A method for separating trace plutonium from a large amount of uranium using solid phase leaching resin

Abstract

The present invention relates to a method for separating trace plutonium from a large amount of uranium by using a solid phase leaching resin, and belongs to the field of spent fuel post-processing. A spent fuel post-processing simulation liquid containing uranium and plutonium is prepared, and the spent fuel post-processing simulation liquid is pumped into a leaching resin column at a first preset flow rate to perform a dynamic test, and the uranium and plutonium concentration in the aqueous phase at the outlet is analyzed at intervals to draw a penetration curve; an eluent is pumped into the leaching resin column after adsorption equilibrium at a second preset flow rate, and the eluent is used to elute plutonium. The method disclosed in the present invention is used to efficiently separate and purify trace plutonium in a large amount of uranium by using an extraction chromatography method having the characteristics of selectivity of solvent extraction and high efficiency of chromatographic separation, and a solid phase leaching resin with a wide range of acidity applications and high selectivity for Pu is used to achieve efficient separation of trace plutonium in a large amount of uranium, and the separation process does not require acid adjustment, and the operation is simple, the method is simple, the operation is simple, and the practicability is strong, which has a strong promotion advantage.

Description

Technical Field

[0001] The invention belongs to the field of spent fuel post-processing, and in particular relates to a method for separating trace plutonium from a large amount of uranium by using solid phase leaching resin. Background Art

[0002] Plutonium is a long-lived and extremely toxic element. Spent fuel reprocessing has very strict requirements for the control of plutonium in uranium products. The uranium-plutonium mass ratio of each process section of the spent fuel reprocessing uranium line is 10 6 The above (where the uranium concentration is generally 50-100g / L), a large amount of uranium matrix greatly interferes with the analysis of plutonium, and the existing analysis method must be strictly separated from uranium before it can be measured. It is also very difficult to separate the uranium matrix to the extent that it does not interfere with instrument measurement. The main reason is that the separation process for removing the uranium matrix is ​​long, and the decontamination factor is unstable, which makes it difficult to meet the requirements for accuracy, timeliness and stability of plutonium determination in uranium product quality control. In addition, when the operating conditions are abnormal, the plutonium content in the spent fuel reprocessing uranium product liquid does not meet the standard, and it is necessary to return to the previous process stage for deep purification. However, there is no other method suitable for deep purification of plutonium in large-volume uranium product liquid in China.

[0003] Currently, there are two main methods for separating trace plutonium from large amounts of uranium in spent fuel reprocessing, namely solvent extraction and ion exchange.

[0004] (1) Solvent extraction method, generally using 2-thenoyltrifluoroacetone (TTA) as the extractant and xylene as the diluent. The extraction distribution coefficient of TTA for Pu(IV) in 1-2 mol / L nitric acid system is greater than 1×10 4 , using the extraction characteristics of TTA in 1mol / L nitric acid system, plutonium can be extracted with TTA, and more than 99% of plutonium can be separated from uranium. Chinese patent CN111474234A discloses a method for analyzing the trace plutonium content in a large amount of uranium in a nuclear fuel reprocessing process, that is, using 0.4-0.6mol / LTTA-xylene solvent, adjusting the price and acid, and extracting and centrifuging, the separation of trace plutonium in a large amount of uranium is achieved. This method involves acid adjustment, and the operation steps are cumbersome. It is not suitable for the separation and purification of plutonium in large volumes of liquid feed, and the extraction system will also cause environmental problems.

[0005] (2) Ion exchange method. There are many reports on the separation of plutonium by anion exchange. The basic principle is to adjust the valence of plutonium to tetravalent, form a complex anion of plutonium nitrate in a nitric acid system (acidity greater than 6.5 mol / L), and exchange and adsorb on anion exchange chromatography. Since the complex anion of plutonium nitrate dissociates to form plutonium ions under low acid conditions and is not adsorbed by anion exchange resin, low acid (acidity less than 0.5 mol / L) can be used to elute plutonium from the resin. Li Huibo et al. (see: Research and Establishment of Separation Methods for Trace Plutonium in Large Amounts of Uranium, Annual Report of China Institute of Atomic Energy, 2006) proposed a combined separation process of quaternary ammonium salt-TBP extraction chromatography-ion exchange, first using extraction chromatography to remove most of the uranium, and then using ion exchange to purify the plutonium. The extraction chromatographic agent is selected as quaternary ammonium salt and TBP, and the adsorption acidity is 4 and 2 mol / L respectively, and the anion exchange resin is selected as 256 type, and the adsorption acidity is 6.5 mol / L. This method involves multiple acid adjustment, adsorption, elution and washing processes, and the operation steps are cumbersome.

[0006] In summary, for the separation of trace plutonium in large amounts of uranium, existing technologies all involve acid adjustment. For example, the solvent extraction method needs to be adjusted to 1-2 mol / L, and the ion exchange method needs to be adjusted to above 6.5 mol / L. However, the acidity of the spent fuel reprocessing uranium line varies greatly in different process sections, resulting in cumbersome operating steps during the acid adjustment process, which is not suitable for the deep purification of plutonium in large volumes of uranium liquid. Summary of the invention

[0007] In view of the defects existing in the prior art, the purpose of the present invention is to provide a method for separating trace plutonium from a large amount of uranium by using a solid phase leaching resin, using an extraction chromatography method having the characteristics of both the selectivity of solvent extraction and the high efficiency of chromatographic separation to efficiently separate and purify trace plutonium in a large amount of uranium, and providing a solid phase leaching resin with a wide range of acidity applications and high selectivity for Pu (IV), so as to achieve efficient separation and purification of trace plutonium in a large amount of uranium.

[0008] To achieve the above purpose, the technical solution adopted by the present invention is: a method for separating trace plutonium from a large amount of uranium using solid phase leaching resin, the method comprising the following steps:

[0009] S1. Prepare spent fuel reprocessing simulation liquid containing uranium and plutonium;

[0010] S2. Pumping the spent fuel reprocessing simulation liquid into the leaching resin column at a first preset flow rate, performing a dynamic test, analyzing the uranium and plutonium concentrations in the water phase at the outlet at regular intervals, and drawing a breakthrough curve;

[0011] S3. Pumping the eluent into the elution resin column after adsorption equilibrium at a second preset flow rate, and eluting plutonium with the eluent.

[0012] Furthermore, in the spent fuel reprocessing simulation liquid in step S1, the U(VI) concentration is 30-110 g / L, the Pu(IV) concentration is 0.5-50 mg / L, and the HNO3 concentration is 0.1-4 mol / L.

[0013] Furthermore, the first preset flow rate is 0.2-0.4 mL / min.

[0014] Furthermore, the second preset flow rate is 0.5-1.5 mL / min.

[0015] Furthermore, the eluent is a mixture of 0.1-0.5 mol / L HNO3 and 0.05-0.2 mol / L H2C2O4.

[0016] Further, the solid phase extraction resin is prepared by the following method:

[0017] S21, synthesis of polyamide ligands by substitution reaction;

[0018] S22, synthesis of silicon-based supports by activation and in situ polymerization;

[0019] S23, using a vacuum impregnation method to load the polyamide ligand synthesized in step S21 onto the silicon-based carrier synthesized in step S22 to synthesize a solid phase leaching resin.

[0020] Furthermore, in step S21, N,N'-dimethylformamide is used as a catalyst to react nitrilotriacetic acid with oxalyl chloride in a dibutylamine solvent to undergo a substitution reaction, and then impurities are removed by vacuum distillation, and then dialkylamine is added to generate a corresponding polyamide ligand product.

[0021] Furthermore, step S21 further comprises refluxing the polyamide ligand mixture, washing it with water, 1M HCl washing solvent solution, 1M NaOH solution and water in sequence, and then drying it.

[0022] Further, step S22 specifically includes first placing the silicon dioxide in a 10-100 mPa vacuum environment, then filling it with nitrogen or an inert gas to normal pressure, then heating it to 100-500° C., constant temperature activation, obtaining activated silicon dioxide, and sealing and storing it in a N2 atmosphere;

[0023] The monomers DVB and styrene are fully mixed with the activated silica in a system with acetophenone and diethyl phthalate as diluents and AIBN and V-40 as initiators, and then nitrogen or inert gas is filled into the system to normal pressure to ensure that the device is basically in an oxygen-free environment. The prepared SiO2-P is washed with acetone and ultrapure water alternately for several times until no obvious impurities appear in the washing liquid, thereby realizing the synthesis of silicon-based carriers.

[0024] Further, step S23 includes dissolving the polyamide ligand in ethanol or acetone solvent, transferring it to a container containing a certain amount of activated silica, performing rotary evaporation to remove the organic solvent therein to obtain a powdered solid, and drying the powdered solid.

[0025] The beneficial technical effect of the present invention is: adopting a method disclosed in the present invention to separate trace plutonium from a large amount of uranium by using a solid phase leaching resin, by preparing a spent fuel post-processing simulation liquid containing uranium and plutonium, pumping the spent fuel post-processing simulation liquid into the leaching resin column at a first preset flow rate, conducting a dynamic test, analyzing the uranium and plutonium concentration in the aqueous phase at the outlet at intervals, and drawing a penetration curve; pumping an eluent into the leaching resin column after adsorption equilibrium at a second preset flow rate, and using the eluent to elute plutonium. The method disclosed in the present invention adopts an extraction chromatography method having the characteristics of selectivity of solvent extraction and high efficiency of chromatographic separation to efficiently separate and purify trace plutonium in a large amount of uranium, adopts a solid phase leaching resin with a wide range of acidity applications and high selectivity for Pu, and realizes efficient separation of trace plutonium in a large amount of uranium, and the separation process does not require acid adjustment, and the operation is simple, the method is simple, the operation is simple, and the practicability is strong, which has a strong promotion advantage. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 A schematic diagram of the structure of a solid phase leaching resin prepared in the method for preparing a solid phase leaching resin according to Example 1 of the present invention;

[0027] Among them, R1~R8 each independently takes CnH 2n+1 (n is an integer, and 2≤n≤12). DETAILED DESCRIPTION

[0028] The present invention is further described below in conjunction with the accompanying drawings and specific embodiments.

[0029] Embodiment 1

[0030] The embodiment of the present invention provides a method for preparing a solid phase leaching resin, wherein the solid phase leaching resin is a silicon-based supported multiamide material, and the method comprises the following steps:

[0031] S21, synthesis of polyamide ligands by substitution reaction;

[0032] With N,N'-dimethylformamide as catalyst, nitrilotriacetic acid and oxalyl chloride are reacted in dibutylamine solvent at 25-35°C for substitution reaction, and then impurities are removed by reduced pressure distillation. Then, dialkylamine is added at below 5°C to generate the corresponding multi-amide ligand product.

[0033] The mixture was then refluxed for 12 hours, washed with water, 1M HCl washing solvent solution, 1M NaOH solution and water in sequence, and then dried at 60°C for 6 hours and stored for later use.

[0034] S22, synthesis of silicon-based supports by activation and in situ polymerization;

[0035] The synthesis of the silicon-based carrier is divided into two sub-steps: activation and in-situ polymerization.

[0036] The activation method is degassing and calcination. Degassing: first place the silicon dioxide in a 10-100mPa vacuum environment for 30-60min, then fill it with inert gas (nitrogen or argon) to normal pressure, then heat it to 100-500°C at a heating rate of 1-5°C / min, and activate it at a constant temperature for 6-12 hours to obtain activated silicon dioxide, which is then sealed and stored in a N2 atmosphere.

[0037] In-situ polymerization: The monomers DVB and styrene are fully mixed with the activated silica in a system with acetophenone and diethyl phthalate as diluents and AIBN and V-40 as initiators for 30 minutes, and then filled with inert gas (nitrogen or argon) to normal pressure to ensure that the device is basically in an oxygen-free environment. The prepared SiO2-P is placed in a G2 sand core funnel and washed with acetone and ultrapure water alternately for 3 times until no obvious impurities appear in the washing liquid, thus realizing the synthesis of the silicon-based carrier.

[0038] S3, using a vacuum impregnation method to load the polyamide ligand synthesized in step S21 onto the silicon-based carrier synthesized in step S22 to synthesize a solid phase leaching resin.

[0039] The multiamide ligand is loaded onto the SiO2-P carrier by vacuum impregnation. The multiamide ligand is dissolved in ethanol or acetone solvent, transferred to a single-necked flask containing a certain amount of activated silica, and the organic solvent is removed by a rotary evaporator. The negative pressure of the rotary evaporator is 30-100mPa, the rotation speed is 80-150r / min, the temperature is increased from 30°C to 60°C, the heating rate is 1-5°C / min, and then the rotary evaporation is continued at 60°C for 30-60min to obtain a powdered solid. Subsequently, the solid is placed in a vacuum drying oven and dried for 12 hours at a temperature of 60°C and a negative pressure of 0.1kPa, and then the product is taken out for use. Note: The loading amount of the multiamide ligand is 5-45wt.%.

[0040] In this embodiment, 3 grams of polyamide ligand are dissolved in ethanol solvent and transferred to a 100 ml single-necked flask containing 7 grams of activated SiO2-P, and the ethanol therein is slowly removed by a rotary evaporator; wherein, the negative pressure of the rotary evaporator is 50 mPa, the rotation speed is 100 r / min, the temperature is increased from 30°C to 60°C, the heating rate is 1°C / min, and then the rotary evaporation is continued at 60°C for 60 minutes to obtain a powdered solid; the solid is placed in a vacuum drying oven and dried for 12 hours at a temperature of 60°C and a negative pressure of 0.1 kPa, and then the product is taken out for use.

[0041] Embodiment 2

[0042] An embodiment of the present invention provides a method for separating trace plutonium from a large amount of uranium, the method comprising the following steps:

[0043] S1. Prepare spent fuel reprocessing simulation liquid containing uranium and plutonium, wherein the concentration of U(VI) is 30-110 g / L, the concentration of Pu(IV) is 0.5-50 mg / L, and the concentration of HNO3 is 0.1-4 mol / L.

[0044] S2. Pumping the spent fuel reprocessing simulation liquid into the leaching resin column at a first preset flow rate, performing a dynamic test, analyzing the uranium and plutonium concentrations in the water phase at the outlet at regular intervals, and drawing a breakthrough curve;

[0045] A solid phase leaching resin column is prepared. In this embodiment, the resin loading amount is 0.5-1 g, the column height is 50-100 mm, and the inner diameter is 2-4 mm. After the column is pretreated with the corresponding acid, a syringe pump is used to pump the simulated liquid into the leaching resin column at a flow rate of 0.2-0.4 mL / min. The uranium and plutonium concentration in the aqueous phase at the outlet is analyzed at regular intervals to draw a penetration curve.

[0046] S3. Pumping the eluent into the elution resin column after adsorption equilibrium at a second preset flow rate, and eluting plutonium with the eluent.

[0047] Using (0.1~0.5)mol / L HN03-(0.05~0.2)mol / L H2C2O4 as eluent, a syringe pump was used to pump the eluent into the leaching resin column after adsorption equilibrium at a flow rate of (0.5~1.5)mL / min. The uranium and plutonium concentrations in the aqueous phase at the outlet were analyzed at regular intervals and a concentration curve was drawn.

[0048] Dynamic experiments showed that for a feed solution of 62g / LU(VI)-30.3mg / L Pu(1V)-0.1~4mol / LHNO3, it was pumped into the resin column at a flow rate of 0.3mL / min. After 1h, the concentration of Pu(IV) in the effluent was less than 0.1mg / L. Subsequently, plutonium was eluted with nitric acid-oxalic acid eluent, and the Pu(IV) recovery rate was >95%.

[0049] Experiments show that the effect of polyamide ligands is not outstanding in low-acid systems (DPu(IV) < 1 at 0.1-0.5 mol / L HNO3). However, after combining this type of ligand with SiO2-P, the high specific surface area and porous characteristics of SiO2-P under low-acid conditions (0.1-0.5 mol / L HNO3) play a major role in the adsorption of Pu(IV). In high acid conditions, polyamide ligands play a major role, thereby showing high selectivity for Pu(IV), wide acidity applicability, and faster adsorption kinetics, avoiding the tedious repeated acid adjustment of the existing process, greatly simplifying the operation, and being suitable for deep purification of plutonium in large volumes of uranium feed liquid. In addition, compared with conventional leaching resins loaded on carriers such as silica gel, the in-situ modified SiO2-P carrier is more stable in binding to the ligand. After ten cycles, the ligand loss rate is less than 1.5%.

[0050] The leaching resin disclosed in the embodiment of the present invention is suitable for deep purification of trace plutonium in a large amount of uranium in a 0.1-4 mol / L HNO3 system, does not require acid adjustment, is easy to operate, and is superior to existing separation materials in related fields.

[0051] It can be seen from the above embodiments that the present invention discloses a method for separating trace plutonium from a large amount of uranium by using a solid phase leaching resin. The leaching resin used is suitable for deep purification of trace plutonium in a large amount of uranium in a 0.1-4 mol / L HNO3 system. The separation process does not require acid adjustment and is easy to operate. It is superior to the existing separation materials in the relevant field. The method is simple, easy to operate, and highly practical, and has a strong promotion advantage.

[0052] The method described in the present invention is not limited to the embodiments described in the specific implementation manner. Those skilled in the art may derive other implementation manners based on the technical solution of the present invention, which also fall within the technical innovation scope of the present invention.

Claims

1. A method for separating trace plutonium from a large amount of uranium using a solid phase leaching resin, the method comprising the following steps: S1. preparing a spent fuel reprocessing simulation liquid containing uranium and plutonium, wherein the HNO3 concentration in the spent fuel reprocessing simulation liquid is 0.1-4 mol / L; S2. Pumping the spent fuel reprocessing simulation liquid into the leaching resin column at a first preset flow rate, performing a dynamic test, analyzing the uranium and plutonium concentration in the water phase at the outlet at regular intervals, and drawing a breakthrough curve; S3, pumping the eluent into the eluting resin column after adsorption equilibrium at a second preset flow rate, and eluting plutonium with the eluent; The solid phase extraction resin is prepared by the following method: S21, synthesis of polyamide ligands by substitution reaction; S22, synthesis of silicon-based supports by activation and in situ polymerization; S23, using a vacuum impregnation method to load the polyamide ligand synthesized in step S21 onto the silicon-based carrier synthesized in step S22 to synthesize a solid phase leaching resin.

2. A method for separating trace plutonium from a large amount of uranium using a solid phase leaching resin as claimed in claim 1, characterized in that: In step S1, the U(VI) concentration in the spent fuel reprocessing simulation liquid is 30-110 g / L, and the Pu(IV) concentration is 0.5-50 mg / L.

3. A method for separating trace plutonium from a large amount of uranium using a solid phase leaching resin as claimed in claim 1, characterized in that: The first preset flow rate is 0.2~0.4mL / min.

4. A method for separating trace plutonium from a large amount of uranium using a solid phase leaching resin as claimed in claim 1, characterized in that: The second preset flow rate is 0.5~1.5mL / min.

5. A method for separating trace plutonium from a large amount of uranium using a solid phase leaching resin as claimed in claim 1, characterized in that: The eluent is a mixture of 0.1-0.5 mol / L HNO3 and 0.05-0.2 mol / L H2C2O4.

6. A method for separating trace plutonium from a large amount of uranium using a solid phase leaching resin as claimed in claim 1, characterized in that: In step S21, N,N'-dimethylformamide is used as a catalyst to react nitrilotriacetic acid with oxalyl chloride in a dibutylamine solvent to undergo a substitution reaction, and then impurities are removed by vacuum distillation, and then a dialkylamine is added to generate a corresponding polyamide ligand product.

7. A method for separating trace plutonium from a large amount of uranium using a solid phase leaching resin as claimed in claim 6, characterized in that: Step S21 also includes refluxing the multiamide ligand mixture, washing it with water, 1M HCl washing solvent solution, 1M NaOH solution and water in sequence, and then drying it.

8. A method for separating trace plutonium from a large amount of uranium using a solid phase leaching resin as claimed in claim 7, characterized in that: Step S22 specifically includes first placing the silicon dioxide in a 10-100 mPa vacuum environment, then filling it with nitrogen or an inert gas to normal pressure, then heating it to 100-500° C., constant temperature activation, obtaining activated silicon dioxide, and sealing and storing it in a N2 atmosphere; The monomers DVB and styrene are fully mixed with the activated silica in a system with acetophenone and diethyl phthalate as diluents and AIBN and V-40 as initiators, and then nitrogen or inert gas is filled into the system to normal pressure to ensure that the device is basically in an oxygen-free environment. The prepared SiO2-P is washed with acetone and ultrapure water alternately for several times until no obvious impurities appear in the washing liquid, thereby realizing the synthesis of silicon-based carriers.

9. A method for separating trace plutonium from a large amount of uranium using a solid phase leaching resin as claimed in claim 8, characterized in that: Step S23 includes dissolving the polyamide ligand in ethanol or acetone solvent, transferring the solution to a container containing a certain amount of activated silica, performing rotary evaporation to remove the organic solvent therein to obtain a powdered solid, and drying the powdered solid.

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