Light water adsorbent and method for separating light water

Abstract

To provide a light water adsorbent that can selectively adsorb light water.SOLUTION: An adsorbent 1 adsorbs light water. The adsorbent 1 is made of titanate. The titanate has a structure in which a plurality of host layers 2 in which octahedron having six oxygen atoms coordinated in titanium atoms are chained to be formed by oxygen atom-bond in a two-dimensional direction are laminated thereon and sodium ions 3 are arranged between the host layers 2. Portions of titanium sites in the host layers 2 are replaced with monovalent-trivalent cations (α). A decrease rate of mass on heating in a temperature range of 120°C-200°C at the time when the titanate is heated from 40°C up to 200°C at a rate of temperature increase 10°C / minute under a nitrogen stream is 0.5 mass% or less.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] This invention relates to a light water adsorbent and a method for separating light water using the light water adsorbent. [Background technology]

[0002] 1 H2 16 Some isotopes of hydrogen or oxygen in water (also known as light water) are radioactive. For example, tritium (T), which has a mass number of 3, is a naturally occurring isotope of hydrogen and is a radioactive substance with a half-life of approximately 12.3 years. Furthermore, water in which the hydrogen atoms constituting the water molecule are replaced by tritium is called tritiated water, and is known to exist in the forms HTO, DTO, and T2O. In particular, tritiated water mainly exists in the form of HTO, and examples of water containing it include radioactive contaminated water generated by accidents at nuclear power plants.

[0003] While it is possible to remove 62 types of radioactive substances (excluding tritium) from radioactively contaminated water using an Advanced Liquid Processing System (ALPS), separating tritiated water from light water remains a problem. One method for separating tritiated water from light water is to electrolyze the light water in radioactively contaminated water containing trace amounts of tritiated water, but this method requires an enormous amount of energy. Other methods for separating tritiated water from light water include distillation using temperature differences and freezing, but these methods are not practical due to issues such as differences in freezing temperatures. Therefore, Patent Document 1 proposes a method for separating and immobilizing tritium from an aqueous solution containing tritium using a tritium separation and immobilization agent that has a layered structure and contains a metal compound with hydroxyl groups. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2019-155248

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, since heavy water such as tritiated water has properties similar to those of light water, it is difficult to obtain sufficient separation ability by a method of selectively adsorbing tritiated water from a large amount of light water as in Patent Document 1 and the like. Further, in the conventional technology, nothing is known about an adsorbent that selectively adsorbs light water.

[0006] The present invention has been made in view of the above circumstances, and an object thereof is to provide a light water adsorbent capable of selectively adsorbing light water and a method for separating light water capable of easily separating light water.

Means for Solving the Problems

[0007] The present invention provides the following light water adsorbent and method for separating light water.

[0008] Item 1 An adsorbent for adsorbing light water, wherein the adsorbent is composed of a titanate, and the titanate has a structure in which a plurality of host layers formed by edge-sharing octahedra in which oxygen atoms are six-coordinated to titanium atoms are linked in a two-dimensional direction, and sodium ions are arranged between the layers of the host layer, and a part of the titanium sites in the host layer is substituted with monovalent to trivalent cations (α), and the heating mass reduction rate in the temperature range of 120°C to 200°C when the titanate is heated from 40°C to 200°C at a heating rate of 10°C / min in a nitrogen stream is 0.5 mass% or less. Light water adsorbent.

[0009] Item 2 The light water adsorbent according to Item 1, wherein the content of sodium ions present between the layers of the host layer is 50 mol% or more and 100 mol% or less with respect to 100 mol% of the ions present between the layers of the host layer.

[0010] Item 3. The light water adsorbent according to Item 1 or Item 2, wherein the cation (α) is at least one of lithium ion and magnesium ion.

[0011] Item 4. The light water adsorbent according to any one of Items 1 to 3, wherein among the titanium sites in the host layer, more than 0 mol% and 40 mol% or less of the titanium sites are substituted with the cation (α).

[0012] Item 5. The light water adsorbent according to any one of Items 1 to 4, wherein the titanate substantially does not contain crystal water.

[0013] Item 6. The light water adsorbent according to any one of Items 1 to 5, wherein the interlayer distance of the host layer is 6 Å or more and 8 Å or less.

[0014] Item 7. The titanate is Na x K y Li 0.27 Ti 1.73 O 3.8~4 (where x is from 0.4 to 0.8, y is from 0 to 0.4, and x + y is from 0.4 to 0.8) and Na x K y Mg 0.4 Ti 1.6 O 3.8~4 (where x is from 0.4 to 0.8, y is from 0 to 0.4, and x + y is from 0.4 to 0.8), and is at least one compound selected from the group consisting of, and is the light water adsorbent according to any one of Items 1 to 6.

[0015] Item 8. The light water adsorbent according to any one of Items 1 to 7, wherein the average particle diameter of the titanate is from 0.1 μm to 100 μm.

[0016] Item 9. A method for separating light water, comprising a step of adsorbing at least a part of the light water onto the light water adsorbent according to any one of Items 1 to 8 by bringing a liquid to be treated containing light water and heavy water into contact with the light water adsorbent.

[0017] Item 10. The method for separating light water according to Item 9, wherein the heavy water contains tritium. [Effects of the Invention]

[0018] According to the present invention, it is possible to provide a light water adsorbent that can selectively adsorb light water, and a method for separating light water that can easily separate light water. [Brief explanation of the drawing]

[0019] [Figure 1] Figure 1 is a schematic diagram showing a light water adsorbent according to one embodiment of the present invention. [Figure 2] Figure 2 is a schematic diagram showing the experimental apparatus used in the tritium enrichment experiments of the examples and comparative examples. [Modes for carrying out the invention]

[0020] The following describes an example of a preferred embodiment of the present invention. However, the following embodiments are merely illustrative. The present invention is not limited in any way to the following embodiments.

[0021] <Light water adsorbent> The light water adsorbent of the present invention is an adsorbent that adsorbs light water. The adsorbent is made of a titanate. The titanate has a structure in which multiple host layers are stacked, each consisting of octahedrons in which 6 oxygen atoms are coordinated to a titanium atom, linked together in a two-dimensional direction with shared edges, and sodium ions are arranged between the host layers. Some of the titanium sites in the host layers are replaced with monovalent to trivalent cations (α). Furthermore, when the titanate is heated from 40°C to 200°C at a heating rate of 10°C / min under a nitrogen atmosphere, the heating mass loss rate in the temperature range of 120°C to 200°C is 0.5% by mass or less.

[0022] The light water adsorbent of the present invention can selectively adsorb light water because the titanate salt has a higher adsorption capacity for light water than for heavy water. The reason for this effect is not clear, but normally, water molecules form aggregates, and it is necessary to break these aggregates when they are incorporated as water of crystallization. In this case, there is a difference in the energy required to break these aggregates between light water and heavy water, and it is thought that when the titanate salt has the crystalline structure described later and there is less than one water molecule incorporated between the layers, light water is more easily adsorbed than heavy water.

[0023] Note that water contains water molecules that do not contain isotopes. 1 H2 16 O (hereinafter referred to as "light water") and, 16 Oxygen isotopes other than O and 1 A water molecule containing at least one of the hydrogen isotopes other than H. 1 H2 16 It contains isotopic water composed of water molecules with a mass greater than that of oxygen. In this invention, among the isotopic water, 1 Water molecules containing hydrogen isotopes other than H (practium) are called "heavy water," and among "heavy water," water molecules containing tritium (water molecules composed of one molecule each of practium, tritium, and oxygen (HTO), water molecules composed of one molecule each of deuterium, tritium, and oxygen (DTO), and water molecules composed of two molecules of tritium and one molecule of oxygen (T2O)) are called "tritiated water."

[0024] In the present invention, when the titanate is heated from 40°C to 200°C at a heating rate of 10°C / min under a nitrogen stream, the heating mass loss rate in the temperature range of 120°C to 200°C is preferably 0% by mass or more, more preferably 0.05% by mass or more, preferably 0.4% by mass or less, and more preferably 0.3% by mass or less. When the heating mass loss rate of the titanate is within the above range, light water can be adsorbed more selectively. The heating mass loss rate of the titanate can be measured, for example, using a differential thermomass-thermal measurement device (NEXTA STA300, manufactured by Hitachi High-Tech Science Corporation). The nitrogen flow rate can be, for example, 50 ml / min to 300 ml / min.

[0025] In this invention, the titanate host layer is formed by a chain of octahedra, each with six oxygen atoms coordinated to a titanium atom, sharing edges in a two-dimensional direction, forming a single layer that serves as a stacking unit. While each host layer is normally electrically neutral, it carries a negative charge due to some of the tetravalent titanium sites being replaced by monovalent to trivalent cations (α) or being vacant. The electrical neutrality of this compound is maintained by compensation from the positive charges of sodium ions, etc., present between the host layers (hereinafter referred to as "interlayers").

[0026] More specifically, Figure 1 is a schematic diagram showing a light water adsorbent according to one embodiment of the present invention. As shown in Figure 1, the light water adsorbent 1 is made of a titanate salt having a crystalline structure in which a plurality of host layers 2 are stacked and sodium ions 3 are arranged between the host layers 2. Furthermore, each host layer 2 is formed by a two-dimensional chain of octahedra in which 6 oxygen atoms are coordinated to titanium atoms, with edges sharing. Note that Figure 1 is a schematic diagram as an example, and the light water adsorbent of the present invention is not limited to the structure shown in the schematic diagram of Figure 1.

[0027] In the present invention, from the viewpoint of further enhancing the selective adsorption of light water, it is preferable that more than 0 mol% and 40 mol% or less of the titanium sites in the host layer are replaced with cations (α), more preferably 5 mol% or more and 30 mol% or less of the titanium sites are replaced with cations (α), and even more preferably 10 mol% or more and 20 mol% or less of the titanium sites are replaced with cations (α).

[0028] Examples of cations (α) include hydrogen ions, oxonium ions, alkali metal ions, alkaline earth metal ions, zinc ions, nickel ions, copper ions, iron ions, aluminum ions, gallium ions, and manganese ions. In particular, from the viewpoint of further enhancing the selective adsorption of light water, it is preferable that the cation (α) be at least one selected from the group consisting of hydrogen ions, oxonium ions, lithium ions, and magnesium ions, and more preferably at least one of lithium ions and magnesium ions.

[0029] Some of the titanium sites in the host layer may be vacant. If vacancies are present, it is preferable that the portion of the titanium sites in the host layer that exceeds 0 mol% and does not exceed 20 mol% is vacant, from the viewpoint of further enhancing the selective adsorption of light water.

[0030] The interlayers of the host layer may contain only sodium ions, or they may contain cations (β) as long as they do not impair the desirable physical properties of the present invention. Examples of cations (β) include hydrogen ions, oxonium ions, alkali metal ions, and alkaline earth metal ions. Among these, alkali metal ions are preferred as cations (β), and potassium ions are more preferred.

[0031] From the viewpoint of further enhancing the selective adsorption of light water, the sodium ion content between the host layers is preferably 50 mol% or more, more preferably 60 mol% or more, preferably 100 mol% or less, and more preferably 80 mol% or less, based on 100 mol% of the ions present between the host layers. From the viewpoint of further enhancing the selective adsorption of light water, the content ratio of cations (β) to sodium ions (cations (β) / sodium ions) between the host layers is preferably 5 / 95 to 50 / 50, and more preferably 10 / 90 to 40 / 60 in molar ratio.

[0032] In the present invention, it is preferable that the titanate is substantially free of crystal water. When the titanate is substantially free of crystal water, the selective adsorption of light water can be further enhanced. In the present invention, "substantially free of crystal water" means that the crystal water content in the titanate is 0.5% by mass or less.

[0033] In the present invention, the interlayer distance of the host layer of the titanate is preferably 6 Å or more and 8 Å or less. By setting the interlayer distance of the host layer within the above range, the selective adsorption of light water can be further enhanced. The interlayer distance of the host layer can be determined by X-ray diffraction measurement.

[0034] More specifically, in the X-ray diffraction pattern, several equally spaced peaks appearing in the low-angle region (generally 2θ = 20° or less) originate from the layered structure of titanate, and the interlayer distance can be calculated from the diffraction angle (2θ) of the first-order peak appearing at the lowest angle. Specifically, it can be calculated using Bragg's equation "d = nλ / 2sinθ" (where d is the interlayer distance (Å), θ is the diffraction angle (2θ) of the first-order peak divided by 2, λ is the wavelength of the CuKα line, which is 1.5418 Å, and n is a positive integer (n=1 for the first-order peak)).

[0035] In the present invention, the titanate is a powdery particle with various shapes, including spherical (including those with slight irregularities on the surface or those with an elliptical cross-section or other shapes that are roughly spherical), columnar (including those with a rod-shaped, cylindrical, prismatic, rectangular, rectangular, roughly cylindrical, roughly rectangular, or other shapes that are roughly columnar overall), plate-shaped, block-shaped, shapes with multiple protrusions (such as amoeba-shaped, boomerang-shaped, cross-shaped, or konpeito-shaped), and irregular shapes. The particle size of the titanate is not particularly limited, but the average particle diameter is preferably 0.1 μm to 100 μm, more preferably 0.5 μm to 50 μm, and even more preferably 1 μm to 20 μm.

[0036] In this invention, "average particle diameter" refers to the particle diameter at 50% cumulative accumulation (50% volume-based cumulative particle diameter) in the particle size distribution determined by laser diffraction and scattering, i.e., D 50 This refers to the median diameter. This volume-based cumulative 50% particle size (D 50 The particle size distribution is determined based on volume, and on a cumulative curve where the total volume is set to 100%, the number of particles is counted from smallest to largest, and the particle size at the point where the cumulative value reaches 50% is the particle diameter. These various particle morphologies and particle sizes can be arbitrarily controlled by the shape of the titanate salt used as the raw material, as described later.

[0037] The titanates described above include Na x K y Li 0.27 Ti 1.73 O 3.8~4 (In the equation, x is 0.4 to 0.8, y is 0 to 0.4, and x+y is 0.4 to 0.8) and Na x K y Mg 0.4 Ti 1.6 O 3.8~4 It is preferable that the compound is at least one compound selected from the group consisting of (wherein x is 0.4 to 0.8, y is 0 to 0.4, and x + y is 0.4 to 0.8).

[0038] The titanate salt constituting the light water adsorbent of the present invention can separate light water from a liquid to be treated that contains both light water and heavy water, and concentrate (reduce the volume of) the heavy water. Therefore, the light water adsorbent of the present invention is expected to be used, for example, to concentrate (reduce the volume of) tritium-containing contaminated water generated by an accident at a nuclear power plant.

[0039] (Method for manufacturing light water adsorbent) The method for producing the light water adsorbent of the present invention is not limited to a specific method as long as the above composition and structure can be achieved. The light water adsorbent of the present invention can be produced, for example, by a production method comprising the steps of (I) mixing a lepidocrocite-type titanate (hereinafter referred to as raw material titanate) having a layered crystalline structure with a sodium salt, and (II) heat-treating the compound obtained in step (I).

[0040] In the above manufacturing method, in step (I), the raw titanate and sodium salt are mixed, causing the interlayer cations of the raw titanate to undergo an ion exchange reaction with sodium ions. Furthermore, in the heat treatment in step (II), the water molecules between the layers of the raw titanate are removed (dehydrated), thereby obtaining a group of spaces between the layers of the resulting titanate that are suitable for the adsorption of light water.

[0041] As for the raw material titanate, A x M y Ti (2-y) O4 [wherein A is one or more alkali metals excluding Li, M is one or more selected from Li, Mg, Zn, Ga, Ni, Cu, Fe, Al, Mn, x is 0.5 to 1.0, y is 0.25 to 1.0], A 0.1~0.8 Li 0.2~0.4 Ti 1.6~1.8 O 3.7~3.95 [In the formula, A is one or more alkali metals excluding Li], A 0.2~0.8 Mg 0.3~0.5 Ti 1.5~1.7 O 3.7~3.95 [In the formula, A is one or more alkali metals excluding Li], A 0.5~0.7 Li (0.27-x) M y Ti (1.73-z) O 3.85~3.95 [In the formula, A is one or more alkali metals excluding Li, M is one or more selected from Mg, Zn, Ga, Ni, Cu, Fe, Al, and Mn (however, in the case of two or more types, combinations of ions with different valencies are excluded), x and z are x=2y / 3 and z=y / 3 when M is a divalent metal, and x=y / 3 and z=2y / 3 when M is a trivalent metal, and y is 0.004≦y≦0.4], etc. Among these, A is preferred as the raw material titanate. 0.5~0.7 Li 0.27 Ti 1.73 O 3.85~3.95 [In the formula, A is one or more alkali metals excluding Li] and A 0.2~0.7 Mg 0.40 Ti 1.6 O 3.7~3.95In the formula, A is at least one selected from the group consisting of one or more alkali metals excluding Li.

[0042] The sodium salt is not particularly limited as long as it is capable of ion exchange with the intercalated cations of the titanate raw material, and examples include sodium chloride, sodium sulfate, sodium carbonate, and sodium nitrate. Among these, sodium chloride is preferred.

[0043] Step (I) is preferably a wet process and can usually be carried out by adding the raw material titanate directly to a solution of sodium salt dissolved in an aqueous medium, or by adding a suspension of the raw material titanate dispersed in an aqueous medium and stirring. The reaction temperature is preferably 5°C to 80°C, and the reaction time is preferably 24 hours to 100 hours. After the reaction, the solids are separated by suction filtration, centrifugation, etc., washed in an aqueous medium, and the solids are dried.

[0044] In this invention, "aqueous medium" refers to water, an organic solvent miscible with water, or a mixture thereof. The aqueous medium in step (I) may be water, a mixture of water and an organic solvent miscible with water, or an organic solvent miscible with water. Among these, water is preferred as the aqueous solvent from the viewpoint of further enhancing reactivity.

[0045] The amount of sodium salt mixed in step (I) is preferably 3 to 9 equivalents relative to the exchangeable cation capacity of the raw titanate. If the amount of sodium salt mixed in step (I) is less than the lower limit, it may not be possible to sufficiently replace the interlayer cations with sodium ions, which may result in low light water adsorption. If the amount of sodium salt mixed in step (I) is greater than the upper limit, it may not be economically viable. In this specification, "exchangeable cation capacity" refers, for example, to the case where the raw titanate is of general formula A x M y Ti (2-y)O4 [wherein the formula A is one or more alkali metals excluding Li, M is one or more selected from Li, Mg, Zn, Ga, Ni, Cu, Fe, Al, Mn, x is 0.5 to 1.0, and y is 0.25 to 1.0] refers to the value expressed as x + my when the valence of M is m.

[0046] In step (II), the target titanate can be obtained by heat-treating the compound (solid) obtained in step (I). The heat treatment is not particularly limited as long as it can be controlled so that the water removed by heating is quickly discharged from the system. The heat treatment temperature is preferably 50°C to 500°C, more preferably 100°C to 300°C, and even more preferably 150°C to 250°C. The heat treatment time is preferably 0.5 hours to 24 hours, more preferably 1 hour to 12 hours, and even more preferably 1 hour to 4 hours.

[0047] <Method for separating light water> The present invention provides a method for separating light water, comprising the step of bringing a liquid to be treated containing light water and heavy water into contact with the above-mentioned light water adsorbent, thereby adsorbing at least a portion of the light water in the liquid to be treated onto the light water adsorbent. The heavy water is 1 Any water molecule containing hydrogen isotopes other than H (light hydrogen) is acceptable, but preferably it is a water molecule containing tritium such as HTO, DTO, and T2O.

[0048] The concentration of tritium in the treated solution is preferably between 1 kBq / g and 1000 kBq / g.

[0049] The method of bringing the liquid to be treated and the light water adsorbent into contact is not particularly limited, and examples include immersing the light water adsorbent in the liquid to be treated, bringing the vapor of the liquid to be treated into contact with the light water adsorbent, and passing the liquid to be treated through a filter containing the light water adsorbent.

[0050] The temperature of the liquid to be treated when it comes into contact with the light water adsorbent is preferably between 0°C and 80°C.

[0051] The preferred contact time for the light water adsorbent with the liquid to be treated is, for example, 30 to 60 days in the method of contacting it with steam. A contact time exceeding 120 days is undesirable because it will also adsorb heavy water, such as tritium water. [Examples]

[0052] The present invention will be described in more detail below based on specific examples. The present invention is not limited in any way to the following examples, and can be implemented with appropriate modifications without changing its essence.

[0053] (Example 1) An aqueous solution was prepared by dissolving 13.07 g of sodium chloride in 500 g of deionized water. Next, 10 g of layered lithium potassium titanate (manufactured by Otsuka Chemical Co., Ltd., trade name "Terraces L-SS"), which contains Li in part of the titan site, was added to the prepared aqueous solution and stirred at room temperature for 96 hours. After stirring, the solution was filtered and washed with water, and dried at 200°C for 1 hour to obtain the titanate.

[0054] (Example 2) An aqueous solution was prepared by dissolving 12.86 g of sodium chloride in 500 g of deionized water. Next, 10 g of layered magnesium potassium titanate (manufactured by Otsuka Chemical Co., Ltd., trade name "Terraces PS"), which contains Mg in part of the titanite, was added to the prepared aqueous solution and stirred at room temperature for 96 hours. After stirring, the solution was filtered and washed with water, and dried at 200°C for 1 hour to obtain the titanate.

[0055] (Comparative Example 1) Molecular sieves 3A (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., pore size 3 Å) were dried at 200°C for 1 hour to prepare the sample for Comparative Example 1.

[0056] (Comparative Example 2) An aqueous solution was prepared by dissolving 21.29 g of anhydrous magnesium chloride in 500 g of deionized water. Next, 10 g of layered lithium potassium titanate (manufactured by Otsuka Chemical Co., Ltd., trade name "Terraces L-SS"), which contains Li in part of the titan site, was added to the prepared aqueous solution and stirred at room temperature for 96 hours. After stirring, the solution was filtered and washed with water, and dried at 200°C for 1 hour to obtain the titanate.

[0057] (Comparative Example 3) An aqueous solution was prepared by dissolving 13.07 g of sodium chloride in 500 g of deionized water. Next, 10 g of layered lithium potassium titanate (manufactured by Otsuka Chemical Co., Ltd., trade name "Terraces L-SS"), which contains Li in part of the titan site, was added to the prepared aqueous solution and stirred at room temperature for 96 hours. After stirring, the solution was filtered and washed with water, and dried at 100°C for 1 hour to obtain the titanate.

[0058] [evaluation] The following evaluations were performed on the samples prepared in the examples and comparative examples.

[0059] (Average particle size) The average particle size of titanate salts was measured using a laser diffraction particle size distribution analyzer (Shimadzu Corporation, model number "SALD-2300"), and the particle size at 50% cumulative volume in the obtained particle size distribution was defined as the average particle size.

[0060] (composition formula) The chemical formula of the titanate was confirmed using an ICP-AES analyzer (Agilent 5110 VDV, manufactured by Agilent Technologies).

[0061] (Interlayer distance) The interlayer distance of the titanate host layer was confirmed by analysis using an X-ray diffraction analyzer (Ultima IV, Rigaku Corporation).

[0062] (Heating mass reduction rate) The heating mass loss rate of titanate was determined as follows: A 10 mg sample of titanate was heated from 40°C to 200°C in a differential thermomass analyzer (Hitachi High-Tech Science Corporation, "NEXTA STA300") under a nitrogen stream (nitrogen flow rate 200 ml / min) at a heating rate of 10°C / min. The mass loss (mass%) obtained by heating from 120°C to 200°C was defined as the heating mass loss rate.

[0063] (Tritium enrichment experiment) The apparatus shown in Figure 2 was prepared, and 5 g of the powder sample 13 obtained in the examples and comparative examples was spread evenly on the bottom of a conical flask 11 (100 mL). Next, a treatment solution 14 containing 380 kBq / g light water (H2O) and HTO was prepared, and 5 g of this treatment solution 14 was placed in a test tube 12 (11 mL) and sealed. At this time, the initial tritium concentration was set to C0 (kBq / g). Next, the conical flask 11 and test tube 12 were left standing in a constant temperature water bath 15 at 30°C for 60 days.

[0064] After standing for 60 days, 1 ml of the treated solution 14 in test tube 12 was taken using a micropipette and mixed with a liquid scintillator (PerkinElmer, "Ultima Gold LLT") to prepare a measurement sample. The radiation dose of this HTO-containing measurement sample was measured using a liquid scintillation counter (Hitachi Aloka Medical, "LSC-6101" and "LSC-7400") to determine the tritium concentration in test tube 12. The measured tritium concentration in test tube 12 after standing for 60 days was defined as C (kBq / g), and the increase / decrease rate was calculated using the following formula (1).

[0065] Percentage change (%) = ((C / C0) × 100 - 100) ... Equation (1)

[0066] A positive increase / decrease rate in equation (1) means that HTO is concentrated, indicating that the powder sample 13 in the Erlenmeyer flask 11 is selectively adsorbing light water. On the other hand, a negative increase / decrease rate in equation (1) means that HTO is diluted, indicating that the powder sample 13 in the Erlenmeyer flask 11 is selectively adsorbing HTO.

[0067] The results are shown in Table 1 below.

[0068] [Table 1]

[0069] As is clear from Table 1, the titanates of Examples 1 and 2, which have a specific structure in which sodium ions are arranged between the layers of the host layer and have a heating mass loss rate of 0.5% by mass or less, showed a positive increase / decrease rate in the tritium concentration experiment, indicating that they selectively adsorb light water and thus the titanates act as light water adsorbents. On the other hand, in Comparative Example 1, which does not use titanates, Comparative Example 2, which has magnesium ions arranged between the layers of the host layer, and Comparative Example 3, which has a heating mass loss rate of titanates greater than 0.5% by mass, the increase / decrease rate in the tritium concentration experiment was negative, indicating that they were not selectively adsorbing light water and thus the titanates did not act as light water adsorbents. [Explanation of Symbols]

[0070] 1…Light water adsorbent 2…Host layer 3…Sodium ions 11…Erlenmeyer flask 12… Test tube 13…Powder Samples 14… Liquid to be treated 15… Constant temperature water bath

Claims

1. An adsorbent that adsorbs light water, The adsorbent consists of a titanate salt, The titanate salt has a structure in which multiple host layers are stacked, each consisting of octahedrons, in which six oxygen atoms are coordinated to a titanium atom, linked together in a two-dimensional direction with shared edges, and sodium ions are arranged between the host layers. A portion of the titanium sites in the host layer is replaced with monovalent to trivalent cations (α), A light water adsorbent wherein the titanate is heated from 40°C to 200°C at a heating rate of 10°C / min under a nitrogen atmosphere, and the heating mass loss rate in the temperature range of 120°C to 200°C is 0.5% by mass or less.

2. The light water adsorbent according to claim 1, wherein the sodium ion content present between the layers of the host layer is 50 mol% or more and 100 mol% or less, relative to 100 mol% of the ions present between the layers of the host layer.

3. The light water adsorbent according to claim 1 or claim 2, wherein the cation (α) is at least one of lithium ions and magnesium ions.

4. The light water adsorbent according to claim 1 or claim 2, wherein more than 0 mol% and 40 mol% or less of the titanium sites in the host layer are replaced with the cation (α).

5. The light water adsorbent according to claim 1 or claim 2, wherein the titanate is substantially free of crystal water.

6. The light water adsorbent according to claim 1 or claim 2, wherein the interlayer distance of the host layer is 6 Å or more and 8 Å or less.

7. where the titanate is Na ｘ K ｙ Li ０．２７ Ti １．７３ O ３．８～４ (where x is 0.4 to 0.8, y is 0 to 0.4, and x + y is 0.4 to 0.8) and Na ｘ K ｙ Mg ０．４ Ti １．６ O ３．８～４ (where x is 0.4 to 0.8, y is 0 to 0.4, and x + y is 0.4 to 0.8), and is at least one compound selected from the group consisting of the light water adsorbent according to claim 1 or claim 2.

8. The light water adsorbent according to claim 1 or claim 2, wherein the average particle size of the titanate is 0.1 μm to 100 μm.

9. A method for separating light water, comprising the step of bringing a liquid to be treated containing light water and heavy water into contact with a light water adsorbent according to claim 1 or claim 2, thereby adsorbing at least a portion of the light water onto the light water adsorbent.

10. The method for separating light water according to claim 9, wherein the heavy water contains tritium.

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