JP2018070401A - Method for producing crystalline silicotitanate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide with an industrial advantage a crystalline silicotitanate having a high capacity to adsorb cesium and strontium in seawater.SOLUTION: The present invention comprises a first step of mixing together a silicic acid source, a sodium compound, a potassium compound, titanium tetrachloride and water to give a mixture gel, and a second step of allowing the resultant mixture gel to undergo reaction. In the first step, the silicic acid source, sodium compound, potassium compound and titanium tetrachloride are added such that Ti/Si=1.2 to 1.5 and MO/SiO=3.8 to 5.0 where M denotes Na and K are satisfied. In the second step, the reaction is performed at 70 to 110°C under atmospheric pressure.SELECTED DRAWING: None

Description

  The present invention relates to a method for producing crystalline silicotitanate particularly useful as an adsorbent for cesium and / or strontium.

  Conventionally, coprecipitation treatment is known as a treatment technique for wastewater containing radioactive substances (see Patent Document 1 below). However, for radioactive cesium and radioactive strontium that are water-soluble, the coprecipitation treatment is not effective, and at present, adsorption removal by an inorganic adsorbent such as zeolite is performed (see Patent Document 2 below).

  However, when radioactive cesium and radioactive strontium flow into seawater, an increase in the sodium concentration of seawater components acts to suppress the ion exchange reaction between cesium and the adsorbent (see Non-Patent Document 1 below). The problem is known. Although not described in Non-Patent Document 1 below, an increase in the sodium concentration of the seawater component also acts to suppress the ion exchange reaction between strontium and the adsorbent.

Crystalline silicotitanate is one of the inorganic adsorbents studied so far for the adsorption of cesium and / or strontium. Crystalline silicotitanates are known in a plurality of compositions such as those having a Ti / Si molar ratio of 1: 1, 5:12, and 2: 1. In addition, Ti / Si It is known that crystalline silicotitanate exists in a molar ratio of 4: 3. In Non-Patent Document 2, products 3B and 3C produced by hydrothermal treatment using an alkoxide of Ti (OET) ₄ as a Ti source and colloidal silica as a Si source are three-dimensional from the X-ray diffraction pattern. Having a typical eight-membered ring structure, and the crystalline silicotitanate having this structure ideally has a composition represented by M ₄ Ti ₄ Si ₃ O ₁₆ (M is Na, K, etc.) The crystalline silicotitanate having this structure is named Grace titanium silicate (GTS-1). Non-Patent Document 3 discloses a crystalline silicotitanate having a Ti / Si molar ratio of 4: 3, titanium tetrachloride as a Ti source, and a mixed solution containing highly dispersed SiO ₂ powder as a Si source. It describes that it was manufactured by heat treatment. This document describes that the synthesized crystalline silicotitanate has strontium ion exchange capacity.

  In addition, the present applicant previously proposed a crystalline silicotitanate having a Ti / Si molar ratio of 4: 3 as an adsorbent for cesium and / or strontium (for example, see Patent Documents 3 to 5).

Japanese Patent Laid-Open No. 62-266499 JP2013-57599A JP-A-2006-74548 JP-A-2006-3151 WO2015 / 14662 pamphlet

JAEA-Research 2011-037 ZEOLITES, 1990, Vol 10, November / December Keiko Fujiwara, “Modification and evaluation of microporous crystals as heat pump adsorbents”, [online], [October 23, 2016 search], Internet <URL: https://kaken.nii.ac.jp/file /KAKENHI-PROJECT-21560846/21560846seika.pdf>

  Conventionally, when producing a crystalline silicotitanate having a Ti / Si molar ratio of 4: 3, hydrothermal synthesis has been performed. However, since a relatively large amount of energy is required for hydrothermal synthesis, development of an industrially advantageous method that is energy-saving and cost-saving and environmentally friendly is desired.

  Therefore, an object of the present invention is to provide a crystalline silicotitanate having a Ti / Si molar ratio of 4: 3, and to produce a crystalline silicotitanate having high cesium and strontium adsorption performance even in seawater, in an energy-saving and cost-saving manner. It is to provide an advantageous manufacturing method.

In the method for producing crystalline silicotitanate proposed in Patent Document 3, the molar ratio of Ti and Si contained in the mixed gel is Ti / Si = 1.2 or more and 1.5 or less, and M ₂ O / Hydrothermal synthesis is performed using a mixed gel having a SiO ₂ molar ratio of preferably 0.6 to 1.1. As a result of intensive studies by the present inventors based on this production method, surprisingly, by using a mixed gel in which the molar ratio of M ₂ O / SiO _{2 is in} a specific range higher than this, the reaction is performed under atmospheric pressure. It has been found that crystalline silicotitanate having excellent crystallinity can be obtained even if it is carried out. Moreover, it was found that the crystalline silicotitanate produced in this way has a high adsorption performance for cesium and strontium even in seawater. The present invention has been completed based on these findings.

That is, the method for producing crystalline silicotitanate to be provided by the present invention has a general formula; M ₄ Ti ₄ Si ₃ O ₁₆ · nH ₂ O (wherein M represents Na and K. n represents 0 to 8). A method for producing a crystalline silicotitanate represented by:
A first step of obtaining a mixed gel by mixing a silicic acid source, a sodium compound, a potassium compound, titanium tetrachloride, and water;
A second step of reacting the mixed gel obtained in the first step,
In the first step, the molar ratio of Ti and Si contained in the mixed gel is Ti / Si = 1.2 or more and 1.5 or less, and the molar ratio of M ₂ O and SiO ₂ is M ₂ O / SiO ₂ = Add a silicic acid source, a sodium compound, a potassium compound and titanium tetrachloride so as to be 3.8 or more and 5.0 or less,
In the second step, the reaction is carried out at 70 to 110 ° C. under atmospheric pressure.

  ADVANTAGE OF THE INVENTION According to this invention, the crystalline silicotitanate excellent in the adsorption removal characteristic of cesium and strontium in seawater can be manufactured by an industrially advantageous method.

1 is an X-ray diffraction chart of the crystalline silicotitanate obtained in Example 1. FIG. FIG. 2 is an X-ray diffraction chart of the crystalline silicotitanate obtained in Example 2. FIG. 3 is an X-ray diffraction chart of the crystalline silicotitanate obtained in Example 3. FIG. 4 is an X-ray diffraction chart of the crystalline silicotitanate obtained in Example 4. FIG. 5 is an X-ray diffraction chart of the crystalline silicotitanate obtained in Example 5. 6 is an X-ray diffraction chart of the crystalline silicotitanate obtained in Comparative Example 1. FIG. 7 is an X-ray diffraction chart of the crystalline silicotitanate obtained in Comparative Example 2. FIG.

Hereinafter, the manufacturing method of the crystalline silicotitanate of this invention is demonstrated based on the preferable form. The production method of the present invention has a general formula in which the molar ratio of Ti: Si = 4: 3; M ₄ Ti ₄ Si ₃ O ₁₆ · nH ₂ O (wherein M represents Na and K. n represents 0 to 0). The number of 8 represents a single-phase crystalline silicotitanate substantially in X-ray diffraction. Since M represents Na and K in the general formula, the crystalline silicotitanate produced according to the present invention contains both sodium and potassium.

In general _formula; represented by _{M 4 Ti 4 Si 3 O 16} · nH 2 O ( wherein, M is in formula represents an alkali metal of Na and K, n denotes a number from 0 to 8..) In crystalline silicotitanate, a more detailed composition is not clear, but the general formula; (Na _x K _(1-x) ) ₄ Ti ₄ Si ₃ O ₁₆ · nH ₂ O (wherein _x exceeds 0) The present inventors presume that the number is less than 1. Therefore, in the present invention, substantially single-phase M ₄ Ti ₄ Si ₃ O ₁₆ .nH ₂ O is mainly composed of crystalline silicotitanate having a molar ratio of Ti: Si = 4: 3 in terms of X-ray diffraction. Crystalline silicon titanate other than the main component, Na ₄ Ti ₉ O ₂₀ · mH ₂ O, K ₄ Ti ₉ O ₂₀ · mH ₂ O, (Na _y K _(1-y) ) ₄ Ti ₉ It means that a clear diffraction peak of a by-product of titanate such as O ₂₀ · mH ₂ O (wherein y represents a number exceeding 0 and less than 1) and TiO ₂ is not observed.

  The present invention provides a first step of mixing a silicic acid source, a sodium compound, a potassium compound, titanium tetrachloride, and water to obtain a mixed gel, and a first step of reacting the mixed gel obtained in the first step under atmospheric pressure. It has two steps.

  Examples of the silicate source used in the first step include sodium silicate. Moreover, the active silicic acid obtained by carrying out cation exchange of the alkali silicate (namely, alkali metal salt of silicic acid) is also mentioned.

  The activated silicic acid is obtained by cation exchange by bringing an aqueous alkali silicate solution into contact with, for example, a cation exchange resin. As a raw material for the alkali silicate aqueous solution, a sodium silicate aqueous solution usually called water glass (water glass No. 1 to No. 4 etc.) is preferably used. This is relatively inexpensive and can be easily obtained. For semiconductor applications that dislike Na ions, an aqueous potassium silicate solution is suitable as a raw material. There is also a method of preparing an alkali silicate aqueous solution by dissolving solid alkali silicate in water. Alkali metasilicates are produced through a crystallization process, so some of them have few impurities. The aqueous alkali silicate solution is diluted with water as necessary.

  The cation exchange resin used when preparing the active silicic acid can be appropriately selected from known ones and is not particularly limited. In the contacting step between the alkali silicate aqueous solution and the cation exchange resin, for example, the alkali silicate aqueous solution is diluted with water so that the silica has a concentration of 3% by mass or more and 10% by mass or less. Contact with a strong acidic or weakly acidic cation exchange resin to dealkalize. Further, if necessary, it can be deanioned by contacting with an OH type strongly basic anion exchange resin. By this step, an active silicic acid aqueous solution is prepared. Regarding the details of the contact conditions between the aqueous alkali silicate solution and the cation exchange resin, various proposals have already been made, and any known contact conditions can be adopted in the present invention.

  Examples of the sodium compound used in the first step include water-soluble inorganic sodium salts such as sodium hydroxide and sodium carbonate. Among these sodium compounds, when sodium carbonate is used, carbon dioxide gas is generated. Therefore, it is preferable to use sodium hydroxide that does not generate such gas from the viewpoint of smoothly promoting the neutralization reaction.

  Moreover, as a potassium compound, water-soluble inorganic potassium salts, such as potassium hydroxide and potassium carbonate, are mentioned, for example. Among these potassium compounds, when potassium carbonate is used, carbon dioxide gas is generated. Therefore, it is preferable to use potassium hydroxide that does not generate such gas from the viewpoint of smoothly promoting the neutralization reaction.

In the first step, the addition ratio of the potassium compound is the ratio of K to the total number of moles of M converted to oxide (M ₂ O) when the number of moles of M defined below is converted to oxide in the mixed gel. in terms of oxides _(K 2 O) molar ratio of _{(K 2 O / M 2 O} ), preferably greater than 0 to 0.6, more preferably 0.1 to 0.6, particularly preferably 0.2 Addition of a sodium compound and a potassium compound so as to be 0.4 or less is preferable from the viewpoint of obtaining a crystalline silicotitanate with further improved cesium and strontium adsorption performance. Here, the number of moles of M in the mixed gel is represented by the following formula.
Number of moles of M = (number of moles of sodium derived from sodium compound) + (number of moles of potassium derived from potassium compound)

When sodium silicate or potassium silicate is used as the above-mentioned silicic acid source, the amount of sodium or potassium contained in the sodium silicate or potassium silicate is included in the calculation of the number of moles of M. In this case, the number of moles of M is obtained by the following formula.
Number of moles of M = (number of moles of sodium derived from sodium silicate) + (number of moles of potassium derived from potassium silicate) + (number of moles of sodium derived from sodium compounds other than sodium silicate) + (other than potassium silicate) Of potassium derived from potassium compounds)

  One feature of the method for producing crystalline silicotitanate of the present invention is that titanium tetrachloride is used as a titanium source. When other titanium compounds such as titanium oxide are used as the titanium source, unreacted titanium oxide tends to remain, and crystalline silicotitanate other than crystalline silicotitanate having a molar ratio of Ti: Si of 4: 3 is present. Easy to generate. Therefore, in the present invention, titanium tetrachloride is used as the titanium source.

  The titanium tetrachloride used in the first step can be used without particular limitation as long as it is industrially available.

  The addition amount of the silicic acid source and titanium tetrachloride may be set to an amount such that Ti / Si, which is the molar ratio of Ti derived from titanium tetrachloride and Si derived from the silicon source in the mixed gel, has a specific ratio. This is one of the characteristics of the method for producing crystalline silicotitanate. For example, in Non-Patent Document 3, titanium tetrachloride is used as the titanium source, but the silicic acid source and titanium tetrachloride are added to the mixed solution in such an amount that the molar ratio of Ti / Si is 0.32. Yes. In contrast, in the present invention, the silicic acid source and titanium tetrachloride are added in such amounts that the Ti / Si molar ratio is 1.2 or more and 1.5 or less. As a result of the study by the present inventors, it is easy to obtain a crystalline silicotitanate having a high degree of crystallinity by setting the Ti / Si molar ratio in the mixed gel in the molar range. The inventors have found that when this crystalline silicotitanate is used as an adsorbent, the adsorption performance of cesium and strontium is particularly improved. From this viewpoint, the ratio of Ti / Si in the mixed gel is more preferably 1.3 or more and 1.4 or less.

The total amount of the SiO ₂ equivalent silicic acid source concentration and the TiO ₂ equivalent titanium tetrachloride concentration in the mixed gel is preferably 1% by mass to 20% by mass, more preferably 2% by mass to 15% by mass, and more. It is preferably 5% by mass or more and 10% by mass or less from the viewpoint of obtaining a crystalline silicotitanate with a high yield.

In the first step, the molar ratio of M ₂ O / SiO ₂ in the mixed gel is 3.8 to 5.0, preferably 4.0 to 5.0, particularly preferably 4.2 to 4.8. Is also one of the characteristics of the method for producing crystalline silicotitanate of the present invention. As a result of investigation by the present inventor, by setting the ratio of M ₂ O / SiO _{2 in} the mixed gel within the range of the above molar ratio, even if the reaction is performed under atmospheric pressure, the X-ray diffraction is substantially reduced. It was found that a single phase with high crystallinity can be obtained with good yield. It has also been found that when this crystalline silicotitanate is used as an adsorbent, the adsorption performance of cesium and strontium becomes high.

In this production method, the reason why the molar ratio of M ₂ O / SiO _{2 in} the mixed gel is set in the above range is that the molar ratio of M ₂ O / SiO _{2 in} the mixed gel is 3.8 or more. , dissolution of the silica component tends to progress crystallization becomes sufficient, while the molar ratio of M _{2 O} / SiO ₂ in the mixed gel 5.0 by below, prevented from dissolution of silica is dominant This is because crystallization is facilitated and 9 titanate is hardly formed as a by-product.

In Patent Document 3, the number of moles of M ₂ O represents the number of sodium and potassium ions in the mixed gel in terms of oxides, in other words, alkali metal such as sodium and potassium and tetrachloride. It is obtained by removing the amount of sodium or potassium used in the neutralization reaction with titanium. In contrast, the “number of moles of M ₂ O” in the present production method represents the above “number of moles of M” in terms of oxide, in other words, included in all raw materials added to the first step. Sodium and potassium expressed in terms of oxides.

In the first step, the silicic acid source, sodium compound and potassium compound, and titanium tetrachloride can be added to the reaction system in the form of an aqueous solution, respectively. In some cases, it can be added in the form of a solid. Furthermore, in a 1st process, the density | concentration of this mixed gel can be adjusted using a pure water with respect to the obtained mixed gel. In particular, in this production method, the yield increases when the molar ratio of H ₂ O / M ₂ O in the mixed gel is 50 or more and 150 or less, preferably 60 or more and 100 or less, particularly preferably 60 or more and 85 or less. It is preferable from the viewpoint. Moreover, since the mixed gel becomes a slurry, it is preferable from the viewpoint of easy stirring efficiency and easy handling of the mixed gel.

  In the first step, the silicic acid source, sodium compound and potassium compound, and titanium tetrachloride can be added in various addition orders. For example, (1) a mixed gel can be obtained by adding titanium tetrachloride to a mixture of a silicic acid source, a sodium compound and a potassium compound, and water (this addition order is simply referred to as “( 1) Implementation ”). The implementation of (1) is preferable in terms of suppressing generation of chlorine from titanium tetrachloride.

  As another order of addition in the first step, (2) an aqueous solution of activated silicic acid (hereinafter sometimes simply referred to as “activated silicic acid”) obtained by cation exchange of an alkali metal silicate, titanium tetrachloride, A mode in which a sodium compound and a potassium compound are added to a mixture of water can also be adopted. Even when this order of addition is adopted, a mixed gel can be obtained in the same manner as in the execution of (1) (this addition order may be simply referred to as “the execution of (2)” hereinafter). Titanium tetrachloride can be added in the form of an aqueous solution or solid form. Similarly, sodium compounds and potassium compounds can also be added in the form of their aqueous solutions or solid forms.

In the implementation of (1) and (2), the total concentration of sodium and potassium (M ₂ O concentration) in the mixed gel is 5% by mass or more and 20% by mass or less, preferably 8% by mass or more. It is preferable to add so that it may become 12 mass% or less from a viewpoint with which a yield will become high and handling of mixed gel becomes easy.

  When sodium silicate is used as the silicate source, the sodium component in the sodium silicate simultaneously becomes the sodium source in the mixed gel. Accordingly, the “total concentration of sodium and potassium in the mixed gel” referred to here is counted as the sum of all sodium and potassium components in the mixed gel.

In the implementation of (1) and (2), the total concentration of sodium and potassium (M ₂ O concentration) in the mixed gel is 0.5% by mass or more and 15.0% by mass in terms of Na ₂ O. %, Particularly 0.7% by mass or more and 13.0% by mass or less of crystalline silicotitanate other than crystalline silicotitanate having a molar ratio of Ti: Si = 4: 3 is by-produced. It is preferable from the viewpoint of suppressing the above. The total Na ₂ O equivalent concentration of sodium and potassium in the mixed gel is calculated by the following equation.
Concentration (mass%) of sodium and potassium in the mixed gel in terms of Na ₂ O = [({Na ₂ O mass} + {K ₂ O mass / 94.2 × 62.0}) / (total mass of the mixed gel) ] X 100

  In the implementation of (1) and (2), it is desirable to add titanium tetrachloride stepwise or continuously as a titanium tetrachloride aqueous solution over a certain period of time in order to obtain a uniform gel. For this reason, a peristaltic pump etc. can be used suitably for addition of titanium tetrachloride.

  The mixed gel obtained in the first step is preferably not less than 0.1 hour, more preferably not less than 0.5 hour and not more than 12 hour before the reaction is performed under atmospheric pressure, which is the second step described later. In view of obtaining a uniform product, aging is preferably performed at 10 ° C. or more and less than 70 ° C., more preferably 10 ° C. or more and 50 or less, and atmospheric pressure. The aging step may be performed, for example, in a stationary state, but it is preferable to perform the stirring under stirring from the viewpoint of obtaining a more uniform product and preventing the formation of by-products.

  In the present invention, the mixed gel obtained in the first step is subjected to a reaction under atmospheric pressure in the second step to obtain crystalline silicotitanate. In the present invention, “under atmospheric pressure” means that the reaction proceeds with the reaction system open to the atmosphere. When the reaction system is opened to the atmosphere, a part of the medium water is evaporated and lost. The evaporated water is converted into liquid water by a cooling means such as a condenser, and the reaction system is circulated. The reaction may be carried out. At the laboratory level, the reaction vessel may be lightly covered with aluminum foil or the like.

  The reaction temperature in the second step is 70 ° C. or higher and 110 ° C. or lower, preferably 90 ° C. or higher and 110 ° C. or lower. This is because when the reaction temperature is lower than 70 ° C., crystallization does not proceed, whereas when the reaction temperature is higher than 110 ° C., the boiling point of the slurry is exceeded, and a pressure vessel, autoclave, etc. are required.

  The reaction time in the second step is not critical in the present production method, and the reaction may be performed for a sufficient time until a single-phase crystalline silicotitanate is produced by X-ray diffraction. In many cases, crystalline silicotitanate having satisfactory physical properties can be produced preferably in 3 hours or more, more preferably in 6 hours or more and 48 hours or less.

  By performing the second step, water-containing crystalline silicotitanate is produced. This water-containing crystalline silicotitanate can be dried, and the resulting dried product can be crushed or pulverized as necessary to form a powder (including granules). Alternatively, the hydrous crystalline silicotitanate may be extruded from an aperture member having a plurality of apertures to obtain a rod-shaped molded body, and the obtained rod-shaped molded body may be dried to be molded into a columnar shape. . Furthermore, the dried rod-shaped molded body may be formed into a spherical shape, or may be pulverized or pulverized into particles. In the latter case, that is, by performing extrusion molding before drying the water-containing crystalline silicotitanate, the yield of the crystalline silicotitanate recovered by the classification method described later can be increased. Here, pulverization refers to an operation of loosening a collection of fine particles. The pulverization is an operation in which a mechanical force is applied to the loosened solid particles to further reduce the particle size.

  Examples of the shape of the hole formed in the aperture member include a circle, a triangle, a polygon, and an annulus. The true circle equivalent diameter of the opening is preferably 0.1 mm or more and 10 mm or less, and more preferably 0.3 mm or more and 5 mm or less. The true circle equivalent diameter here is a diameter of a circle calculated from the area when the area of one hole is defined as a circular area. The drying temperature after extrusion molding can be, for example, 50 ° C. or more and 200 ° C. or less. The drying time can be 1 hour or more and 120 hours or less.

  The dried rod-shaped molded body can be used as an adsorbent as it is, or can be used after lightly loosening. Moreover, you may grind | pulverize and use the rod-shaped molded object after drying. The powdery crystalline silicotitanate obtained by these various methods is preferably further classified and then used as an adsorbent from the viewpoint of increasing the adsorption efficiency of cesium and / or strontium. For the classification, for example, it is preferable to use a first sieve having a nominal opening prescribed in JISZ8801-1 of 1000 μm or less, particularly 710 μm or less. Moreover, it is also preferable to carry out using the 2nd sieve whose said nominal opening is 100 micrometers or more, especially 300 micrometers or more. Furthermore, it is preferable to carry out using these first and second sieves.

According to the production method of the present invention, M ₄ Ti ₄ Si ₃ O ₁₆ .nH ₂ O (wherein M represents Na and K. In the formula, n represents a number of 0 to 8). The crystalline silicotitanate represented by is obtained as a substantially single phase X-ray diffraction. As is apparent from these general formulas, according to the present production method, a crystalline silicotitanate having a Ti: Si molar ratio of 4: 3 is obtained, while crystals having a Ti: Si molar ratio other than 4: 3 are obtained. sex Shirikochitaneto _{and, Na 4 Ti 9 O 20 ·} mH 2 O, K 4 Ti 9 O 20 · mH 2 O, (Na y K (1-y)) in _{4 Ti 9 O 20 · mH 2} O ( wherein, One of the characteristics is that titanate by-products such as y is more than 0 and less than 1 and m is a number from 0 to 10 are not substantially observed by X-ray diffraction.

  The second feature of the crystalline silicotitanate obtained by the production method of the present invention is that it does not contain titanium oxide as an impurity. The absence of titanium oxide can be confirmed by the fact that 2θ = 25 ° which is the peak of titanium oxide is not detected in the diffraction peak obtained by X-ray diffraction measurement of the crystalline silicotitanate.

  The crystalline silicotitanate obtained by the production method of the present invention has high adsorption performance for cesium and strontium even in seawater. Using this characteristic, the crystalline silicotitanate can be molded according to a conventional method as necessary, and the resulting molded product can be suitably used as an adsorbent for cesium and / or strontium.

  As the molding process, for example, after granulating a powdery crystalline silicotitanate or a powdery adsorbent containing it, or by slurrying the powdered crystalline silicotitanate, A method of encapsulating crystalline silicotitanate by dripping into a liquid containing a curing agent such as calcium chloride, a method of attaching and coating a crystalline silicotitanate powder on the surface of a resin core, formed of natural fiber or synthetic fiber Examples thereof include a method in which a powdery crystalline silicotitanate or a powdery adsorbent containing the same is attached to the surface and / or inside of the formed sheet-like substrate and fixed to form a sheet.

  Examples of the granulation method include known methods such as stirring and mixing granulation, rolling granulation, extrusion granulation, crushing granulation, fluidized bed granulation, spray drying granulation (spray drying), A compression granulation etc. can be mentioned. In the granulation process, a binder and a solvent may be added and mixed as necessary. As the binder, known ones such as polyvinyl alcohol, polyethylene oxide, hydroxyethylcellulose, hydroxypropylcellulose, hydroxypropylmethylcellulose, hydroxyethylmethylcellulose, carboxymethylcellulose, hydroxypropylmethylcellulose, methylcellulose, ethylcellulose, starch, cornstarch, molasses, lactose, gelatin , Dextrin, gum arabic, alginic acid, polyacrylic acid, glycerin, polyethylene glycol and polyvinylpyrrolidone. As the solvent, various solvents such as an aqueous solvent and an organic solvent can be used.

  The granulated product obtained by granulating the water-containing crystalline silicotitanate obtained by the production method of the present invention is suitable as an adsorbent for a water treatment system having an adsorption vessel and an adsorption tower filled with a radioactive substance adsorbent. Can be used for In this case, the shape and size of the granular product obtained by granulating the water-containing crystalline silicotitanate is filled in an adsorption vessel or packed tower, and treated water containing cesium and / or strontium is passed through. It is preferable to adjust appropriately so that it may adapt to.

  The granulated product obtained by granulating the water-containing crystalline silicotitanate obtained by the production method of the present invention is recovered by magnetic separation from water containing cesium and / or strontium by further containing magnetic particles therein. It can be used as a possible adsorbent. Examples of magnetic particles include powders of metals such as iron, nickel and cobalt, or powders of magnetic alloys based on these metals, and metal oxides such as iron sesquioxide, iron sesquioxide, cobalt-added iron oxide, barium ferrite and strontium ferrite. Examples thereof include powders of physical magnetic materials. As a method for adding magnetic particles to a granulated granulated silicon silicotitanate, for example, the granulation operation described above may be performed in a state where magnetic particles are contained.

  The crystalline silicotitanate obtained by the production method of the present invention includes, for example, cesium and strontium adsorbents, as well as metal ions such as Pb, Cu, Zn, Cd, Hg, Co, Ni, Fe, Mn, and Ag. It can also be used as an adsorbent.

  The present invention will be specifically described below with reference to examples and comparative examples. However, the present invention is not limited to these. Unless otherwise specified, “%” represents “mass%”. Evaluation devices and materials used in Examples and Comparative Examples are as follows.

<Evaluation equipment>
X-ray diffraction: Bruker D8 AdvanceS was used. Cu-Kα was used as the radiation source. The measurement conditions were a tube voltage of 40 kV, a tube current of 40 mA, and a scanning speed of 0.1 ° / sec.
ICP-AES: Varian 720-ES was used.
Cs and Sr adsorption tests were conducted with a measurement wavelength of cesium (Cs) of 697.327 nm and a measurement wavelength of strontium (Sr) of 216.596 nm. The standard sample used was a Cs: 120 ppm aqueous solution containing 0.3% NaCl and a Sr: 30 ppm aqueous solution containing 0.3% NaCl.

<Materials used>
-Sodium silicate: manufactured by Nippon Chemical Industry Co., Ltd. (SiO ₂ : 28.96%, Na ₂ O: 9.37%, H ₂ O: 61.67%, SiO ₂ / Na ₂ O = 3.1)
-Caustic potash aqueous solution: 48% potassium hydroxide for industrial use (K ₂ O: 40.3%, H ₂ O: 59.7%)
-Caustic soda aqueous solution: Industrial 48% sodium hydroxide (Na ₂ O: 37.2%, H ₂ O: 62.8%)
Titanium tetrachloride aqueous solution: 36.48% aqueous solution manufactured by Osaka Titanium Technologies Co., Ltd. Simulated seawater: 0.3% NaCl aqueous solution containing 100 ppm of Cs and Sr was used as simulated seawater. The simulated seawater was prepared by dissolving Cs chloride and Sr chloride in a 0.3% NaCl aqueous solution such that Cs and Sr were 100 ppm, respectively.

[Examples 1 to 5 and Comparative Examples 1 and 2]
(1) First Step Sodium silicate, 48% caustic soda aqueous solution, 48% caustic potassium aqueous solution and pure water were mixed in the amounts shown in Tables 1 and 2 and stirred to obtain a mixed aqueous solution. To this mixed aqueous solution, the amount of titanium tetrachloride aqueous solution shown in Tables 1 and 2 was continuously added with a peristaltic pump over 0.5 hours to produce a mixed gel. The mixed gel was aged with stirring at room temperature (25 ° C.) for 1 hour after the addition of the aqueous titanium tetrachloride solution.

(2) Second Step After the mixed gel obtained in the first step is put into a beaker, the mouth of the beaker is lightly covered with aluminum foil, and then heated to the temperature shown in Table 1 and Table 2 over 1 hour. The reaction was carried out with stirring while maintaining this temperature. The reaction time was as shown in Tables 1 and 2. The slurry after the reaction was filtered, washed and dried to obtain massive crystalline silicotitanate.

  The compositions determined from the X-ray diffraction structures of the crystalline silicotitanates obtained in the examples and comparative examples are shown in Table 3 below. X-ray diffraction charts are shown in FIGS. Furthermore, the peak intensity of the main peak derived from crystalline silicotitanate observed at 2θ = 10 to 13 ° by X-ray diffraction analysis is shown in Table 3.

  From the results shown in FIGS. 1 to 7 and Table 3, the crystalline silicotitanate obtained in each example is a crystalline silicotitanate having a molar ratio of Ti: Si = 4: 3 by X-ray diffraction. It can be seen that sex silicotitanate is obtained substantially in a single phase. Moreover, it turns out that the crystalline silicotitanate obtained in each Example is remarkably superior to the crystalline silicotitanate of Comparative Examples 1 and 2.

<Cs and Sr adsorption test>
The massive crystalline silicotitanate obtained in Examples 1 to 5 and Comparative Examples 1 and 2 was pulverized in a mortar and classified with a 100 μm sieve to obtain a powder (<100 μm). 0.05 g of this granular adsorbent was placed in a 100 ml plastic container, 100.00 g of simulated seawater was added and the mixture was capped, and the contents were shaken and mixed. The contents of the plastic container were shaken by inverting and erecting the container 10 times. Then, after standing for 1 hour, the contents were shaken again. Subsequently, about 50 ml of the contents were extracted and filtered through 5C filter paper, and the filtrate obtained by filtration was collected. Further, the remaining 50 ml was left as it was, and further shaken again after 23 hours (24 hours after first shaking). The contents were filtered through 5C filter paper, and the filtrate obtained by filtration was collected. Using the collected filtrate as a target, the contents of Cs and Sr in the filtrate were measured using ICP-AES, and the distribution coefficient Kd was determined by the following equation. Moreover, the same test was conducted as Comparative Example 3 using a commercially available crystalline silicotitanate obtained by hydrothermal synthesis. The results are also shown in Table 4.

Distribution coefficient Kd = (C ₀ −C) / C × (V / m)
Here, C ₀ : each concentration before immersion of Cs and Sr.
C: Cs and Sr concentrations 24 hours after addition of adsorbent.
V: Solution volume (ml) of the test solution in a plastic container.
m: Weight of adsorbent (g).

As is apparent from the results shown in Table 4, the crystalline silicotitanate of Examples 1 to 5 obtained by this production method is superior in the adsorption performance of cesium compared to the crystalline silicotitanate of Comparative Examples 1 to 3. I understand that.
Further, the adsorption capacity of the crystalline silicotitanate of Examples 1 to 5 obtained by this production method is superior to that of the crystalline silicotitanate of Comparative Examples 1 and 2, and the water of Comparative Example 3 is used. It can be seen that it has an adsorption capacity equal to or higher than that of commercially available crystalline silicotitanate obtained by thermal synthesis.

Claims (5)

In the method for producing crystalline silicotitanate represented by the general formula: M ₄ Ti ₄ Si ₃ O ₁₆ · nH ₂ O (wherein M represents Na and K, n represents a number of 0 to 8). There,
A first step of obtaining a mixed gel by mixing a silicic acid source, a sodium compound, a potassium compound, titanium tetrachloride, and water;
A second step of reacting the mixed gel obtained in the first step,
In the first step, the molar ratio of Ti and Si contained in the mixed gel is Ti / Si = 1.2 or more and 1.5 or less, and the molar ratio of M ₂ O and SiO ₂ is M ₂ O / SiO ₂ = Add a silicic acid source, a sodium compound, a potassium compound and titanium tetrachloride so as to be 3.8 or more and 5.0 or less,
A method for producing crystalline silicotitanate, wherein the reaction is carried out at 70 ° C. or higher and 110 ° C. or lower under atmospheric pressure in the second step. In the first step, the molar ratio of Ti and Si contained in the mixed gel is Ti / Si = 1.2 or more and 1.5 or less, and the molar ratio of M ₂ O and SiO ₂ is M ₂ O / SiO ₂ = The method for producing crystalline silicotitanate according to claim 1, wherein a silicic acid source, a sodium compound, a potassium compound and titanium tetrachloride are added so as to be 4.0 or more and 5.0 or less. In the first step, the molar ratio (K ₂ O / M ₂ O) of potassium oxide equivalent (K ₂ O) to the total number of moles of sodium and potassium oxide equivalent (M ₂ O) in the mixed gel is: The method for producing crystalline silicotitanate according to claim 1 or 2, which is greater than 0 and 0.6 or less. In the first step, the molar ratio of water (H ₂ O / M ₂ O) to the total number of moles of sodium and potassium oxide conversion (M ₂ O) in the mixed gel is 50 or more and 150 or less. 4. The method for producing crystalline silicotitanate according to any one of items 1 to 3.   The method for producing crystalline silicotitanate according to any one of claims 1 to 4, wherein the first step includes an aging step of aging the mixed gel at 10 ° C or higher and lower than 70 ° C with stirring.

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