JP2015090362A - Method for removing strontium using sediment - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for removing radioactive strontium, capable of corresponding to various environments contaminated with radioactive strontium.SOLUTION: The method for removing radioactive strontium discharged into an environment using an organic polymer fiber 2 with ions absorbed therein and forming a poorly soluble salt with strontium confined in the fiber by reacting with the ions on the fiber to form the poorly soluble salt comprises removing radioactive strontium by immersing the fiber into a contaminated lake or river, etc., to be taken out. By using the fiber as a base material, moldings having various shapes suitable for a contamination situation can be used.

Description

  Among the radioactive pollutants released into the environment due to accidents at facilities related to nuclear power plants, the main ones are cesium, strontium and iodine. Among these, since radioactive iodine has a short half-life of about 8 days, it is very important to deal with it in a short period immediately after the accident. On the other hand, cesium and strontium, which have a long half-life of about 30 years, continue to emit radioactivity for a long period after being released into the environment. Therefore, it is important to remove these two types of radioactive substances from the environment over a long period of time from the occurrence of the accident. Radioactive cesium has materials and technologies with high removal performance such as zeolite and ferrocyanate metal salt insolubilized materials. On the other hand, radioactive strontium often coexists with high concentrations of calcium, magnesium, and the like, and since the ratio of non-radioactive strontium is also large, it is difficult to remove it effectively. The present invention relates to a method for removing radioactive strontium released into the environment.

Conventional technology

  In the Great East Japan Earthquake on March 11, 2011, radioactive materials represented by cesium-137, cesium-134 strontium-90 and iodine-131 were released from the Fukushima Daiichi Nuclear Power Station. These scattered around and caused severe pollution in land, sea and air. There is an urgent need to decontaminate radioactive materials released into the environment as well as within the power plant. Since cesium 137 and strontium-90 both have a long half-life of about 30 years and are the main cause of contamination, decontamination of cesium 137 and strontium-90 is particularly urgent.

  As a method for removing radioactive cesium, an adsorption method using zeolite (Patent Document 1) and a precipitation method using metal ferrocyanide (Patent Document 2) have been performed. A method of selecting or using both removal methods depending on the state of contamination, for example, whether decontamination is fresh water or sea water has been proposed.

  Strontium often coexists with other alkaline earth metals such as calcium and magnesium, and these concentrations are orders of magnitude higher than those of strontium. For example, in seawater, calcium is approximately 400 mg / L and magnesium exceeds 1000 mg / L. Strontium is mostly non-radioactive strontium at about 8 mg / L. Therefore, in order to remove radioactive strontium, non-radioactive strontium must be removed at the same time in the presence of high concentrations of calcium and magnesium of the same family.

  Conventionally, in order to remove radioactive strontium, a method of precipitating with an alkaline pH has been performed. Aggregation and precipitation of calcium, magnesium and strontium as hydroxides are performed.

  However, a white colloidal precipitate is deposited when the pH is raised to remove the magnesium contained in the highest concentration to produce hydroxide. Since this colloidal sediment has a large water content and volume of sludge, it imposes a heavy load on the dehydration apparatus and hinders volume reduction of radioactive waste.

  Sodium titanate has been proposed as an inorganic ion exchanger that selectively adsorbs radioactive strontium (Patent Document 3). Since this adsorbent is granular, only the packed tower method can be used as in the above-described zeolite. Further, since the physical strength of sodium titanate itself is weak, there is a problem that minute sodium titanate that is easily powdered and adsorbs radioactive strontium leaks into the treated water.

  A chelate resin having an iminodiacetic acid group introduced therein is commercially available. Excellent adsorption performance for alkaline earth metal and heavy metal ions. However, with regard to the alkaline earth metal adsorption performance by the chelate resin, the selective adsorption of strontium is the smallest in the raw water with relatively high salt concentration, and strontium leaks first when treated in a packed tower. There was a problem (Non-Patent Document 1). In addition, there is a limitation in the usage method that it can be used only in a packed tower system like sodium titanate.

JP 61-239196 JP 2000-84418 A Special table 2000-502595

Diaion 2, edited and published by Mitsubishi Chemical Corporation, revised on October 31, 2007, p. 249-p. 251 4th edition

  Large-scale facilities such as coagulation sedimentation equipment and sludge treatment equipment are not required, and the usage method is not limited to the packed tower system like chelate resins and titanic acid-based inorganic adsorbents. Seawater, groundwater, lakes and marshes Therefore, there has been a demand for a strontium removal method that can be easily used in various situations such as waterways and storage tanks, and can easily dispose of used adsorbents, thereby minimizing the exposure of workers. The present invention provides a solution to such a problem.

The inventors of the present invention have made extensive studies on a high-performance radioactive strontium removal material using a radiation graft polymerization method.
The inventors have found a radioactive strontium removing material having the characteristics shown in the following (1) to (8) and a radioactive strontium removing method using the material, and have reached the present invention.

(1) A radioactive strontium removing material having a functional group consisting of an ion exchange group or a chelate group in the side chain and adsorbing ions that form a hardly soluble salt with an alkaline earth metal on the functional group

(2) The radioactive strontium removing material according to (1), wherein the radioactive strontium removing material is obtained by introducing a graft chain into an organic polymer base material using a radiation graft polymerization method.

(3) The organic polymer base material described in (2) is composed of a fibrous base material, which is a short fiber, a long fiber, a twisted yarn, a cut fiber, a woven or non-woven fabric that is an aggregate of fibers, and a molded product thereof. Radioactive strontium removal material selected from some wind filters, pleated filters, braids, ropes and moldings

(4) The radioactive strontium-removing material according to (1), (2) or (3), wherein the ions that form the hardly soluble salt are selected from oxalic acid, carbonic acid, sulfuric acid, and phosphate ions

(5) First step of irradiating the fibrous substrate with radiation, graft polymerization of a monomer having an ion exchange group or chelate group, or graft polymerization of a polymerizable monomer that can be converted into an ion exchange group or chelate group, and A strontium removing material comprising a second step of converting to an ion exchange group or a chelate group, and a third step of imparting an ion selected from oxalic acid, carbonic acid, sulfuric acid and phosphate ions using the ion exchange group or chelate group Production method

(6) A method for removing radioactive strontium comprising a first treatment step in which the radioactive strontium removing material according to (1) to (4) is brought into contact with a liquid contaminated with radioactive strontium.

(7) As a step before or after the first treatment step described in (6), the radioactive strontium removing material described in (1) to (4), a material introduced with a sulfonic acid group, or a phosphate group was introduced The method for removing radioactive strontium according to (6), comprising a second treatment step of contacting the material, the material introduced with iminodiacetic acid group, and the radioactive strontium removing material selected from the radioactive strontium removing material loaded with sodium titanate

(8) The radioactive strontium-removing material according to (1) to (4) described in (7), a material introduced with a sulfonic acid group, a material introduced with a phosphate group, a material introduced with an iminodiacetic acid group, titanic acid The radioactive strontium removing material carrying sodium is obtained by introducing a graft side chain into a fibrous base material using a radiation graft polymerization method. (7)

  As graft polymerization is translated as “grafting polymerization” in Japanese, one end is bonded to an existing polymer and the other end is a free end. Since it does not have a cross-linked structure like ordinary ion exchange resins, it is excellent as an adsorptive separation material. For example, since the ion exchange resin has a crosslinked structure, the adsorbed ions need to diffuse into the crosslinked structure. However, in the case of the graft polymerization method, particularly the radiation graft polymerization method, the graft chains swell due to repulsion with the same charge, so that the space for the ions to be diffused and moved is large, and the adsorption sites inside the substrate Is also easily caught.

  In the present invention, a side chain having an ion exchange group or a chelate group is adsorbed with an ion that generates a hardly soluble salt with an alkaline earth metal ion, and then brought into contact with an aqueous solution containing the alkaline earth metal ion, thereby being hardly soluble. This was obtained by the epoch-making knowledge that the target ions can be removed by depositing the salt of the compound in the organic polymer substrate and taking out the material out of the system.

  More specifically, when carbonic acid ions are adsorbed on a material having an anion exchange group on the graft side chain and this material is immersed in an aqueous solution containing a large amount of calcium and magnesium as well as strontium, Calcium and strontium carbonate are deposited inside the substrate. Magnesium having a relatively high solubility is difficult to be generated inside the substrate, and calcium and strontium having a low solubility are generated. It is convenient for the purpose of removing radioactive strontium.

  In the radiation graft polymerization method, radicals can be easily generated in fiber assemblies such as existing organic polymer materials such as fibers, hollow fibers, woven fabrics and non-woven fabrics by irradiating with electron beams or gamma rays. Therefore, a graft side chain can be generated even inside the substrate, and a functional group such as ion exchange can be introduced. Here, strontium carbonate can be deposited inside the substrate by adsorbing carbonate ions. If the base material is selected as a fiber having good moldability, and selected from twisted yarn, rope and braid among various fiber products, a strontium adsorbent can be produced in this shape. Strontium can be removed by putting this material into contaminated water and pulling it up after a predetermined time. Moreover, if it is a sheet-like material like a nonwoven fabric, a strontium adsorbent can be manufactured in a sheet form. Using this material, a cartridge filter such as a pleated filter can be easily manufactured.

  The method of the present invention can remove radioactive strontium in a single operation or can be performed multiple times. It can be used in combination with other methods, for example, conventional granular sodium titanate, zeolite and the like. However, a material using a radiation graft polymerization method is preferable because it can be used in the same shape. For example, when the calcium concentration is high and the removal with the radioactive strontium removing material of the present invention is insufficient, the removal can be reliably performed by repeating the operation twice or more. Moreover, radioactive strontium and radioactive cesium can be simultaneously removed using the cesium removal material by the technique disclosed by Unexamined-Japanese-Patent No. 2013-11599 by the present inventors.

  The material of the present invention is a first step of irradiating an organic polymer substrate, particularly a fibrous substrate, a monomer having an ion exchange group or a chelate group, or can be converted into an ion exchange group or a chelate group. Second step of graft polymerization of polymerizable monomer, and further conversion to ion exchange group or chelate group, ion selected from oxalic acid, carbonic acid, sulfuric acid, phosphate ion is applied using ion exchange group or chelate group It can be manufactured by a process including the third process. It can be easily produced by adsorbing ions that form a hardly soluble salt with an alkaline earth metal to the fixed functional group in the graft chain.

  According to the present invention, calcium and strontium are contained in an organic polymer from a liquid having a very high salt concentration such as seawater and an alkaline earth metal such as magnesium and calcium at a very high concentration. Radioactive strontium can be easily removed by precipitating and taking out the organic polymer out of the system. In particular, when fibers are used, since the molding process is easy, radioactive strontium in harbors and tanks can be effectively removed.

  In the case of a harbor, the twisted yarn is processed into a mall shape and suspended or moored at the harbor so that the contaminated sea water and the mall come into contact with each other by natural convection and diffusion without using power. If the adsorbed fiber is in the form of a mall, it can be easily recovered by winding up. Mole is effective not only in ionic form but also in removing fine particles.

  In the case of tank storage water treatment, it is possible to suspend the adsorbent processed into a mall shape, but it is processed into a cartridge filter and stored in an appropriate housing, and it is routed from a pipe laid in the tank via a pump. May be circulated through the housing, and filtration and adsorption may be performed simultaneously. Since the adsorbent contaminated after use can be disposed of together with the housing, contamination of the surroundings can be avoided as much as possible. By using a cartridge filter, finer particles can be efficiently removed.

Wind type cartridge filter Mall-shaped adsorbent

  Hereinafter, embodiments of the present invention will be described in more detail.

  The radiation graft polymerization method irradiates the substrate with ionizing radiation such as γ rays and electron beams, polymerizes the monomer using radicals generated on the substrate surface or inside the substrate, and then grafts the graft chain from the substrate. It is a way to grow. Graft means “grafting” and represents a state where one end of the graft chain is fixed to the base material and the other end is a free end that is not fixed.

  In the present invention, a radiation graft polymerization method is optimal as a method for introducing a polymer chain having an ion exchange group and / or a chelate group into a side chain. Although there is a method that does not use radiation, it is possible to generate radicals not only on the surface but also inside the existing organic polymer having various shapes, and graft side chains can be generated inside the polymer substrate. As a monomer used in the graft polymerization, a monomer having an ion exchange group or a chelate group, or a monomer that can be converted into an ion exchange group or a chelate group is used, and the ion exchange group or chelate is brought into the base material. A group can be introduced. Therefore, the number of functional groups introduced into the substrate also increases.

  Since the graft chains have such morphological characteristics, small ions to large molecules can easily enter between the graft chains. This is a feature that is greatly different from that of an ion exchange resin having a crosslinked structure. In particular, when a fixed charge such as an ion exchange group or a chelate group is present in the graft chain, the fixed charges repel each other electrostatically, so that the graft chain extends and the graft chains repel each other. For this reason, a wide space is formed between the graft chains.

  In the space between the graft chains thus formed, ions that react with alkaline earth metal ions to form a hardly soluble salt are adsorbed. And if it contacts with the liquid containing alkaline-earth metals, such as radioactive strontium, since a slightly soluble salt with radioactive strontium precipitates and forms inside a base material, radioactive strontium can be removed.

  There are approximately 8 ppm strontium, 350 ppm calcium and 1200 ppm magnesium in sea water. It is not necessary to remove calcium present at a considerably higher concentration than the strontium concentration, but it is removed at the same time depending on the kind of ions adsorbed in advance. For example, when carbonate ions are adsorbed on a graft chain having an anion exchange group and then contacted with seawater, strontium is removed simultaneously with calcium. However, the magnesium present at the highest concentration is not removed.

  When salt concentration is very high like seawater, calcium carbonate precipitation may leak out of the fiber, but it can be suppressed by optimizing the amount of carbonate ions adsorbed and the amount of ion exchange groups introduced. In addition, since the precipitate of calcium carbonate containing strontium carbonate has a relatively high sedimentation rate and the moisture content is not as high as magnesium hydroxide, a filter for solid-liquid separation can be added after contact with this material. .

  Ions other than carbonate ions can be used as long as they form ions that are hardly soluble by reaction with alkaline earth metals. For example, there are oxalate ions, phosphate ions, sulfate ions, and any of them can be used. The material for adsorbing these ions is preferably a graft side chain having an anion exchange group.

  The ionizing radiation applied to the organic polymer molded body includes α rays, β rays, γ rays, electron beams, neutron rays, etc., but penetrates from the surface of the organic polymer molded body as a base material to a deep portion. It is preferable to use gamma rays and electron beams having the ability. Radiation irradiation conditions are not particularly limited, but in order to obtain sufficient grafting efficiency in the next step, it is preferably 5 to 200 kGy, particularly 30 to 100 kGy in a deoxygenated state. At this time, the oxygen concentration may be a concentration at which graft polymerization can be achieved at a required polymerization rate, and is preferably 1% or less, more preferably 100 ppm or less.

  When the organic polymer molded body is irradiated with ionizing radiation, radicals are generated on the surface and inside of the organic polymer molded body. When a monomer having a cation exchange group and / or a chelate group is brought into contact therewith, a monomer having a cation exchange group or an anion exchange group and / or a chelate group is polymerized from the generated radical as a base point. Here, the pre-irradiation graft polymerization method and the simultaneous irradiation graft polymerization method are classified according to the timing of radiation irradiation. The present invention can employ either irradiation method. The pre-irradiation graft polymerization method is a polymerization method in which a base material is irradiated with radiation and then brought into contact with a monomer, and is generally suitable for a method for producing a separation material because the amount of homopolymer is small. . The simultaneous irradiation graft polymerization method is a graft polymerization method in which radiation is irradiated in the presence of a substrate and a monomer. In the present invention, it is more preferable to use a pre-irradiation graft polymerization method with a small amount of homopolymer (homopolymer).

  Here, the liquid phase graft polymerization method is used when the monomer to be contacted is a liquid, and the gas phase graft polymerization method is used when the monomer is a gas. In the present invention, any of the graft polymerization methods of liquid phase or gas phase graft polymerization can be used. That is, a liquid monomer can be brought into contact with the organic polymer molded body irradiated with radiation, or a gaseous monomer can be brought into contact therewith. It is also possible to perform an impregnation polymerization method. This method is a graft polymerization method in which the amount of monomer is calculated in advance so as to obtain a predetermined graft ratio, and the required amount of monomer is immersed in the organic polymer molded body in advance.

  Since ion exchange groups can be introduced to the inside, calcium carbonate and calcium phosphate can be supported not only on the fiber surface but also inside. Since one end of the graft chain is fixed and the other end is not fixed, the graft chains having the same ion exchange group are spread by charge repulsion. By using this ion exchange group, calcium carbonate or strontium carbonate can be precipitated and fixed in the fiber, so that dropping can be prevented. Since particles such as calcium carbonate and strontium carbonate are negatively charged, they are preferably held firmly in the positively charged graft chain. The positively charged functional group includes an anion exchange group, and an anion exchange group having a quaternary ammonium group or a tertiary or lower amino group can be used.

  In the case of introducing an ion exchange group, a monomer having an ion exchange group or capable of being converted into an ion exchange group can be easily introduced by graft polymerization. Assuming that the water to be treated is derived from seawater, the content of alkaline earth metal is increased. In that case, anions suitable for forming a sparingly soluble salt include carbonate ions and oxalate ions. It is preferable to graft polymerize a monomer having an anion exchange group capable of adsorbing these anions.

  As monomers having an anion exchange group, vinylbenzyltrimethylammonium chloride, arylamine, N, N-dimethylaminoethyl acrylate, N, N-dimethylaminoethyl methacrylate, N, N-diethylaminoethyl methacrylate, N, N-dimethylacrylamide, N, N-dimethylaminopropylacrylamide may be mentioned. Moreover, vinyl imidazole etc. are mentioned as a monomer which has a chelate group.

  As monomers having functional groups that can be converted into ion exchange groups and / or chelate groups, acrylonitrile, acrolein, vinylpyridine, styrene, chloromethylstyrene, glycidyl methacrylate, glycidyl acrylate, glycidyl sorbate, glycidyl metaitaconate, glycidyl Examples thereof include vinyl sulfonate, ethyl glycidyl maleate, 2-vinyl pyrrolidone, divinyl benzene, 1-vinyl-2-piperidone, N-vinyl-N-methylacetamide and derivatives thereof. Glycidyl methacrylate (GMA) can be particularly preferably used because various functional groups such as a sulfonic acid group, an amino group and a chelate group can be easily introduced. Styrene and chloromethylstyrene can also be suitably used because ion exchange groups and chelate groups can be easily introduced. For example, GMA is graft-polymerized on an organic polymer molded body, and then contacted with an aqueous solution such as trimethylamine (hydrochloride) or dimethylamine to easily convert an epoxy group into an anion exchange group such as a quaternary ammonium group or a tertiary amino group. Can be converted.

  Styrene and chloromethylstyrene can also be suitably used because ion exchange groups and chelate groups can be easily introduced. For example, when chloromethylstyrene is graft-polymerized to an organic polymer molding and then reacted with trimethylamine, the chloromethyl group present in the graft chain is converted to a quaternary ammonium group.

  As the base material for radiation graft polymerization used in the present invention, single fibers, single fiber aggregates, woven fabrics, nonwoven fabrics, short fibers, short fiber aggregates, hollow fibers, sponge-like void materials, braids, moldings It is preferably selected from those comprising a rope, a bag.

  A commercially available product can be freely selected as the organic polymer molding used as the base material used in the present invention. For example, fibers, non-woven fabrics, woven fabrics, twisted yarns, membranes, porous membranes and the like can be freely selected according to the application. Among these, since the fiber has a large surface area, a high adsorption rate can be expected when used as a radioactive material collection material. Moreover, since the removal of strontium of the present invention uses intra-fiber deposition, a porous material is also preferable in order to prevent leakage to the outside of the fiber.

  In addition to the twisted yarn that is a fiber assembly, the fiber can be easily formed into a sheet shape such as a nonwoven fabric or a woven fabric, and thus is suitable for the use of the present invention. In particular, if the type, location, abundance, usage environment, etc. of the radioactive material are significantly different from those in the normal state, such as the removal of radioactive material at the time of an accident at a radioisotope handling facility, change the usage method and mode of use. It is very advantageous that it can be freely selected or changed. Moreover, since it also has a filter function, ions and particles can be removed simultaneously.

  Examples of the fiber material useful as a base material for the radioactive substance removing material of the present invention include synthetic fibers, cellulosic fibers such as cotton, animal fibers or regenerated fibers, or mixed fibers thereof. Synthetic fibers include polyester, polyamide, acrylic, polyvinyl chloride, polyvinylidene chloride, polyethylene, polypropylene, polyurethane, polyvinyl alcohol, fluorine, and the like. Cellulosic fibers include natural cellulose fibers such as cotton and hemp, viscose rayon, copper ammonia rayon, regenerated cellulose fibers such as polynosic, purified cellulose fibers such as tencel, and semi-synthetic fibers such as acetate and diacetate. It is. Animal fibers include animal hair fibers such as wool, silk and the like. The recycled fiber includes chitin / chitosan fiber, collagen fiber and the like. It is also possible to use blends of these fiber materials.

A functional group consisting of an ion exchange group or a chelate group is introduced into the side chain, and an ion that forms a hardly soluble salt with an alkaline earth metal is adsorbed to the functional group. The ions include oxalic acid, carbonic acid, sulfuric acid, Salts selected from phosphate ions are suitable. The solubility product constants are 3.3 × 10 ^{−9 for} calcium carbonate and 5.4 × 10 ^{−10 for} strontium carbonate. Of these, carbon dioxide and sulfuric acid are preferable in consideration of availability and cost. Sodium carbonate, sodium bicarbonate, and calcium chloride are inexpensive as chemicals having carbonate ions and sulfate ions.

  If an anion exchange group or a monomer that can be converted to an anion exchange group is introduced into the base material by radiation graft polymerization and then brought into contact with an aqueous solution of sodium carbonate, calcium chloride, sodium oxalate, sodium phosphate, etc. Ions selected from oxalic acid, carbonic acid, sulfuric acid, and phosphate ions can be adsorbed to the anion exchange group introduced into the chain. Thus, the radioactive strontium removal material of this invention can be manufactured.

  The method of bringing the radioactive strontium-removing material into contact with the liquid contaminated with radioactive strontium is a short fiber, long fiber, twisted yarn, cut fiber, or fiber aggregate when a fibrous or aggregate of fibers is used as a substrate. Since it can be provided in various shapes such as a woven or non-woven fabric, a wound filter that is a molded product thereof, a braid, a rope, a molding, etc., there are various contact methods. The important points are that the adsorption rate is high because the surface area of the fiber is large, and that ions and particles can be removed simultaneously because it can be easily formed into a filter.

  Various contact methods with contaminated water can be selected depending on the usage environment. A wind filter as shown in FIG. 1, a pleated filter obtained by pleating a nonwoven fabric, a rolled filter or a wound filter can be used. A cartridge filter in which these filters are housed in a filter housing is compact and easy to handle. Since the cartridge filter used in the present invention is used in a distribution system, it has both a filtration function and a function of removing ionic radioactive substances, and the functions can be combined. From the standpoint of trapping the captured radioactive material, it is safer to discard the entire housing. Of course, only the filter body may be replaced depending on the degree of contamination.

  In addition, a molding fiber structure as shown in FIG. 2 or one selected from a cut product thereof can be used. A molding-like structure is a kind of braid having a structure in which fibers and twisted yarns are radially projected from the outside of a rope. In the case of a staying radioactive liquid such as the ocean or lake, the radioactive strontium in the liquid can be adsorbed and removed by hanging this mall. The application method can be selected depending on the contamination status and usage environment. After use, solid-liquid separation can be easily achieved by winding the molding with an appropriate means. Further, post-processing is easy.

  The strontium removal material according to the present invention also removes calcium at the same time. Therefore, depending on the quality of the contaminated water, when the calcium concentration is too high or the coexisting salt concentration is high, the removal of strontium may be insufficient to perform the removal operation using the strontium removal material of the present invention at one time. is there. In that case, the same operation may be performed again. In addition to using the same material, a material carrying sodium titanate (Japanese Patent Application No. 2012-094212) may be used, or a material having a sulfonic acid group introduced, an iminodiacetic acid group introduced. A material or a material into which a phosphate group is introduced may be used.

  The strontium-removed fiber described in Japanese Patent Application No. 2012-094212 is obtained by graft polymerization of styrene sulfonic acid having a sulfonic acid group, which is a representative strong acid cation exchange group, using a radiation graft polymerization method. It is adsorbed, converted to hydrous titanium oxide after being made alkaline, and finally added with an alcohol solution of sodium hydroxide and heated for a predetermined time. This material has a high selectivity for strontium.

  A material having an iminodiacetic acid group can be easily produced from a material obtained by graft polymerization of GMA. It can be obtained by immersing the GMA graft in a dioxane or alcohol solution of about 10% sodium iminodiacetate and heating at 80 ° C. for about 8 to 15 hours. Although depending on the graft ratio of GMA, an iminodiacetic acid group concentration of 2 mmol / g or more calculated from the weight increase rate can be easily obtained.

  A sulfonic acid group is obtained by immersing a GMA graft product having a graft ratio of 100% or more in a solution of sodium sulfite / isopropyl alcohol / water = 20/15/65 (weight) and heating at 80 ° C. for about 10 hours. An acid group concentration of 2 mmol / g or more is obtained. The phosphoric acid group can be obtained by immersing the GMA grafted product in a phosphoric acid solution and heating it at a temperature of 50 to 60 ° C. for several hours.

  Thus, when removing strontium using another adsorbent, the treatment with the adsorbent in the previous stage is also considered as a pretreatment. In any case, when manufactured from a material by a radiation graft polymerization method, it can be molded into the same shape and is suitable. For example, when the product shape is made into a mall shape, it can be processed using two types of twisted yarns in one mall, or the mall of the present invention and other adsorbent moldings can be used together. It can be determined according to the type, amount, usage environment, etc. of the radioactive substance.

Hereinafter, although an Example demonstrates concretely, the aspect of this invention is not restricted to a following example.
(1) Production 1 of strongly basic anion exchange fiber
A bobbin wound with 500 g of twisted yarn made of nylon fiber having a fiber diameter of about 40 μm was placed in a polyethylene bag, and the nitrogen substitution operation of evacuation and introduction of nitrogen gas was repeated three times. This bag was irradiated with 100 kGy of gamma rays. After the irradiation, the irradiated polyethylene fiber woven fabric was put in a foamed polystyrene box as a bag, and dry ice was also put therein and stored at a low temperature. On the other hand, 5 L of chloromethylstyrene (manufactured by AGC Seimi Chemical Co., Ltd.) was passed through 1000 ml of an activated alumina-filled column to remove the polymerization inhibitor contained in chloromethylstyrene. Nitrogen was bubbled through the chloromethylstyrene to deoxygenate. The previously irradiated nylon fiber bobbin was placed in a stainless steel reaction vessel and aspirated for 10 minutes with a vacuum pump, and then deoxygenated by introducing nitrogen. A deoxygenated chloromethylstyrene solution was introduced here, and graft polymerization was performed in a constant temperature water bath at 45 ° C. for 6 hours. After the polymerization, the bobbin was removed by washing with acetone and methanol. From the weight change of the dummy twisted yarn reacted together, it was found that the approximate graft ratio was 62%. The bobbin after the graft polymerization was immersed in a 5% trimethylamine aqueous solution and subjected to a quaternary ammonium reaction at 40 ° C. for 3 hours. The obtained nylon fiber was a strongly basic anion exchange with a neutral salt decomposition capacity of 1.9 meq / g.

(2) Production of strongly basic anion exchange fiber 2
Irradiation was performed under the same conditions as in (1). The nylon fiber after irradiation is taken out, put into a similar stainless steel reaction vessel, immersed in a 10% methanol solution of glycidyl methacrylate previously deoxygenated by bubbling with nitrogen gas, and subjected to graft polymerization at 40 ° C. for 8 hours. % Grafting rate was obtained. Next, it was immersed in a solution having a weight ratio of triethylenediamine / isopropyl alcohol / water = 30/30/40 and reacted at 80 ° C. for 3 hours to introduce triethylenediamine. This fiber was a strongly basic anion exchange fiber having a neutral salt decomposition capacity of 1.3 mmol / g.

(3) Production of Strong Acid Cation Exchange Fiber As in (1), 200 g of gamma ray was irradiated to 500 g of fiber bobbin. After the irradiation, a nylon fiber bobbin in a polyethylene bag was placed in a stainless steel reaction vessel, and a 10% aqueous solution of sodium styrenesulfonate (Nacalai Tesque) that had been deoxygenated beforehand by bubbling with nitrogen gas was introduced. Then, graft polymerization was performed at 40 ° C. for 5 hours. The twisted yarn after the polymerization was immersed in pure water at 50 ° C. and washed for 1 hour. This washing operation was repeated three times. When the dummy twisted yarn after washing was vacuum dried and the weight was measured, it was found that the graft ratio was 63%. A portion of 0.5 g of this twisted yarn was collected and regenerated by dipping in 100 ml of 1N hydrochloric acid. The twisted yarn was washed with pure water until the pH test paper showed no acidity. The twisted yarn was immersed in 100 ml of a 3% sodium chloride aqueous solution for 30 minutes and stirred. A portion of the acidified solution was titrated with a 1N aqueous sodium hydroxide solution to determine the neutral salt decomposition capacity. Thus, a twisted yarn composed of a strongly acidic cation exchange fiber having an ion exchange capacity of 1.76 meq / g was obtained.

(4) Production of sodium titanate-carrying fiber 10 g of the strongly acidic cation exchange fiber of (3) was immersed in 1 L of a 1% aqueous solution of titanium sulfate for 1 hour to adsorb titanium ions. Next, it was immersed in 1% of a sodium hydroxide aqueous solution 5% for 30 minutes to make titanium into hydrous titanium oxide. Further, it was washed twice with 1 L of methanol and then vacuum-dried. This fiber was immersed in a 5% sodium hydroxide ethanol solution and treated at 80 ° C. for 4 hours. The treated fiber was washed with methanol and vacuum dried to obtain a sodium titanate-carrying fiber. The fiber loading was 13% weight gain compared to the weight of the first sulfonated fiber (Na type).

(5) Production of iminodiacetic acid group-containing fiber Radiation graft polymerization was performed under the same conditions as in (2) to obtain a GMA graft product having a graft rate of 121%. This fiber was immersed in a solution of sodium iminodiacetate / dioxane / water = 10/40/50, reacted at 80 ° C. for 8 hours, and chelate fiber having an iminodiacetic acid group introduction rate of 2.3 mmol / g calculated from the weight increase rate Got.

(6) Manufacture of molding fiber structure 1
Using a polypropylene fiber (PP) as a core material, a loop was formed using the three types of fibers of the strongly basic anion exchange fiber 1 produced in (1) and a twisted PP yarn to produce a molding adsorbent. In this molding fiber structure 1, the outer diameter of the fiber assembly was about 100 mm, and the amount of each adsorbent used per 1 m of the molding structure was about 200 g.

(7) Production of molding fiber structure 2
A loop is formed using three types of fibers, ie, a strong basic anion exchange fiber 2 produced in (2) and a twisted PP yarn, using polypropylene fiber (PP) as a core material. The material was manufactured. In the molding fiber structure, the outer diameter of the fiber assembly was about 100 mm, and the amount of each adsorbent used per 1 m of the molding structure was about 200 g.

Production of Strontium Removal Material 1 of the Present Invention The fibers of (1) were placed in the same reaction vessel as bobbins, regenerated with 10 L of 5% aqueous sodium hydroxide solution, and then washed with 10 L of pure water three times. Next, carbonate ions were adsorbed with a 0.5 mol / L sodium carbonate aqueous solution. Similarly, washing was performed 3 times using 10 L of pure water. Thus, the strontium removing material 1 of the present invention was produced.

Production of strontium removing material 2 of the present invention The fibers of (2) were adsorbed with carbonate ions under the same conditions as in Example 1 to produce the strontium removing material 2 of the present invention.

Batch strontium removal test 1
Artificial seawater was diluted to about 50% and used as raw water for a batch strontium removal test. When the water quality of this liquid was measured by ICP-AES (plasma emission analyzer), the magnesium, calcium and strontium concentrations were 510, 160 and 4.7 mg / L in this order. In 200 ml of this solution, 1 g of the carbonate type anion exchange fiber (2) was immersed and stirred for 30 minutes. The magnesium concentration of this supernatant was 480 mg / L, but the calcium concentration was 22 mg / L. The strontium concentration was 0.5 mg / L. That is, only by immersing the carbonate type fiber, magnesium was not removed, and about 90% of calcium and strontium were removed.

Batch strontium removal test 2
1 g of the fiber (4) was further immersed in the liquid obtained by removing the fiber of the batch test of [Example 3], and stirred for 30 minutes. When the supernatant liquid after 30 minutes was analyzed, magnesium was 280 mg / L, and the concentrations of calcium and strontium were both below the ICP-AES quantification limit of 0.5 mg / L. That is, calcium and strontium could be removed by using carbonate type anion exchange fiber and sodium titanate-supported fiber in this order. At this time, no precipitate was observed and the liquid was transparent. From this result, 95% or more of strontium in the 50% diluted seawater solution was removed by two-stage fiber immersion.

(8) Batch strontium removal test 3
1 g of the fiber (5) was further immersed in the batch test solution of [Example 3], and the same test as in Example 3 was performed. When the supernatant liquid after 30 minutes was analyzed, magnesium was 290 mg / L, and the concentrations of calcium and strontium were both below the ICP-AES quantitative limit of 0.5 mg / L. That is, calcium and strontium could be removed by using carbonate type anion exchange fiber and iminodiacetic acid group-introduced fiber in this order. At this time, no precipitate was observed and the liquid was transparent. From this result, 95% or more of strontium in the 50% diluted seawater solution was removed by two-stage fiber immersion.

Batch-type strontium removal test 4 with molding fiber structure 4
After the mall-shaped fiber structure 1 of (6) was previously immersed in sodium hydroxide, it was washed with water. Next, it was immersed in a 0.5 M aqueous sodium carbonate solution to adsorb carbonate ions. 200 L of seawater was taken in a drum can, and the carbonate ion-type molding fiber structure 1 was suspended on a PVC pipe that was passed over the 5 m drum can. The mold-like fiber structure 1 was taken out after 48 hours. The strontium concentration in the sea water was measured to be 0.8 mg / L. Since the strontium concentration of seawater is about 8 mg / L, 90% is removed by simply throwing in the mole-like fiber structure and taking it out after a predetermined time.

Batch-type strontium removal test 5 using molding fiber structure 1 (twice)
The new molding fiber structure 1 manufactured in [Example 6] was immersed for 5 m in the liquid obtained by removing the molding in [Example 6], and the same test was performed. As a result, the strontium concentration in the liquid was 0.5 mg / L or less, which was below the measurement limit of ICP-AES.

Batch type strontium removal test 6 with molding fiber structure 6
(7) A test similar to [Example 6] and [Example 7] was conducted using Production 2 of the molding fiber structure. When the molding fiber structure 2 was used once, 90% of strontium could be removed, and when it was used twice, the strontium concentration in the liquid was 0.5 mg / L or less (removal rate of 95% or more), and the same result was obtained.

Production of Strontium Adsorbing Material 3 of the Present Invention The strongly basic anion exchange fiber obtained in (1) was immersed in a 1M sodium hydroxide solution. Next, after sufficient washing, it was immersed in a 1% sodium oxalate solution to adsorb oxalate ions. The strontium adsorbing material 3 of the present invention could be manufactured.

Batch strontium removal test 7
A batch strontium removal test similar to [Example 3] was performed using the fiber of [Example 10]. The magnesium concentration in the liquid from which the fibers were removed was 480 mg / L, the calcium concentration was 31 mg / L, and the strontium concentration was 1.1 mg / L. That is, just immersing this oxalate-type fiber did not remove magnesium, and about 80% of calcium and strontium were removed.

Batch strontium removal test 8
[Example 11] Further, sodium titanate-carrying fiber was added to this solution in the same manner as in batch strontium removal test 2, and strontium in the solution after stirring was measured. It was removed.

  In seawater, non-radioactive strontium is present at about 8 mg / L, and calcium and magnesium are present in a large excess. Therefore, it has been difficult to remove radioactive strontium from seawater or contaminated water derived from seawater. Since the radioactive strontium removing material of the present invention forms calcium and strontium and a sparingly soluble salt in the fiber, the radioactive strontium can be removed simply by pulling up the fiber after it has been introduced. No power or equipment such as pumps or tanks is required. In addition, it can be molded and applied to malls and filters in places where it is difficult to construct large water treatment facilities such as harbors, rivers, lakes and stagnant water. Since the adsorbent after use is a polymer, volume reduction such as incineration is easy. The present invention is extremely effective while the problem of radioactive contamination associated with the Great East Japan Earthquake is becoming more and more apparent.

1 Inner cylinder 2 Anion exchange fiber material adsorbed with carbonate ions 3 core

Claims (8)

  A radioactive strontium removal material having a functional group consisting of an ion exchange group or a chelate group in the side chain and adsorbing ions that form a hardly soluble salt with an alkaline earth metal to the functional group   2. The radioactive strontium removing material according to claim 1, wherein the radioactive strontium removing material is obtained by introducing a graft chain into an organic polymer base material using a radiation graft polymerization method.   The organic polymer base material according to claim 2 comprises a fibrous base material, a short fiber, a long fiber, a twisted yarn, a cut fiber, a woven or non-woven fabric that is an aggregate of fibers, and a wind filter that is a molded product thereof. Radioactive strontium removal material selected from pleated filter, braid, rope, molding   The radioactive strontium removing material according to claim 1, 2 or 3, wherein the ions forming the hardly soluble salt are selected from oxalic acid, carbonic acid, sulfuric acid, and phosphate ions.   First step of irradiating the fibrous base material with radiation, graft polymerization of a monomer having an ion exchange group or chelate group, or graft polymerization of a polymerizable monomer that can be converted into an ion exchange group or chelate group, and further ion exchange groups Or the 2nd process which converts into a chelate group, The manufacturing method of the strontium removal material including the 3rd process which provides the ion selected from an oxalic acid, carbonic acid, a sulfuric acid, and a phosphate ion using an ion exchange group or a chelate group   The radioactive strontium removal method including the 1st process process which makes the radioactive strontium removal material of Claims 1-4 contact the liquid contaminated with radioactive strontium   As a step before or after the first treatment step according to claim 5, the radioactive strontium removing material according to claims 1-4, a material having a sulfonic acid group introduced therein, a material having a phosphate group introduced therein, an iminodiacetic acid group 7. A method for removing radioactive strontium according to claim 6, further comprising a second treatment step in which the material is contacted with a radioactive strontium removing material selected from a material into which sodium titanate is loaded and a radioactive strontium removing material loaded with sodium titanate.   The material having a sulfonic acid group introduced therein, a material having a phosphoric acid group introduced therein, a material having an iminodiacetic acid group introduced therein, and a radioactive strontium-removing material carrying sodium titanate are applied to a fibrous base material with radiation. 6. The method for removing radioactive strontium according to claim 5, wherein the radioactive strontium is produced using a graft polymerization method.