JP5753760B2 - Purification method of radioactive material contaminated soil - Google Patents

Description

  The present invention relates to a method for reducing radioactive substances contained in soil by removing radioactive substances from soil contaminated with radioactive substances.

  A large amount of radioactive material has been released due to the accident at the nuclear power plant and contaminated the surrounding soil. In order to reduce the radiation dose in areas contaminated with soil and make it possible to live, or to reduce the impact on the health of residents, removal of radioactive materials is required. However, there is a large amount of contaminated soil, and it is difficult to remove all of these soils and put them in strict management. For this reason, it is possible to reuse the soil from which the pollutants have been removed by purifying the contaminated soil, and to separate and strictly control only the portion with a high contamination concentration containing the removed pollutants. .

For example, Patent Document 1 discloses a method for separating a portion containing a large amount of heavy metal or the like as a contaminant by washing soil contaminated with heavy metal or the like.
In this method, acid such as nitric acid, hydrochloric acid, sulfuric acid or the like is added to contaminated soil, and the soil is stirred to wash the soil particles.

JP 11-197643 A

The necessity of purifying a large amount of soil contaminated with radioactive materials has hardly been assumed so far, and an effective method has not been clarified. Although it is conceivable to apply a method for purifying contamination caused by heavy metals as described in Patent Document 1, the contaminants are different and cannot be applied as they are. Therefore, there is a need for an effective method for purification of contamination with radioactive substances.
In addition, a large amount of soil contaminated with radioactive substances already exists, and it is required that these treatments can be carried out with a simple operation using a simple apparatus.

  This invention is made | formed in view of the above situations, and it aims at providing the method of isolate | separating a radioactive substance effectively from the soil contaminated with the radioactive substance.

  In order to solve the above-mentioned problem, the invention according to claim 1 includes an immersion treatment step in which soil contaminated with a radioactive substance is immersed in an aqueous ammonia or ammonium salt solution for a predetermined time, and the soil after the immersion treatment step. After adjusting the solid-liquid ratio, the agitation is performed by rubbing the soil particles with each other and grinding the surface. And the separation treatment step of separating together, the immersion treatment step accommodates the soil in a mesh container in which a mesh-like sheet or a plate-like member having a large number of small holes is used on all or part of the bottom surface and the peripheral surface. Then, the soil is stored in the mesh container and immersed in an immersion tank storing the aqueous ammonia or ammonium salt solution, and the solid-liquid ratio is adjusted before the attrition treatment step. Pulls up the mesh container containing the soil from the dip tank, and maintains the state in which the liquid and fine particles in the soil fall through the mesh-like sheet or plate member for a predetermined time. The present invention provides a method for purifying radioactive material contaminated soil.

  In this method, cesium ions are replaced with ammonium ions by immersing contaminated soil in an aqueous ammonia or ammonium salt solution, and radioactive substances are separated from the surface of the soil particles into aqueous ammonia or aqueous solution, or attrition performed later. It becomes easy to separate from the soil particles by the treatment. Therefore, the effect of the attrition treatment to be performed later is improved, and effective purification can be performed by combining the treatment soaked in an aqueous ammonia or ammonium salt solution and the attrition treatment. The immersion treatment or the attrition treatment can achieve a certain degree of effect even if each of them is performed alone, but by combining these, a remarkable effect exceeding the range predicted from the effect of performing each of them alone can be obtained. It is obtained. The effect of separating heavy metals by immersion treatment can be expected by using high-concentration hydrochloric acid, sulfuric acid, and other acids, as well as by electrolysis and other treatments. However, for radioactive substances, particularly radioactive cesium, ammonia can be expected. It has been found that a great effect can be obtained by immersing water or an ammonium salt in an aqueous solution, and the present invention has been made based on this. Furthermore, when immersed in a high-concentration acid, a treatment for washing away the acid or a treatment for neutralization is required after the purification treatment. Moreover, it is necessary to perform a process such as electrolysis, which requires a large-scale facility. On the other hand, even if ammonia water and ammonium salt remain in the soil after purification, they do not significantly affect the living environment and land use. Moreover, it becomes possible to purify with simple equipment.

The above immersion treatment is performed by storing the soil in a mesh container, so that the soil is immersed in the immersion tank and held until a predetermined time elapses, and then the work of taking out from the immersion tank can be efficiently performed. In addition, when the soil contained in the mesh container is pulled up from the immersion tank and the liquid is allowed to flow down from the mesh container, the solid-liquid ratio is substantially suitable for the attrition treatment, and the attrition treatment is performed with a simple operation after the immersion treatment. It becomes possible.

  The invention according to claim 2 is the method for purifying radioactive material-contaminated soil according to claim 1, wherein the solid-liquid ratio of the soil after the immersion treatment step is adjusted to 1: 0.1 to 1: 0.2. Shall.

  By setting the solid-liquid ratio in the above range, the grinding effect in the attrition treatment can be increased, and the radioactive substance adhering to the soil particles can be effectively peeled off.

The invention according to claim 3 is the method for purifying radioactive material-contaminated soil according to claim 1 or claim 2 , wherein the size of the through holes formed in the mesh-like sheet or plate member is 50 μm or more. It shall be 200 μm or less.

  In this method, the radioactive substance suspended in the ammonia water or the solution is discharged from the soil particles to the outside of the mesh container, and the fine particles of the soil particles to which the radioactive substances are attached are separated before the attrition treatment. And purification can be performed efficiently.

  As described above, in the method for purifying radioactive material-contaminated soil of the present invention, the radioactive material can be efficiently separated from the soil by a simple operation, and the contaminated soil can be purified.

It is a schematic process drawing which shows the purification method of the radioactive substance contaminated soil which is one Embodiment of this invention. It is a schematic sectional drawing which shows the example of the mixer which can be used by the attrition process in the purification method of the radioactive substance contaminated soil which concerns on this invention. It is an enlarged view of the mesh-like sheet | seat or plate-shaped member used with a mesh container.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a schematic diagram showing the steps of a method for purifying radioactive material-contaminated soil according to an embodiment of the present invention.
The equipment for carrying out this method includes a dipping tank 1 containing ammonia water or an aqueous solution of ammonium salt as a dipping agent, and a mesh container 2 capable of dipping contaminated soil into the dipping tank. Then, the soil subjected to the immersion treatment is accommodated and stirred, and the mixer 3 that performs the attrition treatment and the water that has been added to the soil subjected to the attrition treatment, and the radioactive substances separated from the soil particles and the fine particles of the soil particles. Use a separation means 4 for separating turbid water containing particles and coarse particles of soil particles, and a precipitation separation tank 5 for separating water from turbid water into less contaminated water and radioactive substances. Can do.

If the immersion tank 1 can store the aqueous solution of ammonia water or ammonium salt and can soak the mesh container 2 containing the soil, the shape, size, etc. can be appropriately set. .
Further, the mesh container 2 uses a mesh-like sheet or a plate-like member having a large number of small holes on the whole or a part of the bottom surface and the peripheral surface. The aqueous ammonia solution or ammonium salt solution as well as the radioactive substance separated from the soil particles and the fine particles of the soil particles can pass through the pores. This mesh container 2 has a strength that allows soil to be stored and soaked in the immersion tank 1 and pulled up, and has a frame body having sufficient strength, and the mesh-like sheet or plate shape. The member can be supported by reinforcing members arranged at predetermined intervals.

As shown in FIG. 3A, the mesh sheet 2a used for the mesh container 2 is made by weaving synthetic resin fibers or metal wires in a mesh shape. The dimension a is desirably 50 μm or more and 200 μm or less. More preferably, it is 75 μm or more and 150 μm or less.
When the plate-like member 2c having a large number of small holes is used, it is desirable that the inner diameter a of the small holes 2d is similarly 50 μm or more and 200 μm or less, more preferably 75 μm or more, as shown in FIG. And 150 μm or less.

  As the mixer 3 used for the attrition treatment, for example, as shown in FIG. 2A, a mixer having two stirring blades rotating around the same axis can be used. This mixer has a stirring tank 11, an outer stirring blade 12 that rotates around the central axis in the vertical direction near the peripheral wall of the stirring tank 11, and an inner stirring blade 13 that rotates around the same central axis near the center of the stirring tank 11. It has. The two stirring blades 12 and 13 are rotationally driven in opposite directions, and the outer stirring blade 12 rotates more slowly than the inner rotating blade 13. The inner stirring blade 13 includes a plurality of blade bodies 15 projecting from the rotary shaft 14 to the periphery, and rotates at high speed near the center to stir so that the soil particles contained in the soil are rubbed together. The outer stirring blade 12 has a blade body 16 having a shape along the peripheral wall of the stirring tank, and operates to return the soil pressed near the peripheral wall to the vicinity of the center by the centrifugal force generated by the rotation of the inner stirring blade 13. Is.

  In addition, as shown in FIG. 2B, it is also possible to use a two-shaft mixer 30 in which two stirring blades 33a and 33b having vertical rotating shafts 32a and 32b are arranged at predetermined intervals in the stirring tank 31. it can. In the two-shaft mixer 30, the two rotor blades 33a and 33b rotate in the opposite direction or the same direction, whereby the contained soil is stirred and moved between the two rotation regions, and the soil particles are rubbed against each other. The

The separation means 4 separates the fine particles of the soil generated by the attrition treatment and the fine particles originally contained in the soil, and a vibration sieve, a cyclone, a filter, or the like can be used. In the present embodiment, a vibrating screen is used, which is hydrated by the soil fed onto the screen 21, and the coarse particles of the soil and the fine particles contained in the water are divided into two storage tanks 22 and 23. Is contained.
The said precipitation separation tank 5 can use the thing of various aspects, as long as it can isolate | separate the deposit and supernatant water which precipitated using the coagulant | flocculant.

When such a facility is used, the method of the present invention is performed as follows.
A predetermined amount of contaminated soil collected from the contaminated area is accommodated in the mesh container 2 and immersed in an immersion tank 1 in which an immersion treatment agent, that is, an aqueous solution of ammonia water or ammonium salt is stored. The aqueous ammonia or ammonium salt solution preferably has a concentration of 0.1 to 1.5 mol / liter, particularly preferably about 0.2 to 1.0 mol / liter.
The immersion time of the contaminated soil is about 30 minutes to 12 hours, and when the immersion treatment is performed, it is desirable to heat the immersion treatment agent to 50 ° C or higher.
In addition, the kind, density | concentration, and immersion time of the said immersion treatment agent can be suitably adjusted with the soil contamination condition, the soil particle size, etc.

  By the above immersion treatment, radioactive cesium ions are replaced with ammonium ions, and are easily separated from the soil particles. In addition, a part is separated from the soil particles and floats in the immersion treatment agent. The separated radioactive cesium is discharged out of the mesh container 2 during the immersion process or when the mesh container 2 is pulled up from the immersion tank 1, and remains in the immersion tank 1. Further, a part of the fine particles in the soil that can pass through the permeation holes of the mesh container 2 is also discharged out of the mesh container 2 and remains in the immersion tank 1.

After a predetermined soaking time has elapsed, the mesh container 2 containing the soil is pulled up from the soaking tank 1 and the soaking agent contained in the soil is caused to flow down to the soaking tank 1. This is what is called “draining”. By maintaining the mesh container 2 in this manner, the immersion treatment agent held between the soil particles gradually flows down. And it maintains until the predetermined time when the solid-liquid ratio of soil becomes a desirable value for performing the attrition treatment elapses, and then the soil in the mesh container 2 is stirred by the stirring tank 11 of the mixer 3 for performing the attrition treatment. In. Since the predetermined time varies depending on the particle size distribution of the soil, the structure of the mesh container 2, and the like, it is desirable to set in advance by conducting a preliminary test or the like. That is, the liquid is unlikely to flow down in soil containing a large amount of small-diameter soil particles, and the predetermined time for pulling up and maintaining the mesh container 2 is set to be long. On the other hand, the predetermined time can be set shorter in soil containing a large amount of large soil particles.
In addition, although a solid-liquid ratio desirable when performing attrition treatment is 1: 0.1 to 1: 0.2, the solid-liquid ratio is slightly larger than the above value depending on the contamination state, the particle size distribution of soil, and the like. Or small.

The soil thrown into the agitation tank 11 of the mixer 3 is agitated by driving the agitation blades 12 and 13, and the surface is rubbed by the contact with the agitation blades 12 and 13 and the contact between the soil particles. The radioactive material adhering to is peeled off.
When the mixer shown in FIG. 2 (a) is used, the stirring by the mixer can be performed at a rotational speed of 100 to 1000 times / minute and a processing time of about 10 to 30 minutes.

When the attrition treatment is completed, a separation treatment is performed to separate the water containing the fine particles of the soil and the coarse particles of the soil while hydrating and washing the soil. As the separation means used in this separation process, a vibrating screen can be used as shown in FIG. Moreover, you may isolate | separate using a cyclone and a filter. Further, these can be used in combination.
The diameter of the fine particles of the soil separated in this separation treatment step can be about 75 μm to 150 μm, for example.

Depending on the amount of radioactive material remaining, the coarse grain fraction of the soil separated in the separation process can be returned to the original ground when there is little radioactive material. Moreover, you may accommodate in a disposal site. When the amount of the remaining radioactive material is large, the immersion treatment and the attrition treatment are repeated again, and the separation treatment step is performed to separate the radioactive material.
In addition, the coarse grain part of the isolate | separated soil is wash | cleaned with water, and even if the ammonia used by the immersion process remains, it is diluted. For this reason, even if it returns to the original ground, residual ammonia does not become a problem.

On the other hand, the water containing the fine particles separated in the separation treatment step is stored in the precipitation separation tank 5 and subjected to the precipitation separation treatment. In the precipitation separation process, a flocculant is added to the precipitation separation tank 5 to precipitate fine particles, and the supernatant water removes radioactive substances using an adsorbent. Supernatant water in which the radioactive substance becomes a predetermined concentration or less can be reused in the aqueous solution of ammonia water or ammonium salt in the immersion treatment, and can be reused in soil washing in the separation treatment. On the other hand, the precipitated fine particles contain a lot of radioactive substances, and are stored in a disposal site or the like by storing them in a container that shields radiation.
Even if ammonia used in the immersion treatment remains in the supernatant water, it is diluted by hydration after the attrition treatment and further neutralized with an adsorbent. Therefore, it can be reused or disposed of as it is.

  As described above, the coarse particles of soil separated from the soaking process to the separating process are separated from the soaking process when the contained radioactive material is reduced but the target value is not reached. The process up to the process can be repeated until the target value is purified. In addition, after the immersion treatment is again performed on the coarse particles of the soil separated by the separation treatment, the treatment can be terminated by washing.

  The aqueous ammonia or ammonium salt solution used for the dipping treatment can be used multiple times for the soaking of the soil contained in the mesh container. The waste liquid after being used a plurality of times is separated into fine particles in the precipitation separation tank 5 in the same manner as the water containing the fine particles after the attrition treatment. The waste liquid is weakly acidic when an ammonium salt is used as a chemical for immersion treatment, but is strongly alkaline when ammonia water is used, and needs to be neutralized.

  The method for purifying radioactive material-contaminated soil according to the present invention is not limited to the above-described embodiment, and the above-described immersion treatment process to separation treatment process are implemented in other forms that fall within the scope of the present invention. You can also Further, the subsequent steps are not limited at all, and appropriate processing can be performed according to the purpose. Moreover, before performing a soaking process, it can also carry out by adding processes, such as classification of soil.

DESCRIPTION OF SYMBOLS 1: Soaking tank, 2: Mesh container, 3: Mixer, 4: Separation means, 5: Precipitation separation tank, 11: Stirring tank, 12: Outer stirring blade, 13: Inner stirring blade, 14: Rotating shaft, 15: Inner Rotor wing body, 16: Outer rotor wing body,
21: Sieve, 22, 23: Reservoir,
30: 2-shaft mixer, 31: stirring tank, 32: rotating shaft, 33: stirring blade

Claims (3)

An immersion treatment step of immersing the soil contaminated with radioactive material in an aqueous ammonia or ammonium salt solution for a predetermined time;
After adjusting the solid-liquid ratio of the soil after the immersion treatment step, an attrition treatment step of stirring and rubbing the soil particles together to grind the surface;
Including a separation treatment step of adding water to the soil after the attrition treatment step and separating fine particles in the soil together with water,
In the dipping process, soil is accommodated in a mesh container in which a mesh-like sheet or a plate-like member having a large number of small holes is used on all or part of the bottom surface and the peripheral surface, and the soil is accommodated in the mesh container. Dipped in a dipping tank in which the aqueous solution of ammonia water or ammonium salt is stored,
The adjustment of the solid-liquid ratio before performing the attrition treatment step is carried out by pulling up the mesh container containing the soil from the immersion tank and passing through the mesh-like sheet or plate-like member in the liquid and soil. A method for purifying radioactive material-contaminated soil, characterized in that the state in which the particle fraction falls is maintained for a predetermined time.   The method for purifying radioactive material-contaminated soil according to claim 1, wherein the solid-liquid ratio of the soil after the immersion treatment step is adjusted to 1: 0.1 to 1: 0.2. The method for purifying radioactive material-contaminated soil according to claim 1 or 2, wherein the size of the permeation hole formed in the mesh-like sheet or plate member is 50 µm or more and 200 µm or less.

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