JP5708511B2 - Method for producing solid cement of radioactive cesium-containing fly ash - Google Patents

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). Then, for the strength of the solidified product of cement, cement solidified product 1m ³ per 150kg or more, uniaxial compressive strength at the time of performing the landfill is defined separately from the landfill method in the case is not the case with the case of 0.98 megapascals .

  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 found that the 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 was. And if this fly ash is mixed in advance with a water-insoluble and granular cation exchanger in water and added to water to form a slurry, water-soluble radioactive substances such as cesium chloride contained therein When 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 and there is no elution problem even if rainwater permeates. It was found that radioactive cesium can be contained in cement solidified material.

  And it discovered that a cation exchanger could be mixed with fly ash uniformly by blowing this cation exchanger into a flue. In addition, the concentration change of the radioactive material in the fly ash collected from the flue and dust collector is measured, and the elution of radioactive cesium is stabilized by changing the injection amount of the cation exchanger according to the measured value. It was found that it can be suppressed.

  The present invention has been made on the basis of these findings, and the fly ash in the exhaust gas discharged from the incinerator for incineration of radioactive cesium-containing materials or from the melting furnace for melting is collected by a flue dust collector. In the method of adding water and cement to the solidified product, the concentration change of the radioactive material in the fly ash collected from the dust collector is measured, and the positive particle-shaped positive is upstream of the dust collector of the flue. A method for producing a cement solidified product of radioactive cesium-containing fly ash, wherein the ion exchanger is injected, and the amount of the cation exchanger injected is changed according to the measured concentration of radioactive material, and containing radioactive cesium In a method of collecting fly ash in exhaust gas discharged from an incinerator for incineration of materials or a melting furnace for melting by a dust collector of a flue and adding water and cement to this to form a solidified product, the dust collector of the flue Above On the side, the concentration change of the radioactive substance is measured, and a granular cation exchanger is blown, and the amount of the cation exchanger blown is changed according to the measured concentration of the radioactive substance. The present invention provides a method for producing a solidified cement of radioactive cesium-containing fly ash.

  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. 4, since water-soluble radioactive cesium is solidified with cement as it is, 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 process drawing which shows an example of the method by this invention. It is process drawing which shows another example of the method by this invention. It is a figure explaining the conventional method.

The radioactive cesium-containing material is a combustible material containing radioactive cesium that is incinerated, its incinerated ash, molten fly ash, and the like. That is, the incineration ash obtained by incinerating combustibles containing radioactive cesium includes the main ash that is the bottom ash collected at the bottom of the incinerator and the flying ash that is contained in the combustion exhaust gas and collected by a dust collector such as a bag filter. There is ash. 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 cesium content of these fly ash is usually about 0.1 to 10 ppm, of which the radioactive cesium content 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.

  There is no limitation on the type of incinerator, but it can be an ordinary incinerator. Basically, it is a combustion furnace, an inlet for introducing combustible materials containing radioactive cesium, and a flue and smoke window for discharging combustion exhaust gas. It consists of a dust collector installed in the middle of the flue, an outlet for incinerated ash generated as a result of combustion, and the like.

  The melting furnace is a furnace for melting incinerated ash generated in the incinerator into a molten slag, such as a shaft type gasification melting furnace or an electric resistance type ash melting furnace.

  The flue is a passage for the exhaust gas of these incinerators and melting furnaces, and a dust collector that collects fly ash in the exhaust gas is provided in the middle.

  The type of dust collector is not limited, but a typical one is a bag filter.

  In the present invention, the concentration change of the radioactive material of the flue or the dust collector or the fly ash discharged from it is measured. The radioactive material is not only cesium, but it is radioactive cesium that has been discharged from nuclear power plants and has a long half-life. In fact, most of the radioactive material contained in fly ash is radioactive cesium.

  It is sufficient to use a commercially available radioactivity measuring instrument to measure the concentration change of the radioactive substance. Examples of the radioactivity measuring instrument include a Geiger counter and a scintillation counter.

  In the case where the radioactive measuring instrument is mounted on the flue, a seat provided on the side wall of the pipe can be exemplified. In the case of measuring with a dust collector or fly ash discharged from the dust collector, the hopper of the fly ash discharged from the dust collector itself, the clean room, the piping on the exit side, and the like can be exemplified as the attachment position. Radioactivity is measured continuously or intermittently, and the change in radioactivity over time is measured. And in principle, record with a recorder.

  The cation exchanger blown into the flue 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, the ferrocyanide is preferably supported on an inorganic porous material such as silica gel or silica. As examples of preferable ferrocyanides, hexacyanoiron salts such as Prussian blue, potassium ferrocyanide, potassium ferricyanide, potassium hexacyanonickel (II) iron (II), and the like can be given. 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 amount of the cation exchanger to be blown should be about 1 to 100 g, preferably about 10 to 50 g per 100 g of ash in terms of fly ash weight. In the case of an inorganic porous material carrying a ferrocyanide, the amount added can be reduced by about 10 to 20%.

  In the present invention, the amount of cation exchanger blown is increased or decreased based on the measurement result of the concentration change of the radioactive material in the flue or dust collector or the fly ash discharged from the flue, and adjusted so that it falls within the above-mentioned addition amount range. To do. This adjustment does not have to be performed strictly, but may be varied step by step.

  In order to adsorb the radioactive cesium in the fly ash in the mixture of the fly ash and the cation exchanger collected from the dust collector to the cation exchanger, it is necessary to make water into a slurry form. 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.

  After adding water to the mixture, 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.

(Example 1)
An example of the method according to the present invention will be described with reference to the process diagram of FIG.

  Incinerate combustible materials containing radioactive cesium in an incinerator. The exhaust gas generated by incineration passes through the flue and is collected by a bag filter, which is a dust collector, and then discharged from the smoke window to the atmosphere. A cation exchanger inlet is provided upstream of the dust collector in the flue, and zeolite is injected from there. The mixture of fly ash and zeolite collected by the bag filter and dropped into the hopper enters the hopper where it is stirred and temporarily stored. A radioactivity measuring instrument is attached to the hopper, and the amount of zeolite injected is adjusted according to the measured value. From this hopper, it is supplied to a kneading and molding machine by a screw feeder. In this kneading and molding machine, cement is also supplied by a screw feeder, and a chelating agent made of sodium dithiocarbamate and humidified water are also supplied from each tank. In the kneading and molding machine, the radioactive cesium is kneaded and adsorbed on the zeolite, and the solidified product that has been molded and solidified on the curing conveyor enters the pit and is transported to the landfill.

Here, the components of the obtained fly ash were Si: 10 wt%, Al: 2 wt%, Ca: 20 wt%, Na: 4 wt%, K: 4 wt%, Cl: 10 wt%, Pb: 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 An average of 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.

  In the kneading and molding machine, 50 mL of water was added to 100 g of fly ash, and 1 g of a chelating agent made of sodium dithiocarbamate was added to 100 g of fly ash as a heavy metal elution stabilizer.

  30 g of cement was added to 100 g of fly ash and cured on a curing conveyor to produce a cement solidified product.

As a result of conducting the elution test of the above cement solidified based on the Environmental Agency Notification No. 13 method, the elution concentration of radioactive cesium was 100 Bq / L. On the other hand, when the cement solidified product was produced without blowing the cation exchanger into the flue, the elution concentration of radioactive cesium was 1,000 Bq / L.
(Example 2)
Another example of the method according to the present invention will be described with reference to the flow chart of FIG.

  Incinerate combustible materials containing radioactive cesium in an incinerator. The exhaust gas generated by incineration passes through the flue and is collected by a bag filter, which is a dust collector, and then discharged from the smoke window to the atmosphere. A radioactivity measuring instrument is attached to the flue, and the amount of zeolite injected is adjusted according to the measured value. A cation exchanger inlet is provided upstream of the dust collector in the flue, and zeolite is injected from there. The mixture of fly ash and zeolite collected by the bag filter and dropped into the hopper enters the hopper where it is stirred and temporarily stored. From this hopper, it is supplied to a kneading and molding machine by a screw feeder. In this kneading and molding machine, cement is also supplied by a screw feeder, and a chelating agent made of sodium dithiocarbamate and humidified water are also supplied from each tank. In the kneading and molding machine, the radioactive cesium is kneaded and adsorbed on the zeolite, and the solidified product that has been molded and solidified on the curing conveyor enters the pit and is transported to the landfill.

Here, the components of the incineration ash from the incinerator are Si: 5 wt%, Al: 5 wt%, Ca: 15 wt%, Na: 10 wt%, K: 10 wt%, Cl: 17 wt% The concentration of radioactive cesium (total of ¹³⁴ Cs and ¹³⁷ Cs) is 5,500 Bq / kg.

  Moreover, the natural zeolite similar to Example 1 was used for the cation exchanger.

  An average of 65 g of cation exchanger per 100 g of incineration ash was blown into the flue of the incinerator and mixed.

  In the kneading and molding machine, 50 mL of water was added to 100 g of fly ash, and 1 g of a chelating agent made of sodium dithiocarbamate was added to 100 g of fly ash as a heavy metal elution stabilizer.

  30 g of cement was added to 100 g of fly ash and cured on a curing conveyor to produce a cement solidified product.

  As a result of conducting the dissolution test of the above cement solidified based on the Environmental Agency Notification No. 13 method, the elution concentration of radioactive cesium was 90 Bq / L. On the other hand, when the cement solidified product was produced without blowing the cation exchanger into the flue, the elution concentration of radioactive cesium was 1,500 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 (2)

  In a method of collecting fly ash in exhaust gas discharged from an incinerator or a melting furnace for melting radioactive cesium-containing material with a dust collector in a flue and adding water and cement to this to form a solidified product, the dust collector The concentration change of the radioactive material of fly ash collected from the air is measured, and the cation exchanger in the form of a granular material is blown upstream from the dust collector of the flue, and the amount of the cation exchanger blown is measured. A method for producing a solidified cement of radioactive cesium-containing fly ash, characterized by changing the concentration according to the measured concentration of radioactive material.   In a method of collecting fly ash in exhaust gas discharged from an incinerator for incineration of radioactive cesium-containing material or melting melting furnace with a dust collector in a flue and adding water and cement to this to form a solidified product, the smoke At the upstream side of the dust collector on the road, the concentration change of the radioactive material is measured, the granular cation exchanger is blown, and the amount of the cation exchanger blown according to the measured concentration of the radioactive material A method for producing a solidified cement of radioactive cesium-containing fly ash, characterized by changing.

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