JP2015085240A - Molded cesium adsorbent and manufacturing method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a molded cesium adsorbent that improves efficiency of adsorption work for adsorbing radioactive cesium by molding powdered cesium adsorbent into a proper shape to improve convenience of a member for cesium adsorption, and to provide a method for manufacturing the molded cesium adsorbent.SOLUTION: A molded cesium adsorbent, which is formed by molding a cesium adsorbent of Prussian blue, or of Prussian blue and a porous body into a predetermined granular, filamentous, or film-like shape by coagulation of a cellulose excipient, includes: a dissolution step of dissolving the cellulose excipient in a cellulose dissolving solvent to obtain a cellulose solution; a mixing step of mixing the cellulose solution with the cesium adsorbent to obtain an adsorbent mixture; and a coagulation step of bringing the adsorbent mixture into contact with a coagulating liquid to coagulate the adsorbent mixture into a predetermined shape.

Description

  The present invention relates to a molded cesium adsorbent and a method for producing the same, and more particularly to a cesium adsorbent having a formability and a production method therefor.

In nuclear fuel used in general uranium reactors, ²³⁵ U is the main element of fission reaction. ^There are ⁹⁰ Sr, ¹³¹ I, ¹³⁴ Cs, ¹³⁷ Cs and the like as radionuclide nuclides generated by the fission reaction of ²³⁵ U. When the above-mentioned nuclide is diffused in the environment, the presence of ¹³⁷ Cs is particularly problematic from the viewpoint of the half-life length and the amount produced by the fission reaction. ^{Since 137} Cs has a half-life of about 30 years and undergoes β decay, there is a risk of long-term exposure with β-ray irradiation.

Therefore, the diffusion component to the environment, recovery, etc. of the radionuclides ¹³⁷ Cs, etc. from the in nuclear fuel and reactor facilities (radioisotope) is a pressing problem. Immediately after collection, it must be isolated and shielded until it changes to a stable nuclide (stable isotope). Under such circumstances, efficient cesium recovery materials and recovery methods have been studied.

Since cesium is an alkali metal, it is often present in water in the form of Cs ⁺ ions. When recovering cesium in the environment such as soil, there are usually many types of metal compounds and metal ions. Therefore, if only a simple ion exchanger is used, naturally, metal ions other than cesium are also adsorbed, and the selective adsorption efficiency is not good. Therefore, there are problems such as requiring excessive facilities.

  For example, in an announcement by the National Institute of Advanced Industrial Science and Technology (AIST) on August 24, 2011, and thereafter, it has been clarified that Prussian blue exhibits an effect on selective adsorption of cesium. This is a finding that pays attention to the characteristics of being stably taken into the voids because the size of the lattice-like voids of the Prussian blue complex is relatively close to the size of the cesium ions (hydrated cesium ions).

  Prussian blue itself has long been used as a blue dye and paint. As an efficient method for producing Prussian blue, an aqueous solution containing an anionic metal cyano complex and an aqueous solution containing a metal cation are mixed, and crystals of Prussian blue type metal complex having metal atoms derived from both aqueous solutions Next, a solution in which a ligand is dissolved in a solvent and a Prussian blue-type metal complex crystal are mixed to obtain a dispersion of Prussian blue-type metal complex ultrafine particles. There is a technique for obtaining a type metal complex (see Patent Document 1).

When the Prussian blue-type metal complex of Patent Document 1 is a fine particle, the surface area of the particle itself increases and the contact area with the cesium ion increases. Therefore, cesium ions present in water are efficiently adsorbed by Prussian blue. On the other hand, because Prussian blue itself is also dispersed in water, it is not always easy to separate and collect Prussian blue fine particles from the water to be treated. When collecting the Prussian blue fine particles, centrifugal separation or a separate aggregating treatment is required. In particular, there is a high risk of exposure when treating Prussian blue adsorbed with radionuclides such as ¹³⁷ Cs. For this reason, reduction of the time required for processing as much as possible and simplification of processing itself are urgent issues.

  Therefore, a new cesium adsorbent that has improved the convenience of handling Prussian blue while utilizing the selective adsorption performance of cesium included in Prussian blue has been demanded.

  However, many of the existing cesium adsorbing materials such as Patent Document 1 are powdery. For this reason, when a cesium adsorbing substance is introduced into a treatment liquid containing radioactive cesium, the cesium adsorbing substance floats, and therefore, it is necessary to consider separation and recovery after adsorption. Therefore, at present, separate equipment is provided for holding or collecting the cesium adsorbing substance itself. Thus, although an adsorbent exhibiting good cesium adsorption performance has been obtained, further improvement is desired in terms of enhancing its convenience.

JP 2006-256594 A

  The present invention has been proposed in view of the above situation, and by making the adsorbent such as Prussian blue used for adsorption of cesium into an appropriate shape, it is made a more compact state than the state of fine particles for cesium adsorption. The present invention provides a molded cesium adsorbent and a method for producing the same, which enhance the convenience of members and contribute to the efficiency of the adsorption work of radioactive cesium adsorption.

  That is, the invention of claim 1 relates to a molded cesium adsorbent characterized by forming a cesium adsorbent into a predetermined shape with a cellulose-based excipient.

  The invention according to claim 2 relates to the shaped cesium adsorbent according to claim 1, wherein the cesium adsorbent is Prussian blue.

  The invention of claim 3 relates to the shaped cesium adsorbent according to claim 1, wherein the cesium adsorbent is Prussian blue and a porous body.

  The invention according to claim 4 relates to the shaped cesium adsorbent according to claim 3, wherein the porous body is activated carbon or zeolite.

  The invention according to claim 5 relates to the shaped cesium adsorbent according to claim 1, wherein the cesium adsorbent is zeolite.

  The invention according to claim 6 is the molded cesium adsorbent according to any one of claims 1 to 5, wherein the cesium adsorbent is added in an amount of 0.03 to 3.5 times by weight with respect to the cellulose-based excipient. Concerning.

  The invention of claim 7 relates to the molded cesium adsorbent according to any one of claims 1 to 6, wherein the cesium adsorbent is molded into a predetermined shape by coagulation of the cellulose-based excipient.

  The invention according to claim 8 relates to the shaped cesium adsorbent according to any one of claims 1 to 7, wherein the shaped cesium adsorbent is granular, thread-like, or film-like.

  The invention of claim 9 is the method for producing a molded cesium adsorbent according to any one of claims 1 to 8, wherein the cellulose-based excipient is dissolved in a cellulose-dissolving solvent to obtain a cellulose-dissolved solution. A dissolving step, a mixing step of mixing the cellulose solution and the cesium adsorbent to obtain an adsorbent mixed solution, and a coagulation for solidifying the adsorbent mixed solution into a predetermined shape by bringing the adsorbent mixed solution into contact with a coagulating solution. And a process for producing a molded cesium adsorbent.

  Invention of Claim 10 concerns on the manufacturing method of the shaping | molding cesium adsorbent of Claim 9 in which the said cellulose melt | dissolution solvent contains an aprotic polar organic solvent.

  Invention of Claim 11 concerns on the manufacturing method of the shaping | molding cesium adsorbent of Claim 9 in which the said cellulose solution solvent contains an ionic liquid.

  According to the molded cesium adsorbent according to the invention of claim 1, since the cesium adsorbent is formed into a predetermined shape with a cellulose-based excipient, the adsorbent used for adsorbing particulate cesium is put together, and It can be put together in an appropriate shape. As a result, the convenience as a member for cesium adsorption is improved, and it is useful for improving the efficiency of the adsorption work of radioactive cesium adsorption.

  According to the molded cesium adsorbent according to the invention of claim 2, in the invention of claim 1, since the cesium adsorbent is Prussian blue, a new addition to Prussian blue that has been conventionally used for the adsorption removal of radioactive cesium. Can add value.

  According to the shaped cesium adsorbent according to the invention of claim 3, in the invention of claim 1, since the cesium adsorbent is Prussian blue and a porous body, the floatability of Prussian blue is suppressed, and it becomes particulate and easy to handle. Increase.

  According to the molded cesium adsorbent according to the invention of claim 4, in the invention of claim 3, since the porous body is activated carbon or zeolite, the floatability of Prussian blue is suppressed, and it becomes particulate and increases ease of handling. .

  According to the shaped cesium adsorbent according to the invention of claim 5, since the cesium adsorbent is zeolite in the invention of claim 1, it is also suitable for adsorption of cesium which is an alkali metal.

  According to the molded cesium adsorbent according to the invention of claim 6, in the invention of any one of claims 1 to 5, the cesium adsorbent is added in an amount of 0.03 to 3.5 times by weight with respect to the cellulose-based excipient. Therefore, the cesium adsorption ability as an adsorbent is exhibited and a stable shape can be maintained.

  According to the molded cesium adsorbent according to the invention of claim 7, in the invention of any one of claims 1 to 6, the cesium adsorbent is molded into a predetermined shape by coagulation of the cellulose-based excipient. The molded cesium adsorbent containing the cellulose excipient can be obtained by returning to the cellulose excipient while containing the agent.

  According to the molded cesium adsorbent according to the invention of claim 8, in the invention of any one of claims 1 to 7, the molded cesium adsorbent is granular, thread-like, or film-like, so that it can be freely taken into consideration in terms of surface area. Can be made separately.

  According to the method for producing a shaped cesium adsorbent according to the invention of claim 9, the method for producing a shaped cesium adsorbent according to any one of claims 1 to 8, wherein the cellulose-based excipient is dissolved in cellulose. A dissolution step of dissolving in a solvent to obtain a cellulose solution, a mixing step of mixing the cellulose solution and a cesium adsorbent to obtain an adsorbent mixture, and contacting the adsorbent mixture with a coagulation solution A coagulation step for coagulating the agent mixture into a predetermined shape, so that the cellulosic excipient can be handled like a resin so that the adsorbent used for adsorbing particulate cesium can be made into a collective state. Can be combined into a shape.

  According to the method for producing a molded cesium adsorbent according to the invention of claim 10, in the invention of claim 9, since the cellulose-dissolving solvent contains an aprotic polar organic solvent, the cellulose-based excipient is dissolved and dissolved. The fluidity of the later solution can be adjusted.

  According to the method for producing a shaped cesium adsorbent according to the invention of claim 11, in the invention of claim 10, since the cellulose dissolving solvent contains an ionic liquid, pure cellulose can be dissolved.

It is a schematic process drawing explaining the manufacturing method of the shaping | molding cesium adsorbent of this invention. It is a photograph of granular shaped cesium adsorbent. It is a photograph of a filamentous cesium adsorbent. It is a photograph of a film-shaped molded cesium adsorbent.

  A cesium adsorbent having a cesium adsorption capacity is usually indefinite shape such as fine particles and powder. For this reason, when the to-be-treated water containing radioactive cesium is passed, a filtration and separation device for recovering the cesium adsorbent is separately required. Therefore, the molded cesium adsorbent of the present invention uses a cellulose-based excipient to reduce the separation burden of the cesium adsorbent itself while minimizing the decrease in the adsorption capacity of the cesium adsorbent having the ability to adsorb cesium. It is a regular product processed into a predetermined shape.

  The cesium adsorbent constituting the molded cesium adsorbent of the present invention is mainly composed of a cesium adsorbent alone (I), a cesium adsorbent and a composite (II) with a substrate supporting the cesium adsorbent. It is a kind.

  When the cesium adsorbent is used alone (I), the cesium adsorbent is Prussian blue simple substance or zeolite simple substance. The substance itself has the ability to adsorb cesium.

Prussian blue used as a cesium adsorbent is a kind of metal hexacyano complex generally indicated as “Fe ^III ₄ [Fe ^II (CN) ₆ ] ₃ ”, and forms a lattice-like bond. There are also types in which Ni and Co are coordinated as metal elements other than Fe. Cesium is adsorbed and held in the Prussian blue lattice. Therefore, it is conventionally used for the adsorption removal of radioactive cesium. Further, it is possible to add a fixed value to Prussian blue.

  Prussian blue is a powdery substance having a particle size of about 1 to 100 μm, used as a bitumen for dyes and pigments, and has an appropriate shape such as a lump or flake. In this size, Prussian blue can be used alone as a cesium adsorbent. As the Prussian blue itself increases, the surface area of the granules decreases. However, since the bitumen produced and used in the past can be used as it is, the cost is low and the procurement is quantitatively easy.

  Zeolite used for the cesium adsorbent is a crystal having a regular lattice formed of silica and alumina, and the lattice formed in the crystal becomes a minute void. Since the voids act like a sieve, they are effective for adsorption of various elements and ion exchange. Therefore, it is also suitable for adsorption of cesium, which is an alkali metal. In addition, zeolite has been widely used for cesium adsorption.

  Next, in the case of the complex (II) with the cesium adsorbent and the substrate for supporting the cesium adsorbent, the main component that adsorbs cesium is the aforementioned Prussian blue, which is used for supporting the Prussian blue. A porous body is used as the substrate. This porous body is activated carbon or zeolite. When Prussian blue is combined with a porous material, the floatability of Prussian blue is suppressed, and it becomes particulate and increases ease of handling.

  In preparing the complex (II), Prussian blue used for the same is the same as described above. However, in consideration of the penetration of the porous material into the pores, it is more preferable that Prussian blue has a fine particle property. Of course, pigments such as bitumen can be crushed. However, it is easier to use the fine particle property from the beginning. Prussian blue, which is a fine particle property, is a hydrophobic particle having a particle diameter of 10 to 20 nm disclosed in the above-mentioned Patent Document 1 (Japanese Patent Laid-Open No. 2006-256594). By using fine particle properties, high dispersibility in water, organic solvents, and the like is provided. In addition, Prussian blue, which is a fine particle property, is dispersed in water and is suitable for mixing with a porous material.

  In addition, Prussian blue, which is a fine particle property, easily enters the pores of the porous body. Since it is possible not only to adhere to the surface of the porous body but also to enter the inside of the pores, the support performance of the Prussian blue fine particles of the porous body is improved, and easy desorption is suppressed. Further, since Prussian blue itself is in the form of fine particles, the surface area of each fine particle is increased, and the adsorption efficiency of cesium is generally improved.

  The fine particle property Prussian blue is characterized by its production method and is prepared as a complex from the beginning. Since the particle size of Prussian blue is extremely small, the surface area per unit weight increases, and the adsorption effect of cesium generally increases. However, when the particle size of Prussian blue becomes finer, the floating property is increased accordingly, and a problem of fixing property arises. Therefore, in order to improve the floating defect of Prussian blue, which is a fine particle property, it is meaningful to form a composite in combination with a porous material.

  The porous body used in forming the composite is a known activated carbon or zeolite powder. Activated carbon is carbonized, fired, and appropriately pulverized pulverized products of woody plant materials rich in cellulose, such as wood saws, sawdust (wood sawdust) and sawdust generated during processing, waste wood, thinned wood, waste bamboo, felled bamboo, and coconut shells. It is the carbide obtained through the activation of. In addition to plant materials, carbides of various resin products such as old tires and phenol resins can be added. The base activated carbon can be procured relatively inexpensively and quantitatively. Further, it has been conventionally used as an adsorbing and filtering material, and has a wide range of substances to be adsorbed by pores having high stability and safety and developed on the activated carbon surface. The usable zeolite is a pulverized powder of natural zeolite (fluorite) or a pulverized powder of synthetic zeolite.

  Regarding the selection of the particle size of the activated carbon and zeolite powders, it is easy to be mixed with the cellulose-based excipient described below, and it is important to disperse uniformly. In addition, the degree of freedom in shape design is taken into account for the molded cesium adsorbent finally obtained after solidification. Therefore, it becomes difficult to mold with a powder having a large particle size, and the strength of the final molded product tends to vary. Therefore, the activated carbon and zeolite to be used are preferably in a powder form of approximately 0.1 mm or less.

  When preparing the cesium adsorbent of the composite (II), Prussian blue, which is a fine particle, is attached to powdered activated carbon and powdered zeolite previously measured by spraying or dipping. The amount of Prussian blue is adjusted by adjusting the number of spraying and dipping. Then, the activated carbon or zeolite to which Prussian blue is attached is dried. Thus, the cesium adsorbent of the complex (II) is completed.

  The cesium adsorbent of the single substance (I) that is Prussian blue or zeolite alone, or the complex (II) cesium adsorbent in which the Prussian blue is adsorbed on activated carbon or zeolite is not a fixed form by itself. It is a powder. Therefore, the cesium adsorbent is added to the cellulosic excipient and processed into a predetermined shape, and becomes a regular product.

  The cellulose-based excipient that is a main component for shaping is cellulose or a cellulose derivative. For example, there is a purified pulp obtained by pulverizing wood to remove impurities such as lignin to increase the purity of the cellulose component. In addition, it is a processed product appropriately processed from cellulose of such pulp as starting materials, and examples thereof include acetylcellulose (cellulose acetate, cellulose acetate), methylcellulose, carboxymethylcellulose, hydroxypropylcellulose, hydroxypropylmethylcellulose, and the like.

  The cellulosic excipients listed above are usually solid. Therefore, as will be described in the following production method, it is once dissolved in an appropriate solvent to prepare a cellulose solution. The cesium adsorbent of the aforementioned single body (I) or composite body (II) is added to the cellulose solution. And it returns to a cellulose excipient | filler, containing a cesium adsorption agent, through passing through coagulation | solidification of a cellulose solution. In this process, molding into a predetermined shape is possible, and a molded cesium adsorbent containing a cellulose-based excipient is obtained.

  As a result of molding performed in melting and solidification, the molded cesium adsorbent is finished into a granular, thread-like (fibrous), or film-like molded body. By contacting a cellulose solution containing a cesium adsorbent into a coagulation bath, it is possible to freely create a spherical or particle-size granular material to a thread-like (fibrous) or film-like molded product in consideration of the surface area. Although the molded shape is not limited to these, these shapes are preferable in consideration of an increase in the surface area of the molded cesium adsorbent.

  As the amount of cesium adsorbent in the formed cesium adsorbent increases, the amount of cesium adsorbed per unit weight of the formed cesium adsorbent increases. However, the relative proportion of the cellulosic excipient is reduced accordingly, and it becomes difficult to maintain the shape. Therefore, from the balance of both, the cesium adsorbent is converged to an addition amount of 0.03 to 3.5 times by weight with respect to 1 weight of the cellulosic excipient. The range of this addition amount is mainly the range of the cesium adsorbent in a single form (I). In the case of the cesium adsorbent of the composite (II), an addition amount range of 0.14 to 3.5 times by weight is preferable.

  The single cesium adsorbent (I) alone has an adsorption function, and can be adsorbed even at a low concentration. Therefore, the lower limit is 0.03 times by weight. The upper limit can be molded and is 3.5 times the weight from the viewpoint of maintaining strength. In the case of the cesium adsorbent of the complex (II), the lower limit amount is increased in consideration of components that do not directly contribute to the adsorption of cesium. When the addition amount of the cesium adsorbent is less than 0.14 times by weight, the cesium adsorbent itself is small and the adsorbing effect is insufficient. When the added amount of the cesium adsorbent exceeds 3.5 times by weight, it cannot be molded as a molded cesium adsorbent due to insufficient strength, and the molded product which is the object of the present invention cannot be obtained.

  Even when a known thermoplastic resin is used as an excipient, it can be kneaded with a cesium adsorbent and molded, and a predetermined molded product can be obtained. However, since the thermoplastic resin itself does not absorb water, the cesium adsorbent is coated and the cesium adsorption performance is significantly reduced. On the other hand, unlike the thermoplastic resin etc., the said cellulose-type excipient | filler has a water-containing performance, and also is equipped with water resistance. Therefore, the cellulose-based excipient suppresses the detachment of the cesium adsorbent held inside while allowing ions such as cesium to pass therethrough. Thus, since the molded cesium adsorbent is a molded product having a property of allowing cesium to permeate, convenience during use is enhanced.

  About the shaping | molding cesium adsorption material demonstrated so far, the manufacturing method is demonstrated using FIG. First, a cellulose-based excipient that is a structural component of the molded cesium adsorbent is prepared. The cellulose-based excipient is dissolved in a cellulose-dissolving solvent to become a cellulose-dissolved solution. This process is a “dissolution step”. Subsequent to the dissolution step, the above-mentioned cesium adsorbent is mixed in the cellulose solution, and an adsorbent mixed liquid in which the cesium adsorbent is dispersed is generated in the liquid. This process is a “mixing step”. After the mixing step, the adsorbent mixed solution coagulates by contacting with the coagulating solution. Through this solidification, it is formed into a desired shape to produce a solidified molded product. This process is a “coagulation step”. The solidified molded product is appropriately washed, and finally the molded cesium adsorbent of the present invention is completed.

  In the dissolution step, when acetylcellulose is used as the cellulose-based excipient, acetylcellulose is dissolved in a cellulose-dissolving solvent of an aprotic polar organic solvent. The aprotic polar organic solvent is selected from N, N-dimethylacetamide, dimethylsulfoxide, acetonitrile, N, N-dimethylformamide, 1-methyl-2-pyrrolidone (N-methyl-2-pyrrolidone), pyridine and the like. . These organic solvents are used because they dissolve cellulosic excipients and can adjust the fluidity of the solution after dissolution.

  When pure cellulose such as refined pulp is used as the cellulosic excipient, the solubility needs to be further increased because there are few cellulose modification groups. In such a case, the ionic liquid is blended with the cellulose-dissolving solvent together with the aprotic polar organic solvent described above.

  The ionic liquid has a strong charge in the molecule as is obvious. Since cellulose has a large amount of hydroxyl groups in the molecule, it is easily bonded electrostatically by hydrogen bonding or the like. Therefore, the aprotic polar organic solvent is used to enable homogeneous dissolution with an ionic liquid in a short time. If a proton-based solvent is used, an interaction (hydrogen bond) between the proton-based solvent and the ionic liquid occurs, and the hydrogen bond breakage of cellulose by the ionic liquid is inhibited. Therefore, proton-based organic solvents are not suitable.

The ionic liquid is shown as a heterocyclic compound of an imidazolium salt of the formula (i) and a derivative thereof. In the formula, R ₁ is an alkyl group having 1 to 4 carbon atoms, and R ₂ is an alkyl group having 1 to 4 carbon atoms or an allyl group. X is a halogen, pseudohalogen, or carboxyl group.

  As described above, the ionic liquid is an organic compound but a salt having an ionic bond. The ionic liquid moderately combines both the hydrophobicity as an organic substance and the affinity for hydrogen bonds derived from salts. For this reason, it permeates between the crystalline celluloses of the cellulosic excipient to break up hydrogen bonds between molecules or within molecules. At the same time, it is thought to play a role in preventing re-linking by the action of the hydrophobic portion in the molecule.

  Specific examples of ionic liquids of imidazolium salts include 1-butyl-3-methylimidazolium chloride, 1-butyl-3-methylimidazolium bromide, 1-allyl-3-methylimidazolium chloride, 1-allyl-3- Examples include methyl imidazolium bromide, 1-propyl-3-methyl imidazolium bromide, 1-ethyl-3-methyl imidazolium acetate, 1-ethyl-3-methyl imidazolium formate. In addition to the imidazolium salt of the formula (i), other ionic liquids of heterocyclic compounds such as other five-membered rings and six-membered rings can be used sufficiently.

  The cesium adsorbent is a cesium adsorbent alone (I), a composite (II) with a cesium adsorbent and a substrate on which the cesium adsorbent is supported. In the single substance (I), only “Prussian blue (PB)” or “Zeolite (ZL)” is used. The composite (II) is “a composite of activated carbon (AC) and Prussian blue (PB)” or “a composite of zeolite (ZL) and Prussian blue (PB)”. All are the above-mentioned materials.

  The process up to the preparation of the adsorbent mixture is affected by the properties of the solvent, viscosity, dispersibility of the cesium adsorbent, and the like. Therefore, as long as the adsorbent mixed solution can be finally obtained, the order of mixing can be changed as necessary. Alternatively, all may be mixed almost simultaneously. The process of the manufacturing method defined in the present invention is a sequential process mainly considering mass production. On the other hand, for example, since the examples described later are prototypes, the cesium adsorbent is first dispersed in the cellulose-dissolving solvent from the relationship of the equipment used, and then the cellulose-based excipient is added and dissolved. .

  The coagulation liquid used in the coagulation process is water, alcohol or the like. Affinity with aprotic polar organic solvents and ionic liquid water contained in the adsorbent mixture is high. The aprotic polar organic solvent or ionic liquid is transferred to water which is a coagulating liquid by contact with water. Therefore, only the cellulose-based excipient and the cesium adsorbent in the adsorbent mixed solution remain, whereby a solidified molded product is formed. Solidification is a process of confining a cesium adsorbent in a cellulosic excipient using such a phase separation phenomenon.

  In addition, when the adsorbent mixed liquid is solidified, the solidified molded product having a desired shape is finished by changing the contact method with the solidified liquid. For example, when the adsorbent mixed liquid is dropped into the coagulating liquid, a spherical solidified molded product is obtained. Alternatively, after the adsorbent mixed liquid is put into the coagulation liquid, it can be formed into a spherical shape by stirring using an appropriate stirring blade. Further, when the adsorbent mixed liquid is discharged from a nozzle (nozzle) having a small pore diameter, a solid and long solid (fibrous) solidified molded product is obtained. Further, when the adsorbent mixed liquid is discharged from the T die, a film-like (film-like) solidified molded product is obtained. As will be understood from this, many processing techniques for resin processing, fiber and film manufacturing can be used for the production of the solidified molded product. In this way, the adsorbent mixed solution becomes a “formed cesium adsorbent” through the solidified molded product.

  The shaped cesium adsorbent has a powder or fine powder cesium adsorbent contained therein in a desired shape, and has an excipient itself and moisture and ion permeability. Therefore, it combines both the selective adsorption of cesium and the ease of handling by shaping. Therefore, it greatly contributes to reducing the burden of loading cesium into the adsorption treatment apparatus and subsequent collection, and can contribute to improvement of work efficiency.

[Raw materials]
The inventors used the following activated carbon, zeolite, hydrophobic Prussian blue fine particles, and bitumen (Prussian blue pigment) as a cesium adsorbent.
-Activated carbon manufactured by Futamura Chemical Co., Ltd., wood-based activated carbon “Dazai SA1000” (average particle size: 5.1 μm) / (hereinafter referred to as AC)
Zeolite, manufactured by Tosoh Corporation, synthetic zeolite / Zeoram F-9 (powder product) (average particle size: 5.8 μm) / (hereinafter referred to as ZL)
Prussian blue manufactured by Kanto Chemical Co., Inc., Prussian blue nano-dispersion L (particle size: 10 to 20 nm), about 10 wt% aqueous dispersion / (hereinafter referred to as PB1. PB1 is a so-called fine particle dispersion.)
Made by Dainichi Seika Kogyo Co., Ltd., MILORI BLUE 905 (average particle size 0.17 μm) / (hereinafter referred to as PB2, PB2 is a bitumen pigment pulverized product)

Cellulosic excipients and solvents are as follows.
Cellulose-based excipient Acetylcellulose (abbreviation AcC), manufactured by Daicel Corporation, L-20
Cellulose (abbreviated as Cel), manufactured by Nippon Paper Chemical Co., Ltd., dissolved pulp, solvent, etc. Aprotic polar organic solvent, dimethyl sulfoxide (abbreviated as DMSO), manufactured by Kanto Chemical Co., Ltd., N, N-dimethylacetamide (abbreviated as DMAc), Tokyo Chemical Industry -Ionic liquid 1-butyl-3-methylimidazolium chloride (abbreviation BMIMCl), manufactured by Merck

[Preparation of cesium adsorbent]
In the case of the cesium adsorbent alone (I), only Prussian blue (PB2) and only zeolite (ZL) were used as they were. In the case of the cesium adsorbent of the composite (II), a composite of Prussian blue (PB1) and activated carbon (AC) or zeolite (ZL) was used.

[Preparation of complex (II)]
It was added to an aqueous dispersion of PB1 and diluted to a concentration of about 0.1 to 5% by weight from the initial 10% by weight. A diluted solution of PB1 was added little by little to a predetermined amount of activated carbon (AC) or zeolite (ZL) and sufficiently stirred. After being well adapted to the whole, activated carbon or zeolite was put in a dryer and dried at 120 ° C.

[Creation of molded cesium adsorbent]
In the case of using acetyl cellulose A cesium adsorbent and dimethyl sulfoxide (DMSO) which had been measured were dispersed while being mixed. A predetermined amount of acetylcellulose (AcC) was added thereto and stirred until completely dissolved to obtain an adsorbent mixed solution. The coagulation bath was filled with water and stirred gently, and the adsorbent mixture was added dropwise at regular intervals. The solidified molded product solidified in the solidification bath was collected, washed with water as appropriate, and used as a spherical shaped cesium adsorbent (see FIG. 2).

In the case of using cellulose: A cesium adsorbent and N, N-dimethylacetamide (DMAc) that had been measured were dispersed while being mixed. BMIMCl, a kind of ionic liquid weighed here, was added and mixed while heating to 80 ° C. Into this, cellulose (Cel) pulverized into a cotton shape by a pulverizer was added and further stirred to completely dissolve the cellulose to obtain an adsorbent mixed solution. The coagulation bath was filled with water and stirred gently, and the adsorbent mixture was added dropwise at regular intervals. The spherical solidified molded product solidified in the coagulation bath was collected, washed with water as appropriate, and used as a spherical molded cesium adsorbent.

[Created result]
Types of cesium adsorbent {single (I), composite (II)}, and specific amounts (%) of Prussian blue, activated carbon, zeolite, solvent, and cellulosic excipient, and cellulosic shaping Tables 1 to 4 show the weight ratio (adsorbent / excipient) (weight times) of the cesium adsorbent to the agent. Table 1 is a combination of prototype examples 101 to 112, Table 2 is a combination of prototype examples 201 to 203, Table 3 is a combination of prototype examples 301 to 310, and Table 4 is a combination of prototype examples 401 to 404.

  In preparing each prototype, the concentration of the cesium adsorbent and the cellulose-based excipient in the adsorbent mixture was approximately 5% by weight or more. This is because the molding was poor at 3% by weight or less from the previous production. On the other hand, when the amount reached 25% by weight, the decrease in fluidity became remarkable and the dripping became difficult. Therefore, the upper limit concentration was set to approximately 23% by weight.

  The cesium adsorbent of Table 1 was composite (II). An amount of Prussian blue (PB1) corresponding to half of the amount of activated carbon (AC) was added. And it is the granular shaping | molding cesium adsorbent produced by increasing the amount of cesium adsorbent with respect to acetylcellulose (AcC) of a cellulose-type excipient | filler. From prototype examples 101 to 112, the cesium adsorbent could be molded up to 0.13 to 3.5 times the addition of the cellulosic excipient. However, when it exceeded 3.75 times by weight, the amount of the cellulose-based excipient was relatively small, resulting in molding failure. Therefore, the upper limit was 3.5 times by weight.

  The cesium adsorbents in Table 2 were a single body (I) containing only zeolite (ZL) and a composite (II) obtained by attaching Prussian blue (PB1) to zeolite (ZL). The cellulose-based excipient was acetylcellulose (AcC). In any case, it was possible to prepare as a granular shaped cesium adsorbent (prototype examples 201 to 203).

  For the cesium adsorbent in Table 3, the kind of Prussian blue was changed to PB2, and this was used alone (I), and the blend of the cesium adsorbent was increased. The cellulose-based excipient was acetylcellulose (AcC). In any case, it was possible to prepare a granular shaped cesium adsorbent (prototype examples 301 to 310).

  The cesium adsorbents shown in Table 4 were Prussian blue (PB2) alone (I) and activated carbon (AC) in which Prussian blue (PB2) was attached. And the cellulose of the cellulose excipient | filler was melt | dissolved using the ionic liquid (BMIMCl). Also in this example, all were able to be produced as a granular shaping | molding cesium adsorption material (prototype examples 401 thru | or 404).

[About shape]
The photograph in FIG. 2 is a granular shaped cesium adsorbent of Prototype Example 108 in Table 1. The diameter of one grain is a slightly flat body of about 3 mm.

[Measurement and evaluation of cesium adsorption performance]
A test solution was prepared by dissolving cesium chloride (CsCl) in ultrapure water to a concentration of 1 ppm cesium. 0.5 g of the molded cesium adsorbent to be evaluated (each prototype) was weighed in terms of solid content and placed in a 100 mL container. Next, 50 mL of the test solution was put into the above-mentioned container and shaken for 100 minutes using a shaker (manufactured by Taitec Corporation, Triple Shaker, NR-80). Here, a blank test was also conducted by adding only the test solution without using the molded cesium adsorbent of the prototype and shaking it under the same conditions.

  Collect the solution in the container after shaking. Filter using 5C filter paper. The filtrate was quantified by atomic absorption of cesium (Cs). For the measurement, an atomic absorption analyzer (iCE 3000 SERIES AA Spectrometer) manufactured by Thermo Fisher Scientific Co., Ltd. was used.

[Results of cesium adsorption rate]
The amount of cesium in the filtrate of the blank test was used as a reference. The amount of cesium contained in the filtrate added with the shaped cesium adsorbent in each prototype was measured, and the adsorption rate (relative concentration) of cesium was determined by comparison with the blank test. When the relative concentration was 0%, complete adsorption was assumed, and the adsorption rate of cesium was 100%. The results are in Tables 5-8. For each prototype, the type and composition of the cesium adsorbent and the weight ratio (times by weight) of the cesium adsorbent to the cellulosic excipient were specified, and the cesium adsorption rate (%) was specified.

[Consideration of cesium adsorption rate]
According to the results of prototype examples 101 to 112 in Table 5, the cesium adsorption rate tends to increase with an increase in the weight ratio of the cesium adsorbent. However, at 0.13 weight times (prototype example 101), the adsorption rate falls below 90%. Therefore, from the viewpoint of maintaining the cesium adsorption rate of 90%, in the case of the composite (II), the lower limit of the weight times is desirably 0.14, and in order to further improve the performance, it is 0.25. desirable. There is no particular restriction on the upper limit. However, as mentioned above, the upper limit was set to 3.5 times the weight of the prototype 112 because the defective molding and the adsorption performance reached its peak.

  According to the results of Prototype Examples 201 to 203 in Table 6, the cesium adsorbent exhibited a good adsorption ability as a zeolite alone or with a cellulosic excipient (Prototype Example 201). Moreover, as a result of attaching Prussian blue to zeolite, the adsorption capacity was further improved (prototype examples 202 and 203).

  According to the results of prototype examples 301 to 310 in Table 7, the cesium adsorption capacity was also improved in correlation with the amount of PB2 in the cesium adsorbent. Therefore, from the viewpoint of securing an adsorption rate of 90% or more, it is desirable that the lower limit of the weight multiplication is 0.03 (prototype example 302), and further, 0.1 weight times is desirable from a comparison between the prototype examples 303 and 304.

  According to the results of prototype examples 401 to 310 in Table 8, even a molded cesium adsorbent prepared by changing the cellulose-based excipient to cellulose dissolved using an ionic liquid exhibited good adsorption ability.

[Other shapes]
All of the disclosed prototype examples were granular (spherical). Therefore, by changing the way of contact with the coagulation bath, shapes other than granular were also created.

  The adsorbed liquid mixture used in the preparation of the above-mentioned prototype example 108 (see Table 1) was filled in a syringe and dropped in a water coagulation bath while slowly pushing the piston. A spherical solidified molded product solidified in the coagulation bath was collected, washed with water as appropriate, and used as a thread-shaped molded cesium adsorbent. This is a photograph of FIG.

  The adsorbed liquid mixture used in the production of the above-described prototype example 108 (see Table 1) was poured into a stainless steel vat so that the overall thickness was substantially uniform. The water for coagulation was gently poured into it and waited for coagulation in the bat. Thereafter, it was washed with water to obtain a film-shaped molded cesium adsorbent. This is a photograph of FIG.

[Summary]
From the results of the production of a series of molded cesium adsorbents, the types and configurations of cesium adsorbents that can be used were relatively freely selected. Further, even if the cellulose-based excipient is changed as appropriate, it can be molded in the same manner, and the adsorption effect of cesium is not inferior. In addition, by adopting a cellulose-based excipient, it was possible to obtain processability that can be easily formed into various shapes like a resin. For this reason, it became possible to improve the ease of handling, which was difficult to achieve with powdered cesium adsorbents. Furthermore, by adopting the cellulose-based excipient, metal ions such as cesium can permeate. Therefore, both the retention of the cesium adsorbent in the adsorbent and the permeation of the metal ions to be adsorbed can be achieved.

  The shaped cesium adsorbent of the present invention is an adsorbent that adsorbs and holds radioactive cesium, and can be processed into a desired shape unlike conventional powdery adsorbents. Therefore, it can greatly contribute to the improvement of working efficiency in the radioactive cesium adsorption work.

Claims (11)

  A shaped cesium adsorbent comprising a cesium adsorbent molded into a predetermined shape with a cellulose-based excipient.   The shaped cesium adsorbent according to claim 1, wherein the cesium adsorbent is Prussian blue.   The shaped cesium adsorbent according to claim 1, wherein the cesium adsorbent is Prussian blue and a porous body.   The shaped cesium adsorbent according to claim 3, wherein the porous body is activated carbon or zeolite.   The shaped cesium adsorbent according to claim 1, wherein the cesium adsorbent is zeolite.   The shaped cesium adsorbent according to any one of claims 1 to 5, wherein the cesium adsorbent is added in an amount of 0.03 to 3.5 times by weight with respect to the cellulose-based excipient.   The shaped cesium adsorbent according to any one of claims 1 to 6, wherein the cesium adsorbent is formed into a predetermined shape by coagulation of the cellulose-based excipient.   The shaped cesium adsorbent according to any one of claims 1 to 7, wherein the shaped cesium adsorbent is granular, thread-like, or film-like. A method for producing a shaped cesium adsorbent according to any one of claims 1 to 8,
A dissolution step of dissolving the cellulose-based excipient in a cellulose dissolution solvent to obtain a cellulose solution;
A mixing step of mixing the cellulose solution and the cesium adsorbent to obtain an adsorbent mixture;
A solidification step of solidifying the adsorbent mixed liquid into a predetermined shape by bringing the adsorbent mixed liquid into contact with a coagulating liquid. A method for producing a molded cesium adsorbent.   The method for producing a molded cesium adsorbent according to claim 9, wherein the cellulose-dissolving solvent contains an aprotic polar organic solvent.   The method for producing a shaped cesium adsorbent according to claim 9, wherein the cellulose-dissolving solvent contains an ionic liquid.

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