Lithium isotope concentration device, multi-stage lithium isotope concentration device, and lithium isotope concentration method

Abstract

This lithium-isotope enrichment device 1 comprises a treatment tank 7 which is divided into a supply tank 11 and a recovery tank 12 by means of an electrolyte membrane 2 having lithium ion conductivity, and recovers, into the recovery tank 12, an aqueous solution ES for the recovery of 6Li of which the isotope ratio of 6Li is high from a Li-containing aqueous solution FS stored in the supply tank 11. While a power supply 51, which is connected between a second electrode 32 of a porous structure provided on a recovery tank 12-side surface of the electrolyte membrane 2 and a third electrode 33 provided to be spaced apart from the electrolyte membrane 2 in the recovery tank 12, applies a voltage V1 with the second electrode 32 being made to be positive, the lithium-isotope enrichment device 1 connects a first electrode 31 provided in the supply tank 11 to the second electrode 32.

Description

Lithium isotope enrichment device, multistage lithium isotope enrichment device, and lithium isotope enrichment method

[0001] The present invention relates to a lithium isotope enrichment apparatus and a multistage lithium isotope enrichment apparatus for separating lithium isotopes, and a lithium isotope enrichment method.

[0002] Lithium (Li) is 7 Li and 6 There are two stable isotopes of Li, with natural abundances of 92.41 mol% and 7.59 mol%. 7 Li and mass number 6 6 Li has very different properties, e.g. 7 Li is used to adjust the pH (hydrogen ion concentration) of the reactor coolant. 6 Li is used to produce tritium, a fuel for fusion reactors. 7 Li and 6 Li has been enriched and separated into less isotopes, and the amalgamation method, molten salt method, distillation method, and the extraction of lithium ions from seawater, etc. have been developed. + The adsorption method and the electrodialysis method (see, for example, Patent Document 1) are known as methods for selectively recovering methyl methacrylate.

[0003] Compared to the amalgamation method, which uses a large amount of mercury, the molten salt method, which heats lithium compounds at high temperatures, and the distillation method, the adsorption method and the electrodialysis method are relatively superior in terms of environmental impact, etc. On the other hand, these methods have a high transfer speed due to the small mass. 6 Li + However, the isotope separation coefficient is small and the productivity as an enrichment method is low. Therefore, the inventors have found that the isotope separation coefficient is large only for a short time immediately after starting operation in the enrichment of lithium isotopes using lithium recovery technology (e.g., Patent Documents 2, 3, and 5) that selectively recovers Li from seawater or the like by electrodialysis using an electrolyte membrane having lithium ion conductivity, and have invented a method to increase the efficiency by applying a voltage intermittently or by applying positive and negative voltages alternately (Patent Document 4, Non-Patent Document 1).

[0004] A method for concentrating lithium isotopes using a lithium recovery technique by electrodialysis will be described with reference to Figure 31. The lithium isotope enrichment device 101 is configured by an electrolyte membrane 2 having electrodes 131, 132 made of porous membranes attached to both sides, dividing a treatment tank 7 into a supply tank 11 and a recovery tank 12, and connecting a power source 151 between the electrodes 131, 132 with the electrode 131 as the positive electrode. A Li-containing aqueous solution FS such as a lithium hydroxide (LiOH) aqueous solution is introduced into the supply tank 11 as a Li source, and pure water or the like is introduced into the recovery tank 12. 6 The aqueous solution ES for recovering Li is introduced.

[0005] When a voltage is applied from the power source 151, a reaction according to the following formula (1) occurs in the vicinity of the electrode 131 in the Li-containing aqueous solution FS in the supply tank 11, generating oxygen (O2), and hydroxide ions (OH - ) decreases. 6 In the aqueous solution ES for recovering Li, the reaction of the following formula (2) occurs near the electrode 132 to generate hydrogen (H), and OH - Then, in order to maintain the charge balance in each of the aqueous solutions FS and ES, Li in the Li-containing aqueous solution FS increases. + The reaction of the following formula (3) in which Li moves into the electrolyte membrane 2, + but 6 The reaction of the following formula (4) occurs, in which Li contained in the electrolyte membrane 2 (electrolyte) moves to the aqueous solution for Li recovery ES. + Li + (electrolyte).

[0006] Li from the supply tank 11 side to the recovery tank 12 side in the electrolyte membrane 2 + As mentioned above, the movement of 6 Li + The amount of movement per hour is 7 Li + This is particularly noticeable in the short time immediately after the start of operation (start of voltage application), so by connecting a switching element 105s or the like to the power supply 151 and applying voltage intermittently, and alternately repeating short periods of voltage application and stopping, 6Li can be efficiently concentrated (Patent Document 4, Non-Patent Document 1).

[0007] Japanese Patent No. 5429658 Japanese Patent No. 6233877 JP 2019-141807 JP 2019-141808 WO 2023 / 027190

[0008] Shunsuke Honda, Kiyoto Shin-mura, Kazuya Sasaki, “Lithium isotope enrichment by electrochemical pumping using solid lithium electrolytes”, Journal of the Ceramic Society of Japan, Volume 126, Issue 5, pp 331-335, May 2018

[0009] The method described in Patent Document 4 etc. has room for further improvement in order to increase the isotope separation factor.

[0010] The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide a more efficient lithium isotope enrichment apparatus, a multistage lithium isotope enrichment apparatus, and a lithium isotope enrichment method using electrodialysis.

[0011] The present inventors have conducted extensive research into the enrichment of lithium isotopes by electrodialysis and have found that Li + Since the smaller the energy required for isotope transport through the electrolyte, the larger the isotope separation factor, the researchers came up with the idea of ​​minimizing this energy.

[0012] That is, the lithium isotope enrichment device according to the present invention comprises: a lithium ion conductive electrolyte membrane; a treatment tank partitioned into a first tank and a second tank by the lithium ion conductive electrolyte membrane; a first electrode provided in one of the first tank and the second tank; a second electrode having a porous structure provided in contact with a surface of the lithium ion conductive electrolyte membrane on the other tank side; a third electrode provided in the other tank and spaced apart from the second electrode on the opposite side of the lithium ion conductive electrolyte membrane; and a power source that applies the same voltage to the first electrode and the second electrode relative to the third electrode, with the first tank side being positive, and is contained in the first tank. 6 Li and 7 Li and Li in the state of lithium ions, 6 An aqueous solution containing lithium ions with an enriched Li isotope ratio is collected in the second tank.

[0013] The multistage lithium isotope enrichment apparatus according to the present invention comprises two or more of the lithium isotope enrichment apparatuses described above, connected together so that the treatment tanks are integrated, the lithium ion conductive electrolyte membranes of the lithium isotope enrichment apparatuses are arranged spaced apart from each other so as to separate the integrated treatment tank into three or more tanks, and the second tank of one of two adjacent lithium isotope enrichment apparatuses also serves as the first tank of the other.

[0014] Another multistage lithium isotope enrichment apparatus according to the present invention is configured such that, in the lithium isotope enrichment apparatus described above, the first electrode is provided in the first tank, the third electrode is provided in the second tank, and two or more lithium ion conductive electrolyte membranes are provided to partition the treatment tank into three or more tanks in the following order: the first tank, one or more intermediate tanks, and the second tank, and the second electrode is provided in contact with the lithium ion conductive electrolyte membrane that separates the first tank from the adjacent intermediate tank.

[0015] The lithium isotope enrichment method according to the present invention includes a treatment tank partitioned into a first tank and a second tank by a lithium ion conductive electrolyte membrane, and a lithium isotope enrichment solution contained in the first tank. 6 Li and 7Li and Li in the state of lithium ions, 6 The method for enriching lithium isotopes according to the present invention comprises applying the same voltage to a first electrode provided in one of the first and second tanks, a second electrode having a porous structure provided in contact with the surface of the lithium ion conductive electrolyte membrane facing the other tank, and a third electrode provided in the other tank on the opposite side of the lithium ion conductive electrolyte membrane and spaced apart from the second electrode.

[0016] According to the lithium isotope enrichment device and the lithium isotope enrichment method of the present invention, 6 An aqueous solution having a higher Li isotope ratio can be recovered safely and with high productivity. 6 The Li isotope ratio can be made even higher.

[0017] FIG. 1 is a schematic diagram illustrating the configuration of a lithium isotope enrichment apparatus according to a first embodiment of the present invention. FIG. 2 is a schematic diagram of the lithium isotope enrichment apparatus shown in FIG. 1 , illustrating electrodialysis of lithium ions in the lithium isotope enrichment method according to the first embodiment of the present invention. FIG. 3 is a circuit diagram of the lithium isotope enrichment apparatus shown in FIG. 1 , illustrating the lithium isotope enrichment method according to the first embodiment of the present invention. FIG. 4 is an enlarged view of a main part of the lithium isotope enrichment apparatus shown in FIG. 1 , illustrating the behavior of lithium ions in an initial state in electrodialysis of lithium ions. FIG. 5 is an enlarged view of a main part of the lithium isotope enrichment apparatus shown in FIG. 1 , illustrating the behavior of lithium ions immediately after the start of movement in electrodialysis of lithium ions. FIG. 6 is an enlarged view of a main part of the lithium isotope enrichment apparatus shown in FIG. 1 , illustrating the behavior of lithium ions during movement in electrodialysis of lithium ions. FIG. 7 is a model illustrating ion conduction in an electrolyte. FIG. 8 is a graph illustrating the dependence of the amount of movement per hour and the isotope ratio on the applied voltage in electrodialysis of lithium ions, based on a simulation. FIG. 9 is a schematic diagram illustrating the configuration of an isotope enrichment apparatus according to a modified example of the first embodiment of the present invention, and electrodialysis of lithium ions in the lithium isotope enrichment method. 1 is a schematic diagram illustrating the configuration of a multistage lithium isotope enrichment apparatus as a lithium isotope enrichment apparatus according to a modification of the first embodiment of the present invention. FIG. 1 is a schematic diagram illustrating the configuration of a multistage lithium isotope enrichment apparatus according to the first embodiment of the present invention. FIG. 2 is a schematic diagram illustrating the configuration of a lithium isotope enrichment apparatus according to a second embodiment of the present invention. FIG. 3 is a schematic diagram of the lithium isotope enrichment apparatus shown in FIG. 10 , illustrating electrodialysis of lithium ions in a lithium isotope enrichment method. FIG. 4 is a schematic diagram of the lithium isotope enrichment apparatus according to a first modification of the second embodiment of the present invention, illustrating electrodialysis of lithium ions in a lithium isotope enrichment method. FIG. 5 is a schematic diagram of the lithium isotope enrichment apparatus shown in FIG. 12 , illustrating electrodialysis of lithium ions in a lithium isotope enrichment method. FIG. 6 is a schematic diagram illustrating the configuration of a lithium isotope enrichment apparatus according to a second modification of the second embodiment of the present invention. FIG. 7 is a schematic diagram of the lithium isotope enrichment apparatus shown in FIG. 14 , illustrating electrodialysis of lithium ions in a lithium isotope enrichment method. FIG. 8 is a schematic diagram illustrating the configuration of a lithium isotope enrichment apparatus according to a third embodiment of the present invention.20 , illustrating a lithium isotope enrichment method according to a first modification of the third embodiment of the present invention. 21 is a time chart illustrating the transition of applied voltage in a lithium isotope enrichment method according to a third embodiment of the present invention. 22 is a schematic diagram illustrating the configuration of a multistage lithium isotope enrichment apparatus according to a third embodiment of the present invention. 23 is a schematic diagram illustrating a lithium isotope enrichment method using the multistage lithium isotope enrichment apparatus shown in FIG. 18. 24 is a schematic diagram illustrating a lithium isotope enrichment method using the multistage lithium isotope enrichment apparatus shown in FIG. 18. 25 is a schematic diagram illustrating a configuration of a lithium isotope enrichment apparatus according to a first modification of the third embodiment of the present invention. 26 is a time chart illustrating the transition of applied voltage in a lithium isotope enrichment method according to a first modification of the third embodiment of the present invention. 27 is a schematic diagram of the lithium isotope enrichment apparatus shown in FIG. 20 , illustrating a lithium isotope enrichment method according to a first modification of the third embodiment of the present invention. 28 is an enlarged view of a main part of the lithium isotope enrichment apparatus shown in FIG. 20 , illustrating the behavior of lithium ions after the movement of lithium ions has stopped in electrodialysis of lithium ions. 29 is a schematic diagram illustrating another configuration of a lithium isotope enrichment apparatus according to a first modification of the third embodiment of the present invention. 29 is a time chart illustrating the transition of applied voltage in a lithium isotope enrichment method according to a second modification of the third embodiment of the present invention. 26. A schematic diagram illustrating a configuration of a multistage lithium isotope enrichment apparatus according to a first modified example of the third embodiment of the present invention. 27. A schematic diagram illustrating a lithium isotope enrichment method using the multistage lithium isotope enrichment apparatus shown in FIG. 26. A schematic diagram illustrating a lithium isotope enrichment method using the multistage lithium isotope enrichment apparatus shown in FIG. 26. A schematic diagram illustrating a configuration of a multistage lithium isotope enrichment apparatus according to a second modified example of the second embodiment of the present invention. 28. A schematic diagram illustrating a lithium isotope enrichment method using the multistage lithium isotope enrichment apparatus shown in FIG. 28. A schematic diagram illustrating a lithium isotope enrichment method using the multistage lithium isotope enrichment apparatus shown in FIG. 28. A schematic diagram illustrating a lithium isotope enrichment method using the multistage lithium isotope enrichment apparatus shown in FIG. 28. A graph showing the amount of lithium ion migration and lithium isotope separation coefficients according to examples and comparative examples. 29. A schematic diagram of a lithium isotope enrichment apparatus illustrating a conventional lithium isotope enrichment method using electrodialysis.

[0018] Modes (embodiments) for carrying out a lithium isotope enrichment apparatus, a multistage lithium isotope enrichment apparatus, and a lithium isotope enrichment method according to the present invention will be described with reference to the drawings. In the drawings, the size of certain elements may be exaggerated and the shapes may be simplified for clarity. In addition, in the description of each embodiment, elements that are the same as those in the previous embodiment are designated by the same reference numerals, and descriptions thereof will be omitted as appropriate.

[0019] 1, a lithium isotope enrichment apparatus 1 according to a first embodiment of the present invention includes a treatment tank 7, an electrolyte membrane (lithium ion conductive electrolyte membrane) 2, a first electrode 31, a second electrode 32, a third electrode 33, a power source 51, and an agitator (circulation means) 8. The treatment tank 7 is separated by the electrolyte membrane 2 into a supply tank (first tank) 11 that contains a Li-containing aqueous solution FS, 6 and a recovery tank (second tank) 12 that stores an aqueous solution for Li recovery ES. A first electrode 31 is provided in the supply tank 11. A second electrode 32 has a porous structure and is provided to cover the surface of the electrolyte membrane 2 that faces the recovery tank 12. A third electrode 33 is provided in the recovery tank 12, spaced apart from the electrolyte membrane 2 and the second electrode 32. A power source 51 has a positive (+) terminal connected to the first electrode 31 and the second electrode 32, and a negative (-) terminal connected to the third electrode 33. An agitator 8 mixes the Li-containing aqueous solution FS in the supply tank 11 and the Li-containing aqueous solution ES in the recovery tank 12. 6 The lithium recovery aqueous solution ES is circulated through the respective components. Hereinafter, each component constituting the lithium isotope enrichment device according to this embodiment will be described.

[0020] The treatment tank 7 contains a Li-containing aqueous solution FS and 6 The treatment tank 7 is made of a material that does not corrode or change in quality even when it comes into contact with the aqueous solution ES for recovering Li. The treatment tank 7 is not particularly limited in shape, etc., as long as it has a volume corresponding to the required treatment capacity.

[0021] The electrolyte membrane 2 is an electrolyte having lithium ion conductivity, and - Furthermore, it is preferable that the Li-containing aqueous solution FS does not conduct Li. +When the electrolyte membrane 2 contains metal ions other than those mentioned above, it is preferable that the electrolyte membrane 2 does not conduct these metal ions. More preferably, the electrolyte membrane 2 is made of a ceramic material having these properties. Specifically, lithium lanthanum titanium oxide (La 2 / 3-x Li 3x Such an electrolyte membrane 2 has a certain proportion of lattice defects, and the size of the lattice defect sites is small, so that Li + For example, a solid electrolyte having a perovskite (ABO3) structure (A = Li, La, or vacancy, B = Ti) such as LLTO has vacancies (A-site defects) in some A-sites. As will be explained later in the lithium isotope enrichment method, Li is introduced into the A-site defects. + penetrates and Li + Hereinafter, a site where Li can exist, such as the A site, will be referred to as a Li site, and a Li site having a vacancy will be referred to as a Li site defect.

[0022] The first electrode 31 and the second electrode 32 are Li + The third electrode 33 is provided to maintain the same potential between both surfaces of the electrolyte membrane 2 when the lithium-containing aqueous solution FS is moved through the electrolyte membrane 2. The third electrode 33 is paired with the first electrode 31 and is provided to 6 A positive voltage is applied to the aqueous solution ES for recovering Li, and 6 The first electrode 31 is an electrode for forming a lower potential in the Li recovery aqueous solution ES than the surface (hereinafter referred to as the back surface, as appropriate) of the electrolyte membrane 2. For this purpose, the first electrode 31 is provided in the supply tank 11. The second electrode 32 is provided in contact with the surface (back surface) of the electrolyte membrane 2 facing the recovery tank 12. The third electrode 33 is arranged in the recovery tank 12 so as not to come into contact with the electrolyte membrane 2 and the second electrode 32.

[0023] The first electrode 31 is provided in the supply tank 11 and, as shown in FIG. 1 , can be positioned at a distance from the surface of the electrolyte membrane 2 facing the supply tank 11 (hereinafter referred to as the “surface”), allowing the Li-containing aqueous solution FS to contact the entire surface of the electrolyte membrane 2. Such a first electrode 31 preferably has a mesh-like shape or the like through which the aqueous solution passes, increasing the contact area with the Li-containing aqueous solution FS and ensuring continuous replacement of the Li-containing aqueous solution FS contacting the surface of the electrolyte membrane 2 in the supply tank 11. The first electrode 31 is preferably formed from an electrode material that is electronically conductive and stable in the Li-containing aqueous solution FS even when a voltage is applied, and further preferably has catalytic activity for the reaction represented by the following formula (1). Platinum (Pt), for example, is a preferred electrode material for the first electrode 31. Alternatively, carbon (C) can be used for the first electrode 31, and more preferably, carbon (C) can be used, with Pt fine particles supporting catalytic functions on its surface.

[0024] The second electrode 32 is provided in contact with the rear surface of the electrolyte membrane 2, and applies a voltage to a wide range of the electrolyte membrane 2 while applying a voltage to a sufficient area of ​​the rear surface of the electrolyte membrane 2. 6 The second electrode 32 has a porous structure such as a mesh structure so that the aqueous solution for recovering Li can come into contact with the second electrode 32. The second electrode 32 has electronic conductivity and is used for the reaction to proceed and release Li. + It began to contain 6 The second electrode 32 is preferably made of an electrode material that is stable when a voltage is applied even in the aqueous solution ES for Li recovery, and that has catalytic activity for the reactions of the following formulas (1) and (4). The second electrode 32 is preferably made of a material that can be easily processed into the above-mentioned shape. For example, platinum (Pt) is a preferred electrode material for the second electrode 32. In each formula, the Li contained in the electrolyte membrane 2 (electrolyte) + Li + The following formula (4) represents the Li in the electrolyte membrane 2. + is an aqueous solution ( 6 The reaction of transferring to the aqueous solution for Li recovery ES is shown.

[0025] The third electrode 33 is preferably disposed in the recovery tank 12 so as not to come into contact with the electrolyte membrane 2 and the second electrode 32, and is disposed parallel to the second electrode 32. Furthermore, as will be described later, the third electrode 33 6 In order to make the electric field E1 (see FIG. 2) generated in the aqueous solution ES for recovering Li stronger than the voltage V1 applied between the second electrode 32 and the third electrode 33, the third electrode 33 is preferably disposed close to the second electrode 32 to a degree that does not cause a short circuit. 6 The contact area with the aqueous solution for Li recovery ES is increased, and the contact area with the back surface (second electrode 32) of the electrolyte membrane 2 in the recovery tank 12 is increased. 6 The third electrode 33 preferably has a mesh-like shape or the like through which the aqueous solution for Li recovery ES can pass so that the aqueous solution for Li recovery ES can be continuously replaced. 6 The third electrode 33 is preferably formed from an electrode material that is stable when a voltage is applied in the aqueous solution ES for recovering Li, and further, a material that has catalytic activity for the reaction of the following formula (2): Alternatively, the third electrode 33 may be made of carbon (C), copper (Cu), or stainless steel, which are stable at a potential lower than the potential at which the reaction of the following formula (2) occurs, and more preferably, these materials have Pt fine particles that function as a catalyst supported on their surfaces.

[0026] The first electrode 31 may be provided in contact with the surface of the electrolyte membrane 2 (see the first electrode 31B of the modified example of the third embodiment shown in FIG. 20). This first electrode 31 has a porous structure such as a mesh structure, similar to the second electrode 32, so that a voltage is applied to a wide range of the electrolyte membrane 2 while the Li-containing aqueous solution FS comes into contact with a sufficient area of ​​the surface of the electrolyte membrane 2. The first electrode 31 is preferably made of a material that has catalytic activity for the reaction of the following formula (3) in addition to the reaction of the above formula (1), and is also preferably made of a material that can be easily processed into the above shape. The following formula (3) represents the reaction of the Li-containing aqueous solution (Li-containing aqueous solution FS) + represents a reaction in which the hydrogen ions migrate into the electrolyte membrane 2.

[0027] The power supply 51 is a DC power supply, and applies to the first electrode 31 and the second electrode 32 a voltage of the same polarity and magnitude as that of the third electrode 33, with the supply tank 11 side being positive. In the lithium isotope enrichment apparatus 1 according to this embodiment, the power supply 51 has a positive electrode connected to the first electrode 31 and the second electrode 32 and a negative electrode connected to the third electrode 33, and applies a positive voltage V1 (voltage +V1) with respect to the third electrode 33 to the first electrode 31 and the second electrode 32.

[0028] The agitator 8 circulates the Li-containing aqueous solution FS in the supply tank 11 so that the Li-containing aqueous solution FS in contact with the first electrode 31 and the surface of the electrolyte membrane 2 is continuously replaced during operation, and also circulates the Li-containing aqueous solution FS in contact with the second electrode 32 (the back surface of the electrolyte membrane 2) and the third electrode 33. 6 The aqueous solution for Li recovery ES in the recovery tank 12 is continuously replaced. 6 The agitator 8 is provided as needed to circulate the aqueous solution ES for recovering Li. 6 Alternatively, only one of the aqueous solutions FS and ES for Li recovery may be circulated. A known device can be used as the agitator 8, and for example, as shown in Fig. 1, a screw immersed in the aqueous solutions FS and ES may be rotated by a motor. Alternatively, each of the tanks 11 and 12 may be provided with an inlet and an outlet and connected to a circulation tank installed outside the treatment tank 7, and the aqueous solutions FS and ES may be circulated by a pump.

[0029] The Li-containing aqueous solution FS is a Li source that supplies Li, 7 Li and 6 Li cation 7 Li + , 6 Li + At least at the start of operation of the lithium isotope enrichment apparatus 1, 7 Li + , 6 Li + The Li-containing aqueous solution FS contains Li at a natural abundance ratio. + It is preferable that the concentration is higher, and at the start of operation of the lithium isotope enrichment apparatus 1, Li +It is more preferable that the solution is a saturated or supersaturated aqueous solution of the above. 6 The aqueous solution for Li recovery ES is a solution of lithium ions Li recovered from the aqueous solution containing Li FS. + ,especially, 6 Li having a Li isotope ratio higher than that of at least the Li-containing aqueous solution FS + At the start of operation of the lithium isotope enrichment apparatus 1, the aqueous solution is, for example, pure water. 7 Li and 6 Li ( 7 Li + and 6 Li + ) are not distinguished from each other, Li (Li + ) is called.

[0030] The lithium isotope enrichment device 1 further includes a Li-containing aqueous solution FS or 6 The cooling device may be provided to cool the electrolyte membrane 2 via the aqueous solution ES for Li recovery. A known device for cooling a liquid can be used as the cooling device, and it is preferable that the cooling device has a temperature adjustment function. The cooling device is, for example, an immersion type, and a pipe (refrigerant pipe) through which a refrigerant flows is provided in the recovery tank 12. 6 The cooling device is immersed in the aqueous solution for Li recovery ES. The cooling device is only required to be able to keep the electrolyte membrane 2 at a predetermined temperature. 6 The aqueous solution for Li recovery ES does not need to be kept at a uniform liquid temperature. However, depending on the volume of the treatment tank 7, a stirring device may be provided. The refrigerant pipe of the cooling device is the same as the treatment tank 7, and the Li-containing aqueous solution FS and 6 The cooling device is made of a material that does not corrode or otherwise deteriorate even when it comes into contact with the Li recovery aqueous solution ES, and its shape is not particularly limited. For example, in order to efficiently cool the electrolyte membrane 2, the refrigerant pipe is installed in a serpentine shape in accordance with the dimensions of the plate-shaped electrolyte membrane 2, facing closely over a wide area of ​​the electrolyte membrane 2. Depending on the thickness of the electrolyte membrane 2, the refrigerant pipe may be inserted into both the supply tank 11 and the recovery tank 12. The cooling device may also be configured such that the treatment tank 7 has a double structure (jacket tank) and the refrigerant flows inside it (jacket portion). Alternatively, the Li-containing aqueous solution FS or 6The Li recovery aqueous solution ES may be circulated outside the treatment tank 7 by a pump and cooled by a heat exchanger.

[0031] The temperature of the electrolyte membrane 2 will be described in detail later, but it is set to 30° C. or less so that the aqueous solutions FS and ES do not freeze. 6 When the aqueous solution for Li recovery ES is pure water at the start of operation of the lithium isotope enrichment apparatus 1 (start of electrodialysis), the temperature is set to 0° C. or higher. 6 Alternatively, the liquid temperature of the aqueous solution ES for recovering Li can be measured.

[0032] The lithium isotope enrichment device 1 further includes: an operating Li-containing aqueous solution FS; 6 A liquid level sensor or the like may be provided to detect fluctuations in the amount of the aqueous solution ES for Li recovery. In addition, in order to prevent carbon dioxide (CO2) in the atmosphere from unintentionally dissolving in the aqueous solutions FS and ES and causing lithium carbonate (Li2CO3) to precipitate, the lithium isotope enrichment device 1 6 It is preferable that the lithium recovery aqueous solution ES is configured so as not to be exposed to the atmosphere. Furthermore, it is preferable for safety reasons that the lithium isotope enrichment apparatus 1 is provided with an exhaust means for exhausting H and O generated during operation (by the reactions of formulas (1) and (2)) so as not to fill the inside of the apparatus.

[0033] (Method for Enriching Lithium Isotopes) In the method for enriching lithium isotopes according to the present invention, in a treatment tank 7 partitioned into a supply tank 11 and a recovery tank 12 by an electrolyte membrane 2, 6 This is a method for recovering an aqueous Li recovery solution ES in a recovery tank 12. In the lithium isotope enrichment method according to the first embodiment of the present invention, a positive voltage V1 is applied to a first electrode 31 provided in a supply tank 11, a second electrode 32 provided on the back surface of an electrolyte membrane 2, and a third electrode 33 provided in the recovery tank 12 at a distance from the electrolyte membrane 2 and the second electrode 32. First, with reference to Fig. 2 , electrodialysis of lithium ions using the lithium isotope enrichment apparatus according to the first embodiment will be described. In the lithium isotope enrichment apparatus 1 shown in Fig. 2 , the agitator 8 is omitted.

[0034] As shown in FIG. 2, in the lithium isotope enrichment apparatus 1, a power supply 51 applies a positive voltage V1 (voltage +V1) to the first electrode 31 and the second electrode 32, which are short-circuited with respect to the third electrode 33. Then, the following reaction occurs in the supply tank 11. In the vicinity of the first electrode 31, hydroxide ions (OH - ) undergoes the reaction of the following formula (1), and electrons e - is released to the first electrode 31, generating water (H2O) and oxygen (O2), and - In the Li-containing aqueous solution FS, OH - As the charge imbalance decreases, Li + In order to cause the reaction of the following formula (3) in which Li dissolves in the electrolyte membrane 2, + moves to the vicinity of the surface of the electrolyte membrane 2. As a result, the vicinity of the surface of the electrolyte membrane 2 6 Li in the vicinity of the back surface of the electrolyte membrane 2 in the aqueous solution ES for Li recovery + This concentration gradient, i.e., the concentration of Li in the vicinity of the front surface and the rear surface of the electrolyte membrane 2, is + Due to the chemical potential difference between the two, and in order to compensate for the charge imbalance, the reaction of the following formula (3) occurs, and Li + becomes highly concentrated.

[0035] On the other hand, in the recovery tank 12, application of a voltage +V1 causes the following: 6 An electric field E1 (electric field +E1) is generated in the aqueous solution ES for recovering Li from the second electrode 32 toward the third electrode 33, and the following reaction occurs: + Due to the chemical potential difference between Li and Li in the electrolyte membrane 2, + but 6 The reaction of the following formula (4) that moves to the Li recovery aqueous solution ES occurs near the back surface of the electrolyte membrane 2. Furthermore, near this back surface, i.e., near the second electrode 32, 6 OH in aqueous solution ES for Li recovery - The reaction of the following formula (1) occurs, and electrons e -is released to the second electrode 32, generating H2O and O2. 6 The H2O in the aqueous solution ES for Li recovery is electron e - By supplying hydrogen (H) and OH, the reaction of the following formula (2) occurs. - Li in the vicinity of the second electrode 32 + Increased OH - and the decrease in OH - In order to compensate for the charge imbalance caused by the increase in Li + moves to the vicinity of the third electrode 33 along the electric field +E1 generated between the second electrode 32, i.e., the back surface of the electrolyte membrane 2, and the third electrode 33. As a result, Li + The low concentration state continues, and Li is absorbed into the surface layer or the vicinity of the surface of the electrolyte membrane 2. + The chemical potential difference is maintained.

[0036] A series of reactions produces a Li-containing aqueous solution FS, 6 A charge balance is maintained in the aqueous solution for Li recovery ES and the electrolyte membrane 2. In addition, in this series of reactions, the Li-containing aqueous solution FS and 6 The charge compensation in the entire Li recovery aqueous solution ES is maintained by the reaction amount of the reaction of formula (2) (H generation) in the vicinity of the third electrode 33 and the reaction amount of the reaction of formula (1) (O generation) in the vicinity of each of the electrodes 31 and 32. The amount of O generated in the Li-containing aqueous solution FS (the reaction amount of the reaction of formula (1) in the vicinity of the first electrode 31) is calculated by the reaction amount of Li that has migrated through the electrolyte membrane 2. + (the reaction amounts of the reactions of formula (3) and formula (4)). + The amount of (Li + The movement amount) is near the third electrode 33 ( 6 This is equal to or less than the amount of H 2 generated in the aqueous solution for Li recovery ES) and corresponds to the difference between the amount of H 2 generated and the amount of O 2 generated in the vicinity of the second electrode 32.

[0037] From the above, the voltage V1 is set to a voltage at which the electrolysis reaction of water occurs or more, and the Li-containing aqueous solution FS and 6The Li recovery aqueous solution ES is set to +1.229 V (25°C) or more at the same pH (hydrogen ion concentration). In practice, the voltage V1 needs to be set to a value several hundred mV higher than the theoretical voltage of 1.229 V, depending on the electrode performance that determines the electrode reaction overvoltage of each of the electrodes 31, 32, and 33. 6 The higher the pH of the aqueous solution ES for Li recovery, the lower the voltage at which the electrolysis reaction of water occurs. 6 If the pH is low relative to the aqueous solution ES for recovering Li, the voltage at which the electrolysis reaction of water occurs becomes large, and therefore it is necessary to set the voltage V1 to a large value.

[0038] In addition, the stronger the electric field E1 between the second electrode 32 and the third electrode 33, 6 In the aqueous solution ES for Li recovery, + By moving the third electrode 33 away from the electrolyte membrane 2, the chemical potential difference between both sides of the electrolyte membrane 2 can be increased. If the chemical potential difference between both sides of the electrolyte membrane 2 is insufficient, the reaction of formula (1) is unlikely to occur near the first electrode 31, i.e., in the Li-containing aqueous solution FS, and will occur only near the second electrode 32. Therefore, it is preferable that the third electrode 33 be arranged at a short distance from the second electrode 32 so as not to cause a short circuit, and it is also preferable that the voltage V1 be somewhat large, as will be described later.

[0039] Here, the aqueous solution of the Li-containing solution FS in the portion sandwiched between the first electrode 31 and the electrolyte membrane 2 is designated by the symbol “FS E " 6 The aqueous solution for Li recovery ES in the portion sandwiched between the second electrode 32 and the third electrode 33 is designated by the symbol "ES E As shown in FIG. 3, the lithium isotope enrichment device 1 according to this embodiment includes a power supply 51 and 6 Li recovery aqueous solution ES E The lithium isotope enrichment device 1 includes a closed circuit in which the electrodes 11 and 12 are connected in a circular fashion, and currents I1 and I2 flow counterclockwise as indicated by the gray arrows from a power source 51. The lithium isotope enrichment device 1 further includes a branch from the positive electrode of the power source 51 and a Li-containing aqueous solution FS E, and electrolyte membrane 2, and a current I2 flows from current I1 and a branched current I3 as shown by the gray dashed arrow (I1 = I2 + I3). + resistance to movement) is R EL , Li-containing aqueous solution FS E The resistance (resistance between the first electrode 31 and the electrolyte membrane 2) is R FS , 6 Li recovery aqueous solution ES E The resistance (resistance between the second electrode 32 and the third electrode 33) is R ES The lithium isotope enrichment device 1 further includes a reaction resistance R due to the reaction (O generation) of the formula (1) at the first electrode 31. Ox1 , reaction resistance R due to the reaction of formula (1) (O2 generation) at the second electrode 32 Ox2 , the reaction resistance R due to the reaction of formula (2) (H generation) at the third electrode 33 Red Then, the circuit constituting the lithium isotope enrichment device 1 is expressed by the following formula (5). In addition, in the electrolyte membrane 2, when electron transfer property is not exhibited, electrons e - Instead of Li + In the aqueous solutions FS and ES, electrons e - Instead of a part of - , and in the opposite direction Li + and H + will move respectively. V1-(R ES +R Red ) I1 = R Ox2 I2 = (R Ox1 +R FS +R EL ) I3 ... (5)

[0040] In the lithium isotope enrichment device 1, in order to increase productivity, the amount of Li that flows through the electrolyte membrane 2 per hour is + The amount of (Li + It is preferable that the resistance R of the electrolyte membrane 2 is large, that is, the current I3 is large. EL It is preferable that the resistance R of the electrolyte membrane 2 is low. EL is the Li of the aqueous solutions FS and ES in contact with the electrolyte membrane 2. +Since it depends on the defect concentration of Li site in equilibrium with the concentration of Li between both sides of the electrolyte membrane 2, + The larger the concentration gradient, the lower the Li concentration. + It is preferable to strengthen the electric field E1 so that the concentration decreases. However, if the voltage V1 is increased to strengthen the electric field E1, both the current I1 and the current I2 increase. The larger the current I2, the more O2 is generated near the second electrode 32, and the lower the energy efficiency. Therefore, for example, if the power consumption per amount of recovered Li is within an allowable range and a higher Li concentration is obtained, + It is preferable to set the voltage V1 so as to obtain the mobility.

[0041] Furthermore, in order to make the current I3 larger relative to the magnitude of the voltage V1, a resistor R FS , R ES , R Ox1 , R Red Therefore, the first electrode 31 and the third electrode 33 are preferably designed to have a low reaction resistance R Ox1 , R Red It is preferable that the area immersed in the aqueous solutions FS and ES is large so that the resistance R is low, and it is preferable to use a material that has high catalytic activity in the reactions of formula (1) and formula (2). Also, as described above, the distance between the second electrode 32 and the third electrode 33 is set short enough to prevent a short circuit, thereby strengthening the electric field E1 and reducing the resistance R ES Similarly, it is preferable to reduce the distance between the first electrode 31 and the electrolyte membrane 2 to reduce the resistance R FS The first electrode 31 may have a porous structure and be in contact with the surface of the electrolyte membrane 2, and the resistance R FS However, the contact area with the Li-containing aqueous solution FS is reduced, so the reaction resistance R Ox1 Furthermore, since the contact area of ​​the electrolyte membrane 2 with the Li-containing aqueous solution FS on the surface is reduced, the resistance R EL Therefore, it is preferable to arrange the first electrode 31 close to the surface of the electrolyte membrane 2 so as not to prevent contact between the surface of the electrolyte membrane 2 and the Li-containing aqueous solution FS.

[0042] Li +The behavior of the electrolyte membrane 2 when it permeates the electrolyte membrane 2 will be described in detail with reference to Figures 4A to 4C. Figures 4A to 4C are enlarged cross-sectional views of the vicinity of the electrolyte membrane 2 of the lithium isotope enrichment device 1, and the second electrode 32 is in partial contact with the back surface of the electrolyte membrane 2. The aqueous solutions FS and ES are 7 Li + , 6 Li + Only the above are indicated by encircling each one.

[0043] When no voltage is applied, as shown in FIG. 7 Li + , 6 Li + The Li-containing aqueous solution FS floats, alternately adsorbs to and desorbs from the surface of the electrolyte membrane 2, and remains stationary at the Li site in the electrolyte membrane 2. From this state, as shown in FIG. 4B, a positive voltage V1 (voltage +V1) is applied to the first electrode 31 and the second electrode 32, and a negative voltage V2 (voltage +V1) is applied to the third electrode 33. In the figure, a positive charge is represented by a + in a circle, and a negative charge is represented by a - in a circle. Then, the Li in the Li-containing aqueous solution FS + ( 7 Li + , 6 Li + ) tries to dissolve in the electrolyte membrane 2 through the reaction of the following formula (3). At this time, Li adsorbed in the vicinity of the Li site defect on the surface of the electrolyte membrane 2 + In addition, the Li in the electrolyte membrane 2 is converted into the Li site defect as shown in the following reaction formula (4): + but 6 Li on the back surface tries to move to the aqueous solution ES for Li recovery. + but 6 Furthermore, as described above, by applying a voltage V1 between the second electrode 32 and the third electrode 33, as shown in FIG. 6 In the aqueous solution for Li recovery ES, Li near the electrolyte membrane 2 + However, the charged particles are separated from the electrolyte membrane 2 and attracted to the third electrode 33 by electrostatic attraction.

[0044] In addition, the Li-containing aqueous solution FS, i.e., the electrolyte membrane 2, is 6Li in the vicinity of the back surface of the electrolyte membrane 2 in the aqueous solution ES for Li recovery + Since there is a low concentration gradient, Li + tends to move from the front surface side to the back surface side in the electrolyte membrane 2. Specifically, Li of the Li site near the deep side (front surface side) of the electrolyte membrane 2 moves to the vacant Li site defect on the back surface of the electrolyte membrane 2 by the reaction of formula (4). + It jumps (hops) over. + The Li site defect that has become vacant due to the jump of Li is further vacant from the Li site in the vicinity of the surface side. + In other words, Li that has entered the Li site defects on the surface of the electrolyte membrane 2 from the Li-containing aqueous solution FS + jumps to a nearby Li site defect on the deep side (back side), and then jumps to a nearby Li site defect on the back side. + The electrons repeatedly move from the Li site defects of the electrolyte membrane 2 to the neighboring Li site defects, and finally move from the Li site on the back surface to the Li site on the back surface as shown in FIG. 4C according to the reaction of the formula (4). 6 The solution is transferred to the aqueous solution ES for Li recovery.

[0045] Furthermore, on the back surface of the electrolyte membrane 2, as described above, Li in the Li adsorption site on the back surface + However, when a voltage V1 is applied between the second electrode 32 and the third electrode 33, the Li atoms are released from the second electrode 32, i.e., the back surface of the electrolyte membrane 2, by electrostatic repulsion, and the Li atoms are released from the back surface of the electrolyte membrane 2, accelerating the vacancy of Li site defects. On the other hand, on the surface of the electrolyte membrane 2, the Li atoms that have entered the Li site defects on the surface or that have been adsorbed in the vicinity thereof are released. + As a result of the movement of Li atoms to the depth of the electrolyte membrane 2, the Li atoms adsorbed in the vicinity of the vacant Li site defect are absorbed. + The Li-containing aqueous solution FS moves and penetrates, and new Li + These Li + Similarly, Li moves through the electrolyte membrane 2. + By moving, the Li site defect becomes Li + The Li adsorbed on the surface is released through the newly generated Li site defects on the surface of the electrolyte membrane 2.+ can start moving to the back side.

[0046] Li + The inter-site migration (hopping) of E in the electrolyte membrane 2 will be described in more detail with reference to FIG. 5. FIG. 5 is a model for explaining ion conduction in the electrolyte, where x is the position in the thickness direction of the electrolyte membrane 2, E p indicates potential energy. In the electrolyte membrane 2, Li + ( 7 Li + , 6 Li + ) exists stably at the Li site where the potential energy is minimum, but the nearby Li site is a vacancy (represented by a dotted circle), and the activation energy E a When this site defect receives more than 1000 times the energy barrier between the sites, E m can move by jumping over (hopping) a = E D / 2+E m , E D (Defect creation energy). Ions can be assumed to oscillate thermally at the minimum potential energy position with a frequency of Γ0, and can hop at a frequency (hopping rate Γ) corresponding to this frequency (frequency factor) Γ0. The frequency Γ0 is inversely proportional to the square root of the ion's mass. 6 Li has a mass of 7 Since it is 6 / 7 times smaller than Li, the frequency Γ0 7 Li (√(7 / 6)) times, and as will be described in detail later, the average migration speed in the electrolyte membrane 2 is 7 For example, for a Li site defect in the electrolyte membrane 2, two equidistant locations are located nearby. 7 Li + and 6 Li + If exists, 6 Li + It is assumed that the latter will jump preferentially.

[0047] In addition, in the Li site of the electrolyte membrane 2, i.e., in the ground state 7 Li+ , 6 Li + is the zero-point vibration hω I The potential energy increases by the amount of zero-point vibration hω I is isotope dependent, 7 Li + than 6 Li + Similarly, in the excited state, the zero-point vibration hω S teeth 6 Li + is larger. Therefore, 7 Li + Less mass than 6 Li + In both the ground state and the excited state, the zero-point vibration hω I , hω S The potential energy is high considering 6 Li + The potential energy difference between these excited states and the ground state is the energy barrier E m is small (E m ( 7 Li + )>E m ( 6 Li + )), i.e., the activation energy E a is small. As a result, 6 Li + The energy received is 7 Li + Hopping can occur even if the amount is smaller than Li + is the activation energy E of the received energy a The greater the excess over , the greater the mobility μ.

[0048] Also, 6 Li + is better 7 Li + Activation energy E a The surplus energy for the 6 Li +The mobility μ is higher in the case of the frequency Γ0 ratio. Here, FIG. 6 shows the time-dependent mobility μ obtained by simulation when the received energy is the applied voltage between both sides of the electrolyte membrane 2. 6 Li + , 7 Li + Movement amount and movement Li + The simulation shows the dependence of the isotope ratio of 1000 to 10 ... a The distribution of is approximated by a normal distribution. 6 Li + , 7 Li + For each of the received energy, the activation energy E a ( 6 Li + < 7 Li + (Li exceeding the + The ratio of activation energy E a The relative value of the mobility μ was calculated by multiplying the cumulative probability density of the normal distribution with the mean value of Γ0 by the frequency ratio. 7 Li + and 6 Li + The ratio of these compounds was calculated as 1:1.

[0049] As shown in FIG. 6 Li + , 7 Li + The mobility of each increases from 0 in an S-shaped curve as the applied voltage increases. 7 Li + For activation energy E a Small 6 Li + However, the voltage is shifted to the smaller side and is higher by the frequency Γ0 ratio. 6 Li + Therefore, the applied voltage, i.e., the received energy, is 6 Li + The smaller the range of movement, 6 Li+ but 7 Li + And the energy becomes larger. 6 Li + , 7 Li + As the mobilities of these atoms converge, the difference between them becomes smaller, and the isotope ratio converges to (√(7 / 6)) / (1+√(7 / 6)).

[0050] The ion mobility μ is related to the ion diffusion coefficient D by the following formula (6) (T: temperature (K), k: Boltzmann's constant). The diffusion coefficient D is proportional to the hopping rate Γ (a: average distance between sites (jump length), n c : carrier density, f: correlation effect coefficient determined by the ion and its surroundings, d: dimension of the diffusion field). The frequency factor Γ0 in equation (7) is proportional to the temperature T as expressed by the following equation (8), and is also proportional to (Z s vib / Z I vib ) is inversely proportional to the square root of the mass number m, so the frequency factor Γ0 is inversely proportional to the square root of the mass number m (h: Planck's constant, Z s vib : phonon partition function at the saddle point, Z I vib where C is the phonon distribution function in the initial state, and C is a constant. From equations (7) and (8), the diffusion coefficient D is expressed by the following equation (9). From equations (6) and (9), the ion mobility μ is expressed by the following equation (10) (C is a constant). As shown in equation (10), the ion mobility μ is expressed as follows: 7 Li + For mass number m and activation energy E a Small 6 Li + is higher.

[0051] Therefore, in the lithium isotope enrichment method according to the present invention, the Li isotope concentration in the vicinity of the rear surface of the electrolyte membrane 2 is increased by an electric field +E1 generated by an applied voltage +V1 between the second electrode 32 and the third electrode 33. + By reducing the concentration, Li +A concentration gradient is formed, and the first electrode 31 is short-circuited with the second electrode 32 to make the potential difference between both sides of the electrolyte membrane 2 zero, and Li is + migrates in the electrolyte membrane 2. Therefore, as shown in FIG. 6, a voltage is applied between both sides of the electrolyte membrane 2 to cause the electrochemical potential difference to cause Li + Compared to the conventional lithium isotope enrichment method that transfers 6 Li + , 7 Li + receives less energy, and as a result, Li + The amount of movement per hour is small, 6 Li + but 7 Li + Move more relative to

[0052] In the lithium isotope enrichment method according to the present invention, Li + Li in the Li-containing aqueous solution FS, which is upstream in the movement of + The higher the concentration, the + The mobility is increased, resulting in 6 Therefore, the Li-containing aqueous solution FS can be made to have a high concentration rate of Li. + Higher concentrations are preferred, Li + However, as the operation time progresses, the Li content of the Li-containing aqueous solution FS may decrease. + Therefore, for example, every time a predetermined operation application time has elapsed, or when the Li concentration of the Li-containing aqueous solution FS is + When the concentration drops below a predetermined value, it is preferable to replace the Li-containing aqueous solution FS in the supply tank 11, and it is also preferable to circulate the Li-containing aqueous solution FS to the outside of the treatment tank 7 at all times during operation. + The Li remaining in the Li-containing aqueous solution FS due to the movement of + of 6 Li isotope ratio ( 6 Li / ( 7 Li+ 6 Li)) decreases, so the newly moving Li + of 6The decrease in the Li isotope ratio is suppressed, 6 Li can be concentrated more efficiently. In addition, the decrease in the liquid volume of the Li-containing aqueous solution FS due to the reaction of formula (1) can be compensated for.

[0053] In addition, Li in the vicinity of the back surface of the electrolyte membrane 2 + The lower the concentration near the surface, the + The mobility can be increased. 6 In the aqueous solution ES for recovering Li, the electric field +E1 between the second electrode 32 and the third electrode 33 causes Li to be present in the vicinity of the third electrode 33. + By distributing Li unevenly in the vicinity of the back surface of the electrolyte membrane 2, + However, the Li concentration near the surface of the electrolyte membrane 2 can be kept low. + To ensure that the density is higher than near the back surface, 6 The total amount of Li in the aqueous solution ES for recovering Li does not exceed the amount of Li in the aqueous solution FS. + It is preferable that the concentration is 6 As for the aqueous solution ES for recovering Li, since the volume of the solution decreases due to the reactions of formula (1) and formula (2), it is preferable to add water (HO) or the like to the recovery tank 12 as needed. In the lithium isotope enrichment apparatus 1, it is preferable that the liquid levels in the supply tank 11 and the recovery tank 12 are the same during operation.

[0054] As shown in the formula (10), the ion mobility μ also depends on the temperature T, and the degree of this dependency varies with the activation energy E a is affected by. 7 Li + , 6 Li + The mobility of each increases exponentially with increasing temperature, but the activation energy E a Large 7 Li + As a result, as the temperature increases, the mobility of 7 Li + and expensive 6 Li + Therefore, the ratio of the moving Li + of 6 The Li isotope ratio is Li+ The temperature range applicable in this embodiment is equal to or higher than the freezing point and lower than the boiling point of the aqueous solutions FS and ES. 6 When the aqueous solution ES for recovering Li is pure water at the start of electrodialysis, the temperature is 0 to 100° C. For this reason, the temperature of the electrolyte membrane 2 is preferably 20° C. or less, more preferably 15° C. or less, even more preferably 10° C. or less, and even more preferably 5° C. or less.

[0055] Furthermore, aqueous solutions FS, ES, especially 6 The aqueous solution ES for Li recovery may contain a solute that does not permeate the electrolyte membrane 2 so as to lower the freezing point below 0°C. Such a solute is one that the aqueous solutions FS and ES containing it do not corrode the electrolyte membrane 2 or the electrodes 31, 32, 33, etc. Specific examples include salts used as antifreeze agents, such as sodium chloride (NaCl, table salt), magnesium chloride (MgCl2), calcium chloride (CaCl2), and potassium chloride (KCl), or organic solvents such as ethylene glycol. In particular, sodium chloride is preferred because it does not produce precipitates (carbonates) other than lithium carbonate even when carbon dioxide dissolves therein and has a large freezing point depression. According to this method, the electrolyte membrane 2 is cooled to 0°C or below, more preferably below 0°C, 6 The Li isotope ratio can be further increased and efficiently enriched.

[0056] The lithium isotope enrichment device 1 according to this embodiment is configured to: 6 Aqueous solution containing Li with a high Li isotope ratio ( 6 The aqueous solution for Li recovery ES is obtained in the recovery tank 12, 6 If the Li isotope ratio is not satisfied, 6 The aqueous solution for Li recovery ES is introduced into the emptied supply tank 11, while the recovery tank 12 is newly charged. 6 The aqueous solution for Li recovery ES is replaced with pure water and operated. 6 An aqueous solution containing Li with a high Li isotope ratio is obtained in the recovery tank 12. 6Before the aqueous solution for recovering Li ES is introduced into the supply tank 11, the water may be evaporated to concentrate Li, if necessary. 6 Li isotope ratio 6 This is repeated until an aqueous solution ES for recovering Li is obtained.

[0057] 6 After Li concentration is completed (desired 6 Li isotope ratio reached) 6 For example, the water content of the aqueous solution ES for recovering Li may be evaporated as necessary to concentrate Li, and then lithium carbonate (LiCO) may be generated and precipitated by bubbling carbon dioxide (CO) gas or the like. 6 Li can be recovered. 6 After Li concentration is completed 6 The aqueous solution ES for Li recovery is cooled or the water is evaporated to a supersaturated state, thereby generating and precipitating lithium hydroxide (LiOH). 6 Li can also be recovered.

[0058] 6 When a salt other than sodium chloride, such as magnesium chloride, is added to the aqueous solution ES for recovering Li in order to lower the freezing point, it is preferable to evaporate the water before bubbling the carbon dioxide gas and remove the salt precipitated due to the decrease in water by a general method such as filtration before bubbling. Alternatively, Li may be selectively recovered in pure water or the like by performing ordinary electrodialysis or the like (see, for example, Patent Document 3) at a temperature of 0°C or higher, for example, room temperature or higher, before bubbling the carbon dioxide gas.

[0059] ​​(Modification) In the lithium isotope enrichment device according to the present invention, the first electrode and the second electrode provided to equalize the potential between both surfaces of the lithium ion conductive electrolyte membrane may be connected to the negative electrode of a power source. In this case, the third electrode is connected to the positive electrode of the power source and provided in the supply tank. That is, as shown in Fig. 7 , a lithium isotope enrichment device 1A according to a modification of the first embodiment of the present invention includes a treatment tank 7, an electrolyte membrane (lithium ion conductive electrolyte membrane) 2, a first electrode 31A, a second electrode 32A, a third electrode 33A, and a power source 51. The treatment tank 7 is divided into a supply tank (first tank) 11 that contains a Li-containing aqueous solution FS by the electrolyte membrane 2, and 6 and a recovery tank (second tank) 12 that stores an aqueous Li recovery solution ES. A first electrode 31A is provided in the recovery tank 12. A second electrode 32A has a porous structure and is provided to cover the surface of the electrolyte membrane 2 facing the supply tank 11. A third electrode 33A is provided in the supply tank 11, spaced apart from the electrolyte membrane 2 and the second electrode 32A. A power source 51 has a positive (+) terminal connected to the third electrode 33A and a negative (-) terminal connected to the first electrode 31A and the second electrode 32A. The lithium isotope enrichment apparatus 1A has a configuration in which the positions of the first electrode 31A and the second electrode 32A and the third electrode 33A are interchanged with those of the lithium isotope enrichment apparatus 1 according to the first embodiment (see FIG. 1 ). The lithium isotope enrichment apparatus 1A has other configurations similar to those of the lithium isotope enrichment apparatus 1 according to the first embodiment, and may include a stirrer (circulation means) 8, a cooling device, a liquid level sensor, an exhaust means, etc., as necessary.

[0060] The first electrode 31A and the second electrode 32A are provided to equalize the potential between both surfaces of the electrolyte membrane 2, similar to the first electrode 31 and the second electrode 32 of the first embodiment. The third electrode 33A is paired with the first electrode 31A and is applied to the Li-containing aqueous solution FS, similar to the third electrode 33 of the first embodiment. 6This electrode is used to apply a positive voltage to the Li recovery aqueous solution ES. In the lithium isotope enrichment apparatus 1A according to this modification, the first electrode 31A is provided in the recovery tank 12. Accordingly, the second electrode 32A is provided in contact with the surface (front surface) of the electrolyte membrane 2 facing the supply tank 11, and the third electrode 33A is disposed in the supply tank 11 so as not to contact the electrolyte membrane 2 or the second electrode 32A.

[0061] The first electrode 31A is provided in the recovery tank 12 and can be arranged spaced apart from the rear surface of the electrolyte membrane 2, as shown in FIG. 7 . Therefore, the first electrode 31A can have a configuration similar to that of the third electrode 33 of the first embodiment, and is preferably made of a material having catalytic activity for the reaction of the following formula (2). Alternatively, the first electrode 31A may be provided in contact with the rear surface of the electrolyte membrane 2. The second electrode 32A is provided in contact with the front surface of the electrolyte membrane 2. Therefore, the second electrode 32A has a porous structure, such as a mesh structure, similar to the second electrode 32 of the first embodiment. However, similar to the first electrode 31 of the first embodiment, the second electrode 32A is preferably formed of an electrode material that is stable even when a voltage is applied in the Li-containing aqueous solution FS, and further preferably has catalytic activity for the reactions of the following formulas (2) and (3). The third electrode 33A is preferably arranged in the supply tank 11 so as not to contact the electrolyte membrane 2 or the second electrode 32A, and is preferably arranged parallel to the second electrode 32A. Therefore, the third electrode 33A is preferably formed of an electrode material that is stable in the Li-containing aqueous solution FS even when a voltage is applied, similar to the second electrode 32A, and further, is preferably a material that has catalytic activity for the reaction of the following formula (1). Therefore, the third electrode 33A can have a configuration similar to that of the first electrode 31 of the first embodiment.

[0062] In the lithium isotope enrichment apparatus 1A according to this modification, the power supply 51 applies a negative voltage V1 to the first electrode 31A and the second electrode 32A with respect to the third electrode 33A. To this end, the power supply 51 has a positive electrode connected to the third electrode 33A and a negative electrode connected to the first electrode 31A and the second electrode 32A.

[0063] In the lithium isotope enrichment method according to the modified example of the first embodiment of the present invention, a negative voltage V1 is applied to a first electrode 31A provided in a recovery tank 12 and a second electrode 32A provided on the surface of an electrolyte membrane 2, relative to a third electrode 33A provided in a supply tank 11 at a distance from the electrolyte membrane 2 and the second electrode 32A. In other words, a positive voltage V1 (voltage +V1) is applied to the third electrode 33A relative to the first electrode 31A and the second electrode 32A. Hereinafter, electrodialysis of lithium ions using the lithium isotope enrichment apparatus according to the modified example of the first embodiment will be described with reference to FIG. 7 .

[0064] 7, in the lithium isotope enrichment apparatus 1A, a power supply 51 applies a positive voltage V1 (voltage +V1) to the third electrode 33A relative to the first electrode 31A and the second electrode 32A, which are short-circuited to each other. Then, in the supply tank 11, as indicated by the thick gray arrow, an electric field E1 (electric field +E1) is generated in the Li-containing aqueous solution FS from the third electrode 33A toward the second electrode 32A, and the following reaction occurs: In the vicinity of the third electrode 33A, OH in the Li-containing aqueous solution FS is converted into OH. - The reaction of the following formula (1) occurs, and electrons e - is released to the first electrode 31, generating H2O and O2, and - In addition, in the vicinity of the second electrode 32A, the H2O in the Li-containing aqueous solution FS is converted into electrons e - By supplying H and OH, the reaction of the following formula (2) occurs. - In addition, the Li in the Li-containing aqueous solution FS + moves along the electric field +E1 to the second electrode 32A, i.e., the vicinity of the surface of the electrolyte membrane 2. As a result, 6 Li in the vicinity of the back surface of the electrolyte membrane 2 in the aqueous solution ES for Li recovery + This concentration gradient, i.e., the concentration of Li in the vicinity of the front surface and the rear surface of the electrolyte membrane 2, is + The chemical potential difference between these two reacts with each other to produce the reaction of the following formula (3), and Li is reacted with the electrolyte membrane 2 at the surface side (surface layer). + In addition, the Li in the Li-containing aqueous solution FS is converted into a high concentration by the reaction of the following formula (3): +As a result, the OH - and the increase in OH in the vicinity of the third electrode 33A. - The reduction of and the charge imbalance in the synthesis of are compensated.

[0065] Meanwhile, in the recovery tank 12, the following reaction occurs: 6 The H2O in the aqueous solution ES for Li recovery is electron e - By supplying H and OH, the reaction of the following formula (2) occurs. - Generates OH - In order to compensate for the charge imbalance due to the increase in + Due to the chemical potential difference between Li and Li in the electrolyte membrane 2, + but 6 The reaction of the following formula (4) that moves to the aqueous solution ES for recovering Li occurs near the rear surface of the electrolyte membrane 2 .

[0066] A series of reactions produces a Li-containing aqueous solution FS, 6 A charge balance is maintained in the aqueous solution for Li recovery ES and the electrolyte membrane 2. In addition, in this series of reactions, the Li-containing aqueous solution FS and 6 Charge compensation for the entire Li recovery aqueous solution ES is maintained by the reaction amount of the reaction of formula (1) (generation of O2) near the third electrode 33A and the reaction amount of the reaction of formula (2) (generation of H2) near each of the electrodes 31A and 32A. 6 The amount of H generated in the aqueous solution ES for Li recovery (the amount of reaction of the reaction of formula (2) in the vicinity of the first electrode 31A) is calculated based on the amount of Li transported through the electrolyte membrane 2. + (the reaction amounts of the reactions of formula (3) and formula (4)). + The amount of (Li + The amount of movement) is equal to or less than the amount of O2 generated near the third electrode 33A (Li-containing aqueous solution FS) and corresponds to the difference between the amount of O2 generated and the amount of H2 generated near the second electrode 32A.

[0067] The voltage V1 is set to a voltage at which the electrolysis reaction of water occurs, as in the first embodiment. In this way, even if the positions of the first electrode 31A, the second electrode 32A, and the third electrode 33A are interchanged, by applying a voltage with the supply tank 11 side being positive, the Li in the Li-containing aqueous solution FS can be + moves through the electrolyte membrane 2 6 The lithium-containing electrolyte reaches the aqueous solution ES for recovering lithium. + Since the electrons move only due to the chemical potential difference, as in the first embodiment, 6 A Li concentration effect is obtained.

[0068] The lithium isotope enrichment method according to the first embodiment (see FIG. 2) includes the following steps: 6 In the aqueous solution ES for recovering Li, an electric field +E1 is generated, so Li + The electrode (first electrode 31) can be disposed away from the electrolyte membrane 2, thereby increasing the chemical potential difference between both sides of the electrolyte membrane 2. In addition, since the electrode (first electrode 31) can be disposed on the surface (front surface) of the electrolyte membrane 2 facing the supply tank 11, the Li-containing aqueous solution FS can come into contact with the entire surface of the electrolyte membrane 2, and the Li + Therefore, the first embodiment is more likely to adsorb Li. + The mobility can be increased.

[0069] The lithium isotope enrichment apparatus 1 (see FIG. 1 ) according to the first embodiment can also have a cascade structure in which the recovery tank 12 is further partitioned into two or more tanks by one or more electrolyte membranes 2 between the second electrode 32 and the third electrode 33. That is, as shown in FIG. 8 , a lithium isotope enrichment apparatus (multistage lithium isotope enrichment apparatus) 1B according to another modification of the first embodiment of the present invention includes a treatment tank 7A, four electrolyte membranes (lithium ion conductive electrolyte membranes) 22, 23, 24, and 25 arranged in parallel at intervals so as to partition the treatment tank 7A in one direction into five tanks 11, 12, 13, 14, and 15, a first electrode 31 arranged in the tank 11, a second electrode 32 covering the back surface of the electrolyte membrane 22, a third electrode 33 arranged in the tank 15, and a power source 51A. The lithium isotope enrichment apparatus 1B further includes a third electrode 33 in each of the vessels 12, 13, and 14, and an agitator (circulation means) 8 in each of the vessels 11, 12, 13, 14, and 15.

[0070] The lithium isotope enrichment apparatus 1B has a structure in which the recovery tank 12 of the lithium isotope enrichment apparatus 1 according to the above embodiment is partitioned into four tanks 12, 13, 14, and 15 by three electrolyte membranes 23, 24, and 25 between the second electrode 32 and the third electrode 33. In other words, the electrolyte membrane 22 that partitions the tank 11 and the tank 12 corresponds to the electrolyte membrane 2 of the lithium isotope enrichment apparatus 1 according to the above embodiment. The electrolyte membranes 22, 23, 24, and 25 can each have the same configuration as the electrolyte membrane 2 of the lithium isotope enrichment apparatus 1 according to the above embodiment, and when the electrolyte membranes 22, 23, 24, and 25 are not particularly distinguished from one another, they will be referred to as the electrolyte membrane 2 as appropriate.

[0071] In the drawing, the supply tank 11 on the left side contains the Li-containing aqueous solution FS as in the previous embodiment. 6 Contains aqueous solutions ES1, ES2, ES3, and ES4 for recovering Li. 6 The aqueous solutions ES1, ES2, ES3, and ES4 for Li recovery are 6 Similarly to the Li recovery aqueous solution ES, the lithium ions Li recovered from the Li-containing aqueous solution FS +The treatment tank 7A is an aqueous solution for containing the lithium isotope enrichment solution, and is, for example, pure water when the operation of the lithium isotope enrichment apparatus 1B is started. In the lithium isotope enrichment apparatus 1B, the tank 15 at the end opposite to the supply tank 11 serves as a recovery tank. The treatment tank 7A may have any shape having a volume corresponding to the required treatment capacity, and other than that, it may have the same configuration as the treatment tank 7 of the lithium isotope enrichment apparatus 1 according to the above embodiment.

[0072] In the lithium isotope enrichment apparatus 1B, the resistance between the second electrode 32 and the third electrode 33 disposed in the recovery tank 15, i.e., the resistance between the electrolyte membranes 23, 24, 25, 6 Aqueous solutions for Li recovery ES1, ES2, ES3, and 6 It is preferable that the sum of the resistances of the portions of the Li recovery aqueous solution ES4 sandwiched between the electrolyte membrane 25 and the third electrode 33 is low. To suppress this resistance, the electrolyte membranes 22, 23 are preferably spaced apart shortly enough to prevent the third electrode 33 disposed in the tank 12 from shorting out with the second electrode 32, and it is more preferable that the third electrode 33 does not contact the electrolyte membrane 23. It is preferable that the electrolyte membranes 23, 24, 25 are spaced apart shortly enough to prevent contact with the third electrodes 33 disposed in the respective tanks 13, 14. Therefore, it is preferable that the tanks 12, 13, 14 are short in the partition direction of the treatment tank 7A (the left-right direction in FIG. 8 ).

[0073] Similar to the power supply 51 of the above embodiment, the power supply 51A has a positive electrode connected to the first electrode 31 and the second electrode 32 and a negative electrode connected to the third electrode 33. In the lithium isotope enrichment apparatus 1B according to this modification, a third electrode 33 is provided in each of the tanks 12, 13, 14, and 15, and one of the third electrodes 33 is connected to the negative electrode of the power supply 51A. For this purpose, the lithium isotope enrichment apparatus 1B further includes a switching element 5s3 that connects the negative electrode of the power supply 51A to one of the third electrodes 33. Therefore, the resistance between the second electrode 32 and the third electrode 33 changes depending on the third electrode 33 to which it is connected, so the power supply 51A is preferably a variable power supply that changes the applied voltage in stages.

[0074] The agitator 8 circulates the aqueous solutions FS, ES1, ES2, ES3, and ES4 in the tanks 11, 12, 13, 14, and 15, respectively. The lithium isotope enrichment apparatus 1B may further include a cooling device (not shown) for cooling the electrolyte membranes 22, 23, 24, and 25, as necessary. Because the tanks 12, 13, and 14 are narrow as described above, it is preferable that the cooling device be configured such that the treatment tank 7A has a double structure (jacket tank) and a refrigerant circulates inside it. The other elements are as described in the configuration of the lithium isotope enrichment apparatus 1.

[0075] The lithium isotope enrichment method by the lithium isotope enrichment apparatus 1B according to this modification is the same as the method by the lithium isotope enrichment apparatus 1. 7 Li, 6 A Li-containing aqueous solution FS containing Li at a natural abundance ratio is poured into the tank 10, and pure water is poured into the other tanks 12, 13, 14, and 15. As described above, the Li concentration in the electrolyte membrane 2 is + The mobility is calculated by the ratio of Li in the aqueous solution on the upstream side (supply side) to the + Therefore, immediately after the start of operation, the amount of Li in the aqueous solution ES1, which is pure water in the tank 12, is increased by 100%. + Li moves only in the electrolyte membrane 22. + Li in the aqueous solution ES1 + In order to achieve this, the power supply 51A connects the negative electrode to the third electrode 33 in the tank 12 and applies a voltage V1. + When the concentration reaches the predetermined value, the negative electrode of the power source 51A is connected to the third electrode 33 in the tank 13. Then, due to the electric field generated between the second electrode 32 and the third electrode 33 in the tank 13, Li is continuously transferred from the Li-containing aqueous solution FS to the aqueous solution ES in the tank 12. + As the aqueous solution ES moves, Li + At this time, it is preferable to increase the voltage of the power source 51A to maintain the electric field E1 generated in the aqueous solutions ES1 and ES2 between the second electrode 32 and the newly connected third electrode 33.

[0076] Li from the Li-containing aqueous solution FS to the aqueous solution ES1, and from the aqueous solution ES1 to the aqueous solution ES2 + The migration proceeds in parallel, and the aqueous solution ES2 + When the concentration reaches the predetermined value, the negative electrode of the power source 51A is connected to the third electrode 33 in the tank 14, and the voltage of the power source 51A is further increased to transfer Li from the aqueous solution ES to the aqueous solution ES in the tank 14. + This process is repeated until finally, as shown in FIG. 8, by connecting the negative electrode of the power source 51A to the third electrode 33 in the tank 15, Li + The aqueous solutions ES1, ES2, ES3, and ES4 in the tanks 12, 13, 14, and 15 change from pure water at the start of operation to 6 The resulting aqueous LiOH solutions contain different concentrations of Li with different Li isotope ratios. 6 The Li isotope ratio increases in the order FS<ES1<ES2<ES3<ES4. + Even if the isotope separation coefficient due to migration in one electrolyte membrane 2 is not large, 6 Li with a high Li isotope ratio can be recovered from the recovery tank 15.

[0077] The number of electrolyte membranes 2 in the lithium isotope enrichment device 1B is not particularly limited. 6 Li with a high Li isotope ratio can be recovered from the tank at the end on the recovery side. Although all adjacent electrolyte membranes 2, 2 are arranged facing each other in Fig. 8 , they may be bent at 90° at one or two locations and connected, so that adjacent electrolyte membranes 2, 2 are arranged perpendicular to each other. In the tank at the bent portion separated by the perpendicularly arranged electrolyte membranes 2, 2, the third electrode 33 is arranged parallel to the electrolyte membrane 2 on the supply side.

[0078] In the lithium isotope enrichment method using the lithium isotope enrichment apparatus 1B, the Li of the Li-containing aqueous solution FS is + maintain high concentrations of 6In order to suppress the decrease in the Li isotope ratio, it is preferable to replace the Li-containing aqueous solution FS in the supply tank 11 or circulate it with the outside of the treatment tank 7A during operation. Also, it is preferable to add water (HO) or the like to the tanks 12, 13, 14, and 15 as necessary during operation so that the liquid levels in the tanks 11, 12, 13, 14, and 15 are uniform. 6 The aqueous solutions ES1, ES2, ES3, and ES4 for recovering Li may contain a solute that lowers the freezing point below 0°C, and the electrolyte membranes 22, 23, 24, and 25 may be cooled to below 0°C and above the freezing point by a cooling device.

[0079] (Multistage Lithium Isotope Enrichment Apparatus) As described above, the lithium isotope enrichment apparatus 1 according to the first embodiment (see FIG. 1) is a multistage lithium isotope enrichment apparatus for recovering Li from the recovery tank 12. 6 The aqueous solution for Li recovery ES is introduced into the emptied supply tank 11 and operated, 6 An aqueous solution containing Li with a high Li isotope ratio is obtained. Therefore, the recovery tank 12 of the lithium isotope enrichment device 1 and the supply tank 11 of another lithium isotope enrichment device 1 are connected by a flow path such as a pipe, and the supply tank 11 is connected to the recovery tank 12. 6 By configuring the system so that the aqueous solution for Li recovery ES is supplied, 6 The recovery tank 12 can be a multi-stage lithium isotope enrichment device that enriches Li. 6 The aqueous solution ES for recovering Li may be pumped out by, for example, a pump or the like, or the aqueous solution ES may be circulated through an inclined pipe structure with the lithium isotope enrichment device 1 on the upstream side (supply side) installed at a relatively high position. The aqueous solution may be transferred between the lithium isotope enrichment devices 1, 1 at a constant flow rate or at regular intervals.

[0080] Furthermore, a miniaturized multistage lithium isotope enrichment apparatus can be obtained by forming a cascade structure in which the recovery tank 12 of one lithium isotope enrichment apparatus 1 is integrally connected to the supply tank 11 of another lithium isotope enrichment apparatus 1. Hereinafter, a multistage lithium isotope enrichment apparatus according to a first embodiment of the present invention will be described with reference to FIG.

[0081] A multistage lithium isotope enrichment apparatus 10 according to a first embodiment of the present invention includes a treatment tank 7A, three electrolyte membranes (lithium ion conductive electrolyte membranes) 22, 23, and 24 arranged in parallel at intervals so as to partition the treatment tank 7A in one direction into four tanks 11, 12, 13, and 14, a first electrode 31 arranged facing the front surfaces (left surfaces in the figure) of the electrolyte membranes 22, 23, and 24, a second electrode 32 covering the back surfaces of the electrolyte membranes 22, 23, and 24, a third electrode 33 arranged facing the second electrode 32, and three power sources 51. The multistage lithium isotope enrichment apparatus 10 further includes an agitator (circulation means) 8 in each of the tanks 11, 12, 13, and 14. The multistage lithium isotope enrichment apparatus 10 has a structure in which three lithium isotope enrichment apparatuses 1 are connected together so that each treatment tank 7 is integrated into treatment tank 7A, and the recovery tank 12 of one of two adjacent lithium isotope enrichment apparatuses 1, 1 is also used as the supply tank 11 of the other. Therefore, in the multistage lithium isotope enrichment apparatus 10, a third electrode 33 and a first electrode 31 are disposed in each of the tanks 12, 13 except for the tanks 11, 14 at both ends. When the electrolyte membranes 22, 23, 24 are not particularly identified, they will be referred to as the electrolyte membrane 2 as appropriate.

[0082] The tank 11 at the end of the supply tank 11 side of the lithium isotope enrichment apparatus 1 (the left side in FIG. 9 , hereinafter referred to as the supply side) is the supply tank 11 like the lithium isotope enrichment apparatus 1, and contains a Li-containing aqueous solution FS. Tanks 12, 13, and 14 are respectively: 6 Contains aqueous solutions ES1, ES2, and ES3 for recovering Li. 6 The aqueous solutions ES1, ES2, and ES3 for Li recovery are 6 Similarly to the Li recovery aqueous solution ES, the lithium ions Li recovered from the Li-containing aqueous solution FS + At the start of operation of the multistage lithium isotope enrichment apparatus 10, the aqueous solution is, for example, pure water. The side of the lithium isotope enrichment apparatus 1 on which the recovery tank 12 is located (the right side in FIG. 9 ) is referred to as the recovery side. In the multistage lithium isotope enrichment apparatus 10, the tank 14 at the end of the recovery side is the recovery tank.

[0083] In the multistage lithium isotope enrichment apparatus 10, a second electrode 32, a third electrode 33, and a first electrode 31 are arranged in each of the tanks 12 and 13, excluding the tanks 11 and 14 at both ends, in that order from the supply side. The third electrode 33 and the first electrode 31 in the tanks 12 and 13 are arranged with a sufficient distance between them, and therefore the tanks 12 and 13 are designed to have a sufficient length in the partition direction of the treatment tank 7A (the connecting direction, the left-right direction in FIG. 9). In more detail, the resistance ( 6 Resistance R of the portion of the Li recovery aqueous solution ES1, ES2 sandwiched between the third electrode 33 and the first electrode 31 ES ' is the resistance R between the second electrode 32 and the third electrode 33 ES , and the resistance (R FS +R EL ) (see FIG. 3 ), preferably by a larger difference. Note that, similarly to the lithium isotope enrichment device 1, the first electrode 31 may have a porous structure and be provided in contact with the surfaces of the electrolyte membranes 22, 23, and 24.

[0084] The power supply 51 is as described in the configuration of the lithium isotope enrichment apparatus 1. Preferably, the three power supplies 51 of the multistage lithium isotope enrichment apparatus 10 are configured so that they can be connected (driven) independently to the electrodes 31, 32, and 33. It is preferable that the power supplies 51 are not grounded, or that only one power supply in the multistage lithium isotope enrichment apparatus 10 is grounded. In FIG. 9, the positive electrode of the first power supply 51 from the supply side is grounded so that the Li-containing aqueous solution FS in the supply tank 11 is grounded to the reference potential. However, the resistance R between the third electrode 33 and the first electrode 31 in each of the tanks 12 and 13 is ES If ' is sufficiently high, each of the two or more power supplies 51 may be grounded.

[0085] The agitator 8 circulates the aqueous solutions FS, ES1, ES2, and ES3 in the tanks 11, 12, 13, and 14, respectively. The multistage lithium isotope enrichment apparatus 10 may further include a cooling device (not shown) for cooling the electrolyte membranes 22, 23, and 24, as necessary. The other elements are as described in the configuration of the lithium isotope enrichment apparatuses 1 and 1B.

[0086] (Method of Enriching Lithium Isotopes by a Multistage Lithium Isotope Enrichment Apparatus) The method of enriching lithium isotopes by the multistage lithium isotope enrichment apparatus 10 is the same as the method by the lithium isotope enrichment apparatuses 1 and 1B. 7 Li, 6 A Li-containing aqueous solution FS containing Li at a natural abundance ratio is introduced into the tank 11, and pure water is introduced into the other tanks 12, 13, and 14. Then, just as in the lithium isotope enrichment method using the lithium isotope enrichment apparatus 1B (see FIG. 8), immediately after the start of operation, Li is introduced from the Li-containing aqueous solution FS in the supply tank 11 into the aqueous solution ES1, which is pure water in the tank 12. + Li moves only in the electrolyte membrane 22. + Li in the aqueous solution ES1 + It is preferable to increase the concentration. For this purpose, only the first power supply 51 on the supply side is driven. Then, the aqueous solution ES1 is turned on to obtain a predetermined Li concentration. + When the concentration reaches the predetermined value, the second power supply 51 on the supply side is driven to supply Li from the aqueous solution ES1 to the aqueous solution ES2 in the tank 13. + Start moving.

[0087] Li from the Li-containing aqueous solution FS to the aqueous solution ES1, and from the aqueous solution ES1 to the aqueous solution ES2 + The migration proceeds in parallel, and the aqueous solution ES2 + When the concentration reaches the predetermined value, the third power supply 51 on the supply side is driven to supply Li from the aqueous solution ES to the aqueous solution ES in the tank 14. + In this way, by finally driving all the power supplies 51 of the multistage lithium isotope enrichment apparatus 10, the Li isotope + The aqueous solutions ES1, ES2, and ES3 in the tanks 12, 13, and 14 change from pure water at the start of operation to 6The resulting aqueous LiOH solutions contain different concentrations of Li with different Li isotope ratios. 6 The Li isotope ratio increases in the order FS < ES1 < ES2 < ES3. + Even if the isotope separation coefficient due to migration in one electrolyte membrane 2 is not large, 6 Li with a high Li isotope ratio can be recovered from the recovery tank 14.

[0088] The multistage lithium isotope enrichment apparatus 10 is designed so that, during operation, substantially no electric field is generated between the third electrode 33 and the first electrode 31 of each of the vessels 12 and 13, or, if an electric field is generated, the electric field is sufficiently weaker than the electric field +E1 (see FIG. 2 ) generated between the second electrode 32 and the third electrode 33 in the same vessel. To achieve this, as described above, the third electrode 33 and the first electrode 31 are spaced apart sufficiently widely. With this configuration, two or more adjacent power supplies 51 can be driven simultaneously.

[0089] In the lithium isotope enrichment method using the multistage lithium isotope enrichment device 10, the Li of the Li-containing aqueous solution FS is + maintain high concentrations of 6 In order to suppress a decrease in the Li isotope ratio, it is preferable to replace the Li-containing aqueous solution FS in the supply tank 11 or circulate it with the outside of the treatment tank 7A during operation. It is also preferable to add water (HO) or the like to the tanks 12, 13, and 14 as necessary during operation so that the liquid levels in the tanks 11, 12, 13, and 14 are uniform.

[0090] The multistage lithium isotope enrichment device 10 does not have a specific number of electrolyte membranes 2 and electrodes 31, 32, and 33 provided for each electrolyte membrane 2. The larger the number, i.e., the more lithium isotope enrichment devices 1 are connected, the more efficient the lithium isotope enrichment device 1 becomes. 6Li with a high Li isotope ratio can be recovered from the tank at the end on the recovery side. Furthermore, in Fig. 9, the lithium isotope enrichment device 1 is connected in one direction, and all adjacent electrolyte membranes 2, 2 are arranged facing each other. However, for example, the lithium isotope enrichment device 1 may be connected by bending at 90° at one or two locations, and adjacent electrolyte membranes 2, 2 may be arranged perpendicular to each other. In the bent tank separated by the perpendicularly arranged electrolyte membranes 2, 2, the third electrode 33 and the first electrode 31 are also arranged perpendicular to each other. Therefore, it is preferable to arrange them so that the distance between them at the shortest part on the inside of the bend is sufficiently long.

[0091] Two or more lithium isotope enrichment apparatuses 1A (see FIG. 7) according to the modified example of the first embodiment can also be connected to integrate their respective treatment tanks 7 to form a multistage lithium isotope enrichment apparatus. Furthermore, one or more lithium isotope enrichment apparatuses 1 and one or more lithium isotope enrichment apparatuses 1A can also be connected to form a multistage lithium isotope enrichment apparatus.

[0092] [Second embodiment] As described in the first embodiment, during operation, the Li-containing aqueous solution FS contains Li + Therefore, it is preferable to maintain a high concentration. In addition to replacing the Li-containing aqueous solution FS in the supply tank 11 or circulating it with the outside of the treatment tank 7, it is possible to easily change the Li concentration of the Li-containing aqueous solution FS without significantly expanding the apparatus. + In order to maintain the concentration, the following configuration is adopted: A lithium isotope enrichment device according to a second embodiment of the present invention will now be described.

[0093] 10 , a lithium isotope enrichment apparatus 1C according to a second embodiment of the present invention includes a treatment tank 7B, an electrolyte membrane (lithium ion conductive electrolyte membrane for lithium replenishment) 21, an electrolyte membrane (lithium ion conductive electrolyte membrane) 22, a first electrode 31, a second electrode 32, a third electrode 33, a fourth electrode 41, a fifth electrode 42, a power source 51, a power source (lithium replenishment power source) 53, and an agitator (circulation means) 8. The treatment tank 7B is divided into a replenishment tank (lithium replenishment tank) 1z that contains a Li-containing aqueous solution FS′, a supply tank (first tank) 11 that contains a Li-containing aqueous solution FS, and a second tank 12 that contains a Li-containing aqueous solution FS, by the electrolyte membranes 21 and 22. 6and a recovery tank (second tank) 12 that stores an aqueous Li recovery solution ES. The lithium isotope enrichment apparatus 1C is configured such that, compared to the lithium isotope enrichment apparatus 1 (see FIG. 1 ) according to the first embodiment, an electrolyte membrane 21 that separates the treatment tank 7B with a supply tank 11 made of an electrolyte membrane 22, electrodes 41, 42 provided in each of a replenishing tank 1z and the supply tank 11 that are separated from the supply tank 11 by the electrolyte membrane 21, and a power supply 53 connected between the electrodes 41, 42. The remaining configuration is the same as that of the lithium isotope enrichment apparatus 1 according to the first embodiment, and may include a cooling device, a liquid level sensor, an exhaust means, and the like, as necessary.

[0094] The portion of the lithium isotope enrichment apparatus 1C that is composed of the refilling tank 1z, the supply tank 11, the electrolyte membrane 21 separating them, and the electrodes 41, 42, and the power supply 53 is a lithium recovery apparatus that uses a lithium ion conductive electrolyte membrane, similar to the lithium isotope enrichment apparatus 1 (see, for example, Patent Documents 2 and 3). This lithium recovery apparatus transfers lithium ions from the Li-containing aqueous solution FS' contained in the refilling tank 1z to the Li-containing aqueous solution FS contained in the supply tank 11. That is, the lithium isotope enrichment apparatus 1C according to this embodiment is an apparatus with a cascade structure in which the lithium recovery apparatus and the lithium isotope enrichment apparatus 1 according to the first embodiment are connected by integrating their respective treatment tanks with the supply tank 11.

[0095] The electrolyte membrane 22 has the same configuration as the electrolyte membrane 2 of the lithium isotope enrichment device 1 according to the above embodiment. The electrolyte membrane 21 may also have the same configuration as the electrolyte membrane 22.

[0096] The fourth electrode 41 and the fifth electrode 42 are a pair of electrodes for applying a voltage between both sides of the electrolyte membrane 21. The fourth electrode 41 is provided in the refill tank 1z, and the fifth electrode 42 is provided in the supply tank 11, each in contact with or facing the electrolyte membrane 21. Preferably, one or both of the fourth electrode 41 and the fifth electrode 42 have a porous structure and are in contact with the electrolyte membrane 21. More preferably, one of the electrodes is in contact with the electrolyte membrane 21. It is even more preferable that the fourth electrode 41 is in contact with the electrolyte membrane 21, as shown in FIG. 10 (see Patent Document 3). By having at least one of the electrodes 41, 42 in contact with the electrolyte membrane 21, a voltage can be applied across a wide area of ​​the electrolyte membrane 21. Furthermore, because one of the electrodes 41, 42 is in contact with the electrolyte membrane 21 and the other is spaced apart, even if the voltage V3 applied by the power supply 53 connected between the electrodes 41, 42 is relatively large, the potential difference between the two surfaces of the electrolyte membrane 21 is suppressed, and as will be described later, a decrease in the energy efficiency of Li movement in the electrolyte membrane 21 can be suppressed.

[0097] As described above, the fourth electrode 41 is provided in contact with the surface (surface) of the electrolyte membrane 21 facing the refill tank 1z, and has a porous structure, such as a mesh structure, similar to the second electrode 32, so that a voltage can be applied to a wide area of ​​the electrolyte membrane 21 while the Li-containing aqueous solution FS' contacts a sufficient area of ​​the surface of the electrolyte membrane 21. The fourth electrode 41 is formed of an electrode material that is electronically conductive and stable in the Li-containing aqueous solution FS' even when a voltage is applied, and preferably has catalytic activity for the reactions of the following formulas (1) and (3), and is also preferably a material that can be easily processed into the above shape. Platinum (Pt), for example, is a preferred electrode material for the fourth electrode 41.

[0098] The fifth electrode 42 is disposed in the supply tank 11 so as not to contact the electrolyte membrane 21, preferably at a short distance from the electrolyte membrane 21, and preferably parallel to the electrolyte membrane 21. Like the first electrode 31, the fifth electrode 42 has a large contact area with the Li-containing aqueous solution FS and preferably has a mesh-like shape through which the aqueous solution can pass, so that the Li-containing aqueous solution FS in contact with the surface of the electrolyte membrane 2 in the supply tank 11 is continuously replaced. The fifth electrode 42 is formed of an electrode material that is electronically conductive and stable even when a voltage is applied with the Li-containing aqueous solution FS. Furthermore, like the third electrode 33, the fifth electrode 42 is preferably a material that has catalytic activity for the reaction of the following formula (2). Platinum (Pt) is a preferred example of such an electrode material. Alternatively, the fifth electrode 42 can be made of carbon (C), copper (Cu), or stainless steel, which are stable at potentials lower than the potential at which the reaction of the following formula (2) occurs. Preferably, these electrodes have Pt fine particles, which function as a catalyst, supported on their surfaces. The fifth electrode 42 may have a porous structure similar to the fourth electrode 41 and be provided in contact with the electrolyte membrane 21 .

[0099] Furthermore, in the lithium isotope enrichment apparatus 1C, the fifth electrode 42 and the first electrode 31 are disposed in one supply tank 11. The supply tank 11 is designed to have a sufficient length in the partition direction (between the electrolyte membranes 21, 22) so that the fifth electrode 42 and the first electrode 31 are disposed with a sufficient distance between them. More specifically, even if the first electrode 31 is connected to a power source 51 and the fifth electrode 42 is connected to a power source 53, the supply tanks 11 are designed so that substantially no electric field is generated between the fifth electrode 42 and the first electrode 31, or even if an electric field is generated, the electric field is sufficiently weak so as not to inhibit the reactions near the fifth electrode 42 and the first electrode 31.

[0100] The power supply 53 is a DC power supply similar to the power supply 51, and has a positive electrode connected to the fourth electrode 41 and a negative electrode connected to the fifth electrode 42, and applies a positive voltage V3 (voltage +V3) to the fourth electrode 41 with respect to the fifth electrode 42. + The power supply 53 may be a variable power supply so that the mobility can be adjusted.

[0101] The Li-containing aqueous solution FS' is obtained by adding the Li to the Li-containing aqueous solution FS during the operation of the lithium isotope enrichment apparatus 1C. + The Li-containing aqueous solution FS′ is a Li source that supplies Li to maintain a high concentration. 7 Li and 6 Li cation 7 Li + , 6 Li + The aqueous solution containing Li is, for example, an aqueous solution of lithium hydroxide (LiOH) similar to the Li-containing aqueous solution FS. The Li-containing aqueous solution FS' is, for example, an aqueous solution of Li + If the concentration is low, Li in the electrolyte membrane 21 + Since the mobility is low, it is preferable that the mobility is higher at the start of operation of the lithium isotope enrichment apparatus 1C. + It is more preferable that the Li-containing aqueous solution FS is a saturated or supersaturated aqueous solution of the above. 6 As in the first embodiment, the aqueous solution ES for Li recovery is, for example, a saturated or supersaturated aqueous solution of LiOH and pure water at the start of operation of the lithium isotope enrichment apparatus 1C.

[0102] (Lithium isotope enrichment method) A lithium isotope enrichment method using a lithium isotope enrichment apparatus according to a second embodiment of the present invention will be described with reference to Fig. 11. In the lithium isotope enrichment apparatus 1C according to this embodiment, 6 Li in aqueous solution ES for Li recovery + The movement is the same as in the first embodiment (see FIGS. 2 and 4A to 4C). Here, Li is transferred from the Li-containing aqueous solution FS′ in the replenishing tank 1z to the Li-containing aqueous solution FS in the supply tank 11. + The movement will be described below. Note that the agitator 8 is omitted in FIG.

[0103] As shown in FIG. 11 , in the lithium isotope enrichment apparatus 1C, the power supply 53 applies a positive voltage V3 (voltage +V3) to the fourth electrode 41 relative to the fifth electrode 42. Then, the following reaction occurs in the replenishing tank 1z. In the vicinity of the fourth electrode 41, hydroxide ions (OH - ) undergoes the reaction of the following formula (1), and electrons e- is released to the fourth electrode 41, generating water (H2O) and oxygen (O2), and - In the Li-containing aqueous solution FS', OH - As the charge imbalance decreases, Li + The reaction of the following formula (3), in which the compound (II) dissolves in the electrolyte membrane 21 , occurs on the surface of the electrolyte membrane 21 , i.e., in the vicinity of the fourth electrode 41 .

[0104] On the other hand, the application of the voltage +V3 causes the following reaction in the supply tank 11: H2O in the Li-containing aqueous solution FS converts electrons e - By supplying H and OH, the reaction of the following formula (2) occurs. - Then, OH - As the amount of Li increases, the amount of Li in the electrolyte membrane 21 increases in order to maintain the charge balance. + The reaction of the following formula (4) occurs near the back surface of the electrolyte membrane 21. As a result, the Li contained in the Li-containing aqueous solution FS', the electrolyte membrane 21, and the Li-containing aqueous solution FS near the electrolyte membrane 21 + Due to the electrochemical potential difference, Li is released from the Li-containing aqueous solution FS'. + permeates the electrolyte membrane 21 and moves to the Li-containing aqueous solution FS.

[0105] From the reaction of formula (3) to the reaction of formula (4), that is, Li in the Li-containing aqueous solution FS′ + penetration of the electrolyte membrane 21 from the surface to the inside, + and Li in the electrolyte membrane 21 + The transfer of Li to the Li-containing aqueous solution FS is + This is the same as the movement of Li to the Li-containing aqueous solution FS via the electrolyte membrane 21 (electrolyte membrane 2), as described in the first embodiment. However, in the electrolyte membrane 21, the application of the voltage +V3 creates a potential gradient where the potential on the supply tank 11 side is low, so that Li + Regardless of the concentration gradient of Li on the supply tank 11 side, that is, between both sides of the electrolyte membrane 21 + Even if the concentration is high, the electrolyte membrane 21 +moves from the replenishing tank 1z side to the supply tank 11 side.

[0106] The larger the voltage V3, the greater the Li in the electrolyte membrane 21. + Since the mobility is high (see FIG. 6), Li + It is preferable to set the voltage V3 in accordance with the mobility. + Li in the electrolyte membrane 21 due to the electrochemical potential difference + The mobility is higher than that of Li in the electrolyte membrane 22 due to the chemical potential difference alone. + 11, during operation of the lithium isotope enrichment apparatus 1C (while the power supply 51 is running), the power supply 53 is constantly driven to continuously add Li to the Li-containing aqueous solution FS. + Alternatively, the power source 53 may be driven for a short time at regular intervals, and a large voltage V3 may be applied to add Li to the Li-containing aqueous solution FS. + can be moved at high speed.

[0107] Here, the voltage V3 is large, and the potential difference between the two surfaces is large enough to reduce some of the transition metal ions constituting the electrolyte membrane 21 (for example, if the electrolyte membrane 21 is LLTO, Ti 4+ +e - →Ti 3+ ) voltage or more, the electrolyte membrane 21 exhibits electronic conductivity. Then, the electrons e - generates Joule heat, so Li + The energy efficiency in the movement drops sharply, and even if the voltage V3 is further increased, the increase + The mobility does not increase. Specifically, although it depends on the electronic conductivity of the electrolyte membrane 21 and the electrode performance that determines the electrode reaction overvoltage, when a voltage exceeding 2.0 V is applied as a potential difference between the two surfaces of the electrolyte membrane 21, electronic conductivity may be exhibited in the electrolyte membrane 21. In the lithium isotope enrichment device 1C, one of the electrodes 41, 42 that sandwich the electrolyte membrane 21 from both sides is disposed away from the electrolyte membrane 21. Therefore, even if the voltage V3 is increased to a certain extent, the potential difference between the two surfaces of the electrolyte membrane 21 is unlikely to reach this voltage, but if it is further increased, it will reach this voltage, so it is preferable to set it at or below this voltage.

[0108] According to the lithium isotope enrichment apparatus 1C of this embodiment, the Li-containing aqueous solution FS is constantly or periodically 6 Li isotope ratio is natural ratio Li + Since the amount of Li in the Li-containing aqueous solution FS is replenished, + Maintain high concentrations of 6 Since the rate of decrease in the Li isotope ratio can be slowed down, long-term continuous operation is possible without circulating the Li-containing aqueous solution FS with the outside. However, if the operation continues for a certain period of time, a large amount of Li remaining in the Li-containing aqueous solution FS will 7 Li + By 6 The Li isotope ratio is significantly lower than the natural ratio, and the Li of the Li-containing aqueous solution FS' is + The concentration of Li in the electrolyte membrane 21 decreases to + Since the mobility decreases and the energy efficiency decreases, it is preferable to replace the Li-containing aqueous solutions FS' and FS in the replenishing tank 1z and the supply tank 11.

[0109] (First Modification) The lithium isotope enrichment apparatus 1C according to this embodiment is configured to add Li to the Li-containing aqueous solution FS by a known lithium recovery method. + Therefore, the Li to be replenished in the Li-containing aqueous solution FS is + However, Li can be recovered from seawater. + In low concentration aqueous solutions, Li + The mobility of Li on the surface of the electrolyte membrane 21 + Since the rate is limited by the diffusion of Li, it is difficult to increase the voltage V3, and the energy efficiency is low. Furthermore, chloride ions contained in seawater deteriorate the catalytic activity of the fourth electrode 41 and are adsorbed on the surface of the electrolyte membrane 21, resulting in the formation of Li + The mobility decreases. + Li from an aqueous solution containing a low concentration of + In order to efficiently replenish the

[0110] 12 , a lithium isotope enrichment apparatus 1D according to a first modification of the second embodiment of the present invention includes a treatment tank 7B, an electrolyte membrane (lithium ion conductive electrolyte membrane for lithium replenishment) 21, an electrolyte membrane (lithium ion conductive electrolyte membrane) 22, a first electrode 31, a second electrode 32, a third electrode 33, a fourth electrode 41, a fifth electrode 42, a sixth electrode 44, a power source 51, a power source (lithium replenishment power source) 53, a power source 55, an ion exchange membrane 6, and an agitator (circulation means) 8. The treatment tank 7B is circulated by the ion exchange membrane 6 and the electrolyte membranes 21, 22 into a raw material tank 1y containing a Li-containing aqueous solution SW, a replenishment tank (lithium replenishment tank) 1z containing a Li-containing aqueous solution FS′, a supply tank (first tank) 11 containing a Li-containing aqueous solution FS, 6 and a recovery tank (second tank) 12 for storing an aqueous Li recovery solution ES. The lithium isotope enrichment apparatus 1D is configured by adding an ion exchange membrane 6 that separates the treatment tank 7B from the replenishment tank 1z side of the electrolyte membrane 21, a sixth electrode 44 provided in the raw material tank 1y separated from the replenishment tank 1z by the ion exchange membrane 6, and a power supply 55 connected between the electrodes 44 and 41 to the lithium isotope enrichment apparatus 1C according to the second embodiment (see FIG. 10 ). Note that in the lithium isotope enrichment apparatus 1D, the fourth electrode 41 is provided in contact with the surface of the electrolyte membrane 21 facing the replenishment tank 1z. The remaining configuration is the same as that of the lithium isotope enrichment apparatus 1C according to the previous embodiment, and may include a cooling device, a liquid level sensor, an exhaust means, and the like, as necessary.

[0111] The ion exchange membrane 6 is Li + As a result, the Li-containing aqueous solution FS' in the replenishing tank 1z conducts cations containing at least Cl. - The ion exchange membrane 6 is a cation exchange membrane that allows cations to pass through and blocks anions, and a Li + , K + , Na +Examples of suitable ion exchange membranes include monovalent cation-permselective ion exchange membranes that allow only monovalent cations to pass through, such as monovalent cations (e.g., monovalent cations), and bipolar monovalent ion-permselective ion exchange membranes that allow only monovalent ions to pass through. These ion exchange membranes may be known, such as SELEMION (registered trademark) CMV (manufactured by AGC Engineering Co., Ltd.) and NEOSEPTA CSE (manufactured by ASTOM Corporation) as cation exchange membranes, SELEMION (registered trademark) CSO (manufactured by AGC Engineering Co., Ltd.) as monovalent cation-permselective ion exchange membranes, and NEOSEPTA CIMS (manufactured by ASTOM Corporation) as bipolar monovalent ion-permselective ion exchange membranes. In the lithium isotope enrichment apparatus 1D, a short distance between the sixth electrode 44 and the fourth electrode 41 is preferred. Therefore, the ion exchange membrane 6 is preferably positioned so as to shorten the distance from the electrolyte membrane 21 (fourth electrode 41). Therefore, the replenishing tank 1z is preferably short in the direction of the partition of the treatment tank 7B.

[0112] The sixth electrode 44 is paired with the fourth electrode 41 to detect Li in the Li-containing aqueous solution SW. + The sixth electrode 44 is an electrode for transferring cations including cations (including cations of ... - ), the sixth electrode 44 is preferably made of a material having catalytic activity for the reaction of the following formula (11): As such an electrode material, for example, carbon (C), platinum (Pt), or carbon supporting platinum fine particles as a catalyst is preferable.

[0113] The power supply 55 is a DC power supply similar to the power supply 53, and has a positive electrode connected to the sixth electrode 44 and a negative electrode connected to the fourth electrode 41, i.e., connected in series to the positive electrode of the power supply 53. The power supply 55 applies a voltage V5 to generate an electric field E3 (see FIG. 13) in the Li-containing aqueous solution SW, FS', thereby + The cations containing Li are moved to the Li-containing aqueous solution FS', and the surface of the electrolyte membrane 21 is set to a relatively low potential in the Li-containing aqueous solution FS'. + The power supplies 53 and 55 are preferably configured to be capable of being turned on and off independently of each other.

[0114] The Li-containing aqueous solution SW is added to the Li-containing aqueous solution FS during the operation of the lithium isotope enrichment device 1D. + The Li-containing aqueous solution SW is a Li source that supplies Li via the Li-containing aqueous solution FS' to maintain a high concentration. + In addition to that, K + , Na + , Ca 2+ Other metal ions M such as n+ Examples of such aqueous solutions include seawater, brine discarded after extracting salt from seawater, groundwater such as hot spring water, and an aqueous solution obtained by crushing used lithium ion secondary batteries and dissolving them in acid and then adjusting the pH. The Li-containing aqueous solution FS' is, as in the above embodiment, 7 Li and 6 Li cation 7 Li + , 6 Li + The aqueous solution containing the lithium isotope enrichment device 1D may be pure water before starting operation (isotope enrichment). 6 As in the first embodiment, the aqueous solution ES for Li recovery is, for example, a saturated or supersaturated aqueous solution of LiOH and pure water at the start of operation of the lithium isotope enrichment apparatus 1D.

[0115] A lithium isotope enrichment method using a lithium isotope enrichment apparatus according to a first modified example of the second embodiment of the present invention will be described with reference to Fig. 13. In the lithium isotope enrichment apparatus 1D according to this modified example, pure water is contained in the replenishing tank 1z as the Li-containing aqueous solution FS', and first, the power supply 55 is driven to extract Li from the Li-containing aqueous solution SW contained in the raw material tank 1y. + Li in the Li-containing aqueous solution FS' is transferred by transferring cations including + When the concentration of Li reaches a certain level, it is preferable to start driving the power supply 53. Hereinafter, the Li concentration of the Li-containing aqueous solution FS′ in the replenishing tank 1z to the Li-containing aqueous solution FS in the supply tank 11 will be referred to as the Li concentration. + The movement will be described below. Note that the agitator 8 is omitted in FIG.

[0116] In the lithium isotope enrichment apparatus 1D, the power supplies 55 and 53 connected in series can be regarded as one power supply (referred to as power supply 55-53). The power supply 55-53 applies a positive voltage (V5+V3) to the sixth electrode 44 with respect to the fifth electrode 42. At the same time, the power supply 53 applies a positive voltage V3 to the fourth electrode 41 with respect to the fifth electrode 42. Then, the following reactions occur in the raw material tank 1y and the replenishing tank 1z. In the vicinity of the sixth electrode 44 and the fourth electrode 41, the OH in the Li-containing aqueous solutions SW and FS' is converted into OH. - The reaction of the following formula (1) occurs, and electrons e - Electrons e are released to the sixth electrode 44 and the fourth electrode 41 to generate H2O and O2. - The Li-containing aqueous solution SW releases Cl. - When the electrons are included in the electron transport layer 44, the reaction of the following formula (11) further occurs near the sixth electrode 44, and electrons e - In the Li-containing aqueous solution SW, OH - As the amount of anions and other negative ions decreases, the positive ions Li + and M n+ moves to the Li-containing aqueous solution FS'. In the Li-containing aqueous solution FS', OH - As the charge balance decreases, Li +The reaction of the following formula (3), in which the ions migrate into the electrolyte membrane 21 , occurs on the surface of the electrolyte membrane 21 , i.e., in the vicinity of the fourth electrode 41 .

[0117] Furthermore, an electric field E3 is generated between the electrodes 44, 41 of the Li-containing aqueous solution SW, FS′ by application of a voltage V5 from the power source 55, and a potential gradient is formed in which the sixth electrode 44 has a higher potential than the surface of the electrolyte membrane 21 on which the fourth electrode 41 is provided. - and Cl - is attracted to the sixth electrode 44 by electrostatic attraction. + The cations containing the cations permeate the ion exchange membrane 6 and are attracted to the surface of the electrolyte membrane 21 .

[0118] Meanwhile, in the supply tank 11, the following reaction occurs as in the previous embodiment: Near the fifth electrode 42, H O in the Li-containing aqueous solution FS converts electrons e - By supplying H and OH, the reaction of the following formula (2) occurs. - Then, OH - As the amount of Li increases, the amount of Li in the electrolyte membrane 21 increases in order to maintain the charge balance. + The reaction of the following formula (4) occurs in the vicinity of the electrolyte membrane 21 .

[0119] In the lithium isotope enrichment apparatus 1D according to this modification, as described above, a potential gradient is formed in the Li-containing aqueous solution FS' by applying the voltage V5 from the power supply 55, and thus the cations Li + is attracted to the surface of the electrolyte membrane 21 (fourth electrode 41) by electrostatic attraction, and becomes relatively concentrated in this vicinity. + Even at low concentrations, Li + can be sufficiently diffused to the surface of the electrolyte membrane 21, and Li in the electrolyte membrane 21 + The mobility does not decrease.

[0120] The stronger the electric field E3, the + is attracted to the surface of the electrolyte membrane 21 and +However, when the voltage V5 is increased to strengthen the electric field E3 and reach the voltage at which water electrolysis occurs (+1.229 V vs. SHE, 25°C), the reaction of formula (2) occurs in the Li-containing aqueous solution FS' near the fourth electrode 41, generating H2. This reaction involves the electron e - Therefore, the reaction of the above formula (1) in the vicinity of the fourth electrode 41 is different from the reaction of the above formula (1) in - When the vicinity of the fourth electrode 41, i.e., the surface of the electrolyte membrane 21 on the side of the refill tank 1z, reaches the H generating potential, some of the transition metal ions constituting the electrolyte membrane 21 are reduced (for example, if the electrolyte membrane 21 is LLTO, Ti 4+ +e - →Ti 3+ ) potential, and the electrolyte membrane 21 exhibits electron transfer properties. As a result, as described above, + The energy efficiency of the transfer of hydrogen rapidly decreases. Therefore, voltage V5 is set to be lower than the voltage at which H2 is generated near the fourth electrode 41 (see Patent Document 5). The voltage at which H2 is generated is actually approximately the theoretical voltage for water electrolysis under standard conditions or several hundred mV higher, depending on the electrode performance that determines the electrode reaction overvoltage of each of the electrodes (electrodes 44 and 41 for voltage V5) and the pH of the solution near the electrodes. Furthermore, in this modified example, even if voltage V5 is equal to or higher than the aforementioned value, if voltage V3 is somewhat higher than voltage V5, the potential of the surface of electrolyte membrane 21 on the raw material tank 1y side (high potential side) does not decrease below the H2 generation potential, and H2 is not generated.

[0121] Furthermore, when the voltage V5 exceeds a certain magnitude relative to the potential difference between the two surfaces of the electrolyte membrane 21, a current flows from the fourth electrode 41 to the negative electrode of the power source 55, that is, the fourth electrode 41 generates electrons e -, and the reaction of formula (2) occurs nearby, generating H2. As a result, electron transfer properties are exhibited in the electrolyte membrane 21. Therefore, it is preferable that the voltage V5 is large enough to prevent current from flowing from the fourth electrode 41 toward the negative electrode of the power source 55. To achieve this, for example, an ammeter may be connected in series to the fourth electrode 41 (connecting the ammeter between the fourth electrode 41 and the connection between the power sources 55 and 53) and voltages V3 and V5 may be applied while measuring the current (see Patent Document 5).

[0122] In the lithium isotope enrichment apparatus 1D according to this modification, the raw material tank 1y may be open to the sea or the like via a filter or the like. Furthermore, the lithium isotope enrichment apparatus 1D may not include the ion exchange membrane 6, i.e., the treatment tank 7B may be partitioned into three compartments, as in the lithium isotope enrichment apparatus 1C according to the previous embodiment, and seawater or the like may be stored in the replenishing tank 1z as the Li-containing aqueous solution FS'. Application of a voltage V5 causes Cl in the Li-containing aqueous solution FS' to be removed. - Since anions such as Cl are repelled from the fourth electrode 41 and the electrolyte membrane 21, the anions such as Cl are repelled from the fourth electrode 41 and the electrolyte membrane 21 even without the ion exchange membrane 6. - is difficult to be adsorbed on the surface of the electrolyte membrane 21, and the fourth electrode 41 is - Since the electrolyte membrane 21 is not easily deteriorated by Li, + The mobility does not decrease. + is attracted to the fourth electrode 41, i.e., the surface of the electrolyte membrane 21, and Li + Furthermore, the absence of the ion exchange film 6 makes it possible to strengthen the electric field E3 relative to the voltage V5.

[0123] According to the lithium isotope enrichment apparatus 1D of this modification, Li is added to the Li-containing aqueous solution FS from the Li-containing aqueous solution SW such as seawater. + Therefore, for the Li-containing aqueous solution FS, before the operation (isotope enrichment) of the lithium isotope enrichment apparatus 1D is started, pure water is stored in the supply tank 11, and Li is supplied from the Li-containing aqueous solution SW via the Li-containing aqueous solution FS′. +In other words, the lithium isotope enrichment apparatus 1D can be a cascade structure lithium recovery / isotope enrichment combined apparatus in which the lithium recovery apparatus, the lithium isotope enrichment apparatus 1, and the treatment tank are integrated. In this case, first, the power sources 53 and 55 are driven to convert the Li-containing aqueous solution FS into the target Li. + After the LiOH aqueous solution is adjusted to a certain concentration (for example, a saturated LiOH aqueous solution), the power supply 51 is driven to start isotope enrichment.

[0124] (Second Modification) The lithium isotope enrichment apparatus 1D according to the above modification can be a combined lithium recovery and isotope enrichment apparatus. However, when converting a high-concentration Li solution such as a saturated aqueous solution of LiOH from pure water, + To make an aqueous solution, a large amount of Li + Therefore, it takes time to start isotope enrichment. + In order to increase the mobility, the following configuration was adopted.

[0125] 14 , a lithium isotope enrichment apparatus 1E according to a second modification of the second embodiment of the present invention includes a treatment tank 7B, an electrolyte membrane (lithium ion conductive electrolyte membrane for lithium replenishment) 21, an electrolyte membrane (lithium ion conductive electrolyte membrane) 22, a first electrode 31, a second electrode 32, a third electrode 33, a fourth electrode 41, a fifth electrode 42A, an auxiliary electrode 43, a sixth electrode 44, an auxiliary electrode 43, a power source 51, a power source (lithium replenishment power source) 53, a power source 54, a power source 55, an ion exchange membrane 6, and an agitator (circulation means) 8. The treatment tank 7B is configured by the ion exchange membrane 6 and the electrolyte membranes 21, 22 to contain a raw material tank 1y containing a Li-containing aqueous solution SW, a replenishment tank (lithium replenishment tank) 1z containing a Li-containing aqueous solution FS′, a supply tank (first tank) 11 containing a Li-containing aqueous solution FS, 6and a recovery tank (second tank) 12 that stores the Li recovery aqueous solution ES. The lithium isotope enrichment apparatus 1E is configured such that, compared to the lithium isotope enrichment apparatus 1D (see FIG. 12 ) according to the first modified example of the second embodiment, a fifth electrode 42A has a porous structure similar to the fourth electrode 41 and is in contact with the electrolyte membrane 21, a sub-electrode 43 is provided in the supply tank 11 facing the fifth electrode 42A and spaced apart from the electrolyte membrane 21 and the fifth electrode 42A, and a power source 54 is connected between the electrodes 42A and 43. The rest of the configuration is the same as that of the lithium isotope enrichment apparatus 1D according to the modified example, and may include a cooling device, a liquid level sensor, an exhaust means, and the like, as necessary.

[0126] The fifth electrode 42A is an electrode paired with the fourth electrode 41 for applying a voltage between both surfaces of the electrolyte membrane 21 and for relatively increasing the potential of the surface (back surface) of the electrolyte membrane 21 facing the supply tank 11 in the Li-containing aqueous solution FS. To this end, the fifth electrode 42A has a porous structure and is provided in contact with the surface of the electrolyte membrane 21 facing the supply tank 11. The fifth electrode 42A is formed of an electrode material that is electronically conductive and stable in the Li-containing aqueous solution FS even when a voltage is applied. The fifth electrode 42A is preferably formed of a material that has catalytic activity for the reactions of the following formulas (1) and (4), and is also preferably a material that can be easily processed into the above-described shape. Platinum (Pt), for example, is a preferred electrode material for the fifth electrode 42A.

[0127] The auxiliary electrode 43 is an electrode for forming a lower potential than the back surface of the electrolyte membrane 21 in the Li-containing aqueous solution FS and is also an electrode paired with the fourth electrode 41 for applying a voltage. Therefore, the auxiliary electrode 43 is preferably arranged in the supply tank 11 facing the fifth electrode 42A without contacting the electrolyte membrane 21 or the fifth electrode 42A, and is preferably arranged parallel to the fifth electrode 42A. Furthermore, as described below, the auxiliary electrode 43 is preferably arranged close enough to the fifth electrode 42A to prevent short-circuiting. Furthermore, the auxiliary electrode 43 preferably has a mesh-like shape or the like to increase the contact area with the Li-containing aqueous solution FS. The auxiliary electrode 43 is preferably formed from an electrode material that is electronically conductive and stable in the Li-containing aqueous solution FS even when a voltage is applied, and further preferably has catalytic activity for the reaction represented by the following formula (2). Platinum (Pt), for example, is a preferred electrode material for the auxiliary electrode 43. Alternatively, the auxiliary electrode 43 may be made of carbon (C), copper (Cu), or stainless steel, which are stable at a potential lower than the potential at which the reaction of the following formula (2) occurs. It is more preferable that these materials have Pt fine particles, which function as a catalyst, supported on their surfaces.

[0128] The power supply 54 is a DC power supply like the power supply 53, and has a positive electrode connected to the fifth electrode 42A and a negative electrode connected to the sub-electrode 43, i.e., connected in series to the negative electrode of the power supply 53. The power supply 54 applies a voltage V4 to create a lower potential in the Li-containing aqueous solution FS than the rear surface of the electrolyte membrane 21, thereby suppressing the development of electronic conductivity in the electrolyte membrane 21.

[0129] A lithium isotope enrichment method using a lithium isotope enrichment apparatus according to a second modified example of the second embodiment of the present invention will be described with reference to Fig. 15. In a lithium isotope enrichment apparatus 1E according to this modified example, pure water is contained as the Li-containing aqueous solutions FS' and FS in the replenishing tank 1z and the supply tank 11. Then, as in the lithium isotope enrichment apparatus 1D according to the first modified example (see Fig. 13), first, the power supply 55 is driven to extract Li from the Li-containing aqueous solution SW contained in the raw material tank 1y. + Li in the Li-containing aqueous solution FS' is transferred by transferring cations including +When the concentration of Li reaches a certain level, it is preferable to start driving the power supplies 53 and 54. + The movement will be described below. Note that the agitator 8 is omitted in FIG.

[0130] In the lithium isotope enrichment apparatus 1E, the power supplies 55, 53, and 54 connected in series can be regarded as a single power supply (referred to as power supplies 55-53-54). Similarly, the power supplies 53 and 54 can be regarded as a single power supply (referred to as power supplies 53-54). The power supplies 55-53-54 apply a voltage (V5+V3+V4) to the sixth electrode 44 that is positive with respect to the sub-electrode 43. At the same time, the power supplies 53-54 apply a voltage (V3+V4) to the fourth electrode 41 that is positive with respect to the sub-electrode 43. Then, in the raw material tank 1y and the replenishing tank 1z, similar to the lithium isotope enrichment apparatus 1D described above, the reaction of the following formula (1) occurs near the sixth electrode 44 and the fourth electrode 41, and further the reaction of the following formula (11) occurs near the sixth electrode 44. As a result, the Li in the Li-containing aqueous solution FS' increases. + The reaction of the following formula (3) occurs near the fourth electrode 41, in which the reactant moves into the electrolyte membrane 21.

[0131] Meanwhile, the following reaction occurs in the supply tank 11. In the vicinity of the sub-electrode 43, the application of a voltage (V3+V4) from the power source 53-54 causes H2O in the Li-containing aqueous solution FS to convert electrons e - By supplying H and OH, the reaction of the following formula (2) occurs. - Then, H is generated near the sub-electrode 43. + Since the amount of Li in the electrolyte membrane 21 decreases, the amount of Li in the electrolyte membrane 21 decreases near the back surface of the electrolyte membrane 21, i.e., the fifth electrode 42A. + The reaction of the following formula (4) occurs, in which OH moves to the Li-containing aqueous solution FS. At the same time, the power supply 54 applies a positive voltage V4 of a predetermined magnitude based on the voltages V3 and V5 to the fifth electrode 42A relative to the sub-electrode 43. Then, in the vicinity of the fifth electrode 42A, OH in the Li-containing aqueous solution FS moves to the - The reaction of the following formula (1) occurs, and electrons e -is released to the fifth electrode 42A, generating H2O and O2. As a result, an imbalance in charge occurs in the vicinity of the fifth electrode 42A, resulting in an excess of cations due to the reaction of the following formula (1) and the reaction of the following formula (4). However, to compensate for the deficiency of cations that occurs near the sub-electrode 43 due to the reaction of the following formula (2), Li is released from the vicinity of the fifth electrode 42A to the vicinity of the sub-electrode 43. + As a result, the imbalance of the charges in the Li-containing aqueous solution FS is eliminated. The relative relationship between the magnitudes of the voltages V3 and V4 will be described later.

[0132] In the lithium isotope enrichment apparatus 1E according to this modification, the effect of applying the voltage V5 is the same as that of the lithium isotope enrichment apparatus 1D according to the first modification. In this modification, the application of the voltage V4 also generates an appropriate potential difference in the Li-containing aqueous solution FS, with the fifth electrode 42A being positive. Then, the electrons e supplied from the sub-electrode 43 to the Li-containing aqueous solution FS - moves from the fifth electrode 42A on the back surface of the electrolyte membrane 21 to the positive electrode of the power supply 54, and the potential of the fifth electrode 42A is maintained high at approximately the O2 generating potential. Since the O2 generating potential is higher than the reduction potential of the transition metal ions constituting the electrolyte membrane 21, the electrons e - Therefore, the voltage V3 can be set to a voltage equal to or greater than the applied voltage that causes the electrolyte membrane 21 to reach the reduction potential of at least one transition metal ion constituting the electrolyte membrane 21. In other words, when such a large voltage V3 is applied without applying the voltage V4, electrons e are transferred from the negative electrode side (supply tank 11 side) of the electrolyte membrane 21. - However, in this modification, as described above, the application of voltage V4 prevents the electrolyte membrane 21 from reaching the reduction potential of the transition metal ions, and the electrolyte membrane 21 absorbs electrons e - does not transmit.

[0133] If the voltage V4 is not large enough relative to the potential difference between the two surfaces of the electrolyte membrane 21, i.e., the voltage V3, a current flows from the fifth electrode 42A to the negative electrode of the power source 53, i.e., the fifth electrode 42A is charged with electrons e -, and the reaction of formula (2) occurs in the vicinity of the fifth electrode 42A, generating H2. As a result, electron transfer properties are exhibited in the electrolyte membrane 21. Therefore, the voltage V4 is set to a value that prevents current from flowing from the fifth electrode 42A toward the negative electrode of the power source 53. However, as the voltage V4 increases within this range, the current flowing from the power source 54 to the fifth electrode 42A increases, and the generation of O2 (reaction of formula (1)) in the vicinity of the fifth electrode 42A and the generation of H2 (reaction of formula (2)) in the vicinity of the sub-electrode 43 become greater than the value of Li + The voltage V5 is set to be lower than the voltage at which H2 is generated near the fourth electrode 41 or the fifth electrode 42A, and the higher the voltage V5 is within this range, the more the amount of Li transferred to the Li-containing aqueous solution FS increases. + In this modification, even if voltage V5 is equal to or greater than the theoretical voltage for water electrolysis, taking into account the electrode performance of electrodes 44 and 41, as described in the first modification, if voltage V4 is somewhat higher than voltages V3 and V5, the potentials on both sides of electrolyte membrane 21 do not drop below the H generation potential, and voltages V3 and V5 can be set to even higher values. However, as described above, an excessively high voltage V4 reduces energy efficiency. Therefore, as in the first modification, an ammeter may be connected in series to fourth electrode 41 and another ammeter may be connected in series to fifth electrode 42A (connecting an ammeter between the connection between power supplies 53 and 54 and fifth electrode 42A), and voltages V3, V5, and V4 may be applied while measuring the currents of the respective electrodes (see Patent Document 5).

[0134] The Li-containing aqueous solution FS targets Li + When the concentration reaches, for example, a saturated LiOH aqueous solution, the power supply 51 is driven to start isotope enrichment. + Li in the electrolyte membrane 21 due to the electrochemical potential difference + The mobility is higher than that of Li in the electrolyte membrane 22 due to the chemical potential difference alone. + Since the voltage V3 can be made higher than the mobility, the voltage V5 can be further reduced as needed, and the power supply 54 can be stopped (see FIGS. 14 and 13).

[0135] The lithium isotope enrichment apparatuses 1C, 1D, and 1E according to the second embodiment and its modified examples may be configured to be connected to the supply tank 11 of the lithium isotope enrichment apparatus 1A (see FIG. 7) according to the modified example of the first embodiment. Similarly, the lithium isotope enrichment apparatuses 1C, 1D, and 1E may be configured to be connected to the supply tank 11 of the lithium isotope enrichment apparatus 1B (see FIG. 8) or the multistage lithium isotope enrichment apparatus 10 (see FIG. 9).

[0136] [Third Embodiment] According to the first embodiment, immediately after the start of voltage application shown in FIG. 4B, Li adsorbed on the surface of the electrolyte membrane 2 + in 7 Li + , 6 Li + is the Li concentration in the Li-containing aqueous solution FS + However, 7 Li + and 6 Li + Due to the difference in the migration speed between the Li site defects of the electrolyte membrane 2 and the Li site defects of the electrolyte membrane 2, 6 Li + is the Li-containing aqueous solution FS 6 Li isotope ratio ( 6 Li / ( 7 Li+ 6 Li)) and migration between Li site defects in the electrolyte membrane 2, and 6 Lithium can also be transferred to the aqueous solution ES. 6 Li + As a result, the Li adsorbed on the surface of the electrolyte membrane 2 + Among them, 6 Li + The surface is then filled with new 7 Li + , 6 Li + is adsorbed from the Li-containing aqueous solution FS in its isotope ratio. By repeating this behavior, the Li adsorbed on the surface of the electrolyte membrane 2 gradually + of 6 The Li isotope ratio decreases. Furthermore, the Li remaining in the Li-containing aqueous solution FS + of 6Since the Li isotope ratio decreases, the amount of Li newly adsorbed on the surface of the electrolyte membrane 2 increases. + of 6 The Li isotope ratio decreases, and as a result, the Li that moves through the electrolyte membrane 2 + of 6 The Li isotope ratio is significantly reduced. + of 6 The Li isotope ratio is maximum immediately after the start of application of the voltage +V1, and then decreases exponentially as the application time passes (see Patent Document 4). + Slow in 7 Li + The isotope ratio of Li increases, + ( 7 Li + + 6 Li + ) decreases in movement per unit time.

[0137] Therefore, in order to extract the state immediately after the start of voltage application, the following configuration is adopted: A lithium isotope enrichment device according to a third embodiment of the present invention will now be described.

[0138] 16 , a lithium isotope enrichment apparatus 1F according to a third embodiment of the present invention includes a treatment tank 7, an electrolyte membrane (lithium ion conductive electrolyte membrane) 2, a first electrode 31, a second electrode 32, a third electrode 33, a power supply device 5 incorporating a power supply 51, and an agitator (circulation means) 8. The treatment tank 7 is divided into a supply tank (first tank) 11 containing a Li-containing aqueous solution FS by the electrolyte membrane 2, 6 and a recovery tank (second tank) 12 that contains an aqueous solution for Li recovery ES. The lithium isotope enrichment apparatus 1F is configured such that a switching element 5s1 is connected to a power supply 51 to repeatedly apply a voltage for a short period of time, with the application stopped between each. The lithium isotope enrichment apparatus 1F has the same configuration as the lithium isotope enrichment apparatus 1 according to the first embodiment, except for the power supply 5, and may include a cooling device, a liquid level sensor, an exhaust means, etc., as necessary.

[0139] The power supply device 5 includes a power supply 51, a switching element 5s1 connected to the power supply 51, and a drive circuit for the switching element 5s1, and is configured to intermittently apply a DC voltage from the power supply 51. The switching element 5s1 switches the power supply 51 ON / OFF, i.e., switches the connection / disconnection between the power supply 51 and the electrodes 32, 33, and in Fig. 16 connects the negative electrode of the power supply 51 to the third electrode 33. Ideally, the power supply device 5 should have a built-in capacitor or the like to have high time response so as to output a rectangular wave as shown in Fig. 17.

[0140] (Method for Enriching Lithium Isotopes) In the method for enriching lithium isotopes according to the third embodiment of the present invention, a positive voltage V1 (voltage +V1) is applied to the first electrode 31 and the second electrode 32 relative to the third electrode 33, as in the first embodiment. However, the voltage +V1 is applied for only a short time, and after the voltage application is stopped, the application of the voltage +V1 is repeated for a short time. In this way, the application of the voltage +V1 for a short time enriches Li + After moving a small amount, the application is stopped to return the state to the state before the voltage application started or a state close to that (initialization). + When the movement of Li has progressed to a certain extent, as described above, the Li adsorbed on the surface of the electrolyte membrane 2 + teeth, 6 Li + Since the Li preferentially moves into the electrolyte membrane 2, the Li remaining in the Li-containing aqueous solution FS at this point + than 6 It is considered that the Li isotope ratio is low (see FIG. 4C). When the application of the voltage +V1 is stopped and the state is set to a non-voltage application state, the reaction of formula (1) occurs near the first electrode 31 in the Li-containing aqueous solution FS: 6 Since the reactions of formulas (1) and (2) in the vicinity of the electrodes 32 and 33 in the aqueous solution ES for recovering Li stop, Li is released to compensate for the charge imbalance. + As a result, in the Li-containing aqueous solution FS, 6 Li in aqueous solution ES for Li recovery + are suspended in the aqueous solutions FS and ES, respectively, and are repeatedly adsorbed to and released from the front and back surfaces of the electrolyte membrane 2 (see FIG. 4A).

[0141] When the application of voltage +V1 is started again from this state, new Li appears on the surface of the electrolyte membrane 2 as shown in FIG. 4B. + This Li adsorbed on the surface of the electrolyte membrane 2 + is the Li content in the Li-containing aqueous solution FS at this point. + Therefore, the Li adsorbed on the surface of the electrolyte membrane 2 immediately before the application of the previous voltage +V1 was stopped (see FIG. 4C) + than 6 As a result, even with the short application of voltage +V1, 6 In this way, by repeatedly applying the voltage +V1 for a short time, it is possible to recover Li with a high Li isotope ratio. 6 It is possible to recover Li with a high Li isotope ratio, and it is possible to increase the amount of Li recovered per energization time.

[0142] One continuous application time of voltage +V1 (electrodialysis period) t ED , and the application stop time (t CYC -t ED , t CYC : period) is not particularly defined (see FIG. 17 ), 6 It is preferable that the electrodialysis period t is set so that the recovery efficiency of Li is sufficiently high. ED The shorter the time, the more Li is recovered. 6 The Li isotope ratio increases, and specifically, the application stop time (t CYC -t ED ) is short, the molecules adsorbed on the surface of the electrolyte membrane 2 by the application of the voltage +V1 immediately before. 7 Li with a high isotope ratio + On the other hand, if the time during which the voltage is not applied is excessively long, the electrodialysis period t ED Period t CYC The ratio to the total time is lowered, resulting in a decrease in time efficiency (productivity).

[0143] 16 is configured such that the first electrode 31 and the second electrode 32 are always connected, but may be configured such that the connection between the first electrode 31 and the second electrode 32 is disconnected when the power supply 51 is OFF. However, it is preferable to configure the device so that the first electrode 31 and the second electrode 32 are never disconnected when the power supply 51 is ON, that is, so that only one of the first electrode 31 or the second electrode 32 is never connected to the power supply 51. When a voltage is applied between the third electrode 33 and either the first electrode 31 or the second electrode 32, even if an electrolysis reaction of water occurs, Li + However, the isotope separation coefficient due to the isotope migration through the electrolyte membrane 2 is small, resulting in a decrease in energy efficiency.

[0144] The lithium isotope enrichment apparatus 1F according to this embodiment, like the lithium isotope enrichment apparatus 1 according to the first embodiment, 6 The aqueous solution for Li recovery ES is introduced into the supply tank 11. 6 Replace with aqueous solution ES (pure water) for Li recovery and 6 Li isotope ratio 6 The operation can be repeated until the aqueous solution for Li recovery ES is obtained. Furthermore, in the lithium isotope enrichment apparatus 1F, similar to the lithium isotope enrichment apparatus 1B (see FIG. 8 ) according to the modified example of the first embodiment, the recovery tank 12 can be further partitioned into two or more tanks by one or more electrolyte membranes 2 between the second electrode 32 and the third electrode 33, forming a cascade structure.

[0145] (Multistage Lithium Isotope Enrichment Apparatus) In the lithium isotope enrichment apparatus 1F according to this embodiment, similar to the lithium isotope enrichment apparatus 1 according to the first embodiment, the recovery tank 12 and the supply tank 11 of another lithium isotope enrichment apparatus 1F are connected by a pipe or the like to each other, and the lithium isotope enrichment apparatus 1F is enriched in stages. 6In addition, by forming a cascade structure in which the recovery tank 12 of the lithium isotope enrichment apparatus 1F is integrally connected to the supply tank 11 of another lithium isotope enrichment apparatus 1F, a multistage lithium isotope enrichment apparatus like the multistage lithium isotope enrichment apparatus 10 (see FIG. 9) according to the first embodiment can be formed. In such a multistage lithium isotope enrichment apparatus, the multiple power supply devices 5 may be synchronized or asynchronous, and further, the period t CYC and electrodialysis period t ED The power supply devices 5 may be different in type, or a power supply device 5 (power supply 51) that applies continuously and a power supply device 5 that applies intermittently may be mixed.

[0146] In the multistage lithium isotope enrichment apparatus according to the present embodiment, the third electrode 33 and the first electrode 31 disposed in each of the integrated recovery tank 12 and supply tank 11 can be integrated by aligning the cycles of the power supply devices so that adjacent ones do not apply voltage simultaneously. That is, as shown in Fig. 18 , a multistage lithium isotope enrichment apparatus 10A according to the third embodiment of the present invention includes a treatment tank 7A, four electrolyte membranes (lithium ion conductive electrolyte membranes) 22, 23, 24, and 25 arranged in parallel at intervals so as to partition the treatment tank 7A in one direction into five tanks 11, 12, 13, 14, and 15, a first electrode 31 disposed opposite the front surfaces (left surfaces in the figure) of the electrolyte membranes 22, 23, 24, and 25, a second electrode 32 covering the back surfaces of the electrolyte membranes 22, 23, 24, and 25, a third electrode 33 disposed opposite the second electrode 32 in the tank 15 at the end on the recovery side, and a power supply unit 50 having four built-in power supplies 51. The multistage lithium isotope enrichment apparatus 10A further includes an agitator (circulation means) 8 in each of the vessels 11, 12, 13, 14, and 15.

[0147] The multistage lithium isotope enrichment apparatus 10A has a structure in which four lithium isotope enrichment apparatuses 1F are connected so that each treatment tank 7 is integrated with the treatment tank 7A, and one recovery tank 12 of two adjacent lithium isotope enrichment apparatuses 1, 1 doubles as the supply tank 11 of the other. Furthermore, the third electrode 33 of this one recovery tank 12 is also doubled as the first electrode 31 arranged in the other supply tank 11. That is, the first electrode 31 in each of the tanks 12, 13, and 14 doubles as the third electrode 33. Therefore, these first electrodes 31 are preferably formed from a material having catalytic activity for the reactions of the following formulas (1) and (2). Furthermore, in each of the tanks 12, 13, and 14, the resistance between the first electrode 31 and the second electrode 32 facing the supply side thereof is equal to or greater than the resistance R between the second electrode 32 and the third electrode 33. ES (See FIG. 3 ) and is preferably arranged close to the second electrode 32 to a degree that does not cause a short circuit, so that the temperature is sufficiently low. For this reason, it is preferable that each tank except for the tanks 11 and 15 at both ends is short in the partition direction (connection direction) of the treatment tank 7A. With this configuration, the multistage lithium isotope enrichment apparatus 10A according to this embodiment can reduce the number of parts and can be made smaller in size by shrinking in the connection direction. Note that, similar to the lithium isotope enrichment apparatus 1, the first electrode 31 may have a porous structure and be provided in contact with the surfaces of the electrolyte membranes 22, 23, 24, and 25.

[0148] The power supply device 50 includes four power supply devices 5A1, 5A2, 5A3, and 5A4, each equipped with a power supply 51, arranged in this order from the supply side. The power supply devices 5A1, 5A2, 5A3, and 5A4 each correspond to the power supply device 5 of the lithium isotope enrichment device 1F, and will be referred to as the power supply device 5A as appropriate unless otherwise specified. The power supply device 5A, like the power supply device 5, includes switching elements 5s that form a three-pole switch that simultaneously connects / disconnects in order to apply a DC voltage intermittently. a1 , 5s a2 , 5s c (collectively referred to as switching elements 5s as appropriate). a1 , 5s a2The first electrode 31 and the second electrode 32, which face each other with one electrolyte membrane 2 sandwiched therebetween, are both connected to the positive electrode of the power source 51. c The negative electrode of the power source 51 is connected to the third electrode 33 or the first electrode 31 that is placed in the same tank as the second electrode 32 that is connected to the positive electrode of the power source 51 .

[0149] The power supply unit 50 is further configured so that the power supply units 5A of adjacent lithium isotope enrichment apparatuses 1F do not simultaneously connect the power supply 51 to the electrodes 31, 32, and 33, i.e., do not simultaneously connect the switching element 5s. To achieve this, two or more adjacent power supply units 5A of the lithium isotope enrichment apparatuses 1F are grouped together, and one unit from each group alternately connects the switching element 5s. Here, the power supply units 5A of two adjacent lithium isotope enrichment apparatuses 1F are grouped together, and the power supply units 5A1 and 5A3, and the power supply units 5A2 and 5A4, are driven synchronously. 18, the power supplies 51 of the synchronized power supply units 5A are connected in series, with the negative terminal of the power supply 51 of power supply unit 5A1 connected to the positive terminal of the power supply 51 of power supply unit 5A3, the negative terminal of the power supply 51 of power supply unit 5A2 connected to the positive terminal of the power supply 51 of power supply unit 5A4, and the positive terminals of the power supplies 51 of power supplies 5A1 and 5A2 grounded to a reference potential. Alternatively, the power supplies 51 of the power supply units 50 do not need to be connected to each other. In this case, it is preferable that the power supplies 51 of none of the power supply units 5A are grounded, or that only one of the synchronized power supply units 5A is grounded. The power supply unit 50 may also be configured with one power supply 51 each for the synchronized power supply units 5A1 and 5A3, and for the synchronized power supply units 5A2 and 5A4. The power supply device 50 is required to connect the power supply 51 to two adjacent tanks 12, 13, 14, and 15 so that the voltage +V1 is not applied between two electrodes within one tank at the same time, and to short-circuit the first electrode 31 and the second electrode 32 that face each other across the electrolyte membrane 2 when the power supply 51 is connected. The circuit configuration shown in FIG. 18 is one example.

[0150] In the multistage lithium isotope enrichment apparatus 10A, the power supply units 5A1 and 5A3, and the power supply units 5A2 and 5A4 are driven in synchronization with each other, and the power supply units 5A do not simultaneously apply the voltage +V1 to adjacent lithium isotope enrichment apparatuses 1F. CYC is the same and the electrodialysis period t ED is the period t CYC Less than 1 / 2 of (t ED <t CYC The power supply units 5A1 and 5A3 and the power supply units 5A2 and 5A4 are set to the electrodialysis period t ED The multistage lithium isotope enrichment apparatus 10A is driven so as not to overlap with the power supplies 5A1, 5A2, 5A3, and 5A4. Hereinafter, a lithium isotope enrichment method using the multistage lithium isotope enrichment apparatus 10A will be described with reference to FIGS. 19A and 19B. Note that in FIGS. 19A and 19B, the power supplies 51 of the power supply devices 5A1, 5A2, 5A3, and 5A4 are respectively indicated as power supplies 51(1), 51(2), 51(3), and 51(4). Furthermore, the agitator 8 is omitted from the multistage lithium isotope enrichment apparatus 10A shown in FIGS. 19A and 19B.

[0151] As shown in FIG. 19A , when power supply devices 5A1 and 5A3 connect power supplies 51(1) and 51(3) via switching element 5s and apply voltage +V1, power supply devices 5A2 and 5A4 disconnect switching element 5s. As a result, the first electrode 31 and second electrode 32, which face each other across electrolyte membranes 22 and 24, are short-circuited and connected to the positive pole of power supplies 51(1) and 51(3). The first electrode 31 in the same tank 12 or 14 as this second electrode 32 is connected to the negative pole. Meanwhile, the second electrode 32 in tank 13 and the second electrode 32 and third electrode 33 in tank 15 are in an open state. At this time, within tanks 12 and 14, the first electrode 31 is connected to the negative pole of power supplies 51(1) and 51(3) and functions as third electrode 33, generating an electric field +E1 between the second electrode 32 and first electrode 31. Then, Li +The Li-containing aqueous solution FS in the supply tank 11 passes through the electrolyte membrane 22 to move to the aqueous solution ES in the tank 12, and passes through the electrolyte membrane 24 from the aqueous solution ES in the tank 13 to move to the aqueous solution ES in the tank 14. Since there is no potential difference between the second electrode 32 on the back side of the electrolyte membranes 22 and 24 and the aqueous solutions FS and ES on the front side (supply side), the Li + On the other hand, in the electrolyte membrane 23 (between the aqueous solution ES1 and the aqueous solution ES2) and the electrolyte membrane 25 (between the aqueous solution ES3 and the aqueous solution ES4), the movement of Li + does not move.

[0152] Next, as shown in FIG. 19B , when power supply devices 5A2 and 5A4 connect power supplies 51(2) and 51(4) via switching element 5s and apply voltage +V1, power supply devices 5A1 and 5A3 disconnect switching element 5s. As a result, the first electrode 31 and second electrode 32, which face each other across electrolyte membranes 23 and 25, are short-circuited and connected to the positive electrodes of power supplies 51(2) and 51(4), respectively. The first electrode 31 in tank 13 and the third electrode 33 in tank 14, which are the same as second electrode 32, are connected to the negative electrodes, while the second electrode 32 in tanks 12 and 14 are open. At this time, the first electrode 31 in tank 13 is connected to the negative electrode of power supply 51(2) and functions as third electrode 33. An electric field +E1 is generated between the second electrode 32 and first electrode 31 (third electrode 33) in tanks 13 and 15. As a result, Li + moves from the aqueous solution ES1 in the tank 12 through the electrolyte membrane 23 to the aqueous solution ES2 in the tank 13, and from the aqueous solution ES3 in the tank 14 through the electrolyte membrane 25 to the aqueous solution ES4 in the tank 15. Since there is no potential difference between the second electrode 32 on the back side of the electrolyte membranes 23 and 25 and the aqueous solutions ES1 and ES3 on the front side (supply side), the Li + On the other hand, in the electrolyte membrane 22 (between the aqueous solution FS and the aqueous solution ES1) and the electrolyte membrane 24 (between the aqueous solution ES2 and the aqueous solution ES3), the movement of Li + does not move.

[0153] In addition, since no electric field is generated between the first electrode 31 in the tank 11 on the supply side of the electrolyte membrane 22 and the aqueous solution ES on the recovery side, the Li adsorbed on the surface of the electrolyte membrane 22 due to the movement in the electrolyte membrane 22 immediately before shown in FIG. + Similarly, since no electric field is generated between the first electrode 31 in the tank 13 on the supply side of the electrolyte membrane 24 and the aqueous solution ES3 on the recovery side, the Li adsorbed on the surface of the electrolyte membrane 24 moves within the electrolyte membrane 24. + On the other hand, as shown in Fig. 19A, when the switching elements 5s of the power supply devices 5A1 and 5A3 are connected, no electric field is generated between the first electrode 31 in the tank 12 on the supply side of the electrolyte membrane 23 and the aqueous solution ES on the recovery side, and therefore, the Li that had been adsorbed on the surface of the electrolyte membrane 23 during the movement in the electrolyte membrane 23 immediately before, as shown in Fig. 19B, is released. + Similarly, since no electric field is generated between the first electrode 31 in the tank 14 on the supply side of the electrolyte membrane 25 and the aqueous solution ES on the recovery side, the Li adsorbed on the surface of the electrolyte membrane 25 moves through the electrolyte membrane 25. + is released and floats in the aqueous solution ES3.

[0154] In this way, multistage lithium isotope enrichment apparatus 10A is operated by alternately connecting and disconnecting switching element 5s between power supply devices 5A1, 5A3 and power supply devices 5A2, 5A4. As a result, voltage +V1 is intermittently applied, and electric field +E1 is generated alternately in each of tanks 12, 14 and tanks 13, 15, thereby increasing the isotope separation coefficient for each electrolyte membrane 2.

[0155] In this embodiment, just as in the lithium isotope enrichment method using the multistage lithium isotope enrichment apparatus 10, immediately after the start of operation, Li is introduced from the Li-containing aqueous solution FS in the supply tank 11 to the aqueous solution ES1, which is pure water in the tank 12. + Li moves only in the electrolyte membrane 22. + Li in the aqueous solution ES1 + It is preferable to increase the concentration. For this purpose, only the power supply device 5A1 is driven. Then, the aqueous solution ES1 is turned on to obtain a predetermined Li concentration. +When the concentration reaches the predetermined value, the power supply device 5A2 is driven to alternately switch the connection / disconnection of the switching element 5s with the power supply device 5A1. + When the concentration is reached, power supply device 5A3 is driven in synchronization with power supply device 5A1, and finally all power supply devices 5A of the power supply device 50 are driven.

[0156] As with the multistage lithium isotope enrichment apparatus 10, the more lithium isotope enrichment apparatuses 1F are connected to the multistage lithium isotope enrichment apparatus 10A, the more efficient the enrichment. 6 Li with a high Li isotope ratio can be recovered from the tank at the end of the recovery side. In this case, the power supply unit 50 synchronizes every other power supply unit 5A1, 5A3, 5A5, ... as one set, and synchronizes the power supply units 5A2, 5A4, 5A6, ... as one set, and alternately connects / disconnects the two sets. Also, the multistage lithium isotope enrichment apparatus 10A may be configured such that the power supply unit 50 drives three or more adjacent power supply units 5A as one set. For example, during the electrodialysis period t ED period t CYC Less than 1 / 3 of (t ED <t CYC / 3), three adjacent power supply units 5A can be grouped together. In this case, power supply units 5A1, 5A4, 5A7, ... are synchronized, power supply units 5A2, 5A5, 5A8, ... are synchronized, and power supply units 5A3, 5A6, 5A9, ... are synchronized.

[0157] Furthermore, similar to the multistage lithium isotope enrichment apparatus 10, the multistage lithium isotope enrichment apparatus 10A may be formed by connecting lithium isotope enrichment apparatuses 1F by bending them at one or two positions by 90 degrees, and arranging adjacent electrolyte membranes 2, 2 perpendicular to each other. In the bent portion of the tank separated by the perpendicularly arranged electrolyte membranes 2, 2, the first electrode 31 does not also serve as the third electrode 33, i.e., the third electrode 33 and the first electrode 31 are arranged perpendicular to each other and spaced apart so as not to short-circuit.

[0158] The lithium isotope enrichment apparatus 1A (see FIG. 7) according to the modified example of the first embodiment can also be provided with a power supply device 5 having a built-in power supply 51 connected to a switching element 5s1, as with the lithium isotope enrichment apparatus 1F according to the third embodiment. Two or more such lithium isotope enrichment apparatuses can be connected so that their treatment tanks 7 are integrated to form a multistage lithium isotope enrichment apparatus. Furthermore, as with the multistage lithium isotope enrichment apparatus 10A, the first electrode 31A and the third electrode 33A disposed in the integrated recovery tank 12 and supply tank 11, respectively, can be integrated.

[0159] The lithium isotope enrichment apparatus 1F and the multistage lithium isotope enrichment apparatus 10A according to this embodiment, like the lithium isotope enrichment apparatus 1 and the multistage lithium isotope enrichment apparatus 10 according to the first embodiment, can be used to enrich Li in the Li-containing aqueous solution FS as in the lithium isotope enrichment apparatuses 1C, 1D, and 1E according to the second embodiment and its modified examples (FIGS. 10 to 15). + It is also possible to add a configuration to supplement the above.

[0160] (First Modification) In the lithium isotope enrichment device according to the third embodiment, the isotope separation factor can be further increased by applying a voltage intermittently. However, in a state where no voltage is applied, it takes time for the lithium ions adsorbed on the surface of the electrolyte membrane to be sufficiently released. 6 It is difficult to achieve both high Li enrichment and improved productivity. Therefore, in order to actively separate lithium ions from the electrolyte membrane, the following configuration is adopted. Hereinafter, a lithium isotope enrichment device according to a modified example of the third embodiment of the present invention will be described.

[0161] 20 , a lithium isotope enrichment apparatus 1G according to a first modification of the third embodiment of the present invention includes a treatment tank 7, an electrolyte membrane (lithium ion conductive electrolyte membrane) 2 that partitions the treatment tank 7 into two tanks, a supply tank (first tank) 11 and a recovery tank (second tank) 12, a first electrode 31B, a second electrode 32, a third electrode 33, an auxiliary electrode 34, a power supply unit 5G incorporating a power supply 51 and an auxiliary power supply 52, and an agitator (circulation means) 8. The first electrode 31B and the second electrode 32 have a porous structure, and the first electrode 31B covers the surface of the electrolyte membrane 2 facing the supply tank 11, while the second electrode 32 covers the surface of the electrolyte membrane 2 facing the recovery tank 12. The third electrode 33 is provided in the recovery tank 12 and spaced apart from the electrolyte membrane 2 and the second electrode 32. The auxiliary electrode 34 is provided in the supply tank 11 and spaced apart from the electrolyte membrane 2 and the first electrode 31B. The power supply 51 has a positive electrode connected to the first electrode 31B and the second electrode 32, and a negative electrode connected to the third electrode 33. The auxiliary power supply 52 has a positive electrode connected to the first electrode 31B, and a negative electrode connected to the auxiliary electrode 34. Therefore, the lithium isotope enrichment apparatus 1G according to this modification is similar to the lithium isotope enrichment apparatus 1F according to the third embodiment shown in FIG. 16 in that, in the supply tank 11, the first electrode 31 is replaced with a first electrode 31B provided in contact with the surface of the electrolyte membrane 2, an auxiliary electrode 34 is further added, and an auxiliary power supply 52 is added that is connected to the first electrode 31B and the auxiliary electrode 34. The rest of the configuration is the same as that of the lithium isotope enrichment apparatus 1F, and may include a cooling device, a liquid level sensor, an exhaust means, and the like, as necessary.

[0162] The first electrode 31B is provided in the supply tank 11, similar to the first electrode 31 of the first embodiment, and is further provided in contact with the surface of the electrolyte membrane 2. This first electrode 31B has a porous structure, such as a mesh structure, similar to the second electrode 32, so that a voltage is applied to a wide range of the electrolyte membrane 2 while the Li-containing aqueous solution FS comes into contact with a sufficient area of ​​the surface of the electrolyte membrane 2. The first electrode 31B is preferably made of a material that has catalytic activity for the reactions of the following formulas (1) and (3), and is also preferably a material that can be easily processed into the above-mentioned shape. Platinum (Pt), for example, is a preferred electrode material for the first electrode 31B.

[0163] The auxiliary electrode 34 is an electrode that enables a lower potential to be formed in the Li-containing aqueous solution FS than the surface of the electrolyte membrane 2. Therefore, the auxiliary electrode 34 is preferably arranged in the supply tank 11 so as not to contact the electrolyte membrane 2 and the first electrode 31B and to be parallel to the first electrode 31B. Furthermore, as will be described later, the auxiliary electrode 34 is preferably arranged close enough to the first electrode 31B to prevent a short circuit, in order to make the electric field E2 (see FIG. 22 ) generated in the Li-containing aqueous solution FS stronger than the voltage V2 applied between the auxiliary electrode 34 and the first electrode 31B. Furthermore, the auxiliary electrode 34 preferably has a mesh-like shape or the like that allows the aqueous solution to pass through, so that the Li-containing aqueous solution FS in contact with the surface of the electrolyte membrane 2 (first electrode 31B) in the supply tank 11 is continuously replaced. The sub-electrode 34, like the first electrode 31B, is preferably made of an electrode material that is electronically conductive, stable even when a voltage is applied in the Li-containing aqueous solution FS, and easily processed into the above-mentioned shape. Examples of such electrode materials for the sub-electrode 34 include platinum (Pt), but carbon (C) may also be used.

[0164] The power supply unit 5G includes two DC power supplies 51 and 52, as well as switching elements 5s1 and 5s2 and their drive circuits. DC voltages are alternately applied from the power supplies 51 and 52. In other words, the power supply unit 5G includes two DC pulse power supplies, one of which is turned on and the other is turned off in synchronization. The power supply 51 is the main power supply, and, as in the first embodiment, it intermittently applies a positive voltage V1 (voltage +V1) relative to the third electrode 33 to the first electrode 31B and the second electrode 32 via the switching element 5s1. The secondary power supply 52 has its positive terminal connected to the first electrode 31B and its negative terminal connected to the secondary electrode 34. It applies a negative voltage V2 (voltage −V2) relative to the first electrode 31B to the secondary electrode 34 when the power supply 51 is not applying the voltage +V1, as shown in FIG. 21 . Ideally, the power supplies 51 and 52 should incorporate a capacitor or the like for high time response, so as to output a rectangular wave as shown in FIG. 21 . The magnitude of the voltage V1 is set to be equal to or greater than the voltage at which the electrolysis reaction of water occurs, as in the first embodiment, and the voltage V2 is preferably less than the voltage at which the electrolysis reaction of water occurs in the Li-containing aqueous solution FS.

[0165] As in the first embodiment, the switching element 5s1 switches the connection / disconnection between the negative electrode of the power source 51 and the third electrode 33 (turning the power source 51 ON / OFF). The switching element 5s2 alternately switches the connection of the first electrode 31B between the second electrode 32 (and the positive electrode of the power source 51) and the positive electrode of the auxiliary power source 52. During this connection, there may be a period during which the first electrode 31B is not connected to either electrode. However, as in the first embodiment, it is preferable that the first electrode 31B is also connected to the power source 51 when the power source 51 is connected between the second electrode 32 and the third electrode 33. Therefore, it is preferable that the switching element 5s2, in conjunction with the switching element 5s1, always connects the first electrode 31B to the second electrode 32 when the power source 51 is connected between the second electrode 32 and the third electrode 33 (the power source 51 is ON), as shown in FIG. 20 . 22, only when the power supply 51 is not connected between the second electrode 32 and the third electrode 33 (when the power supply 51 is OFF), the first electrode 31B is connected to the auxiliary power supply 52. ​​The timing of application of the voltages V1 and V2 will be described in detail later.

[0166] As described above, the power supply device 5G is only required to be able to apply voltages V1 and V2 of predetermined polarity and magnitude alternately between the electrodes 31B, 32 and the third electrode 33 and between the sub-electrode 34 and the first electrode 31B, and the circuit configuration shown in Fig. 20 is merely an example. For example, the power supply device may include a variable power supply that can switch between two voltage levels, V1 and V2, with its positive electrode connected to the first electrode 31B, a switching element that switches the connection destination of the negative electrode of the variable power supply between the third electrode 33 and the sub-electrode 34, and a switching element that switches the connection and disconnection between the first electrode 31B (the positive electrode of the variable power supply) and the second electrode 32. Alternatively, two DC power supplies may be connected in series via switching elements, with two power supplies applying voltage V1 and one power supply applying voltage V2 (not shown). 20, when the power supply device 5G applies a voltage +V1 between the electrodes 31B, 32 and the third electrode 33, the sub-electrode 34 is in an open state, and when the power supply device 5G applies a voltage −V2 between the sub-electrode 34 and the first electrode 31B, the second electrode 32 and the third electrode 33 are in an open state (see FIG. 22). Alternatively, the power supply device 5G may be configured such that when the voltage +V1 is applied between the electrodes 31B, 32 and the third electrode 33, the sub-electrode 34 is connected to the same potential as the first electrode 31B.

[0167] A lithium isotope enrichment method according to a first modification of the third embodiment of the present invention alternately performs the following steps: a first step of applying a voltage V1 between a first electrode 31B provided on the front surface of the electrolyte membrane 2, a second electrode 32 provided on the back surface, and a third electrode 33 provided in the recovery tank 12 at a distance from the electrolyte membrane 2 and the second electrode 32, with the electrodes 31B and 32 being positive; and a second step of applying a voltage V2 between a sub-electrode 34 provided in the supply tank 11 at a distance from the electrolyte membrane 2 and the first electrode 31B and the first electrode 31B, with the sub-electrode 34 being negative. Hereinafter, a lithium isotope enrichment method using a lithium isotope enrichment apparatus according to this modification will be described with reference to FIGS. 20 , 22 , 23 , 2 , and 4A-4C . In the lithium isotope enrichment apparatus 1G shown in FIG. 22 , the power supply 51 is turned off and omitted, and the agitator 8 is also omitted.

[0168] The behavior of lithium ions during application of voltage V1 (see FIG. 20), including immediately after the start of application, is as described in the first embodiment (see FIGS. 2 and 4A to 4C). Furthermore, as described in the third embodiment, when the application of voltage +V1 is stopped, the Li ions adsorbed on the surface of the electrolyte membrane 2 + However, these Li + Until just before, the Li atoms were attracted to the deeper side (back side) of the electrolyte membrane 2 to compensate for the imbalance in charge caused by the application of the voltage +V1, and therefore do not immediately leave the surface of the electrolyte membrane 2 even when the application of the voltage +V1 is stopped. Therefore, in this modification, when the application of the voltage +V1 is stopped, the auxiliary power supply 52 starts to apply a negative voltage V2 (voltage -V2) with respect to the first electrode 31B to the auxiliary electrode 34 (see FIG. 22). The application of the voltage -V2 generates a potential gradient in the Li-containing aqueous solution FS, with the vicinity of the surface of the electrolyte membrane 2 being positive and the vicinity of the auxiliary electrode 34 being negative. Therefore, as shown in FIG. 23, the Li atoms adsorbed on the surface of the electrolyte membrane 2 are attracted to the deeper side (back side) of the electrolyte membrane 2 to compensate for the imbalance in charge caused by the application of the voltage +V1. + However, they quickly detach due to electrostatic repulsion.

[0169] By applying the voltage −V2, Li is removed from the surface of the electrolyte membrane 2 in a short time. + Therefore, when the application of the voltage −V2 is stopped and the application of the voltage +V1 by the power supply 51 is started again, new Li + This Li adsorbed on the surface of the electrolyte membrane 2 + is the Li adsorbed on the surface of the electrolyte membrane 2 immediately before the previous application of the voltage +V1 was stopped (see FIG. 4C), as in the first embodiment. + than 6 In this way, by applying the voltage −V2 during the period when the application of the voltage +V1 is stopped, the Li isotope ratio is higher than in the non-application state as in the first embodiment. + is easily removed from the surface of the electrolyte membrane 2, so the application of the voltage +V1 is stopped after a time (t CYC -t ED Even if the time t1 is short, the effect of intermittent application can be obtained. 6 The operation time for recovering Li can be shortened, thereby improving productivity.

[0170] The higher the voltage V2, the stronger the electric field E2 (electric field −E2) in the Li-containing aqueous solution FS from the surface of the first electrode 31B, i.e., the electrolyte membrane 2, to the sub-electrode 34, and the stronger the Li + is attracted to the sub-electrode 34 at high speed, and the Li adsorbed on the surface of the electrolyte membrane 2 + is removed in a shorter time. On the other hand, when the voltage V2, i.e., the potential difference between the first electrode 31B and the sub-electrode 34, exceeds a certain value, the electrolysis reaction of HO (reactions of formulas (1) and (2)) occurs in the Li-containing aqueous solution FS, and the energy efficiency decreases. Therefore, it is preferable to set the voltage V2 to a value that does not cause the electrolysis reaction of HO, and at most is smaller than the voltage V1. It is preferable to arrange the sub-electrode 34 at a short distance from the first electrode 31B so that the electric field E2 is strong against such a voltage V2.

[0171] One continuous application time of voltage −V2 (reset period) t RST is not specifically specified, 6 It is preferable that the reset period t be set so that the Li recovery efficiency is sufficiently high. RST is the Li adsorbed on the surface of the electrolyte membrane 2 by the application of the voltage +V1 immediately before. + It is sufficient that the distance is sufficiently separated, preferably completely separated. 6 The recovery efficiency of Li was not improved, and the electrodialysis period t ED Period t CYC (≧t ED +t RST ) becomes lower, and time efficiency (productivity) decreases. RST The stronger the electric field E2, that is, the higher the voltage V2, and the shorter the distance between the sub-electrode 34 and the first electrode 31B, the shorter the time required to obtain the effect.

[0172] It is also preferable that the voltage +V1 and the voltage −V2 are not applied simultaneously. + Since the concentration of is relatively low near the surface of the electrolyte membrane 2, when the voltage −V2 is applied while the voltage +V1 is applied, 6 Li in aqueous solution ES for Li recovery +The movement of Li is hindered, resulting in a decrease in energy efficiency. + of 6 It is preferable that the voltage −V2 is not applied immediately after the start of application of the voltage +V1 at which the Li isotope ratio is maximized. On the other hand, during the non-application period t int1 , t int2 However, there may be a non-voltage application period t int1 , t int2 If the time is long, the productivity will decrease. Therefore, the application of voltage +V1 (electrodialysis period t ED ) After the application of voltage −V2 (reset period t RST ) (t int1 ≧0), and it is more preferable to start applying the voltage −V2 as soon as possible after the application of the voltage +V1 is stopped. int1 =0) is more preferable. RST ) After the stop of application of voltage +V1 (electrodialysis period t ED ) (t int2 ≧0), and it is preferable that the application of voltage +V1 is started after the application of voltage −V2 is stopped (t int2 It is preferable that the timings for starting and stopping the application of the voltage +V1 and the voltage −V2 are set in accordance with the timing accuracy of the power supply device 5G, etc., so that the voltage +V1 and the voltage −V2 are not applied simultaneously.

[0173] The application period of voltage −V2 (reset period t RST ), it is preferable to disconnect the first electrode 31B and the second electrode 32. For this purpose, for example, during the application period of the voltage +V1 (electrodialysis period t ED ) and connect the first electrode 31B and the second electrode 32. If the second electrode 32 is connected to the first electrode 31B when the voltage -V2 is applied, depending on the magnitude of the voltage V2, 6 Li in aqueous solution ES for Li recovery +flows back into the Li-containing aqueous solution FS. Therefore, as in the lithium isotope enrichment apparatus 1F according to the third embodiment (see FIG. 16 ), the first electrode 31B and the second electrode 32 can be configured to be constantly connected, but in this case, it is preferable to set the voltage V2 to be lower than the voltage at which electrolysis of water occurs.

[0174] In a lithium isotope enrichment device 1F according to the third embodiment (see FIG. 16 ), the first electrode 31 is disposed spaced apart from the electrolyte membrane 2. Therefore, in this modification, the positions of the first electrode 31B and the auxiliary electrode 34 may be interchanged. That is, as shown in FIG. 24 , a lithium isotope enrichment device 1H according to another configuration of the first modification of the third embodiment differs from the lithium isotope enrichment device 1G according to the modification (see FIG. 20 ) in that it includes a first electrode 31 spaced apart from the electrolyte membrane 2, a porous auxiliary electrode 34A in contact with the surface of the electrolyte membrane 2, and a power supply device 5H that connects the positive electrode of a secondary power supply 52 to the auxiliary electrode 34A and alternately switches the connection destination of the first electrode 31 between the second electrode 32 and the negative electrode of the secondary power supply 52 using a switching element 5s2. The first electrode 31 has the same configuration as in the first embodiment. The auxiliary electrode 34A preferably has a porous structure such as a mesh structure similar to the first electrode 31B of the lithium isotope enrichment device 1G so that the Li-containing aqueous solution FS comes into contact with a sufficient area of ​​the surface of the electrolyte membrane 2, and is made of a material that has catalytic activity for the reaction of the following formula (3). Furthermore, when the voltage +V1 is applied, both the first electrode 31 and the auxiliary electrode 34A (the first electrode 31B and the auxiliary electrode 34) may be connected to the second electrode 32 (the positive electrode of the power source 51).

[0175] (Second Modification) In the lithium isotope enrichment apparatuses 1G and 1H according to the first modification of the third embodiment, Li + When the application of the voltage +V1 that moves the Li in the electrolyte membrane 2 is stopped, a voltage -V2 is applied between the sub-electrode 34 and the first electrode 31B (the first electrode 31 and the sub-electrode 34A) in the supply tank 11 to form a potential gradient in the Li-containing aqueous solution FS in which the potential near the surface of the electrolyte membrane 2 is high, thereby causing the Li adsorbed on the surface of the electrolyte membrane 2 to be transferred. + However, when the application of the voltage +V1 was resumed, the Li in the Li-containing aqueous solution FS +Since the concentration is relatively low near the surface of the electrolyte membrane 2, Li + It takes time for Li to be adsorbed, and immediately after the application of the voltage +V1 is restarted, + The mobility of the electrons is not high and the energy efficiency is insufficient.

[0176] Therefore, by applying a voltage −V2 (second step), Li + After the Li is temporarily removed from the surface of the electrolyte membrane 2 (see FIGS. 22 and 23), a voltage +V2 with reversed polarity is applied between the sub-electrode 34 and the first electrode 31B (third step), and the Li + The application of the voltage +V1 may be resumed after the low concentration of the lithium isotope enrichment apparatus 1G, 1H is resolved. To this end, the secondary power supplies 52 of the power supply devices 5G, 5H of the lithium isotope enrichment apparatus 1G, 1H are configured to be able to apply voltages with reversed polarity. Specifically, as shown in FIG. 25 , when the power supply 51 is not applying the voltage +V1, the secondary power supply 52 first applies the voltage −V2 during one stop period of the voltage +V1, and then reverses the polarity and applies the voltage +V2.

[0177] As explained in the modified example, after the application of the voltage +V1, the application of the voltage −V2 causes the Li adsorbed on the surface of the electrolyte membrane 2 to be removed as shown in FIG. + For details, please see Li + is released from the surface of the electrolyte membrane 2, which is positively charged, by electrostatic repulsion. + is unevenly distributed in the vicinity of the sub-electrode 34 due to electrostatic attraction, and as a result, Li + The lithium isotope enrichment method according to this modification applies a voltage −V2 from the secondary power supply 52, and then reverses the polarity of the secondary power supply 52 to apply a voltage +V2. The application of the voltage +V2 generates a potential gradient in the Li-containing aqueous solution FS, with the vicinity of the surface of the electrolyte membrane 2 being negative and the vicinity of the secondary electrode 34 being positive. Then, the Li that was unevenly distributed in the vicinity of the secondary electrode 34 due to the application of the voltage −V2 immediately before is released. + is quickly separated from the sub-electrode 34 by electrostatic repulsion, and Li +The electrostatic repulsion on the surface of the electrolyte membrane 2 is quickly released, and the relative Li + The low concentration state is resolved. Furthermore, the Li that was unevenly distributed near the sub-electrode 34 + and Li floating in the Li-containing aqueous solution FS. + However, they are attracted to the negatively charged surface of the electrolyte membrane 2 by electrostatic attraction, and become highly concentrated in the vicinity, and some of them are adsorbed onto the surface. + is the Li content in the Li-containing aqueous solution FS at this point. + It has the same isotopic ratio as

[0178] When the application of the voltage +V2 is stopped and the application of the voltage +V1 is started again by the power supply 51, the Li adsorbed on the surface of the electrolyte membrane 2 is removed as shown in FIGS. 4B and 4C. + In this way, after applying the voltage −V2 between the sub-electrode 34 and the first electrode 31B, the polarity is reversed and the voltage +V2 is applied, and then the application of the voltage +V1 is resumed. 6 A large amount of Li with a high Li isotope ratio can be recovered.

[0179] The voltage applied between the sub-electrode 34 and the first electrode 31B does not have to be the same in magnitude between the negative and positive. As the voltage +V2 increases, the electric field (referred to as electric field +E2) in the Li-containing aqueous solution FS from the sub-electrode 34 to the surface of the electrolyte membrane 2 becomes stronger, and Li + moves away from the sub-electrode 34 at high speed and is attracted to the surface of the electrolyte membrane 2. + The low concentration state is resolved in a shorter time, and furthermore, Li is deposited on the surface of the electrolyte membrane 2. + On the other hand, as explained in the above embodiment, it is preferable to set the voltage to a level that does not cause the electrolysis reaction of H2O in the Li-containing aqueous solution FS.

[0180] One continuous application time of voltage +V2 (preparation period) t PREP is not particularly specified, and the electrodialysis period t ED and reset period t RST Similarly, 6It is preferable that the preparation period t is set so that the recovery efficiency of Li is sufficiently high. PREP is the Li near the surface of the electrolyte membrane 2 generated by the application of the immediately preceding voltage -V2. + It is sufficient to eliminate the low concentration state, and further Li + It is preferable that the concentration of Li becomes high near the surface of the electrolyte membrane 2 and that a large amount of Li is adsorbed on the surface. + Even if the electrode is attracted, the Li + There is a limit to the improvement of the mobility of PREP If is long, the electrodialysis period t ED Period t CYC The ratio to the production time decreases, and productivity decreases. PREP is the reset period t RST Similarly, the higher the voltage V2 is and the shorter the distance between the sub-electrode 34 and the first electrode 31B, the shorter the time required to obtain the effect.

[0181] Reset period t RST and preparation period t PREP If there is a long non-application period during which neither the voltage -V2 nor +V2 is applied between the sub-electrode 34 and the first electrode 31B, productivity will decrease. Therefore, it is preferable to start applying the voltage +V2 as soon as possible after the application of the voltage -V2 is stopped, and it is even more preferable to start applying the voltage +V2 at the same time as the application of the voltage -V2 is stopped, as shown in FIG. 25. In addition, the application of the voltage +V2 (preparation period t PREP ) After stopping the application of voltage +V1 (electrodialysis period t ED ) until the start of the no-voltage application period t int3 If the time is long, productivity decreases, and the effect of applying the voltage +V2 also decreases. Therefore, it is preferable to start applying the voltage +V1 as soon as possible after stopping the application of the voltage +V2. It is preferable to start applying the voltage +V1 at the same time as stopping the application of the voltage +V2 (t int3 = 0) is more preferable. ED ) the voltage +V2 may be applied. Therefore, after the application of the voltage +V1 is started, the application of the voltage +V2 may be stopped. In this case, PREPis set assuming that it is from the start of application of voltage +V2 to the start of application of voltage +V1.

[0182] The lithium isotope enrichment apparatuses 1G and 1H according to this modification, like the lithium isotope enrichment apparatuses 1 and 1F according to the first and third embodiments, are configured to: 6 The aqueous solution for Li recovery ES is introduced into the supply tank 11. 6 Replace with aqueous solution ES (pure water) for Li recovery and 6 Li isotope ratio 6 The operation can be repeated until the aqueous solution for Li recovery ES is obtained. Furthermore, in the lithium isotope enrichment apparatuses 1G and 1H, similar to the lithium isotope enrichment apparatus 1B according to the modified example of the first embodiment (see FIG. 8 ), the recovery tank 12 can be further partitioned into two or more tanks by one or more electrolyte membranes 2 between the second electrode 32 and the third electrode 33, forming a cascade structure.

[0183] The lithium isotope enrichment apparatus 1A (see FIG. 7 ) according to the modified example of the first embodiment can be equipped with a power supply device, such as the power supply device 5G of the lithium isotope enrichment apparatus 1G, that switches the voltage between two levels, V1 and V2, and that switches the connection / disconnection of the first electrode 31A to the second electrode 32A. With this lithium isotope enrichment apparatus, the third electrode 33A functions as the auxiliary electrode 34 of the lithium isotope enrichment apparatus 1G, and isotope enrichment similar to the lithium isotope enrichment method according to the first modified example of the third embodiment (see FIG. 21 ) can be performed. Specifically, a first step (see FIG. 7 ) in which a positive voltage V1 (voltage +V1) is applied to the third electrode 33A relative to the first electrode 31A and the second electrode 32A, and a second step (see FIG. 7 ) in which a negative voltage V2 (voltage −V2) is applied to the third electrode 33A relative to the second electrode 32A, are alternately performed. In the second step, it is preferable to disconnect the first electrode 31A from the second electrode 32A and place it in an open state, etc. Furthermore, similar to the lithium isotope enrichment method according to the second modified example of the third embodiment (see FIG. 25 ), after the second step, a third step may be executed in which a positive voltage V2 (voltage +V2) with respect to the second electrode 32A is applied to the third electrode 33A.

[0184] (Multistage Lithium Isotope Enrichment Apparatus) In the lithium isotope enrichment apparatuses 1G and 1H according to the modified example of the third embodiment, similar to the lithium isotope enrichment apparatus 1 according to the first embodiment, the recovery tank 12 and the supply tank 11 of another lithium isotope enrichment apparatus 1G or 1H are connected by a pipe or the like, and lithium isotope is enriched in stages. 6 A multistage lithium isotope enrichment apparatus for enriching Li can be formed. Furthermore, by forming a cascade structure in which the recovery tank 12 of the lithium isotope enrichment apparatus 1G, 1H is integrally connected to the supply tank 11 of another lithium isotope enrichment apparatus 1G, 1H, a multistage lithium isotope enrichment apparatus like the multistage lithium isotope enrichment apparatus 10 according to the first embodiment (see FIG. 9 ) can be formed.

[0185] A multistage lithium isotope enrichment apparatus (not shown) in which lithium isotope enrichment apparatuses 1G are connected includes a single tank partitioned on both sides by electrolyte membranes 2, 2, and in this order from the supply side, a second electrode 32, a third electrode 33, a sub-electrode 34, and a first electrode 31B. This tank is designed to be long enough in the partition direction (connection direction) so that the third electrode 33 and the sub-electrode 34 are spaced apart from each other with a sufficient distance. Specifically, the tank is designed so that even if at least one of the third electrode 33 and the sub-electrode 34 is connected to a power source 51 or a power source 52, an electric field is not substantially generated between the third electrode 33 and the sub-electrode 34, or even if an electric field is generated, the electric field is sufficiently weaker than the electric field E1 (see FIG. 2 ) and the electric field E2 (see FIG. 22 ) generated in the same tank. In addition, in a multistage lithium isotope enrichment apparatus in which lithium isotope enrichment apparatus 1H are connected, the second electrode 32, the third electrode 33, the first electrode 31, and the auxiliary electrode 34A are arranged in this order from the supply side in a single tank separated on both sides by electrolyte membranes 2, 2, excluding the tanks at both ends, and therefore the third electrode 33 and the first electrode 31 are arranged with a sufficient distance between them.

[0186] The method of enriching lithium isotopes by the multistage lithium isotope enrichment apparatus according to this modification is the same as the method by the lithium isotope enrichment apparatuses 1G and 1H. In addition, as in the method by the multistage lithium isotope enrichment apparatus 10 according to the first embodiment, first, Li is enriched only between the first tank (tank 11) and the second tank (tank 12) from the supply side. + The aqueous solution ES1 in the tank 12 is then transferred to a predetermined Li +It is preferable to reach a concentration of

[0187] In a multistage lithium isotope enrichment apparatus in which lithium isotope enrichment apparatuses 1G according to a modified example of the third embodiment are connected, the third electrode 33 and the auxiliary electrode 34 arranged in each of the integrated recovery tank 12 and supply tank 11 can be integrated by aligning the periods so that adjacent power supply units do not apply positive voltages at the same time. That is, as shown in FIG. 26 , a multistage lithium isotope enrichment apparatus 10B according to a first modified example of the third embodiment of the present invention includes a treatment tank 7A, four electrolyte membranes (lithium ion conductive electrolyte membranes) 22, 23, 24, and 25 arranged in parallel at intervals so as to partition the treatment tank 7A in one direction into five tanks 11, 12, 13, 14, and 15, a first electrode 31B covering the front surfaces (the surfaces on the left in the figure) of the electrolyte membranes 22, 23, 24, and 25, a second electrode 32 covering the back surfaces of the electrolyte membranes 22, 23, 24, and 25, a third electrode 33 arranged opposite the second electrode 32, an auxiliary electrode 34 arranged opposite the first electrode 31B in the tank 11 at the supply side end, and a power supply unit 50B having four built-in power sources 51 and four built-in auxiliary power sources 52.

[0188] The multistage lithium isotope enrichment apparatus 10B has a structure in which four lithium isotope enrichment apparatuses 1G (see FIG. 20 ) are connected together so that each treatment tank 7 is integrated with a treatment tank 7A. The recovery tank 12 of one of two adjacent lithium isotope enrichment apparatuses 1G, 1G doubles as the supply tank 11 of the other. Furthermore, the third electrode 33 disposed in one recovery tank 12 doubles as the auxiliary electrode 34 disposed in the other supply tank 11. That is, the third electrode 33 in each of the tanks 12, 13, and 14 doubles as the auxiliary electrode 34. Furthermore, in each of the tanks 12, 13, and 14, the third electrode 33 is preferably disposed close enough to the first electrode 31B facing the recovery side thereof to prevent short-circuiting, so that the resistance between the third electrode 33 and the first electrode 31B facing the recovery side thereof is sufficiently low. Therefore, each tank, except for the tanks 11 and 15 at both ends, is preferably short in the partition direction (connection direction) of the treatment tank 7A. With this configuration, the multistage lithium isotope enrichment apparatus 10B according to this modification can reduce the number of parts and can be made smaller in size by shrinking it in the connecting direction.

[0189] The power supply device 50B includes four power supply devices 5B1, 5B2, 5B3, and 5B4, arranged in order from the supply side, each including a power supply 51 and a secondary power supply 52. ​​The power supply devices 5B1, 5B2, 5B3, and 5B4 correspond to the power supply device 5G of the lithium isotope enrichment device 1G, and will be referred to as the power supply device 5B as appropriate unless otherwise specified. The power supply device 5B includes switching elements 5s, which constitute three-pole switches that simultaneously connect / disconnect the power supply 51 and the secondary power supply 52, in order to alternately apply DC voltage to the power supply 51 and the secondary power supply 52, just like the power supply device 5G. 1a1 , 5s 1a2 , 5s 1c (collectively referred to as switching element 5s1 as appropriate) and switching element 5s forming a two-pole switch 2a , 5s 2c In each of the power supply devices 5B, the switching element 5s1 and the switching element 5s2 are configured not to be connected at the same time. 1a1 , 5s 1a2 The first electrode 31B and the second electrode 32, which face each other with one electrolyte membrane 2 sandwiched therebetween, are both connected to the positive electrode of the power source 51. 1c The switching element 5s connects the negative electrode of the power source 51 to the third electrode 33, which is disposed in the same tank as the second electrode 32 connected to the positive electrode of the power source 51. 2a , 5s 2c The positive and negative electrodes of the auxiliary power supply 52 are connected to the first electrode 31B and the third electrode 33 or the auxiliary electrode 34, which are arranged in the same tank. In addition, since the third electrode 33 also serves as the auxiliary electrode 34, the switching element 5s of the adjacent power supply device 5B 1c is the switching element 5s 2c It can be used for both purposes.

[0190] The power supply unit 50B is further configured so that the power supply units 5B of adjacent lithium isotope enrichment apparatuses 1G do not simultaneously connect the power supply 51 to the electrodes 31B, 32, and 33, i.e., do not simultaneously connect the switching element 5s1. Alternatively, when one of the adjacent power supply units 5B connects the power supply 51, the other may connect the auxiliary power supply 52 to the first electrode 31B and the third electrode 33 or the auxiliary electrode 34. To achieve this, two or more adjacent power supply units 5B of the lithium isotope enrichment apparatus 1G are grouped together, and one unit from each group alternately connects the switching element 5s1. Here, two adjacent power supply units 5B are grouped together, and the power supply units 5B1 and 5B3, and the power supply units 5B2 and 5B4 are driven synchronously. In addition, the power supply unit 50B may have a state where the power supply units 5B1 and 5B3 are connected to the power supply 51 and a state where the power supply units 5B2 and 5B4 are connected to the secondary power supply 52. ​​Similarly, the state where the power supply units 5B1 and 5B3 are connected to the secondary power supply 52 may have a state where the power supply units 5B2 and 5B4 are connected to the power supply 51. Therefore, the power supply unit 50B is connected because the negative electrodes of the supply-side power supplies 51 and the recovery-side secondary power supplies 52 of two adjacent power supply units 5B can be connected to the same third electrode 33 at the same time.

[0191] 26, the positive electrodes of the supply-side secondary power supplies 52 of two adjacent power supply units 5B may or may not be connected to the positive electrodes of the recovery-side power supplies 51. It is also preferable that the power supplies 51 and the secondary power supplies 52 are not grounded, or that only one of the power supplies 51 or the secondary power supplies 52 of the synchronized power supply units 5B (the power supplies 51 of the power supply units 5B1 and 5B2 in FIG. 26) is grounded to the reference potential. Furthermore, the power supply unit 50B may be configured such that the synchronized power supply units 5B1 and 5B3, and the synchronized power supply units 5B2 and 5B4 each have one power supply 51 and one secondary power supply 52. The power supply unit 50B is required to connect the power supply 51 to two adjacent tanks 12, 13, 14, and 15 so that the voltage +V1 is not applied between the second electrode 32 and the third electrode 33 within one tank at the same time, and when the power supply 51 is connected, to short-circuit the first electrode 31B that faces the second electrode 32 across the electrolyte membrane 2, and to prevent the auxiliary power supply 52 from being connected to this first electrode 31B. The circuit configuration of the power supply unit 50B shown in Figure 26 is one example.

[0192] Similar to the multistage lithium isotope enrichment apparatuses 10 and 10A (see FIGS. 9 and 18), the multistage lithium isotope enrichment apparatus 10B preferably further includes a stirrer (circulation means) 8 for circulating the aqueous solutions FS, ES, ES, ES, and ES in the tanks 11, 12, 13, 14, and 15, respectively. The multistage lithium isotope enrichment apparatus 10B may further include a cooling device (not shown) for cooling the electrolyte membranes 22, 23, 24, and 25, as necessary. The other elements are as described in the configurations of the lithium isotope enrichment apparatuses 1, 1F, and 1G and the multistage lithium isotope enrichment apparatuses 10 and 10A.

[0193] In the multistage lithium isotope enrichment apparatus 10B, the power supply units 5B1 and 5B3, and the power supply units 5B2 and 5B4 are driven in synchronization with each other, and adjacent power supply units 5B do not simultaneously apply the voltage +V1. CYC is the same and the electrodialysis period t ED and reset period t RST are the periods t CYC Less than 1 / 2 of (t ED <t CYCThe power supply units 5B1 and 5B3 and the power supply units 5B2 and 5B4 are set to the electrodialysis period t ED The power supplies 51 and sub-power supplies 52 of the power supply devices 5B1, 5B2, 5B3, and 5B4 are respectively indicated as power supplies 51(1), 51(2), 51(3), and 51(4), and sub-power supplies 52(1), 52(2), 52(3), and 52(4).

[0194] 27A , when power supply units 5B1 and 5B3 connect power supplies 51(1) and 51(3) using switching element 5s1 and apply voltage +V1, power supply units 5B2 and 5B4 may disconnect switching element 5s1 and connect secondary power supplies 52(2) and 52(4) using switching element 5s2 and apply voltage −V2. As a result, first electrode 31B and second electrode 32, which face each other across electrolyte membranes 22 and 24, are short-circuited and connected to the positive electrodes of power supplies 51(1) and 51(3), respectively, and third electrode 33, which is located in the same tank 12 or 14 as second electrode 32, is connected to the negative electrode. Furthermore, third electrode 33 is connected to the negative electrode of secondary power supplies 52(2) and 52(4), and first electrode 31B, which is located in the same tank 12 or 14, is connected to the positive electrode. On the other hand, the second electrode 32 and the third electrode 33 in the tanks 13 and 15, and the auxiliary electrode 34 in the tank 11 are in an open state. At this time, in the aqueous solutions ES1 and ES3 in the tanks 12 and 14, respectively, an electric field +E1 is generated between the second electrode 32 and the third electrode 33, and an electric field -E2 is generated between the third electrode 33 and the first electrode 31B. Then, Li + The Li-containing aqueous solution FS in the supply tank 11 permeates through the electrolyte membrane 22 to the aqueous solution ES in the tank 12, and then permeates through the electrolyte membrane 24 from the aqueous solution ES in the tank 13 to the aqueous solution ES in the tank 14. The Li-containing aqueous solution FS in the supply tank 11 permeates through the electrolyte membrane 22 to the aqueous solution ES in the tank 12, and then permeates through the electrolyte membrane 24 to the aqueous solution ES in the tank 14. + is quickly released by the electric field −E2.

[0195] 27B , when power supply units 5B2 and 5B4 connect power supplies 51(2) and 51(4) using switching element 5s1 to apply voltage +V1, power supply units 5B1 and 5B3 may disconnect switching element 5s1 and connect secondary power supplies 52(1) and 52(3) using switching element 5s2 to apply voltage -V2. As a result, first electrode 31B and second electrode 32, which face each other across electrolyte membranes 23 and 25, are short-circuited and connected to the positive electrodes of power supplies 51(2) and 51(4), respectively, and third electrode 33 in the same tanks 13 and 15 as second electrode 32 is connected to the negative electrode. Furthermore, secondary electrode 34 in tank 11 and third electrode 33 in tank 13 are connected to the negative electrodes of secondary power supplies 52(1) and 52(3), respectively, and first electrode 31B in the same tanks 11 and 13 is connected to the positive electrode. On the other hand, the second electrode 32 and the third electrode 33 in the tanks 12 and 14 are in an open state. At this time, an electric field -E2 is generated in the aqueous solution FS in the tank 11, an electric field +E1 is generated in the aqueous solution ES4 in the tank 15, and an electric field +E1 is generated between the second electrode 32 and the third electrode 33, and an electric field -E2 is generated between the third electrode 33 and the first electrode 31B in the aqueous solution ES2 in the tank 13. Then, Li + moves from the aqueous solution ES1 in the tank 12 through the electrolyte membrane 23 to the aqueous solution ES2 in the tank 13, and from the aqueous solution ES3 in the tank 14 through the electrolyte membrane 25 to the aqueous solution ES4 in the tank 15. In addition, Li in the aqueous solutions FS and ES2 that were adsorbed on the surfaces of the electrolyte membranes 22 and 24 + is quickly released by the electric field −E2.

[0196] In this manner, multistage lithium isotope enrichment apparatus 10B is operated by alternately connecting and disconnecting switching elements 5s1, 5s2 between power supplies 5B1, 5B3 and power supplies 5B2, 5B4. This causes voltage +V1 to be applied intermittently, generating an electric field +E1 between the rear surface of electrolyte membrane 2 and third electrode 33 in each of vessels 12, 14 and vessels 13, 15, alternating between the rear surface of electrolyte membrane 2 and third electrode 33. This increases the isotope separation factor for each of electrolyte membranes 2. Furthermore, in the adjacent vessel on the supply side, application of voltage −V2 subsequently generates an electric field −E2 between sub-electrode 34 or third electrode 33 and the surface of electrolyte membrane 2. This further increases the isotope separation factor even if the application of voltage +V1 is stopped for a short period of time.

[0197] The multistage lithium isotope enrichment apparatus 10B may be configured by connecting lithium isotope enrichment apparatuses 1H (see FIG. 24 ) so that the recovery tank 12 of one of two adjacent lithium isotope enrichment apparatuses 1H, 1H doubles as the supply tank 11 of the other. In this case, the third electrode 33 of one of the recovery tanks 12 is also used as the first electrode 31 disposed in the other supply tank 11.

[0198] In the multistage lithium isotope enrichment apparatus 10B according to this modification, similarly to the lithium isotope enrichment apparatuses 1G and 1H, the auxiliary power supply 52 may apply a voltage −V2 and then reverse the polarity to apply a voltage +V2 (see FIG. 25). As described above, two adjacent power supply units 5B are used as a pair, and therefore the application time (reset period) t RST and the application time of voltage +V2 (preparation period) t PREP The sum of (t RST +t PREP ) is the period t CYC Less than 1 / 2 of (t ED <t CYC / 2).

[0199] The multistage lithium isotope enrichment apparatus 10B according to this modification may be configured such that the power supply unit 50B drives three or more adjacent power supply units 5B as a group, similar to the multistage lithium isotope enrichment apparatus 10A according to the third embodiment. ED period t CYC Less than 1 / 3 of (t ED <t CYC / 3), three adjacent power supply devices 5B can be grouped into one set. RST and preparation period t PREP are each period t CYC Less than 1 / 3 of (t RST <t CYC / 3,t PREP <t CYC / 3), a voltage +V1 is applied to each of the three adjacent connected lithium isotope enrichment devices 1G (electrodialysis period t ED ), voltage −V2 is applied (reset period t RST ), voltage +V2 application (preparation period t PREP In such a multistage lithium isotope enrichment apparatus, the third electrode 33 and the first electrode 31B disposed in the integrated recovery tank 12 and supply tank 11 can be integrated, and the second electrode 32 and the sub-electrode 34 disposed in the recovery tank 12 and supply tank 11 can be integrated.

[0200] That is, as shown in FIG. 28 , a multistage lithium isotope enrichment apparatus 10C according to a second modified example of the third embodiment of the present invention includes a treatment tank 7A, six electrolyte membranes (lithium ion conductive electrolyte membranes) 22, 23, 24, 25, 26, and 27 arranged in parallel at intervals so as to partition the treatment tank 7A in one direction into seven tanks 11, 12, 13, 14, 15, 16, and 17, a first electrode 31B covering the front surfaces (the surfaces on the left in the figure) of the electrolyte membranes 22, 23, 24, 25, 26, and 27, a second electrode 32 covering the back surfaces of the electrolyte membranes 22, 23, 24, 25, 26, and 27, an auxiliary electrode 34 arranged opposite the first electrode 31B in the tank 11 at the end on the supply side, a third electrode 33 arranged opposite the second electrode 32 in the tank 15 at the end on the recovery side, and a power supply unit 50C having six built-in power sources 51 and six built-in auxiliary power sources 52.

[0201] The multistage lithium isotope enrichment apparatus 10C has a structure in which six lithium isotope enrichment apparatuses 1G (see FIG. 20 ) are connected together so that each treatment tank 7 is integrated with a treatment tank 7A, and the recovery tank 12 of one of two adjacent lithium isotope enrichment apparatuses 1G, 1G doubles as the supply tank 11 of the other. Furthermore, the third electrode 33 disposed in one of the recovery tanks 12 is also served as the first electrode 31B disposed in the other supply tank 11, and the second electrode 32 disposed in one of the recovery tanks 12 doubles as the auxiliary electrode 34 disposed in the other supply tank 11. That is, the first electrode 31B in each of tanks 12, 13, 14, 15, and 16 doubles as the third electrode 33, and the second electrode 32 doubles as the auxiliary electrode 34. Furthermore, in each of the tanks 12, 13, 14, 15, and 16, the second electrode 32 and the first electrode 31B are preferably arranged close enough to each other to prevent short-circuiting and to ensure sufficiently low resistance between them. Therefore, each tank, except for the tanks 11 and 17 at both ends, is preferably short in the partition direction (connection direction) of the treatment tank 7A. With this configuration, the multistage lithium isotope enrichment apparatus 10C according to this modification can reduce the number of parts and can be made smaller by shrinking in the connection direction.

[0202] The power supply unit 50C includes six power supply units 5C1, 5C2, 5C3, 5C4, 5C5, and 5C6, arranged in order from the supply side, each equipped with a power supply 51 and a sub-power supply 52. ​​The power supply units 5C1, 5C2, 5C3, 5C4, 5C5, and 5C6 each correspond to the power supply unit 5G of the lithium isotope enrichment unit 1G, and will be referred to as the power supply unit 5C as appropriate unless otherwise specified. In the power supply unit 5C, the power supply 51 and the sub-power supply 52 alternately apply DC voltage, similar to the power supply unit 5G, and the first electrode 31B and the second electrode 32 in the vessels 12 to 16 function as the third electrode 33 and the sub-electrode 34. Furthermore, the power supply unit 50C includes three adjacent power supply units 5C, and these power supply units 5C1 and 5C4, 5C2 and 5C5, and 5C3 and 5C6 are driven synchronously. For this purpose, the power supply device 5C includes a three-position switching element 5s that constitutes a four-pole switch that simultaneously switches the connection destination and connection / disconnection of the electrodes 31B, 32, 33, and 34. 31 , 5s 32 , 5s33 , 5s 34 (collectively referred to as switching element 5s as appropriate).

[0203] Switching element 5s 31 is a triple-throw switch that switches the connection destination of the first electrode 31B between three options: the positive electrode of the power source 51, the positive electrode of the auxiliary power source 52, and the negative electrode of either the auxiliary power source 52 or the power source 51. 32 The switching element 5s switches the connection of the second electrode 32 between three options: the positive electrode of the power source 51, the negative electrode of the auxiliary power source 52, or disconnection. 33 The switching element 5s switches between connecting and disconnecting the third electrode 33 to the negative electrode of the power supply 51. 34 The switching element 5s switches the connection of the auxiliary electrode 34 between three options: the negative electrode of the auxiliary power supply 52, the positive electrode of the auxiliary power supply 52, or disconnection. In addition, the first electrode 31B and the second electrode 32 disposed in the tanks 12 to 16 also serve as the third electrode 33 and the auxiliary electrode 34, respectively. 33 Only the power supply device 5C6 at the recovery side has a switching element 5s 34 are provided only in the power supply device 5C1 at the supply side end.

[0204] In addition, in the power supply device 50C, the negative electrodes of the supply-side power supplies 51 and the recovery-side secondary power supplies 52 of two adjacent power supply devices 5C are connected because they can be connected to the same first electrode 31B at the same time. Furthermore, as shown in FIG. 28 , the positive electrodes of the supply-side secondary power supplies 52 of two adjacent power supply devices 5C may or may not be connected to the positive electrodes of the recovery-side power supplies 51. It is preferable that the power supplies 51 and the secondary power supplies 52 are not grounded, or that only one of the power supplies 51 or the secondary power supplies 52 of the synchronized power supply devices 5C is grounded to a reference potential. Furthermore, the power supply device 50C may be configured such that each of the synchronized power supply devices 5C1 and 5C4, the power supply devices 5C2 and 5C5, and the power supply devices 5C3 and 5C6 has one power supply 51 and one secondary power supply 52. The power supply unit 50C connects the power supply 51 to two adjacent tanks among the tanks 12, 13, 14, 15, 16, and 17 so that the voltage +V1 is not applied simultaneously between two electrodes within one tank. When the power supply 51 is connected, the first electrode 31B, which faces the second electrode 32 across the electrolyte membrane 2, is short-circuited, and at this time, the auxiliary power supply 52 is not connected to this first electrode 31B, but is connected after the power supply 51 is disconnected. The circuit configuration of the power supply unit 50C shown in Figure 28 is one example.

[0205] Similar to the multistage lithium isotope enrichment apparatuses 10 and 10A (see FIGS. 9 and 18 ), the multistage lithium isotope enrichment apparatus 10C preferably further includes a stirrer (circulation means) 8 for circulating the aqueous solutions FS, ES, ES, ES, ES, ES, and ES in the tanks 11, 12, 13, 14, 15, 16, and 17, respectively. The multistage lithium isotope enrichment apparatus 10C may further include a cooling device (not shown) for cooling the electrolyte membranes 22, 23, 24, 25, 26, and 27, as necessary. The other elements are as described in the configurations of the lithium isotope enrichment apparatuses 1, 1F, and 1G and the multistage lithium isotope enrichment apparatuses 10, 10A, and 10B.

[0206] In the multistage lithium isotope enrichment apparatus 10C, the power supply units 5C1 and 5C4, the power supply units 5C2 and 5C5, and the power supply units 5C3 and 5C6 are driven in synchronization with each other, and adjacent power supply units 5C are driven so that they do not simultaneously apply the voltage +V1. Furthermore, in each of the tanks 12 to 16 except for the tanks 11 and 17 at both ends, the voltage +V1 applied between the second electrode 32 and the first electrode 31B functioning as the third electrode 33 also serves as the voltage +V2 applied between the second electrode 32 functioning as the auxiliary electrode 34 and the first electrode 31B. For this reason, all the power supply units 5C are driven in synchronization with each other with a period t CYC is the same and the electrodialysis period t ED , reset period t RST , and the preparation period t PREP are the periods t CYC Less than 1 / 3 of (t ED <t CYC / 3,t RST <t CYC / 3,t PREP <t CYC The power supply units 5C1 and 5C4, the power supply units 5C2 and 5C5, and the power supply units 5C3 and 5C6 are set to the electrodialysis period t ED are driven so as not to overlap.

[0207] A lithium isotope enrichment method using the multistage lithium isotope enrichment apparatus 10C will be described below with reference to Figures 29A, 29B, and 29C. In Figures 29A, 29B, and 29C, the power supplies 51 and sub-power supplies 52 of the power supply devices 5C1, 5C2, 5C3, 5C4, 5C5, and 5C6 are respectively referred to as power supplies 51(1), 51(2), 51(3), 51(4), 51(5), and 51(6), and sub-power supplies 52(1), 52(2), 52(3), 52(4), 52(5), and 52(6). Also in Figures 29A, 29B, and 29C, the third electrode 33 in the tank 17 and the switching element 5s connected thereto are respectively referred to as power supplies 51(1), 51(2), 51(3), 51(4), 51(5), and 51(6). 33 is omitted.

[0208] 29A , while power supply units 5C1 and 5C4 are connected to power supplies 51(1) and 51(4) and applying voltage +V1, the other power supply units 5C2, 5C3, 5C5, and 5C6 disconnect power supply 51, while power supply units 5C3 and 5C6 connect auxiliary power supplies 52(3) and 52(6) and apply voltage −V2. As a result, first electrode 31B and second electrode 32, which face each other across electrolyte membrane 22 and 25, are short-circuited and connected to the positive electrodes of power supplies 51(1) and 51(4), respectively, and first electrode 31B, which is located in the same tank 12 or 15 as second electrode 32, is connected to the negative electrode. Furthermore, second electrode 32 and first electrode 31B, which face each other in tank 13 or 16, are connected to the negative and positive electrodes of auxiliary power supplies 52(3) and 52(6), respectively. On the other hand, the auxiliary electrode 34 in the tank 11, the second electrode 32 in the tank 14, and the second electrode 32 and the third electrode 33 in the tank 17 (see FIG. 28) are in an open state. At this time, an electric field +E1 is generated in the aqueous solutions ES1 and ES4 in the tanks 12 and 15, respectively. Then, the Li + is attracted to the surfaces of the electrolyte membranes 23 and 26. Also, Li in the Li-containing aqueous solution FS in the supply tank 11 + moves through the electrolyte membrane 22 to the aqueous solution ES1. Similarly, Li in the aqueous solution ES3 in the tank 14 + The hydrogen permeates the electrolyte membrane 25 and moves to the aqueous solution ES4. At this time, O2 is generated near the electrodes 31B and 32 that cover both sides of the electrolyte membranes 22 and 25, and H2 is generated near the first electrodes 31B that cover the surfaces of the electrolyte membranes 23 and 26 (not shown). In addition, an electric field -E2 is generated in the aqueous solutions ES2 and ES5 in the tanks 13 and 16, respectively, and the Li in the aqueous solutions ES2 and ES5 that was adsorbed on the surfaces of the electrolyte membranes 24 and 27 is + will quickly withdraw.

[0209] Next, as shown in FIG. 29B , power supply units 5C1 and 5C4 connect secondary power supplies 52(1) and 52(4) and apply voltage −V2, while power supply units 5C2 and 5C5 connect power supplies 51(2) and 51(5) and apply voltage +V1. As a result, first electrode 31B and second electrode 32, which face each other across electrolyte membranes 23 and 26, are short-circuited and connected to the positive electrodes of power supplies 51(2) and 51(5), respectively. The first electrode 31B in the same tank 13 or 16 as second electrode 32 is connected to the negative electrode. Furthermore, the facing secondary electrode 34 or second electrode 32 and first electrode 31B in tank 11 or 14 are connected to the negative and positive electrodes of secondary power supplies 52(1) and 52(4), respectively. Meanwhile, the second electrode 32 in tank 12 or 15, and the second electrode 32 and third electrode 33 in tank 17 (see FIG. 28 ) are in an open state. At this time, an electric field −E2 is generated in each of the aqueous solutions FS and ES3 in the tanks 11 and 14, and the Li adsorbed on the surface of the electrolyte membranes 22 and 25 tries to permeate the aqueous solutions FS and ES3. + In addition, an electric field +E1 is generated in each of the aqueous solutions ES2 and ES5 in the tanks 13 and 16. Then, the Li + is attracted to the surfaces of the electrolyte membranes 24 and 27. Also, Li in the aqueous solution ES1 in the tank 12 + moves to the aqueous solution ES2 through the electrolyte membrane 23. Similarly, Li in the aqueous solution ES4 in the tank 15 + permeates the electrolyte membrane 26 and moves into the aqueous solution ES. At this time, O is generated near the electrodes 31B and 32 covering both sides of the electrolyte membranes 23 and 26, and H is generated near the first electrodes 31B covering the surfaces of the electrolyte membranes 24 and 27 (not shown).

[0210] 29C , power supplies 5C2 and 5C5 connect secondary power supplies 52(2) and 52(5) to apply voltage −V2, power supplies 5C3 and 5C6 connect power supplies 51(3) and 51(6) to apply voltage +V1, and power supply 5C1 then connects power supply 52(1) with the polarity reversed to apply voltage +V2. As a result, first electrode 31B and second electrode 32, which face each other across electrolyte membrane 24 and 27, are short-circuited and connected to the positive electrodes of power supplies 51(3) and 51(6), respectively, and first electrode 31B or third electrode 33 (see FIG. 28 ), which is located in the same tank 14 or 17 as second electrode 32, is connected to the negative electrode. Furthermore, second electrode 32 and first electrode 31B, which face each other in tank 12 or 15, are connected to the negative and positive electrodes of secondary power supplies 52(2) and 52(5), respectively. In addition, the facing auxiliary electrode 34 and first electrode 31B in the tank 11 are connected to the positive and negative electrodes of the auxiliary power supply 52(1). Meanwhile, the second electrode 32 in the tanks 13 and 16 is in an open state. At this time, an electric field -E2 is generated in the aqueous solutions ES1 and ES4 in the tanks 12 and 15, respectively, and the Li + In addition, an electric field +E2 is generated in the Li-containing aqueous solution FS in the supply tank 11, and an electric field +E1 is generated in the aqueous solutions ES3 and ES6 in the tanks 14 and 17, respectively. + is attracted to the surfaces of the electrolyte membranes 22 and 25. Also, Li in the aqueous solution ES in the tank 13 + moves through the electrolyte membrane 24 to the aqueous solution ES. Similarly, Li in the aqueous solution ES in the tank 16 + permeates the electrolyte membrane 27 and moves into the aqueous solution ES. At this time, O is generated near the electrodes 31B and 32 covering both sides of the electrolyte membranes 24 and 27, and H is generated near the first electrode 31B covering the surface of the electrolyte membrane 25 and the third electrode 33 in the tank 17 (not shown).

[0211] 29A , power supplies 5C3 and 5C6 connect sub-power supplies 52(3) and 52(6) to apply voltage −V2, and power supplies 5C1 and 5C4 connect power supplies 51(1) and 51(4) to apply voltage +V1. In this manner, multistage lithium isotope enrichment apparatus 10C operates by alternately connecting and disconnecting power supplies 51 and 52 between power supplies 5C1 and 5C4, power supplies 5C2 and 5C5, and power supplies 5C3 and 5C6. This causes voltage +V1 to be applied intermittently, generating electric fields +E1 alternately in tanks 12 and 15, tanks 13 and 16, and tanks 14 and 17, thereby increasing the isotope separation coefficient for each electrolyte membrane 2. Furthermore, thereafter, in the adjacent tank on the supply side, a voltage −V2, a voltage +V2, or a voltage +V1 is applied in sequence, and an electric field −E2, an electric field +E2, or an electric field +E1 is generated in sequence, so that the isotope separation factor can be further increased even if the period during which the application of the voltage +V1 is stopped is short.

[0212] Similar to the multistage lithium isotope enrichment apparatus 10A, the multistage lithium isotope enrichment apparatuses 10B and 10C according to this modification may be formed by connecting the lithium isotope enrichment apparatus 1G by bending it at one or two points by 90 degrees, and arranging adjacent electrolyte membranes 2, 2 perpendicular to each other. In the bent portion of the tank separated by the perpendicularly arranged electrolyte membranes 2, 2, the third electrode 33 and the sub-electrode 34 are not shared with other electrodes, i.e., the second electrode 32, the third electrode 33, the sub-electrode 34, and the first electrode 31B are all arranged, and the third electrode 33 and the sub-electrode 34 are arranged perpendicular to each other and spaced apart so as not to short-circuit.

[0213] The lithium isotope enrichment apparatuses 1G and 1H and the multistage lithium isotope enrichment apparatuses 10B and 10C according to the modified third embodiment, like the lithium isotope enrichment apparatus 1 and the multistage lithium isotope enrichment apparatus 10 according to the first embodiment, do not add Li to the Li-containing aqueous solution FS as in the lithium isotope enrichment apparatuses 1C, 1D, and 1E according to the second embodiment and its modified examples (FIGS. 10 to 15). + It is also possible to add a configuration to supplement the above.

[0214] The lithium isotope enrichment device and the lithium isotope enrichment method according to the present invention have been described above as embodiments for carrying out the present invention, but examples in which the effects of the present invention have been confirmed will be described below. It goes without saying that the present invention is not limited to these examples and the above embodiments, and that various changes and modifications based on these descriptions are also included in the spirit of the present invention.

[0215] The amount of change in lithium isotope ratio was measured for the lithium isotope enrichment apparatus according to the first embodiment of the present invention shown in FIG. 1 and the lithium isotope enrichment apparatus shown in FIG. 31 as a comparative example.

[0216] (Preparation of Lithium Isotope Enrichment Apparatus) The lithium isotope enrichment apparatus was prepared using a plate-shaped La 10 ... 0.57 Li 0.29 TiO3 (lithium ion conductive ceramics LLTO, manufactured by Toho Titanium Co., Ltd.) was used. Grid-shaped electrodes measuring 19.5 mm x 20.5 mm, 10 μm thick, 0.5 mm wide, and spaced 0.5 mm apart, were formed as the first and second electrodes in the center of each side of the electrolyte membrane. Lead wires were then formed to connect these electrodes to a power source. The first and second electrodes and lead wires were formed by screen-printing Pt paste onto the surface of the electrolyte membrane and firing it at 900°C for 1 hour in air. A 30 mm x 40 mm Ni mesh electrode was used as the third electrode. The electrolyte membrane with the electrodes formed on it was placed in an acrylic treatment tank, partitioned into a supply tank and a recovery tank. The third electrode was placed in the recovery tank so that it faced the second electrode on the electrolyte membrane surface (distance between the third electrode and the electrolyte membrane: 50 mm). The treatment tank was then placed in a thermostatic chamber with temperature control. The first electrode and the second electrode were connected by a lead wire, and a power source was connected between these electrodes and the third electrode, with the first electrode serving as a positive electrode, to form the lithium isotope enrichment device of Example 1.

[0217] In the comparative lithium isotope enrichment apparatus, a power source was connected between the first and second electrodes, with the first electrode serving as the positive electrode, without using a third electrode (see FIG. 31 ). Similarly to Example 1, an electrode was formed on only one side of the electrolyte membrane using Pt paste, and the electrolyte membrane was installed in a treatment tank with this electrode serving as the second electrode. A 30 mm × 40 mm Pt mesh electrode was placed in the supply tank as the first electrode, facing the electrolyte membrane (distance between the first electrode and the electrolyte membrane: 50 mm), to form the lithium isotope enrichment apparatus of Example 2 (see FIG. 1 ).

[0218] As the Li-containing aqueous solution, 7 Li: 92.23 mol%, 6 A 1 mol / L lithium hydroxide aqueous solution containing 7.77 mol% Li was prepared, and 150 ml of the solution was poured into the supply tank of the lithium isotope enrichment device so that the first electrode was completely immersed. Further, the lithium hydroxide aqueous solution was stored in a tank installed outside the treatment tank of the lithium isotope enrichment device in a thermostatic bath as a replacement. Meanwhile, a recovery tank was filled with 6 150 ml of pure water was added as an aqueous solution for recovering Li so that the second electrode and the third electrode were completely immersed. The liquid temperatures of the lithium hydroxide aqueous solution and the pure water in the thermostatic bath were adjusted to 20°C.

[0219] (Lithium Isotope Enrichment Experiment) In Examples 1 and 2, a DC voltage of 2.0 V was applied between the first electrode and the second and third electrodes for 12 hours. In Comparative Example, a DC voltage of 2.0 V was applied between the first electrode and the second electrode for 12 hours. 2.0 V was the voltage at which the LLTO (electrolyte membrane) was enriched with Li. + The voltage at which the material exhibits conductivity and electronic conductivity is not exhibited or is sufficiently small. + In order to suppress changes in the concentration of the lithium hydroxide aqueous solution in the supply tank due to the movement, the lithium hydroxide aqueous solution was replenished from an external tank to the supply tank at a constant rate by a liquid transfer pump while a voltage was being applied, and was also pumped out at the same rate.

[0220] After the experiment, the aqueous solution in the recovery tank was collected and 7 Li, 6 The amount of Li was measured using an inductively coupled plasma mass spectrometer (ICP-MS) (Elan drc-e, manufactured by PerkinElmer Co., Ltd.).7 Li, 6 From the amount of Li, Li + amount of movement( 7 Li, 6 Li), Li per hour of voltage application time + Movement amount (Li + mobility), and 6 The Li isotope separation factor was calculated. 6 The Li isotope separation factor is (of the aqueous solution in the recovery tank after voltage application) 6 Li / 7 Li) molar ratio) / (( of the lithium hydroxide aqueous solution in the supply tank before voltage application) 6 Li / 7 Li) molar ratio). + Movement amount (Li per application time of voltage + V1) + Travel amount, Li + mobility), and by applying voltage for 12 h 6 The Li isotope separation factors are shown in Table 1 and FIG.

[0221]

[0222] As shown in Table 1 and FIG. 30, in comparison with the comparative example in which a voltage was applied between both surfaces of the electrolyte membrane, in Examples 1 and 2 in which the potential difference between both surfaces of the electrolyte membrane was set to 0 V and a potential difference was provided in the recovery tank, 6 The Li isotope separation factor was high. + By moving only due to the chemical potential difference, 6 It was confirmed that the Li concentration effect was obtained. Furthermore, even if the first electrode was in contact with or separated from the electrolyte membrane, 6 The Li isotope separation coefficients were similar. + The mobility was comparable to that of the comparative example.

[0223] DESCRIPTION OF SYMBOLS 1, 1A, 1C to 1H Lithium isotope enrichment apparatus 1B Lithium isotope enrichment apparatus (multistage lithium isotope enrichment apparatus) 10, 10A, 10B, 10C Multistage lithium isotope enrichment apparatus 11 Supply tank (first tank) 12 Recovery tank (second tank) 1z Replenishment tank (lithium replenishment tank) 1y Raw material tank 2 Electrolyte membrane (lithium ion conductive electrolyte membrane) 21 Electrolyte membrane (lithium replenishment lithium ion conductive electrolyte membrane) 22, 23, 24, 25, 26, 27 Electrolyte membrane (lithium ion conductive electrolyte membrane) 31, 31A, 31B First electrode 32, 32A Second electrode 33, 33A Third electrode 34, 34A Sub-electrode 41 Fourth electrode 42, 42A Fifth electrode 50, 50B, 50C Power supply device 5, 5G, 5H Power supply device 5A1 to 5A4, 5B1 to 5B4, 5C1 to 5C6 Power supply device 51, 51A Power supply 52 Sub-power supply 6 Ion exchange membrane 7, 7A, 7B Treatment tank 8 Agitator (circulation means) FS Li-containing aqueous solution ES 6 Li recovery aqueous solution

Claims

1. a lithium ion conductive electrolyte membrane; a treatment tank partitioned into a first tank and a second tank by the lithium ion conductive electrolyte membrane; a first electrode provided in one of the first and second tanks, and a porous second electrode provided in contact with a surface of the lithium ion conductive electrolyte membrane facing the other tank; a third electrode provided in the other tank on the opposite side of the lithium ion conductive electrolyte membrane from the second electrode and spaced apart from the second electrode; a power source that applies the same voltage to the first electrode and the second electrode with respect to the third electrode, with the first tank side being positive; contained in the first tank, 6 Li and 7 Li and Li in the state of lithium ions, 6 A lithium isotope enrichment apparatus, characterized in that an aqueous solution containing lithium ions with a high Li isotope ratio is recovered in the second tank.

2. the first electrode is provided in the first tank, the second electrode is provided in contact with a surface of the lithium ion conductive electrolyte membrane facing the second tank, the third electrode is provided in the second tank, 2. The lithium isotope enrichment device according to claim 1, wherein the power supply applies a positive voltage to the first electrode and the second electrode relative to the third electrode.

3. a sub-electrode provided in the first tank and spaced apart from the first electrode; one of the first electrode and the sub-electrode is spaced from the first tank side surface of the lithium ion conductive electrolyte membrane, and the other has a porous structure and is in contact with the first tank side surface; 3. The lithium isotope enrichment device according to claim 2, wherein the power supply alternately applies a positive voltage to the first electrode and the second electrode with respect to the third electrode, and applies a voltage between the first electrode and the sub-electrode with one of the electrodes being negative.

4. 4. The lithium isotope enrichment device according to claim 3, wherein the power supply applies the voltage between the first electrode and the auxiliary electrode with one side positive after applying the voltage between the first electrode and the auxiliary electrode with one side negative and before applying the voltage between the first electrode and the second electrode with the positive voltage relative to the third electrode.

5. 3. The lithium isotope enrichment device according to claim 2, wherein the power supply applies the voltage intermittently.

6. the treatment tank is partitioned into a lithium replenishment tank, the first tank, and the second tank in this order; a lithium ion conductive electrolyte membrane for lithium replenishment that separates the lithium replenishment tank from the first tank; a fourth electrode disposed within the lithium replenishment reservoir; a fifth electrode disposed in the first vessel in contact with or facing the lithium ion conducting electrolyte membrane for lithium replenishment; a lithium replenishment power source connected between the fourth electrode and the fifth electrode, with the fourth electrode as a positive electrode; The lithium replenishment tank contains 6 Li and 7 6. The lithium isotope enrichment device according to claim 1, wherein lithium ions are transferred from an aqueous solution containing Li in the form of lithium ions to the aqueous solution contained in the first tank.

7. A multistage lithium isotope enrichment apparatus comprising two or more connected lithium isotope enrichment apparatuses according to any one of claims 1 to 5, A multistage lithium isotope enrichment apparatus, characterized in that two adjacent lithium isotope enrichment apparatuses are connected via an aqueous solution transfer means that allows the aqueous solution contained in one of the second tanks to flow into the other of the first tanks.

8. A multistage lithium isotope enrichment apparatus comprising two or more lithium isotope enrichment apparatuses according to any one of claims 1 to 5, connected together so that the treatment tanks are integrated, the lithium ion conductive electrolyte membranes of the lithium isotope enrichment device are arranged apart from each other so as to separate the integrated treatment tank into three or more tanks; A multistage lithium isotope enrichment apparatus, wherein the second tank of one of two adjacent lithium isotope enrichment apparatuses also serves as the first tank of the other.

9. A multistage lithium isotope enrichment apparatus comprising two or more lithium isotope enrichment apparatuses according to claim 5, connected together so that the treatment tanks are integrated, the lithium ion conductive electrolyte membranes of the lithium isotope enrichment device are arranged apart from each other so as to separate the integrated treatment tank into three or more tanks; A multistage lithium isotope enrichment apparatus, characterized in that, in two adjacent lithium isotope enrichment apparatuses, the second tank of one also serves as the first tank of the other, and the third electrode of one also serves as the first electrode of the other.

10. A multistage lithium isotope enrichment apparatus comprising two or more lithium isotope enrichment apparatuses according to claim 3 or 4, connected together so that the treatment tanks are integrated, the lithium ion conductive electrolyte membranes of the lithium isotope enrichment device are arranged apart from each other so as to separate the integrated treatment tank into three or more tanks; A multistage lithium isotope enrichment apparatus, characterized in that, in two adjacent lithium isotope enrichment apparatuses, the second tank of one also serves as the first tank of the other, and the third electrode of one also serves as the first electrode or the auxiliary electrode of the other.

11. A multistage lithium isotope enrichment apparatus comprising two or more lithium isotope enrichment apparatuses according to claim 3 or 4, connected together so that the treatment tanks are integrated, the lithium ion conductive electrolyte membranes of the lithium isotope enrichment device are arranged apart from each other so as to separate the integrated treatment tank into three or more tanks; A multistage lithium isotope enrichment apparatus, characterized in that, of two adjacent lithium isotope enrichment apparatuses, the second tank of one also serves as the first tank of the other, the second electrode of one also serves as the auxiliary electrode of the other, and the third electrode of one also serves as the first electrode of the other.

12. A multistage lithium isotope enrichment apparatus comprising the lithium isotope enrichment apparatus according to any one of claims 2 to 4, two or more of the lithium ion conductive electrolyte membranes are provided, and the treatment tank is partitioned into three or more tanks in the order of the first tank, one or more intermediate tanks, and the second tank; a second electrode provided in contact with the lithium ion conductive electrolyte membrane separating the first tank from the adjacent intermediate tank;

13. a lithium ion conductive electrolyte membrane for replenishing lithium, which further partitions the partitioned treatment chamber so that a lithium replenishment chamber is provided at the end of the first chamber side; a fourth electrode disposed within the lithium replenishment reservoir; a fifth electrode disposed in the first reservoir adjacent to the lithium replenishment reservoir in contact with or facing the lithium replenishment lithium ion conductive electrolyte membrane; a lithium replenishment power source connected between the fourth electrode and the fifth electrode, with the fourth electrode as a positive electrode; The lithium replenishment tank contains 6 Li and 7 9. The multistage lithium isotope enrichment apparatus according to claim 8, wherein lithium ions are transferred from an aqueous solution containing Li in the form of lithium ions to the aqueous solution contained in the first tank adjacent to the lithium replenishment tank.

14. In a treatment tank partitioned into a first tank and a second tank by a lithium ion conductive electrolyte membrane, 6 Li and 7 Li and Li in the state of lithium ions, 6 A method for enriching lithium isotopes, in which an aqueous solution containing lithium ions having a high Li isotope ratio is recovered in the second tank, a first electrode provided in one of the first and second tanks, a second electrode having a porous structure provided in contact with a surface of the lithium ion conductive electrolyte membrane facing the other tank, and a third electrode provided in the other tank and spaced apart from the second electrode on the opposite side of the lithium ion conductive electrolyte membrane.

15. the first electrode is provided in the first tank, the second electrode is provided in contact with a surface of the lithium ion conductive electrolyte membrane facing the second tank, and the third electrode is provided in the second tank; 15. The method for enriching lithium isotopes according to claim 14, wherein a positive voltage is applied to the first electrode and the second electrode relative to the third electrode.

16. 16. The method for enriching lithium isotopes according to claim 14, wherein the voltage is applied intermittently.

17. a first step of applying the positive voltage between the first electrode, the second electrode and the third electrode; a second step of applying a voltage between the first electrode and a sub-electrode provided in the first tank at a distance from the first electrode, with a positive voltage being applied to one of the first electrode and the sub-electrode, the one having a porous structure and in contact with a surface of the lithium ion conductive electrolyte membrane facing the first tank, and a negative voltage being applied to a other of the first electrode and the sub-electrode spaced from the surface.

18. a third step of applying a voltage between the auxiliary electrode and the first electrode in a direction opposite to that of the second step; 18. The method for enriching lithium isotopes according to claim 17, wherein the first step, the second step, and the third step are repeated in this order.

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