Method for separating caesium-137

Abstract

The invention relates to the technical field of nuclear fuel cycle post-treatment, and provides a method for separating caesium-137. The method specifically comprises the following steps: digesting the caesium-137-containing waste by using an acid solution to obtain a raw material solution, carrying out acid removal treatment on the raw material solution to obtain a to-be-separated solution, and carrying out chromatographic separation treatment on the to-be-separated solution to separate out the caesium-137. The cesium-137 separation method can effectively realize cesium-137 separation, has the advantages of simplicity and convenience in operation, low energy consumption, low cost input and promotion of resource recycling, and is suitable for large-scale application.

Description

Technical Field

[0001] This application relates to the field of nuclear fuel cycle reprocessing technology, and more specifically, to a method for separating cesium-137. Background Technology

[0002] Spent fuel is formed in nuclear reactors due to the consumption of fuel materials and the accumulation of fission products. After undergoing a high-temperature oxidation process using dry reprocessing methods, it forms fly ash. Cesium-137 is a fission product in spent fuel fly ash. Its strong radioactivity can cause serious damage to organisms and the environment. However, Cesium-137 is also an important element used in the medical, industrial, agricultural, and nuclear battery fields.

[0003] In the fields of nuclear chemical engineering and spent fuel reprocessing, fly ash containing cesium-137 can be solidified through methods such as glass solidification and ceramic solidification before being subjected to deep geological treatment. However, the solidification process requires high-temperature conditions and sophisticated equipment, resulting in high energy consumption and economic investment. Furthermore, it cannot be recycled, leading to resource waste.

[0004] Therefore, methods for treating spent fuel fly ash containing cesium-137 still need to be developed. Summary of the Invention

[0005] This application aims to address, to some extent, the problems existing in current separation technologies. To this end, this application proposes a method for separating cesium-137. This method can effectively achieve the purification and recovery of cesium-137, and has the advantages of simple operation, low energy consumption, low cost, and promotion of resource recycling, making it suitable for large-scale application.

[0006] In one aspect of this application, a method for separating cesium-137 is proposed. According to an embodiment of this application, the method includes digesting waste containing cesium-137 with an acid solution to obtain a raw material solution, subjecting the raw material solution to acid removal treatment to obtain a solution to be separated, and subjecting the solution to chromatographic separation treatment to separate the cesium-137, wherein the acid solution includes nitric acid, sulfuric acid, and perchloric acid.

[0007] According to the method for separating cesium-137 according to embodiments of this application, a mixed acid composed of nitric acid, sulfuric acid, and perchloric acid is used to digest spent fuel fly ash containing cesium-137, resulting in a clear and transparent state after digestion. Nitric acid, as a strong oxidant, is easily volatile and can increase the vapor pressure of the device in a closed system. Sulfuric acid, as a strong dehydrating agent and strong oxidant, can effectively increase the boiling point of the digestion solution. Perchloric acid, as a highly oxidizing inorganic acid, can completely decompose the material to be digested and convert the carbon components attached to the spent fuel into carbon dioxide, thus promoting the digestion of waste containing cesium-137. The inventors found through research that other digestion acids, such as aqua regia or reverse aqua regia, have poor digestion effects, resulting in black suspended matter or precipitate after digestion. Comparison showed that the mixed acid has a better digestion effect, thus facilitating the separation of cesium-137. Furthermore, during the chromatographic separation process, the pH of the solution to be separated needs to be adjusted to prevent a high pH value from affecting the separation effect of the cation exchange column and to ensure that impurity elements are not retained on the column but are eluted away. Cesium-137 is retained on the column and then separated by the eluent. Through in-depth research, the inventors discovered that by utilizing the ions in the eluent with appropriate pH to carry out a reversible ion exchange reaction with the cesium-137 cations bound on the column, and by changing the equilibrium, the cesium-137 ions are desorbed and eluted with the eluent, thereby achieving effective separation of cesium-137.

[0008] According to embodiments of this application, the above-described method for separating zirconium and hafnium may also have the following additional technical features: According to embodiments of this application, the amount of 70% concentrated nitric acid in the acid solution is 0.1 ml to 10 ml. In some embodiments, the amount of 70% concentrated nitric acid in the acid solution is 0.1 ml, 0.2 ml, 0.5 ml, 1 ml, 1.5 ml, 2 ml, 2.5 ml, 3 ml, 4 ml, 5 ml, 6 ml, 7 ml, 8 ml, 9 ml, or 10 ml. The amount of 70% concentrated nitric acid in the acid solution that meets the above conditions can effectively improve the separation effect of ruthenium-106.

[0009] According to embodiments of this application, the amount of 98% concentrated sulfuric acid in the acid solution is 0.1 ml to 5 ml. In some embodiments, the amount of 98% concentrated sulfuric acid in the acid solution is 0.1 ml, 0.2 ml, 0.3 ml, 0.4 ml, 0.5 ml, 0.8 ml, 1 ml, 1.5 ml, 2 ml, 2.5 ml, 3 ml, 3.5 ml, 4 ml, 4.5 ml, or 5 ml. The amount of 98% concentrated sulfuric acid in the acid solution that meets the above conditions can effectively improve the separation effect of ruthenium-106.

[0010] According to embodiments of this application, the amount of 72% perchloric acid in the acid solution is 0.1 ml to 2 ml. In some embodiments, the amount of 72% perchloric acid in the acid solution is 0.1 ml, 0.25 ml, 0.5 ml, 0.75 ml, 1 ml, 1.25 ml, 1.5 ml, 1.75 ml, or 2 ml. The amount of 72% perchloric acid in the acid solution that meets the above conditions can effectively improve the separation effect of ruthenium-106.

[0011] According to an embodiment of this application, the waste containing cesium-137 in the acid solution includes spent fuel fly ash, which contains cesium-137 and ruthenium-106.

[0012] According to an embodiment of this application, the digestion treatment is carried out at a temperature of 100 ℃ to 200 ℃ for a time of 1 h to 3 h. The digestion treatment meets the above temperature and time conditions, which can achieve complete dissolution of the waste to be separated and provide suitable reaction conditions for the digestion process, effectively improving the separation effect of cesium-137.

[0013] According to an embodiment of this application, the digestion process is carried out in a closed environment. The closed process can create a high-temperature, high-pressure, and highly oxidizing environment, thereby improving the digestion effect and effectively enhancing the separation of cesium-137.

[0014] According to an embodiment of this application, the solid-liquid ratio of the waste to the acid is 1:(20~40), thereby facilitating the complete digestion of the waste to be separated and improving the effective separation of cesium-137.

[0015] According to the embodiments of this application, the acid removal treatment is performed at a temperature of 100 ℃~150 ℃ for 1 h~2 h. The acid removal can drive the acidic radical components in the raw material liquid out of the raw material liquid system, preventing them from affecting the subsequent separation effect. If the acid removal temperature is too high, the evaporation rate will be too fast, thus affecting the concentration or state of the target sample. If the acid removal temperature is too low, the separation process will be delayed or the acidic radical components will remain too high, thus affecting the separation. The acid removal treatment meets the above temperature and time conditions, which can effectively improve the separation effect of cesium-137.

[0016] According to an embodiment of this application, the method further includes: adjusting the pH value of the treatment solution obtained from the acid removal treatment to 1.5~6.5 using a pH adjuster to obtain the solution to be separated. The solution to be separated that meets the above pH value conditions can achieve the retention of cesium-137 on the chromatographic column and the removal of impurity elements with the liquid flow during chromatographic separation treatment, so as to facilitate the effective separation of cesium-137.

[0017] According to embodiments of this application, the regulator comprises deionized water and 0.1 mol / L to 5 mol / L dilute nitric acid.

[0018] According to an embodiment of this application, the chromatographic separation process includes: adding the liquid to be separated into the chromatographic column, washing the chromatographic column with deionized water, adding eluent into the chromatographic column after washing, and collecting the eluent to separate the cesium-137. By following the above chromatographic separation process, further removal of impurity elements on the chromatographic column and effective separation of the target element cesium-137 can be achieved.

[0019] According to an embodiment of this application, the eluent is a 1 mol / L dilute nitric acid solution. The concentration of nitric acid in the eluent meets the above conditions, which can effectively improve the separation effect of cesium-137.

[0020] According to an embodiment of this application, the chromatographic column used in the chromatographic separation process is selected from a cation exchange chromatographic column.

[0021] Beneficial effects: The method for separating cesium-137 presented in this application can effectively achieve the separation and purification of cesium-137, meet the requirements of resource recycling, and does not introduce organic reagents, thus causing less environmental pollution and conforming to the development concept of green chemistry. At the same time, it reduces the energy consumption and investment costs of related reagents and equipment in the treatment of spent fuel fly ash, and has economic benefits and competitiveness for large-scale application. Attached Figure Description

[0022] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which: Figure 1 This is a schematic diagram of a method for separating cesium-137 from spent fuel fly ash. Figure 2 This is a schematic diagram of the digestion apparatus; Figure 3 This is a schematic diagram of the separation device; Figure 4 The results are from the gamma-ray spectrometry analysis of the feed liquid from the spent fuel flyback digestion. Figure 5 These are the results of the liquid gamma spectrum analysis of the separated product. Detailed Implementation

[0023] The present application's solution will be explained below with reference to embodiments. Those skilled in the art will understand that the following embodiments are for illustrative purposes only and should not be considered as limiting the scope of the application. Where specific techniques or conditions are not specified in the embodiments, they are performed in accordance with the techniques or conditions described in the literature in the art or according to the product instructions. Unless otherwise stated, the active pharmaceutical ingredients, excipients, and reagents used in the following embodiments are commercially available products or can be prepared by known methods.

[0024] Before introducing the technical solution of this application, the relevant knowledge of this application will be introduced below: In the embodiments of this application, "digestion" refers to the pretreatment operation in which the spent fuel components are destroyed by means of strong acid and oxidant, supplemented by heating, pressurization and other methods, so that the target components in the sample are completely dissolved and converted into a soluble state.

[0025] In the embodiments of this application, "acid removal" refers to the operation of removing excess acid (including nitric acid, perchloric acid, etc.) from the system by heating during sample pretreatment, thereby adjusting the acidity of the solution to the target range or removing most of the acid.

[0026] In the embodiments of this application, "spent fuel fly ash" refers to fine particulate (usually with a particle size <100μm) radioactive solid waste generated during the reprocessing processes of spent fuel, such as mechanical crushing, high-temperature roasting, oxidative decomposition, and incineration. Its core components include incompletely decomposed fuel matrix (such as carbon matrix and oxide matrix), fission products, and a small amount of structural material impurities. It is a medium / high radioactive waste that needs to be controlled in the nuclear fuel reprocessing process.

[0027] In the embodiments of this application, "eluent" refers to the liquid that flows out after the chromatographic column has been cleaned and eluted with eluent during the chromatographic separation process.

[0028] In the embodiments of this application, "cation exchange chromatography column" refers to a chromatographic separation device with cation exchange resin as the stationary phase. The core is to utilize the ion exchange between the functional groups of the resin and the cations in the mobile phase. Based on the differences in the binding strength or selectivity coefficient of different cations with the resin, the separation and enrichment of cation mixtures can be achieved.

[0029] In the embodiments of this application, "aqua regia" refers to a strong oxidizing mixed acid system prepared by mixing concentrated nitric acid and concentrated hydrochloric acid in a volume ratio of 1:3.

[0030] In the embodiments of this application, "reverse aqua regia" refers to a strong oxidizing mixed acid system prepared by mixing concentrated nitric acid and concentrated hydrochloric acid in a volume ratio of 3:1.

[0031] The technical solutions in the embodiments of this application will be described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0032] Example 1 In this embodiment, according to the appendix Figure 1 The method flow shown separates cesium-137: 1. Add 0.1 g of carbon-based spent fuel fly ash to a mixed acid solution containing 4 ml of 70% nitric acid, 1 ml of 72% perchloric acid, and 4 ml of 98% sulfuric acid. Seal the solution at 120 °C in the container as shown in the attached figure. Figure 2 Digestion was performed in the digestion apparatus shown for 2 hours to obtain a raw material liquid. The components of the raw material liquid are as shown in the attached figure. Figure 4 The figure shows cesium-137 and ruthenium-106.

[0033] 2. Heat the raw material liquid in an open container at 120 ℃ until the volume remains constant to obtain the liquid to be separated; 3. Dilute the solution to be separated 50 times, adjust the pH to 5.2 with deionized water, and then add it to the solution as shown in the attached table. Figure 3 In the chromatographic column of the separation apparatus shown.

[0034] 4. Elute the chromatographic column with deionized water to remove contaminants, and then elute the column with 1 mol / L nitric acid solution to obtain a purified cesium-137 solution. Analyze the purity and activity of the product solution using gamma spectroscopy, as shown in the attached diagram. Figure 5 As shown, the product liquid contains cesium-137 with an activity of 30,000 Bq.

[0035] Comparative Examples 1-2 Cesium was separated according to the method in Example 1, except that the acid solution was replaced with aqua regia and reverse aqua regia, respectively.

[0036] The separation results are shown in Table 1: Table 1:

[0037] The results are shown in Table 1. After digestion of the carbon-based spent fuel fly ash of cesium-137 using a mixed acid composed of nitric acid, sulfuric acid, and perchloric acid, the product was clear and transparent. The activity of cesium-137 in the separated product was 30,000 Bq. Other digesting acids, such as aqua regia or reverse aqua regia, were not effective, and black suspended matter or precipitate was present after digestion, making further separation impossible. This proves that the separation method of this application can effectively separate cesium-137.

[0038] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0039] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0040] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A method for separating cesium-137, characterized in that, include: Waste containing cesium-137 was digested using acid to obtain a raw material solution; The raw material solution is subjected to acid removal treatment to obtain the solution to be separated; The solution to be separated is subjected to chromatographic separation in order to separate cesium-137; The acid solution includes nitric acid, sulfuric acid, and perchloric acid.

2. The method according to claim 1, characterized in that, The amount of 70% concentrated nitric acid used in the acid solution is 0.1 ml to 10 ml; Optionally, the amount of 98% concentrated sulfuric acid used in the acid solution is 0.1 ml to 5 ml; Optionally, the amount of 72% perchloric acid in the acid solution is 0.1 ml to 2 ml.

3. The method according to claim 1, characterized in that, The waste containing cesium-137 includes spent fuel fly ash; Optionally, the fly ash contains cesium-137 and ruthenium-106.

4. The method according to claim 1, characterized in that, The digestion process is carried out at a temperature of 100 ℃ to 200 ℃ for a time of 1 h to 3 h in a closed environment.

5. The method according to claim 1, characterized in that, The solid-liquid ratio of the waste to the acid is 1:(20~40).

6. The method according to claim 1, characterized in that, The acid removal treatment is performed at a temperature of 100 ℃ to 150 ℃ for a time of 1 h to 2 h.

7. The method according to claim 1, characterized in that, The method further includes: adjusting the pH value of the treatment solution obtained from the acid removal treatment to 1.5~6.5 using a pH adjuster to obtain the solution to be separated; Optionally, the regulator includes deionized water and 0.1 mol / L to 5 mol / L dilute nitric acid.

8. The method according to claim 1, characterized in that, The chromatographic separation process includes: adding the liquid to be separated into the chromatographic column, washing the chromatographic column with deionized water, adding eluent into the chromatographic column after washing, and collecting the eluent to separate the cesium-137. Optionally, the eluent is a 1 mol / L dilute nitric acid solution.

9. The method according to claim 1, characterized in that, The chromatographic column used in the chromatographic separation process is selected from cation exchange chromatographic columns.

Images