JP6309699B2 - Method for producing adsorbent containing crystalline silicotitanate - Google Patents

Description

  The present invention particularly relates to a method for producing an adsorbent containing crystalline silicotitanate that can be suitably used for selectively and efficiently separating and recovering cesium and / 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 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.

Therefore, the use of crystalline silicotitanate as a cesium adsorbent has been studied (see Non-Patent Document 1 below). For crystalline silicotitanate (hereinafter sometimes referred to as “CST”), Patent Document 3 uses an alkoxide of Si (OET) ₄ as the Si source and Ti (OET) _{4 as} the Ti source, A method for hydrothermal synthesis of titanosilicate TS-1 using tetrapropylammonium hydroxide is disclosed. Further, as a method for synthesizing a CST adsorbent having selectivity for cesium, Non-Patent Document 2 uses a alkoxide similar to TS-1 as a Ti source and a Si source, and a molar ratio of Ti: Si is 1: 1. And a mixture using Na compound as a mold is hydrothermally synthesized to produce crystals close to Na ₂ Ti ₂ O ₃ (SiO ₄ ) · 2H ₂ O with a molar ratio of Ti: Si of 2: 1. It has been reported that a powder (Na _1.64 H _0.36 Ti ₂ O ₃ (SiO ₄ ) · 1.84H ₂ O) can be obtained.

  In addition, the inventors previously obtained a mixed gel by adding a silicic acid source, a sodium compound and / or potassium compound, titanium tetrachloride, and water in Patent Document 4 below, and then obtaining the mixed gel. The adsorbent useful for adsorption removal of cesium and strontium from seawater containing crystalline silicotitanate having a Ti / Si molar ratio of 4/3 was proposed by hydrothermal reaction of the resulting mixed gel.

Japanese Patent Laid-Open No. 62-266499 JP2013-57599A JP-A-56-96720 US2016 / 107140A1

JAEA-Research 2011-037 Chem. Mater. , 6, 1994, pp. 2364-2368

Conventionally, crystalline silicotitanate having a Ti / Si molar ratio of 2/1 is known as an adsorbent for strontium and cesium, but an expensive raw material such as an alkoxide is used as the Si source and / or Ti source. Further, since there is a problem of wastewater treatment of alcohol as a by-product, it has been desired to develop an industrially advantageous method, in particular, a method for providing an adsorbent excellent in adsorption ability of cesium and / or strontium. .
Accordingly, an object of the present invention is to produce an adsorbent containing crystalline silicotitanate having a Ti / Si molar ratio of 2/1 by X-ray diffraction, which is excellent in adsorbability of cesium and strontium even in seawater. In an advantageous manner.

  As a result of intensive studies in order to solve the above problems, the present inventor, in the method for producing an adsorbent containing crystalline silicotitanate having a Ti / Si molar ratio of 4/3 described in Patent Document 4, The crystalline silicotitanate obtained when the niobium source is contained in the mixed gel and subjected to the hydrothermal reaction contains a crystalline silicotitanate having a Ti / Si molar ratio of 2/1 in X-ray diffraction. And the adsorbent containing the crystalline silicotitanate was found to be particularly excellent in the ability to adsorb cesium from seawater and further strontium. As a result of further investigation, a solution containing at least a silicic acid source, an alkali metal compound and water and subjected to a hydrothermal reaction on a mixed gel obtained by adding titanium tetrachloride to a niobium-containing mixed gel is a cesium and strontium adsorption performance In particular, the present inventors have found that the adsorption performance of strontium is greatly improved, and the present invention has been completed.

That is, the present invention has a general formula: A ₂ Ti ₂ O ₃ (SiO ₄ ) · nH ₂ O (wherein A represents one or two alkali metal elements selected from Na and K. n represents A method for producing an adsorbent comprising Nb in crystalline silicotitanate represented by the formula:
A first step of obtaining a niobium-containing mixed gel by mixing a silicic acid source, an alkali metal compound, a niobium source , titanium tetrachloride and water ;
A niobium-containing mixed gel obtained by the first step is hydrothermally reacted, and the niobium-containing mixed gel of the first step is a liquid containing at least a silicic acid source, an alkali metal compound, and water. The present invention provides a method for producing an adsorbent characterized by being obtained by adding titanium tetrachloride.

FIG. 1 is an X-ray diffraction chart of an adsorbent containing the crystalline silicotitanate obtained in Example 1 and Example 8. FIG. 2 is an X-ray diffraction chart of the adsorbent containing the crystalline silicotitanate obtained in Examples 2 to 5. FIG. 3 is an X-ray diffraction chart of the adsorbent containing the crystalline silicotitanate obtained in Examples 6-7. 4 is an X-ray diffraction chart of an adsorbent containing crystalline silicotitanate obtained in Example 10. FIG.

Detailed Description of the Invention

Hereinafter, the present invention will be described based on preferred embodiments thereof.
The adsorbent obtained by this production method is obtained by adding Nb to crystalline silicotitanate, and a general formula in which the molar ratio of Ti / Si is 2/1 by X-ray diffraction; A ₂ Ti ₂ O ₃ (SiO ₄ ) · nH ₂ O (wherein A represents one or two alkali metal elements selected from Na and K. n represents a number of 0 to 2). It contains sex silicotitanate.
In the present invention, “a general formula in which the molar ratio of Ti / Si is 2/1 by X-ray diffraction; A ₂ Ti ₂ O ₃ (SiO ₄ ) · nH ₂ O (where A is Na and K Is a crystalline silicotitanate represented by 1 or 2 kinds of alkali metal elements selected from the above, and n represents a number of 0 to 2. ”in X-ray diffraction analysis It means that the diffraction peak pattern of crystalline silicotitanate can be confirmed, and does not necessarily mean that the molar ratio of Ti / Si is 2/1 in the composition of the adsorbent. The adsorbent obtained by this production method preferably has a diffraction peak pattern of the crystalline silicotitanate as a main component in X-ray diffraction analysis. The diffraction peak pattern of the crystalline silicotitanate is confirmed as the main component when the adsorbent is subjected to X-ray diffraction analysis as the main peak in the range of 2θ = 5 to 80 °. It means that a diffraction peak of titanate is observed. Preferably, the main peak in the scanning range is observed at a position of 2θ = 10 ° to 13 °. In addition to this range, the crystalline silicotitanate has a diffraction peak in any one or more of 14 ° to 16 °, 25 ° to 28 °, 26 ° to 29 °, 33 ° to 36 °. It is preferred that it be observed. X-ray diffraction analysis can be performed under the conditions described in the examples described later.

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

  Examples of the silicate source used in the first step include alkali silicates such as sodium silicate and potassium silicate. Moreover, the active silicic acid obtained by carrying out cation exchange of the alkali silicate (namely, alkali metal salt of silicic acid) can also be used.

  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.

  The alkali metal compound used in the first step is, for example, a compound containing sodium or potassium. Examples of the compound containing sodium include sodium hydroxide and sodium carbonate. Moreover, potassium hydroxide, potassium carbonate, etc. are mentioned as a compound containing potassium. Among these alkali metal compounds, when carbonate is used, carbon dioxide gas is generated. Therefore, it is preferable to use a hydroxide that does not generate such gas from the viewpoint of smoothly promoting the neutralization reaction.

In this production method, the reaction is carried out by containing a niobium source in the mixed gel, so that the reaction system of the present invention contains crystalline silicotitanate having a Ti / Si molar ratio of 2/1 by X-ray diffraction. An adsorbent can be generated.
Examples of the niobium source used in the first step include niobium hydroxide, niobium oxide, niobium oxalate, and niobium ammonium oxalate. Among these, niobium hydroxide is more reactive than niobium oxide. In addition, it is preferable from the viewpoint of being cheaper than niobium oxalate and its salt.

  In the method for producing an adsorbent of the present invention, it is one of the features that titanium tetrachloride is used as a titanium source. When another titanium compound such as titanium oxide or titanium alkoxide is used as the titanium source, the reaction is difficult to proceed and usually requires a reaction time of not less than 100 hours at 170 ° C. In the production method, the reaction time is shortened by using titanium tetrachloride as a titanium source, and the adsorbent having excellent adsorption performance containing crystalline silicotitanate having a Ti / Si molar ratio of 2/1 by X-ray diffraction. Can be manufactured.

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

  In the first step, the silicic acid source, the alkali metal compound, the niobium source 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 the first step, a mixed gel before adding a niobium source obtained by adding titanium tetrachloride to a liquid containing a silicic acid source and an alkali metal compound (hereinafter sometimes simply referred to as “mixed gel”) Alternatively, if necessary, the concentration of the niobium-containing mixed gel can be adjusted using pure water with respect to the niobium-containing mixed gel.

In the first step, it is also one of the features that a niobium-containing mixed gel is obtained by adding titanium tetrachloride to a mixture of at least a silicic acid source, an alkali metal compound and water.
In this production method, the adsorbent obtained by subjecting the niobium-containing mixed gel obtained by adding titanium tetrachloride to a mixture of at least a silicic acid source, an alkali metal compound and water, is particularly A material having high adsorption performance of strontium is obtained, and further, there is an advantage that generation of chlorine from titanium tetrachloride can be suppressed.

  Titanium tetrachloride in the first step can be added in the form of an aqueous solution or solid form.

In the first step, the procedure for preparing the niobium-containing mixed gel may be either (1) or (2).
(1) Titanium tetrachloride is added to a liquid containing a silicic acid source, an alkali metal compound, water and a niobium source.
(2) Titanium tetrachloride is added to a liquid containing a silicic acid source, an alkali metal compound and water to obtain a mixed gel, and a niobium source is added to the mixed gel.
In the case of (1), as a preparation procedure of a liquid containing a silicic acid source, an alkali metal compound, water and a niobium source before adding titanium tetrachloride, four kinds of materials may be mixed at the same time, and at different timings. May be mixed. There are various examples of mixing at different timings. For example, there is a method in which a niobium source is further added to a liquid obtained by mixing a silicic acid source, an alkali metal compound and water and mixed.

In the first step, mixing a silicic acid source, an alkali metal compound, a niobium source, titanium tetrachloride and water so as to be a niobium-containing mixed gel having a composition represented by the following molar ratio is a target CST. The yield can be increased to a satisfactory level, and by-product generation of impurities such as remaining titanium oxide, amorphous silicate compounds other than CST, niobium-containing silicate titanate, etc. can be suppressed as much as possible. From the viewpoint of being able to.
_{(Nb 2 O 5 + TiO 2} ) / SiO 2 = 0.70~2.50, preferably 0.81 to 2.2,
A ₂ O / SiO ₂ = 0.65 to 3.50, preferably 1.00 to 3.00
H ₂ O / SiO ₂ = 40 to 180, preferably 50 to 150
In this production method, the number of moles of A ₂ O in the mole ratio of A ₂ O / SiO ₂ is the number of sodium and potassium ions in the niobium-containing mixed gel expressed in terms of oxides, in other words, It is obtained by subtracting the amount of sodium or potassium used for the neutralization reaction with titanium tetrachloride from the total amount of sodium and potassium in the niobium-containing mixed gel.

Viewpoint of obtaining an adsorbent having improved adsorption performance by X-ray diffraction single phase CST, particularly when the molar ratio of A ₂ O / SiO _{2 in} the niobium-containing mixed gel is 1.3 to 2.5 To preferred.
Furthermore, the molar ratio of H ₂ O / A ₂ O in the niobium-containing mixed gel is 20 to 100, preferably 30 to 80, particularly 40 to 70, from the viewpoint of obtaining an adsorbent with further improved adsorption performance.

The amount of niobium source added is 0.03 to 0.35, preferably 0.05 to 0.29 in terms of the molar ratio of niobium to titanium (Nb ₂ O ₅ / TiO ₂ ) in the niobium-containing mixed gel. It is preferable from the viewpoint that the production of the target Nb-containing CST can be promoted and the production of the by-product Nb-containing silicate titanate can be suppressed.

When an alkali silicate such as sodium silicate or potassium silicate is used as the silicic acid source, sodium and potassium, which are alkali metal components contained in the alkali silicate, are simultaneously regarded as NaOH and KOH. It is also an alkaline component. Therefore, the A ₂ O is calculated as the sum of all alkali components.

By combining the adjustment of the alkali metal concentration of the selection and niobium-containing mixed gel silicic acid source, X-rays diffraction to Ti: molar ratio of Si 2: 1 the production of crystalline Shirikochitaneto other than crystalline Shirikochitaneto Can be suppressed as much as possible. When alkali silicate is used as the silicic acid source, the alkali metal concentration in the niobium-containing mixed gel is 2.6% by mass or more in terms of A ₂ O, whereby a crystal having a Ti: Si molar ratio of 5:12 is obtained. The production of silicotitanate can be effectively suppressed. On the other hand, the alkali metal concentration in the niobium-containing mixed gel is 9.4% by mass or less in terms of A ₂ O, whereby the molar ratio of Ti: Si However, it is possible to effectively suppress the production of 1: 1 crystalline silicotitanate.

  In the first step, 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 niobium-containing mixed gel obtained in the first step is 20 ° C. or higher and 100 ° C. or lower under atmospheric pressure for 0.5 hour or more and 2 hours or less before performing the hydrothermal reaction which is the second step described later In order to obtain a uniform product, aging is preferably performed at 20 ° C. or higher and 70 ° C. or lower. 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 niobium-containing mixed gel obtained in the first step is subjected to a hydrothermal reaction as the second step to obtain an adsorbent containing crystalline silicotitanate. The hydrothermal reaction is not particularly limited as long as the crystalline silicotitanate can be synthesized. The hydrothermal reaction temperature is preferably 120 ° C. or higher and 200 ° C. or lower, more preferably 140 ° C. or higher and 200 ° C. or lower. The hydrothermal reaction time is preferably 6 hours or more and 100 hours or less, more preferably 12 hours or more and 80 hours or less. In the hydrothermal reaction, the niobium-containing mixed gel is usually reacted under pressure in an autoclave at a temperature within the above range and for a time within the above range. 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 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.

The adsorbent obtained by this production method has a general formula: A ₂ Ti ₂ O ₃ (SiO ₄ ) · nH ₂ O (wherein A represents one or two alkali metal elements selected from Na and K). N represents a number of 0 to 2.) The crystalline silicotitanate represented by Nb is contained, and the content of Nb in the adsorbent is 2% by mass or more as Nb ₂ O _5. , Preferably 5 to 20% by mass, particularly preferably 10 to 20% by mass. Further, the content of Ti in the adsorbent is 20% by mass or more, preferably 25 to 45% by mass as TiO ₂ . Further, the content of Si in the adsorbent is 5 to 30% by mass, preferably 10 to 25% by mass as SiO ₂ . Further, the total amount of Na and K in the adsorbent is 5 to 40% by mass, preferably 10 to 25% by mass as A ₂ O.
In the adsorbent obtained by the present production method, the Xb-ray diffraction agrees with the diffraction peak pattern of crystalline silicotitanate having a Ti / Si molar ratio of 2/1. It is thought that it exists in the form of partly substituted with Ti of the sex silicotitanate.
It should be noted that the adsorbent obtained by the present production method preferably has as few by-products as possible such as alkali silicate niobate and niobium-containing alkali silicate titanate resulting from the production method, but the range does not impair the effects of the present invention. The content may contain by-products resulting from the production method.

  The adsorbent obtained by this production method can be suitably used as an adsorbent for metals such as cesium, strontium, antimony, lead, zinc, mercury, copper, cadmium, and mercury.

  The adsorbent obtained by this production method is particularly excellent in cesium adsorption / removal properties, and in addition, has high strontium adsorption / removal properties. Using this characteristic, the molded article obtained by molding according to a conventional method can be further used as an adsorbent for cesium and / or strontium.

  As the molding process, for example, a powdery crystalline silicotitanate or a powdery adsorbent containing the same is granulated, or an adsorbent containing the powdery crystalline silicotitanate is slurried. A method of encapsulating an adsorbent by dropping it into a liquid containing a hardener such as calcium chloride, a method of applying an adsorbent powder to the surface of a resin core material, a sheet formed of natural fibers or synthetic fibers Examples thereof include a method in which a powdery adsorbent or a powdery adsorbent containing the adsorbent is attached to the surface and / or inside of the 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 granular product obtained by granulating the adsorbent obtained by the production method of the present invention can be suitably used as an adsorbent for a water treatment system having an adsorption vessel and an adsorption tower filled with a radioactive substance adsorbent. I can do it.
In this case, the shape and size of the granular product obtained by granulating the adsorbent is suitable for filling the adsorption vessel or packed tower and passing the treated water containing cesium and / or strontium. Thus, it is preferable to appropriately adjust the shape and size.

In addition, the granular product obtained by granulating the adsorbent obtained by the production method of the present invention can be recovered as an adsorbent by magnetic separation from water containing cesium and / or strontium by further containing magnetic particles. Can be used. 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 of incorporating magnetic particles into a granulated product obtained by granulating an adsorbent, for example, the above-described granulation processing operation may be performed in a state where magnetic particles are contained.

Further, in this production method, the adsorbent obtained by the above production method can be used as an adsorbent that can selectively and efficiently adsorb strontium out of cesium and strontium in water by further heat treatment. .
In addition, the adsorbent to be heat-treated may be a powder (including granules) obtained after the second step or a molded product thereof.

  The heat treatment temperature is 250 ° C. or higher and 800 ° C. or lower. Examples of the apparatus used for the heat treatment include a box-type firing furnace and a rotary kiln. Note that an electric furnace or the like can be used in a laboratory scale. The atmosphere for the heat treatment may be an oxygen-containing atmosphere such as the air, an inactive atmosphere such as nitrogen or argon, or a reducing atmosphere.

When the temperature of the heat treatment is 250 ° C. or higher, the cesium adsorption performance can be lowered. Moreover, the temperature of heat processing shall be 800 degrees C or less, and the strontium adsorption performance of the adsorbent obtained can be made high. From these viewpoints, the temperature of the heat treatment is preferably 250 ° C. or higher and 800 ° C. or lower, more preferably 300 ° C. or higher and 700 ° C. or lower, and particularly preferably 400 ° C. or higher and 600 ° C. or lower.
The heat treatment time in the above temperature range is, for example, preferably 0.5 hours or more, and more preferably 1 hour or more and 24 hours or less.

  The obtained heat-treated product may be used as an adsorbent as it is, or may be used as an adsorbent after appropriately performing various treatments such as washing, drying and molding.

  The heat-treated adsorbent obtained by the above production method can be used in various applications as an adsorbent that is a powder-like unmolded product or a molded product such as a rod or particle (including granules). When the heat-treated adsorbent obtained by the production method of the present invention is used as a molded body, it can be carried out by the same method as described above.

  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>
Sodium silicate (No. 3 sodium silicate): manufactured by Nippon Chemical Industry Co., Ltd. (SiO ₂ : 28.5%, Na ₂ O: 9.2%, H ₂ O: 62.3%, SiO ₂ / Na ₂ O = 3.1).
・ 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.-Niobium hydroxide: Commercially available product (containing Nb ₂ O ₅ : 76.5 wt%)
Simulated seawater (1): A 0.3% NaCl aqueous solution containing 100 ppm of Cs and Sr was used as simulated seawater. Simulated seawater (1) is NaCl (99.5%): 3.0151 g, SrCl ₂ .6H ₂ O (99%): 0.3074 g, CsNO ₃ (99%): 0.1481 g, H ₂ O: 996. 5294g was obtained by mixing.
Simulated seawater (2): A 0.3% NaCl aqueous solution containing 1 ppm of Cs and Sr, 37 ppm of K, 40 pppm of Ca and 125 ppm of Mg was used as simulated seawater (2). Simulated seawater (2) was prepared using NaCl, SrCl ₂ .6H ₂ O, CsCl, MgSO ₄ , CaSO ₄ .2H ₂ O, KCl, and H ₂ O.

[Example 1]
(1) First Step No. 3 sodium silicate 115 g, caustic soda aqueous solution 670.9 g, and ion-exchanged water 359.1 g were mixed and stirred to obtain a mixed aqueous solution. To this mixed aqueous solution, 25.5 g of niobium hydroxide (Nb ₂ O ₅ : 76.5% by mass) was added and mixed with stirring, and then 412.3 g of titanium tetrachloride aqueous solution was continuously added over 0.5 hour with a peristaltic pump. Thus, a niobium-containing mixed gel was produced. The gel was aged at room temperature (25 ° C.) for 1 hour after the addition of the aqueous titanium tetrachloride solution.

(2) Second Step The niobium-containing mixed gel obtained in the first step was placed in an autoclave, heated to 160 ° C. over 1 hour, and then reacted for 18 hours with stirring while maintaining this temperature.

The slurry after the reaction was filtered, and the obtained cake was extruded using a circular aperture member having a diameter of 0.6 mm, dried and classified to obtain a granular material having a particle size of 300 μm or more and 600 μm or less.
The obtained granular material was subjected to X-ray diffraction measurement. The result is shown in FIG. Moreover, the composition analysis by ICP-AES was performed about the granular material. The results are shown in Table 2.
From the results of FIG. 1, it was confirmed by X-ray diffraction that the obtained granular material was mainly composed of crystalline silicotitanate represented by Na ₂ Ti ₂ O ₃ (SiO ₄ ) · 2H ₂ O. The presence of a slight heterogeneous phase (Na ₁₂ (Ti ₂ O ₂ ) (Nb ₁₂ SiO ₄₀ ) (H ₂ O) ₄ ) was also confirmed.

<Adsorption test of Cs and Sr>
0.5 g of this granular adsorbent was taken in a 100 ml plastic container, 100.00 g of simulated seawater (1) was added, the lid 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, and the adsorption rate of Cs and Sr of the adsorbent was determined from the results. The obtained adsorption rate is shown in Table 3 below.

[Examples 2 to 7]
No. 3 sodium silicate, caustic soda aqueous solution, ion exchange water, niobium hydroxide and titanium tetrachloride aqueous solution were added in the amounts shown in Table 1, and in the second step, the reaction temperature was 170 ° C. for 72 hours. Except for the above, the reaction was carried out in the same manner as in Example 1, then, a granular adsorbent was prepared in the same manner as in Example 1, and the adsorption test of Cs and Sr was conducted. The results are shown in Table 3 below. As a result of X-ray diffraction analysis, it was confirmed by X-ray diffraction that the obtained granular material was mainly composed of crystalline silicotitanate represented by Na ₂ Ti ₂ O ₃ (SiO ₄ ) · 2H ₂ O. did. The presence of a slight amount of foreign phase (Na ₁₂ (Ti ₂ O ₂ ) (Nb ₁₂ SiO ₄₀ ) (H ₂ O) ₄ ) was also confirmed, and the composition was analyzed by ICP-AES for the granular material. It shows in Table 2.

Example 8
100 g of the granular adsorbent obtained in Example 1 was placed in an alumina container, heated in the atmosphere over 2 hours, and then calcined at 500 ° C. for 2 hours. The granular material after firing was taken out into the atmosphere together with the container and cooled to obtain an adsorbent. Further, the adsorption test of Cs and Sr was conducted in the same manner as in Example 1. The results are shown in Table 3 below.
The obtained adsorbent was measured by X-ray diffraction. The results are also shown in FIG.

[Examples 9 to 12]
No. 3 sodium silicate, caustic soda aqueous solution, ion exchange water, niobium hydroxide and titanium tetrachloride aqueous solution were added in the amounts shown in Table 4, and the reaction was carried out in the second step except that the reaction temperature was 190 ° C. Reaction was carried out in the same manner as in Example 1, and then a granular adsorbent having an Nb ₂ O ₅ content of 16.8% by mass was prepared in the same manner as in Example 1.
As a result of X-ray diffraction analysis, the granular material obtained in Example 10 is a crystalline silicotitanate expressed by X-ray diffraction with a single-phase Na ₂ Ti ₂ O ₃ (SiO ₄ ) · 2H ₂ O. It was confirmed. FIG. 4 shows an X-ray diffraction pattern of the adsorbent obtained in Example 10.

[Comparative Example 1]
In Example 10, a caustic soda aqueous solution, ion-exchanged water and titanium tetrachloride were mixed and stirred to obtain a mixed solution. To this mixed solution, 62.0 g of niobium hydroxide (Nb ₂ O ₅ : 76.5% by mass) was obtained. In addition, after stirring and mixing, the reaction was performed in the same manner as in Example 10 except that No. 3 sodium silicate was added to obtain a niobium-containing mixed gel, and then Nb ₂ O ₅ was processed in the same manner as in Example 10. A granular adsorbent having a content of 14.9% by mass was prepared.

[Comparative Example 2]
In Example 10, the reaction was performed in the same manner as in Example 10 except that 1003.7 g of a 24% by mass aqueous titanium sulfate solution was used instead of the titanium tetrachloride aqueous solution, and then Nb ₂ O was performed in the same manner as in Example 10. A granular adsorbent having a ₅ content of 16.6% by mass was prepared.

<Adsorption test of Sr and Cs>
0.05 g of the adsorbent containing the granular crystalline silicotitanate obtained in Examples 9 to 12 and Comparative Examples 1 and 2 is taken in a 1000 ml plastic container, and 1000.00 ml of simulated seawater (2) is added to the lid. After mixing, the contents were shaken. 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 content of Sr in the filtrate was measured using ICP-AES, and the distribution coefficient Kd was determined by the following equation.
For Examples 9 and 10 and Comparative Examples 1 and 2, the collected filtrate was measured using ICP-AES, the Cs content in the filtrate was measured, and the distribution coefficient Kd was obtained from the following equation. It was.
These results are shown in Table 5.

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

According to the present invention, a crystalline silicotitanate having an excellent cesium and / or strontium adsorption / removal property in seawater and having a Ti / Si molar ratio of 2/1 is obtained by X-ray diffraction using an inexpensive raw material. The containing adsorbent can be provided in an industrially advantageous manner.

Claims (12)

General formula: A ₂ Ti ₂ O ₃ (SiO ₄ ) · nH ₂ O (wherein A represents one or two alkali metal elements selected from Na and K. n represents a number from 0 to 2). A method for producing an adsorbent in which Nb is contained in the crystalline silicotitanate represented by:
A first step of obtaining a niobium-containing mixed gel by mixing a silicic acid source, an alkali metal compound, a niobium source, titanium tetrachloride and water;
A niobium-containing mixed gel obtained by the first step is hydrothermally reacted, and the niobium-containing mixed gel of the first step is a liquid containing at least a silicic acid source, an alkali metal compound, and water. all SANYO obtained by addition of titanium tetrachloride,
(1) Titanium tetrachloride is added to a solution containing a silicate source, an alkali metal compound, water and a niobium source, or (2) Titanium tetrachloride is added to a solution containing the silicate source, alkali metal compound and water. A method for producing an adsorbent , comprising adding a mixed gel to add a niobium source to the mixed gel . The method for producing an adsorbent according to claim 1, wherein in the first step, the composition of the niobium-containing mixed gel is the following molar ratio.
(Nb ₂ O ₅ + TiO ₂ ) / SiO ₂ = 0.70 to 2.50,
A ₂ O / SiO ₂ = 0.65~3.50
H ₂ O / SiO ₂ = 40 to 180 The method for producing an adsorbent according to claim 1 or 2, wherein in the first step, the molar ratio of Nb ₂ O ₅ / TiO ₂ in the niobium-containing mixed gel is 0.03 to 0.35.   The method for producing an adsorbent according to any one of claims 1 to 3, wherein in the first step, the silicic acid source is an alkali silicate.   The method for producing an adsorbent according to any one of claims 1 to 4, wherein in the first step, the alkali metal compound is a hydroxide.   The method for producing an adsorbent according to any one of claims 1 to 5, wherein in the first step, the niobium source is a hydroxide. The method for producing an adsorbent according to any one of claims 1 to 6, wherein in the first step, the molar ratio of H ₂ O / A ₂ O in the niobium-containing mixed gel is 20 to 100.   The method for producing an adsorbent according to any one of claims 1 to 7, wherein a hydrothermal reaction temperature in the second step is 120 to 200 ° C. The method for producing an adsorbent according to any one of claims 1 to 8 , wherein the adsorbent is used as a metal adsorbent. The method for producing an adsorbent according to claim 9 , wherein the metal to be adsorbed is cesium and / or strontium. The manufacturing method of the adsorption agent which heat-processes the adsorption agent obtained by the manufacturing method of any one of Claims 1 thru | or 8 further. The method for producing an adsorbent according to claim 11 , wherein the adsorbent is used as an adsorbent for strontium.