High wear-resistant silica titanate molded article and method for manufacturing the same

Abstract

To provide a highly abrasion resistant molded body of silico-titanate of better high abrasion resistance relative to a conventional molded body of silico-titanate, and a method of producing the same.SOLUTION: There are provided a highly abrasion resistant molded body of silico-titanate including 5 pts.wt. or more and 30 pts.wt. or less of an inorganic oxide relative to 100 pts.wt. of silico-titanate, with the mean particle diameter of the inorganic oxide being 1 nm or larger and 15 nm or smaller, and a method of producing the highly abrasion resistant molded body of silico-titanate.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a molded body containing silicon titanate having a chitinite structure and an oxide, more particularly to a highly wear-resistant molded body using a small particle size inorganic oxide binder, a method for producing the molded body, and an adsorbent using the molded body. The molded body of the present invention is useful, for example, in applications for adsorptive removal treatment of cesium and strontium in seawater and groundwater.

Background Art

[0002] Due to the accident that occurred at the Fukushima Daiichi Nuclear Power Plant in 2011, a large amount of radioactive waste liquid containing radionuclides has been generated. Contaminated water continues to be generated by groundwater flowing in daily, etc., and an adsorbent capable of selectively capturing radionuclides is required. Among them, silicon titanate has attracted attention as an adsorbent capable of simultaneously adsorbing Cs and Sr contained at high concentrations in contaminated water. In treatment facilities such as the currently used Sally (SARRY, Simplified Active Water Retrieve and Recovery System (simple contaminated water treatment system) cesium removal device) and ALPS (ALPS, multi-nuclide removal device), powdered silicon titanate cannot be used, so a method of filling a column with a molded silicon titanate adsorbent and passing contaminated water through it is adopted. Generally, it has been found that the adsorption capacity of silicon titanate decreases by intense heating, and since a molded body cannot be created by firing at a high temperature as in the case of a zeolite molded body, etc., the strength of the adsorbent has become a problem.

[0003] Non-Patent Document 1 discloses the removal of cesium from cesium-containing wastewater using a pelletized silicotitanate. However, when cesium-containing wastewater is passed through a column packed with this pelletized silicotitanate, a portion of the silicotitanate dissolves or wears away, clogging the column. Therefore, a problem with the silicotitanate disclosed in Non-Patent Document 1 is that its ability to treat cesium-containing wastewater is reduced. To prevent column clogging, methods have been disclosed in which components that dissolve or wear away are removed from the silicotitanate by treating it with an alkaline solution beforehand.

[0004] Patent Document 1 proposes a silicatitanate molded article useful for adsorption and removal of cesium and strontium from seawater and groundwater, which is obtained by drying and molding a powder containing one or more oxides selected from the group consisting of silica, alumina, zirconia, and tungsten oxide as an inorganic binder, and silicatitanate having a sicinakite structure.

[0005] Patent Document 2 proposes a silicotitanate molded article characterized by containing crystalline silicotitanate particles represented by the general formula: A2Ti2O3(SiO4)·nH2O (wherein A represents one or two alkali metal elements selected from Na and K, and n represents a number from 0 to 2), having a particle size distribution in which 90% or more of the particles by volume are in the range of particle size 1 μm to 10 μm, and an oxide of one or more elements selected from the group consisting of aluminum, zirconium, iron, and cerium.

[0006] Patent Document 3 proposes a method for producing a silicotitanate composition, characterized by treating a silicotitanate composition, which includes a silicotitanate crystal with a sicinakite structure and a crystal having a peak at at least one of 2θ=8.7±0.5°, 2θ=10.0±0.5°, 2θ=27.8±0.5°, or 2θ=29.4±0.5°, and a peak at 2θ=21.8±0.5°, with a Na2O content of 1.0% by weight or more and 12.0% by weight or less, and a Na / Ti molar ratio of 0.1 or more and 1.0 or less, with an acidic aqueous solution.

[0007] In the method described in Non-Patent Document 1, the processing capacity decreases unless the adsorbent is pre-treated. In the methods described in Patent Documents 1, 2, and 3, although the adsorbent can withstand abrasion during water flow, it cannot withstand mechanical abrasion that occurs during the filling and retrieval of the adsorbent. [Prior art documents] [Patent Documents]

[0008] [Patent Document 1] Japanese Patent Publication No. 2016-102053 [Patent Document 2] Japanese Patent Publication No. 2019-014613 [Patent Document 3] Japanese Patent Publication No. 2019-189516 [Non-patent literature]

[0009] [Non-Patent Document 1] May Nyman, et al, “Characterization of UOP IONSIV IE-911”, SANDIA REPORT, SAND2001-0999, Printed June 2001, Sandia National Laboratories [Overview of the Initiative] [Problems that the invention aims to solve]

[0010] The present invention aims to provide a silica titanate molded article that has abrasion resistance to withstand mechanical shocks that occur during filling of an adsorption tower, etc., by using small-particle-sized silica particles as a binder, and also has high selective adsorption characteristics for cesium and strontium, a method for producing the molded article, and an adsorbent containing the molded article. [Means for solving the problem]

[0011] The inventors diligently investigated the above-mentioned problems. As a result, they found that a molded body using a small particle size binder, a molded body of silicate titanate having a sicinakite structure, and containing a specific oxide, exhibits significantly reduced wear when subjected to mechanical impacts during filling into an adsorption tower, etc. Furthermore, they found that wear is significantly reduced even when used in adsorption treatment under conditions where the aqueous solution to be treated flows at a high flow rate, and that it exhibits high selective adsorption characteristics for cesium and strontium in aqueous solutions such as seawater or groundwater. In other words, the present invention relates to a highly wear-resistant silicate titanate molded body containing 5 to 30 parts by weight of an inorganic oxide per 100 parts by weight of silicate titanate, wherein the average particle size of the inorganic oxide is 1 nm to 15 nm, a method for manufacturing the molded body, and an adsorption method using the molded body.

[0012] In detail, the present invention is as follows: [1] A highly wear-resistant silicatitanate molded article containing 5 to 30 parts by weight of an inorganic oxide per 100 parts by weight of silicatitanate, wherein the average particle size of the inorganic oxide is 1 nm to 15 nm. [2] The highly wear-resistant silicatitanate molded article according to [1] above, wherein the silicatitanate comprises crystals having a sicinakite structure and crystals having peaks at least one of 2θ=8.7±0.5°, 2θ=10.0±0.5°, 2θ=27.8±0.5°, or 2θ=29.4±0.5°, and a peak at 2θ=21.8±0.5°. [3] The highly wear-resistant silicatitanate molded article according to [1] or [2] above, wherein the inorganic oxide comprises at least one of silicon oxide, zirconium oxide, aluminum oxide, titanium oxide, and tungsten oxide. [4] A highly wear-resistant silicon titanate molded article according to any of the above items [1] to [3], wherein the partition coefficient for cesium adsorption is 800,000 mL / g or more. [5] A highly wear-resistant silicon titanate molded article according to any of the above items [1] to [4], wherein the partition coefficient for strontium adsorption is 4,000 mL / g or more. [6] A method for producing a highly wear-resistant silicatitanate molded article according to any of the above [1] to [5], wherein 100 parts by weight of silicatitanate is mixed with an inorganic oxide sol containing 5 to 30 parts by weight of an inorganic oxide, 1 to 10 parts by weight of a molding aid, and 40 to 100 parts by weight of water, and then kneaded to obtain a kneaded product containing these, and the kneaded product is molded and then dried, wherein the average particle size of the inorganic oxide is 1 nm to 15 nm. [7] A method for adsorbing at least one of cesium or strontium using a highly wear-resistant silicon titanate molded body as described in any of the above items [1] to [5].

[0013] The silicon titanate molded article of the present invention will be described in detail below.

[0014] The silicon titanate molded article of the present invention contains an inorganic oxide as an inorganic binder. The inorganic oxide is at least one selected from the group consisting of silicon dioxide (e.g., silica), zirconium oxide, aluminum oxide, titanium oxide, and tungsten oxide, more preferably at least one of silicon dioxide or zirconium oxide, and particularly preferably silicon dioxide.

[0015] The silica titanate molded article of the present invention contains 5 to 30 parts by weight of inorganic oxide per 100 parts by weight of silica titanate, preferably 5 to 20 parts by weight, and more preferably 5 to 15 parts by weight. If the amount of inorganic oxide is less than 5 parts by weight, the bonding force will be high and the strength of the molded article will be low. If the amount of inorganic oxide exceeds 30 parts by weight, the adsorption capacity per unit weight or per unit volume of the molded article will be low.

[0016] The average particle size of the inorganic oxide contained in the silica titanate molded article of the present invention is 1 nm or more and 15 nm or less, preferably 3 nm or more and 13 nm or less. If it is less than 1 nm, the extrusion moldability deteriorates significantly and is therefore undesirable from a manufacturing standpoint, and if it exceeds 15 nm, the strength of the molded article deteriorates significantly.

[0017] The silicotitanate contained in the silicotitanate molded body of the present invention has a sitinakite structure. Thereby, the silicotitanate molded body of the present invention has a high selective adsorption property for cesium and strontium. Here, the sitinakite structure is one of the crystal structures, as described in E.V. Sokolova et al., Sov. Phys. Dokl. 34, 583 (1989) (hereinafter referred to as "Reference 1"), or M.J. Buerger et al., W.A. DollAse, Z. KRISTALLOGR., 125, 92 (1967) (hereinafter referred to as "Reference 2"), or the powder X-ray diffraction (hereinafter referred to as "XRD") pattern described in sitinakite in the American Mineralogist Crystal Structure Database (http: / / ruff.geo arizona.edu. / AMS / amcsd.php, search date: July 1, 2014, hereinafter referred to as "Reference HP1"). It is a crystal structure attributed to the characteristic peaks shown. If the molded body of the present invention has the peak, the silicotitanate contained may be either a silicotitanate having a sitinakite structure alone or a silicotitanate composition described later.

[0018] The silicotitanate contained in the silicotitanate molded body of the present invention may contain niobium. Thereby, the silicotitanate molded body of the present invention has a higher selective adsorption property for cesium and strontium.

[0019] The Nb / Ti molar ratio of the silicotitanate molded body of the present invention is preferably 0.1 or more, more preferably 0.2 or more, and particularly preferably 0.4 or more. Thereby, the silicotitanate molded body of the present invention has higher adsorption performance for cesium, strontium, and particularly strontium. Usually, if the Nb / Ti molar ratio is 1.5 or less, sufficient adsorption performance is exhibited.

[0020] The Na / Ti molar ratio of the silicon titanate molded body of the present invention is preferably 0.1 or more and 1.0 or less, more preferably 0.3 or more and 1.0 or less, and particularly preferably 0.5 or more and 1.0 or less. Thereby, the Sr adsorption performance is enhanced.

[0021] The Na2O content of the silicon titanate molded body of the present invention is preferably 1.0% by weight or more and 12.0% by weight or less, more preferably 3.0% by weight or more and 12.0% by weight or less, and particularly preferably 5.0% by weight or more and 12.0% by weight or less. Thereby, the Sr adsorption performance is enhanced.

[0022] The shape of the silicon titanate molded body of the present invention is, for example, at least one selected from the group consisting of columnar, disk-shaped, hollow, polyhedral, spherical, substantially spherical, three-lobed, and massive, more preferably at least one selected from the group consisting of columnar, spherical, and three-lobed, and particularly preferably spherical and columnar. The length of the molded body is not particularly limited, but is preferably 0.1 mm or more and 5 mm or less.

[0023] The silicon titanate molded body of the present invention has high selectivity for cesium adsorption. Therefore, the distribution coefficient of the silicon titanate molded body of the present invention for cesium adsorption is preferably 800,000 mL / g or more, more preferably 1,000,000 mL / g or more, and particularly preferably 2,000,000 mL / g or more. If the distribution coefficient for cesium adsorption is 800,000 mL / g or more, coexisting components other than cesium in the treatment solution, for example, calcium, magnesium, etc. in seawater, are less likely to be adsorbed, and cesium adsorption can be carried out more efficiently.

[0024] The silicon titanate molded article of the present invention exhibits high selectivity for strontium adsorption. Therefore, the silicon titanate molded article of the present invention preferably has a partition coefficient for strontium adsorption of 4,000 mL / g or more, more preferably 10,000 mL / g or more, and particularly preferably 20,000 mL / g or more. If the partition coefficient for strontium adsorption is 4,000 mL / g or more, coexisting components other than strontium in the treatment solution, such as calcium and magnesium in seawater, will be less likely to be adsorbed, and strontium adsorption can be performed more efficiently.

[0025] The turbidity of the silicon titanate molded body of the present invention after abrasion testing is preferably 200 or less, more preferably 150 or less, and particularly preferably 100 or less. A turbidity of 200 or less after abrasion testing reduces the likelihood of crushed adsorbent material being generated, which can cause clogging at the bottom of purification equipment or in piping, when the silicon titanate molded body of the present invention is used as an adsorbent and packed into columns or the like. The abrasion test is performed by placing 2g of the adsorbent in a container with 100ml of pure water and rotating the container with a mix rotor at 40rpm for 4 hours. The turbidity is then measured using a high-sensitivity turbidimeter (TR-55, manufactured by Kasahara Chemical Industry Co., Ltd.).

[0026] The silicon titanate molded article of the present invention has a bulk density of 0.5 g / cm³. 3 Preferably, it should be above this level, and even more preferably 0.55 g / cm³. 3 Preferably, it is 0.60 g / cm³ or more, and especially 0.60 g / cm³. 3 Preferably, the bulk density is 0.5 g / cm³. 3 As a result, cesium and strontium can be adsorbed with a smaller amount of adsorbent. This allows for a reduction in the volume of the packed bed, such as the column, enabling miniaturization of the processing equipment. On the other hand, the bulk density is 0.95 g / cm³. 3 Preferably, the bulk density is 0.95 g / cm³. 3 The following conditions make it less likely for the flow of the treated aqueous solution within the column to be uneven, thereby suppressing a decrease in the column's adsorption performance.

[0027] The silicatitanate in the silicatitanate molded article of the present invention is preferably silicatitanate having a sicinakite structure with a high degree of crystallinity. High crystallinity allows for more selective adsorption treatment of cesium and strontium. Silicotitanate obtained by a neutralization method using a metal salt as a raw material, or silicatitanate obtained by a hydrolysis method using a metal alkoxide as a raw material, is preferred, with silicatitanate obtained by the neutralization method being preferred. Silicotitanate obtained by the neutralization method has a particularly high degree of crystallinity and therefore has a higher selective adsorption capacity.

[0028] The silicatitanate molded article of the present invention may contain at least silicatitanate having a sicinakite structure (hereinafter also referred to as "S-type silicatitanate"). However, it may also be a composition containing silicatitanate with a crystalline structure other than the sicinakite structure, or a substance other than silicatitanate. Specifically, examples include a silicate composition containing S-type silicate and niobium, and having diffraction peaks at least at 2θ=8.7±0.5°, 2θ=10.0±0.5°, 2θ=27.8±0.5°, or 2θ=29.4±0.5°, or a silicate composition containing S-type silicate and niobium, and having peaks at at least one of 2θ=8.7±0.5°, 2θ=10.0±0.5°, 2θ=27.8±0.5°, or 2θ=29.4±0.5°, and having a diffraction peak at 2θ=21.8±0.5°. By including such a composition, the silicate molded article of the present invention has higher strontium adsorption characteristics.

[0029] In this specification, 2θ is the value (°) of the X-ray diffraction angle in an XRD pattern using a CuKα line (wavelength λ = 1.5405 Å) as the source.

[0030] The composition containing the silicatitanate molded article of the present invention is not particularly limited in terms of the state of niobium, as long as the composition contains niobium. For example, niobium may be a niobium-containing compound, or any of the group consisting of niobium salts, niobium silicates, niobium titanates, and Nb-Si-Ti oxides. Furthermore, niobium may be contained in S-type silicatitanate.

[0031] The composition of the silicotitanate molded article of the present invention is preferably a silicotitanate composition containing a crystalline substance having diffraction peaks at 2θ = 27.8 ± 0.5° and 2θ = 29.4 ± 0.5° (hereinafter also simply referred to as "crystalline substance A") and S-type silicotitanate. Here, as crystalline substance A, at least one of the group consisting of crystalline silicotitanate other than S-type silicotitanate, titanate, niobate, silicate, niobsilicate, niobititanate, and Nb-Si-Ti-based oxides can be listed, preferably a crystalline silicotitanate other than S-type silicotitanate, and more preferably a silicotitanate having a vinogradovite structure (hereinafter also referred to as "V-type silicotitanate").

[0032] V-type silicotitanate is a crystalline silicotitanate that possesses an XRD peak corresponding to vinogradovite in the American Mineralogist Crystal Structure Database (http: / / ruff.geo.arizona.edu. / AMS / amcsd.php, accessed March 20, 2015, hereinafter referred to as "Reference HP2"). V-type silicotitanate has characteristic XRD peaks at least at 2θ = 27.8 ± 0.5° and 2θ = 29.4 ± 0.5°.

[0033] If the composition of the silicatitanate molded article of the present invention includes S-type silicatitanate and crystalline silicatitanate other than S-type silicatitanate (hereinafter also referred to as "non-S-type silicatitanate"), the silicatitanate composition only needs to contain S-type silicatitanate and non-S-type silicatitanate, and may be at least one of the following: a mixture of S-type silicatitanate and non-S-type silicatitanate, or a silicatitanate consisting of a mixed crystal of S-type silicatitanate and non-S-type silicatitanate.

[0034] The composition of the silicotitanate molded article of the present invention is preferably a silicotitanate composition comprising a crystalline substance (hereinafter also simply referred to as "crystalline substance B") having peaks at at least one of 2θ=8.7±0.5°, 2θ=10.0±0.5°, 2θ=27.8±0.5°, or 2θ=29.4±0.5°, and having a diffraction peak at 2θ=21.8±0.5°, and S-type silicotitanate. Here, as crystalline substance B, at least one of the group consisting of crystalline silicotitanate other than S-type silicotitanate, titanates, niobates, silicates, niobsilicates, niobititanates, and Nb-Si-Ti oxides can be listed, preferably at least one of niobates or silicates, and more preferably niobates.

[0035] Here, if the aforementioned XRD peak is present, the crystalline substance B may be two or more compounds, and is preferably two or more niobate salts.

[0036] If crystalline substance B contains a niobate salt, the composition of the niobate salt contained in the silicotitanate composition is NaxNbyOz·nH2O (where x=1~20, y=1~30, z=5~80, n=10~100).

[0037] The composition comprising the silicatitanate molded article of the present invention may also be a composition comprising S-type silicatitanate, crystalline substance A, and crystalline substance B.

[0038] Next, the method for producing the silicon titanate molded article of the present invention will be described.

[0039] (Mixing process) In the mixing process, inorganic oxide sol, silicate, and water are mixed together.

[0040] In the mixing step, the obtained silicate, inorganic oxide sol, and water are mixed to obtain a mixture.

[0041] The inorganic oxide sol can be one or more sols selected from silica sol, alumina sol, zirconia sol, and tungsten oxide sol. Silica sol and / or zirconia sol are particularly preferred, and silica sol is even more preferred. Using silica sol, or at least one of zirconia sol, or even more specifically silica sol, allows the firing temperature in the firing process to be lowered to 250°C or below.

[0042] The average particle size of the inorganic oxide in the inorganic oxide sol is 1 nm to 15 nm, preferably 3 nm to 13 nm. If it is less than 1 nm, the extrusion moldability deteriorates significantly, which is undesirable from a manufacturing standpoint, and if it exceeds 15 nm, the strength of the molded article deteriorates.

[0043] The amount of inorganic oxide in the inorganic oxide sol is preferably 5 to 30 parts by weight per 100 parts by weight of silicate titanate, more preferably 5 to 20 parts by weight, and particularly preferably 5 to 15 parts by weight. If the amount of inorganic oxide is less than 5 parts by weight, the strength of the molded article deteriorates significantly. If the amount of inorganic oxide exceeds 30 parts by weight, the adsorption capacity per unit weight of the molded article decreases.

[0044] For every 100 parts by weight of silica titanate, the amount of water (including water derived from sol) is 40 parts by weight or more and 100 parts by weight or less, preferably 50 parts by weight or more and 90 parts by weight or less. If the amount is less than 40 parts by weight or more than 100 parts by weight, molding may become difficult.

[0045] In the mixing process, it is preferable to first mix the above-mentioned silicate titanate and inorganic oxide sol, and then add water while mixing. Any mixing method is acceptable as long as a mixture with the following final composition is obtained. During the mixing process, molding aids and pH adjusters can be added as needed, either before the start of mixing or at the same time as adding water.

[0046] Silicone titanate: 100 parts by weight Inorganic oxide: 5 parts by weight or more and 30 parts by weight or less Water: 40 parts by weight or more and 100 parts by weight or less, more preferably 60 parts by weight or more and 80 parts by weight or less The molding aid can be any compound that has the function of increasing the viscosity of the mixture. One or more can be selected from the group consisting of carboxymethylcellulose, polyvinyl alcohol, and sodium tripolyphosphate. Carboxymethylcellulose (hereinafter referred to as "CMC") is a particularly preferred molding aid. The amount of the molding aid is 1 part by weight or more and 10 parts by weight or less, preferably 2 parts by weight or more and 8 parts by weight or less, per 100 parts by weight (anhydrous basis) of silicate titanate. If the amount is less than 1 part by weight, the moldability will decrease, and if it exceeds 10 parts by weight, the compressive strength will decrease.

[0047] The pH adjuster can be any compound that adjusts the viscosity of the mixture. Examples include one or more compounds selected from the group consisting of nitric acid, sulfuric acid, acetic acid, sodium hydroxide, and ammonia. Particularly preferred pH adjusters include at least one of acetic acid or ammonia, and more specifically, acetic acid.

[0048] The mixing can be done using any one of the following methods: Henschel mixer, ribbon blender, kneader, Nauter mixer, or mix maller.

[0049] (molding process) In the molding process, the mixture obtained in the mixing process is molded using any molding method. For example, if the mixture is to be molded into cylindrical, trefoil, or polygonal shapes, an extrusion molding method can be used. Furthermore, the extruded body can be crushed and granulated to obtain a molded body of any size. Alternatively, if the mixture is to be molded into bead shapes, a rolling granulation method can be used. Examples of rolling granulation methods include blade type, pan type, drum type, and blade agitator type rolling granulation.

[0050] (Firing process) A silicon titanate molded body can be obtained by firing the molded body obtained in the molding process. By firing the molded body, the pressure resistance strength of the obtained silicon titanate molded body is increased. The firing temperature is preferably 80°C to 500°C, more preferably 100°C to 300°C, and even more preferably 110°C to 200°C. By using an oxide sol as an inorganic binder, even when firing at a low temperature of 80°C to 500°C, a silicon titanate molded body with improved mechanical strength and sufficient wear resistance can be obtained. The firing holding time can be 0.5 hours or more, and more preferably 1 hour or more. The firing atmosphere can be an oxidizing atmosphere, for example, air. Furthermore, a preferred firing atmosphere is firing in an airflow of 5 L / min or more, and more preferably 20 L / min or more. This tends to further improve the sinterability of the molded body.

[0051] (Treatment with acidic solution) The performance of the silicon titanate molded body obtained in the firing process can be improved by treating it with an acidic solution. To facilitate treatment with an acidic aqueous solution using an appropriate amount of treatment liquid, the pH of the acidic aqueous solution is preferably 1 to 6.5, more preferably 1.5 to 6.5, and even more preferably 2 to 6.5.

[0052] The acidic aqueous solution can contain at least one of the following: hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, boric acid, or carbonate. Buffer solutions with a pH between 1 and 6.5 are also acceptable.

[0053] The treatment temperature with the acidic aqueous solution should be between 30°C and 90°C, more preferably between 30°C and 80°C, or even more preferably between 30°C and 70°C. The silicate titanate composition treated with the acidic aqueous solution can be in powder or molded form. Treatment with the acidic aqueous solution can be carried out by either a batch method or a column method, and the treatment time can be between 0.5 hours and 24 hours.

[0054] The amount of acidic aqueous solution varies depending on the pH and temperature of the acidic solution, but it can be between 1 and 50 times the amount of the silicate titanate composition before acid treatment.

[0055] In the column method, the acidic aqueous solution can be passed through in a single pass, or the solution discharged from the column outlet can be returned to the column inlet for circulation; both upflow and downflow methods are acceptable. The flow rate of the acidic aqueous solution depends on the shape of the column, but it should be between 5 cm / min and 50 cm / min as an empty column velocity.

[0056] The method for producing the silicate composition is described below.

[0057] The pre-acid-treated silicotitanate composition must contain a citinakite structure. The presence of the citinakite structure is necessary for the Sr adsorption performance to be exhibited. Because the pre-acid-treated silicotitanate composition has higher Sr adsorption performance, it is preferable that it contains crystals with a citinakite structure and crystals having a peak at at least one of the following angles: 2θ=8.7±0.5°, 2θ=10.0±0.5°, 2θ=27.8±0.5°, or 2θ=29.4±0.5°. The Na2O and Na / Ti molar ratio of the pre-acid-treated silicotitanate composition is not particularly limited.

[0058] The silica titanate composition before acid treatment contains a doped metal (at least one selected from the group consisting of niobium, tantalum, vanadium, antimony, manganese, copper, and iron). Among the doped metals, niobium (Nb) is preferred. To improve Sr adsorption performance, a doped metal / Ti molar ratio of 0.01 to 1.5 is preferred, 0.3 to 1.5 is more preferred, and 0.5 to 1.0 is even more preferred.

[0059] A method for producing a silicotitanate composition before acid treatment includes a gel step of mixing an inorganic titanium compound, an inorganic silicon compound, water, and an alkali metal hydroxide to obtain a silicotitanate gel, a crystallization step of crystallizing the silicotitanate gel, and a molding step of molding the silicotitanate composition obtained in the crystallization step.

[0060] In the gel process, an amorphous silicate titanate gel is obtained by mixing an inorganic titanium compound, an inorganic silicon compound, water, and an alkali metal hydroxide. In the gel process, an inorganic titanium compound is used as the titanium source, and an inorganic silicon compound is used as the silicon source. These titanium and silicon sources do not contain any hazardous or toxic substances, including organic alkoxy metal compounds. Furthermore, the inorganic titanium compound and inorganic silicon compound are soluble in aqueous alkali metal hydroxide solutions. Also, no organic substances such as alcohols are generated when the inorganic titanium compound and inorganic silicon compound are mixed. Therefore, the titanium and silicon sources are easier to handle than organic alkoxy metal compounds such as organic alkoxy titanium compounds or organic alkoxy silicon compounds. Moreover, because they are inexpensive, inorganic titanium salts and inorganic silicon compounds are more suitable for industrial use.

[0061] Examples of inorganic titanium compounds include at least one from the group consisting of titanium sulfate, titanium oxysulfate, sodium metatitanate, and titanium chloride. More preferred inorganic titanium compounds include at least one of titanium sulfate or titanium oxysulfate, and even more specifically, titanium oxysulfate.

[0062] Examples of inorganic silicon compounds include at least one from the group consisting of sodium silicate, silica sol, fumed silica, and white carbon. Since it is relatively easy to dissolve them in aqueous solutions of alkali metal hydroxides, the inorganic silicon compound is preferably at least one of sodium silicate or silica sol, and more preferably sodium silicate.

[0063] Examples of alkali metal hydroxides include at least one from the group consisting of lithium hydroxide, sodium hydroxide, and potassium hydroxide. Because they are inexpensive, the alkali metal hydroxide is preferably at least one of sodium hydroxide or potassium hydroxide, and sodium hydroxide is preferred.

[0064] The water may be the water contained in an aqueous solution of each ingredient, or it may be water mixed separately from each ingredient.

[0065] In the gel process, an amorphous silicotitanate gel (hereinafter also simply referred to as "silicotitanate gel") is produced by mixing an inorganic titanium compound, an inorganic silicon compound, water, and an alkali metal hydroxide. It is preferable to mix the inorganic titanium compound, the inorganic silicon compound, water, and the alkali metal hydroxide in the following molar ratios.

[0066] Si / Ti molar ratio: 0.5 to 2.0 H2O / Ti molar ratio: 20 to 150 M / Ti molar ratio: 1.0 to 5.0 (M is one alkali metal selected from the group Li, Na, and K, and M is preferably Na.) Furthermore, the following molar ratios are more preferable.

[0067] Si / Ti molar ratio: 1.0 or higher, 2.0 or lower H2O / Ti molar ratio: 20 to 150 M / Ti molar ratio: 1.0 to 5.0 (M is one alkali metal selected from the group Li, Na, and K, and M is preferably Na.) The Si / Ti molar ratio should be between 0.5 and 2.0, preferably between 0.8 and 1.8, and more preferably between 1.0 and 1.7. A Si / Ti molar ratio of 0.5 to 2.0 allows for efficient acquisition of the pre-acid-treated silicotitanate composition. The H2O / Ti molar ratio is preferably between 20 and 150, and more preferably between 40 and 100. An H2O / Ti molar ratio of 20 or higher reduces the viscosity of the resulting silicotitanate gel, making it easier to stir. An H2O / Ti molar ratio of 150 or lower tends to result in a higher yield of the pre-acid-treated silicotitanate composition.

[0068] The M / Ti molar ratio is preferably 1.0 to 5.0, more preferably 1.5 to 4.5, and particularly preferably 2.5 to 4.5. A mixture with an M / Ti molar ratio of 1.0 to 5.0 allows for efficient production of a pre-acid-treated silicate titanate composition.

[0069] The silicotitanate gel contains a doped metal (at least one selected from the group consisting of niobium, tantalum, vanadium, antimony, manganese, copper, and iron). The pre-acid treated silicotitanate composition obtained from the silicotitanate gel containing the doped metal has higher adsorption properties for Cs and Sr. Because the resulting pre-acid treated silicotitanate composition has higher adsorption properties for Cs and Sr, niobium can be cited as a particularly preferred doped metal.

[0070] A silicotitanate gel containing a doped metal can be obtained by at least one of the following methods: mixing an inorganic titanium compound, an inorganic silicon compound, water, an alkali metal hydroxide, and a doped metal source; or adding a doped metal source to a silicotitanate gel.

[0071] The doped metal source is preferably at least one of the group consisting of metals, alloys, and compounds containing the doped metal. Examples of compounds containing the doped metal include at least one of the group consisting of hydroxides, chlorides, nitrates, and sulfates containing the doped metal. To further improve the adsorption properties of Cs and Sr of the silicotitanate composition, the doped metal source can be at least one of compounds containing the doped metal, a hydroxide or nitrate containing the doped metal, or even a hydroxide of the doped metal.

[0072] The doped metal contained in the silica titanate gel is preferably in a molar ratio of doped metal to titanium (hereinafter also referred to as the "Mdope / Ti molar ratio") of 0.01 to 1.5. Having the Mdope / Ti molar ratio within this range reduces the generation of by-products that do not contribute to the adsorption of Cs and Sr, thereby improving the adsorption characteristics of Cs and Sr.

[0073] Seed crystals can also be mixed into the silicate titanate gel. Mixing seed crystals into the silicate titanate gel allows the gel to crystallize in a shorter time. The seed crystals can be any crystalline silicate, for example, silicate with a cicinakite structure. The amount of seed crystals relative to the silicate titanate gel is preferably 0.5% by weight or more and 10% by weight or less, and more preferably 0.5% by weight or more and 5% by weight or less.

[0074] A silicotitanate composition is obtained by crystallizing the silicotitanate gel.

[0075] In the crystallization step, a silicotitanate gel obtained by mixing an inorganic titanium compound, an inorganic silicon compound, water, and an alkali metal hydroxide and doped metal source is crystallized. In other words, the method for producing the pre-acid-treated silicotitanate composition uses silicon and titanium sources that are not classified as hazardous or toxic substances, and does not use structure-directing agents. Structure-directing agents are usually expensive compounds. By producing the pre-acid-treated silicotitanate composition without using structure-directing agents, the silicotitanate composition can be produced at a lower cost. In the crystallization step, the silicotitanate gel may be crystallized while being stirred. Crystallization is also possible without stirring, but stirring shortens the crystallization time.

[0076] The crystallization temperature should be between 150°C and 230°C, preferably between 160°C and 220°C, and more preferably between 170°C and 200°C. A crystallization temperature of 150°C or higher tends to result in higher crystallinity of the resulting silicatitanate. A temperature of 230°C or lower is sufficient for the use of general-purpose reaction vessels.

[0077] The crystallization time should be between 12 and 120 hours. If the crystallization time is 12 hours or more, the crystallinity of the silicotitanate contained in the resulting silicotitanate composition tends to be high. On the other hand, if the crystallization time is 120 hours or less, a silicotitanate composition with sufficient Cs or Sr adsorption properties can be obtained.

[0078] In the crystallization process, a pre-acid-treated silicotitanate composition can be obtained by crystallizing the silicotitanate gel. Furthermore, the process may include one or more steps of cooling, solid-liquid separation, washing, and drying the pre-acid-treated silicotitanate composition obtained by crystallization.

[0079] There are no particularly limiting cooling conditions when cooling a crystallized silicate composition.

[0080] When filtering a crystallized silicate composition, any solid-liquid separation method can be used. Examples include vacuum-assisted solid-liquid separation and membrane separation.

[0081] When washing a crystallized silicatitanate composition before acid treatment, pure water can be used as washing water in an amount of 2 to 10 times the weight of the silicatitanate composition. Furthermore, the pure water can be heated to a temperature of 60°C to 90°C and used as washing water. The washing method can be the same as that used for solid-liquid separation described above.

[0082] When drying the crystallized, pre-acid-treated silicate composition, it is recommended to dry the silicate composition in air at a temperature of 50°C to 200°C, and more specifically, 70°C to 150°C. After drying, if the silicate composition has aggregated, it can be appropriately crushed using a mortar and pestle, grinder, or the like.

[0083] By going through these steps after crystallization, the silicotitanate composition before acid treatment can be made into a powder. [Effects of the Invention]

[0084] The silica titanate molded articles of the present invention have high wear resistance due to the use of small-particle-sized silica particles as a binder, and are less likely to generate fine powder even when subjected to mechanical shocks such as those that occur during filling of adsorption towers, thus reducing the likelihood of blockage of adsorption towers by fine powder. [Examples]

[0085] The present invention will be described in more detail below with reference to examples. However, the present invention is not limited to these examples.

[0086] <Powder X-ray diffraction measurement> The XRD pattern of the sample was measured using a general-purpose X-ray diffractometer (product name: UltimaIV, manufactured by RIGAKU). The measurement conditions were as follows:

[0087] X-ray source: CuKα ray (λ = 1.5405 Å) Scanning condition: 0.1° per second Divergence slit: 1.00 deg Scattering slit: 1.00 deg Receiving slit: 0.30 mm Measurement range: 2θ = 5.0° - 60.0° The obtained XRD pattern was compared with the XRD peaks of silicotitanate with a chitinite structure described in the reference HP to identify the chitinite structure.

[0088] <Composition analysis of the silicotitanate composition and analysis of Cs and Sr concentrations> The composition analysis of the silicotitanate composition and the analysis of Cs and Sr concentrations were measured by a general ICP method. For the measurement, a general ICP-AES (device name: OPTIMA 7300DV, manufactured by PERKINELMER) was used.

[0089] <Measurement of the average particle size of the inorganic oxide sol> The specific surface area of the dried inorganic oxide sol was measured by the gas adsorption method (BET method), and the particle size converted as spherical particles (BET method converted particle size) was taken as the average particle size. The dried inorganic oxide sol was pretreated under vacuum at 110 °C for 2 hours. The nitrogen adsorption isotherm was measured at the liquid nitrogen temperature (77 K) using a constant volume method gas adsorption measurement device (product name: BELSOPE mini II, manufactured by Microtrac·BEL). The BET surface area was calculated from the obtained adsorption isotherm in the range of relative pressure of 0.1 or less. Then, the particle size converted as spherical particles (BET method converted particle size) was calculated and taken as the average particle size.

[0090] <Wear test> 2 g of the molded body was placed in a container together with 100 ml of pure water, and the container was rotated at 40 rpm for 4 h using a mix rotor for treatment.

[0091] <Evaluation of Sr adsorption characteristics> The lower half of a glass column with an inner diameter of 8 mm and a length of 25 cm, fitted with a jacket, was packed with glass beads to a height of approximately 10 cm. 4.5 mL of a molded silicate composition was then measured and packed onto the column. The jacket was temperature-controlled by flowing water adjusted to 30°C. The column was packed with pure water to prevent air from entering between the particles of the molded composition. After packing, 150 mL of pure water was flowed through the column. The test solution was prepared using commercially available Marine Art SF-1 (manufactured by Tomita Pharmaceutical Co., Ltd.) to achieve the following concentrations: Cs (1 mg / L), Sr (1.6 mg / L), Na (1992 mg / L), K (64 mg / L), Mg (236 mg / L), and Ca (82 mg / L). Since Marine Art SF-1 does not contain Cs, the concentration was adjusted by adding a standard solution for atomic absorption (1000 mg / L) to achieve a Cs concentration of 1 mg / L.

[0092] The test solution was passed through the glass column at a rate of 0.181 L / hr, and the Sr and Cs concentrations were analyzed by collecting the solution effluent from the glass column. The endpoint was defined as when the Sr concentration of the effluent reached 0.2 ppm or 7 days after the start of flow. The adsorption characteristics were evaluated based on the amount of flowable liquid that could be passed through by that time. A higher flow rate indicates higher adsorption performance.

[0093] Synthesis Example 1 Preparation of silica titanate powder 1743 g of pure water, 406 g of a 48% aqueous solution of sodium hydroxide, 171 g of niobium hydroxide, and 286 g of amorphous silica titanate gel (as solid content) were added and thoroughly mixed to obtain the raw material composition. The composition of the raw material composition, with TiO2 set to 1 in molar ratio, was SiO2:1.4, Nb2O5:0.3, Na2O:1.75, and H2O:109.

[0094] This raw material composition was sealed in a 4L stainless steel autoclave (product name: TAS-4 type, manufactured by Pressure-Resistant Industrial Glass) and heated at 180°C for 24 hours while rotating at 196 rpm. The product after heating was separated into solid and liquid phases, the obtained solid phase was washed with a sufficient amount of pure water, and dried at 100°C to obtain a powder product. The composition of the powder product, expressed as a molar ratio with TiO2 as 1, was SiO2:0.94, Nb2O5:0.28, and Na2O:0.75.

[0095] Example 1 A molded body was prepared by mixing 12 parts by weight of silica sol (product name: ST-30, manufactured by Nissan Chemical Corporation), 6 parts by weight of carboxymethylcellulose (product name: F-20LC, manufactured by Nippon Paper Industries Corporation), and 76 parts by weight of water (including water derived from the sol) with 100 parts by weight of the obtained powder product. The molded body was cylindrical with a diameter of 0.4 mm and a length of 0.4 to 2 mm. The average particle size of the silica contained in the silica sol used was 12 nm. The obtained cylindrical molded body was treated with an acidic aqueous solution. A 0.1 mol / L hydrochloric acid aqueous solution was used as the acidic aqueous solution. 550 mL of the silica titanate molded body was packed into a glass column, and 3300 mL of 0.1 mol / L hydrochloric acid aqueous solution (pH=1) was circulated at a linear velocity of 13.5 cm / min. At this time, the temperature of the hydrochloric acid aqueous solution was adjusted to 40°C. The circulation time of the hydrochloric acid aqueous solution was 18 hours. After treatment with the acidic aqueous solution, the body was washed with pure water and dried at 150°C. The turbidity of the obtained molded body after abrasion testing was 58.

[0096] The resulting molded article contained 12 parts by weight of silica per 100 parts by weight of silica titanate, and the average particle size of the silica was 12 nm.

[0097] Example 2 A molded body was prepared by mixing 12 parts by weight of silica sol (product name: ST-XS, manufactured by Nissan Chemical Corporation), 6 parts by weight of carboxymethylcellulose (product name: F-20LC, manufactured by Nippon Paper Industries Corporation), and 76 parts by weight of water (including water derived from the sol) with 100 parts by weight of the obtained powder product. The average particle size of the silica contained in the silica sol used was 5 nm. The molded body was cylindrical with a diameter of 0.4 mm and a length of 0.4 to 2 mm. The obtained cylindrical molded body was treated with an acidic aqueous solution. A 0.1 mol / L hydrochloric acid aqueous solution was used as the acidic aqueous solution. 550 mL of the silica titanate molded body was packed into a glass column, and 3300 mL of 0.1 mol / L hydrochloric acid aqueous solution (pH=1) was circulated at a linear velocity of 13.5 cm / min. At this time, the temperature of the hydrochloric acid aqueous solution was adjusted to 40°C. The circulation time of the hydrochloric acid aqueous solution was 18 hours. After treatment with the acidic aqueous solution, the body was washed with pure water and dried at 110°C. The turbidity of the obtained molded body after abrasion testing was 52.

[0098] The resulting molded article contained 12 parts by weight of silica per 100 parts by weight of silica titanate, and the average particle size of the silica was 5 nm.

[0099] Comparative Example 1 A molded body was prepared by mixing 12 parts by weight of silica sol (product name: ST-ZL, manufactured by Nissan Chemical Corporation), 6 parts by weight of carboxymethylcellulose (product name: F-20HC, manufactured by Nippon Paper Industries Corporation), and 76 parts by weight of water (including water derived from the sol) with 100 parts by weight of the obtained powder product. The molded body was cylindrical with a diameter of 0.4 mm and a length of 0.4 to 2 mm. The average particle size of the silica contained in the silica sol used was 80 nm. The obtained cylindrical molded body was treated with an acidic aqueous solution. A 0.1 mol / L hydrochloric acid aqueous solution was used as the acidic aqueous solution. 550 mL of the silica titanate molded body was packed into a glass column, and 3300 mL of 0.1 mol / L hydrochloric acid aqueous solution (pH=1) was circulated at a linear velocity of 13.5 cm / min. At this time, the temperature of the hydrochloric acid aqueous solution was adjusted to 40°C. The circulation time of the hydrochloric acid aqueous solution was 18 hours. After treatment with the acidic aqueous solution, the body was washed with pure water and dried at 110°C. The turbidity of the obtained molded body after abrasion testing was 252.

[0100] The resulting molded article contained 12 parts by weight of silica per 100 parts by weight of silica titanate, and the average particle size of the silica was 80 nm.

[0101] Comparative Example 2 A molded body was prepared by mixing 12 parts by weight of silica sol (product name: ST-30L, manufactured by Nissan Chemical Corporation), 6 parts by weight of carboxymethylcellulose (product name: F-20HC, manufactured by Nippon Paper Industries Corporation), and 76 parts by weight of water (including water derived from the sol) with 100 parts by weight of the obtained powder product. The molded body was cylindrical with a diameter of 0.4 mm and a length of 0.4 to 2 mm. The average particle size of the silica contained in the silica sol used was 45 nm. The obtained cylindrical molded body was treated with an acidic aqueous solution. A 0.1 mol / L hydrochloric acid aqueous solution was used as the acidic aqueous solution. 550 mL of the silica titanate molded body was packed into a glass column, and 3300 mL of 0.1 mol / L hydrochloric acid aqueous solution (pH=1) was circulated at a linear velocity of 13.5 cm / min. At this time, the temperature of the hydrochloric acid aqueous solution was adjusted to 40°C. The circulation time of the hydrochloric acid aqueous solution was 18 hours. After treatment with the acidic aqueous solution, the body was washed with pure water and dried at 110°C. The turbidity of the obtained molded body after abrasion testing was 178.

[0102] The resulting molded article contained 12 parts by weight of silica per 100 parts by weight of silica titanate, and the average particle size of the silica was 45 nm.

[0103] Comparative Example 3 A molded body was prepared by mixing 12 parts by weight of smectite clay (trade name: LAPONITE-RD, manufactured by BYK), 6 parts by weight of carboxymethylcellulose (trade name: F-20LC, manufactured by Nippon Paper Industries), and 76 parts by weight of water (including water derived from the sol) with 100 parts by weight of the obtained powder product. The molded body was cylindrical with a diameter of 0.4 mm and a length of 0.4 to 2 mm. The obtained cylindrical molded body was treated with an acidic aqueous solution. A 0.1 mol / L hydrochloric acid aqueous solution was used as the acidic aqueous solution. 550 mL of the silicate titanate molded body was packed into a glass column, and 3300 mL of 0.1 mol / L hydrochloric acid aqueous solution (pH=1) was circulated at a linear velocity of 13.5 cm / min. At this time, the temperature of the hydrochloric acid aqueous solution was adjusted to 40°C. The circulation time of the hydrochloric acid aqueous solution was 18 hours. After treatment with the acidic aqueous solution, it was washed with pure water and dried at 150°C. The turbidity of the obtained molded body after abrasion testing was 169.

[0104] The resulting molded article contained 0 parts by weight of inorganic oxide relative to 100 parts by weight of silicate titanate. [Industrial applicability]

[0105] The present invention provides a silica titanate molded body that has abrasion resistance to withstand mechanical shocks that occur during packing into an adsorption column, etc., by using small-particle-sized silica particles as a binder, and also has high selective adsorption characteristics for cesium and strontium, a method for manufacturing the molded body, and an adsorbent using the molded body. The obtained silica titanate molded body can suppress the deterioration of column performance due to the generation of fine powder from the molded body during column packing and when the liquid to be treated is passed through it, and can efficiently treat harmful ions such as cesium or strontium that coexist in seawater and groundwater.

Claims

1. A highly wear-resistant silicatitanate molded article comprising 5 to 30 parts by weight of an inorganic oxide per 100 parts by weight of silicatitanate, wherein the average particle size of the inorganic oxide is 1 nm to 15 nm, and the silicatitanate comprises crystals with a sicinakite structure and crystals having peaks at least one of 2θ = 8.7 ± 0.5°, 2θ = 10.0 ± 0.5°, 2θ = 27.8 ± 0.5°, or 2θ = 29.4 ± 0.5°, and a peak at 2θ = 21.8 ± 0.5°.

2. The highly wear-resistant silicon titanate molded article according to claim 1, wherein the inorganic oxide comprises at least one of silicon oxide, zirconium oxide, aluminum oxide, titanium oxide, and tungsten oxide.

3. A highly wear-resistant silica titanate molded article according to claim 1 or claim 2, wherein the partition coefficient for cesium adsorption is 800,000 mL / g or more.

4. A highly wear-resistant silicon titanate molded article according to claim 1 or claim 2, wherein the partition coefficient for strontium adsorption is 4,000 mL / g or more.

5. A method for producing a highly wear-resistant silicatitanate molded article according to claim 1 or 2, wherein 100 parts by weight of silicatitanate is mixed with an inorganic oxide sol containing 5 to 30 parts by weight of an inorganic oxide, 1 to 10 parts by weight of a molding aid, and 40 to 100 parts by weight of water, and then kneaded to obtain a kneaded product containing these, and the kneaded product is molded and then dried, the average particle size of the inorganic oxide being 1 nm or more and 15 nm or less.

6. A method for adsorbing at least one of cesium or strontium using a highly wear-resistant silicon titanate molded body according to claim 1 or claim 2.