JP7498566B2 - Granular Structure - Google Patents

Description

The present invention relates to a granular structure for use in an aqueous medium.

For adsorbents used to remove harmful substances from water, catalysts used in chemical reactions in aqueous media, etc., granular structures made by granulating porous particles with a binder are used for convenience during use.

In this case, granulation methods such as rolling granulation, extrusion granulation, and spray drying are used. For example, Patent Document 1 describes the production of agglomerates of radioactive material decontamination particles with a specific pore volume by spray drying.

JP 2014-228282 A

Here, in order to allow the porous particles in the granular structure after granulation to exert their inherent adsorption capacity and delay breakthrough in the breakthrough curve as much as possible, it is necessary not only to increase the porosity inside the particles, but also to design pores that communicate with the outside so that water can easily enter the pores. However, with conventional granulation methods, it has not been possible to fully exert the inherent adsorption capacity of the porous particles (adsorbent powder).

In other words, the granules obtained by the rolling granulation method and the extrusion granulation method have a relatively small porosity, which is thought to impair the inherent adsorption capacity of the porous particles. Furthermore, the rolling granulation method produces a broad particle size distribution after granulation, so in order to produce particles of the required diameter, operations such as crushing of coarse particles or regranulation of fine powder are necessary, which tends to reduce yields.

On the other hand, the spray drying method not only produces a large porosity in the granulated material, allowing it to exert its original adsorption capacity, but also produces a sharp particle size distribution after granulation, making it possible to produce particles of the required particle size with good yield. However, the spray drying method is not a sustainable method because it uses large amounts of water and heat. In addition, the particle strength of the granulated material is low, making it difficult to say that it is suitable for granulation for applications that require strength, such as adsorbents and catalysts.

The present invention therefore relates to a granulated material made of porous particles, which has a high inherent adsorption capacity, can fully exert catalytic activity, and has a granular structure with high particle strength.

After examining various granulation methods, the inventors discovered that a granulation method using a container-rotating granulator and a multi-fluid nozzle can produce granular structures with high porosity, high inherent adsorption capacity of porous particles, sufficient catalytic activity, and sufficient particle strength with good yield, and thus completed the present invention.

The present invention provides a granular structure in which hydrophilic porous particles are bonded together via a binder, wherein the ratio of voids having an area of ³⁰ μm2 or more in the central cross-sectional area of the granular structure is 5% or more and 15% or less when dry, the water absorption capacity obtained by subtracting the ratio when impregnated with water from the ratio when dry is 4% or more and 15% or less, and the particle strength of the granular structure is 400 gf/mm2 ^or more and 2000 gf/ ^mm2 or less.

The granular structure of the present invention is obtained by granulating porous particles with a binder, and is capable of fully exerting the inherent adsorption capacity or catalytic activity of the porous particles, while also having sufficient particle strength.

1 is an adsorption isotherm plotting the amount of adsorption versus the equilibrium supernatant concentration when A-type zeolite is used as the porous particles. 1 is a Langmuir plot in which the equilibrium supernatant concentration is plotted against the divisor of the equilibrium supernatant concentration by the adsorption amount when A-type zeolite is used as the porous particles.

[Granular structure]
In the granular structure of the present invention, from the viewpoint of exerting the inherent adsorption capacity of the porous particles, the ratio of voids having an area of 30 μm2 or ^more in its cross-sectional area (hereinafter sometimes simply referred to as "porosity") is 5% or more, preferably 6% or more, more preferably 7% or more, and even more preferably 7.5% or more, when dry, and from the viewpoint of maintaining the particle strength and bulk density of the granular structure, it is 15% or less, preferably 14% or less, more preferably 12% or less, and even more preferably 10% or less.

In addition, from the viewpoint that water easily penetrates into the pores of the granular structure of the present invention, the water-holding capacity obtained by subtracting the porosity when water-impregnated from the porosity when dry is 4% or more, preferably 5% or more, more preferably 5.5% or more, and even more preferably 6% or more, and from the viewpoint of maintaining particle strength, it is 15% or less, preferably 14% or less, more preferably 12% or less, and even more preferably 10% or less.

In the present invention, the porosity of the granular structure was measured by placing the granular structure in a glass capillary, and analyzing the cross-sectional image of the powder taken with an X-ray CT (manufactured by Bruker Micro CT) using the image processing software ImageJ. That is, the cross-sectional image of the center of the powder was binarized, and the ratio of the void area to the powder area was calculated to determine the powder porosity. The detectable void size was the resolution of the device (0.8 μm).

Furthermore, from the viewpoint that the granular structure of the present invention can be suitably used in applications requiring strength such as adsorbents and catalysts, the particle strength of the granular structure is 400 gf/ ^mm2 or more, preferably 450 gf/ ^mm2 or more, more preferably 500 gf/ ^mm2 or more, and even more preferably 550 gf/ ^mm2 or more, and from the viewpoint that it can be easily reduced in volume after adsorption or the like, the particle strength is 2000 gf/mm2 or ^less , preferably 1800 gf/ ^mm2 or less, more preferably 1500 gf/ ^mm2 or less, and even more preferably 1200 gf/ ^mm2 or less.

Hydrophilic porous particles used in the granulation of the granular structure of the present invention include zeolite, silicotitanate, ferrocyanide, titanic acid, etc., and among these, A-type zeolite, mordenite, clinoptilolite, and chabazite, which are types of zeolite, are preferred.

The porosity of the hydrophilic porous particles is preferably 15% or more, more preferably 18% or more, and even more preferably 20% or more, from the viewpoint of obtaining sufficient adsorption capacity, and is preferably 60% or less, more preferably 55% or less, and even more preferably 50% or less, from the viewpoint of maintaining the skeleton of the crystal structure.

The average particle size of the hydrophilic porous particles is preferably 1 μm or more, more preferably 2 μm or more, and even more preferably 3 μm or more, from the viewpoint of improving adsorption efficiency, and is preferably 100 μm or less, more preferably 50 μm or less, even more preferably 10 μm or less, and even more preferably 7 μm or less, from the viewpoint of ease of forming a granular structure.

Binders used in the granulation of the granular structure of the present invention include silicates, fatty acids, waxes, etc., and among these, silicates are preferred. From the viewpoint of forming a granular structure, the silicate preferably contains one or two types selected from sodium silicate and potassium silicate, and more preferably contains sodium silicate. The total content of sodium silicate and potassium silicate in the silicate is preferably 95% by mass or more, more preferably 99% by mass or more, even more preferably 99.5% by mass or more, and even more preferably substantially 100% by mass.

_{Examples of sodium silicate include sodium metasilicate (Na2SiO3), sodium orthosilicate (Na4SiO4), sodium disilicate (Na2Si2O5 ) , sodium tetrasilicate ( Na2Si4O9 ) and} their hydrates. As the sodium silicate material, sodium silicate No. 1, No. 2, No. ₃ as described in JIS K1408, as well as water glass of various molar ratios can usually be used.

Sodium silicate is generally expressed by the molecular formula _{Na2O.nSiO2.mH2O} . The coefficient n ( _{the molecular ratio of SiO2 to Na2O ) is called} the molar ratio and can be expressed by the following formula:

The physical properties of sodium silicate vary depending on the molar ratio. From the viewpoint of improving the handling properties when using the granular structure, the molar ratio is preferably 2.0 or more, more preferably 2.4 or more, even more preferably 2.8 or more, and even more preferably 3.0 or more. From the viewpoint of improving the sprayability during production, the molar ratio is preferably 4.0 or less, more preferably 3.5 or less, and even more preferably 3.3 or less.

The mass ratio of the binder to the hydrophilic porous particles constituting the granular structure of the present invention (binder/hydrophilic porous particles) is preferably 0.05 or more, more preferably 0.1 or more, and even more preferably 0.2 or more, from the viewpoint of improving the handling properties when the granular structure is used, and is preferably 1 or less, more preferably 0.8 or less, and even more preferably 0.7 or less, from the viewpoint of adsorption efficiency.

The average particle size of the granular structure of the present invention is preferably 50 μm or more, more preferably 80 μm or more, and even more preferably 100 μm or more, from the viewpoint of improving the handling properties when the granular structure is used, and is preferably 2000 μm or less, more preferably 1000 μm or less, and even more preferably 800 μm or less, from the viewpoint of improving the adsorption efficiency.

〔Production method〕
The granular structure of the present invention can be produced by a method including a step of granulating hydrophilic porous particles in a rotating container rotary granulator by spraying an aqueous solution of a binder with a multi-fluid nozzle (hereinafter referred to as the "spray agglomeration method").

In general, the granulation method using a rotary container granulator makes it possible to uniformly fluidize the powder, and furthermore, the shear force applied to the powder is suppressed by the mixing mechanism involving lifting of particles by rotation and sliding and falling due to their own weight. Therefore, the granulation method using a rotary container granulator can be said to be a non-compact granulation method. As a result, the granular structure of the present invention obtained by this method has a large porosity compared to granules obtained by other granulation methods.

Furthermore, the granulation method described above allows for the production of granulated material with a suitable particle size with good yield. This is believed to be because the binder is sprayed in advance as fine droplets of an aqueous solution using a multi-fluid nozzle, and then fed into the container-rotating granulator, preventing the formation of large liquid lumps that would form coarse particles.

In the above-mentioned manufacturing method, the binder concentration in the aqueous binder solution to be sprayed is preferably 10% by mass or more, more preferably 20% by mass or more, and even more preferably 30% by mass or more, from the viewpoint of a concentration suitable for binding the hydrophilic porous particles together, and is preferably 65% by mass or less, more preferably 60% by mass or less, and even more preferably 58% by mass or less, from the viewpoint of ease of handling and of spraying as droplets to suppress coarsening of particles and to increase the strength of the granular structure. The binder concentration (solid content) in the aqueous binder solution can be determined by the method described in the Examples.

In addition, the aqueous binder solution may contain polymers, inorganic particles, etc., and may also contain lower alcohols having 1 to 3 carbon atoms, etc., as long as they do not impair the effects of the present invention.

(Rotary container type granulator)
As the container rotation type granulator, drum type granulator and pan type granulator are preferred. As the drum type granulator, there is no particular limitation as long as the drum-shaped cylinder rotates to perform processing. A horizontal or slightly inclined drum type granulator can also be used. These devices may be either a batch type or a continuous type.

If the wall friction coefficient between the hydrophilic porous particles and the inner wall of the container rotation type granulator is small and it is difficult to apply sufficient upward motive force to the hydrophilic porous particles, it is preferable to provide multiple baffles on the inner wall of the container to assist mixing. By providing baffles, it is possible to impart upward motive force to the hydrophilic porous particles, improving powder mixability and solid-liquid mixability.

There are no particular limitations on the operating conditions of the container-rotating granulator, so long as the hydrophilic porous particles in the granulator can be made to flow and be stirred as uniformly as possible. From the viewpoint of producing granular structures with sufficient particle strength with a good yield, the Froude number defined by the following formula is preferably 0.005 or more, more preferably 0.01 or more, and even more preferably 0.05 or more, and from the viewpoint of obtaining non-compacted granules, it is preferably 1.0 or less, more preferably 0.6 or less, and even more preferably 0.4 or less.

In addition, in drum-type granulators or pan-type granulators where granulation progresses by the rotation of the main body, V and R are the values of the main body, in horizontal or vertical granulators equipped with main wings or crushing wings, V and R are the values of the main shaft, and in pan-type granulators equipped with crushing wings, V and R are the values of the crushing wings.

(Multi-fluid nozzle)
In the present invention, the aqueous solution of the binder is supplied using a multi-fluid nozzle. By using the multi-fluid nozzle, the droplets can be made fine and dispersed. The multi-fluid nozzle is a nozzle that mixes and atomizes the liquid and the atomization gas (air, nitrogen, etc.) by passing them through independent flow paths to the vicinity of the nozzle tip, and examples of the multi-fluid nozzle include a two-fluid nozzle, a three-fluid nozzle, and a four-fluid nozzle. In addition, the mixing section of the aqueous binder solution and the atomization gas may be either an internal mixing type in which the mixture is performed within the nozzle tip, or an external mixing type in which the mixture is performed outside the nozzle tip.

Examples of such multi-fluid nozzles include internal mixing type two-fluid nozzles manufactured by Spraying Systems Japan, Kyoritsu Alloy Manufacturing Co., Ltd., Ikeuchi Co., Ltd., etc., external mixing type two-fluid nozzles manufactured by Spraying Systems Japan, Kyoritsu Alloy Manufacturing Co., Ltd., Atmax Co., Ltd., etc., and external mixing type four-fluid nozzles manufactured by Fujisaki Electric Co., Ltd., etc.

The droplet size of the binder aqueous solution can be adjusted to a desired range by adjusting the balance between the flow rate of the binder aqueous solution and the flow rate of the atomization gas. That is, to reduce the droplet size, the flow rate of the atomization gas may be increased for a constant flow rate of the binder aqueous solution, or the flow rate of the binder aqueous solution may be decreased for a constant flow rate of the atomization gas.
For example, when a two-fluid nozzle is used, the flow rate of the atomization gas can be easily adjusted by adjusting the spray pressure of the atomization gas. The atomization gas spray pressure is preferably 0.05 MPa or more from the viewpoint of liquid dispersion, and is preferably 1 MPa or less from the viewpoint of equipment load. There is no particular restriction on the spray pressure of the binder aqueous solution, but it is preferably, for example, 1 MPa or less from the viewpoint of equipment load.

The average droplet size of the binder aqueous solution is preferably 200 μm or less, more preferably 150 μm or less, and even more preferably 100 μm or less, from the viewpoint of producing granular structures with sufficient particle strength with good yield, and is preferably 10 μm or more, more preferably 20 μm or more, even more preferably 30 μm or more, and even more preferably 50 μm or more, from the viewpoint of improving handling properties during use.

The smaller the droplet size, the lower the flow rate of the binder aqueous solution and the lower the productivity. However, for example, by using multiple multi-fluid nozzles and lowering the flow rate per nozzle, it is possible to increase the addition speed while maintaining the fineness of the droplets. One or more multi-fluid nozzles are sufficient, but 2 to 20 nozzles can also be used.

The average droplet size of the binder aqueous solution is calculated on a volume basis, and is a value measured, for example, using a laser diffraction particle size distribution analyzer (Spraytec, manufactured by Malvern Instruments).

The temperature of the aqueous binder solution when sprayed using a multi-fluid nozzle is preferably from 5 to 50° C., more preferably from 10 to 30° C., from the viewpoint of spray stability.
From the viewpoint of obtaining a granulated product with a sharp particle size distribution, the addition rate of the aqueous binder solution is preferably 35 parts by mass/min or less, more preferably 20 parts by mass/min or less, and even more preferably 10 parts by mass/min or less, and is preferably 1 part by mass/min or more, more preferably 2 parts by mass/min or more, and even more preferably 3 parts by mass/min or more, relative to 100 parts by mass of the hydrophilic porous particles. The above ranges are suitable when sodium silicate No. 1, No. 2, or No. 3 described in JIS K1408 is used.

From the same viewpoint as above, the addition rate of the binder (solid content) is preferably 30 parts by mass/min or less, more preferably 18 parts by mass/min or less, and even more preferably 9 parts by mass/min or less, and is preferably 0.4 parts by mass/min or more, more preferably 0.8 parts by mass/min or more, and even more preferably 1.2 parts by mass/min or more, relative to 100 parts by mass of the hydrophilic porous particles.

(Drying)
In the present invention, in order to increase the particle strength and obtain a stable granulated product even when the structure is used in water, it is preferable to further dry the obtained granular structure. Examples of the drying method include shelf drying, fluidized bed drying, reduced pressure drying, microwave drying, etc. Among them, shelf drying and fluidized bed drying are preferable from the viewpoint of equipment.

In order to prevent the collapse of the granular structure during drying, a drying method that applies as little strong shear force as possible is preferable. For example, examples of batch methods include drying using an electric shelf dryer or hot air dryer, and drying using a batch fluidized bed, while examples of continuous methods include fluidized bed, rotary dryers, and steam tube dryers.

The drying temperature can be appropriately determined taking into consideration the drying speed, but is preferably 60°C or higher, more preferably 100°C or higher, and even more preferably 120°C or higher. In order to reduce the heat load, the upper limit is preferably 300°C or lower, more preferably 250°C or lower, and even more preferably 200°C or lower.

The drying time varies depending on the active ingredient and amount of the aqueous binder solution used in the production, but is adjusted appropriately so that the particle strength of the granular structure falls within the range described above. The drying time is usually about 10 minutes to 24 hours, more preferably about 20 minutes to 15 hours, and even more preferably about 30 minutes to 8 hours.

The moisture content in the resulting granular structure is preferably 10% by mass or less, more preferably 7% by mass or less, and even more preferably 5% by mass or less, from the viewpoint of increasing particle strength and forming a stable granulated product even when the structure is used in water, and is preferably 0.5% by mass or more, more preferably 0.8% by mass or more, and even more preferably 0.5% by mass or less, from the viewpoint of productivity.

[Application]
The granular structure of the present invention is useful as an adsorbent for harmful substances in water, a catalyst for liquid phase reaction systems of polar solvents, etc. For example, it can be used for treating contaminated water containing radioactive substances in nuclear power generation, treating wastewater containing harmful metals and organic matter discharged from factories, and as a hydrogenation catalyst for processing oils and fats.

Examples 1 to 2, Comparative Examples 1 to 3
Using A-type zeolite or mordenite as the porous particles and sodium silicate as the binder, granular structures were produced by the production methods shown in Examples 1 and 2 and Comparative Examples 1 to 3. Table 1 shows the composition of the raw materials used in the production of the granular structures, the composition, average particle size and water content of the obtained granular structures. The water content of the granular structures was measured as follows.

<Measurement of Moisture Content of Granular Structure>
2 g of the sample was evenly spread on an aluminum container with a diameter of 11.5 cm, and then the volatile free moisture was measured using an infrared moisture meter (FD240, manufactured by Kett Electric Laboratory Co., Ltd.) in the moisture standard moisture measurement mode at a temperature of 105°C under Auto conditions (the measurement was terminated when the change in the measurement value was within 0.05% in 30 seconds, which was considered to be the final measurement value), and the moisture content was calculated by subtracting the volatile free moisture content. The moisture content shown in Table 1 is an external ratio to the solid content.

Example 1 (spray agglomeration method)
A type zeolite (manufactured by Zeobuilder, product name: Zeolite (powder), average particle size: about 3 μm) was charged into a 75 L drum-type granulator (φ40 cm × L60 cm) equipped with a baffle plate in the blending ratio shown in Table 1, and while mixing under the conditions of drum rotation speed 30 rpm / Froude number 0.2 / drum angle 12.6°, sodium silicate aqueous solution (manufactured by Fuji Chemical Co., Ltd., product name: No. 3 sodium silicate, molar ratio: 3.0-3.3, Baume degree: 40-53, solid content: 54.3%) was sprayed and added using one external mixing type two-fluid nozzle (manufactured by Atmax Co., Ltd.) to granulate. The batch size was 6.9 kg. The median diameter of the sprayed droplets of the sodium silicate aqueous solution was 69 μm.
After spraying the aqueous sodium silicate solution, mixing was continued for 1 minute, after which the mixture was discharged from the drum granulator and dried at 150° C. for 720 minutes using an electric dryer to obtain the granular structure of Example 1.

Comparative Example 1 (Spray Granulation Method)
A type zeolite (manufactured by Zeobuilder, product name: Zeolite (powder), average particle size approximately 3 μm), an aqueous sodium silicate solution (manufactured by Fuji Chemical, product name: No. 3 sodium silicate, molar ratio: 3.0-3.3, Baume degree: 40-53, solid content: 54.3%), and water were mixed in the proportions shown in Table 1 using a turbine blade (DHC-10 manufactured by Inoue Seisakusho) to obtain an aqueous slurry with a solid content of 50.0%. The aqueous slurry was prepared by first putting water into a mixing tank, then adding the aqueous sodium silicate solution, and then adding the zeolite and mixing.
The resulting water slurry was spray-dried at an air temperature of 170° C. to obtain the granular structure of Comparative Example 1.

Comparative Example 2 (rolling granulation method)
In the blending ratio shown in Table 1, A-type zeolite (manufactured by Zeobuilder, product name: Zeolite (powder), average particle size approximately 3 μm) was mixed in a 2 L high-speed mixer (manufactured by Fukae Powtec: LFS-2, agitator rotation speed 300 rpm, chopper rotation 1300 rpm) while sodium silicate aqueous solution (manufactured by Fuji Chemical Industry Co., Ltd., product name: No. 3 sodium silicate, solid content: 55.1%) was added dropwise and tumbling granulated. The batch size was 0.3 kg. The median diameter of the droplets of the sodium silicate aqueous solution was approximately 500 μm.
After the sodium silicate aqueous solution was added dropwise, mixing was continued for 5 minutes, after which the mixture was discharged from the 2 L mixer and dried at 120° C. for 4 hours using an electric shelf dryer to obtain a granular structure of Comparative Example 2.

Comparative Example 3 (Extrusion Granulation Method)
In the proportions shown in Table 1, A-type zeolite (Zeobuilder, product name: Zeolite (powder), average particle size approximately 3 μm) was mixed with a Nauta mixer (Hosokawa Micron: LV-1, maximum rotation speed) while a sodium silicate aqueous solution (Fuji Chemical Industry, product name: No. 3 sodium silicate, solid content: 55.1%) was added dropwise. The batch size was 0.6 kg. The median diameter of the droplets of the sodium silicate aqueous solution was approximately 500 μm.
After the sodium silicate aqueous solution was added, mixing was continued for 10 minutes, and then the mixture was discharged from the mixer. The discharged mixture was extrusion granulated using a Dome Gran (Dalton: DG-L1, φ1.5 mm screen, rotation speed 50 rpm). The extrusion granules were received in a tray, sized using a Power Mill (Dalton: P-02S, φ5.0 mm screen), and then dried at 140° C. for 4 hours using an electric shelf dryer to obtain the granular structure of Comparative Example 3.

Example 2 (spray agglomeration method)
Mordenite (manufactured by Tosoh Corporation, product name: HSZ-642NAA, average particle size: 12 μm) was charged into a 75 L drum type granulator (φ40 cm × L60 cm) equipped with a baffle plate in the blending ratio shown in Table 1, and while mixing under the conditions of drum rotation speed 30 rpm / Froude number 0.2 / drum angle 12.6°, sodium silicate aqueous solution (manufactured by Fuji Chemical Co., Ltd., product name: No. 3 sodium silicate, molar ratio: 3.0-3.3, Baume degree: 40-53, solid content: 54.3%) was sprayed and added using one external mixing type two-fluid nozzle (manufactured by Atmax Co., Ltd.) to granulate. The batch size was 8.9 kg. The median diameter of the sprayed droplets of the sodium silicate aqueous solution was 69 μm.
After spraying the aqueous sodium silicate solution, mixing was continued for 1 minute, after which the mixture was discharged from the drum granulator and dried at 150° C. for 720 minutes using an electric dryer to obtain the granular structure of Example 2.

Test example (evaluation of granular structure)
For the granular structures of Examples 1 and 2 and Comparative Examples 1 to 3 obtained above, the saturated adsorption capacity of the porous particles, the breakthrough capacity, porosity, water absorption capacity, and particle strength of the granular structures were measured, and the results are shown in Table 3. Each granular structure was sieved to have a particle size within the range shown in Table 3 and used in the following measurements.
As a reference example, the same measurement was carried out on natural zeolite, and the results are also shown in Table 3.
As the granular structure of natural zeolite, Z-05 (particle size 0.5-1.0 mm) manufactured by Zieklite was used. As it contains a small amount of fine powder, it was washed with water to remove the fine powder before evaluation. As the porous particles, SGW (particle size 10 μm) manufactured by Zieklite was used. SGW is a crushed product of Z-05.

<Method for measuring saturated adsorption capacity of porous particles>
1 g of porous particles was weighed into a 100 mL beaker for 100 mL of 300, 500, 800, 1000, 5000, 10000, and 15000 ppm CsCl aqueous solution, and the equilibrium supernatant concentration of Cs after 24 hours of stirring using a stirrer piece was measured by the following method. The amount of adsorption was calculated from the initial concentration and the equilibrium supernatant concentration.
FIG. 1 shows an adsorption isotherm in which the adsorption amount is plotted against the equilibrium supernatant concentration when type A zeolite is used as the porous particles, and FIG. 2 shows a Langmuir plot in which the equilibrium supernatant concentration is plotted against the divisor of the equilibrium supernatant concentration by the adsorption amount.
The saturated adsorption capacity of the porous particles was calculated from the slope of equation (2) which represents the Langmuir plot by modifying the following Langmuir equation (1).

<Method of measuring breakthrough volume of granular structure>
2.0 g of the granular structure produced in the above Examples and Comparative Examples was placed in a 2 mL column (Econocolumn chromatography column #7370707 manufactured by Bio-Rad Laboratories), and a 1000 ppm CsCl solution was passed through at a flow rate of 1 mL/min using an SJ-1211II-L peristaltic pump manufactured by ATTO Corporation. The solution was fractionated into 10 mL portions using a fraction collector DC-1000 manufactured by Tokyo Rikakikai Co., Ltd., and the Cs concentration was analyzed by the following method to obtain a breakthrough curve. The time at which the concentration exceeded 1% of the initial concentration was defined as the breakthrough time, and the amount of adsorption up to that time was defined as the breakthrough capacity of the granular structure.

(Method of measuring Cs concentration)
The Cs concentration was measured using an inductively coupled plasma mass spectrometer (ICP-MS). The device used was a Thermo Fisher Scientific iCAP Qs, and ¹³³ Cs was measured in He collision mode. A calibration curve was created using an atomic absorption standard solution (Cs 1000μg/mL, Kanto Chemical Co.) diluted with 1% nitric acid. Samples were prepared by diluting with 1% nitric acid so that they fell within the calibration curve range and then used for measurement.

(Method of measuring void ratio)
The porosity was measured in full scanning mode using an X-ray CT scanner (Bruker Micro CT, SKYSCAN1272). The measurement conditions were voltage 50 kV, current 200 μA, resolution 4904 × 3280 pixels, and resolution 0.8 μm. The acquired images were binarized using the image processing software ImageJ with a threshold set to 35, and the porosity of void areas of ³⁰ μm2 or more was calculated using the command Analyze Particles in ImageJ.

(Method of Measuring Particle Strength)
A particle hardness measuring device (Grano, manufactured by Okada Seiko Co., Ltd.) was used, one granular structure was placed on the stage inside the device, and the indenter was lowered at a speed of 100 μm/sec to measure the load at which the granular structure collapsed. At this time, measurements were taken for 10 granular structures, and the number average value was shown.

Claims (2)

A granular structure in which hydrophilic porous particles are bound to each other via a binder,
a mass ratio of the binder to the hydrophilic porous particles constituting the granular structure (binder/hydrophilic porous particles) is 0.2 or more and 0.7 or less;
the hydrophilic porous particles are zeolite;
the binder is a silicate;
The ratio of voids having an area of ³⁰ μm2 or more in the central cross-sectional area of the granular structure is 5% or more and 15% or less when dry,
The water absorption capacity obtained by subtracting the ratio when soaked in water from the ratio when dry is 4% or more and 15% or less, and
The particle strength of the granular structure is 400 gf/mm ² or more and 2000 gf/mm ² or less;
Granular structure. The granular structure according to claim 1, which is an adsorbent for harmful substances in water.