阅读说明：本技术 一种四价钚离子的萃取方法 (Extraction method of tetravalent plutonium ions ) 是由 肖成梁 徐雷 于 2019-11-11 设计创作，主要内容包括：本发明涉及核燃料循环及废液处理技术领域,公开了一种四价钚离子的萃取方法,包括以下步骤：利用式(1)的邻菲罗啉衍生物与稀释剂混合形成有机相,从水相中萃取四价钚离子；水相为含有四价钚离子的酸性水溶液。本发明以邻菲罗啉衍生物作为萃取剂,从含有多种锕系离子的水相中选择性的萃取出四价钚,萃取能力强,萃取速度快,特别是从含有五价镎和六价铀的硝酸水溶液中对四价钚萃取分离效率非常高,萃取率最高可达99％,在核工业废液处理领域中具有良好的应用前景。<Image he="295" wi="690" file="DDA0002268051930000011.GIF" imgContent="drawing" imgFormat="GIF" orientation="portrait" inline="no"></Image>(The invention relates to the technical field of nuclear fuel circulation and waste liquid treatment, and discloses a method for extracting tetravalent plutonium ions, which comprises the following steps: mixing phenanthroline derivative shown in formula (1) with a diluent to form an organic phase, and extracting tetravalent plutonium ions from the aqueous phase; the aqueous phase is an acidic aqueous solution containing tetravalent plutonium ions. The method takes the phenanthroline derivative as an extracting agent to selectively extract the tetravalent plutonium from the aqueous phase containing various actinide ions, has strong extraction capability and high extraction speed, particularly has very high extraction and separation efficiency of the tetravalent plutonium from the nitric acid aqueous solution containing the pentavalent neptunium and the hexavalent uranium, has the highest extraction rate of 99 percent, and has good application prospect in the field of nuclear industry waste liquid treatment.)

1. A method for extracting tetravalent plutonium ions, characterized by comprising the steps of: mixing phenanthroline derivative shown in formula (1) with a diluent to form an organic phase, and extracting tetravalent plutonium ions from the aqueous phase; the water phase is an acidic aqueous solution containing tetravalent plutonium ions;

wherein R is C₁-C₁₀Linear or branched alkyl groups of (a).

2. A method for extracting a tetravalent plutonium ion according to claim 1, wherein R is n-butyl.

3. A method of extracting tetravalent plutonium ions according to claim 1, wherein said organic phase contains phenanthroline derivatives in an amount of 0.005 to 0.1 mol/L.

4. A method of extracting tetravalent plutonium ions according to claim 1, wherein said diluent is at least one of kerosene, 3-nitrobenzotrifluoride, n-octanol, cyclohexanone and cyclohexane.

5. A method of extracting tetravalent plutonium ions according to claim 1, wherein said acidic aqueous solution is an aqueous nitric acid solution, wherein the concentration of nitric acid is 0.01 to 5 mol/L.

6. A method of extracting tetravalent plutonium ions according to claim 1 or 3, characterized in that said volume ratio of organic phase to aqueous phase is 0.2-5: 1.

7. A method for extracting tetravalent plutonium ions according to claim 1, wherein said method for extracting is characterized in that the extraction time is 1s to 3 h.

8. A method of extracting tetravalent plutonium ions according to claim 1 or 7, wherein said extraction is performed at a temperature of 15-30 ℃.

Technical Field

The invention relates to the technical field of nuclear fuel circulation and waste liquid treatment, in particular to a method for extracting tetravalent plutonium ions.

Background

Nuclear power has become an important option for replacing fossil energy, reducing greenhouse gas emission and solving energy crisis in countries in the world in the 21 st century. However, in order to realize safe and effective utilization of nuclear energy, the safe treatment and disposal of spent fuel has become a bottleneck in the development of nuclear power, and directly restricts the sustainable development of nuclear energy. The extraction and separation technology of radioactive elements is closely related to the post-treatment of Spent Fuel (SNF) in the process of Nuclear energy sustainable development.

The aim of post-treatment of spent fuel is mainly to recover Uranium (U) and Plutonium (Pu) therein, and currently, the separation and Recovery of Uranium and Plutonium are mainly completed by Plutonium and Uranium Extraction (PUREX) process, and the process has been applied to large-scale industrialization. The strong nitric effluents resulting from the separation of uranium and plutonium, referred to as highly radioactive wastes (HLW), contain, in addition to the compounds with long-term radiotoxicity (t)^1/2>10³-10⁶Trivalent actinide ions such as trivalent americium and trivalent curium in the year), and also minor actinide ions such as pentavalent neptunium (np (v)) and tetravalent plutonium (pu (iv)) which are highly radiotoxic.

CN 104894372A discloses a method for extracting and separating trivalent lanthanide and trivalent actinide ions, which uses di (2,4, 4-trimethylpentyl) dithiophosphinic acid as an extracting agent, uses long-chain alkane as a diluent, utilizes a weak acid buffer system to effectively stabilize the pH value of an aqueous phase of an extraction system, does not need to adjust the pH value of the system again in the extraction process, extracts and separates the trivalent actinide elements from the aqueous phase with high selectivity, and most of the trivalent lanthanide elements are remained in the aqueous phase. The invention has high-efficiency and stable extraction and separation performance on trivalent lanthanide and trivalent actinide ions, and has better application prospect in the field of advanced nuclear fuel cycle.

CN 107958717A discloses a method for separating trivalent actinide and lanthanide ions based on synergistic effect, which adopts fat-soluble dithiophosphinic acid as an extracting agent, and dilutes the extracting agent to form an organic phase which is subjected to extraction reaction with a water phase, wherein the water phase is an acidic aqueous solution which is added with a water-soluble organic weak acid complexing agent and contains trivalent lanthanide and actinide ions, and the trivalent lanthanide and actinide ions are extracted and separated through the synergistic effect of the extracting agent and the complexing agent; the volume ratio of the organic phase to the aqueous phase is 0.2-2; the pH value of the acidic aqueous solution is 2-4; the invention has the advantages of good separation performance, good stability and simple and convenient operation.

However, in order to eliminate or minimize the potential radioactive toxicity of trivalent actinides and actinides such as np (v), pu (iv) to the environment and humans over a long period of time, it is necessary to separate and recover np (v), pu (iv), etc. from HLW and use them. Plutonium is a radioactive element, is an important raw material in the atomic energy industry, can be used as a fission agent of nuclear fuel and nuclear weapons, and has great significance for separating and recovering the plutonium, but the PUREX process in the prior art is to extract and separate U and Pu by adjusting price at the same time, and the industrial process for separately extracting plutonium still needs to be explored

At present, oxygen-containing ligands and tributyl phosphate are mainly used in industry to extract Pu (IV) in spent fuel, and the ligands have certain extraction capability to different actinide ions with different valence states, so that the defects of low selectivity, low extraction efficiency and the like exist. CN 106893878A discloses a method for recovering plutonium from radioactive spent fuel, which comprises extracting pu (iv) in the water solution of the radioactive spent fuel with an organic solvent containing tributyl phosphate; and adding an organic solvent containing dimethyl hydroxylamine into the organic phase to reduce the tetravalent plutonium into the trivalent plutonium and then carrying out back extraction, and adding a dilute acid aqueous solution into the organic phase to back extract the plutonium into the aqueous phase for recovery. Although the method improves the recovery efficiency of plutonium, the extraction method still has the defects of complicated process, incomplete reduction of tetravalent plutonium possibly, and low efficiency.

Disclosure of Invention

The invention aims to provide a method for directly extracting tetravalent plutonium, which takes phenanthroline derivatives as an extracting agent to extract Pu (IV) from an aqueous phase containing actinide ions with different valence states, has good selectivity to Pu (IV), and has the highest extraction efficiency of 99 percent.

In order to achieve the purpose, the invention adopts the technical scheme that:

a method for extracting tetravalent plutonium ions, comprising the steps of: mixing phenanthroline derivative shown in formula (1) with a diluent to form an organic phase, and extracting tetravalent plutonium ions from the aqueous phase; the water phase is an acidic aqueous solution containing tetravalent plutonium ions;

wherein R is C₁-C₁₀Linear or branched alkyl groups of (a).

Further, R is C₁-C₆Straight chain alkyl or C₁-C₆Branched alkyl groups of (a).

More preferably, R is n-butyl, and the phenanthroline derivative is C4-POPhen, and the structure of the phenanthroline derivative is shown as a formula (2);

the rigid phenanthroline mother ring (Phen) shown in the formula (3) in the C4-POPhen structure has strong radiation resistance, excellent extraction kinetics performance and coordination capacity with actinides, and tributyl phosphate (TBP) shown in the formula (4) in the C4-POPhen structure is a main stream extractant structure in the traditional spent fuel post-processing Purex process, and has the advantages of small volatility, simple synthesis method, irradiation decomposition resistance and strong Pu (IV) extraction capacity. The extraction efficiency of C4-POPhen on Pu (IV) obtained by combining Phen with a functional fragment of TBP is very high.

The content of the phenanthroline derivative in the organic phase is 0.005-0.1mol/L, the phenanthroline derivative serving as an extracting agent has too low content and incomplete extraction, and the extracting agent has too high content, so that emulsification and uneven dispersion of the extracting agent are easily caused in the extraction process.

The diluent is at least one of kerosene, 3-nitrotrifluorotoluene, n-octanol, cyclohexanone and cyclohexane.

Preferably, the diluent is 3-nitrobenzotrifluoride, the volatility is small, the density is high, the solubility in a water phase is extremely low, phase separation is easy, the solubility to phenanthroline derivative molecules is good, and the extraction efficiency is very favorably improved.

The acidic aqueous solution is nitric acid aqueous solution, wherein the concentration of nitric acid is 0.01-5 mol/L. The acidity of the acidic aqueous solution has a great influence on the extraction rate and the selectivity of the extractant, and the extraction is not favored by over-high or over-low acidity.

Preferably, the concentration of nitric acid in the acidic aqueous solution is 0.5-3mol/L, and the extraction rate of Pu (IV) in the acidity is above 97%, and can reach 99% at most.

The water phase also contains other impurity ions, such as np (V), U (VI) and other actinide ions with different valence states, the method can independently extract Pu (IV) from the actinide ion mixture with different valence states, the selectivity of Pu (IV) is good, and the extraction efficiency is high.

The volume ratio of the organic phase to the aqueous phase is 0.2-5: 1.

In the extraction method, the extraction time is the extraction time conventional in the art, and usually the time for reaching the extraction equilibrium is the end point, preferably 1s-3h, and more preferably 1-2 h. Within the time range, the extraction can be balanced, the higher extraction efficiency is also considered, and the irradiation time of the ligand for receiving radioactive elements is shortened, so that secondary pollutants generated by radiolysis are reduced.

In the extraction method, the extraction temperature is the extraction temperature conventional in the field, and is preferably 15-30 ℃. The extraction effect is good at the temperature, and the extraction system does not need to be heated or cooled to consume extra electric energy in the extraction process.

The preparation method of the phenanthroline derivative shown in the formula (1) comprises the following steps: in an organic solvent, under the action of a catalyst and an acid-binding agent, a compound shown as a formula (5) and a compound shown as a formula (6) react to obtain:

wherein X is halogen and R is as defined above.

The organic solvent may be any organic solvent conventionally used in the art, and toluene is preferred in the present invention.

The catalyst may be conventional in the art for such reactions, and the preferred catalyst of the present invention is 1,1' -bis (diphenylphosphino) ferrocene and/Pd (OAc)₂. The combination of the two catalysts has the best catalytic efficiency and higher reaction yield.

The acid-binding agent can be an acid-binding agent which is conventional in the reaction in the field, and triethylamine is preferred in the invention. The triethylamine is weak in alkalinity, and continuously reacts with generated hydrochloric acid to form salt in the reaction process, so that the catalyst 1,1' -bis (diphenylphosphino) ferrocene and palladium acetate are not deactivated due to too strong alkalinity, and the yield of the synthesis reaction is ensured.

The compound shown as the formula (5) reacts with Pd (OAc)₂The mol ratio of 1,1' -bis (diphenylphosphino) ferrocene, the compound shown in the formula (6) and triethylamine is 10: (0.5-2): (1-3): (20-30):(20-30).

In the preparation method of the phenanthroline derivative shown in the formula (1), the reaction temperature is the reflux temperature of the organic solvent.

In the preparation method of the phenanthroline derivative shown in the formula (1), the reaction progress can be monitored by adopting thin-layer chromatography (TLC) in the reaction process, the compound shown in the formula (5) is completely reacted, and the reaction is stopped, wherein the reaction time is preferably 2-5 h.

The extraction method provided by the invention has the advantages that the phenanthroline derivative is used as an extracting agent, Pu (IV) is selectively extracted from the aqueous phase containing various actinide ions, the extraction capacity is strong, and the extraction speed is high. Especially, Pu (IV) is selectively extracted and separated from the nitric acid aqueous solution containing Np (V), U (VI), the extraction efficiency can reach 99 percent to the maximum, and the method has good application prospect in the field of nuclear industry waste liquid.

Before this, the inventors found that the phenanthroline derivative has a good extraction effect on trivalent lanthanide ions, but an extraction agent capable of coordinating with trivalent lanthanide ions cannot be generally used for coordinating pu (iv) ions, and the application background and the separation objects of the trivalent lanthanide ions and pu (iv) ions are substantially different. However, through many experiments, the inventor unexpectedly finds that the phenanthroline derivative has strong coordination capacity to Pu (IV), and shows excellent selectivity to Pu (IV) in the nitric acid solution in which Np (V), U (VI) exist simultaneously, and Pu (IV) can be separated from the nitric acid solution independently, which has great significance to the technical field of post-treatment of spent fuel.

Drawings

FIG. 1 is a nuclear magnetic spectrum of C4-POPhen prepared in example 1;

FIG. 2 is a graph showing the distribution ratio of U (VI), Np (V) and Pu (IV) separated from the aqueous phase by using C4-POPhen prepared in example 1 as an extractant as a function of the concentration of nitric acid.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is further described in detail with reference to the following embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention. Those skilled in the art should understand that they can make modifications and equivalents without departing from the spirit and scope of the present invention, and all such modifications and equivalents are intended to be included within the scope of the present invention.

In the following examples, all the raw materials were purchased from commercial sites, wherein the distribution ratio D is the ratio of the content of metal ions in the equilibrium organic phase to the content of metal ions in the equilibrium aqueous phase after the completion of the first extraction (the content of metal ions in the equilibrium aqueous phase was determined by liquid flash method, and then the content of metal ions in the equilibrium organic phase was determined by the subtraction method), i.e., the ratio D is the ratio

D＝C_org/C_aq＝(C’_aq-C_aq)/C_aq(5)

In the formula (1), C_orgShowing the concentration of metal ions in the equilibrium organic phase after the completion of one extraction; c_aqShowing the concentration of metal ions in the equilibrium water phase after the completion of the primary extraction; c'_aqThe concentration of metal ions in the aqueous phase before the first extraction is indicated.

The extraction rate E is the percentage of the amount of extracted substances transferred from the water phase to the organic phase in the extraction process to the total amount of the extracted substances in the raw water phase, namely:

E＝100％×(C’_aq-C_aq)/C’_aq(6)

in the formula (2), C_aqShowing the concentration of metal ions in the equilibrium water phase after the completion of the primary extraction; c'_aqThe concentration of metal ions in the aqueous phase before the first extraction is indicated.

The separation coefficient SF is the ratio of the distribution ratio of two substances to be separated between two phases when extraction separation is performed under certain conditions, and is also called an extraction separation factor. E.g. Pu (IV) phaseSeparation factor SF for U (VI)_Pu(IV)/U(VI)Is defined as:

SF_Pu(IV)/U(VI)＝D_Pu(IV)/D_U(VI)(7)

in the formula (7), D_Pu(IV)Represents D_Pu(IV)Distribution ratio D of_U(VI)Represents D_U(VI)The distribution ratio of (a).