JP2015010848A - Adsorbent for decontaminating radiation material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a decontamination adsorbent more inexpensive than zeolite, having adsorption power to a radioactive material in the same degree as zeolite or higher.SOLUTION: An adsorbent for decontaminating a radioactive material is obtained by burning a material formed by pulverizing (1) diatomaceous earth, mud or clay, or (2) a material formed by solidifying naturally diatomaceous earth, or a mudstone or a claystone. Further, the adsorbent for decontaminating a radioactive material is obtained by pulverizing a material formed by burning and solidifying diatomaceous earth, mud or clay.

Description

  The present invention relates to an adsorbent for decontamination of radioactive substances obtained by processing mud, clay or diatomaceous earth as a raw material.

  There is a need for technological development to decontaminate water, trees, buildings, soil, etc. that are contaminated with radioactive materials released in the accident 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 decontaminating radioactive cesium (cesium 134 and 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 size 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 an adsorbent that is cheaper than zeolite and has an adsorbing power for radioactive materials that is equal to or higher than that of zeolite.
Also, an adsorbent that decontaminates radioactive substances that can be removed to radioactive materials by using simple equipment and methods and removes radioactive substances contained in sediment or water at the bottom of the water. It is to be.

  As a result of intensive studies to solve the above-mentioned problems, the present inventor made mud, clay or diatomaceous earth as a raw material, and contaminated water containing radioactive substances in the radioactive material decontamination adsorbent obtained by processing. As a result of the contact, the present inventors have found that the decontamination adsorbent has the property of adsorbing radioactive cesium at the same level or higher as that of zeolite, and has led to the present invention.

That is, the present invention provides (1) diatomaceous earth, mud or clay,
Or
(2) To provide an adsorbent for decontamination of radioactive material, characterized in that it is obtained by firing a diatomaceous earth solidified, crushed mudstone or claystone. .
Hereinafter, this aspect of the present invention is referred to as “Aspect 1”.

In addition, the present invention provides an adsorbent for decontamination of radioactive material, which is obtained by pulverizing a diatomaceous earth, mud or clay fired and hardened.
Hereinafter, this embodiment is referred to as “embodiment 2”.

  Moreover, this invention provides the decontamination method characterized by decontaminating a radioactive substance from the contaminated water containing the collect | recovered radioactive substance using said adsorption agent for radioactive substance decontamination.

  In addition, the present invention provides a connecting mat in which a plurality of bags filled with the above-mentioned radioactive material decontamination adsorbents are connected to a river, a lake, a dam, a pond, a rice field, or an agricultural waterway (hereinafter referred to as these, A decontamination method characterized by decontaminating radioactive substances contained in the sediment or water of the bottom of the water by sinking to the bottom of the bottom of the water (which may be simply abbreviated as “river etc.”) Is to provide.

  In addition, the present invention is included in the water by forming a weir of a river, a dam, a rice field, or an agricultural waterway with a fence or a net packed with an adsorbent for decontamination of the above-mentioned radioactive substance, and collecting it after a certain time. The present invention provides a decontamination method characterized by decontaminating a radioactive substance.

  Further, the present invention uses the above-described adsorbent for decontamination of radioactive material, and decontaminates the radioactive material adhering to a tree or a building using an abrasive water jet method. A method is provided.

According to the present invention, an adsorbent for decontamination of a radioactive substance (hereinafter simply referred to as “adsorbent”) that is less expensive than zeolite and has an adsorption power for radioactive substances of the same or higher level than zeolite. Can be provided).
In particular, since cesium ions are adsorbed, radioactive materials such as cesium 134 and cesium 137 can be removed.

  If the adsorbent of the present invention is used, it is possible to remove radioactive substances by adsorption from contaminated water containing radioactive substances recovered by washing trees, buildings, soil, etc., and the radioactive substances are concentrated. In state, it can be moved, landfilled or disposed of.

Moreover, if a mat mated with the adsorbent of the present invention or a mat mated with a bag packed with the adsorbent is submerged in the bottom of the water, a radioactive material in water can be adsorbed by a simple method. If the mat or the connecting mat is pulled up, the adsorbent adsorbing the radioactive substance can be removed from the water with a simple device or method.
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.

  Moreover, it is possible to remove the radioactive substance contained in the water from the water with a simple device or method by configuring the weir with a basket or net packed with the adsorbent of the present invention and collecting it after a certain time.

  In addition, the adsorbent of the present invention is dispersed in a liquid such as water and sprayed onto a structure such as a tree or a building, that is, the abrasive body is worn by using an abrasive water jet method or the like. In addition, the radioactive substance attached to the structure can be removed from the structure with little damage.

It is the longitudinal cross-sectional schematic of an example of the mobile contamination water decontamination apparatus used with the decontamination method of this invention. It is explanatory drawing which shows an example of the mat | matte used with the decontamination method of this invention in which the partition was provided inside. It is explanatory drawing when the decontamination method 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 used for the purpose of adsorbing and removing the radioactive substance contained in the contaminated water from the “contaminated water containing the collected radioactive substance”, or using the “mat or connecting mat packed with it” at the bottom of the water. After subsidence, or by collecting "weirs composed of ridges or nets filled with it", it can be used for the purpose of adsorbing and removing radioactive substances contained in sediment or water at the bottom of the water. The present invention relates to an “adsorbent for decontamination of radioactive material” which is used for the purpose of removing radioactive material adhering to trees or buildings by spraying “water containing it”.

  The “adsorbent for decontamination of radioactive substances” of the present invention exists in a wide range by adsorbing radioactive substances contained in structures in polluted water, in sediment at the bottom of rivers, in water in rivers, etc. It is used for concentrating radioactive material and confining it in a small volume.

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 “mud” used in the present invention refers to those having a volume average particle size of 6.25 μm or less, and the “mudstone” refers to sedimentary rocks formed by consolidation of “mud”.
The “clay” used in the present invention refers to those having a volume average particle size of 4 μm or less, and the “clay rock” refers to sedimentary rocks in which “clay” is consolidated by compression and dehydration.
Here, “sedimentary rock” refers to rocks formed by solidification of materials deposited on the bottom of the sea, such as the bottom of the sea, the bottom of a lake, or the surface, subject to physical and scientific changes.

  The mud, clay, diatomaceous earth, or mudstone, claystone, or “naturally consolidated diatomaceous earth” used in the present invention can be any of those produced in various places, but diatomaceous earth from Iwaki City, Fukushima Prefecture. Is preferable for use in the present invention because it has an excellent adsorption function for radioactive substances.

The chemical composition of the metal contained in the “adsorbent for decontamination of radioactive material” of 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.

Naturally consolidated diatomaceous earth, mudstone or claystone (above, embodiment 1), or "calculated and solidified diatomaceous earth", "thinned and solidified mud", or "fired clay There is no particular limitation on the method of pulverizing the "solidified product" (above aspect 2), such as a method of using a hammer, a method of using centrifugal force, a method of using a crushing device, a method of pulverizing by blasting, etc. Known methods can be used.
The crusher (pulverizer) is not particularly limited, but is a primary crusher such as a jaw crusher; A roller mill or the like.

  In order to obtain an adsorbent having a number average particle size of 0.5 mm to 30 mm, it is preferable to use a pulverizer such as a hammer mill, a jet mill, or a ball mill. In order to obtain an adsorbent having a number average particle diameter of 15 cm to 25 cm, it is preferable to use a crusher such as a jaw crusher, a roll crusher, or a cone crusher.

<Aspect 1>
Aspect 1 of the present invention
(1) Diatomaceous earth, mud or clay,
Or
(2) An adsorbent for decontamination of a radioactive material, characterized in that it is obtained by firing pulverized diatomaceous earth that is naturally consolidated, mudstone or claystone.

  There is no particular limitation on the method of calcination of diatomaceous earth, mud or clay, or diatomaceous earth that is naturally consolidated, mudstone or claystone. 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. When sintered in the range of 500 ° C to 1500 ° C, even when the particle size is small, it does not melt when mixed with water when placed in water. It is easy to remove moisture and easily reduce the total volume of water and adsorbent. Moreover, there exists an effect that the adsorption | suction power of a radioactive substance raises or does not fall.
Moreover, although baking time is not specifically limited, 1 to 10 hours are preferable, 1.5 to 7 hours are more preferable, and 2 to 4 hours are especially preferable. If the firing time is too short, it may not be sufficiently sintered and the adsorption function may be reduced. Also, when mixed with water, it becomes “sloppy”, making it difficult to remove water and difficult to handle.
More preferably, firing is performed by combining a preferred firing temperature and a preferred firing time.

<Aspect 2>
Aspect 2 of the present invention is an adsorbent for decontamination of radioactive materials, characterized in that it is obtained by pulverizing diatomaceous earth, mud or clay that has been fired and hardened.
That is, it is obtained by pulverizing artificially hardened material.

The “diatomaceous earth fired and hardened” used in the present invention is obtained by compressing and molding diatomaceous earth and then firing and solidifying it.
The “mud fired and hardened” used in the present invention is a product obtained by compressing and forming mud and then firing and solidifying it.
The term “clay baked and hardened” used in the present invention is a product obtained by compressing and molding clay and then baking and solidifying it.
Examples of “a baked and hardened diatomaceous earth”, “a fired and hardened mud” or “a fired and hardened clay” used in the present invention include, for example, tiles, bricks, etc. However, in addition to existing tiles, bricks and the like, the adsorbent of the present invention may be fired and hardened.

The diatomaceous earth, mud or clay can be compressed and molded by a known technique.
The firing conditions are the same as the firing conditions described above when firing diatomaceous earth, mud or clay, or “ground diatomaceous earth, mudstone or claystone”.

<Usage Mode Common to Aspect 1 and Aspect 2>
The present invention can provide a decontamination method characterized by decontaminating a radioactive substance using the adsorbent obtained as described above.
The “decontamination” of the “decontamination method” in the present invention means that a radioactive substance existing in a wide range is concentrated (contained in a small volume portion) by adsorbing the radioactive substance to an adsorbent, and the radioactive substance This means that the adsorbent adsorbed by is moved to a predetermined location.

<Decontamination method using contaminated water decontamination equipment>
By using the adsorbent of the present invention obtained as described above, a decontamination method characterized by decontaminating a radioactive substance from contaminated water containing the radioactive substance can be provided. As the contaminated water decontamination apparatus using the adsorbent of the present invention, a known contaminated water decontamination apparatus can be used. FIG. 1 shows an example of a preferable contaminated water decontamination apparatus.

FIG. 1 is an example of a contaminated water decontamination apparatus. The contaminated water decontamination apparatus is mobile and can be carried on a truck bed.
A water supply pipe 6 for injecting contaminated water containing a radioactive substance (hereinafter sometimes simply referred to as “contaminated water”) and an adsorbent 17 for decontamination of the radioactive substance in the upper part of the treatment tank 2 “Adsorbent spray nozzle 20 for radioactive material decontamination” sprayed from above is provided.
A drainage valve 8 is provided on the wall of the treatment tank 2, and a sedimentation chamber 10 is attached to the bottom via a water stop valve 9. Further, a drain valve 12 for discharging the adsorbent having the radioactive substance adsorbed to the bottom of the precipitation chamber 10 to the external container 11 is provided.

After the contaminated water is injected into the treatment tank 2 from the water supply pipe 6, the adsorbent of the present invention is dispersed from the upper part of the contaminated water in the treatment tank 2 through the spray nozzle 20.
The radioactive material is adsorbed in the process of settling of the adsorbent of the present invention, and the adsorbent adsorbed with the radioactive material is stored in the precipitation chamber 10. And the water stop valve | bulb 9 is closed and the water from which the radioactive substance was removed is drained from the drain valve 8 outside.

After draining, the drain valve 12 of the sedimentation chamber 10 is opened, and the adsorbent adsorbed with radioactive material is collected in the container 11.
For example, by using the apparatus shown in FIG. 1, the adsorbent of the present invention from which the radioactive substance has been removed and to which the radioactive substance has been adsorbed can be separated and recovered separately.

  Although the time from spraying the adsorbent of the present invention to collecting the decontaminated water is not particularly limited, it is preferably 1 hour or more. The amount of the decontamination adsorbent to be dispersed is not particularly limited, but is preferably 0.2 g to 20 g, more preferably 0.5 g to 10 g, and particularly preferably 1 g to 5 g per kg of contaminated water.

The average particle diameter of the adsorbent of the present invention used for this is not particularly limited, but the number average particle diameter is preferably 1 μm to 10 mm, more preferably 4 μm to 5 mm, and particularly preferably 10 μm to 1 mm.
The volume average particle size / number average particle size value is preferably 5 or less.

<Decontamination method using mat or connecting mat>
A mat filled with the adsorbent of the present invention obtained as described above, or a connecting mat obtained by connecting a plurality of bags filled with the adsorbent, a river, a lake, a dam, a pond, a rice field, or the bottom of an agricultural waterway It is possible to provide a decontamination method characterized by decontaminating radioactive substances contained in the sediment or water in the bottom of the water by being submerged in water and recovered after a certain time.

The mat has a mesh having a size that prevents the adsorbent for decontamination from flowing out and clogging, and a partition is provided inside to prevent the adsorbent from being biased.
The size of the mesh 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 is preferably 0.05 mm to 20 mm in terms of one side of the rectangle, 0.1 mm -17 mm is more preferable, 0.3 mm to 15 mm is particularly preferable, and 1 mm to 10 mm is still more preferable. The partition can be provided by a known method.

The size of the mat 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 is from the edge. It preferably has a length to the end.
Further, since radioactive materials tend to stay in the stagnation, the size of the portion is also preferable.

A partition that prevents the adsorbent from being biased is provided inside the mat. The preferred size of the portion partitioned by the partition 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 number of the mat-separated portions is not particularly limited, but is preferably 10 to 1600, more preferably 20 to 800, and particularly preferably 40 to 400.
An explanatory view showing an example of the mat is shown in FIG.

The connection mat is a connection of a plurality of bags filled with the adsorbent of the present invention.
The bag has a mesh size that prevents the adsorbent from flowing out and clogging. The size and shape of the mesh are the same as the mat.
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 number of the bags connected is appropriately adjusted according to the size of rivers, lakes, dams, ponds, rice fields, agricultural waterways, etc., and the number is not particularly limited, but is preferably 10 to 1600, preferably 20 to 800. More preferably, 40 to 400 is particularly preferable.

The size of the connecting mat is determined by the size of the river, lake, dam, pond, rice field, or agricultural waterway, but the width of the connecting mat is narrow if the river, pond, rice field, agricultural waterway, etc. are thin or small. It preferably has a length from the end to the end.
Further, since radioactive materials tend to stay in the stagnation, the size of the portion is also preferable.
Although the magnitude | size of a connection mat 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 for connecting a plurality of bags is not particularly limited, and the meshes forming the mesh may be tied with a string, or may be connected with a dedicated connecting device made of plastic or metal.

The average particle diameter of the adsorbent used in the method for decontaminating radioactive substances contained in the bottom sediment or water is not particularly limited, but the number average particle diameter is preferably 0.1 mm to 30 mm, 0 .3 mm to 20 mm is more preferable, 1 mm to 15 mm is particularly preferable, and 1.5 mm to 10 mm is still more preferable. 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.

In order to pull up from rivers, lakes, dams, ponds, rice fields, agricultural waterways, etc., means 24 for lifting from the bottom of the water are provided at both ends of the mat 22 or the connecting mat.
3A and 3B are explanatory diagrams when the mat 22 is used in rivers, agricultural waterways, and the like.
By fixing the means 24 for pulling up from the bottom of the water using a pillar, a pile, a crane or the like, the mat 22 can be prevented from moving due to the water flow.
The means 24 for lifting from the bottom of the water is also preferably used for lifting the mat 22 from the bottom of the water.
The means 24 for pulling up from the bottom of the water is not particularly limited, but a rope, a wire, or the like can be used.

  The time from when the mat 22 or the connecting mat is submerged to the bottom of a river or dam to the time it is lifted is not particularly limited, but is preferably 1 week to 10 years, more preferably 1 month to 5 years, A period of 2 months to 3 years is particularly preferred.

<Decontamination method using weir>
Decontamination of radioactive substances contained in water by forming a weir of a river, a dam, a rice field or an agricultural waterway with a basket or net packed with the adsorbent of the present invention obtained as described above, and collecting after a certain time The decontamination method characterized by this can be provided.

The size of the mesh of the ridge or mesh 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 preferably 1 to 20 cm in terms of one side of the rectangle. -15 cm is more preferable, and 5-10 cm is particularly preferable.
The material of the ridge or net is preferably a metal, natural fiber, or synthetic fiber.

  The size of the net is determined by the size of the river, dam, rice field, or agricultural waterway, but the width of the weir consisting of a paddle or net packed with adsorbent is the length from end to end of the river etc. It is preferable to have.

The average particle diameter of the adsorbent used in the decontamination method is characterized by decontaminating radioactive substances contained in water with a basket or net packed with an adsorbent, although the number average particle is not particularly limited. The diameter is preferably 0.5 cm to 25 cm, more preferably 5 cm to 18 cm, and particularly preferably 15 cm to 25 cm.
The volume average particle size / number average particle size value is preferably 5 or less.

  There is no particular limitation on the time from when the weirs are provided with the hoe or net packed with the adsorbent to when the hoe or net is collected. A period of 1 week to 10 years is preferable, a period of 1 month to 5 years is more preferable, and a period of 2 months to 3 years is particularly preferable.

<Decontamination method of spraying adsorbent with water>
A decontamination method in which the adsorbent of the present invention described above is sprayed together with water to decontaminate radioactive substances attached to trees or buildings is also preferable as a use mode of the adsorbent of the present invention.
A decontamination method using the adsorbent of the present invention obtained as described above, and decontaminating a radioactive substance attached to a tree or a building using an abrasive water jet method or a wet blast method. Can be provided.

  To decontaminate the radioactive material stuck to trees or structures without peeling off the skin of the tree by spraying from the nozzle a mixture of adsorbent and water supplied at a constant water pressure to the nozzle head Can do. In particular, there is an effect that it is possible to remove radioactive substances adhered to the skin of trees or the grooves or irregularities on the surface of the building.

The average particle diameter of the adsorbent used in the decontamination method, which is characterized by decontaminating radioactive substances attached to trees or buildings, is preferably 1 to 100 μm, and preferably 2 to 70 μm, as the number average particle diameter. More preferably, 5-50 micrometers is especially preferable.
The volume average particle size / number average particle size value is preferably 5 or less.

The water pressure when used for a tree is preferably 0.6 to 10 MPa, more preferably 0.8 to 5 MPa, and particularly preferably 1 to 2 MPa.
The water pressure when used in a building is preferably 1 to 15 MPa, more preferably 2 to 12 MPa, and particularly preferably 5 to 10 MPa.
If the water pressure is higher than the above, the skin of the tree or the surface of the building may be scraped off. In addition, if the water pressure is lower than the above-described water pressure, there is a case where radioactive substances attached to trees or buildings cannot be sufficiently removed.

When water that does not contain the adsorbent of the present invention is jetted, higher water pressure may be required, and in that case, the skin of the tree or the surface of the building may be scraped off.
Radioactive substances adhering to the inside of the irregularities of trees or buildings may not be removed unless they are injected at a higher water pressure than the above water pressure (for example, it is necessary to inject water at a so-called ultra-high pressure). When the water containing the adsorbent of the present invention is jetted, the radioactive material adhering to the inside of the irregularities of the tree or the building is removed with the above-described water pressure without jetting water at an ultra-high pressure. It is possible.
Further, by using the above method, that is, by spraying water containing the adsorbent of the present invention, decontamination can be performed without using a large amount of water.

It is preferable to lay a sheet for storing water under the tree or building so as to prevent water from penetrating into the soil.
The contaminated water collected on the sheet is preferably subjected to a decontamination method using the contaminated water decontamination apparatus.

  In the decontamination method characterized in that the radioactive substance is decontaminated using the adsorbent for decontamination of the radioactive substance obtained as described above, the radioactive substance spread throughout the water has a small volume part (mass part) ) To facilitate subsequent disposal. 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 radioactive material decontamination adsorbent>
Diatomaceous earth produced in Iwaki City, Fukushima Prefecture was used as a raw material for the adsorbent. 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) 10 g (1 part by mass with respect to the contaminated water) of the adsorbent for decontamination obtained by the above method was stirred. Soaked in time.
Then, the adsorbent for decontamination was taken out and the absorbed 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 decontamination adsorbent obtained by the above method, the amount of adsorbed radiation was measured in the same manner as in Example 1 using zeolite having the same number average particle size 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 could be adsorbed by immersion for 1 hour under stirring, the adsorbent of the present invention and the contaminated water were mixed using a contaminated water cleaning device, and recovered after a certain time, A radioactive substance contained in the contaminated water can be decontaminated.

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.

Since we were able to adsorb radioactive cesium by immersion for 1 hour under stirring, weirs of rivers, dams, rice fields, or agricultural waterways were constructed with firewood or nets packed with the adsorbent of the present invention. By collecting after time, radioactive substances contained in the water can be decontaminated.
It is expected that the actual period from the installation of the weir to the recovery of the fence or net is preferably 1 week to 10 years.

  Since it was possible to adsorb radioactive cesium by immersion for 1 hour under stirring, it is possible to decontaminate radioactive substances adhering to trees or buildings by spraying the adsorbent of the present invention together with water. is there.

Example 2
<Preparation of radioactive material decontamination adsorbent>
The diatomaceous earth produced in Iwaki City, Fukushima Prefecture used in Example 1 was used as a raw material. The diatomaceous earth was pulverized to a number average particle size of 0.05 mm with a ball mill and fired in air at 1100 ° C. for 3 hours to obtain a decontamination adsorbent. The obtained decontamination adsorbent had a number average particle diameter of 0.05 mm.

<Verification test for decontamination ability of contaminated trees>
The adsorbent for decontamination was mixed with water supplied to the nozzle head at a water pressure of 1 MPa, and the mixture was sprayed from the nozzle onto the contaminated tree.
The skin of the tree before and after decontamination was scraped off, and the radiation dose was measured according to a conventional method using SEG-EMS (manufactured by Seiko EG & G).
As a result, the radiation dose of the epidermis of the tree before decontamination was 13100 Bq / kg, whereas the radiation dose of the epidermis of the tree after decontamination was 1550 Bq / kg.
The surface of the tree was neither scraped nor scratched.
From the above, it was found that radioactive materials attached to trees or buildings can be decontaminated by spraying the adsorbent of the present invention together with water using an abrasive water jet method or the like.

Example 3
<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) was immersed in 10 g of the adsorbent obtained by the above method (1 mass% with respect to the contaminated water) for 1 hour with stirring. .
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.
Since radioactive cesium was able to be adsorbed by immersion for 1 hour under stirring, the adsorbent of Example 1 is effective for all the decontamination methods described in Example 1.

  By using the adsorbent for decontamination of radioactive material according to the present invention, in particular, the radioactive material accumulated in the sediment at the bottom of rivers, the bottom of dams and ponds, and the bottom of agricultural canals is decontaminated and diffused. In addition, the radioactive substances adhering to the structure can be efficiently removed, so that it is possible to prevent migration to humans and other animals and plants, and it is widely used in adsorbents and fields where they are used. .

DESCRIPTION OF SYMBOLS 1 Contaminated water decontamination apparatus 2 Processing tank 3 Contaminated water tank 4 Contaminated water 6 Supply pipe 8 Drain valve 9 Water stop valve 10 Sedimentation chamber 11 Container 12 Drain valve 17 Adsorbent for decontamination of radioactive material 20 Decontamination of radioactive material Adsorbent spray nozzles 22 Mats with partitions inside 23 Parts of the mats separated by partitions 24 Means for lifting from the bottom 25 Partitions

Claims (9)

(1) Diatomaceous earth, mud or clay,
Or
(2) An adsorbent for decontamination of a radioactive material, characterized in that it is obtained by firing a pulverized diatomaceous earth that is naturally consolidated, mudstone or claystone.   An adsorbent for decontamination of a radioactive material, characterized in that it is obtained by pulverizing diatomaceous earth, mud or clay that has been hardened by baking. The chemical composition is
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,
The adsorbent for decontamination of radioactive substances according to claim 1 or claim 2.   4. The decontamination of a radioactive substance according to claim 1, wherein the firing is performed in an oxygen atmosphere at a firing temperature of 500 ° C. to 1500 ° C. and a firing time of 1 to 10 hours. Adsorbent.   A decontamination method comprising decontaminating a radioactive substance from contaminated water containing the radioactive substance using the radioactive substance decontamination adsorbent according to any one of claims 1 to 4.   A plurality of mats filled with the radioactive material decontamination adsorbent according to any one of claims 1 to 4 or a plurality of bags filled with the radioactive material decontamination adsorbent. Decontamination of radioactive materials contained in the sediment or water of the bottom of the river, lakes, dams, ponds, rice fields, or by subtracting it from the bottom of an agricultural waterway and collecting it after a certain time. Characterized decontamination method.   A river, a dam, a rice field, or a weir of an agricultural waterway is composed of a fence or a net packed with the radioactive material decontamination adsorbent according to any one of claims 1 to 4, and collected after a certain time. A decontamination method characterized by decontaminating radioactive substances contained in water.   A decontamination method comprising spraying the radioactive material decontamination adsorbent according to any one of claims 1 to 4 together with water to decontaminate the radioactive material adhering to a tree or a building. Method.   The decontamination method according to claim 8, wherein the decontamination method is performed using an abrasive water jet method.

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