JP6180838B2 - Soil decontamination method and apparatus - Google Patents

Description

  The present invention relates to a decontamination method and apparatus 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 and is expected to affect the long term. The Therefore, removal of cesium from contaminated soil and sludge is desired. Several proposals have been made for 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 in the surface layer of the contaminated soil at a predetermined interval, and by energizing between these electrodes, the pollutants are accumulated at the electrodes, and plants with high accumulation of harmful substances are cultivated in the contaminated soil, A method for removing the pollutant by absorbing the plant is disclosed (for example, see Patent Document 2). However, these methods have a problem that it is difficult to perform on-site processing because they require electrode installation and energization. Moreover, in the method including the process of plant cultivation, there also exists a problem that processing requires a long time.

  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 wastewater, 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. Not suitable for. (For example, refer to 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).

  Furthermore, a method has been proposed in which contaminated soil is immersed in an organic acid solution and cesium is eluted in the solution, and then cesium is recovered using an adsorbent. There is concern that sufficient decontamination is not possible because of the difference.

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

  The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a soil decontamination method and apparatus capable of simply and efficiently decontaminating soil containing radioactive cesium. To do.

One aspect of the soil decontamination method according to the present invention is a soil decontamination method for decontaminating soil containing radioactive cesium, wherein the soil is contacted with a first eluent containing potassium hydroxide, and the soil A first elution step of eluting cesium in the first eluent, and the soil and a second eluent containing oxalic acid are contacted, and the cesium in the soil is brought into contact with the second eluent. It has a second elution step of eluting, and performing a plurality of times the first elution step and the second elution step are alternately respectively during.

One aspect of the soil decontamination apparatus according to the present invention is a soil decontamination apparatus for decontaminating soil containing radioactive cesium, wherein the treatment tank contains the soil, and the treatment tank contains potassium hydroxide. And a second eluent containing oxalic acid in the treatment tank by supplying a first eluent supplying means for eluting the cesium in the soil into the first eluent. The second eluent supply means for eluting cesium in the soil into the second eluent, and the temperature of the first eluent and the second eluent in the treatment tank are 60 ° C. or more and 100 ° C., respectively. It has a heating device which makes it below ° C.

  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 graph which shows the elution rate in the elution using potassium hydroxide and oxalic acid. It is a graph which shows the relationship between the temperature of a potassium hydroxide aqueous solution, and an elution rate. It is a graph which shows the relationship between the density | concentration of potassium hydroxide aqueous solution, and an elution rate. It is a graph which shows the relationship between the soil classification at the time of using potassium hydroxide and oxalic acid, and an elution rate. It is a graph which shows the relationship between the elution rate at the time of using oxalic acid and a soil classification. It is a graph which shows the elution rate in the elution using hydrochloric acid and sodium hydroxide.

  FIG. 1 is a diagram showing a schematic configuration of a soil decontamination apparatus used for decontamination of soil containing radioactive cesium in the present embodiment.

  A soil decontamination apparatus 1 shown in FIG. 1 has a treatment tank 2 for containing soil S. The soil decontamination apparatus 1 includes a potassium hydroxide aqueous solution tank 4 connected to the treatment tank 2 by a supply line 3, a cleaning liquid tank 6 connected to the treatment tank 2 by a supply line 5, and a supply line to the treatment tank 2. 7 and an oxalic acid aqueous solution tank 8 connected by 7. Transfer pumps 9, 10, and 11 are inserted in the supply lines 3, 5, and 7, respectively.

  In the soil decontamination apparatus 1, the potassium hydroxide aqueous solution tank 4, the transfer pump 9 and the supply line 3 constitute a first eluent supply means, and the oxalic acid aqueous solution tank 8, the transfer pump 11 and the supply line 7 are the first. 2 eluent supply means. Further, the cleaning liquid tank 6, the transfer pump 10, and the supply line 5 constitute cleaning means.

  Furthermore, the soil decontamination apparatus 1 has an adsorption tower 12, and the treatment tank 2 and the water inlet 12 </ b> A of the adsorption tower 12 are connected by a suction line 13. A circulation line 14 that circulates the first eluent L1, the second eluent L2, and the cleaning liquid W between the treatment tank 2 and the adsorption tower 12 is provided at the outlet 12B of the adsorption tower 12 with an open / close valve 15. The first eluent L1, the second eluent L2, and the cleaning liquid W are sent to the circulation line 14 to the potassium hydroxide aqueous solution tank 4, the oxalic acid aqueous solution tank 8, and the cleaning liquid tank 6, respectively. Thus, the open / close valves 16, 18, and 17 are inserted. In the soil decontamination apparatus 1, the circulation line 14 and the open / close valves 15 to 18 constitute a circulation means.

  A discharge line 20 for discharging the first eluent L 1, the second eluent L 2, and the cleaning liquid W is connected to the circulation line 14 via an open / close valve 19.

  A transfer pump 21 that transfers the first eluent L1, the second eluent L2, and the cleaning liquid W is inserted in the suction line 13. Further, a filter 22 for removing the solid content in the first eluent L1, the second eluent L2, and the cleaning liquid W is provided at the intake port of the suction line 13 located below the liquid level in the processing tank 2. Is provided.

  The processing tank 2 is provided with a heating device 23 such as a heater for heating the first eluent L1 and the second eluent L2 in the processing tank 2 to a predetermined temperature. Further, the treatment tank 2 is preferably provided with a stirring device such as a stirring bar. Note that an ultrasonic application device may be provided instead of or in addition to the stirring bar.

  The processing tank 2, the supply lines 3, 5, and 7, the suction line 13, the circulation line 14, and the discharge line 20 constituting the soil decontamination apparatus 1 are made of a material having high corrosion resistance. As such a material, stainless steel having high corrosion resistance is preferable.

  Moreover, the capacity | capacitance of the processing tank 2 is suitably determined according to the quantity of the soil S which should be processed.

  The filter 22 is not particularly limited as long as it does not allow the soil S to pass therethrough. For example, a filter made of a hollow fiber membrane made of polyethylene, polysulfone, polypropylene or the like can be used.

  The adsorption tower 12 contains an adsorbent that adsorbs cesium in the first eluent L1, the second eluent L2, and the cleaning liquid W.

  The adsorbent is not particularly limited as long as it has a high adsorption performance with respect to cesium. 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.

  Further, the amount of the adsorbent is appropriately determined according to the type of adsorbent and the cesium concentrations in the first eluent L1 and the second eluent L2.

Next, a soil decontamination method using the soil decontamination apparatus 1 shown in FIG. 1 will be described.
The soil decontamination method of this embodiment performs the 1st elution process using potassium hydroxide aqueous solution as 1st eluent L1 with respect to soil S, and then performs the washing process using the washing | cleaning liquid W as needed. Then, a second elution step using an oxalic acid aqueous solution as the second eluent L2 is performed.

The soil S is a soil containing radioactive cesium, and may contain sludge, sand and the like.
In general, the soil itself is an aggregate of particles, and the particles themselves are on the order of μm to mm, so that the soil is in contact with the first eluent L1 and the second eluent L2. An area can be enlarged and the elution of cesium from the soil S demonstrated below can be performed efficiently and effectively.

  The soil S consists of 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 an aqueous potassium hydroxide solution or an aqueous oxalic acid solution, a part of the laminated structure is broken and cesium inside elutes into the aqueous solution.

  In the soil S having different soil properties, the types and structures of the components constituting the soil S, the structure of the soil S, and the like may be different, and the elution rate of cesium may be different depending on the eluent used. In the soil decontamination method of the present embodiment, a part of the structure of the soil S was broken in the first elution step, and the internal cesium was removed, and then it was not destroyed in the first elution step in the second elution step. The remaining structure of the soil S is partially broken to remove this internal cesium. Therefore, it is possible to efficiently decontaminate various soils S regardless of the soil quality.

  In FIG. 1, the soil S and the first eluent L1 are shown separately, but in reality, the above-described stirring and mixing operation and the mode (form, size, etc.) of the soil S are accompanied. Thus, the soil S is dispersed in the first eluent L1. Here, for convenience of explanation of the present embodiment, the soil S and the first eluent L1 are separated and described. The same applies to the second eluent L2 and the cleaning liquid W.

  In the first elution step, the soil S containing radioactive cesium is accommodated in the treatment tank 2, and a potassium hydroxide aqueous solution is supplied from the potassium hydroxide aqueous solution tank 4 to the treatment tank 2 as the first eluent L1 by the transfer pump 9. The first eluent L1 is heated by the heating device 23. Moreover, the 1st eluent L1 is stirred as needed. As a result, cesium contained in the soil S is eluted into the first eluent L1.

  The concentration of the potassium hydroxide aqueous solution is appropriately set according to the type of soil S. The concentration of the potassium hydroxide aqueous solution is, for example, preferably 0.05 mol / L or more and 1.0 mol / L or less, and more preferably 0.5 mol / L or more and 1.0 mol / L or less.

  In the first elution step, the first eluent L1 is preferably heated to 60 ° C. or higher and 100 ° C. or lower, more preferably 95 ° C. or higher and 100 ° C. or lower. Particularly preferably, heating is performed at about 95 ° C. Thereby, the elution rate can be improved and cesium can be efficiently eluted.

  Next, the first eluent L1 containing cesium is supplied to the adsorption tower 12 by the transfer pump 21. At this time, the first eluent L1 passes through the filter 22, so that the solid content in the first eluent L1 is removed.

  In the adsorption tower 12, the first eluent L1 comes into contact with the adsorbent, so that cesium in the first eluent L1 is removed. The first eluent L1 from which cesium has been removed is discharged out of the system through the discharge line 20.

  In the present embodiment, after the first elution step, a cleaning step is performed as necessary.

  In the cleaning step, the cleaning liquid W is supplied from the cleaning liquid tank 6 to the processing tank 2 by the transfer pump 10 and stirred as necessary. Simultaneously with or in place of stirring the cleaning liquid W, the cleaning liquid W may be continuously passed through the treatment tank 2. Moreover, you may heat the washing | cleaning liquid W with the heating apparatus 23 as needed. Thereby, the potassium hydroxide in the soil S can be efficiently dissolved in the cleaning liquid W and reduced. As the cleaning liquid W, water is generally used.

  After a predetermined time, the cleaning liquid W in the processing tank 2 is supplied to the adsorption tower 12 by the transfer pump 21. At this time, since the cleaning liquid W passes through the filter 22, the solid content in the cleaning liquid W is removed.

  In the adsorption tower 12, when the cleaning liquid W comes into contact with the adsorbent, cesium in the cleaning liquid W is removed. The cleaning liquid W from which cesium has been removed is discharged from the discharge line 20.

  Thus, the potassium hydroxide remaining in the treatment tank 2 or in the soil S can be reduced by dissolving and removing the potassium hydroxide in the soil S in the washing liquid in the washing step. Therefore, in the second elution step, it is possible to suppress an increase in the amount of oxalic acid used that reacts with the remaining potassium hydroxide. Moreover, the potassium oxalate remaining in the soil S can be reduced.

  In the present embodiment, a second elution step is performed following the cleaning step. In the second elution step, the oxalic acid aqueous solution is supplied from the oxalic acid aqueous solution tank 8 as the second eluent L2 into the processing tank 2 by the transfer pump 11, and the second eluent L2 is heated by the heating device 23. Moreover, the 2nd eluent L2 is stirred as needed. Thereby, the cesium remaining in the soil S in the first elution step is eluted in the second eluent L2.

  The concentration of the oxalic acid aqueous solution is appropriately set according to the type of soil S. The concentration of the oxalic acid aqueous solution is preferably a concentration that dissolves iron in the soil S. Such a concentration is preferably 0.05 mol / L or more and 1.0 mol / L or less, and more preferably 0.5 mol / L or more and 1.0 mol / L or less.

  In the second elution step, the second eluent L2 is preferably heated to 60 ° C. or higher and 100 ° C. or lower, more preferably 95 ° C. or higher and 100 ° C. or lower. Particularly preferably, heating is performed at about 95 ° C. Thereby, the elution rate can be improved and cesium can be efficiently eluted.

  Next, the second eluent L2 in the processing tank 2 is supplied to the adsorption tower 12 by the transfer pump 21. At this time, the second eluent L2 passes through the filter 22, so that the solid content in the second eluent L2 is removed.

  In the adsorption tower 12, the second eluent L2 comes into contact with the adsorbent, so that cesium in the second eluent L2 is removed. The second eluent L2 from which cesium has been removed is discharged out of the system through the discharge line 20.

  In the present embodiment, it is preferable that the first elution step and the second elution step described above are alternately repeated twice or more. Thereby, the elution rate can be improved.

  In this case, it is preferable to perform the washing step in the same manner as described above after the second elution step. Thereby, by reducing the oxalic acid remaining in the soil S in the treatment tank 2, the required amount of potassium hydroxide and the amount of generated potassium oxalate in the first elution step can be reduced.

  In the present embodiment, the first eluent L1 and the second eluent L2 that have passed through the adsorption tower 12 are discharged out of the system and discarded. Therefore, the total use amount of each of the first eluent L1 and the second eluent L2 is such that oxalic acid in the second eluent L2 is 0 with respect to 1 mol of potassium hydroxide in the first eluent L1. It is preferable that it is the quantity used as the ratio of .5 mol. Thereby, the waste liquid which is a mixed liquid of the potassium hydroxide aqueous solution and the oxalic acid aqueous solution becomes neutral, and it becomes possible to reduce the disposal cost.

In addition, the first eluent L1, the second eluent L2, and the cleaning liquid W that have passed through the adsorption tower 12 can be circulated and used without being discharged out of the system. Specifically, in each step, the first eluent L1 is supplied from the adsorption tower 12 to the potassium hydroxide aqueous solution tank 4 through the circulation line 14, and the second eluent L2 is supplied from the adsorption tower 12 to the circulation line 14. The oxalic acid aqueous solution tank 8 can be supplied to the processing tank 2 and then supplied again to the treatment tank 2 for recycling. Similarly, the cleaning liquid W can be recycled by being supplied from the adsorption tower 12 to the cleaning liquid tank 6 through the circulation line 14 and again to the processing tank 2.
In this case, since the cesium concentration in the first eluent L1, the second eluent L2, and the cleaning liquid W can be kept low at all times, the elution of cesium can be performed quickly and efficiently, and is high in a short time. Elution rate can be obtained.

  Thus, according to this embodiment, soil containing radioactive cesium can be easily and efficiently decontaminated even when the soil quality is different.

Example 1
In this example, the elution rate when the second elution step was performed after the first elution step was examined.
Specifically, 5 g of soil having a soil classification of sandy loam soil was mixed with 250 ml of 0.5 mol / L potassium hydroxide aqueous solution as the first eluent (liquid-solid ratio (eluent volume [ml] / soil Mass [g]) was immersed in 50 ml / g) and heated with stirring.

  Elution was performed with the temperature of the first eluent being 95 ° C. and the elution time being 1 hour. Thereafter, the first eluent was discharged. Next, the remaining soil is immersed in a 0.5 mol / L oxalic acid aqueous solution as a second eluent at a liquid-solid ratio of 50 ml / g, and the temperature of the second eluent is 95 ° C. and the elution time is set while stirring. Elution was performed for 1 hour.

The radioactivity of the soil before elution and the radioactivity of the soil after each elution were measured, and the elution rate was calculated as follows.
Elution rate [%] = (1−Radioactivity in soil after elution [Bq] ÷ Radioactivity in soil before elution [Bq]) × 100
The results are shown in the graph of FIG. 2 with the elution rate as the vertical axis.

  2 that the elution rate after performing the second elution step after the first elution step is 80% or more. Furthermore, the reaction product of potassium hydroxide and oxalic acid is potassium oxalate, and the method of this example has less influence on farmland than the method using hydrochloric acid and sodium hydroxide aqueous solution, and is suitable for decontamination. Turned out to be.

(Example 2)
In this example, the relationship between the temperature of the aqueous potassium hydroxide solution and the elution rate was examined.
Specifically, the elution rate is obtained by immersing soil containing radioactive cesium in a 0.5 mol / L potassium hydroxide aqueous solution, which is the first eluent, at a liquid-solid ratio of 50 ml / g, and heating while stirring. Was measured.

The relationship between the temperature of the eluent and the elution rate is shown in the graph of FIG. 3 with the elution rate on the vertical axis and the eluent temperature on the horizontal axis.
From FIG. 3, it was found that when the temperature of the first eluent was 60 ° C. or higher, an elution rate of 10% or higher was obtained, and when the temperature of 95 ° C. or higher was obtained, an elution rate of 65% or higher was obtained. For this reason, it is understood that the temperature of the first eluent is preferably 60 ° C. or higher, and more preferably 95 ° C. or higher.

(Example 3)
In this example, the relationship between the concentration of the potassium hydroxide aqueous solution and the elution rate was examined.
Specifically, the soil was immersed in aqueous potassium hydroxide solutions (first eluent) having a liquid-solid ratio of 50 ml / g and different concentrations. The elution was carried out with the temperature of the first eluent set at 95 ° C. and the elution time set at 1 hour, and the elution rate was measured.

  The relationship between the concentration of the potassium hydroxide aqueous solution and the elution rate is shown in the graph of FIG. 4 with the elution rate on the vertical axis and the potassium hydroxide concentration on the horizontal axis. From these results, it was found that an elution rate of 10% or more can be obtained when the concentration of the potassium hydroxide aqueous solution is 0.05 mol / L or more, and an elution rate of 65% or more can be obtained when the concentration is 0.5 mol / L or more. For this reason, the concentration of the potassium hydroxide aqueous solution is preferably 0.05 mol / L or more, and more preferably 0.5 mol / L or more.

(Example 3)
In this example, the elution rate when the first elution step and the second elution step were alternately repeated twice for soil of different soil classifications was examined.
Specifically, elution was performed as follows for soils with soil classification of light soil, sandy soil, sandy soil, and soil.

First, the soil was immersed in a 0.5 mol / L potassium hydroxide aqueous solution as the first eluent at a liquid / solid ratio of 50 ml / g and heated with stirring. Elution was performed with the temperature of the first eluent being 95 ° C. and the elution time being 1 hour. Thereafter, the first eluent was discharged.
Next, the remaining soil was immersed in a 0.5 mol / L oxalic acid aqueous solution as the second eluent at a liquid / solid ratio of 50 ml / g and heated with stirring. Elution was performed with the temperature of the second eluent being 95 ° C. and the elution time being 1 hour. Thereafter, the second eluent was discharged.
Such an operation was repeated twice and the elution rate was measured. The results are shown in the graph of FIG. 5 with the elution rate as the vertical axis.

  From FIG. 5, it was found that an elution rate of 90% or more can be obtained after the elution using an aqueous potassium hydroxide solution and an aqueous oxalic acid solution is alternately repeated twice.

(Comparative Example 1)
In this comparative example, only the oxalic acid aqueous solution was used as the eluent, and the elution rate when elution was performed on soils of different soil classifications was examined.

  Specifically, soil whose soil classification is sandy clay, loam sand, sandy clay, and clay is immersed in a 0.5 mol / L oxalic acid aqueous solution as an eluent at a liquid-solid ratio of 50 ml / g. And warmed with stirring. Elution was performed at an eluent temperature of 95 ° C. and an elution time of 1 hour. The elution rate at this time was measured. The results are shown in the graph of FIG. 6 with the elution rate as the vertical axis for each soil.

  From FIG. 6, it was found that when the elution was performed only with the oxalic acid aqueous solution, the elution rate varied depending on the soil classification.

(Comparative Example 2)
In this comparative example, the sandy loam soil was eluted using hydrochloric acid and an aqueous sodium hydroxide solution as an eluent.

  Specifically, the sandy loam soil was immersed in a 1 mol / L hydrochloric acid aqueous solution as an eluent at a liquid-solid ratio of 50 ml / g and heated with stirring. Elution was carried out at a hydrochloric acid eluent temperature of 95 ° C. and an elution time of 1 hour, and the elution rate was measured. Next, the eluted hydrochloric acid eluent was discharged, and the remaining soil was immersed with a 0.5 mol / L sodium hydroxide aqueous solution as an eluent at a liquid-solid ratio of 50 ml / g and heated with stirring. Elution was carried out at a sodium hydroxide eluent temperature of 95 ° C. and an elution time of 1 hour, and the elution rate was measured. These results are shown in the graph of FIG. 7 with the elution rate as the vertical axis.

  From FIG. 7, the elution rate was about 30% after elution with hydrochloric acid, and the elution rate was about 55% after elution with an aqueous sodium hydroxide solution. Further, it has been found that this method has a problem that sodium chloride produced from hydrochloric acid and sodium hydroxide remains in the soil and is not suitable for decontamination of soil such as farmland.

  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 1 ... Soil decontamination apparatus 2 ... Treatment tank 3,5,7 ... Supply line 4 ... Potassium hydroxide aqueous solution tank 6 ... Cleaning liquid tank 8 ... Oxalic acid aqueous solution tank 9,10,11,21 ... Transfer pump 12 ... Adsorption tower 12A ... inlet 12B ... outlet 13 ... suction line 14 ... circulation lines 15, 16, 17, 18, 19 ... open / close valve 20 ... discharge line 22 ... filter 23 ... heating device S ... soil L1 ... first eluent L2 ... Second eluent W: cleaning solution.

Claims (11)

A soil decontamination method for decontaminating soil containing radioactive cesium,
A first elution step of bringing the soil into contact with a first eluent containing potassium hydroxide to elute cesium in the soil into the first eluent;
The soil and contacting the second eluate containing oxalic acid, and have a second elution step of eluting the cesium in said soil in the second eluate,
The soil decontamination method, wherein the first elution step and the second elution step are alternately performed a plurality of times .   In the first eluent and the second eluent, the first eluent and the second eluent used in the first elution step and the second elution step are brought into contact with an adsorbent. The soil decontamination method according to claim 1, further comprising a removal step of removing cesium. The first eluent and the second eluent are circulated and used by bringing the first eluent and the second eluent in contact with the adsorbent into contact with the soil. The soil decontamination method according to claim 2 . The soil decontamination method according to any one of claims 1 to 3 , wherein the concentration of potassium hydroxide in the first eluent is 0.05 mol / L or more and 1.0 mol / L or less. Wherein the temperature of the first eluate and the second eluate, soil decontamination method of any one of claims 1 to 4, characterized in that at most 100 ° C. 60 ° C. or higher, respectively. 2. A cleaning step of removing potassium hydroxide remaining in the soil by bringing the soil into contact with a cleaning solution between the first elution step and the second elution step. The soil decontamination method of any one of thru | or 5 . The amount of the first eluent and the amount of the second eluent is 0.5 mol of oxalic acid in the second eluent with respect to 1 mol of potassium hydroxide in the first eluent. The soil decontamination method according to any one of claims 1 to 6 , characterized in that A soil decontamination device for decontaminating soil containing radioactive cesium,
A treatment tank containing the soil;
First eluent supply means for supplying a first eluent containing potassium hydroxide to the treatment tank and eluting cesium in the soil into the first eluent;
A second eluent supply means for supplying a second eluent containing oxalic acid to the treatment tank and eluting cesium in the soil into the second eluent;
A soil decontamination apparatus, comprising : a heating device that sets a temperature of the first eluent and the second eluent in the treatment tank to 60 ° C. or more and 100 ° C. or less, respectively . The soil decontamination apparatus according to claim 8, further comprising an adsorption tower that contains an adsorbent that adsorbs cesium in the first eluent and the second eluent. The soil decontamination apparatus according to claim 9 , further comprising a circulation unit that circulates the first eluent and the second eluent between the adsorption tower and the treatment tank. The soil decontamination apparatus according to any one of claims 8 to 10 , further comprising cleaning means for supplying a cleaning liquid to the treatment tank to remove potassium hydroxide remaining in the soil.

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