JP6472118B2 - Radioion extraction method and radioion extraction system - Google Patents

Description

  The present invention relates to a radioactive ion extraction method and a radioactive ion extraction system. In particular, the present invention relates to a method for extracting radioactive ions from a decontamination target material such as soil, and a radioactive ion extraction system.

  After the Fukushima Daiichi nuclear accident caused by the Great East Japan Earthquake that occurred on March 11, 2011, decontamination of radioactive materials including radioactive cesium ions has become a major issue. One of the most difficult issues is the development of technology for efficiently and safely extracting and separating radioactive cesium ions trapped in soil clay minerals. This technology is key to reducing the amount of radioactive soil waste.

  Conventionally, a method is known in which sodium tetraphenylborate and soil containing cesium ions are mixed and heated at several hundred degrees for two weeks to extract cesium ions from the soil (see, for example, Non-Patent Document 1). . In addition, a method for separating cesium ions from soil using Prussian blue has been studied (see, for example, Non-Patent Document 2). Furthermore, a method for separating cesium ions from soil by boiling contaminated soil with dilute sulfuric acid, washing with water and dehydrating has been studied (for example, see Non-Patent Document 3). In addition, a flocculant composition for treating wastewater containing udon powder, rice flour or wheat flour, which includes a mallow family troro-aoi genus component and a flocculant component, and a mallow troro-aoi genus component dried and crushed okra It is known (for example, refer to Patent Document 1).

Patent No. 4422202

Clays and Clay min. 13th Nat. Clay Conf. 247-261 Toru Kawamoto and two others, “Succeeded in extracting cesium in the soil with low-concentration acid, and recovered it with Prussian blue nanoparticle adsorbents to significantly reduce radioactive waste”, [online], (Germany) National Institute of Advanced Industrial Science and Technology, [Search on March 11, 2013], Internet <URL: http://www.aist-renkeisensya.jp/innovation-online/pdf/press/110831.pdf> Hiroshi Kasuyasu, “Cleaning and improving the environment of soil contaminated with radioactive cesium”, [online], Ministry of Agriculture, Forestry and Fisheries, [Search on March 11, 2013], Internet <URL: http: //www.maff.go .jp / mobile / kinkyu / tohoku_saigai / jyosen / kenkyu06.html ＞

  However, the extraction method described in Non-Patent Document 1 is not suitable for practical use because it requires not only heat treatment at high temperature but also heat treatment for 2 weeks. Further, in the method using the Prussian blue nanoparticle adsorbent described in Non-Patent Document 2, since cyanide is used, there is a risk of discharging cyanide into the environment, and the soil is subjected to acid treatment. As a result, radioactive cesium ions are eluted, which may destroy the structure of clay minerals.

  Further, in the methods described in Non-Patent Document 2 and Non-Patent Document 3, since it is necessary to use an acid, not only the material and location of the container that can handle the acid are limited, but the structure of the clay mineral is also limited. It can be destroyed. Furthermore, when radioactive cesium ions are extracted from soil using the flocculant composition described in Patent Document 1, it is necessary to coagulate and solidify the soil itself, so that the amount of waste increases and the soil is coagulated and solidified. There are many steps up to this point, and there are difficulties in putting it to practical use.

  Accordingly, an object of the present invention is to provide a radioactive ion extraction method and a radioactive ion extraction system that can quickly and easily extract radioactive ions from a decontamination target substance at room temperature.

  In order to achieve the above object, the present invention stores a mixed solution of a decontamination target substance containing radioactive ions and an aqueous solution of a precipitation reagent that reacts with the radioactive ions to produce a radioactive solid containing the radioactive ions. A method for extracting radioactive ions is provided, which includes a solid production step in which a container is rotated while revolving around a revolution axis, and a mixed solution is stirred and mixed to produce a radioactive solid containing radioactive ions.

  In order to achieve the above object, the present invention stores a mixed solution of a decontamination target substance containing radioactive ions and an aqueous solution of a precipitation reagent that reacts with the radioactive ions to produce a radioactive solid containing the radioactive ions. A radioactive ion extraction system is provided that includes a storage unit, and a stirring and mixing unit that rotates the sample storage unit while revolving around a revolution axis and stirs and mixes the mixed solution.

  According to the radioactive ion extraction method and the radioactive ion extraction system according to the present invention, a radioactive ion extraction method and a radioactive ion extraction system that can quickly and easily extract radioactive ions from a decontamination target material at room temperature. Can be provided.

It is a flowchart of extraction of the radioactive ion which concerns on the 1st Embodiment of this invention. It is a schematic diagram of the autorotation / revolution mixer used for extraction of the radioactive ion which concerns on the 1st Embodiment of this invention. It is a functional block diagram of the radioactive ion extraction system which concerns on the 2nd Embodiment of this invention.

[First Embodiment]
FIG. 1 shows a flow of extraction of radioactive ions according to the first embodiment of the present invention. FIG. 2 shows an outline of a rotation / revolution mixer used for extraction of radioactive ions according to the first embodiment of the present invention.

  In the method for extracting radioactive ions according to the present embodiment, the radioactive ions of the decontamination target material such as soil capturing the radioactive ions are replaced with non-radioactive ions in a short time at room temperature. This is a method for extracting radioactive ions from a target substance.

  Specifically, the radioactive ion extraction method includes the following steps. First, a mixed solution of a decontamination target substance that captures radioactive ions between the surfaces or layers, and an aqueous solution of a precipitation reagent that generates radioactive solids (ie, solid salts) containing radioactive ions by an ion exchange reaction with the radioactive ions. Is stored in the sample container (storage process: step 10; hereinafter, step is expressed as “S”). Next, the sample container is rotated while revolving around the revolution axis, and the mixed solution is stirred and mixed to generate a radioactive solid containing radioactive ions (solid generation step: S20). Subsequently, the decontamination target material from which the radioactive ions have been removed and the radioactive solid are separated (separation step: S30).

Here, the radioactive ions are radioactive cesium ions. The decontamination target substances include, for example, phlogopite (chemical formula: KMg ₃ AlSi ₃ O ₁₀ (OH, F) ₂ ) containing radioactive ions between the surfaces or layers and biotite (chemical formula: K (Mg, Fe) ₃ AlSi). It is a soil containing a layered silicate mineral such as ₃ O ₁₀ (OH, F) ₂ ).

  As the precipitation reagent, a compound that forms a solid salt hardly soluble in water when reacted with ions is used. Specifically, sodium tetraphenylborate or barium chloride can be used as the precipitation reagent in the present embodiment. The amount of the precipitation reagent used is preferably an amount that can replace at least all of the radioactive ions contained in the decontamination target substance. For example, it is preferable to use 1 mol or more of precipitation reagent for 1 mol of radioactive ions contained in the decontamination target substance. In addition, the greater the amount of precipitation reagent used, the shorter the time required for ion exchange between radioactive ions in the decontamination target substance and ions of the precipitation reagent. Further, when radioactive cesium ions are contained in the decontamination target substance, it is most preferable to use sodium tetraphenylborate.

  In the solid production process, the sample container 30 is rotated and revolved to give a complicated up-down convection to the mixed solution to stir and mix to promote the ion exchange reaction. Here, a solid production | generation process performs stirring and mixing at normal temperature and a normal pressure. Specifically, as shown in FIG. 2, the solid generation process is a rotation / revolution type that can rotate the sample container 30 around the rotation axis 20 while revolving the sample container 30 around the rotation axis 10. Use a mixer. In the solid generation step, a sample container 30 is rotated at a predetermined rotation speed while revolving around the rotation axis at a predetermined rotation speed using a rotation / revolution mixer. The rotation speed is set to a predetermined speed with respect to the revolution speed. As an example, the revolution speed is set to 2000 rpm, and the rotation speed is set to 800 rpm. The revolution speed and the rotation speed are not limited to these speeds, and can be appropriately changed.

  Moreover, a solid production | generation process can stir and mix a mixed solution by adding the acceleration more than the gravitational acceleration in the ground surface to a mixed solution by rotating and revolving the sample container 30. FIG. In the present embodiment, in the solid production step, a gravitational acceleration of about 400 G can be applied to the mixed solution. And in this Embodiment, a solid production | generation process is continued for the time about 30 minutes or more and 30 hours or less, for example. In addition, the inclination angle with respect to the revolution axis 10 of the sample container 30 can be provided so that it can be changed according to the revolution speed.

  In the separation step, a decontamination target material from which radioactive ions have been removed and a radioactive solid containing the radioactive ions are separated using a technique such as filtration, centrifugation, or elutriation.

(Effects of the first embodiment)
In the method for extracting radioactive ions according to the present embodiment, the precipitation reagent and the decontamination target substance are stirred and mixed in the sample container 30 that rotates while revolving around the revolution axis. The radioactive ions can be removed from the decontamination target material with high efficiency. Thereby, according to the method for extracting radioactive ions according to the present embodiment, compared to the conventional method that requires heating at a high temperature of several hundred degrees, the method that uses a high concentration acid, and the method that uses a very harmful reagent, Clay minerals and salts containing radioactive ions such as radioactive cesium ions can be separated safely and easily quickly under conditions of room temperature.

  Moreover, since the extraction method of the radioactive ion which concerns on this Embodiment uses the precipitation reagent which produces | generates a solid salt hardly soluble in water when it reacts with ion, a radioactive ion can be easily separated from a decontamination target substance as a solid salt. . Thereby, according to the radioactive ion extraction method according to the present embodiment, all or most of the radioactive ions can be decontaminated from the decontamination target substance, so that the amount of waste requiring strict management can be greatly reduced. .

  For example, when the decontamination target material is soil containing radioactive cesium ions and the precipitation reagent is sodium tetraphenylborate, the radioactive ion extraction method according to the present embodiment allows the radioactive cesium in the soil to be Ions are replaced by sodium tetraphenylborate sodium ions. Thereby, since radioactive cesium ions can be removed from the soil without destroying the structure of the soil (that is, the structure of the clay mineral), the soil after decontamination can be reused as normal soil.

[Second Embodiment]
FIG. 3 shows an example of a functional configuration of the radioactive ion extraction system according to the second embodiment of the present invention.

  The radioactive ion extraction system 1 according to the second embodiment can realize part or all of the steps and functions of the radioactive ion extraction method according to the first embodiment as a system.

  The radioactive ion extraction system 1 is a sample container as a sample storage unit that stores a mixed solution of a decontamination target substance containing radioactive ions and an aqueous solution of a precipitation reagent that reacts with the radioactive ions to generate a radioactive solid containing the radioactive ions. 30, the sample container 30 is rotated while revolving around the revolution axis, and the stirring and mixing unit 40 that stirs and mixes the mixed solution, and the separation unit that separates the decontamination target material from which radioactive ions have been removed and the radioactive solid 50.

  The stirring and mixing unit 40 is, for example, a rotation / revolution mixer, and can apply acceleration exceeding the gravitational acceleration on the ground surface to the mixed solution in the sample container 30. The separation unit 50 is a filtration device, a centrifuge, or a water tank (eltriation) device.

  The radioactive cesium ion was extracted from the clay mineral which adsorb | sucked the radioactive cesium ion with the following processes using the extraction method of the radioactive ion which concerns on embodiment of this invention.

  First, 2.0 g of sodium tetraphenylborate (manufactured by Kanto Chemical Co., Inc.) was weighed and dissolved in 50 ml of ion-exchanged water to prepare a sodium tetraphenylborate aqueous solution. Next, 2.0 g of a clay mineral adsorbing radioactive cesium ions and 30 ml of an adjusted sodium tetraphenylborate aqueous solution were mixed to prepare a mixed solution. As the clay mineral used in this example, phlogopite with 1480 ppm of radioactive cesium ions adsorbed was used. Subsequently, the mixed solution prepared using a rotation / revolution mixer was stirred and mixed at room temperature and normal pressure.

  In this example, THINKY AR-100 manufactured by Shinky Corporation was used as a rotating / revolving mixer. The revolution speed was set to 2000 rpm, and the rotation speed was set to 800 rpm. The stirring time was set to 30 hours.

  After stirring and mixing, the mixed solution was a suspension. This suspension was allowed to stand to precipitate clay minerals, and cesium tetraphenylborate was recovered from the supernatant. Then, the cesium tetraphenylborate recovered from the precipitated clay mineral and the supernatant is analyzed by an atomic absorption spectrophotometer (manufactured by Shimadzu Corporation: AA-6200 and AA-7000), and how much radioactive cesium is determined from the clay mineral. It was calculated whether it could be extracted.

As a result, it was shown that 77% or more of radioactive cesium ions could be recovered as a cesium tetraphenylborate salt when using the method for extracting radioactive ions according to this example. The concentration of radioactive cesium ions in the clay mineral used in this example is about 1000 times the concentration of radioactive cesium ions in soil contaminated by Fukushima Daiichi Nuclear Power Plant. It is considered that approximately 100% of radioactive cesium ions can be extracted from the actual soil by applying the radioactive ion extraction method according to the present embodiment to the contaminated actual soil. In addition, the concentration of radioactive cesium ions in soil contaminated by the Fukushima Daiichi nuclear power plant is the result of soil monitoring in the radiation monitoring information by the Ministry of Education, Culture, Sports, Science and Technology (URL: http://radioactivity.mext.go.jp/en/ contents / 6000/5622/24 / 116_0313.pdf) (the value obtained by converting the Bq value of ¹³⁷ Cs into g).

(Comparative example)
Sodium tetraphenylborate was replaced with an alkylammonium salt to prepare a mixed solution in the same manner as in Example 1, and the mixed solution was heated for 24 hours without using a rotation / revolution mixer. As a result, the amount of radioactive cesium ions that could be extracted from the clay mineral was about 5%.

  First, 35.8 g of barium chloride was weighed and dissolved in 100 ml of ion exchange water to prepare a saturated barium chloride aqueous solution. Next, 1.0 g of phlogopite adsorbing radioactive cesium ions and 20 ml of an adjusted saturated barium chloride aqueous solution were mixed to prepare a mixed solution. Then, this mixed solution was stirred for 90 minutes by a rotation / revolution mixer in the same manner as in Example 1. The revolution speed was set to 2000 rpm, and the rotation speed was set to 800 rpm.

  After stirring and mixing, the mixed solution was a suspension. This suspension was filtered and washed, and the obtained solid (cesium chloride) was dried. As a result, cesium ions could be extracted from the phlogopite.

  Thus, according to the method for extracting radioactive ions according to the present embodiment, radioactive ions (for example, radioactive cesium ions) that are difficult to extract due to being strongly trapped by clay minerals in the soil are converted into strong acids or It was shown that extraction and separation can be performed efficiently and at high speed at room temperature without using dangerous reagents.

  While the embodiments and examples of the present invention have been described above, the embodiments and examples described above do not limit the invention according to the claims. In addition, not all combinations of features described in the embodiments and examples are necessarily essential to the means for solving the problems of the invention.

DESCRIPTION OF SYMBOLS 1 Radioactive ion extraction system 10 Revolving shaft 20 Rotating shaft 30 Sample container 40 Agitation mixing part 50 Separation part

Claims (4)

A sample container storing a mixed solution of a decontamination target substance containing radioactive cesium ions and an aqueous solution of barium chloride, which is a precipitation reagent that reacts with the radioactive ions to produce radioactive solids containing the radioactive ions, A method for extracting radioactive ions, comprising: a solid generation step of generating a radioactive solid containing the radioactive ions by rotating around an axis while revolving, and stirring and mixing the mixed solution. The method for extracting radioactive ions according to claim 1, wherein the solid generation step adds acceleration exceeding gravitational acceleration on the ground surface to the mixed solution. The method for extracting radioactive ions according to claim 1, further comprising a separation step of separating the decontamination target material from which the radioactive ions have been removed and the radioactive solid. A decontamination substance containing radioactive cesium ions, and the sample storage unit for storing a mixed solution of an aqueous solution of barium chloride as a precipitating reagent to produce radioactive solid containing the radioactive cesium said radioactive cesium ions react with ions,
A radioactive ion extraction system comprising: a stirring and mixing unit that rotates the sample storage unit while revolving around a revolution axis and stirs and mixes the mixed solution.

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