JP3264940B2 - Method for separating transition elements in solution - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method of separating transition elements from the solution containing a transition element (e.g. a radioactive waste liquid).

[0002]

2. Description of the Related Art Conventionally, there are the following methods for separating a transition element from a solution. For example, a method for separating transuranium elements from radioactive liquid waste is described in IAE, Technical Document, 337 (1985) pp. 97-112 (IAEA-TECDOC-337 (1)).
985) PP97-112).
This is a method of causing precipitation of an iron compound in a radioactive waste liquid and co-precipitating the transuranium element in the waste liquid.
JP-A-57-170827 discloses that a ferrous salt and a neutralizing agent are added to wastewater containing a trace amount of Rh to reduce the wastewater p.
A method of adjusting H and precipitating Rh with iron is described.

[0003]

[SUMMARY OF THE INVENTION A conventional method of the former is effective against transuranium elements, other transition elements, in particular ruthenium, problem of low separation efficiency for Techne Chi um is is there. The latter conventional method is also not directed to the separation of ruthenium and Techne Ji um.

An object of the present invention is a method of separating transition elements in the solution, the transition element other than transuranium elements, in particular ruthenium, to provide an effective method against separation of Techne Ji um is there.

[0005]

The method for separating transition elements in a solution according to the present invention is as described in each claim. In the present specification, the zero-valent metal means the metal itself that is not in the form of ions or compounds, and is preferably in the form of a metal powder.

[0006] As the zero-valent metal to be added to the solution, zero-valent iron is suitable, but other than that, zero-valent metals such as chromium, manganese, cobalt, nickel, copper, and zinc may be used. . Also, as the polyvalent metal compound to be added to the solution,
Trivalent or divalent iron compounds are preferred, but otherwise,
A polyvalent metal compound, such as chromium or a rare earth element, which is soluble in a solution and generates a hydroxide precipitate in an alkaline region may be used.

[0007]

The divalent iron ions and / or 3
Polyvalent metal ions, such as multivalent iron ions, form hydroxide precipitates in the solution when the solution is alkaline. At this time, a rare earth element such as an actinoid element is taken into the precipitate or adsorbed on the precipitate to coprecipitate. As a result, most of the transition elements move into the precipitate together with the polyvalent metal and can be separated from the solution. On the other hand, part of the transition elements such as ruthenium or Techne Ji um, so exist stably in the solution without coprecipitation polyvalent metal precipitation, but is reduced by 0-valent metal in solution, the multi Behaves with the precipitation of the valent metal. In this way, the transition elements such as ruthenium or Techne Chi um that can exist stably in the solution can also be separated from the solution.

The polyvalent metal ion may be an ion generated by dissolving the polyvalent metal compound added to the solution, or a part of the zero-valent metal added to the solution may be oxidized in the solution. It may be an ion generated. Or,
An ion generated by at least a part of the trivalent iron compound added to the solution being reduced in the solution may be used. An oxidizing agent or a reducing agent may be added to the solution for the above oxidation or reduction.

[0009]

EXAMPLES first invention described below, the second, third, fourth embodiment, when applying the present invention as a method for removing transuranic elements, ruthenium and Texnai Chi um from among radioactive liquid waste It shows about.

First, a first embodiment will be described with reference to FIG.
FIG. 1 is a diagram showing a basic device configuration used in the present embodiment. The low-level radioactive waste liquid 6 generated from the reprocessing step of spent nuclear fuel is put into the precipitation tank 1, and a mixture (mixed iron) 7 of zero-valent iron and a soluble trivalent iron compound is added. Next, a pH adjuster 11 is added to adjust the pH in the solution to an alkaline range, thereby causing precipitation of iron hydroxide. Transuranic elements contained in the radioactive liquid waste, nuclides such as ruthenium or Techne Chi <br/> um is co-precipitated with the above precipitate. On this occasion,
When the stirring mechanism 10 is used, the precipitation is effectively generated. After the sediment has sufficiently grown, the treated waste liquid 9 is taken out by the sediment removing mechanism (filter) 2 while preventing the sediment from being mixed. Then, the precipitate 8 is finally taken out. Transuranic elements in the effluent by the above procedure, ruthenium and Texnai Chi um is removed from the waste liquid as a precipitate body.

The separation performance of transuranium elements (americium and neptunium) and ruthenium according to the present embodiment will be described with reference to FIG. FIG. 2 shows the results of experimentally determining a decontamination coefficient (DF) as an index of the separation performance. DF is a value obtained by dividing the concentration of the element contained in the original solution by the concentration of the element in the solution after the treatment, and the higher the DF, the better the separation performance. The method of obtaining DF = 10 ³ is a fairly effective separation method. FIG. 2 shows the experimental results of the two separation methods indicated by a and b in comparison. a is the case of a conventional method of adding a soluble trivalent iron compound to form a ferric hydroxide precipitate to coprecipitate a transition element,
It can be seen that it is effective for americium (Am) and neptunium (Np) but not for ruthenium (Ru). b is the experimental result of the method according to the present example, and it can be seen that the separation performance of ruthenium (Ru) is also improved by adding zero-valent iron in addition to the soluble trivalent iron compound. Although not shown in FIG. 2, Techne Ji <br/> um (Tc) also shows the same behavior as ruthenium (Ru).

According to this embodiment, not only the transuranium element but also Ru and Tc can be effectively removed from the radioactive waste liquid. In addition, since only iron and iron compounds are added as additives and only pH operation is performed, the treatment of precipitation is easy,
It also has the advantage of simple operation.

In this embodiment, the same effect can be obtained by adding a metal which dissolves in a solution, such as zero-valent chromium, manganese, cobalt, nickel, copper or zinc, instead of zero-valent iron. Furthermore, exhibits instead chrome trivalent iron compound soluble, such as rare earth elements, the same effect can be added polyvalent metal compound soluble to produce a hydroxide precipitate with an alkaline region.

Next, a second embodiment of the present invention will be described with reference to FIG. The radioactive waste liquid 6 whose pH has been adjusted to an alkaline region in advance is put into the precipitation generating tank 1,
A mixture of zero-valent iron, a soluble divalent iron compound, and a trivalent iron compound (mixed iron) 7 is added to form a precipitate of iron hydroxide. After the sedimentation, the slurry solution containing the sediment is transferred by the slurry transfer pump 3 to the sediment removal mechanism 2 via the on-off valve 5, where the sediment is separated from the solution by a filter. The solution 9 after the treatment is transferred to a solution storage tank as it is, while the precipitate 8 attached to the filter is transferred to another storage tank by the backwash water 12 via the on-off valve 5. Since the precipitate 8 contains long-lived nuclides such as transuranium elements, it is strictly stored and managed, and will be stabilized and solidified in the future. Since the radioactive waste liquid 9 after the treatment does not contain a long-lived nuclide, a relatively simple treatment such as concentration can be performed.

According to this embodiment, a transition element such as a transuranium element, Ru, Tc, or a rare earth element is co-precipitated from the radioactive waste liquid into the iron hydroxide precipitate, and this precipitate is effectively removed from the waste liquid. Can be removed from

In this embodiment, a method using an ordinary filter is adopted as a method for separating a precipitate, but a pulse filter method,
The same effect can be obtained by using a vacuum filtration method, a gravity separation method, or a centrifugal separation method. Although water was used as the backwash water 12, the same effect can be obtained by using another solution.

A third embodiment according to the present invention will be described with reference to FIG. The radioactive waste liquid 6 is put into the precipitation tank 1, zero-valent iron 13 is added, and a part of the zero-valent iron is oxidized in the waste liquid 6 to obtain divalent iron ions and / or trivalent iron ions. Is added to the radioactive waste liquid 6.
In this way, zero-valent iron and 2 are contained in the radioactive waste liquid 6 in the tank 1.
A valent iron ion and / or a trivalent iron ion coexist. Next, a pH adjuster 11 is added to make the waste liquid alkaline, and a precipitate of iron hydroxide is generated. At this time, the pH in the solution is monitored and controlled by the pH measuring mechanism 14. The radioactive waste liquid after the formation of the precipitate is transferred to another tank by the pump 3 while the precipitation removing mechanism 2 avoids mixing of the precipitate. The precipitate 8 from which the treated waste liquid 9 has been removed is also transferred to another tank and stored and managed. The hydroxide precipitation of iron is relatively stable and suitable for long-term storage as it is.

According to the present embodiment, the solution containing zero-valent iron
Although it is necessary to generate trivalent iron ions and / or trivalent iron ions, only zero-valent iron (preferably a powder) (or a mixture obtained by mixing an oxidizing agent as necessary) is used as an additive. Just prepare. Further, fine adjustment of the solution pH is facilitated by the pH measurement mechanism. Further, since no sediment enters the pump 3, an ordinary liquid transfer pump can be used. Transuranium elements, ruthenium and
And technetium separation performance is the same as that of the method shown in the first embodiment (see FIG. 2).

In this embodiment, zero-valent iron is used as an additive. However, similar effects can be obtained by using a zero-valent metal (powder) such as nickel or cobalt which dissolves in a solution and produces a precipitate in an alkaline region. To play.

Next, a fourth embodiment will be described. Zero-valent iron and a soluble trivalent iron compound are added to the radioactive liquid waste placed in the precipitation tank, and at least a part of trivalent iron ions generated from the trivalent iron compound is contained in the radioactive liquid waste. Is added to the radioactive waste liquid so as to generate divalent iron ions by the reduction. This reducing agent may be previously blended with the above-mentioned zero-valent iron and trivalent iron compounds to be added.
In this way, zero-valent iron and divalent iron ions and / or trivalent iron ions coexist in the radioactive waste liquid in the tank. Next, as in the third embodiment, the waste liquid is made alkaline, causing precipitation of iron hydroxide, and separated and transferred in the same manner as described above.

[0021]

[0022]

FIG. 5 shows the operating procedure according to the invention,
This is shown in a block flow with attention paid to the adjustment of.
In the present invention, the pH adjustment of the waste liquid 6 is relatively important, and three methods are conceivable. In the first method, the pH of the waste liquid is first adjusted to 7 or less, preferably 4 or less, and then the additive according to the present invention, for example, mixed iron is added.
Is adjusted to 7 or more, preferably 9 or more and 13 or less to generate a precipitate. At this time, since the transition element is contained in the precipitate, it can be separated from the waste liquid by precipitation separation. In the second method, when the pH of the waste liquid is originally lower than 7, a mixed iron is first added, the pH is adjusted to 7 or more, and then the generated precipitate is separated. The third method is the pH of the waste liquid.
Is adjusted to 7 or more, and mixed iron is added to generate a precipitate. In this case, if the pH of the waste liquid is originally 7 or more, the pH adjustment process is naturally unnecessary. As described above, in any of the methods, the transition element can be separated from the waste liquid by a relatively simple procedure.

[0024]

According to the present invention, it is included in the solvent solution Ruteni
Since the presence and technetium can be coprecipitated along with the polyvalent metal hydroxide precipitate, Contact ruthenium from solvent solution
And technetium can be separated with high efficiency . Ma
And, when the solution is radioactive waste, transuranic elements and Techne Chi um and γ long lived nuclides from the radioactive liquid waste
Since ruthenium, which is a radionuclide, can be separated, waste liquids can be easily handled, and the volume of the high-risk radionuclide can be reduced.
Effect contribute to the stable storage there Ru.

[Brief description of the drawings]

FIG. 1 is a diagram of an apparatus used in a first embodiment of the present invention.

FIG. 2 is a diagram illustrating the effect of the present invention in comparison with a conventional technique.

FIG. 3 is a diagram of an apparatus used in a second embodiment of the present invention.

FIG. 4 is a diagram of an apparatus used in a third embodiment of the present invention.

FIG. 5 is an exemplary diagram of an operation flow according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Precipitation production tank 2 ... Precipitation removal mechanism 3 ... Slurry transfer pump 6 ... Waste liquid 7 ... Precipitating agent 11 ... pH adjuster

Continuation of the front page (51) Int.Cl. ⁷ Identification symbol FI G01N 31/00 G01N 31/00 Y 31/02 31/02 G21F 9/10 G21F 9/10 (56) References JP-A-50-140799 ( JP, A) JP-A-62-204200 (JP, A) Katsuo Ito, Coprecipitation reaction of technetium ion with iron hydroxide, Journal of the Atomic Energy Society of Japan, Japan, Atomic Energy Society of Japan, February 28, 1982, Vol. 24 No. 2, pp. 64-68 (58) Fields investigated (Int. Cl. ⁷ , DB name) C02F 1/70 C01G 55/00 C01G 57/00 C02F 1/62 G01N 31/00 G21F 9/10

Claims (11)

(57) [Claims] At least ruthenium and technetium
Produces hydroxides in solutions containing alkaline in the alkaline region
A polyvalent metal compound, ruthenium and
Reduces technetium and produces hydroxide in the alkaline region
A 0-valent metal to produce the addition, the solution is the condition under a and the polyvalent metal ion that is alkaline
Under the condition that zero-valent metal coexists, hydroxylation of the polyvalent metal
A method for separating transition elements in a solution, comprising coprecipitating a substance with ruthenium and technetium . (2) at least a transuranium element, ruthenium and
And technetium in a solution containing
A polyvalent metal compound that forms a chloride;
Reduces ruthenium and technetium and reduces alkalinity
It was added and 0-valent metal to produce a hydroxide in range, a condition under that the solvent <br/> solution is alkaline and the polyvalent metal
Under the condition that the above-mentioned ion and the zero-valent metal coexist,
Hydroxides of valent metals and transuranium elements, ruthenium and te
The method of separating transition elements dissolved solution you characterized by co-precipitation and Kunechiumu. 3. The polyvalent metal compound and the zero-valent gold
After the genus is added to the solution, the solution is made alkaline.
3. The method according to claim 1, wherein
The method of separating transition elements in solution according to. 4. The method according to claim 1 , wherein said solution adjusted to be alkaline has
Adding said polyvalent metal compound and said zero-valent metal
The method for separating a transition element in a solution according to claim 1, wherein: 5. The method according to claim 1, wherein said solution is alkaline.
The polyvalent metal compound and the zero-valent metal are added to the solution.
3. The method according to claim 1, further comprising:
A method for separating a transition element from a solution according to any of the above items . 6. At least ruthenium and technetium
The solution containing the acid is acidified and the hydroxide is removed in the alkaline region.
The resulting polyvalent metal compound and ruthenium dissolved in the solution
And technetium in the alkaline region
Adding a zero-valent metal that forms an oxide to the solution;
The solution is made alkaline, and the solution is made alkaline.
And the polyvalent metal ion and the
Under the condition that a zero-valent metal coexists, the hydroxide of the metal and
It specially co-precipitates ruthenium and technetium.
A method for separating transition elements in a solution. 7. At least a transuranium element, ruthenium and
Acid and the solution containing technetium
Metal compounds that form hydroxides in the
To reduce ruthenium and technetium
A solution in which a zero-valent metal that forms a hydroxide in the potash region is added to the solution
And then make the solution alkaline and add the solution
Is alkaline and the polyvalent metal
Under conditions where ions and the zero-valent metal coexist, the metal
Hydroxide and transuranium, ruthenium and technetic
A method for separating transition elements in a solution, comprising coprecipitating the transition element with a solution. 8. The method according to claim 1, wherein the polyvalent metal compound is a divalent iron compound.
And / or a trivalent iron compound, wherein the zero-valent metal is
Claim 1 or Claim 2 which is zero-valent iron.
8. The method for separating a transition element from a solution according to any one of items 7 to 7 . 9. The method according to claim 8, wherein said zero-valent metal is Fe, Ni and Co.
The method for separating transition elements in a solution according to any one of claims 1 to 7, wherein the method is any of the following. 10. At least transuranium element, ruthenium
And radioactive waste containing technetium
Metal compounds that form hydroxides in the
To reduce ruthenium and technetium
Adds a zero-valent metal that produces hydroxide in the potash region
And under the condition that the radioactive waste liquid is alkaline
And the ion of the polyvalent metal and the zero-valent metal coexist
Under the conditions, the hydroxide of the polyvalent metal and the transuranium element,
Co-precipitated with ruthenium and technetium
A method for separating transition elements in a solution. 11. The polyvalent metal compound is a divalent iron compound.
And / or a trivalent iron compound, wherein said zero-valent metal
Is zero-valent iron.
Method for separating transition elements in solution.