JP2013057599A - Method for processing radioactive contaminated water - Google Patents

Abstract

PROBLEM TO BE SOLVED: To efficiently process massive radioactive contaminated water.SOLUTION: A method for processing radioactive contaminated water is a method for processing the radioactive contaminated water containing radioactive nuclides containing at least radioactive cesium, and includes: a preprocessing process of performing preprocessing by adding ferrocyanide iron and zeolite-based adsorbent for adsorbing the radioactive nuclides to the radioactive contaminated water, and mixing and stirring the resulting mixture; a coagulant addition and mixing process of adding an inorganic coagulant to the preprocessed contaminated water preprocessed in the preprocessing process, adding then a solution of an organic coagulant to the preprocessed contaminated water, mixing the resulting mixture, and performing granulation of a solid containing the ferrocyanide iron and the zeolite-based adsorbent; and a solid-liquid separation process of performing solid-liquid separation of the mixture to be obtained in the coagulant addition and mixing process by sedimentation by a thickener device 23.

Description

  The present invention relates to a method for treating radioactive contaminated water containing a radionuclide containing radioactive cesium.

  Conventionally, as a technique for processing a waste liquid containing a radionuclide, a processing method described in Patent Document 1 below is known. In this treatment method, nickel sulfate, potassium ferrocyanide, ferric sulfate and sodium hydroxide are added to the waste liquid to coprecipitate radioactive materials. Then, by adding a polymer flocculant simultaneously with or after the addition of ferric sulfate, the fine particles generated by the coprecipitation reaction are aggregated, and the precipitate containing the radionuclide is recovered by centrifugation.

JP 62-266499 A

  However, when a large amount of radioactively contaminated water is to be treated, it is necessary to separate a large amount of liquid components and precipitates, but the centrifugal separation method is not suitable for separating a large amount of objects. The above-mentioned waste liquid treatment method using the method is not suitable for treating a large amount of radioactively contaminated water. In view of such circumstances, an object of the present invention is to efficiently process a large amount of radioactively contaminated water.

  The method for treating radioactive contaminated water of the present invention is a method for treating radioactive contaminated water containing a radionuclide containing at least radioactive cesium, wherein an adsorbent that adsorbs the radionuclide is added to the radioactive contaminated water, mixed and agitated before mixing. After adding an inorganic flocculant to the pretreatment step to be treated and the pretreated contaminated water pretreated in the pretreatment step, an aqueous solution of an organic flocculant is added and mixed, and the solid containing the adsorbent A flocculant addition mixing step for granulating the product, and a solid-liquid separation step for solid-liquid separation of the mixed liquid obtained in the flocculant addition mixing step by sedimentation separation.

  In this treatment method, the radionuclide is adsorbed on the adsorbent by the pretreatment step, the solid containing the adsorbent is granulated by the flocculant addition mixing step, and the solid containing the radionuclide is granulated by the solid-liquid separation step. Things are separated. In the solid-liquid separation process, sedimentation separation is used, so by preparing a large-capacity tank for retaining the mixed liquid, the mixed liquid after granulation can be efficiently processed in large quantities to produce a solid containing radionuclides. Can be separated.

  In the solid-liquid separation step, the solid-liquid separation may be performed by using a thickener device that has a retention tank for retaining the mixed liquid and extracts solids precipitated in the mixed liquid from the lower part of the retention tank. If the thickener device is used, the solid matter containing the radionuclide at a high concentration is unevenly distributed in the lower part of the retention tank, so that a protective structure for reducing the influence of radioactivity can be provided only in the lower part of the thickener device.

  In the pretreatment step, the first adsorbent and the second adsorbent are used as the adsorbent, and after adding the first adsorbent to the radioactive polluted water, mixing and stirring, 2 adsorbents may be added and mixed and stirred. According to this configuration, the amount of adsorbent used can be suppressed by using two types of adsorbents in two stages in order according to their characteristics.

  In this case, the radioactively contaminated water may further contain radioactive strontium as a radionuclide, the first adsorbent may be iron ferrocyanide, and the second adsorbent may be a zeolite-based adsorbent. Ferric ferrocyanide mainly adsorbs cesium, and zeolitic adsorbent has the property of adsorbing cesium and strontium. Therefore, by using iron ferrocyanide as the first adsorbent first, radioactive cesium in the radioactively contaminated water is first adsorbed and reduced by iron ferrocyanide, and from that state, the zeolite adsorbent is used as the second adsorbent. By using the agent, the adsorption capacity of the zeolite-based adsorbent can be exhibited mainly for the adsorption of radioactive strontium. Therefore, since radioactive strontium in radioactively contaminated water is efficiently reduced by the zeolite adsorbent, the required amount of the zeolite adsorbent can be suppressed and the amount used can be suppressed.

  According to the method for treating radioactive contaminated water of the present invention, a large amount of radioactive contaminated water can be treated efficiently.

It is a figure which shows an example of the radioactive contamination water treatment facility in which the processing method of radioactive contamination water of this invention is performed. It is a table | surface which shows the result of our test.

  Hereinafter, embodiments of a method for treating radioactive contaminated water according to the present invention will be described in detail with reference to the drawings.

  A radioactively contaminated water treatment facility 1 shown in FIG. 1 includes a radioactively contaminated water tank 3 that stores radioactive contaminated water to be treated, and an oil / water separator 5 that separates and removes oil from the radioactively contaminated water. The radioactive contaminated water contains a radionuclide. The radioactively contaminated water is obtained, for example, by previously removing soil particles from radioactive turbid water containing soil particles and radionuclides. The radionuclide in the radioactively contaminated water contains at least radioactive cesium and radioactive strontium, and the radioactivity per volume of the radioactively contaminated water is, for example, about 100 Bq / mL.

  The facility 1 also includes two pretreatment tanks 7a and 7b to which radioactive contaminated water that has been treated by the oil / water separator 5 is sent. In the pretreatment tanks 7a and 7b, two kinds of adsorbents are sequentially added to the radioactive contaminated water and mixed and stirred. Of these, the first type of adsorbent added first is ferric ferrocyanide (first adsorbent), and has the property of adsorbing radioactive cesium in radioactively contaminated water. A second type of adsorbent added later is a zeolite-based adsorbent (second adsorbent), and has the property of adsorbing radioactive cesium and radioactive strontium in radioactive contaminated water. The zeolite adsorbent refers to synthetic zeolite, natural zeolite, artificial zeolite, and a mixture obtained by mixing two or three of them.

  The facility 1 includes an iron ferrocyanide mixed water tank 9 for supplying ferric ferric iron mixed water to the pretreatment tanks 7a and 7b with a fixed supply pump. Here, for example, ferric ferrocyanide mixed water is supplied so that about 0.5% by weight of iron ferrocyanide is supplied to the radioactively contaminated water (raw water). The facility 1 also includes a zeolite mixed water tank 11 for supplying zeolite-based adsorbent mixed water to the pretreatment tanks 7a and 7b with a fixed supply pump. Here, for example, the zeolite-based adsorbent mixed water is supplied so that about 0.5 wt% of the zeolite-based adsorbent is supplied to the radioactively contaminated water (raw water). The pretreatment tanks 7a and 7b are composed of two tanks having the same configuration in order to perform the parallel mixing of the mixing and stirring process of the first type of adsorbent on one side and the mixing and stirring process of the second type of adsorbent on the other side. They are installed in parallel, and their functions and processing contents are the same.

  The treated water from the treated water storage tank 13 is supplied to the ferrocyanide mixed water tank 9. Then, the ferric ferrocyanide powder is added to and mixed with the treated water to prepare ferric ferrocyanide mixed water in which iron ferrocyanide is mixed and dissolved. Similarly, the treated water from the treated water storage tank 13 is also supplied to the zeolite mixed water tank 11. Then, the zeolite-based adsorbent in a state where the zeolite-based adsorbent is mixed and dissolved is prepared by charging and mixing the powdered zeolite-based adsorbent into the treated water. The treated water storage tank 13 is supplied with treated water generated in a treated water facility 31 described later. In this case, it is not essential to use treated water generated in the treated water facility 31, and fresh water (such as tap water) is supplied to the ferrocyanide mixed water tank 9 and the zeolite mixed water tank 11. May be.

  The facility 1 also includes an agitation granulation tank 17 in the subsequent stage of the pretreatment tanks 7a and 7b. In the agitation granulation tank 17, an inorganic flocculant is added to the pretreated contaminated water after being treated in the pretreatment tanks 7a and 7b, and then an aqueous solution of an organic flocculant is added and mixed and stirred ( Granulation process). For example, PAC (polyaluminum chloride) is used as the inorganic flocculant. As the organic flocculant, for example, a polyacrylamide flocculant (polymer flocculant) is used. The facility 1 stores an inorganic flocculant storage tank 19 that stores the inorganic flocculant and supplies it to the stirring granulation tank 17, and an organic that prepares an aqueous solution of the organic flocculant and supplies it to the stirring granulation tank 17. System flocculant preparation tank 21. The amount of PAC or polymer flocculant charged into the pretreated contaminated water is determined by, for example, a jar test.

  When the inorganic flocculant is added to the pretreated contaminated water, solid particles in the pretreated contaminated water aggregate to form an aggregate. Further, when an organic flocculant is added, the aggregates gather to form a larger aggregate (floc), and the solid component tends to settle. The solid matter in the pretreated contaminated water contains iron ferrocyanide adsorbed with radioactive cesium and a zeolite adsorbent adsorbed with radioactive strontium. Therefore, these solid matters are included in the above floc. In addition, when soil particles remain in the raw water (the radioactively contaminated water in the radioactively contaminated water tank 3), the soil particles are also included in the above flock.

  Further, the facility 1 includes a thickener device 23 that is located at the rear stage of the stirring granulation tank 17. The thickener device 23 includes a retention tank 23 a that retains the mixed liquid from the stirring granulation tank 17. The liquid mixture supplied to the retention tank 23a is in a state where the floc, which is a solid component, and the liquid component are mixed. In the thickener device 23, when the mixed liquid introduced from the stirring granulation tank 17 is allowed to stand in the retention tank 23a, the floc settles on the bottom of the retention tank 23a due to gravity. And the extraction port 23b is provided in the bottom part of the retention tank 23a, The floc which is unevenly distributed in the bottom vicinity is isolate | separated from a supernatant liquid, and is extracted from the extraction port 23b as a concentrated slurry.

  After the concentrated slurry is sent to the slurry tank 27, it is filled into the concentrated slurry drum by the drum filling device 29 and carried out of the system. The concentrated slurry contains radionuclides such as radioactive cesium and radioactive strontium, and the radioactivity per volume of the concentrated slurry is, for example, about 2000 Bq / mL. On the other hand, the supernatant liquid of the retention tank 23 a is sent to the treated water facility 31. In the treated water facility 31, the radionuclide remaining in the supernatant is removed, and after the concentration of the radionuclide is sufficiently reduced, the radionuclide is discharged out of the system.

  In addition, as shown in the figure, a radiation detection device RM is provided at a necessary place on each transfer line connecting between tanks and devices, and the above-mentioned radioactive contaminated water, mixed liquid, and concentrated slurry are contained. Radiation dose is measured and managed.

  Then, the processing method of the radioactive contamination water performed in the radioactive contamination water processing facility 1 demonstrated above is demonstrated.

(Pretreatment first step)
The radioactively contaminated water in the radioactively contaminated water tank 3 is alternately sent to the two pretreatment tanks 7a and 7b after the oil content is removed by the oil / water separator 5. In addition, since the process of the radioactive contamination water in the pretreatment tanks 7a and 7b is the same, the process in the pretreatment tank 7a is demonstrated here. First, ferric ferrocyanide mixed water is supplied from the ferrocyanide mixed water tank 9 to the radioactively contaminated water in the pretreatment tank 7a and stirred and mixed. Thereby, radioactive cesium in radioactive contaminated water is adsorbed by ferrocyanide. Stirring is continued for 1 hour, for example.

(Pretreatment second step)
Thereafter, the zeolitic adsorbent mixed water from the zeolite mixed water tank 11 is supplied to the radioactively contaminated water in the pretreatment tank 7a and stirred and mixed. Thereby, radioactive strontium in radioactive polluted water is adsorbed by the zeolite adsorbent. Stirring is continued for 1 hour, for example. Thereafter, radioactively contaminated water (pretreated contaminated water) in the pretreatment tank 7 a is sent to the stirring granulation tank 17.

(Flocculant-added mixing first step)
An inorganic flocculant is added from the inorganic flocculant storage tank 19 to the pretreated contaminated water in the stirring granulation tank 17 and mixed by stirring. When an inorganic flocculant is added to the pretreated contaminated water, the charge of the negatively charged solid particles is neutralized by the positively charged inorganic flocculant, so that the solid particles gather in the pretreated contaminated water. Thus, an aggregate is formed. This aggregate includes particles of iron ferrocyanide adsorbed with radioactive cesium and particles of zeolitic adsorbent adsorbed with radioactive strontium.

(Flocculant-added and mixed second step)
Next, the aqueous solution of the organic flocculant from the organic flocculant preparation tank 21 is added to the pretreated contaminated water in the stirring granulation tank 17 and stirred and mixed. When the organic flocculant is added, the aggregates gather to form a larger aggregate (floc), and a mixed liquid in which the flocs, which are solid components, are mixed with the liquid component is generated. The floc in the liquid mixture is large and is likely to settle in the liquid component. The liquid mixture is sent to the thickener device 23.

(Solid-liquid separation process)
In the thickener device 23, the liquid mixture is successively sent from the stirring granulation tank 17 to the staying tank 23a, and the liquid mixture stays in the staying tank 23a for a certain period of time. The residence time of the mixed liquid is, for example, about 1 to 2 hours. The floc in the mixed liquid settles below the staying tank 23a by gravity. A floc (concentrated slurry) separated from the supernatant liquid is sent from the withdrawal port 23b to the slurry tank 27 by withdrawing the floc that is unevenly distributed in the vicinity of the bottom of the retention tank 23a from the withdrawal port 23b. On the other hand, the supernatant liquid is sequentially collected in the retention tank 23 a and sent to the treated water facility 31. In the treated water facility 31, the remaining radionuclide is removed by a predetermined water treatment, and the treated water in a state where the concentration of the radionuclide is sufficiently lowered is discharged out of the system.

(Drum filling process)
The concentrated slurry sent to the slurry tank 27 is filled into the concentrated slurry drum by the drum filling device 29 and carried out of the system. In the concentrated slurry, the radionuclides (radiocesium and strontium) originally contained in the radioactively contaminated water are concentrated and contained, and as a result, the radionuclide-containing material is concentrated and reduced in volume. If soil particles remain in the raw water (the radioactively contaminated water in the radioactively contaminated water tank 3), the soil particles are also contained in the concentrated slurry and discharged out of the system.

  Then, the effect by the processing method of radioactive contamination water mentioned above is demonstrated.

  In the above-described treatment method, the radionuclide is adsorbed on the adsorbent (iron ferrocyanide and zeolite adsorbent) in the pretreatment step, and the solid containing the adsorbent is granulated in the flocculant addition mixing step. The solid matter containing the radionuclide is separated by a solid-liquid separation process. In the solid-liquid separation step, sedimentation separation by gravity is used. Therefore, by preparing a large-capacity thickener device 23, the liquid mixture can be efficiently processed in large quantities. That is, sedimentation separation using the thickener device 23 and the like is relatively easy to increase in scale as compared with other solid-liquid separation methods such as centrifugation, and is suitable for treatment of a large amount of turbid water. Therefore, the throughput of the entire radioactive contaminated water treatment can be increased, and a large amount of radioactive contaminated water can be treated efficiently.

  In addition, even when soil particles remain in the raw water (the radioactively contaminated water in the radioactively contaminated water tank 3), the soil particles are finally contained in the concentrated slurry and discharged out of the system. If the degree is about 100 ppm or less, the soil particles are also well removed.

  Further, since the thickener device 23 is used in the solid-liquid separation step, a solid substance containing a high concentration of radionuclide can be recovered from the drawing port 23b at the bottom of the retention tank 23a. The floc (concentrated slurry) that has settled at the bottom of the retention tank 23a has the highest radioactivity in the system, but since this concentrated slurry is unevenly distributed in the lower part of the retention tank 23a, the effect of radioactivity is reduced. The protective structure may be provided intensively in the lower part of the retention tank 23a. Therefore, radiation protection measures can be taken relatively easily. For example, about the lower half of the thickener device 23, the conveying line for the concentrated slurry to the slurry tank 27, the slurry tank 27, and the drum filling device 29 are subjected to radiation shielding measures.

  In addition, the pretreatment process using the adsorbent is divided into two stages. In the first pretreatment process, ferric ferrocyanide is added to the radioactive contaminated water, and then in the second pretreatment process, the zeolite adsorbent is used. Is added. Here, iron ferrocyanide mainly adsorbs cesium, and zeolitic adsorbent has a property of adsorbing cesium and strontium. Therefore, by using ferrocyanide in the first pretreatment first step, radioactive cesium in the radioactive contaminated water is first adsorbed and reduced by iron ferrocyanide, and in the second pretreatment step, the zeolitic adsorption is performed. By using the agent, the adsorption capacity of the zeolite-based adsorbent can be exhibited mainly for the adsorption of radioactive strontium.

  Therefore, in the pretreatment second step, radioactive strontium in the radioactively contaminated water is efficiently reduced by the zeolite adsorbent, so that the necessary amount of the zeolite adsorbent can be suppressed and the amount used can be suppressed. In addition, since the zeolite-based adsorbent is an expensive adsorbent, it contributes to the cost reduction of the entire radioactive contaminated water treatment. That is, if the pretreatment second step is executed first, the zeolite adsorbent adsorbs not only radioactive strontium but also much radioactive cesium. As a result, the ability to treat radioactive strontium by the zeolite-based adsorbent decreases, and the necessary amount of the zeolite-based adsorbent increases, which is not preferable.

  Although one embodiment of the present invention has been described above, the present invention is not limited to the above-described embodiment, and may be modified without changing the gist described in each claim.

  For example, in the embodiment, the radioactively contaminated water to be treated contains radioactive cesium and radioactive strontium, but the treatment method of the present invention uses radioactively contaminated water that hardly contains radioactive strontium (for example, radioactive cesium is used as a radionuclide). Mainly contained radioactive contaminated water) may be treated.

  In the embodiment, two types of adsorbents (iron ferrocyanide and zeolite-based adsorbent) are used. However, the processing method of the present invention may use only one type of adsorbent. For example, when treating radioactively contaminated water that contains almost no radioactive strontium (for example, radioactively contaminated water that mainly contains radioactive cesium as a radionuclide), use only ferric ferrocyanide to reduce the radioactivity of the treated water. It is thought that it can be sufficiently reduced. Further, even when radioactively contaminated water containing radioactive cesium and radioactive strontium is treated, it is considered that the radioactivity of the treated water can be sufficiently reduced using only the zeolite-based adsorbent.

(Example)
The present inventors performed Tests 1 to 9 in which radioactively contaminated water A to D shown in Table 1 (FIG. 2) was treated with ferrocyanide and / or zeolite adsorbent. The treatment in each test 1 to 9 is the same as the contaminated water treatment by the radioactive contaminated water treatment facility 1 described above except for the combination of the first adsorbent and the second adsorbent. The first adsorbent shown in Table 1 is an adsorbent added to the radioactive contaminated water in the pretreatment first step, and the second adsorbent is an adsorbent added to the radioactive contaminated water in the pretreatment second step. In addition, in each of the pretreatment first step and the pretreatment second step, after each adsorbent was added, stirring was continued for 1 hour.

  The radioactive contaminated water A is radioactive contaminated water that is expected to contain mainly radioactive cesium as a radionuclide. The radioactive contaminated water B is a radioactive contaminated water that is expected to contain radioactive cesium and a small amount of radioactive strontium as radionuclides. The radioactive contamination water C is radioactive contamination water expected to contain radioactive cesium and radioactive strontium as radionuclides. The radioactively contaminated water C is expected to contain radioactive cesium and radioactive strontium as radionuclides, and is further radioactively contaminated water containing soil particles. The radioactivity per volume of each raw water and each treated water was measured using a germanium semiconductor detector. The turbidity of raw water and treated water was measured using a throwing light scattering type measuring instrument.

  According to Test 1 and Test 2, when raw water is mainly contaminated with radioactive cesium, the activity per volume of treated water is 0.1 by using either iron ferrocyanide or zeolite adsorbent. Bq / mL could be achieved.

  According to Test 3 and Test 5, when radioactive strontium is contained in raw water, a radioactivity of 0.1 Bq / mL per volume of treated water is achieved even when only ferric ferrocyanide is used as an adsorbent. I couldn't. This is probably because ferric ferrocyanide hardly adsorbs radioactive strontium in the raw water, and radioactive strontium remains in the treated water. On the other hand, according to Test 4 and Test 6, it was possible to achieve a radioactivity of 0.1 Bq / mL per volume of treated water by using only the zeolite adsorbent for the same raw water. Thereby, it was found that the zeolitic adsorbent has the ability to treat both radioactive cesium and radioactive strontium.

  Comparing test 6 and test 7, test 7 uses zeolitic adsorbent by using ferric ferrocyanide (first adsorbent) prior to using zeolitic adsorbent (second adsorbent). It was found that the amount can be reduced compared to test 6. In Test 7, instead of reducing the amount of zeolitic adsorbent used, the amount of ferrocyanide used is increased. However, since the zeolitic adsorbent is more expensive than ferric ferrocyanide, the adsorbent combination of Test 7 can reduce the entire cost of treating contaminated water.

  Test 7 and test 8 are compared. Compared with Test 7, in Test 8 in which the order of charging ferric ferrocyanide and zeolitic adsorbent was changed, the radioactivity per volume of treated water was 20-30 Bq / mL and was not sufficiently reduced. This is because the zeolitic adsorbent previously introduced as the first adsorbent adsorbs not only radioactive strontium but also much radioactive cesium, and as a result, the ability to treat radioactive strontium by the zeolite adsorbent decreases, and finally It is thought that radioactive strontium remained in the treated water. Therefore, in the order of adsorbent input in Test 8, it is necessary to increase the input amount of the zeolite adsorbent in order to sufficiently reduce the radioactivity of the treated water. On the other hand, as shown in Test 7, it was found that the amount of the zeolite-based adsorbent used can be reduced by the charging order in which the first adsorbent is iron ferrocyanide and the second adsorbent is the zeolite-based adsorbent.

  Comparing test 7 and test 9, it was found that the turbidity component can be reduced even when the turbidity component (such as soil particles) is contained in the raw water. Further, comparing Test 9 and Test 10, in Test 9, the removal rate of turbidity components was 95%, but in Test 10, the removal rate of turbidity components was reduced to 92.5%. That is, it was found that the removal rate of turbidity components was higher when the turbidity of raw water was 100 ppm than when the turbidity of raw water was 200 ppm. Thus, it was found that if the turbidity of the raw water is about 100 ppm, the soil particles contained in the radioactive contaminated water can be sufficiently removed by the treatment of the radioactive contaminated water treatment facility 1.

  DESCRIPTION OF SYMBOLS 1 ... Radioactive water treatment facility, 7a, 7b ... Pretreatment tank, 9 ... Ferrous ferricide (first adsorbent) mixed water tank, 11 ... Zeolite (second adsorbent) mixed water tank, 19 ... Inorganic coagulation Agent storage tank, 21... Organic flocculant preparation tank, 23. Thickener device, 23 a. Retention tank, 23 b.

Claims (4)

A method for treating radioactive contaminated water containing a radionuclide containing at least radioactive cesium,
A pretreatment step of adding an adsorbent that adsorbs the radionuclide to the radioactively contaminated water, mixing and stirring, and pretreating;
After adding an inorganic flocculant to the pretreated contaminated water pretreated in the pretreatment step, an organic flocculant aqueous solution is added and mixed to granulate the solid matter containing the adsorbent. A coagulant addition mixing step to be performed;
And a solid-liquid separation step of solid-liquid separation of the liquid mixture obtained in the flocculant addition mixing step by sedimentation separation. In the solid-liquid separation step,
The solid-liquid separation is performed using a thickener device that has a retention tank for retaining the mixed liquid and extracts the solid matter settled in the mixed liquid from a lower portion of the retention tank. Treatment method of radioactive contaminated water. In the pretreatment step,
As the adsorbent, two kinds of a first adsorbent and a second adsorbent are used,
3. The radioactive contamination according to claim 1 or 2, wherein the first adsorbent is added to the radioactive contaminated water and mixed and stirred, and then the second adsorbent is further added and mixed and stirred. Water treatment method. The radioactively contaminated water further includes radioactive strontium as the radionuclide,
The method for treating radioactive polluted water according to claim 3, wherein the first adsorbent is ferric ferrocyanide, and the second adsorbent is a zeolite adsorbent.

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