JP2014077720A - Cation adsorbent particle and manufacturing method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide cation adsorbent particles with a high mechanical strength used for removing and collecting radioactive materials, which are easily separated from decontamination objects while ensuring removal performance of radioactive material.SOLUTION: The manufacturing method of cation adsorbent particles includes the steps of: preparing a slurry by mixing a dispersion liquid of nanoparticle inorganic ion exchangers with a solution containing a gel material; forming a capsule-like structure which has a surface layer of gel enriched with calcium and contains nanoparticle inorganic ion exchangers being dispersed therein by allowing the slurry to come into contact with a solution which contains calcium; and forming the particles by drying the capsule-like structure to solidify the same.

Description

  The present invention relates to cation adsorbent particles and a method for producing the same.

Research has been conducted on the use of ion exchange materials as a method for separating and removing specific radioactive elements from radioactive liquid waste discharged as a result of nuclear power generation or the like. Ions to be separated / removed are radioactive elements such as cesium, strontium, and americium.
If a large amount of radioactive material is diffused due to unspecified reasons such as an accident at a nuclear power plant or related facility, it is necessary to remove, recover, and reduce the volume from the environment. Among them, cesium 134 and cesium 137, which are radioactive elements, are known to be scattered over long distances, and countermeasures thereof are a major issue. More specifically, it is the diffusion of radioactive materials originating from the accident at the Fukushima Daiichi Nuclear Power Station that occurred after March 2011. Among the radioactive materials diffused in this accident, cesium 134 and cesium 137 became particularly problematic after a long time in an area some distance away. From this, this removal, collection | recovery, and the volume reduction method are calculated | required (nonpatent literature 1, nonpatent literature 2).

The collection of outdoor radioactive materials such as farmland, schoolyards, building outer walls and roads is often performed by washing with water, and in this case, a liquid (contaminated water) containing a large amount of radioactive materials is generated. There is also a method of recovering radioactive material by crushing the surface of a building or pavement surface. In this case as well, a large amount of contaminated water is recovered by recovering the radioactive material by washing the fragments with water or acid. Will occur.
Furthermore, a large amount of contaminated water is generated by cooling a damaged nuclear reactor.

  A cation adsorbent such as zeolite or Prussian blue particles can be used to recover the radioactive substances in the contaminated water (Patent Document 1, Patent Document 2, Patent Document 3, and Non-Patent Document 1). Radioactive material recovery methods using cation adsorbents such as zeolite and Prussian blue include adsorption methods using non-woven fabrics carrying cation adsorbents and adsorption methods using coagulant precipitation agents. There has been a problem that the nonwoven fabric or the like adsorbing the substance and the coagulating precipitation agent are bulky both in terms of mass and volume, and the effect of substantially reducing the volume of contaminants is small.

A method of stirring Prussian blue particles themselves in contaminated water and a method of passing contaminated water through a column packed with Prussian blue particles themselves are considered. There have been problems such as falling, clogged columns, and particles that have fallen into the decontaminated product.
As a cesium separation / recovery agent combined with a carrier, sodium alginate and an inorganic ion exchanger were kneaded and then immersed in an aqueous calcium chloride solution to use a calcium alginate gel as a carrier, and this supported an inorganic ion exchanger. The structure has been reported (Patent Document 3, Non-Patent Document 3). However, since this method proceeds the reaction until it completely gels to the inside, it takes a long time to synthesize, and it is difficult to construct a structure having a large size of 1 mm or more and to obtain strong particles. .

JP 2000-84418 A Japanese Patent Laid-Open No. 9-173832 Japanese Patent Application No. 2001-164326

2011 Atomic Energy Society Autumn Meeting Special Symposium on Fukushima Daiichi Nuclear Power Station Accident Japan Atomic Energy Agency /20110919yamagishi.pdf] Ministry of Economy, Trade and Industry Disaster Waste Safety Evaluation Study Group (5th) [http://www.env.go.jp/jishin/attach/haikihyouka_kentokai/05-mat_1.pdf] WM’02 Conference, February 24-28, 2002, Tucson, AZ [http://www.wmsym.org/archives/2002/Proceedings/17/277.pdf]

  An object of the present invention is to provide a cation adsorbent particle having high mechanical strength and easy separation from a decontamination target while ensuring the ability to remove the radioactive material, which is used for the removal and recovery of the radioactive material. An object of the present invention is to provide a technique that can be manufactured in a timely manner and that can flexibly change the size of particles.

  In order to solve the above-mentioned problems, the inventors of the present invention have first made a capsule-like structure having a gel-like surface layer enriched with calcium and containing dispersed nano-particle inorganic ion exchangers. Then, by drying, it is possible to easily produce spherical particles with a narrow particle size distribution width, high mechanical strength, and easy separation from the decontamination target, while ensuring the ability to remove radioactive substances. Found a method with easy size control.

That is, the present invention relates to the following.
[1] A method for producing cation adsorbent particles, the step of preparing a slurry by mixing a dispersion of nanoparticle inorganic ion exchanger with a solution containing a gel raw material,
The slurry is brought into contact with a solution containing calcium to form a capsule-like structure having a gel-like surface layer enriched with calcium and containing dispersed nano-particle inorganic ion exchangers, and drying The said manufacturing method including the process of solidifying a capsule-like structure and shape | molding particle | grains.
[2] The nanoparticle inorganic ion exchanger is represented by the following formula (A):
A _p Fe [Fe (CN) ₆ ] _y · zH ₂ O (A)
Where
A is an atom derived from a cation, p is a number from 0 to 2, y is a number from 0.6 to 1.5, and z is a number from 0.5 to 10;
The production method according to [1], which is Prussian blue represented by:
[3] The method according to [1] or [2], wherein the gel raw material is sodium alginate.
[4] The production method according to any one of [1] to [3], wherein the capsule-like structure is dried in a state in which the inside is not completely gelled and contains a dispersion of the nanoparticle inorganic ion exchanger. .
[5] Cation adsorbent particles produced by the production method according to any one of [1] to [4].
[6] The nanoparticle inorganic ion exchanger is represented by the following formula (A):
A _p Fe [Fe (CN) ₆ ] _y · zH ₂ O (A)
Where
A is an atom derived from a cation, p is a number from 0 to 2, y is a number from 0.6 to 1.5, and z is a number from 0.5 to 10;
The cation adsorbent particle according to [5], which is Prussian blue represented by:
[7] The following formula (A)
A _p Fe [Fe (CN) ₆ ] _y · zH ₂ O (A)
Where
A is an atom derived from a cation, p is a number from 0 to 2, y is a number from 0.6 to 1.5, and z is a number from 0.5 to 10;
Cationic adsorbent particles formed by supporting and combining Prussian blue nanoparticles represented by

According to the production method of the present invention, an adsorbent containing an inorganic ion exchanger such as Prussian blue, which is rich in cation adsorption such as Cs, can be produced easily and in large quantities continuously. The resulting particles are spherical and have a narrow particle size distribution and high surface strength. For this reason, the adsorption tower and the adsorption column can be easily packed, the generation of fine powder due to the rubbing and contact of the particles is small, and the elution of the adsorbent and the like can be avoided.
In large-scale adsorption towers and adsorption columns, particle destruction becomes a problem due to the self-weight of the particles and the pressure associated with liquid flow. Since the broken particles and fine powder are mixed into the object to be processed or clogged in the piping, these preventions are important problems. However, the particles obtained by the present invention have sufficient strength and can be used for large-scale adsorption towers and the like. Further, the particles used in the adsorption column may be desirably particles having a relatively large size exceeding 1 mm in order to ensure the speed of passing water to be treated. By using the method of the present invention, such an adsorbent exceeding 1 mm can be produced.

It is a measurement result of the particle size distribution of the particle 5 produced in Example 6. 2 is a photograph of particles 1 produced in Example 2. 3 is a measurement result of particle size distribution of particles 1 produced in Example 2. FIG. It is a figure which shows the result of the adsorption | suction characteristic test (shaking method) of cesium. It is a figure which shows the result of the adsorption characteristic test (column method) of cesium.

In the present invention, the cation adsorbent particles have a gel-like surface layer enriched with calcium, and a capsule-like structure containing nanoparticle inorganic ion exchangers dispersed therein is first prepared, and then the capsule-like structure is formed. It is obtained by a production method including a step of drying the body, and as a result, particles having high strength and adsorbent content can be formed.
The cation adsorbent particles of the present invention typically comprise a step of preparing a slurry by mixing a dispersion of nanoparticle inorganic ion exchanger with a solution containing a gel raw material (slurry preparation step), and the slurry. A step of forming a capsule-like structure having a surface layer enriched with calcium by being brought into contact with a calcium-containing solution and containing a nanoparticle inorganic ion exchanger dispersed therein (capsule-like structure forming step), drying Thus, it is obtained from a process including a step (particle forming step) of solidifying the capsule structure and forming strong particles.

The cation adsorbent particles in the present invention are those that adsorb and recover cations by the ion exchange ability of the nanoparticle inorganic ion exchanger contained in the particles. Accordingly, it is possible to select a nanoparticle inorganic ion exchanger having high selectivity for the cation that is the target of adsorption recovery.
Examples of the nanoparticle inorganic ion exchanger include A-type zeolite that selectively adsorbs strontium ions and Cyanex 302 that selectively adsorbs palladium.
For the purpose of adsorption / recovery of cesium, in addition to Prussian blue, Prussian blue analog fine particles in which some of the iron atoms of Prussian blue are replaced with copper, zinc, nickel, etc., zeolite, bentonite, crown ether, titanium Examples thereof include silicates, and Prussian blue and Prussian blue analogues are preferable, and Prussian blue is more preferable from the viewpoint of the adsorption ability of radioactive substances.

  The primary particle diameter of the nanoparticle inorganic ion exchanger is not limited to this, but is typically 1 to 50 nm, preferably 1 to 20 nm. The reason why the mechanical strength of the particles of the present invention is extremely high is not necessarily clear. However, since the nanoparticles have a large surface energy, the particles are likely to condense, which may be involved in the strength of the particles of the present invention.

In particular, the following formula (A)
A _p Fe [Fe (CN) ₆ ] _y · zH ₂ O (A)
Where
A is an atom derived from a cation, p is a number from 0 to 2, y is a number from 0.6 to 1.5, and z is a number from 0.5 to 10;
Prussian blue represented by
Preferably, iron ions forming hexacyanoiron ions are +2 valent, and other iron ions are +3 valent.
A is an atom derived from a cation. Examples of the cation include monovalent ions such as alkali metal ions and ammonium ions.
p is a number from 0 to 2; In order to improve the dispersibility, it is preferable to increase the number.
y is a number from 0.6 to 1.5. Prussian blue crystals currently marketed as pigments have a y value of 1. This value is closely related to the water solubility of the nanoparticles and is also derived from the defect structure inside the lattice. Regarding the former, the dispersibility is remarkably increased by increasing the proportion of hexacyano iron ions in the ions exposed on the surface of the nanoparticles. This is thought to be due to the fact that the surface of the nanoparticles is negatively charged due to the occupation of hexacyanoiron ions, thereby improving the dispersibility in a polarizing solvent such as water. That is, dispersibility can be improved by increasing y.

  On the other hand, the amount of lattice defects of hexacyanoiron ions in the lattice is also important for the value of y. Including estimation, Prussian blue nanoparticles obtained in the present invention contain a large amount of hexacyanoiron ion lattice defects in the lattice, and it is understood that water is coordinated to the lattice defect portion. The This is estimated from the high water content of the nanoparticles obtained by the present invention described later, that is, a large z. That is, more water can be present in the crystal, and as a result, it is understood that this has the effect of increasing the adsorptivity of cations such as Cs.

  When producing insoluble nanoparticles, y is preferably 0.7 to 0.8, and more preferably 0.74 to 0.76. On the other hand, when producing water-soluble nanoparticles, y is preferably 0.85 to 1.2, and more preferably 0.85 to 0.96. For example, when 0.8 to 0.85 is selected as the value of y, nanoparticles having a high viscosity can be obtained although they are dispersed in water to some extent. This may be particularly effective when used in a process such as carrying the nanoparticles on an organic member. On the other hand, when y exceeds 1.0, it is possible to generate thixotropy, that is, a characteristic that the viscosity increases with time. By using a material having a high viscosity, it becomes easy to maintain the shape of the slurry prepared in the slurry preparation step, and as a result, it becomes easy to give flexibility to the formability of the final adsorbent.

z is 0.5 or more, and preferably 1 to 10. It is more preferably 2 to 8, and further preferably 3 to 8. The moisture content referred to here is a value in a state where drying is continued to a certain extent after standing still in room conditions (for example, 25 ° C., relative humidity 40%, 24 hours). Of course, when Prussian blue is in a wet state, z can be increased in any way, but such an increased value usually does not affect the adsorption capacity.
It is preferable that the coordination number (z) of this water is 0.5 or more, and it is considered that the larger the value, the higher the cation adsorptivity. The reason for this, including estimation, is that, as described above, it is understood that cations such as Cs are not only adsorbed on the crystal surface but also absorbed in the crystal, and are absorbed by the water in the crystal. It is thought that it is efficiently transported to the inside and a larger amount of cations are adsorbed.

  The dispersion of the nanoparticle inorganic ion exchanger in the slurry preparation step of the production method of the present invention refers to a dispersion of the nanoparticle inorganic ion exchanger in the solution. The dispersed state here refers to a state in which the nanoparticle inorganic ion exchanger is uniformly present in the solution during the time for which the capsule-shaped structure forming step is performed. That is, it is not necessary to maintain the state for a very long time, and in that sense, not only the dispersed state and the dissolved state that are generally used, but also the suspended state is not limited to the nanoparticle inorganic ion exchange in the capsule structure forming process. It's good if body precipitation doesn't matter. As the dispersion solvent, water, an organic solvent, a mixture of an organic solvent and water, or the like can be used. Examples of the organic solvent include alcohols such as methanol and ethanol, and toluene. Water is preferable from the viewpoints of economy and safety. In the case where it is insoluble or hardly soluble in water, it can be used after being dispersed in an organic solvent using a nitrogen-containing dispersant or the like. Examples of the nitrogen-containing dispersant include amine compounds having an alkyl group having 3 to 20 carbon atoms (including pyridine compounds), but the number of carbon atoms is 3 to 6 in order to efficiently carry out the drying step in the particle forming step. Is preferable, and 3 and 4 are particularly preferable. At this time, the alkyl group may have an unsaturated bond, and may be an alkenyl group or an alkynyl group. Specific examples include oleylamine, stearylamine, propylamine, hexylamine and the like. Regarding the nitrogen-containing dispersant, the pamphlet of International Publication No. 2008/081923 can be referred to. The organic solvent for dissolving or dispersing Prussian blue is not particularly limited, and examples thereof include toluene, hexane, octane, and methyl acetate.

In the present invention, the dispersion of the nanoparticle inorganic ion exchanger may contain impurities such as other salts or ions, and may contain additives such as a surfactant.
In the present invention, the concentration of the nanoparticle inorganic ion exchanger in the dispersion of the nanoparticle inorganic ion exchanger is not particularly limited as long as the ion exchanger is dispersed, but typically 20 wt% to It is 0.1% by weight, preferably 10% by weight to 1% by weight, more preferably 5% by weight to 1% by weight.

  In the present invention, the gel raw material is not particularly limited as long as it can generate a gel by ion exchange with calcium ions and can ensure the strength of the cation adsorbent particles. Sodium alginate, gellan gum, carrageenan, gelatin, carboxymethylcellulose calcium and the like, and sodium alginate is particularly preferable from the viewpoint of increasing the strength of the gel film formed on the surface. Moreover, 1 type or 2 or more types of gel raw materials can also be used in combination.

As the solvent of the solution containing the gel raw material, water, an organic solvent, a mixture of an organic solvent and water, or the like can be used. Examples of the organic solvent include alcohols such as methanol and ethanol, and toluene. Water is preferable from the viewpoint of safety and price.
In the present invention, the solution containing the gel raw material may contain a surfactant.
The concentration of the gel raw material in the solution containing the gel raw material is not particularly limited as long as the gel raw material is dissolved, but typically 0.5 wt% to 5.0 wt%, preferably 1.0 wt%. -3.0 wt%.

In this invention, a slurry is obtained by mixing the dispersion liquid of a nanoparticle inorganic ion exchanger and the solution containing a gel raw material. The slurry here may also be uniform during the time of forming a gel-like coating on the surface in the capsule-shaped structure forming step, and is not only in a dissolved state or a dispersed state, but also in a suspended state. Etc.
The mixing ratio is important from the viewpoint of increasing the content of the nanoparticle inorganic ion exchanger contained in the final particulate adsorbent, and it is desirable to increase the ratio of the nanoparticle inorganic ion exchanger as much as possible. Typically, the ion exchanger is 50 to 84% by weight, preferably 70 to 82% by weight, particularly preferably 75 to 81% by weight, based on the gel raw material.
The method for mixing the dispersion of the nanoparticle inorganic ion exchanger and the sodium alginate solution is not particularly limited as long as it can be uniformly dispersed. For example, mechanical stirring can be used, and mixing by ultrasonic waves can also be used. .

Although the solution containing calcium will not be specifically limited if a calcium ion is included in a solution, For example, a calcium salt solution is mentioned. The calcium salt is not limited as long as it is a compound that dissociates in a solution and releases calcium ions, and organic calcium salts and inorganic calcium salts can be used. For example, calcium chloride, calcium nitrate, calcium acetate, calcium citrate and the like can be mentioned.
As a solvent of the solution containing calcium, water, alcohol, a mixture of alcohol and water, or the like can be used. Furthermore, pH adjustment and the like can be performed as necessary.

  When the calcium-containing solution is a calcium salt solution, the concentration of the calcium salt is not particularly limited as long as the calcium salt is dissolved, but typically 0.5 wt% to 20.0 wt%, preferably It is 1.0% by weight to 10.0% by weight, more preferably 1.0% by weight to 5.0% by weight.

  In the present invention, the mixing method of the slurry obtained by mixing the dispersion of the nanoparticle inorganic ion exchanger and the solution containing the gel raw material and the solution containing calcium is not particularly limited. For example, the former is the latter solution. There is a method of dropping into a granular composite ion exchanger. In addition, when the viscosity of the slurry is sufficiently high, a method of immersing in a solution containing calcium after making it into a fiber with an extruder or the like can also be used. From the viewpoint of obtaining spherical particles having a narrow particle size distribution width, the former is preferably dropped into the latter solution.

In the present invention, a gel-like surface layer enriched with calcium is formed on the surface of the obtained product by mixing the dispersion of the nanoparticle inorganic ion exchanger and the solution containing the gel raw material. Thus, a capsule-like structure in which the nanoparticle inorganic ion exchanger is dispersed in a strong surface layer enriched with calcium is formed. The capsule shape typically has an outer shell and contains a substance inside. The outer shell may be a gel-like film.
What is important here is that it is not necessary to gel all of the capsule-like structure. The inside does not have to be gelled, and even if it contains a dispersion liquid of nanoparticle inorganic ion exchanger in liquid form, it can produce a strong adsorbent by drying and solidifying in the next particle forming step. It becomes possible. From this, the present invention can produce a granular adsorbent in a short time.
Therefore, the capsule-like structure in which the nanoparticle inorganic ion exchanger of the present invention is dispersed and contained has a strong gel-like surface layer enriched with calcium in one embodiment, where the surface layer is an inorganic nanoparticle. An ion exchanger may be included, and the inside of the surface layer is in a gel or slurry in which nanoparticle inorganic ion exchangers are dispersed or a mixed form thereof. That is, a gel body or a slurry or a mixed form thereof can be a carrier for a nanoparticle inorganic ion exchanger. The slurry may contain a nanoparticle inorganic ion exchanger in liquid form.

In the present invention, the capsule-like structure is dried until solidified. In the present invention, solidification means forming a state in which the strength as an adsorbent is improved by heating the capsule-like structure and evaporating the internal solvent sufficiently.
The drying temperature is not particularly limited as long as the capsule-like structure can be solidified, but it is typically 40 ° C. or higher from the viewpoint of rapid processing. Preferably it is 40 to 120 degreeC, Most preferably, it is 50 to 90 degreeC. However, when the heat resistance of the cation exchanger to be used is low, the drying temperature needs to be adjusted accordingly. The drying time may be a time sufficient to solidify the capsule-like structure, and can be appropriately set according to the drying temperature. As drying conditions, for example, 50 ° C. to 70 ° C. for 10 hours or longer, and 70 ° C. to 90 ° C. for 5 hours or longer are preferable.

  In the present invention, the particle size of the cation adsorbent particles is not particularly limited, but it is possible to produce particles having a size larger than that of Patent Document 3, specifically, production of particles exceeding 1 cm. Is also possible. However, 5 mm or less is practical to ensure the ability to remove radioactive substances. Moreover, when using for a column use, since it is necessary to fix to column shape, 1 micrometer or more is preferable and 10 micrometers or more are more preferable.

One aspect of the present invention is a step of preparing a slurry by mixing a dispersion of nanoparticle inorganic ion exchangers with cation adsorbent particles and a solution containing a gel raw material,
The slurry is brought into contact with a solution containing calcium to form a capsule-like structure having a gel-like surface layer enriched with calcium and containing dispersed nano-particle inorganic ion exchangers, and drying Thus, the present invention relates to the particles produced by the production method including the step of solidifying the capsule-like structure and forming the particles. Therefore, the cation adsorbent particles of the present invention are formed by supporting nanoparticles on a carrier and compositing them.

In one embodiment, the cation adsorbent particles of the present invention have a calcium-enriched surface layer, and dry a capsule-like structure in which Prussian blue nanoparticles represented by the formula (A) are dispersed and contained. Thus, the particles are produced by a production method including a step of solidifying to form particles. Accordingly, Prussian blue nanoparticles represented by the above formula (A) are supported on a carrier and combined. The particles are capable of reducing elution of Prussian blue, and have strength that can reduce breakage in actual adsorption work, even though Prussian blue is contained at a high content of 70% or more. It is preferable in the accompanying point.
The Prussian blue represented by the formula (A) is typically a nanoparticle having a relatively small primary particle size (for example, about 3 to 100 nm), and although not necessarily obvious, the plurality of primary particles are heated. It is considered that the particles have a property of growing by bonding. Although the specific surface area is decreased by increasing the primary particles and the adsorption ability may be reduced to a certain extent, the nanoparticles are bonded to the carrier inside the capsule-like structure by heating, which is higher than the carrier. It is thought that adhesiveness can be realized. This is considered to make it possible to create stronger particles.

The cation adsorbent particles of the present invention can selectively adsorb cations according to the adsorption characteristics such as the adsorption selectivity of the nanoparticle inorganic ion exchanger.
The partition coefficient (Kd) in the adsorption of Prussian blue Cs ions represented by the above formula (A), which is an embodiment of the cation adsorbent particles of the present invention, depends on the concentration of coexisting ions and is not particularly limited. It can be 1000 mL / g or more, preferably 10,000 mL / g or more, more preferably 10,000 mL / g or more. Although there is no upper limit in particular, it is practical that it is 100 million mL / g or less.

  The cation adsorbent particles of the present invention can be obtained by immersing the adsorbent in a certain amount of sample containing the target ions for a certain period of time, by immersing the target ions in the column, and by immobilizing the ions in the column and passing the material through It can be applied to a column method for adsorbing ions. The cation adsorbent particles of the present invention have sufficient strength, are spherical, and have excellent mechanical strength. Therefore, in the dipping method, the cation adsorbent particles can be easily recovered without destroying them. In the immersion method, the immersion process and the subsequent solid-liquid separation of the adsorbent particles and the sample are performed sequentially, or the sample is injected into the container having the adsorbent particles and discharged simultaneously. It is possible to do so. In addition, since the cation adsorbent particles obtained by the present invention have a certain particle size, most of them are generally used in the solid-liquid separation work associated with the dipping method, such as membrane filtration and centrifugation. These methods are available. In the column method, the adsorption tower and the adsorption column can be easily packed, and the generation of fine powder due to the rubbing and contacting of the particles is small, so that it can be used for a large-scale adsorption tower. Further, since the particles of the present invention have a narrow particle size distribution, they can be easily packed in a column and can maintain a stable adsorption ability over a long period of time.

Hereinafter, the present invention will be described in detail based on examples, but the present invention is not construed as being limited thereto.
<Example 1> Preparation of Prussian blue dispersion 145 g of sodium ferrocyanide decahydrate was dissolved in 600 mL of water. This is designated as raw material liquid 1. 162 g of iron nitrate nonahydrate was dissolved in 300 mL of an aqueous solution in water. This is designated as raw material liquid 2. Raw material liquid 1 was added to raw material liquid 2 and stirred for 5 minutes to obtain a Prussian blue dispersion. This was washed with a centrifuge to remove sodium nitrate as a by-product.

<Example 2> Preparation of particles (gelator: sodium alginate)
775.0 g of Prussian blue dispersion prepared in Example 1 and 425.0 g of water were mixed. This was mixed with 2400.0 g of a 1.5% aqueous sodium alginate solution. This is designated as Droplet 1. Separately, an aqueous calcium chloride solution was prepared and used as Reaction Solution 1. The dripping liquid 1 was dripped at the reaction liquid 1 at 3.4 ml / min using the pump (Drip port (nozzle) diameter: 1.15 mm). Here, the dropping position was adjusted so that a droplet was formed. These operations produced a dark blue gel. Only the resulting gel was taken out (1820 g), washed with water, and dried with a dryer (90 ° C., 20 hours). The obtained particles are referred to as “Particle 1”.

<Example 3>
Particles 2 were produced in the same manner as in Example 2. Table 1 shows the production conditions and yield of each particle.

The composition of particles 1 and 2 is shown in Table 2.

<Example 4> Preparation of particles (gelling agent: gellan gum)
12.9 g of the Prussian blue dispersion prepared in Example 1 and 27.1 g of water were mixed. This was mixed with 20 g of a 1.0% deacylated gellan gum aqueous solution. This is designated as Droplet 2. Separately, an aqueous calcium chloride solution was prepared and used as Reaction Solution 1. The dripping liquid 2 was dripped at the reaction liquid 1 at 3.4 ml / min using the pump. Here, the dropping position was adjusted so that a droplet was formed. These operations produced a dark blue gel. Only the resulting gel was taken out (35 g), washed with water, and dried with a dryer (50 ° C., 20 hours). The obtained particles are designated as “Particle 3”.

<Example 5> Preparation of particles (gelator: κ-carrageenan)
“Particle 4” was obtained in the same manner as in Example 4 except that the acylated gellan gum was changed to κ-carrageenan.

<Example 6> Preparation of particles having different particle diameters [0125] "Particle 5" was prepared in the same manner as in Example 2 except that the diameter of the dropping port (nozzle) was changed from 1.15 mm to 0.4 mm. Obtained. The particle diameter of the particles 5 was 0.8 mm. Thus, the particle diameter could be changed only by changing the outlet diameter. FIG. 1 shows the result of particle size distribution.

<Example 7>
Using particles 1 and 2, particle strength, particle size distribution, and particle shape were measured. The particle strength was evaluated by dropping 15 g of agate on the particles. The particle size distribution was prepared by measuring the particle diameter of the plurality of particles 1 with a caliper. The particle shape was confirmed visually. Table 3 shows the strength measurement results, Table 4 shows the particle shape results, FIG. 2 shows a photograph of the obtained particles, and FIG. 3 shows the particle size distribution results.

<Example 8>
Using particle 1, a cesium adsorption experiment was conducted. After cesium nitrate was dissolved in ultrapure water, 10 mg of particle 1 was immersed in 10 mL of an aqueous solution prepared with a cesium ion concentration of 1000 ppb (1 ppb is 1 billion), and shaken at 600 rpm for 24 hours. After treatment at 5000 rpm for 10 minutes, solid-liquid separation was performed, and the cesium ion concentration in the solution was measured with an inductively coupled plasma mass spectrometer (NexION 300D (trade name, manufactured by PerkinElmer Japan Co., Ltd.). Shown in

<Example 9>
An adsorption test was performed using the particles 5, and cesium adsorption characteristics were confirmed. 12.5 mg was collected, immersed in 10 mL of an aqueous solution having a Cs concentration of 1 ppm prepared using pure water, and shaken at a cycle of 600 rpm. FIG. 4 shows the result of measuring the Cs concentration in the aqueous solution in the same manner as in Example 8 every 1, 2, 4, 6, 12, and 24 hours. Thus, even if the solid-liquid ratio was a very high value of 800, cesium in the aqueous solution was almost completely adsorbed in about 5 hours. The distribution coefficient Kd after 24 hours was 742400. This value is sufficiently higher than that of Non-Patent Document 3, and one of the reasons is that the concentration of Prussian blue as a cation exchanger is 80%, which is higher than that of Non-Patent Document 3.

<Example 10>
Since the particulate adsorbent according to the present invention has a gel-like coating especially enriched with calcium on the surface, elution during use of the cation exchanger can be avoided. Specific examples are shown below.
1.2480 g (corresponding to 1.000 g of PB) of particles 1 was filled in a Terumo 5 mL syringe, and a syringe filled with glass fibers before and after was prepared. The ash leachate obtained by washing the ash generated when wood is incinerated (extracted with a solid / liquid ratio of 1/25 milliQ water and adjusted to pH 5) was poured at a rate of 5 mL / min, and the initial distillation was 10 mL. As a fraction, fractions of 9 fractions of 50 mL and 1 fraction of 45 mL were collected. The Fe concentration of the fraction was quantified by ICP-MS. The column was immersed in ultrapure water for 15 hours or longer for experiments. The results are shown in Table 6. As a result, the Fe concentration detected when Prussian blue was eluted was a very low value of 20 ppb or less for all fractions.

As a comparison, the same Prussian blue used when the particles 1 were produced was granulated to a particle size of 60 μm by spray drying. Table 7 shows the results of similar experiments using particles that do not contain other constituent materials such as alginic acid. In this case, the iron concentration per fraction exceeded 200 ppb, and higher elution of Fe was observed compared to the case of particle 1.
<Example 11>
Since the particulate adsorbent obtained by the present invention can be easily controlled in size, it can also be used as a column material.
A cesium nitrate aqueous solution in which 10 ppm of cesium ions were dissolved was passed through a syringe produced by the same operation as in Example 10 at 5 mL / min. However, the syringe was evaluated for three cases of one, two series, and three series. The first fraction was collected as a 10 mL drain, and the subsequent fractions were collected every 25 mL or 50 mL. The result of quantifying the Cs concentration of the fraction by ICP-MS is shown in FIG. As a result, the cesium concentration can be reduced to about 20% of the initial concentration even with one syringe, and can be reduced to about 1/2000 by connecting three in series. From this result, it was found that the convection time of the aqueous solution in the column was 30 seconds or less, and the cesium concentration could be reduced to 1/1000.

Claims (7)

A method for producing cation adsorbent particles, a step of preparing a slurry by mixing a dispersion of nanoparticle inorganic ion exchanger with a solution containing a gel raw material,
The slurry is brought into contact with a solution containing calcium to form a capsule-like structure having a gel-like surface layer enriched with calcium and containing dispersed nano-particle inorganic ion exchangers, and drying The said manufacturing method including the process of solidifying a capsule-like structure and shape | molding particle | grains. The nanoparticle inorganic ion exchanger has the following formula (A)
A _p Fe [Fe (CN) ₆ ] _y · zH ₂ O (A)
Where
A is an atom derived from a cation, p is a number from 0 to 2, y is a number from 0.6 to 1.5, and z is a number from 0.5 to 10;
The manufacturing method of Claim 1 which is Prussian blue represented by these.   The method according to claim 1 or 2, wherein the gel raw material is sodium alginate.   The manufacturing method as described in any one of Claims 1-3 with which a capsule-shaped structure is dried in the state in which the inside is not gelatinized completely but contains the dispersion liquid of a nanoparticle inorganic ion exchanger.   Cation adsorbent particle manufactured by the manufacturing method as described in any one of Claims 1-4. The nanoparticle inorganic ion exchanger has the following formula (A)
A _p Fe [Fe (CN) ₆ ] _y · zH ₂ O (A)
Where
A is an atom derived from a cation, p is a number from 0 to 2, y is a number from 0.6 to 1.5, and z is a number from 0.5 to 10;
The cation adsorbent particle according to claim 5, which is Prussian blue represented by: The following formula (A)
A _p Fe [Fe (CN) ₆ ] _y · zH ₂ O (A)
Where
A is an atom derived from a cation, p is a number from 0 to 2, y is a number from 0.6 to 1.5, and z is a number from 0.5 to 10;
Cationic adsorbent particles formed by supporting and combining Prussian blue nanoparticles represented by