Method for reducing concentration of nitric acid in feed liquid in spent fuel post-treatment process

Abstract

The invention relates to a method for reducing the concentration of nitric acid in feed liquid in a spent fuel post-treatment process, which comprises the following steps: mixing the feed liquid containing nitric acid as a water phase with an organic phase in volume, stirring, extracting acid, and standing to obtain the organic phase and the water phase after acid extraction; the organic phase obtained after acid extraction and a carbonate aqueous solution are mixed in an isovolumetric mode and stirred, then standing layering is conducted, a first organic phase is obtained, the first organic phase and deionized water are mixed in an isovolumetric mode and stirred, standing is conducted after washing is conducted, a regenerated organic phase is obtained, and the regenerated organic phase is repeatedly used. Compared with the prior art, the method is used for deacidifying the specific acid-containing feed liquid, the nitric acid concentration can be reduced by two orders of magnitude, the speed is high, and the content of lanthanide metal ions in the feed liquid is almost not lost. In addition, a solvent extraction method is adopted for deacidification, the compatibility of the operation process and the existing spent fuel post-treatment process is high, and the method has great advantages in the aspect of industrialization.

Description

Technical Field

[0001] The invention relates to the technical field of spent fuel post-processing, and in particular to a method for reducing the nitric acid concentration of liquid feed in the process of spent fuel post-processing. Background Art

[0002] In the wet process of nuclear fuel reprocessing, nitric acid is widely used in dissolution, oxidation, extraction, etc., and its concentration has an important influence on the reprocessing process. Therefore, in the reprocessing of acidic (nitric acid) spent fuel, due to changes in treatment process conditions or (evaporation) concentration, it is usually necessary to reduce the concentration of free nitric acid in the feed liquid to meet the pretreatment requirements. At present, the method of denitrification is usually used to reduce the concentration of nitric acid in the feed liquid, which is mainly divided into biological denitrification, electrochemical denitrification, chemical reduction denitrification, etc.

[0003] Among them, biological denitrification has good denitrification efficiency, but the reaction rate is slow, the denitrification cycle is long, the bacteria have strict requirements on the system environment (for example, they are more sensitive to the concentration of metal ions therein), are difficult to control, and produce organic residues; although electrochemical denitrification is relatively safe and easy to control, electrode maintenance and energy consumption limit its industrial application; chemical reduction denitrification mainly uses formaldehyde, formic acid and other substances to reduce nitric acid for denitrification, but its reaction temperature is usually 90-100°C, the energy consumption is high, the addition rate of formaldehyde or formic acid must be strictly controlled, and there is a risk of explosion.

[0004] The above methods each have their own advantages and disadvantages. Therefore, developing a method for reducing the nitric acid concentration of the feed liquid with simple steps, easy operation, mild conditions and rapidity is of great significance and necessity for the subsequent further processing or concentration of the feed liquid. Summary of the invention

[0005] The purpose of the present invention is to overcome the defects of the above-mentioned prior art and provide a method for reducing the nitric acid concentration of the liquid in the spent fuel reprocessing process. The organic amine extractant used is low in cost, simple to operate, mild in conditions, and highly safe; the extractant used can be recycled and reused, saving energy and economic costs.

[0006] The purpose of the present invention can be achieved by the following technical solutions:

[0007] The present invention provides a method for reducing the concentration of nitric acid in a feed liquid during spent fuel reprocessing, comprising the following steps:

[0008] S1: mixing the feed liquid containing nitric acid as the aqueous phase with the organic phase in equal volumes and stirring, extracting the acid and then letting it stand to obtain the organic phase and aqueous phase after the acid extraction;

[0009] S2: The organic phase obtained after acid extraction in S1 is mixed with an equal volume of a carbonate aqueous solution and stirred, and then allowed to stand to separate into layers to obtain a first organic phase, and the first organic phase is mixed with an equal volume of deionized water and stirred, and then allowed to stand after washing to obtain a regenerated organic phase, which is reused.

[0010] Furthermore, in S1, the concentration of nitric acid in the aqueous phase is (0.1-0.3) mol / L, and the metal ions contained in the aqueous phase are one or more of Zr, Y, La, Ce, Pr, Nd, Sm, Eu, and Gd.

[0011] Furthermore, the concentration of the metal ions is (0-500) pm.

[0012] Furthermore, in S1, the organic phase includes a nitric acid extractant, a phase modifier and a diluent.

[0013] Further, in S1, the nitric acid extractant is an alkaline organic amine compound, and the alkaline organic amine compound includes one of tri-n-octylamine, di-iso-octylamine, di-n-octylamine, and tri-iso-octylamine, and the structural formula is shown below; preferably, the alkaline organic amine compound is tri-n-octylamine;

[0014]

[0015] Furthermore, the volume fraction of the alkaline organic amine compound in the organic phase is 15%-30%.

[0016] Furthermore, the phase modifier is tributyl phosphate, the structural formula of which is shown below. The volume fraction of the tributyl phosphate in the organic phase is 10%-30%.

[0017]

[0018] Furthermore, the diluent is kerosene.

[0019] Furthermore, in S2, the carbonate aqueous solution is one of ammonium carbonate and sodium carbonate.

[0020] Furthermore, in S1 and S2, the stirring time is (4-6) minutes.

[0021] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0022] 1. The present invention reduces the acidity of the aqueous phase of a specific acid-containing feed solution, and the nitric acid concentration can be reduced by two orders of magnitude at a relatively fast rate, and the content of lanthanide metal ions in the feed solution is almost not lost.

[0023] 2. The organic amine extractant tri-n-octylamine used in the present invention has low cost, simple operation, mild conditions and high safety; in addition, tri-n-octylamine can be recycled and reused, saving energy and economic costs.

[0024] 3. The present invention adopts a solvent extraction method for acid reduction, and its operation process is highly compatible with the existing spent fuel reprocessing process, and has great advantages in industrialization. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 A flow chart for reducing the concentration of nitric acid in the liquid during spent fuel reprocessing;

[0026] Figure 2 is a graph of the total metal ion extraction efficiency of TOA recycled in Experimental Example 1;

[0027] Figure 3 is the pH value of the aqueous solution after extraction in the TOA recycling process in Experimental Example 1. DETAILED DESCRIPTION

[0028] The specific implementation methods of the present invention are described in detail below through examples. These examples are implemented on the premise of the scheme described in the present invention, and provide detailed implementation methods and specific operating processes, but the protection scope of the present invention is not limited to the following examples.

[0029] The present invention is further described below in conjunction with the accompanying drawings and specific embodiments. Any features such as component models, material names, connection structures, preparation methods, materials, structures or composition ratios not clearly described in this technical solution are deemed to be common technical features disclosed in the prior art.

[0030] Example 1

[0031] This embodiment provides a method for reducing the nitric acid concentration of the feed liquid during the spent fuel reprocessing process, such as Figure 1 As shown, the following process is included:

[0032] Preparation of feed solution: prepare acid-containing feed solution, i.e., aqueous phase feed solution, according to Zr (0.4 g / L), Y (0.014 g / L), La (0.0008 g / L), Ce (0.019 g / L), Pr (0.019 g / L), Nd (0.14 g / L), Sm (0.08 g / L), Eu (0.027 g / L), and Gd (0.025 g / L) (nitrate), and the concentration of nitric acid is 0.15 mol / L.

[0033] Preparation of organic phase: using kerosene as diluent and 30% by volume of tributyl phosphate as phase modifier, prepare an organic phase with 15% by volume of tri-n-octylamine (TOA).

[0034] Solvent extraction operation: At room temperature, take 10 mL of the aqueous phase and 15% tri-n-octylamine organic phase in a 50 mL extraction centrifuge tube and mix for 5 minutes, then let stand for 5 minutes to allow the two phases to separate quickly. Place the extraction centrifuge tube in a centrifuge to separate the two phases and obtain the aqueous phase①.

[0035] Regeneration of organic phase: At room temperature, 5 mL of the organic phase after acid extraction was mixed with 5 mL of 0.2 mol / L sodium carbonate aqueous solution and stirred for 5 minutes to remove acid; then let it stand, the two phases separated quickly within 5 minutes, and no third phase or emulsification occurred. Then centrifuge, take out the first organic phase, mix 5 mL of the first organic phase with 5 mL of deionized water in equal volumes and stir for 5 minutes for washing; then let it stand, the two phases separated quickly within 5 minutes, and no third phase or emulsification occurred. Then separate the obtained organic phase, i.e. the regenerated organic phase, which can be directly put into use again.

[0036] Example 2

[0037] The difference between this embodiment and embodiment 1 is that the organic phase is configured with 20% volume fraction of tri-n-octylamine, and the rest of the contents are the same as those in embodiment 1, to obtain a water phase ②.

[0038] Example 3

[0039] The difference between this embodiment and embodiment 1 is that the organic phase is configured with 30% volume fraction of tri-n-octylamine, and the rest of the contents are the same as those in embodiment 1, to obtain an aqueous phase ③.

[0040] pH test of the liquid before and after extraction: Before extraction, 5 mL of the aqueous phase liquid was tested with a pH meter, and the pH was 0.75. Then, the pH of the aqueous phases ①, ②, and ③ were tested with a pH meter, and the pH values ​​were 3.15, 3.58, and 3.80, respectively.

[0041] ICP test before and after extraction of the liquid: Before extraction, take 5 mL of the liquid for ICP test and record the initial concentration of element ions C0. Then, ICP test the aqueous phases ①, ②, and ③ respectively and record the concentration of element ions C after extraction. n Extraction efficiency = (C0-C n ) / C0, the results are shown in Table 1, 15% tri-n-octylamine organic phase hardly extracts metal ions; 20% tri-n-octylamine and 30% tri-n-octylamine organic phases extract trace or small amounts of metal ions.

[0042] Table 1. Extraction efficiency of metal ions in aqueous phase with different concentrations of TOA

[0043]

[0044] Note: “ / ” indicates no extraction was detected.

[0045] Example 4

[0046] In this embodiment, the regenerated organic phase obtained in Example 1 is recycled, and the specific process is as follows:

[0047] The obtained regenerated organic phase was used as an extractant for solvent extraction, and the extracted sample was subjected to pH and ICP tests; then the organic phase was regenerated, and these two steps were repeated 4 times. Figure 2 and Figure 3 As shown, Figure 2 The extraction efficiencies of TOA cycles 1-5 were 1.08%, 1.47%, 1.96%, 1.61% and 2.13%, respectively. In the five test results, the nitric acid content in the feed solution decreased from 0.15 mol / L to pH>3, and there was no significant difference in the ICP test results, that is, the metal ions were almost not extracted.

[0048] Comparative Example 1

[0049] This comparative example provides a comparison of the effects of four organic amines in the deacidification process, including the following processes:

[0050] Preparation of feed solution: prepare acid-containing feed solution, i.e., aqueous phase feed solution, according to Zr (0.4 g / L), Y (0.014 g / L), La (0.0008 g / L), Ce (0.019 g / L), Pr (0.019 g / L), Nd (0.14 g / L), Sm (0.08 g / L), Eu (0.027 g / L), and Gd (0.025 g / L) (nitrate), and the concentration of nitric acid is 0.15 mol / L.

[0051] Preparation of organic phase: using kerosene as diluent and 30% by volume of tributyl phosphate as phase modifier, the organic amines are prepared as di-n-octylamine, diisooctylamine, tri-n-octylamine and triisooctylamine, and the volume fraction of the organic phase is 10%.

[0052] Solvent extraction operation: At room temperature, 10 mL of the aqueous phase liquid and each of the four organic phases were taken in a 50 mL extraction centrifuge tube and mixed for 5 minutes, then allowed to stand for 5 minutes, and the two phases were quickly separated. After the extraction centrifuge tube was placed in a centrifuge, the two phases were separated to obtain the aqueous phase. The pH of the aqueous phase was tested separately, and the results are shown in Table 2. Although di-isooctylamine and di-n-octylamine had better deacidification effects, emulsification occurred during the extraction process; tri-n-octylamine and tri-isooctylamine did not emulsify during the extraction process, but the deacidification effect of tri-n-octylamine was significantly better than that of tri-isooctylamine.

[0053] Table 2 Acid removal effect and emulsification phenomenon of different organic amines

[0054]

[0055] The above description of the embodiments is to facilitate the understanding and use of the invention by those skilled in the art. It is obvious that those skilled in the art can easily make various modifications to these embodiments and apply the general principles described herein to other embodiments without creative work. Therefore, the present invention is not limited to the above embodiments, and improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the present invention should be within the scope of protection of the present invention.

Claims

1. A method for reducing the concentration of nitric acid in the feed liquid during spent fuel reprocessing, It is characterized in that The following steps are involved: S1: mixing the feed liquid containing nitric acid as the aqueous phase with the organic phase in equal volumes and stirring, extracting the acid and then letting it stand to obtain the organic phase and aqueous phase after the acid extraction; S2: The organic phase obtained after acid extraction in S1 is mixed with an equal volume of a carbonate aqueous solution and stirred, and then allowed to stand to separate into layers to obtain a first organic phase, and the first organic phase is mixed with an equal volume of deionized water and stirred, and then allowed to stand after washing to obtain a regenerated organic phase, which is reused.

2. A method for reducing the concentration of nitric acid in the feed liquid during spent fuel reprocessing according to claim 1, It is characterized in that In S1, the concentration of nitric acid in the aqueous phase is (0.1-0.3) mol / L, and the metal ions contained in the aqueous phase are one or more of Zr, Y, La, Ce, Pr, Nd, Sm, Eu, and Gd.

3. A method for reducing the concentration of nitric acid in the feed liquid during the spent fuel reprocessing process according to claim 2, It is characterized in that The concentration of the metal ions is (0-500) pm.

4. A method for reducing the concentration of nitric acid in the feed liquid during the spent fuel reprocessing process according to claim 1, It is characterized in that In S1, the organic phase comprises a nitric acid extractant, a phase modifier and a diluent.

5. A method for reducing the concentration of nitric acid in the feed liquid during the spent fuel reprocessing process according to claim 4, It is characterized in that The nitric acid extractant is an alkaline organic amine compound, and the alkaline organic amine compound includes one of tri-n-octylamine, di-iso-octylamine, di-n-octylamine and tri-iso-octylamine.

6. A method for reducing the concentration of nitric acid in the feed liquid during the spent fuel reprocessing process according to claim 5, It is characterized in that The volume fraction of the alkaline organic amine compound in the organic phase is 15%-30%.

7. A method for reducing the concentration of nitric acid in the feed liquid during the spent fuel reprocessing process according to claim 4, It is characterized in that The phase modifier is tributyl phosphate, and the volume fraction of the tributyl phosphate in the organic phase is 10%-30%.

8. A method for reducing the concentration of nitric acid in the feed liquid during the spent fuel reprocessing process according to claim 4, It is characterized in that The diluent is kerosene.

9. A method for reducing nitric acid concentration in liquid feed during spent fuel reprocessing according to claim 1, It is characterized in that In S2, the carbonate aqueous solution is one of ammonium carbonate and sodium carbonate.

10. A method for reducing nitric acid concentration in liquid feed during spent fuel reprocessing according to claim 1, It is characterized in that In S1 and S2, the stirring time is 4-6 minutes.

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