JP2013096781A - Method for manufacturing cement solidification matter of fly ash containing radioactive cesium - Google Patents

Abstract

[PROBLEMS] To develop a means for landfill treatment of incinerated ash with high radioactive cesium content and long-term landfill without melting radiocesium.
The object is to mix fly ash containing radioactive cesium with a water-insoluble and granular cation exchanger, add water to form a slurry, and then add cement to solidify. It solves by the manufacturing method of the cement solidified material of the radioactive cesium containing fly ash characterized by the above-mentioned.
[Selection] Figure 1

Description

  The present invention relates to a method for producing a solidified cement of fly ash or molten fly ash containing radioactive cesium.

Combustible waste discharged from facilities that handle radioactive materials such as nuclear power plants is incinerated, and the incineration ash generated during the incineration contains radioactive materials. Since radioactive cesium has a long half-life of ¹³⁴ Cs for about 2 years and ¹³⁷ Cs for about 30 years, it must be carefully stored. In particular, recently, a large amount of radioactive material has been released due to an accident at a nuclear power plant in Fukushima Prefecture, causing pollution over a wide area, and the treatment of incinerated ash from combustible materials from the contaminated area has also become a problem.

Therefore, the Ministry of the Environment has a guideline for incineration ash with radioactive cesium concentration exceeding 8,000 Bq / kg and 100,000 Bq / kg or less to make solidified by adding cement and covering the periphery of the cement solidified by landfill. (Non-Patent Document 1). Further, regarding the strength of the cement solidified material, 150 / kg or more per 1 m ³ , and the landfilling method when the uniaxial compressive strength at the time of landfill disposal is 0.98 megapascal or not are separately defined.

  On the other hand, there is also a report of determining the uniaxial compressive strength by changing the blending ratio as a method for solidifying incinerated ash containing harmful substances (Non-patent Document 2).

  Moreover, when solidifying the incinerated ash of radioactive waste with cement, a method of converting heavy metal chlorides such as lead chloride produced by incineration to a state having low solubility in water is also disclosed (Patent Document 1). ). For this conversion, an alkali metal hydroxide, an alkaline earth metal hydroxide, or the like is used.

JP 2008-256660 A

Ministry of the Environment, Abandoned Opportunity No. 110831001, Environment Abandoned Production No. 110831001, August 31, 2011 Kawato et al., “Cement solidification test of incineration ash I—Basic solidification characteristics of simulated incineration ash”, JAEA-Technology 2010-013, July 2010, p1-38.

  Incinerated ash cement solids may have cracks. In such a case, when rainwater penetrates, radioactive cesium is eluted from the cracks. Therefore, conventional landfill methods include methods of changing the structure of the landfill disposal site to provide a partition wall layer, putting it in a concrete container, or treating waste water from the disposal site. However, it is necessary to pay close attention to prevent radioactive cesium from leaking out. Even if these methods are used, if there is an unexpected situation such as a trouble during transportation, a crack in the disposal site due to an earthquake, or a trouble in the wastewater treatment facility, it will be radioactive. There is concern that cesium may leak.

  As a result of intensive studies to solve the above-mentioned problems, the present inventor has a small amount of radioactive cesium in the main ash, which is the bottom ash of the incineration ash, and cesium is an oxidation that is hardly soluble in water. It is known that fly ash collected from the flue has a high content of radioactive cesium, and most of it is contained in the form of water-soluble cesium chloride, etc. It has been. This fly ash is mixed with a cation exchanger in the form of a half-particle that is slightly insoluble in water in advance, and if water is added to form a slurry, water-soluble cesium chloride and the like contained therein If radioactive cesium begins to dissolve and the radioactive cesium is adsorbed on the cation exchanger, and the cement is solidified in this state, the radioactive cesium is adsorbed on the cation exchanger even if rainwater permeates. And found that radioactive cesium can be contained in cement solidified material.

  The present invention has been made on the basis of such knowledge. A water-insoluble, granular cation exchanger is mixed with fly ash containing radioactive cesium, and water is added to form a slurry. Then, the present invention provides a method for producing a solidified cement of radioactive cesium-containing fly ash characterized by adding cement and then solidifying.

  An outline of the method of the present invention is shown in FIG. As shown in the figure, by adding pulverized cation exchanger and water to the contaminated fly ash and mixing, the radioactive cesium is adsorbed on the cation exchanger, and cement is added to this to form a solidified product. A stable solidified product from which radioactive cesium does not elute even when landfilled can be obtained.

  On the other hand, in the conventional method, as shown in FIG. 3, since the water-soluble radioactive cesium is solidified with cement as it is, the radioactive cesium is eluted when rainwater permeates from a crack or the like.

  According to the present invention, fly ash containing radioactive cesium can be stably contained in a cement solidified product, and elution from a landfill site can be prevented.

It is a figure explaining the method of this invention. It is a processing flow explaining the method of this invention. It is a figure explaining the conventional method.

The incineration ash obtained by incinerating combustibles containing radioactive cesium includes main ash that is the bottom ash collected at the bottom of the incinerator and fly ash that is contained in the combustion exhaust gas and collected by a dust collector such as a bag filter. is there. There is also a molten fly ash that is generated when the main ash is heated and melted in a melting furnace to be slag and collected by a dust collector such as a bag filter. The present invention can be applied to both fly ash generated from an incinerator and fly ash generated from a melting furnace. The content of cesium in these fly ash is usually about 0.1 to 10 ppm. Among them, the content of radioactive cesium varies depending on the radioactivity concentration, but the initial ash radiation concentration is equal to ¹³⁴ Cs and ¹³⁷ Cs. For example, if each of them is 500 Bq / kg (that is, 1,000 Bq / kg in total), ¹³⁴ Cs is about 10 pg / kg and ¹³⁷ Cs is about 155 pg / kg, which is a very small amount.

  The cation exchanger added to the fly ash is preferably one that can adsorb radioactive cesium efficiently. In addition, since radioactive cesium does not elute with rainwater or the like after adsorption, it is preferably insoluble in water, particularly insoluble in water, and is preferably a granular material from the viewpoint of uniform mixing.

  Examples of preferred cation exchangers include inorganic cation exchangers such as zeolite, bentonite, heteroborates such as ammonium molybdate, tungstophosphate, and Ni-based or Fe-based ferrocyanide. Examples of organic cation exchangers include ion exchange resins and crushed ion exchange membranes. The ion exchange resin and the ion exchange membrane have an ion exchange group that is an acid group, and may be either strongly acidic or weakly acidic. The larger cation exchange capacity is preferable, and it is 50 meq / 100 g or more, preferably 100 meq / 100 g or more. The upper limit is not particularly limited, but is practically about 120 meq / 100 g, particularly about 200 meq / 100 g. The particle size is preferably fine from the viewpoint of uniform dispersion. However, if the particle size is too small, there are problems in handling such as easy aggregation, and if it is too large, the adsorption ability is not preferable. Therefore, the average particle size is about 0.01 to 200 μm, preferably about 0.1 to 50 μm. Although a particle shape is not ask | required, a spherical shape, a crushing shape, etc. can be illustrated.

In particular, it is preferable to carry iron cyanide on the cation exchanger. Examples of preferable iron cyanide include hexacyanoiron salts such as Prussian blue, potassium ferrocyanide, potassium ferricyanide and the like. As a loading method, it is preferable to sequentially impregnate Ni (NO ₃ ) ₂ and K ₄ Fe (CN) ₆ salt solution to precipitate insoluble ferrocyanide in the pores.

  The addition amount of the cation exchanger may be about 1 to 100 g, preferably about 20 to 50 g, per 100 g of fly ash. When iron cyanide is supported, the amount added can be reduced by about 10 to 20%.

  In order to adsorb the radioactive cesium in the fly ash in the form of a slurry and adsorb it on the cation exchanger, water must be present. If the amount of water added is too small, the adsorption of radioactive cesium to the cation exchanger will be insufficient, and if it is too large, it will hinder subsequent cement solidification, and countermeasures are required. Therefore, the amount of water for causing the mixture of fly ash and cation exchanger to exist in the form of a slurry is 10 to 90% by weight, preferably 20 to 70% by weight, based on the fly ash. When the addition amount of water is less than 10% by weight with respect to the fly ash, the mixture of the fly ash and the cation exchanger does not become a slurry and is insufficiently adsorbed on the cation exchanger. Furthermore, if the amount of water added exceeds 90% by weight with respect to fly ash, it takes a long time until the cement is solidified.

  The cation exchanger and water should be added to the fly ash as long as the radioactive cesium in the fly ash can be sufficiently adsorbed by the cation exchanger, regardless of which cation exchanger or water is added first. Both may be added simultaneously. It is preferable to blow the cation exchanger into the flue before the dust collector in terms of improving the mixing property of the cation exchanger to the fly ash. After adding the cation exchanger and water to the fly ash, the mixture is stirred and mixed so that the radioactive cesium is sufficiently adsorbed on the cation exchanger. For that purpose, elution of water-soluble radioactive cesium from the fly ash and movement of the eluted radioactive cesium to the cation exchanger are necessary, and it is preferable to leave for about 10 to 20 minutes after mixing. Cement may be added at the time of this stirring and mixing, but it is preferable to add the cement after adsorbing it to the cation exchanger of radioactive cesium from the viewpoint of sufficient adsorption.

  A heavy metal stabilizer for preventing elution of lead, cadmium and the like may be added to the slurry thus produced together with water. As the heavy metal elution stabilizer, a chelating agent such as sodium dithiocarbamate or a phosphate compound can be used.

The type of cement is not particularly limited, and various portland cements such as ordinary portland cement and early-strength portland cement, blast furnace cement, low alkaline cement, and granulated slag cement can be used. The amount of cement is 150 kg or more per 1 m ^{3 of} cement solidified material as shown in the attached document of Non-Patent Document 1, and the uniaxial compressive strength at the time of landfill disposal is 0.98 megapascals. Although it depends on the type of cement and the like, it is usually about 10 to 50% by weight with respect to fly ash. The cement can also contain gravel, sand, and other aggregates. If the cement mixture is deficient in moisture, the insufficient amount of water is added and kneaded, then poured into a mold and cured until a set strength is obtained. Landfill with.

  The fly ash and the cation exchanger were mixed based on the processing flow shown in FIG.

Here, the components of the fly ash used were: Si: 10 wt%, Al: 2 wt%, Ca: 20 wt%, Na: 4 wt%, K: 4 wt%, Cl: 10 wt%, Pb: 0 The concentration of radioactive cesium (total of ¹³⁴ Cs and ¹³⁷ Cs) is 10,000 Bq / kg.

  The cation exchanger used was natural zeolite (manufactured by New Tohoku Chemical Industry) having the following properties.

・ Silicon oxide (SiO ₂ ): 70% by weight
Aluminum oxide (Al ₂ O ₃ ): 10% by weight
・ Calcium oxide (CaO): 2% by weight
・ Average particle size: 30μm
Exchange capacity: 110 meq / 100 g cation 30 g of cation exchanger per 100 g of fly ash was blown into the flue of the incinerator and mixed.
The flue, in order to remove the HCl and SO _X, but is blown acid gas removal agent such as slaked lime, the amount of the sum of the acid gas removal agent and dust amount was fly ash amount.

  Furthermore, 50 mL of water was added to 100 g of fly ash and mixed with an agitator for about 10 minutes to form a slurry. During mixing and stirring, 1 g of a chelating agent composed of sodium dithiocarbamate as a heavy metal elution stabilizer was added to 100 g of fly ash.

  To this slurry mixture, 30 g of cement was added to 100 g of fly ash, kneaded for about 20 minutes, and then cured for about 1 day to produce a cement solidified product.

  As a result of carrying out the dissolution test of the above-mentioned cement solidified based on the Environmental Agency Notification No. 46, the dissolution concentration of radioactive cesium was 100 Bq / L. On the other hand, when a cement solidified product was produced only with fly ash without using a cation exchanger, the elution concentration of radioactive cesium was 1,000 Bq / L.

  According to the present invention, since radioactive cesium can be landfilled without leaking, it can be widely used for landfill treatment of radioactive cesium-containing fly ash.

Claims (4)

  A radioactive cesium characterized by mixing fly ash containing radioactive cesium with a water-insoluble and granular cation exchanger, adding water to form a slurry, and then adding cement to solidify it. A method for producing a solidified cement containing fly ash.   2. The method for producing a solidified cement of radioactive cesium-containing fly ash according to claim 1, wherein the cation exchanger is blown into a flue before the dust collector.   The method for producing a solidified cement of radioactive cesium-containing fly ash according to claim 1 or 2, wherein the cation exchanger has an average particle size of 0.1 to 50 µm.   4. The method for producing a solidified cement of radioactive cesium-containing fly ash according to claim 1, wherein the cation exchanger has a cation exchange capacity of 100 to 200 meq / 100 g cation.

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