JP2017136521A - Strontium absorbent - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an absorbent excellent in selective absorption removal of Sr of Cs and Sr in sea water or the like and a manufacturing method of an absorber suitable for manufacturing the absorber.SOLUTION: The strontium absorber consists of amorphous or low crystalline silicon and titanium-containing compound. In the case of low crystalline, it is preferable to exhibit a peak derived from silico-titanate represented by the general formula; A'TiSiOnHO, where A exhibits one or more alkali metal selected from Na and K and n represents the number of 0-8 in an X ray diffraction analysis. It is preferable that the silicon and titanium-containing compound is amorphous and weight reduction at 150°C to 300°C in a thermogravimetric analysis is 7 mass% or less. Further it is also preferably to contain titanate represented by the general formula; ATiOmHO, where A represents one or more alkali metal selected from Na and K and m represents the number of 0-10.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an adsorbent capable of selectively and efficiently separating or recovering strontium in seawater, and a production method suitable for the adsorbent.

  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).

Further, as an adsorbent capable of adsorbing both cesium and strontium, the applicant of the present application has previously described A ′ ₄ Ti ₄ Si ₃ O ₁₆ .nH ₂ O (A ′ is Na and / or K, and n is 0 to 8). Table with a crystalline Shirikochitaneto represented by indicating the number.) _{of, a 4 Ti 9 O 20 ·} mH 2 O (a is Na and / or K, m is a number of 0.) The composition containing the titanate produced is reported (refer the following patent document 3).

Japanese Patent Laid-Open No. 62-266499 JP2013-57599A Japanese Patent Laying-Open No. 2015-188782

As described above, the composition containing crystalline silicotitanate and titanate described in Patent Document 3 has the ability to adsorb both cesium and strontium.
However, in some cases, when this composition is used for the treatment of a liquid containing radioactive strontium and radioactive cesium, the radiation dose of the adsorbent after adsorption is too high due to adsorption of cesium in addition to strontium. Processing may be difficult. In order to cope with such a case, an adsorbent having high strontium adsorption performance while low cesium adsorption performance is desired.
Accordingly, an object of the present invention is to provide an adsorbent capable of selectively and efficiently adsorbing strontium out of cesium and strontium in water, and an industrially advantageous production method for the adsorbent.

  As a result of intensive research to solve the above problems, the present inventors have surprisingly found that amorphous or low crystalline silicon and titanium-containing compounds have low cesium adsorption performance, while strontium adsorption. Found high efficiency.

  That is, the present invention provides a strontium adsorbent comprising an amorphous or low crystalline silicon and titanium-containing compound.

The present invention is also a method for producing the strontium adsorbent,
General formula; A ′ ₄ Ti ₄ Si ₃ O ₁₆ .nH ₂ O (where A ′ represents one or two alkali metals selected from Na and K, and n represents a number of 0 to 8. The crystalline silicotitanate represented by) is calcined at 250 ° C. or higher and 800 ° C. or lower, and a method for producing a strontium adsorbent is provided.

The strontium adsorbent of the present invention has a high adsorption performance of strontium while the adsorption performance of cesium is low.
The method for producing a strontium adsorbent of the present invention can produce the above strontium adsorbent by an industrially advantageous method.

FIG. 1 is an X-ray diffraction chart after baseline correction of the adsorbent of Comparative Example 1 (Production Example 1) and the adsorbent of Example 1. FIG. 2 is a TG-DTA curve of crystalline silicotitanate obtained in Comparative Example 1 (Production Example 1). FIG. 3 is an X-ray diffraction chart after baseline correction of the adsorbent of Comparative Example 2 (Production Example 2) and the adsorbent of Example 2. FIG. 4 is a TG-DTA curve of a mixture of crystalline silicotitanate and titanate obtained in Comparative Example 2 (Production Example 2). FIG. 5 is a TG-DTA curve of the crystalline silicotitanate obtained in Example 1. FIG. 6 is an X-ray diffraction chart after baseline correction of the adsorbent of Comparative Example 3 and the adsorbent of Example 3. FIG. 7 is an X-ray diffraction chart after baseline correction of the adsorbent of Comparative Example 4 and the adsorbent of Comparative Example 5. FIG. 8 is a TG-DTA curve of the titanate obtained in Comparative Example 4. FIG. 9 shows the results of an adsorbent batch adsorption test. (A) is a test result of each adsorbent of Example 1 and Comparative Example 1, and (b) is a test result of each adsorbent of Example 2 and Comparative Example 2. FIG. 10 shows the results of an adsorbent batch adsorption test. (A) is a test result of each adsorbent of Example 3 and Comparative Example 3, and (b) shows a test result of each adsorbent of Comparative Examples 4 and 5. FIG. 11 is a photograph showing the results of the water resistance test of the adsorbents of Example 2-2 and Comparative Example 2. FIG. 12 is a graph showing measurement results of Sr and Cs adsorption amounts in the adsorption tests of the adsorbents of Example 2-2 and Comparative Example 2. (A) is the Cs adsorption amount, and (b) is the Sr adsorption amount.

The strontium adsorbent of the present invention is composed of an amorphous or low crystalline silicon- and titanium-containing compound.
Amorphous silicon and titanium-containing compound is based on the premise that it contains silicon and titanium, and uses Cu—Kα as a radiation source, and powder X-ray diffraction measurement in a scanning range of 2θ = 5 to 70 ° The crystal peak derived from the silicon- and titanium-containing compound is not observed.

  The low-crystalline silicon and titanium-containing compound is based on the premise that it contains silicon and titanium, and when this is subjected to the same powder X-ray diffraction measurement as described above, a minute crystal derived from the silicon and titanium-containing compound. The crystal peak is observed.

When a fine crystal peak of the silicon- and titanium-containing compound of the present invention as measured by powder X-ray diffraction as described above is observed, the peak is represented by the general formula: A ′ ₄ Ti ₄ Si ₃ O ₁₆ .nH ₂ O ( In the formula, A ′ is one or two alkali metals selected from Na and K, and n is a peak derived from silicotitanate represented by 0 to 8). For example, as for the peak derived from the silicotitanate, a strongest main peak or halo peak is observed at, for example, 2θ = 8 to 13 °, more typically 2θ = 10 to 13 °. The minute peak is preferably a peak having a maximum intensity (cps) of 350 cps or less, more preferably a peak having a maximum intensity (cps) of 300 cps or less, and a maximum intensity (cps) of 250 cps or less. The peak is particularly preferably. In order to obtain a silicon- and titanium-containing compound exhibiting such a minute peak, the firing temperature, firing time, etc. in the preferred production method of the present invention described later may be adjusted.

In the present invention, the weight loss rate when the temperature of the amorphous or low crystalline silicon- or titanium-containing compound powder or granule is increased to 150 to 300 ° C. is 7% or less, preferably 2% or less. However, while the adsorption performance of cesium is low, it is preferable from the viewpoint of having a high adsorption performance of strontium. The silicon- and titanium-containing compound whose weight reduction rate is less than or equal to this upper limit may be an anhydride, or may have crystal water or water of hydration, but from the above viewpoint, it may be an anhydride. preferable. On the other hand, in general, there are many crystalline silicon and titanium-containing compounds including crystalline silicotitanate represented by the following general formula: A ′ ₄ Ti ₄ Si ₃ O ₁₆ .nH ₂ O (n is 1 to 8). In this case, a large endothermic peak due to the disappearance of crystal water is observed at 150 to 300 ° C. when TG-DTA measurement is performed. The weight reduction rate is measured by the method described in Examples described later.

The silicon and titanium-containing compound used in the present invention preferably has a molar ratio of Ti: Si of 4: 3. The molar ratio of Ti: Si in the silicon and titanium-containing compound and the adsorbent can be determined by the following method. In the case of obtaining by this method, considering that the molar ratio is based on semi-quantitative analysis, the molar ratio of Ti: Si is from 4: 2 to 4, particularly from 4: 2.5 to 3.5. It is also preferable that the ratio is in a range corresponding to the molar ratio of 4: 3. A silicon- and titanium-containing compound has a general formula; A ′ ₄ Ti ₄ Si ₃ O ₁₆ .nH ₂ O (wherein A ′ represents one or two alkali metals selected from Na and K, and n is 0 to 0). In general, the molar ratio of Ti: Si is in the above-described range in the case of the fired product of crystalline silicotitanate represented by the number of 8. In order to obtain an amorphous or low-crystalline silicon and titanium-containing compound having a Ti: Si molar ratio within the above range, the adsorbent of the present invention can be produced by a suitable production method of the present invention described later. Good. For example, a general formula which is a preferable mixture described later; A ₄ Ti ₉ O ₂₀ · mH ₂ O (wherein A represents one or two alkali metals selected from Na and K, and m is 0 to 10) The Ti: Si molar ratio of the adsorbent of the present invention is described above as the preferred Ti: Si molar ratio of silicon and titanium-containing compounds. A range similar to the above range is also preferable.
<How to find the molar ratio of Ti / Si>
(A) A silicon- and titanium-containing compound or adsorbent is put into a suitable container (aluminum ring or the like), sandwiched between dies, and pelletized by applying a pressure of 10 MPa with a press. This sample was subjected to a fluorescent X-ray apparatus (device name: ZSX100e, tube: Rh (4 kW), atmosphere: vacuum, analysis window: Be (30 μm), measurement mode: SQX analysis (EZ scan), measurement diameter: 30 mmφ, (stock ) All elements are measured with Rigaku). The content (mass%) of SiO ₂ and TiO _{2 in} the silicon- and titanium-containing compound or adsorbent is calculated by the SQX method, which is a semi-quantitative analysis method.
(B) The obtained content (mass%) of SiO ₂ and TiO ₂ is divided by the respective molecular weights to obtain the number of moles of SiO ₂ and TiO _{2 in} 100 g of silicon and titanium-containing compound or adsorbent.

The silicon and titanium-containing compound used in the present invention preferably contains one or two alkali metals selected from Na and K. The silicon and titanium-containing compound preferably has a molar ratio of A ′: Si in the silicon and titanium-containing compound of 4: 3 when one or two alkali metals selected from Na and K are A ′. . Here, A ′ represents one or two alkali metals selected from Na and K. The molar ratio of A ′: Si in the silicon and titanium-containing compound or adsorbent can be determined by the following method. When obtaining by this method, considering that the molar ratio is based on semi-quantitative analysis, the molar ratio of A ′: Si is from 4: 2 to 4, particularly from 4: 2.5 to 3.5. A range having a width is also preferable as corresponding to the molar ratio of 4: 3. A silicon- and titanium-containing compound has a general formula; A ′ ₄ Ti ₄ Si ₃ O ₁₆ .nH ₂ O (wherein A ′ represents one or two alkali metals selected from Na and K, and n is 0 to 0). In general, the molar ratio of A ′: Si falls within the above range. In order to obtain an amorphous or low-crystalline silicon and titanium-containing compound having a molar ratio of A ′: Si within the above range, the adsorbent of the present invention can be produced by a suitable production method of the present invention described later. Good. Further, for example, when the above-mentioned titanate which is a preferable mixture is not contained, the molar ratio of A ′: Si in the adsorbent of the present invention is the above-described preferable molar ratio of A ′: Si of silicon and titanium-containing compound It is preferable that it is the range similar to the range quoted by.

<How to find the molar ratio of A '/ Si>
(A) A silicon- and titanium-containing compound or adsorbent is put into a suitable container (aluminum ring or the like), sandwiched between dies, and pelletized by applying a pressure of 10 MPa with a press. This sample was subjected to a fluorescent X-ray apparatus (device name: ZSX100e, tube: Rh (4 kW), atmosphere: vacuum, analysis window: Be (30 μm), measurement mode: SQX analysis (EZ scan), measurement diameter: 30 mmφ, (stock ) All elements are measured with Rigaku). The content (mass%) of Na ₂ O, K ₂ O and SiO _{2 in} the silicon and titanium-containing compound or adsorbent is calculated by calculating by the SQX method which is a semi-quantitative analysis method.
(B) The obtained content (mass%) of Na ₂ O, K ₂ O and SiO ₂ is divided by the respective molecular weights, and the number of moles of Na ₂ O + K ₂ O in 100 g of silicon and titanium-containing compound or adsorbent and SiO 2 Obtain the number of moles of ₂ and calculate the above ratio.

The silicon and titanium-containing compound used in the present invention is preferably an oxide. The silicon- and titanium-containing compound is preferably free of metal elements or metalloid elements other than Na, K, Si, and Ti, and is particularly free of transition metal elements or rare earth elements other than titanium, and / or It is preferable that an alkaline earth metal element is not contained and / or a metalloid element other than Si is not contained. Other elements preferably not containing silicon and titanium-containing compounds include halogen elements; sulfur; selenium; phosphorus; nitrogen; carbon. The silicon and titanium-containing compound used in the present invention is preferably a silicon titanate, and is a compound represented by the above general formula; A ′ ₄ Ti ₄ Si ₃ O ₁₆ .nH ₂ O. May be.

The adsorbent and silicon- and titanium-containing compound used in the present invention are preferably a fired product of crystalline silicotitanate represented by the above general formula; A ′ ₄ Ti ₄ Si ₃ O ₁₆ .nH ₂ O. When the crystalline silicotitanate represented by the above general formula; A ′ ₄ Ti ₄ Si ₃ O ₁₆ .nH ₂ O is fired, the obtained low crystalline or amorphous fired product, particularly amorphous fired Even if the composition can identify the composition by composition analysis or the like, the chemical structure cannot be identified by X-ray diffraction measurement. In addition, the characteristics of the fired product may vary depending on the firing conditions, etc., and excessive experiments are required to find all the characteristics or physical properties (parameters) characteristic of the specific fired product. It is also difficult to specify the contained compound by characteristics other than the matters described in this specification. Thus, it is very difficult to specify the structure and characteristics of an amorphous or low crystalline material, particularly an amorphous fired product. For this reason, the low-crystalline or amorphous silicon and titanium-containing compounds, which are a fired product of crystalline silicotitanate represented by the above general formula; A ′ ₄ Ti ₄ Si ₃ O ₁₆ .nH ₂ O, There are circumstances where the structure or properties cannot be directly specified by matters other than those described herein, or are nearly impractical.

As described above, the adsorbent of the present invention has the general formula: A ₄ Ti ₉ O ₂₀ · mH ₂ O (wherein A represents one or two alkali metals selected from Na and K, and m represents 0 It is preferable that the titanate represented by this is contained. Hereinafter, this titanate may be referred to as the titanate or simply titanate. The adsorbent of the present invention contains this titanate because the main peak of the titanate is measured when the adsorbent of the present invention is measured by X-ray diffraction in the range of the above-mentioned radiation source and diffraction angle. This can be confirmed by being observed as a broad peak at 2θ = 8 to 14 °. The main peak of the titanate is usually detected at 2θ = 8 to 10 ° as a peak derived from a hydrated salt having a crystal orientation of (010) and m in the general formula (2) of 5 to 7. The However, in a preferable production method of the adsorbent of the present invention, titanate may be fired as described later, and in that case, 2θ = 9 slightly higher than 2θ = 8 to 10 ° is preferable. A broad peak of the main peak of the titanate appears at ˜14 °, particularly at 2θ = 10-14 °.

  The titanate in which the main peak is observed at 2θ = 8 to 10 ° has a slight cesium adsorption performance, although the strontium adsorption performance is high. On the other hand, the titanate in which the main peak is observed at a higher angle than 2θ = 8 to 10 ° is preferable in that the cesium adsorption performance is sufficiently reduced although the strontium adsorption performance is lowered. Therefore, when the adsorbent of the present invention is measured by X-ray diffraction, the main peak of the titanate is preferably observed at 2θ = 9 to 14 °, particularly 2θ = 10 to 14 °. In order to obtain the adsorbent of the present invention containing a titanate exhibiting such a peak, in the production method of the present invention described later, the raw material contains titanate before firing, and the firing time and temperature What is necessary is just to adjust the time.

  In the adsorbent of the present invention, when the silicon and titanium-containing compound further contains titanate, the main peak of the silicon and titanium-containing compound and titanate overlaps at 2θ = 10 to 14 °. In some cases, the main peak of the silicon and titanium-containing compound may not be observed on the X-ray chart, but the main peak of the silicon and titanium-containing compound does not need to be clearly observed on the X-ray chart.

In the specific titanate in the adsorbent of the present invention, the interlayer is preferably in a specific range. Specifically, the interlayer thickness of the titanate is preferably 0.63 nm or more and 0.88 nm or less, and more preferably 0.65 nm or more and 0.80 nm or less. The present inventors consider that such an interlayer is related to the position of the X-ray diffraction peak. Specifically, the main peak is observed at the diffraction angle (2θ) = 8 to 10 ° between the titanate layers where the main peak is observed at a higher angle than the diffraction angle (2θ) = 8 to 10 °. It is narrower than the titanate interlayer (usually about 0.90 to 0.95 nm). Such narrowing of the layers seems to be related to the low cesium adsorption performance of titanate in the adsorbent. The titanate interlayer can be measured by X-ray diffraction analysis. Specifically, the 2θ of the diffraction peak obtained from the 001 plane diffraction of titanate is measured, the 001 plane spacing (d) of titanate is calculated by the following Bragg diffraction formula, and the obtained d is Interlayer (nm).
λ = 2 dsin θ
(In the formula, d represents the 001 plane spacing of titanate, θ represents the diffraction angle, and λ is 0.15418 nm.)

  In order to make the interlayer of the titanate contained in the adsorbent of the present invention in the above range, in the production method of the present invention described later, the raw material contains titanate before firing, and the firing time and temperature What is necessary is just to adjust the time.

  When the adsorbent of the present invention contains the titanate, the molar ratio of the titanate to the silicon and titanium-containing compound obtained by composition analysis (the former: the latter) is 1: 0.25 to It is preferably 0.45, and more preferably 1: 0.3 to 0.4. Specifically, this molar ratio is determined by the following method. In order to make the molar ratio of the adsorbent of the present invention within the above range, the amount ratio of the raw material containing titanate and crystalline silicotitanate before firing may be adjusted in the production method of the present invention described later. .

<How to find the molar ratio of silicon and titanium-containing compound to titanate>
(A) The adsorbent is put in a suitable container (aluminum ring or the like), sandwiched between dies, and pelletized by applying a pressure of 10 MPa with a press machine to obtain a measurement sample. This sample was subjected to a fluorescent X-ray apparatus (device name: ZSX100e, tube: Rh (4 kW), atmosphere: vacuum, analysis window: Be (30 μm), measurement mode: SQX analysis (EZ scan), measurement diameter: 30 mmφ, (stock ) All elements are measured with Rigaku). The content (mass%) of SiO ₂ and TiO ₂ in the adsorbent is calculated by calculating by the SQX method which is a semi-quantitative analysis method.
(B) the obtained content of SiO ₂ and TiO ₂ (mass%) divided by the respective molecular weight, obtaining the number of moles of SiO ₂ and TiO ₂ in the adsorbent 100 g.
(C) One third of the number of moles of SiO _{2 in} the adsorbent determined above is the amount of silicon- and titanium-containing compound (A ′ ₄ Ti ₄ Si ₃ O ₁₆ .nH ₂ O-derived compound) in the adsorbent. Assumes moles. Further, assuming that the number of moles of Ti atoms in 1 mole of silicon and titanium-containing compound is 4, the number of moles of the titanate in the adsorbent is determined by the following formula (1).
(D) The above ratio is obtained from the number of moles of the obtained silicon and titanium-containing compound and the number of moles of titanate.

  The adsorbent of the present invention may contain other components such as various binders in addition to the silicon- and titanium-containing compound and the titanate, but from the viewpoint of enhancing the adsorption performance, The amount is preferably low. In the adsorbent, the total content of components other than the silicon and titanium-containing compound and the titanate is preferably 10% by mass or less, and more preferably 5% by mass or less.

The adsorbent of the present invention preferably has a BET specific surface area within a specific range. Specifically, it is preferable that the BET specific surface area of 20 m ² / g or more, further preferably 20 m ² / g or more 100 m ² / g or less, or less 50 m ² / g or more 100 m ² / g Is more preferable. The adsorbent of the present invention having a BET specific surface area in this range has very good selective adsorption performance of strontium. The BET specific surface area is measured by a BET one-point method using Flowsorb II2300 (trade name) manufactured by Shimadzu Corporation. The gas used is a nitrogen helium mixed gas (nitrogen 30 vol%).

  Since the adsorbent of the present invention contains both amorphous or low crystalline silicon and titanium-containing compounds, it can achieve both low cesium adsorption performance and high strontium adsorption performance, so cesium is selected from strontium and cesium. Can be adsorbed efficiently.

  Examples of the form of the adsorbent of the present invention include powder, granules, and molded bodies other than granules (spherical and cylindrical), and the like, and preferably in the form of powder or granules.

  When the adsorbent of the present invention is a granule, it preferably has a particle size of 200 μm or more and 1000 μm or less. Since the adsorbent of the present invention composed of granules of this particle size does not have particles finer than 200 μm or is extremely small even if present, the adsorbent of the present invention is packed in an adsorption tower and passed through. In this case, it is possible to prevent the problem that particles are clogged in the adsorption tower. Moreover, when the particle size is 1000 μm or less, it is easy to improve the adsorption performance of the adsorbent.

  Specifically, when the adsorbent of the present invention is a granular material, when the sieve according to JIS Z8801 standard has a sieve having an opening of 212 μm and the sieve having an aperture of 1 mm, the adsorbent of the present invention It is preferable that 98% by mass or more, particularly 99% by mass or more pass through a sieve having an opening of 1 mm, and 98% by mass or more, particularly 99% by mass or more should not pass through a sieve having an opening of 212 μm. In particular, the adsorbent of the present invention is preferably composed of a granular material having a particle size of 300 μm or more and 600 μm or less. Specifically, when a sieve having an opening of 300 μm according to JIS Z8801 standard and a sieve having an opening of 600 μm are used, 98 mass% or more, particularly 99 mass% or more of the adsorbent of the present invention is the above-mentioned 600 μm. It is preferable that 98% by mass or more, particularly 99% by mass or more, does not pass through the 300 μm sieve.

  The preferable content of silicon and titanium-containing compounds (or silicon and titanium-containing compounds and titanates) in the adsorbent of the present invention varies depending on the form. For example, when the adsorbent is used while being fixed to a non-woven fabric, the amount of silicon and titanium-containing compound in the adsorbent (or the total amount of silicon and titanium-containing compound and titanate) is preferably 90% by mass or more, particularly 95 It is preferable that it is mass% or more. Further, when the adsorbent is in a form granulated with a binder, the amount of silicon and titanium-containing compound in the adsorbent (or the total amount of silicon and titanium-containing compound and titanate) is preferably 70% by mass or more, In particular, it is preferably 80% by mass or more. When the adsorbent contains a binder component, the amount of the binder component in the adsorbent is preferably about 1% by mass to 30% by mass, and preferably about 1% by mass to 20% by mass. Is more preferable. As the binder component, various binders described later can be used.

  Then, the suitable manufacturing method of the strontium adsorption agent of this invention is demonstrated.

In this production method, the general formula: A ′ ₄ Ti ₄ Si ₃ O ₁₆ .nH ₂ O (where A ′ represents one or two alkali metals selected from Na and K, and n is 0 to 8). The raw material containing the crystalline silicotitanate represented by (hereinafter also referred to as “the crystalline silicotitanate” or simply “crystalline silicotitanate”) is fired at 250 ° C. or higher and 800 ° C. or lower. When X-ray diffraction measurement is performed on the raw material containing crystalline silicotitanate at the above temperature, a peak derived from silicotitanate represented by the general formula is not observed, or a minute amount derived from the silicotitanate An amorphous or low crystalline silicon- and titanium-containing compound with a peak observed is obtained. These compounds are highly effective in the present invention in terms of achieving both high strontium and low cesium adsorption performance.

The raw material containing crystalline silicotitanate may have only crystalline silicotitanate, or may contain other components other than crystalline silicotitanate. As other components other than the crystalline silicotitanate, a titanate represented by the general formula: A ₄ Ti ₉ O ₂₀ · mH ₂ O is preferable. When obtaining a raw material containing crystalline silicotitanate, when the raw material is subjected to X-ray diffraction measurement within the range of the above-mentioned radiation source and diffraction angle, the peak with the highest intensity among the peaks of crystalline silicotitanate (hereinafter referred to as main peak) Is also observed in the diffraction angle (2θ) range of 10-13 °, and in addition to this, the crystalline silicon is also observed in the range of 27 ° -29 ° and / or 34 ° -35 °. More preferably, a titanate peak is detected. When obtaining a raw material containing crystalline silicotitanate and titanate, the main peak of titanate is preferably observed at diffraction angle (2θ) = 8-10 °, in addition to this, 27-29 ° and More preferably, the titanate peak is further detected in the range of 47 to 49 °. The ratio of the main peak height of the titanate to the main peak height of the crystalline silicotitanate is preferably 5% or more and 70% or less, more preferably 5% or more and 60% or less. It is more preferable that it is not less than 50% and not more than 50%.

  The ratio of the peak height described in the present specification is performed based on the X-ray diffraction peak pattern corrected for the baseline. Baseline correction is performed by the sonneveld-visser method. The peak height is obtained from the diffraction peak pattern as follows. First, a straight line is obtained by connecting two bottom points of one peak. Then, a perpendicular line is drawn from the peak apex to intersect with the straight line, and the distance between the obtained intersection and the peak apex is defined as the peak height.

When the raw material containing the crystalline silicotitanate contains the titanate, the preferred molar ratio is mentioned above as the preferred molar ratio of the silicon and titanium-containing compound and the titanate in the adsorbent of the present invention. The molar ratio similar to the molar ratio can be mentioned. The method for obtaining the molar ratio between the crystalline silicotitanate and the titanate in the raw material is the same as the method for obtaining the molar ratio between the silicon and titanium-containing compound and the titanate in the adsorbent.

  The amount of components other than crystalline silicotitanate in the raw material containing crystalline silicotitanate (excluding the titanate) is preferably 10% by mass or less, and more preferably 5% by mass or less.

  As the crystalline silicotitanate in the raw material containing the crystalline silicotitanate used in the present invention, a commercially available product may be used, but for example, it may be produced by the following production method. First, the manufacturing method will be described in detail.

In this production method, a silicate source, a sodium compound and / or a potassium compound, titanium tetrachloride, and water are mixed to produce a mixed gel, and the mixed gel obtained in the first step is mixed with water. A second step for heat reaction,
In the first step, a silicic acid source and titanium tetrachloride are added so that the molar ratio of Ti and Si contained in the mixed gel is Ti / Si = 0.5 or more and 3.0 or less. According to this production method, both a raw material containing only crystalline silicotitanate as a titanium compound and a raw material containing both crystalline silicotitanate and titanate can be produced.

  Examples of the silicic acid 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. With respect to 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.

  Examples of the sodium compound used in the first step include 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. Examples of the potassium compound used in the first step include potassium hydroxide and potassium carbonate, and potassium hydroxide is preferred for the same reason as the sodium compound.

  In the case where a sodium compound and a potassium compound are used in the first step, the ratio of the number of moles of the potassium compound to the total number of moles of the sodium compound and the potassium compound is preferably more than 0% and 50% or less. % Or less is more preferable.

  In this production method, the silicic acid source and titanium tetrachloride are added in such amounts that the Ti / Si ratio (molar ratio) is 0.5 or more and 3.0 or less. When obtaining a raw material containing only crystalline silicotitanate as a titanium compound, the Ti / Si ratio in the mixed gel is preferably 1.2 or more and 1.5 or less. When a raw material containing crystalline silicotitanate and titanate is obtained, the Ti / Si ratio in the mixed gel is preferably 1.8 or more and 2.2 or less.

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% or more and 40 mass% or less, and A ₂ O and SiO ₂ occupy in the mixed gel. It is desirable to add the silicic acid source and titanium tetrachloride so that the molar ratio of A ₂ O / SiO ₂ = 0.5 or more and 3.0 or less. Here, A represents Na and K. By adjusting the addition amount of the silicic acid source and titanium tetrachloride within the above range, the yield of the desired crystalline silicotitanate can be increased to a satisfactory level.

In addition, when obtaining the raw material which contains only crystalline silicotitanate as a titanium compound, a silicic acid source and titanium tetrachloride should be added so that the molar ratio of A ₂ O / SiO ₂ is 0.5 or more and 2.5 or less. In the case of obtaining a raw material containing crystalline silicotitanate and titanate, a silicate source and a molar ratio of A ₂ O / SiO _{2 in} the mixed gel = 1.0 to 1.8 It is preferable to add titanium tetrachloride.

  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, sodium compound, 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. 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 silicic acid source, sodium compound, 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 silicate source, a sodium compound and / or a potassium compound, and water (this addition order is simply referred to as “additional order” hereinafter). (It may be called “Implementation of (1)”.) 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 A mode in which a sodium compound and / or a potassium compound is added to a mixture of these can also be employed. 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 in the mixed gel is 0.5% by mass or more and 15% by mass or less, particularly 0.7% by mass in terms of Na ₂ O. It is preferable to add so that it may become 13 to 13 mass%. The total Na ₂ O equivalent mass of sodium and potassium in the mixed gel and the total Na ₂ O equivalent concentration of sodium and potassium in the mixed gel (hereinafter referred to as “total concentration of sodium and potassium (the potassium compound is used in the first step) If not, the sodium concentration) ”is calculated by the following formula.
Total Na ₂ O equivalent mass (g) of sodium and potassium in the mixed gel = number of moles of sodium ions derived from sodium silicate + number of moles of sodium ions derived from sodium compounds such as sodium hydroxide + potassium hydroxide, etc. Number of moles of potassium ion derived from potassium compound-number of moles of chloride ion derived from titanium tetrachloride) × 0.5 × Na ₂ O molecular weight

Concentration (mass%) in terms of Na ₂ O of the total of sodium and potassium in the mixed gel =
Total Na ₂ O equivalent mass of sodium and potassium in the mixed gel / (water content in the mixed gel + total Na ₂ O equivalent mass of sodium and potassium in the mixed gel) × 100

Suppressing the formation of crystalline silicotitanate other than crystalline silicotitanate with a molar ratio of Ti: Si of 4: 3 by combining the selection of the silicate source with the adjustment of the total concentration of sodium and potassium in the mixed gel Can do. When sodium silicate or potassium silicate is used as the silicic acid source, the molar ratio of Ti: Si is set to 2.0% by mass or more in terms of Na ₂ O in terms of the total concentration of sodium and potassium in the mixed gel. It becomes possible to effectively suppress the formation of 5:12 crystalline silicotitanate, while the total concentration of sodium and potassium in the mixed gel is 6.0% by mass or less in terms of Na ₂ O, It becomes possible to effectively suppress the formation of crystalline silicotitanate having a molar ratio of Ti: Si of 1: 1. Also, when using the active silicic acid obtained by the alkali silicate to cation exchange as silicic acid source, by setting more than 1.0 mass% in terms of Na ₂ O, Ti: molar ratio of Si 5: It is possible to effectively suppress the formation of 12 crystalline silicotitanate, while the total concentration of sodium and potassium in the mixed gel is 6.0% by mass or less in terms of Na ₂ O, so that Ti: Production of crystalline silicotitanate having a Si molar ratio of 1: 1 can be effectively suppressed.

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. Therefore, the “Na ₂ O equivalent mass (g) of sodium in the mixed gel” referred to here is counted as the sum of all sodium 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 90 hours or shorter, more preferably 12 hours or longer and 80 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 it is as a raw material containing the crystalline silicotitanate, or it can be used by lightly loosening it. Moreover, you may grind | pulverize and use the rod-shaped molded object after drying. The crystalline silicotitanate of each shape is preferably further classified and then used as a raw material for firing from the viewpoint of increasing the adsorption efficiency of strontium of the adsorbent of the present invention. 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 800 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.

With the above production method, it is possible not only to produce a substantially single phase raw material of crystalline silicotitanate by X-ray diffraction by selecting reaction conditions as appropriate, but also at a stretch of raw materials containing crystalline silicotitanate and titanate. Can be manufactured.
In addition, the raw material containing crystalline silicotitanate and titanate may produce crystalline silicotitanate and titanate at a time by the above production method, or crystalline silicotitanate as in the above production method. May be prepared by X-ray diffraction single phase and then mixed with a commercially available or known titanate to obtain a raw material containing crystalline silicotitanate and titanate.

  The raw material containing the crystalline silicotitanate obtained as described above is fired at 250 ° C. or higher and 800 ° C. or lower. Examples of the apparatus used for firing 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 firing atmosphere may be an oxygen-containing atmosphere such as the air, an inactive atmosphere such as nitrogen or argon, or a reducing atmosphere.

By setting the firing temperature to 250 ° C. or higher, the cesium adsorption performance can be lowered. Moreover, the temperature of baking shall be 800 degrees C or less, and the strontium adsorption | suction performance of the adsorbent obtained can be made high. From these viewpoints, the firing temperature is preferably 250 ° C. or more and 800 ° C. or less, more preferably 300 ° C. or more and 700 ° C. or less, particularly preferably 400 ° C. or more and 600 ° C. or less, and 400 ° C. It is particularly preferable that the temperature is 500 ° C. or lower.
The firing 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 fired 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 adsorbent obtained by the above production method can be used for various applications as an adsorbent that is an unmolded body that is in the form of a powder or a molded body that is, for example, a rod or a particle (including granules). When the strontium adsorbent of the present invention is used as a molded body, the raw material that is an unshaped body such as a powder may be fired, and then the raw material that is the unshaped body may be molded, or the crystalline silicon titanate or the After the raw material containing crystalline silicotitanate and titanate is previously molded into various predetermined shapes such as rods and particles (including granules), this molded body may be fired.

  Examples of the molding process include a granulation process for forming a powdery raw material or an adsorbent into granules, or a slurry of a powdery raw material or an adsorbent and dropping it into a liquid containing a hardener such as calcium chloride. The method of encapsulating the raw material or adsorbent, the method of coating the surface of the resin core material with the raw material or adsorbent powder, the surface and / or the interior of the sheet-like substrate formed of natural fibers or synthetic fibers A powdery raw material or an adsorbent is attached to 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, hydroxyethyl cellulose, hydroxypropyl cellulose, hydroxypropyl methyl cellulose, hydroxyethyl methyl cellulose, carboxymethyl cellulose, hydroxypropyl methyl cellulose, methyl cellulose, ethyl cellulose, starch, corn starch, molasses, lactose, molding Examples include 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.

Further, the granular adsorbent of the present invention can be used as an adsorbent that can be recovered by magnetic separation from water containing cesium and / or strontium by further containing magnetic particles. 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 the magnetic particles into the granular adsorbent, for example, the granulation operation described above may be performed in a state where the magnetic particles are contained.

In addition, when the strontium adsorbent of the present invention is used for various adsorbing sheets and mats such as non-woven fabrics, it is used by adding it when processing the material as a powder. As a specific method for fixing the adsorbent to the nonwoven fabric, there is a method in which a powdered adsorbent is dispersed in water together with an emulsified resin binder, impregnated with the nonwoven fabric, and then dried. Examples of the resin binder include latex binder, polyacrylate, polymethacrylate, acrylate copolymer, methacrylate copolymer, styrene butadiene copolymer, styrene acrylic copolymer, ethylene vinyl acetate copolymer, and nitrile rubber. , Acrylonitrile butadiene copolymer, polyvinyl alcohol and the like. As the nonwoven fabric, for example, those composed of polyester and / or polyolefin fibers are used.
Thus, even if it makes the form which wound the nonwoven fabric which apply | coated the adsorbent, for example with the surface which apply | coated the adsorbent inside, it can be used suitably for water treatment.

  The adsorbent formed into a granular shape or the like obtained by the above-described method for producing a strontium adsorbent or the adsorbent fixed to the nonwoven fabric as a powder is water having an adsorption container and an adsorption tower filled with a radioactive substance adsorbent. It can be suitably used as an adsorbent for a treatment system or a water treatment material.

The present invention further provides a method for adsorbing strontium, wherein a strontium adsorbent comprising an amorphous or low crystalline silicon- and titanium-containing compound is contacted with a solution containing cesium and strontium. In this case, there is no limitation on the amount of cesium and strontium in the solution containing cesium and strontium, but to give an example, from the viewpoint of sufficiently exhibiting the selective adsorptivity of the adsorbent of the present invention, containing strontium, It is preferable to contain 0.01 ppm or more of strontium, and it is particularly preferable to contain 1 ppm or more. Further, from the same viewpoint, when cesium is contained, it is preferable to contain 0.01 ppm or more of cesium, and particularly preferably 1 ppm or more. As these upper limits, for example, strontium is preferably 1000 ppm or less, particularly 500 ppm or less, because the high adsorption performance of the adsorbent of the present invention is easily exhibited. When the strontium concentration is less than or equal to this upper limit, cesium is preferably 2000 ppm or less, particularly preferably 1000 ppm or less from the viewpoint of clearly showing the selective adsorptivity of the adsorbent of the present invention.

  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.
TG-DTA: TGDSCl manufactured by METTLER TOLEDO was used in an air atmosphere. Measurement temperature range: 25 ° C. to 1000 ° C., temperature increase rate: Measure the weight of the sample at 150 ° C. and the weight of the sample at 300 ° C. when the temperature rises at 10 ° C./min, and calculate the weight reduction rate from the following formula did. Reference: component α-alumina. The sample amount was 180 mg.
Weight reduction rate (%) = (A−B) / A × 100
(A: sample weight at 150 ° C., B: sample weight at 300 ° C.)

<Materials used>
No. 3 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 soda aqueous solution: Industrial 25% sodium hydroxide (NaOH: 25%, H ₂ O: 75%).
Caustic potash: solid reagent potassium hydroxide (KOH: 85%).
-Titanium tetrachloride aqueous solution: 36.48% aqueous solution manufactured by Osaka Titanium Technologies Co., Ltd.

[Production Example 1]
<Synthesis of crystalline silicotitanate>
(1) First step No. 3 sodium silicate 60 g, caustic soda aqueous solution 224.3 g, caustic potash 34.6 g and ion-exchanged water 82.5 g were mixed and stirred to obtain a mixed aqueous solution. To this mixed aqueous solution, 203.3 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. Ti / Si molar ratio in the mixed gel: 1.33, K ₂ O / Na ₂ O molar ratio: 25/75, SiO ₂ equivalent concentration a: 2.83%, TiO ₂ equivalent concentration b: 5.14%, a + b: 7.97, A ₂ O / SiO ₂ molar ratio: 0.926, Na ₂ O equivalent concentration: 3.71%.

(2) Second Step The mixed gel obtained in the first step was put in an autoclave, heated to 170 ° C. over 1 hour, and reacted for 96 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 μm, dried, and classified to obtain a granular material having a particle size of 300 μm to 600 μm. The obtained granular material was subjected to X-ray diffraction measurement. The result is shown in FIG. From the result of the X-ray diffraction measurement shown in FIG. 1, the obtained granular material has a general formula: A ′ ₄ Ti ₄ Si ₃ O ₁₆ .nH ₂ O (where A ′ is one selected from Na and K, or It was judged as a single phase of crystalline silicotitanate represented by the following formula: In FIG. 1 and subsequent figures, “GTS” represents the crystalline silicotitanate.
Further, a TG-DTA curve of the obtained “GTS” is shown in FIG. In FIG. 2, the thick line is the DTA curve, and the thin line is the TG curve. As shown in the DTA curve of FIG. 2, an endothermic peak accompanying dehydration of crystalline silicotitanate was observed at around 200 ° C. When the obtained crystalline silicotitanate was analyzed by TG-DTA, the weight reduction rate was 8.8%.

{Reference experiment}
100 g of the granular material obtained in Production Example 1 was placed in an alumina container, heated in an electric furnace over the course of 2 hours in the atmosphere, and then fired at 250 ° C., 400 ° C., 500 ° C., and 600 ° C. for 2 hours, respectively. The obtained fired product was subjected to TG-DTA measurement at a heating rate of 10 ° C./min from 25 ° C. to 1000 ° C., and the weight reduction rate was measured. The results are shown in Table A.

[Production Example 2]
<Synthesis of crystalline silicotitanate and titanate mixture>
(1) First Step 90 g of sodium silicate No. 3, caustic soda aqueous solution 667.49 g and pure water 84.38 g were mixed and stirred to obtain a mixed aqueous solution. To this mixed aqueous solution, 443.90 g of titanium tetrachloride aqueous solution was continuously added over 1 hour and 20 minutes with a peristaltic pump to produce a mixed gel. The mixed gel was aged at room temperature for 1 hour after the addition of the aqueous titanium tetrachloride solution. Ti / Si molar ratio in the mixed gel: 2, K ₂ O / Na ₂ O molar ratio: 0/100, SiO ₂ equivalent concentration a: 2.00%, TiO ₂ equivalent concentration b: 5.30%, a + b: The molar ratio was 7.30, A ₂ O / SiO ₂ molar ratio: 1.56, Na ₂ O equivalent concentration: 3.22%.

(2) Second Step The mixed gel obtained in the first step was placed in an autoclave, heated to 170 ° C. over 1 hour, and then reacted for 24 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 μm, dried, and classified to obtain a granular material having a particle size of 300 μm to 600 μm. The obtained granular material was subjected to X-ray diffraction measurement. The result is shown in FIG. From the result of the X-ray diffraction measurement shown in FIG. 3, the obtained granular material is the main phase Na ₄ Ti ₄ Si ₃ O ₁₆ .nH ₂ O, and Na ₄ Ti ₉ O ₂₀ .mH ₂ O is detected. It was confirmed to be a mixture of crystalline silicotitanate and the titanate. The granular material is 2θ = 8 to 10 ° with respect to the height of the main peak (MP) derived from Na ₄ Ti ₄ Si ₃ O ₁₆ · 6H ₂ O observed in the range of 2θ = 10 to 13 °. The ratio of the height of MP derived from Na ₄ Ti ₉ O ₂₀ · 5-7H ₂ O observed in the range was 38.5%. According to the composition analysis of the above method, the molar ratio of Na ₄ Ti ₄ Si ₃ O ₁₆ .nH ₂ O: Na ₄ Ti ₉ O ₂₀ .mH ₂ O was 1: 0.37.
Moreover, the TG-DTA curve of the mixture of crystalline silicotitanate and titanate is shown in FIG. An endothermic peak accompanying dehydration of the mixture was observed at around 70-80 ° C and around 200 ° C.
As a result of X-ray diffraction analysis, the interlayer of titanate was 0.90 nm (2θ = 9.8 °).

[Comparative Example 1]
The granular material obtained in Production Example 1 was used as the adsorbent of Comparative Example 1 as it was.

[Example 1]
100 g of the granular material obtained in Production Example 1 was put in an alumina container, heated in an electric furnace in the air atmosphere over 2 hours, and then baked at 500 ° C. for 2 hours. Thereby, the adsorbent of Example 1 was obtained. The obtained adsorbent was subjected to X-ray diffraction measurement by the above method. The result is shown in FIG. As shown in FIG. 1, although the peak derived from crystalline silicotitanate almost disappeared, a minute peak (peak intensity 220 cps) that was considered to be derived from the silicotitanate was observed as a main peak at 2θ = 10-13 °. Therefore, it was confirmed that the adsorbent of Example 1 contained an amorphous or low crystalline silicon- and titanium-containing compound containing the silicotitanate.
Further, the obtained adsorbent was subjected to TG-DTA measurement at a heating rate of 10 ° C./min from 25 ° C. to 1000 ° C., and the weight reduction rate was measured to be 1.1%. The obtained TG-DTA is shown in FIG.

[Comparative Example 2]
The granular material obtained in Production Example 2 was used as the adsorbent of Comparative Example 2 as it was.

[Example 2-1]
100 g of the granular material obtained in Production Example 2 was put in an alumina container, heated in an air atmosphere over 2 hours, and then fired at 400 ° C. for 2 hours. This obtained the adsorbent of Example 2-1. The obtained adsorbent was subjected to X-ray diffraction measurement by the above method. The result is shown in FIG. As shown in FIG. 4, it was confirmed that the main peak observed at 2θ = 10 to 13 ° derived from crystalline silicotitanate was reduced (peak intensity 150 cps), resulting in low crystalline silicotitanate. Further, the main peak of the titanate moved slightly to the high angle side. In FIG. 4 and subsequent figures, SNT represents the titanate.
Further, as a result of X-ray diffraction analysis, the interlayer of the titanate fired at 400 ° C. was 0.89 nm (2θ = 9.9 °).

[Example 2-2 and Example 2-3]
An adsorbent was produced in the same manner except that Example 2-1 and the firing temperature were changed to 500 ° C. (Example 2-2) or 600 ° C. (Example 2-3), and X-ray diffraction measurement was performed in the same manner. It was. The results are shown in FIG. As shown in FIG. 3, according to the X-ray diffraction charts of the adsorbents obtained in Examples 2-2 and 2-3, a clear peak derived from crystalline silicotitanate was not observed (there is a peak). Even if the main peak of titanate at 2θ = 10-14 ° overlaps, the strength is 350 cps or less), it is confirmed that it is an amorphous or low crystalline silicon and titanium-containing compound. It was. Moreover, it was confirmed that the main peak of the titanate observed at 2θ = 8 to 10 ° of the titanate moves to the high angle side (2θ = 10 to 14 °).
As a result of X-ray diffraction analysis, the titanate layer of the 500 ° C. fired product was 0.76 nm (2θ = 11.6 °), and the titanate layer of the 600 ° C. fired product was 0.74 nm (2θ = 12.0 °).

[Comparative Example 3]
In the same manner as in Production Example 1, a first step was performed to obtain a mixed gel. The obtained mixed gel is put in an autoclave, heated to 170 ° C. over 2 hours, and then reacted for 96 hours with stirring while maintaining this temperature, and the slurry containing the crystalline silicotitanate is reacted. (First slurry) was obtained.
Further, 1742.94 g of an aqueous caustic soda solution, 719.09 g of caustic potash, and 3671.54 g of pure water were mixed and stirred to obtain a mixed aqueous solution. To this mixed aqueous solution, 1616 g of titanium tetrachloride aqueous solution was continuously added over 1 hour by a peristaltic pump to produce a mixed gel. The molar ratio of K ₂ O / Na ₂ O in the mixed gel was 1/1, and the concentration in terms of TiO ₂ was 3.22%. The mixed gel was heated to 98 ° C. over 2 hours after the addition of the aqueous titanium tetrachloride solution, and then reacted for 6 hours with stirring while maintaining this temperature. After the reaction containing the titanate Slurry (second slurry) was obtained.
The molar ratio of the ratio of the crystalline silicotitanate and the titanate (the ratio when the Ti in each of the first slurry and the second slurry is the total amount, the crystalline silicotitanate and the titanate). The first slurry and the second slurry were stirred and mixed so that the ratio was 1: 1. The obtained mixture was filtered, and the obtained solid was washed to obtain a dried product. This was used as the adsorbent of Comparative Example 3. The obtained adsorbent was subjected to X-ray diffraction measurement by the above method. The result is shown in FIG. As shown in FIG. 6, in the X-ray diffraction chart of the adsorbent of Comparative Example 3, peaks derived from the crystalline silicotitanate and the titanate were observed.
As a result of X-ray diffraction analysis, the interlayer of the titanate was 0.89 nm (2θ = 9.9 °).

Example 3
In place of the granular material obtained in Production Example 1, 100 g of the adsorbent obtained in Comparative Example 3 was placed in an alumina container, heated in an air atmosphere over 2 hours, and then calcined at 500 ° C. for 2 hours. Example 3 Of adsorbent was obtained. The obtained adsorbent was subjected to X-ray diffraction measurement by the above method. The result is shown in FIG. As shown in FIG. 6, the peak derived from crystalline silicotitanate is small or disappears (even if the peak exists, the main peak of titanate at 2θ = 10 to 14 ° is overlapped, The strength was 350 cps or less), and it was confirmed to be a low-crystalline or amorphous silicon- and titanium-containing compound. In the X-ray diffraction chart of Example 3 in FIG. 6, the main peak of the titanate is considered to have moved to the high angle side (2θ = 10-14 °).
As a result of X-ray diffraction analysis, the titanate interlayer was 0.79 nm (2θ = 11.2 °).

[Comparative Example 4]
The post-reaction slurry containing the titanate obtained in Comparative Example 3 was filtered, and the resulting solid was washed to obtain a dried product. This was used as the adsorbent of Comparative Example 4. The obtained adsorbent was subjected to X-ray diffraction measurement by the above method. The result is shown in FIG.
Moreover, the TG-DTA curve of the obtained titanate is shown in FIG. In FIG. 8, a thick line is a DTA curve, and a thin line is a TG curve. As shown in the DTA curve of FIG. 8, an endothermic peak accompanying dehydration was observed near 100 ° C.
As a result of X-ray diffraction analysis, the interlayer of the titanate was 0.95 nm (2θ = 9.3 °).

[Comparative Example 5]
100 g of the adsorbent of Comparative Example 4 was put in an alumina container, heated in an air atmosphere over 2 hours, and then calcined at 500 ° C. for 2 hours to obtain an adsorbent of Comparative Example 5. The obtained adsorbent was subjected to X-ray diffraction measurement by the above method. The result is shown in FIG.
As shown in FIG. 6, it was confirmed that the main peak observed at 2θ = 8 to 10 ° of the titanate moved to the high angle side (2θ = 10 to 14 °).
As a result of X-ray diffraction analysis, the titanate interlayer was 0.77 nm (2θ = 11.5 °).

The adsorbents of Example 1, Examples 2-1 to 2-3, Example 3, and Comparative Examples 1 to 5 were each pulverized in a mortar, passed through a sieve with an opening of 100 μm, and each of the examples and comparative examples was passed through a sieve. It was set as the sample of this. Among these, the BET specific surface area was measured by the above method for each sample of Example 1, Examples 2-1 to 2-3, Example 3, and Comparative Examples 1 to 3. The results are shown in Table 1 below. Moreover, each sample of these Example 1, Examples 2-1 to 2-3, Example 3, and Comparative Examples 1-5 was used for the following <batch adsorption test>.
<BET specific surface area>

<Batch adsorption test>
Simulated seawater having the following composition was used.
<Composition of simulated seawater>
NaCl: 0.3%, Cs: 100 ppm, Sr: 100 ppm

  0.1 g of a sample was taken in a 100 ml plastic container, 60.0 g of simulated seawater was added, the lid was put on, and the container was tilted 10 times. Then, after standing for 1 hour, the mixture was shaken 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. For the filtrate collected at the second time (with an adsorption time of 24 hours), the content of Cs and Sr in the filtrate was measured using ICP-AES to determine the adsorption rate. The results are shown in FIGS. 9 and 10 below.

  As is apparent from the description of FIGS. 9 and 10, the adsorbents of Example 1, Examples 2-1 to 2-3, and Example 3 containing amorphous or low crystalline silicon and titanium-containing compounds were compared. It can be seen that it has high strontium adsorption performance comparable to the crystalline silicotitanate of Examples 1 to 3 or a mixture thereof and titanate, and low cesium adsorption performance can be realized. On the other hand, it can be seen that the titanate fired product of Comparative Example 5 has lost both the adsorption performance of strontium and cesium.

The adsorbents of Example 2-2 and Comparative Example 2 were subjected to the following <Water resistance test>.
<Water resistance test>
1 g of the adsorbent of Example 2 and Comparative Example 2 and 20 g of pure water were placed in a 200 ml container. After irradiating a 28 kHz ultrasonic wave for 10 seconds, the collapse of the molded body and the turbidity of pure water were visually confirmed. As shown in the photograph of FIG. 11, it was confirmed that the sample of Example 2-2 was thinner than the sample of Comparative Example 2 after the ultrasonic irradiation. Therefore, it turns out that water resistance improves by baking.

The adsorbents of Example 2-2 and Comparative Example 2 were subjected to the following <Column adsorption test>.
<Column adsorption test>
A column having an inner diameter of φ12 mm was used. The column was filled with the adsorbent sample so that the height was 4.5 cm (volume: 5 ml). Simulated seawater having the following composition was passed through the column. The liquid flow rate was 16.7 (ml / min), LV = 8.9 (m / h), and SV = 200 (1 / h). The cesium concentration and strontium concentration in the test solution sampled periodically were measured by ICP-AES, and the ratio of the concentration C after passing through to the initial concentration Co (Co / C) was determined. FIG. 12 shows a result in which the vertical axis indicates the numerical value represented by C / C ₀ and the horizontal axis indicates the total flow rate (BV) of the simulated seawater with respect to the volume of 5 ml.
Simulated seawater composition: NaCl: 0.13%, Mg: 63ppm, Ca: 20ppm, K: 19ppm, Cs: 120ppm, Sr: 30ppm, pH 5.5-6

  From the results shown in FIG. 12, the adsorbent of the present invention containing an amorphous or low crystalline silicon- and titanium-containing compound is crystalline silicotitanate before firing even when packed in a column and when the strontium concentration is low. It can be seen that it exhibits high strontium adsorption performance and low cesium adsorption performance equivalent to a mixture of citrate and titanate.

Claims (9)

  A strontium adsorbent comprising an amorphous or low crystalline silicon and titanium-containing compound.   2. The strontium adsorbent according to claim 1, wherein the silicon and titanium-containing compound has a weight loss of 150% by mass or less at 150 ° C. to 300 ° C. in thermogravimetric analysis. Furthermore, it is a general formula: A ₄ Ti ₉ O ₂₀ · mH ₂ O (wherein A represents one or two alkali metals selected from Na and K, and m represents a number of 0 to 10). The strontium adsorbent of Claim 1 or 2 containing the titanate represented.   The strontium adsorbent according to claim 3, wherein a main peak derived from the titanate is observed in a range of 2θ = 8 to 14 ° in X-ray diffraction measurement.   The strontium adsorbent according to claim 3 or 4, wherein a distance between layers in the layer structure of the titanate is 0.63 nm or more and 0.88 nm or less. Amorphous or low crystalline silicon and titanium-containing compounds have the general formula: A ′ ₄ Ti ₄ Si ₃ O ₁₆ .nH ₂ O (where A ′ is one or two selected from Na and K) The strontium adsorbent according to any one of claims 1 to 5, which is a fired product of crystalline silicotitanate represented by an alkali metal and n is a number of 0 to 8. A method for producing a strontium adsorbent according to claim 1,
General formula; A ′ ₄ Ti ₄ Si ₃ O ₁₆ .nH ₂ O (where A ′ represents one or two alkali metals selected from Na and K, and n represents a number of 0 to 8. A method for producing a strontium adsorbent, in which a raw material containing a crystalline silicotitanate represented by (2) is calcined at 250 ° C. or higher and 800 ° C. or lower. The raw material containing the crystalline silicotitanate has a general formula: A ₄ Ti ₉ O ₂₀ · mH ₂ O (wherein A represents one or two alkali metals selected from Na and K, and m represents 0 to 0). The manufacturing method of the strontium adsorption agent of Claim 7 containing the titanate represented by the number of 10.).   A method for adsorbing strontium, comprising bringing the strontium adsorbent according to any one of claims 1 to 6 into contact with a solution containing cesium and strontium.