JP3144160B2 - How to remove radioactive materials in water - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to uranium, wastewater and wastewater generated from nuclear power plants, spent nuclear fuel reprocessing plants, nuclear fuel processing plants and facilities using radioactive materials.
The present invention relates to a method for removing radioactive substances such as thorium and ruthenium.

[0002]

2. Description of the Related Art For example, wastewater or wastewater containing radioactive substances generated from nuclear facilities or the like is subjected to some treatment to reduce the concentration of radioactive substances when it is released to the environment, and the concentration is regulated by law (nuclear raw material substances). , Nuclear fuel materials and nuclear reactor regulations). As the treatment method, an evaporation concentration method, an ion exchange resin method, a coagulation sedimentation method and the like are employed. Waste liquid treatment in a spent nuclear fuel reprocessing plant is performed by an evaporative concentration method which is excellent in removing radioactive substances. However, this method uses steam as a heat source or uses an evaporator or the like, so that the equipment scale is large and the cost is large. In a nuclear fuel processing plant or a facility using radioactive materials, depending on the type of radioactive material to be removed, for example, in the case of thorium, it should be removed by ion exchange resin, and ruthenium should be physically removed. There has been proposed a method of removing by an activated carbon adsorption method or the like utilizing a mechanical adsorption mechanism or the like. The two methods using the chemical or physical adsorption means can simplify the equipment, and can achieve the target removal performance by optimizing the length of the adsorption column. Therefore, the life of the resin or the activated carbon is short, and the generation of the waste resin or the activated carbon is inevitable, and the secondary waste including the radioactive substance is increased. To minimize the load on such adsorbents,
Further, a coagulation sedimentation method, which is known as one of the methods for removing radioactive substances in a waste liquid, has been adopted as a primary treatment technique. In this case, the coagulation and sedimentation method is an exhaustion of general industry.
R> A hydroxide coprecipitation method using iron or aluminum as a carrier, which is widely used in water treatment technology. According to this coprecipitation method, a large amount of waste liquid can be treated at a time, and the cost is low.

[0003]

However, according to the conventional coagulation sedimentation method using a coprecipitant such as iron or aluminum, it depends on the type of radioactive substance to be removed.
For example, in the case of uranium, the removal efficiency is reduced to 9 by performing decarboxylation in water prior to the coagulation and precipitation.
It is possible to achieve up to about 0%. However, if the removal efficiency is about 90%, there is an inconvenience that the standard defined in the above law cannot be satisfied.
In addition, ruthenium contained in wastewater containing radioactive substances can form various types of nitrosyl ruthenium compounds with different chemical forms by nitric acid coexisting during the treatment process. Magazine "Radiochimica Acta" 29
1981, pp. 159-166).
However, conventional coagulation sedimentation removes only certain nitrosyl ruthenium compounds and leaves other nitrosyl compounds, so that the removal rate cannot be improved and an economical process cannot be realized. There was a problem.

[0004] The present invention has been made in view of such problems, and an object of the present invention is to provide a radioactive substance such as uranium, thorium, ruthenium or the like contained in water in a water treatment technique by a coagulation sedimentation method. It is an object of the present invention to provide a method for removing radioactive substances in water, which can remove water with high efficiency.

[0005]

In order to achieve the above object, a method for removing radioactive material in water according to the present invention comprises adding a metal ion to water containing a radioactive material, and mixing the radioactive material in the water with the added metal. The main reaction for forming a complex with the ions and the side reaction for producing hydroxides of the added metal ions are carried out so that the radioactive substance is adsorbed on the resulting cohesive precipitate. In the method for removing radioactive substances in water according to the present invention, the hydrogen ion concentration of the water containing radioactive substances is adjusted to a pH value of 3.5 to 1.
It is in the range of 3.5. Further, in the method for removing radioactive substances in water according to the present invention, the metal ion is at least one of a zinc ion and a magnesium ion.

[0006]

According to the present invention, in the case of uranium and thorium contained in water, hydrogen ions are dissociated and ionized, and each of the uranium and thorium is dissolved in water.
There are many forms of trivalent and tetravalent ions, and ruthenium is said to have a complex divalent to octavalent valence. In the presence of such ions, particularly zinc ions and magnesium By adding the ions, compounds and hydroxides of uranium, thorium and ruthenium and the added metal ions are precipitated, whereby uranium, thorium and ruthenium can be removed with extremely high efficiency. Further, according to the present invention, by using a substance capable of releasing zinc ions and magnesium ions, the pH range for the formation of the precipitate can be widened, and the removal efficiency can be further increased. And the concentration of ruthenium will be reduced to a level that can be released to the environment.

[0007]

An embodiment in which uranium, thorium and ruthenium are removed by the method for removing radioactive substances in water according to the present invention will be described below.

[0008]First embodiment Referring to FIGS. 1, 2 and Table 1, radiation in water according to the invention
A first embodiment of the method for removing a volatile substance will be described. First, test water
As uranium (²³⁸U) 0.2Bq / ml concentration and bird
Umm (²³⁴Th) pH containing 0.2 Bq / ml concentration
The waste liquid at a temperature of 18 ° C. in 1 is used. Where the test water is
Nuclear power plant, spent nuclear fuel reprocessing plant, nuclear fuel
Effluent generated from processing plants and facilities using radioactive materials
And drainage are selected. And in these waters uranium and
And thorium are uranyl cations (UO_Two ²⁺) And Uranas
Ion (U⁴⁺) Or thorium ion (Th⁴⁺)
PH value in the presence but in the presence of such ions
Substance capable of releasing the metal ion into test water of 7.8, eg
For example, zinc nitrate, magnesium nitrate or zinc oxide or acid
Salt obtained by dissolving magnesium halide in aqueous alkaline solution
Add the base metal solution. This allows the metal ion
By adding, for example, according to the following reaction formula,
Genus ion (Me²⁺) And uranium complex is MeUO_Four・ Me
O and MeU_TwoO ₇・ To precipitate MeO etc.
is there. This metal ion releasing substance is limited to the above example
Not release zinc or magnesium ions
Any substance can be used. 2Me²⁺+ U_TwoO₇ ^2-+ H_TwoO → MeU_TwoO₇・ MeO
+ 2H⁺ Me²⁺: Zn²⁺, Mg²⁺

In this embodiment, the addition of the metal ion is
Uranium in test water ⁽²³⁸ U) concentration 0.2Bq / m
1 and two test waters containing a thorium ( ²³⁴ Th) concentration of 0.2 Bq / ml and adjusted to a temperature of 18 ° C. at a pH of 1 were prepared. The test was performed by adding a basic metal solution adjusted with a 10% aqueous sodium hydroxide solution to a concentration of 100 mg / l in test water. The zinc ion, magnesium ion and their mixture ions to be added to the test water are appropriately selected in consideration of the hydrogen ion concentration of the test water in order to efficiently precipitate and form the insoluble complex of uranium and thorium. Among them, zinc ion is superior in the ability to adsorb the radioactive substance.

The hydrogen ion concentration in the test water is preferably within a certain range and the higher the higher the range, the better the result. Obtainable. That is, pH 3.5 to 13.5, preferably pH 6.8 to 1
A range of 1.5 is preferred. If the pH is lower than 3.5, no precipitation or complex formation is performed, and if the pH is higher than 13.5, the precipitate is immediately redissolved even if precipitation and complex formation are once performed. To adjust the pH value, sodium hydroxide, sodium carbonate, lime, or the like can be used, but sodium hydroxide is particularly preferable. Therefore, in this example, the pH value of the test water was adjusted with a 10% aqueous sodium hydroxide solution and set to a predetermined value. The pH adjustment of the test water may be performed prior to or simultaneously with the addition of the metal ions.

The test water to which the above zinc or magnesium ions have been added and the pH value has been adjusted is further stirred for 15 minutes at a temperature of 19 ° C., and after standing for a certain period of time, the precipitated product is filtered to obtain a filtrate. And separated. As described above, most of uranium and thorium dissolved in the test water precipitate as a poorly soluble complex, and are separated into solid and liquid by an appropriate method such as filtration. Here, the reaction time and the temperature of the test water can be set without being limited to the above examples as long as the reaction time is within a range of about 5 to 60 minutes and the temperature is about 10 to 90 ° C.

FIG. 1 shows the results of measurement of the concentration of radioactivity remaining in the filtrate after filtration of the precipitated product in test water at a temperature of 19 ° C. at various pH values as described above. As is clear from FIG. 1, in the case of the test water to which zinc ions were added, it was found that the radioactive substance was almost completely removed in the pH range of 6.8 to 11.5. Also, in the case of adding magnesium ions, the range of the pH value has shifted to a slightly higher side, but the radioactive substance has been almost completely removed as in the case of adding zinc ions.

FIG. 2 shows the results of measuring the concentration of radioactivity remaining in the filtrate after filtration of the precipitate product at each time in test water at a temperature of 19 ° C. with the reaction time in the range of 5 to 90 minutes as described above. Is shown. As is apparent from FIG. 2, in the case of the test water to which zinc ions were added, the radioactive substance was almost completely removed when the reaction time was 60 minutes or more. Similarly, even when magnesium ions are added, radioactive substances are almost completely removed.

Table 1 shows that, as described above, substances capable of releasing zinc, magnesium and iron ions were added to the test water so that the concentration of each metal ion became 100 mg / l, and the test substance was prepared using sodium hydroxide. The result of measuring the uranium concentration in the filtrate after solid-liquid separation by an appropriate method such as filtration by using a proportional counter with a pH value of the test water of 8 to form a precipitate of hydroxide is shown. As shown in Table 1, it is apparent that zinc ions and magnesium ions are superior in uranium removal rate as compared with iron ions conventionally used. In particular, when zinc ions were used, uranium was removed to such an extent that it could not be detected in the test solution, which is considered to be caused by the following complex formation reaction and coprecipitation reaction with hydroxide. . 2Zn ²⁺ + U ₂ O ₇ ^2- + H ₂ O → ZnU ₂ O ₇ .ZnO
+ 2H ⁺

Second Embodiment This embodiment has a thorium ( ²³⁴ Th) concentration of 0.5 Bq /
After adding concentrated nitric acid to 500 liters of the test solution to adjust the pH value to 1 or less, zinc oxide (zinc weight: 50 mg) was added, and the pH value was adjusted to 8 with an aqueous sodium hydroxide solution. Conditions such as temperature and time are the same as those in the first embodiment. After the filtration, the thorium concentration in the filtrate was measured using a GM counter, and the results are shown in Table 2. It was confirmed that thorium as well as uranium can be removed by zinc ion treatment.

Third Embodiment This embodiment uses ruthenium (Ru) chemical forms of Ru (NO) (NO ₃ ) ₃ and Na ₂ RuO ₄ as test water, and each test water has a Ru concentration of 50 mg / l. 200 ml was prepared, and zinc oxide was added to each test water as the weight of the coprecipitated carrier.
0 mg was added, and the pH of the solution was adjusted with an aqueous sodium hydroxide solution.
A value of 8 was used to generate a precipitated product,
Conditions such as temperature and time are the same as those in the first embodiment.
Table 3 shows the results of quantifying the ruthenium concentration in the filtrate after solid-liquid separation by an appropriate method such as filtration by ICP emission spectrometry.

[0017] Fourth Embodiment In this embodiment, ruthenium ⁽¹⁰⁶ Ru) concentration 0.25B
Nitric acid was added to 200 ml of the q / ml test solution to adjust the pH value to 1.
Then, zinc oxide (zinc weight: 50 mg) was added, and the pH was adjusted to 8 with an aqueous sodium hydroxide solution. Conditions such as temperature and time were the same as those in the first embodiment. is there. After filtration, the ruthenium concentration in the filtrate was measured by γ-ray spectrometry, and the results are shown in Table 4. It was confirmed that ruthenium could be removed by zinc ion treatment.

[0018]

As described above, according to the present invention, radioactive substances such as uranium, thorium, ruthenium, etc. can be economically and economically removed from waste liquid and waste water generated from nuclear facilities and the like. .

[Brief description of the drawings]

FIG. 1 is a diagram showing the relationship between the hydrogen ion concentration (pH) of test water to which zinc ions and magnesium ions are respectively added and the residual radioactivity concentration (Bq / ml) after the test.

FIG. 2 is a diagram showing a relationship between a reaction elapsed time (min) and a residual radioactivity concentration (Bq / ml) in test water.

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁷ , DB name) G21F 9/10 G21F 9/06

Claims (4)

(57) [Claims] 1. A main reaction in which a metal ion is added to water containing a radioactive substance to cause a complex formation reaction between the radioactive substance in the water and the additional metal ion, and a hydroxide of the additional metal ion is formed. A radioactive substance in water, wherein the radioactive substance is adsorbed on the resulting cohesive precipitate. 2. The method according to claim 1, wherein the radioactive substance contained in the water contains uranium, thorium and ruthenium. 3. The method according to claim 1, wherein the additional metal ion is at least one of a zinc ion and a magnesium ion. 4. The method for removing a radioactive substance in water according to claim 1, wherein the hydrogen ion concentration of the water containing the radioactive substance has a pH value of 3.5 to 13.5.