JP5818095B2 - Cleaning treatment method for cesium contaminated soil - Google Patents

Description

  The present invention relates to a method for cleaning cesium-contaminated soil.

  Conventionally, as a method of separating and removing these harmful substances from soil contaminated with organic compounds, oils and other harmful substances, water is added to the contaminated soil to form a slurry, which is then sent to a floating separator, to which a surfactant is added. And a method for floating and separating harmful substances from contaminated soil by adding an alkaline agent (see, for example, Patent Document 1).

  By the way, as a purification method for contaminated soil containing radioactive substances such as cesium adhering to the surface of the soil particles, for example, the contaminated soil is classified into coarse particles, sand and fine particles by a wet sieve device and a hydrocyclone. In addition to collecting the contaminants together with the floss generated by the scrubber and the flotation device with respect to the sand obtained by the classification process, the washed washed sand is dehydrated and recovered, and further classified. The fine particle fraction classified by the above, the floss obtained by the flotation treatment, and the treatment solution produced by the dehydration are put into a coagulating sedimentation apparatus and separated into a concentrated residue and treated water.

  In general, scrubbing with a scrubber is also applied, for example, to washing heavy metal-contaminated soil. In this case, water is added to the soil to form a slurry, and then the soil particles collide with each other by stirring. Thus, the soil surface layer is stripped off to remove heavy metals adhering to the surface layer of soil particles, and the soil is purified.

JP-A-63-72391

However, the above-described conventional scrubbing treatment in contaminated soil cleaning has the following problems.
That is, cesium is taken into the sand obtained by the classification process in the purification process described above in a state where cesium has entered the surface layer of the soil particles. Therefore, in order to increase the cleaning effect of cesium-contaminated soil, the surface layer of soil particles is stripped thickly and cesium is taken in by increasing the stirring speed by increasing the rotational speed and driving force of the scrubber in the scrubbing process. It is necessary to sufficiently remove the surface layer of soil particles. However, if the scrubbing process is performed excessively, the collision between the soil particles becomes large, and the part that is stripped off by scrubbing is not only the surface layer of the soil particles but also the internal part where cesium is not taken in. Since the amount to be taken increases, there is a problem that the amount of residue containing cesium increases and the disposal cost also increases.

  The present invention has been made in view of the above-described problems, and can maintain the purification effect and reduce the volume of residues containing cesium generated by the scrubbing treatment, thereby reducing the disposal cost. An object of the present invention is to provide a method for cleaning cesium-contaminated soil.

In order to achieve the above object, the cleaning method for cesium-contaminated soil according to the present invention is a cleaning method for cesium-contaminated soil that cleans contaminated soil contaminated with cesium and separates and removes cesium from the contaminated soil. In addition, the first step of classifying the slurry-like earth and sand obtained by adding water to the contaminated soil and separating the coarse particles by wet sieving classification into the sand and fine particles is classified in the first step. Add a chemical agent consisting of acid to the treated sand and perform a surface treatment to make the soil particles surface brittle, and remove the surface layer of the sand treated in the second step by stirring. cesium a third step of separating, a fourth step of recovering the froth caused by flotation treatment withdrawal was peeled by the third step, the cesium contained in the cleaning sand of the fourth step A fifth step of extracting with a solution of the extracted drug and further obtaining a low-concentration low-concentration washing sand by dehydration, and a fourth step using the fine particles obtained from the fine particles obtained in the first step as an adsorbent The sixth step of removing cesium from the floss and the treatment solution according to the fifth step, coagulating and separating it into separated sludge and water, dehydrating the precipitated sludge and separating it into a concentrated residue and treated water; It is characterized by having.

  In the present invention, the surface layer portion of the classified sand component is incorporated in a state where cesium has entered, but in the second step, by adding acid to the sand component, the surface of the soil particles of the soil component ( Surface treatment can be performed in which the surface layer part) reacts with the acid and becomes brittle and easily broken. Furthermore, the sand particles surface-treated in the third step are stirred by scrubbing or the like, so that the soil particles collide with each other, so that the surface layer of the soil particles made brittle by the acid is peeled off and can be separated.

Thus, by making only the soil particle surface brittle before stirring, it is possible to efficiently peel off and separate only the particle surface layer with a small collision force during stirring. Therefore, the power required for stirring can be reduced, and it is possible to suppress an increase in the thickness dimension to be peeled off as in the case of stirring with a large driving force. That is, it is possible to suppress peeling off the inside of the soil particles themselves (parts other than the surface layer) from which cesium has not been taken in by stirring. Accordingly, it is possible to reduce the generation amount of useless residues containing cesium while maintaining the purification effect, and it is possible to reduce the amount of waste and the cost of waste disposal.
Moreover, since it is possible to peel off only the soil particle surface layer with a weaker stirring force than in the past, there is also an advantage that the thickness control of the soil particles during the stirring becomes easy.

  In the cleaning method for cesium-contaminated soil according to the present invention, it is preferable to add a surfactant together with the stirring in the third step.

  In the present invention, the soil particle surface of sand becomes brittle by reacting with an acid in the second step, and the effect of scrubbing can be maintained by the dispersing action of the surfactant on the detached part separated by scrubbing.

  According to the cleaning method for cesium-contaminated soil of the present invention, only the surface of the soil particles in the sand is made brittle with an acid in advance, so that only the surface portion of the sand is efficiently peeled off by stirring by the scrubbing treatment. Since it can be peeled thinly, it is possible to reduce the volume of the residue containing cesium generated by the scrubbing treatment while maintaining the purification effect, and to reduce the disposal cost.

It is a flowchart which shows typically the washing process process of the cesium contamination soil by embodiment of this invention.

  Hereinafter, a cleaning method for cesium-contaminated soil according to an embodiment of the present invention will be described with reference to the drawings.

  As shown in FIG. 1, the cleaning method for cesium-contaminated soil according to the present embodiment relates to a method for cleaning contaminated soil G0 contaminated with cesium and separating and removing cesium from contaminated soil G0.

  That is, the cleaning treatment method for cesium-contaminated soil is a slurry-like soil G1 obtained by adding water to the contaminated soil G0 and performing wet sieving classification to separate the coarse particles G2 into sand S1 and fine particles S2. Further, a classification process 1 (first process) for classifying treatment, and a surface treatment process 2 (first process) for adding a chemical comprising acid 7 to the sand component S1 classified in the classification process 1 to make the soil particle surface of the sand component S1 brittle. 2 step) and a scrubbing step 3 (third step) for peeling off the surface layer portion of the sand S3 surface-treated in the surface treatment step 2 by stirring.

Further, in the present cleaning method, a cleaning step 4 (fourth step) for recovering the detached material separated in the scrubbing step 3 by the floss F generated by the flotation processing, and a cesium contained in the cleaning sand S4 of the cleaning step 4 Is extracted with a solution of the cesium extraction agent 8, and the low-concentration washed sand S5 having a lower concentration is obtained by dehydration. The cesium extraction step 5 (fifth step) and the fine particle portion S2 obtained in the classification step 1 are adsorbed. The fine particle S2 is used to remove cesium from the Floss F in the washing step 4 and the processing solution E in the cesium extraction step 5, and to coagulate and precipitate to separate the precipitated sludge and water. And an adsorption step 6 (sixth step) for separating the concentrated residue T and the treated water W.

(Classification process 1)
First, in the classification step 1, the wet sieving apparatus 11 is used to separate the coarse particles G2 from the cesium-contaminated soil (contaminated soil G0) having a strong adsorptivity to the soil to form the slurry-like sediment G1. Is done. Here, the wet sieving apparatus 11 sorts foreign matter by vibration sieving, ultrasonic sieving, specific gravity sorting, etc., and classifies it into gravel / coarse sand and lower slurry-like earth and sand G1. Is provided inside. As the wet sieving device 11, a commercially available known device can be used. In addition, the washing | cleaning efficiency in the washing | cleaning process 4 can be improved by isolate | separating the coarse particle content G2 with the wet sieve apparatus 11. FIG.

Next, the hydrocyclone 12 is used to classify the earth and sand G1 from which the coarse particles G2 have been removed into a sand S1 and a fine particles S2. At this time, cesium is contained in the sand component S1 and the fine particle component S2.
The hydrocyclone 12 is composed of a container having a cylindrical bottom structure, for example, and includes an upper inlet for introducing slurry mixed with earth and sand, a lower outlet for extracting underflow, and an upper outlet for extracting overflow. It has. The slurry-like earth and sand G1 that has entered from the upper inflow port is rotated at a high speed in the circumferential direction of the cylindrical container, thereby causing a rotational motion, which becomes a rotational flow and proceeds toward the top of the cone. At this time, particles having a high specific gravity in the slurry gather on the peripheral wall due to centrifugal force, gradually move toward the underflow outlet (lower outlet), and are concentrated and discharged. On the other hand, particles having a low specific gravity with the liquid rise as a vortex in the center of the cylindrical container and are discharged from the overflow outlet (upper outlet). A known device can be used as the hydrocyclone 12. Since cesium adheres to and adsorbs to the fine particle portion S2, most of the cesium can be removed from the cleaning soil by classification with the hydrocyclone 12. The number of classification processes is appropriately set, but it is preferably performed once or more.

(Surface treatment process 2)
Next, in the surface treatment step 2, the sand component S1 classified in the classification step 1 is stored in the surface treatment tank 13, and the acid 7 is added to the sand component S1 in the surface treatment tank 13, whereby the sand component S1. A surface treatment is performed in which the surface (surface layer portion) of the soil particles is made weak by reacting with the acid 7. Here, examples of the acid 7 that is a drug to be added include hydrochloric acid, sulfuric acid, nitric acid, and hydrofluoric acid.

(Scrubbing process 3)
Subsequently, in the scrubbing step 3, by using the scrubber 14, the surface layer portion of the sand S3 weakened in the surface treatment step 2 is peeled off by the scrubbing by stirring to take off cesium. The surface layer portion of the sand content S3 is removed.
The scrubber 14 is provided with a stirring tank and a stirring blade, and mechanically mixes and stirs using the stirring blade and the like, and the soil particles collide with each other and rub against each other, thereby destroying the soil surface (surface layer). And it is for making it peel with the cesium taken in by the surface layer by peeling off. As the scrubber 14, a known device can be used, and an attrition scrubber having a high wear effect may be used, or a normal scrubber may be employed.

(Washing process 4)
Next, in the washing step 4, using the flotation device 15, the detachment (surface layer portion of soil particles containing cesium) from the scrubbing step 3 out of the sand S3 charged from the scrubber 14 into the flotation device 15 is filtered. In addition to being recovered by the floss F generated by the rotation process, the washing sand S4 from which the detached matter has been removed is taken out.
That is, in the flotation device 15, bubbles are generated and the separated matter (surface layer portion of soil particles containing cesium) separated by the scrubber 14 is raised to the liquid level together with the bubbles, and is recovered as froth F together with the bubbles from the liquid level. , And sent to the coagulation sedimentation apparatus 18 used in the adsorption step 6.

(Cesium extraction process 5)
Next, in the cesium extraction step 5, residual cesium remaining in the washing sand S <b> 4 taken out in the washing step 4 is extracted with a solution of the cesium extraction agent 8 in the extraction tank 16, and further concentrated using the dehydration apparatus 17. The low secondary cleaning sand (low concentration cleaning sand S5) is dehydrated. Here, as the cesium extraction agent 8, for example, an alkali metal such as a potassium compound, or an acidic substance such as ammonia or nitric acid can be used.
The dehydration processing device 17 is a known pressure filtration device (belt filter press) or the like, and includes a filter made of a filter cloth or the like and a press machine. In addition, the process solution E at this time is sent to the coagulation sedimentation apparatus 18 used in the adsorption process 6.

(Adsorption process 6)
Next, in the adsorption process 6, the Floss F from the washing process 4 and the treatment solution E from the cesium extraction process 5 are sent to the coagulation sedimentation apparatus 18, and the fine particle fraction S2 separated by the hydrocyclone 12 from the classification process 1 is also coagulated. It is sent to the precipitation device 18. The coagulating sedimentation apparatus 18 separates the clear treated water W by adding and stirring the coagulant to the suspension water containing fine particles, causing fine suspended matters in the water to settle as large sedimentation sludge. The coagulation sedimentation device 18 is provided with a press dewatering device 19. The press dewatering device 19 is a known pressure filtration device (belt filter press) or the like, and includes a filter made of a filter cloth or the like and a press machine.
Then, the fine particle S2 is used as an adsorbent, and cesium (Floss F, treatment solution E) is adsorbed and removed on the fine particle S2, and is coagulated and separated into precipitated sludge and water. The precipitated sludge is dehydrated by 19 and separated into concentrated residue T and treated water W.

Next, the effect | action of the washing | cleaning processing method of the cesium contamination soil of the structure mentioned above is demonstrated in detail.
As shown in FIG. 1, in the present embodiment, cesium has been incorporated in the surface layer portion of the sand S1 classified in the classification process 1, but in the surface treatment process 2, this sand S1. By adding the acid 7 to the surface, the surface treatment (surface layer portion) of the soil particles having the sand content S1 reacts with the acid 7, and can be subjected to a surface treatment that is brittle and easily broken.
Furthermore, since the sand particles S3 surface-treated in the scrubbing step 3 are agitated by scrubbing with the scrubber 14, the soil particles collide with each other, so that the surface layer of the soil particles made brittle by the acid 7 is peeled off and separated. be able to.

By making the soil particle surface only brittle before stirring in this way, only the particle surface layer can be efficiently peeled off and separated with a small collision force during stirring by the scrubbing treatment. Therefore, the power required for stirring can be reduced, and it is possible to suppress an increase in the thickness dimension to be peeled off as in the case of stirring with a large driving force. That is, it is possible to suppress peeling off the inside of the soil particles themselves (parts other than the surface layer) from which cesium has not been taken in by stirring. Accordingly, it is possible to reduce the generation amount of useless residues containing cesium while maintaining the purification effect, and it is possible to reduce the amount of waste and the cost of waste disposal.
Moreover, since it is possible to peel off only the soil particle surface layer with a weaker stirring force than in the past, there is also an advantage that the thickness control of the soil particles during the stirring becomes easy.

As described above, in the cleaning method for cesium-contaminated soil according to the present embodiment, only the surface of the soil particle surface of the sand component S1 is made brittle with the acid 7 in advance, so that only the surface layer portion of the sand component S1 is agitated by the scrubbing process. Can be peeled off efficiently and can be peeled thinly, so that the residue containing cesium generated by the scrubbing treatment can be reduced while maintaining the purification effect, and the disposal cost can be reduced. Can be achieved.
The

  As mentioned above, although embodiment of the washing | cleaning processing method of the cesium contaminated soil by this invention was described, this invention is not limited to said embodiment, It can change suitably in the range which does not deviate from the meaning.

For example, in the cleaning treatment method for cesium-contaminated soil according to the present embodiment, the detachment containing cesium generated by the scrubbing process is collected by the flotation device 15 and is treated in the adsorption step 6. The recovery method is not limited to this, and it is possible to recover by an appropriate recovery method that is generally known. For example, in the present embodiment, the cesium extraction process 5 is used to remove cesium from the washing sand taken out by the flotation device 15 using the cesium extraction agent 8, but this process can be omitted.
Moreover, in this Embodiment, although it is set as the method of utilizing fine particle content S2 as an adsorbent in adsorption | suction process 6, it is not limited to employ | adopting such a collection | recovery method.

Moreover, you may make it add surfactant with the stirring in the scrubbing process 3 (3rd process) of embodiment mentioned above. In this case, in the surface treatment step 2, the soil particle surface of the sand S1 reacts with the acid 7 and becomes brittle, and the scrubbing effect can be maintained by the dispersing action of the surfactant on the detached part separated by scrubbing.
Here, examples of the surfactant include fatty acid salts, dodecyl sulfate, oleate, xanthate, alkyl sulfonate, lignin sulfonate, and other general surfactants.

  Furthermore, conditions such as time and amount of addition when acid 7 is added in surface treatment step 2 are the type of acid 7 to be added, the type and amount of sand, and the amount of cesium incorporated in the soil particle surface layer. The optimal setting may be made according to conditions such as the surface layer thickness.

  In addition, it is possible to appropriately replace the components in the above-described embodiments with known components without departing from the spirit of the present invention.

1 Classification process (1st process)
2 Surface treatment process (2nd process)
3 Scrubbing process (3rd process)
4 Cleaning process (4th process)
5 Cesium extraction process (5th process)
6 Adsorption process (6th process)
7 Acid 8 Cesium extractant 11 Wet sieving device 12 Hydrocyclone 13 Surface treatment tank 14 Scrubber 15 Flotation device 16 Extraction tank 17 Dehydration treatment device 18 Coagulation sedimentation device E Treatment solution F Floss G0 Contaminated soil (cesium contaminated soil)
G1 Earth and sand G2 Coarse particles S1, S3 Sand and S2 Fine particles S4 Washed sand S5 Low-concentration washed sand T Concentrated residue W Treated water

Claims (2)

A method for cleaning cesium-contaminated soil that cleans contaminated soil contaminated with cesium and separates and removes cesium from the contaminated soil,
A first step in which water is added to the contaminated soil, and the slurry-like earth and sand separated by wet sieving and separated into coarse particles is further classified into sand and fine particles;
A second step of adding a chemical agent consisting of acid to the sand classified in the first step, and performing a surface treatment to make the soil particle surface brittle of the sand;
A third step in which the surface layer portion of the sand treated in the second step is peeled off by stirring and separated;
A fourth step of recovering the separated material separated by the third step by floss generated by a flotation treatment;
A fifth step of extracting cesium contained in the washing sand of the fourth step with a solution of a cesium extraction agent and further obtaining a low concentration washing sand having a low concentration by dehydration;
Using the fine particles obtained in the first step as an adsorbent, the fine particles are used to remove cesium from the floss in the fourth step and the treatment solution in the fifth step, and to coagulate and precipitate A sixth step of separating the precipitated sludge into water and dewatering the precipitated sludge into a concentrated residue and treated water;
A method for cleaning cesium-contaminated soil, comprising:   The method for cleaning cesium-contaminated soil according to claim 1, wherein a surfactant is added together with the stirring in the third step.

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