JP2020163265A - Classification cleaning treatment method of contaminated soil - Google Patents

Abstract

To improve characteristics of recycled soil obtained by a classification cleaning treatment.SOLUTION: At the time of start of a classification cleaning treatment of removal soil to which a modifier containing a polymer water-absorbing resin is added, for example, a swelling inhibitor such as calcium chloride or ferrous sulfate heptahydrate is added to the removal soil. Thereby, an amount of the polymer water-absorbing resin remaining in purified soil Sp purified by the classification cleaning treatment can be reduced. The classification cleaning treatment can achieve passage of more soil particles of less than 75 μm, and accordingly the amount of the soil particles of less than 75 μm contained in purified soil Sp can be reduced. Specifically, an amount of Cs having a high possibility that a comparatively large amount of Cs is adsorbed in the soil particles of less than 75 μm can be reduced, and accordingly a dose of the purified soil Sp can be lowered. Thereby, characteristics of the purified soil Sp can be improved.SELECTED DRAWING: Figure 11

Description

The present invention relates to a method for classifying and cleaning contaminated soil, for example, a method for classifying and cleaning for reusing contaminated soil that has been intermediately stored.

The removed soil generated by decontamination and the like is crushed and separated in order to be stored and stored for about 30 years. In this separation treatment, for example, by adding a modifier of about 3 wt% of the target soil, the highly viscous soil is modified into a sand shape to facilitate separation from tree branches, leaves, etc. Modification treatment is applied to improve the processing capacity. This modifier contains a trace amount of a super absorbent polymer, a high-performance flocculant, and the like.

In order to reduce the volume of soil to be used for final disposal of the removed soil after such separation treatment, adjustments have been made for reuse, such as reusing low-dose soil as embankment material and roadbed. ing. As a treatment method for this reuse, in order to reduce the concentration of radioactive cesium, the removed soil is separated into coarse particles and fine particles by a classification washing treatment, and the amount of radioactive cesium adsorbed is relatively large. Fine particles (generally, for example, soil particles that have passed through a sieve of less than 75 μm) are separated and extracted, while coarse particles are reused as a material to suppress public exposure during reuse. Is being considered as one of the processing methods.

For example, in Patent Document 1, regarding a paper diaper using a super absorbent polymer, the used paper diaper material is recycled and the pulp component and non-woven fabric / vinyl used in the paper diaper are collected so that they can be reused. The technology is disclosed.

Japanese Unexamined Patent Publication No. 2000-84533

However, since the removed soil after the separation treatment contains a polymer water-absorbent resin, although the content is not high, the polymer water-absorbent resin in the removed soil undergoes water-containing expansion during the classification cleaning treatment, resulting in a sieve. Because it causes clogging without passing through the soil, swollen high-molecular-weight water-absorbent resin and soil particles of less than 75 μm do not pass through the sieve and are contained in a large amount in the recycled soil (hereinafter referred to as regenerated soil). It ends up. As described above, since the superabsorbent polymer is contained, the water content is always high, and there is a risk that the characteristics of the regenerated soil may deteriorate, such as absorbing water and expanding.

In addition, since radioactive cesium is likely to be adsorbed and accumulated in a relatively large amount on soil particles of less than 75 μm, soil particles of less than 75 μm do not pass through the sieve and are contained in a large amount in the regenerated soil, so that they are regenerated together with the modifier. Radioactive cesium may be left in the soil, which may increase the dose of regenerated soil.

The present invention has been made from the above-mentioned technical background, and an object of the present invention is to improve the characteristics of regenerated soil.

In order to solve the above problems, the method for classifying and cleaning contaminated soil according to claim 1 applies a swelling inhibitor to the contaminated soil at the start of the classifying cleaning process for contaminated soil containing a polymer water-absorbent resin. It is characterized by being added.

The invention according to claim 2 is the invention according to claim 1, wherein by changing the addition amount of the swelling inhibitor, the amount of soil particles passing through the sieve and the sieve can be passed through the classification cleaning treatment. It is characterized in that the amount of soil particles remaining is controlled.

The invention according to claim 3 is the invention according to claim 1 or 2, wherein the contaminated soil is the removed soil, and the removed soil is added to the removed soil having a relatively high concentration of pollutants. It is characterized in that the amount of the swelling inhibitor added is larger than the amount of the swelling inhibitor added to the removed soil having a relatively low concentration of pollutants.

The invention according to claim 4 is characterized in that, in the invention according to any one of claims 1 to 3, the swelling inhibitor contains calcium chloride or ferrous sulfate heptahydrate.

The invention according to claim 5 is characterized in that, in the invention according to claim 1, the swelling inhibitor contains calcium chloride, and the amount of calcium chloride added is 0.25 to 5 wt%. ..

The invention according to claim 6 is characterized in that, in the invention according to claim 5, the amount of calcium chloride added is 1 to 5 wt%.

The invention according to claim 7 is the invention according to claim 1, wherein the swelling inhibitor contains ferrous sulfate heptahydrate, and the amount of the ferrous sulfate heptahydrate added is 0. It is characterized by being 1 to 5 wt%.

The invention according to claim 8 is characterized in that, in the invention according to claim 7, the amount of the ferrous sulfate heptahydrate added is 0.5 to 3 wt%.

The invention according to claim 9 is the invention according to claim 3, wherein the swelling inhibitor contains calcium chloride, and the amount of calcium chloride added to the removed soil having a relatively low pollutant concentration is It is 0.25 to 1 wt%, and the amount of calcium chloride added to the removed soil having a relatively high pollutant concentration is 1 to 5 wt%.

The invention according to claim 10 is the invention according to claim 3, wherein the swelling inhibitor contains ferrous sulfate heptahydrate, and sulfuric acid is added to the removed soil having a relatively low concentration of pollutants. The amount of ferrous heptahydrate added is 0.1 to 0.5 wt%, and the amount of ferrous sulfate heptahydrate added to the removed soil having a relatively high concentration of contaminants is It is characterized by being 0.5 to 3 wt%.

According to the present invention, it is possible to improve the characteristics of the regenerated soil obtained by the classification washing treatment.

It is a conceptual diagram showing the flow of treatment of removed soil, which is being studied in the national government. It is a conceptual diagram of a main part of a treatment facility for removed soil in an interim storage facility. It is explanatory drawing of an example of a receiving sorting facility. It is explanatory drawing for demonstrating the principle of the classification cleaning process. (A) is a plan view of a main part of a superabsorbent polymer resin, and (b) is a diagram showing a chemical formula of the superabsorbent polymer resin of FIG. 5 (a). (A) is a diagram showing the behavior of COO groups constituting the superabsorbent polymer resin, and (b) is a plan view of a main part of the superabsorbent polymer resin before and after water absorption. (A) is a diagram showing the relationship between the addition rate of the modifier and the water content of the residue remaining without passing through the 75 μm sieve, and (b) is the addition rate of calcium chloride and the residue remaining without passing through the 75 μm sieve. The figure which shows the relationship with the water content of a minute, (c) is the figure which shows the relationship between the addition rate of ferrous sulfate heptahydrate and the water content of the residue which does not pass through a 75 μm sieve. It is the figure which showed the result which can be seen from FIG. 7 (b) and (c) collectively. It is a schematic block diagram of an example of the classification cleaning facility which concerns on one Embodiment of this invention. It is a schematic block diagram of another example of the classification cleaning facility which concerns on one Embodiment of this invention. It is a flow chart which shows the classification washing method of the removed soil which concerns on one Embodiment of this invention. (A) and (b) are diagrams showing the amount of soil (dry weight) that has passed through a 75 μm sieve when calcium chloride and ferrous sulfate heptahydrate are used as swelling inhibitors, respectively. It is a figure which showed the result which can be seen from FIG.

Hereinafter, embodiments as an example of the present invention will be described in detail with reference to the drawings. In addition, in the drawing for demonstrating the embodiment, the same constituent elements are in principle given the same reference numerals, and the repeated description thereof will be omitted. In addition, here, soil containing radioactive substances is exemplified as soil containing pollutants. In this case, the pollutant concentration of soil containing pollutants is the radiation concentration of soil containing radioactive substances.

(First Embodiment)

FIG. 1 is a conceptual diagram showing the flow of treatment of removed soil, which is being studied in the national government.

According to the flow of this treatment, the removed soil and the like are classified into soils S1 to S4 according to the radiation cesium (Cs) concentration (pollutant concentration, radiation concentration), and are temporarily stored in the intermediate storage facility Fi. During this period, volume reduction treatment is performed and the purified product is reused as a recycled material. In addition, the concentrate produced by volume reduction treatment will be disposed of at the final disposal site. Soil S1 has a Cs concentration of 8000 Bq / kg or less, soil S2 has a Cs concentration of 8000 to 20000 Bq / kg or less, soil S3 has a Cs concentration of 200,000 to 80,000 Bq / kg or less, and soil S4 has a Cs concentration of 80000 Bq / kg or more. is there.

According to this plan, the soils S1 to S4 are transported to the receiving and sorting facility Fs of the interim storage facility Fi, and are subjected to sorting treatment to remove foreign substances in the soil. In this separation treatment, as described above, a modifier containing a super absorbent polymer or the like is added to the soil. A part of the soils S1 and S2 after the separation treatment is recovered as regenerated soil after being appropriately subjected to radioactivity attenuation treatment and the like. Further, the soil S3 after the separation treatment is subjected to the classification cleaning treatment at the classification cleaning facility Fc. In this classification cleaning treatment, for example, what remains as a group of soil particles of 75 μm or more is recovered as regenerated soil. On the other hand, in the above-mentioned classification cleaning treatment, for example, the concentrate extracted as a group of soil particles of less than 75 μm is heat-treated at the heat treatment facility Ft to become slag or a calcined product, and the cleaning treatment facility after the heat treatment. It is divided into those that are subjected to cleaning treatment at Fw and are finally disposed of at the final disposal site.

FIG. 2 is a conceptual diagram of a main part of a soil removal facility in an interim storage facility.

In the interim storage facility, a receiving sorting facility Fs and a classification cleaning facility Fc are installed. At the receiving and sorting facility Fs, foreign substances such as combustibles are removed by performing a sorting treatment on the received removed soil. In the classification cleaning facility Fc, by performing the classification cleaning treatment on the removed soil that has been subjected to the classification treatment, for example, gravel having a particle size of about 2 mm or more, sand having a particle size of about 2 to 0.075 mm, etc. And, it is classified into silt, clay, etc. with a particle size of about 0.075 mm or less.

FIG. 3 is an explanatory diagram of an example of a receiving and sorting facility.

In the receiving and sorting facility Fs, the unloading facility Fu, the bag breaking facility Fb, and the sorting facility Fss are installed in order along the moving direction of the removed soil. The removed soil is placed on a truck TR or the like in a state of being housed in a packaging material CB such as a flexible container bag or the like, and is carried to an unloading facility Fu.

The unloading facility Fu is a facility that receives the packaging material CB carried by a truck TR or the like and transfers it to the belt conveyor BC1 by a crane CR or the like. At this stage, the removed soil is contained in the packaging material CB and is difficult to scatter to the outside. Therefore, the unloading facility Fu is installed in a simple building having a roof or the like.

The bag-breaking facility Fb is a facility that breaks the packaging material CB carried by the belt conveyor BC1 with the bag-breaking machine BM. The bag-breaking facility Fb and the subsequent sorting facility Fss are installed in a building having a roof, a peripheral wall, and the like so that dust due to the removed soil does not spread to the surroundings.

The sorting facility Fss is a facility that removes foreign substances such as combustibles from the soil removed after the bag breaking process and sorts them. For example, two sieving machines SV1 and SV2 arranged in series are connected to each part 3 It has two belt conveyors BC2 and BC4. That is, the removed soil or the like discharged from the bag breaking machine BM is stored in the sieve machine SV1 in the previous stage through the belt conveyor BC2. The removed soil from which the foreign matter FM1 such as the packaging material residue has been removed by the sieving machine SV1 is housed in the sieving machine SV2 at the subsequent stage through the belt conveyor BC3. The removed soil from which foreign substances FM2 such as tree branches, leaves, roots, etc. have been removed by this sieve SV2 is sent to the subsequent stage as the removed soil after sorting through the belt conveyor BC4.

By the way, in this sorting facility Fss, as described above, by adding and mixing a modifier of about 3 wt% of the target soil to the removed soil on the belt conveyor BC3 in the front stage of the sieve SV2, the highly viscous removed soil is sanded. It is modified into a shape to facilitate the separation of tree branches, leaves, roots, etc., and for example, the removed soil having a particle size of 20 mm or less is efficiently recovered.

As the modifier, for example, a material having a composition in which a silica-based, gypsum-based or zeolite-based material is used as a base material and a small amount of a super absorbent polymer, a high-performance flocculant or the like is added is often used. Therefore, the superabsorbent polymer compounded in the modifier is contained in a small amount in the removed soil after the separation.

However, if the removed soil contains a superabsorbent polymer, the superabsorbent polymer in the removed soil absorbs and expands during the classification cleaning treatment after the separation treatment, so that the resin does not pass through the sieve and is clogged. Therefore, the swollen super absorbent polymer and soil particles of less than 75 μm do not pass through the sieve and are contained in a large amount in the regenerated soil. As described above, since the superabsorbent polymer is contained, the water content is always high, and there is a risk that the characteristics of the regenerated soil may deteriorate, such as absorbing water and expanding. In addition, since radioactive cesium is likely to be adsorbed and accumulated in a relatively large amount on soil particles of less than 75 μm, soil particles of less than 75 μm do not pass through the sieve and are contained in a large amount in the regenerated soil, so that they are regenerated together with the modifier. Radioactive cesium may be left in the soil, which may increase the dose of regenerated soil. Therefore, there is a risk that the characteristics of the regenerated soil (particle size characteristics, water content, radiation concentration depending on the amount of Cs contained) will deteriorate.

Therefore, in the present embodiment, at the start of the classification cleaning treatment of the removed soil after separation, a swelling inhibitor is added to the removed soil as an additive for suppressing (controlling) the water-containing swelling property of the superabsorbent polymer. .. As a result, the swelling of the superabsorbent polymer resin in the removed soil can be suppressed or prevented, so that clogging of the sieve due to the expanded superabsorbent polymer resin can be reduced or eliminated. Therefore, the amount of the polymer water-absorbent resin contained in the residual removed soil can be reduced, so that the characteristics (particle size characteristics, water content, radiation concentration depending on the content of Cs) of the remaining removed soil (that is, regenerated soil) are improved. Can be made to.

Further, by adjusting the amount of the swelling inhibitor added to the removed soil, the state of clogging of the sieve due to the swelling of the polymer water-absorbent resin contained in the removed soil can be adjusted, so that the sieve of 75 μm The amount of a group of soil particles (removed soil) that passes through the sieve and the amount of a group of soil particles (removed soil) that remain without passing through a 75 μm sieve can be controlled.

First, the classification cleaning process will be described with reference to FIG. FIG. 4 is an explanatory diagram for explaining the principle of the classification cleaning process. In FIG. 4, different hatches are attached to the fine particle Pf, the pollutant Ph, and the like in order to make the drawing easier to see. The pollutant Ph and the like are heavy metal elements such as arsenic and radioactive substances.

The left side of FIG. 4 shows the removed soil Sc in which the coarse particle Pc, the fine particle Pf, the pollutant Ph, and the like are mixed. In the classification cleaning treatment, the removed soil Sc is subjected to cleaning treatment and polishing treatment using a machine, and the particle size is classified to separate the particle size classification on which pollutants Ph and the like are adsorbed, or This is a treatment method in which a pollutant Ph or the like is dissolved in a cleaning liquid and the pollutant Ph or the like is extracted from the removed soil Sc. By this classification washing treatment, the purified soil Sp in the upper right of FIG. 4 can be obtained, and the dehydrated cake Sd (concentration of contamination) in the lower right of FIG. 4 can be extracted. The purified soil Sp is soil with a specified radiation dose or less.

Next, the principle of swelling of the super absorbent polymer described above and the swelling inhibitor that suppresses the swelling will be described with reference to FIGS. 5 and 6. 5 (a) is a plan view of a main part of the super absorbent polymer, FIG. 5 (b) is a diagram showing the chemical formula of the superabsorbent polymer of FIG. 5 (a), and FIG. 6 (a) is a polymer absorbent polymer. The figure which shows the behavior of the COO group which constitutes a resin, FIG. 6B is a plan view of the main part of a super absorbent polymer before and after water absorption. The left side of the arrow in FIG. 6B indicates before water absorption, and the right side of the arrow indicates after water absorption.

As shown in FIG. 5A, the super absorbent polymer has a network-like structure. When this polymer water-absorbent resin comes into contact with water, as shown in FIG. 5 (b), Na ions coordinated to the COO groups constituting the polymer water-absorbent resin dissolve into the water and the COO group becomes negative. It becomes the basis. Then, as shown in FIG. 6 (a), the COO groups adjacent to each other repel each other to swell the network, and as shown in FIG. 6 (b), water is taken into the network. This is the principle of swelling.

Therefore, when an environment is created in which more polyvalent cations have a higher adsorption power to the COO group than Na ions, the polyvalent cations are coordinated again to the COO group, and the taken-in water is discharged. Swelling performance is suppressed. Therefore, by using a polyvalent cation reagent having a high ionization tendency and a higher affinity for the COO group as a swelling inhibitor, the superabsorbent polymer water-absorbent resin that has absorbed water and swelled can be dehydrated.

As a specific example of such a swelling inhibitor, for example, calcium chloride can be used. In the case of calcium chloride, it can be procured at low cost. However, when calcium chloride is used, acceptance is restricted as waste containing chloride when a group of soil particles smaller than 75 μm (removed soil) recovered by dehydration is disposed of at a final disposal site, etc. May occur. In that case, for example, ferrous sulfate heptahydrate can be used as a swelling inhibitor containing no chloride ion. The swelling inhibitor may be any material that exhibits the principle of swelling inhibition, and is not limited to calcium chloride or ferrous sulfate heptahydrate, and can be changed in various ways.

Next, the water content of the residual portion of the removed soil that has not passed through the 75 μm sieve due to the classification washing treatment will be described with reference to FIGS. 7 and 8. FIG. 7 (a) shows the relationship between the addition rate of the modifier and the water content of the residual residue that did not pass through the 75 μm sieve, and FIG. 7 (b) shows the addition rate of calcium chloride and the 75 μm sieve. The figure showing the relationship between the water content of the residue remaining without passing through, FIG. 7 (c) shows the relationship between the addition rate of ferrous sulfate heptahydrate and the water content of the residue remaining without passing through the 75 μm sieve. FIG. 8 is a diagram showing the results that can be seen from FIGS. 7 (b) and 7 (c).

The amount of the residual component remaining without passing through the 75 μm sieve by the classification cleaning treatment depends on the water-containing swelling property of the superabsorbent polymer contained in the modifier. That is, as a result of the superabsorbent polymer swelling and the water content of the removed soil that has been classified and washed without using a swelling inhibitor, the residual content that does not pass through the 75 μm sieve is larger than that of the soil particles alone. Will also increase. In fact, as shown in FIG. 7 (a), as the addition rate of the modifier added to the removed soil increases, the water content of the residual component that does not pass through the 75 μm sieve increases, and the water content in the residual component increases. There is a residual condition. For example, when 3 wt% of the modifier is added to the removed soil that has passed through the 2 mm sieve and no swelling inhibitor is added, the water content of the residual residue that has not passed through the 75 μm sieve has reached 54%. ..

On the other hand, according to the study of the inventor, when the swelling inhibitor was added to the removed soil at the start of the classification washing treatment, it passed through a 75 μm sieve as shown in FIGS. 7 (b) and 7 (c). It was possible to reduce the water content of the remaining residue.

That is, as shown in FIGS. 7 (b) and 8 when calcium chloride is used as the swelling inhibitor, the swelling property of the residual residue that does not pass through the 75 μm sieve is suppressed (water content is controlled). The preferable amount of the swelling inhibitor added is, for example, 0.25 or more and 5 wt% or less, and in particular, the water content can be reduced by 23 points by adding 1.0 wt% of the swelling inhibitor, and no swelling inhibitor is used. The water content could be reduced to 31% with respect to (water content of 54%).

Further, as shown in FIGS. 7C and 8, when ferrous sulfate heptahydrate is used as the swelling inhibitor, the swelling property of the residual residue that does not pass through the 75 μm sieve is suppressed (moisture content). The amount of the swelling inhibitor added is preferably 0.1 or more and 5 wt% or less, and in particular, the water content is reduced by 25 points by adding 1.5 wt% or 3 wt% of the swelling inhibitor. It was possible to reduce the water content to 29% compared to the case where the swelling inhibitor was not used (water content was 54%).

By using the swelling inhibitor in this way, the characteristics of the removed soil (regenerated soil) after the classification washing treatment can be improved. For example, when the residual residue that does not pass through the 75 μm sieve is reused as an embankment or the like, the swelling property can be suppressed, so that draining can be facilitated, and the efficiency and trafficability of the compaction work, etc. Can be improved.

Next, an example of the classification cleaning facility of the present embodiment will be described with reference to FIGS. 9 and 10. 9 and 10 are schematic configuration diagrams of an example of a classification cleaning facility according to the present embodiment. In FIGS. 9 and 10, the solid line arrow indicates the flow of pollutants and the like, the broken line arrow indicates the drainage flow, and the alternate long and short dash line arrow indicates the flow of the removed soil. The dotted arrow in FIG. 9 indicates the flow of wash water.

As shown in FIG. 9, the classification cleaning facility Fc includes a cleaning treatment device WM, a classification treatment device CM, a separation treatment device DM, a dehydration treatment device DHM, and a wastewater treatment device DWM.

The cleaning processing apparatus WM is composed of, for example, a drum washer. This cleaning treatment device WM is a device that performs cleaning treatment and polishing treatment on the removed soil Sc contained in the drum D by rotating the drum D while sprinkling water in the drum D. In the present embodiment, for example, the above-mentioned swelling inhibitor is put into the drum D of the cleaning treatment apparatus WM.

The classification processing device CM is a device that performs classification processing, and for example, a vibrating sieve (not shown) and a cyclone are integrally provided. The muddy water sent from the cleaning treatment device WM is centrifuged by the cyclone of the classification treatment device CM. This separated heavy soil portion is placed on a vibrating sieve of the classification treatment device CM and drained. That is, the earth and sand that has fallen on the net of the vibrating sieve is drained while moving laterally on the net, and eventually spills from the edge of the net. Further, the water drained by the vibrating sieve is mixed with the muddy water sent one after another from the cleaning treatment apparatus WM and supplied to the cyclone again. Here, for example, a group of soil particles having a size of less than 75 μm is extracted and sent to the subsequent stage, while a group of soil particles having a size of 75 μm or more is obtained as purified soil Sp. Instead of the drum washer and the vibrating sieve, for example, a trommel or a high mesh separator may be used. Further, in order to improve the classification cleaning performance, for example, a bubble floating type separation device or a gravity type separation device may be used as the classification processing device CM.

The separation processing apparatus DM is composed of, for example, a thickener. The separation processing device DM is a device that separates solid particles in muddy water sent from the classification processing device CM as slurry. The solid particles settle on the bottom of the treatment tank T of the separation treatment apparatus DM, and the supernatant liquid is stored in the treatment tank T.

The dehydration processing apparatus DHM is composed of, for example, a filter press. In the dehydration processing apparatus DHM, the mud-like fine particles are filled in a bag-shaped filter and dehydrated by applying a high pressure, and the dehydrated cake Sd is taken out. For example, a belt press may be used instead of the filter press.

The wastewater treatment device DWM is a device that purifies the wastewater (including pollutants) sent from the dehydration treatment device DHM. The purified water purified by the wastewater treatment device DWM is sent to the cleaning treatment device WM and the classification treatment device CM again.

The configuration of the classification cleaning facility Fc shown in FIG. 10 is almost the same as that in FIG. Here, the drainage flow is slightly different. That is, the washing water obtained by the separation treatment device DM is supplied to the cleaning treatment device WM and the classification treatment device CM, and the waste water (including pollutants) obtained by the dehydration treatment device DHM is supplied to the separation treatment device DM. It has become like.

Next, an example of the classification cleaning method of the removed soil of the present embodiment will be described with reference to FIG. 9 along with the flow chart of FIG. FIG. 11 is a flow chart showing a method for classifying and cleaning the removed soil according to the present embodiment.

First, the removed soil Sc, water, and the swelling inhibitor are put into the drum D of the cleaning treatment device WM, and then the drum D is rotated to mix and stir to wash and polish the removed soil Sc in the drum D (FIG. 11 steps 100).

Subsequently, the removed soil (muddy water) after the washing treatment is sent to the classification treatment device CM, and the classification treatment is performed to extract a group of soil particles (fine particle Pf (see FIG. 4)) having a size of less than 75 μm. A group of soil particles (coarse particle Pc (see FIG. 4)) having a thickness of 75 μm or more is taken out as a residual component (step 101 in FIG. 11). After the conformity with the standard is confirmed by the purification confirmation survey, this residual amount becomes the purified soil Sp (regenerated soil) (step 102 in FIG. 11).

After that, the fine-grained Pf (see FIG. 4) that has passed through the classification treatment device CM and has concentrated contamination is coagulated and precipitated in the separation treatment device DM, and then dehydrated in the dehydration treatment device DHM (step 103 in FIG. 11). ), It is discharged as a dehydrated cake Sd. Since the dewatered cake Sd is highly contaminated, it is treated as contaminated soil and carried out to a retreated contaminated soil treatment facility or the like (step 104 in FIG. 11).

As described above, in the present embodiment, the swelling of the superabsorbent polymer contained in the removed soil is suppressed by adding the swelling inhibitor to the removed soil at the start of the classification cleaning treatment of the removed soil as described above. Alternatively, since it can be prevented, clogging of the sieve due to the expanded polymer water-absorbent resin can be reduced or eliminated.

Therefore, the amount of the modifier (polymer water-absorbent resin) remaining in the purified soil Sp can be reduced, so that the characteristics (for example, particle size characteristics and water content) of the purified soil Sp (regenerated soil) can be improved. Can be improved.

In addition, since clogging of the sieve is reduced or eliminated during the classification cleaning treatment, more soil particles of less than 75 μm can be passed through the classification cleaning treatment, so that the soil is included in the purified soil Sp (regenerated soil). The amount of soil particles smaller than 75 μm can be reduced. That is, since the amount of Cs that is likely to be adsorbed and accumulated in a relatively large amount on soil particles of less than 75 μm can be reduced, the dose of purified soil Sp can be reduced. Therefore, it is possible to improve the characteristics of the purified soil Sp (for example, reduce the radiation concentration depending on the amount of Cs contained).

(Second Embodiment)

Generally, it is known that a large amount of Cs is adsorbed on soil particles passing through a 75 μm sieve, but according to the above embodiment, the amount of the swelling inhibitor added is adjusted in the process of the classification cleaning treatment. Then, since the state of clogging of the sieve due to the swelling of the polymer water-absorbent resin contained in the removed soil can be adjusted, the amount of soil passing through the 75 μm sieve can be controlled. That is, by adjusting the amount of the swelling inhibitor added, the amount of Cs contained in the residual soil (regenerated soil) that does not pass through the 75 μm sieve can be adjusted.

Here, FIGS. 12 (a) and 12 (b) show the amount of soil (dry weight) that passed through a 75 μm sieve when calcium chloride and ferrous sulfate heptahydrate were used as swelling inhibitors, respectively. Shown. Further, FIG. 13 is a diagram showing the results obtained from FIG. 12 collectively.

As shown in FIGS. 12A and 13, when calcium chloride is used as the swelling inhibitor, when the amount of the swelling inhibitor added is, for example, 0.25 or more and less than 1 wt%, it passes through a 75 μm sieve. The amount of soil to be added is relatively small, and in particular, the amount of the swelling inhibitor added is 0.75 wt%, and the amount of soil passing through the 75 μm sieve is the minimum (56% reduction). In this case, since the residual amount remaining without passing through the 75 μm sieve increases, the effect of reducing the amount of Cs in the regenerated soil is suppressed.

Further, when calcium chloride is used as the swelling inhibitor, if the amount of the swelling inhibitor added is, for example, 1 or more and less than 5 wt%, the amount of soil passing through the 75 μm sieve becomes relatively large, and in particular, swelling. The amount of the inhibitor added is 3 wt%, and the amount of soil passing through the 75 μm sieve is the maximum (24% increase). In this case, the residual amount that does not pass through the 75 μm sieve is reduced, so that the effect of reducing the amount of Cs in the regenerated soil is promoted.

On the other hand, as shown in FIGS. 12B and 13, when ferrous sulfate heptahydrate is used as the swelling inhibitor, the amount of the swelling inhibitor added is, for example, 0.1 or more, 0. When it is less than 5 wt%, the amount of soil passing through the 75 μm sieve is relatively small, and in particular, when the amount of the swelling inhibitor added is 0.1 wt%, the amount of soil passing through the 75 μm sieve is the minimum (38% reduction). It becomes. In this case, since the residual amount remaining without passing through the 75 μm sieve increases, the effect of reducing the amount of Cs in the regenerated soil is suppressed.

Further, when ferrous sulfate heptahydrate is used as the swelling inhibitor, when the amount of the swelling inhibitor added is, for example, 1.5 or more and 3 wt% or less, the amount of soil passing through the 75 μm sieve is relative. In particular, the amount of the swelling inhibitor added is 1.5 wt%, and the amount of soil passing through the 75 μm sieve is the maximum (up 108%). In this case, the residual amount that does not pass through the 75 μm sieve is reduced, so that the effect of reducing the amount of Cs in the regenerated soil is promoted.

In this way, the amount of the swelling inhibitor added when the amount of soil passing through the 75 μm sieve is smaller or larger than that of the soil without the swelling inhibitor added (additive amount = 0 wt%). Although it can be discriminated, it can be understood that the amount of the swelling inhibitor added is a boundary value that suppresses or promotes the amount of Cs in the regenerated soil.

Since this and the premise of reuse of soil containing Cs is not to exceed 8000 Bq / kg, in the present embodiment, swelling is suppressed in soil of 8000 Bq / kg or less and soil exceeding 8000 Bq / kg. Try to change the amount of the agent added. This makes it possible to carry out rational purification treatment. An application example will be described below for each case.

First, a method of adding a swelling inhibitor used when the target of the classification cleaning treatment is soil having a relatively high Cs concentration (soils S2, S3, etc. in FIG. 1) will be described.

In this case, when calcium chloride is used as the swelling inhibitor, the amount of calcium chloride added is, for example, in the range of 1 or more and 5 wt% or less. When ferrous sulfate heptahydrate is used as the swelling inhibitor, the amount added thereof is, for example, in the range of 0.5 or more and 3 wt% or less. As a result, it is possible to increase the number of soil particles having a size of less than 75 μm that pass through the sieve during the classification cleaning treatment, so that the Cs concentration of the regenerated soil (residual residue that does not pass through the 75 μm sieve) can be reduced.

Next, a method of adding the swelling inhibitor used when the target of the classification cleaning treatment is soil having a relatively low Cs concentration (soil S1 or the like in FIG. 1) will be described.

In this case, when calcium chloride is used as the swelling inhibitor, the amount of calcium chloride added is, for example, in the range of 0.25 or more and less than 1 wt%. When ferrous sulfate heptahydrate is used as the swelling inhibitor, the amount added thereof is, for example, in the range of 0.1 or more and less than 0.5 wt%. As a result, it is possible to reduce the amount of soil particles having a size of less than 75 μm that passes through the sieve during the classification washing process, so that the amount of regenerated soil (residual residue that does not pass through the 75 μm sieve) can be increased.

(Third Embodiment)

In the first embodiment described above, the case where the soil S3 (see FIG. 1) is used as the target removed soil has been described. Here, although the soils S1 and S2 are not washed, they are carried to the interim storage facility Fi (see FIG. 1), the modifier is added, and the foreign matter is removed, and then the soil is stored in the interim storage facility Fi. Is being done. In addition, it is legally required that this soil be excavated within 30 years and reused or transported to a final disposal site. It is also assumed that the soils S1 and S2 also have swelling properties due to the influence of water during storage and contact with water after excavation.

Therefore, in the present embodiment, even in the soils S1 and S2 that are not subjected to the classification cleaning treatment, the swelling inhibitor is added and stirred after the soils S1 and S2 are dug out. As a result, swelling in soils S1 and S2 can be suppressed. In addition, the characteristics of soils S1 and S2 (for example, particle size characteristics and water content) can be improved.

Although the invention made by the present inventor has been specifically described above based on the embodiments, the embodiments disclosed in the present specification are exemplary in all respects and are limited to the disclosed technology. is not. That is, the technical scope of the present invention is not limitedly interpreted based on the description in the above-described embodiment, but should be interpreted according to the description of the claims, and the scope of claims. All changes are included as long as they do not deviate from the description technology and the technology equivalent to the above and the gist of the claims.

In the above description, the case where the classification cleaning treatment method for contaminated soil of the present invention is applied to the classification cleaning treatment method for removed soil has been described, but for example, even in the treatment of industrial waste such as dehydrated sludge, high molecular weight water absorption. Since a treatment agent containing a resin may be used, it can be applied as a measure for suppressing swelling in that case.

Fi Intermediate storage facility Fs receiving and sorting facility Fc classification washing facility BM bag breaking machine SV1, SV2 sieving machine BC1 to BC4 Belt conveyor WM washing treatment device CM classification treatment device DM separation treatment device DHM dehydration treatment device DWM wastewater treatment device S1 to S4 soil Sc-removed soil Sp Purified soil Sd Dewatered cake Pf Fine grain Pc Coarse grain Ph Contaminant

Claims (10)

A method for classifying and cleaning contaminated soil, which comprises adding a swelling inhibitor to the contaminated soil at the start of the classification and cleaning treatment of contaminated soil containing a polymer water-absorbent resin. The first aspect of claim 1, wherein the amount of soil particles that pass through the sieve and the amount of soil particles that do not pass through the sieve and remain in the classification cleaning treatment are controlled by changing the amount of the swelling inhibitor added. How to classify and clean contaminated soil. The contaminated soil is the removed soil, and the amount of the swelling inhibitor added to the removed soil having a relatively high pollutant concentration is added to the removed soil having a relatively low pollutant concentration. The method for classifying and cleaning contaminated soil according to claim 1 or 2, wherein the amount is larger than the amount of the swelling inhibitor added. The method for classifying and cleaning contaminated soil according to any one of claims 1 to 3, wherein the swelling inhibitor contains calcium chloride or ferrous sulfate heptahydrate. The method for classifying and cleaning contaminated soil according to claim 1, wherein the swelling inhibitor contains calcium chloride, and the amount of calcium chloride added is 0.25 to 5 wt%. The method for classifying and cleaning contaminated soil according to claim 5, wherein the amount of calcium chloride added is 1 to 5 wt%. The contaminated soil according to claim 1, wherein the swelling inhibitor contains ferrous sulfate heptahydrate, and the amount of the ferrous sulfate heptahydrate added is 0.1 to 5 wt%. Classification cleaning method. The method for classifying and cleaning contaminated soil according to claim 7, wherein the amount of ferrous sulfate heptahydrate added is 0.5 to 3 wt%. The swelling inhibitor contains calcium chloride, and the amount of calcium chloride added to the removed soil having a relatively low pollutant concentration is 0.25 to 1 wt%, and the removal having a relatively high pollutant concentration. The method for classifying and cleaning contaminated soil according to claim 3, wherein the amount of calcium chloride added to the soil is 1 to 5 wt%. The swelling inhibitor contains ferrous sulfate heptahydrate, and the amount of ferrous sulfate heptahydrate added to the removed soil having a relatively low concentration of pollutants is 0.1 to 0.5 wt. The contamination according to claim 3, wherein the amount of ferrous sulfate heptahydrate added to the removed soil having a relatively high concentration of pollutants is 0.5 to 3 wt%. Classification cleaning method of soil.

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