JP6356567B2 - Method for producing crystalline silicotitanate - Google Patents

Description

  The present invention relates to a method for producing crystalline silicotitanate that can be suitably used for selectively and efficiently separating and recovering cesium or strontium in seawater.

  Conventionally, coprecipitation treatment is known as a treatment technique for wastewater containing radioactive substances (see Patent Document 1 below). However, for water-soluble radioactive cesium and radioactive strontium, the coprecipitation treatment is not effective and is currently being adsorbed and removed by an inorganic adsorbent such as zeolite (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.

Crystalline silicotitanate is one of the inorganic adsorbents studied so far for the adsorption of cesium and / or strontium. Crystalline silicotitanates are known to have a plurality of types of compositions such as those with a Ti / Si ratio of 1: 1, 5:12, and 2: 1. It is known that there is crystalline silicotitanate in which is 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. It has a typical 8-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 hydrothermal treatment of a crystalline silicotitanate having a Ti / Si ratio of 4: 3, titanium tetrachloride as a Ti source, and a highly dispersed SiO ₂ powder as a Si source. The fact that it was manufactured by applying is described. This document describes that the synthesized crystalline silicotitanate has strontium ion exchange capacity.

Japanese Patent Laid-Open No. 62-266499 JP2013-57599A

JAEA-Research 2011-037 ZEOLITES, 1990, Vol 10, November / December Keiko Fujiwara, “Modification and evaluation of microporous crystals as heat pump adsorbents”, [online], [March 3, 2014 search], Internet <URL: http://kaken.nii.ac.jp/pdf /2011/seika/C-19/15501/21560846seika.pdf>

Conventionally, many studies on crystalline silicon titanate have been made on the sodium salt type, and the study has hardly been made on the potassium salt type.
Conventionally, crystalline silicotitanate has been known as an adsorbent for strontium and cesium, and further improvement in the adsorption performance of cesium is desired, and the adsorption performance of strontium is also required.
Accordingly, an object of the present invention is to provide an industrially advantageous method for producing crystalline silicotitanate which is effective in cesium adsorbents and further strontium adsorbents in seawater.

As a result of intensive studies to solve the above problems, the present inventors have added a silicic acid source, a potassium compound, titanium tetrachloride, and water, and the ratio of Ti: Si is a specific ratio, In addition, K ₄ Ti ₉ O ₂₀ · mH ₂ O and other crystalline silicotitanates are by-produced by hydrothermal reaction of the mixed gel obtained so that the molar ratio of K ₂ O and SiO ₂ becomes a specific ratio. The crystalline silicotitanate represented by the target general formula; K ₄ Ti ₄ Si ₃ O ₁₆ .nH ₂ O (wherein n represents 0 to 8) is X-ray diffraction simple. It has been found that crystalline silicotitanate, which is a phase and useful as an adsorbent for cesium and strontium from seawater, can be efficiently obtained, and the present invention has been completed.

That is, the present invention is a method for producing crystalline silicotitanate represented by the general formula: K ₄ Ti ₄ Si ₃ O ₁₆ .nH ₂ O (wherein n represents 0 to 8),
A first step of mixing a silicate source, a potassium compound, titanium tetrachloride and water to obtain a mixed gel;
A second step of hydrothermal reaction of 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 = 0.5 or more and 3.0 or less, and the molar ratio of K ₂ O and SiO ₂ is K ₂ O / SiO ₂ = 0. The present invention provides a method for producing crystalline silicotitanate, wherein a silicic acid source, a potassium compound and titanium tetrachloride are added so as to be 5 or more and 3.0 or less.

According to the present invention, crystalline silicotitanate having excellent adsorption and removal characteristics of cesium and strontium can be produced even in seawater by an industrially advantageous method. Further, according to the present invention, a crystal represented by the general formula of single phase in X-ray diffraction ;; K ₄ Ti ₄ Si ₃ O ₁₆ .nH ₂ O (wherein n represents 0 to 8). Sex silicotitanate can be easily produced.

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.

  The first step in the method for producing crystalline silicotitanate of the present invention is a step of producing a mixed gel by mixing a silicate source, a potassium compound, titanium tetrachloride and water.

  Examples of the silicate source used in the first step include potassium 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 potassium compound used in the first step include potassium hydroxide and potassium carbonate. 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.

  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 a titanium source, unreacted titanium oxide remains or crystalline siliconates other than crystalline silicon titanate having a molar ratio of Ti: Si of 4: 3 are formed. Cheap. 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 silicate source and titanium tetrachloride are added to the mixed solution in such an amount that the Ti / Si ratio is 0.32. In contrast, in the present invention, the silicic acid source and titanium tetrachloride are added in such an amount that the Ti / Si ratio is 0.5 or more and 3.0 or less. As a result of investigations by the present inventors, by setting the Ti / Si ratio in the mixed gel to the above molar range, crystals as crystalline silicotitanate represented by K ₄ Ti ₄ Si ₃ O 1 ₆ .nH ₂ O are obtained. It was found that a high degree of conversion was easily obtained, and that the adsorption performance of cesium was particularly improved when this crystalline silicotitanate was used as an adsorbent. From this viewpoint, the Ti / Si ratio in the mixed gel is preferably 1.0 or more and 3.0 or less, more preferably 1.1 or more and 2.5 or less, and 1.2 or more and 2.2 or less. More preferably, it is as follows.

Further, 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 2.0 mass% to 40 mass%, preferably 3 to 30 mass%, more preferably 5 to 5 mass%. 20% by mass is preferable from the viewpoint of obtaining crystalline silicotitanate with high yield.

In the present invention, the molar ratio of K ₂ O / SiO ₂ in the mixed gel is 0.5 or more and 3.0 or less, preferably 0.7 or more and 1.5 or less, more preferably 0.9 or more and 1.5 or less. This is also one of the characteristics of the method for producing crystalline silicotitanate of the present invention. As a result of the study by the present inventors, the crystallinity represented by K ₄ Ti ₄ Si ₃ O 1 ₆ .nH ₂ O is set by setting the ratio of K ₂ O / SiO _{2 in} the mixed gel to the above molar range. As silicotitanate, those having a higher degree of crystallinity were obtained with good yield, and it was found that the adsorption performance of cesium was further improved particularly when this crystalline silicotitanate was used as an adsorbent.

  In the first step, the silicic acid source, potassium compound and titanium tetrachloride can each be added to the reaction system in the form of an aqueous solution. In some cases, it can be added in the form of a solid. Further, in the first step, if necessary, the concentration of the mixed gel can be adjusted using pure water for the obtained mixed gel.

  In the first step, the silicate source, 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 potassium compound and water (this addition order is simply referred to as “implementation of (1) below”). ”Sometimes.) The implementation of (1) is preferable in that the generation of chlorine from titanium tetrachloride is suppressed.

  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 alkali silicate, titanium tetrachloride and water It is also possible to adopt a mode in which a potassium compound is added to the mixture. 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, the potassium compound can also be added in the form of its aqueous solution or in the form of a solid.

In the implementation of (1) and (2), the potassium compound has a potassium concentration in the mixed gel of 0.5% by mass or more and 15.0% by mass or less, particularly 0.7% by mass or more and 13% by mass in terms of K ₂ O. It is preferable to add so that it may become the following. K ₂ O in terms of potassium in the mixed gel weight and the concentration of K ₂ O in terms of potassium in the mixed gel (hereinafter referred to as "potassium concentration") is calculated by the following equation.

K ₂ O equivalent weight of potassium in the mixed gel (g)
= Moles of potassium ions from potassium silicate + moles of potassium ions from potassium compound such as potassium hydroxide - four moles of chloride ions from the titanium chloride) × 0.5 × K ₂ O molecular weight

Concentration (mass%) of potassium in the mixed gel in terms of K ₂ O
= K ₂ O equivalent weight of potassium in the mixed gel / (Moisture content in the mixed gel + K ₂ O equivalent weight of potassium in the mixed gel) × 100

In the present invention, the mixed gel is preferably substantially free of Na from the viewpoint of suppressing the production of crystalline silicotitanate other than the crystalline silicotitanate, which is the objective.
In the present invention, “substantially not containing Na” means a concentration in terms of Na ₂ O, and the concentration in the mixed gel is less than 0.5 mass%.

By combining the selection of the silicic acid source and the adjustment of the potassium concentration in the mixed gel, the production of crystalline silicotitanate other than the crystalline silicotitanate having a molar ratio of Ti: Si of 4: 3 can be suppressed. When potassium silicate is used as the silicic acid source, the production of crystalline silicotitanate having a molar ratio of Ti: Si of 5:12 is effectively suppressed by setting it to 2.8% by mass or more in terms of K ₂ O. On the other hand, it is possible to effectively produce crystalline silicotitanate having a molar ratio of Ti: Si of 1: 1 by setting the potassium concentration in the mixed gel to 6% by mass or less in terms of K ₂ O. It becomes possible to suppress. When activated silicic acid obtained by cation exchange of alkali silicate is used as a silicic acid source, the molar ratio of Ti: Si is 5:12 by making it 1% by mass or more in terms of K ₂ O. It becomes possible to effectively suppress the formation of crystalline silicotitanate, while the molar ratio of Ti: Si is 1: 1 by setting the potassium concentration in the mixed gel to 6% by mass or less in terms of K ₂ O. It is possible to effectively suppress the formation of crystalline silicotitanate.

When potassium silicate is used as the silicate source, the potassium component in the potassium silicate simultaneously becomes a potassium source in the mixed gel. Therefore, the “K ₂ O equivalent weight (g) of potassium in the mixed gel” mentioned here is counted as the sum of all potassium components in the mixed gel.

  In the implementation of (1) and (2), it is desirable to add titanium tetrachloride stepwise or continuously as an aqueous titanium tetrachloride 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 may be aged at 10 ° C. or higher and 100 ° C. or lower for a time period of 0.1 hour or longer and 5 hours or shorter before performing a hydrothermal reaction which is the second step described later. From the viewpoint of obtaining a uniform product. The aging step may be performed, for example, in a stationary state, or may be performed in a stirring state using a line mixer or the like.

  In the present invention, the mixed gel obtained in the first step is subjected to a hydrothermal reaction as the second step to obtain crystalline silicotitanate. The hydrothermal reaction is not particularly limited as long as the crystalline silicotitanate can be synthesized. Usually, in an autoclave, the temperature is preferably 120 ° C. or higher and 200 ° C. or lower, more preferably 140 ° C. or higher and 180 ° C. or lower, preferably 6 hours or longer and 72 hours or shorter, more preferably 12 hours or longer and 36 hours or shorter. React under pressure. The reaction time can be selected according to the scale of the synthesizer.

  The water-containing crystalline silicotitanate obtained in the second step can be dried, and the obtained 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 in which a plurality of apertures are formed to obtain a rod-shaped molded body, and the obtained rod-shaped molded body may be dried to form a columnar shape. 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, when extrusion is performed before drying, the yield of crystalline silicotitanate recovered by a classification method described later can be increased. Here, pulverization refers to an operation of loosening particles that are gathered into a lump, and pulverization refers to an operation of applying mechanical force to the loosened solid particles to make them finer.

  Examples of the shape of the hole formed in the opening member include a circle, a triangle, a polygon, and a ring shape. 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 a circle 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 being loosened lightly. 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.

The crystalline silicotitanate obtained by the production method of the present invention is represented by the general formula; K ₄ Ti ₄ Si ₃ O ₁₆ .nH ₂ O (wherein n represents 0 to 8). The first feature of the crystalline silicotitanate obtained by the production method of the present invention is that the molar ratio of Ti: Si is 4: 3, as is apparent from the above general formula. That the molar ratio of Ti: Si in the crystalline silicotitanate is this value can be confirmed by structural analysis of the crystalline silicotitanate by X-ray diffraction and composition analysis by ICP.

  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 is particularly excellent in the cesium adsorption / removal property, and in addition, the strontium adsorption / removal property is also high. Using this characteristic, the crystalline silicotitanate can be molded according to a conventional method if necessary, and the molded product obtained thereby can be suitably used as an adsorbent for cesium and / or strontium.

  Examples of the molding process include granulation for forming a powdery crystalline silicotitanate or a powdery adsorbent containing it into a granular form, and slurrying a powdered crystalline silicotitanate to obtain calcium chloride, etc. A method of encapsulating crystalline silicotitanate by dropping into a liquid containing a curing agent, a method of applying a crystalline silicotitanate powder to the surface of a resin core, and a sheet formed of natural fibers or synthetic fibers 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 the inside of the shaped 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), and compression granulation. A grain 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, polyvinylpyrrolidone and the like. 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.
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 the shape and size as appropriate so as to adapt to this.

In addition, a granular 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. It can be used as a possible adsorbent. Examples of magnetic particles include metals such as iron, nickel, and cobalt, or powders of magnetic alloys based on these metals, metal oxides such as iron trioxide, iron sesquioxide, cobalt-added iron oxide, barium ferrite, and strontium ferrite. Examples thereof include powders of magnetic system.
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.

  EXAMPLES The present invention will be specifically described below with reference to examples and comparative examples, but the present invention is not limited to these examples. 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.
The Cs and Sr adsorption tests were performed with a Cs measurement wavelength of 697.327 nm and a Sr measurement wavelength of 216.596 nm. Standard samples used were Cs: 100 ppm, 50 ppm and 10 ppm aqueous solutions containing 0.3% NaCl, and Sr: 100 ppm, 10 ppm and 1 ppm aqueous solutions containing 0.3% NaCl.

<Materials used>
Potassium silicate: manufactured by Nippon Chemical Industry Co., Ltd. (SiO ₂ : 26.5%, K ₂ O: 13.5%, H ₂ O: 60.00%, SiO ₂ / K ₂ O = 3.09).
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: solid reagent potassium hydroxide (KOH: 85%)
・ Caustic soda aqueous solution; industrial 25% sodium hydroxide (NaOH: 25%, H ₂ O: 75%)
-Titanium tetrachloride aqueous solution: 36.48% aqueous solution manufactured by Osaka Titanium Technologies Co., Ltd.-Titanium dioxide: Ishihara Sangyo ST-01
Simulated seawater: 0.3% NaCl aqueous solution containing 100 ppm of Cs and Sr was used as simulated seawater. Simulated seawater is composed of NaCl (99.5%): 3.0151 g, SrCl · 6H ₂ O (99%): 0.3074 g, CsNO ₃ (99%): 0.1481 g, H ₂ O: 996.5294 g. I got it.

[Example 1]
<Synthesis of crystalline silicotitanate>
(1) First Step 114.5 g of potassium silicate, 336.0 g of 85% caustic potash and 635.4 g of pure water were mixed and stirred to obtain a mixed aqueous solution. To this mixed aqueous solution, 527.1 g of titanium tetrachloride aqueous solution was continuously added over 0.5 hour with a peristaltic pump to produce a mixed gel. The mixed gel was aged by standing at room temperature (25 ° C.) for 1 hour after the addition of the aqueous titanium tetrachloride solution. At this time, the molar ratio of Ti and Si in the mixed gel was Ti: Si = 2: 1. The concentration of SiO ₂ in the mixed gel was 1.88%, the concentration of TiO ₂ was 5.00%, and the concentration of K ₂ O was 5.41%.

(2) Second Step The mixed gel obtained in the first step was placed in an autoclave, heated to 140 ° C. over 1 hour, and then reacted for 24 hours with stirring while maintaining this temperature. The slurry after the reaction was filtered, washed and dried to obtain massive crystalline silicotitanate. Table 1 below shows the compositions determined from the X-ray diffraction structure and ICP-AES composition analysis of the obtained crystalline silicotitanate. An X-ray diffraction chart of the obtained crystalline silicotitanate is shown in FIG.

<Adsorption test of Cs and Sr>
The obtained bulk crystalline silicotitanate was granulated (300 to 600 μm) by mortar grinding and classification with 600 μm and 300 μm sieves. 0.5 g of this granular crystalline silicotitanate was placed in a 100 ml plastic container, 100.00 g of simulated seawater was added, the cap was capped, and the contents were shaken and mixed. The contents were shaken by inverting the plastic container 10 times (the same applies hereinafter). Then, after standing for 1 hour, the contents were shaken and mixed again, about 50 ml was filtered with 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). And it filtered with 5 C filter paper, and the filtrate obtained by filtration was extract | collected. Using the collected filtrate as a target, the contents of Cs and Sr in the filtrate were measured using ICP-AES. The results are shown in Table 6 below.

[Example 2]
<Synthesis of crystalline silicotitanate>
(1) First Step 163.6 g of potassium silicate, 322.4 g of 85% caustic potash and 744.8 g of pure water were mixed and stirred to obtain a mixed aqueous solution. To this mixed aqueous solution, 502.0 g of titanium tetrachloride aqueous solution was continuously added over 0.5 hour with a peristaltic pump to produce a mixed gel. The mixed gel was aged by standing at room temperature (25 ° C.) for 1 hour after the addition of the aqueous titanium tetrachloride solution. At this time, the molar ratio of Ti and Si in the mixed gel was Ti: Si = 1: 0.75. Further, the SiO ₂ concentration in the mixed gel was 2.50%, the TiO ₂ concentration was 4.43%, and the K ₂ O concentration was 5.35%.

(2) Second Step The mixed gel obtained in the first step was placed in an autoclave, heated to 140 ° C. over 2 hours, and then reacted for 18 hours with stirring while maintaining this temperature. The slurry after the reaction was filtered, washed and dried to obtain massive crystalline silicotitanate. Table 2 below shows the compositions determined from the X-ray diffraction structure and ICP-AES composition analysis of the obtained crystalline silicotitanate. An X-ray diffraction chart of the obtained crystalline silicotitanate is shown in FIG. The results of the adsorption test of the obtained crystalline silicotitanate are also shown in Table 6.

Example 3
<Synthesis of crystalline silicotitanate>
(1) First Step 129.0 g of potassium silicate, 380.6 g of 85% caustic potash and 635.4 g of pure water were mixed and stirred to obtain a mixed aqueous solution. To this mixed aqueous solution, 600.0 g of titanium tetrachloride aqueous solution was continuously added over 0.5 hour with a peristaltic pump to produce a mixed gel. The mixed gel was aged by standing at room temperature (25 ° C.) for 1 hour after the addition of the aqueous titanium tetrachloride solution. At this time, the molar ratio of Ti and Si in the mixed gel was Ti: Si = 2: 1. The concentration of SiO ₂ in the mixed gel was 1.96%, the concentration of TiO ₂ was 5.26%, and the concentration of K ₂ O was 5.68%.

(2) Second Step The mixed gel obtained in the first step was placed in an autoclave, heated to 140 ° C. over 1 hour, and then reacted for 24 hours with stirring while maintaining this temperature. The slurry after the reaction was filtered, washed and dried to obtain massive crystalline silicotitanate. The composition determined from the X-ray diffraction structure of the obtained crystalline silicotitanate and elemental analysis by ICP is shown in Table 3 below. Further, an X-ray diffraction chart of the obtained crystalline silicotitanate is shown in FIG. The results of the adsorption test of the obtained crystalline silicotitanate are also shown in Table 6.

Example 4
<Synthesis of crystalline silicotitanate>
(1) First Step 114.5 g of potassium silicate, 300.6 g of 85% caustic potash and 670.8 g of pure water were mixed and stirred to obtain a mixed aqueous solution. To this mixed aqueous solution, 527.1 g of titanium tetrachloride aqueous solution was continuously added over 0.5 hour with a peristaltic pump to produce a mixed gel. The mixed gel was aged by standing at room temperature (25 ° C.) for 1 hour after the addition of the aqueous titanium tetrachloride solution. At this time, the molar ratio of Ti and Si in the mixed gel was Ti: Si = 2: 1. The SiO ₂ concentration in the mixed gel was 1.88%, the TiO ₂ concentration was 5.00%, and the K ₂ O concentration was 3.23%.

(2) Second Step The mixed gel obtained in the first step was placed in an autoclave, heated to 140 ° C. over 2 hours, and then reacted for 18 hours with stirring while maintaining this temperature. The slurry after the reaction was filtered, washed and dried to obtain massive crystalline silicotitanate. The composition determined from the X-ray diffraction structure of the obtained crystalline silicotitanate and elemental analysis by ICP is shown in Table 4 below. Further, FIG. 4 shows an X-ray diffraction chart of the obtained crystalline silicotitanate. The results of the adsorption test of the obtained crystalline silicotitanate are also shown in Table 6.

[Comparative Example 1]
No. 3 sodium silicate 90 g, caustic soda aqueous solution 121.2 g and pure water 776.1 g were mixed and stirred to obtain a mixed aqueous solution. To this mixed aqueous solution, a slurry prepared by mixing and dispersing 68.2 g of titanium dioxide in 270 g of ion-exchanged water was continuously added to the mixed solution over 5 minutes to obtain a mixed gel. The mixed gel was aged at room temperature for 1 hour after the addition of titanium dioxide. This mixed gel is put in an autoclave and heated to 170 ° C. over 1 hour. Then, while maintaining this temperature, the reaction is carried out for 24 hours with stirring, and the slurry after the reaction is filtered, washed and dried to obtain crystalline silicon. Titanate was obtained. The molar ratio of Ti and Si in the mixed gel was Ti: Si = 2: 1. The concentration of SiO ₂ in the mixed gel was 1.97%, the concentration of TiO ₂ was 5.15%, and the concentration of Na ₂ O was 2.59%. The obtained crystalline silicotitanate was subjected to the same analysis and adsorption test as in Example 1. Table 3 below shows the compositions determined from the X-ray diffraction structure and ICP-AES composition analysis of the obtained crystalline silicotitanate. As a result, the presence of titanium oxide as an impurity was confirmed. The results of the adsorption test for Cs and Sr are shown in Table 6 below.

As is apparent from the results shown in Tables 1 to 4 and Table 6, it can be seen that according to this example, crystalline silicotitanate represented by K ₄ Ti ₄ Si ₃ O ₁₆ .6H ₂ O can be obtained. It can be seen that the crystalline silicotitanate can adsorb and remove Cs and Sr contained in the simulated seawater with a high adsorption rate. In addition, by adopting the conditions of the examples, unreacted titanium source remains or suppresses by-production of crystalline silicotitanate other than crystalline silicotitanate having a molar ratio of Ti: Si of 4: 3, Single phase crystalline silicotitanate can be obtained.

Claims (6)

A method for producing a crystalline silicotitanate represented by a general formula: K ₄ Ti ₄ Si ₃ O ₁₆ .nH ₂ O (where n represents 0 to 8),
A first step of mixing a silicate source, a potassium compound, titanium tetrachloride and water to obtain a mixed gel;
A second step of hydrothermal reaction of 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 = 0.5 or more and 3.0 or less, and the molar ratio of K ₂ O and SiO ₂ is K ₂ O / SiO ₂ = A method for producing crystalline silicotitanate, comprising adding a silicic acid source, a potassium compound and titanium tetrachloride so as to be 0.5 or more and 3.0 or less.   The method for producing crystalline silicotitanate according to claim 1, wherein in the first step, the mixed gel contains substantially no Na. In the first step, the molar ratio of Ti and Si contained in the mixed gel is Ti / Si = 1.0 to 3.0 and the molar ratio of K ₂ O and SiO ₂ is K ₂ O / SiO _2. The crystalline silicotitanate according to claim 1, wherein a silicic acid source, a potassium compound, and titanium tetrachloride are added so as to be 0.7 to 1.5. Manufacturing method. In the first step, the silicic acid source and the quaternary silicate source and the quaternary silicate are converted so that the total amount of the SiO ₂ converted silicate source concentration and the TiO ₂ converted titanium tetrachloride concentration is 2.0% by mass or more and 40% by mass or less. Titanium chloride is added, The manufacturing method of the crystalline silicotitanate as described in any one of Claim 1 or 2 characterized by the above-mentioned.   The method for producing crystalline silicotitanate according to any one of claims 1 to 4, wherein in the first step, the potassium compound is potassium hydroxide.   The method for producing crystalline silicotitanate according to any one of claims 1 to 5, wherein in the first step, the silicate source is potassium silicate.