JP2014232058A - Mesoporous ceramic applied to technology of removing environmental pollutant using natural porous inorganic mineral capable of burying processed product underground - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of efficiently removing a radioactive material and storing and managing it safely for a long time.SOLUTION: A radioactive material is firmly adsorbed to a mesoporous ceramic having a specific pore structure, or a material containing a radioactive material is mixed into a mesoporous ceramic raw material. Then, the product is molded and burned to immobilize the radioactive material. Thus, the radioactive material can be safely stored underground for a long time.

Description

  The present invention relates to a mesoporous ceramic for adsorbing an environmental substance, which is expected to be disposed of with regard to a decontamination technique for environmental pollutants, a manufacturing method thereof, and a technique for immobilizing an environmental substance adsorbed by a ceramic technique.

  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.

  Patent applications have already been filed for mesoporous ceramics using diatomaceous earth and Kanuma earth. The ceramics use tile-shaped ceramics as humidity conditioning materials, bulk ceramics as deodorants, or vase-shaped ceramic containers, plate-shaped ceramics, or pipe-shaped ceramics as water-permeable ceramics and breathable ceramics. . These uses are for the purpose of permeation and storage of air and water. This patent is a ceramic that uses the same mesoporous raw material, but aims to adsorb and remove radioactive substances, which is a major social issue. Previous information on mesoporous ceramics does not suggest that it has a function of adsorbing radioactive materials. The inventors of the present invention have found that mesoporous ceramics, such as cesium, which is an alkali metal, and strontium, which is an alkaline earth metal, have a strong binding property with a natural mineral containing a large amount of a silica component and have a large specific surface area. Due to its strong binding force, ceramics as an adsorbent that can be safely stored for a long period of time and an adsorption removal method using the same have been devised. Zeolite minerals or clay minerals have been put into practical use as radioactive material adsorbents and have been studied. However, these minerals have a crystal structure broken at a temperature of 700 ° C. or higher, and the adsorption capacity is significantly reduced. In addition, even if it cannot be sintered at a lower temperature than the crystal breaks and it becomes a semi-sintered state that forms a shape, it will come into contact with moisture and cause phenomena such as swelling and collapse, and it should be used as a stable adsorbent There was a problem.

  In patent document 1, it describes in the diatomaceous earth ceramic for obtaining a humidity control function as a humidity control building material. In this document, there is no description that diatomaceous earth ceramics suggests that mesoporous ceramics have a function of adsorbing radioactive substances such as cesium and strontium, and there is no description of material properties of mesoporous ceramics for realizing it.

  In Patent Document 2, radioactive adsorption is a foam of PE resin or PP resin, a fine powder of iron ferrocyanide is mixed into a resin raw material, and the material of this mixture is molded into the shape of a foam-molded gold saccharose, Methods have been proposed to improve contact with radioactive material and improve absorption.

  In Patent Document 3, it is proposed to separate by disposing a liquid containing a contaminant in one tank untreated by an osmosis membrane and moving a radioactive substance to the other tank by electroosmosis. Also in this method, the separated radioactive substance is present in the liquid, and there is no method for storing and managing this, and it is difficult to store it safely for a long time.

  Patent Document 4 is a radioactive substance removing agent composed of a metal alginate with a porous body having a particle diameter of 1 mm or more as a base particle, and comprising a clay mineral, a hardly soluble ferrocyan compound, activated carbon, and zeolite. Granular adsorbents have been proposed to facilitate post-treatment. This method makes post-treatment easier compared to powder or organic adsorbents, but does not show the material properties of the adsorbents for the adsorption of mineral adsorbents at high concentrations, and the long-term safety after adsorption. It does not refer to safe storage.

  Patent Document 5 defines the mesopore state as a characteristic of the synthesized porous material. However, the material relates to calcium phosphate and adsorbs a physiologically active substance, a biocatalyst, and the like. It is not intended to adsorb radioactive material, and does not suggest the mesoporous ceramic for adsorbing radioactive material of this patent.

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 expected to separate at low temperatures. 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 that is a mineral or ferrocyan compound that is an organic substance is used, but it is described that there is a problem in the disposal thereof. P-862 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.

Non-Patent Document 3 describes a simple method for measuring the opening diameter and the amount of fine pores that define the material properties of mesoporous ceramics. Gas adsorption and mercury intrusion methods have been widely used to measure the specific surface and pore distribution of porous materials, but recently instrumental analysis has also been used. As a simple method for simply evaluating the pore distribution of the mesoporous material, a simple method using a constant temperature and humidity chamber was used.

Patent Publication 10-2044 Patent Publication 2013-057534 Patent Publication 2006-194621 Patent Publication 2013-068438 Patent Publication 2006-131470

Report on 2011 “Decontamination Technology Demonstration Test Project” August 2012 Ministry of the Environment, Water and Air Environment Bureau CERAMICS JAPAN 2012.11.1, P-859 to P-863 “Wall and humidity control” PP. 40-45 Wall Material Association (February 8, 1991)

  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 nuclides and has a function of blocking the inflow of water and air from the outside.

  To convert waste contaminated with radioactive materials into materials with low radioactivity, remove as much radioactive material as possible from the contaminated waste and reduce it to a pollution concentration of 100 Bq / Kg or less, which can be disposed of in the same way as general waste. Is preferred. Furthermore, it is preferable to decontaminate the treated waste as low as possible. For that purpose, it is necessary to adsorb the radioactive substance at a high concentration by the adsorbent.

  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 disposal amount decreases. A form in which the amount of adsorption can be adjusted is preferable. For example, when the adsorbent is powder, a column or the like can be inserted to adjust the contact time with the contaminants 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 are used as organic substances, and zeolites and clay minerals are used as inorganic substances because of their large adsorbed amounts.

  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 network structure in the crystal. When the crystal structure of zeolite is heated to 700 ° C. or higher, the crystal structure is broken and cannot be ceramicized (solidified). If solidification is attempted after adsorption, the crystals may be 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.

  Cyanide compounds and chelating substances may be used as adsorbents. Since these are mainly composed of an organic substance or used as a binder, they cannot be used at high temperatures. These adsorbents are sometimes used for decontamination of cooling water of nuclear fuel that has adsorbed radioactive material. In storage of pollutants, it is said that heat will be 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, cyanide compounds may generate toxic cyanide by decomposition.

In order to solve these problems, in the present invention, mesoporous ceramics having high adsorption ability of radioactive substances and excellent heat resistance were developed as adsorbents from various test studies. Mesoporous ceramics is mainly made of diatomaceous earth, blended with clay minerals to facilitate molding, and formed into an arbitrary shape, and then fired at a temperature of, for example, 800 ° C. to form ceramics. Diatomaceous earth has a lot of silica components and is made of an amorphous material. From its origin, diatomaceous earth has mesopores of 4 to 20 nanometers, and macropores are mixed by using ceramics. The silica component is as large as 76% or more, and is a porous body with a specific surface area as large as 4200 cm ² / g. Since it has many silica components and is porous, it is highly reactive with ionic substances such as cesium and strontium, which are radioactive substances. Further, it can be used up to a temperature of 800 ° C. at which the mesopores collapse. By applying diatomaceous earth ceramics as a radioactive material adsorption and decontamination material, it has become possible to solve the problems of conventional adsorption materials.

A wide range of forests around the power plant was contaminated by an explosion at the nuclear power plant. It has been found that radioactive substances attached to forest trees or grasses are liberated by firing at 800 ° C. or lower. The released radioactive material is attached to the ash contained in the plant. Ash is composed of fine inorganic substances, but is not necessarily in an optimum form for adsorbing radioactive substances. The concentration of cesium adsorbed by the burned ash is
From the report of “No.22 Demonstration of decontamination / waste volume reduction technology by washing and incineration of radioactively contaminated wood and bark” (p-73), it is less than 10,000 Bq / Kg and less than 130,000 Bq / Kg. is there. If the adsorption capacity of the baked ash is small, the required processing volume becomes large, requiring a lot of labor, cost and space. Diatomaceous earth ceramics can be used in an environment of 800 ° C. or lower. When the temperature range where the adsorption amount is large was investigated by always installing in the flue of the firing furnace, it was 600 to 800 ° C., and the adsorption amount was 98000 to 257000 Bq / Kg. The concentration of the burned ash at this time is 60 Bq / Kg, which is a level at which general waste treatment is possible. The current waste contamination concentration is 100,000 Bq / Kg, but if the management method is changed based on an appropriate burying treatment method, it can be decontaminated to a higher concentration by diatomaceous earth ceramics and increase the volume reduction rate. It is preferable for waste management and disposal. It can also be used for disposal of radioactive materials by firing treatment, for treatment of sewage sludge and disposal of general incineration waste.

  The cooling water used for cooling the nuclear fuel is highly contaminated with radioactive materials. High-concentration contaminated water uses ferrocyan compounds, mineral substances such as zeolite, chelate compounds, and the like as radioactive material adsorbents. Among these adsorbents, organic minerals or clay minerals having a crystal structure may be decomposed and lose their functions when subjected to heat treatment for post-treatment. In the case of storage and processing after decontamination work, the organic matter may decompose due to heat generation and release the adsorbed radioactive material. Further, minerals such as zeolite and bentonite that adsorb radioactive substances by their crystal structure may have their crystal structure collapsed by heat treatment such as vitrification and discharge the adsorbed radioactive substances. On the other hand, since mesoporous ceramics are not crystalline components but amorphous, the crystalline form does not change by heating. The fine pores of the mesopores may sinter at 900 ° C. or higher, reducing the adsorption function. Diatomaceous earth ceramics adsorbed with radioactive substances are firmly bonded to alkali metal cesium and alkaline earth metal strontium, and do not separate radioactive substances by contact with low-temperature flowing water or air. For long-term management and storage, the mesoporous ceramic composition does not cause sintering that reduces mesopores at 800 ° C or lower, and the open pores are reduced to 1% or lower by heating at about 1200 ° C. After being adjusted so that the radioactive substance is adsorbed, moisture can be removed, and after drying, firing at about 1200 ° C. can perform porcelain treatment to block water and air from the outside.

  The present invention provides a ceramic capable of adsorbing radioactive cesium or the like. The effect of ceramics can be used at high temperatures, and by refiring to promote porcelain, the effect of blocking water and air from the outside can be obtained. to enable. In order to make ceramics, it is molded into an arbitrary shape and sintered at a sintering temperature. If the sintering temperature is low, sufficient sintering cannot be performed, and if it is placed in water, it will swell and collapse. Swelling / disintegration is a phenomenon in which, when semi-sintered ceramics are placed in water, the bonding of particles is cut and the shape cannot be maintained. When the firing temperature is high, the pores of the porous body are crushed and the adsorption performance is lowered. Zeolite is a crystalline mineral and has crystal pores that can adsorb cesium, etc., so it adsorbs radioactive substances such as cesium, but if it is sintered at a temperature that does not cause swelling collapse, the crystal breaks and adsorbs. It cannot be sintered at a temperature that maintains its function.

  The mesoporous ceramic for adsorbing a radioactive substance according to the present invention has a pore structure in which pores having an opening having a diameter of 16 nm or less contain 0.05 ml / g or more and pores having a diameter of 4 nm or less contain 0.01 ml / g. In the ceramic, the radioactive material can be easily adsorbed up to 100,000 Bq / Kg in a short time. The adsorbed radioactive material can be safely stored for a long period of time without being dissolved even if it comes into contact with water or air during storage because it binds firmly. The measurement of pores having a diameter of 16 nm or more and 4 nm or less of the opening was performed by a simple method using a constant temperature and humidity chamber. As raw materials before firing, diatomaceous earth, allophane, zeolite, or the like can be used alone or in plural, but it is important to adjust the selection of raw materials, firing conditions and the like so as to be a prescribed mesoporous. The reason why the upper limit of pores of 16 nm and 4 nm or less is not defined is, as shown in the examples, 0.105 to 0.248 ml / g and 0.039 to 0.058 ml / g, respectively. These values are preferably large for radioactive substance adsorption, but do not exceed the values of the raw materials. The formulation is determined in consideration of sinterability and adsorptivity, but these values are set as large as possible.

Here, 4 nm was used as one standard. A pore volume of 4 nm or less is called a micropore, and adsorbs fine particles and ions. One standard of 16 nm is that the pore volume of 16 nm or less represents the sum of micropores and mesopores, and serves as an index for adsorbing more various kinds of radioactive substances.

In the ceramic of the present invention, zeolite or diatomaceous earth is filled with diatomaceous earth so that pores having an opening diameter of 16 nm or less contain 0.10 ml / g or more and pores 4 nm or less contain 0.02 ml / g or more. The composition for blending raw materials such as allophane is determined. After forming into an arbitrary shape, it is fired to produce.
Firing is performed at a temperature not lower than the degree of swelling and collapse and not higher than a temperature at which the fine pores are not crushed, and these temperatures are in the range of approximately 700 ° C. or higher and 900 ° C. or lower, depending on the composition. The blending composition is composed of 30 to 90% by weight of diatomaceous earth, 10 to 30% by weight of clay as a molding aid, and 0 to 40% by weight of minerals such as zeolite and allophane.

  The mesoporous ceramic produced as described above has an ability to adsorb radioactive substances of 100 million Bq / Kg or more. In addition, it has been sufficiently confirmed even insoluble in water and hydrochloric acid. Currently, only the substances of 100,000 Bq / Kg or less are regulated by the storage regulations. In order to comply with this, it is necessary to adjust the amount of adsorption so as to be below this value. If this regulation is relaxed, for example, if disposal of 1 billion Bq / Kg becomes possible, the volume of the adsorbing aid will be 1 / 10,000, and the disposal volume will be significantly reduced. However, in this case, the radioactivity generated from the unit volume will be correspondingly increased, so it is necessary to consider such as deep underground.

  In the ceramic of the present invention, after adsorbing the radioactive substance, it can be fixed by sintering with the radioactive substance by re-firing. Ceramics adsorbed with a radioactive substance have different open composition, and the open pores are almost 0% (that is, 1% or less), and it is possible to eliminate contact with air or water during storage. Even if the ambient atmosphere of the storage is subjected to unforeseen harsh conditions, the radioactive material does not dissolve in the surroundings and enables safe storage over a long period of time. By adjusting the content ratio of sintering aids such as alkali, alkaline earth components, iron oxide, titanium oxide, etc., firing at 900 ° C. or lower does not proceed at the firing temperature of the ceramic, but refires. Therefore, it is possible to obtain a blending composition in which the open pores are almost 0%. The sintering aids have different temperatures at which the sintering reaction starts, and feldspars, which are natural minerals containing a large amount of alkali components and alkaline earth components, start a melting reaction at 1000 ° C. or higher. At most 1000 ° C. or less, no melting reaction occurs. By adjusting the type and amount of the firing aid, mesoporous ceramics are formed at 900 ° C or lower, and mesoporous ceramics that promote the sintering reaction at temperatures of 1000 ° C or higher are devised to adsorb more radioactive substances. Then, by refiring, we developed ceramics that do not leak radioactive materials to the outside.

  In the ceramics of the present invention, air containing a radioactive substance is obtained by forming the ceramic into an arbitrary shape after adsorbing the radioactive substance using natural porous mineral powder particles and firing at 700 ° C. or higher. Many radioactive substances can be adsorbed to the ceramics in a short time without making a large load on the equipment by improving the contact between the liquid and the ceramic and reducing the resistance of these fluids. As a preferable shape, it can be formed into a honeycomb shape, a rod shape, a cylindrical shape, or the like with an appropriate adjustment of the mesh size and fired to obtain a ceramic.

Ceramics using natural minerals can be formed into an arbitrary shape, dried and then sintered in a firing furnace to form ceramics. Decontamination of the radioactive substance of the present invention is performed via a gas or a liquid. The fluid containing the radioactive substance preferably has 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, and a shape suitable for the fluid is required. Set. The formed raw material mixture is sintered in a firing furnace after drying. In sintering, it is necessary to obtain a sufficient bond so as not to break during the decontamination operation, and it is necessary to give sufficient thermal energy. However, if the firing temperature is too high, the mesopores are sintered with heat. In addition, the decontamination performance by adsorption decreases. Corresponding to the chemical composition of the raw material mixture, the sintering temperature is preferably 700 ° C to 900 ° C.

  The installation method in the mesoporous ceramic decontamination apparatus is different. In the case of incineration of organic matter in trees, grass, or agricultural production, radioactive materials are adsorbed and removed from polluted combustion gases, but cylindrical ceramics are placed at a temperature of 800 ° C or below of the flue. Tile mesoporous ceramics can be installed on the furnace wall. When no mesoporous ceramics is installed, radioactive materials adhere to the calcined ash, but before adhering to the calcined ash, contacting the mesoporous ceramics with the calcining gas reduces the contamination concentration of the calcined ash, and the general waste and The same disposal becomes possible. Contaminants may adhere to the metal and heat insulating material on the surface of the firing furnace. By arranging tile-shaped mesoporous ceramics on the surface, the life of the firing furnace can be extended.

  Water that cools nuclear reactors and nuclear fuel is highly contaminated with radioactive materials. To decontaminate the high-concentration contaminants, immerse the ceramics in a storage tank, replace the ceramics with new ones at a predetermined concentration, and gradually reduce the contamination concentration until the predetermined concentration is reached. Repeat the 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 mesoporous ceramic is a porous ceramic having open pores while maintaining mesopores by appropriately adjusting the chemical composition of the ceramic, and is a sintered body having no open pores at a firing temperature of 1000 ° C. or higher. It is possible to make ceramics. Firing at a low temperature (for example, 800 ° C.) that does not crush the mesopores melts the slightly vitrified component at the fine contact portion of the raw material to form a semi-sintered ceramic. The starting firing aid can be made into a porcelain shape that begins to sinter at 1000 ° C. or higher and has a firing temperature of about 1200 ° C. and almost no open pores. Such adjustment can be achieved by blending natural feldspar minerals. A mesoporous ceramic decontaminated with a radioactive substance at a high concentration can be made into a ceramic ceramic with approximately 0% open pores by re-firing at 1000 ° C. or higher, preferably 1200 ° C. The radioactive substance bonded to the mesoporous ceramic is not separated during the firing process, and can be adsorbed and removed in the furnace even if trace components are separated. The ceramics thus made porcelain are not separated by a temperature of 1000 ° C. or less, or by contact with water, for example, in contact with a high-concentration hydrochloric acid solution. Even in such ceramics made of porcelain, radiation is generated, so that it can be disposed of in the ground at a predetermined distance from humans and organisms.

  It is difficult to separate radioactive materials from calcined ash, rubble, sewage sludge, etc., which have already been combined with inorganic materials and radioactive materials. By pulverizing these materials to a particle size of several mm or less and blending a predetermined amount with a mesoporous ceramic raw material, by firing at a temperature of 1000 ° C. or higher, preferably 1200 ° C., the open pores are almost 0%. It can be a porcelain ceramic. The radioactive substance bonded to the mesoporous ceramic is not separated during the firing process, and can be adsorbed and removed in the furnace even if trace components are separated. The ceramics thus made porcelain are not separated by a temperature of 1000 ° C. or less, or by contact with water, for example, in contact with a high-concentration hydrochloric acid solution. Even in such ceramics made of porcelain, radiation is generated, so that it can be disposed of in the ground at a predetermined distance from humans and organisms.

In order to express the function of mesoporous ceramics, the mesoporous was subjected to an evaluation test of firing characteristics and pore distribution. Both are pore capacities corresponding to the pore diameters of diatomaceous earth and zeolite produced in Hokkaido.
Samples No, A, M, and J are mesoporous diatomaceous earths, but their production areas are different, and their strata and rock quality are also different. No and N are zeolites and are clinoptilolite type.

表１は、各種原料の細孔径と細孔容量を示した。
表１ 珪藻土およびゼオライトの細孔径と細孔容量

Table 1 shows the pore diameters and pore capacities of various raw materials.
Table 1 Pore diameter and pore volume of diatomaceous earth and zeolite

表２は、原料Ｎｏ．Ａの焼成温度による細孔容量の変化を示しものである。
表２ Ｎｏ.Ａ 珪藻土の焼成温度と細孔容量

Table 2 shows the raw material No. The change of the pore capacity | capacitance with the calcination temperature of A is shown.
Table 2 No. A Diatomite firing temperature and pore volume

表３は、Ｎｏ．Ｍ原料の焼成温度による細孔容量の変化を示したものである。
表３ Ｎｏ.Ｍ 珪藻土の焼成温度と細孔容量

Table 3 shows no. The change of the pore volume with the firing temperature of the M raw material is shown.
Table 3 No. M Diatomite firing temperature and pore volume

表４は、Ｎｏ．Ｊ原料の焼成温度による細孔容量の変化を示したものである。
表４ Ｎｏ.Ｊ 珪藻土の焼成温度と細孔容量

Table 4 shows no. The change of the pore volume with the firing temperature of J raw material is shown.
Table 4 No. J Diatomite firing temperature and pore volume

表５は、Ｎｏ．Ｎ原料の焼成温度による細孔容量の変化を示したものである。
表５ Ｎｏ．Ｎ ゼオライトの焼成温度と細孔容量

Table 5 shows no. This shows the change in pore volume depending on the firing temperature of the N raw material.
Table 5 No. N Zeolite firing temperature and pore volume

  Cylindrical material with an outer diameter of 40 mm, an inner diameter of 30 mm, and a length of 35 mm is prepared by mixing 50% by weight of the raw material (Sample No. A), 30% by weight of the raw material (Sample No. N) and 20% by weight of clay for ceramics, and by extrusion molding. After drying, it was kept at 850 ° C. for 1 hour to obtain the mesoporous ceramic (sample 1) of the present invention. Similarly, the mesoporous ceramics of the present invention held at 700 ° C. and 800 ° C. were prepared (referred to as Sample 2 and Sample 3, respectively). Similarly, ceramics fired at 600 ° C., 900 ° C., 1000 ° C., 1100 ° C., 1200 ° C. and 1300 ° C. (comparative samples 1, 2, 3, 4, 5 and 6 respectively) were used.

  The water absorption ratios of these samples in firing at each temperature are as follows. The amount of pores having an opening diameter of 16 nm or less and the amount of pores having a size of 4 nm or less are as shown in Table 4, and swelling and destruction of these ceramics and cesium Table 6 shows the amount of strontium adsorbed.

表６は、メソポーラスセラミックスの一例の配合組成に対して、材料特性、セシウム、ストロンチウムの吸着特性を示すものである。

Table 6 shows material characteristics, cesium, and strontium adsorption characteristics with respect to a blend composition of an example of mesoporous ceramics.

  A simple method using a constant temperature and humidity chamber was used as the measurement method for the diameter of the opening 16 nm and similarly 4 nm. Swelling breakage was determined by putting one sample into a 500 ml polybeaker and 300 ml of water, and checking if the shape was deformed after 1 hour. “None” indicates a result in which no deformation is observed, and occurrence indicates a result in which the deformation is recognized. The amount of adsorption of cesium and strontium is non-radioactive using cesium chloride and strontium chloride, put 1 ppm solution and test sample with solution / sample = 10, soak and shake for 5 hours. Analysis was carried out. From the difference in the residual concentration of cesium and strontium in the solution in which the sample was not immersed and the solution in which the sample was added, the elution ratio of the component remaining in the solution was determined.

  From the above results, radioactive material adsorption characterized by a pore structure containing 0.05 ml / g or more of pores having an opening diameter of 16 nm or less and 0.01 ml / g of pores having a diameter of 4 nm or less In the mesoporous ceramics for use, the adsorption amount of cesium and strontium is large, and it is excellent as an adsorbent. In order to obtain such results, diatomaceous earth and zeolite containing pores having an opening diameter of 16 nm or less containing 0.10 ml / g or more and pores having 4 nm or less containing 0.01 ml / g or more are used. After molding into an arbitrary shape as a main raw material, sintering to such an extent that swelling water breakage does not occur, and in a firing temperature range such that micropores and mesopores do not decrease, depending on the chemical composition and blending ratio of the raw materials, 700 ~ It can be produced by firing at 900 ° C. When the ceramics adsorbed with the radioactive material is 1% or less open pores, the circulation of water and air to the outside is closed, and the adsorbed radioactive material is not melted out to the outside. Such temperature varies depending on the chemical composition and blending ratio of the raw material, but at 1000 ° C., the water absorption rate is almost several percent or less, at 1100 ° C. or more, the water absorption rate is 0.5% or less, and the open pores are Nearly zero.

  Using a sample (sample 2) calcined at 800 ° C. with a sample having the same blending ratio as in Example 2, using a sample adsorbing non-radioactive cesium by the same method, a 1 ppm solution and test with 10 solutions / sample = 10 The sample was put and immersed for 5 hours by shaking, and the amount of cesium eluted in the solution was measured. The elution test was performed in the same manner as the adsorption test. After the sample adsorption test was performed, the sample dried at 120 ° C. for 2 hours was immersed in water and 1N hydrochloric acid as the sample 2-1, respectively. The amount of elution was determined by measuring cesium dissolved in the solution. Thus, the dried sample was further subjected to a heat treatment of holding at 200 ° C., 400 ° C., 600 ° C., and 800 ° C. for 2 hours to obtain Samples 2-2, 2-3, 2-4, and 2-5, respectively. . These samples were heat-treated with water and 1N normal hydrochloric acid in the same manner as Sample 2-1, and then an elution test was performed. The results are shown in Table 5.

表７は、セシウムの吸着試験の後の熱処理によって、溶出量の変化を示したものである。
表７ 吸着後の熱処理による溶出量の変化

Table 7 shows the change in the amount of elution by the heat treatment after the cesium adsorption test.
Table 7 Changes in elution amount due to heat treatment after adsorption

As shown in the results of Table 7, the components adsorbed by the adsorption test are less than 1% in the elution test in water, and cesium (non-radioactive substance) seems to be firmly bonded to the mesoporous ceramics. Seen. With 1N hydrochloric acid, elution of cesium is observed after drying at 120 ° C. and heat treatment at 200 ° C., but no elution is observed even with 1N normal hydrochloric acid by heat treatment at 400 ° C. or higher.

  After firing, 70% by weight of powdered sewage sludge, diatomaceous earth no. 10% by weight of A, 10% by weight of clay for ceramics, and 10% by weight of anti-feldspar feldspar as a natural feldspar raw material were blended to prepare a blended soil. The cesium chloride solution was added so that the water content was 20% by weight, and the ratio of cesium chloride contained in the finished blended soil was 1 ppm with respect to the solid content. This blended soil was molded with a kneading extruder so as to have a diameter of 10 mm and a length of 10 to 15 mm, dried, and then fired in the atmosphere for 1 hour at 1200 ° C. The water absorption of this fired product was 0.2%. About 20 g of this sample was taken and the dissolution test was carried out in the same manner as in Example 2. The elution test was carried out with water and 1N hydrochloric acid solution, but no elution was detected. In this way, even contaminated materials that have already been contaminated with radioactive materials and difficult to separate the components are blended with the ceramic raw material of the present invention and fired while absorbing the radioactive materials scattered during firing. It was found that the contained radioactive material can be immobilized.

表８に配合土の焼成前と焼成後の、セシウムの溶出試験の結果を示す。
表８ 配合土の焼成前と焼成後の、セシウムの溶出試験の結果

Table 8 shows the results of the cesium elution test before and after firing the blended soil.
Table 8 Results of cesium dissolution test before and after mixing

  As seen in the examples, the mesoporous ceramics of the present invention have a great effect on the adsorption and immobilization of radioactive substances, and a great effect on adsorption and decontamination of various forms of radioactive substances scattered in the nuclear accident. The 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. Ceramic materials are shaped and fired according to the application, and environmental substances are removed over a wide range, including disposal of NO _X and SO _X , which are environmental substances, removal of odorous substances (deodorization), and adsorption removal of oil mist. It can be expected to be used in the future.

Claims (5)

  A mesoporous ceramic for adsorbing a radioactive material, characterized by a pore structure containing 0.05 ml / g or more of pores having an opening diameter of 16 nm or less and 0.01 ml / g or more of pores having a diameter of 4 nm or less .   After molding into diatomaceous earth and zeolite containing 0.10 ml / g or more of pores having an opening diameter of 16 nm or less and 0.01 ml / g or more of pores of 4 nm or less as main raw materials 2. The mesoporous ceramic according to claim 1, wherein the mesoporous ceramic is produced by firing at a temperature that does not swell and collapse and that does not decrease the pores.   A ceramic characterized in that after adsorbing a radioactive substance with the ceramic according to claim 1, the ceramic is sintered and fixed with the radioactive substance by refiring the ceramic at a temperature at which the open pores become zero or more.   A ceramic produced by blending a material adsorbing a radioactive substance and the ceramic according to claim 1 as a raw material, forming into an arbitrary shape, and firing at a temperature at which open pores become zero or more. A ceramic produced by adsorbing a radioactive substance using the natural porous mineral powder granule according to claim 1, forming into an arbitrary shape, and firing at a temperature at which open pores become zero or more.