JP2016099264A - Radioactive material adsorbing ceramics for safe disposal of radioactive material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a radioactive-substance-adsorption porous ceramic material that has high performance of adsorbing radioactive substances and is excellent in a dry and wet resistance.SOLUTION: A ceramic adsorption agent is formed by carrying out first burning of a compound including: a radioactive substance adsorption agent made of one type or a plurality of types of components of inorganic substances, such as a radioactive substance adsorption material of diatomaceous earth, zeolite, calcium phosphate, titanium oxide and the like, excellent in performance of adsorption of radioactive substances, as a main raw material; a caking additive; and a burning auxiliary material and the like. After having undergone adsorption processing, the ceramic adsorption agent is further burned at a high temperature, thereby enabling being disposed of in the underground and the like for a long term safely.SELECTED DRAWING: None

Description

The present invention relates to a ceramic for adsorbing environmental substances that allows for the final disposal of decontamination technology for environmental pollutants. In particular, the present invention relates to a ceramic material in which an environmental substance is a radioactive substance, and the radioactive substance is adsorbed or mixed with ceramics and fired into a dense body.

  Various decontamination techniques have been researched and proposed in various fields for decontamination of radioactive materials that have caused serious environmental pollution. Most of the techniques are techniques for removing pollutants and separating and concentrating radioactive substances from the pollutants, and there is no decontamination technique in anticipation of final disposal. Therefore, effective decontamination technology remains invisible.

  As a method for decontaminating radioactive substances, each decontamination method has been proposed depending on its form. The water that cools the nuclear fuel in the reactor contains a high concentration of radioactive material. Along with the explosion of the nuclear reactor, radioactive materials are dissipated outside the reactor, riding in an air stream, dissolving in the rain, and a wide range of forest trees, houses, buildings, roads, field soil, etc. around the reactor Is attached to the substance. Radioactive material scattered in the air may adhere to dust and enter the body in the form of fine particles. Radioactive materials adhering to trees and soils are an important problem because they continue to emit radioactivity over a long period of time, causing damage to the health of people and animals living in this area.

  The radioactive material adsorbent is required not only to adsorb the radioactive material but also to exclude components other than the radioactive material and selectively adsorb the radioactive material. So far, at the Fukushima Daiichi Power Station, where there was an explosion, there was radioactive cesium and radioactive strontium generated from the fuel of the power plant in the cooling water of the power generation vessel. Seawater is mixed, and sodium ions, potassium ions, magnesium ions, calcium ions, non-radioactive cesium ions, non-radioactive strontium ions, and the like are present. In the presence of such ions, radioactive cesium, radioactive strontium, etc. must be adsorbed and removed.

  Examples of the adsorbent include zeolite, mordenite, diatomaceous earth, silica gel, titanium oxide, calcium phosphate, and ferrocyanide. Zeolite, mordenite, and iron ferrocyanide have a crystal structure, and have a pore crystal structure or a layered crystal structure in the crystal. Cesium ions and strontium ions can be taken into these crystal structures and removed by adsorption.

  In Patent Document 1, components other than cesium and strontium are precipitated and removed from a mixture of various ionic components, passed through a zeolite column that selectively adsorbs cesium and strontium, removed, and then glass melted and solidified. It is different from the adsorbent of the present invention, and does not suggest the technique of the present invention.

  In Patent Document 2, an insoluble ferrocyan compound is brought into contact with zeolite to make an adsorbent for cesium and strontium, and after adsorbing the component from an aqueous solution containing the component, it is molded and fired to form a ceramic solid body. A method is described. The purpose of bringing the insoluble ferrocyan compound into contact with the zeolite is to decompose the pore crystal structure of the insoluble ferrocyan compound in the firing to form a ceramic solid, the adsorbed cesium and strontium volatilize, and the zeolite adsorbs the volatiles. This is different from the technique of the present application in which a dense ceramic is formed by firing and is stable with respect to external stress, and is not suggested.

  Patent documents 3 and 4 relate to calcium phosphate ceramics. Calcium phosphate is applied to artificial bones and the like as bioceramics. Depending on the application, it may be used in dense ceramics or in porous ceramics. In any case, it does not describe that the radioactive material is adsorbed by the porous body, sintered into a dense body, made insoluble in water or solution, and can be safely disposed of. It is not a suggestion.

In addition to these patent documents, various countermeasure tests have been carried out after an explosion accident occurred due to the 2011 off the Pacific coast of Tohoku Earthquake and many radioactive materials were scattered. According to "No. 1 Development of dry cesium removal technology from radioactive material contaminated soil" in Non-Patent Document 1 (P-31), cesium adhering to contaminated soil may not be released even by heating at 1200 ° C. It has been reported. The cesium combined with the soil means that the cesium is firmly bonded to the extent that the bond with the soil cannot be cut by heating at 1200 ° C. According to the “No. 13 Decontamination Technology by Ultra High Pressure Water Surface Treatment Method“ J Remover ”” (P-55) in the non-patent document, “Radioactivity attached to road surface by ultra high pressure water (maximum 280 MPa). As the water pressure increases, the decontamination rate increases, and it can be estimated that the radioactive material is chemically bonded and physical separation is effective. According to “No.20 Proposal of Radioactive Contaminated Water Purification System Using Adhesive Aggregation Precipitant with Iron Ferrocyanide” (P-69) in the patent literature, the pool water is converted to radioactive material by ferrocyanide. It shows that it can be removed by adsorption. According to “No.22 Demonstration of decontamination and waste volume reduction technology by washing and incineration of radioactively contaminated wood and bark” (p-73), organic substances such as trees are released by combustion in incinerators. , Adheres to the burned ash. Compared to radioactive materials attached to contaminated soil, it is estimated that they are separated at a low temperature. As other matters, the test results of removal of radioactive materials by particle size classification such as soil and calcined ash and separation / removal by chemicals have been reported.

  P-859 to 863 of Non-Patent Document 2 includes the status of radioactive material contamination caused by the Tohoku-Pacific Ocean Earthquake, the form of contamination, decontamination methods for highly-contaminated water and debris in power plants, and waste treatment by decontamination. Problems etc. are described. As the adsorbent, zeolite or ferrocyan compound, which is a mineral, is used, but it is described that there is a problem in disposal thereof. P862 describes that the adsorbed radioactive substance cesium 137 is an exothermic nuclide and is heated from 360 ° C. to 500 ° C. during storage. P867 states that “Cs-adsorbing insoluble ferrocyan compounds are easily decomposed by heat and accompanied by Cs volatilization at high temperatures. Furthermore, there is a concern about the generation of cyanide in inert and reducing atmospheres”. Furthermore, these adsorbents are not suitable for storing adsorbents.

Patent Publication No. 8-105998 Patent Publication 2014-016311 Patent Publication 5-97551 Patent Publication 2010-018459

2011 “Decontamination Technology Demonstration Test” Results Report August 2012 Ministry of the Environment Water and Air Environment Bureau CERAMICS JAPAN 2012.11.1

  The problem of decontamination of radioactive materials is the problem of removing radioactive materials from objects with radioactive materials attached or dissolved to make them safe with low radioactivity, and the high concentration of adsorbents that adsorb radioactive materials. There are two problems of adsorbing radioactive material on the surface, reducing its volume, and whether it can be safely managed or disposed of over a long period of time. In order to realize the former, it is necessary to remove as much pollutants as possible from the pollutants, and to increase the pollutant concentration of the adsorbent, that is, to increase the volume reduction rate. In order to solve the latter problem, it has heat resistance against heat generated by the exothermic nuclide and has a function of blocking the inflow of water and air from the outside.

  Radioactive materials that are not dissolved in water and scattered from the nuclear power plant to the outside may adhere to soil, trees, and the like. For example, cesium adhering to an inorganic material containing a silica component is difficult to bind firmly and separate. As described in Non-Patent Document 1, the scattered radioactive material is collected as sewage sludge, or the burned ash that is incinerated by adhering to trees, grass, and agricultural byproducts contains an inorganic component in the burned ash, and cesium Binds to the inorganic component and cannot be separated even at calcination at 1200 ° C. In order to dispose of such incinerated ash safely, components that adsorb radioactive materials, such as zeolite, diatomaceous earth, titanium oxide, silica gel, etc., are blended, and standard ceramic processes such as extrusion and press molding are used. The ceramic can be molded, can form a dense body at 1100 ° C. to 1200 ° C., and can be safely stored for a long period of time. Depending on the components of the substance including the radioactive material to be disposed, the mixing ratio of the feldspar component, the silica component, and the alumina component can be adjusted, and the sintering temperature can be adjusted.

  In order to convert waste contaminated with radioactive materials into materials with low radioactivity, the radioactive material in the waste is reduced by removing as much radioactive material as possible from the contaminated waste and disposed of at a general waste disposal site. Is preferably 8000 Bq / Kg or less, and in order to be able to use general waste as a valuable resource, the contamination concentration is more preferably 100 Bq / Kg or less. For that purpose, it is preferable to adsorb the radioactive substance at a high concentration by the adsorbing ceramics.

  Adsorbents as treatments for radioactive materials must also be disposed of. A special disposal method is defined for the contamination concentration of 8000 Bq / Kg to 100,000 Bq / Kg. Increasing the concentration of adsorbent contamination is preferable because the volume reduction rate increases and the amount of disposal decreases. A form in which the amount of adsorption can be adjusted is preferred. For example, when the adsorbent is powder, it can be inserted into a column or the like, and the contact time with the contaminant can be adjusted to adjust the contamination concentration of the radioactive substance. The adsorbent preferably has a large adsorption amount and a high adsorption rate. As adsorbents, ferrocyan compounds, zeolites and clay minerals are used because of their large adsorbed amount.

  When the adsorbent is powder, separation of contaminants and adsorbent becomes a problem. If the pollutant is a gas or liquid, it can be contacted with the adsorbent when it is passed through the column. However, it is difficult to reduce the passage resistance through the column and to separate the adsorbent from the pollutant. It is.

  If the pollutant is solid and it is difficult to contact the adsorbent, the radioactive material is liberated by chemicals, etc., and adsorbed by contact with the adsorbent, or burned and bonded to the burned ash. It is practiced to dissolve the radioactivity in water and separate it with an adsorbent. The problem is that it is difficult to separate radioactive materials from solid pollutants and it cannot be efficiently decontaminated.

  Zeolite, which is a crystalline mineral, traps and adsorbs radioactive substances such as cesium in a pore network structure or a layered structure in the crystal. When the crystal structure of zeolite is heated to 700 ° C. or higher, the crystal structure is broken and the adsorption ability of radioactive substances cannot be maintained. If it is less than 700 degreeC, adsorption | suction capability can be maintained, but if a molded object repeats drying and immersion in water, the shape of a molded object cannot be hold | maintained. In order to solidify after adsorption, it is necessary to mix low melting point glass or the like and sinter as a solid. When the crystalline component is baked at a high temperature, the crystal is broken and the adsorbed radioactive material may be scattered. In order to dispose of zeolite adsorbed with radioactive material, problems remain to be solved such as the problem of stability of binding with radioactive material.

  Cyanides and chelating substances may be used as adsorbents. Since these are components that decompose at low temperatures, they cannot be densified at high temperatures. These adsorbents are sometimes used for decontamination of cooling water of nuclear fuel that has adsorbed radioactive material. It is said in Non-Patent Document 2 that in the storage of pollutants, heat is generated at 300 ° C. or 500 ° C. due to nuclear heat generation during storage for several decades. Organic matter can decompose at high temperatures and release absorbed radioactive material. In addition, it is said that ferrocyan compounds may generate toxic cyanide by decomposition in a reducing flame atmosphere.

  In order to solve these problems, in the present invention, ceramics having high adsorption ability of radioactive substances and excellent heat resistance have been developed as adsorbents from various test studies. The ceramic is mainly composed of a radioactive material adsorbent composed of one or a plurality of components of an inorganic material excellent in the adsorptivity of radioactive material, for example, diatomaceous earth, zeolite, calcium phosphate, titanium oxide and the like. And the mixture which consists of a baking auxiliary material etc. is first baked, and the porous body excellent in the moisture resistance is formed. Wet and dry resistance is a condition in which semi-sintered ceramics are immersed in water from a dry state and held for a certain period of time, and the dry state and the immersed state are repeated to evaluate whether the shape can be maintained. It is the characteristic which shows the resistance which can maintain a shape even if it repeats.

In order to perform the adsorption process efficiently, the porous adsorbent improves the contact between the adsorbent and a fluid such as contaminated water or combustion gas, increases the adsorption performance, and separates the adsorbent and the fluid. It is necessary to improve. For that purpose, it is preferable that there are many voids and the contact area is large. In addition, the fluid and the adsorbent need to be in contact with each other so that the adsorbent can maintain its shape. For this purpose, it is necessary that the primary calcination has an excellent radioactive adsorption function and that the adsorption performance is not deteriorated, and that the wet and dry resistance is excellent, and a corresponding composition must be selected.

In order to store the porous adsorbent adsorbing the radioactive substance safely for a long period of time, it is preferable that the adsorbent does not scatter in a powder form and does not elute in contact with a liquid such as water. Ceramics so that the mixing ratio of the porous adsorbent adsorbing the radioactive substance is adjusted so that the water absorption is 1% or less at the secondary firing temperature of 1100 ° C. to 1300 ° C., and the radioactive substance can be adsorbed. After adjusting the mixing ratio and adsorbing the radioactive substance to the porous adsorbent, it can be fired as it is to form a dense ceramic with a water absorption of 1% or less. The treatment process of the adsorbent is simplified, and a safe adsorbent-treated product can be easily prepared for long-term storage.

  In order to create a dense ceramic by secondary firing, the adsorbent compounding amount is set so that the inorganic adsorbing material becomes the target adsorbing amount according to the radioactive material of the substance to be decontaminated. In addition, as other components, the blending ratio of the clay component serving as a molding aid and the feldspar component serving as a sintering aid is determined. In the primary firing for forming the porous body, firing at as low a temperature as possible is preferable, but a temperature of 700 ° C. to 900 ° C. at which components such as clay and feldspar begin to decompose in a temperature range in which the adsorption capacity of the adsorbent does not decrease. A range is preferred. In order to maintain the adsorption characteristics, it is necessary to form a porous body having a certain level or higher of the wet and dry characteristics by this primary firing. Secondary firing is preferably in the secondary temperature range of 1100 ° C to 1300 ° C. It is preferable that the temperature range from the temperature at which the water absorption rate is 1% or less to the softening and melting is wider. By using natural raw materials, the temperature range is widened and the firing management is facilitated.

Due to the explosion at the nuclear power plant, extensive forests, fields, streets and schools around the power plant were contaminated. In some areas, sewage sludge accumulates surrounding contaminants, and the burned ash of sewage sludge contains a high concentration of radioactive substances. A radioactive material impregnated with a radioactive substance is blended into a raw material mixture for ceramics preparation consisting of a binder, a firing aid, etc., mixed, molded, and fired to form a dense body, thereby ensuring safe radiation over a long period of time. Made material-adsorbing ceramics possible. Firing after adsorption preferably has a temperature range of 1100 ° C to 1300 ° C. However, the work is easier if the water absorption is 1% or less and the temperature range until softening and melting is wider.

  The present invention provides a ceramic adsorbent that enables adsorption of radioactive cesium or the like and makes it safe to store an adsorbate for a long period of time. The effect of using ceramics is that in the disposal of contaminated water, the contact resistance between the contaminated water and the adsorbent is reduced, and the contaminated water can pass at an arbitrary speed. The ceramic adsorbed with the contaminants can be fired as it is without any steps such as molding after drying.

In disposal of contaminated soil or sewage sludge incineration ash, it can be molded into a spherical or cylindrical body so that it can be stored for a long period of time, and it does not change due to heat of reaction during storage, or by contact with liquids such as water Elution is eliminated and long-term safe storage becomes possible.

  The radioactive substance-adsorbing ceramic of the present invention can be formed into an arbitrary shape such as a spherical shape, a cylindrical shape, or a ring shape, and after drying, primary firing in a firing furnace can be made into a ceramic. Decontamination of the radioactive substance of the present invention is performed via a gas or a liquid. The fluid containing a radioactive substance needs to have good contact with ceramics, but at the same time, it is preferable to reduce the pressure loss of the fluid, and a sufficient space is required in the flow path, which is suitable for it. Set the shape. The blended, mixed, and molded raw material mixture is subjected to primary firing in a firing furnace after drying. In the primary firing, it is necessary that the wet and dry resistance is excellent so as not to break during the adsorption work. If the firing temperature is too high, the ceramics are sintered, or the adsorption properties of the adsorbent are lowered, and the decontamination performance by adsorption is lowered. Corresponding to the chemical composition of the raw material mixture, the primary firing temperature is preferably 700 ° C to 900 ° C.

  Water that cools nuclear reactors and nuclear fuel is highly contaminated with radioactive materials. To carry out decontamination of the high-concentration contaminants, immerse the ceramics in a decontamination container, replace with new ceramics when the predetermined concentration is reached, and sequentially reduce the contamination concentration until the predetermined concentration is reached. Repeat this operation. In order to decontaminate the flowing liquid from the tank, the ceramics are installed in the passage, and the upstream decontaminated ceramics are sequentially replaced to remove the flowing contaminated water to a predetermined concentration. Dyeing can be performed.

  The radioactive substance adsorbing ceramic of the present invention is adjusted to a ceramic composition appropriately, and is made into a porous ceramic having a water absorption of 25% or more by primary firing, and a water absorption of 1 by secondary firing at 1100 ° C. or more. % Or less can be made into a dense ceramic sintered body. Primary firing that does not collapse by repeatedly drying and immersing the porous body in water (for example, 600 ° C.) may swell and disintegrate, but the firing aid that starts melting at 1000 ° C. absorbs water at 1000 ° C. or higher. There is a tendency for the rate to decrease, and at a firing temperature of about 1200 ° C., a porcelain shape having almost no water absorption rate can be obtained. Such adjustment can be achieved by blending an appropriate amount of feldspar mineral and adjusting the secondary firing temperature.

  The adsorption limit of radioactive materials in adsorbed ceramics is determined by the disposal method of ceramics that adsorbed radioactive materials, and ceramics that have adsorbed radioactive materials up to their concentration become porcelain with a water absorption rate of almost zero by secondary firing. Therefore, radioactive materials are not eluted by water or acid. Ceramics that have adsorbed radioactive material are determined by radiation depending on the concentration of the radioactive material. Therefore, disposal is possible by isolating the corresponding distance from people, animals and plants.

  In the case of polluted gas in incineration of trees, grass or agricultural by-products, radioactive material is adsorbed and removed from the contaminated combustion gas. It is said that radioactive materials generated by incineration do not adhere to incineration ash or its furnace wall and are not released to the outside from the dust collector. That is, radioactive material generated during firing adheres to the furnace wall or incineration ash and is collected. A large amount of incineration ash is generated because the incineration ash has a limited ability to adsorb radioactive materials. In this case, for example, cylindrical ceramics can be installed at a position of 800 ° C. or lower of the flue, or tile ceramics can be installed on the furnace wall of the flue. When no radioactive substance adsorbing ceramics are installed, radioactive substances adhere to the calcined ash, but before adhering to the calcined ash, contacting the calcining gas with the radioactive substance adsorbing ceramics reduces the contamination concentration of the calcined ash, The same disposal as general waste becomes possible. Contaminants may adhere to the metal and heat insulating material on the surface of the firing furnace. By placing tile-shaped radioactive material adsorbing ceramics on the surface, the life of the firing furnace can be extended.

  Ceramics that have adsorbed radioactive material to a predetermined concentration must be stored safely for a long period of time. Radioactive materials generate radiation with a half-life. If contacted with water or acidic water, it may elute and there is a possibility of secondary disaster. As a means for this, in the present invention, the radioactive substance is adsorbed to the porous ceramics to a predetermined concentration, and then subjected to secondary firing to be trapped in the porcelain and prevented from being eluted. Since the radioactive substance bonded to the baked ash and the radioactive substance attached to the soil and the inorganic component are not easily separated, the secondary calcination can be adjusted to become a porcelain and solidified into ceramics. For example, sewage sludge incineration ash is blended with an inorganic adsorbent suitable for adsorbing incineration ash, a binder, and a firing aid, and made into a porcelain shape having a water absorption of 1% or less by secondary firing. Can do. Since the chemical composition of sewage sludge incineration ash varies depending on the district or season, sintering characteristics by secondary firing may differ. In that case, it can mix | blend by adjusting the quantity of a binder and a baking adjuvant.

As a sample of the present invention, 40% by weight of Wakkanai diatomaceous earth, 40% by weight of clinoptilolite-type zeolite, and 20% of Seto gileme clay are blended, and a cylindrical sample having an outer diameter of 15 mm and a length of 20 mm is formed by extrusion molding. It was prepared, dried, and held at 800 ° C. for 1 hour to obtain a mesoporous ceramic (sample 1). Similarly, mesoporous ceramics of the present invention maintained at 700 ° C. and 800 ° C. were prepared (referred to as Sample 2 and Sample 3, respectively). Similarly, for comparison, ceramics subjected to primary firing at 600 ° C., 1000 ° C., 1100 ° C., and 1200 ° C. (comparative samples 1, 2, 3, and 4 respectively) were used.

  Samples 1, 2, and 3 as samples of the present invention, and Comparative Sample 1, Comparative Sample 2, Comparative Sample 3, and Comparative Sample 4 as comparative samples are measured for water absorption as a simple evaluation method for denseness by firing. did. A cylindrical sample was set up vertically and immersed in water for 1 hour to determine swelling water breakage. When the powder collapsed from the ceramic or the shape could not be maintained, it was determined that swelling water breakage occurred. A simulation test of the radioactive material adsorption test was conducted. In the adsorption simulation test, about 3 g of ceramics was used in a non-radioactive cesium 1 ppm solution, and the non-radioactive cesium solution weight / sample weight was set to 10, and the adsorption test was performed by immersion for 5 hours. The non-radioactive cesium residue in the solution was analyzed by ICP-MS, and the results are shown in Table 1.

Table 1 shows the measurement results of the water absorption rate, swelling water breakage, cesium, and strontium adsorption with respect to the firing temperature of diatomaceous earth ceramics.

As a result of the adsorption amount shown in Table 1, since the ratio of 10 parts of 1 ppm solution with respect to 1 part of the sample, the adsorption amount of 1 part of the adsorbent is 9.9 ppm or more when it is 99% or more. Represents 0.1 ppm or less. The concentration of radioactive material of 1 ppm is calculated based on the formula of “g / Bq = half-life (seconds) × atomic weight / 6.022 × 1023 × 0.6931”. 1 ppm and 1 ppm of strontium 90 are 33.3 × 10 ⁸ Bq / L and 25.6 × 10 ⁸ Bq / L, respectively, which are sufficiently larger than the high-concentration contaminated water in the power plant and the contaminated soil. It is a numerical value.

After the radioactive material was adsorbed on the porous adsorbent, it was evaluated whether the adsorbed radioactive material was separated and lost its adsorption ability in the course of secondary firing. A sample in which primary firing was performed at 800 ° C. with the mesopore ceramic of the mixing ratio of Example 1 was used, and a sample on which non-radioactive cesium was adsorbed in the same manner as in Example 1 was used. The adsorption simulation test was performed in the same manner as in Example 1. After performing the adsorption simulation test, the dried ceramic was used as Sample 4-1. The dried sample was further subjected to secondary firing that was held at 1300 ° C. for 1 hour to obtain a dense ceramic 4-2. These ceramics were dissolved and analyzed as ICP-MS measurement data. The results are shown in Table 2.

Table 2 shows the results of the cesium adsorption test on ceramics with different primary firings.
Table 2 Changes in elution amount due to heat treatment after adsorption

In the cesium analysis results of Samples 4-1 and 4-2 of Example 2, no difference was recognized in the analysis accuracy. This indicates that cesium adsorbed on the mesoporous ceramic is not reduced in the process of secondary firing at 1300 ° C. The mechanism by which mesoporous ceramics adsorb cesium has not been elucidated, but it is presumed that the silica component contained in mesoporous ceramics and cesium were combined, and mesoporous ceramics (diameter 4 nm to 20 nm in diameter) existing in mesoporous ceramics. The presence of pores increases the chance of this binding, adsorbs a large amount of radioactive material, and the binding is strong. It is estimated that the secondary firing at 1300 ° C does not cause a reduction in the analytical accuracy. The This phenomenon coincides with a phenomenon in which cesium adhering to an inorganic substance cannot separate calcined ash and cesium even when calcined at 1200 ° C.

Using a sample (sample 2) calcined at 800 ° C. with a sample having the same blending ratio as in Example 1, using a sample adsorbing non-radioactive cesium by the same method, a 1 ppm solution and a test with solution / sample = 10 The sample was put and immersed for 5 hours by shaking, and the amount of cesium eluted in the solution was measured. In the dissolution test, after performing the sample adsorption test in the same manner as the adsorption test, the dried sample was immersed in water and 1N hydrochloric acid as sample 2-1, and cesium dissolved in water and 1N normal hydrochloric acid was measured. The elution amount was determined. Thus, the dried sample was further subjected to a heat treatment of holding at 800 ° C., 1000 ° C., 1100 ° C., and 1200 ° C. for 2 hours to obtain Samples 2-2, 2-3, 2-4, and 2-5, respectively. . For these samples, water and 1N normal hydrochloric acid were used as a solution in the same manner as in Example 2, and the liquid weight / sample weight ratio was 10. Shaking immersion was performed for 5 hours, and the eluate was measured by ICP-MS. The results are shown in Table 2. Heat treatment was performed, and the amount of cesium dissolved in the hydrochloric acid solution was measured. The results are shown in Table 1.

Table 3 shows the change in the amount of elution by the heat treatment after the cesium adsorption test.
Table 3 Changes in elution amount due to heat treatment after adsorption

No elution is observed even with 1N normal hydrochloric acid by heat treatment at 1100 ° C. or higher. As shown in the results of Table 2, the components adsorbed by the adsorption test are less than 1% in the elution test in water, but with 1N hydrochloric acid, the drying of 120 ° C. and the heat treatment at 1100 ° C. Although elution is observed, when the recalcination temperature is 1100 ° C. or higher and the water absorption is less than 1%, cesium is seen to be firmly bonded to the adsorbed ceramic.

  10% by weight of Wakkanai diatomaceous earth, 70% by weight of calcium phosphate manufactured by Ohira Chemical Industry Co., Ltd. and 20% by weight of Seto gypsum clay, 25% by weight of water, dried on gypsum board, 10 to 20 mm in bulk And firing at 800 ° C. for 2 hours to obtain calcium phosphate ceramics.

The solution shown in the initial value of Example 1 was immersed in shaking for 5 hours, and an adsorption test was performed. Both strontium Sr and cesium Cs used non-radioactive elements. The reason for adding calcium, magnesium, potassium, and sodium ion components to the eluate is to confirm the alienation effect of the adsorbed amount of strontium and cesium dispersed in seawater.

Table 4 shows the change in the amount of elution by the heat treatment after the cesium adsorption test.
Table 4 Change in elution amount due to heat treatment after adsorption

Although the adsorption amount of cesium and strontium may decrease due to the presence of seawater cation in the adsorption solution, as described above, the adsorption capacity of the ceramic adsorbent exceeds 1 ppm, and seawater is mixed in. Even in this case, the adsorption capacities of 1 ppm of non-radioactive cesium and strontium are 33.3 × 10 ⁸ Bq / L and 25.6 × 10 ⁸ Bq / L, which are sufficiently large values.

  As seen in the examples, the radioactive substance-adsorbing ceramics of the present invention have a great effect on the adsorption and fixation of radioactive substances, and adsorb and decontaminate various forms of radioactive substances scattered in the nuclear accident. A big effect can be expected, and industrial applicability is great.

Although this specification has described in detail the decontamination of radioactive materials, it can also be expected to remove other environmental materials. Forming and firing ceramics according to the application, disposing of NO _X and SO _X , one of the environmental substances, removing deodorant substances (deodorizing), removing and removing oil mist, and so on It can be used for removal.

Claims (3)

  In the adsorbing component capable of adsorbing and decontaminating radioactive substances, the adsorbing component of the radioactive substance is mainly composed of a component capable of adsorbing a radioactive substance composed of one or a plurality of radioactive substance adsorbing materials such as diatomaceous earth, zeolite, calcium phosphate, titanium oxide, A radioactive substance-adsorbing porous ceramic, characterized in that it is a porous body that does not collapse by repeated drying and wetting, and retains the ability to adsorb radioactive substances, by firing a mixture comprising a binder, a firing aid, and the like.   A radioactive substance-adsorbing ceramic, comprising a radioactive substance adsorbed to the porous ceramic according to claim 1 and then calcined at a high temperature to form a dense body. A radioactive substance-adsorbing ceramic characterized in that a powdery substance containing a radioactive substance is blended, mixed, molded, and fired into a raw material mixture composed of a binder, a firing aid and the like to form a dense body.