Uranium recovery method

Abstract

The invention provides a method for recovering uranium from waste organic phase feed liquid, which comprises the following steps: mixing uranium-containing waste organic phase feed liquid with a complexing eluent, layering, collecting a uranium-containing aqueous phase solution, adjusting the pH value of a uranium-containing washing water phase to generate a diuranate precipitate, filtering, and collecting the diuranate precipitate, the complexing eluent comprising sodium pyrophosphate and nitric acid. The complexing eluent provided in the method has a good elution effect on uranium in the organic phase, uranium in the uranium-containing waste organic phase can be eluted and recycled through a simple method, and radioactive contamination is reduced.

Description

Technical Field

[0001] The invention relates to the field of spent fuel reprocessing and radioactive waste treatment, in particular to a method for recovering uranium, and more particularly to a method for recovering uranium from waste organic phase liquid in a spent fuel reprocessing process. Background Art

[0002] The PUREX (Plutonium Uranium Reduction Extraction) process is currently the only commercial spent fuel reprocessing process. The main purpose of this process is to extract uranium and plutonium from spent fuel and separate some useful nuclides at the same time. 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. The 30% TBP-kerosene-HNO3 system used in this process will undergo radiation degradation and chemical degradation under the dual 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, etc. The degradation products can continue to undergo secondary reactions to generate long-chain alkyl phosphates, etc.

[0003] The degradation products of TBP-kerosene will accumulate continuously during the process operation and scientific research debugging. Some degradation products have strong complexing ability for metal ions, which will cause the retention of metal ions in the organic phase (such as uranium, plutonium, ruthenium, etc.). The degradation process of the entire system is very complex, and the products are also diverse, which has a great impact on the operation of the process. During the accident conditions and scientific research debugging, the pilot plant produced a large amount of waste organic phase liquid with high plutonium and uranium concentrations. However, after being treated by the existing washing and stripping processes of the pilot plant, the concentrations of plutonium and uranium in it are difficult to reduce. These high-plutonium and high-uranium waste organic phase liquids cannot be combined with normal operating liquids, nor can they be directly discharged, which has a great interference with the production and testing of spent fuel reprocessing facilities. In order to reduce the damage of the accumulation of degradation products and metal ions to the extraction process, Na2CO3 is often 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, relevant literature and patents have previously reported that a new type of eluent (2,6-pyridinedicarboxylic acid) can elute more than 99.9% of the plutonium in the organic phase to the aqueous phase, and the plutonium recovery rate is more than 99%. Despite this, the treated waste organic phase liquid still contains a large amount of uranium and radiation degradation products, such as dibutyl phosphate and other substances. Since dibutyl phosphate has a strong complexing ability for uranium and plutonium, conventional dilute acid and dilute alkali are difficult to compete with the radiolytic degradation products. Therefore, the conventional dilute acid washing method of organic phase uranium is not applicable here. The presence of uranium will also affect the normal discharge of the organic phase and the reuse of solvents.

[0004] Therefore, for the contaminated solvent produced by this post-processing process, which has a long storage time and high concentrations of degradation products and uranium, it is urgent to develop a method for recovering uranium from the waste organic phase. Summary of the invention

[0005] In view of this, the main purpose of the present invention is to provide a solution for eluting and recovering uranium in a waste organic phase, which has a good elution effect on uranium and is simple to operate.

[0006] To this end, the present invention provides a method for recovering uranium, the method comprising: mixing a uranium-containing waste organic phase with a complexing eluent, collecting a uranium-containing aqueous phase after phase separation, adjusting the pH of the uranium-containing aqueous phase to generate a 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 spent organic phase includes uranium, kerosene, tributyl phosphate, and dibutyl phosphate.

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

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

[0010] In some embodiments, the volume ratio of the uranium-containing spent 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 be greater than 13 by using 50%-52% by mass of NaOH solution or 25%-28% by mass of ammonia water.

[0012] In some embodiments, the recovery method further comprises, after collecting the diuranate precipitate, washing the diuranate precipitate with 0.1 mol / L-0.5 mol / L NaOH or ammonia solution.

[0013] In some embodiments, the mixing is performed by shaking or stirring.

[0014] In some embodiments, after the uranium-containing waste organic phase feed liquid is mixed with the complexing eluent, the mixed solution is allowed to separate into phases by standing or centrifuging.

[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 includes sodium pyrophosphate with a concentration of 0.16 to 0.5 mol / L and nitric acid with a concentration of 0.1 to 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 standing or centrifugal phase separation, collecting the uranium-containing aqueous phase, adding a NaOH solution with a mass proportion of 50% to 52% or ammonia water with a mass proportion of 25% to 28% to adjust the pH of the uranium-containing aqueous phase to greater than 13, generating a diuranate precipitate, and filtering and collecting the diuranate precipitate.

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

[0017] The method of the present invention adopts a complexing eluent formed by pyrophosphate and an inorganic salt to mix with a waste organic phase containing uranium. Based on the strong coordination ability of pyrophosphate to hexavalent uranium in an acidic solution, the uranium element in the organic phase is eluted into the aqueous phase by complexing elution, and then the uranium is precipitated in the form of diuranate by adjusting the pH of the aqueous phase, thereby realizing the recovery of uranium. In addition, the treated organic phase can meet the requirements of distillation. The method of the present invention has an elution efficiency of more than 99% for uranium, can realize efficient recovery of uranium, and the method of the present invention is simple to operate. It is expected that the method of the present invention has good application prospects in the treatment of waste organic phases in spent fuel reprocessing plants and the deep purification of polluted solvents in normal operation. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 This is a process flow chart 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 an embodiment of the present invention after being dissolved and tested. DETAILED DESCRIPTION

[0020] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in combination with the embodiments of the present invention and the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0021] Throughout the specification, unless otherwise specifically stated, the terms used herein should be understood as meanings commonly used in the art. Therefore, unless otherwise defined, all technical and scientific terms used herein have the same meanings as those generally understood by those skilled in the art to which the present invention belongs. In the event of a conflict, the present specification takes precedence.

[0022] It should be noted that, in the embodiments of the present invention, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a method or device including a series of elements includes not only the elements explicitly stated, but also other elements not explicitly listed, or also includes elements inherent to the implementation of the method or device. In the absence of further restrictions, an element defined by the sentence "includes a ..." does not exclude the existence of other related elements in the method or device including the element.

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

[0024] In the prior art, there is a lack of suitable and effective recovery methods for uranium in the degradation products and contaminated solvents with high uranium content that are generated during the spent fuel reprocessing process and have been stored for a long time.

[0025] In view of this, the present invention provides a method for recovering uranium, the method comprising: mixing a uranium-containing waste organic phase with a complexing eluent, collecting a uranium-containing aqueous phase after phase separation, adjusting the pH of the uranium-containing aqueous phase to produce a diuranate precipitate, filtering and collecting the diuranate precipitate, wherein the complexing eluent comprises sodium pyrophosphate and nitric acid. In the present application, the sodium pyrophosphate in the complexing eluent comprises a pyrophosphate radical, which has a strong coordination ability for hexavalent uranium in the acidity range of 0.1 to 1 mol / L, and the nitric acid in the complexing eluent can provide the above acidity range, on the one hand, preventing the uranium-containing waste organic phase from emulsifying with the complexing detergent, which is conducive to rapid phase separation, and on the other hand, through the combination of sodium pyrophosphate and nitric acid, the hexavalent uranium in the uranium-containing waste organic phase can be combined, so that the uranium in the organic phase can be eluted into the aqueous phase in the form of complexing with sodium pyrophosphate. In the present application, the nitric acid can be the nitric acid added when preparing the complexing eluent, or it can be the nitric acid 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] The method of the present invention can elute more than 99% of the uranium in the uranium-containing waste organic phase into the aqueous phase, so that the uranium content in the uranium-containing waste organic phase is reduced to 10%. -3 g / L, so that the radioactivity level of the organic phase is reduced to a low radioactivity level, for example, in accordance with the low radioactivity level specified in the radioactive environmental standard (for example, GB9833-88), and the requirements for the next step of distillation of the organic phase solvent are met, and the recovery of uranium can be achieved by simply adjusting the pH of the uranium-containing aqueous phase obtained after elution. The method of the present invention has an elution efficiency of more than 99% for uranium, and can achieve efficient recovery of uranium. The method of the present invention is simple to operate, and it is expected that the method of the present invention has good application prospects in the treatment of waste organic phases in spent fuel reprocessing plants and the deep purification of polluted solvents in normal operation.

[0027] In the present application, the uranium-containing waste organic phase can be freshly generated high-uranium content organic phase waste from the spent fuel reprocessing process, or it can be a waste organic phase that has been stored for a long time (storage time is greater than 5 years). The fresh or long-stored uranium-containing waste organic phase generated in the spent fuel reprocessing process usually includes tributyl phosphate (TBP), hydrogenated kerosene, metal elements such as uranium and plutonium, 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 treated by the present application, tributyl phosphate (TBP) and / or dibutyl phosphate (HDBP) have a strong coordination ability for uranium, and uranium usually exists in the form of complex with TBP and / or HDBP, which may form polymers after being left for a long time, and conventional acids, alkalis or other complexing agents are difficult to complex and elute the uranium in the organic phase.

[0029] In some embodiments, in the complexing eluent, the concentration of the sodium pyrophosphate is 0.16 to 0.5 mol / L. By making the concentration of sodium pyrophosphate within the above range, it is beneficial for the sodium pyrophosphate to fully combine with the uranium in the uranium-containing waste organic phase to improve the elution efficiency of uranium. Exemplarily, in the complexing eluent, the concentration of the sodium pyrophosphate 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 between the ranges consisting of any two of them.

[0030] In some embodiments, the concentration of nitric acid is 0.1 mol / L to 1.0 mol / L. By making the concentration of nitric acid in the above range, it is helpful to provide a suitable acidity range. On the one hand, it is ensured that the complex organic phase does not emulsify and promotes phase separation. On the other hand, it can promote the combination of pyrophosphate and uranium, thereby improving the elution efficiency of the complex eluent for uranium. Exemplarily, the concentration of 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 between the ranges consisting of any two of them.

[0031] In some embodiments, the volume ratio of the uranium-containing waste organic phase to the complexing eluent is 1:1 to 1:5. By making the volume ratio of the uranium-containing waste organic phase to the complexing eluent within the above range, it is beneficial for the complexing eluent to fully complex with the uranium in the uranium-containing waste organic phase, thereby improving the elution efficiency of uranium. 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 between the ranges consisting of any two of them.

[0032] In some embodiments, the pH of the uranium-containing aqueous phase is adjusted to be greater than 13 by using a 50%-52% by mass NaOH solution or a 25%-28% by mass ammonia water. By adjusting the pH of the uranium-containing aqueous phase to be greater than 13, it is beneficial to fully precipitate the uranium in the uranium-containing aqueous phase in the form of diuranate, improve the recovery rate of uranium, and remove sodium pyrophosphate. By adding the above-mentioned concentration of sodium hydroxide solution or ammonia water, it is beneficial to improve the efficiency of precipitation and reduce the volume of the solution during precipitation, thereby simplifying the operation of the subsequent filtration step, and by using NaOH solution or ammonia water treatment, no new impurity elements are introduced, the operation steps are simplified, and a uranium product of the normal process can be obtained after purification.

[0033] In some embodiments, the recovery method further comprises, after collecting the diuranate precipitate, washing the diuranate precipitate with a 0.1 mol / L-0.5 mol / L NaOH solution or ammonia water. Washing the diuranate with the above-mentioned dilute NaOH solution or ammonia water is conducive to removing impurity ions on the surface of the diuranate and avoiding new contamination caused by the dissolution of the diuranate during the elution process.

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

[0035] In some embodiments, after the uranium-containing waste organic phase feed liquid is mixed with the complexing eluent, the mixed solution is separated into layers by standing or centrifuging.

[0036] The following combination Figure 1 The process flow chart shown describes the method of the present application in detail.

[0037] In some embodiments, the method comprises mixing a uranium-containing waste organic phase with a complexing eluent by shaking or stirring, wherein the complexing eluent comprises sodium pyrophosphate with a concentration of 0.16 to 0.5 mol / L and nitric acid with a concentration of 0.1 to 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 standing or centrifugal stratification, collecting the uranium-containing aqueous phase, adding a NaOH solution with a mass proportion of 50% to 52% or ammonia water with a mass proportion of 25% to 28% to adjust the pH of the uranium-containing aqueous phase to greater than 13, generating a diuranate precipitate, and filtering and collecting the diuranate precipitate.

[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-0.5 mol / L to obtain purified sodium diuranate.

[0039] The present invention is further explained below in conjunction with specific embodiments. It should be understood that these specific embodiments are merely illustrative and do not limit the scope of the present invention.

[0040] Example

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

[0042] Hydrogenated kerosene, wherein the uranium content is 3.5g / L, the nitric acid content is 0.1mol / L, the dibutyl phosphate (HDBP) content is 0.1mol / L, and the content of other degradation products and metal ions is not determined. The appearance of the feed liquid is a yellow-brown clear solution.

[0043] Example 1

[0044] (1) Preparation of complexing eluent:

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

[0046] (2) Elution of uranium:

[0047] Take 1.0 mL of uranium-containing waste organic phase in 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 the aqueous phase are separated, take the organic phase to test the uranium concentration, and calculate the uranium elution rate according to the following formula:

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

[0049] (3) Collecting the aqueous solution after eluting uranium in the above step (2), adjusting the pH of the aqueous solution to above 13 with a concentrated NaOH solution with a mass percentage of 50%, gradually precipitating a yellow precipitate from the solution, discarding the supernatant, washing the precipitate with a 0.01 mol / L dilute NaOH solution, and finally collecting the precipitate to obtain pure sodium diuranate solid, thereby achieving the purpose of uranium recovery.

[0050] Figure 2 The Raman spectrum of the sodium diuranate recovered in Example 1 of the present application after being dissolved in 0.1 mol / L dilute nitric acid is shown. As can be seen from the figure, there is no characteristic peak of pyrophosphate in the sodium diuranate recovered by the method of the present application, indicating that there is no sodium pyrophosphate impurity in the diuranate precipitate, and the purpose of purification is achieved.

[0051] Example 2-3

[0052] Example 2-3 Uranium was recovered in a similar manner to Example 1, except that the concentration of nitric acid in the complexing eluent was adjusted with reference 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, so the calculated elution rate is >99.8%.

[0056] Embodiment 5-7

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

[0058] Example 5-7 recovers uranium in a similar manner to Example 1, except that the volume ratio of the uranium-containing waste organic phase to the complexing eluent in step (2) is adjusted with reference to the parameters shown in Table 2. The uranium elution rate is tested and calculated, and the results are shown in Table 2.

[0059] Table 2

[0060]

[0061] From the above results, it can be seen that the uranium-containing waste organic phase is treated with the complexing eluent provided by the method of the present invention, wherein the concentration of the metaphosphate in the complexing eluent is in the range of 0.16-0.5 mol / L, the concentration of the inorganic acid is in the range of 0.1-1.0 mol / L, and the volume ratio of the uranium-containing waste organic phase: the complexing eluent in the elution step is in the range of 1:1 to 1:5, which can effectively elute the uranium in the uranium-containing waste organic phase, and the uranium elution efficiency is as high as more than 99%. The method of the present application is simple to operate and can be applied 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 changes made by using the contents of the present invention specification and drawings under the inventive concept of the present invention, or directly / indirectly applied in other related technical fields are included in the patent protection scope of the present invention.

Claims

1. A method for recovering uranium, characterized in that: The method comprises: mixing a uranium-containing waste organic phase with a complexing eluent, collecting a uranium-containing aqueous phase after phase separation, adjusting the pH of the uranium-containing aqueous phase to generate a diuranate precipitate, filtering and collecting the diuranate precipitate, wherein the complexing eluent comprises sodium pyrophosphate and nitric acid.

2. The method according to claim 1, characterized in that The uranium-containing waste organic phase comprises uranium, kerosene, tributyl phosphate and dibutyl phosphate.

3. The method according to claim 1 or 2, characterized in that: In the complexing eluent, the concentration of the sodium pyrophosphate is 0.16-0.5 mol / L, and the concentration of the nitric acid is 0.1 mol / L-1.0 mol / L.

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

5.

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

6. The method according to claim 1 or 2, characterized in that: The recovery method further comprises, after collecting the diuranate precipitate, washing the diuranate precipitate with a 0.1 mol / L-0.5 mol / L NaOH solution or ammonia water.

7. The method according to claim 1 or 2, characterized in that: The mixing is performed by shaking or stirring.

8. The method according to claim 1 or 2, characterized in that: After the uranium-containing waste organic phase feed liquid is mixed with the complexing eluent, the mixed solution is separated into phases by standing or centrifuging.

9. The method according to claim 1, characterized in that: The method comprises: mixing a uranium-containing waste organic phase with a complexing eluent by shaking or stirring, wherein the complexing eluent comprises sodium pyrophosphate with a concentration of 0.16 to 0.5 mol / L and nitric acid with a concentration of 0.1 to 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 phase separation by standing or centrifugation, collecting a uranium-containing aqueous phase, adding a NaOH solution with a mass proportion of 50% to 52% or ammonia water with a mass proportion of 25% to 28% to adjust the pH of the uranium-containing aqueous phase to greater than 13, generating a diuranate precipitate, and filtering and collecting the diuranate precipitate.

10. The method according to claim 9, characterized in that The diuranate precipitate is washed with a NaOH solution having a concentration of 0.1-0.5 mol / L to obtain purified diuranate.

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