circulated to obtain plutonium-238 product liquid meeting the product requirement, and the crude product liquid of the neptunium-237 is purified and circulated to obtain neptunium-237 product liquid meeting the product requirement; by changing the feeding valence state of the neptunium plutonium in the feeding feed liquid of one cycle to Np (IV) -Pu (IV), the process flow of extracting the plutonium-238 from the irradiated neptunium target dissolving liquid and recovering the neptunium-237 can be simplified, and the construction cost can be reduced. Meanwhile, the method provided by the invention reduces high-level areas and can reduce the radiation and defense difficulty. In addition, the method provided by the invention reduces the use of saline reagents, and can reduce the amount of radioactive solid waste; and through optimizing the flow design, the purification rate of extracting plutonium from the irradiated neptunium target dissolving liquid can be improved.

Drawings

Fig. 1 is a schematic flow diagram of a new process for extracting plutonium-238 from an irradiated neptunium target dissolution liquor and recovering neptunium-237, according to an embodiment of the present invention;

fig. 2 is a flow diagram of a disclosed plutonium-238 extraction chemistry separation process in accordance with an embodiment of the present invention;

fig. 3 is a schematic process diagram of a new method for extracting plutonium-238 from an irradiated neptunium target dissolution solution and recovering neptunium-237, according to an embodiment of the present invention.

Detailed Description

The technical solutions in the embodiments of the present invention will be further clearly and completely described below with reference to the accompanying drawings and examples, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, rather than all embodiments, and all other embodiments obtained by a person of ordinary skill in the art without any creative work based on the examples of the present invention belong to the protection scope of the present invention.

There are few known processes for extracting plutonium-238 from irradiated neptunium targets and recovering neptunium-237, among which chinese patent CN111020244A discloses "a method for extracting and separating plutonium-238 from irradiated neptunium targets and recovering neptunium-237", and the chemical separation scheme is shown in fig. 2. Wherein the neptunium plutonium chemical separation section mainly comprises a cycle, a plutonium purification cycle, and a neptunium purification cycle.

One cycle (i.e., 1NA-1 NB-1A-1B) is a neptunium plutonium splitting cycle, which is required to achieve splitting of the neptunium plutonium from the splits, and splitting between the neptunium plutonium. Therefore, the valence states of the neptunium and plutonium in the feed liquid are respectively adjusted to Np (IV) -Pu (III), the neptunium is extracted into an organic phase in the 1NA section, the plutonium and the fission remain in an aqueous phase (namely, 1 NAW), so that the neptunium is separated from the plutonium and the neptunium and the fission is realized, and then the neptunium is back extracted into the aqueous phase in the 1NB section; the 1NAW dressing is prepared as 1AF into stage 1A, plutonium is extracted into the organic phase, while the splits remain in the aqueous phase (i.e. 1 AW), thus achieving the separation of plutonium from the splits, followed by the reductive stripping of plutonium into the aqueous phase in stage 1B, which is the end of the cycle. From the foregoing, it can be easily seen that there are two high-lying areas during neptunium plutonium separation (1 NA) and plutonium extraction (1A), increasing the radiation protection difficulty and the construction cost; meanwhile, the seasoning (namely 1NAW oxidation) and the extraction process (namely 1A) of the plutonium are added in one cycle, and the investment of manpower, material resources and operation cost is also more required.

The neptunium purification cycle (i.e. the 2NA-2NB section) requires a further purification of the neptunium. In the patent, the feed valence of neptunium in the feed liquid is Np (VI), the adopted oxidant is metavanadate, the plutonium is Pu (IV), and the neptunium plutonium is extracted into a water phase at 2NA, so that the neptunium and the split sheet are further separated, and the purification effect of the split sheet in the neptunium is improved; hydrazine and derivatives thereof are used as selective reduction stripping agents in the 2NB to selectively reduce the neptunium to Np (V) and further strip the neptunium to an aqueous phase, while the plutonium is still Pu (IV) and remains in an organic phase, thereby realizing the re-separation of the neptunium plutonium and improving the purification of the plutonium in the neptunium. From the foregoing, it can be easily found that the use of metavanadate as the oxidant increases the salt content in the waste liquid, which brings difficulty to the treatment of radioactive waste liquid, and increases the amount of radioactive solid waste in the subsequent steps; meanwhile, hydrazine and derivatives thereof are used as selective reduction stripping agents in a stripping section (namely a 2NB section) of the neptunium purification cycle, so that the neptunium can be stripped into an aqueous phase, and 5-10% of plutonium can be stripped into the aqueous phase, thereby reducing the purification of the plutonium in the neptunium product.

In view of the important applications of plutonium-238 in national economic production and national defense construction, it is important to extract plutonium-238 from irradiated neptunium target dissolution liquid and recover neptunium-237 safely, efficiently and with as little radioactive waste as possible.

The novel method for extracting plutonium-238 and recovering neptunium-237 from irradiated neptunium target dissolving liquid provided by the embodiment of the invention mainly comprises the technical processes of adjusting the valence and the acid of the irradiated neptunium target dissolving liquid, performing one cycle, performing plutonium purification cycle, performing neptunium purification cycle and the like. The process for extracting the plutonium-238 from the irradiated neptunium target dissolving liquid and recovering the neptunium-237 is simplified by changing the feeding valence of the neptunium plutonium so as to reduce the construction cost; the high-level areas are reduced to reduce the radiation and defense difficulty; reducing the use of saline reagents to reduce the amount of radioactive solid waste; the purification of plutonium in neptunium is improved by the process design.

The method for obtaining the irradiated neptunium target solution comprises the following steps: first, neptunium-237 is recovered from spent fuel reprocessing, recovered ²³⁷ Np is made into a neptunium-237 target (aluminum and magnesium matrix), then the neptunium-237 target is irradiated in a reactor, and after the neptunium-237 target is irradiated in the reactor and discharged, the target product plutonium-238 and the rest target material neptunium-237 and other radioactive elements are contained and uniformly dispersed in a high-purity aluminum ring machine body. The aluminum matrix of the neptunium target is then dissolved in the form of aluminum nitrate by mercury-catalyzed dissolution, during which the neptunium plutonium oxide does not dissolve but remains in the form of an oxide powder. After the aluminum matrix is dissolved and separated, the NpO can be treated at normal temperature and normal pressure by adopting a catalytic indirect electrochemical oxidation technology taking Ag (II) as a catalyst ₂ 、PuO ₂ And dissolving to obtain an irradiated neptunium target dissolving solution, wherein the main component of the irradiated neptunium target dissolving solution is a neptunium nitrate/plutonium solution.

As shown in fig. 1 and fig. 3, the present invention provides a new method for extracting plutonium-238 from an irradiated neptunium target dissolution solution and recovering neptunium-237, the method including the following steps:

s1, adjusting the valence and the acid of the irradiated neptunium target solution: reducing the neptunium in the irradiated neptunium target dissolving liquid into a tetravalent state and simultaneously reducing the plutonium into a trivalent state by adding a reducing agent into the irradiated neptunium target dissolving liquid or adopting an electrochemical reduction method; and then, adjusting the valence states of the neptunium plutonium to be tetravalent by adopting a first oxidant, and adjusting the acidity of the irradiated neptunium target solution by using nitric acid to prepare a circulating feed liquid 1AF.

Specifically, in step S1, the first oxidant may be nitrous gas or N ₂ O ₄ And the like, but is not limited thereto.

Specifically, in step S1, in the obtained first-cycle feed liquid 1AF, the valence states of the neptunium plutonium are Np (IV) -Pu (IV), respectively.

Specifically, the concentration of the nitric acid is 1-10mol/L; and adjusting the acidity of the irradiated neptunium target solution to 2-5mol/L by using the nitric acid.

S2, a cycle: the method comprises the steps of neptunium plutonium co-extraction 1A, plutonium reduction and back extraction 1B and neptunium back extraction cycle 1C. Specifically, the step S2 includes the following specific steps:

s21, neptunium plutonium co-extraction 1A, using an organic solvent containing di (1-methylheptyl) methylphosphonate as a neptunium plutonium co-extraction agent 1AX, co-extracting Np (IV) and Pu (IV) in the recycle feed liquid 1AF in the step S1 into a neptunium plutonium co-extraction organic phase 1AP, and introducing fission elements into a neptunium plutonium co-extraction aqueous phase 1AW, so as to realize separation of neptunium plutonium and fission elements.

Specifically, in step S21, the volume percentage of the di (1-methylheptyl) methylphosphonate in the organic solvent containing di (1-methylheptyl) methylphosphonate is 5-50%. In a specific embodiment, the organic solvent containing the methyl phosphonic acid di (1-methyl heptyl) ester adopts 5-50% (v/v) P350-kerosene.

S22, performing reduction and back extraction 1B on the plutonium, taking the collected neptunium plutonium co-extraction organic phase 1AP as a reduction and back extraction feed 1BF of the plutonium, reducing Pu (IV) to Pu (III) by using a first plutonium reduction and back extraction agent 1BX, performing back extraction on the plutonium into a reduction and back extraction aqueous phase of the plutonium by utilizing the difference of distribution coefficients of Np (IV) and Pu (III), and still retaining the neptunium in the reduction and back extraction organic phase 1BN of the plutonium to realize the separation of the neptunium plutonium and obtain a crude product liquid 1BP of the plutonium-238.

Specifically, in step S22, the first plutonium reduction stripping agent 1BX may be a salt-free reducing agent in an acidic medium, the salt-free reducing agent being one or a combination of more of hydroxylamine, dimethylhydroxylamine, hydrazine, and the like, but is not limited thereto; the acidic medium is nitric acid.

Specifically, after the first plutonium reduction and stripping agent 1BX reduces Pu (IV) to Pu (III) and strips plutonium into the reduction and stripping aqueous phase of plutonium, the method further includes the following steps: and (3) performing additional extraction on the neptunium in the reduction and back-extraction aqueous phase of the plutonium by using a first additional extraction agent 1BS, wherein the reduction and back-extraction aqueous phase product of the plutonium obtained after the additional extraction is the crude product liquid 1BP of the plutonium-238.

S23, a reverse extraction cycle 1C of the neptunium, namely, taking a reduction and reverse extraction organic phase 1BN of the collected plutonium as a reverse extraction cycle feed 1CF of the neptunium, using dilute acid as a first neptunium reverse extraction agent 1CX, and reversely extracting the tetravalent neptunium in an organic phase into a reverse extraction cycle water phase of the neptunium to obtain a crude product liquid 1CN of the neptunium-237, wherein the crude product liquid can be used as a feed liquid for neptunium purification cycle, further purification and concentration.

Specifically, in step S23, the first neptunium stripping agent 1CX is (0.2-0.3) mol/LHNO ₃ 。

S3, plutonium purification cycle: performing seasoning treatment on the crude product liquid 1BP of the plutonium-238 obtained in the step S22 to obtain a plutonium purification cycle process feed liquid 2AF; and (3) carrying out chemical separation on the plutonium purification cycle process feed liquid 2AF, and finally obtaining plutonium-238 product liquid 2BP meeting product requirements.

Specifically, in step S3, the process of seasoning the crude plutonium-238 liquid 1BP includes: oxidizing the plutonium-238 in the crude product liquid 1BP of the plutonium-238 to tetravalent by using a second oxidizing agent, and adjusting the concentration of nitric acid in the crude product liquid 1BP of the plutonium-238 to 2-5mol/L to prepare a feed liquid 2AF in the plutonium purification cycle process.

Specifically, the second oxidant may be nitrous gas, N ₂ O ₄ And the like, but is not limited thereto.

Specifically, the process of chemically separating the plutonium purification cycle process feed liquor 2AF comprises: plutonium extraction 2A, plutonium stripping cycle 2B. In plutonium extraction 2A, an organic solvent containing di (1-methylheptyl) methylphosphonate is used as plutonium extraction agent 2AX, plutonium and a very small amount of neptunium are extracted into plutonium extraction organic phase 2AP, and further separation of plutonium from lobe elements and plutonium from neptunium is realized. In the plutonium stripping cycle 2B, a second plutonium reduction stripping agent 2BX is added to the plutonium extraction organic phase 2AP to reduce plutonium to Pu (III), and Pu (III) is stripped into the plutonium stripping cycle aqueous phase, while a very small amount of neptunium remains in the plutonium stripping cycle organic phase 2BW, so that neptunium in plutonium is removed again.

In a particular embodiment, the second plutonium reduction stripping agent 2BX can be a salt-free reducing agent in an acidic medium, the salt-free reducing agent being a combination of one or more of hydroxylamine, dimethylhydroxylamine, hydrazine, and the like, but is not so limited; the acidic medium is nitric acid.

Specifically, after the second plutonium reduction stripping agent 2BX reduces plutonium to Pu (III) and strips Pu (III) back into the back-extraction circulating aqueous phase of plutonium, the method further includes the steps of: and (3) performing additional extraction on the neptunium in the back extraction circulating water phase of the plutonium by adopting a second additional extraction agent 2BS, wherein a back extraction circulating water phase product of the plutonium obtained after the additional extraction is plutonium product liquid 2BP.

S4, neptunium purification cycle: seasoning the crude product liquid 1CN of the neptunium-237 in the step S23 to prepare a neptunium purification cycle process feed liquid 2NAF; and (3) carrying out chemical separation on feed liquid 2NAF in the neptunium purification circulation process, and finally obtaining product liquid 2NBP of neptunium-237, which meets the product requirement.

Because the nitrous acid existing in the system can slowly oxidize the tetravalent neptunium to pentavalent, and in the process, part of the tetravalent neptunium in the crude product liquid 1CN of the neptunium-237 may be oxidized to pentavalent, a reducing agent needs to be added to perform seasoning treatment on the crude product liquid 1CN of the neptunium-237, so that the pentavalent neptunium possibly existing in the crude product liquid 1CN of the neptunium-237 is reduced to tetravalent; meanwhile, the reducing agent added in the neptunium purification cycle can also reduce the tetravalent plutonium in the crude product liquid 1CN of the neptunium-237 into trivalent plutonium, so that the trivalent plutonium enters the extraction aqueous phase 2NAW of the neptunium in the extraction 2NA process of the neptunium, and the separation of the neptunium and the plutonium is realized.

Specifically, in step S4, the seasoning treatment process of the crude product liquid 1CN of neptunium-237 is as follows: and (2) reducing the neptunium in the crude product liquid 1CN of the neptunium-237 to a tetravalent state and reducing the plutonium to a trivalent state by adopting a reducing agent, and adjusting the concentration of nitric acid in the crude product liquid 1CN of the neptunium-237 to 2-5mol/L to prepare a feed liquid 2NAF in the neptunium purification cycle process.

Specifically, the reducing agent may be a salt-free reducing agent such as hydrazine and a derivative thereof, but is not limited thereto.

Specifically, the process of chemically separating the feed liquid 2NAF in the neptunium purification cycle process comprises: extraction of neptunium 2NA, back extraction of neptunium 2NB. Extraction of neptunium the 2NA process is: an organic solvent containing di (1-methyl heptyl) methylphosphonate is used as a neptunium extracting agent 2NAX, and the neptunium is extracted into an organic phase 2NAP for extracting the neptunium, so that the further separation of the neptunium from lobe elements and the neptunium from plutonium is realized. The back-extraction cycle of neptunium 2NB procedure is: and adding a second neptunium stripping agent 2NBX into the neptunium extraction organic phase 2NAP, so that the neptunium is stripped from the neptunium extraction organic phase 2NAP to a neptunium stripping circulating water phase, and the stripping circulating water phase of the stripped neptunium is the neptunium product liquid 2NBP.

In a particular example, the second neptunium stripping agent 2NBX may be (0.2-0.3) mol/LHNO3, but is not limited thereto.

Example 1 method for recovering plutonium from a plutonium-containing feed solution by two extraction-back extraction processes

The new method for extracting the plutonium-238 and recovering the neptunium-237 from the irradiated neptunium target dissolving solution provided by the embodiment is used for recovering the plutonium from the plutonium-containing feed solution through two extraction-back extraction processes, and comprises the following steps:

s1, adjusting the valence and the acid of the irradiated neptunium target solution, and adopting N ₂ O ₄ Adjusting the valence states of tetravalent neptunium and trivalent plutonium in the irradiated neptunium target dissolving liquid, adjusting the valence states of the neptunium and the trivalent plutonium to be tetravalent, and adjusting the acidity of the irradiated neptunium target dissolving liquid by nitric acid; the prepared one-cycle feed liquid 1AF comprises the following components: tetravalent neptunium at a concentration of 2g/L, tetravalent plutonium at a concentration of 0.5g/L, nitric acid at a concentration of 3mol/L, and a trace amount of fragmentation elements.

S2, circulating, comprising the following specific steps:

s21, neptunium plutonium co-extraction 1A, introducing 1AF into an extraction tank of 1A, introducing 5-50% (v/v) P350-kerosene serving as a neptunium plutonium co-extraction agent 1AX into the extraction tank of 1A, and introducing 3-4mol/L HNO ₃ The neptunium plutonium co-extract obtained was washed AS detergent 1 AS. After the co-extraction and washing, more than 99.9% of plutonium and 99.5% of neptunium are extracted and enter the neptunium-plutonium co-extraction organic phase 1AP, and the lobe splitting element enters the neptunium-plutonium co-extraction aqueous phase 1AW, so that the effective separation of the plutonium, the neptunium and the lobe splitting element is realized.

S22, plutonium reduction and back extraction 1B, introducing the collected neptunium-plutonium co-extraction organic phase 1AP serving as plutonium reduction and back extraction feed 1BF into a 1B back extraction tank, and introducing (0.2-0.5) mol/L dimethylhydroxylamine- (0.1-0.5) mol/L hydrazine- (1-2) mol/L HNO into the 1B back extraction tank ₃ As the first plutonium reduction stripping agent 1BX, 5-50% (v/v) P350-kerosene was introduced as a make-up agent 1BS. The first plutonium reduction stripping agent 1BX reduces Pu (IV) to Pu (III), causing Pu to strip from the organic phase to the plutonium reduction stripping aqueous phase, leaving neptunium still as Np (IV) in plutonium reduction stripping organic phase 1 BN; and a first supplement extraction agent 1BS is adopted to supplement and extract the neptunium in the aqueous phase through the reduction and back extraction of the plutonium. The reduction and back extraction water phase product of the plutonium obtained after the back extraction is crude product liquid 1BP of plutonium-238, which can be used as plutonium purification cycle for further purification and concentrationAnd (4) feeding the material liquid.

In the process of reducing and back-extracting the plutonium by 1B, the back-extraction rate of the plutonium is more than 99.9 percent, and the back-extraction rate of the neptunium is lower than 0.5 percent.

S23, a reverse extraction cycle 1C of the neptunium, introducing a reduction reverse extraction organic phase 1BN of the collected plutonium into a 1C reverse extraction tank as a reverse extraction cycle feed 1CF of the neptunium, and introducing (0.2-0.3) mol/LHNO into the 1C reverse extraction tank ₃ As the first neptunium stripping agent 1CX, a stripping recycle aqueous phase which causes the neptunium to strip from the organic phase to the neptunium. The obtained reverse extraction circulation water phase product of the neptunium is crude product liquid 1CN of the neptunium-237, and can be used as liquid for neptunium purification circulation, further purification and concentration.

During the reverse extraction cycle 1C of neptunium, the reverse extraction rate of neptunium is greater than 99.5%.

S3, plutonium purification cycle: by using N ₂ O ₄ The plutonium in the crude product liquid 1BP of the plutonium-238 is oxidized into the quadrivalence, and the concentration of nitric acid in the crude product liquid 1BP of the plutonium-238 is adjusted to 2-5mol/L, so that a feed liquid 2AF in the plutonium purification cycle process is prepared; and (3) sequentially carrying out plutonium extraction 2A and plutonium back extraction circulation 2B on the feed liquid 2AF in the plutonium purification circulation process, and finally obtaining plutonium-238 product liquid 2BP meeting the product requirements.

In plutonium extraction 2A, 2AF is introduced into a 2A extraction tank, 5-50% (v/v) P350-kerosene serving as a plutonium extractant 2AX is also introduced into the 2A extraction tank, plutonium and a very small amount of neptunium are extracted into an organic plutonium extraction organic phase 2AP, and further separation of the plutonium from lobe elements and further separation of the plutonium from the neptunium is realized.

In the plutonium stripping cycle 2B, the plutonium-extracted organic phase 2AP is introduced into a 2B stripping tank as a plutonium stripping cycle feed 2BF, and (0.2-0.5) mol/L dimethylhydroxylamine- (0.1-0.5) mol/L hydrazine- (1-2) mol/L HNO is also introduced into the 2B stripping tank ₃ As second plutonium reduction stripping agent 2BX, plutonium is reduced to Pu (III) and stripped into the plutonium stripping cycle aqueous phase 2BP, while a very small amount of neptunium remains in the plutonium stripping cycle organic phase 2 BW; and 5-50% (v/v) of P350-kerosene is introduced into the 2B back-extraction tank to be used as a second back-extraction agent 2BS to carry out back-extraction on the neptunium in the back-extraction circulating aqueous phase of the plutonium. And the back extraction circulating water phase of the plutonium obtained after the back extraction is the plutonium product liquid 2BP, so that the neptunium in the plutonium is removed again.

Example 2 process for recovery of neptunium from crude 1CN of neptunium-237 in step S23 of example 1

Performing seasoning treatment on the crude product liquid 1CN of the neptunium-237 to prepare feed liquid 2NAF in the neptunium purification cycle process; and (3) carrying out chemical separation on the feed liquid 2NAF in the neptunium purification cycle process, and finally obtaining the neptunium-237 product liquid 2NBP meeting the product requirement.

The process of seasoning treatment of the crude product liquid 1CN of the neptunium-237 comprises the following steps: and (3) reducing the neptunium in the crude product liquid 1CN of the neptunium-237 to quadrivalent by adopting hydrazine and reducing the plutonium in the crude product liquid 1CN of the neptunium-237 to trivalent, and adjusting the concentration of nitric acid in the crude product liquid 1CN of the neptunium-237. The neptunium purified cycle process feed liquid 2NAF prepared after the seasoning treatment comprises the following components: tetravalent neptunium with a concentration of 8g/L, nitric acid with a concentration of 2mol/L, and a trace amount of schizophrenic element.

The chemical separation process of the feed liquid 2NAF in the neptunium purification cycle process comprises the following steps: extraction of neptunium 2NA, back extraction of neptunium 2NB.

Extraction of neptunium the 2NA process is: 2NAF is introduced into a 2NA extraction tank, 5-50% (v/v) P350-kerosene serving as a neptunium extracting agent 2NAX is also introduced into the 2NA extraction tank, 3-6mol/L HNO ₃ As a detergent 2NAS, the neptunium is extracted into an extraction organic phase 2NAP of the neptunium, achieving a further separation of the neptunium from lobe elements, and the neptunium from plutonium. After extraction more than 99.9% of the Np is extracted into the extracted organic phase 2NAP of the neptunium.

The back-extraction cycle of neptunium 2NB procedure is: the extracted organic phase of neptunium, 2NAP, was introduced into the 2NB stripping tank as the stripping cycle feed 2NBF for neptunium, and (0.2-0.3) mol/LHNO was also introduced into the 2NB stripping tank ₃ And as a second neptunium stripping agent 2NBX, stripping the neptunium from the neptunium extraction organic phase 2NAP to a reverse extraction circulating water phase of the neptunium, wherein the reverse extraction circulating water phase of the obtained neptunium is the product liquid 2NBP of the neptunium.

During the reverse extraction of the neptunium from the extraction organic phase 2NAP of the neptunium to the back extraction circulating aqueous phase of the neptunium, the reverse extraction rate of the neptunium is 99.5%.

The method of the present invention is not limited to the specific embodiments described above, which are merely illustrative of the present invention, which may be embodied in other specific forms or other specific forms without departing from the spirit or essential characteristics thereof. The described embodiments are, therefore, to be considered in all respects as illustrative and not restrictive. The scope of the invention should be indicated by the appended claims, and any changes that are equivalent to the intent and scope of the claims are also intended to be included within the scope of the invention.

Claims (10)

1. A new process for extracting plutonium-238 from a solution of irradiated neptunium target and recovering neptunium-237, characterized in that it comprises the following steps:

s1, adjusting the valence and the acid of the irradiated neptunium target solution: the neptunium in the irradiated neptunium target dissolving liquid is reduced to be tetravalent, and the plutonium is reduced to be trivalent; then, adjusting the valence states of the neptunium and plutonium to be tetravalent by adopting a first oxidant, and adjusting the acidity of the irradiated neptunium target dissolving liquid by using nitric acid to prepare a circulating feed liquid;

s2, circulating, comprising the following specific steps:

s21, performing neptunium plutonium co-extraction, and adopting a neptunium plutonium co-extraction agent to extract Np (IV) and Pu (IV) in the feed liquid in the first circulation together to enter a neptunium plutonium co-extraction organic phase;

s22, performing reduction and back extraction on plutonium, namely reducing Pu (IV) in the neptunium plutonium co-extracted organic phase to Pu (III) by adopting a first plutonium reduction and back extraction agent, and back extracting the Pu (III) into a reduction and back extraction aqueous phase of the plutonium to obtain a crude product liquid of the plutonium-238;

s23, performing back extraction circulation on the neptunium, and enabling the neptunium in the plutonium reduction and back extraction organic phase to enter a back extraction circulation water phase of the neptunium by adopting a first neptunium back extraction agent to obtain a crude product liquid of neptunium-237;

s3, plutonium purification cycle: seasoning the crude plutonium-238 product liquid to obtain a plutonium purification cycle process feed liquid; and the plutonium purification cycle process feed liquid is subjected to chemical separation to obtain plutonium-238 product liquid meeting the product requirements;

s4, neptunium purification cycle: performing seasoning treatment on the crude product liquid of the neptunium-237 to prepare feed liquid of the neptunium purification cycle process; and the feed liquid in the neptunium purification cycle process is chemically separated to obtain the product liquid of neptunium-237, which meets the product requirements.

2. A new process for extracting plutonium-238 from irradiated neptunium target dissolution liquor and recovering neptunium-237, according to claim 1, characterized in that in step S1, the first oxidant is nitrous gas or N ₂ O ₄ ；

The concentration of the nitric acid is 1-10mol/L;

and adjusting the acidity of the irradiated neptunium target solution to 2-5mol/L by using the nitric acid.

3. A new process for extracting plutonium-238 and recovering neptunium-237 from an irradiated neptunium target dissolution liquor according to claim 1, characterized in that in step S21, the neptunium plutonium co-extractant is an organic solvent containing di (1-methylheptyl) methylphosphonate;

in the organic solvent containing the methyl phosphonic acid di (1-methylheptyl) ester, the volume percentage content of the methyl phosphonic acid di (1-methylheptyl) ester is 5-50%.

4. A new method for extracting plutonium-238 from an irradiated neptunium target dissolution solution and recovering neptunium-237, according to claim 1, characterized in that in step S22, the first plutonium reduction stripping agent is a salt-free reducing agent in an acidic medium;

the salt-free reducing agent is one or a combination of more of hydroxylamine, dimethylhydroxylamine and hydrazine;

the acidic medium is nitric acid.

5. A new process for extracting plutonium-238 and recovering neptunium-237 from irradiated neptunium target dissolution according to claim 1, characterized in that, in step S22, after the Pu (IV) in said neptunium plutonium co-extracted organic phase is reduced to Pu (III) with a first plutonium reduction stripping agent and the Pu (III) is stripped into a plutonium reduction stripping aqueous phase, it comprises the following steps:

performing supplementary extraction on the neptunium in the reduction back extraction aqueous phase of the plutonium by adopting a first supplementary extraction agent;

the first extraction supplement is an organic solvent containing methyl phosphonic acid di (1-methyl heptyl) ester.

6. A new method for extracting plutonium-238 and recovering neptunium-237 from irradiated neptunium target dissolution liquor according to claim 1, characterized in that, in step S23, the first neptunium stripping agent is (0.2-0.3) mol/L HNO ₃ 。

7. A new method for extracting plutonium-238 from irradiated neptunium target dissolution liquid and recovering neptunium-237, according to claim 1, characterized in that in step S3, the seasoning of said plutonium-238 raw product liquid is performed by:

oxidizing the plutonium-238 in the crude plutonium-238 product liquid to tetravalent by using a second oxidizing agent, and adjusting the concentration of nitric acid in the crude plutonium-238 product liquid to 2-5mol/L to prepare the feed liquid in the plutonium purification cycle process.

8. A new process for extracting plutonium-238 from an irradiated neptunium target dissolution liquor and recovering neptunium-237, according to claim 1, characterized in that, in step S3, the chemical separation of the plutonium purification cycle feed liquor comprises the following steps:

s31, plutonium is extracted, and plutonium and neptunium in feed liquid in the plutonium purification cycle process are extracted into an plutonium extraction organic phase by adopting a plutonium extraction agent;

and S32, a back-extraction cycle of the plutonium, namely adding a second plutonium reduction and back-extraction agent into the plutonium extraction organic phase to reduce the plutonium to Pu (III) and back-extract the Pu (III) into a back-extraction cycle aqueous phase of the plutonium, wherein the neptunium is remained in the back-extraction cycle organic phase of the plutonium.

9. A new process for extracting plutonium-238 and recovering neptunium-237 from an irradiated neptunium target dissolution liquor, according to claim 1, characterized in that: in step S4, the seasoning treatment method for the crude product liquid of neptunium-237 is as follows:

and reducing the neptunium in the crude product liquid of the neptunium-237 to the tetravalent state and the plutonium to the trivalent state by adopting a reducing agent, and adjusting the concentration of nitric acid in the crude product liquid of the neptunium-237 to 2-5mol/L to prepare the feed liquid in the neptunium purification cycle process.

10. A new process for extracting plutonium-238 and recovering neptunium-237 from an irradiated neptunium target dissolution liquor, according to claim 1, characterized in that: in step S4, the method for chemically separating the feed liquid of the neptunium purification cycle includes the following steps:

s41, extracting the neptunium, namely extracting the neptunium in feed liquid in the neptunium purification cycle process by adopting a neptunium extracting agent to enter an organic extraction phase of the neptunium;

s42, a back extraction circulation of the neptunium, wherein a second neptunium back extraction agent is added into the extracted organic phase of the neptunium, so that the neptunium is back extracted from the extracted organic phase of the neptunium to a back extraction circulation water phase of the neptunium.

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