A method for selective dissolution and separation of lanthanides from spent fuel

Abstract

The application provides a selective dissolution and separation method of lanthanide elements in spent fuel. The method comprises the following steps: adding a mixture of lanthanide oxide and uranium dioxide into an aqueous solution of hydroxyethylidene tripepiperazine ammonium hydrochloride or an aqueous solution of butyl hydroxyethylidene tripepiperazine ammonium hydrochloride, and heating and stirring to selectively dissolve the lanthanide oxide. Then, centrifugal separation is performed, the dissolved lanthanide oxide is in the solution, and the undissolved actinide compound uranium dioxide solid is recovered, so that the lanthanide elements and the actinide elements in the spent fuel are efficiently separated. The application is based on the good dissolution behavior of the hydroxyethylidene tripepiperazine ammonium hydrochloride compound with radiation resistance to the lanthanide elements, and applies the selective dissolution and separation technology to the spent fuel reprocessing. Compared with the traditional solvent extraction method, the method avoids the use of organic solvents and a large amount of waste liquid, the used alkaloid hydroxyethylidene tripepiperazine ammonium hydrochloride compound is non-toxic and harmless, green and environment-friendly, low in cost, strong in radiation resistance, simple in process flow, and easy to be applied in industrialization.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of separation of lanthanide and actinide in spent fuel reprocessing, and particularly relates to selective dissolution separation of lanthanide in spent fuel and solid-state recovery of actinide in a specific chemical dissolution separation system. BACKGROUND

[0002] With the sustained development of nuclear power, the spent fuel treatment problem of nuclear power plants is increasingly prominent, which has caused great threat to human living environment. The spent fuel generally contains 95% of UO2, 1% of Pu and minor actinide MAs, and 4% of fission products. However, the content of lanthanide is relatively large, accounting for 30% of the total amount of these fission products. Some lanthanides (Sm, Nd, Gd, etc.) have a high neutron absorption cross section, such as 149 Sm (σ = 74500b), which is called neutron poison, can hinder the subsequent transmutation of minor actinides and must be effectively separated and removed.

[0003] Lanthanide and actinide have similar electronic structure and ionic radius, and their physical and chemical properties are very similar. The separation between them has always been one of the hot issues in the field of spent fuel reprocessing. Most of the current separation researches are to separate and remove lanthanide from spent fuel by solvent extraction method, which has the disadvantages of complex separation process, more high-level liquid waste, serious environmental pollution, etc. Therefore, it is still necessary to develop new separation methods to realize the effective separation between lanthanide and actinide.

[0004] Since the matrix of spent fuel is UO2, the amount of lanthanide compound fission product is very small, and the existing form is Ln2O3. According to the different basic physical and chemical properties of lanthanide oxide Ln2O3 and spent fuel matrix UO2, a chemical system with lanthanide dissolution function is used as the dissolution separation medium, and a selective dissolution separation technology is proposed to complete the efficient separation of lanthanide and spent fuel matrix UO2. While separating and removing lanthanide, the solid-state recovery of actinide is also realized.

[0005] Betaine hydrochloride is a common alkaloid, and its chemical structure is similar to amino acid and choline, which is widely used in daily chemical, feed and food additive fields. There is no related report on its application in the separation of lanthanide and actinide in spent fuel. SUMMARY

[0006] The purpose of the present application is to provide a simple and efficient method for separating lanthanide in spent fuel, while realizing the solid-state recovery of reusable actinide uranium dioxide, which has the characteristics of green environmental protection, simplicity and easy operation.

[0007] To achieve the above objectives, the present invention uses an aqueous solution of an alkaloid betaine hydrochloride compound as a chemical dissolution system, which is betaine hydrochloride (shown in Formula I) or butyl betaine hydrochloride (shown in Formula II).

[0008]

[0009] The simple and efficient method for separating lanthanides from spent fuel utilizes the different solubilities of lanthanide oxides and nuclear fuel matrix UO2 in aqueous solutions of betaine hydrochloride compounds. By controlling conditions such as temperature, solid-liquid ratio, and dissolution time, the lanthanide oxides are selectively dissolved in the solution. Through centrifugation, the efficient separation of lanthanides and actinides from spent fuel is achieved.

[0010] The method for separating lanthanides from spent fuel provided by the present invention includes the following steps: adding a mixture containing lanthanide oxides and actinide compound uranium dioxide to an aqueous solution of betaine hydrochloride compound, heating and stirring to selectively dissolve the lanthanide oxides in the solution, and then centrifuging to recover the actinide compound uranium dioxide in solid form.

[0011] In the above method, the mixture containing lanthanide oxides and actinide compounds uranium dioxide refers to a mixture of uranium dioxide powder and lanthanide oxides, wherein the lanthanide oxides are selected from one or more of La2O3, Nd2O3, Sm2O3, Eu2O3, and Gd2O3, and the content is between 0.5% and 25%.

[0012] In the above method, the concentration of the aqueous solution of the betaine hydrochloride compound (such as betaine hydrochloride or butyl betaine hydrochloride) can be 0.05M to 2M, specifically 0.5M, 1M or 2M.

[0013] The betaine hydrochloride compounds described above did not undergo radiation cracking after irradiation testing. When the irradiation dose was less than or equal to 1000 kGy, the chemical separation system had no effect on the selective dissolution and separation of lanthanides and the solid-state recovery of actinides, indicating that the chemical dissolution and separation system can withstand a certain degree of radioactivity and has certain practical significance in spent fuel reprocessing.

[0014] In the above method, the solid-liquid ratio of the mixture containing lanthanide oxides and uranium dioxide to the chemical dissolution system with lanthanide separation function (such as an aqueous solution of betaine hydrochloride compounds) is 10-100 g / L.

[0015] The heating and stirring conditions are as follows: temperature 30-70℃, magnetic stirring speed 600-1000 r / min, and time 30-240 min.

[0016] Separation tests show that in aqueous solutions of betaine hydrochloride compounds, the solubility of lanthanide oxides is over 96%, the solid recovery rate of actinide compound uranium dioxide is over 95%, and the separation factor reaches over 2000. This method has a very beneficial separation effect.

[0017] During their research, the inventors of this invention discovered that aqueous solutions of betaine hydrochloride or its derivative butyl betaine hydrochloride possess unique solubility properties for lanthanide oxides. Under mild conditions, it can efficiently and selectively dissolve lanthanide oxides, while uranium dioxide remains insoluble. Therefore, the inventors have, for the first time, applied this technology to the field of spent fuel reprocessing, proposing a selective dissolution and separation technique to solve the problem of separating lanthanides and actinides from spent fuel, and to broaden the application range of betaine hydrochloride.

[0018] Compared with the prior art, the present invention has the following beneficial effects:

[0019] (1) This invention provides a novel approach to the separation of lanthanides and the recovery of actinides in the reprocessing of spent fuel. It achieves efficient separation of lanthanides and actinides through dissolution and separation alone. The whole process has the advantages of being mild, green, environmentally friendly, simple in equipment, easy to operate, and highly efficient.

[0020] (2) This invention uses betaine hydrochloride, a common biological agent, as a chemical dissolution system. The raw materials are readily available, the cost is low, and the radiation resistance is good. It can be directly used for experimental treatment after being dissolved in water without adding any reagents. The chemical system is simple, generates less waste, and has good prospects for industrial application.

[0021] (3) Based on the excellent solubility of betaine hydrochloride in lanthanide oxides, this invention selectively dissolves lanthanide compounds. After centrifugation, the lanthanide compounds are efficiently removed, and the solid-state recovery of actinide compound uranium dioxide is also achieved. The separation efficiency of lanthanide compounds can reach about 96%, and the recovery efficiency of uranium dioxide is over 95%. The process is simple and easy to scale up. Attached Figure Description

[0022] Figure 1 This is a schematic diagram illustrating the separation principle of the present invention.

[0023] Figure 2 This is the separated EDX spectrum of Example 1 in this invention.

[0024] Figure 3 This is a diagram showing the separation effect of betaine hydrochloride on radiation resistance in Example 2 of this invention.

[0025] Figure 4 This is a diagram showing the separation effect of the lanthanide mixture and UO2 in Example 3 of this invention. Detailed Implementation

[0026] The present invention will be further described below with reference to specific embodiments, but the present invention is not limited to the following embodiments. Unless otherwise specified, the methods described are conventional methods. Unless otherwise specified, the raw materials are all available from publicly available commercial sources.

[0027] The formula for calculating the separation factor used in the following embodiments is as follows:

[0028]

[0029] Where SF is the separation factor, E Nd and E u These refer to the solubility rates of Nd₂O₃ and UO₂, respectively.

[0030] Example 1:

[0031] A mixture containing lanthanide oxide Nd₂O₃ (5 wt%) and uranium dioxide (95 wt%) was added to an unirradiated 0.5 M betaine hydrochloride aqueous solution at a solid-liquid ratio of 60 g / L. The mixture was heated and stirred at 40 °C for 120 min to selectively dissolve and separate the lanthanides. Centrifugation followed, with the lanthanide oxides dissolved in the upper layer of the betaine hydrochloride aqueous solution, and the lower solid layer containing undissolved uranium dioxide. Tests showed that the dissolution and removal rate of lanthanide oxide Nd₂O₃ was 96%, the recovery rate of uranium dioxide was 95%, and the separation factor reached 2000, achieving highly efficient separation of lanthanides and actinides.

[0032] Example 2:

[0033] A mixture containing lanthanide oxide Nd₂O₃ (8 wt%) and uranium dioxide (92 wt%) was added to a 1 M betaine hydrochloride aqueous solution irradiated with γ-rays at a dose between 300 and 1000 kGy and a solid-liquid ratio of 50 g / L. The mixture was heated and stirred at 50 °C for 100 min to selectively dissolve and separate the lanthanides. Centrifugation was then performed, with the lanthanide oxides dissolved in the solution and the undissolved solid uranium dioxide recovered. Tests showed that the dissolution removal rate of lanthanide oxide Nd₂O₃ was 96%, the recovery rate of uranium dioxide was 95%, and the separation factor reached approximately 2000, achieving highly efficient separation of lanthanides and actinides.

[0034] Example 3:

[0035] A mixture containing various lanthanide oxides and uranium dioxide (Nd₂O₃, Sm₂O₃, Eu₂O₃, Gd₂O₃, and UO₂ contents of 5.34%, 5.8%, 6.28%, 6.33%, and 76.55%, respectively) was added to a 2M aqueous solution of betaine hydrochloride at a solid-liquid ratio of 40 g / L. The mixture was heated and stirred at 40°C for 180 min to selectively dissolve and separate the lanthanides. Centrifugation was then performed, with the lanthanide oxides dissolved in the solution and the undissolved solid uranium dioxide recovered. Tests showed that the dissolution and removal rates of all lanthanide oxides reached 97%, and the recovery rate of uranium dioxide was 94%, achieving highly efficient separation of lanthanides and actinides (UO₂).

[0036] Example 4:

[0037] A mixture containing 10% lanthanide oxide Sm₂O₃ and 90% uranium dioxide was added to an unirradiated 1M butyl betaine hydrochloride aqueous solution at a solid-liquid ratio of 50 g / L. The mixture was heated and stirred at 30°C for 120 min to selectively dissolve and separate the lanthanides. Centrifugation followed, revealing the dissolved lanthanides in the upper layer of the hydrochloric acid-betaine aqueous solution, while the lower solid layer contained undissolved uranium dioxide. Tests showed a 97% removal rate of lanthanide oxide Sm₂O₃ and a 96% recovery rate of uranium dioxide, achieving highly efficient separation of lanthanides and actinides.

Claims

1. A method for selectively dissolving and separating lanthanides from spent fuel, comprising the following steps: adding a mixture containing lanthanide oxides and uranium dioxide to a chemical dissolution system with lanthanide dissolving function, heating and stirring to selectively dissolve the lanthanide oxides in the solution, and then centrifuging to recover the actinide compound uranium dioxide in solid form, thereby achieving efficient separation between lanthanides and actinides; The chemical dissolution system with lanthanide dissolving function is an aqueous solution of betaine hydrochloride compounds.

2. The method according to claim 1, characterized in that: The mixture containing lanthanide oxides and actinide compounds uranium dioxide refers to a mixture of uranium dioxide powder and lanthanide oxides, wherein the lanthanide oxides are selected from one or more of La2O3, Nd2O3, Sm2O3, Eu2O3, and Gd2O3, and the mass content is between 0.5% and 25%.

3. The method according to claim 1 or 2, characterized in that: The concentration of the aqueous solution of the betaine hydrochloride compound is 0.05M~2M.

4. The method according to claim 3, characterized in that: The betaine hydrochloride compound is selected from at least one of the following: betaine hydrochloride, butyl betaine hydrochloride.

5. The method according to claim 1 or 2, characterized in that: The solid-liquid ratio of the mixture containing lanthanide oxides and uranium dioxide to the chemical dissolution system with lanthanide separation function is 10~100g / L.

6. The method according to claim 1 or 2, characterized in that: The heating and stirring refers to a temperature of 30~70℃, a magnetic stirring speed of 600~1000r / min, and a time of 30~240min.

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