JP2015010852A - Method for decontaminating radioactive material contained in sediment on water bottom or in water - Google Patents

Abstract

PROBLEM TO BE SOLVED: To decontaminate a radioactive material contained in water or in sediment on a water bottom by a simple device or method.SOLUTION: A connection mat 1 formed by connecting a plurality of bags 2 packed with an adsorbent obtained by pulverizing-burning diatomaceous earth or the like is sunk onto a water bottom, and then recovered, to thereby decontaminate a radioactive material contained in sediment on the water bottom or in the water.

Description

  The present invention relates to a method for decontaminating radioactive substances contained in sediment or water in the bottom using an adsorbent obtained by pulverizing and firing mudstone or claystone.

  There is a need for technological development to decontaminate water and soil contaminated by radioactive materials released in accidents at nuclear power plants. Radioactive materials released from the nuclear power plant into the atmosphere diffused by the flow of wind, poured down to the surface by rain, etc., and entered rivers, dams, ponds, paddy fields / fields, and forests.

  The radioactive substance is a general term for substances containing radioactive elements, and includes radioactive cesium (cesium 134, cesium 137), radioactive iodine (iodine 131), and radioactive strontium (strontium 90). In particular, technical development for decontamination of radioactive cesium (cesium 134, cesium 137) having a long half-life is required, and various methods are being studied.

  In addition, there is a need for technological development to decontaminate radioactive materials contained in sediments and water, such as riverbed waterbeds, lakes and dams, and agricultural waterways. For example, there is a method of discharging radioactive material-contaminated sediment deposited on the bottom of the water, but the treatment of the generated waste is a problem.

  In Patent Document 1, granulated particles containing zeolite particles and magnetic particles in contact with water to adsorb harmful components such as radioactive substances to the granulated particles, and granulated by adsorbing harmful components in the water There has been proposed a water purification method characterized by magnetically separating material particles from water.

  Patent Document 2 is characterized in that a radioactive substance treating agent obtained by dispersing natural zeolite fine particles having an average particle diameter of 5.0 μm or less obtained by pulverizing natural zeolite made of mordenite in water is added to radiation-contaminated wastewater. A treatment method for radiation-contaminated wastewater is proposed.

  However, the zeolite used in the technique described in Patent Document 1 or 2 has a problem that it is expensive, is excellent in economic efficiency, and has an adsorptive power with respect to a radioactive substance at the same level or higher than that of zeolite. No decontamination method using the adsorbent has been provided yet.

JP 2005-177709 A JP 2012-247405 A

An object of the present invention is to provide a method for decontaminating a radioactive substance using an adsorbent that is less expensive than zeolite and has an adsorbing power to the same or higher level of radioactive substance as zeolite.
In addition, by providing a method for decontaminating radioactive materials that can remove adsorbents that have adsorbed radioactive materials from water with a simple device or method, and move them to a predetermined location with a simple device or method. is there.

  As a result of intensive studies to solve the above-mentioned problems, the present inventor made contact with contaminated water containing a radioactive substance to the adsorbent obtained by pulverizing and firing mudstone or claystone, It has been found that the adsorbent has the property of adsorbing radioactive cesium at the same level or higher as that of zeolite.

That is, the present invention is a method for decontaminating radioactive substances contained in sediment or water in the bottom of a water by sinking a connecting mat in which a plurality of bags filled with an adsorbent are connected to the bottom of the water and then collecting the mat. The adsorbent is obtained by pulverizing, after pulverizing mudstone or clay rock, which is naturally agglomerated diatomaceous earth, and the bag has a mesh size that prevents the adsorbent from flowing out and clogging. Provided is a method for decontaminating a radioactive substance, characterized in that means for pulling up from the bottom of the water is provided at both ends of the connecting mat.
Hereinafter, this aspect of the present invention is referred to as “Aspect 1”.

Further, the present invention is a method for decontaminating radioactive materials contained in sediment or water in the bottom of the water by sinking a mat filled with an adsorbent to the bottom of the water, and recovering the mat, wherein the adsorbent is made of diatomaceous earth. It is obtained by pulverizing and firing natural solidified mudstone or claystone, and the mat has a mesh size that prevents the adsorbent from flowing out and clogging. The present invention provides a method for decontaminating a radioactive substance, characterized in that a partition is provided in the mat so as not to be biased, and means are provided at both ends for lifting from the bottom of the water.
Hereinafter, this embodiment is referred to as “embodiment 2”.

ADVANTAGE OF THE INVENTION According to this invention, the decontamination method excellent in economical efficiency and adsorption power using the adsorption agent which is cheaper than a zeolite and has the adsorption power with respect to the radioactive substance of the same grade or more as a zeolite can be provided.
In particular, since cesium ions are adsorbed, radioactive materials such as cesium 134 and cesium 137 can be removed.

In addition, if the mat or connecting mat filled with the adsorbent is submerged in the bottom of the water, the radioactive material in the water can be adsorbed by a simple method, and the adsorbent that adsorbs the radioactive material by a simple device or method Can be removed from the water.
When the adsorbent is dispersed on the bottom of the water, it is not easy to take out only the “adsorbent adsorbing radioactive material” other than earth and sand from the water, but according to the present invention, the process can be facilitated.

Further, if the mat or the connecting mat is collected, it can be easily moved to another place such as a disposal site in a state where the radioactive substance is concentrated.
That is, it is easy to move the adsorbent adsorbed with the radioactive substance, which is the latter half of the “decontamination” in the present invention, to a predetermined location.

It is a perspective view which shows an example of the connection mat which used for the method of decontaminating the radioactive substance of this invention which connected the some bag (Aspect 1). It is a perspective view which shows an example of the mat | matte used for the method of decontaminating the radioactive substance of this invention in which the partition was provided inside (aspect 2). It is explanatory drawing when the method of decontaminating the radioactive substance of this invention is used by a river (a) and an agricultural waterway (b).

  Hereinafter, the present invention will be described, but the present invention is not limited to the following specific embodiments, and can be arbitrarily modified within the scope of the technical idea.

<Common to Aspect 1 and Aspect 2>
The present invention is a method for decontaminating radioactive materials contained in sediment or water in the bottom of the water, in sediments of the bottom of rivers, lakes, dams, ponds, rice fields, agricultural waterways, or rivers, lakes, dams, It is useful for decontamination of radioactive materials contained in water itself such as ponds, rice fields, and agricultural waterways.
In the present invention, “decontamination” means that the radioactive material contained in a wide range is concentrated (contained in a small volume) by adsorbing the radioactive material contained in the sediment or water in the bottom of the water to the adsorbent. This refers to up to moving the adsorbent adsorbed with the radioactive substance to a predetermined location.

The “diatomaceous earth” used in the present invention is a deposit made of diatom remains.
When diatoms grow in large quantities in the sea or lakes and die, the dead bodies settle on the bottom of the water. The organic matter in the carcass is gradually decomposed, and finally only the shell composed mainly of silicon dioxide remains. The soil made of fossil diatoms thus made is diatomaceous earth. In many cases, it is derived from the Cretaceous or later strata.

The “mudstone” used in the present invention refers to a sedimentary rock formed by depositing and solidifying mud (particles having an average particle size of 6.25 μm or less).
The “clay rock” used in the present invention is a sedimentary rock in which clay (particles having an average particle size of 4 μm or less) is consolidated by compression and dehydration.
Here, the “sedimentary rock” is a rock formed by solidifying a substance deposited on the surface of the seabed, lake bottom, or the like or on the surface of the earth by physical or chemical changes.

  The diatomaceous earth used in the present invention is naturally consolidated, mudstone or claystone can be any of those produced in various places. Since it has an excellent adsorption function for a substance, it is preferable for use in the present invention.

The chemical composition of the metal contained in the adsorbent used in the present invention is not particularly limited, but in terms of oxide of the metal,
SiO ₂ 50~80 parts by weight,
_{2 to} 20 parts by mass of Al ₂ O ₃ ,
1 to 10 parts by mass of Fe ₂ O ₃ ,
0.1-6 parts by mass of CaO,
MgO 0.1-5 parts by mass,
TiO ₂ 2 parts by mass or less,
Na ₂ O 3 parts by mass or less,
5 parts by mass of K ₂ O or less,
Is preferred.

Particularly preferably,
55 to 75 parts by mass of SiO ₂
Al ₂ O ₃ 5 to 15 parts by weight,
2-7 parts by mass of Fe ₂ O ₃ ,
0.2 to 5 parts by mass of CaO,
0.5-3 parts by mass of MgO,
TiO ₂ 1 part by mass or less,
Na ₂ O 2 parts by mass or less,
It is 3 parts by mass or less of K ₂ O.

There is no particular limitation on the method of pulverizing mudstone or claystone, but it is possible to use a known method such as a method using a hammer, a method using centrifugal force, a method using a crushing device, or a method of pulverizing by blasting. it can.
There are no particular limitations on the pulverizing apparatus (pulverizer), but examples include pulverizers using impact or grinding such as hammer mills and mortars; media mills such as ball mills and bead mills; jet mills; roller mills and the like. The adsorbent in the present invention is preferably a relatively coarse particle having a number average particle diameter of 0.1 mm to 30 mm, and therefore a pulverizer such as a hammer mill or a ball mill is preferable.

  There is no particular limitation on the method of firing the diatomaceous earth that is naturally consolidated, mudstone or claystone and then firing it. A known method such as a method using a baking apparatus can be used, and the method is preferably performed in an oxygen atmosphere, and particularly preferably performed in air.

Although it does not specifically limit about baking temperature, It is preferable to bake at 500 to 1500 degreeC, It is more preferable to bake at 800 to 1400 degreeC, It is especially preferable to bake at 700 to 1000 degreeC.
Moreover, although baking time is not specifically limited, 1 to 10 hours are preferable and 2-3 hours are especially preferable.

By firing, even when the particle size is small, when mixed in water, it mixes with water and does not melt, so it is easy to remove moisture at the disposal site after pulling up from the bottom of the water, and water and adsorbent It is easy to reduce the total volume.
Moreover, there exists an effect that the adsorption | suction power of a radioactive substance raises or does not fall.

The average particle diameter of the adsorbent obtained by the above method is not particularly limited, but the number average particle diameter is preferably 0.1 mm to 30 mm, more preferably 0.3 mm to 20 mm, particularly preferably 1 mm to 15 mm, More preferably, it is 1.5 mm to 10 mm. When the number average particle size is 0.1 mm to 30 mm, the adsorbent is prevented from flowing out and clogging from the mesh of the bag when used in a bag.
The volume average particle size / number average particle size value is preferably 5 or less.

<Aspect 1>
In the first aspect of the present invention, the adsorbent obtained by the above method is put in a bag having a mesh size that prevents the adsorbent from flowing out and clogging. FIG. 1 is a perspective view showing an example of a connection mat according to the first aspect in which a plurality of bags are connected.
The shape of one bag is not particularly limited, but when viewed from above, a rectangle or a circle is preferable, a rectangle is more preferable, and a square is particularly preferable.
The size of one bag is not particularly limited, but in the case of a rectangle, the length of one side is preferably 5 cm to 150 cm, more preferably 10 cm to 100 cm, and particularly preferably 15 cm to 70 cm.

  The size of the mesh of the bag is not particularly limited as long as the adsorbent does not flow out or clog, and the shape of the mesh may be rectangular or hexagonal, but it is preferably 0.05 mm to 20 mm in terms of one side of the rectangle. .1 mm to 17 mm is more preferable, 0.3 mm to 15 mm is particularly preferable, and 1 mm to 10 mm is still more preferable.

  As shown in FIG. 1, a plurality of bags 2 filled with an adsorbent are connected to form a connection mat 1. The number to be connected is appropriately adjusted according to the size of rivers, lakes, dams, ponds, fields, agricultural waterways, etc., and the number is not particularly limited, but preferably 10 to 1600, more preferably 20 to 800, 40 to 400 is particularly preferable.

The size of the connecting mat 1 is determined by the size of rivers, lakes, dams, ponds, rice fields, or agricultural waterways, but if the river, pond, rice field, agricultural waterways, etc. are thin or small, the width of the connecting mat 1 is It is preferable to have a length from end to end.
Further, since radioactive materials tend to stay in the stagnation, the size of the portion is also preferable.
Although the magnitude | size of the connection mat 1 is not limited, 2m-50m are preferable in conversion of the length of one side of a rectangle, 3m-30m are more preferable, 5m-20m are especially preferable.

  The connecting means 4 for connecting a plurality of bags is not particularly limited, and the nets forming the mesh may be tied with a string, or may be connected with a dedicated connecting device made of plastic or metal.

<Aspect 2>
In the second aspect of the present invention, instead of the bag, a mat having a mesh with a size that prevents the adsorbent from flowing out and clogging and having a partition in which the adsorbent is not biased is used. . In FIG. 2, the perspective view which shows an example of the mat | matte in which the partition was provided inside of the aspect 2 is shown.

The size of the mat 22 provided with a partition inside can be appropriately changed depending on the size of the river, lake, dam, pond, and agricultural waterway. The preferred size of the mat 22 provided with partitions inside the second aspect is the same as the preferred size of the connecting mat of the first aspect.
Further, the preferred shape and size of the mesh of aspect 2 are the same as the preferred shape and size of the mesh of aspect 1.

In the aspect 2, the partition 25 in which the adsorbent is not biased is provided inside the mat 22 provided with a partition inside. The preferred size of the portion delimited by the partition 25 is the same as the preferred size of the bag of aspect 1.
The number of the divided portions of the mat 22 provided with a partition inside the aspect 2 is the same as the preferable number of the bags of the aspect 1.
The partition is provided by a known method.

<Common to Aspect 1 and Aspect 2>
In order to pull up from a river, lake, dam, pond, rice field, agricultural waterway, etc., means 3 for pulling up from the bottom of the water to the ends of mat 22 in aspect 1 or mat 22 provided with a partition in aspect 2 (24) is provided.
3 (a) and 3 (b) are explanatory diagrams when the connecting mat 1 or the mat 22 provided with a partition is used in a river, an agricultural waterway or the like.
By fixing the means 3 for pulling up from the water bottom using a pillar, a pile, a crane or the like, it is possible to prevent the connecting mat 1 or the mat 22 provided with a partition inside from being moved by the water flow.
The means 3 (24) for lifting from the bottom of the water is also preferably used for lifting the connecting mat 1 or the mat 22 provided with a partition inside from the bottom of the water.

  The means 3 (24) for lifting from the bottom of the water is not particularly limited, and a rope, a wire, or the like can be used.

  The time until the connecting mat 1 or the mat 22 provided with a partition in the interior is submerged on the bottom of a river or a dam and then lifted is not particularly limited, but is preferably 1 week to 10 years. A period of 5 years is more preferable, and a period of 2 months to 3 years is particularly preferable.

The present invention is a method for decontaminating radioactive substances contained in (1) the sediment at the bottom of the water or (2) in the water. When water flows, the water enters the inside from the mesh and is adsorbed in the present invention. By contacting the agent, the radioactive material in the water is adsorbed by the adsorbent.
The radioactive material to be adsorbed may be the radioactive material that has been in the water from the beginning (in the case of (2) above), or the radioactive material that is mixed in or adsorbed to the sediment at the bottom of the water is once in the water. In some cases, the radioactive material is transferred (in the case of (1) above). In this case, the radioactive substance is transferred from the bottom sediment to the adsorbent in the present invention.

  In the connected mat 1 pulled up or in the mat 22 provided with a partition inside, an adsorbent adsorbed with a radioactive substance is contained, and the radioactive substance spread throughout the water is in a small volume part (mass part). So that it can be easily disposed of later. The adsorbent adsorbed with the radioactive substance moves to a predetermined place and is disposed of according to a conventional method.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples. However, the present invention is not limited to these examples unless it exceeds the gist.

Example 1
<Preparation of adsorbent>
We used natural and consolidated diatomaceous earth produced in Iwaki City, Fukushima Prefecture. The chemical composition of the metal of this Iwaki diatomaceous earth is shown in Table 1 (numerical values are converted to oxides, and the unit of the table is parts by mass).
The diatomaceous earth was pulverized to a number average particle diameter of 3 mm with a hammer mill and fired in air at 1100 ° C. for 3 hours to obtain an adsorbent. The obtained decontamination adsorbent had a number average particle diameter of 3 mm.

<Verification test for adsorption performance of radioactive materials>
1000 g of contaminated water containing radioactive material (contaminated to 780 Bq / kg by cesium 134 and cesium 137) was immersed in 10 g of the adsorbent obtained by the above method (1 part by mass with respect to the contaminated water) for 1 hour. .
Thereafter, the adsorbent was taken out and the adsorbed radiation dose was measured. The radiation dose was measured according to a conventional method using SEG-EMS (manufactured by Seiko EG & G).

Comparative Example 1
In Example 1, instead of the adsorbent obtained by the above method, the amount of radiation adsorbed was measured in the same manner as in Example 1 using zeolite having the same number average particle diameter and particle size distribution.
The results are summarized in Table 2 below.

From the results in Table 2, the radiation dose reduction rate (b / a) due to the use of the adsorbent of the present invention was higher than when zeolite was used. From the above, it has been found that there is at least the same or more adsorptive power to radioactive cesium as zeolite.
Since the radioactive cesium was able to be adsorbed by immersion for 1 hour under stirring, a mat filled with the adsorbent of the present invention or a bag filled with the adsorbent was connected to the bottom of a river, a dam or the like. The radioactive matte contained in the sediment or water in the bottom of the water can be decontaminated by sinking the connected mat and allowing it to stand and recover for a certain period of time.
It is expected that the actual period of standing on the bottom of the water is preferably 1 week to 10 years.

Example 2
<Preparation of adsorbent>
Clay rock produced on the coast of Iwaki City, Fukushima Prefecture was crushed to a number average particle size of 3 mm with a hammer mill.
The pulverized product was calcined in air at 1100 ° C. for 3 hours to obtain an adsorbent. The number average particle diameter of the obtained adsorbent was 3 mm.

<Verification test for adsorption performance of radioactive materials>
1000 g of contaminated water containing radioactive material (contaminated to 780 Bq / kg by cesium 134 and cesium 137) 10 g of the adsorbent obtained by the above method (1 part by mass with respect to 100 parts by mass of contaminated water) Soaked in time.
Thereafter, the adsorbent was taken out and the adsorbed radiation dose was measured. The radiation dose was measured according to a conventional method using SEG-EMS (manufactured by Seiko EG & G).
The results of Comparative Example 1 described above are summarized in Table 3 below.

  From the results in Table 3, it was found that the adsorbent of the present invention obtained from clay rock has an adsorption power for radioactive cesium that is equal to or higher than that of zeolite.

  By using the method for decontaminating radioactive materials according to the present invention, in particular, radioactive materials accumulated in the sediment at the bottom of rivers, the bottom of dams and ponds, and the bottom of agricultural canals are decontaminated and diffused. Since it is possible to reduce and prevent migration to humans and other animals and plants, it is widely used in adsorbents and fields where they are used.

DESCRIPTION OF SYMBOLS 1 Connection mat 2 Bag packed with adsorbent 3 Means for raising from bottom 4 Connection means 22 Mat provided with partition inside 23 Part of mat partitioned by partition 24 Means for lifting from bottom 25 Partition

Claims (6)

A method of decontaminating radioactive materials contained in sediment or water in the bottom of the water by collecting a connecting mat in which a plurality of bags filled with an adsorbent are connected and sinking to the bottom of the water,
The adsorbent is obtained by pulverizing and firing a diatomaceous earth naturally solidified mudstone or claystone,
The bag has a mesh size that prevents the adsorbent from flowing out and clogging;
Means for pulling up from the bottom of the water is provided at both ends of the connecting mat.
A method for decontaminating radioactive materials characterized by the above. A method of decontaminating radioactive material contained in sediment or water in the bottom by collecting a mat filled with an adsorbent after sinking to the bottom,
The adsorbent is obtained by pulverizing and firing a diatomaceous earth naturally solidified mudstone or claystone,
The mat has a mesh of a size that prevents the adsorbent from flowing out and clogging, and is provided with a partition that prevents the adsorbent from being biased within the mat, and is pulled up from the bottom of the water at both ends. Means are provided for,
A method for decontaminating radioactive materials characterized by the above.   The method for decontaminating a radioactive substance according to claim 1 or 2, wherein the bottom is a bottom of a river, a lake, a dam, a pond, a rice field, or an agricultural waterway.   The radioactive substance according to any one of claims 1 to 3, wherein the radioactive substance is decontaminated in the sediment or water of the bottom by sinking to the bottom of the water and collecting it after 1 week to 10 years. How to decontaminate.   The method of decontaminating a radioactive substance according to any one of claims 1 to 4, wherein the adsorbent has a number average particle diameter of 0.1 mm to 30 mm.   The radioactive material according to any one of claims 1 to 5, wherein the firing is performed in an oxygen atmosphere at a firing temperature of 500 ° C to 1500 ° C, a firing time of 1 to 10 hours. How to dye.

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