JP7217581B2 - Method for classifying and cleaning polluted soil - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for classifying and washing contaminated soil, and for example, to a method for classifying and washing for reuse of contaminated soil that has been intermediately stored.

The removed soil generated by decontamination, etc. is subjected to crushing, sorting, etc. in order to store it for about 30 years. In this sorting process, for example, by adding a modifier of about 3 wt% of the target soil, the highly viscous soil is modified into a sandy state to make it easier to separate from tree branches and leaves. A modification process is applied to improve the processing capacity. This modifier contains a very small amount of a high-molecular-weight water-absorbing resin, a high-performance flocculant, and the like.

In order to reduce the volume of the removed soil after such sorting and disposal, adjustments are made for reuse, such as reusing soil with low radiation doses as red bean paste for embankment materials and roadbeds. 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 classification and washing, and the amount of radioactive cesium adsorbed is relatively large. To reduce public exposure during reuse by separating and extracting fine particles (generally, for example, soil particles that have passed through a sieve of less than 75 μm) and reusing coarse particles as materials. is considered as one of the treatment methods.

In addition, for example, in Patent Document 1, regarding paper diapers using high-molecular water-absorbing resin, recycling treatment of used paper diaper materials and recovery of pulp components, non-woven fabrics, and vinyl used in paper diapers so that they can be reused. technology is disclosed.

JP-A-2000-84533

However, since the removed soil after the sorting process contains high-molecular-weight water-absorbing resin, although the content is not large, during the classification and washing process, the high-molecular-weight water-absorbing resin in the removed soil swells as it absorbs water and sieves. Since clogging occurs without passing through the sieve, the swollen polymer water-absorbing resin and soil particles of less than 75 μm do not pass through the sieve, and are contained in large amounts in the soil to be reused (hereinafter referred to as reclaimed soil). end up As described above, since the polymer water-absorbent resin is contained, the water content is always high, and there is a possibility that the properties of the reclaimed soil may deteriorate, such as swelling due to absorption of water.

In addition, since there is a high possibility that radioactive cesium will be adsorbed and accumulated in soil particles of less than 75 μm in relatively large amounts, soil particles of less than 75 μm do not pass through the sieve and are contained in the reclaimed soil in large amounts, so that it can be regenerated together with the reforming material. Radioactive cesium may be left in the soil, potentially increasing the dose of reclaimed soil.

The present invention has been made in view of the above technical background, and aims to improve the characteristics of reclaimed soil.

In order to solve the above problems, the method for classifying and washing contaminated soil according to claim 1 of the present invention is a classifying and washing method for classifying and washing contaminated soil containing a polymer water absorbent resin, At the start of the classification and washing process, a swelling inhibitor is added to the contaminated soil, the swelling inhibitor contains ferrous sulfate heptahydrate, and the added amount of the ferrous sulfate heptahydrate is 0.5. It is characterized by being 5 to 3 wt%.

The invention according to claim 2 is based on the invention according to claim 1 , wherein the amount of soil particles passing through the sieve and the amount of soil particles passing through the sieve in the classification and washing process are changed by changing the addition amount of the swelling inhibitor. It is characterized by controlling the amount of residual soil particles.

ADVANTAGE OF THE INVENTION According to this invention, it becomes possible to improve the characteristic of the reclaimed soil obtained by the classification washing process.

FIG. 2 is a conceptual diagram showing the flow of treatment of removed soil, which is being studied by the national government, etc. FIG. FIG. 2 is a conceptual diagram of the main part of the removed soil processing facility in the interim storage facility; It is an explanatory diagram of an example of a receiving and sorting facility. FIG. 3 is an explanatory diagram for explaining the principle of the classification cleaning process; FIG. 5(a) is a plan view of the main part of the water absorbent polymer, and FIG. 5(b) is a diagram showing the chemical formula of the water absorbent polymer shown in FIG. 5(a). (a) is a diagram showing the behavior of a COO group that constitutes the polymer water-absorbing resin, and (b) is a plan view of the main part of the polymer water-absorbing resin before and after water absorption. (a) is a diagram showing the relationship between the addition rate of the modifier and the moisture content of the residue that does not pass through the 75 μm sieve, and (b) is the addition rate of calcium chloride and the residue that does not pass through the 75 μm sieve. (c) is a diagram showing the relationship between the addition rate of ferrous sulfate heptahydrate and the moisture content of the residue that does not pass through a 75 μm sieve. It is the figure which showed collectively the result understood from FIG.7(b), (c). 1 is a schematic configuration diagram of an example of a classifying and washing facility according to an embodiment of the present invention; FIG. FIG. 4 is a schematic configuration diagram of another example of the classifying and washing facility according to one embodiment of the present invention; 1 is a flowchart showing a method for classifying and cleaning removed soil according to an embodiment of the present invention; FIG. (a) and (b) are diagrams showing 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. It is the figure which showed collectively the result understood from FIG.

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment as an example of the present invention will be described in detail below with reference to the drawings. In the drawings for describing the embodiments, in principle, the same components are denoted by the same reference numerals, and repeated description thereof will be omitted. Moreover, soil containing radioactive substances is exemplified here as the soil containing contaminants. In this case, the concentration of contaminants in soil containing contaminants means 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 by the government.

According to this processing flow, the removed soil and the like are classified into soils S1 to S4 according to the radioactive cesium (Cs) concentration (contaminant concentration, radiation concentration) and temporarily stored in the interim storage facility Fi. During this time, volume reduction treatment is performed, and the purified material is reused as a recycled material. In addition, the concentrate generated by volume reduction treatment, etc. will be disposed of at the final disposal site. The soil S1 has a Cs concentration of 8000 Bq/kg or less, the soil S2 has a Cs concentration of 8000 to 20000 Bq/kg or less, the soil S3 has a Cs concentration of 200000 to 80000 Bq/kg or less, and the soil S4 has a Cs concentration of 80000 Bq/kg or more. be.

According to this plan, the soils S1 to S4 are transported to the receiving and sorting facility Fs of the interim storage facility Fi, where they are subjected to sorting treatment and foreign matter in the soil is removed. In this sorting treatment, as described above, a modifier containing a polymer water-absorbing resin or the like is added to the soil. Some of the soils S1 and S2 after the sorting treatment are appropriately subjected to radioactivity attenuation treatment, etc., and then collected as reclaimed soil. Further, the soil S3 after the sorting treatment is subjected to the sorting and washing treatment in the sorting and washing facility Fc. In this classifying and washing treatment, for example, a group of soil particles of 75 μm or more that remain as a group is collected as reclaimed soil. On the other hand, in the above-described classification and cleaning process, for example, the concentrate extracted as a group of soil particles of less than 75 μm is subjected to heat treatment in the heat treatment facility Ft to become slag or baked products, and after the heat treatment, the cleaning treatment facility In Fw, it is divided into those subjected to cleaning treatment and the like and finally disposed of at the final disposal site.

FIG. 2 is a conceptual diagram of the main part of the removed soil processing facility in the interim storage facility.

The interim storage facility has a receiving and sorting facility Fs and a sorting and washing facility Fc. At the receiving and sorting facility Fs, the received removed soil is sorted to remove foreign substances such as combustibles. In the classification and washing facility Fc, the removed soil that has been subjected to classification and washing is subjected to classification and washing, for example, gravel with a particle size of about 2 mm or more and sand with a particle size of about 2 to 0.075 mm. and silt/clay 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, an unloading facility Fu, a bag-breaking facility Fb and a sorting facility Fss are installed in order along the moving direction of the removed soil. The removed soil is placed in a packaging material CB such as a flexible container bag and placed on a truck TR or the like and transported to the unloading facility Fu.

The unloading facility Fu is a facility for receiving the packaging material CB carried by the truck TR or the like and transferring it to the belt conveyor BC1 by the crane CR or the like. At this stage, the removed soil is contained in the packaging material CB and is unlikely to scatter outside, so the unloading facility Fu is installed in a simple building with a roof or the like.

The bag-breaking equipment Fb is equipment for breaking the packaging material CB conveyed 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 and peripheral walls, etc., so that dust caused by the removed soil does not spread around.

The sorting facility Fss is a facility for removing foreign substances such as combustibles from the removed soil after bag breaking treatment and sorting it. It has platform belt conveyors BC2 to BC4. That is, the removed soil and the like discharged from the bag breaker BM are received by the sieving machine SV1 in the preceding stage through the belt conveyor BC2. The removed soil from which foreign matter FM1 such as packaging material residue has been removed by the sieving machine SV1 is received in the subsequent sieving machine SV2 through the belt conveyor BC3. The removed soil from which foreign substances FM2 such as tree branches, leaves, roots, etc. have been removed by the sieve SV2 is sent to the subsequent stage through the belt conveyor BC4 as separated removed soil.

By the way, in this sorting facility Fss, as described above, on the belt conveyor BC3 in front of the sieve SV2, a modifier of about 3% by weight of the target soil is added to the removed soil and mixed to convert the highly viscous removed soil into sand. The soil is modified into a shape to make it easier to separate tree branches, leaves, roots, etc., and for example, the removed soil with a particle size of 20 mm or less is efficiently collected.

Modifiers are often composed of, for example, silica, gypsum, or zeolite-based materials as base materials, and small amounts of high-molecular-weight water-absorbing resins, high-performance flocculants, and the like added thereto. For this reason, the removed soil after the separation described above contains a very small amount of the polymer water-absorbent resin and the like blended in the modifier.

However, if the removed soil contains a polymer water-absorbent resin, the polymer water-absorbent resin in the removed soil will not pass through the sieve and cause clogging during the classification and washing process after the sorting process due to water absorption and swelling of the polymer water-absorbent resin. As a result, the swollen high-molecular-weight water-absorbing resin and soil particles of less than 75 μm do not pass through the sieve and are included in the reclaimed soil in large amounts. As described above, since the polymer water-absorbent resin is contained, the water content is always high, and there is a possibility that the properties of the reclaimed soil may deteriorate, such as swelling due to absorption of water. In addition, since there is a high possibility that radioactive cesium will be adsorbed and accumulated in soil particles of less than 75 μm in relatively large amounts, soil particles of less than 75 μm do not pass through the sieve and are contained in the reclaimed soil in large amounts, so that it can be regenerated together with the reforming material. Radioactive cesium may be left in the soil, potentially increasing the dose of reclaimed soil. Therefore, there is a possibility that the characteristics of the reclaimed soil (particle size characteristics, moisture content, and radiation concentration depending on the amount of Cs contained) may be degraded.

Therefore, in the present embodiment, a swelling inhibitor is added to the removed soil as an additive for suppressing (controlling) the hydrous swelling property of the polymer water-absorbent resin at the start of the classification and washing treatment of the removed soil after sorting. . As a result, it is possible to suppress or prevent the swelling of the polymer water-absorbing resin in the removed soil, so that clogging of the sieve due to the swollen polymer water-absorbing resin can be reduced or eliminated. Therefore, the amount of polymer water-absorbing resin contained in the remaining removed soil can be reduced, so the characteristics of the remaining removed soil (that is, the reclaimed soil) (particle size characteristics, moisture content, radiation concentration depending on the amount of Cs contained) are improved. can be made

In addition, by adjusting the amount of the swelling inhibitor added to the removed soil, it is possible to adjust the state of clogging of the sieve due to swelling of the polymer water absorbent resin contained in the removed soil. It is possible to control the amount of soil particles that pass through the sieve (removed soil) and the amount of soil particles that do not pass through the 75 μm sieve and remain (removed soil).

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 addition, in FIG. 4, in order to make the drawing easier to see, the fine particles Pf and the contaminants Ph, etc. are hatched differently. Contaminants Ph and the like are, for example, heavy metal elements such as arsenic and radioactive substances.

The left side of FIG. 4 shows the removed soil Sc in which coarse particles Pc, fine particles Pf, contaminants Ph, etc. are mixed. In the classification and cleaning process, the removed soil Sc is washed and polished using a machine, and the particle size is classified to separate particle size categories in which contaminants Ph and the like are adsorbed, or In this treatment method, the pollutants Ph and the like are dissolved in the cleaning liquid and the pollutants Ph and the like are extracted from the removed soil Sc. Through this classification and washing process, the purified iso-soil Sp on the upper right of FIG. 4 can be obtained, and the dehydrated cake Sd (concentration of contamination) on the lower right of FIG. 4 can be extracted. In addition, the purified soil Sp is soil having a radiation dose equal to or less than a specified level.

Next, the principle of swelling of the above-described polymer water-absorbing resin and the swelling suppressing agent for suppressing the swelling will be described with reference to FIGS. 5 and 6. FIG. FIG. 5(a) is a plan view of the main part of the polymer water-absorbent resin, FIG. 5(b) is a diagram showing the chemical formula of the polymer water-absorbent resin in FIG. 5(a), and FIG. 6(a) is the polymer water-absorbent FIG. 6(b) is a diagram showing the behavior of COO groups that constitute the resin, and FIG. In addition, the left side of the arrow in FIG. 6B indicates the state before water absorption, and the right side of the arrow indicates the state after water absorption.

As shown in FIG. 5(a), the polymer water absorbent resin has a network structure. When this polymer water-absorbing resin comes into contact with water, as shown in FIG. base. Then, as shown in FIG. 6(a), the COO groups adjacent to each other repel each other to swell the mesh, and as shown in FIG. 6(b), the mesh takes in moisture. This is the principle of swelling.

Therefore, when an environment is created in which more polyvalent cations, which have a higher adsorptive power to COO groups than Na ions, are present, polyvalent cations are coordinated again to COO groups, causing behavior to expel the taken-in moisture. Swelling performance is suppressed. Therefore, by using a polyvalent cation reagent having a high ionization tendency and a higher affinity with COO groups as a swelling inhibitor, it is possible to dehydrate the polymer water-absorbent resin that has been swollen by absorbing water.

As a specific example of such a swelling inhibitor, for example, calcium chloride can be used. Calcium chloride can be procured inexpensively. However, when calcium chloride is used, when a group of soil particles of less than 75 μm (removed soil) collected by dehydration treatment is disposed of at a final disposal site, etc., acceptance is restricted as waste containing chlorides. may occur. In that case, ferrous sulfate heptahydrate, for example, can be used as a swelling inhibitor that does not contain chloride ions. Examples of the swelling inhibitor are not limited to calcium chloride and ferrous sulfate heptahydrate, but may be variously modified as long as they exhibit the principle of swelling inhibition described above.

Next, the moisture content of the residual portion of the removed soil that did not pass through the 75 μm sieve after the classification and washing process and remains is described with reference to FIGS. 7 and 8. FIG. FIG. 7(a) is a diagram showing the relationship between the addition rate of the modifier and the moisture content of the residue that did not pass through the 75 μm sieve, and FIG. 7(b) is the addition rate of calcium chloride and the 75 μm sieve. A diagram showing the relationship between the moisture content of the residue that does not pass through and the moisture content of the residue that remains without passing through the 75 μm sieve. FIG. FIG. 8 is a diagram summarizing the results obtained from FIGS. 7(b) and 7(c).

The amount of the residue that did not pass through the 75 μm sieve after the classification and washing treatment and remained depends on the water-swelling property of the polymer water-absorbing resin contained in the modifier. That is, in the removed soil that has been classified and washed without using a swelling inhibitor, the high-molecular-weight water-absorbing resin swells and the water content increases, and as a result, the remaining residue that does not pass through the 75 μm sieve is less than 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 residue that does not pass through the 75 μm sieve and remains increases, and water content in the residue increases. A residual condition has arisen. For example, when 3 wt% of the modifier is added to the removed soil that has passed through a 2 mm sieve and no swelling inhibitor is added, the residual moisture content that does not pass through the 75 μm sieve reaches 54%. .

On the other hand, according to the inventor's study, when a swelling inhibitor is added to the removed soil at the start of the classification and washing process, as shown in FIGS. It was possible to lower the moisture content of the remaining residue.

That is, as shown in FIGS. 7(b) and 8, when calcium chloride is used as a swelling inhibitor, the swelling property of the residue remaining after not passing through a 75 μm sieve is suppressed (controlling the water content). A preferable addition amount of the swelling inhibitor is, for example, 0.25 or more and 5 wt% or less. (Water content is 54%), the water content was able to be reduced to 31%.

In addition, as shown in FIGS. 7(c) and 8, when ferrous sulfate heptahydrate is used as the swelling inhibitor, the swelling of the residue that does not pass through the 75 μm sieve is suppressed (moisture content The amount of the swelling inhibitor preferably added to control) is, for example, 0.1 or more and 5 wt% or less, and in particular, the addition of 1.5 wt% or 3 wt% of the swelling inhibitor reduces the water content by 25 points. It was possible to reduce the water content to 29% compared to the case where no swelling inhibitor was used (the water content was 54%).

By using the swelling inhibitor in this manner, the properties of the removed soil (regenerated soil) after the classification and washing treatment can be improved. For example, when the residue that does not pass through this 75 μm sieve is reused as embankment, etc., swelling can be suppressed, so drainage can be facilitated, efficiency of compaction work, trafficability, etc. can be improved.

Next, an example of the classifying and washing facility of this embodiment will be described with reference to FIGS. 9 and 10. FIG. 9 and 10 are schematic configuration diagrams of an example of a classifying and washing facility according to this embodiment. 9 and 10, solid line arrows indicate the flow of contaminants and the like, broken line arrows indicate the flow of waste water, and dashed line arrows indicate the flow of removed soil. Further, dotted arrows in FIG. 9 indicate the flow of washing water.

As shown in FIG. 9, the classification and washing facility Fc has a washing treatment device WM, a classification treatment device CM, a separation treatment device DM, a dehydration treatment device DHM, and a waste water treatment device DWM.

The cleaning equipment WM is composed of, for example, a drum washer. This washing treatment apparatus WM is an apparatus for washing and polishing the removed soil Sc accommodated in the drum D by rotating the drum D while sprinkling water inside it. In the present embodiment, for example, the above-described swelling inhibitor is put into the drum D of the cleaning apparatus WM.

The classifying device CM is a device that performs a classifying process, and includes, for example, a vibrating sieve machine and a cyclone (not shown) integrally. The muddy water sent from the cleaning equipment WM is centrifuged by the cyclone of the classification equipment CM. This separated heavy soil portion is applied to a vibrating sieve of the classifier CM and drained. That is, the sediment that has fallen on the net of the vibrating sieve is drained while moving laterally on the net, and eventually spills over the edge of the net. Also, the water drained by the vibrating sieve is mixed with the muddy water successively sent from the cleaning equipment WM and supplied to the cyclone again. Here, for example, a group of soil particles of less than 75 μm is extracted and sent to the subsequent stage, while a group of soil particles of 75 μm or more is obtained as the purified, etc. soil Sp. For example, a trommel or a high-mesh separator may be used instead of the drum washer or vibrating sieve. Further, in order to improve the classification and washing performance, for example, a bubble floating separator or a gravity separator may be used as the classifier CM.

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

The dehydration apparatus DHM is composed of, for example, a filter press. In the dehydration treatment apparatus DHM, a bag-like filter is filled with muddy fine particles, and high pressure is applied to dehydrate the fine particles, and the dewatered cake Sd is taken out. A belt press, for example, may be used instead of the filter press.

The waste water treatment device DWM is a device for purifying waste water (including contaminants) sent from the dehydration treatment device DHM. The purified water purified by the wastewater treatment equipment DWM is sent again to the washing treatment equipment WM and the classification treatment equipment CM.

The configuration of the classifying and washing facility Fc shown in FIG. 10 is substantially the same as that shown in FIG. Here, the drainage flow is slightly different. That is, the washing water obtained in the separation treatment equipment DM is supplied to the washing treatment equipment WM and the classification treatment equipment CM, and the waste water (including contaminants) obtained in the dehydration treatment equipment DHM is supplied to the separation treatment equipment DM. It's like

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

First, the removed soil Sc, water, and a swelling inhibitor are put into the drum D of the washing treatment apparatus WM, and then the drum D is rotated to mix and stir, and the removed soil Sc in the drum D is washed and polished (Fig. 11 step 100).

Subsequently, the removed soil (mud water) after the washing treatment is sent to the classifier CM, and a group of soil particles (fine particle fraction Pf (see FIG. 4)) of less than 75 μm is extracted by classifying. A group of soil particles (coarse particle fraction Pc (see FIG. 4)) of 75 μm or more is taken out as a residue (step 101 in FIG. 11). After the conformity to the standard is confirmed by the purification confirmation investigation, this residual portion becomes purified soil Sp (regenerated soil) (step 102 in FIG. 11).

After that, the fine particles Pf (see FIG. 4) that have passed through the classifier CM and have concentrated contamination are coagulated and sedimented in the separation treatment equipment DM, and then subjected to dehydration treatment in the dehydration treatment equipment DHM (step 103 in FIG. 11). ) and discharged as dehydrated cake Sd. This dehydrated cake Sd is treated as contaminated soil because the contamination is concentrated, and is transported to a reprocessing contaminated soil treatment facility or the like (step 104 in FIG. 11).

As described above, in the present embodiment, by adding the swelling inhibitor to the removed soil at the start of the classification and washing treatment of the removed soil as described above, swelling of the polymer water absorbent resin contained in the removed soil is suppressed. Or it can be prevented, so clogging of the sieve due to the swollen high-molecular-weight water-absorbing resin can be reduced or eliminated.

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

In addition, since the clogging of the sieve is reduced or eliminated during the classification and washing process, more soil particles of less than 75 μm can be passed through the classification and washing process, so it is included in the purified soil Sp (regenerated soil). It can reduce the amount of soil particles smaller than 75 μm that are absorbed. That is, since the amount of Cs, which is likely to be adsorbed and accumulated in soil particles of less than 75 μm in a relatively large amount, can be reduced, the dose of purified soil Sp can be reduced. Therefore, the properties of the purified soil Sp can be improved (for example, the radiation concentration due to the amount of Cs contained can be reduced).

(Second embodiment)

Generally, it is known that a large amount of Cs is adsorbed on soil particles that pass through a 75 μm sieve. As a result, it is possible to control the clogging of the sieve due to the swelling of the polymer water-absorbing resin contained in the removed soil, so that the amount of soil that passes through the 75 μm sieve can be controlled. That is, by adjusting the addition amount of the swelling inhibitor, it is possible to adjust the amount of Cs contained in the residual soil (regenerated soil) that does not pass through the 75 μm sieve.

Here, FIGS. 12A and 12B 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. showing. FIG. 13 is a diagram summarizing the results obtained from FIG.

As shown in FIGS. 12( a ) 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 that passes through a 75 μm sieve is the smallest (56% reduction), especially at an additive amount of 0.75 wt % of the swelling inhibitor. In this case, the amount of residue that does not pass through the 75 μm sieve is large, so the effect of reducing the amount of Cs in the reclaimed 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 that passes through a 75 μm sieve is relatively large, and in particular, swelling At 3 wt% inhibitor loading, the amount of soil that passes through a 75 μm sieve is maximized (24% increase). In this case, the residue that does not pass through the 75 μm sieve is reduced, so the effect of reducing the amount of Cs in the reclaimed soil is promoted.

On the other hand, as shown in FIGS. 12(b) and 13, when ferrous sulfate heptahydrate is used as the swelling inhibitor, the addition amount of the swelling inhibitor is, for example, 0.1 or more and 0.1 or more. At less than 5 wt%, the amount of soil that passes through a 75 μm sieve is relatively small, especially when the amount of swelling inhibitor added is 0.1 wt%, the amount of soil that passes through a 75 μm sieve is minimal (38% reduction). becomes. In this case, the amount of residue that does not pass through the 75 μm sieve is large, so the effect of reducing the amount of Cs in the reclaimed 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 a 75 μm sieve is relatively In particular, when the added amount of the swelling inhibitor is 1.5 wt %, the amount of soil that passes through a 75 μm sieve becomes maximum (108% increase). In this case, the residue that does not pass through the 75 μm sieve is reduced, so the effect of reducing the amount of Cs in the reclaimed soil is promoted.

In this way, when the amount of soil passing through a 75 μm sieve decreases or increases compared to the soil to which the swelling inhibitor is not added (the amount of added material = 0 wt%), the amount of the swelling inhibitor added is However, it can be understood that the addition amount of the swelling inhibitor is a boundary value for suppressing or promoting the amount of Cs in the reclaimed soil.

Because of this and the premise of reusing Cs-containing soil is not to exceed 8000 Bq / kg, in the present embodiment, swelling is suppressed in soil of 8000 Bq / kg or less and in soil exceeding it. Vary the amount of agent added. This makes it possible to carry out a rational purification process. Application examples for each case will be described below.

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

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

Next, a method of adding a swelling inhibitor used when soil having a relatively low Cs concentration (soil S1 in FIG. 1, etc.) is to be subjected to the classification and washing process will be described.

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

(Third Embodiment)

In the first embodiment, the case where the soil S3 (see FIG. 1) is the target removed soil has been described. Here, although the soils S1 and S2 are not subjected to washing treatment, they are carried to the intermediate storage facility Fi (see FIG. 1) and stored in the intermediate storage facility Fi after being subjected to foreign matter removal treatment by adding a modifier. being done. Also, the law stipulates that this soil must be excavated and reused or transported to a final disposal site within 30 years. Also, it is assumed that the soil S1 and S2 will also become swellable due to the influence of moisture during storage and contact with moisture after excavation.

Therefore, in the present embodiment, even in the soils S1 and S2 that are not subjected to the classification and washing treatment, the swelling inhibitor is added and stirred after the soils S1 and S2 are excavated. Thereby, swelling in soil S1 and S2 can be controlled. Also, the properties of the soils S1 and S2 (for example, particle size properties and moisture content) can be improved.

Although the invention made by the present inventor has been specifically described based on the embodiments, the embodiments disclosed in this specification are illustrative in all respects and are limited to the disclosed technology. isn't it. That is, the technical scope of the present invention should not be construed in a restrictive manner based on the description of the above embodiments, but should be construed according to the description of the scope of claims. All modifications are included as long as they do not deviate from the description technology and equivalent technology and the gist of the claims.

In the above description, the method for classifying and washing contaminated soil of the present invention is applied to the method for classifying and washing removed soil. Since a treatment agent containing a resin is sometimes used, it can be applied as a measure for suppressing swelling in that case.

Fi Intermediate storage facility Fs Receiving separation facility Fc Classification and washing facility BM Bag breaker SV1, SV2 Sieve machine BC1-BC4 Belt conveyor WM Washing device CM Classification device DM Separation device DHM Dehydration device DWM Wastewater treatment device S1-S4 Soil Sc Removed soil Sp Purified soil Sd Dehydrated cake Pf Fine particle fraction Pc Coarse particle fraction Ph Contaminant

Claims (2)

A classifying and cleaning method for classifying and cleaning contaminated soil containing a polymer water-absorbing resin,
adding a swelling inhibitor to the contaminated soil at the start of the classifying and washing treatment of the contaminated soil,
A method for classifying and cleaning contaminated soil, wherein the swelling inhibitor contains ferrous sulfate heptahydrate, and the amount of the ferrous sulfate heptahydrate added is 0.5 to 3 wt % . 2. The amount of soil particles that pass through the sieve and the amount of residual soil particles that do not pass through the sieve in the classifying and washing process are controlled by changing the amount of the swelling inhibitor added. A method for classifying and cleaning contaminated soil.

Images