JP2016024183A - Radioactive iodine removal material and method for producing the same, and radioactive iodine removal method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a material for removal of radioactive iodine from contaminated water containing a high concentration of salts, and a method for producing the same.SOLUTION: The present invention provides a radioactive iodine adsorption material in which a radiation graft polymerization method is used to support silver or silver compounds on a graft chain having a functional group such as an ion exchange group, a chelate group and a hydrophilic group in a polymer base material. Particularly suitably can be used is one in which a graft chain is formed in fiber (such as twist yarn, woven fabric, and nonwoven fabric), and a functional group such as an ion exchange group is used to support and deposit silver compounds even inside the fiber.SELECTED DRAWING: Figure 4

Description

  The present invention relates to a material for removing radioactive iodine leaked due to an accident at the Fukushima Daiichi Nuclear Power Station, a method for producing the material, and a method for removing radioactive iodine using the material.

Like the cesium and strontium, radioactive iodine leaked out due to the 3.11 earthquake. Since radioactive iodine causes great damage to the thyroid gland, it must be prevented from spreading into the environment as much as possible. Iodine is often released into the atmosphere, and its chemical form is complex such as iodine (I ₂ ) hypoiodous acid (HIO), methyl iodide (CH ₃ I), and those adsorbed on particles. Among these, methyl iodide is nonionic compared to other iodine compounds, and thus the removal method is complicated. Activated carbon or impregnated activated carbon has often been used to remove these. As chemical substances to be attached to the impregnated activated carbon, triethylenediamine, silver, potassium iodide, and the like are used, although depending on the object to be removed.

  Activated carbon can adsorb various kinds of radioactive materials by physical adsorption. Regarding radioactive iodine, triethylenediamine is supported on activated carbon and used for adsorption of organic iodine such as methyl iodide. In addition, silver is used to remove iodine and hydroiodic acid. However, activated carbon has the problems of being heavy and difficult to dispose of waste. Furthermore, granular activated carbon can only be packed and used in boxes and columns and used in a distribution system. Problems such as difficulty in quickly removing radioactive iodine present at unsteady sites caused by the accident at the Fukushima Daiichi NPS There was a point.

  Radioactive iodine adsorbing materials other than activated carbon have also been proposed. In Patent Document 1, silver is supported on an ion exchange fiber, and iodine in a gas phase and a liquid phase can be removed. In this prior art, silver is adsorbed on an ion exchange fiber to remove organic iodine such as inorganic iodine or methyl iodide in the gas phase or liquid phase. In Examples, there is an example in which silver is supported on a material provided with a cation exchange group such as a carboxyl group, and iodine such as methyl iodide is removed in a gas phase with this fiber. However, there is no disclosure about removing radioactive iodine from a liquid containing a high concentration of salts such as sodium chloride.

  In Patent Document 2, a functional group capable of adsorbing silver ions using a radiation graft polymerization method, for example, a graft chain having a cation exchange group is introduced, and the reaction between silver ions adsorbed on the cation exchange group and an iodine compound results in radioactive activity. There is a proposal to remove iodine released into the gas. However, since this technique is intended for removing iodine in the gas phase, there is no idea to remove iodine ions in the liquid phase from a solution having a particularly high salt concentration.

In Patent Document 3, N-alkyl-N-vinylalkylamide (for example, N-vinylpyrrolidone) is graft-polymerized on a fiber base material as a monomer, and removal performance against iodine in the air (particularly iodine (I ₂ )) is imparted. I can do it. However, since this is a technique for removing iodine in the gas phase, it is not a technique for iodine ions in the liquid phase.

From the above examples, the techniques proposed so far are mainly for removing iodine in the gas phase, and there are very few techniques for removing iodine from an aqueous solution. In particular, it is not easy to remove iodine from a solution having a relatively high salt concentration, and the multi-nuclide removal equipment (ALPS) installed at the Fukushima Daiichi Nuclear Power Station does not have a significant removal effect. The concentration of radioactive iodine in the treated water has changed around the reported concentration. In addition, although it is said that the iodine in aqueous solution has many forms of I < ^- > or IO < ₃ > ^- , the removal of iodine ion (I < ^- >) is described here.

  For removing iodine in an aqueous solution, an ion exchange resin or silver impregnated activated carbon is used. Ion exchange resins are excellent adsorbents, but it is difficult to selectively remove only iodine ions when the salt concentration is high. For example, when iodine ions are removed from seawater or liquid contaminated with seawater, the removal rate and the adsorption capacity are usually extremely small. In particular, since seawater is used to cool the nuclear reactor, the concentration of salts such as sodium chloride is very high in the nuclear power plant, and it is difficult to remove iodine coexisting with these salts.

  Non-Patent Document 1 shows an example in which iodine ions are removed from the presence of chlorine ions in silver-impregnated activated carbon. In this case, the mechanism of iodine removal is a reaction in which iodine reacts with the supported silver chloride to form hardly soluble silver iodide (Agl). Speaking of the reaction formula, it is described that chlorine ions in silver chloride exchange with iodine ions, but the details are not clear. When silver chloride is impregnated into the pores of activated carbon, there is a risk of leakage into the water to be treated because the interaction between silver chloride or silver iodide and activated carbon is small. In addition, since activated carbon is granular, the method of use is limited to a packed tower system such as ALPS, so it cannot be used depending on the contaminated environment in many cases.

  Therefore, a material that can efficiently remove iodine ions from an aqueous solution having a high salt concentration at high speed and can be used anywhere has not been proposed. In particular, at the site of contamination where the removal rate of radioactive iodine concentration in the treated water is not sufficient and only the removal performance around the notification concentration can be maintained as in the Fukushima Daiichi Nuclear Power Station, along with the removal of radioactive cesium and radioactive strontium, There is an urgent need to propose a radioactive iodine removal material.

JP-A-63-12345 JP 2000-254446 A JP2000-2558592

J. et al. inorg, nucl. Chem. Vol. pp. 583-587, Pergamon Press Ltd. . 1981. Printed in Great Britain

Task

When removing radioactive iodine from contaminated water containing radioactive iodine, not only when the salt concentration of contaminated water is low, but also when the salt concentration is high, such as in seawater, radioactive iodine can be quickly removed and removed. No adsorbent was desired. In view of the problem, the present invention has been devised as a result of earnest research and development on the removal of iodine ion (I ⁻ ) present in an aqueous solution having a high salt concentration.

Means for solving the problem

  This invention provides the radioactive iodine removal material which has the following characteristics, its manufacturing method, and the radioactive iodine removal method using this adsorption material.

(1) A radioactive iodine removing material in which at least silver or a silver compound is added to an organic polymer base material having a functional group selected from an ion exchange group, a chelate group, or a hydrophilic group in a graft side chain

(2) The functional group irradiates the organic polymer substrate with radiation and has a functional group selected from an ion exchange group, a chelate group, or a hydrophilic group, or from an ion exchange group, a chelate group, or a hydrophilic group. The radioactive iodine removing material according to (1), which is introduced by graft polymerization of a monomer that can be converted into a selected functional group

(3) The functional group is an amino functional group containing a sulfonic acid group, a carboxyl group, a phosphoric acid group, a quaternary ammonium group, an amino acid group, an aminophosphoric acid group, an iminodiacetic acid group, or a primary to tertiary amino group. Or a radioactive iodine removing material according to (1) or (2), wherein the material is selected from amidoxime groups, hydroxamic acid groups, amide groups, and hydroxyl groups

(4) The organic polymer substrate is a fiber, a cut fiber, a twisted yarn that is an aggregate of fibers, a woven fabric, a nonwoven fabric, a porous hollow fiber, a porous flat membrane, a sponge-like void material, or a processed product thereof ( The radioactive iodine removing material according to 1), (2) or (3)

(5) Bags, wind filters, pleated filters, roll filters, braids, molds, etc., in which the processed product is water permeable to the organic polymer substrate but not the substrate. The radioactive iodine removing material according to (1), (2), (3) or (4), which is more selected

(6) After irradiating the organic polymer substrate with radiation, it has a functional group selected from an ion exchange group, a chelate group, or a hydrophilic group, or is selected from an ion exchange group, a chelate group, or a hydrophilic group By graft polymerization of a monomer that can be converted into a functional group, a graft side chain is introduced into the organic polymer fiber, and then at least a water-soluble silver salt is brought into contact, whereby silver imparts a silver compound to the fiber surface and inside. (1), (2), (3), (4) or the method for producing a radioactive iodine removing material according to (5)

(7) The functional group is an amino functional group containing a sulfonic acid group, a carboxyl group, a phosphoric acid group, a quaternary ammonium group, an amino acid group, an aminophosphoric acid group, an iminodiacetic acid group, or a primary to tertiary amino group. Or (1), (2), (3), (4), (5) or (6) selected from those having an amidoxime group, hydroxamic acid group, amide group, hydroxyl group or convertible Method for producing radioactive iodine removing material

(8) After contacting the water-soluble silver salt described in (6), a liquid containing at least chloride ions is contacted to deposit silver chloride on the surface and / or inside of the organic polymer substrate ( 1), (2), (3), (4), (5), (6) a method for producing a radioactive iodine removing material according to (7) or (8)

  One end of the graft side chain is bonded to the base polymer, and the other end is a free end. Therefore, it has very high mobility, and ions and particles easily enter between the graft chains, so that the adsorption rate is high. In particular, since the radiation graft polymerization method can freely select a substrate, a fiber substrate having a large surface area can be selected. As a result, the adsorption rate can be further improved. In addition, since the graft chain can be generated not only on the surface of the substrate but also inside, a large amount of functional groups can be introduced into the graft chain unlike a simple surface modification, and it is excellent as a separation functional material. In the ion exchange reaction, chelate reaction, etc., the adsorbed ions reach not only the surface but also the deep part of the graft chain and the inside of the substrate and are captured.

  Since silver ions can be supported using ion exchange reaction or chelate reaction, silver ions can be adsorbed in the base polymer. Insoluble silver halides such as silver chloride can also be deposited and supported inside the base polymer. For this reason, the adsorbed silver ions and the supported silver chloride can be used to remove iodine ions.

  There are several methods for imparting silver or a silver compound to a graft chain having a functional group depending on the type of the functional group. In the case of a cation exchange group typified by a sulfonic acid group or a chelate group typified by an iminodiacetic acid group, it is easy to introduce silver ions and they can be used as they are without reacting with halide ions. It is. It can also be used by reacting with halide ions, and can be selected depending on the use environment.

  Anion exchange groups typified by quaternary ammonium groups cannot adsorb silver ions. However, silver chloride can be deposited and supported by contact with an aqueous silver nitrate solution after conversion to a halogen ion type such as a chloride ion type. Silver chloride ultrafine particles are formed on the surface and inside of the substrate. Here, since the functional group has a positive charge, it can adsorb and hold negatively charged colloidal fine particles. Some will fall off, but many will be retained on the surface or inside of the substrate. Since one end of the graft chain is not fixed, it can be expected that multipoint adsorption occurs between the silver halide grains and the graft side chain.

The immobilized silver chloride can adsorb iodine ions. Although the adsorption mechanism is not yet clear, basically, the solubility of silver iodide is as small as 8.5 × 10 ⁻¹⁷ , so that the chloride ion of silver chloride (solubility is 2.8 × 10 ⁻¹⁰ ) And iodide ions are substituted, or it can be understood that the iodide ions are extracting silver.

  In this adsorption mechanism, iodine ions can be removed even in a liquid having a high salt concentration such as seawater. Therefore, even when a large amount of seawater is introduced as in the Fukushima Daiichi Nuclear Power Station, radioactive iodine can be removed. Conventionally, in an ion exchange reaction, when there are a large amount of anion components such as chloride ions coexisting, the performance deterioration is remarkable. However, this silver chloride-supported material does not deteriorate performance. In the case of a cation exchange group, a repulsive force is generated against the approach of iodine ions to the adsorbent, but a material having an anion exchange group typified by a quaternary ammonium group is preferable because iodine ions can be freely taken inside. .

  As described above, a strong retention force is exerted by multipoint adsorption of silver halide grains by the graft chain, and a functional group having an anion exchange group or anion exchange chelate group in that iodine ions are easily accessible between the graft chains. Groups are preferred. As such a functional group, there is the most common trimethylammonium group as a strongly basic anion exchange group, which can be suitably used. As a method for introducing this functional group, a monomer having a trimethylammonium group, for example, vinylbenzyltrimethylammonium chloride (VBTAC) can be used.

  Since the radiation graft polymerization method can generate radicals up to the inside of the base material with respect to the base polymer of various shapes, and can carry out the graft polymerization method, for example, fibers, woven fabrics and non-woven fabrics that are aggregates of fibers, Functional groups can be introduced into twisted yarns, void materials and particles. Among them, the fiber has a large surface area and a high adsorption rate, so that it is suitable for removing a dilute substance in a large amount of liquid as in the case of removing radioactive iodine.

  The method of introducing an ion exchange group or chelate group into an organic polymer substrate by radiation graft polymerization is a method in which a monomer having an ion exchange group or a chelate group is contacted after irradiating the substrate with radiation such as gamma rays or electron beams. The graft side chain can be generated on the base material by graft polymerization by a method such as bringing a monomer that can be converted into an ion exchange group or a chelate group into contact. At this time, since radicals are generated even inside the base material, a graft chain is generated not only on the surface of the base material but also inside the base material.

  Functional groups include sulfonic acid groups, carboxyl groups, phosphoric acid groups, quaternary ammonium groups, amino acid groups, aminophosphoric acid groups, iminodiacetic acid groups, amino functional groups containing one or more primary to tertiary amino groups, amidoxime groups, It can be selected from those having a hydroxamic acid group, an amide group or a hydroxyl group. A functional group can be introduced into the graft side chain by radiation graft polymerization of a monomer having these functional groups or capable of being converted into functional groups.

  Since the fiber has a good molding process, various contact methods such as a mooring method and a filter method are possible as well as a column packing method applied with a granular adsorbent. A filter wound with a twisted yarn or a non-woven fabric can simultaneously remove fine particles and ions. It is also possible to contact the cut fibers as a slurry. Therefore, the usage method according to the contamination site inside and outside the nuclear power plant is possible. In the case of contaminated water mixed with seawater, the chlorine ion concentration is high, but it can be removed by the radioactive iodine removing material of the present invention.

  When the radioactive iodine adsorbing material of the present invention is actually used for liquid decontamination, it is possible to re-fix or remove excessively supported silver ions and silver chloride particles by washing with a sodium chloride aqueous solution in advance. It is preferable because dropping of silver chloride grains and the like can be reduced.

  The treatment method of the liquid containing radioactive iodine by the radioactive iodine adsorbing material of the present invention can be appropriately selected depending on the state of contamination and the method of use. For example, it can be processed into a filter shape, and both particle and ion adsorption removal functions can be imparted by circulating the pump. In addition, it can be used in the form of a mall and moored in a lake or harbor.

Effect of the invention

  According to the present invention, silver halide fine particles can be deposited and supported on a graft side chain having a functional group such as an ion exchange group or a chelate group. By using radiation graft polymerization, it is possible to use various base materials, especially fibers with a large surface area. Using the graft chains introduced into these fibers, the surface of the fiber and the interior of the silver compound represented by silver chloride are strengthened. It was possible to deposit and support the material. And it turned out that this hardly soluble silver chloride can be utilized for adsorption | suction of an iodine ion. By making it possible to propose a fibrous adsorbent that can be molded freely, the internal and external radioactive iodine diffused from the Fukushima Daiichi Nuclear Power Station can be quickly removed.

  Chemical structure of triethylenediamine   Introduction route of triethylenediamine into nylon fiber by radiation graft polymerization   Mall-shaped adsorbent   Wind filter

  The radioactive iodine removing material used in the present invention is obtained by adding at least silver or a silver compound to an organic polymer base material having a functional group selected from an ion exchange group, a chelate group, or a hydrophilic group on a graft side chain. The radiation graft polymerization method is the most suitable method for introducing the graft side chain. Hereinafter, an example using the radiation graft polymerization method will be described.

  The radiation graft polymerization method is a method of irradiating a substrate with ionizing radiation such as γ-rays or electron beams and utilizing a radical generated on the surface of the substrate or inside the substrate (hereinafter referred to as “monomer”). Is a method of growing a graft chain from a substrate.

  A characteristic of the radiation graft polymerization method is that radicals can be easily generated not only on the surface of the substrate but also inside the substrate by irradiation with radiation. Therefore, since the monomer can be polymerized not only on the substrate surface but also inside the substrate, the number of graft chains introduced into the substrate increases, and thus the number of functional groups introduced into the substrate also increases. .

  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. 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. The radioactive iodine adsorbing material of the present invention can form and hold silver or a silver compound between the graft chains. Due to the mobility of the graft chain, the silver compound is firmly fixed by multipoint adsorption. Iodine ions can easily enter the spaces between the graft chains thus formed, which is advantageous for adsorption and removal.

  The number and length of graft chains introduced into the substrate can be controlled by the radiation dose and graft rate. When the irradiation dose is large, the radical generation amount is large, and the number of graft chains is increased. The graft rate means the rate of weight increase before and after graft polymerization. The larger the graft rate, the longer the length of the graft chain. Usually, the longer the graft chain length, the higher the functional group concentration and the higher the removal rate and the adsorption capacity, but the lower the physical strength, so that it can be appropriately selected depending on the type of substrate used and the method of use. In the case of an ion exchange group or a chelate group, the graft ratio is usually about 20 to 150%.

  In the radiation graft polymerization method, the organic polymer base material can be selected from various shapes. However, as the radioactive iodine removing material of the present invention, a fiber that can be easily processed and expected to have a large surface area and a large adsorption rate is suitable.

  Examples of the fiber material that can be used as the substrate include synthetic fibers, cellulosic fibers such as cotton, animal fibers, 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.

  In the radiation graft polymerization method, first, the fiber material to be graft-polymerized is irradiated with radiation. Irradiation conditions are not particularly limited, but 5 to 200 kGy, particularly 30 to 100 kGy are preferable in a deoxygenated state in order to obtain sufficient graft efficiency. 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. Examples of radiation that can be suitably used for the purpose of the present invention include, but are not limited to, α rays, β rays, gamma rays, electron beams, ultraviolet rays, and the like. Industrially, gamma rays or electron beams are suitable.

  The graft polymerization performed next is divided into a pre-irradiation graft polymerization method and a simultaneous irradiation graft polymerization method depending on the timing of irradiation, and either irradiation method can be employed in the present invention. The pre-irradiation graft polymerization method is a polymerization method in which the base material is irradiated with radiation in advance and then brought into contact with the monomer, and is suitable as 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, both the pre-irradiation graft polymerization method and the simultaneous irradiation graft polymerization method can be used, but the pre-irradiation graft polymerization method in which the amount of homopolymers (homopolymer) produced is small is more preferable.

  Depending on whether the monomer to be contacted is liquid or gas, it is divided into a liquid phase graft polymerization method and a gas phase graft polymerization method, respectively. In the present invention, any of the graft polymerization methods of liquid phase or gas phase graft polymerization can be used. Further, there is an impregnation polymerization method as a graft polymerization method located between the liquid phase and the gas phase graft polymerization method. This method is a graft polymerization method in which the amount of monomer is controlled so as to obtain a predetermined graft ratio in advance and the substrate is immersed in the base material. The present invention can also be used for this graft polymerization method.

  Examples of the polymerizable vinyl monomer that can be introduced into the fiber by the radiation graft polymerization method of the present invention include a polymerizable vinyl monomer having various functional functional groups, or a secondary reaction after grafting the polymerizable vinyl monomer. A polymerizable vinyl monomer which can introduce a functional functional group by performing can be used.

As a functional group to be introduced using a radiation graft polymerization method, an ion exchange group or a chelate group is preferable. For example, as the ion exchange group, a sulfonic acid group, a carboxyl group, a phosphoric acid group, a quaternary ammonium group, an amino group, and the like can be used. As chelate groups, amino acid groups typified by iminodiacetic acid groups, chelate groups containing a plurality of carboxyl groups, amino functional groups, aminophosphate groups, amidoxime groups, hydroxamic acids containing one or more primary ^to tertiary amino groups Those selected from the group can be used. Since sulfonic acid groups and quaternary ammonium groups, which are typical ion exchange groups, swell the graft chain by charge repulsion, a wide space is formed and is suitable for supporting silver compounds and adsorbing iodine ions.

  Examples of the monomer having an ion exchange group include acrylic acid, methacrylic acid, styrene sulfonic acid, vinyl sulfonic acid, methacryl sulfonic acid, allyl sulfonic acid and alkali metal salts thereof, vinylbenzyltrimethylammonium chloride (VBTAC), arylamine, N , N-dimethylaminoethyl acrylate, N, N-dimethylaminoethyl methacrylate, N, N-diethylaminoethyl methacrylate, N, N-dimethylacrylamide, N, N-dimethylaminopropylacrylamide and the like can be used.

  A typical anion exchange group is a quaternary ammonium group. There exists (VBTAC) as a monomer which has this ion exchange group. When this monomer is graft polymerized to the fiber, it may coexist with a monomer having a nonionic hydrophilic group depending on the fiber material. For example, N-vinyl-2-pyrrolidone, hydroxyethyl methacrylate and the like can be easily graft-polymerized by using a mixed monomer. Further, N, N-diethylaminoethyl methacrylate having a tertiary amine may be used in combination.

  Monomers that can be converted into ion exchange groups or chelate groups by performing a secondary reaction include acrylonitrile, acrolein, vinylpyridine, styrene, chloromethylstyrene, glycidyl methacrylate (GMA), glycidyl acrylate, glycidyl sorbate, and glycidyl metaitaconate. Glycidyl vinyl sulfonate, ethyl glycidyl maleate, 2-vinyl pyrrolidone, divinyl benzene, 1-vinyl-2-piperidone, N-vinyl-N-methylacetamide and derivatives thereof.

  In the case of GMA, various functional groups such as a cation exchange group such as a sulfonic acid group and a carboxyl group, a chelate group such as an iminodiacetic acid group, and an anion exchange group such as a quaternary ammonium group can be easily introduced. . In addition, styrene and chloromethylstyrene can be easily used because ion exchange groups and chelate groups can be easily introduced.

  When a quaternary ammonium group is introduced into the GMA graft chain, for example, the quaternary ammonium group can be introduced by bringing the GMA graft fiber into contact with a trimethylamine hydrochloride aqueous solution and reacting at a predetermined temperature for a predetermined time. In addition, triethylenediamine (TEDA) does not have an amine odor like trimethylamine, so that not only the workability is good, but also a neutral salt decomposition capacity of 1.5 meq / g or more and a quaternary ammonium group concentration can be introduced in a large amount.

  The method for supporting silver ions or silver compounds can be appropriately selected depending on the type of functional group. For example, to support silver chloride on the anion exchange group, the salt form of the anion exchange group is converted to the chloride ion type in advance, and then the silver chloride precipitate is easily supported inside the substrate by contacting with the silver nitrate solution. it can. In order to convert the quaternary ammonium group to the chloride ion type, it can be easily prepared by contacting with a 0.1 to 1 M sodium chloride solution. Further, any chloride ion type monomer can be used as it is because the graft product after graft polymerization is a chloride ion type.

  A chloride ion-type anion exchange group is brought into contact with a water-soluble silver salt such as silver nitrate to carry silver chloride inside the fiber. Silver ions diffuse and move between the swollen graft chains, depriving the chloride ions adsorbed on the anion exchange groups, and forming extremely insoluble silver chloride in the vicinity thereof. The produced insoluble silver chloride particles have a negative charge, are attracted electrostatically to the graft chain having a positive charge, and are firmly fixed by multipoint adsorption. Thus, since fine silver chloride particles are supported in a donut shape from the fiber surface layer toward the center, falling off during use can be prevented. Even in aqueous solutions with extremely high chloride ion concentrations, such as seawater, silver chloride particles do not fall off.

  In the case of a cation exchange group, silver ions can be adsorbed by adjusting the salt type to H type or Na type and then contacting with a silver nitrate solution. Even in this state, it can be used for adsorption of iodine in the gas phase. Further, after adsorbing silver ions, silver chloride can be deposited and supported by contacting with chemicals containing chloride ions, for example, sodium chloride aqueous solution. Hydrochloric acid can be used in the same manner instead of sodium chloride. If the silver chloride that is leaking into the liquid has a lot of white turbidity, it may be washed with a sodium chloride aqueous solution or pure water until the white turbidity disappears as appropriate. When immersed in a liquid to be treated having a high chlorine ion concentration while adsorbing silver ions, silver chloride is generated and leaks into the liquid to be treated. Therefore, if it wash | cleans previously with sodium chloride aqueous solution etc. and it is set as silver chloride particle | grains, the leakage of the precipitation at the time of use can be suppressed.

  Chelate groups can also be supported according to the case of ion exchange groups. The iminodiacetic acid group, which is a typical chelate group, can carry a silver compound in the same manner as the weakly acidic cation exchange group. In the case of an anionic chelate group such as polyamine, a silver compound can be supported as in the case of an anion exchange group.

  In order to implement the present invention most effectively, a material having an anion exchange group or an anion exchange chelate group in the graft chain is preferred. This is because, when the silver chloride is supported, an electrostatic adsorption force acts between the negatively charged precipitate and the positively charged functional group, and can be firmly held by multipoint adsorption. In addition, since iodine of adsorbed ions is an anion, it diffuses and moves inside the material to exchange anions. Among the anion exchange groups, a strongly basic anion exchange group having a quaternary ammonium group is preferable.

  The above-described material into which TEDA is introduced has a functional group of both a quaternary ammonium group and a highly reactive tertiary amino group, and thus is more preferable. TEDA has the chemical structure shown in FIG. 1 and has two highly reactive tertiary amino groups in the molecule. Therefore, one amino group is bonded to the epoxy group of the GMA of the graft chain and quaternary ammonium is formed, and at the same time, the other amino group is bonded to another graft chain to form a crosslinked structure. Silver can be prevented from falling off, which is very suitable for the use of the present invention.

  The TEDA introduction route is shown in FIG. Thus, glycidyl methacrylate (GMA) is graft-polymerized on the fiber by a radiation graft polymerization method. Then, TEDA can be easily introduced by heating an aqueous solution of 10% to 50% TEDA, optionally with an alcohol such as isopropyl alcohol, at a temperature of 50 to 80 ° C. for several hours. In TEDA-introduced fiber, one end of two tertiary amines of TEDA is bonded to GMA to form a quaternary ammonium, but the other end is a tertiary amine, and both amines can be used for ion exchange. In this way, a strongly basic anion exchange fiber having a neutral salt decomposition capacity of about 1.5 meq / g can be easily obtained.

  Further, TEDA tertiary amines are very reactive and highly nucleophilic, so the amine at the other end is also easily bonded to another graft chain. In this case, since a crosslinked structure is formed in the graft chain, it is suitable for holding the silver halide grains inside the adsorbent.

  The degree of crosslinking can be analyzed by titration. The quaternary ammonium group produced by crosslinking is capable of decomposing neutral salts such as sodium chloride. For example, when the Cl type is regenerated to OH type by immersing it in a sodium hydroxide solution of about 1M, and then immersed in an aqueous sodium chloride solution, sodium hydroxide is produced by adsorbing Cl ions. This sodium hydroxide (NaOH) is obtained by neutralization titration with hydrochloric acid or sulfuric acid whose concentration is accurately known. Since the amount of amine introduced can be known from the change in weight before and after the introduction of the functional group, the amino group involved in crosslinking can be calculated from this value and the value of the quaternary ammonium group determined previously.

  If there are many crosslinks, it will affect the adsorption rate and loading, so 5% to 75% of the introduced TEDA is suitable. In the case of 5% or less, the amount of quaternary ammonium groups is small, and sufficient electrostatic adsorption force does not work. On the other hand, if it is 75% or more, the flexibility of the fiber is reduced and the strength is lowered.

  When carrying out the graft polymerization, a crosslinking agent such as divinylbenzene can be used in combination. In addition, crosslinking agents such as triallyl isocyanate and ethylene glycol dimethacrylate can be used. The supported silver chloride particles can be used to prevent dropping off.

  When salt concentration is high like seawater, it can be used because it can fix excess silver ions and wash away excess silver chloride particles by washing with an aqueous solution that is equivalent to or higher than seawater. It is possible to completely prevent the silver chloride grains from falling off.

  When cation exchange groups are used, silver chloride particles can be supported by first adsorbing silver ions by ion exchange and then contacting with a sodium chloride aqueous solution. However, both the silver chloride particles and the cation exchange groups have negative charges. Therefore, the holding power is not strong as compared with the case where silver chloride is supported on the anion exchange group, but it can be used appropriately depending on conditions such as the use environment. In the case of a cation exchange group, it is preferable to use the cation exchange group while adsorbing silver ions when the concentration of the coexisting salts is low even in the gas phase or the liquid phase. It can be determined appropriately according to the usage environment.

  In the case of iminodiacetic acid group, it is a cation-exchangeable chelate group, so the retention of silver halide grains is not as great as when silver chloride is supported on the anion exchange group. It can be used by setting the sheath carrying amount appropriately. An anionic chelating group such as ethylenediamine can be suitably used because of its electrostatic adsorption force.

  Various methods can be proposed for contacting the radioactive iodine-removing fiber with the radioactive iodine-containing liquid depending on the use environment, the state of contamination, and the like.

  When using cut fibers obtained by cutting this radioactive iodine removal fiber, the cut fiber and radioactive iodine-containing water are mixed or stirred, and water can pass through the radioactive iodine removal fiber that has adsorbed radioactive iodine after the lapse of a predetermined time, but radioactive The usage method which filters with the solid-liquid separator which does not pass an iodine removal fiber is possible. A solid-liquid separator such as a wire mesh or net is sufficient. This method uses the good fluidity of the cut fiber, does not require any adsorption device, and can be brought into contact with the contaminated water without any trouble by the pump flow. After contacting for a predetermined time, it can be separated by sieving. If a polymeric woven or non-woven fabric is used as a sieve, the post-adsorption operation is facilitated by sealing the adsorbent-collected fabric in a bag shape. It is also possible to dry after hanging in the air and draining the liquid.

  As shown in FIG. 3, the radioactive iodine-removed fiber processed into a mole shape (braided shape) can be used for the treatment of stagnant water such as when decontaminating rivers, lakes, harbors and tanks containing radioactive iodine. A molding is a kind of braid having a structure in which fibers and twisted threads are projected radially (looped) on the outside of a rope. When full-scale introduction of a processing apparatus is difficult, it is also possible to apply a method of suspending or mooring these fiber materials for a predetermined period and recovering the radioactive iodine removing material fiber that has adsorbed the radioactive iodine after the predetermined period has elapsed. Since the fibers are long, the radioactive iodine-removed fibers can be recovered simply by pulling one end. The recovered fibers are easy to dispose of as radioactive waste, such as volume reduction and incineration.

  A cotton or cut fiber stored in a net-shaped bag or a long sheet or one having a long thread fixed to the flow path can be used in the same manner as the molding adsorbent. .

  Conventional radioactive iodine adsorbents are packed in a column and used in a distribution system using a pump or the like, but such a method of use is also possible. The cut fiber can be packed in a column as it is and used. In addition, if the column is filled with a bag containing cut fibers in a net, handling after use is easy. Since the fiber has a filling rate of at most 40%, there are many voids and low pressure loss. Therefore, high-speed processing is possible using a large adsorption speed.

  A twisted yarn that is an aggregate of fibers is wound around a core of a perforated pipe and molded into a wind filter shape as shown in FIG. A pleated filter obtained by pleating a nonwoven fabric can also be used. A roll filter obtained by winding a non-woven fabric or a woven fabric as it is can also be used. These filters can be used by being housed in a housing as a cartridge filter, and in addition to radioactive iodine ions, those adhering to the particles can be removed at the same time.

  Hereinafter, although the radioactive iodine removal material by this invention and its evaluation result are shown in the following Example, the range of this invention is not necessarily limited.

(1) Production of Radioactive Iodine Removal Fiber 1 Using a twisted yarn made of nylon fiber having a diameter of about 40 μm, gamma rays were irradiated at 20 kGy. The irradiated fibers were immersed in a 10% methanol solution of glycidyl methacrylate (GMA), and graft polymerization was performed at 40 ° C. for 6 hours. The fiber after the reaction was taken out, washed with methanol three times, and the weight after drying was measured. From the weight increase rate, the graft rate was 106%. A 20% aqueous solution of triethylenediamine (TEDA) was neutralized with hydrochloric acid, and isopropyl alcohol was added to 40%. GMA graft fiber was immersed in this solution and reacted at 70 ° C. for 5 hours to introduce triethylenediamine. When the neutral salt decomposition capacity of this fiber was measured, a strongly basic anion exchange fiber of 1.53 meq / g could be produced. The TEDA-introduced fiber was treated with 0.1M hydrochloric acid. After washing with water, it was immersed in a 0.5M aqueous silver nitrate solution for 1 hour to carry silver chloride in the fiber. Further, it was washed with 1M sodium chloride aqueous solution. Thereafter, it was washed 5 times with pure water. By this washing, the cloudiness disappeared completely. In this way, a radioactive iodine removing fiber 1 having a quaternary ammonium group bonded to the graft side chain and a tertiary amine not bonded to the graft side chain could be produced.

(2) Production of radioactive iodine-removed fiber 2 The same base fiber as in (1) was irradiated with the same gamma ray, and then, by weight, vinylbenzyltrimethylammonium chloride (VBTAC) 20%, n-vinyl 2pyrrolidone 10% and It was immersed in a 70% water monomer solution and graft polymerization was carried out at 40 ° C. for 6 hours. The graft rate was 41%. The neutral salt decomposition capacity of this fiber was 0.4 meq / g. The fiber was immersed in an aqueous 0.5 M silver nitrate solution for 1 hour to carry silver chloride in the fiber. Further, it was washed with 1M sodium chloride aqueous solution. Thereafter, it was washed 5 times with pure water. By this washing, the cloudiness disappeared completely. A radioactive iodine removing fiber 2 in which silver chloride was supported on a strongly basic anion exchange fiber could be produced.

(3) Production of radioactive iodine removing fiber 3 The GMA-grafted fiber of (1) is immersed in a solution of sodium sulfite 10%, isopropyl alcohol 15% and water 75% by weight, immersed in a constant temperature bath at 80 ° C., 10 Reacted for hours. This fiber was a strongly acidic cation exchange fiber having a neutral salt decomposition capacity of 2.1 meq / g. This fiber was brought into contact with a 0.5 M aqueous silver nitrate solution for 1 hour to adsorb silver ions. Thus, the radioactive iodine removal fiber 3 by which silver ion was carry | supported by the strongly acidic cation exchange fiber was able to be manufactured.

(4) Production of radioactive iodine removing fiber 4 A 1M sodium chloride aqueous solution was brought into contact with the radioactive iodine removing fiber 3 described in (3) for 40 minutes to carry silver chloride. At this time, since white turbidity occurred, washing was performed with an aqueous sodium chloride solution until the white turbidity disappeared. Thus, the radioactive iodine removal fiber 4 by which silver chloride was carry | supported by the strong acidic cation exchange fiber was able to be manufactured.

(5) Iodine ion adsorption test A 0.5 M sodium chloride aqueous solution having a salt concentration almost the same as the salt concentration of seawater was prepared. Next, potassium iodide was added to an iodine ion concentration of 10 mg / l to obtain a stock solution for evaluating iodine removal performance. Next, 1 g of 10 mm cut fibers of radioactive iodine removing fibers 1 to 4 was added to 100 ml of this stock solution, and the mixture was stirred for 1 hour and filtered through a 0.45 μm Millipore filter. It was as Table 1 when the iodine ion concentration of the filtrate was measured by ICP-AES.

  Currently, contaminated water is being treated at the multi-nuclide removal facility at the Fukushima Daiichi Nuclear Power Station. With this facility, it is possible to remove radioactive cesium and radioactive strontium sufficiently, but although radioactive iodine is below the reported concentration, it is not clear enough. Therefore, it is possible to apply a method of filling the radioactive iodine removing fiber of the present invention into an adsorption tower of an existing apparatus or a high-performance multi-nuclide removing facility for performing a more advanced treatment.

1 Loop 2 Core 3 Core 4 Radioactive iodine adsorption fiber

Claims (8)

  A radioactive iodine removing material in which silver or a silver compound is added to an organic polymer having a functional group selected from an ion exchange group, a chelate group, or a hydrophilic group in a graft side chain   The functional group is irradiated with radiation and has a functional group selected from an ion exchange group, a chelate group, or a hydrophilic group on the organic polymer base material, or is selected from an ion exchange group, a chelate group, or a hydrophilic group. The radioactive iodine removing material according to claim 1 introduced by graft polymerization of a monomer that can be converted into a functional group.   The functional group is a sulfonic acid group, a carboxyl group, a phosphoric acid group, a quaternary ammonium group, an amino acid group, an aminophosphoric acid group, an iminodiacetic acid group, an amino functional group containing a primary or tertiary amino group, or an amidoxime group. The radioactive iodine removing material according to claim 1 or 2, wherein the material is selected from hydroxamic acid groups, amide groups, and hydroxyl groups.   The organic polymer base material is a fiber, a cut fiber, a twisted yarn that is an aggregate of fibers, a woven fabric, a nonwoven fabric, a porous hollow fiber, a porous flat membrane, a sponge-like void material, or a processed product thereof. The radioactive iodine removing material according to 2 or 3   The processed product is selected from a bag shape, a wind filter, a pleated filter, a roll filter, a braid shape, and a mold shape that are stored in a bag that allows water to pass through the organic polymer base material but not the base material. The radioactive iodine removing material according to claim 1, 2, 3, or 4   After irradiating the organic polymer substrate with radiation, it has a functional group selected from an ion exchange group, a chelate group, or a hydrophilic group, or a functional group selected from an ion exchange group, a chelate group, or a hydrophilic group. By graft polymerization of a convertible monomer, a graft side chain is introduced into an organic polymer base material, and then at least a water-soluble silver salt is brought into contact with the surface, and / or silver gives a silver compound to the inside of the base material. A method for producing a radioactive iodine removing material according to claim 1, 2, 3, 4, 5 or 6   A liquid containing at least chloride ions is contacted after contacting the water-soluble silver salt, and silver chloride is precipitated on the surface and / or inside of the organic polymer substrate. Method for producing radioactive iodine removing material according to 5, 6 or 7   The monomer is a sulfonic acid group, a carboxyl group, a phosphoric acid group, a quaternary ammonium group, an amino acid group, an aminophosphoric acid group, an iminodiacetic acid group, an amino functional group containing one or more primary to tertiary amino groups, an amidoxime group, 6. The method for producing a radioactive iodine removing material according to claim 5, wherein the material has a hydroxamic acid group, an amide group or a hydroxyl group or is selected from those capable of being converted.