JPH0685869B2 - Separation method of cesium in nitric acid-containing aqueous solution - Google Patents

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to an improvement in a method for separating cesium from an aqueous solution containing nitric acid. More specifically, the present invention relates to a method for efficiently separating and recovering radioactive cesium in a high-level radioactive waste liquid containing high-concentration nitric acid, which is generated from a nuclear-related facility such as a spent nuclear fuel reprocessing facility.

[0002]

2. Description of the Related Art In recent years, as a method for reprocessing spent nuclear fuel, the Purex method is becoming the mainstream. In this method, a high-level radioactive waste liquid containing a high concentration of nitric acid (2-4M) accompanying the processing is used. Occurs. The safe treatment and disposal method for such high-level radioactive waste liquid has not been established yet, and the most effective treatment method at this time is the development of a treatment method in which the high-level radioactive waste liquid is collectively vitrified. Is being promoted.

However, in this method, for example, (1) radioactive cesium such as ¹³⁷ Cs ¹³⁴ Cs is liable to volatilize during vitrification treatment, which is difficult to cope with. (2) Elution of radioactive nuclide from vitrified body during flooding It is difficult to completely suppress the radioactivity, and radioactive cesium is the nuclide that is most likely to be eluted. (3) Strong radioactivity and a large amount of heat generated ensure the safety of handling and transporting vitrified materials, and long-term There are problems such as being a major factor that makes it difficult to make preliminary evaluations of stability during storage and storage.

As a means for solving such a problem,
It is considered that radioactive cesium and strontium, which account for 90% or more of the total radioactivity, should be removed in advance. In addition, these radionuclides have great utility value in industry, and in particular, radioactive cesium is expected to be in great demand in the future as an irradiation source for sterilization of excess sludge and various foods accompanying the treatment of activated sludge such as municipal sewage. .

For these reasons, a method of preliminarily separating radioactive strontium and cesium from a high-level radioactive liquid waste has attracted attention in recent years ["An Alternative Strategic For Commercial High Level Radio Active Management (an al
ternative strategy for co
mmercial high-level radio
-Active management), IAEA-
SM-261 / 34 ", page 461 (1983)
Year)]. In particular, radioactive cesium occupies most of the gamma-ray source in the waste liquid, so even if only these are removed, the cost required for shielding the gamma-ray is greatly reduced when processing the residual portion and handling and transporting the canister. Therefore, a large effect can be expected in combination with the effective use of recovered radioactive cesium.

Further, recently, as an ideal treatment / disposal technology for high-level radioactive waste liquid, nuclides in the waste liquid are separated into groups, useful components are utilized as resources, and useless and long-lived nuclides are eliminated. The group separation / annihilation treatment method that aims at the final safe treatment / disposal is performed, and in this case also, the separation of radioactive cesium, which is the main nuclide from the high-level radioactive liquid waste, is an important elemental technology. Becomes

Examples of the method for removing cesium from the high-level radioactive liquid waste include an adsorption method using an inorganic ion exchanger or a selective ion exchange resin, a solvent extraction method using crown ether, a heavy metal salt and a soluble ferrocyanide or ferricyanide. A coprecipitation method using a compound salt and a chemical treatment method using a cesium precipitation reagent are known. Among these methods, decontamination coefficient (initial concentration ÷ concentration after decontamination), radiation resistance,
From the viewpoint of heat resistance, it is suitable for adsorption methods using zeolites such as mordenite, heteropolyacid salts such as ammonium phosphomolybdate, acidic salts of polyvalent metals such as titanium phosphate, and inorganic ion exchangers such as insoluble ferrocyanide. The emphasis is on development.

However, when such an adsorption method using an inorganic ion exchanger is applied to a high-level radioactive waste liquid containing high-concentration nitric acid, a zeolite-based one is unsuitable because it is weakly soluble in acid. In addition, as an adsorbent for high-level radioactive liquid waste, one that does not adsorb actinide is required [[Technology and Roll of C
s and Sr Separation in Disposal Strategy of High Level Waste (T
technology and role of Cs a
nd Sr separation in dispo
sal strategy of high level
l waste) IAEA-TECDOC-337 ", page 31 (1985)], heteropolyacid salts such as ammonium phosphomolybdate have poor separability from actinides, and polyvalent metals such as titanium phosphate. The acidic salt-based compounds have a slight difficulty in the adsorption power and selective adsorptivity in the highly acidic region, but have excellent acid resistance, but like the heteropolyacid-based compounds, they are separable from actinides. Has the disadvantage of being inferior to.

On the other hand, it is known that insoluble ferrocyanide does not adsorb actinides [[An Assessment of the Application of Inorganic Ion Exchangers to the Treatment]・ Intermediate Level ・
Weightlessness (An assessment of the th
e application of inorgani
c ion exchanges to the t
reatment of intermediate
level wastes) AERE-R11088 "
Pp. 118 (1984)], the cesium adsorption power is greatly different between in the presence of hydrochloric acid and in the presence of nitric acid, and is significantly reduced in the latter ["Journal of Nuclear Science and Technology (Journ.
al of Nuclear Science and
Technology, "Volume 4, Page 190 (1967)," Journal of Inorganic and Nuclear Chemistry (Journ).
al of Inorganic and Nucle
arChemistry) ", Vol. 34, page 1427 (1972)]. Since this tendency is remarkable especially in the case of copper-based ferrocyanide, a high-concentration nitric acid aqueous solution is used as an eluent for desorbing cesium from cesium-adsorbed copper-based ferrocyanide by utilizing this property. It is said that.

Therefore, if the cesium adsorption ability of the insoluble ferrocyanide in a high-concentration nitric acid aqueous solution can be increased, its usefulness is expected to be significantly enhanced. By the way, insoluble ferrocyanide lacks the ability to adsorb cesium in nitric acid because it is oxidized by nitric acid and converted to ferricyanide.If there is a means to prevent this oxidation, it is not possible to use cesium as an adsorbent. It will be possible. However, since a reducing agent which is considered to be effective in preventing oxidation is susceptible to oxidation by nitric acid, no compound effective in preventing oxidation of ferrocyanide in the presence of high-concentration nitric acid has been found so far.

[0011]

Under the above circumstances, the present invention provides an adsorbent for cesium in an aqueous solution containing nitric acid, particularly a cesium nuclide in a high-level radioactive waste liquid containing high-concentration nitric acid and an insoluble ferrocyanide. The object of the present invention is to provide a method of efficiently separating and recovering.

[0012]

Means for Solving the Problems The present inventor has conducted extensive research in order to achieve the above-mentioned object. First, the cesium in an aqueous solution containing nitric acid is brought into contact with the adsorbent composed of an insoluble ferrocyanide. We have found some compounds effective for preventing the oxidation of the ferrocyanide by nitric acid during the adsorption separation. The present invention has been made based on this finding.

That is, according to the present invention, when cesium in an aqueous solution containing nitric acid is adsorbed and separated using an adsorbent composed of an insoluble ferrocyanide, thioglycolic acid, hydroiodic acid, sulfanilic acid, sulfanilamide, and dihydroxytoluene are used. And separation of cesium in a nitric acid-containing aqueous solution, which comprises contacting the nitric acid-containing aqueous solution with an adsorbent in the presence of at least one selected from these derivatives or in the presence of a hydrazine derivative. It provides a method.

In the method of the present invention, an insoluble ferrocyanide is used as the adsorbent. This insoluble ferrocyanide is insoluble or insoluble in water obtained by reacting a salt or hydroxide containing a metal other than a divalent or more alkaline earth metal with a salt or acid containing a ferrocyanide ion. A substance, or the porous body obtained by allowing the reaction to be carried out in the voids of an inorganic porous body such as silica gel or an organic porous body such as an anion or cation exchange resin, is used as a carrier, On the other hand, it has an excellent adsorption capacity.

In the method of the present invention, thioglycolic acid is used as an antioxidant in order to prevent the oxidation of the ferrocyanide by nitric acid and increase its cesium adsorption power.
Hydroiodic acid, sulfanilic acid, sulfanilamide,
It is necessary to use one selected from dihydroxytoluene and derivatives thereof. These may be used alone or in combination of two or more.

Further, a hydrazine derivative can also be used. As the hydrazine derivative, for example, methylhydrazine, phenylhydrazine, sulfanylhydrazine-p-sulfonic acid, 1,1-diphenylhydrazine, tolylhydrazine and salts thereof are suitable. One of these hydrazine derivatives may be used,
Two or more kinds may be used in combination, and may be used in combination with the antioxidant.

Since the necessary addition amount of these antioxidants in the method of the present invention varies depending on the nitric acid concentration in the raw material solution used, impurities contained, etc., a preliminary test is conducted in accordance with each condition to obtain the optimum amount. Select.

Although the mechanism of action of these antioxidants is not always clear, is it possible to decompose nitrite groups?
Additives that react with this to produce nitroso compounds and diazonium salts were often effective even in trace amounts, so that nitrite groups coexisting in trace amounts in nitric acid are catalytically involved in nitric acid oxidation of insoluble ferrocyanides. However, it is considered that the effect of the antioxidant is due to the action of removing the nitrite group.

In general, the effect of the antioxidant greatly differs depending on the magnitude of the cesium adsorption force of the insoluble ferricyanide corresponding to each insoluble ferrocyanide. Since copper-based insoluble ferrocyanide and the like have a low cesium adsorbing power of ferricyanide which is an oxidized form thereof, the effect of the antioxidant is particularly strong.

Utilizing such a property, for example, a method in which cesium adsorption is performed by the method of the present invention and an oxidizing solution such as a high-concentration nitric acid solution containing no antioxidant for desorption is used as an eluent is preferable. Bring effect. In general, the insoluble ferrocyanide has a higher cesium adsorption force than the corresponding ferricyanide, and therefore the effect of the antioxidant on cesium separation is almost always observed.

The nitric acid concentration of the nitric acid-containing aqueous solution used in the method of the present invention is not particularly limited, but the nitric acid concentration of the aqueous solution containing nitric acid at a concentration higher than that for oxidizing the insoluble ferrocyanide in the absence of an antioxidant is It is desirable to apply the inventive method in terms of effect. The nitric acid oxidation of ferrocyanide depends on its type, processing time, processing temperature, etc., but when the nitric acid concentration is 1 M or more, it progresses fairly rapidly even at room temperature. When the method of the present invention is applied to a cesium-containing nitric acid aqueous solution, the oxidation of ferrocyanide can be almost completely prevented even when the nitric acid concentration is 3 M or more, and the cesium adsorption force is remarkably higher than that in the case where no antioxidant is present. improves.

[0022]

According to the present invention, when cesium in a nitric acid-containing aqueous solution is adsorbed and separated using an adsorbent composed of an insoluble ferrocyanide, the presence of a specific antioxidant enables the presence of the antioxidant. The cesium adsorption power of the adsorbent can be significantly improved as compared with the case where
The cesium can be efficiently separated.

Therefore, the method of the present invention can be applied to efficiently separate cesium from a high-level radioactive waste liquid having a high radioactive cesium content generated from, for example, a Purex method reprocessing facility. It is extremely valuable for the development of effective utilization technology of radioactive cesium in the waste liquid.

[0024]

The present invention will be described in more detail by way of examples, which should not be construed as limiting the invention thereto. The residual cesium in the treatment liquid was analyzed by an atomic absorption photometric method (air-acetylene flame) or an atomic emission photometric method (air-acetylene flame). The analysis was carried out in the presence of 0.1 M potassium chloride as a sensitizer. From the measurement result of the residual cesium concentration, the distribution coefficient (Kd) was calculated by the following formula as an index of the cesium adsorption force of each adsorbent.

[Equation 1] However, Co: cesium initial concentration (M), C: cesium residual concentration (M), W: adsorbent weight (g), L: liquid amount (m
l)

Example 1 0.01 g of anhydrous copper potassium ferrocyanide (K
₂ Cu ₃ Fe (CN) ₆ ) was weighed into an Erlenmeyer flask with a screw cap, and 10 ⁻³ M cesium ion and 10 ⁻⁵ M were added thereto.
3M nitric acid solution containing M sodium thioglycolate 1
0 ml was added, and the mixture was shaken in a constant temperature water bath at 25 ° C. for 24 hours. As a result of measuring the residual cesium concentration in the treatment liquid, it was 3.07 × 10 ⁻⁶ M. The Kd of these is calculated to be 3.2 × 10 ⁵ ml / g.

Examples 2 to 14 As in Example 1, except that the type and concentration of the antioxidant shown in Table 1 were present in place of 10 ⁻⁵ M sodium thioglycolate. Carried out. The results are shown in Table 1.

Comparative Example The same procedure as in Example 1 was carried out except that sodium thioglycolate was not used. The results are shown in Table 1.

[Table 1] From this table, it can be seen that in the presence of each antioxidant, the Kd value remarkably increases as compared with the case without each antioxidant.

Claims (3)

[Claims] 1. When cesium in an aqueous solution containing nitric acid is adsorbed and separated using an adsorbent composed of an insoluble ferrocyanide, thioglycolic acid, hydriodic acid, sulfanilic acid, sulfanilamide, dihydroxytoluene and their derivatives. A method for separating cesium from a nitric acid-containing aqueous solution, which comprises contacting the nitric acid-containing aqueous solution with an adsorbent in the presence of at least one selected from the above. 2. When the cesium in the nitric acid-containing aqueous solution is adsorbed and separated using an adsorbent composed of an insoluble ferrocyanide, the nitric acid-containing aqueous solution and the adsorbent are contacted in the presence of a hydrazine derivative. Method for separating cesium from nitric acid-containing aqueous solution. 3. The hydrazine derivative is methylhydrazine,
The method for separating cesium from a nitric acid-containing aqueous solution according to claim 2, which is at least one selected from phenylhydrazine, sulfanylhydrazine-p-sulfonic acid, 1,1-diphenylhydrazine, tolylhydrazine and salts thereof.