JP3365473B2 - Purification method of uranyl nitrate - Google Patents

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for precipitating and recovering uranyl nitrate crystals from a nitric acid solution containing uranium. More specifically, the present invention relates to a method for purifying uranyl nitrate in which a uranyl nitrate crystal is precipitated and recovered from a uranium-containing nitric acid solution generated in a nuclear fuel reprocessing step or the like.

[0002]

2. Description of the Related Art Conventionally, a method is known in which a solution of a spent nuclear fuel is cooled to a temperature below the freezing point to deposit uranyl nitrate and recover it. For example, in Japanese Examined Patent Publication No. 6-31802, a uranyl nitrate aqueous solution is cooled to −10 to −35 ° C. in a batch pure purification method of uranium or plutonium recovered in a spent nuclear fuel material reprocessing step. JP-A-4-140698 describes a method for separating uranium and plutonium from a uranium-plutonium mixed solution, in which the uranyl nitrate-plutonium nitrate mixed solution is cooled to -20 to -40 ° C. ing. Further, in Japanese Patent Laid-Open No. 4-218797, in a method for reprocessing spent nuclear fuel, a dissolved liquid of spent nuclear fuel is -10.
It is disclosed to be cooled to ~ -30 ° C.

[0003]

However, in any of the above-mentioned conventional methods, the nitric acid solution containing uranium must be cooled to a temperature below the freezing point, so that a large-scale cooling device is required. Further, cooling below the freezing point may cause precipitation of ice or nitric acid hydrate, which reduces the purity of the uranyl nitrate crystal and complicates subsequent steps. An object of the present invention is to provide a method for purifying uranyl nitrate, which does not require a large-scale cooling device and can recover highly pure uranyl nitrate crystals in high yield.

[0004]

The invention according to claim 1 is
This is a method for purifying uranyl nitrate in which a nitric acid solution containing uranium is maintained at 0 to 25 ° C. and the nitric acid concentration of the nitric acid solution is increased to precipitate uranyl nitrate crystals from the nitric acid solution and recover the crystals. When the nitric acid solution is kept at 0 to 25 ° C. to increase the nitric acid concentration, the solubility of uranyl nitrate in the nitric acid solution becomes small, and uranyl nitrate crystals are deposited in high yield. The invention according to claim 2 is the invention according to claim 1, a method of increasing the nitric acid concentration of the nitric acid solution by adding a high concentration of nitric acid of 60 to 98 percent in nitric acid solution. According to this method
Without cooling the nitric acid solution below the freezing point as before,
It is possible to easily increase the nitric acid concentration of the nitric acid solution and precipitate the uranyl nitrate crystal by the operation of adding high-concentration nitric acid whose concentration is easily adjusted.

The invention according to claim 3 is the invention according to claim 1, wherein when the nitric acid concentration of the nitric acid solution is increased by evaporating and concentrating the nitric acid solution, the temperature of the nitric acid solution is 0 ° C.
When maintaining near, increase nitric acid concentration to 7-8N
Or if the temperature of the nitric acid solution is kept near 25 ° C
Is a method of increasing the nitric acid concentration to 4 to 5N . In this method, the nitric acid solution can be easily concentrated to evaporate and concentrate without evaporating and concentrating the nitric acid solution without cooling the nitric acid solution below the freezing point and without using high-concentration nitric acid, which is difficult to handle. Crystals can be precipitated. The invention according to claim 4 is the invention according to any one of claims 1 to 3 , wherein the uranium-containing nitric acid solution having a temperature higher than 25 ° C is cooled to be maintained at a temperature of 0 to 25 ° C. Is. According to this method, the solubility of uranyl nitrate is lowered by cooling, and the concentration of nitric acid solution is increased, whereby uranyl nitrate crystals can be more efficiently precipitated at room temperature.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, in order to increase the nitric acid concentration of a nitric acid solution containing uranium, the nitric acid solution is added to 0-2.
The temperature is kept at 5 ° C., and 60-98% highly concentrated nitric acid is added to the nitric acid solution, or the nitric acid solution is concentrated by evaporation. In the invention according to claims 2 to 4, the holding temperature of the nitric acid solution is 25.
If the temperature exceeds ° C, uranyl nitrate is not likely to precipitate as crystals, which is not preferable. If the holding temperature is lower than 0 ° C, the same problems as in the conventional case occur. The temperature of nitric acid solution is 0
If the nitric acid concentration is selected to be 7 to 8 N when the temperature is kept in the vicinity of 0 ° C., the solubility of uranyl nitrate in the nitric acid solution becomes small and the recovery rate becomes high. Further, when the temperature of the nitric acid solution is kept near 25 ° C., if the nitric acid concentration is selected to be 4 to 5 N, the solubility of uranyl nitrate in the nitric acid solution becomes small,
Higher recovery rate.

[0007]

EXAMPLES Next, examples of the present invention will be described in order to show specific embodiments of the present invention. <Example 1> 50 ml of a nitric acid solution of uranyl nitrate was prepared. This nitric acid solution has a uranium concentration of 622 gU / l and a nitric acid concentration of 2.2 N at 40 ° C. This nitric acid solution at a temperature of 40 ° C. was placed in a constant temperature bath at a temperature of 15 ° C. and maintained at the same temperature. Then, 17.9 ml of 60% nitric acid was added to the nitric acid solution and stirring was continued. Precipitated. Then, the precipitated crystals and the mother liquor were separated by filtration. When the nitric acid concentration of the mother liquor was measured, it increased to 6.8N.
The recovery rate of the obtained uranyl nitrate crystals is shown in Table 1 below.

Example 2 50 ml of a nitric acid solution of uranyl nitrate was prepared. This nitric acid solution has a uranium concentration of 293 gU / l and a nitric acid concentration of 2.0 N at 5 ° C. This nitric acid solution at a temperature of 5 ° C. was placed in a constant temperature bath at a temperature of 5 ° C., 11.5 ml of 98% nitric acid was added to the nitric acid solution, and stirring was continued, whereby crystals of uranyl nitrate were precipitated. Then, the precipitated crystals and the mother liquor were separated by filtration. When the nitric acid concentration of the mother liquor was measured, it increased to 7.0N. The recovery rate of the obtained uranyl nitrate crystals is shown in Table 1 below.

Example 3 50 ml of a nitric acid solution of uranyl nitrate was prepared. This nitric acid solution has a uranium concentration of 389 gU / l and a nitric acid concentration of 1.0 N at 5 ° C. The nitric acid solution at a temperature of 5 ° C. was placed in a constant temperature bath at a temperature of 5 ° C., and 10.9 ml of 98% nitric acid was added to the nitric acid solution, and stirring was continued. As a result, crystals of uranyl nitrate were precipitated. Then, the precipitated crystals and the mother liquor were separated by filtration. When the nitric acid concentration of the mother liquor was measured, it increased to 5.7N. The recovery rate of the obtained uranyl nitrate crystals is shown in Table 1 below.

Example 4 50 ml of a nitric acid solution of uranyl nitrate was prepared. This nitric acid solution has a uranium concentration of 414 gU / l and a nitric acid concentration of 1.1 N at 0 ° C. This nitric acid solution at a temperature of 0 ° C. was placed in a constant temperature bath at a temperature of 0 ° C. and kept at the same temperature, and then 10.9 ml of 98% nitric acid was added to this nitric acid solution, and stirring was continued. Precipitated. Then, the precipitated crystals and the mother liquor were separated by filtration. When the nitric acid concentration of the mother liquor was measured, it increased to 6.9N. The recovery rate of the obtained uranyl nitrate crystals is shown in Table 1 below.

<Example 5> 100 ml of a nitric acid solution of uranyl nitrate was prepared. This nitric acid solution has a uranium concentration of 206 gU / l and a nitric acid concentration of 2.3 N at 25 ° C. By heating the nitric acid solution, the water content of the nitric acid solution was evaporated and the solution was concentrated to about 50 ml. This nitric acid solution was placed in a constant temperature bath at a temperature of 25 ° C. and kept at the same temperature, and as a result, crystals of uranyl nitrate were precipitated. Then, the precipitated crystals and the mother liquor were separated by filtration. When the nitric acid concentration of the mother liquor was measured, it increased to 5.3N. The recovery rate of the obtained uranyl nitrate crystals is shown in Table 1 below.

[0012]

[Table 1]

As is clear from Table 1, in any of Examples 1 to 5, uranyl nitrate crystals were obtained at a high recovery rate of 50% or more.

[0014]

As described above, according to the present invention, the nitric acid solution containing uranium is kept at 0 to 25 ° C.
Uranyl nitrate crystals were precipitated from the nitric acid solution by increasing the nitric acid concentration of the liquid and collected, so that it is possible to recover the uranyl nitrate crystals in a high yield without cooling the nitric acid solution containing uranium below the freezing point. You can Therefore,
Compared with the conventional method in which the nitric acid solution containing uranium must be cooled to a temperature below the freezing point, there is an advantage that a large-scale cooling device is not required. Further, since uranyl nitrate is precipitated at a temperature equal to or higher than the freezing point, highly pure uranyl nitrate crystals can be obtained without precipitation of ice or nitric acid hydrate.

─────────────────────────────────────────────────── ─── Continuation of front page (72) Kenji Nishimura Inventor, Kenji Nishimura, Naka-machi, Naka-gun, Naka-gun, Ibaraki Prefecture, No. 1002, Mukaiyama, No. 14 14 No. 14 at Mitsubishi Materials Corporation, Naka Energy Laboratory (72) Inventor, Sumio Yamagami, Naka-gun, Ibaraki Prefecture Nakamachi, Oka, Mukaiyama, Rokujinto, No. 1002 14 14 Mitsubishi Materials Corporation, Naka Energy Laboratory (56) References JP-A-4-140698 (JP, A) JP-A-60-205398 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C01G 43/00 G21C 19/46

Claims (4)

(57) [Claims] 1. A nitric acid solution containing uranium is kept at 0 to 25 ° C.
A method for purifying uranyl nitrate, which comprises holding and increasing the nitric acid concentration of the nitric acid solution to precipitate and recover uranyl nitrate crystals from the nitric acid solution. 2. A purification process according to claim 1, wherein increasing the nitric acid concentration of said nitric acid solution by adding a high concentration of nitric acid of 60 to 98 percent in nitric acid solution. Wherein when increasing the nitrate concentration of the nitric acid solution by evaporation of the nitric acid solution, the temperature of the nitric acid solution
Is maintained near 0 ° C., the nitric acid concentration should be 7 to 8
Or increase the temperature of the nitric acid solution to around 25 ° C.
The refining method according to claim 1 , wherein the nitric acid concentration is increased to 4 to 5 N when it is held . 4. A 25 Purification process according to any one of claims 1 to 3 kept at a temperature of 0 to 25 ° C. by cooling the high temperature of the uranium-containing nitric acid solution than ° C..