JP2013096983A - Method for decontaminating soil and soil decontaminating agent - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a decontamination method and a decontaminating agent capable of inexpensively collecting requisite minimum contaminated soil for a wide-range and uneven contaminated soil surface layer without causing secondary contamination.SOLUTION: The decontamination method includes: an application/gelatinization step of applying or spraying a decontaminating agent containing a monovalent metal salt of alginic acid and a polyvalent metal salt other than the alginic acid, on the contaminated soil surface layer and gelatinizing it; and a decontaminating agent removal step of removing the gelatinized decontaminating agent adsorbing and including the contaminated soil surface layer.

Description

Detailed Description of the Invention

The present invention relates to a soil decontamination method and a soil decontamination agent, and more particularly, to a decontamination technique for soil in which a radioactive substance adheres to a surface layer.

In nuclear power facilities such as nuclear power generation and nuclear power research and radioactive waste treatment facilities, the surrounding soil may be contaminated with radioactive materials such as iodine, strontium, cesium, and plutonium due to the handling of radioactive materials. . In addition, when these facilities become uncontrollable due to damage such as natural disasters, and an accident occurs in which radioactive materials are released into the atmosphere, radioactive materials may accumulate in a wide area and soil may be contaminated.

Many radioactive substances have long half-lives, and those deposited on the soil surface continue to emit strong radiation over a long period of time, so there is a high risk of health damage due to radiation exposure for those living in the vicinity. Therefore, decontamination as early as possible is desired for soil on which radioactive materials are deposited.

Conventionally, when pollutants such as radioactive substances accumulate on the soil, a decontamination method has been used in which the topsoil is dug and collected by a construction machine such as a shovel car and transported to a final disposal site. However, it is only a small depth from the surface that is contaminated by radioactive materials, but excavators and other equipment dig up and recover the top soil considerably, so the amount of soil to be disposed of is more than necessary. There was a problem that would become. The larger the area to be decontaminated, the greater the cost of transporting and disposing of the collected earth and sand.
In addition, during each excavation, collection, and transportation work, there is a problem that dust containing contaminants is scattered together with dust, and the possibility of secondary contamination that affects the surrounding environment is increased.

In recent years, the following processing methods have been proposed for such problems.

  Patent Document 1 is a decontamination sheet having a curing sheet in which an adhesive is attached to one side of a polymer sheet. Further, Patent Document 2 is characterized in that a gel decontamination agent composed of a surface active decontamination agent and a photocatalyst is photocatalyzed to form a coating film on the contaminated surface and decontamination is performed by removing the film. Further, Patent Document 3 is characterized in that a water-soluble emulsion made of a styrene-butadiene copolymer or the like is applied to a surface to be decontaminated and is decontaminated into a film.

JP 7-318693 A JP-A-11-101894 JP-T-2004-533499

  However, in the decontamination method as in Patent Document 1, the contaminant cannot be taken in more than the surface area of the pressure-sensitive adhesive, and furthermore, it cannot be sufficiently decontaminated on the uneven soil surface. In addition, the decontamination method and decontamination agent as disclosed in Patent Document 2 are expensive in photocatalysts, and need a radiation generator such as ultraviolet rays and X-rays for gelation, and can be applied to a wide range of soils. It is difficult to do. Furthermore, a decontamination agent containing a styrene-butadiene copolymer or the like as in Patent Document 3 is difficult to biodegrade, and it is difficult to dispose of the solid topsoil. There was a problem of remaining inside and putting a burden on the environment.

  As a result of diligent research to solve the above-mentioned problems, the present inventor adsorbs and removes the contaminated soil surface with a gel made of alginate in order to decontaminate the soil surface contaminated with radioactive substances. Has been found to be effective, leading to the present invention.

That is,
(1) A decontaminant mainly composed of a monovalent metal salt of alginic acid and a polyvalent metal salt other than alginates is applied or sprayed on the surface of the soil to be decontaminated, and the soil is formed by the alginate gel formed. The present invention relates to a decontamination method comprising a step of solidifying a surface layer and a removal step of peeling and removing the solidified decontaminated soil surface layer from the ground.

(2) Further, in the solidifying step according to claim 1, a decontamination agent (A) mainly composed of a monovalent metal salt of alginic acid and a decontamination mainly composed of a polyvalent metal salt other than alginates. 2. The decontamination method according to claim 1, wherein the decontamination method is divided into the agent (B), and A or B is continuously sprayed or applied to the surface of the surface of the soil to be decontaminated for gelation.

(3) The decontamination agent according to (1) to (2), wherein the monovalent metal salt of alginic acid is at least one of sodium alginate, potassium alginate, or ammonium alginate ( It is related with the decontamination agent of any one of 1)-(2).

(4) Moreover, it is a decontamination agent as described in (1)-(3), Comprising: The polyvalent metal salt other than an alginate is a compound which consists of calcium, zinc, copper, barium, iron, aluminum, nickel, and manganese. It is related with the decontamination agent of any one of said (1)-(3) characterized by being at least one.

  The present invention applies or spreads a decontamination agent applying the properties of alginic acid that gels by an ion exchange reaction. Even if it covers a wide and uneven ground surface, it covers evenly and gels the topsoil. Can be removed. Further, since this decontaminating agent gels and solidifies at room temperature without using a special device or curing agent, the decontamination treatment is easy and the cost for decontamination can be reduced. In addition, since only the contaminated layer on the surface layer of the soil can be solidified and separated and removed, the amount of contaminated soil to be collected can be kept to a minimum and the costs for recovery and disposal can be reduced. It is also possible to reduce the size of the collection ground for the recovered topsoil to be processed. In addition, since the topsoil to be collected is gelled and solidified into a film, dust is not generated during decontamination work, transportation, etc., and the operator sucks radioactive materials or scatters around Can be prevented. Furthermore, since the main component of the decontamination agent according to the present invention is alginic acid derived from a natural plant, the residue after treatment is easily biodegraded, and the burden on the environment is small.

  It is a front sectional view showing one embodiment of the decontamination method and decontamination agent concerning the present invention, and is a figure which applied or sprayed the decontamination agent on the surface of the soil layer to be decontaminated.   BRIEF DESCRIPTION OF THE DRAWINGS It is a front sectional view which shows one Embodiment of the decontamination method and decontamination agent which concerns on this invention, Comprising: It is a figure which shows the decontamination agent which carried out adsorption inclusion of the surface layer to be decontaminated and gelatinized.   It is a front sectional view showing one embodiment of the decontamination method and decontamination agent concerning the present invention, and is the figure which removed the decontamination agent which carried out adsorption inclusion of the decontamination soil surface layer from the soil, and was gelatinized.

  EXAMPLES Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited thereto.

As a first example,
A decontamination agent (A) composed of an aqueous sodium alginate solution and a decontamination agent (B) composed of an aqueous calcium chloride solution are prepared.

  Next, the decontaminating agent (A) is applied to or spread on the surface of the contaminated soil by any means such as a brush or roller, shower or spray. Subsequently, the decontamination agent (B) is applied to the surface of the soil to be decontaminated as shown in FIG. 1 by any means such as a brush, roller, shower or spray. At this time, there is no restriction | limiting in particular in the order and frequency | count of apply | coating a decontaminating agent (A) and a decontaminating agent (B).

  By contacting and mixing the decontaminating agent (A) and the decontaminating agent (B), an ionic crosslinking reaction is caused by alginic acid molecules and calcium ions in the decontaminating agent, and gelation occurs. At this time, as shown in FIG. 2, since the decontamination agent includes the soil surface layer in the gel, contaminants such as radioactive substances are solidified together with the soil.

  When the gelation proceeds sufficiently after a predetermined time has elapsed, as shown in FIG. 3, the topsoil solidified with the gelled decontamination agent can be peeled off and removed from the ground.

As a second example,
A decontamination agent (C) containing sodium alginate and calcium sulfate and sodium pyrophosphate and glucono delta lactone as a gelation time adjusting agent is prepared and dissolved to obtain an aqueous solution.

  The solution of the decontaminating agent (C) is applied or spread on the surface of the soil to be decontaminated by any means such as a brush, roller, shower or spray.

  The sodium alginate and calcium salt contained in the decontamination agent (C) are ionized after penetrating into the top soil by the action of the gelation time adjusting agent and gelled by a crosslinking reaction. At this time, as shown in FIG. 2, the decontamination agent includes the soil surface layer in the gel, so that contaminants such as radioactive substances are solidified together with the soil.

  When the gelation proceeds sufficiently after a predetermined time has elapsed, as shown in FIG. 3, the topsoil solidified with the gelled decontamination agent can be peeled off and removed from the ground.

  In this example, the soil surface layer could be peeled from the surface by about 5 mm in any of the examples. According to non-patent literature (34th Atomic Energy Commission document No. 1, 2011, page 15), the removal of 5mm from the surface layer of radioactive material contaminated soil shows that the dose rate drops to one third. This example is presumed to have a sufficient decontamination effect.

Claims (4)

  A decontamination agent mainly composed of a monovalent metal salt of alginic acid and a polyvalent metal salt other than alginate is applied to or spread on the surface of the soil to be decontaminated, and the soil surface layer is solidified by the formed alginate gel. A decontamination method comprising: a step of removing and removing the solidified decontaminated soil surface layer from the ground.   In the solidification process according to claim 1, a decontamination agent (A) containing a monovalent metal salt of alginic acid as a main component, and a decontamination agent (B) containing a polyvalent metal salt other than an alginate as a main component; 2. The decontamination method according to claim 1, wherein A and B are continuously sprayed or applied to the surface layer of the soil to be decontaminated and gelled.   3. The decontamination reagent according to claim 1, wherein the monovalent metal salt of alginic acid is at least one of sodium alginate, potassium alginate, or ammonium alginate. The decontamination agent according to item 1.   It is a decontamination agent of Claims 1-3, Comprising: Polyvalent metal salts other than an alginate are at least one of the compounds which consist of calcium, zinc, copper, barium, iron, aluminum, nickel, and manganese. The decontamination agent according to any one of claims 1 to 3.

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