Method for recovering uranium

Abstract

The application provides a method for recovering uranium from waste organic phase feed liquid, comprising mixing the waste organic phase feed liquid containing uranium with a complex eluent, collecting a water phase solution containing uranium after delamination, adjusting the pH of the uranium-containing elution water phase to generate a diuranate precipitate, filtering and collecting the diuranate precipitate, wherein the complex eluent comprises sodium pyrophosphate and nitric acid. The complex eluent provided in the method of the application has good elution effect on uranium in the organic phase, and can elute and recover uranium in the waste organic phase containing uranium through a simple method, thereby reducing radioactive pollution.

Description

Technical Field

[0001] This invention relates to the fields of spent fuel reprocessing and radioactive waste treatment, specifically to a method for recovering uranium, and more specifically to a method for recovering uranium from the waste organic phase liquid in a spent fuel reprocessing process. Background Technology

[0002] The PUREX (Plutonium Uranium Reduction Extraction) process is currently the only commercially available spent fuel reprocessing process. Its main purpose is to extract uranium and plutonium from spent fuel, while also separating some useful nuclides. This process is a multi-cycle solvent extraction process. The aqueous phase is a nitric acid solution containing metal ions, the organic phase extractant is tributyl phosphate (TBP), and the diluent is chemically inert hydrogenated kerosene, hydrogenated tetrapropylene (TPH), or n-dodecane, etc. The 30% TBP-kerosene-HNO3 system used in this process undergoes both radioactive and chemical degradation under the combined effects of radiation and chemical reagents such as nitric acid. The main degradation products include dibutyl phosphate (HDBP), monobutyl phosphate (H2MBP), phosphoric acid, and alcohols. These degradation products can further undergo secondary reactions to generate long-chain alkyl phosphates, etc.

[0003] The degradation products of TBP-kerosene accumulate continuously during process operation and research commissioning. Some degradation products have a strong complexing ability with metal ions, resulting in the retention of metal ions (such as uranium, plutonium, and ruthenium) in the organic phase. The degradation process of the entire system is complex and the products are diverse, significantly impacting process operation. During accident operations and research commissioning, the pilot plant generated a large amount of waste organic phase feed liquid with high plutonium and uranium concentrations. However, even after treatment by the existing washing and back-extraction processes in the pilot plant, the concentrations of plutonium and uranium were difficult to reduce. These waste organic phase feed liquids with high plutonium and high uranium content could neither be combined with the feed liquids of normal operation nor be directly discharged, causing significant interference to the production and testing of spent fuel reprocessing facilities. To mitigate the harmful effects of degradation products and metal ion accumulation on the extraction process, Na2CO3 is commonly used to wash dibutyl phosphate (HDBP), monobutyl phosphate (H2MBP), and H3PO4 in the organic phase to reduce the retention of metal ions. Regarding the elution of plutonium from this type of waste organic phase liquid, previous literature and patents have reported a novel eluent (2,6-pyridinedicarboxylic acid) that can elute more than 99.9% of the plutonium from the organic phase to the aqueous phase, with a plutonium recovery rate of over 99%. However, the treated waste organic phase liquid still contains a large amount of uranium and radiation degradation products, such as dibutyl phosphate. Because dibutyl phosphate has a strong complexing ability for uranium and plutonium, conventional dilute acids and alkalis are insufficient to compete with these radiation degradation products. Therefore, the conventional method of washing uranium from the organic phase with dilute acid is not applicable here, and the presence of uranium also affects the normal discharge of the organic phase and solvent reuse.

[0004] Therefore, for the waste solvents generated by this reprocessing process, which have long storage times and high concentrations of degradation products and uranium, there is an urgent need to develop a method for recovering uranium from the waste organic phase. Summary of the Invention

[0005] In view of this, the main objective of the present invention is to provide a method for eluting and recovering uranium from waste organic phases. This method has a good elution effect on uranium and is simple to operate.

[0006] Therefore, the present invention provides a method for recovering uranium, the method comprising: mixing a uranium-containing waste organic phase with a complexing eluent, separating the phases and collecting the uranium-containing aqueous phase, adjusting the pH of the uranium-containing aqueous phase to generate diuranate precipitate, filtering and collecting the diuranate precipitate, wherein the complexing eluent comprises sodium pyrophosphate and nitric acid.

[0007] In some embodiments, the uranium-containing waste organic phase includes uranium, kerosene, tributyl phosphate, and dibutyl phosphate.

[0008] In some embodiments, the concentration of sodium pyrophosphate in the complexing eluent is 0.16–0.5 mol / L.

[0009] In some embodiments, the concentration of the nitric acid is 0.1 mol / L to 1.0 mol / L.

[0010] In some embodiments, the volume ratio of the uranium-containing waste organic phase to the complexing eluent is 1:1 to 1:5.

[0011] In some embodiments, the pH of the uranium-containing aqueous phase is adjusted to a value greater than 13 using a NaOH solution with a mass ratio of 50%-52% or ammonia solution with a mass ratio of 25%-28%.

[0012] In some embodiments, the recovery method further includes washing the uranate precipitate with a 0.1 mol / L to 0.5 mol / L NaOH or ammonia solution after collecting the uranate precipitate.

[0013] In some implementations, the mixing is carried out by shaking or stirring.

[0014] In some embodiments, the uranium-containing waste organic phase liquid is mixed with a complexing eluent, and the mixed solution is separated into phases by standing or centrifugation.

[0015] In some embodiments, the method includes mixing a uranium-containing waste organic phase with a complexing eluent by shaking or stirring, wherein the complexing eluent comprises sodium pyrophosphate at a concentration of 0.16–0.5 mol / L and nitric acid at a concentration of 0.1–1.0 mol / L, and the volume ratio of the uranium-containing waste organic phase to the complexing eluent is 1:1 to 1:5; after settling or centrifuging to separate the phases, collecting the uranium-containing aqueous phase, adding 50%–52% NaOH solution or 25%–28% ammonia solution by mass to adjust the pH of the uranium-containing aqueous phase to greater than 13, generating diuranate precipitate, filtering and collecting the diuranate precipitate.

[0016] In some embodiments, the uranate precipitate is washed with a 0.1-0.5 mol / L NaOH or ammonia solution to obtain purified uranate.

[0017] The method of this invention uses a complex eluent formed by pyrophosphate and inorganic salts mixed with a uranium-containing waste organic phase. Based on the strong coordination ability of pyrophosphate for hexavalent uranium in acidic solution, uranium is eluted from the organic phase into the aqueous phase through complexation elution. Then, by adjusting the pH of the aqueous phase, the uranium precipitates as diuranate, thereby achieving uranium recovery. Furthermore, the treated organic phase meets the requirements for distillation. The method of this invention achieves a uranium elution efficiency of over 99%, enabling highly efficient uranium recovery. Moreover, the method is simple to operate and is expected to have good application prospects in the treatment of waste organic phases in spent fuel reprocessing plants and the deep purification of waste solvents in normal operation. Attached Figure Description

[0018] Figure 1 This is a process flow diagram of uranium recovery according to one embodiment of the present invention;

[0019] Figure 2 This is a Raman spectrum of sodium diuranate recovered according to one embodiment of the present invention after being dissolved. Detailed Implementation

[0020] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments and accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0021] 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 invention pertains. In the event of any conflict, this specification shall prevail.

[0022] It should be noted that, in the embodiments of the present invention, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a method or apparatus that includes a list of elements includes not only the elements expressly stated, but also other elements not expressly listed, or elements inherent to implementing the method or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other related elements in the method or apparatus that includes that element.

[0023] It should be noted that the terms "first," "second," and "third" used in the embodiments of this invention are merely to distinguish similar objects and do not represent a specific ordering of objects. It is understood that "first," "second," and "third" can be interchanged in a specific order or sequence where permissible. It should be understood that the objects distinguished by "first," "second," and "third" can be interchanged where appropriate so that the embodiments of the invention described herein can be implemented in an order other than those illustrated or described herein.

[0024] In the existing technology, there is a lack of suitable and effective methods for recovering uranium from waste solvents with long storage time, degradation products, and high uranium content generated in the spent fuel reprocessing process.

[0025] In view of this, the present invention provides a method for uranium recovery, the method comprising: mixing a uranium-containing waste organic phase with a complexing eluent; collecting the uranium-containing aqueous phase after phase separation; adjusting the pH of the uranium-containing aqueous phase to generate diuranate precipitate; filtering and collecting the diuranate precipitate; wherein the complexing eluent comprises sodium pyrophosphate and nitric acid. In this application, the sodium pyrophosphate in the complexing eluent comprises pyrophosphate ions, which have a strong coordination ability for hexavalent uranium within an acidity range of 0.1–1 mol / L. Furthermore, the nitric acid in the complexing eluent provides this acidity range, preventing emulsification between the uranium-containing waste organic phase and the complexing eluent, facilitating rapid phase separation; and, through the combination of sodium pyrophosphate and nitric acid, binding the hexavalent uranium in the uranium-containing waste organic phase, thereby eluting the uranium in the organic phase into the aqueous phase through complexation with sodium pyrophosphate. In this application, the nitric acid can be nitric acid added during the preparation of the complexing eluent or nitric acid derived from the uranium-containing waste organic phase. When the uranium-containing waste organic phase contains a certain concentration of nitric acid, sodium pyrophosphate can form a complex eluent with the nitric acid in the uranium-containing waste organic phase without the need to add additional nitric acid.

[0026] By separating the organic and aqueous phases, retaining the uranium-containing aqueous phase, and adjusting the pH of the aqueous phase to alkaline, the uranium in the aqueous phase precipitates as diuranate, which can then be separated by filtration. The method of this invention can elute more than 99% of the uranium from the uranium-containing waste organic phase into the aqueous phase, reducing the uranium content in the uranium-containing waste organic phase to 10%. -3 The method reduces the radioactivity level of the organic phase to a low level, such as meeting the low radioactivity level specified in radioactive environmental standards (e.g., GB9833-88), thus satisfying the requirements for the next step of organic phase solvent distillation. Uranium recovery can be achieved by simply adjusting the pH of the uranium-containing aqueous phase obtained after elution. The method of this invention achieves a uranium elution efficiency of over 99%, enabling highly efficient uranium recovery. Furthermore, the method is simple to operate and is expected to have good application prospects in the treatment of waste organic phases in spent fuel reprocessing plants and the deep purification of waste solvents in normal operation.

[0027] In this application, the uranium-containing waste organic phase can be either freshly generated high-uranium-content organic phase waste from the spent fuel reprocessing process or waste organic phase that has been stored for a long time (more than 5 years). Fresh or long-stored uranium-containing waste organic phases generated during the spent fuel reprocessing process typically include tributyl phosphate (TBP), hydrogenated kerosene, uranium, plutonium and other metallic elements, nitric acid, dibutyl phosphate (HDBP), and other radiolysis products.

[0028] In some embodiments, the uranium-containing waste organic phase includes uranium, kerosene, tributyl phosphate (TBP), and dibutyl phosphate (HDBP). In the uranium-containing waste organic phase processed in this application, TBP and / or HDBP have a strong coordination ability for uranium. Uranium typically exists in a complexed form with TBP and / or HDBP, and may form polymers after prolonged storage. Conventional acids, bases, or other complexing agents are insufficient to complex and elute the uranium from this organic phase.

[0029] In some embodiments, the concentration of sodium pyrophosphate in the complexing eluent is 0.16–0.5 mol / L. Maintaining the sodium pyrophosphate concentration within this range facilitates its thorough binding with uranium in the uranium-containing waste organic phase, thereby improving the elution efficiency of uranium. Exemplarily, the concentration of sodium pyrophosphate in the complexing eluent can be 0.16 mol / L, 0.23 mol / L, 0.24 mol / L, 0.28 mol / L, 0.32 mol / L, 0.36 mol / L, 0.40 mol / L, 0.45 mol / L, 0.5 mol / L, or a value within a range of any two of these values.

[0030] In some embodiments, the concentration of the nitric acid is 0.1 mol / L to 1.0 mol / L. Maintaining the nitric acid concentration within this range helps to provide a suitable acidity range, ensuring that the complex organic phase does not emulsify and promoting phase separation, while also promoting the binding of pyrophosphate with uranium, thereby improving the elution efficiency of the complexing eluent for uranium. Exemplarily, the concentration of the nitric acid is 0.1 mol / L, 0.25 mol / L, 0.5 mol / L, 0.75 mol / L, 1.0 mol / L, or a value within a range of any two of these values.

[0031] In some embodiments, the volume ratio of the uranium-containing waste organic phase to the complexing eluent is 1:1 to 1:5. Maintaining this volume ratio within the aforementioned range facilitates thorough complexation between the complexing eluent and the uranium in the waste organic phase, thereby improving the uranium elution efficiency. Exemplarily, the volume ratio of the uranium-containing waste organic phase to the complexing eluent can be 1:1, 1:2, 1:3, 1:4, 1:5, or a value within a range of any two of these values.

[0032] In some embodiments, the pH of the uranium-containing aqueous phase is adjusted to a value greater than 13 using a 50%-52% (w / w) NaOH solution or a 25%-28% (w / w) ammonia solution. Adjusting the pH of the uranium-containing aqueous phase to a value greater than 13 facilitates the precipitation of uranium in the aqueous phase as diuranate, improving uranium recovery and simultaneously removing sodium pyrophosphate. Adding the aforementioned concentrations of sodium hydroxide solution or ammonia solution improves precipitation efficiency and reduces the solution volume during precipitation, thus simplifying subsequent filtration steps. Furthermore, the use of NaOH solution or ammonia solution does not introduce new impurity elements, simplifying the operation and yielding a uranium product suitable for normal processes after purification.

[0033] In some embodiments, the recovery method further includes washing the uranate precipitate with a 0.1 mol / L to 0.5 mol / L NaOH solution or ammonia after collecting the precipitate. Washing the uranate precipitate with a dilute NaOH solution or ammonia of the above concentration helps remove impurity ions from the surface of the uranate precipitate and avoids new contamination caused by the dissolution of the uranate precipitate during the elution process.

[0034] In some embodiments, the uranium-containing waste organic phase liquid is mixed with the complexing eluent by shaking or stirring, and the mixing time can be, for example, 5 minutes.

[0035] In some embodiments, the uranium-containing waste organic phase liquid is mixed with a complexing eluent, and the mixed solution is allowed to separate into layers by standing or centrifugation.

[0036] The following combination Figure 1 The process flow diagram shown illustrates the method of this application in detail.

[0037] In some embodiments, the method includes mixing a uranium-containing waste organic phase with a complexing eluent by shaking or stirring, wherein the complexing eluent comprises sodium pyrophosphate at a concentration of 0.16–0.5 mol / L and nitric acid at a concentration of 0.1–1.0 mol / L, and the volume ratio of the uranium-containing waste organic phase to the complexing eluent is 1:1 to 1:5; after separation by standing or centrifugation, the uranium-containing aqueous phase is collected, and the pH of the uranium-containing aqueous phase is adjusted to greater than 13 by adding 50%–52% NaOH solution or 25%–28% ammonia solution to generate diuranate precipitate, which is then filtered and collected.

[0038] In some embodiments, the sodium diuranate precipitate is washed with a dilute NaOH or ammonia solution with a concentration of 0.1 mol / L to 0.5 mol / L to obtain purified sodium diuranate.

[0039] The present invention will be further explained and illustrated below with reference to specific embodiments. It should be understood that these specific embodiments are merely exemplary and do not limit the scope of the present invention.

[0040] Example

[0041] The uranium-containing waste organic phase used in Examples 1-4 below is an organic phase feed liquid generated during the research and commissioning of the reprocessing process at the China Institute of Atomic Energy. The main chemical composition of this organic phase feed liquid includes: 30% (volume percentage) tributyl phosphate (TBP) and 70% (volume percentage)...

[0042] Hydrogenated kerosene, containing 3.5 g / L uranium, 0.1 mol / L nitric acid, and 0.1 mol / L dibutyl phosphate (HDBP), with other degradation products and metal ion contents not determined. The solution is a clear, yellowish-brown liquid.

[0043] Example 1

[0044] (1) Preparation of complexing eluent:

[0045] Weigh a certain amount of Na4P2O7 solid and add it to a 15mL centrifuge tube. Then add 0.1mol / L nitric acid solution to prepare a complexing elution solution with Na4P2O7 concentration of 0.16mol / L and HNO3 concentration of 0.1mol / L.

[0046] (2) Elution of uranium:

[0047] Take 1.0 mL of uranium-containing waste organic phase into a 15 mL centrifuge tube, add 1.0 mL of the complexing eluent solution prepared in step (1) above, shake in an air bath for 5 minutes, centrifuge until the organic phase and aqueous phase separate, take the organic phase to test the uranium concentration, and calculate the uranium elution rate according to the following formula:

[0048] Uranium elution rate = (Uranium content in the initial organic phase - Uranium content in the eluted organic phase) / Uranium content in the initial organic phase × 100%. The calculation results of the elution rate are shown in Table 1.

[0049] (3) Collect the aqueous solution after uranium elution in step (2) above, adjust the pH of the aqueous solution to above 13 with a 50% NaOH solution by mass, and a yellow precipitate will gradually precipitate out of the solution. Discard the supernatant, wash the precipitate with a 0.01 mol / L dilute NaOH solution, and finally collect the precipitate to obtain pure sodium diuranate solid, thus achieving the purpose of uranium recovery.

[0050] Figure 2 The image shows the Raman spectrum of sodium diuranate recovered in Example 1 of this application after being dissolved in 0.1 mol / L dilute nitric acid. As can be seen from the image, the sodium diuranate recovered by the method of this application does not contain the characteristic peak of pyrophosphate, indicating that the sodium diuranate precipitate no longer contains the impurity of sodium pyrophosphate, thus achieving the purpose of purification.

[0051] Examples 2-3

[0052] Examples 2-3 involved uranium recovery using a method similar to that of Example 1, except that the concentration of nitric acid in the complexing eluent was adjusted according to the parameters shown in Table 1. The uranium elution rate was tested and calculated, and the results are shown in Table 1.

[0053] Table 1

[0054]

[0055] Note: The data marked with * in the table are because the concentration of uranium in the organic phase after elution is lower than the instrument detection limit, therefore the calculated elution rate is >99.8%.

[0056] Examples 5-7

[0057] The uranium-containing waste organic phase used in Examples 5-7 was a waste organic phase liquid that had been stored for many years during the research and debugging of the pilot plant's post-processing flow. Its main chemical composition was: 30% (volume percentage) tributyl phosphate (TBP) and 70% (volume percentage) hydrogenated kerosene, with a uranium content of 3.6 g / L, a plutonium content of 0.04 g / L, a total acid content of 0.3 mol / L, and a dibutyl phosphate (HDBP) content of 0.3 mol / L. Before this experiment, the liquid had been stored for approximately 8 years and appeared as a bright yellow organic phase solution.

[0058] Examples 5-7 were performed using a method similar to that of Example 1, except that the volume ratio of uranium-containing waste organic phase to complexing eluent in step (2) was adjusted according to the parameters shown in Table 2. The uranium elution rate was tested and calculated, and the results are shown in Table 2.

[0059] Table 2

[0060]

[0061] The results above show that the complexing eluent provided by the method of this invention effectively treats uranium-containing waste organic phases. Specifically, the concentration of metaphosphate in the complexing eluent is in the range of 0.16-0.5 mol / L, the concentration of inorganic acid is in the range of 0.1-1.0 mol / L, and the volume ratio of uranium-containing waste organic phase to complexing eluent in the elution step is in the range of 1:1 to 1:5. This method can effectively elute uranium from the uranium-containing waste organic phase, achieving an uranium elution efficiency of over 99%. The method of this application is simple to operate and applicable to the treatment of waste organic phases in spent fuel reprocessing plants.

[0062] The above description is only a preferred embodiment of the present invention and does not limit the patent scope of the present invention. All equivalent structural transformations made under the inventive concept of the present invention using the contents of the present invention specification and drawings, or direct / indirect applications in other related technical fields, are included within the patent protection scope of the present invention.

Claims

1. A method for recovering uranium, characterized in that, The method includes: mixing a uranium-containing waste organic phase with a complexing eluent, separating the phases and collecting the uranium-containing aqueous phase, adjusting the pH of the uranium-containing aqueous phase to generate diuranate precipitate, filtering and collecting the diuranate precipitate, wherein the uranium-containing waste organic phase includes uranium, kerosene, tributyl phosphate and dibutyl phosphate, the complexing eluent includes sodium pyrophosphate and nitric acid, wherein the concentration of sodium pyrophosphate in the complexing eluent is 0.16 ~ 0.5 mol / L, and the concentration of nitric acid is 0.1 mol / L ~ 1.0 mol / L.

2. The method according to claim 1, characterized in that, The volume ratio of the uranium-containing waste organic phase to the complexing eluent is 1:1 to 1:

5.

3. The method according to claim 1 or 2, characterized in that, The pH of the uranium-containing aqueous phase is adjusted to a value greater than 13 using a NaOH solution with a mass ratio of 50%-52% or ammonia solution with a mass ratio of 25%-28%.

4. The method according to claim 1 or 2, characterized in that, The recovery method further includes washing the uranate precipitate with a 0.1 mol / L - 0.5 mol / L NaOH solution or ammonia after collecting the precipitate.

5. The method according to claim 1 or 2, characterized in that, The mixing is carried out by shaking or stirring.

6. The method according to claim 1 or 2, characterized in that, After mixing the uranium-containing waste organic phase liquid with a complexing eluent, the mixed solution is allowed to stand or centrifuged to separate the phases.

7. The method according to claim 1, characterized in that, The method includes mixing a uranium-containing waste organic phase with a complexing eluent by shaking or stirring, wherein the complexing eluent comprises sodium pyrophosphate at a concentration of 0.16 ~ 0.5 mol / L and nitric acid at a concentration of 0.1 ~ 1.0 mol / L, and the volume ratio of the uranium-containing waste organic phase to the complexing eluent is 1:1 ~ 1:5; after settling or centrifuging to separate the phases, collecting the uranium-containing aqueous phase, adding 50%-52% NaOH solution or 25%-28% ammonia solution by mass to adjust the pH of the uranium-containing aqueous phase to greater than 13, generating diuranate precipitate, filtering and collecting the diuranate precipitate.

8. The method according to claim 7, characterized in that, The uranate precipitate was washed with a NaOH solution with a concentration of 0.1-0.5 mol / L to obtain purified uranate.

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