JP2014100700A - Method for decontaminating contaminated soil - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for decontaminating contaminated soil capable of abating, simply and inexpensively without being encumbered with land limitations, harmful substance contents at least within a contaminated soil surface layer portion.SOLUTION: The provided method includes an aqueous solution spraying step S1 of spraying an aqueous deuterated sulfuric acid solution onto a contaminated soil wherein at least the surface layer portion thereof is contaminated with harmful substances, a water spraying step S2 of spraying water onto the surface layer portion sprayed with the aqueous deuterated sulfuric acid solution, and a drying step S3 of drying the surface layer portion sprayed with the water. Harmful substances are precipitated from surface layer to deep layer portions of the contaminated soil by repeatedly executing the water spray step S2 and drying step S3.

Description

  The present invention relates to a decontamination method for contaminated soil.

  As a decontamination technique for radioactive substances, particularly radioactive cesium in farmland soil, the one described in Non-Patent Document 1 is known. For example, techniques such as stripping topsoil and stirring and removing soil with water are listed. However, these methods are difficult to apply to land such as forests where it is difficult to remove the soil, and large machinery such as heavy machinery is required for the removal work, resulting in high costs. Furthermore, the problem of processing the removed contaminated soil also arises.

Ministry of Agriculture, Forestry and Fisheries, September 14, 2011 “About radioactive material removal technology (decontamination technology) of farmland soil” http: // www. s. affrc. go. jp / docs / press / 110914

  In view of such a conventional situation, an object of the present invention is to provide a decontamination method for contaminated soil that reduces the amount of harmful substances in the surface layer of the contaminated soil easily and inexpensively without being restricted by land.

  In order to achieve the above object, the decontamination method for contaminated soil according to the present invention is characterized by an aqueous solution spraying step in which a deuterated sulfuric acid aqueous solution is sprayed on contaminated soil having at least a surface layer contaminated with harmful substances, the deuterated sulfuric acid aqueous solution Spraying water on the surface layer portion sprayed, and drying step for drying the surface layer portion sprayed with water, and repeatedly performing the water spraying step and the drying step to remove the harmful substances from the contaminated soil. The purpose is to settle from the surface layer portion to the deep layer portion.

According to the above configuration, the deuterated sulfuric acid aqueous solution is first sprayed on the contaminated soil surface layer, and then water is sprayed on the surface layer portion on which the deuterated sulfuric acid aqueous solution is sprayed. Here, a single grain of the soil aggregates due to the aggregation effect of the deuterated sulfuric acid aqueous solution, and water is vaporized by a drying process after water spraying, resulting in a gap in the soil. Although water vaporizes (evaporates), deuterium sulfuric acid (D ₂ SO ₄ ) does not vaporize, and deuterated sulfuric acid that has not contributed to the agglomeration effect remains in the surface layer portion. Therefore, when water is sprayed again, the remaining deuterated sulfuric acid moves to the lower layer through the gap generated by the previous step together with the harmful substances, and the lower layer similarly causes single-grain agglomeration. And by making it dry, water evaporates and a clearance gap arises also in a lower layer. Therefore, by repeating the watering process and the drying process, the remaining deuterated sulfuric acid (D ₂ SO ₄ ) is gradually moved to the lower layer together with the harmful substances and promotes the agglomeration of the soil. The gap can be extended to the deep layer. Thus, since it is only necessary to repeat the watering step and the drying step after the aqueous solution spraying step, the decontamination work can be easily performed without being restricted by the land, and the surface layer portion can be removed without removing the soil. The amount of harmful substances can be reduced.

Here, in the aqueous solution spraying step, it is desirable to spray the deuterated sulfuric acid so that the deuterated sulfuric acid is 0.0003 volume% or more and 0.002 volume% or less with respect to 1 m ^{3 of the} contaminated soil. When the deuterated sulfuric acid is less than 0.0003% by volume with respect to the soil, the agglomeration of the soil due to the above-described aggregation effect is not sufficiently promoted. On the other hand, even if deuterated sulfuric acid exceeds 0.002% by volume with respect to the soil, the agglomeration effect is not improved so much and the cost becomes high.

  In the aqueous solution spraying step, the deuterated sulfuric acid aqueous solution may be sprayed in a heated state. According to experiments by the inventors, it has been found that when the deuterated sulfuric acid aqueous solution is sprayed in a heated state, more harmful substances move (outflow) from the contaminated soil than at room temperature. This is considered that the coagulation effect of the deuterated sulfuric acid aqueous solution is promoted as compared to room temperature. Therefore, according to the said structure, it becomes possible to move more harmful substances to a lower layer with the residual deuterium sulfuric acid.

  Furthermore, in the watering step, the water is preferably hot water. According to the experiments by the inventors, it has been found that, by heating the soil sprayed with the deuterated sulfuric acid aqueous solution, more harmful substances move (run out) from the contaminated soil. Therefore, according to the above configuration, by spraying hot water after spraying the deuterated sulfuric acid aqueous solution, more harmful substances can be moved to the lower layer by the remaining deuterated sulfuric acid.

  Moreover, after the said drying process, it is good to have further the aqueous solution re-spreading process of spraying the said deuterated sulfuric acid aqueous solution again on the dried surface layer part. As described above, deuterated sulfuric acid that has not contributed to the aggregation effect does not vaporize and remains in the surface layer portion, but the residual amount gradually decreases. Therefore, by spraying the deuterated sulfuric acid aqueous solution again after the drying step, the deuterated sulfuric acid is replenished, and further, soil aggregation in the deep layer portion is promoted, and harmful substances can be settled deeper.

  The aqueous solution spraying step may be performed before snowfall, and the water spraying step immediately after the aqueous solution spraying step may be performed by snow melting of snow accumulated on the surface layer portion. In this case, it is not necessary to artificially sprinkle water after spraying the deuterated sulfuric acid aqueous solution, and the soil agglomeration effect works gradually as in the case of watering several times, so that the permeability is improved.

  Moreover, you may make it perform the said watering process with the rain water which rained on the said surface layer part. There is no need for artificial watering, the work load can be reduced, and decontamination can be performed more easily. Moreover, if the drying process is natural drying, the operation is further simplified.

  The harmful substance is, for example, radioactive cesium. Because of the above-mentioned heavy water aggregation effect, the radioactive cesium in the surface layer can be settled into the deep layer together with water, so that the air dose can be easily reduced without removing the soil.

  In order to achieve the above object, another feature of the decontamination method for contaminated soil according to the present invention includes a mixing step of mixing contaminated soil contaminated with a hazardous substance and a deuterated sulfuric acid aqueous solution, and passing this mixture for a predetermined time. A dehydration step of dehydrating afterwards, and separating the harmful substances extracted from the contaminated soil into the deuterated sulfuric acid aqueous solution from the mixture by the dehydration step.

  According to the inventors' experiments, it was found that in a mixture in which contaminated soil and deuterated sulfuric acid aqueous solution are mixed, most of the harmful substances move (outflow) from the contaminated soil to the deuterated sulfuric acid aqueous solution after a predetermined time. . This is considered that a gap is generated in the soil by mixing the contaminated soil and the deuterated sulfuric acid aqueous solution, and harmful substances are flowing into the aqueous solution through the gap. Therefore, according to the said structure, a hazardous | toxic substance can be isolate | separated and collect | recovered from a contaminated soil via deuterated sulfuric acid aqueous solution, and a contaminated soil can be wash | cleaned efficiently.

  In this case, it is desirable to further include a heating step of heating the mixture for the predetermined time after the mixing step. According to the inventors' experiments, it has been found that more harmful substances move (outflow) at higher temperatures than at normal temperatures. Therefore, according to the above configuration, more harmful substances can be separated, and the cleaning efficiency (decontamination efficiency) is improved.

  According to the feature of the decontamination method for contaminated soil according to the present invention, it is possible to reduce the amount of harmful substances at least on the surface layer of the contaminated soil easily and inexpensively without being restricted by land.

  Other objects, configurations, and effects of the present invention will become apparent from the following embodiments of the present invention.

It is a flowchart which shows the process of the decontamination method of the contaminated soil which concerns on this invention. It is a figure explaining the state of the soil in each process, (a) is a solution spraying process, (b) is a watering process, (c) is a drying process, (d) is a watering process again after (c). The state, (e), shows the state after the drying step after (d). It is a graph which shows the relationship between the heavy water density | concentration in the closest distance (3.2A) between water molecule oxygen atoms, and intensity | strength. It is a figure explaining the aggregation effect in the soil by a deuterated sulfuric acid solution, (a) shows before spraying of a deuterated sulfuric acid solution, (b) shows the state after spraying of a deuterated sulfuric acid solution. It is a graph which shows the result of a particle size test. It is a graph which shows the result of having compared the radiation dose in the test soil of the normal temperature which added the deuterated sulfuric acid aqueous solution which concerns on this invention, and the heated test soil, (a) is a comparison result of soil, (b) is The comparison result of a liquid component is shown. It is a graph which shows the time change of the radiation dose of the liquid component extracted from the test soil of the state heated by adding deuterated sulfuric acid aqueous solution, (a) shows cesium 134, (b) shows cesium 137. It is a graph which shows the measurement result of the radiation dose of the liquid component extracted from the test soil heated by adding water and the deuterated sulfuric acid aqueous solution, and (a) is cesium 134 per 1 g of soil, (b ) Shows cesium 137 per gram of soil, (c) shows cesium 134 per ml of liquid component, and (d) shows cesium 137 per ml of liquid component. It is a graph which shows the result which carried out the relative comparison of the radiation dose of the liquid component extracted from the test soil which added water and heated, and the test soil which added deuterated sulfuric acid aqueous solution, and (a) is cesium 134, (b) is The result of cesium 137 is shown. It is a graph which shows the result of having compared the radiation dose in the normal temperature test soil which added water, and the normal temperature test soil which added the deuterated sulfuric acid aqueous solution, (a) is a comparison result of soil, (b) is a liquid component. A comparison result is shown. It is a graph which shows the result which carried out the relative comparison of the radiation dose in the test soil heated by adding dilute sulfuric acid and the deuterated sulfuric acid aqueous solution, (a) is a comparison result of soil, (b) is a liquid component. The comparison result of is shown.

Next, the present invention will be described in more detail with reference to the accompanying drawings as appropriate.
[Outline of contaminated soil]
In the decontamination method for contaminated soil according to the present invention, for example, as shown in FIG. 2 (a), radioactive cesium Cs as a harmful substance distributed on the surface layer 2 (surface GL) of the soil 1 is converted into the surface layer 2. Without removing the soil, the water 1 is allowed to settle from the surface layer portion 2 to the deep layer portion 3 through the water W. In addition, the deep layer part 3 points out the part deeper than crop and planting depth, for example.

[Outline of decontamination process]
As shown in FIGS. 1 and 2, the decontamination method includes an aqueous solution spraying step S1 in which the surface layer 2 is sprayed with the deuterated sulfuric acid aqueous solution AL on the surface layer 2 of the soil 1 contaminated with radioactive cesium Cs, and the deuterated sulfuric acid. It consists of a water spraying step S2 for spraying water W onto the surface layer portion 2 sprayed with the aqueous solution AL, and a drying step S3 for drying the surface layer portion 2 sprayed with water W. The watering step S2 is performed, for example, artificially with an appropriate period. Moreover, drying process S3 is performed by natural drying.

[Production method of deuterated sulfuric acid aqueous solution]
In the present embodiment, the above-described deuterated sulfuric acid aqueous solution AL is prepared, for example, by mixing deuterated sulfuric acid: water at a volume ratio of 1: 9. Moreover, the pH of this deuterated sulfuric acid aqueous solution is adjusted within the range of 1.0-2.5. In the soil after the sprinkling step, the deuterium concentration per 1 m ^{3 of} soil can be 0.0003 vol% to 0.002 vol%. In addition, you may dilute to 30 times or more and 100 times or less with water so that it may become the content rate with respect to the soil mentioned later, for example.

[Effect of deuterated sulfuric acid aqueous solution]
Here, FIG. 3 shows the logarithm of the relationship between the concentration of heavy water and the strength at the closest distance (3.2 A) between water molecules and oxygen atoms. As shown in the figure, within the range of 0.002% by volume of heavy water concentration 0.0003% by volume or more with respect to the soil 1 m ^3, whose distance between oxygen atoms close interaction between water molecules (intermolecular force ) Is considered strong. If the amount is less than 0.0003% by volume, the interaction is lowered, and the aggregation effect described later is hardly exhibited. On the other hand, even if it exceeds 0.002% by volume, there is no significant difference in the interaction and there is no significant difference in the aggregation effect. FIG. 3 is a graph relating to the concentration of heavy water (D ₂ O), but it is estimated that the same applies to deuterated sulfuric acid (D ₂ SO ₄ ).

[Aggregating effect]
By the way, in the soil 1, as shown to Fig.4 (a), the single grain 1a and the aggregate 1b exist. In addition, the aggregate 1b is obtained by solidifying the single grain 1a. In the soil, the single grains 1a accumulate and concentrate over time, etc., and there are few gaps and the water permeability and air permeability are reduced (single grain structure). In this state, rainwater or the like does not penetrate into the deep layer portion 3 of the soil 1, and the state where the radioactive cesium Cs is distributed in the surface layer portion 2 continues.

  When the deuterated sulfuric acid aqueous solution AL is sprayed on the surface layer 2 in such soil, as shown in FIG. 4 (b), the single particles 1a are attracted to each other and aggregate due to the interaction between the water molecules described above. Grains 1b are formed. By this agglomeration, as shown in the figure, gaps 4 are generated between the agglomerates 1b to improve water permeability and air permeability (aggregate structure). As a result, radioactive cesium Cs settles (moves) from the surface layer portion 2 to the deep layer portion 3. Therefore, the radioactive cesium Cs of the surface layer part 2 of the soil 1 decreases, and the air dose (radiation dose) in the vicinity of the ground surface can be reduced.

[Verification experiment]
The inventor conducted various experiments in order to verify the above effects.
1) Water permeability test The test soil was sprayed with 0.5 l / m ^{2 of} an aqueous solution of deuterated sulfuric acid diluted 30-fold with water, and the same amount of water was sprayed onto the soil. PH and water permeability (mm / h) were measured for a certain period of time with a portion and a non-sprayed portion.

  As shown in Table 1, in the state where water was sprayed after one month from spraying, the water permeability improved in both the sprayed part and the non-sprayed part, but the sprayed part has higher water permeability. This is presumably because soil aggregates due to the agglomeration effect of deuterated sulfuric acid described above and many gaps are formed.

  In addition, in the dry state without watering after 2 months from spraying, the water permeability was significantly improved in both the sprayed part and the non-sprayed part compared to after January, but the sprayed part was more water-permeable. Is expensive. This is because water content is high because the moisture content is originally low in the dry state, and the sprayed part is further aggregated due to the agglomeration effect of deuterated sulfuric acid and there are many gaps, so that water permeability is further increased. Will be higher.

2) Grain size test (soil investigation)
A soil sample before treatment in which a deuterated sulfuric acid aqueous solution is not sprayed on the soil, and a soil sample 1 after sprayed in which a deuterium sulfate aqueous solution having a dilution ratio of 50 times and 100 times is sprayed on a volume (water + soil sample) 1000 cc , 2 were each subjected to a particle size test. The particle size test (precipitation analysis) is a method performed based on the sedimentation theory (Stokes), and measures the amount of sedimentation from time to time after dispersing the sample and water. The vertical axis represents the transmission mass percentage (%), and the horizontal axis represents the particle size (mm).

  As shown in FIG. 5, in the soil sample before the treatment, about 40% of soil particles having a particle size of 0.008 mm or less were present, and a large amount of clay having a particle size of less than 0.005 mm was present. On the other hand, in the soil samples sprayed with the deuterated sulfuric acid aqueous solution, the soil particles having a particle size of 0.008 mm or less are greatly reduced to about 5%, and the clay content having a particle size of less than 0.005 mm is 3 to 4%. It became about. And the soil particle in the range whose particle size is 0.008 mm-0.1 mm increased significantly. From this, it is considered that by spraying the deuterated sulfuric acid aqueous solution, the particles having a smaller particle size are aggregated by the aggregation effect of the deuterated sulfuric acid aqueous solution to become particles having a larger particle size, and a gap is generated between the particles. . In addition, there is no big difference by a dilution rate from a test result, and it is more economical to use the deuterated sulfuric acid aqueous solution with a high dilution rate.

[Detailed description of decontamination process]
Next, each step of the decontamination method will be described in detail with reference to FIG.
First, as shown in FIG. 2A, for example, 50 cc of deuterated sulfuric acid aqueous solution is sprayed per 1 m ³ of soil, and deuterated sulfuric acid DS is distributed in the upper layer portion 2a of the surface layer portion 2 (aqueous solution spraying step S1). Next, as shown in FIG. 5B, water W is sprayed on the surface layer portion 2 (watering step S2). Let the watering amount be the amount which becomes the saturated state of water of the surface layer part 2 (water content 100%). Thereby, the deuterium concentration per 1 m ^{3 of} soil is set to 0.0003 vol% to 0.002 vol%, and the upper layer portion 2a of the surface layer portion 2 is shown in FIG. Such agglomeration occurs.

  Next, as shown in FIG.2 (c), the surface layer part 2 is naturally dried (drying process (S3)). Thereby, the water W is vaporized and a gap is generated in the upper layer portion 2a. On the other hand, the deuterated sulfuric acid DS that did not contribute to the aggregation effect remains in the upper layer portion 2a without being vaporized. Then, as shown in FIG. 4D, water is sprayed again to bring the moisture in the surface layer portion 2 into a saturated state (water content 100%). As a result, the remaining deuterated sulfuric acid DS penetrates into the lower layer 2b and promotes soil agglomeration as in the previous watering step. Moreover, radioactive cesium Cs settles in the lower layer part 2b like the figure (e) through the clearance gap | interval produced | generated by the water sprinkling process S2 and the drying process S3 with the water W. FIG. Thereafter, by drying again, a gap is also generated in the lower layer portion 2b due to the aggregation effect of the deuterated sulfuric acid DS. In this way, by repeating the watering step and the drying step, the deuterated sulfuric acid DS gradually permeates toward the deep layer portion 3 and creates a gap. And radioactive cesium Cs settles from the surface layer part 2 to the deep layer part 3 through the clearance gap formed sequentially.

Next, a second embodiment according to the present invention will be described. In the following embodiments, similar members are denoted by the same reference numerals.
In said 1st embodiment, normal temperature deuterated sulfuric acid aqueous solution was used for the aqueous solution spraying process, and normal temperature water was used for the watering process. However, in the second embodiment, the deuterated sulfuric acid aqueous solution heated in the aqueous solution spraying process is used, and hot water is used in the sprinkling process. Thereby, a hazardous | toxic substance can be moved to a soil lower layer more efficiently.

Here, the inventor conducted the following tests to confirm the usefulness of the present invention.
[Test 1]
Add the deuterated sulfuric acid aqueous solution of the present application to the test soil, warm it at room temperature (Example B) and about 90 ° C. (Example A) for 120 minutes, and then separate the soil and liquid components, It was measured. For the measurement (analysis method) of radiation dose, gamma-ray spectrometry using a germanium semiconductor detector of the Ministry of Education, Culture, Sports, Science and Technology Radioactivity Measurement Method Series 7 was used. FIG. 6 shows the results of relative comparisons based on the large measured values. As shown in the figure, the radiation amount in the soil is lower and the radiation amount of the liquid component is higher in the heated state than at normal temperature. As a result, it can be presumed that in the heated state, aggregation due to the aggregation effect is promoted, and more harmful substances can move to the lower layer.

[Test 2]
The deuterated sulfuric acid aqueous solution of the present application was added to the test soil and heated at about 90 ° C. for 60 minutes and 120 minutes, after which the soil and liquid components were separated, and the radiation dose was measured in the same manner as described above. FIG. 7 shows the measurement results of radiation doses of cesium 134 and 137 per 1 ml of liquid. The values shown in the figure show relative values based on the radiation dose of the test soil. Since this value indicates the relative value of the radiation dose of the liquid component, it can be regarded as the decontamination rate of the contaminated soil. For reference, the results at room temperature for 10 minutes are also shown. As shown in the figure, the relative value increases with time. Therefore, by spraying the hot water after spraying the heated deuterated sulfuric acid aqueous solution, the warmed state can be continued, and the soil agglomeration is further promoted, thereby making it more harmful. It can be assumed that the substance can move to the lower layer.

[Test 3]
What added each deuterated sulfuric acid aqueous solution and water of this application to test soil was heated at about 90 degreeC for 120 minutes, after that, it isolate | separated into soil and a liquid component, and measured the radiation dose similarly to the above. The measurement results are shown in FIG. As shown in the figure, the heated deuterated sulfuric acid aqueous solution has a lower radiation dose from the soil and a higher radiation dose from the liquid than water alone. Moreover, the comparison result with the water of the radiation dose of cesium 134 and 137 per 1 ml of liquid after progress for 120 minutes is shown in FIG. The values shown in the figure show relative values based on the radiation dose of the test soil. As shown in the figure, the radiation dose of the deuterated sulfuric acid aqueous solution is higher than that of water. From these results, it was confirmed that more cesium (hazardous substance) can be moved to the lower layer by spraying the deuterated sulfuric acid aqueous solution.

[Test 4]
The test 3 (FIG. 9) was a comparison between the deuterated sulfuric acid aqueous solution and water in a heated state, but the same test was performed at room temperature. The result is shown in FIG. The value shown in the figure is a relative value based on a large measured value. As shown in the figure, even at room temperature, the deuterated sulfuric acid aqueous solution has a lower radiation dose from the soil and a higher radiation dose from the liquid than water alone. In other words, even at room temperature, deuterated sulfuric acid aqueous solution can move more harmful substances to the lower soil layer than water.

[Test 5]
Although the above tests 2 to 4 were a comparison with water, a comparison was made with dilute sulfuric acid having a pH equivalent to that of the deuterated sulfuric acid aqueous solution of the present application (about 4.3). In this test, heating was performed at about 95 ° C. for 120 minutes. The result is shown in FIG. In this figure, the same relative values as in FIG. 10 are used. As shown in the figure, the amount of radiation from the soil and the amount of radiation from the liquid are higher in the deuterated sulfuric acid aqueous solution than in the dilute sulfuric acid. That is, it can be seen that the deuterated sulfuric acid aqueous solution can move pollutants to the lower soil layer more efficiently than dilute sulfuric acid.

  By the way, in said 1st and 2nd embodiment, the example which spreads deuterated sulfuric acid aqueous solution and sprinkles water on the soil of a natural state was demonstrated. However, the present invention is not limited to this, and even in contaminated soil from which the surface layer portion of the contaminated soil has been removed and isolated by decontamination work, in the same manner as in the above embodiment, the deuterated sulfuric acid aqueous solution is sprayed and sprinkled to contaminate harmful substances. It can be separated from the soil. In such a case, since the contaminated soil is isolated, for example, the contaminated soil can be heated without heating the deuterated sulfuric acid aqueous solution to be sprayed and the water to be sprinkled. Even in this case, similarly to the second embodiment, harmful substances can be removed more efficiently than at normal temperature.

  However, in the first and second embodiments, it takes time to spread (permeate) deuterated sulfuric acid throughout the contaminated soil. Therefore, in the third embodiment, the contaminated soil and the deuterated sulfuric acid aqueous solution are mixed, and the mixture is dehydrated after a predetermined time. Since the soil and the deuterated sulfuric acid aqueous solution are mixed (stirred), the deuterated sulfuric acid can be spread over the entire soil in a shorter time than in the above embodiments in which the deuterated sulfuric acid aqueous solution is sprayed on the soil. Therefore, as shown in each test result, harmful substances can be extracted from the contaminated soil in a short time, and a large amount of contaminated soil can be treated. The pH of the deuterated sulfuric acid aqueous solution in the third embodiment is preferably 1.0 or more and 5.0 or less. If it is in this numerical range, the effect similar to said each embodiment can be acquired in a short time. More preferably, the pH of the deuterated sulfuric acid aqueous solution is 1.0 or more and 3.0 or less.

  As a third embodiment, for example, a deuterated sulfuric acid aqueous solution (for example, in the range of pH = 1.0 to 3.0) and contaminated soil of each of the above embodiments and a contaminated soil are put into a container such as a tank, Heat. Thereafter, the mixture is pressurized and dehydrated to separate the soil and liquid components. As shown in the above tests 1 to 4, since the pollutant (cesium) moves from the contaminated soil to the liquid component, harmful substances are removed (separated) from the contaminated soil by the dehydration process. In this way, by mixing and treating the contaminated soil and the deuterated sulfuric acid aqueous solution, it is not necessary to repeat watering and drying, and a large amount of contaminated soil can be decontaminated in a short time. In addition, although it is possible to process a mixture at normal temperature without heating, as shown in the said test 1, the extraction efficiency of a harmful substance improves by heating (high temperature).

Finally, the possibilities of yet another embodiment of the present invention will be described.
In the first and second embodiments, as shown in FIG. 1, after the aqueous solution spraying step S1, the watering step S2 and the drying step S3 were repeated. However, as shown by the alternate long and short dash line in the figure, an aqueous solution respraying step S4 may be provided after the drying step S3. By providing the aqueous solution respreading step S4, deuterated sulfuric acid in the surface layer portion 2 that is decreased by repeatedly performing the watering step S2 and the drying step S3 can be supplemented, and further the soil agglomeration in the deep layer portion Can be promoted. In addition, what is necessary is just to perform aqueous solution re-spreading process S4, observing the state of soil etc. suitably.

  In said 1st embodiment, watering process S2 was performed by artificial watering. However, it is not limited to artificial watering, and rain may be used. Further, the aqueous solution spraying step may be performed before snowfall, and the water spraying step S2 immediately after the aqueous solution spraying step S1 may be performed by snow melting. As a result, the work load is reduced. Furthermore, when snowmelt is used, the occurrence of snowmelt differs depending on the day or time, so that the soil cohesion effect works gradually and the permeability is improved in the same manner as when water is sprayed several times.

  Moreover, in said 1st, 2nd embodiment, although drying process S3 was performed by natural drying, it can also be performed artificially. However, the above embodiment is excellent in that the work load increases.

  In each of the above embodiments, radioactive cesium has been described as an example of a harmful substance. However, the present invention is not limited to this, and other radioactive substances can also be applied. Further, not only radioactive substances but also substances such as heavy metals such as cadmium, chromium and lead are applicable.

  In the first and second embodiments, the deuterated sulfuric acid aqueous solution was prepared by mixing deuterated sulfuric acid: water at a volume ratio of 1: 9. However, the deuterated sulfuric acid aqueous solution is not limited to this mixing ratio, and may be adjusted so that the deuterated sulfuric acid is 0.0003 vol% or more and 0.002 vol% or less with respect to the contaminated soil. Similarly, the dilution factor and the application amount may be appropriately set so as to be in the above numerical range.

  The present invention can be used as a decontamination method for soil contaminated with harmful substances such as radioactive cesium, without being limited to the use and type of land such as farmland, parks, and forests. Moreover, it can utilize also with respect to the contaminated soil removed from each above-mentioned land.

1: soil, 1a: single grain, 1b: aggregate, 2: surface layer part, 3: deep layer part, 4: gap, AL: deuterated sulfuric acid aqueous solution, DS: deuterated sulfuric acid, Cs: radioactive cesium (toxic substance), GL: ground surface, W: water

Claims (10)

An aqueous solution spraying process in which a deuterated sulfuric acid aqueous solution is sprayed on contaminated soil with at least the surface layer contaminated with harmful substances,
A watering step of spraying water on a surface layer portion sprayed with the deuterated sulfuric acid aqueous solution;
Having a drying step of drying the surface layer portion to which the water has been dispersed;
A decontamination method for contaminated soil in which the harmful substances are settled from a surface layer portion to a deep layer portion of the contaminated soil by repeatedly performing the watering step and the drying step. Decontamination method of contaminated soil according to claim 1, wherein the deuterium sulfate to spray the deuterium aqueous sulfuric acid solution so that the contaminated soil 1 m ³ 0.0003 vol% 0.002% by volume or less with respect. The decontamination method for contaminated soil according to claim 1 or 2, wherein in the aqueous solution spraying step, the deuterated sulfuric acid aqueous solution is sprayed in a heated state. The decontamination method for contaminated soil according to claim 3, wherein in the watering step, the water is hot water. The decontamination method for contaminated soil according to any one of claims 1 to 4, further comprising an aqueous solution respraying step of spraying the deuterated sulfuric acid aqueous solution again on the dried surface layer portion after the drying step. The decontamination method for contaminated soil according to any one of claims 1, 2, and 5, wherein the aqueous solution spraying step is performed before snowfall, and the water spraying step immediately after the aqueous solution spraying step is performed by thawing the snow accumulated on the surface layer portion. . The decontamination method for contaminated soil according to any one of claims 1, 2, and 5, wherein the watering step is performed using rainwater that has fallen on the surface layer. The method for decontamination of contaminated soil according to any one of claims 1 to 7, wherein the harmful substance is radioactive cesium. A mixing step of mixing contaminated soil contaminated with harmful substances and deuterated sulfuric acid aqueous solution;
Having a dehydration step of dehydrating the mixture after a predetermined time;
A decontamination method for contaminated soil, wherein a harmful substance flowing out from the contaminated soil into the deuterated sulfuric acid aqueous solution by the dehydration step is separated from the mixture. The decontamination method for contaminated soil according to claim 9, further comprising a heating step of heating the mixture for the predetermined time after the mixing step.

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