JP6152764B2 - Cesium adsorbent manufacturing method and cesium adsorbent - Google Patents

Description

  The present invention relates to a method for producing a cesium adsorbent using ferric ferrocyanides and a cesium adsorbent. More specifically, it is an adsorbent that has a high cesium adsorption capacity and a small amount of cyanide elution, contains a large amount of cations other than cesium, and efficiently removes cesium from waste liquids with low cesium concentrations. The present invention relates to a method for producing a cesium adsorbent.

Various methods have been studied for the recovery and removal of radioactive cesium from waste liquids generated from facilities related to the use of nuclear energy such as spent fuel reprocessing facilities. Radioactive cesium is produced by a fission reaction such as uranium 235, but it is an alkali metal that has a long half-life and is easy to elute, so it is contained in various treatment liquids at nuclear facilities. It is known that cesium can be adsorbed and removed by using a specific zeolite when other cations do not coexist in the waste liquid containing cesium.
However, in the event of an accident at a nuclear facility, when radioactive cesium is released into the atmosphere and mixed with rainwater and falls to the ground, or waste liquid or treated water containing radioactive cesium flows into seawater or a pond, etc. A large amount of coexisting alkali metals such as sodium and potassium and alkaline earth metals such as calcium are included. In such a case, since cesium cannot be adsorbed and removed with high selectivity in zeolite, a method of efficiently removing radioactive cesium is eagerly desired.

  As a means for removing radioactive cesium from a liquid in which other metal ions coexist, such as seawater, it is well known that a poorly water-soluble ferrocyanide compound has excellent cesium adsorption ability. Typical poorly water-soluble ferrocyanide metal compounds are ferrocyanide, cobalt ferrocyanide, nickel ferrocyanide, copper ferrocyanide, zinc ferrocyanide, and silver ferrocyanide.

  However, generally poorly water-soluble ferrocyanide compounds are fine powders and have a primary particle size of about 50 nm to 100 nm, so if used as an adsorbent as they are, they are dispersed in water and are very difficult to recover in their entirety. It is difficult to use as a filter medium in an adsorption tower or the like. For this reason, it has been studied to use a poorly water-soluble ferrocyanide compound supported on a porous material or the like, or to form a powder of poorly water-soluble ferrocyanide into granules using a binder.

For example, Patent Document 1 describes the use of a combustible cesium adsorbent in which a poorly water-soluble ferrocyanide compound is supported in the pores of activated carbon.
Patent Document 2 discloses a cesium adsorbent having high cesium adsorption capacity and carrying a copper salt-based poorly water-soluble hexacyanoiron (II) salt (also known as copper ferrocyanide) in the pores of a porous carrier. Have been described.
However, in the methods of Patent Document 1 and Patent Document 2, since the ratio of the poorly water-soluble ferrocyanide compound supported on the porous carrier is small, it is useful if the amount of radioactive waste is small, but a particularly large amount of cesium is contained. When adsorbing cesium contained in water, a large amount of an adsorbent carrying a metal ferrocyanide compound is required, which increases the amount of radioactive waste.

  On the other hand, Patent Document 3 and Patent Document 4 propose a cesium adsorbent obtained by mixing and complexing a poorly water-soluble ferrocyanide compound and a fine metal oxide. However, by simply mixing and combining a poorly water-soluble ferrocyanide metal compound and a particulate metal oxide, it is not possible to bind sufficiently when the content of the particulate hardly water-soluble ferrocyanide compound is increased, When this cesium adsorbent was immersed in water containing cesium to adsorb cesium, there was a problem that the poorly water-soluble ferrocyanide fine particles that could not be bound were dispersed in water. A poorly water-soluble ferrocyanide compound such as ferrocyanide is a solid, but its particle size is extremely small as described above, so it is easy to pass through a filter that filters water for analysis. It is quantified as cyan in the all-cyan analysis specified in the Pollution Control Law. Further, if the fine particles are discharged in a state where the radioactive cesium is adsorbed, there is a possibility that secondary contamination by radioactive substances may occur.

From this, the inventors of the present invention in Patent Document 5 solidified the particulate metal oxide and the poorly water-soluble ferrocyanide compound into particles, impregnated with a metal alkoxide, and improved the binding property by performing a condensation reaction. We have proposed a cesium adsorbent that has high strength and is more suitable as a filter medium.
The cesium adsorbent obtained by the methods of Patent Document 1 and Patent Document 2 has a content of poorly water-soluble ferrocyanide compound of only about several to no more than about 20% of the total weight of the adsorbent, In the method proposed by the present inventors, the ratio of the poorly water-soluble ferrocyanide compound to the entire adsorbent can be easily increased to 50% or more, and the adsorption capacity can be greatly increased. Moreover, due to the reinforcing effect by the condensation reaction of the metal alkoxide, dispersion of the poorly water-soluble ferrocyanide metal compound fine particles in water can be suppressed.

  As described above, the method of forming a poorly water-soluble ferrocyanide compound using a binder or the like can increase the concentration of poorly water-soluble ferrocyanide metal in the adsorbent and increase the amount of cesium adsorbed per adsorbent as described above. This is preferable. On the other hand, as a substance that is industrially mass-produced as a poorly water-soluble ferrocyanide compound and that can be used in each country under laws such as the Japanese laws concerning the examination and production of chemical substances, There are only ferric ferrocyanides that are manufactured as blue pigments. Therefore, the method of forming a poorly water-soluble ferrocyanide compound using a binder or the like has an advantage that iron ferrocyanides that can be easily obtained can be used.

However, when the present inventors conducted experiments on cesium adsorption using ferrocyanide, it was found that when used in the cesium removal step, ferrocyanide ions are eluted in the water after cesium removal. .
In more detailed investigations, it was found that when cesium is adsorbed and removed from an aqueous solution containing salt such as seawater, ferrocyanide ions are more likely to be eluted when cesium is adsorbed and removed from an aqueous solution having a low cesium ion concentration.
Further, as conventionally known, ferric ferrocyanides are easily decomposed in a liquid having a high pH, and as a result, a large amount of ferrocyanide ions are eluted. When radioactive cesium leaks from the nuclear power plant to the sea area due to an accident, etc., the cesium concentration is often low, the presence of a large amount of salt, and a high pH (normally the pH of seawater is as high as about 8 to 8.4) Therefore, ferrocyanide ions are likely to elute if used for cesium adsorption in such an environment.

  Ferrocyanide ions contain cyanide ions as ligands, and ferrocyanide ions may decompose in the environment to generate toxic free cyanide, and the emission concentration must be lowered. For example, in Japan's Water Pollution Control Law, among the criteria for hazardous substances listed in Appendix 1 of the Ordinance Ordinance 1 of the Ministerial Ordinance for Establishing Wastewater Standards, the wastewater standard value for cyan is 1 mg / L as the total cyanide amount. Excess drainage cannot be discharged into the environment. For this reason, the water after adsorbing and removing cesium needs to have a total cyan density less than the reference value. This total cyanide includes not only free cyanide ions, which are highly toxic per se, but also cyanide present as a ligand in cyano complexes such as ferricyanide and ferricyanide in which the central metal iron is oxidized. It becomes a target.

  The present invention intends to significantly suppress elution of cyanide during cesium adsorption by reacting a molded article containing ferrocyanide with a solution in which a metal salt having a lower ionization tendency than iron is reacted. It is what.

Japanese Patent Laid-Open No. 2-207839 Japanese Patent Laid-Open No. 11-76807 JP 2012-250904 A JP 2012-251994 A JP 2013-29498 A

  In view of the above situation, the present invention provides a method for producing a cesium adsorbent with very little elution of ferrocyanide ions when a cesium adsorbent containing ferrocyanide is used to remove cesium. Objective.

As a result of intensive studies to solve the above problems, the present inventors have brought a solid containing iron ferrocyanide into contact with a metal salt solution containing a metal salt having a lower ionization tendency than iron. It has been found that elution of ferrocyanide ions or ferricyanide ions can be remarkably suppressed, and the present invention has been completed.
The metal ionization tendency can be quantified by measuring the standard electrode potential of the metal salt solution.

  That is, the method for producing a cesium adsorbent according to claim 1 includes a material containing iron ferrocyanide composed of at least ferrocyanide ions and iron ions, and a metal having a standard electrode potential higher than −0.40V. It is a manufacturing method of a cesium adsorbent characterized by including the process of making a metal salt solution react.

  The method for producing a cesium adsorbent according to claim 2, wherein an acid and / or a chelate compound is dissolved in a metal salt solution to be reacted with a material containing ferric ferrocyanides. It is a manufacturing method of a cesium adsorbent.

The method for producing a cesium adsorbent according to claim 3 is characterized in that, after the step of reacting the material containing iron ferrocyanide and the metal salt solution, a step of contacting any of the following liquids is performed. A method for producing a cesium adsorbent according to claim 1 or claim 2.
(1) A step of contacting a solution having a pH of 7 to 9.
(2) The process made to contact the solution of a chelate compound.
(3) A step of contacting a solution containing a chelate compound having a pH of 7 to 9.
(4) The process which makes acidic aqueous solution contact, and is subsequently made to contact the solution of pH 7-9.

  The method for producing a cesium adsorbent according to claim 4, wherein the ferrocyanide is ferric ferrocyanide, ferric ferrocyanide ammonium, ferric sodium ferrocyanide and ferric ferrocyanide. It is any of potassium, It is a manufacturing method of the cesium adsorbent in any one of Claims 1-3.

  The method for producing a cesium adsorbent according to claim 5, wherein the kind of metal element constituting the metal salt contained in the metal salt solution is copper, tin, or nickel. It is a manufacturing method of the cesium adsorbent in any one.

  The method for producing a cesium adsorbent according to claim 6 is characterized in that the material containing ferric ferrocyanide is formed by solidifying ferric ferrocyanide into a solid with a binder. The method for producing a cesium adsorbent according to any one of Items 6.

  The method for producing a cesium adsorbent according to claim 7 is the method for producing a cesium adsorbent according to claim 6, wherein the binder is a metal oxide.

  The manufacturing method of the cesium adsorbent of Claim 8 is a cesium adsorbent obtained by the manufacturing method in any one of Claims 1-7.

  The cesium adsorbent obtained by the production method of the present invention is excellent in cesium adsorption performance, and can remove cesium by a simple method. Furthermore, even if contaminated water containing cesium contains a large amount of cations such as alkali metals and alkaline earth metals such as seawater, it can efficiently adsorb and remove cesium, and the cesium adsorbed water Elution of cyanide compounds such as ferrocyanide ions and ferricyanide ions can be greatly reduced.

The ferrocyanide in the present invention can be used without any particular limitation. For example, it is represented by a chemical formula of the general formula Fe (III) xMy [Fe (II) (CN) ₆ ] z, M represents a metal component, ferrocyanide ion is a tetravalent anion, and Fe (III) is Since it is a trivalent cation, it satisfies the relationship (3x + M valence × y = 4z, where x and z are both 1 or more). In this formula, M may or may not be present, but if included, consists of one or more cations. When M is a plurality of cations, two or more of the same cations may be used, or two or more types of cations may be used. Since this chemical formula is an explanation of ferric ferrocyanides, when water-soluble salts such as ammonium ferrocyanide used in the ferrous ferrocyanide manufacturing process remain, x is less than 1 Is also applied to ferrocyanide components excluding these mixed components. For this reason, naturally, even if ferrocyanide other than ferrocyanide is mixed, the process of the present invention can be applied.

Ferrocyanide is produced as a blue pigment and is a compound that is hardly soluble in water and is known to adsorb cesium ions. Specific examples thereof include ferric ferrocyanide represented by the composition formula Fe (III) ₄ [Fe (II) (CN) ₆ ] ₃ and the composition formula NH ₄ Fe (III) [Fe (II) (CN ) ₆ ] ferric iron ferrocyanide, NaFe (III) [Fe (II) (CN) ₆ ] ferric ferric sodium salt, KFe (III) [Fe (II) Ferric ferrocyanide potassium represented by (CN) ₆ ] can be used.

  In the production method of the present invention, finely ferric ferrocyanide can be used as it is, but it is preferable to use a powder that has been processed into a shape suitable for cesium adsorption removal in advance such as granular using a binder or the like. preferable. The reason for this is that when the ferrous ferrocyanide fine powder is reacted with the metal salt solution in the method of the present invention and the subsequent washing and drying steps are performed, since the ferrocyanide is very fine, the washing step This is because not only is it difficult to separate the liquid from the cleaning liquid, but there is also a lot of powder loss during the process.

  Examples of the binder include organic substances and inorganic substances. Examples of the organic binders include organic polymers such as polyacrylonitrile, ethylene vinyl acetate copolymer, polyamide, polyester, polyvinyl alcohol, and polysaccharides, or epoxy resins, acrylic resins, and unsaturated polyesters. Examples thereof include curable resins. Since it is used in contact with water containing cesium, it is preferable to use one having a polar functional group. In the case of using a water-soluble polymer, it is preferably used after crosslinking with a crosslinking agent.

  As the inorganic binder, metal oxide, clay, fine powder such as glass, and the like can be used. Alternatively, a metal oxide precursor such as a metal alkoxide or sodium silicate can be used and gelled to form a metal oxide, which can be used as a binder. Since radioactive cesium decays by emitting gamma rays, the organic matter is easily decomposed and is not suitable for long-term storage. Therefore, it is more preferable to use an inorganic compound as a binder.

In the present invention, when iron ferrocyanide is hardened with a binder and formed into a granular shape or the like, it is preferable to use a metal oxide as the binder, in particular, metal oxide fine particles such as colloidal silica. Is preferred.
Although the metal oxide fine particles have water molecules adsorbed on the surface and do not sinter when heated at 100 to 150 ° C., the water molecules adsorbed between the particles are removed and the metal oxide fine particles are Can stick to each other and harden to the extent that they do not disintegrate easily in water. Moreover, particulate inorganic substances such as glass and clay can be used in combination. These metal oxides and fine inorganic particles are mixed with fine ferrocyanide powder in a state of being dispersed in a liquid such as water, and then poured into a mold or the like, extruded, or rolled and granulated. It is possible to mold by molding by a method and heating as necessary to volatilize and remove a liquid such as water. In addition, when a powdered metal oxide is used, it can be mixed in a liquid such as ferrocyanide and water without being previously dispersed in water.

  In the above method, the removal of liquid such as water does not provide sufficient strength of the molded product, and the water resistance is low, so that the molded product is rubbed or submerged in water so that the fine particles of iron ferrocyanide Is easy to fall off from the molded product. For this reason, it is preferable to reinforce these particles by chemically bonding them together with a metal alkoxide.

The metal oxide, glass, clay, and the like are materials that are usually sintered or melted at a high temperature of 500 to 1000 ° C. or more, thereby generating a strong binding force, but ferrocyanide is less than that. Such a sintering process cannot be adapted due to decomposition at temperature.
The metal alkoxide can not only condense itself to form a cross-linked metal oxide, but it can also be shared by condensation reaction with the metal oxide, hydroxyl groups present on the surface of inorganic particles such as glass and clay. Since a bond can be formed, a chemical bond can be formed at a temperature lower than that at which ferric ferrocyanides decompose, and a strong molded body can be obtained. By this, it can suppress that the fine particle of ferrocyanide is more firmly fixed in the molded body, and falls off in the process of adsorbing cesium.

As the fine particle metal oxide, silica, titania, alumina, zirconia, etc. can be used without any particular limitation, but the metal oxide having a particle diameter of 1 to 100 nm is excellent in binding properties of ferrocyanide. Therefore, it is preferable.
Moreover, what has a hydroxyl group (hydroxy group) on the surface is preferable from the bridge | crosslinking by a condensation reaction by a metal alkoxide can be anticipated. Specifically, a metal oxide having a titanol group, an aluminal group, or a silanol group, or a metal oxide having a hydroxyl group (hydroxy group) on the surface with fine particles made of titania, alumina, silica, and zirconia can be used.
In particular, a colloidal material dispersed in water using water as a dispersion medium is preferable because it is easy to disperse and is easy to handle.
Among such metal oxides, colloidal silica is the most typical, and is preferable because waste can be easily disposed of by vitrification of a remover that has adsorbed radioactive cesium.

  Further, when the metal oxide is used in the form of fine particles, it is preferable to use a liquid such as water as a dispersion medium and mix it with the ferrocyanide.

  In the present invention, the metal oxide preferably used includes silicic anhydride (silica fine particles) having a particle diameter of 5 to 30 nm. Among these, colloidal silica dispersed in a colloidal form in water or an organic solvent is preferable, and a water dispersion type is more preferable. In the case of water-dispersed colloidal silica, since a large number of hydroxyl groups are present on the surface of the silica fine particles, a strong molded body that is easily mixed with hydrophilic ferrocyanide is obtained.

  Furthermore, the water-dispersed colloidal silica is divided into an acidic aqueous dispersion type and a basic aqueous dispersion type, both of which can be used. Ferric ferrocyanides can be used in a basic atmosphere with a pH exceeding 10 or an acidic atmosphere with a pH of 1 or less. Since it is easy to decompose | disassemble, it is preferable to use the thing of the range of pH 2-9. In addition, even if it is outside the preferable pH range, it can be used by adjusting the pH to a preferable range by adding an acid or a base.

As a specific colloidal silica, a commercial product can be used as it is. For example, as a commercial product dispersed in an acidic aqueous solution, Snowtex O (trade name) manufactured by Nissan Chemical Industries, Ltd., JGC Catalysts & Chemicals Cataloid SN (trade name) manufactured by Co., Ltd., and as a commercial product dispersed in a basic aqueous solution, Snowtex C (trade name), Snowtex 30 (trade name) and Snowtex manufactured by Nissan Chemical Industries, Ltd. 40 (trade name), Cataloid S30 (trade name) and Cataloid S40 (trade name) manufactured by JGC Catalysts & Chemicals Co., Ltd. may be mentioned.
Further, as commercial products dispersed in an organic solvent, MA-ST (trade name), IPA-ST (trade name), NBA-ST (trade name) manufactured by Nissan Chemical Industries, Ltd., etc., and Catalyst Chemical Industry Co., Ltd. OSCAL1132 (brand name), OSCAL1232 (brand name), etc. which are manufactured are mentioned.

  Specific examples other than colloidal silica include an aqueous dispersion of alumina (alumina sol 200, alumina sol 520 manufactured by Nissan Chemical Industries, Ltd.), an aqueous dispersion of zirconia (nanouse ZR-30BF manufactured by Nissan Chemical Industries, Ltd.), titania An aqueous dispersion (Taika Corporation Anatas TKS-203) and the like can be mentioned.

  As the metal oxide fine particles, those supplied as a powder without being dispersed in a liquid can be used. In this case, the powdered metal oxide, ferrocyanide and water or other solvent are directly mixed and stirred, and the solvent is removed by volatilization, thereby forming the same process as when using the metal oxide dispersion. Can do. Examples of such metal oxide powder include fumed silica (Aerosil manufactured by Nippon Aerosil Co., Ltd.).

  In the present invention, the method for mixing the ferrocyanide and the metal oxide is not particularly limited, and a known mixing method can be used. Since it is desirable to mix uniformly, it is preferable to mix in advance using a kneader such as a kneader before molding.

  In addition to the above method, a method generally known as a method for producing silica gel can be used as a method of binding and molding fine particles of ferrocyanide with a metal oxide. That is, it is a method of depositing silica gel by adding a catalyst such as sulfuric acid to a liquid containing sodium silicate as a metal oxide precursor. In this case, since the pH of sodium silicate is high, if ferrous ferrocyanide fine particles are dispersed and mixed on the catalyst solution side and mixed with sodium silicate, the ferrocyanide is difficult to decompose during production.

  The material containing iron ferrocyanide in the present invention is preferably subjected to a treatment for reinforcing strength after the iron ferrocyanide is molded with a binder or the like.

In order to perform the treatment for reinforcement, a method may be mentioned in which iron ferrocyanide is formed into a granular shape with a metal oxide or the like and then impregnated with a metal alkoxide such as alkoxysilane and cured.
By using this method, the strength of the adsorbent in water is increased, the content of ferric ferrocyanide, which is an active ingredient for cesium adsorption, can be increased, and a large amount of cesium can be adsorbed with a small amount of adsorbent. It is most preferable from the viewpoint that
In order to improve cesium adsorption performance, the proportion of ferrocyanide in the cesium adsorbent is preferably 50 to 95% by mass, more preferably 60 to 85% by mass.

  On the other hand, metal oxides act as a binder for particulate ferric ferrocyanides and have the effect of improving shape retention when cesium adsorbents are immersed in water containing cesium. The total of the fine metal oxide and metal alkoxide-derived metal oxide is preferably 5 to 50% by mass, more preferably 15 to 40% by mass.

  In the step of forming into a granular shape or the like, other components may be added for the purpose of adjusting the fluidity during the forming process. For example, glass, silica, alumina, various clay minerals and flow modifiers, foaming agents, antifoaming agents, dispersing agents and the like are exemplified.

  As the material containing iron ferrocyanide in the present invention, a material obtained by solidifying iron ferrocyanide with a binder such as a metal oxide and molding it into a solid form such as a granule as described above may be used. When ferrocyanide is synthesized, the primary particles are usually produced as fine particles having a size of several tens to several hundreds of nanometers. Once such fine particles are dispersed in water, it becomes very difficult to separate and recover, so it is necessary to facilitate separation of water and adsorbent. As a method for separating water and adsorbent by a simple method, a separation method using a filtration tower is known. For this reason, it is easy to adsorb and remove radioactive cesium dissolved in water by forming it into a shape suitable for filling the filtration tower.

  Filter towers are widely used as a means for removing impurities contained in liquids, and are used, for example, in the production of drinking water and pure water. As for the filtration tower, what filled sand, activated carbon, and ion exchange resin inside is generally known. The filling material to be filled in is required to have a large surface area and absorb a large amount of impurities, to have a low resistance when flowing a liquid, and to be free from contamination by the filling material itself. As described above, ferrocyanide is produced as fine particles having a very small size, and a method for increasing the crystal size to a size suitable as a filter medium is not known. For this reason, it is not preferable to fill the filtration tower as it is because the liquid flow resistance becomes too large, and fine particles are liable to leak. Therefore, it is necessary to form a shape suitable for filtration, such as solidified with a binder or granular.

In the present invention, when an adsorbent prepared by solidifying ferric ferrocyanide with a metal oxide binder is packed in a filtration tower, the particle size of the granules is about 0.1 mm to 5 mm in average particle size. It can be preferably used.
The particle size is designed considering various factors such as the length of the adsorption tower, the flow rate of the flowing liquid, the cross-sectional area, and the concentration of cesium contained in the water contaminated by cesium, so it is limited to the particle size shown here. It is not something.

  The shape of the cesium adsorbent of the present invention is not limited to a granular shape, and may be formed into a cylindrical shape, a pipe shape, a spherical shape, or a honeycomb shape as necessary. It may be fixed.

  A molding method in the case of using, as a material containing iron ferrocyanide, a material obtained by molding iron ferrocyanide using a particulate metal oxide such as colloidal silica as a binder will be described. First, a dispersion of iron ferrocyanide and a particulate metal oxide and, if necessary, a liquid such as water are mixed and molded, and then heated by a method such as ventilation drying. The heating condition is not particularly limited as long as it is not higher than the decomposition temperature of the ferric ferrocyanide. However, in order to sufficiently heat, for example, it is preferable to heat at a temperature of 120 ° C. to 150 ° C. for 2 hours to 3 hours.

  When colloidal silica is used as the binder, the one heated at 120 ° C. to 150 ° C. is hardly disintegrated even when placed in water or an alcohol solution of a metal alkoxide, and the shape can be maintained. On the other hand, when heated at 100 ° C. for 3 hours, when immersed in an alcohol solution of water or a metal alkoxide, for example, a particle having a diameter of about 3 mm is converted into an alcohol solution of the metal alkoxide in a cross-linking step using a metal alkoxide described later. When immersed, it disintegrates into several pieces, but the one dried at 130 ° C. for 2 hours did not disintegrate even when immersed in water or an alcohol solution of a metal alkoxide.

  In addition, even if it is a disintegrated particle | grain, since it reinforces by bridge | crosslinking with a metal alkoxide and water resistance improves, it can be used as a filter medium depending on the magnitude | size after disintegration. However, if the heating temperature is too low, there is a problem that it becomes difficult to control the size of the formed granule, which is not preferable.

  In addition, when mixing ferric ferrocyanides and a particulate metal oxide binder, at a high temperature from the beginning in the drying process after pouring the paste kneaded into a mold using water or an organic solvent. When heated, problems such as the generation of many bubbles inside the adsorbent and the adsorbent becoming brittle are likely to occur. When the solvent is water, the solvent is first heated at a temperature lower than 100 ° C. It is preferable to remove most of the solvent once at a temperature lower than the boiling point of.

When the ferrocyanide is solidified with a metal oxide binder and molded, in order to increase the hardness and strength of the molded product, it is preferable to immerse the molded product in a metal alkoxide solution, and then filter and heat again.
Metal alkoxides can be bonded to each other by hydrolysis and condensation to form metal oxides, and a condensation reaction can occur between hydroxyl groups such as silanol groups and metal alkoxides, which can be chemically bonded. It is presumed that the alkoxysilane that has penetrated into the inside not only hardens alone, but also has a function of bonding metal oxide particles. For this reason, a remarkable reinforcing effect is obtained.
In addition, there is no limitation in particular about the immersion method to a metal alkoxide solution, the filtration method, and drying conditions, A well-known method is applicable.

  Examples of the metal alkoxide include lower alkoxides of metals selected from silicon, aluminum, zirconium and titanium. Examples of the lower alkoxide include methoxide, ethoxide, propoxide, butoxide, and isomers thereof such as isopropoxide, sec-butoxide, and t-butoxide, and one or more of these can be used.

  Specific examples of metal alkoxides include silicon tetraethoxide (ethyl silicate), silicon tetramethoxide (methyl silicate), silicon tetrabutoxide (butyl silicate), propyl silicate, aluminum triisopropoxide, zirconium tetrabutoxide, titanium tetraisooxide. A propoxide etc. are mentioned. Among these, silicon tetramethoxide and silicon tetramethoxide are preferable.

When these metal alkoxides use partial hydrolysates, the reaction is completed in a short time. Such a partial hydrolyzate includes a partial hydrolyzate of tetramethoxysilane (trade name: methyl silicate 51, manufactured by Colcoat Co., Ltd.), a partial hydrolyzate of tetraethoxysilane (trade name: ethyl silicate 40, manufactured by Colcoat Co., Ltd.), etc. Can be illustrated.
In addition, it is preferable to use an alcohol such as methyl alcohol or a water-soluble solvent such as acetone in combination with the metal alkoxide because water necessary for the hydrolysis reaction can be dissolved.

  Furthermore, if necessary, a curing catalyst and water necessary for hydrolysis can be added to the alkoxysilane solution. As such curing catalysts, inorganic acids such as hydrochloric acid, sulfuric acid and phosphoric acid, organic acids such as acetic acid, citric acid, maleic acid and malic acid, inorganic bases such as sodium hydroxide, ammonia and tetramethylammonium hydroxide are used. it can.

  However, the present inventors have studied that when an acid or base is used as a catalyst, the reaction of metal alkoxide is promoted and a crosslinking reaction can be caused at a lower temperature. On the other hand, a poorly water-soluble ferrocyanide Will be decomposed and the amount of ferrocyanide ions eluted will increase, so to suppress the dissolution of ferrocyanide ions, instead of adding acid or base as a catalyst, The condensation reaction is preferably carried out by raising the heating temperature or setting the heating time longer.

  Although the said heating conditions will not be specifically limited if it is below the decomposition temperature of the said iron ferrocyanide, In order to fully heat, it is preferable to heat at 100-150 degreeC for 2 hours-3 hours, for example. At that time, it may be heated in an inert gas atmosphere so that the ferrocyanide is not oxidized.

The present invention dissolves a metal salt of a metal whose ionization tendency is lower than that of iron, in which ferrocyanide is solidified with a binder and is formed into a granular solid such as a granule for application to a simple apparatus such as a filtration tower. Accordingly, the present invention provides a method for producing a cesium adsorbent that suppresses the elution of ferrocyanide while maintaining the cesium adsorption performance by reacting with the liquid.
As described above, ferrocyanide is decomposed when cesium is adsorbed from water.

  As a method for quantifying ferrocyanide ion concentration, the method shown in Reference Document 1 (Attachment test method in the notice of the Food Health Department No. 07712001 dated July 12, 2002) is widely known. Ferrocyanide This is a quantitative method in which ferrous sulfate is added to a sample containing ions and the absorbance of the product is measured using light with a wavelength of 720 nm. Reference 2 [Mori, Nishioka, Yamashita, Nozaki, Tsukamoto, Kagawa Prefecture] According to Environmental Health Research Center Bulletin No. 2 pp72-74 (2003)], ferricyanide ions in which iron, the central metal of the complex, is oxidized from divalent to trivalent are the same as ferrocyanide ions. In order to show the absorbance, it is reported that the two cannot be distinguished at a wavelength of 720 nm.

  In this document, as a method for discriminating ferricyanide ions out of these two types of complex ions, it is proposed to use a wavelength of 304 nm or 423 nm, which is a characteristic absorption wavelength of ferricyan ions. The water in which cesium was adsorbed and removed by a cesium adsorbent prepared using ammonium ferrocyanide was analyzed by these two methods, and the ferrocyanide quantified by the method of Reference Document 1 When the ion concentration was compared with the ferricyanide ion concentration determined by the method of Reference Document 2, it was found that a lot of ferricyanide ions were actually contained.

  Therefore, the concentration quantified and reported as ferrocyanide ion in Reference 3 [Hideki Hiraoka, Daisuke Kamiya, Toagosei Group Research Annual Report TREND (16) p31-36 (2013)] is actually ferrocyanide ion. And the total amount of ferricyanide ions.

  In addition, as described in Reference Document 4 [Hayashi Eiko, 2010 Toray Science Education Award Winning Works, pp27-30 (2011)], ferrocyanide ion (also known as hexacyanoferrate (II) ion as anion) ), Ferricyanide ions (also known as hexacyanoferrate (III) ions), and the properties of salts obtained from combinations of divalent and trivalent iron ions as cations. From the combination of ferrocyanide ions and trivalent iron ions, or from the combination of ferricyanide ions and divalent iron ions, amber-colored precipitation can occur in water, and these are the same substance. A combination of ferrocyanide ions and divalent iron can form a white precipitate in water. However, in the combination of ferricyanide ions and trivalent iron ions, precipitation does not occur in water, resulting in a brown liquid.

  Iron ferrocyanide compounds have been previously said to be very stable substances, but as stated above, the present inventors have found that when iron in complex ions is oxidized to ferricyanide ions, The insoluble crystals could not be maintained, and it was thought that ions dissociated and dissolved in water. The amount of dissociation is very small in view of the amount of ferrocyanide used, but it is a problem level in terms of drainage standards as a cyanide compound.

  For this reason, the present inventor considers that the amount of cyanide eluted is reduced if iron ferrocyanide in the vicinity of the surface where oxidation is likely to occur even in the adsorbent is converted to a compound that is more difficult to dissolve. Has been reached. The surface in this case means both the surface of the granule and the surface of the pores in the granule, for example, in the case of a granular adsorbent formed from ferrocyanide.

  In the present invention, iron ferrocyanide is contained in a solution in which a metal salt of a metal having a lower ionization tendency than iron is dissolved in a material containing iron ferrocyanide, such as one formed by solidifying ferrocyanide with a binder. The reaction is performed for a necessary time by a method such as dipping the material, and then the excess metal salt is washed away and dried. Such a treatment provides a method for making it difficult to elute cyanide compounds such as ferrocyanide ions at the time of cesium adsorption.

  The reason why such an effect can be obtained is not clear, but since the effect can be obtained by using a metal salt having a lower ionization tendency than iron as described below, a molded product of ferrocyanide irons. It is estimated that the iron in ferrocyanide melts in the vicinity of the surface including the pore surface inside the metal, and is replaced with a metal with a low ionization tendency, thereby changing to a more stable metal cyano complex salt. .

The metal salt that can be used in the metal salt solution for treating the material containing ferrocyanide in the present invention has a lower ionization tendency of the constituent metal than iron, and the standard electrode potential is −0. It is a metal salt solution of metals higher than 40V.
The ionization tendency of metals is widely known as an order of the susceptibility to ions in a solution of simple metals. Although there are some objections, K> Ca from the order of high ionization tendency. It is widely recognized that the order is>Na>Mg>Al>Zn>Fe>Ni>Sn>Pb>(H)>Cu>Hg>Ag>Pt> Au.

This order can be said to be an order from a low standard electrode potential to a high standard electrode potential. However, since it is easy to be an ion from a single substance, for example, ferrous ions (Fe ²⁺ ), second When iron ions (Fe ³⁺ ) are present, it is appropriate to compare with the standard electrode potential of ferrous ions (Fe ²⁺ ).

  According to Reference 5 [The Chemical Society of Japan, “Chemical Handbook (Basic Edition II)”, revised edition 5, Maruzen, pp581-584 (2004)], the standard electrode potential in an aqueous solution at 25 ° C. for the above metal is K (-2.925V)> Ca (-2.84V)> Na (-2.714V)> Mg (-2.356V)> Al (−1.676V)> Zn (−0.7626V)> Fe (−0.44 V)> Ni (−0.257 V)> Sn (−0.1375 V)> Pb (−1.263 V)> (H) (0 V)> Cu (0.340 V)> Hg (0.7960 V) )> Ag (0.7991 V)> Pt (1.188 V)> Au (1.52 V), which is consistent with the order of ionization tendency.

  The above 16 types of metal and hydrogen ionization tendencies have been used in, for example, Japanese school education and do not cover all metals but have standard electrode potentials that can be used in connection with the present invention. Examples of the metal include Cd (−0.4025V), Co (−0.277V), Sb (0.1504V), and Bi (0.3172). On the other hand, the purpose of the cesium adsorbent is to remove radioactive cesium ions dissolved in water, so if toxic metals dissolve in the water from which cesium has been removed, this must be removed as necessary. Therefore, it is necessary to decide the metal salt to be used in consideration of toxicity.

  Therefore, the metal constituting the preferred metal salt that can be used in the present invention is nickel, cobalt, tin, antimony, bismuth, copper, etc., preferably copper, tin and nickel, and further, the electrode potential with iron The copper salt is most preferable in that it is highly effective in suppressing the elution of cyanide and can be well below the drainage standard (3 mg / l) stipulated in the Japanese Water Pollution Control Law.

  Examples of metal salts that can be used include halide salts, nitrates, sulfates, and organic acid salts such as acetates. The preferred solvent used in the metal salt solution is often water, but the halide can also be dissolved in an alcohol, or can be used in a mixed solvent of water and alcohol.

  The method of reacting the material containing ferrocyanide with the metal salt solution is not particularly limited, but the method of immersing the material containing ferrocyanide in the metal salt solution, or spraying the metal salt solution with ferrocyanide, etc. For example, a method of spraying on a material containing ferric compounds. Any method may be used as long as the material containing the ferrocyanide and the metal salt solution are in contact with each other.

As said reaction temperature, 90 degrees C or less is preferable, More preferably, it is 60 degrees C or less, More preferably, it is 30 degrees C or less. On the low temperature side, there is no particular problem as long as it is above the temperature at which the metal salt solution does not freeze. When the temperature exceeds 90 ° C., the cyanide compound tends to be easily eluted.
Moreover, as reaction time, if it is immersion time, for example, 30 minutes or more and within 24 hours are preferable. If it is less than 30 minutes, the solution may not be sufficiently immersed, and the effect of preventing elution of cyanide may be small, and if it is 24 hours or more, the work efficiency decreases.

  It is preferable to dissolve an acid and / or a chelate compound in the metal salt solution as necessary before or during the reaction with the material containing ferrocyanide.

For example, it is preferable to dissolve a small amount of acid such as hydrochloric acid in a metal salt solution. When the ferric ferrocyanide solidified with a binder is immersed in these liquids, the pH of the liquid may increase, for example, when the silanol group in the silica constituting the binder is a sodium salt or the like. . In this case, the metal ions constituting the metal salt precipitate as hydroxides, and it is difficult not only to remove the precipitates, but also when the precipitates precipitate inside the ferrocyanide compact, When used, it is difficult for cesium ions to enter the molded body, and it is preferable to add an acid for the purpose of preventing such a phenomenon.
If the amount of acid added is too large, the amount of cyanide that elutes when adsorbing cesium using the obtained cesium adsorbent may not be able to be controlled. Is good. More preferably, it is 2-20 mol%, More preferably, it is 5-10 mol%.

  Similarly, a chelate compound is preferably added as a method for preventing the precipitation of hydroxide. There are many types of chelating agents, and there are no particular limitations, but any chelating agent that does not form a hydroxide of these metals by coordination with iron, copper, nickel, tin, cobalt or the like can be used. For example, examples of aminocarboxylic acid-based chelates include ethylenediaminetetraacetic acid (abbreviation EDTA), nitrilotriacetic acid (abbreviation NTA), diethylenetriaminepentaacetic acid (abbreviation DTPA), hydroxyethylenetriacetic acid (abbreviation HEDTA), triethylenetetraminehexaacetic acid ( Abbreviation TTHA), 1,3-propanediaminetetraacetic acid (abbreviation PDTA), 1,3-diamino-2-hydroxypropanetetraacetic acid, hydroxyethyliminodiacetic acid (abbreviation HIDA), dihydroxyethylglycine (abbreviation DHEG), o, o′-bis (2-aminoethyl) ethylene glycol-N, N, N ′, N′-tetraacetic acid (abbreviation GEDTA), L-glutamic acid diacetic acid (abbreviation GLDA), ethylenediaminedisuccinic acid (abbreviation EDDS), and the like. Can be mentioned. Examples of phosphonic acid chelates include hydroxyethylene diphosphonic acid (abbreviation HEDP), nitrilotris (methylenephosphonic acid) (abbreviation NTMP), 2-phosphono-1,2,4-butanetricarboxylic acid, ethylenediaminetetra ( Methylenephosphonic acid) (abbreviation EDTMP) and the like. In addition, bipyridine, citric acid and the like can be mentioned. Among these chelating agents, those that have an acidic group such as EDTA but are not soluble in water may use part or all of the acidic group as sodium salt, potassium salt, etc. in order to increase water solubility. it can.

  Although the addition amount of a chelating agent changes with chelate compounds, when taking EDTA as an example, it is good to set it as 1-100 mol% with respect to the metal salt to add. More preferably, it is 1-50 mol%, More preferably, it is 1-10 mol%.

  After reacting the ferrocyanide and the metal salt solution, it is preferable to wash away the excess metal salt. This is because if excess metal salt remains, the water from which radioactive cesium has been removed may be contaminated with metal ions.

  Also in this case, it is preferable that the remaining metal is easily removed by dissolving an acid or a chelate in the cleaning solution on the same principle as in the case of reacting a material containing an iron ferrocyanide compound with a metal salt solution. Furthermore, although the reason is not clear, if the acid remains, the elution of the cyanide compound may increase during the removal of cesium, and in order to prevent this, the pH of the sodium bicarbonate dissolved in the 7-9 aqueous solution and the chelate dissolved therein It is better to wash with a cleaning solution. Since the cesium adsorbent obtained by the present invention is used to remove water contamination, it is washed with tap water at the end of these washing steps and dried so that unnecessary things do not dissolve. Is preferred.

The cesium adsorbent that has been treated to prevent elution of cyanide compounds such as ferrocyanide ions and ferricyanide ions can be packed in an adsorption tower as it is, and contaminated water containing cesium is supplied to the adsorption tower filled with the cesium adsorbent. Thus, cesium is removed from the contaminated water by contacting with the cesium adsorbent.
The conditions for bringing the cesium adsorbent into contact with the contaminated water are not particularly limited, but conditions such as the adsorbent filling amount and the contaminated water flow rate can be appropriately selected according to the cesium concentration in the contaminated water.

As described above, the method for suppressing the elution of cyanide from a cesium adsorbent in the present invention suppresses the decomposition of ferrocyanide.
On the other hand, the cesium adsorbent in the present invention is treated with an inorganic polymer flocculant such as polyaluminum chloride or polyferric sulfate and then treated with a weak alkaline aqueous solution, or an antioxidant is included in the cesium adsorbent. Use of the method in combination is preferable because elution of ferrocyanide ions and ferricyanide ions can be further suppressed.
When processing with an inorganic type polymer flocculant, it is necessary to perform the said processing method after implementing the method of this invention. This is because an active ingredient such as polyaluminum chloride is dissolved by the presence of an acid.

  In addition, the process of compounding antioxidants when molding ferrous ferrocyanides, or immersing a solution of antioxidants in the molded ferrocyanide and drying, will also dissolve cyanide compounds. It has an inhibitory effect and can be used in combination with the method of the present invention.

Hereinafter, the present invention will be described more specifically with reference to Examples and Comparative Examples.
<Granulation example 1>
800 g ferric ferrocyanide ammonium (Daiichi Seika Kogyo Co., Ltd., trade name MIRORI BLUE 905) and 500 g of colloidal silica dispersion (Nissan Chemical Industry Co., Ltd., trade name Snowtex O40) (200 g as solid content) The mixture was placed in a table kneader and kneaded for 10 minutes.
The mixture obtained by kneading was placed in a stainless steel tray and stretched to a thickness of about 5 mm. This was heated at 70 ° C. for 1 hour in a draft dryer and subsequently heated at 130 ° C. for 3 hours to obtain a lump of dried formulation. This was crushed with a crusher to remove fine particles passing through a sieve having a pore size of 1 mm and large particles not passing through a pore size of 2 mm, thereby obtaining a granular granulated product having a particle size of about 1 to 2 mm. In this state, ferric ferrocyanide ammonium content is 80%.
Next, 96 g of water is added to a solution composed of 500 g of methyl silicate (trade name: Methyl silicate 51, manufactured by Colcoat Co., Ltd.) and 500 g of methanol, and the resulting granulated product is immersed in this solution for 2 hours. After that, the excess solution was removed by filtration, and the granulated material impregnated with the solution was heated again at 120 ° C. for 3 hours with a draft dryer. The obtained product is designated as granulated product 1.
Since the rate of weight increase after completion of the reaction with methyl silicate is about 10%, the ferric ammonium ferrocyanide content in the obtained granulated product is about 73%.

<Granulation example 2>
Granulated product 2 was obtained in the same manner as granulation example 1 except that ferric ferrocyanide (a reagent manufactured by ACROS) was used instead of ferric ferric ammonium.

<Granulation example 3>
Granulated product 3 was obtained in the same manner as granulation example 1 except that ferric potassium ferrocyanide was used in place of ferric ferrocyanide ammonium.
In addition, the potassium ferrocyanide used in the granulation example 3 was synthesized and used in the following procedure. 162.2 g (1 mol) of anhydrous iron (III) chloride was taken and dissolved while adding water to make a total of 2000 ml. In a separate container, dissolve potassium ferrocyanide trihydrate (aka: potassium hexacyanoferrate (II) trihydrate, manufactured by Wako Pure Chemical Industries, Ltd.) 422.4 g (1 mol) while adding water. The total volume was 2000 ml. When the aqueous potassium ferrocyanide solution was added little by little while stirring the prepared aqueous iron chloride solution, a dark blue-colored precipitate was generated, and after the entire amount was mixed, the mixture was further stirred for 5 hours. The product dispersed in this liquid was precipitated with a centrifuge, and the supernatant was discarded. Add 3000 ml of ultrapure water to the container in which the precipitate remained, stir, further centrifuge and discard the supernatant 10 times, then remove the precipitate into an evaporating dish, vacuum dry at 50 ° C. overnight, and then mortar By grinding, 148 g of amber powder was obtained. The X-ray diffraction (XRD) pattern of this powder supported the FCC structure. Since the ratio of iron to potassium was 2.00: 1.04 as analyzed by fluorescent X-ray, this compound was obtained by the FeFe (III) [Fe (II) (CN) ₆ ] ₃ structure. It is potassium ferric Russian. This synthesis operation was repeated to obtain the required amount.

<Granulation example 4>
Granulated product 4 was obtained in the same manner as granulation example 1 except that ferric ferric sodium sodium was used instead of ferric ferric ammonium.
Ferric ferrocyanide sodium was synthesized in Granulation Example 3 except that sodium ferrocyanide decahydrate (reagent manufactured by Wako Pure Chemical Industries, Ltd.) was used instead of potassium ferrocyanide trihydrate. And synthesized and used in the same manner as ferric ferrocyanide potassium.

<Granulation example 5>
Disperse 216 g of ferric ferrocyanide (ACROS reagent) in 20 liters of 4N sulfuric acid, and add 20 liters of sodium silicate (SiO ₂ / Na ₂ O ratio 3.3) silica solution with 18% silica concentration. Then, a silica hydrosol was produced by mixing and reacting, and this was allowed to stand for 1 hour to obtain a gelled silica hydrogel. This was washed with water to remove sodium sulfate, and then 28% by weight aqueous ammonia was added to adjust the pH to 8.0, followed by aging at 80 ° C. for 12 hours. Furthermore, after drying at 120 ° C. for 12 hours with a ventilating dryer, this is crushed with a crusher to remove fine particles passing through a sieve having a pore diameter of 1 mm and large particles not passing through a pore diameter of 2 mm, and the particle size is about 1 A granulated product of ˜2 mm was obtained.
Next, the granulated product obtained in a solution consisting of 96 g of water was immersed in a solution consisting of 500 g of methyl silicate (methyl silicate 51 manufactured by Colcoat Co., Ltd.) and 500 g of methanol, and left for 2 hours. Subsequently, the excess solution was removed by filtration, and the granulated product impregnated with the solution was heated again at 120 ° C. for 3 hours with an air dryer to obtain a granulated product 5 treated with silicate.

<Example 1>
Put 8.6 g (0.064 mol) of cupric chloride and 50 ml of water in a polyethylene container, stir, dissolve uniformly, add water to make a total volume of 64 ml, and add 1.0 mol of cupric chloride. / L aqueous solution was prepared. This is the first immersion liquid. In the following Examples and Comparative Examples 2-5, 10-15, the solution which first immerses the granulated material containing ferrocyanide is used as the first immersion liquid, and its components are described in Table 1 and Table 2. To do. To this first immersion liquid, 5 g of granulated product 1 (content of ferric iron ferric ammonium was about 0.013 mol) was added, and the container was shaken lightly to stir the inside to remove bubbles. When left as it was for 20 hours, a pale precipitate was generated around the granulated material. The contents of the container were poured into a 100 mesh polypropylene net shaped like a funnel to separate and remove excess liquid. Further, the granulated product in the mesh was put in 200 ml of water together with the mesh, and the operation of raising and lowering the mesh several times and pulling it up from the water was repeated three times, and then immersed in 200 ml of water (pH 7) for 1 hour and pulled up with the mesh. Following immersion in the first immersion liquid, the liquid that is simply washed with water and then immersed is used as the second immersion liquid, and the components are listed in Tables 1 and 2. Furthermore, when the mesh is added to 200 ml of fresh water and the mesh is raised and lowered several times and then pulled up from the water repeatedly, the whitish precipitate gradually breaks out and comes out of the mesh. After repeating several times, the white precipitate became almost inconspicuous, so the washing operation was terminated. Next, the granulated material was spread on a glass petri dish. After leaving it in the air for 3 hours, it was put in a dryer and dried at 120 ° C. for 2 hours to obtain a cesium adsorbent.
As a result of a cesium adsorption test conducted using 100 ml of artificial seawater having a pH of 8.2 containing 0.01 ppm of cesium using 0.625 g of this adsorbent, the cesium removal rate after being immersed for 24 hours was 90% or more. On the other hand, the concentration of ferrocyanide ions contained in the water after the test (which can be said to be a quantitative value including ferricyanide ions from the description of Non-Patent Document 3, hereinafter referred to as ferrocyanide ions) is 0.12 ppm. In addition, the elution amount of the ferrocyan compound was greatly reduced as compared with Comparative Examples described later.

<Example 2>
Put 8.6 g (0.064 mol) of cupric chloride, 50 ml of water and 0.64 ml of 1N hydrochloric acid in a polyethylene container, stir, dissolve uniformly, and then add water to make the total volume 64 ml. An aqueous solution of 1.0 mol / l cupric copper and 0.01 mol / l hydrochloric acid was prepared. 5g of granulation example 1 was added here, the container was shaken lightly, the inside was stirred, and the bubble was removed. When left as it was for 20 hours, no whitish precipitate was observed. The contents of the container were poured into a 100 mesh polypropylene net shaped like a funnel to separate and remove excess liquid. Further, the granulated product in the mesh was put in 200 ml of water together with the mesh, and the operation of raising and lowering the mesh several times and pulling it up from the water was repeated three times, and then immersed in 200 ml of water (pH 7) for 1 hour and pulled up with the mesh. Further, the entire mesh was put in 200 ml of new water, and the operation of raising and lowering the mesh several times and then pulling it up from the water was repeated three times to complete the washing operation. Next, the granulated material was spread on a glass petri dish. After leaving it in the air for 3 hours, it was put in a dryer and dried at 120 ° C. for 2 hours to obtain a cesium adsorbent.
As a result of conducting the cesium adsorption test similar to Example 1 about this adsorbent, the cesium removal rate was 90% or more. On the other hand, the concentration of ferrocyanide ions contained in the water after the test was 0.12 ppm, and the elution amount of the ferrocyanide compound was greatly reduced as compared with Comparative Examples described later.

<Example 3>
Subsequent to the operation of immersing in an aqueous solution of cupric chloride 1.0 mol / l and hydrochloric acid 0.01 mol / l and rinsing with water, a solution immersed for 1 hour (second immersion solution) is a 1% aqueous sodium bicarbonate solution (pH 8). .5) A cesium adsorbent was obtained in the same manner as in Example 2 except that
As a result of conducting the cesium adsorption test similar to Example 1 about this adsorbent, the cesium removal rate was 90% or more. On the other hand, the concentration of ferrocyanide ions contained in the water after the test 1 was 0.12 ppm, and the elution amount of the ferrocyan compound was greatly reduced as compared with the comparative examples described later.

<Examples 4 and 5>
A cesium adsorbent was obtained in the same manner as in Example 2 except that the hydrochloric acid concentration of the granule immersion treatment solution was 0.1 mol / l in Example 4 and 0.5 mol / l in Example 5.
As a result of conducting a cesium adsorption test similar to Example 1 for these adsorbents, the cesium removal rate was 90% or more in both Examples 4 and 5. On the other hand, the concentration of ferrocyanide ions contained in the water after the test was 0.52 ppm in Example 4 and 0.89 ppm in Example 5. Although the elution amount of the ferrocyan compound was smaller than that of the comparative example described later, there was a tendency that the effect of inhibiting the elution of the ferrocyan compound decreased as the concentration of hydrochloric acid used in the first immersion liquid increased.

<Example 6>
Instead of hydrochloric acid, 0.52 g of a 50% aqueous solution of tripotassium ethylenediaminetetraacetate (abbreviated symbol EDTA3K) (manufactured by Nagase ChemteX Corporation, trade name Clewat 3K, specific gravity 1.33) is added, and 1.0 mol of cupric chloride is added. A cesium adsorbent was obtained in the same manner as in Example 2 except that an aqueous solution of EDTA3K 0.01 mol / l was prepared. In this case, even when the granulated product 1 was immersed in an aqueous cupric chloride solution for 20 hours, no whitish precipitate was observed.
As a result of conducting the cesium adsorption test similar to Example 1 about this adsorbent, the cesium removal rate was 90% or more. On the other hand, the concentration of ferrocyanide ions contained in the water after the test was 0.20 ppm, and the elution amount of the ferrocyan compound was greatly reduced as compared with the comparative examples described later.

<Example 7>
An aqueous solution of nickel chloride 1.0 mol / l and hydrochloric acid 0.01 mol / l was prepared using 15.2 g of nickel chloride hexahydrate (NiCl ₂ .6H ₂ O) instead of cupric chloride. Except for the above, a cesium adsorbent was obtained in the same manner as in Example 2.
As a result of conducting the cesium adsorption test similar to Example 1 about this adsorbent, the cesium removal rate was 90% or more. On the other hand, the concentration of ferrocyanide ions contained in the water after the test was 1.1 ppm, and the elution amount of the ferrocyan compound decreased compared to the comparative example described later.

<Example 8>
A cesium adsorbent was obtained in the same manner as in Example 7 except that the hydrochloric acid concentration in the granulated product immersion treatment liquid was changed to 0.1 mol / l.
As a result of conducting the cesium adsorption test similar to Example 1 about this adsorbent, the cesium removal rate was 90% or more. On the other hand, the concentration of ferrocyanide ions contained in the water after the test was 1.3 ppm. The elution amount of the ferrocyan compound was small as compared with the comparative examples described later.

<Example 9>
Subsequent to the operation of immersing in a 1.0 mol / l aqueous solution of cupric chloride and washing with water, the liquid immersed for 1 hour (second immersion liquid) was changed to an EDTA3K 0.01 mol / l aqueous solution (pH 7.7). A cesium adsorbent was obtained in the same manner as in Example 1.
As a result of conducting the cesium adsorption test similar to Example 1 about this adsorbent, the cesium removal rate was 90% or more. On the other hand, the concentration of ferrocyanide ions contained in the water after the test was 0.21 ppm, and the elution amount of the ferrocyanide compound was greatly reduced as compared with Comparative Examples described later. In addition, a pale precipitate was generated during immersion in the aqueous cupric chloride solution as in Example 1. However, even when hydroxide precipitation occurred, it was considered that the precipitate was easily removed by immersion in the solution containing the chelate compound. It is done.

<Example 10>
Subsequent to the operation of immersing in an aqueous solution of cupric chloride 1.0 mol / l and hydrochloric acid 0.01 mol / l and rinsing with water, the liquid immersed for 1 hour (second immersion liquid) is EDTA3K 0.01 mol / l, 1% A cesium adsorbent was obtained in the same manner as in Example 2 except that an aqueous sodium hydrogen carbonate solution (pH 8.4) was used.
As a result of conducting the cesium adsorption test similar to Example 1 about this adsorbent, the cesium removal rate was 90% or more. On the other hand, the concentration of ferrocyanide ions contained in the water after the test was 0.13 ppm, and the elution amount of the ferrocyanide compound was greatly reduced as compared with Comparative Examples described later.

<Example 11>
Example 1 was used except that 16.0 g of copper sulfate pentahydrate was used in place of cupric chloride to prepare an aqueous solution of copper sulfate 1.0 mol / l and hydrochloric acid 0.01 mol / l. A cesium adsorbent was obtained.
As a result of conducting the cesium adsorption test similar to Example 1 about this adsorbent, the cesium removal rate was 90% or more. On the other hand, the concentration of ferrocyanide ions contained in the water after the test was 0.14 ppm, and the elution amount of the ferrocyanide compound was greatly reduced as compared with Comparative Examples described later.

<Examples 12 to 15>
In place of granulated product 1, granulated product 2 in Example 12, granulated product 3 in Example 13, granulated product 4 in Example 14, and granulated product 5 in Example 15 were used. A cesium adsorbent was obtained in the same manner as in Example 2.
These adsorbents were subjected to the same cesium adsorption test as in Example 1, and as a result, the cesium removal rate was 90% or more. On the other hand, the concentrations of ferrocyanide ions contained in the water after the test are 0.10 ppm, 0.25 ppm, 0.28 ppm, and 1.4 ppm in Examples 12 to 15, respectively. Compared with the comparative example using the product, the elution amount of the ferrocyan compound was greatly reduced.

<Comparative Example 1>
The granulated product 1 was directly subjected to the same cesium adsorption test as in Example 1. As a result, the cesium removal rate was 90% or more. On the other hand, the concentration of ferrocyanide ions contained in the water after the test was 2.2 ppm, and the elution amount of the ferrocyanide compound was larger than that of the example.

<Comparative example 2>
A cesium adsorbent was obtained in the same manner as in Example 1 except that the granulated product 1 was immersed in ultrapure water for 20 hours instead of the copper chloride aqueous solution.
The adsorbent was subjected to the same cesium adsorption test as in Example 1. As a result, the cesium removal rate was 90% or more. On the other hand, the concentration of ferrocyanide ions contained in the water after the test was 1.9 ppm, and the amount of ferrocyanide compound eluted was larger than that of the Example, which was a result close to the result of Comparative Example 1. It was found that no effect was obtained with water containing no salt such as copper chloride.

<Comparative Examples 3-5>
The granulated product 1 was replaced with a 0.01 mol / l salt aqueous solution of hydrochloric acid in Comparative Example 3 instead of an aqueous copper chloride solution, a 0.1 mol / l aqueous solution of hydrochloric acid in Comparative Example 4, and a 0.5 mol / l aqueous solution of hydrochloric acid in Comparative Example 5 A cesium adsorbent was obtained in the same manner as in Example 1 except that each was immersed for 20 hours.
Each of these adsorbents was subjected to the same cesium adsorption test as in Example 1, and as a result, the cesium removal rate was 90% or more. On the other hand, the concentration of ferrocyanide ions contained in the water after the test is 2.0 ppm in Comparative Example 3, 2.8 ppm in Comparative Example 4, and 6.7 ppm in Comparative Example 5, and is a ferrocyan compound compared to Examples. The elution amount of was increased, and the elution of the ferrocyan compound tended to increase as the concentration of hydrochloric acid in the immersion liquid increased.

<Comparative Examples 6-9>
Instead of the granulated product 1, the granulated product 2 was used in Comparative Example 6, the granulated product 3 was used in Comparative Example 7, the granulated product 4 was used in Comparative Example 8, and the granulated product 5 was used in Comparative Example 9 as it was. As a result of performing the same cesium adsorption test as in Example 1, the cesium removal rate was 90% or more. On the other hand, the concentration of ferrocyanide ions contained in the water after the test is 1.8 ppm in Comparative Example 6, 2.6 ppm in Comparative Example 7, 2.7 ppm in Comparative Example 8, and 3.8 ppm in Comparative Example 9, The elution amount of the ferrocyan compound was larger than that in the example.

<Comparative Examples 10-12>
In Comparative Example 10, the metal salt solution to be immersed was 1.0 mol / l of zinc chloride and 0.01 mol / l aqueous solution of hydrochloric acid, and in Comparative Example 11, 1.0 mol / l of zinc chloride and 0.1 mol / l aqueous solution of hydrochloric acid, Comparative Example 12 Then, a cesium adsorbent was obtained in the same manner as in Example 2 except that the aqueous solution was zinc chloride 1.0 mol / l and hydrochloric acid 0.5 mol / l.
Each of these adsorbents was subjected to the same cesium adsorption test as in Example 1, and as a result, the cesium removal rate was 90% or more. On the other hand, the concentrations of ferrocyanide ions contained in the water after the test were 3.2 ppm in Comparative Example 10, 5.2 ppm in Comparative Example 11, and 9.4 ppm in Comparative Example 12, which are ferrocyan compounds compared to Examples. There was a tendency that the elution amount of the ferrocyan compound increased as the hydrochloric acid concentration in the immersion liquid increased. Thus, zinc chloride had no effect of inhibiting elution of ferrocyanide compounds.

<Comparative Examples 13-15>
In Comparative Example 13, the metal salt solution to be immersed was 1.0 mol / l of iron (III) chloride, an aqueous solution of 0.01 mol / l hydrochloric acid, and in Comparative Example 14, 1.0 mol / l of iron (III) chloride, 0.1 mol / l of hydrochloric acid. The aqueous cesium adsorbent was obtained in the same manner as in Example 2, except that the aqueous solution of Comparative Example 15 was 1.0 mol / l of iron (III) chloride and 0.5 mol / l of hydrochloric acid.
Each of these adsorbents was subjected to the same cesium adsorption test as in Example 1, and as a result, the cesium removal rate was 90% or more. On the other hand, the concentration of ferrocyanide ions contained in the water after the test was 2.1 ppm in Comparative Example 13, 2.7 ppm in Comparative Example 14, and 7.9 ppm in Comparative Example 15, which is a ferrocyan compound compared to Examples. There was a tendency that the elution amount of the cyanide compound increased as the concentration of hydrochloric acid in the immersion liquid increased. Thus, iron (III) chloride did not have an effect of inhibiting elution of ferrocyan compound.

  About Examples 1-15, the composition of immersion liquid and the result of the cesium adsorption test were put together in Table 1.

  About Comparative Examples 1-15, the composition of immersion liquid and the result of the cesium adsorption test were put together in Table 2.

<Evaluation method>
Preparation of artificial seawater containing cesium Ultra pure water equipment (Advantech Toyo Co., Ltd.) made of cesium chloride and artificial seawater (Nippon Pharmaceutical Co., Ltd., trade name: Daigo Artificial Seawater SP) so that the cesium concentration becomes 0.01 ppm. It adjusted using the ultrapure water obtained using brand name: RFU554CA), and simulated cesium pollution seawater was adjusted.

<Evaluation method for immersing adsorbent in seawater containing a certain amount of cesium>
0.625 g of the cesium adsorbent prepared in each Example and Comparative Example and 50 ml of the simulated contaminated water were placed in a 100 ml polyethylene container and shaker (trade name: WATER BATH INCUBATOR MODEL BT- manufactured by Yamato Scientific Co., Ltd.). In 3), the mixture was shaken at room temperature of 25 ° C. for 24 hours, and then filtered through a membrane filter having a pore size of 0.45 μm, and the concentrations of cesium and ferrocyanide ions and the metal concentration were quantified by the following method.

<Quantitative method of cesium>
After 1 ml of nitric acid was added to 1 g of the filtrate obtained by the above filtration, it was diluted 100 times with ultrapure water, and further 0.2 ml of nitric acid was added to 2 g of the diluted solution, and then diluted 10 times with ultrapure water. An analytical solution was obtained.
Using an ICP mass spectrometer (trade name Agilent 7500cs, manufactured by Agilent Technology Co., Ltd.) as an analysis solution, a calibration curve was obtained using simulated contaminated water prepared in advance as a cesium concentration standard solution, and the cesium concentration of the sample was quantified.

<Quantification method of ferrocyanide ion concentration>
Add 3 g of ferrous sulfate heptahydrate to a 100 ml volumetric flask, add 80 ml of water, add 1 ml of sulfuric acid to dissolve uniformly, and then add pure water to make 100 ml to make a ferrous sulfate aqueous solution. did. 2 g of water after the cesium adsorption test and 0.5 ml of the aqueous ferrous sulfate solution prepared previously were placed in a 20 ml volumetric flask, and the whole was adjusted to 20 ml with pure water. After 30 minutes, the absorbance at a wavelength of 720 nm was measured using a UV-VIS spectrophotometer (V-550 manufactured by JASCO Corporation), and compared with a calibration curve prepared in advance using an aqueous potassium ferrocyanide solution, ferrocyanide ions The concentration was quantified. This method is a quantification method by a colorimetric method that is widely known based on Reference Document 1. According to Reference Document 2, ferricyanide ions in which the central metal of the complex is oxidized are ferrocyanide ions. It is reported that they cannot be distinguished from each other because they show the same absorbance. In Reference 2, since the absorbance characteristics at 720 nm are similar for both ferrocyanide ions and ferricyanide ions, it can be used as a method for quantifying the total amount of these cyano complexes. It can be said that it is appropriate to use it for investigating the immersion effect.

Claims (5)

Seen containing a material containing at least consisting of ferrocyanide ions and iron ions ferrocyanide ferrous metal, a step of standard electrode potential reacting a high metal of the metal salt solution than -0.40V,
The material containing iron ferrocyanide is formed by solidifying ferrocyanide iron with a binder,
A method for producing a cesium adsorbent , wherein the binder is a metal oxide .   The method for producing a cesium adsorbent according to claim 1, wherein an acid and / or a chelate compound is dissolved in a metal salt solution to be reacted with a material containing ferrocyanide. 3. The cesium adsorbent according to claim 1, wherein after the step of reacting the ferrocyanide-containing material and the metal salt solution, a step of contacting any of the following liquids is performed. Manufacturing method.
(1) A step of contacting a solution having a pH of 7 to 9.
(2) The process made to contact the solution of a chelate compound.
(3) A step of contacting a solution containing a chelate compound having a pH of 7 to 9.
(4) The process which makes acidic aqueous solution contact, and is subsequently made to contact the solution of pH 7-9.   The ferric ferrocyanide is any one of ferric ferrocyanide, ferric ammonium ferrocyanide, sodium ferrocyanide and potassium ferrocyanide. The manufacturing method of the cesium adsorbent in any one.   The method for producing a cesium adsorbent according to any one of claims 1 to 4, wherein the metal element constituting the metal salt contained in the metal salt solution is copper, tin or nickel.