JP2024028388A - Novel silicotitanate composition and method for producing the same - Google Patents

Abstract

The present invention provides a novel silicotitanate composition capable of selectively adsorbing and removing monovalent and divalent harmful ions from a solution with a high salt concentration, and a method for producing the same. SOLUTION At least 2θ=11.3±0.3°, 2θ=14.6±0.3°, 2θ=26.5±0.2°, 2θ=27.5±0.2°, 2θ =28.1±0.2° and 2θ=29.4±0.2°, and is selected from at least Si, Ti, and Nb, V, Ta, Zr, Mo, and W. A silicotitanate composition characterized in that it contains one or more metals. [Selection diagram] Figure 1

Description

The present invention relates to novel silicotitanate compositions and methods for their production.

There is a need for an adsorbent that can selectively adsorb radioactive elements (such as cesium and strontium) contained in radioactively contaminated water generated at nuclear facilities.

As an adsorbent capable of adsorbing radioactive elements, Patent Document 1 discloses a strontium adsorbent containing niobium. According to Patent Document 1, this strontium adsorbent is a silicotitanate having a sichinakite structure, and in powder X-ray diffraction using CuKα radiation as a radiation source, at least 2θ=27.8° and 2θ=29.4 It is characterized by having a diffraction peak at °.

JP2016-209857

Radioactively contaminated water may include seawater, and such contaminated water contains high concentrations of salts such as sodium, calcium, and magnesium, making it difficult to adsorb and remove radioactive elements using conventional adsorbents. It was difficult.

As a result of intensive studies to solve the above problems, the present inventors have determined that a metal composition having a specific X-ray diffraction peak (at least one or more selected from Nb, V, Ta, Zr, Mo, and W) has a specific X-ray diffraction peak. A silicotitanate composition containing at least one metal selected from Nb, V, Ta, Zr, Mo, and W, which is crystallized from a raw material (containing a metal), has selective ion exchange ability. The present invention has been completed based on the discovery that the present invention is excellent. That is, the present invention has an X-ray diffraction peak at 2θ = 28.1 ± 0.2° that is not present in the silicotitanate of Patent Document 1, and is free from at least Nb, V, Ta, Zr, Mo, and W. The present invention relates to a silicotitanate composition containing one or more selected metals, a method for producing the same, and uses thereof.

The novel silicotitanate composition of the present invention has higher selectivity than conventional ion exchangers, and removes trace amounts of radioactive elements from contaminated water containing large amounts of alkali metals and/or alkaline earth metals, such as seawater. (cesium and strontium) can be adsorbed and removed.

The novel silicotitanate composition of the present invention selectively removes harmful monovalent and divalent ions in addition to cesium and strontium, particularly ions such as thallium, rubidium, barium, cadmium, and zinc from solutions with high salt concentrations. Can be removed by adsorption.

The present invention will be explained in detail below.

The novel silicotitanate composition of the present invention selectively adsorbs and removes monovalent or divalent harmful ions, especially ions such as thallium, cesium, rubidium, barium, strontium, cadmium, and zinc from solutions with high salt concentration. It is suitable for

The novel silicotitanate compositions of the present invention have at least 2θ=11.3±0.3°, 2θ=14.6±0.3°, 2θ=26.5±0.2°, 2θ=27.5± It has X-ray diffraction peaks at 0.2°, 2θ=28.1±0.2°, and 2θ=29.4±0.2°. Regarding the X-ray diffraction peak of the silicotitanate composition of the present invention, when the peak intensity of the 2θ=11.3±0.3° peak is set as 100, the relative intensities of the other peaks are within the range shown in Table 1 below. It is preferable that The X-ray diffraction peak was measured using a general powder X-ray diffractometer using CuKα rays (λ=1.5405 Å) as a radiation source.

The novel silicotitanate composition of the present invention is characterized by containing Si and Ti, and further containing one or more metals selected from Nb, V, Ta, Zr, Mo, and W. . The metal is preferably a metal of Group 5 on the periodic table, more preferably Nb or V, and particularly preferably Nb. The metal is expressed as a molar ratio to Ti, and M/Ti=0.05 to 1.0 (M represents one or more metals selected from Nb, V, Ta, Zr, Mo, and W.) It is preferably 0.1 to 0.8, and more preferably 0.1 to 0.8. By decreasing the M/Ti molar ratio, the selectivity to monovalent harmful metals can be increased, and by increasing the M/Ti molar ratio, the selectivity to divalent harmful metals can be increased.

In the novel silicotitanate composition of the present invention, the Si/Ti molar ratio is preferably Si/Ti = 0.5 to 1.5, and preferably Si/Ti = 0.5 to 1.2. is more preferable.

Furthermore, the novel silicotitanate compositions of the present invention may contain alkali metals or alkaline earth metals. Examples of the alkali metals include sodium and potassium, and examples of the alkaline earth metals include magnesium and calcium. The alkali metal or alkaline earth metal is preferably sodium or potassium, more preferably sodium. The content of the alkali metal or alkaline earth metal, expressed as a molar ratio to Ti, is preferably A/Ti≦2.0 (A represents an alkali metal or alkaline earth metal), and A/Ti≦ More preferably, it is 1.5. Since some or all of the alkali metals or alkaline earth metals contained can be ion-exchanged, the lower limit of A/Ti is 0, but in terms of being excellent as an adsorbent, A/Ti is 0.01 or more. It is preferably 0.05 or more, more preferably 0.1 or more.

The novel silicotitanate composition of the present invention can also be used by previously ion-exchanging a part of the alkali metal or alkaline earth metal it contains with ions that are easily ion-exchanged, such as protons.

The novel silicotitanate composition of the present invention contains at least an alkali source, a silicon source, a titanium source, and one or more metal sources selected from Nb, V, Ta, Zr, Mo, and W, and has the following composition: A reaction mixture that satisfies the conditions (all of which represent the molar ratio of elements) can be produced by maintaining a temperature of 80° C. or higher and 220° C. or lower, preferably 100° C. or higher and 200° C. or lower.

A/Ti=2 or more and 7 or less (A represents an alkali metal or alkaline earth metal.)
Si/Ti=0.5 or more and 2 or less M/Ti=0.05 or more and 1 or less (M represents one or more metals selected from Nb, V, Ta, Zr, Mo, and W.)
H ₂ O/Ti = 30 or more and 300 or less In the reaction mixture, A/Ti is preferably 2.5 or more and 6 or less.

In the reaction mixture, Si/Ti is preferably 0.8 or more and 1.8 or less.

In the reaction mixture, M/Ti is preferably 0.1 or more and 0.9 or less.

In the reaction mixture, H ₂ O/Ti is preferably 50 or more and 200 or less.

Regarding the above metal source, it is essential to use a pyrochlore-structured hydrated oxide containing one or more metals selected from Nb, V, Ta, Zr, Mo, and W.

Note that the metal source in the present invention contains one or more metals selected from Nb, V, Ta, Zr, Mo, and W, since it can increase selectivity to divalent harmful metals. A hydrated oxide with a pyrochlore structure is preferable, and a hydrated oxide with a pyrochlore structure containing Nb is more preferable.

The raw material for the alkali source described above is preferably an alkali metal compound or an alkaline earth metal compound, and is not particularly limited. Part is preferably a water-soluble hydroxide, and sodium hydroxide, potassium hydroxide, etc. can be used. Further, hydroxides, chlorides, carbonates, etc. of these alkali metals or alkaline earth metals can be used in combination.

The silicon source is not particularly limited, but water-soluble silicates such as sodium silicate and potassium silicate, water glass, highly reactive amorphous silica, and the like can be used.

The titanium source is not particularly limited, but includes, for example, titanium sulfate, titanium oxysulfate, sodium metatitanate, or titanium chloride. Among these, titanium sulfate or titanium oxysulfate is preferred, and titanium sulfate is more preferred.

The novel silicotitanate composition of the present invention is prepared by sealing the reaction mixture of these raw materials in a heat-resistant and pressure-resistant container such as an autoclave, and maintaining the temperature at 80°C or higher and 220°C or lower, preferably 100°C or higher and 200°C or lower. can be manufactured. During the reaction, in order to keep the reaction system homogeneous, it is preferable to stir the contents, but the contents may be allowed to stand still. The novel silicotitanate composition of the present invention can be recovered from the reaction product using general solid-liquid separation methods such as filtration and centrifugation. The novel silicotitanate composition of the present invention recovered here may be further subjected to washing and drying treatments.

The novel silicotitanate composition of the present invention can also be made into a molded body. The molding method is not particularly limited. It is also possible to use a binder for molding, and examples of the binder used include inorganic binders such as clay, alumina, and silica. Further, when molding, organic molding aids such as cellulose, inorganic molding aids such as phosphates, etc. can be used as molding aids. The shape of the molded body is not particularly limited, but may be, for example, granular, spherical, cylindrical, trefoil, elliptical, bale-shaped, ring-shaped, or the like.

By bringing the novel silicotitanate composition of the present invention into contact with water to be treated (for example, water containing harmful metal ions such as thallium and cesium), harmful metal ions in the water to be treated can be adsorbed and removed. When performing such a treatment operation, the method of bringing the novel silicotitanate composition of the present invention into contact with the water to be treated is not particularly limited. For example, a method of dispersing the novel silicotitanate composition of the present invention in water to be treated and solid-liquid separation, a method of dispersing the novel silicotitanate composition of the present invention in the water to be treated, or a method of applying the novel silicotitanate composition of the present invention as a powder or as a molded body as a filter medium. General methods such as a method of filtering the treated water and a method of filling a column with the novel silicotitanate composition of the present invention in the form of a molded body and passing the water to be treated are applicable.

1 is an XRD pattern of the product obtained in Example 1. 1 is an XRD pattern of hydrated niobium oxide having a pyrochlore structure used as a raw material in Example 1. 1 is an XRD pattern of the product obtained in Example 2. 3 is an XRD pattern of the product obtained in Example 3. 3 is an XRD pattern of the product obtained in Example 4.

EXAMPLES Hereinafter, the present invention will be explained in more detail with reference to Examples, but the present invention is not limited thereto.

In the examples, the purity (%) of hydrated niobium oxide is expressed as niobium oxide equivalent weight %, where the loss on ignition at 600° C. is regarded as water or hydroxyl group. That is, "65% by weight hydrated niobium oxide" in Examples refers to "hydrated niobium oxide whose loss on ignition at 600° C. was 35% by weight."

<Powder X-ray diffraction measurement>
The powder X-ray diffraction pattern was measured in the range of 2θ = 5° to 60° using a powder X-ray diffractometer (trade name: Ultima IV, manufactured by Rigaku) using copper Kα rays as a radiation source.

Example 1
Pure water, 48% by weight sodium hydroxide solution, 65% by weight hydrated niobium oxide having a pyrochlore structure, precipitated silica gel, and 30% by weight titanium sulfate solution were mixed to prepare a reaction mixture having the following molar composition.

Na/Ti=3.5
Nb/Ti=0.6
Si/Ti=1.5
_H2O /Ti=110
56 g of this reaction mixture was placed in a stainless steel airtight pressure-resistant container with a volume of 80 ml, and held at 180° C. for 24 hours while rotating around a horizontal axis at 45 rpm.

The product was filtered, washed with water, and then dried at 110° C. overnight to obtain a novel silicotitanate composition of the present invention.

The composition of the obtained silicotitanate composition of the present invention, expressed in molar ratio of oxides, was as follows.

_0.62Na2O : _0.29Nb2O5 : _{0.92SiO2 : TiO2}
Na/Ti=1.24
Si/Ti=0.92
Nb/Ti=0.58
The X-ray diffraction pattern of the obtained novel silicotitanate composition of the present invention is shown in FIG. Further, the results of determining the peak positions (2θ) and the relative intensities of the peaks are shown in Table 2 (the table lists only diffraction peaks with relative intensities of 20% or more).

Figure 2 shows the X-ray diffraction pattern of hydrated niobium oxide with a pyrochlore structure used as a raw material. The X-ray diffraction peaks at 2θ = 28.1° and 2θ = 29.4° of the novel silicotitanate composition of the present invention in Example 1 are approximately The peak is shifted to the high angle side by 0.15°, and it is clear that the peak is not due to mixing of unreacted raw materials.

Example 2
Pure water, 48% by weight sodium hydroxide solution, 65% by weight hydrated niobium oxide having a pyrochlore structure, precipitated silica gel, and 30% by weight titanium sulfate solution were mixed to prepare a reaction mixture having the following molar composition.

Na/Ti=3.0
Nb/Ti=0.6
Si/Ti=1.5
_H2O /Ti=110
56 g of this reaction mixture was placed in a stainless steel airtight pressure container with a volume of 80 ml, and held at 180° C. for 24 hours while rotating around a horizontal axis at 45 rpm.

The product was filtered, washed with water, and then dried at 110° C. overnight to obtain a novel silicotitanate composition of the present invention.

The composition of the obtained silicotitanate composition of the present invention, expressed in molar ratio of oxides, was as follows.

_0.67Na2O : _{0.30Nb2O5 : 1.07SiO2} : _TiO2
Na/Ti=1.34
Si/Ti=1.07
Nb/Ti=0.60
The X-ray diffraction pattern of the obtained novel silicotitanate composition of the present invention is shown in FIG. Further, the results of determining the peak positions (2θ) and the relative intensities of the peaks are shown in Table 3 (the table lists only the diffraction peaks with relative intensities of 20% or more).

Example 3
Pure water, 48% by weight sodium hydroxide solution, 65% by weight hydrated niobium oxide having a pyrochlore structure, precipitated silica gel, and 30% by weight titanium sulfate solution were mixed to prepare a reaction mixture having the following molar composition.

Na/Ti=5.5
Nb/Ti=0.6
Si/Ti=1.5
_H2O /Ti=110
56 g of this reaction mixture was placed in a stainless steel airtight pressure-resistant container with a volume of 80 ml, and held at 180° C. for 24 hours while rotating around a horizontal axis at 45 rpm.

The product was filtered, washed with water, and then dried at 110° C. overnight to obtain a novel silicotitanate composition of the present invention.

The composition of the obtained silicotitanate composition of the present invention, expressed in molar ratio of oxides, was as follows.

_0.61Na2O : _0.29Nb2O5 : _{0.89SiO2 : TiO2}
Na/Ti=1.23
Si/Ti=0.89
Nb/Ti=0.58
The X-ray diffraction pattern of the obtained novel silicotitanate composition of the present invention is shown in FIG. Further, the results of determining the peak positions (2θ) and the relative intensities of the peaks are shown in Table 4 (the table lists only diffraction peaks with relative intensities of 20% or more).

Example 4
Pure water, 48% by weight sodium hydroxide solution, 65% by weight hydrated niobium oxide having a pyrochlore structure, precipitated silica gel, and 30% by weight titanium sulfate solution were mixed to prepare a reaction mixture having the following molar composition.

Na/Ti=4.0
Nb/Ti=0.6
Si/Ti=0.8
_H2O /Ti=110
56 g of this reaction mixture was placed in a stainless steel airtight pressure-resistant container with a volume of 80 ml, and held at 180° C. for 24 hours while rotating around a horizontal axis at 45 rpm.

The product was filtered, washed with water, and then dried at 110° C. overnight to obtain a novel silicotitanate composition of the present invention.

The composition of the obtained silicotitanate composition of the present invention, expressed in molar ratio of oxides, was as follows.

_0.66Na2O : _{0.29Nb2O5 : 0.70SiO2} : _TiO2
Na/Ti=1.33
Si/Ti=0.70
Nb/Ti=0.57
The X-ray diffraction pattern of the obtained novel silicotitanate composition of the present invention is shown in FIG. Further, the results of determining the peak positions (2θ) and the relative intensities of the peaks are shown in Table 5 (the table lists only diffraction peaks with relative intensities of 20% or more).

Example 5 (ion exchange test)
An ion exchange capacity test of the novel silicotitanate composition of the present invention obtained in Example 1 was carried out as follows.
<Preparation of ion exchange test solution>
The ion exchange test solution simulates 5-fold diluted seawater, and contains the chloride of each component and SPEX's ICP standard solution -331 was added so that the concentration of each element was 1 ppm. Since this solution is strongly acidic, a 48% by weight NaOH solution was added dropwise to adjust the pH to 6.5. Note that at this time, the above-mentioned fluctuation in ion concentration is so small that it can be ignored. At this time, since a precipitate was generated, a colorless transparent solution filtered through a membrane filter with a pore size of 0.1 μm was used as an ion exchange test solution.
<Ion exchange test>
In the ion exchange test, 80 ml of the above ion exchange test liquid was placed in a 100 ml polybottle, and the silicotitanate composition of the present invention obtained in Example 1 was added in dry weight of 0 mg (Blank test) and 4 mg (50 ppm to the test liquid). ) or 8 mg (100 ppm relative to the test solution) was added, and the mixture was shaken at a vibration frequency of 200 rpm for 24 hours in a water bath maintained at 25°C.

The test solution after the test is filtered through a membrane filter with a pore size of 0.1 μm to separate the adsorbent, and the concentration of ions remaining in the test solution is measured using ICP-AES (equipment name: OPTIMA3000DV, manufactured by PERKIN-ELMER) and ICP- Quantification was performed using MS (device name: NExION300S, manufactured by PERKIN-ELMER).

<Ion exchange removal rate (%)>
The ion exchange removal rate (%) was calculated using the following formula. Note that the ion species targeted for ion exchange removal rate (%) measurement are shown in Table 6.

Table 6 shows the ion exchange removal rate of the silicotitanate composition of the present invention.

As shown in Table 6, the silicotitanate composition of the present invention can be obtained from a high salt concentration solution containing Na: 2120 ppm, Mg: 254 ppm, Ca: 80 ppm, K: 76 ppm, trace amounts (about 1 ppm) of Tl, Cs, Ba could be removed by ion exchange with very good selectivity and a high removal rate. Furthermore, the silicotitanate composition of the present invention can remove trace amounts (approximately 1 ppm) of Zn, Sr, Rb, and Cd by ion exchange with good selectivity and high removal rate, similar to the above-mentioned Tl, Cs, and Ba. was completed. Ions contained in the ion exchange test solution that are not listed in Table 6 could not be quantified because they were precipitated and removed during pH adjustment or due to insufficient sensitivity of ICP.

The novel silicotitanate composition of the present invention selectively removes harmful metal ions from wastewater contaminated with harmful metal ions such as thallium, cadmium, and zinc, and from seawater and river water contaminated with radioactive cesium and strontium. It is useful for applications such as adsorption to and abatement of harmful substances.

Claims (4)

It has an X-ray diffraction peak at least at 2θ=28.1±0.2°, contains at least Si, Ti, and Nb, and has a Si/Ti molar ratio of 0.5 to 1.5. A silicotitanate composition. The silicotitanate composition according to claim 1, characterized in that it contains an alkali metal or an alkaline earth metal. Claim characterized in that the content of the alkali metal or alkaline earth metal, expressed as a molar ratio to Ti, is A/Ti≦2.0 (A represents an alkali metal or an alkaline earth metal). The silicotitanate composition according to 1 or 2. The silicotitanate composition according to claim 1 or 2, wherein the Nb has a molar ratio of Nb/Ti of 0.05 to 1.0.