JPH05164896A - Absorbent for radioactive nuclear species and disposal method for radioactive waste liquid - Google Patents

Abstract

PURPOSE:To enhance durability of absorbent as well as to enable radioactive nuclear species to be selectively absorbed by processing waste solution with absorbent consisting of activated carbon the specific surface area of which is equal to or more than a specified value, impregnated with functional groups in an amino methyle phosphonic acid series. CONSTITUTION:The absorbent consists of activated carbon the specific area of which is equal to or more than 600m<2>/g, impregnated with functional groups in an amino methyl phosphonis acid series. Functional groups in an amino methyl phosphonic acid series to be impregnated with are a part or the whole of hydrogen atoms directly connected to first class or second class nitrogen atoms of alkyl amino groups which are substituted with methylene phosphonic acid groups. A first method for processing radioactive waste solution is to process waste solution with activated carbon impregnated with functional groups in an amino methyl phosphonic acid series. A second meth is to process waste solution with activated carbon in a fiber shape, and with activated carbon impregnated with functional groups in an amino methyl phosphonic acid groups. Since material absorbed by two methods is somewhat different, surface coverage and selective absorption are thereby enhanced because of their synergetic effect.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an adsorbent useful for adsorbing radionuclides and a method for treating radioactive waste liquid.

[0002]

2. Description of the Related Art Among various waste liquids of a facility for reprocessing spent nuclear fuel generated in a nuclear power plant, long-lived β and γ nuclides such as cesium, radionuclides such as uranium and plutonium (hereinafter referred to as TRU nuclides) .)It is included. In the treatment of these radioactive waste liquids, it is necessary to separate and remove the radionuclide in the waste liquid to reduce the radiation level in order to reduce the exposure.

Conventionally, ion exchange resins and chelate resins have been used to remove metals in general waste liquids. But,
In the case of the radioactive waste liquid, there is a problem that the ion exchange resin or the chelate resin made of an organic polymer is easily deteriorated by the chemical action of radiation and cannot be used. Further, even if it can be used, there is a problem in its selectivity. For example, there is no adsorbent or treatment method capable of selectively separating and removing a trace amount of TRU nuclide such as plutonium contained in a large amount of uranium waste liquid. The current situation.

Inorganic adsorbents can be considered as an adsorbent having durability against radiation, but in the present circumstances, no one having excellent adsorbability has been obtained. On the other hand, as an adsorbent in which an inorganic functional group is supported on an organic matrix, there is disclosed in Japanese Patent Laid-Open No.
Japanese Patent No. 4530 proposes an adsorbent in which ferrocyanate is supported on acrylic fiber. However, this functional group has no selective adsorption of TRU nuclide, and there is a problem in durability because the matrix is an organic substance.

Further, Japanese Patent Publication No. 60-51491 discloses a phenolic chelate resin having an aminomethylphosphonic acid functional group and describes that it is excellent in uranium adsorption. There was no ability to selectively adsorb plutonium in uranium.

[0006]

As described above, each of the conventional adsorbents has a problem in durability against radiation and has a problem that it cannot selectively adsorb TRU nuclide in the radioactive liquid waste. .. An object of the present invention is to provide a radioactive nuclide adsorbent that is durable against radiation and capable of selectively adsorbing TRU nuclide, and a method for treating radioactive waste liquid.

[0007]

Means for Solving the Problems As a result of earnest studies to solve such problems, the inventors of the present invention have added aminomethylphosphonic acid functional groups to powdered granular activated carbon or fibrous activated carbon having an inorganic skeleton. The present inventors have found that the adsorbent adhering to the present invention has excellent resistance to radiation, and that it can selectively and reliably separate and remove a trace amount of TRU nuclide such as plutonium contained in the uranium waste liquid.

That is, the present invention has the following configuration. (1) An adsorbent for a radionuclide, comprising an activated carbon having a specific surface area of 600 m ² / g or more and an aminomethylphosphonic acid functional group attached thereto.

(2) A method of treating radioactive waste liquid, which comprises treating with the adsorbent of (1) above when separating and removing the TRU nuclide contained in the radioactive waste liquid.

(3) A method for treating radioactive waste liquid, which comprises treating the radioactive waste liquid with fibrous activated carbon having a specific surface area of 600 m ² / g or more and the adsorbent of (1) above.

The present invention will be described in detail below.

The adsorbent of the present invention has a specific surface area of 600 m ² / g.
The above-mentioned activated carbon is an aminomethylphosphonic acid functional group impregnated, but the activated carbon that constitutes the adsorbent may be powdered, granular, or fibrous, and the raw material for the activated carbon is wood, coconut shell, or coal. , Tar pitch, organic fibers such as rayon and acrylic fibers may be used. Among them, fibrous activated carbon is preferably used because it can be produced with a large specific surface area and can be easily molded into a sheet, a cartridge, a molded product or the like.

The specific surface area of activated carbon used for impregnation is 6
00 m ² / g or more is required, and the larger the specific surface area is, the more the adsorption amount is increased, which is practically preferably 1500 to 2500 m ² / g. The specific surface area of activated carbon used for impregnation is 6
If it is less than 00 m ² / g, the adsorption amount is too low to be used. In addition,
Although the specific surface area of the adsorbent in which the aminomethylphosphonic acid-based functional group is attached to activated carbon is smaller than that before the attachment, the specific surface area after the attachment is preferably 300 m ² / g or more.

In the adsorbent of the present invention, the aminomethylphosphonic acid-based functional group impregnated on the activated carbon has methylenephosphone as a part or all of the hydrogen atoms directly bonded to the nitrogen atom of the primary and / or secondary alkylamino group. It has been substituted with an acid group. As a production method, a reaction of ethylenediamine or polyethyleneimine with formalin and phosphorous acid, a reaction of salicylamine or p-hydroxybenzylamine shown in Chemical formula 1 with formalin and phosphorous acid, and reaction of methylolated phenol with polyethyleneimine It is possible to employ a reaction of a fish with formalin or phosphorous acid.

[0015]

[Chemical 1]

The functional group can be impregnated on the activated carbon by a method of adding activated carbon to react at the raw material stage, a method of advancing the reaction by adding activated carbon after a partial reaction, a method of adsorbing a reaction product on activated carbon, or the like. Can be adopted. Moreover, the form of the activated carbon when the aminomethylphosphonic acid functional group is attached is not particularly limited, and may be formed into a sheet or a cartridge.

The amount of aminomethylphosphonic acid functional group to be attached to the activated carbon is 10 phosphonic acid per 1 kg of activated carbon.
It is preferably mg or more. The larger the amount of impregnation, the more the amount of ionic adsorption of nuclides increases, but the pores of activated carbon are blocked and the amount of physical adsorption decreases, so depending on the type of nuclide present in the waste liquid, the state of the waste liquid, etc. Adjust the amount of impregnation.

Next, the method for treating the radioactive liquid waste of the present invention will be described. The first method of the present invention is to treat the radioactive liquid waste with activated carbon having an aminomethylphosphonic acid functional group attached thereto. By attaching an aminomethylphosphonic acid functional group, even ordinary activated carbon has excellent selectivity. An adsorbent obtained by impregnating the above-mentioned functional groups on fibrous activated carbon is preferable because the activity further increases the selective adsorption.

The second method of the present invention comprises fibrous activated carbon,
That is, the radioactive liquid waste is treated with activated carbon having an aminomethylphosphonic acid functional group attached thereto. What is adsorbed by the fibrous activated carbon is slightly different from that adsorbed by the activated carbon having a functional group attached thereto. Therefore, when both are treated, the synergistic effect thereof can improve the adsorption rate and selective adsorption. The reason for this is, for example, that the first stage is fibrous activated carbon, the second stage is
When treated with activated carbon containing a stage aminomethylphosphonic acid functional group, the first stage fibrous activated carbon adsorbs a trace amount of organic matter contained in the waste liquid and a complex-forming product of TRU nuclide such as plutonium, It is considered that the activated carbon containing the aminomethylphosphonic acid type functional group in the second stage selectively adsorbs TRU nuclides such as plutonium as compared with uranium due to the effect of the functional group.

The fibrous activated carbon used in the second method needs to have a specific surface area of 600 m ² / g or more, as in the case of the fibrous activated carbon to be impregnated to obtain the adsorbent of the present invention.
It is preferably from 00 to 2500 m ² / g.

In the present invention, any conventional means may be adopted as a concrete means for treating the radioactive waste liquid. For example, a batch method using an adsorption tank, a column liquid passing method using an adsorption tower, or a combination thereof can be used. Alternatively, the adsorbent may be formed into a sheet, a cartridge or the like, and a liquid passing method using the adsorbent may be adopted. In general, a column flow method and a cartridge flow method are preferable, but when an adsorbent impregnated with powdered activated carbon is used, a batch method is preferably used.

In the column flow method, the adsorption tower is filled with the adsorbent to pass the radioactive waste liquid, and the thickness of the adsorbent packed layer is preferably 200 mm or more, particularly preferably 500 to 2000 mm. If the thickness of the filling layer is less than 200 mm, leakage due to leakage easily occurs, which is not preferable. The liquid passing speed varies depending on the properties of the liquid, but it is preferably SV (space velocity) of 0.5 hr ^-1 or more, particularly ¹ to 10 hr ^-1 .

The cartridge flow method is a method in which a cartridge formed in a cylindrical shape or a column shape is set in a housing case and the liquid is passed. In the case of a cartridge, the handling of mounting and demounting is easy, and the disposal of the used cartridge is simple, and it is very effective especially when handling radioactive substances. The method of molding the cartridge is, for example,
There are methods such as wet molding of fibrous activated carbon, molding of granular or powdered activated carbon into a sheet with an organic binder by a papermaking method or dry method, or a method of molding a fibrous activated carbon sheet and winding and consolidating it into a cartridge. .. When molding into a cartridge, a small amount of an inorganic binder or an organic binder may be blended.

[0024]

In the present invention, as the adsorbent, by using activated carbon having an aminomethylphosphonic acid functional group having excellent selective adsorption and durability, it is possible to remove radioactive nuclide-containing waste liquid, particularly uranium waste liquid. It becomes possible to selectively adsorb TRU nuclides such as plutonium, and it is possible to easily treat the radioactive waste liquid which has been difficult in the past.

[0025]

EXAMPLES Next, the present invention will be specifically described by way of examples.

Example 1 24 parts by weight of polyethyleneimine having a molecular weight of about 600, phosphorous acid 16
By weight, 45% by weight of 37% formalin and 1% by weight of 98% sulfuric acid were mixed at room temperature and dissolved to obtain a uniform liquid. Then, a fibrous activated carbon (A- manufactured by Unitika Ltd.
20: Specific surface area 2116 m ² / g) 100 g and water sufficient for the above liquid and fibrous activated carbon to be dipped were added, and reacted at 120 ° C. for 3 hours while stirring. Then, the reaction product was filtered, washed, and dried to obtain an aminomethylphosphonic acid-based functional group-impregnated fibrous activated carbon. In this adsorbent, the amount of functional groups attached was 9.1 g / kg in terms of phosphorus amount and the specific surface area was 1360 m ² / g.

1 g of the impregnated fibrous activated carbon thus obtained was mixed with uranium (U) concentration of 432 mg / ml and plutonium (Pu) concentration of 1.2.
It was dipped in 20 ml of a uranium waste liquid of × 10 ⁻³ mg / ml and subjected to adsorption treatment for 24 hours. As a result, the Pu adsorption rate was 60% and the U adsorption rate was 20%.

Example 2 35 parts by weight of phenol, 15 parts by weight of diethylenetriamine,
Phosphorous acid 26 parts by weight, 37% formalin 115 parts by weight, 98% sulfuric acid
63 parts by weight were mixed at room temperature and dissolved to obtain a uniform liquid. Then, the palm shell activated carbon (granular:
After adding 150 g of a specific surface area of 900 m ² / g) and water for immersing the above liquid and activated carbon, the mixture was reacted at 120 ° C. for 3 hours while stirring. Then, the reaction product was filtered, washed, and dried to obtain an aminomethylphosphonic acid-based functional group-impregnated activated carbon. This adsorbent has a functional group loading of 10.5 g / phosphorus.
kg, specific surface area was 380 m ² / g.

1 g of the obtained impregnated activated carbon was added to uranium (U).
Concentration 432mg / ml, Plutonium (Pu) concentration 1.2 × 10 ^-3
It was immersed in 20 ml of a uranium waste liquid of mg / ml and subjected to adsorption treatment for 24 hours. As a result, the Pu adsorption rate was 36% and the U adsorption rate was
It was 15%.

Comparative Example 1 Using the unimpregnated coconut shell activated carbon used in Example 2,
Adsorption treatment of the uranium waste liquid was performed in the same manner as in Example 2. As a result, the Pu adsorption rate was 12%, and the U adsorption rate was 13%, which were low.

Example 3 Non-impregnated fibrous activated carbon (A-20 manufactured by Unitika Ltd .: specific surface area 2116 m ² / g) was packed in a glass column having an inner diameter of 14.8 mm and a height of 500 mm in an amount of 9.0 g. The height of the packed bed at this time is
It was 400 mm. Further, the aminomethylphosphonic acid-based functional group-impregnated fibrous activated carbon obtained in Example 1 was filled in a glass column having the same size as described above in an amount of 9.0 g. The height of the packed bed was 400 mm. The former column is connected to the first stage and the latter column is connected to the second stage in series, and the uranium concentration is 0.26 mg / ml.
A uranium waste liquid having a plutonium concentration of 3.9 × 10 ⁻⁵ mg / ml was subjected to a liquid flow treatment of 500 ml at a flow rate of 176 ml / hr. As a result, the adsorption amount of Pu 1.95 × 10 ^-2 mg, the adsorption rate 100%, U
The adsorption amount was 105 mg, and the adsorption rate was 80%.

[0032]

The adsorbent of the present invention has a specific surface area of 600 m ² /
Since an aminomethylphosphonic acid-based functional group is attached to g or more of activated carbon, the carbon has durability against radiation and can selectively adsorb TRU nuclide.

Therefore, if the radioactive waste liquid is treated by using this adsorbent, it becomes possible to selectively and reliably separate and remove a trace amount of TRU nuclide such as plutonium contained in a large amount of uranium waste liquid. ..

When the radioactive waste liquid is treated by using the adsorbent of the present invention and the fibrous activated carbon in combination, the synergistic effect of the treatment results in
It is possible to improve the adsorption rate and the selective adsorption property.

Claims (4)

[Claims] 1. An adsorbent for a radionuclide, comprising an activated carbon having a specific surface area of 600 m ² / g or more and an aminomethylphosphonic acid functional group attached thereto. 2. The adsorbent according to claim 1, wherein the activated carbon is fibrous activated carbon. 3. A method for treating radioactive waste liquid, which comprises treating with the adsorbent according to claim 1 in separating and removing the radionuclide contained in the radioactive waste liquid. 4. A method for treating radioactive waste liquid, which comprises treating the radioactive waste liquid with a fibrous activated carbon having a specific surface area of 600 m ² / g or more and the adsorbent according to claim 1.