JP6376428B2 - Decontamination method for cesium contaminated soil - Google Patents

Description

  The present invention relates to a method for decontaminating soil contaminated with radioactive substances, and more specifically, by adsorbing and removing radioactive substances from soil contaminated with radioactive substances to detoxify the soil or reduce radioactive substances in the soil. By reducing the amount of radioactive waste generated, or by reducing radioactive substances in the soil, compared to managing the contaminated soil itself as radioactive waste, it is possible to suppress the transition from contaminated soil to plants The present invention relates to a decontamination method for radioactive material contaminated soil.

  Radioactive material scattering caused by the Great East Japan Earthquake has not been stopped in the power plant, but has spread over a wide range of surrounding areas, and radiation exceeding the standard value has been detected. Decontamination of radioactive material-contaminated soil in these areas Has become a serious problem.

  Contamination due to radioactive material splashing in particular contaminates the soil near the surface of the earth. As a method for treating soil contaminated with radioactive material, stripping off the topsoil to remove only the soil near the contaminated surface or contaminated ground. Attempts have been made to replace the soil on the soil that has been excavated and the soil that is not contaminated in the ground, or in the rice fields, etc. Yes.

  However, in the case of stripping off the topsoil, the stripped topsoil itself must be stored and managed as radioactive waste, so securing a place for storing a large amount of soil is a major issue. And in the case of top-and-bottom return, the soil contaminated with radioactive material will exist underground, so there is a concern that the radioactive material will migrate to the ground part through deep rooted plants. In the case of scratching, there is a risk that radioactive material will flow out to the surrounding land and rivers with water.

  Needless to say, it is desirable to treat soil contaminated with radioactive material by removing the radioactive material that is the source of contamination and detoxifying the soil, and storing the removed radioactive material safely in another location. At that time, a method for reducing the amount of radioactive waste that must be safely stored and managed as much as possible becomes extremely important.

  The present invention is a method for decontaminating soil contaminated with radioactive substances using an adsorbent, and the adsorbent can be recovered easily and safely, and the amount of generated radioactive waste is reduced. Alternatively, an object of the present invention is to provide a method capable of suppressing the transition from contaminated soil to plants by reducing radioactive substances in the soil.

  The present inventors have intensively studied, and radioactive radioactive material adsorbent in the form of a powder, or a sheet-like adsorbent in which a radioactive substance adsorbent is held in a sheet or a bag-like adsorbent filled in a bag with a radioactive substance adsorbent. The present inventors have found that the above problem can be solved by bringing the soil contaminated with a substance into contact with water through water, and have reached the present invention.

  That is, the present invention relates to a granular adsorbent that adsorbs a radioactive substance, a sheet-like adsorbent that holds the adsorbent in a sheet, or a bag-like adsorbent filled with the adsorbent in a bag, on a land or temporary storage site. Radioactive material contaminated soil is brought into contact with water, and the radioactive material in the soil is adsorbed to the granular adsorbent, sheet adsorbent or bag adsorbent, detoxifying the soil or reducing the radioactive material in the soil, and radioactive Provided is a method for decontaminating radioactive material-contaminated soil, characterized in that a granular adsorbent adsorbing a substance, a sheet adsorbent or a bag adsorbent is treated as a radioactive waste.

  Uses a radioactive material adsorbent such as zeolite, or a sheet-like adsorbent holding the adsorbent in a sheet or a bag-like adsorbent filled in a bag. Can be recovered. Since only the sheet-like adsorbent or the bag-like adsorbent becomes radioactive waste, the amount of radioactive waste generated can be reduced. Or when reducing the radioactive substance in soil, the management level of the said soil can be lowered | hung and processing cost can be reduced.

The graph which shows the relationship between the particle diameter of a zeolite, and a cesium removal rate. The graph which shows the relationship between the immersion time of a bag-shaped adsorbent filled with zeolite, and cesium concentration. The graph which shows the zeolite addition amount to soil, and the cesium transfer inhibitory rate to a plant.

Details will be described below.
The sheet-like adsorbent used in the present invention is a material in which a water-permeable sheet-like material is supported or sandwiched with an adsorbent such as zeolite. Alternatively, the sheet end portion and an appropriate portion of the sheet are bonded, folded, stitched, or zeolite is bonded to the sheet with an adhesive component and supported. The bag-like adsorbent is obtained by enclosing an adsorbent such as zeolite in a bag-like material capable of passing water, and the material constituting the bag is cloth, porous plastic, metal, or the like.

(Test Example 1)
The relationship between the particle size of zeolite and the adsorption performance of radioactive materials was tested. Cesium was used as a model material for radioactive materials.
5 g of various zeolites (31 species) having different average particle diameters were added to 200 ml of seawater (cesium concentration 2 ppm) to which cesium chloride had been added, and allowed to stand at 10 ° C. for 24 hours. 5 ml of the supernatant was sampled, filtered through a 0.45 μm filter, the Cs concentration in the filtrate after filtration was measured, and the removal rate of cesium was determined. The relationship between the zeolite particle size and the Cs removal rate is shown in FIG.
A zeolite with a smaller particle size (that is, a larger surface area) has a better Cs removal rate, and a powdery zeolite with an average particle size of 13 to 50 μm showed a better Cs removal rate.
For example, it is 90% for Tosoh mordenite 640HOA (φ13 μm), 74% for Zeofir 1424 (φ1.0 to 1.4 mm) made by Shintohoku Chemical Industry, and Zeophyl 614 (φ1.4 to 4.4 made by Shintohoku Chemical Industry). 0 mm), it was 76%.

(Test Example 2)
As zeolite, Mordenite 640HOA manufactured by Tosoh and Zeophyl 1424 manufactured by New Tohoku Chemical Industry were selected, and pure water was used instead of the seawater of Test Example 1, and the Cs removal rate in pure water was measured. The Cs removal rate after 24 hours is shown in Table 1 in comparison with the results measured in the seawater of Test Example 1.

(Test Example 3)
Extra fine fiber cloth (manufactured by Teijin Co., Ltd., Microguard (registered trademark), material: polyester 75% / nylon 25%), Soxhlet extraction cylindrical filter paper (manufactured by Advantech), sandbag bag cloth, sandbag bag felt cloth, 26 μm A bag or sheet was prepared from a mesh wire mesh and Kiriyama filter paper (No. 3), and a bag-shaped adsorbent was prepared by filling zeolite having an average particle diameter of 13 μm or 30 to 50 μm. The produced bag-like adsorbent was immersed in a beaker containing water and shaken, and the outflow state of zeolite was observed.
As a result, bag-like or sheet-like adsorbents made with ultra-fine fiber cloth, Soxhlet extraction cylindrical filter paper, and Kiriyama filter paper are water-permeable, and water remains clear even after shaking, and no spillage of zeolite is observed. It was. On the other hand, in the bag-shaped adsorbent prepared with sandbag cloth, sandbag felt cloth, and 26 mesh wire mesh, water was clouded by shaking, and the outflow of zeolite was observed.

(Test Example 4)
Soxhlet extraction cylindrical filter paper (manufactured by Advantech) is filled with 5 g of zeolite, and the opening is sealed with a Teflon (registered trademark) tape and a binding band (Insulok (registered trademark)). Created. Further, after folding the Kiriyama filter paper (No. 3) in half and filling 5 g of zeolite in the center, it was folded twice on three sides and sealed with staples to prepare a sheet-like adsorbent. A bag-like adsorbent or a sheet-like adsorbent was immersed in 200 ml of seawater in which cesium chloride was dissolved (cesium concentration was about 2.3 ppm), and changes in the concentration of cesium in seawater were measured. Three types of zeolite were used: Tosoh mordenite 640HOA (φ13 μm), Shintohoku Chemical Industries Zeophil 614 (φ1.4 to 4.0 mm), Shintohoku Chemical Industries Zeophyl 1424 (φ1.0 to 1.4 mm). . The results are shown in FIG.

  As shown in FIG. 2, the cesium removal rate after immersion for 400 hours was about 90% for Tosoh mordenite 640HOA (φ13 μm), and about 65 to 70% for the other two types. Therefore, it was found that even when a bag-shaped adsorbent was used, if the immersion time was increased, the removal rate was equivalent to that obtained when zeolite was directly added to the seawater of (Test Example 1).

(Test Example 5)
A test was conducted on the effect of zeolite to suppress the migration of cesium in soil to young plants.
Cesium was added to 100 to 500 g (dry weight) of field simulated soil consisting of black soil 5, red ball soil 3 and vermiculite 2 to create a model soil of radioactive material contaminated soil. As zeolite, 0.1 to 2.5% of Zeophyl 1424 manufactured by Shin-Tohoku Chemical Industry was added to the field simulated soil, and the mixture was mixed by mixing to about 5 mm in the topsoil. Mini sunflowers, Japanese radish, and broccoli were cultivated from seeds, and the amount of cesium transferred to the plant seedlings was measured.

  Analysis of cesium in plant larvae was performed as follows. That is, the leaves and stems of each plant are collected, dried, pulverized in a mortar, and immersed in 60% nitric acid for 1 hour. Subsequently, it filtered, the filtrate was diluted and the analysis sample was adjusted and the quantity of the cesium in a sample was measured by ICP-MS.

Table 2 shows the results of measuring the effect of suppressing cesium migration to mini sunflower and kaiware radish when 2.5% of zeolite is added to the soil, compared to the case where zeolite is not added. About the mini sunflower, 10 samples were collected and measured on the 15th day of cultivation (state of 4 to 6 true leaves). As for radish radish, 14 samples were collected and measured on the 16th day of cultivation (in a state of growing about 10 cm and 2 true leaves).
Moreover, the result of having measured the addition amount of Zeophyl 1424 by Shin-Tohoku Chemical Industry and the inhibitory effect of cesium migration to broccoli is shown in FIG.

  It can be seen from Table 2 and FIG. 3 that the amount of cesium transferred to the young plant can be suppressed to about 1/10 by adding zeolite to the soil.

( Example 1 )
As a pretreatment for decontamination of contaminated soil, it was immersed in water in the presence of clay, and a study was carried out to transfer Cs in the contaminated soil to clay with higher adsorptivity. Silica sand No. 3 to which Cs was added was used as simulated contaminated sand.

<Preparation of simulated contaminated sand and migration test of Cs to bentonite>
Add cesium chloride (Kanto Chemical, cesium chloride 99.8%) to 5 g of silica sand No. 3 (particle size 0.8-5.0 mm) so that cesium becomes 2.00 ppm (0.5 ml of 20 ppm solution is added) In order to adsorb cesium well to silica sand No. 3, it was allowed to stand at room temperature for 34 days as simulated contaminated sand.
Put simulated contaminated sand in a 550 ml wide mouth screw bottle, add 200 ml of pure water, add 1-15 g of bentonite (powder) as clay mineral, cover and draw 10 times / 5 seconds circle by hand. In this way, the mixed solution which was blended with bentonite and homogenized with simulated contaminated sand was allowed to stand in a 10 ° C. water bath for 24 hours or 6 days (Test Nos. Y1 to Y4 in Table 3). For comparison, a similar test was also performed without adding bentonite (Test No. Y5 in Table 3).

<Removing silica sand>
Silica sand No. 3 was collect | recovered with the 300 micrometer mesh sieve for the said liquid mixture after standing still. The supernatant liquid obtained by centrifuging the filtrate (bentonite and pure water) was washed with silica sand on the sieve to remove the bentonite adhering to the surface, and then transferred to an aluminum dish at 80 ° C. for 2 hours. Dried. The recovered silica sand No. 3 was 4.98 g or more in any migration test, and it was confirmed that the silica sand No. 3 was recovered with a loss of less than 0.5%.
Moreover, the said supernatant liquid was sampled, it filtered with the 0.45 micrometer membrane filter, and Cs density | concentration was measured by ICP-MS. The measurement result is shown as the Cs concentration in the transition test solution in Table 3. As a result, elution of 0.01 ppm of Cs was observed only in the system to which bentonite was not added (Test No. Y5 in Table 3), but in other systems, it was below the detection limit.

<Measurement of Cs concentration remaining in silica sand (dissolution test of Cs in silica sand No. 3)>
The recovered silica sand No. 3 (4.98 to 4.99 g) was transferred to a 50 ml heat-resistant centrifuge tube (Zarstat, 50 ml self-supporting centrifuge tube), and 40 ml of 0.5M ammonium nitrate solution (Wako Pure Chemicals, ammonium nitrate 99.0%). The mixture was stirred 10 times / 5 seconds up and down by hand, and then an elution test was performed at 80 ° C. for 3 hours under a 150 prm shaking condition.
5 ml of this supernatant was sampled, the sampled solution was filtered through a 0.45 μm membrane filter, and the Cs concentration was measured by ICP-MS.

  The Cs concentration measured by ICP-MS is shown in Table 3 as the Cs concentration in the eluate.

<Calculation of residual Cs concentration in silica sand and Cs reduction rate in silica sand>
For silica sand No. 3 added and adsorbed with 2.00 ppm of Cs and silica sand No. 3 not added with Cs, prepared in <Preparation of simulated contaminated sand and test for Cs transfer to bentonite> Measurement of Cs Concentration (Cs Elution Test in Silica Sand No. 3)> The Cs concentration was measured by ICP-MC as 0.241 ppm and 0.007 ppm, respectively (Test No. in Table 3). Y8, Y9 (In Table 3, 2 digits after the decimal point are shown). If the Cs concentration originally contained in Silica Sand No. 3 is X, the Cs elution rate of both is equal,
0.241 / ((X + 2.00) × 5/40) = 0.007 / (X × 5/40). From this, the Cs concentration X originally contained in the silica sand 3 is 0.060 ppm. From these values, the elution rate of Cs from the silica sand is determined to be 0.241 / (0.06 + 2.00) × 40/5 = 0.93 (40 in the formula is 0.5 M ammonium nitrate added) The amount of the solution 5 was 93% from the amount of silica sand used in the test.

Since the Cs dissolution rate is assumed to be the same in the transition test to bentonite, the Cs concentration in the silica sand in the transition test to bentonite (Test Nos. Y1 to Y4 in Table 3) and the comparative test in which no bentonite is added The Cs concentration in the silica sand (Test No. Y5 in Table 3) is calculated as follows.
Residual Cs concentration in quartz sand (ppm) = (Cs concentration in eluate / 0.93) × (40/5)

  The test results are summarized in Table 3.

The Cs concentration of the simulated sand before the test was 2.06 ppm, and the Cs concentration of the simulated contaminated sand was 1.62 ppm when no bentonite was added, whereas the transition test was performed for 24 hours with the addition of bentonite. Furthermore, the Cs concentration in the simulated contaminated sand was 0.85 to 0.64 ppm, indicating a tendency to decrease according to the amount of bentonite added. Thereby, it was confirmed that Cs once adsorbed on the silica sand transferred to a substance having higher Cs adsorptivity through water.
In addition, even when the amount of bentonite added is 1 g, the Cs concentration in the simulated contaminated sand was further reduced to 0.44 ppm in the system in which the transition time was 6 days. It is suggested that becomes larger.

( Example 2 )
A transfer test of cesium in the soil to zeolite was performed using zeolite. As the soil, horticultural black soil (water content of 33% in a natural state) that can be obtained in large quantities was used.

<Creation of simulated contaminated soil>
Cesium chloride (Kanto Chemical; 99.8% cesium chloride) was added to 100 g of black clay (with a particle size of 2 mm or less with a 2 mm sieve) so that the cesium content would be 2.00 ppm (20.0 ppm solution added 10 ml) And what was left to stand for 14 days at room temperature in order to make cesium adsorb | suck to soil well was made into the simulation contaminated soil.

<Adsorbent>
As an adsorbent, Zeophyl 614 (φ1.4-4.0 mm) manufactured by Shin-Tohoku Chemical Industry, which is sized to 2-4 mm with a sieve, and two types of zeolite, Tosoh mordenite 640HOA (φ13 μm), and for craft use Three types of bentonite (in powder form) were tested. The amount of adsorbent used was 5 to 20 g.
The adsorbent is added by two methods, namely, the method of directly adding granules in the case of ZEOPHYL 614 and the method of adding in a bag, and in the case of mordenite 640 and bentonite for craft use. The method was carried out.
The bag-filled adsorbent was prepared by making the ultrafine fiber cloth used in Test Example 3 into a bag shape, enclosing 10 g of the adsorbent into the bag, and bending the ends 3 times and fastening them with a gem clip about every 1 cm.

<Transition test of Cs to adsorbent>
After adding 100 g of simulated contaminated soil and 200 ml of pure water to a 550 ml wide mouth screw bottle, add the adsorbent directly or in a bag, cover, and stir up and down by hand for 10 seconds. The mixed solution was allowed to stand at room temperature for 24 hours or 7 days (Test Nos. Y31 to Y39 in Table 4).
Similarly, a control example (test No. Y40) to which no adsorbent was added was tested by allowing it to stand at room temperature for 7 days.

<Removal of adsorbent>
24 hours or 7 days after the adsorbent was added, 5 ml of the supernatant of the above mixture was collected, filtered through a 0.45 μm membrane filter, and the Cs concentration was measured by ICP-MS. , Cs was not detected, and it was confirmed that Cs was not eluted. Thereafter, in the system to which zeolite was added directly, the zeolite was recovered from the test system using a sieve having a sieve size of 2 mm. The zeolite on the sieve was washed three times with the supernatant obtained by centrifuging the mixed solution of black clay and water in the filtrate, and all the black soil adhering to the zeolite was recovered on the liquid side.
In the system in which the adsorbent was added in a bag, the adsorbent was taken out by shaking the bag and pulling it up from the liquid while dropping the black soil on the bag surface.

<Measurement of Cs concentration remaining in black soil (dissolution test of Cs in black soil)>
An elution test was performed to quantify Cs remaining in the black soil. That is, weighed the recovered zeolite in the wet state, and determined the amount of water loss from the test system from the difference in weight from before the zeolite transfer test. After removing the adsorbent, the same amount of pure water was removed. The total amount of pure water was 200 ml, the same as before adsorbent addition. Next, 8 g of ammonium nitrate was added and dissolved to obtain a 0.5 M ammonium nitrate solution as a test solution.
About the said test liquid, the elution test was done on 80 degreeC * 3 hours and 150 prm shaking conditions.
5 ml of the supernatant was sampled, the sampled liquid was filtered through a 0.45 μm membrane filter, and the Cs concentration was measured by ICP-MS.

  The Cs concentration measured by ICP-MS is shown in Table 4 as the Cs concentration in the eluate.

<Calculation of residual Cs concentration in black soil and Cs reduction rate in black soil>
In the same manner as in Test Example 6, the residual Cs concentration in black soil and the Cs reduction rate in black soil were calculated. That is, in the above-described <Cs migration test to Cs adsorbent>, black soil with 2.00 ppm of Cs added and adsorbed (Test No. Y40 in Table 4) and black soil without Cs added (Test in Table 4) No. Y41), the Cs concentration was measured by ICP-MC in the same manner as in <Measurement of Cs concentration remaining in silica sand (elution test of Cs in silica sand No. 3)>. It was 041 ppm (in Test Nos. Y40 and Y41 in Table 4, up to two decimal places are shown). Assuming that the Cs concentration originally contained in the black soil is X, both Cs elution rates are equal.
0.526 / ((X + 2.00) × 100/200) = 0.041 / (X × 100/200) holds, and from this, the Cs concentration X originally contained in the black soil is calculated to be 0.17 ppm. From these values, the dissolution rate of Cs from the black soil was determined to be 0.526 / (0.17 + 2.00) × 200/100 = 0.48 (200 in the formula is 0.5M ammonium nitrate which is a test solution) From the amount of solution, 100 is the amount of black soil used in the test), it was 48%.

Since the Cs elution rate is assumed to be the same in the transfer test to the adsorbent, the Cs concentration in the black soil in the transfer test to the adsorbent (Test Nos. Y31 to Y39 in Table 4) is as follows. Is calculated as follows.
Residual Cs concentration in black soil (ppm) = (Cs concentration in eluate / 0.48) × (200/100)

  The test results are summarized in Table 4.

The Cs concentration of black soil (Y40), which is a simulated contaminated soil, was 2.17 ppm, whereas the Cs concentration in the black soil after the transition test using zeolite as an adsorbent and allowed to stand for 7 days was 1.5-1. There was a tendency to decrease to 3 ppm depending on the amount of zeolite added. (Y31-Y33)
Comparing the case where the standing time is 24 hours and 7 days in the system to which 20 g of zeolite is added, the Cs concentration in the black soil is reduced for 7 days, and the longer standing time has the effect of reducing Cs. Suggested (Y33, 34).
When Zeolite is put in a cloth bag, the Cs reduction effect is lower than when it is put directly (Comparison between Y32 and Y35), but Cs is lower than that when the standing time is shortened by increasing the standing time. It was suggested that the reduction effect increases (comparison of Y36 and Y37). The effect of reducing Cs by increasing the standing time was the same even when bentonite was used as the adsorbent (comparison of Y38 and Y39).

( Example 3 )
A transfer test of cesium in soil to ferrocyanide by ferrocyanide was conducted. As the soil, horticultural black soil (water content of 33% in a natural state) that can be obtained in large quantities was used.

<Creation of simulated contaminated soil>
Put 5g of black clay (with a particle size of 2mm or less with a 2mm sieve) into a 50ml heat-resistant centrifuge tube (Zarstat, 50ml self-supporting centrifuge tube), add cesium chloride (Kanto Chemical; 99.8% cesium chloride), A simulated contaminated soil was added at 2.00 ppm (0.5 ml of a 20.0 ppm solution) and left for 337 days at room temperature in order to adsorb cesium well to the soil.

<Preparation of non-woven fabric carrying ferrocyanide>
To 100 ml of a 2.5% solution of potassium ferrocyanide (potassium hexacyanoiron II acid trihydrate, reagent grade Kanto Chemical Co., Ltd.) on a non-woven fabric (BEMCOT M-1 size 14.5 × 15.5 cm, weight 0.64 g) After soaking at 80 ° C. for 5 minutes, the cloth was squeezed to remove excess solution and dried at 60 ° C. for about 2 hours. The weight of the cloth at this time was 0.71 g.
Add about 6 ml of a 9% solution of ferric chloride (iron (III) chloride hexahydrate reagent special grade Wako Pure Chemical Industries, Ltd.) until the entire fabric turns amber and ferrocyanate on the nonwoven fabric. Iron (Prussian blue) was produced and dried in a wet state at 60 ° C. for about 2 hours. The weight of the cloth at this time was 1.05 g.
Next, rinse with 100 ml of pure water three times to wash off excess ferrocyanide, then immerse in 100 ml of a 15% solution of sodium chloride for 15 minutes to fix the ferrocyanide and fix with 150 ml of pure water. After washing with water once to remove excess salt, it was dried at 60 ° C. for about 2 hours to obtain a non-woven fabric carrying iron ferrocyanide. The weight of the cloth at this time was 0.70 g.

<Transition test of Cs to iron ferrocyanide-supporting nonwoven fabric>
To 5 g of simulated contaminated soil (created in 0046), add 0.7 g of the ferrocyanide-supporting nonwoven fabric and 40 ml of pure water prepared above, cover, and stir up and down by hand 10 times / 5 seconds. The well mixed liquid was allowed to stand at room temperature for 24 hours.

<Removal of adsorbent>
24 hours after the adsorbent was added, 5 ml of the supernatant of the above mixture was collected, filtered through a 0.45 μm membrane filter, and the Cs concentration was measured by ICP-MS, but Cs was detected. It was confirmed that Cs was not eluted. Thereafter, the iron ferrocyanide-supporting non-woven fabric was shaken and pulled up from the mixed solution while removing black soil on the cloth surface. Next, the cloth was squeezed and the liquid mixed with black clay was returned to the test system.

<Measurement of Cs concentration remaining in black soil (dissolution test of Cs in black soil)>
An elution test was performed to quantify Cs remaining in the black soil. That is, the collected wet ferrocyanide-supporting nonwoven fabric was weighed, and the weight difference between the ferrous ferrocyanide-supported nonwoven fabric before the transfer test was determined as the amount of water loss from the test system. After subtracting water, ammonium nitrate was added so that the test solution was a 0.5 M ammonium nitrate solution.
It was 3.43g when the collect | recovered iron ferrocyanide carrying | support nonwoven fabric was weighed.
From this, the loss of water from the test system was calculated to be 2.73 g, and this amount was subtracted from the initial amount of pure water added of 40 ml, and the amount of ammonium nitrate added was 1.49 g.
After capping and stirring well by hand 10 times / 5 seconds up and down, the elution test was conducted for 3 hours under conditions of shaking at 80 ° C. and 150 rpm, and 1 ml of the supernatant was sampled. The sampled solution was filtered through a 0.45 μm membrane filter, and the Cs concentration was analyzed by ICP-MS.
Thereafter, the recovered ferricyanide-carrying nonwoven fabric was dried, weighed after removing water, and found to be 1.92 g. From this, it was confirmed that the actual loss from the test solution was 1.22 g of soil and 1.51 g of water.

  The Cs concentration measured by ICP-MS is shown in Table 5 as the Cs concentration in the eluate.

<Calculation of residual Cs concentration in black soil and Cs reduction rate in black soil>
In the same manner as in Test Example 6, the residual Cs concentration in black soil and the Cs reduction rate in black soil were calculated. That is, in the above <Cs migration test to Cs adsorbent>, black soil added with 2.00 ppm of Cs and adsorbed (Test No. Y56 in Table 5) and black soil without Cs added (Test in Table 5) No. Y57), the Cs concentration was measured by ICP-MC in the same manner as in <Measurement of Cs concentration remaining in silica sand (elution test of Cs in silica sand No. 3)>. It was 025 ppm (in Test Nos. Y56 and Y57 in Table 5, two digits after the decimal point are shown). Assuming that the Cs concentration originally contained in the black soil is X, both Cs elution rates are equal.
0.156 / ((X + 2.00) × 5/40) = 0.025 / (X × 5/40) holds, and from this, the Cs concentration X originally contained in the black soil is calculated as 0.38 ppm. From these values, the elution rate of Cs from black soil was determined to be 0.156 / (0.38 + 2.00) × 40/5 = 0.52 (40 in the formula is 0.5 M ammonium nitrate which is a test solution) The amount of the solution 5 was 52% from the amount of the black soil subjected to the test.

Since the Cs elution rate is assumed to be the same in the transfer test to the adsorbent, the Cs concentration in the black soil (Test No. Y55 in Table 5) in the transfer test to the adsorbent is as follows. Calculated.
Residual Cs concentration in black soil (ppm) = (Cs concentration in eluate / 0.52) × (40−1.51) / (5-1.22)
(In the formula, 40-1.51 is an amount in consideration of the loss of the 0.5M ammonium nitrate solution, which is the test solution, and 5-1.22 is an amount in consideration of the loss of black soil used in the test.)

  The test results are summarized in Table 5.

While the Cs concentration of black soil (Y56), which is a simulated contaminated soil, was 2.38 ppm, the Cs concentration in the black soil after the migration test was left to stand for 1 day using an iron ferrocyanide-supporting nonwoven fabric as the adsorbent. It was 1.75 ppm, and the tendency for Cs density | concentration in black clay to reduce was seen by the ferrocyanide carrying | support nonwoven fabric (Y55).
Note that Prussian blue, which is an iron ferrocyanide, is an insoluble cyano complex that is insoluble in water and is generally used as a blue pigment in paints, inks, crayons, and the like. Cyanide ions are strongly bound to iron atoms, so they are not easily released, have low toxicity, and can be used orally under the control of doctors. However, in heat and high alkali conditions, there is no concern that cyanide may be liberated in some cases, so when using Prussian blue, avoid using it in a long-term open system and make it a manageable closed system. It seems desirable to use.

Claims (1)

Adsorbing cesium, a sheet-like adsorbent comprising a particulate adsorbent or ferric ferrocyanide or zeolite consisting of bentonite or zeolite from carrying nonwoven, is contacted through the water in the cesium contaminated soil land or temporary storage, stirred after,
The contaminated soil, by leaving more than 24 hours while adding the powder particulate adsorbent or sheet-like adsorbent to the water, the cesium in the soil, adsorbed onto a particulate adsorbent or sheet-like adsorbents in Rukoto, to reduce the cesium soil壌中,
A method for decontamination of cesium- contaminated soil, wherein the granular adsorbent adsorbed with cesium or the sheet adsorbent is treated as radioactive waste.

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