Composition and method for concentrating boron isotope water-soluble system

Abstract

Provided is a method for concentrating boron isotope 10B with high concentration efficiency.　This method for concentrating boron isotope 10B involves agitating an aqueous boric acid solution and a resin (preferably, a resin having a specific gravity of 0.9 to 1.5) in the presence of a cation, and then isolating the obtained floc.

Description

Method and composition for enriching boron isotopes in aqueous systems

[0001] One aspect of the present invention is the boron isotope １０ This relates to a method for concentrating B in an aqueous solution.

[0002] Among naturally occurring elements, many elements have two or more stable isotopes. Since the chemical properties of isotopes of an element are very similar to each other, in many cases it is not necessary to distinguish between isotopes and to care about their slight differences. For example, the isotope ratio of boron contained in natural boric acid is １０ B / １１ B is approximately 0.248 ( １０ B: １１ B = 19.9%:80.1%). This value varies slightly depending on geological conditions, and the range of 10B / 11B is generally considered to be 0.235 to 0.255. On the other hand, when utilizing the nuclear properties of isotopes, a specific isotope may be required. For example, boron is used in neutron capture therapy for cancer, but in this case, what is required is not the element boron but an isotope of boron. １０ B. When neutron capture therapy for cancer is performed, １０ What is required is a concentrate of B of 99% or more.

[0003] Until now, separation of boron isotopes has been carried out industrially using BF ３ This has been achieved by distillation of the anisole complex (Non-Patent Document 1). This system has a large separation factor α = 1.039 (2°C), but its strong corrosiveness is a problem.

[0004] In the ion exchange method, boric acid B(OH) present in the aqueous solution ３ and the hydrated product B(OH) ４ － Utilizing the isotope effect between B(OH) ３ is a triangular planar structure, B(OH) ４ － has a regular tetrahedral structure, and when these two coexist, the light isotope １０ B is B(OH) ４ － , heavy isotopes １１ B is B(OH) ３When an anion exchange resin is added to this system, B(OH) ４ － is adsorbed on the anion exchange resin, and B(OH) ３ remains in the external solution phase. As a result, the isotope effect between the complex species is observed as isotope fractionation inside and outside the ion exchanger. In this way, B(OH) ３ and B(OH) ４ － When the isotope effect of α was measured, the equilibrium constant of the isotope exchange reaction in an aqueous system was found to be α = 1.019 at room temperature (Non-Patent Document 2).

[0005] Urgell et al. used an ion exchange resin column packed with a strongly basic ion exchange resin, Dowex 2x8 200-400 mesh, and expanded the boric acid adsorption zone up to 25 m, achieving a boric acid adsorption rate of over 50%. １０ However, this system uses alkali to regenerate the resin, which causes the generation of carbon dioxide gas during elution and development, making long-distance chromatography difficult.

[0006] On the other hand, Kakihana et al. found that when using the weakly basic anion exchange resin DIAION WA21, the boric acid band is eluted with pure water and remains in a regenerated state without generating carbon dioxide, and long-distance chromatography can be performed stably (Non-Patent Documents 2 and 4). With this method, the boric acid adsorption band was developed up to 256 m, and 90% of the band was at the end. １０ I got a B.

[0007] Until now, boron isotopes in aqueous systems １０ Anion exchange resins and aminopolyol-type anion exchange resins have been used to concentrate B, but the equilibrium constant for the isotope exchange reaction of boron isotopes in aqueous systems is α = 1.019, as mentioned above, and it has been thought that this value cannot be exceeded. Furthermore, it has been reported that the equilibrium constant decreases due to pressure load in column-based methods (Non-Patent Documents 5 and 6).

[0008] AA Palko: Industria1 and Engineering Chem., 51,119 (1959).H. Kakihana, M. Kotaka, S. Satoh, M. Nomura, and M. Okamoto: Bull. Chem. Soc. Jpn., 50, 158 (1977).MM Urgell, J. Ig1esias, J. Casas et al.: Third UN International Conf. on the Peaceful Uses of Atomic Energy, A / CONF. 28 / P / 491 (1964).Y. Sakuma, M. Aida, M. Okamoto and H. Kakihana: Bull. Chem. Soc. Jpn., 53,1860 (1980).Musashi et al. JNST 43, 461 (2006). Masaaki Musashi et al., Abstracts of the 55th Annual Meeting of the Geochemical Society of Japan, 2008, Boron isotope fractionation between solid and liquid phases: Effects of hydration and pressure (https: / / doi.org / 10.14862 / geochemproc.55.0.351.0)

[0009] One aspect of the present invention is to provide a method for producing a boron isotope with high enrichment efficiency. １０ The object of the present invention is to provide a method for concentrating B.

[0010] The present inventors have conducted extensive research to solve the above-mentioned problems, and as a result, have found that when an aqueous solution of boric acid and a resin are stirred in the presence of cations, the boron isotopes in the resulting flocs are １０ The inventors have found that B is concentrated in the soluble form of the soluble form, and have thus completed one embodiment of the present invention.

[0011] That is, the gist of one aspect of the present invention is as follows: (1) A method for producing a boron isotope extracting agent, comprising stirring an aqueous boric acid solution and a resin in the presence of a cation, and then separating the resulting flocs. １０(2) The method according to (1) above, wherein the specific gravity of the resin is 0.9 to 1.5. (3) The method according to (1) or (2) above, wherein the resin is a homopolymer or copolymer of acrylonitrile or methacrylonitrile. (4) The method according to any one of (1) to (3) above, wherein a hydroxide or salt of an alkali metal or alkaline earth metal is added as a cation source. (5) Separating the upper layer of the flocs and analyzing the boron isotopes. １０ (6) The method according to any one of (1) to (4) above, which increases the enrichment efficiency of B. (7) The method according to any one of (1) to (4), which increases the enrichment efficiency of B. (8) The method according to any one of (1) to (4), which increases the enrichment efficiency of B. (9) The method according to any one of (1) to (4), １０ The method according to any one of (1) to (5) above, wherein B is obtained as a solution. (7) The separated floc is treated with nitric acid to remove boron isotopes. １０ (8) The method according to any one of (1) to (5), wherein B is obtained as a solution. (9) The method according to any one of (1) to (5), wherein the separated flocs are combusted to extract boron isotopes. １０ (9) A method according to any one of (1) to (5), for obtaining B as a solid. (10) A composition comprising boron, a resin, and a cation, wherein the boron, the resin, and the cation form flocs, and the boron isotopes in the boron in the flocs are １０ B and １１ Molar ratio of B ( １０ B / １１ (B) is greater than 0.248. (10) The composition according to (9), wherein the resin is polyacrylonitrile. (11) The composition according to (9) or (10), wherein the flocs have a Stokes diameter and specific gravity such that the flocs do not settle within a settling time of 6 hours or less, in the relationship between the specific gravity and settling time of the flocs according to the Stokes equation. (12) The composition according to (11), wherein the Stokes diameter is 30 μm or less and the specific gravity is 1.01 to 1.10. This specification incorporates the disclosure of Japanese Patent Application No. 2024-025116, from which the present application claims priority.

[0012] In one embodiment of the present invention, a boron isotope is enriched by an isotope exchange reaction when a boric acid solution and a resin are stirred in the presence of cations to form flocs. １０ This is a groundbreaking method that can concentrate B more strongly and can be done using safe and inexpensive equipment.

[0013] Until now, natural boric acid has been converted to boron trifluoride by reacting with hydrogen fluoride, and then repeatedly bonded and separated with Lewis bases such as ether or anisole, which have unshared electron pairs, to form boron isotopes. １０ However, boron trifluoride and its complexes are highly corrosive, making the construction and management of the facilities extremely complicated and expensive. In addition, hydrogen fluoride, the raw material for boron trifluoride, is highly toxic and requires strict management.

[0014] Even today, enriched boron isotopes exist in this environment. １０ The supply of B is in a state of global shortage. On the other hand, compounds required for neutron capture therapy contain boron isotopes. １０ Compounds containing B are essential, and there is a significant imbalance between supply and demand.

[0015] Therefore, the economic effect of one embodiment of the present invention will be immeasurable, and will contribute not only to the development of medicine but also to the current use of boron isotopes. １０ It is positioned as an invention that solves the supply shortage of B.

[0016] Figure 1 shows the isotope exchange equilibrium in aqueous systems and the B(OH) ３ trigonal planar structure and B(OH) ４ － Figure 2 shows the tetrahedral structure of B(OH) ４ － cation (Na ＋ This shows the neutralization mechanism of B(OH). This operation causes a second-stage enrichment process by isotope exchange reaction, and simultaneously B(OH) ４ －It is believed that this neutralizes the regular tetrahedron structure of the boric acid, eliminating their mutual recoil forces, and as a result, promotes the formation of basal flocs. Figure 3 shows the presumed mechanism of action of the method of one embodiment of the present invention. As shown in the figure, boric acid molecules that have become negative ions due to the addition of hydroxyl groups to boric acid are neutralized by sodium cations, and hydrogen bonds are formed between the hydroxyl groups of boric acid and the nitrile groups of polyacrylonitrile (PAN). As a result, it is presumed that the formation of basal flocs leads to further cross-linking between them, resulting in aggregation. Figure 4A shows the results of Example 1. Figure 4A shows the results of the qualitative experiment on floc formation using Na ＋ The results of an experiment to confirm the effect of cations are shown in Table 1. ＋ Figure 4B shows the flocculation and volume increase rate of PAN by cations (sedimentation time 24 hours). Figure 4B shows the results of Example 1. Figure 4B shows the flocculation and volume increase rate of PAN by cations (sedimentation time 24 hours). ＋ The results of an experiment to confirm the effect of cations are shown in Table 1. ＋ Figure 5 shows the flocculation and volume increase rate of PAN by cations (sedimentation time 48 hours). Figure 5A shows the results of Example 2. Figure 5B shows the K in a qualitative experiment of flocculation. ＋ The results of an experiment to confirm the influence of cations are as follows: ＋ 5A and 5B show the flocculation and volume increase rate of PAN by cations (sedimentation time 24 hours). Fig. 5B shows the results of Example 2. Fig. 5B shows the K in a qualitative experiment of flocculation. ＋ The results of an experiment to confirm the influence of cations are as follows: ＋ Figure 6 shows the flocculation and volume increase rate of PAN by cations (sedimentation time 48 hours). Figure 6 shows the results of Example 3. Figure 6 shows the effect of Li in a qualitative experiment on flocculation. ＋ The results of an experiment to confirm the influence of cations are as follows: ＋ Figure 7 shows the flocculation and volume increase rate of PAN by cations (sedimentation time 48 hours). Figure 7 shows the results of Example 4. Figure 7 shows the effect of Ca in a qualitative experiment on flocculation. ２＋ The results of an experiment to confirm the influence of cations are shown in Table 1. ２＋The graph shows the floc formation and volume increase rate of PAN due to cations (sedimentation time: 48 hours). Figure 8 shows a schematic diagram of the flocs that accumulate in the upper layer of the polyacrylonitrile precipitate. The upper layer of flocs can be visually observed as coarse precipitates. (A) shows the polyacrylonitrile (PAN) precipitate (coarse structure), i.e., the state in which flocs are formed and crosslinks are generated by boric acid, resulting in aggregation. The graph shows the flocs that are concentrated by floc formation. １０ B / １１ Boric acid with a high B ratio accumulates. (B) shows a PAN precipitate (dense structure), i.e., a layer of PAN not involved in floc formation, through which the boric acid from the raw solution has penetrated. This is a simulation result using Stokes' equation, and is a graph showing the relationship between particle specific gravity and settling time for particles with particle diameters of 20 μm, 25 μm, and 30 μm. The dotted line frame shown in (1) represents the initial precipitate, PAN resin (no floc formation). This is a simulation result using Stokes' equation, and is a graph showing the relationship between particle specific gravity and settling time for particles with particle diameters of 10 μm, 15 μm, 20 μm, 25 μm, and 30 μm. The dotted line frame shown in (2) represents white precipitates of PAN flocs, with particle diameters ranging from 10 μm to 25 μm and specific gravities of 1.01 to 1.10. 1 is a graph showing the results of a simulation using Stokes' equation, illustrating the relationship between particle specific gravity and settling time for particles with diameters of 5 μm, 10 μm, 15 μm, 20 μm, 25 μm, and 30 μm. The dotted-line frame indicated by (3) shows floating white particles of PAN flocs, with particle diameters of 5 μm or less and specific gravities of 1.01 to 1.06.

[0017] The boric acid aqueous solution used in one embodiment of the present invention contains a boron isotope １０ There are no limitations as long as it contains B, and for example, an aqueous solution of natural boric acid or natural boric acid treated according to the method of one aspect of the present invention or other methods to obtain a boron isotope. １０ An example is an aqueous solution of boric acid in which the concentration of B is partially increased.

[0018] The cation used in one embodiment of the present invention includes boron isotopes. １０There are no limitations as long as it is capable of forming flocs containing B, and examples thereof include alkali metals such as lithium, sodium, potassium, rubidium, and cesium; alkaline earth metals such as magnesium, calcium, strontium, and barium; and cations such as aluminum, montmorillonite, and alum.

[0019] Examples of the raw material for the cation (cation source) include hydroxides or salts, and preferred examples include sodium hydroxide, potassium hydroxide, sodium bicarbonate, sodium acetate, lithium hydroxide, calcium hydroxide, etc. Preferred examples of the raw material for the cation (cation source) include sodium hydroxide, potassium hydroxide, sodium bicarbonate, sodium acetate, lithium hydroxide, calcium hydroxide, etc. As can be seen from Figures 4A and 4B and Figures 5A and 5B, alkali metal cations such as sodium hydroxide and potassium hydroxide are desirable.

[0020] The resin used in one embodiment of the present invention is a resin containing boron isotopes. １０ There are no limitations as long as it is capable of forming flocs containing B, and resins having a specific gravity of preferably 0.9 to 1.5, and more preferably 1.05 to 1.2, are mentioned.

[0021] Preferred examples of the resin used in one aspect of the present invention include homopolymers or copolymers of acrylonitrile or methacrylonitrile, such as polyacrylonitrile, partial hydrolysates of polyacrylonitrile, polyacrylamide, etc. Examples of acrylonitrile copolymers include copolymers of acrylonitrile and vinyl acetate, for example, acrylonitrile copolymers containing vinyl acetate in an amount of usually 1 to 10% by weight, and in one embodiment 5 to 7% by weight, based on the total weight of the copolymer. In one aspect of the present invention, even in the case of polyacrylonitrile copolymers, boron isotopes can be added. １０ B Concentration of boric acid is possible.

[0022] The resin used in one embodiment of the present invention is in the form of a boron isotope １０ There are no limitations as long as it can form flocs containing B, and it may be in the form of powder, short fibers, strips, etc., but short fibers and strips are preferred.

[0023] The particle shape of the powdered resin is arbitrary, with the particle diameter preferably being several microns to 150 μm, more preferably 1 to 30 μm. The length of the short fibers is not particularly limited, but is preferably 0.001 to 1 mm, more preferably 0.1 to 30 μm. In another embodiment, commercially available powdered resins may be used, for example, 100% polyacrylonitrile. The particle diameter of 100% polyacrylonitrile is 30 to 100 μm. In one embodiment, 100% polyacrylonitrile is adjusted by pulverization to a particle diameter of several microns, for example, 1 μm to 10 μm, and in one embodiment, 2 μm to 8 μm. In another embodiment, 100% polyacrylonitrile having a particle diameter of 30 μm to 100 μm may be mixed with 100% polyacrylonitrile pulverized as described above to adjust the particle diameter to several microns. In a further embodiment, the molecular weight of the resin consisting of 100% polyacrylonitrile is typically 10,000 to 200,000, in one embodiment 50,000 to 180,000, in one embodiment 100,000 to 160,000, for example, about 150,000, as a weight average molecular weight. In one embodiment, the particle size is a value measured by a sieve analysis method. In one embodiment, the particle size of 100% polyacrylonitrile is the Stokes diameter calculated using the Stokes equation. In one embodiment, the Stokes diameter of 100% polyacrylonitrile calculated using the Stokes equation is, for example, 30 μm or less, in one embodiment 25 μm or less, in one embodiment 20 μm or less, in one embodiment 19 μm or less, in one embodiment 18 μm or less, in one embodiment 17 μm or less, in one embodiment 16 μm or less, and in one embodiment 15 μm or less. Since 100% polyacrylonitrile includes those that do not completely settle in the suspension, i.e., those with molecular-level sizes, the lower limit of the Stokes diameter of 100% polyacrylonitrile calculated using the Stokes equation is not limited. In one aspect of the composition of the present invention, the Stokes diameter of 100% polyacrylonitrile calculated using the Stokes equation is usually 0.5 μm or more (corresponding to the lower limit of the particle size calculated using the Stokes equation), in one embodiment 0.6 μm or more, in one embodiment 0.8 μm or more, and in one embodiment 1 μm or more.In one aspect of the present invention, by setting the particle size and molecular weight of the resin as described above, flocs are more likely to form when stirred in the presence of an aqueous boric acid solution and resin cations, and boron isotopes are more likely to be formed by an isotope exchange reaction. １０ This makes it easier to concentrate B.

[0024] The mixing procedure of the boric acid solution, resin, and cation source is １０ There are no particular limitations as long as flocs containing B can be formed, and the following methods are listed as preferred mixing procedures.

[0025] (1) The mixing ratio of natural boric acid to water is usually 175 to 1,750 mL of water per 1 g of natural boric acid (equivalent to a boron concentration of 100 to 1,000 ppm), and the boric acid is dissolved over a sufficient period of time (usually 60 to 180 minutes) to prepare an aqueous boric acid solution containing natural boron. However, the use of a saturated aqueous solution of boric acid (with a boron (B) concentration of approximately 9,960 ppm at 25°C) is not excluded.

[0026] (2) Water (usually 5 to 10 mL per 1 g of resin) is added to a resin (e.g., polyacrylonitrile), and the mixture is hydrated for preferably 1 to 3 hours. Subsequently, the aqueous boric acid solution prepared in (1) above (usually 10 to 50 mL per 1 g of resin) is added to obtain a suspension. In another embodiment, water (usually 5 to 10 mL per 1 g of resin) is added to a resin (e.g., polyacrylonitrile), and the mixture is hydrated for preferably 1 to 3 hours. Subsequently, the aqueous boric acid solution prepared in (1) above (usually 5 to 50 mL per 1 g of resin) is added to obtain a suspension.

[0027] (3) A cation source is added, and the mixture is stirred at room temperature, preferably for 6 hours or more, more preferably for 6 to 48 hours. In another embodiment, a cation source is added, and the mixture is stirred at room temperature, preferably for 2 hours or more, for example, for 2 hours to 5 days, more preferably for 6 to 48 hours. The pH of the mixture is preferably adjusted to 7.0 to 9.5, more preferably 7.5 to 8.5. Therefore, it is preferable to use an alkali metal or alkaline earth metal hydroxide, for example, sodium hydroxide, as the cation source.

[0028] (4) Next, the mixed solution is allowed to stand for preferably 1 to 28 days, more preferably 2 to 5 days, and the upper layer of the settled resin is collected and filtered with filter paper or centrifuged to obtain a floc fraction. In another embodiment, the mixed solution is then allowed to stand for preferably 1 to 28 days, more preferably 2 to 5 days, and the entire mixed solution is filtered with filter paper or centrifuged to obtain a floc fraction. The floc fraction is then treated with a mineral acid, preferably 0.05 to 2N (mol / L) hydrochloric acid, to obtain a boron isotope fraction. １０ The boric acid is washed out, which is enriched with B. Examples of mineral acids include hydrochloric acid and nitric acid.

[0029] The upper layer of flocs can be recovered by specific techniques, such as filtration, centrifugation, or electrophoresis, or the liquid phase in which the flocs are suspended can be collected before they settle.

[0030] The resin from which boric acid has been released from the floc portion can be reused as a resin in one embodiment of the present invention.

[0031] Furthermore, if the flock is burned, boron isotopes will be released. １０ Furthermore, boron isotopes can be extracted from the resin by treating the flocs with concentrated hydrochloric acid or concentrated nitric acid. １０ B can be obtained as a solid.

[0032] By repeating the above steps (1) to (4), １０ B / １１ B ratio is 9 / 1 ( １０ Boric acid with a B concentration of 90% or more can be obtained.

[0033] The mechanism of action of one embodiment of the present invention is believed to be as follows: (1) B(OH) ４ － During the neutralization of the cation to the tetrahedral structure of B(OH), a second enrichment process occurs due to an isotope exchange reaction, and at the same time, the neutralized B(OH) ４ －- The cation complexes eliminate the mutual recoil forces, promoting the formation of basal flocs (Figs. 2 and 3). (2) The basal flocs become aggregated clusters (coarse flocs) with various sizes and densities, and the lower density flocs accumulate in the upper layer. The upper layer flocs are enriched in boron isotopes with higher concentrations. １０ B is contained (Figure 8).

[0034] Therefore, one aspect of the present invention is to provide a method for producing boron isotopes by a method of one aspect of the present invention. １０ A composition containing B-enriched flocs, specifically a composition containing boron, resin, and cations, in which the boron, resin, and cations form flocs, and the boron isotopes in the boron in the flocs are １０ B and １１ Molar ratio of B ( １０ B / １１ B) is greater than 0.248.

[0035] The boron, resin, and cations in the composition of one embodiment of the present invention may be the same as those used in the method of one embodiment of the present invention. Note that the counter anion of the cation may vary depending on the cation source used.

[0036] Here, "floc" refers to a mixture of resin such as PAN resin, hydrated boric acid, and Na that neutralizes it. ＋ When cations such as these are mixed in water, hydrogen bonds are formed between the cyano groups in the resin and the hydroxyl groups of the boric acid, resulting in the formation of aggregated particles. Note that flocs include not only those suspended in suspension, but also those that have become solid after the water used as a solvent has been removed.

[0037] In the composition of one aspect of the present invention, the boron isotopes in the boron in the flocs １０ B and １１ Molar ratio of B ( １０ B / １１ B) is a naturally occurring boron isotope １０ Abundance ratio of B (molar ratio) ( １０ B / １１In the composition of one aspect of the present invention, the boron isotope in the boron is greater than 0.248. １０ B and １１ Molar ratio of B ( １０ B / １１ In one embodiment, B) is 0.250 or more, in one embodiment 0.260 or more, in one embodiment 0.270 or more, in one embodiment 0.280 or more, in one embodiment 0.290 or more, in one embodiment 0.300 or more, in one embodiment 0.320 or more, in one embodiment 0.340 or more, in one embodiment 0.360 or more, in one embodiment 0.380 or more, in one embodiment 0.400 or more, and in one embodiment 0.420 or more. In one embodiment of the composition of the present invention, the boron isotope in the boron １０ B and １１ Molar ratio of B ( １０ B / １１ The upper limit of B) is not limited because the method of one embodiment of the present invention is carried out multiple times, i.e., by sequentially performing enrichment steps (stages), the boron isotopes in the boron in the composition can be increased. １０ B and １１ Molar ratio of B ( １０ B / １１ In the composition of one embodiment of the present invention, the boron isotope in the boron １０ B and １１ Molar ratio of B ( １０ B / １１ B) is in one embodiment 1000 or less, in one embodiment 500 or less, in one embodiment 200 or less, and in one embodiment 100 or less.

[0038] In a composition according to one aspect of the present invention, the particle size of the flocs is not limited. In a composition according to one aspect of the present invention, the Stokes diameter of the flocs calculated using the Stokes equation is typically 30 μm or less, in one embodiment 25 μm or less, in one embodiment 20 μm or less, in one embodiment 19 μm or less, in one embodiment 18 μm or less, in one embodiment 17 μm or less, in one embodiment 16 μm or less, and in one embodiment 15 μm or less. In a composition according to one aspect of the present invention, the formed flocs include those that do not completely settle in the suspension, i.e., flocs of molecular size, and therefore the lower limit of the Stokes diameter of the flocs calculated using the Stokes equation is not limited. In a composition according to one aspect of the present invention, the Stokes diameter of the flocs calculated using the Stokes equation is typically 0.5 μm or more (corresponding to the lower limit of the particle size calculated using the Stokes equation), in one embodiment 0.6 μm or more, in one embodiment 0.8 μm or more, and in one embodiment 1 μm or more.

[0039] In the composition of one aspect of the present invention, the density (specific gravity) of the floc is not limited. In the composition of one aspect of the present invention, the specific gravity of the floc is usually 1.01 to 1.10, in one embodiment 1.01 to 1.09, in one embodiment 1.01 to 1.08, in one embodiment 1.01 to 1.07, and in one embodiment 1.01 to 1.06. Here, the specific gravity is determined by comparing a standard substance with water (density 1.00 g / cm ３ ) is the value when

[0040] In a composition according to one embodiment of the present invention, the flocs have a Stokes diameter and specific gravity such that they do not settle within a settling time of 6 hours or less, in the relationship between the specific gravity of the flocs and the settling time according to the Stokes equation. In a composition according to one embodiment of the present invention, the flocs have a Stokes diameter and specific gravity such that they do not settle within a settling time of 24 hours or less, in the relationship between the specific gravity of the flocs and the settling time according to the Stokes equation. In a composition according to one embodiment of the present invention, the flocs have a Stokes diameter and specific gravity within the dotted line frame in Figure 10 and / or a Stokes diameter and specific gravity within the dotted line frame in Figure 11. In a composition according to one aspect of the present invention, the flocs have a Stokes' diameter and specific gravity such that they do not settle within a settling time of 6 hours or less, in the relationship between the specific gravity of the flocs and the settling time according to the Stokes' equation, the Stokes' diameter is usually 30 μm or less, in one embodiment 25 μm or less, in one embodiment 20 μm or less, in one embodiment 19 μm or less, in one embodiment 18 μm or less, in one embodiment 17 μm or less, in one embodiment 16 μm or less, and in one embodiment 15 μm or less, and the specific gravity is usually 1.01 to 1.10, in one embodiment 1.01 to 1.09, in one embodiment 1.01 to 1.08, in one embodiment 1.01 to 1.07, and in one embodiment 1.01 to 1.06. In a composition according to one aspect of the present invention, the flocs have a Stokes' diameter and specific gravity such that they do not settle within a settling time of 24 hours or less, in the relationship between the specific gravity of the flocs and the settling time according to the Stokes' equation, and the Stokes' diameter is usually 20 μm or less, in one embodiment 19 μm or less, in one embodiment 18 μm or less, in one embodiment 17 μm or less, in one embodiment 16 μm or less, and in one embodiment 15 μm or less, and the specific gravity is usually 1.01 to 1.10, in one embodiment 1.01 to 1.09, in one embodiment 1.01 to 1.08, in one embodiment 1.01 to 1.07, and in one embodiment 1.01 to 1.06.

[0041] In the composition of one aspect of the present invention, the boron content is not limited. In the composition of one aspect of the present invention, the boron content is, relative to the total weight of the composition, usually 0.5 wt% or more, in one embodiment 1 wt% or more, in one embodiment 2 wt% or more, in one embodiment 5 wt% or more, in one embodiment 10 wt% or more, in one embodiment 20 wt% or more, in one embodiment 30 wt% or more, in one embodiment 40 wt% or more, in one embodiment 50 wt% or more, in one embodiment 60 wt% or more, in one embodiment 70 wt% or more, and usually 99 wt% or less, in one embodiment 95 wt% or less, and in one embodiment 90 wt% or less.

[0042] In the composition of one aspect of the present invention, the content of the resin, for example, polyacrylonitrile, is not limited. In the composition of one aspect of the present invention, the content of the resin, for example, polyacrylonitrile, relative to the total weight of the composition, is usually 0.1 wt% or more, in one embodiment 0.2 wt% or more, in one embodiment 0.5 wt% or more, in one embodiment 1 wt% or more, in one embodiment 2 wt% or more, and in one embodiment 5 wt% or more, and is usually 99 wt% or less, in one embodiment 95 wt% or less, in one embodiment 90 wt% or less, in one embodiment 70 wt% or less, in one embodiment 50 wt% or less, in one embodiment 30 wt% or less, in one embodiment 20 wt% or less, and in one embodiment 10 wt% or less.

[0043] In the composition of one aspect of the present invention, the cation content is not limited. In the composition of one aspect of the present invention, the cation content is typically 0.1 wt % or more, in one embodiment 0.2 wt % or more, in one embodiment 0.5 wt % or more, in one embodiment 1 wt % or more, in one embodiment 2 wt % or more, and in one embodiment 5 wt % or more, relative to the total weight of the composition, and typically 50 wt % or less, in one embodiment 40 wt % or less, in one embodiment 35 wt % or less, in one embodiment 30 wt % or less, in one embodiment 20 wt % or less, and in one embodiment 10 wt % or less. Alternatively, in the composition of one aspect of the present invention, the cation content is such that, when 1 g of the composition is added to 100 mL of water, the pH is adjusted to typically 7.0 to 9.5, and in one embodiment 7.5 to 8.5.

[0044] In the composition of one aspect of the present invention, the weight ratio of boron to resin, for example, polyacrylonitrile (boron / resin) is not limited, but is usually 0.01 or more, in one embodiment 0.05 or more, in one embodiment 0.1 or more, in one embodiment 0.5 or more, and in one embodiment 1 or more, and is usually 100 or less, in one embodiment 20 or less, in one embodiment 10 or less, and in one embodiment 5 or less.

[0045] In the composition of one aspect of the present invention, the weight ratio of boron to cations (boron / cation) is not limited, but is usually 0.01 or more, in one embodiment 0.05 or more, in one embodiment 0.1 or more, in one embodiment 0.5 or more, and in one embodiment 1 or more, and is usually 100 or less, in one embodiment 20 or less, in one embodiment 10 or less, and in one embodiment 5 or less.

[0046] In the composition of one aspect of the present invention, the weight ratio of cations to resin, for example, polyacrylonitrile (cation / resin) is not limited, but is usually 0.01 or more, in one embodiment 0.05 or more, in one embodiment 0.1 or more, and in one embodiment 0.5 or more, and is usually 100 or less, in one embodiment 10 or less, in one embodiment 5 or less, and in one embodiment 2 or less.

[0047] The composition of one embodiment of the present invention may comprise flocs containing boron, resin, and cations. The composition of one embodiment of the present invention may contain a solvent in addition to the flocs containing boron, resin, and cations. The solvent is not limited to, but includes water, organic solvents such as alcohols (e.g., methanol, ethanol, propanol), ethers, ketones (e.g., acetone), acetonitrile, and mixtures of two or more of these.

[0048] The composition of one embodiment of the present invention can be produced by the method of one embodiment of the present invention. For example, the composition of one embodiment of the present invention can be produced by collecting the upper layer of the settled resin in (4) in (1) to (4) described above as the preferred mixing procedures for mixing an aqueous boric acid solution, a resin, and a cation source. That is, in the upper layer of the settled resin in (4), boron isotopes are exchanged with a resin, for example, polyacrylonitrile, by isotope exchange reaction.１０ Since B is concentrated, the composition of one embodiment of the present invention can be produced by collecting the upper layer of the settled resin in (4) as is, or by filtering or centrifuging the upper layer of the settled resin in (4) with filter paper, or by optionally filtering or centrifuging the upper layer of the settled resin in (4) with filter paper and then redispersing it in a solvent, for example, water or an organic solvent. Furthermore, in this case, by controlling the settling time, a composition can be produced in which the Stokes diameter of the flocs calculated by Stokes' equation is adjusted to fall within the above range. Alternatively, the composition can be produced by filtering or centrifuging the entire mixed liquid described as another embodiment of (4) with filter paper to obtain a composition, and optionally redispersing the obtained composition in a solvent, for example, water or an organic solvent. Naturally, by repeating the operations (1) to (4), １０ B / １１ A composition having a larger B ratio can be produced. In addition, by repeating the steps (1) to (4), １０ B / １１ After producing a composition with a higher B ratio, the composition is filtered using a specific mesh to remove excess resin while preserving the amount of resin required to stabilize the formed flocs, and / or to remove some of the cations using an ion exchange resin or the like, thereby producing a composition with a high boron content. Note that the lower layer of the settled resin in (4) and the portion other than the flocs separated by filtration or centrifugation are not adsorbed to polyacrylonitrile or have been converted to boron isotopes by an isotope exchange reaction. １１ Contains more B.

[0049] Next, one embodiment of the present invention will be described in more detail by showing examples, but the embodiment of the present invention is not limited to these.

[0050] (Example 1) When polyacrylonitrile forms flocs with boric acid, boron isotopes １０ B Boric acid (boron isotope １０ B 99% content) and natural boric acid (boron isotope １０The amount of flocs produced in each case was examined, and the effect of sodium cations was investigated. Boric acid causes aggregation of part of the resin, increasing the volume of the resin. By comparing this increase in volume with that in the control experiment, the amount of flocs produced was evaluated as the volume increase rate. The control experiment was carried out using polyacrylonitrile without boric acid and sodium cations (Na ＋ ) was added to the same system.

[0051] (1) 0.63 g of natural boric acid (molecular weight: 61.83; Wako Pure Chemical Industries, Ltd., product number 021-02195) was dissolved in 200 mL of pure water over a sufficient period of time to prepare a boric acid aqueous solution containing 500 ppm of natural boron. １０ B Boric acid aqueous solution (boron isotope １０ The boric acid 10B (containing 99% boric acid) was prepared using boric acid 10B, 99% (Cambridge Isotope Laboratories, Inc.), with a molecular weight of 61.0 and adjusted to 500 ppm. Here, 500 ppm corresponds to a concentration of 50 mM.

[0052] (2) 40 mL of pure water was added to 5 g of polyacrylonitrile (Sigma-Aldrich, product number 181315; weight average molecular weight (Mw) 150,000, density 1.184 g / mL), and the mixture was hydrated for 1 hour. Subsequently, 10 mL of the boric acid aqueous solution containing 500 ppm of natural boron prepared in (1) above was added to prepare a 50 mL suspension. This procedure yielded a suspension of boric acid aqueous solution containing 100 ppm of natural boron. More specifically, the procedure is as follows. 40 mL of pure water was added to 5 g of polyacrylonitrile (Sigma-Aldrich, product number 181315; weight average molecular weight (Mw) 150,000, density 1.184 g / mL), and the mixture was hydrated for 1 hour. At this time, the primary particle size of the polyacrylonitrile was 30 μm on average, but it was further pulverized before use. The primary particle size was measured by a sieving method. Subsequently, 10 mL of the 50 mM boric acid aqueous solution prepared in (1) above was added to prepare a suspension with a total volume of 50 mL. By this operation, natural boron or １０A suspension of a 10 mM aqueous boric acid solution containing 100 ppm of boron (B) was obtained.

[0053] (3) Then, 0.125 mL of 1N aqueous sodium hydroxide solution was added to adjust the pH to 7.5, and after thorough stirring, the mixture was left standing at room temperature for 2 days. As a control, polyacrylonitrile and sodium cation (Na ＋ The same system was used except that boric acid was added. The amount of polyacrylonitrile precipitate in the suspension was measured as a percentage of the water surface based on photography. Photography in the sedimentation experiment was carried out 24 hours and 48 hours after standing. The volume increase rate under each condition was measured using the amount of polyacrylonitrile precipitate in a suspension without boric acid added as a control.

[0054] The results are shown below: As shown in the 24-hour time course in Figure 4A, the boron isotopes １０ B Boric acid aqueous solution (boron isotope １０ In the case of polyacrylonitrile containing 99% boron (B), the volume increase rate was 1.23 times that of the control without boric acid. Furthermore, as shown in Figure 4B after 48 hours, the boron isotope １０ B Boric acid aqueous solution (boron isotope １０ The volume increase rate of polyacrylonitrile in the case of the aqueous solution of natural boric acid (containing 99% boron) was 1.21 times that of the control without boric acid. １０ In the case of the SiO2 alloy (containing 19% boron), a volume increase rate of 1.04 times was obtained in FIG. 4A. １０ A significant difference was observed between the B boric acid solution and the natural boric acid solution. １０ In the case of the SiO2 alloy (containing 19% boron), a volume increase rate of 1.04 times was obtained, as shown in FIG. 4B. １０ A significant difference was observed between the B boric acid solution and the natural boric acid solution. １０ It was shown that boric acid (B) greatly promotes the formation of basal flocs. In addition, an experiment was also conducted in which the pH was adjusted to 8.0-8.5 in (3), but the results were the same as in the experiment in which the pH was adjusted to 7.5.

[0055] (Example 2) When polyacrylonitrile forms flocs with boric acid, boron isotopes １０ B Boric acid (boron isotope １０ B 99% content) and natural boric acid (boron isotope １０ The amount of flocs produced in each case was examined, and potassium cation (K ＋ Control experiments were carried out using the same system but omitting the boric acid and adding potassium cations to polyacrylonitrile.

[0056] (1) 0.63 g of natural boric acid (molecular weight: 61.83; Wako Pure Chemical Industries, Ltd., product number 021-02195) was dissolved in 200 mL of pure water over a sufficient period of time to prepare a boric acid aqueous solution containing 50 mM of natural boron. １０ B Boric acid aqueous solution (boron isotope １０ For the 10B (containing 99% boron), Cambridge Isotope Laboratories, Inc. Boric Acid, 10B, 99%, was used, which are natural boron and １０ Natural boron and boron isotopes at 50 mM concentration, containing 100 ppm of B boron １０ An aqueous solution of boric acid containing 99% boron was prepared.

[0057] (2) 40 mL of pure water was added to 5 g of polyacrylonitrile (Sigma-Aldrich product number 181315; weight average molecular weight (Mw) 150,000, density 1.184 g / mL), and the mixture was hydrated for 1 hour. At this time, the primary particle size of the polyacrylonitrile was 30 μm on average, but it was further pulverized before use. The primary particle size was measured by a sieving method. Subsequently, 10 mL of the boric acid aqueous solution containing 50 mM boron, as prepared in (1) above, was added. This operation yielded a suspension of 10 mM boric acid aqueous solution in a total volume of 50 mL.

[0058] (3) Then, 0.125 mL of 1N aqueous sodium hydroxide solution was added to adjust the pH to 8.0-8.5, and after thorough stirring, the mixture was left to stand at room temperature and the precipitation experiment was started. ＋ The same system was used except that boric acid was added. The amount of polyacrylonitrile precipitate in the suspension was measured as a percentage of the water surface based on photographs taken at 24 and 48 hours. The volume increase rate under each condition was measured using the amount of polyacrylonitrile precipitate in a suspension without boric acid added as a control.

[0059] The results are shown in Figure 5A for the 24-hour period and in Figure 5B for the 48-hour period. １０ B Boric acid aqueous solution (boron isotope １０ The volume increase rate of polyacrylonitrile in the case of the aqueous solution of natural boric acid (containing 99% boron) was 1.30 times and 1.23 times, respectively, compared to the control without boric acid. １０ In the case of the SiO2 alloy (containing 19% boron), the volume increase rates were 1.19 times and 1.17 times, respectively, as shown in Figures 5A and 5B. １０ A significant difference was observed between the boric acid solution in B and the natural boric acid solution. ＋ ) and sodium cation (Na ＋ ) as well as boron isotopes １０ It was shown that boric acid significantly promoted basal floc formation.

[0060] (Example 3) When polyacrylonitrile forms flocs with boric acid, boron isotopes １０ B Boric acid (boron isotope １０ B 99% content) and natural boric acid (boron isotope １０ The amount of flocs generated in each case was examined, and lithium cation (Li ＋ Control experiments were carried out using the same system but omitting the boric acid and adding lithium cations to polyacrylonitrile.

[0061] The preparation of (1) and (2) was carried out in the same manner as in Examples 1 and 2. Then, 0.125 mL of a 1N aqueous solution of lithium hydroxide was added, the pH was adjusted to 8.0 to 8.5, and the mixture was thoroughly stirred and then allowed to stand at room temperature to initiate the precipitation experiment. As a control, a mixture of polyacrylonitrile and lithium cation (Li) was prepared by removing only boric acid. ＋ The same system was used except that boric acid was added. The amount of polyacrylonitrile precipitate in the suspension was measured as a percentage of the water surface after 48 hours based on photographs. The volume increase rate under each condition was measured using the amount of polyacrylonitrile precipitate in a control suspension without boric acid as the standard.

[0062] The results are shown in Figure 6. １０ B Boric acid aqueous solution (boron isotope １０ The volume increase rate of polyacrylonitrile in the case of the aqueous solution of natural boric acid (containing 99% boron) was 1.07 times that of the control without boric acid. １０ In the case of the lithium cation (Li 19%), a volume increase of 1.03 times was observed. ＋ ) in the case of １０ Although there was a difference in the concentration effect between the boric acid solution B and the natural boric acid solution, the difference was not large. ＋ ) and potassium cation (K ＋ ) unlike boron isotopes １０ It was shown that boric acid only slightly promoted basal floc formation.

[0063] (Example 4) When polyacrylonitrile is flocculated with boric acid, boron isotopes are released. １０ B Boric acid (boron isotope １０ B) and natural boric acid (boron isotope 99% １０ The amount of floc formation in each case was examined, and the effect of divalent calcium cations was investigated. As a control, polyacrylonitrile without boric acid and calcium cations (Ca ２＋ The amount of flocs produced was evaluated in the same manner as in Examples 1 to 3, by measuring the rate of increase in volume due to aggregation of the resin.

[0064] (1) 0.63 g of natural boric acid (molecular weight: 61.83; Wako Pure Chemical Industries, Ltd., product number 021-02195) was dissolved in 200 mL of pure water over a sufficient period of time to prepare a boric acid aqueous solution containing 500 ppm of natural boron. １０ B Boric acid aqueous solution (boron isotope １０ B (containing 99% boron) was prepared using Cambridge Isotope Laboratories, Inc. Boric Acid, 10B, 99%, with 500 ppm of boron isotope. １０ An aqueous solution of boric acid containing 99% boron was prepared, where 500 ppm corresponds to a concentration of 50 mM.

[0065] (2) 30 mL of purified water was added to 5 g of polyacrylonitrile (Sigma-Aldrich Product No. 181315; weight average molecular weight (Mw) 150,000, density 1.184 g / mL) and hydrated for 1 hour. Subsequently, 10 mL of the boric acid aqueous solution prepared in (1) above, each containing 500 ppm of boron, was added. Here, 500 ppm corresponds to a concentration of 50 mM.

[0066] (3) Then, 10 mL of a 12.5 mM calcium hydroxide aqueous solution was added, and the pH was adjusted to 8.5, to make a 50 mL suspension. Since calcium hydroxide has low solubility in water, the concentration of the calcium hydroxide aqueous solution was set to 12.5 mM. This procedure yielded a suspension of boric acid aqueous solution containing 100 ppm of boron. Here, 100 ppm corresponds to a concentration of 10 mM. After thorough stirring, the suspension was left to stand at room temperature for 3 days. As a control, a suspension of polyacrylonitrile and calcium cations (Ca ２＋ The same system was used, but with boric acid added. The sedimentation amount of polyacrylonitrile in the suspension was measured as a percentage of the water surface based on photography. Photography in the sedimentation experiment was carried out 48 hours and 3 days after standing. The volume increase rate under each condition was measured based on the sedimentation amount of polyacrylonitrile in a suspension without boric acid added as a control.

[0067] The results are shown in Figure 7.１０ B Boric acid aqueous solution (boron isotope １０ The volume increase rate of polyacrylonitrile in the case of the aqueous solution of natural boric acid (containing 99% boron) was 1.05 times that of the control without boric acid. １０ The volume increase rate of the 1.04-fold increase was observed for the 19% boron (B) cation, and the difference between the two was very small. １０ B Boric acid contributed little to floc formation. There was no difference in the results between the standing time of 48 hours and 3 days.

[0068] From the results of Example 1, it is clear that sodium cation (Na ＋ ) can form basic flocs through hydrogen bonds between the hydroxyl groups of boric acid and the nitrogen of the nitrile groups in the polyacrylonitrile suspension to neutralize the repulsive force of the negatively charged borate ions (Fig. 3). It is assumed that the isotope selection process required for enrichment occurs during this process, and the boron isotopes １０ It is believed that there was a large difference in floc formation between B boric acid and natural boric acid. ＋ ), potassium cation (K ＋ ) can form basic flocs through hydrogen bonds between the hydroxyl groups of boric acid and the nitrogen of the nitrile groups in the polyacrylonitrile suspension to neutralize the repulsive force of the negatively charged borate ions (Fig. 3). It is assumed that the isotope selection process required for enrichment occurs during this process, and the boron isotopes １０ It is believed that there was a large difference in the floc formation between B boric acid and natural boric acid. ＋ ), the sodium cation (Na ＋ ) and potassium cation (K ＋ ) the volume increase rate was lower than that of the other isotopes. Because lithium has a very small ionic radius and high electronegativity, it interacts more strongly with water molecules than other alkali metals such as sodium and potassium, which is thought to be due to its properties of having a strong hydration energy. On the other hand, in Example 4, １０No significant difference was observed between B boric acid and natural boric acid. The reason for this is that calcium cations have a divalent positive charge and can ionically bond with two boric acids at the same time. Therefore, the boron isotopes １０ During the competitive process of floc formation between B boric acid and natural boric acid, boron isotopes １０ It is speculated that there was not enough opportunity for the two isotopes to be exchanged into the two isotopes necessary for enrichment of B boric acid. １０ B To concentrate boric acid, monovalent sodium cation (Na ＋ ) is considered to be effective. Furthermore, the boron isotope that acts on the floc formation process １０ B To concentrate boric acid, monovalent potassium cation (K ＋ ) is also considered to be effective. Hydrogen bonds are involved in the floc formation by boric acid, and the hydrogen bond energy of the nitrogen atom of the nitrile group of polyacrylonitrile is O-H...:N, which is 6.9 kcal / mol. On the other hand, the hydrogen bond energy of water is OH...:O, which is 5.0 kcal / mol, and is slightly stronger than that of water, so it can exist in water. The bond between two boric acids by calcium cations is an ionic bond, which is much larger than a hydrogen bond. Therefore, Ca ２＋ Once the two boric acids are bound by the cation, the boron isotopes in the subsequent floc formation process １０ B Opportunity for enrichment of boric acid, i.e. boron isotopes １０ B Boric acid and １１ It is assumed that there will be less opportunity for enrichment through exchange of B boric acid.

[0069] Example 5 (1) 0.63 g of natural boric acid (molecular weight: 61.83; Wako Pure Chemical Industries, Ltd., product number 021-02195) was dissolved in 200 mL of pure water over a sufficient period of time to prepare an aqueous boric acid solution containing 500 ppm of natural boron. Here, 500 ppm corresponds to a concentration of 50 mM.

[0070] (2) 80 mL of pure water was added to 10 g of polyacrylonitrile (Sigma-Aldrich Product No. 181315; weight-average molecular weight (Mw) 150,000, density 1.184 g / mL), and the mixture was hydrated for 1 hour. Subsequently, 20 mL of the boric acid aqueous solution containing 500 ppm of natural boron prepared in (1) above was added to prepare a 100 mL suspension. Here, 500 ppm corresponds to a 50 mM concentration. This procedure yielded a suspension of boric acid aqueous solution containing 100 ppm of natural boron. Here, 100 ppm corresponds to a 10 mM concentration.

[0071] (3) Then, 0.5 mL of 1N aqueous sodium hydroxide solution was added, and the mixture was stirred at room temperature for 2 days and 5 days.

[0072] (4) Next, the upper layer containing the polyacrylonitrile resin flocs was collected after 2 days and 5 days (Fig. 8). The upper layer was filtered with 30 mL of 0.5 N hydrochloric acid and analyzed for boron isotopes. １０ The aqueous boric acid solution enriched with boron B was washed out.

[0073] (5) Boron isotopes １０ B: Each boric acid solution with enriched boron was analyzed by inductively coupled plasma mass spectrometry (ICP-MS) to determine the amount of １０ B / １１ The B ratio was measured. An Agilent 7500 quadrupole ICP-MS was used as the ICP-MS. As a control, an aqueous boric acid solution containing 100 ppm of natural boron was used by diluting the initially used aqueous boric acid solution containing 500 ppm of natural boron five times (hereinafter referred to as the "stock solution"). Here, 500 ppm corresponds to a 50 mM concentration, and 100 ppm corresponds to a 10 mM concentration.

[0074] The results are shown in Table 1. That is, boron isotopes １０ B Before enrichment of boron １０ B / １１ The B ratio was 0.247 (raw solution of natural boric acid solution) and the concentrated boric acid solution obtained by stirring for 2 days. １０ B / １１ The boron isotope ratio obtained after 5 days of stirring was 0.283. １０B. Concentrated boric acid aqueous solution １０ B / １１ The B ratio was 0.283.

[0075]

[0076] The enrichment factor (K) in Table 1 is the enriched boron isotope １０ B. Concentrated boric acid aqueous solution １０ B / １１ The B ratio of the original boric acid aqueous solution containing natural boron is １０ B / １１ It is defined as the value divided by the B ratio. Therefore, the concentration ratio (K) is different from the separation factor (α).

[0077] From these results, averaging the two-day mixing experiment and the five-day mixing experiment, １０ B / １１ The result of the B ratio measurement was K=1.14.

[0078] However, boron isotopes １０ B. Concentrated boric acid aqueous solution １０ B / １１ The B ratios for the two-day and five-day stirring periods happened to be close to each other, but when the dry weight of the polyacrylonitrile residue after filtration was measured later, the amounts of polyacrylonitrile collected were 1.043 g and 2.313 g for the two-day and five-day stirring periods, respectively. In other words, it was thought that some of this polyacrylonitrile was present in a localized state and involved in floc formation.

[0079] (Example 6) In the flocculation concentration method using polyacrylonitrile (PAN), the PAN flocs in the boric acid solution exhibited different settling velocities, and non-uniform settling was observed. As a result, it was empirically found that the PAN flocs accumulated in the upper part of the settling layer (Figure 8). In addition, the boron isotope １０It was found that the concentration of boron (B) tends to be relatively high in PAN flocs with a slow settling velocity. Therefore, the settling velocity of PAN flocs in a boric acid solution was calculated, and a simulation was performed using Stokes' equation to evaluate the relationship between the particle size of the PAN flocs and the settling time, as well as the density. Based on the results, a method for separating PAN flocs was considered.

[0080] 5 g of polyacrylonitrile (Sigma-Aldrich, product number 181315; weight-average molecular weight (Mw) 150,000, density 1.184 g / mL) was added to 100 mL of purified water and hydrated for 2 hours. Subsequently, 1.545 g of natural boric acid was dissolved in 400 mL of purified water. The hydrated PAN suspension (100 mL) was added to 400 mL of aqueous boric acid solution to prepare a total volume of 500 mL of boric acid solution containing 500 ppm of natural boron (10B:11B = 19%:81%). The pH was adjusted to 8.0-8.5 by adding 5N sodium hydroxide solution. 5 g of PAN was suspended in a total volume of 500 mL of 50 mM aqueous boric acid solution containing 500 ppm of boron. The 500 mL measuring cylinder was sealed with a special lid and then shaken to mix. The mixture was left at room temperature for 72 hours, and the amount of sediment was measured over time.

[0081] (1) Initial Sediment: As a result of the sedimentation experiment, the sedimentation of coarse PAN particles was observed visually within 30 minutes of the start of the experiment, with a volume of 25 mL. Six hours after the start of the experiment, a total of 34 mL of sedimentation was observed, with an additional 9 mL of sedimentation. The boundary between the initial sediment and the sediment formed later was not clearly distinguishable. (2) White Sediment: Twenty-four hours after the start of the experiment, a visually identifiable white sediment layer formed at the top, with a volume of 1.25 mL. After 60 hours, the volume of the white sediment layer increased to 4.5 mL and to 5.2 mL after 72 hours. (3) Suspended White Particles: After 72 hours, the volume of the white sediment layer stopped increasing, but unsettled white particles were observed in suspension. The brightness of these suspended particles gradually changed from the top to the bottom, with the upper layer being nearly transparent and becoming darker toward the bottom. From the above results, it was found that the sediments could be classified into three groups: (1) initial sediment, (2) white sediment, and (3) floating white particles.

[0082] Based on these results of the settling phenomenon, a simulation was carried out using Stokes' equation to evaluate the relationship between the particle size and settling time of PAN flocs formed in the boric acid aqueous solution, as well as the settling characteristics of PAN that did not form flocs. The Stokes' equation is as follows: v = D ２ (ρp-ρf)g / 18η The definitions of each symbol are as follows: v: terminal velocity [m / s] D: particle diameter [m] ρp: particle density [kg / m ３ ] ρf: density of fluid [kg / m ３ ] (The density of the boric acid solution is 1000 kg / m ３ ) g: Gravitational acceleration [m / s ２ ] = 9.81 m / s ２ η: viscosity of fluid [Pa s] (50 mM boric acid aqueous solution, 25 ° C, 0.895 mPa s)

[0083] Simulation results showed that the settling time for commercially available PAN with an average particle size of 30 μm was calculated to be approximately 10 minutes. It was estimated that it would take 60 seconds for a particle size of 100 μm and 6 hours for a particle size of 5 μm. Therefore, PAN particles that have not formed flocs through reaction with boric acid are expected to settle within 6 to 9 hours. Therefore, the initial sediment can be considered to consist almost entirely of PAN particles (Figure 9). The white sediment (PAN floc) observed after 24 hours was estimated to have a particle size of 10 to 25 μm and a density of 1.01 to 1.10 (dotted frame in Figure 10). These results suggest that PAN flocs have variable particle sizes and non-uniform properties.

[0084] As a result of the simulation, the floating white particles (PAN flocs) observed 72 hours after the start of the simulation were estimated to have a maximum particle size of approximately 5 μm and a density of 1.01 to 1.06 (shown within the dotted line frame in Figure 11). Based on these results, it was found that in order to further improve the separation efficiency of PAN, it is effective to crush the PAN as finely as possible and hydrate it.

[0085] In the present invention, it is important to properly adjust the particle size and molecular weight of the PAN resin and to finely grind it. This facilitates the formation of flocs during stirring in a boric acid aqueous solution in the presence of cations, and also facilitates the isotope exchange reaction of boron isotopes. １０ This will create an environment in which B can be concentrated more efficiently.

[0086] (Example 7) By using the flocculation enrichment method of one embodiment of the present invention using polyacrylonitrile in an aqueous solution of boron isotopes, the α value (separation factor) defined as [10B / 11B] Resin / [10B / 11B] Liquid was determined using ICP-MS. The ICP-MS was an Agilent 7800 quadrupole ICP-MS, and sodium cation (Na ＋ The α value was calculated under the condition that α was added.

[0087] 1 g of polyacrylonitrile (Sigma-Aldrich, product number 181315; weight-average molecular weight (Mw) 150,000, density 1.184 g / mL) was added to 8 mL of purified water and carefully crushed and hydrated. Subsequently, 1 mL of the 50 mM natural boric acid aqueous solution prepared in Example 1(1) was added, and 1 N sodium hydroxide solution was added to adjust the pH to approximately 8.5. Distilled water was then added to prepare a 10 mL suspension. The suspension was placed in a 50 mL Erlenmeyer flask and stirred with a magnetic stirrer at room temperature for 48 hours. The suspension was filtered to obtain filtrate A1 (liquid) from the PAN (entire PAN, including the upper layer of floc). 10 mL of 0.5 N hydrochloric acid was added to the filtered residue (resin) and stirred for washing. This was then filtered to obtain the first 0.5 N hydrochloric acid extract A2. Again, 10 ml of 0.5N hydrochloric acid was added to the residue, which was stirred and washed, and then filtered to obtain a second 0.5N hydrochloric acid extract A3.

[0088] The filtrate A1 collected from the entire polyacrylonitrile including the flocculation in the upper layer, the first hydrochloric acid extract A2 obtained by the first extraction from the residue with 0.5 N hydrochloric acid, and the second hydrochloric acid extract A3 obtained by further extraction with 0.5 N hydrochloric acid were measured for 10B concentration using ICP-MS (Agilent 7800 quadrupole ICP-MS) to obtain the 10B count number (CPS) value for each.

[0089] Sodium cation (Na ＋ The enrichment separation factor α of the boron isotope 10B after stirring for 48 hours under the condition of adding 10B / 11B resin / [10B / 11B liquid] is shown in Table 2. The enrichment separation factor of 10B is defined as α = [10B / 11B] resin / [10B / 11B] liquid.

[0090]

[0091] From Table 2, sodium cation (Na ＋The separation factors for 10B of the first hydrochloric acid extract A2 and the second hydrochloric acid extract A3 were α = 1.20 and α = 1.22, respectively, which were good values. Here, the count value (CPS) for the first hydrochloric acid extract A2 was one order of magnitude higher than that for the second hydrochloric acid extract A3, but the values ​​were very close. From these results, it was determined that most of the boric acid forming flocs with polyacrylonitrile was extracted from the flocs with 0.5 N hydrochloric acid. If this α = 1.20 had been corrected as in Example 5, it is highly likely that it would have been an even higher value.

[0092] From the above results, it was found that the equilibrium constant α of the isotope exchange reaction in aqueous solution was high by the flocculation enrichment method according to one embodiment of the present invention. By repeating the enrichment operation according to one embodiment of the present invention, highly enriched boron isotopes were obtained. １０ Boron isotopes in the flocculation process can be obtained safely and efficiently. １０ It was suggested that the enrichment mechanism of B boric acid involves other factors that cannot be explained solely by the equilibrium constant α = 1.019 of the isotope exchange reaction in aqueous solution, such as the isotope effect in the neutralization process by cations and a multi-stage enrichment mechanism in the floc formation process.

[0093] Example 8 An experiment was carried out in the same manner as in Example 5, except that polyacrylonitrile (Sigma-Aldrich product number 181315; weight average molecular weight (Mw) 150,000, density 1.184 g / mL) was replaced with an acrylonitrile copolymer containing 5 to 7 wt % of vinyl acetate based on the total weight of the copolymer. In this quantitative experiment, the concentration ratio was calculated using the results of measurements made using inductively coupled plasma mass spectrometry (Agilent 7500 quadrupole ICP-MS).

[0094] As a result, the boron isotopes in polyacrylonitrile copolymers were １０ It was found that it is possible to concentrate boron isotopes of B boric acid. Specifically, in the case of the polyacrylonitrile copolymer, the boron isotopes of the same weight of 100% polyacrylonitrile are １０The enrichment efficiency was about 90% compared to that of B. All publications, patents, and patent applications cited herein are hereby incorporated by reference in their entirety.

Claims

1. A boron isotope extraction method comprising stirring an aqueous solution of boric acid and a resin in the presence of a cation, followed by separating the resulting flocs. １０ Concentration method of B.

2. The method according to claim 1, wherein the specific gravity of the resin is 0.9 to 1.

5.

3. The method of claim 1, wherein the resin is a homopolymer or copolymer of acrylonitrile or methacrylonitrile.

4. The method according to any one of claims 1 to 3, wherein a hydroxide or salt of an alkali metal or alkaline earth metal is added as a cation source.

5. Separate the upper layer of the floc and analyze for boron isotopes. １０ The method according to claim 4, wherein the concentration efficiency of B is increased.

6. The separated flocs are treated with hydrochloric acid or nitric acid to separate the boron isotopes. １０ 5. The method of claim 4, wherein B is obtained as a solution.

7. Burn the separated flocs to extract boron isotopes. １０ 5. The method of claim 4, wherein B is obtained as a solid.

8. A composition comprising boron, a resin, and a cation, wherein the boron, the resin, and the cation form flocs, and the boron isotopes in the boron in the flocs are １０ B and １１ Weight ratio of B ( １０ B / １１ B) is greater than 0.

248.

9. The composition of claim 8, wherein said resin is polyacrylonitrile.

10. The composition according to claim 9, wherein the flocs have a Stokes' diameter and density such that the flocs do not settle within 6 hours or less in the relationship between the specific gravity and settling time according to the Stokes' equation.

11. The composition according to claim 10, wherein the Stokes diameter is 30 μm or less and the specific gravity is 1.01 to 1.10.

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