JP2015200585A - Treating method of radioactive waste liquid - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of stably treating a radioactive waste liquid containing a radioactive electrolyte by electrodialysis for a long term.SOLUTION: The method includes at least a treatment process of treating a radioactive waste liquid 1 containing a radioactive electrolyte using an electrodialysis device 4 in which cation exchange films and anion exchange films are alternately arranged between a negative electrode and a positive electrode, and obtaining a concentrated solution 5 including a concentrated radionuclide. As each cation exchange film, a cation exchange film having a micro phase separation structure is used. The micro phase separation structure includes a polyvinyl alcohol copolymer having an anionic polymer segment having an anionic group and a vinyl alcohol polymer segment, and the domain size (X) is in a range of 0 nm<X≤150 nm.

Description

  The present invention relates to a treatment method for treating radioactive liquid waste by electrodialysis using a novel ion exchange membrane.

So far, a method for separating and removing radionuclides from a radioactive liquid waste using an ion exchange membrane is known (Patent Document 1).
For example, in Patent Document 1, as a radioactive waste treatment method, a used waste salt recycle is dissolved in water to form an aqueous solution, and then the aqueous solution is recovered as an alkali metal treatment solution by electrodialysis. The processing method is known.

  Generally, in water, there are organic substances, particularly macromolecules (hereinafter also referred to as giant organic ions) that become charged by ionization or intramolecular polarization. Therefore, when desalting from an aqueous solution of a salt containing giant organic ions by ion exchange membrane electrodialysis, so-called membranes in which the giant organic ions in the liquid to be treated adhere to the ion exchange membrane and lower the performance of the membrane. The problem of organic pollution occurs. When organic contamination occurs, the electrical resistance of the membrane is increased, the current efficiency is lowered, the solution pH is changed, and the electrodialysis performance is lowered.

In recent years, a technology for treating radioactive waste liquid derived from seawater has been demanded by using a large amount of seawater as cooling water for a nuclear reactor. Seawater contains a larger amount of giant organic ions than purified water.
Therefore, when performing the treatment for removing the radionuclide present in the radioactive liquid waste derived from seawater, there is a possibility that the problem that the membrane performance deteriorates due to membrane contamination caused by giant organic ions in the seawater may become more prominent. .

  Conventionally, ion exchange membranes that easily transmit giant organic ions or the like as ion exchange membranes that suppress organic contamination, or ion exchange membranes that prevent penetration of giant organic ions into the membrane at the membrane surface layer have been proposed. Yes. As a method for facilitating membrane permeation of giant organic ions or the like, a method of loosening the membrane structure is known (Non-Patent Document 1). However, when the membrane structure is loosened, ion selectivity is inevitably lowered, and as a result, efficient desalting cannot be performed.

  On the other hand, ion exchange membranes that prevent the invasion of giant organic ions into the membrane include those in which a thin layer of neutral, amphoteric or opposite ion exchange groups is formed on the membrane surface, and the membrane structure is dense. The effect is more remarkable as the molecular weight of the larger organic ions and the larger the molecular weight. For example, an anion exchange membrane (Patent Document 2) and the like in which an oppositely charged sulfonic acid group is introduced into the surface layer portion of a resin membrane having an anion exchange group to suppress the penetration of organic anions into the membrane has been reported. . There has also been reported an ion exchange membrane in which organic contamination is suppressed by introducing hydrophilic polyether into the membrane surface or inside to make the membrane surface hydrophilic (Patent Document 3).

JP 2003-294888 A Japanese Patent Publication No.51-40556 Japanese Patent Laid-Open No. 2003-082130

Desalination, 13, 105 (1973)

  However, although the ion exchange membrane disclosed in Patent Document 2 or 3 has a certain degree of organic contamination resistance, the resistance of the ion exchange membrane by the oppositely charged layer provided on the surface layer of the resin membrane ( (Hereinafter referred to as “membrane resistance”) has a drawback of significantly increasing. In addition, a film having a hydrophilic group introduced into the surface or inside has a problem that the hydrophilic group portion modified in the vicinity of the surface is lost due to long-term use or brushing washing of the film, resulting in a decrease in organic contamination.

  Therefore, an object of the present invention is to obtain an ion exchange membrane excellent in organic contamination resistance and to perform electrodialysis using this ion exchange membrane when processing radioactive waste liquid by electrodialysis, that is, An object of the present invention is to provide a method for treating a radioactive liquid waste that can concentrate radionuclides in the radioactive liquid waste in a concentration chamber by performing electrodialysis using an ion exchange membrane having excellent organic contamination resistance.

  As a result of intensive studies to solve the above-mentioned problems, the inventors of the present invention have developed a micro-layer in a cation exchange membrane including an anionic polymer segment having an anionic group and a vinyl alcohol copolymer having a vinyl alcohol polymer segment. Phase separation is affected by the salt content mixed as an impurity in the vinyl alcohol copolymer, and by forming a film with a reduced salt content, the domain size is reduced and microphase separation is suppressed. , Thereby providing excellent electrical characteristics such as charge density and membrane resistance. Furthermore, by making it more hydrophilic than conventional ion exchange membranes such as styrenedivinylbenzene, it provides organic contamination resistance with almost no increase in membrane resistance. As a result, the present invention has been completed.

That is, the present invention is a method for treating a radioactive liquid waste containing at least a radioactive electrolyte,
The radioactive liquid waste is treated with an electrodialysis apparatus in which a cation exchange membrane and an anion exchange membrane are alternately arranged between a cathode and an anode to obtain a concentrated solution in which the radionuclide contained in the radioelectrolyte is concentrated. At least a processing step,
The cation exchange membrane contains an anionic polymer segment having an anionic group and a polyvinyl alcohol copolymer having a vinyl alcohol polymer segment, and the domain size (X) is in the range of 0 nm <X ≦ 150 nm. A method for treating radioactive liquid waste, comprising using a cation exchange membrane having a certain microphase separation structure.
In the present invention, microphase separation means that in a copolymer containing two or more types of chain polymers, the same kind of polymer segments aggregate together and a repulsive interaction acts between different polymer segments. A periodic structure obtained by forming a periodic self-organized structure from nanoscale to submicron scale. In the present invention, the domain means a mass formed by aggregating polymer segments of the same kind in one or a plurality of polymer chains.

  The vinyl alcohol polymer segment is a segment formed from a vinyl alcohol polymer not containing an anionic group, and electrodialysis is performed using a cation exchange membrane containing a vinyl alcohol copolymer having the segment. It is preferable.

  It is preferable that a cross-linked structure is introduced into the vinyl alcohol copolymer.

  The crosslinked structure is preferably introduced by reacting a vinyl alcohol copolymer with a dialdehyde compound.

  The vinyl alcohol copolymer is preferably an anionic block copolymer having a vinyl alcohol polymer block and an anionic polymer block having an anionic group.

  The vinyl alcohol copolymer is preferably an anionic graft copolymer having a vinyl alcohol polymer block and an anionic polymer block having an anionic group.

  The radioactive waste liquid may be a radioactive waste liquid containing a seawater component.

  Further, the radioactive waste liquid may further contain a non-radioactive electrolyte, and the cations of the non-radioelectrolyte may be concentrated together with the radionuclide in the treatment step of obtaining the concentrated liquid. The non-radioactive electrolyte may be an inorganic acid or an inorganic salt. Further, the inorganic salt is preferably sodium chloride or potassium chloride.

  The radioactive electrolyte is selected from the group consisting of Co, Mn, Fe, Sr, Y, I, Cs, Pu, Ce, Ru, Am, Cm, Te, U, Mo, Sb, Nd, Ce, and Np. A radionuclide derived from at least one species may be included.

  According to the method for treating a radioactive liquid waste according to the present invention, the cation exchange membrane used in the electrodialysis treatment is composed of a vinyl alcohol copolymer having an anionic polymer segment and a vinyl alcohol polymer segment. Since the ion exchange membrane is formed by reducing the content of salts contained as impurities in the vinyl alcohol copolymer, the microphase separation of the anionic polymer segment and the vinyl alcohol polymer segment Is suppressed, and a film having a domain size larger than 0 nm and 150 nm or less is formed.

  For this reason, as the cation exchange membrane, since the vinyl alcohol polymer segment has high hydrophilicity, the membrane resistance is low, and the microphase separation is suppressed as described above, so that the ion path structure is densely formed and durable. The electrodialysis can be performed stably and efficiently over a long period of time. By performing electrodialysis treatment on radioactive waste liquid using such a cation exchange membrane, the cation exchange membrane can be stably subjected to electrodialysis over a long period of time while maintaining low electrical resistance without being contaminated with organic matter. It is possible to efficiently separate and concentrate the radioactive liquid waste.

It is a transmission electron microscope (TEM) photograph of the ion exchange membrane (CEM-5) used in Example 5, which is an example of a cation exchange membrane used in the method of the present invention. It is a TEM photograph of the ion exchange membrane (CEM-7) used in Example 7, which is an example of a cation exchange membrane used in the method of the present invention. 4 is a TEM photograph of an ion exchange membrane (CEM-8) used in Comparative Example 1. 4 is a TEM photograph of an ion exchange membrane (CEM-9) used in Comparative Example 2. 10 is a TEM photograph of an ion exchange membrane (CEM-10) used in Comparative Example 3. It is explanatory drawing of the apparatus used for the measurement of the membrane resistance of the cation exchange membrane of this invention. It is explanatory drawing for demonstrating the electrodialysis method in one Embodiment of this invention.

The present invention is a method for treating a radioactive liquid waste containing at least a radioactive electrolyte,
The radioactive liquid waste is treated with an electrodialysis apparatus in which a cation exchange membrane and an anion exchange membrane are alternately arranged between a cathode and an anode to obtain a concentrated solution in which the radionuclide contained in the radioelectrolyte is concentrated. At least a processing step.
The feature of the present invention is that, in concentrating the radionuclide by electrodialysis, it contains a polyvinyl alcohol copolymer having an anionic polymer segment having an anionic group and a vinyl alcohol polymer segment as a cation exchange membrane, and a domain The point is that a cation exchange membrane having a microphase separation structure having a size (X) in the range of 0 nm <X ≦ 150 nm is used. Therefore, the cation exchange membrane used in the present invention will be described in detail below.

(Cation exchange membrane)
The cation exchange membrane used in the present invention is composed of an anionic polymer segment having an anionic group and a polyvinyl alcohol copolymer having a vinyl alcohol polymer segment. Usually, an anionic polymer segment and a vinyl alcohol polymer segment are bonded by a covalent bond to constitute a polyvinyl alcohol copolymer. In the present invention, the polymer segment means a polymer chain containing the same repeating unit in which two or more of the same monomer units are linked, and is a polymer block in a block copolymer, a trunk chain or a branch in a graft polymer. It is used as a term encompassing polymer blocks corresponding to chains. In the anionic polymer segment having an anionic group, the anionic group may be contained at the end of the polymer, so that the unit having the anionic group may not be a repeated unit.
As described above, the cation exchange membrane used in the present invention is composed of an anionic polymer segment having an anionic group and a polyvinyl alcohol copolymer having a vinyl alcohol polymer segment. In addition, in addition to this copolymer, a polyvinyl alcohol polymer not having an anionic group not bonded to an anionic polymer segment, an anionic polymer not bonded to a vinyl alcohol polymer, It may be included so as not to affect the separation structure.

  The cation exchange membrane used in the present invention is formed by reducing the content of salts contained in the polyvinyl alcohol copolymer, so that the polyvinyl alcohol copolymer constituting the membrane exhibits a microphase separation structure. The inventors have found that the domain size can be made 150 nm or less. The cation exchange membrane of the present invention is usually used practically after the vinyl alcohol polymer segment is crosslinked, but the ion size is determined by specifying the domain size (X) in the range of 0 nm <X ≦ 150 nm. It is possible to obtain a cation exchange membrane useful for electrodialysis having no change in structure, stable membrane structure, and excellent electrical characteristics such as charge density and membrane resistance. The domain size (X) becomes smaller as the salt content is lowered, and can be set to 0 nm <X ≦ 130 nm, and further 0 nm <X ≦ 100 nm.

  Since the cation exchange membrane used in the present invention is composed of the polyvinyl alcohol copolymer having the vinyl alcohol polymer segment as described above, it is a hydrophilic ion exchange membrane. This has the advantage that contamination due to adhesion of organic pollutants in the liquid to be treated can be suppressed. Here, that the constituent polymer is hydrophilic means that the polymer has hydrophilicity in a structure having no functional group (anionic group) necessary for the anionic polymer. As described above, since the constituent polymer is a hydrophilic polymer, a cation exchange membrane having a high degree of hydrophilicity is obtained, and organic contaminants in the liquid to be treated adhere to the cation exchange membrane and the performance of the membrane. The problem of lowering can be reduced. In addition, there is an advantage that the film strength is increased.

(Anionic polymer)
The anionic polymer constituting the anionic polymer segment used in the present invention is a polymer containing an anionic group in the molecular chain. The anionic group may be contained in any of the main chain, side chain, and terminal. Examples of the anionic group include a sulfonate group, a carboxylate group, and a phosphonate group. In addition, functional groups that can be converted into sulfonate groups, carboxylate groups, and phosphonate groups at least partially in water, such as sulfonic acid groups, carboxyl groups, and phosphonic acid groups are also included in the anionic groups. Of these, a sulfonate group is preferred because of its large ion dissociation constant. The anionic polymer may contain only one type of anionic group or may contain a plurality of types of anionic groups. Moreover, the counter cation of an anionic group is not specifically limited, A hydrogen ion, an alkali metal ion, etc. are illustrated. Of these, alkali metal ions are preferred from the viewpoint of less equipment corrosion problems. The anionic polymer may contain only one type of counter cation or may contain a plurality of types of counter cation.

  The anionic polymer used in the present invention may be a polymer composed only of a structural unit containing the anionic group, or may be a polymer further containing a structural unit not containing the anionic group. Good. Moreover, it is preferable that these polymers have a crosslinking property. An anionic polymer may consist of only one type of polymer, or may include a plurality of types of anionic polymers. Moreover, you may be a mixture of these anionic polymers and another polymer. Here, the polymer other than the anionic polymer is preferably not a cationic polymer.

As an anionic polymer, what has the structural unit of the following general formula (1) and (2) is illustrated.

[Wherein R 5 represents a hydrogen atom or a methyl group. G is -SO 3 H, -SO 3 - representing the M + - M +, -PO 3 H, -PO 3 - M +, -CO 2 H or -CO 2. M + represents an ammonium ion or an alkali metal ion. ]

  Examples of the anionic polymer containing the structural unit represented by the general formula (1) include 2-acrylamido-2-methylpropanesulfonic acid homopolymer or copolymer.

[Wherein R ⁵ represents a hydrogen atom or a methyl group, and T represents a phenylene group or a naphthylene group in which the hydrogen atom may be substituted with a methyl group. G is synonymous with the general formula (1). ]

  Examples of the anionic polymer containing the structural unit represented by the general formula (2) include homopolymers or copolymers of p-styrene sulfonate such as sodium p-styrene sulfonate.

  Examples of the anionic polymer include homopolymers or copolymers of sulfonic acids such as vinyl sulfonic acid and (meth) allyl sulfonic acid or salts thereof, fumaric acid, maleic acid, itaconic acid, maleic anhydride, itaconic anhydride. Examples include dicarboxylic acids such as acids, homopolymers or copolymers of derivatives or salts thereof.

In the general formula (1) or (2), G is preferably a sulfonate group, a sulfonic acid group, a phosphonate group, or a phosphonic acid group that gives a higher charge density. In the general formulas (1) and (2), examples of the alkali metal ion represented by M ⁺ include sodium ion, potassium ion, and lithium ion.

(Vinyl alcohol polymer segment)
In the present invention, as the polyvinyl alcohol constituting the vinyl alcohol polymer segment, those obtained by saponifying a vinyl ester polymer obtained by polymerizing a vinyl ester monomer and using the vinyl ester unit as a vinyl alcohol unit are used. Examples of the vinyl ester monomers include vinyl formate, vinyl acetate, vinyl propionate, vinyl valelate, vinyl laurate, vinyl stearate, vinyl benzoate, vinyl pivalate, vinyl versatate, and the like. Of these, vinyl acetate is preferably used.
When the vinyl ester monomer is copolymerized, a monomer that can be copolymerized, if necessary, within a range that does not impair the effects of the invention (preferably 50 mol% or less, more preferably 30 mol% or less). It may be copolymerized.
Examples of the monomer copolymerizable with the vinyl ester monomer include olefins having 3 to 30 carbon atoms such as ethylene, propylene, 1-butene and isobutene; acrylic acid and salts thereof; methyl acrylate and acrylic acid. Acrylic acid such as ethyl, n-propyl acrylate, i-propyl acrylate, n-butyl acrylate, i-butyl acrylate, t-butyl acrylate, 2-ethylhexyl acrylate, octadecyl acrylate Esters; methacrylic acid and salts thereof; methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, i-propyl methacrylate, n-butyl methacrylate, i-butyl methacrylate, t-butyl methacrylate, methacrylic acid 2 -Ethylhexyl, dodecyl methacrylate, Methacrylic acid esters such as octadecyl tacrylate; acrylamide, N-methylacrylamide, N-ethylacrylamide, N, N-dimethylacrylamide, diacetoneacrylamide, acrylamidepropanesulfonic acid and its salt, acrylamidopropyldimethylamine and its salt, N Acrylamide derivatives such as methylolacrylamide and its derivatives; methacrylamide, N-methylmethacrylamide, N-ethylmethacrylamide, methacrylamidepropanesulfonic acid and its salts, methacrylamidepropyldimethylamine and its salts, N-methylolmethacrylamide and Methacrylamide derivatives such as derivatives thereof; N such as N-vinylformamide, N-vinylacetamide, N-vinylpyrrolidone Vinyl amides; Vinyl ethers such as methyl vinyl ether, ethyl vinyl ether, n-propyl vinyl ether, i-propyl vinyl ether, n-butyl vinyl ether, i-butyl vinyl ether, t-butyl vinyl ether, dodecyl vinyl ether, stearyl vinyl ether; acrylonitrile, methacrylonitrile, etc. Nitriles; vinyl halides such as vinyl chloride, vinylidene chloride, vinyl fluoride and vinylidene fluoride; allyl compounds such as allyl acetate and allyl chloride; maleic acid and its salts or esters; itaconic acid and its salts or its Examples include esters; vinylsilyl compounds such as vinyltrimethoxysilane; and isopropenyl acetate.

  The structural units other than the anionic group in the polyvinyl alcohol-based copolymer can be independently selected, but the copolymer is preferably composed of monomers having the same structural unit. . Thereby, since the affinity between domains becomes high, the mechanical strength of a cation exchange membrane increases. The polyvinyl alcohol copolymer preferably has 50 mol% or more of the same structural unit, more preferably 70 mol% or more.

  Moreover, since it is desirable that it is hydrophilic, it is particularly preferable that the same structural unit is a vinyl alcohol unit. By having a vinyl alcohol unit, the domains can be chemically crosslinked with a crosslinking agent such as glutaraldehyde, so that the mechanical strength of the cation exchange membrane can be further increased.

  As described above, in the present invention, the polyvinyl alcohol copolymer having an anionic polymer segment and a vinyl alcohol polymer segment has a structure in which the anionic polymer segment and the vinyl alcohol polymer segment are bonded. preferable.

  The cation exchange membrane used in the present invention is composed of a polyvinyl alcohol copolymer having a vinyl alcohol polymer segment in the anionic polymer segment as described above, but the polyvinyl alcohol copolymer is anionic. It may be composed of a mixture including a vinyl alcohol polymer containing no group.

(Block or graft copolymer)
In the present invention, the polyvinyl alcohol copolymer preferably has a block copolymer or graft copolymer in which the anionic polymer segment and the vinyl alcohol polymer segment. Among these, a block copolymer is more preferably used. By doing this, the vinyl alcohol polymer block responsible for the function of improving the strength of the entire cation exchange membrane, suppressing the degree of swelling of the membrane, and maintaining the shape, and the amount of anionic group responsible for the permeation of the cation The anionic polymer block obtained by polymerizing the polymer can share the role, and both the ion permeation function and the dimensional stability of the cation exchange membrane can be achieved. The structural unit of the polymer block obtained by polymerizing the anionic group monomer is not particularly limited, and examples thereof include those represented by the general formulas (1) to (2). Among these, from the viewpoint of easy availability, as the monomer constituting the anionic polymer, p-styrene sulfonate or 2-acrylamido-2-methylpropane sulfonate is used. Anionic block copolymer containing an anionic polymer block obtained by polymerizing an acid salt and a vinyl alcohol polymer block, or an anionic polymer obtained by polymerizing 2-acrylamido-2-methylpropanesulfonate A block copolymer comprising a block and a vinyl alcohol polymer block is preferably used.
The graft copolymer includes an anionic polymer segment as a backbone and a vinyl alcohol polymer segment as a branched chain, and a vinyl alcohol polymer segment as a backbone and an anionic polymer segment as a branch. Sometimes it is a chain. Although it is not particularly limited in the present invention, a graft copolymer having vinyl alcohol as a main chain and an anionic polymer segment as a branched chain is preferable from the viewpoint of easily obtaining strength properties. A known method is applied as the graft copolymerization method.

(Method for producing block copolymer)
The method for producing a block copolymer containing an anionic polymer block obtained by polymerizing an anionic monomer used in the present invention and a vinyl alcohol polymer block is mainly classified into the following two methods. . (1) a method in which a desired block copolymer is produced and then an anionic group is bonded to a specific block; and (2) at least one anionic group monomer is polymerized to form a desired block copolymer. It is a method for producing a polymer. Among these, for (1), one or more types of monomers are block copolymerized in the presence of polyvinyl alcohol having a mercapto group at the terminal, and then one or more types of polymer in the block copolymer are copolymerized. For the method of introducing an ionic group into the coalescing component, (2), a block copolymer is produced by radical polymerization of at least one anionic group monomer in the presence of polyvinyl alcohol having a mercapto group at the terminal. However, these methods are preferable because of industrial ease. In particular, the type and amount of constituent monomers in each block of an anionic polymer block obtained by polymerizing a vinyl alcohol block and an anionic group monomer in the block copolymer can be easily controlled. A method of producing a block copolymer by radical polymerization of at least one anionic group monomer in the presence of a group-containing polyvinyl alcohol is preferred. The block copolymer containing a polymer block obtained by polymerizing the anionic group monomer thus obtained and a vinyl alcohol polymer block contains unreacted polyvinyl alcohol having a mercapto group at the terminal. It doesn't matter.

  The vinyl alcohol polymer having a mercapto group at the end used for the production of these block copolymers can be obtained, for example, by the method described in JP-A-59-187003. That is, a method of saponifying a vinyl ester polymer obtained by radical polymerization of a vinyl ester monomer such as vinyl acetate in the presence of thiolic acid can be mentioned. A method for obtaining a block copolymer using a polyvinyl alcohol having a mercapto group at the terminal thus obtained and an anionic group monomer is described in, for example, JP-A-59-189113. Method. That is, a block copolymer can be obtained by radical polymerization of an anionic group monomer in the presence of polyvinyl alcohol having a mercapto group at the terminal. This radical polymerization can be carried out by a known method such as bulk polymerization, solution polymerization, pearl polymerization, emulsion polymerization, etc., but mainly contains a solvent capable of dissolving polyvinyl alcohol containing a mercapto group at the terminal, such as water or dimethyl sulfoxide. It is preferable to carry out in the medium. As the polymerization process, any of a batch method, a semi-batch method, and a continuous method can be employed.

  The radical polymerization is carried out by using a normal radical polymerization initiator such as 2,2′-azobisisobutyronitrile, benzoyl peroxide, lauroyl peroxide, diisopropyl peroxycarbonate, 4,4′-azobis- (4-cyano Pentanoic sodium), 4,4'-azobis- (4-cyanopentanoic ammonium), 4,4'-azobis- (4-cyanopentanoic potassium), 4,4'-azobis- (4- Cyanopentanoic lithium), 2,2′-azobis {2-methyl-N- [1,1′-bis (hydroxymethyl) -2-hydroxyethyl] propionamide}, potassium persulfate, ammonium persulfate, etc. However, in the case of polymerization in an aqueous system, vinyl alcohol can be used. Redox initiation by mercapto group at the terminal of polymer and oxidant such as potassium bromate, potassium persulfate, ammonium persulfate, hydrogen peroxide, 2′-azobis [2-methyl-N (2-hydroxyethyl) propionamide] Etc. are also possible. In particular, those that do not generate ionic residues after decomposition are particularly preferred.

  Alkaline substances are usually used as catalysts for saponification reactions of vinyl ester polymers. Examples thereof include alkali metal hydroxides such as potassium hydroxide and sodium hydroxide, and alkali metal alkoxides such as sodium methoxide. It is done. The saponification catalyst may be added all at once in the early stage of the saponification reaction, or a part thereof may be added in the early stage of the saponification reaction, and the rest may be added and added during the saponification reaction. Examples of the solvent used for the saponification reaction include methanol, methyl acetate, dimethyl sulfoxide, diethyl sulfoxide, dimethylformamide and the like. Of these solvents, methanol is preferred. The saponification reaction can be carried out by either a batch method or a continuous method. After completion of the saponification reaction, the remaining saponification catalyst may be neutralized as necessary, and usable neutralizing agents include organic acids such as acetic acid and lactic acid, and ester compounds such as methyl acetate. .

(Degree of saponification of vinyl alcohol polymer)
Although the saponification degree of a vinyl alcohol polymer is not specifically limited, It is preferable that it is 40-99.9 mol%. If the degree of saponification is less than 40 mol%, the crystallinity is lowered and the strength of the cation exchange membrane may be insufficient. The saponification degree is more preferably 60 mol% or more, and further preferably 80 mol% or more. Usually, the saponification degree is 99.9 mol% or less. At this time, the saponification degree when the polyvinyl alcohol is a mixture of plural kinds of polyvinyl alcohols refers to the average saponification degree of the whole mixture. The saponification degree of polyvinyl alcohol is a value measured according to JIS K6726.

(Polyvinyl alcohol polymerization degree)
The viscosity average degree of polymerization of the polyvinyl alcohol constituting the vinyl alcohol polymer segment (hereinafter sometimes simply referred to as the degree of polymerization) is not particularly limited, but is preferably 50 to 10,000. When the degree of polymerization is less than 50, there is a possibility that the cation exchange membrane cannot maintain sufficient strength in practical use. More preferably, the degree of polymerization is 100 or more. If the degree of polymerization exceeds 10,000, the viscosity of the aqueous polymer solution is too high, making it difficult to apply, and possibly causing defects in the resulting film. The degree of polymerization is more preferably 8000 or less. At this time, the polymerization degree in the case where the polyvinyl alcohol is a mixture of plural kinds of polyvinyl alcohols means an average polymerization degree as the whole mixture. In addition, the viscosity average polymerization degree of polyvinyl alcohol is a value measured according to JIS K6726. The polymerization degree of polyvinyl alcohol containing no ionic group used in the present invention is also preferably within the above range.

(Content of anionic group monomer unit)
The content of the anionic group monomer unit in the vinyl alcohol copolymer constituting the cation exchange membrane is not particularly limited, but the content of the anionic group monomer unit of the copolymer, that is, the above The ratio of the number of anionic group monomer units to the total number of monomer units in the copolymer is preferably 0.1 mol% or more. When the content of the anionic group monomer unit is less than 0.1 mol%, the effective charge density in the cation exchange membrane is lowered, and the electrolyte permselectivity may be lowered. The content of the anionic group monomer unit is more preferably 0.5 mol% or more, and further preferably 1 mol% or more. Moreover, it is preferable that content of an anionic group monomer unit is 50 mol% or less. When the content of the anionic group monomer unit exceeds 50 mol%, the degree of swelling of the cation exchange membrane increases, the effective charge density in the cation exchange membrane decreases, and the electrolyte permselectivity may decrease. There is. The content of the anionic group monomer unit is more preferably 30 mol% or less, and further preferably 20 mol% or less. When the polyvinyl alcohol copolymer is a mixture of a polymer containing an anionic group and a polymer not containing an anionic group, or a mixture of a plurality of polymers containing an anionic group The content of anionic group monomer units refers to the ratio of the number of anionic group monomer units to the total number of monomer units in the mixture.

(Method for producing cation exchange membrane)
The cation exchange membrane production method of the present invention is characterized by a vinyl alcohol polymer segment and a polyvinyl alcohol copolymer (preferably a block copolymer) comprising an anionic polymer segment having an anionic group as constituent components. ) As a main component, and the salt in the copolymer is reduced and the phase separation domain size is reduced by forming a film. The salts referred to herein have an anionic group that constitutes an anionic polymer segment having an anionic group, such as sulfate and acetate which are impurities contained in the polyvinyl alcohol constituting the vinyl alcohol polymer segment. Examples thereof include metal salts such as bromide salts, chloride salts, nitrates, and phosphates contained as impurities in the monomer. These salts are inevitably mixed as impurities in the polyvinyl alcohol copolymer, and the present inventors have mixed these impurities into the anionic heavy polymer in the polyvinyl alcohol copolymer at the time of film formation. It has been found that the microphase separation of the coalesced segment is increased to adversely affect the membrane characteristics. In the present invention, the phase separation domain size of the membrane can be reduced by reducing the content of salts contained in the polyvinyl alcohol copolymer to form a membrane. At this time, the ratio (weight ratio) (C) / (P) of the weight (C) of the salt to the weight (P) of the polyvinyl alcohol-based copolymer needs to be 4.5 / 95.5 or less. In order to reduce the separation domain size, it is 4.0 / 96.0 or less, more preferably, 3.5 / 96.5 or less, and the weight ratio (C) / (P) is 4.5 / 95.5. If it exceeds 1, the microphase separation domain size of the anionic group polymer segment will increase, and when used as a cation exchange membrane, the ion path structure will change, and a durable cation exchange membrane cannot be obtained. .

The content of the salt contained in the polyvinyl alcohol copolymer is not particularly limited in order to reduce it to a predetermined value or less. For example, for impurities contained in the polyvinyl alcohol constituting the vinyl alcohol polymer segment, polymer flakes are used. Can be reduced by washing with water.
In addition, impurities contained in the polymer constituting the anionic polymer segment can be reduced by reprecipitation purification in a poor solvent of a polymer solution obtained by dissolving the polymer in an appropriate solvent, thereby purifying the polymer. Can do.
In the present invention, the salt content only needs to be reduced as described above. Therefore, one or both of polyvinyl alcohol and anionic polymer are purified to reduce the content to the above-described content. Just do it.

(Film formation)
The polyvinyl alcohol copolymer having a salt content adjusted as described above is dissolved in a solvent composed of water, a lower alcohol such as methanol, ethanol, 1-propanol, 2-propanol, or a mixed solvent thereof, A film having a predetermined thickness can be formed by extruding from a die, forming into a film, and removing the solvent by volatilization. The film forming temperature when the film is formed on a plate or a roller is not particularly limited, but a temperature range of about room temperature to about 100 ° C. is usually appropriate. Solvent removal can be performed by heating as appropriate.

(Film thickness)
The cation exchange membrane used in the present invention preferably has a film thickness of about 30 to 1000 μm from the viewpoint of performance, mechanical strength, handling properties, etc. required as an electrolyte membrane for electrodialysis. When the film thickness is less than 30 μm, the mechanical strength of the film tends to be insufficient. On the other hand, when the film thickness exceeds 1000 μm, the membrane resistance increases and sufficient ion exchange properties are not exhibited, so that the electrodialysis efficiency tends to decrease. Preferably it is 40-500 micrometers, More preferably, it is 50-300 micrometers.

(Crosslinking treatment)
The cation exchange membrane used in the present invention is preferably subjected to a crosslinking treatment after film formation. By performing the crosslinking treatment, the mechanical strength of the resulting cation exchange membrane is increased. The method for the crosslinking treatment is not particularly limited, and may be a method of chemically bonding the molecular chains of the polymer or introducing physical bonds by heat treatment or the like.

  When chemically bonding, a method of immersing in a solution containing a crosslinking agent is usually used. Examples of the crosslinking agent include polyvinyl alcohol acetalizing agents such as glutaraldehyde, formaldehyde, and glyoxal. The concentration of the crosslinking agent is usually 0.001 to 10% by volume of the crosslinking agent relative to the solution. The crosslinking reaction can be performed by treating the polyvinyl alcohol copolymer with the above aldehyde in water, alcohol or a mixed solvent thereof under acidic conditions to chemically introduce a crosslinking bond. . After the crosslinking reaction, it is preferable to remove unreacted aldehyde, acid and the like by washing with water.

  Moreover, as a method for the crosslinking treatment, physical crosslinking may be introduced between the molecular chains by performing a heat treatment. By performing the heat treatment, physical crosslinking occurs, and the mechanical strength of the resulting ion exchange membrane is increased. The method of heat treatment is not particularly limited, and a hot air dryer or the like is generally used. Although the temperature of heat processing is not specifically limited, In the case of polyvinyl alcohol, it is preferable that it is 50-250 degreeC. If the temperature of the heat treatment is less than 50 ° C., the mechanical strength of the obtained ion exchange membrane may be insufficient. The temperature is more preferably 80 ° C. or higher, and further preferably 100 ° C. or higher. When the temperature of the heat treatment exceeds 250 ° C., the crystalline polymer may be melted. The temperature is more preferably 230 ° C. or less, and further preferably 200 ° C. or less.

  In the manufacturing method, both heat treatment and chemical crosslinking treatment may be performed, or only one of them may be performed. When both the heat treatment and the crosslinking treatment are performed, the crosslinking treatment may be performed after the heat treatment, the heat treatment may be performed after the crosslinking treatment, or both may be performed simultaneously. It is preferable from the viewpoint of the mechanical strength of the resulting ion exchange membrane to perform a crosslinking treatment after the heat treatment.

(Ion exchange capacity)
In order to express sufficient ion exchange properties for use as a cation exchange membrane for electrodialysis, the ion exchange capacity of the resulting vinyl alcohol copolymer is preferably 0.30 meq / g or more, More preferably, it is 0.50 meq / g or more. The upper limit of the ion exchange capacity of the vinyl alcohol copolymer is preferably 3.0 meq / g or less because if the ion exchange capacity becomes too large, hydrophilicity increases and it becomes difficult to suppress the degree of swelling.

(Charge density)
Further, in order to develop sufficient electrical characteristics to be used as a cation exchange membrane for electrodialysis, the charge density of the obtained cation exchange membrane is preferably 0.6 mol / dm ³ or more. More preferably, it is 0.0 mol / dm ³ or more. As the charge density of the cation exchange membrane, a higher one is preferred, but in view of the membrane resistance, the one having a relatively low membrane resistance and expressing the charge density is preferred.

  The cation exchange membrane of the present invention can be reinforced and used by laminating with a support such as a nonwoven fabric, a woven fabric, or a porous body, if necessary.

(Anion exchange membrane used in electrodialysis treatment)
In the electrodialysis treatment of the present invention, the anion exchange membrane used together with the cation exchange membrane is not particularly limited, and is a membrane made of a polymer having a strongly basic group such as a quaternary ammonium group, a primary grade. A film made of a polymer having a weakly basic functional group such as an amino group, a secondary amino group, or a tertiary amino group can be appropriately selected and used.

(Radioactive liquid waste)
In the present invention, the radioactive liquid waste contains at least a radioelectrolyte to be concentrated. Moreover, the radioactive waste liquid may further contain a non-radioactive electrolyte.
The electrolyte means a substance that ionizes into a cation and an anion when dissolved in a solvent. Examples of the electrolyte include acids (for example, inorganic acids, organic acids having a molecular weight of 1000 or less), bases, and salts. Examples of the salts include inorganic salts, organic salts (salts of organic acids having a molecular weight of 1000 or less), metal complex salts, and the like.

Examples of the metal complex salts include chelating agents represented by EDTA (ethylenediaminetetraacetic acid), organic acids such as citric acid and oxalic acid, inorganic acids, reducing agents, other corrosion inhibitors, and other metal components. It may be a salt complexed by a coordination bond or a hydrogen bond. For example, the metal component (M) is complexed with a chelating agent (Y ⁿ⁻ ) to form a metal complex salt (eg MY ²⁻ ). It may be.

  The electrolyte to be concentrated may be a radioactive substance or both a radioactive substance and a non-radioactive substance. For example, when the radioactive liquid waste further contains a non-radioactive electrolyte, the cations of the non-radioelectrolyte may be concentrated together with the radionuclide in the treatment step of obtaining a concentrated liquid.

  The radioactive electrolyte is not particularly limited as long as it is a radioactive electrolyte.For example, Co, Mn, Fe, Sr, Y, I, Cs, Pu, Ce, Ru, Am, Cm, Te, U, Examples thereof include an electrolyte containing a radionuclide derived from at least one selected from the group consisting of Mo, Sb, Nd, Ce, and Np.

  The non-radioactive electrolyte is not particularly limited as long as it is an electrolyte containing a stable isotope, and is appropriately determined according to the components of the radioactive liquid waste. The non-radioactive electrolyte may be, for example, an organic acid, an organic salt, an inorganic acid, an inorganic salt or the like containing various stable isotope metal elements, preferably an inorganic acid or an inorganic salt (for example, sodium chloride, potassium chloride). Etc.).

  In the present invention, the radioactive liquid waste may contain an organic solvent or an aqueous solvent. The aqueous solvent may be water, a neutral aqueous solution containing water, an acidic aqueous solution such as sulfuric acid, hydrochloric acid, or aqua regia, or an alkaline aqueous solution such as sodium hydroxide.

  Further, the radioactive liquid waste may contain seawater. For example, when seawater is contained in radioactive waste liquid, the waste liquid may be formed by using seawater as cooling water in such waste liquid. In that case, the radioactive liquid waste contains various seawater components (alkali metal salts such as sodium chloride and potassium chloride; alkaline earth metal salts such as magnesium chloride, magnesium sulfate, calcium chloride and calcium sulfate) derived from seawater. It may be. Further, at least one of the seawater components (preferably sodium chloride and potassium chloride) may be concentrated together with the radionuclide by electrodialysis.

Such liquid to be treated, the concentration of radionuclide at least one may be a low-level (radioactive concentration 3.7 × less than ¹⁰ -4 Bq / cm ³ or more 0.37Bq / cm ^3), a mid-level (less than radioactive concentration 0.37Bq / cm ³ or more 37Bq / cm ³⁾ may be, may be a high level (radioactive concentration 3.7 × ¹⁰ 4 Bq / cm ³ or higher).
The concentration may be, for example, 100,000 to 100,000 Bq / cm ³ .

(Electrodialysis)
In the method for treating radioactive liquid waste according to the present invention, the electrodialysis apparatus is configured by arranging the cation exchange membrane and the anion exchange membrane between the anode and the cathode using the cation exchange membrane according to the present invention. Any known electrodialyzer can be used without particular limitation. For example, an anion exchange membrane and a cation exchange membrane are alternately arranged, such as a filter press type or unit cell type having a basic structure in which a desalination chamber and a concentration chamber are formed by the ion exchange membrane and a chamber frame. Such an electrodialyzer can be preferably used.
Note that the number of membranes used in the electrodialysis apparatus or the channel spacing (membrane spacing) between the desalting chamber and the concentrating chamber is appropriately selected depending on the type of organic matter to be treated and the amount of treatment. Since organic substances, particularly giant organic ions, become charged by ionization or intramolecular polarization, when the cation exchange membrane of the present invention is used as a cation exchange membrane, various organic substances, particularly seawater, are used. It is possible to improve the organic contamination resistance against derived giant organic ions (for example, humic substances such as humic acid and fulvic acid, saccharides, etc.).

  The method of the present invention for treating the radioactive waste liquid, which is the liquid to be treated, using such an electrodialyzer, is obtained by alternating the radioactive waste liquid with a cation exchange membrane and an anion exchange membrane between a cathode and an anode. At least a treatment step of obtaining a concentrated solution in which the electrolyte is concentrated.

  The electrodialyzer consists of a desalination chamber partitioned by an anion exchange membrane on the anode side and a cation exchange membrane on the cathode side, and a concentration chamber partitioned by a cation exchange membrane on the anode side and an anion exchange membrane on the cathode side. And.

  When the liquid to be treated is supplied to the desalting chamber while being energized, the cation moves toward the cathode in the desalting chamber and permeates the cation exchange membrane and moves to the concentration chamber. On the other hand, in the concentration chamber, cations cannot permeate the anion exchange membrane and are concentrated in the concentration chamber. Similarly, the anion moves from the desalting chamber to the concentration chamber and is concentrated in the concentration chamber.

By energizing the electrodialyzer in this way, the electrolyte to be concentrated in the radioactive waste liquid supplied into the desalting chamber is dissociated into anions and cations, and the anion exchange membrane and the cation exchange membrane respectively. Since it permeates and is discharged to the concentration chamber side, the electrolyte present in the liquid to be treated can be concentrated in the concentration chamber over time. And from the to-be-processed liquid, the quantity of the electrolyte of concentration object can be reduced, and the desalination liquid in which the quantity of the radionuclide was reduced can be obtained from a desalination chamber. Depending on the concentration of the radionuclide in the solution, the desalting solution may be appropriately treated by known or conventional means used in radioactive waste liquid treatment, or may be further subjected to electrodialysis treatment. In such electrodialysis, the voltage, current density, and treatment time applied to the electrodialyzer may be appropriately determined depending on the types and concentrations of the inorganic electrolyte and organic electrolyte to be removed.
Since the electrolyte to be concentrated contains at least a radioactive substance, the radionuclide can be concentrated in the concentration chamber by electrodialysis, and the amount of radionuclide can be reduced by separating the radionuclide from the liquid to be treated.

  For example, as shown in FIG. 3, the liquid to be treated (model liquid) 1 is once transferred to the liquid tank 2 to be treated, and then supplied to the electrodialyzer 4 by the circulation pump 3 to perform electrodialysis. During electrodialysis, concentration is performed while circulating between the electrodialysis apparatus 4 and the concentrated water tank 5 with the circulation pump 3, and the concentrated liquid finally concentrated is discharged through the concentrated water tank. On the other hand, desalting is performed while circulating between the electrodialysis apparatus 4 and the liquid tank 2 to be treated by the circulation pump 3, and the final desalted liquid is discharged through the liquid tank to be treated.

  The concentrate containing the radionuclide obtained from the concentration chamber (or the concentrated treatment obtained from the concentration treatment) may then be processed by a solidification step. The solidification step is not particularly limited as long as the concentrated treatment liquid can be solidified. For example, in the solidification step, the material may be directly solidified with a solidifying material such as cement, asphalt, or plastic, or may be vitrified. The obtained solidified product may be stored and stored in the site as a highly radioactive solid waste.

  The waste liquid containing radionuclides may be discarded after further concentration treatment by reverse osmosis membrane filter method, evaporation concentration method, etc., and pH adjustment agent, coprecipitation agent and flocculant may be added to the waste liquid for elution. A coprecipitation / aggregation treatment step of solid-liquid separation by changing the radionuclide contained in the liquid into a hardly soluble metal hydroxide may be provided. Further, if necessary, the radioactive liquid waste may be treated by a direct incineration method, a thermal decomposition method, a wet oxidation decomposition method or the like to reduce the volume.

  That is, the method of the present invention can separate and concentrate radioactive substances, and can reduce the cost for membrane cleaning and the like because there is little membrane contamination by organic contaminants. Further, the concentration of the radioactive substance makes it possible to reduce the volume in the radioactive substance solidification process.

  Examples are given below to describe the present invention in more detail, but the present invention should not be limited to these examples. In the examples, “%” and “parts” are based on weight unless otherwise specified.

  The characteristics of the cation exchange membranes shown in Examples and Comparative Examples were measured by the following methods.

1) Membrane moisture content (H)
The dry weight of the ion exchange membrane was measured in advance, and then the wet weight was measured when it was immersed in deionized water and reached a swelling equilibrium. The membrane water content (H) was calculated by the following equation.
H = <(Ww−Dw) /1.0> / <(Ww−Dw) /1.0+ (Dw / 1.3)>
Here, 1.0 and 1.3 indicate the specific gravity of water and polymer, respectively.
-H: membrane water content [-]
Dw: dry weight of membrane [g]
Ww: wet weight of the film [g]

2) Measurement of cation exchange capacity A cation exchange membrane is immersed in a 1 mol / L aqueous HCl solution for 10 hours or more. Thereafter, the hydrogen ion type was replaced with the sodium ion type with 1 mol / L NaNO ₃ aqueous solution, and the liberated hydrogen ions were quantified by acid-base titration (Amol).

Next, the same cation exchange membrane is immersed in a 1 mol / L NaCl aqueous solution for 4 hours or more, washed thoroughly with ion exchange water, dried in a hot air drier at 105 ° C. for 8 hours, and the weight when dried W (G) was measured.
The ion exchange capacity was calculated by the following formula.
Ion exchange capacity = A × 1000 / W [mmol / g-dry membrane]

3) Measurement of the salt in the polyvinyl alcohol copolymer The amount of the salt in the polyvinyl alcohol copolymer was determined by Soxhlet extraction of the film before crosslinking of the polyvinyl alcohol copolymer with a methanol solution for 48 hours. The product was dried and then measured by ion chromatography ICS-5000 (manufactured by DIONEX).

4) Measurement of membrane resistance The membrane resistance was measured by sandwiching a cation exchange membrane in a two-chamber cell having a platinum black electrode plate as shown in Fig. 2, and filling a 0.5 mol / L-NaCl solution on both sides of the membrane. The resistance between the electrodes at 25 ° C. was measured by (frequency 10 cycles / second), and was determined by the difference between the resistance between the electrodes and the resistance between the electrodes when no cation exchange membrane was installed. The membrane used for the above measurement was previously equilibrated in a 0.5 mol / L-NaCl solution.

5) Measurement of domain size A cation exchange membrane immersed in distilled water was cut into a 1 cm square to prepare a measurement sample. This measurement sample was stained with lead acetate (II) and then observed using a TEM (transmission electron microscope) to obtain an image of a particle group in the measurement sample. The obtained image was subjected to image processing using image processing software “WINROOF” manufactured by Mitani Corporation, and the maximum particle size of each particle was determined. The maximum particle size was determined for about 400 particles, and the particle size at which the cumulative frequency of the maximum particle size was 50% was defined as the domain size of the anionic group polymer segment of the cation exchange membrane.

<Production of PVA-1 (Synthesis of polyvinyl alcohol copolymer with mercapto group at molecular end)>
Polyvinyl alcohol (PVA-1) having a mercapto group at the molecular end shown in Table 1 was synthesized by the method described in JP-A-59-187003. Table 1 shows the polymerization degree and saponification degree of PVA-1.

<NaSS-1 (anionic monomer)>
The polystyrene sulfonate sodium monomer (NaSS: manufactured by Tosoh Corporation) shown in Table 2 was used as it was. The salt content was measured by ion chromatography ICS-5000 (manufactured by DIONEX). The impurities in the monomer other than the total salt amount shown in Table 2 were moisture.

<Preparation of NaSS-2>
1000 g of sodium polystyrene sulfonate monomer (NaSS: manufactured by Tosoh Corp.), 950 g of pure water, 40 g of sodium hydroxide, 1 g of sodium nitrate were dissolved at 60 ° C. for 1 hour, cooled to 20 ° C. and recrystallized. Thereafter, the polystyrenesulfonic acid monomer crystals were separated by centrifugal filtration, and the crystals were dried to obtain NaSS-2 (purified polystyrenesulfonic acid monomer) shown in Table 2. The salt content was measured by ion chromatography ICS-5000 (manufactured by DIONEX).

<Synthesis of P-1 (anionic block copolymer)>
A 1 L four-necked separable flask equipped with a reflux condenser and a stirring blade was 660 g of water, 80 g of PVA-1 shown in Table 1 as a vinyl alcohol polymer having a mercapto group at the end, and 46.6 g of NaSS-1. The resulting mixture was heated to 95 ° C. with stirring to dissolve the vinyl alcohol polymer and NaSS-1. The system was purged with nitrogen for 30 minutes while bubbling nitrogen into the aqueous solution. After purging with nitrogen, the mixture was cooled to 90 ° C., and 13 ml of a 5.4% solution of 2,2′-azobis [2-methyl-N (2-hydroxyethyl) propionamide] was sequentially added to the above aqueous solution over 1.5 hours. After the addition and start and advance of block copolymerization, the system temperature is increased to 90.
The polymerization was further continued for 1 hour, and then cooled, and then cooled to obtain a PVA- (b) -p-sodium styrenesulfonate aqueous solution having a solid concentration of 15%. A part of the obtained aqueous solution was dried, dissolved in heavy water, and subjected to 1H-NMR measurement at 400 MHz. As a result, the amount of modification of the sodium parastyrenesulfonate unit was 10 mol%. Table 3 shows the properties of the obtained anionic block copolymer.

<Synthesis of P-2>
The type and amount of the anionic group-containing monomer were changed to those shown in Table 3. Except for this, a PVA- (b) -p-sodium styrenesulfonate aqueous solution having a solid concentration of 15% was obtained in the same manner as P-1. Table 3 shows the properties of the obtained anionic block copolymer.

<Synthesis of P-3>
In a 1 L four-necked separable flask equipped with a reflux condenser and a stirring blade, 616 g of water, 80 g of PVA-1 shown in Table 1 as a vinyl alcohol polymer having a mercapto group at the end, and 46. NaSS-1 were obtained. 6 g was charged and heated to 95 ° C. with stirring to dissolve the vinyl alcohol polymer and NaSS-1, and then cooled to room temperature. 1/2 N sulfuric acid was added to the aqueous solution to adjust the pH to 3.0. The system was heated to 90 ° C., and the system was purged with nitrogen for 30 minutes while bubbling nitrogen into the aqueous solution. After nitrogen substitution, 63 mL of a 2.5% aqueous solution of potassium persulfate was sequentially added to the aqueous solution over 1.5 hours to start and proceed with block copolymerization, and then the system temperature was increased to 90 ° C. for 1 hour. The polymerization was further continued to proceed, followed by cooling to obtain a PVA- (b) -p-sodium styrenesulfonate block copolymer aqueous solution having a solid concentration of 15%. A part of the obtained aqueous solution was dried, dissolved in heavy water, and subjected to 1H-NMR measurement at 400 MHz. As a result, the amount of modification of the sodium p-styrenesulfonate unit was 10 mol%. Table 3 shows the properties of the obtained anionic block copolymer.

<Synthesis of P-4 to 5>
The type and amount of the anionic group-containing monomer were changed to those shown in Table 3. Except for this, a PVA- (b) -p-sodium styrenesulfonate aqueous solution having a solid concentration of 15% was obtained in the same manner as P-3. Table 3 shows the properties of the obtained anionic block copolymer.

<Synthesis of P-6>
A 6 L separable flask equipped with a stirrer, temperature sensor, dropping funnel and reflux condenser was charged with 2450 g of vinyl acetate, 762 g of methanol, and 27 g of sodium 2-acrylamido-2-methylpropanesulfonate (AMPS) under stirring. After the system was purged with nitrogen, the internal temperature was raised to 60 ° C. To this system, 20 g of methanol containing 0.8 g of 2,2′-azobisisobutyronitrile (AIBN) was added to initiate the polymerization reaction. While adding 568 g of methanol solution containing 25% by mass of sodium 2-acrylamido-2-methylpropanesulfonate (AMPS) to the system from the start of polymerization, the polymerization reaction was stopped for 4 hours, and then the polymerization reaction was stopped. The solid content concentration in the system when the polymerization reaction was stopped, that is, the solid content with respect to the entire polymerization reaction slurry was 30% by mass. Subsequently, methanol vapor was introduced into the system to drive out unreacted vinyl acetate monomer, thereby obtaining a methanol solution containing 30% by mass of a vinyl ester copolymer.

  In a methanol solution containing 30% by mass of this vinyl ester copolymer, the molar ratio of sodium hydroxide to vinyl acetate units in the copolymer is 0.02, and the solid content concentration of the vinyl ester copolymer is 30% by mass. Then, a methanol solution containing 10% by mass of methanol and sodium hydroxide was added in this order with stirring, and the saponification reaction was started at 40 ° C.

  Immediately after the saponification reaction has occurred, a gelled product is formed and taken out from the reaction system and pulverized. Then, when 1 hour has passed since the gelated product was formed, methyl acetate was added to the pulverized product. By carrying out neutralization, an aqueous solution of a random copolymer of polyvinyl alcohol-poly (sodium 2-acrylamido-2-methylpropanesulfonate) in a swollen state was obtained. To this swollen anionic polymer, 6 times the amount of methanol (6 times the bath ratio) of methanol was added and washed under reflux for 1 hour, and the polymer was collected by filtration. The polymer was dried at 65 ° C. for 16 hours. When the obtained polymer was dissolved in heavy water and subjected to 1H-NMR measurement at 400 MHz, the content of the anionic monomer in the anionic polymer, that is, the monomer unit in the polymer The ratio of the number of sodium 2-acrylamido-2-methylpropane sulfonate monomer units to the total number of 5 mol% was 5 mol%. Table 4 shows the properties of the obtained anionic random copolymer.

<Production of CEM-1>
The resin of P-3 was diluted to a concentration of 10 wt%, and the resin from which salts were removed by reprecipitation with 1 volume of methanol of the resin solution was taken out. At this time, the salt content (C) was 4.5 wt%. Next, a necessary amount of distilled water was added to prepare an aqueous solution having a concentration of 15 wt%. This aqueous solution was poured into a cast board made of acrylic having a length of 270 mm and a width of 210 mm to remove excess liquid and bubbles, and then dried on a hot plate at 50 ° C. for 24 hours to prepare a film.

  The film thus obtained was heat treated at 160 ° C. for 30 minutes to cause physical crosslinking. Subsequently, the film was immersed in an aqueous electrolyte solution of 2 mol / L sodium sulfate for 24 hours. Concentrated sulfuric acid was added to the aqueous solution so that the pH was 1, and then the film was immersed in a 1.0% by volume glutaraldehyde aqueous solution and stirred with a stirrer at 25 ° C. for 24 hours to carry out a crosslinking treatment. Here, as the glutaraldehyde aqueous solution, a product obtained by diluting “glutaraldehyde” (25% by volume) manufactured by Ishizu Pharmaceutical Co., Ltd. with water was used. After the crosslinking treatment, the film was immersed in deionized water, and the film was immersed until the film reached a swelling equilibrium while exchanging the deionized water several times in the middle to obtain a cation exchange membrane.

(Evaluation of ion exchange membrane)
The cation exchange membrane thus prepared was cut into a desired size to prepare a measurement sample. Using the obtained measurement sample, the membrane water content, charge density, cation exchange capacity, membrane resistance were measured and the phase separation domain size was evaluated according to the above methods. The results obtained are shown in Table 5. Moreover, according to said method, the measurement of evaluation of sucrose leak rate, ethanol leak rate, desalination rate, and organic-contamination resistance was performed. The results obtained are shown in Table 6.

<Production of CEM-2>
The resin of P-3 was diluted to a concentration of 10 wt%, and the resin from which salts were removed by reprecipitation with twice the volume of methanol as the resin solution was taken out. Next, a necessary amount of distilled water was added to prepare an aqueous solution having a concentration of 15 wt%. This aqueous solution was poured onto an acrylic cast plate having a length of 270 mm and a width of 210 mm to remove excess liquid and bubbles, and then dried on a hot plate at 50 ° C. for 24 hours to prepare a film. At this time, the salt content (C) was 4.0 wt%. Except for this, the membrane characteristics of the cation exchange membrane were measured in the same manner as CEM-1. The obtained measurement results are shown in Table 5.

<Preparation of CEM-3>
An aqueous solution of P-2 was poured onto an acrylic cast plate having a length of 270 mm and a width of 210 mm to remove excess liquid and bubbles, and then dried on a hot plate at 50 ° C. for 24 hours to prepare a film. At this time, the salt content (C) was 2.8 wt%. Except for this, the membrane characteristics of the cation exchange membrane were measured in the same manner as CEM-1. The obtained measurement results are shown in Table 5.

<CEM-4 production>
In CEM-3, the membrane characteristics of the cation exchange membrane were measured in the same manner as in CEM-3 except that the heat treatment temperature was changed as shown in Table 5. The obtained measurement results are shown in Table 5.

<CEM-5 production>
The resin of P-3 was diluted to a concentration of 10 wt%, and the resin from which salts were removed by reprecipitation with 5 times the volume of methanol of the resin solution was taken out. Next, a necessary amount of distilled water was added to prepare an aqueous solution having a concentration of 15 wt%. This aqueous solution was poured onto an acrylic cast plate having a length of 270 mm and a width of 210 mm to remove excess liquid and bubbles, and then dried on a hot plate at 50 ° C. for 24 hours to prepare a film. At this time, the salt content (C) was 2.0 wt%. Except for this, the membrane characteristics of the cation exchange membrane were measured in the same manner as CEM-1. The obtained measurement results are shown in Table 5.

<CEM-6 production>
The P-3 resin was diluted to a concentration of 10 wt%, and the resin from which salts were removed by reprecipitation with 10 times the volume of methanol of the resin solution was taken out. Next, a necessary amount of distilled water was added to prepare an aqueous solution having a concentration of 15 wt%. This aqueous solution was poured into a cast board made of acrylic having a length of 270 mm and a width of 210 mm to remove excess liquid and bubbles, and then dried on a hot plate at 50 ° C. for 24 hours to prepare a film. At this time, the salt content (C) was 1.5 wt%. Except for this, the membrane characteristics of the cation exchange membrane were measured in the same manner as CEM-1. The obtained measurement results are shown in Table 5.

<Production of CEM-7 to 11>
The membrane characteristics of the cation exchange membrane were measured in the same manner as CEM-1 except that the cation exchange resin was changed to the contents shown in Table 5. The obtained measurement results are shown in Table 5.

1 (a), 1 (b), 1 (c), 1 (d) and 1 (e) are TEM photographs of cation exchange membranes using block copolymers having different salt contents. (See Table 5 for salt content). From the TEM photographs of FIGS. 1 (a) to 1 (e), the phase separation structure varies depending on the salt content, and the domain size decreases with decreasing salt-containing weight (C) / block copolymer weight (P). I understand that In particular, in FIG. 1 (b) [ CEM-7] in which the weight (C) of the contained salt is the smallest at a modification amount of 10 mol%, the compatibility of the film is improved and the domain size is as very small as 4 nm. . On the other hand, in FIG. 1 (C) [CEM-8] having the largest salt content (C), phase separation was severe and voids were generated.

  From the results in Table 5, the cation exchange membrane using the block copolymer (P) having a salt content weight (C) of 4.0% or less is a membrane having a domain size of 150 nm or less and a low membrane resistance. It can be seen that it is excellent as a cation exchange membrane (CEM-1 to 7). Furthermore, it can be seen that a film having a salt-containing weight (C) of 3.5% or less has a domain size of 130 nm or less and a low film resistance (CEM-2 to 7). On the other hand, a cation exchange membrane using a block copolymer having a salt content of more than 4.0% has a domain size larger than 150 nm, a high membrane resistance, and exhibits characteristics as a cation exchange membrane. None (CEM-8-10). In particular, when the salt content (C) is large, the phase separation of the polymer segment of the membrane is severe, and voids are generated in the entire ion exchange membrane, and satisfactory characteristics as an ion exchange membrane are not expressed (CEM-8). . In CEM-9, purified NaSS-2 is used, but since KPS is used as the polymerization initiator, the salt content in the obtained cation exchange resin is high.

<Example 1>
As a model seawater solution containing radioactive liquid waste, an electrodialysis shown in FIG. 3 using an aqueous solution containing 0.5 mol / L sodium chloride, 300 ppm humic acid, and CsCl (1000 ppm as the Cs concentration in the aqueous solution). Salt concentration was carried out by a production method using an apparatus. The liquid to be treated (model liquid) 1 was once transferred to the liquid tank 2 to be treated, and then supplied to the electrodialyzer 4 by the circulation pump 3 to perform electrodialysis. During electrodialysis, concentration is performed while circulating between the electrodialyzer 4 and the concentrated water tank 5 with the circulation pump 3, and circulation between the electrodialyzer 4 and the liquid tank 2 to be treated is performed with the circulation pump 3. Desalting was performed. The electrodialysis apparatus 4 is a small electrodialysis apparatus CH-0 type (manufactured by AGC Engineering Co., Ltd.) using CEM-1 as a cation exchange membrane and Selemion AMV (manufactured by AGC Engineering Co., Ltd.) as an anion exchange membrane. Then, the stack was assembled alternately between the cathode and anode electrodes, and a concentration test was conducted at 25 ° C. at a current density of 1 A / dm ^{2 for} 7 hours. Table 6 shows the results of measuring the salt concentration of the concentrated solution after 7 hours and the degree of organic contamination (voltage increase rate after 7 hours of operation from the voltage at the start).

<Examples 2 to 7>
A desalting test of the radioactive liquid waste was performed in the same manner as in Example 1 except that the cation exchange membrane used was changed to the contents shown in Table 6. The results obtained are shown in Table 6.

<Comparative Examples 1-4>
A desalting test of the radioactive liquid waste was performed in the same manner as in Example 1 except that the cation exchange membrane used was changed to the contents shown in Table 6. The results obtained are shown in Table 6.

<Comparative Example 5>
Measurement was performed under the same conditions as in Example 1 using a commercial product CMV (manufactured by AGC Engineering Co., Ltd.) as the cation exchange membrane. The results are shown in Table 6.

  As is apparent from the results of Table 6, in the production method according to the present invention, the concentration of NaCl and CsCl in the concentrated solution is obtained by electrodialysis using a cation exchange membrane having a microphase separation structure with a domain size of 150 nm or less. It is found that the film resistance is high and the increase in film resistance is low (contamination of the film is small) (Examples 1-7). In particular, it has been shown that the NaCl and Cs concentrations of the concentrated solution become higher when the domain size is 100 nm or less (Examples 3 to 7).

  On the other hand, a cation exchange membrane (Comparative Examples 1 and 2) with severe phase separation, a cation exchange membrane having a microphase separation structure with a domain size of 180 nm (Comparative Example 3), and a cation exchange membrane with no confirmed phase separation structure ( When Comparative Example 4) is used, it can be seen that the salt concentration of the concentrate is lower than that of Examples 1-7. It can also be seen that electrodialysis using a commercially available cation exchange membrane has a remarkably high rate of increase in electricity and is easily contaminated with the membrane (Comparative Example 5). From the above, when electrodialysis is carried out using a cation exchange membrane made of a vinyl alcohol copolymer and suppressing the phase separation of the polymer segment within the range of 0 nm <X ≦ 150 nm, It turns out that it is excellent in the concentration property and is excellent in stain resistance.

A cation exchange membrane comprising a vinyl alcohol copolymer having an anionic polymer segment and a vinyl alcohol polymer segment according to the present invention is excellent in membrane resistance and stain resistance. Therefore, radionuclides can be concentrated conveniently by electrodialyzing radioactive wastewater (especially radioactive wastewater containing seawater components) with this ion exchange membrane, and the concentrated radionuclides are efficiently removed. There is industrial applicability.

Although the preferred embodiments of the present invention have been described above by way of example, those skilled in the art can make various modifications, additions and substitutions without departing from the scope and spirit of the present invention disclosed in the claims. It will be understandable.

A Ion exchange membrane B Platinum electrode C NaCl aqueous solution D Water bath E LCR meter 1 Liquid to be treated 2 Liquid tank to be treated 3 Circulating pump 4 Electrodialyzer 5 Concentrated water tank

Claims (13)

A method for treating a radioactive liquid waste containing at least a radioactive electrolyte,
The radioactive liquid waste is treated with an electrodialysis apparatus in which a cation exchange membrane and an anion exchange membrane are alternately arranged between a cathode and an anode to obtain a concentrated solution in which the radionuclide contained in the radioelectrolyte is concentrated. At least a processing step,
The cation exchange membrane contains an anionic polymer segment having an anionic group and a polyvinyl alcohol copolymer having a vinyl alcohol polymer segment, and the domain size (X) is in the range of 0 nm <X ≦ 150 nm. A method for treating radioactive liquid waste, comprising using a cation exchange membrane having a certain microphase separation structure.   The vinyl alcohol polymer segment is a segment formed from a vinyl alcohol polymer not containing an anionic group, and is performed using a cation exchange membrane containing a vinyl alcohol copolymer having the segment. The method for treating radioactive liquid waste according to claim 1.   The method for treating a radioactive liquid waste according to claim 1 or 2, wherein a crosslinked structure is introduced into the vinyl alcohol copolymer.   The method for treating a radioactive liquid waste according to claim 3, wherein the crosslinked structure is introduced by reacting a vinyl alcohol copolymer with a dialdehyde compound.   The said vinyl alcohol-type copolymer is an anionic block copolymer which has a vinyl alcohol polymer block and an anionic polymer block which has an anionic group, The any one of Claims 1-4 characterized by the above-mentioned. A method for treating radioactive liquid waste according to 1.   The said vinyl alcohol-type copolymer is an anionic graft copolymer which has a vinyl alcohol polymer block and an anionic polymer block which has an anionic group, The any one of Claims 1-4 characterized by the above-mentioned. A method for treating radioactive liquid waste according to 1.   The method for treating a radioactive liquid waste according to any one of claims 1 to 6, wherein an ion exchange capacity of the cation exchange membrane is 0.30 meq / g or more. The membrane resistance of the said cation exchange membrane is 10 ohm-cm < ² > or less, The processing method of the radioactive waste liquid of any one of Claims 1-7 characterized by the above-mentioned.   The said radioactive waste liquid is a radioactive waste liquid containing a seawater component, The processing method of the radioactive waste liquid of any one of Claims 1-8 characterized by the above-mentioned.   The radioactive waste liquid further contains a non-radioactive electrolyte, and in the treatment step of obtaining the concentrated liquid, the cations of the non-radioactive electrolyte are concentrated together with the radionuclide. The processing method of radioactive liquid waste as described in a term.   The method for treating a radioactive liquid waste according to claim 10, wherein the non-radioactive electrolyte is an inorganic acid or an inorganic salt.   The method for treating a radioactive liquid waste according to claim 11, wherein the inorganic salt is sodium chloride and / or potassium chloride.   The radioactive electrolyte is at least selected from the group consisting of Co, Mn, Fe, Sr, Y, I, Cs, Pu, Ce, Ru, Am, Cm, Te, U, Mo, Sb, Nd, Ce, and Np. The method for treating a radioactive liquid waste according to claim 1, comprising a radionuclide derived from one species.

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