JP6347766B2 - Method for producing radioactive cesium-removing concrete product and method for removing radioactive cesium - Google Patents

Description

  The present invention relates to a concrete product for removing radioactive cesium and a method for removing radioactive cesium using the same.

  When a large-scale accident occurs at a nuclear power plant, soil and groundwater are contaminated due to environmental pollution caused by the release of a large amount of radioactive material. In addition, sludge generated at various sewage treatment plants and general waste treatment plants The incineration ash generated in Japan also contains high-level radioactive pollutants, and the development of treatment methods is urgently needed.

The main radionuclides released in the nuclear power plant accident are ¹³⁴ Cs (half-life 2.06 years) and ¹³⁷ Cs (half-life 30.07 years). ¹³⁷ Cs has a long half-life and is expected to have an adverse effect over a long period of time. In particular, the treatment of soil, fallen leaves, sewage sludge, and incinerated ash contaminated with ¹³⁴ Cs and ¹³⁷ Cs is a major issue. In addition, ¹³⁴ Cs and ¹³⁷ Cs scattered in a wide area flow along slopes by rain and snow in mountain forest areas, accumulate in swamps, concentrate to form high-concentration hot spots, and flow down swamps. ¹³⁴ Cs and ¹³⁷ Cs combine with chloride ions to form cesium chloride, which is extremely easy to dissolve in water and contaminates groundwater and fields. The development of decontamination treatment technology that safely and efficiently removes the ionized state of ¹³⁴ Cs and ¹³⁷ Cs has been sought and intensively studied.

For example, in Patent Document 1, as a method for treating radioactive cesium and strontium in high-level radioactive waste, it is selectively adsorbed on synthetic mordenite, zeolite or a mixture thereof, and an adsorbent is prepared to obtain a sintered solidified body. The technology is disclosed.
Patent Document 2 discloses that a radioactive cesium in an aqueous solution is adsorbed together with another alkali metal such as sodium or potassium or an alkaline earth metal such as calcium or magnesium, from an alkali metal or alkaline earth other than radioactive cesium. By removing the at least part of the metal and repeating the operation of adsorbing the radioactive cesium again to the vacant adsorption site, by utilizing most of the adsorption sites of the zeolite for the adsorption of radioactive cesium, There has been disclosed a decontamination technique that makes high use of zeolite as an adsorbent material and enables volume reduction of secondary waste generated by decontamination work.
Patent Document 3 discloses a radioactive substance adsorbing layer (clay) in which the ratio of the mass content of the hardly soluble ferrocyan compound to the filling volume is 0.4 g / L to 11 g / L or less in a path through which radioactively contaminated water flows. (Mineral or zeolite) 1 and a radioactive substance adsorbing layer 2 (clay mineral or zeolite) 2 having a ratio of the mass of the hardly soluble ferrocyan compound to the filling volume of more than 11 g / L and not more than 550 g / L. An apparatus for treating radioactive sewage comprising a configuration in which a radioactive substance adsorbing layer 1 is disposed on the upstream side is disclosed.
In Patent Document 4 and Patent Document 5, a mineral component other than cesium is eluted from a substance containing radioactive cesium into a first solvent (water or the like), and then radioactive cesium is removed from the substance treated with the first solvent into the second solvent. A method for treating a radioactive cesium-containing substance is disclosed that is extracted with (such as oxalic acid), adsorbed on the extracted radioactive cesium adsorbent and recovered, and the recovered radioactive cesium is mixed with an immobilizing material and stabilized.
Patent Document 6 discloses a method for treating radioactive liquid waste containing radioactive cesium using zeolite adsorbed with a ferrocyanide compound as an adsorbent.

Japanese Patent No. 2807811 JP 2013-117450 A JP 2015-25670 A Japanese Patent No. 5684102 JP 2013-88391 A Japanese Examined Patent Publication No. 62-43519

However, the above prior art has the following problems.
・ Patent Document 1 is intended for radioactive cesium or radioactive strontium contained in extremely high-level radioactive waste generated at nuclear power plants. It requires enormous energy and cannot be used for the purpose of decontamination of low-level radioactive cesium diffused widely in the atmosphere due to a nuclear power plant accident.
・ Patent Document 2 is treated with powdered zeolite (Example), so that powder containing a large amount of radioactive cesium is not easy to handle and workability is poor, and zeolite adsorbed with radioactive cesium is cemented Since it is solidified in a container or placed in a radiation shielding container for final disposal (see paragraph [0008]), there is a problem that the work is complicated and there is a high risk of being exposed to an explosion and lacks safety. .
-Patent Document 3 has to prepare a plurality of radioactive substance adsorbing layers, and lacks productivity and installation workability, and the radioactive substance adsorbing layer is formed with particles of 1 mm to 5 mm, and granular ones are left as they are. Since it has a high possibility of scattering because it is handled, it has a problem of lack of productivity and handleability after adsorbing radioactive cesium.
Patent Documents 4 and 5 require the work to stabilize the radioactive cesium recovered by the adsorbent with a fixing agent, and there is a risk of being exposed to radiation in the course of the work, and it is not safe, and the radioactive cesium extractant There is a problem that the treatment of radioactive liquid waste such as oxalic acid is complicated and lacks safety and workability.
-In Patent Document 6, since the ferrocyanide compound having very high radiocesium adsorption property is directly attached to the zeolite, the radioactive contamination level of the zeolite after the treatment is locally high, and further, on the fine powder. Since it is handled as it is, there is a high possibility that it will be scattered, and there is a problem that it may cause trouble at the stage of disposal of zeolite after adsorption of radioactive cesium.
・ In recent years, the consumption of coal ash and aluminum discharged in large quantities due to the increase in thermal power plants has been increasing year by year, and the treatment of aluminum dross residual ash, which is industrial waste, has become a social problem. Therefore, there is a strong demand for effective use of these industrial wastes.

  The present invention solves the above problems and responds to demands. Radiocesium released in water such as rivers, rivers and lakes and radioactive cesium released from soil by applying fertilizer such as ammonium sulfate to fields. In addition to its excellent adsorptivity, it has excellent retention of radioactive cesium, and in particular, it can be easily installed in mountainous areas and in the waterways of radioactively contaminated water, so it is easy to install and adsorbs a considerable amount of radioactive cesium. In addition to excellent workability in disposal, it is not only excellent in safety during work, but also a concrete product for removing radioactive cesium that can be made from coal ash, aluminum dross residual ash, and cement material for effective use of industrial waste. And can be easily installed in mountains, rivers, lakes, catchments, ditches, slopes, etc., where high-level radioactive cesium flows, and long-term radioactive cesium can be installed The purpose is to provide a method for removing radioactive cesium using a concrete product for radioactive cesium removal that is excellent in decontamination workability that can adsorb efficiently and decontaminate running water efficiently after decontamination and can be removed by simple work And

In order to achieve the above object, a concrete product for removing radioactive cesium and a method for removing radioactive cesium using the same according to the present invention have the following configurations.
In the method for producing a concrete product for removing radioactive cesium according to claim 1 of the present invention, a synthetic zeolite obtained by synthesizing coal ash and aluminum dross residual ash in an alkaline solution is used as Ni, Co, Cu, Mn, It was obtained by immersing in an aqueous solution of any one of the acidic metal salts of Zn to exchange ions with metal ions in the synthetic zeolite, impregnating with ferrocyanide ions, and precipitating an insoluble ferrocyan compound inside. artificial zeolite (a) and cement material (b) is a / b = 3 / 7~7 / 3, are perforated and aggregate, water were mixed, then an arrangement for molding.
With this configuration, the following effects can be obtained.
(1) Since synthetic zeolite synthesized with coal ash and aluminum dross residual ash is used, industrial waste is effectively used.
(2) The optimum zeolite can be synthesized simply by changing the blending amount of the aluminum dross residual ash according to the type of coal ash and the Al content of the aluminum dross residual ash.
(3) Since impregnation with any one metal ion of Ni, Co, Cu, Mn, Zn or ion exchange of Na ions with the metal ion, impregnation with ferrocyanide ions to precipitate an insoluble ferrocyan compound. Ferrocyanide ions can be stably retained in the concrete product, and radioactive cesium can be adsorbed without change over time.
(4) The radioactive cesium can be firmly held in the concrete product with the metal ferrocyanide compound to prevent leakage.
(5) When the concrete product is a flat block or interlocking block, it is easy to install in rivers, rivers, lakes, drains, etc., and the amount of radioactive cesium adsorbed per unit is large. After leaving it alone, it can be easily replaced with civil engineering equipment, resulting in excellent workability.
(6) In the case where the concrete product is a flat block or an interlocking block, it can be easily and mass-produced with existing manufacturing equipment, and is excellent in productivity and excellent in transportability from the production site to the installation location.
(7) If the concrete product is ball-shaped, donut-shaped, or Raschig ring-shaped, it can be easily placed in a gabion or net, and can be easily collected and moved with civil engineering equipment when replacing it. It is excellent in workability.
(8) Concrete products are excellent in water permeability, and artificial zeolite containing an insoluble ferrocyan compound fixed in the concrete products does not show elution of radioactive cesium in water and is difficult to fly even in a dry state.

Here, clinker ash and fly ash are preferably used as the coal ash. This is because the content of SiO ₂ or Al ₂ O ₃ is higher than that of BM ash or PFBC ash. In addition, BM ash and PFBC ash can also be mixed and used for clinker ash and fly ash. These mixing ratios are appropriately determined depending on the contents of SiO ₂ and Al ₂ O ₃ in clinker ash and fly ash.
Since PFBC ash has a size of 3 to 10 μm, it can be used as it is, and fly ash can be used as it is because particles with a particle size of 0.1 mm or less account for 90% or more. Since BM ash has a large particle size, it is used after being pulverized.

Almidros residual ash is not particularly limited as long as it is a by-product in the aluminum melting step of melting aluminum raw material made of aluminum or aluminum alloy. The composition of aluminum dross residual ash, metal aluminum 8-15% by weight, 50 to 60 wt% aluminum oxide (Al ₂ O _3), aluminum nitride (AlN) 5 to 15 wt%, iron (Fe) 0.5 to 2 mass%, silicon (Si) 0.5-10 mass%, magnesium (Mg) 0-6 mass%, alkali (Na + K) 1.5-3 mass%, calcium (Ca) 0-1 mass%, chlorine ( A material such as Cl) 1 to 6% by mass and fluorine (F) 0.5 to 2% by mass is preferably used.

The synthetic zeolite is produced by adding coal ash to the supernatant obtained by reacting aluminum dross residual ash in an aqueous alkali solution at 85 to 99 ° C. for 4 to 10 hours and stirring.
-As alkaline aqueous solution, 1.5-3.5M aqueous solution, such as caustic soda, is used suitably.
The mixing ratio of coal ash and aluminum dross residual ash is 0.7 to 1 when the coal ash is fly ash and the coal ash is 1 while the aluminum dross residual ash has an Al content of 25 to 35%. Used at a rate of .4.
-The synthetic zeolite has a particle size of 30 to 55 μm. This is because the particle size is almost the same as the particle size of cement, so that it can be mixed uniformly with cement and can adsorb radioactive cesium to the entire concrete product without any spots.
Synthetic zeolite is preferably X-type zeolite for efficiently adsorbing cesium, but mordenite type or A-type zeolite may also be used.

-As the first method for producing artificial zeolite, synthetic zeolite is immersed in an aqueous solution of one of the acid metal salts of Ni, Co, Cu, Mn, and Zn, and the sodium in the synthetic zeolite is stirred. performed with metal ions ion-exchange etc. and Ni or the like, and then washed with water neutralization, it is immersed in a water-soluble ferrocyanide compound solution.
The concentration of the ferrocyan compound aqueous solution is preferably adjusted to an M concentration of about twice that of the acidic metal salt 1. However, it is used at 1M or less.
Then, after filtering and washing, a method of drying is mentioned.
Further, as a second method, an aqueous solution of ferricyanide compound (concentration: 0) is added to an aqueous solution (concentration: 0.3 to 0.6M) of any one of Ni, Co, Cu, Mn, and Zn. 7 to 1.4M), the precipitate formed is separated into solid and liquid, the precipitate is washed with water, water is further added, synthetic zeolite is added, and the mixture is sufficiently kneaded with a kneader, after filtered washed to wash away ferrocyanide compound unreacted, method of drying is used.
Nitric acid salts such as nitrates, chlorides, sulfates and acetates are used. Of these, nitrate is preferably used.
-As a ferrocyanide compound of ferrocyanide ion aqueous solution, potassium ferrocyanide, sodium ferrocyanide, etc. can be mentioned.

According to a second aspect of the present invention, there is provided a method for producing a concrete product for removing radioactive cesium, wherein a precipitate obtained by mixing an aqueous solution of an acidic metal salt of Ni, Co, Cu, Mn and Zn and an aqueous solution of a ferrocyan compound is used. Artificial zeolite (a) and cement material obtained after kneading with synthetic zeolite obtained by synthesizing coal ash and aluminum dross residual ash in an alkaline solution after separation and washing with water and filtration washing (B) has a configuration in which a / b = 3/7 to 7/3, aggregate and water are mixed and then molded.
With this configuration, in addition to the effects obtained in the first aspect, the following actions can be obtained.
(1) Since the ferrocyan compound is also exposed on the surface of the artificial zeolite, the contact surface with the radioactive cesium is wide and the adsorption power of cesium is excellent.
(2) Since the ferrocyanic compound can be ion-exchanged up to the equilibrium amount, the adsorption efficiency is excellent.

Here, the kind of acidic metal salt or ferrocyanide of any one of Ni, Co, Cu, Mn, and Zn, the contents of coal ash and aluminum dross ash, and the contents of synthetic zeolite are the same as in claim 1. Description is omitted.
-When 0.08 to 1.2 weight of ferrocyanide is blended with 1 weight of synthetic zeolite, it is preferable because it is efficiently dispersed on the surface of the synthetic zeolite.
The concentration of the acidic metal salt solution of any one of Ni, Co, Cu, Mn, and Zn is 0.05 to 1.2M. As the concentration becomes lower than 0.05M, the ion exchange ability tends to be lacking, and as the concentration becomes higher than 1.2M, the ion exchange equilibrium amount is exceeded, which is not preferable.
The concentration of the ferrocyanide ion aqueous solution is 40 to 65% of the concentration of the acidic metal salt solution. It is preferable to use an aqueous ferrocyanide ion solution having a concentration of 40 to 65% because ion exchange equilibrium can be approached.

In claims 1 and 2, the artificial zeolite and the cement are used in a blending ratio (weight ratio) of 30 to 70/70 to 30 for the artificial zeolite with respect to the cement 100.
As the cement, Portland cement, blast furnace cement, fly ash cement, alumina cement or the like is used.
-As a form of the concrete product for radioactive cesium removal, a flat block or interlocking block with a size of a × b × c (for example, a = 3 to 10 cm, b = 5 to 15 cm, c = 15 to 30 cm), Examples thereof include a ball shape, a donut shape, a cylindrical tube shape, a Raschig ring shape, and a plate shape having a diameter of 2 to 10 cm.
Next, the manufacturing method will be specifically described.
The artificial zeolite (b) is blended with the cement (b) so that (b) / (b) is 3/7 to 7/3. When the blending ratio is less than 3/7, the mechanical strength is low, and when the blending ratio is more than 7/3, the adsorption ability of radioactive cesium is lowered, which is not preferable. In addition, the aggregate and admixture are mixed with water in the same amount as when manufacturing ordinary concrete products. After the kneaded mixture is poured into the mold, vibration is applied using a jolt squeeze machine. Then, molding is performed by applying a predetermined pressure under the condition, and then the obtained molding is cured to obtain a concrete product for removing radioactive cesium.

Method of manufacturing concrete products for radioactive cesium removal of Claim 3 of the present invention, concrete consisting of a flat block or interlocking blocks obtained by the production method of concrete products for radioactive cesium removal according to claim 1 or 2 A cyan adsorbent layer that adsorbs ferrocyanide partially dissolved in running water is formed on one surface of the product .
With this configuration, in addition to the effects obtained in the first or second aspect, the following actions can be obtained.
(1) Even if a part of ferrocyanide ions is dissolved in the running water from the concrete product, since it has a cyan adsorbent layer, it can adsorb and capture ferrocyanide ions and is excellent in safety.
(2) Although the ferrocyanic compound is not toxic, it is not preferable because the total cyan amount specified by the environmental standards and wastewater standards increases. It is possible to prevent an increase in the total cyan content.
(3) Since the ferrocyanide ions adsorbed on the cyan adsorbent layer further adsorb radioactive cesium, the adsorption efficiency is excellent.

Here, activated carbon, anion exchange resin, or the like is preferably used as the cyan adsorbent layer.
As the activated carbon, coal-based, petroleum-based, coconut tree-based, wood-based and the like are used. Also, felt-like and cloth-like activated carbon fibers can be used.
As an anion exchange resin, if it is a strong base anion exchange resin, things, such as a granular form, a fiber form, and a film | membrane form, can be used. For example, a strong base anion exchange resin having a matrix composed of a styrene / divinylbenzene copolymer may be mentioned.
The cyan adsorbent layer is formed by, for example, forming an activated carbon or anion exchange resin to a thickness of several millimeters after filling a slurry made of artificial zeolite and cement material into the mold when manufacturing the block. The cyan adsorbent layer obtained above is provided and pressure is applied, or the cyan adsorbent layer is set and integrated immediately after molding of the block, or cyan formed in a sheet form on one side of the block product The adsorbent layer may be integrated later with an adhesive or the like.

According to a fourth aspect of the present invention, there is provided a method for removing radioactive cesium from a concrete product obtained by the method for producing a radioactive cesium-removing concrete product according to the first or second aspect or the concrete product according to the third aspect. Lay it in parallel with the flow of running water at the hot spot at the bottom of the lake, the bottom of the lake, the drainage ditch or the gutter, or create it in a bowl shape through mortar, etc., and create it in the bottom of the riverbed or lake, the drainage ditch or the gutter It is set in the hot spot of the bottom part of this material in the direction perpendicular | vertical to the flow of flowing water, and has the structure made to contact the flowing water containing radioactive cesium.
With this configuration, the following effects can be obtained.
(1) Since the concrete product has a large capacity of adsorption of radioactive cesium, even if it is installed in a hot spot of radioactive cesium, it absorbs radioactive cesium over a long period of time, so there is no need to replace it frequently and workability Excellent.
(2) Since the shape of the concrete product for removing radioactive cesium is large and excellent in mechanical strength, it is easy to set in running water, and it is easy to replace and collect after adsorption, resulting in excellent workability.
(3) The recovered concrete product for removing radioactive cesium stably retains radioactive cesium inside and does not leak the radioactive cesium, so it is excellent in disposal work, storage and storage.
(4) Since the concrete product manufactured by mixing artificial zeolite with cement has an extremely large amount of water retention, even if a concrete product that absorbs running water containing radioactive cesium ions is exposed from the running water, Since ion exchange can be performed in the system, it can be installed on slopes such as hillsides, and radioactive cesium can be decontaminated over a wide range.
Here, when the concrete product is formed of a flat block and an interlocking block and has a cyan adsorbent layer on one surface thereof, the concrete adsorbent layer is installed on the downstream side.

-The manufacturing method of the concrete product for radioactive cesium removal of this invention has the following effects.
(1) An existing concrete product manufacturing facility can be used to easily manufacture by the same operation as a normal concrete product, and a method for manufacturing a radioactive cesium removing concrete product excellent in productivity can be realized.
(2) Since it can manufacture with industrial wastes, such as coal ash and aluminum dross residual ash, the manufacturing method of the concrete product for radioactive cesium removal excellent in resource-saving property is realizable.
( 3 ) The ferrocyan compound is extremely excellent in radioactive cesium adsorption ability and stably retains radioactive cesium after adsorption. Therefore, a method for producing a radioactive cesium removal concrete product excellent in radioactive cesium removal workability is provided. realizable.
( 4 ) When the concrete product is manufactured in blocks, the adsorption capacity of radioactive cesium per piece is large, so it can be opened and replaced or recovered for a considerable period of time just by installing it once. The manufacturing method of the concrete product for radioactive cesium removal excellent in the property and installation workability is realizable.
-The removal method of radioactive cesium of this invention has the following effects.
(1) Concrete products containing zeolite, is excellent in water permeability, it is possible to adsorb radioactive cesium in flowing deep of the concrete product can be realized method of removing radioactive cesium superior in adsorption efficiency.
(2) Since the concrete product for removing radioactive cesium is rich in formability, it is possible to realize a method for removing radioactive cesium that can selectively construct a concrete product having an optimal shape according to the installation location.
(3) Since there is a large amount of radioactive cesium ions adsorbed per unit, it is possible to realize a method for removing radioactive cesium that is long in replacement time, easy to plan replacement work, excellent in workability, and excellent in labor saving.

Change in decontamination rate of concrete blocks made by adding various zeolites over time Change in decontamination rate of concrete blocks made by adding various zeolites over time Concentration dependence of decontamination rate of Ni ferrocyanide and influence of metal species

-The concrete product for removing radioactive cesium of the present invention is obtained by dissolving aluminum dross residual ash, which is industrial waste, in an alkaline aqueous solution such as caustic soda, and then adding coal ash, which is industrial waste, to the supernatant of the alkali treatment liquid. Stir to obtain a synthetic zeolite. The obtained synthetic zeolite is subjected to ion exchange of Ni and Ni or impregnated with Ni ions in an acidic solution of nickel of a predetermined concentration, and then a solution of ferrocyanide ions of a predetermined concentration is added, and Ni ferrocyanide is synthesized into a synthetic zeolite. It is impregnated into an artificial zeolite.
The obtained artificial zeolite, cement, coarse aggregate made of crushed sand, slag, crushed stone, and ceramic pieces having a particle size of 5 mm to 10 mm, crushed sand having a particle size of 5 mm or less, slag, crushed stone, fine pieces made of ceramic pieces, etc. Aggregates and the like are mixed and kneaded according to a conventional method to obtain a concrete slurry. Next, the obtained concrete slurry is obtained by molding with a mold having a predetermined shape.
As another production method, an acidic solution of nickel of a predetermined concentration and a solution of ferrocyanide ions of a predetermined concentration are mixed, and the synthetic zeolite is mixed and kneaded with an insoluble ferrocyanide, to produce an artificial zeolite, Using the obtained artificial zeolite, it is obtained by molding a concrete slurry obtained in the same manner as described above with a mold having a predetermined shape.
-The method for removing radioactive cesium using the concrete product for removing radioactive cesium of the present invention is to lay it as it is in the running water of the installation site when the concrete product is in a block shape, or to store it in a net or the like if it is not in a block shape. And install in running water.

  EXAMPLES Hereinafter, although this invention is demonstrated more concretely based on an Example and a comparative example, this invention is not limited to these Examples.

(Production of synthetic zeolite)
Almidros residual ash (aluminum content 5 to 30%) 4 kg of caustic soda treatment solution in which 3.2 kg / 40 of caustic soda solution was dissolved was added and stirred with coal ash 5 to 6 kg, and then with water After washing and drying, a synthetic zeolite having an average particle size of 40 μm is obtained.

(Manufacture of artificial zeolite)
Synthetic zeolite (A-1): synthetic zeolite 1.5Kg was immersed in 0.1M nickel nitric acid aqueous solution at room temperature for 2 days, Na ions and Ni ions were exchanged, filtered and then ion exchanged The zeolite is immersed in a 0.05 M aqueous potassium ferrocyanide solution for 2 days to precipitate insoluble nickel ferrocyanide inside. Then, it washed by filtration, cut | disconnected the water | moisture content, it was made to dry at 90 degreeC for 3 hours, and the artificial zeolite (A-1) was obtained.
・ Artificial zeolite (A-2): To a precipitate formed by adding a 0.25M potassium ferrocyanide aqueous solution to a 0.5M nickel nitrate aqueous solution (the solution part is aspirated and removed with an aspirator and then washed with water) After repeating several times, add an appropriate amount of water) Add synthetic zeolite (1.5 kg), knead well, finally filter, drain moisture, and dry at 90 ° C. for 3 hours to artificial zeolite (A-2) Got.

(Manufacture of concrete products for removing radioactive cesium)
-About 1.5 kg of artificial zeolite (A-1) and 2.25 kg of cement so that the ratio (a / b) of artificial zeolite (a) to cement (b) is (a / b = 4/6) Then, after 10.9 kg of aggregate, 0.02 kg of admixture and 0.52 kg of water were mixed and kneaded, the cement slurry was poured into the mold and then subjected to 60 Hz vibration with a jolt squeeze machine. It was molded by applying a pressure of ² t / 0.5 m ² . The resulting molded product is naturally cured and dried for 7 days, and is a block-shaped concrete product for removing radioactive cesium having a size of about 6 cm × 10 cm × 20 cm and an average weight of about 2.85 kg (hereinafter referred to as (A-1B)). Got a block). Similarly, the ratio of artificial zeolite (a) to cement (b) is a / b = 3/7 (A-1 A), 5/5 (A-1 C), 6/4 (A-1 D). Each block (hereinafter collectively referred to as (A-1) block) was prepared by adjusting cement and other materials so that A, b, c, and d indicate that a / b is a block of 3/7, 4/6, 5/5, 6/4, respectively. The same applies hereinafter.
-Using artificial zeolite (A-2), block-shaped concrete products for removing radioactive cesium in the same way as the block (A-1) (A-2 B), (A-2 B), (A-2 C) , (A-2 D) blocks were created (hereinafter collectively referred to as (A-2) blocks).
-As a reference sample, manufactured and provided by Dr. Kortov, Dr. Ural University, Russia, using groconite purchased from Chiyoda Technol Co., Ltd. as a material, the same block as (A-1) block A concrete product for removing radioactive cesium was prepared (hereinafter referred to as (C-1) block).
・ Synthetic zeolite that has not been treated with chemicals as a material, (A-1 B), (A-1 B), (A-1 C) Block-like concrete product (D-1 B) in the same manner as the block , (D-1 B), (D-1 C) are created (hereinafter collectively referred to as (D-1) block).
-Using a natural zeolite as a material, a block-shaped concrete product was produced in the same manner as the (A-1) block (hereinafter referred to as (E-1) block).

(Adjustment of radioactive cesium aqueous solution)
For the radioactive cesium aqueous solution, the fallen leaves collected in Kawamata Town, Fukushima Prefecture were soaked in water and subjected to an ultrasonic cleaner. Further, the solution was concentrated by reducing the volume by removing water with a mantle heater.

(Evaluation of removal rate of radioactive cesium)
Place 50g of radioactive cesium aqueous solution in U8 container (volume: about 100cc), immerse each block in it, place it on high purity germanium semiconductor detector at room temperature 25 ° C, and measure the radioactive concentration in the solution every elapsed days did. As appropriate, each block was temporarily removed from the container, and the radioactive cesium concentration in the solution was measured with a high-purity germanium semiconductor detector. Further, the cesium concentration in the solution portion of the CsCl aqueous solution that was not radioactive was measured with an atomic absorption analyzer, and the cesium concentration in the block was measured with a fluorescent X-ray analyzer. From these, the reduction rate of radioactivity was measured, and the removal rate of radioactive cesium was evaluated.

(Experimental results and discussion)
Each block of (D-1b), (D-1b), (D-1c) (with 30-50% by weight of cement powder replaced with synthetic zeolite) was replaced with 0.12 mM CsCl aqueous solution (about 4L), and the Cs ion removal rate was determined from the change over time of the Cs ion concentration in the aqueous solution. The results are shown in (Table 1).
As is clear from this (Table 1), after 1 day, the removal rate of Cs ions was 32 to 38%, and gradually increased as the immersion time increased from 5 days, and the blending ratio of synthetic zeolite after 11 days. However, after 20 days, it was found that the removal rate was 46 to 62% and the blending ratio of the synthetic zeolite was not significantly different between 40% and 50%.

(Evaluation of mechanical strength)
Since mechanical strength becomes a problem when the cement content in the block decreases, the dimensions and bending strength test results of the concrete block were evaluated based on the water retention amount and water absorption amount. The results are shown in (Table 2) and their mechanical strength was evaluated. The results are shown in (Table 3).
As is clear from (Table 3) , a large difference in bending strength appears, and it can be seen that the synthetic zeolite with a compounding ratio of 50% is slightly below the standard value (5.0 or more). Thereafter, these results were comprehensively judged, and a product containing 40% of zeolite was prepared and compared.

(Evaluation of the residual ratio of ¹³⁷ Cs in radioactive cesium aqueous solution)
A small piece of each block (A-1b), (C-1), and (D-1) (cube with a side of about 3 cm) is taken and immersed in an aqueous solution of radioactive cesium to obtain a solution of the aqueous solution of radioactive cesium. Radioactivity was measured with a high-purity germanium semiconductor detector, and the residual ratio of ¹³⁷ Cs in the radioactive cesium aqueous solution was measured. The results are shown in FIG.
As is clear from this (FIG. 1), it was found that in all samples, the radioactivity decreased sharply in the first few days and then gradually decreased with the passage of time. It was found that the (D-1) block had the lowest reduction effect, and that after 30 days it almost returned to its original value. The (A-1) block was expected to have a value close to about 0.4 from (Table 1), but it was 0.6. This shows that even if radioactive Cs ions are incorporated into the zeolite, the zeolite itself is not sufficient to block the radioactivity. Produced and provided by Dr. Kortov, Ural University in Russia, and the residual rate of radioactive Cs ions in the (C-1) block made with groconite purchased from Chiyoda Technol Co., Ltd. It is a chemical treatment, and it is thought that the effect of the chemical treatment has a great influence.

(Evaluation of radioactivity reduction effect of radioactive cesium)
Radioactivity reduction effect was evaluated using each block of (A-1 B), (A-2 B), (C-1), and (E-1). The result is shown in FIG. The (A-1 b) block in which the inorganic porous body was impregnated with Ni ions in advance and the insoluble ferrocyanide was precipitated inside was reduced almost the same as the (D-1) block not subjected to the chemical treatment (FIG. 1). Only showed an effect. This is probably because artificial zeolite prepared from coal ash and aluminum dross residual ash had extremely few sites capable of exchanging Ni ions. On the other hand, when the (A-2b) block prepared by kneading the insoluble Ni ferrocyanide with the artificial zeolite was used, the reduction effect at the initial stage of immersion was the (C-1) block using the chemically treated sea green stone. Although it is inferior to, it has been found that the same reduction effect is exhibited when the number of days of immersion is increased.

  These samples were used to analyze changes in CsCl aqueous solution and Cs ion concentration in each block when immersed in a CsCl aqueous solution (Cs concentration of about 800 ppm), and the results are shown below.

(Evaluation by atomic absorption analysis)
A calibration curve for atomic absorption analysis was prepared using a standard cesium aqueous solution, and the analysis was performed after 1 day and after 6 days. After 17 days, a calibration curve was prepared and the concentration was measured. The results are shown in (Table 4) to (Table 6).

人工ゼオライトのみの（Ｄ−１）ブロックでも水溶液中のＣｓ濃度は減少し、数値的に見れば、十分Ｃｓを吸着できる能力を持っていることがわかる。（Ａ−２ｂ）ブロックは、１日目で大きなＣｓの減少がみられる。しかし、後述するようにコンクリートブロック中のＣｓ濃度は、浸漬時間と共に増加していることから、コンクリートブロック内に吸着（収蔵）されていることは間違いがないと思料される。グロコナイトを用いた（Ｃ−１）ブロックは、時間と共にＣｓの吸着能の高さを増していった。

Even with the artificial zeolite-only (D-1) block, the Cs concentration in the aqueous solution decreases, and from a numerical viewpoint, it can be seen that it has the ability to sufficiently adsorb Cs. (A-2b) A large decrease in Cs is observed on the first day. However, since the Cs concentration in the concrete block increases with the immersion time as described later, it is considered that there is no mistake that the Cs concentration is absorbed (stored) in the concrete block. The (C-1) block using groconite increased the adsorbability of Cs with time.

(Evaluation by fluorescent X-ray analysis)
In the fluorescent X-ray analysis, a predetermined amount of Cs ₂ CO ₃ and alumina were mixed to prepare a calibration curve. The calibration curve results are shown in (Table 7).
Subsequently, the decontamination rate of the radioactivity Cs was measured. The results are shown in (Table 8).
After 6 days for both the sea green stone and the artificial zeolite, the Cs Lα ray could not be confirmed, and comparing with the data on the 17th day, it can be seen that the Cs concentration in the block (A-2b) is extremely high compared to the others. In any case, it was found that the (A-2b) block and the (C-1) block have a high decontamination rate of radioactive Cs.

Since the weight of the block used for the analysis is different, it is as follows when converted per unit weight.

(Evaluation of Ni concentration and metal ion species)
(A-2b) Block prepared by changing the concentration of Ni ferrocyanide in the block to 0.05, 0.1, 0.5M, and (A-2b) Ni ion in the block, metal ion species of Co, Cu The reduction effect of radioactive cesium was evaluated for the blocks made by changing to. The result is shown in FIG. As is clear from FIG. 3, the reduction effect of radioactive cesium is not very effective when the concentration of Ni ferrocyanide is 0.05 or 0.1M, and a concentration of 0.5M or more is necessary. It was. The effect of reducing radioactive cesium when Ni ions are changed to Co and Cu metal ion species in the block (A-2b) is as follows: Co>Ni> Cu. It was found that Co has the highest reduction effect and a high value exceeding 90%. In addition, it was thought that Mn and Zn can be used although they have a slightly lower effect than Cu.

Next, the method for removing radioactive cesium of the present invention can be achieved by simply laying the concrete product for removing radioactive cesium on the bottom of rivers, lakes, drains, ditches, etc., which are hot spots for radioactive cesium. Radiocesium ions liberated in water such as water, rivers and lakes, and fertilizers such as ammonium sulfate from soil can be adsorbed and decontaminated by radioactive cesium ions. .
Specifically, when the concrete product for removing radioactive cesium is in the form of a block or a tube, it is submerged in running water or installed in a dam shape for decontamination in running water.
If the concrete product for removing radioactive cesium is spherical or Raschig ring-shaped, it is housed in a snake cage or net.
Thereby, radioactive cesium ions in running water can be efficiently decontaminated.

  The concrete product for removing radioactive cesium of the present invention is made of industrial waste coal ash, aluminum dross residual ash and cement material, and is released from radioactive cesium or soil released in water such as rivers, rivers, lakes, etc. It has excellent adsorptivity to radioactive cesium liberated by applying fertilizer, and it has excellent retention of radioactive cesium, and can be easily installed especially in mountainous areas and radioactive water channels. Providing a concrete product for removing radioactive cesium that not only excels in waste workability after adsorbing a considerable amount of radioactive and radioactive cesium, and is excellent in safety during work, but also enables effective use of industrial waste. It can be easily installed in mountainous rivers, rivers, lakes, and watersheds where high-level radioactive cesium flows, efficiently adsorbs radioactive cesium, and effectively decontaminates running water, Dyed After provides method of removing radioactive cesium excellent decontamination workability can be removed by a simple operation.

Claims (4)

A synthetic zeolite obtained by synthesizing coal ash and aluminum dross residual ash in an alkaline solution is immersed in an aqueous solution of an acidic metal salt of any one of Ni, Co, Cu, Mn, and Zn . Artificial zeolite (a) and cement material (b) obtained by impregnating ferrocyanide ions and precipitating an insoluble ferrocyan compound inside after ion exchange with metal ions have a / b = 3/7 to A method of manufacturing a concrete product for removing radioactive cesium, comprising mixing 7/3, aggregate, and water, and then molding. A precipitate obtained by mixing an aqueous solution of an acidic metal salt of Ni, Co, Cu, Mn, and Zn and an aqueous solution of a ferrocyan compound is separated and washed with water, and then coal ash and aluminum dross ash are synthesized in an alkaline solution. The artificial zeolite (a) and the cement material (b) obtained by kneading with the synthetic zeolite obtained and then washed with water and filtered and washed are a / b = 3/7 to 7/3, A method for producing a concrete product for removing radioactive cesium, characterized by mixing water and then molding. Cyan adsorption that adsorbs ferrocyanide partially dissolved in running water on one surface of a concrete product comprising a flat block or an interlocking block obtained by the method for producing a radioactive cesium-removing concrete product according to claim 1 or 2. A method for producing a concrete product for removing radioactive cesium, comprising forming a material layer . The concrete product obtained by the method for producing a radioactive cesium-removing concrete product according to claim 1 or 2 or the concrete product according to claim 3 is used as a hot spot at the bottom of a riverbed or lake, a drainage ditch or a side ditch, Lay it parallel to the flow of running water, or make it into a bowl shape through mortar, etc., and lay it in a hot spot at the bottom of a riverbed or lake, drainage ditch or gutter vertically to the flow of running water. And a method for removing radioactive cesium, wherein the method is brought into contact with running water containing radioactive cesium.

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