JP6178116B2 - Soil decontamination apparatus and method - Google Patents

Description

  The present invention relates to a decontamination apparatus and method for soil containing radioactive cesium.

  For example, when a large-scale accident occurs at a nuclear power plant, there is a concern that a large amount of radionuclide is scattered, causing environmental pollution of soil, trees, buildings, buildings, oceans, lakes, and the like. Therefore, there is an urgent need to develop a method for treating soil, buildings, buildings, sludge and incinerated ash containing radionuclides.

Most of the radionuclides contained in soil and sludge contaminated with radionuclides are cesium 134 and cesium 137. In particular, cesium 137 has a long half-life of 30.2 years. The Therefore, removal of cesium from contaminated soil and sludge is desired.
Several proposals have been made regarding the removal of such radioactive contaminants.

  For example, after mixing pollutants including radioactive substances and chemical species such as cations and anions, a potential gradient is generated between the anode and the cathode, and these cations or anions are moved to the cathode and the anode, respectively. It has been proposed that a matrix material having an affinity for a radioactive substance is disposed and adsorbed, and the contaminants are precipitated by reducing the pH of these systems to a predetermined value or less to remove the radioactive substance ( For example, see Patent Document 1.)

  In addition, at least one set of electrodes is embedded at a predetermined interval on the surface layer of the contaminated soil, and energizing between these electrodes accumulates the pollutants with the electrodes, and cultivates plants with a high accumulation of harmful substances in the contaminated soil. A method for removing the pollutant by absorbing the plant is disclosed (for example, see Patent Document 2).

  However, in these methods, there is a problem that it is difficult to perform on-site processing because it is necessary to install electrodes and energize them. Moreover, since the process of plant cultivation is included, the subject that processing requires a long time also exists.

  In addition, methods using environmentally friendly synthetic inorganic ion adsorbents and inorganic arsenic adsorbents have also been proposed. This method can be used for the production of land water such as oceans, rivers, lakes, and groundwater, and agricultural chemicals, alloys, and semiconductors. Although it is useful for separation / removal of waste water, there is a problem that the adsorbent used for adsorption cannot be removed in soil or sludge (see, for example, Patent Document 3).

  In addition, methods for removing radionuclides from contaminated water and soil using lichens, their metabolites and synthetic metabolites have also been proposed, but the target nuclides are uranium and plutonium, and cesium is removed. (For example, refer patent document 4). In addition, methods have been proposed to deal with soluble heavy metal pollutants present in the geological or seafloor layers, but by stabilizing, they prevent the heavy metal pollutants from being fluidized again by groundwater and remove cesium. (For example, refer to Patent Document 5).

Japanese Patent No. 4128620 JP 2007-289897 A Japanese Patent No. 3557461 JP 2002-1047489 A JP-A-6-39055

  An object of this invention is to provide the soil decontamination apparatus and method which can decontaminate the soil containing radioactive cesium simply and efficiently.

One aspect of the soil decontamination apparatus according to the present invention is a soil decontamination apparatus for decontaminating soil containing radioactive cesium, containing the soil and an eluent containing an acid solution, and removing cesium in the soil. A treatment tank to be eluted by the eluent, an adsorption tower containing an adsorbent that adsorbs cesium in the eluent, a first pipe connecting the treatment tank and a water inlet of the adsorption tower, and the adsorption a second pipe connecting the tower water outlet and said processing bath, is interposed in said first pipe, a transfer pump for circulating between the eluent the processing bath and the adsorption tower, wherein A heating apparatus for heating the eluent in the treatment tank, and a heat exchanger for exchanging heat between the eluent in the first pipe and the eluent in the second pipe. And

One aspect of the soil decontamination method according to the present invention is a soil decontamination method for decontaminating soil containing radioactive cesium, containing the soil and an eluent containing an acid solution in a treatment tank, A first step of eluting the cesium in the eluent, and supplying the eluent to an adsorption tower containing an adsorbent that adsorbs cesium to adsorb the cesium in the eluent to the adsorbent. 2 and a third step of supplying the eluent from the adsorption tower to the treatment tank, wherein the eluent in the treatment tank is hydrochloric acid having a pH of 0.9 or less, The temperature of the eluent is controlled to be 95 ° C. or higher and 100 ° C. or lower, the eluent is circulated between the treatment tank and the adsorption tower, and the first to third steps are continuously repeated. It is characterized by.

  According to the present invention, soil containing radioactive cesium can be easily and efficiently decontaminated.

It is a figure showing roughly the soil decontamination device of an embodiment. It is a figure showing roughly the soil decontamination device of an embodiment. It is a graph which shows the relationship between the frequency | count of elution of an Example, and an elution rate. It is a graph which shows the relationship between the eluent pH of an Example, and an elution rate. It is a graph which shows the relationship between the temperature of the eluent of an Example, and an elution rate. It is a graph which compares the elution rate by the soil decontamination method of an Example and a comparative example. It is a graph which shows the change of the elution rate at the time of using repeatedly the eluent of a comparative example.

(First embodiment)
FIG. 1 is a diagram illustrating a schematic configuration of a decontamination apparatus according to the present embodiment.

  A decontamination apparatus 10 shown in FIG. 1 includes a treatment tank 11 that contains an eluent L and soil S, an adsorption tower 12, and a first pipe 13 that connects the treatment tank 11 and a water inlet 12A of the adsorption tower 12. And a second pipe 14 that connects the water outlet 12B of the adsorption tower and the treatment tank 11. An adsorbent 121 for adsorbing and removing cesium in the eluent L is accommodated in the adsorption tower 12.

  A transfer pump 15 that circulates the eluent L between the treatment tank 11 and the adsorption tower 12 is interposed in the first pipe 13. The water intake 13 </ b> A of the first pipe 13 is located below the liquid level in the processing tank 11, and includes a filter 16 for removing solid content in the eluent L.

  In the decontamination apparatus 10, the eluent L containing cesium is removed from the eluent L by the filter 16, and is sent from the treatment tank 11 to the adsorption tower 12 via the first pipe 13 by the transfer pump 15. It is done. When the eluent L comes into contact with the adsorbent 121 in the adsorption tower 12, cesium in the eluent L is adsorbed by the adsorbent 121 and removed. Next, the eluent L is sent from the water outlet 12 </ b> B of the adsorption tower 12 to the treatment tank 11 through the second pipe 14. As described above, the decontamination apparatus 10 is a continuous apparatus that adsorbs and removes cesium in the eluent L by the adsorbent 121 and circulates and uses the eluent L from which cesium has been removed.

  The processing tank 11 is provided with a heating device 17 such as a heater for heating the eluent L in the processing tank 11 to a predetermined temperature. Moreover, it is preferable to install a stirring device such as a stirrer in the treatment tank 11. Note that an ultrasonic application device may be provided instead of or in addition to the stirring bar.

  The processing tank 11, the 1st piping 13, and the 2nd piping 14 which comprise the decontamination apparatus 10 are comprised from a material with high corrosion resistance. The processing tank 11 may be a glass container such as a beaker at the laboratory level, but is preferably a processing tank made of stainless steel or the like having high corrosion resistance at a practical level. The first pipe 13 and the second pipe 14 are also preferably pipes made of stainless steel or the like with high corrosion resistance.

  Moreover, the capacity | capacitance of the processing tank 11 is suitably selected according to the quantity of the soil S which should be processed, and the aspect of the 1st and 2nd piping is suitably determined with the circulating flow volume of the eluent L required for a process.

  Next, a decontamination method using the decontamination apparatus 10 shown in FIG. 1 will be described.

  First, as shown in FIG. 1, the soil S containing radioactive cesium and the acid solution as the eluent L are accommodated in the treatment tank 11, and the eluent L is heated by the heating device 17. Further, the eluent L is stirred as necessary. As a result, cesium contained in the soil S is eluted into the eluent L. (First step).

  In addition, in FIG. 1, although the soil S and the eluent L are described separately, actually, the above-described stirring and mixing operation and the mode (form, size, etc.) of the soil S are accompanied. The soil S is dispersed in the eluent L. However, here, for convenience of explanation of the present embodiment, the soil S and the eluent L are described separately.

  The soil S is a soil containing radioactive cesium, and may contain sludge, sand and the like.

  The soil S generally contains Si, Al, Fe, Ca, Na, K, Mg, and the balance. These elements are usually present in the soil S as oxides or predetermined salts, and the remainder includes organic matter produced by animals and plants.

  The soil S has a laminated structure composed of oxides of the elements described above, and most of the cesium exists in a form taken into the laminated structure. By immersing the soil S in the eluent L made of an acid solution, a part of the laminated structure is broken and cesium inside elutes as ions.

  Generally, soil itself is an aggregate of particles, and the particles themselves are on the order of μm to about mm, so that the contact area with the eluent L can be increased, which will be described below. Extraction of cesium from the soil S can be performed efficiently and effectively.

  As the acid solution, for example, an aqueous solution of hydrochloric acid, sulfuric acid, nitric acid, oxalic acid or the like is preferably used, and among them, an aqueous solution of hydrochloric acid or oxalic acid is preferable. When sulfuric acid and oxalic acid, which are divalent acids, are used as the acid solution, the amount of acid (number of moles) required for the treatment can be reduced compared to the monovalent acid.

  The concentration of the acid solution is appropriately set according to the type of soil S. The concentration of the acid solution is preferably 0.05 mol / L or more and 1.0 mol / L or less.

  The hydrogen ion concentration of the acid solution is preferably equal to or higher than the hydrogen ion concentration capable of dissolving iron contained in the soil S. This is because, when the soil S contains a large amount of iron, the acid solution dissolves the iron contained in the soil S to decompose the soil S and facilitate the outflow of cesium inside the soil S to the outside. For example, when hydrochloric acid is used, the hydrogen ion concentration of the acid solution is preferably 1.5 or less at pH, and more preferably 0.9 or less at pH.

  In addition, when dissolving cesium of soil S with an acid solution as described above, the dissolution rate is preferably increased by heating the eluent L to 80 ° C. or higher and 100 ° C. or lower, more preferably 95 ° C. or higher and 100 ° C. or lower. And can be eluted efficiently.

The eluent L containing cesium in the above process is sent from the processing tank 11 to the adsorption tower 12 via the first pipe 13 by the transfer pump 15.
At this time, the solid content in the eluent L is removed by passing through the filter 16.

  The filter 16 is not limited as long as it does not allow the soil S to pass through. For example, a filter made of a hollow fiber membrane made of polyethylene, polysulfone, polypropylene or the like can be used.

  In the adsorption tower 12, cesium in the eluent L is removed by the eluent L coming into contact with the adsorbent 121 accommodated in the adsorption tower 12. (Second step).

  The adsorbent 121 is not particularly limited as long as it has high adsorption performance for cesium, and for example, ferrocyanide, silicotitanate, and zeolite can be used.

  Examples of the ferrocyanide include potassium ferrocyanide, sodium ferrocyanide, calcium ferrocyanide, iron ferrocyanide, nickel ferrocyanide, and copper ferrocyanide. Examples of the zeolite include mordenite zeolite, chabazite zeolite, clinoptilolite zeolite, A zeolite, Y zeolite, and X zeolite. Further, the silicic titanic acid may be a salt such as barium silicotitanate or strontium silicotitanate.

  As the adsorbent 121, for example, when circulating the eluent L at a temperature of 95 ° C. or higher, zeolite is preferable from the viewpoint of heat resistance, and mordenite zeolite is particularly preferable. .

  Further, the amount of the adsorbent 121 to be filled is appropriately determined according to the type of the adsorbent 121 and the cesium concentration in the eluent L.

  As described above, the eluent L from which cesium has been removed by contact with the adsorbent 121 is sent to the processing tank 11 via the second pipe 14. (Third step). In the treatment tank 11, the soil S is treated again with the eluent L, and cesium elutes in the eluent L as described above. (First step).

  Note that the circulation flow rate of the eluent L in the decontamination apparatus 10 is appropriately determined depending on the cesium concentration in the eluent L and the amount and type of the adsorbent. The circulation flow rate can be adjusted by changing the discharge amount of the transfer pump 15.

  In the soil decontamination method of the present embodiment, the above-described series of steps (first to third steps) are continuously repeated to remove cesium in the eluent L containing cesium, and this is used as the eluent L. It is intended for recycling. Thereby, the cesium density | concentration of the eluent L is always kept low, and the elution of the cesium contained in the soil S is accelerated | stimulated. Therefore, the removal process of cesium can be performed simply, quickly and efficiently, and a large elution rate can be obtained in a short time compared with the batch process.

(Embodiment 2)
The decontamination apparatus 20 shown in FIG. 2 is heat which performs heat exchange between the eluent L in the first pipe 13 and the eluent L in the second pipe 14 in the decontamination apparatus 10 shown in FIG. An exchanger 18 is provided. Since the other components are the same as those of the decontamination apparatus 10 shown in FIG. 1, the same reference numerals are given to the components having the same functions, and redundant description is omitted.

  In the decontamination apparatus 20, the eluent L in the treatment tank 11 is sucked by the transfer pump 15, and exchanges heat with the eluent L in the second pipe 14 in the process of passing through the first pipe 13. To do. Thereby, the eluent L in the first pipe 14 is cooled and its temperature is lowered. Thereafter, as in Embodiment 1, the eluent L is sent to the adsorption tower 12 where cesium contained in the eluent L is removed. The temperature of the eluent L sent out from the adsorption tower 12 is lowered in the process of flowing through the adsorption tower 12. The eluent L having a lowered temperature exchanges heat with the eluent L in the first pipe 13 in the heat exchanger 18 while passing through the second pipe 14. As a result, the eluent L in the second pipe 14 is heated and sent to the treatment tank 11 in a state where its temperature has risen. (Fourth step). At this time, since the heat released when the eluent L in the first pipe 13 is cooled heats the eluent L in the second pipe 14, these are separately heated and cooled. In comparison, the thermal efficiency in the decontamination apparatus 20 can be improved.

  For this reason, in this embodiment, as the adsorbent 121, an adsorbent that dissolves in a high-temperature acid, specifically, ferrocyanide, silicotitanic acid, or the like can be used.

  Further, the heat exchanger 18 can be used without any particular limitation as long as the temperature of the eluent L in the first pipe can be equal to or lower than the heat resistant temperature of the adsorbent 121.

Thus, in the decontamination apparatus 20 of this embodiment, the heat exchange between the cooled eluent L and the heated eluent L suppresses the release of heat to the outside of the processing system, and the thermal efficiency. Can be improved. Furthermore, since an adsorbent having low heat resistance and acid resistance can be used, the degree of freedom in designing the decontamination apparatus 20 can be increased.
Moreover, since the cesium density | concentration in the eluent L is always kept low similarly to Embodiment 1, the elution of the cesium in the soil S is accelerated | stimulated, and the radioactive cesium contained in the soil S is simply, rapidly and efficiently. Removed.

Example 1
In this example, the relationship between the number of elutions and the elution rate when soil containing radioactive cesium was eluted with hydrochloric acid was examined.

  Specifically, in a 500 ml beaker, 5 g of soil containing radioactive cesium and 250 ml of hydrochloric acid having a concentration of 0.5 mol / L as an eluent (volume of hydrochloric acid aqueous solution [ml] / soil mass [g] (liquid-solid ratio) 50 ml / g) was accommodated and heated with stirring to a temperature of 95 ° C.

The radioactivity of the soil before elution and the radioactivity of the soil after elution was carried out batchwise with an eluent temperature of 95 ° C. and an elution time of 1 hour, and the elution rate was calculated as follows.
Elution rate [%] = (1−Radioactivity in soil after elution [Bq] ÷ Radioactivity in soil before elution [Bq]) × 100

  Then, after elution, the eluent was discharged from the beaker, and the remaining soil was immersed in fresh 0.5 mol / L hydrochloric acid at a liquid-solid ratio of 50 ml / g. Subsequently, elution was performed as described above, and the elution rate was measured. Such a treatment was repeated four times. The results are shown in the graph of FIG. 3 with the vertical axis representing the elution rate and the horizontal axis representing the number of times of elution.

  From FIG. 3, it was found that the elution rate of cesium was increased by increasing the number of times of elution, and an elution rate of 70% could be obtained when the number of times of elution was four times. From this, it was found that if the eluted cesium is removed from the eluent and the cesium concentration in the eluent is kept low at all times, the elution of cesium in the soil is promoted and the eluent can be used efficiently.

(Example 2)
In this example, the relationship between the pH of the eluent and the elution rate was examined when the soil containing radioactive cesium was eluted with an eluent having a different pH.

  Specifically, as in Example 1, soil containing radioactive cesium at a liquid-solid ratio of 50 ml / g was immersed in hydrochloric acid having a pH of 0.9. The eluent was heated, the temperature was set to 95 ° C., and batch processing was performed 5 times (5 hours) with an elution time of 1 hour, and the elution rate was measured.

  Next, the pH of hydrochloric acid to be used was changed between 0.9 and 1.5, elution was performed in the same manner as described above, and the respective elution rates were measured. The results are shown in the graph of FIG. 4 with the vertical axis representing the elution rate and the horizontal axis representing the pH of the eluent.

  From FIG. 4, it has been found that when the pH of the eluent is 1.5 or less, the elution rate is 40% or more, and when the pH is 0.9 or less, the elution rate is 65% or more.

(Example 3)
In this example, the relationship between the temperature of the eluent and the elution rate when the soil containing radioactive cesium was eluted with hydrochloric acid was examined.

  In the treatment of Example 1, the elution rate was measured when elution was carried out batchwise for 1 hour with the temperature of the eluent being 40 ° C., 60 ° C., 85 ° C., 90 ° C., and 95 ° C., respectively. When the eluent was at 95 ° C., batch processing was performed for 4 hours, and the elution rate was measured 1 hour, 2 hours, 3 hours, and 4 hours after the start of elution. The results are shown in the graph of FIG. 5 with the vertical axis representing the elution rate and the horizontal axis representing the temperature of the eluent.

In FIG. 5, the black diamonds are the results of batch processing for 1 hour at each temperature, and the diamonds are the results after performing the treatment at 95 ° C. for 2, 3 and 4 hours.
From the figure, it was found that an elution rate of 58% or more was obtained at an eluent temperature of 95 ° C. That is, it is understood that the temperature of the eluent is preferably 95 ° C. or higher. It was also found that when the elution time was extended at an eluent temperature of 95 ° C., the elution rate slightly increased, but no significant improvement was observed.

Example 4
In this example, changes in elution rate over time were compared between the case where the soil containing radioactive cesium was repeatedly eluted using a batch method and the case where the elution was performed continuously using the configuration of the embodiment.
Specifically, in each case, 0.5 mol / L hydrochloric acid was used as the eluent, the eluent temperature was 95 ° C., and the liquid-solid ratio was 50 ml / g.

  In batch-type elution, elution for 1 hour was repeated 4 times under the above conditions.

In the continuous elution, in the configuration of the embodiment, the filter 16 is a hollow fiber membrane filter, and the adsorbent 121 is zeolite. Elution was performed for 3 hours by setting the circulation flow rate (SV) in the adsorption tower 12 to 10 h- ¹ .

  The results are shown in the graph of FIG. 6 with the vertical axis representing the elution rate and the horizontal axis representing the elution time. In FIG. 6, a diamond indicates a case where elution is performed in the configuration of the embodiment, and a black square indicates a case where elution is performed in a batch type.

From the figure, in the batch method, the elution rate is about 70% after 3 hours (after 3 repetitions), but in the continuous elution of the embodiment, the elution rate is 70% in 2 hours. found. The total amount of the acid solution required at this time is ½ of the batch type. This is because in the continuous method, the initially added acid solution is circulated and used as the eluent, whereas in the batch method, the soil is separated and recovered from the eluent every time and the acid solution is newly added to the soil. is there.
Further, it can be seen that when the elution time is the same, a higher elution rate can be obtained in the continuous method than in the batch method.

(Comparative Example 1)
In this comparative example, the change in the elution rate when the eluent was repeatedly used was examined.
Specifically, the soil is immersed in 0.5 mol / L hydrochloric acid as an eluent at a liquid-solid ratio of 50 ml / g, and the elution temperature is 95 ° C., and the elution time is 1 hour. went.
Thereafter, the eluate after elution was separated from the soil and taken out, and fresh untreated soil was immersed in the eluent to perform elution in the same manner as described above.

Such an operation was repeated 5 times, and the elution rate was measured. The results are shown in the graph of FIG. 7 with the vertical axis representing the elution rate and the horizontal axis representing the number of times of elution.
From FIG. 7, it was found that when the eluent was used twice, the elution rate was 30% or less, and the elution rate further decreased as the number of times the eluent was used. From this, it can be seen that as the number of times of use increases, the elution rate decreases, and as a result, the amount of eluent used increases. Thus, it can be seen that radioactive cesium contained in the soil is not efficiently removed when the eluent is repeatedly used.

  As mentioned above, although several embodiment of this invention was described, these embodiment was posted as an example and is not intending limiting the range of invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the scope of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are included in the invention described in the claims and the equivalents thereof.

DESCRIPTION OF SYMBOLS 10, 20 ... Decontamination apparatus 11 ... Treatment tank 12 ... Adsorption tower 12A ... Water inlet 12B ... Water outlet 121 ... Adsorbent 13 ... First piping 13A ... Water intake 14 ... Second piping 15 ... Transfer pump 16 ... Filter 17 ... Heating device 18 ... Heat exchanger S ... Soil L ... Eluent

Claims (6)

A soil decontamination device for decontaminating soil containing radioactive cesium,
A treatment tank containing the soil and an eluent containing an acid solution, and eluting the cesium in the soil into the eluent;
An adsorption tower containing an adsorbent that adsorbs cesium in the eluent;
A first pipe connecting the treatment tank and a water inlet of the adsorption tower;
A second pipe connecting the water outlet of the adsorption tower and the treatment tank;
A transfer pump interposed in the first pipe for circulating the eluent between the processing tank and the adsorption tower ;
A heating device for heating the eluent in the processing tank;
A soil decontamination apparatus , comprising: a heat exchanger that exchanges heat between the eluent in the first pipe and the eluent in the second pipe . The acid solution is hydrochloric acid, sulfuric acid, soil decontamination apparatus according to claim 1 Symbol mounting, characterized in that an aqueous solution containing at least one selected from nitric acid and oxalic acid. The soil decontamination apparatus according to claim 1 or 2 , wherein the adsorbent is at least one selected from ferrocyanide, silicotitanate and zeolite. A soil decontamination method for decontaminating soil containing radioactive cesium,
A first step of storing the soil and an eluent containing an acid solution in a treatment tank, and eluting cesium in the soil into the eluent;
Supplying the eluent to an adsorption tower containing an adsorbent that adsorbs cesium, and adsorbing the cesium in the eluent to the adsorbent;
A third step of supplying the eluent from the adsorption tower to the treatment tank,
The eluent in the treatment tank is hydrochloric acid having a pH of 0.9 or less,
The temperature of the eluent in the treatment tank is controlled to be 95 ° C. or higher and 100 ° C. or lower,
A soil decontamination method, wherein the eluent is circulated between the treatment tank and the adsorption tower, and the first to third steps are continuously repeated. Between the second step and the third step, there is a fourth step of performing heat exchange between the eluent supplied to the adsorption tower and the eluent supplied to the treatment tank. The soil decontamination method according to claim 4 , wherein the soil decontamination method is characterized. 6. The soil decontamination method according to claim 4 , wherein the adsorbent is at least one selected from ferrocyanide, silicotitanate and zeolite.

Images