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

Abstract

A lithium isotope concentration device (10) has a treatment tank (1) divided into a supply tank (11) and a recovery tank (12) by an electrolyte membrane (2) having lithium ion conductivity, and the electrolyte membrane (2) is cooled by a cooling device (6) using a Li-containing aqueous solution (ASi) in the supply tank (11), whereby 6 A low temperature at which the Li isotope separation factor is large, and a positive voltage is applied to the electrode (31) on the supply tank (11) side by a power source (5) connected between the electrodes (31), (32) provided on both sides of the electrolyte membrane (2).

Description

Technical Field

[0001] This invention relates to a lithium isotope concentration apparatus for separating lithium isotopes, a multi-stage lithium isotope concentration apparatus, and a lithium isotope concentration method. Background Technology

[0002] Lithium (Li) exists 7 Li and 6 The natural abundance ratio of these two stable isotopes, Li, is 92.41 mol% and 7.59 mol%, respectively. (Mass number 7) 7 Li and a mass number of 6 6 The properties of Li vary considerably, for example 7 Li is used to adjust the pH (hydrogen ion concentration) of the coolant in nuclear reactors. On the other hand, 6 Li is used in the production of tritium (tritium), a fuel for nuclear fusion reactors. Therefore, a technology has been developed to... 7 Li and 6 Li can be concentrated and separated into states with fewer isotopes of another substance. Known methods include amalgamation, molten salt methods, distillation, and selective recovery of lithium ions (Li) from seawater. + Methods such as adsorption and electrodialysis (e.g., Patent Document 1).

[0003] From an environmental impact perspective, adsorption or electrodialysis methods are superior to amalgamation methods (which use large amounts of mercury), molten salt methods (which involve heating lithium compounds at high temperatures), or distillation methods. Furthermore, these methods utilize the high-speed transport of large quantities of recovered materials due to their small mass. 6 Li + While the principle is similar, the isotope separation coefficient is small, resulting in low productivity as a concentration method. Therefore, the inventors discovered that in the concentration of lithium isotopes using electrodialysis, the isotope separation coefficient is large only in the short period after the start of operation, and thus invented a method to improve efficiency by intermittently applying voltage (Patent Document 2, Non-Patent Document 1). [Existing Technical Documents] [Patent Literature]

[0004] Patent Document 1: Japanese Patent Publication No. 5429658 Patent Document 2: Japanese Patent Publication No. 2019-141808 [Non-patent literature]

[0005] Non-patent document 1: Shunsuke Honda, Kiyoto Shin-mura, Kazuya Sasaki, "Lithiumisotope enrichment by electrochemical pumping using solid lithiumelectrolytes", Journal of the Ceramic Society of Japan, Volume 126, Issue 5, pp331-335, May 2018 Summary of the Invention [The technical problem that the invention aims to solve]

[0006] The method described in Patent Document 2, etc., has room for further improvement in order to increase the isotope separation coefficient.

[0007] The present invention was made in view of the aforementioned problems, and the technical problem to be solved is to provide a safe and more efficient lithium isotope concentration device and a multi-stage lithium isotope concentration device, as well as a lithium isotope concentration method. [Technical solutions used to solve technical problems]

[0008] The inventors have conducted in-depth research on the concentration of lithium isotopes using electrodialysis, and have found that... 7 Li + and 6 Li + The mobility of the particles exhibits different degrees of temperature and voltage dependence, leading to the consideration of setting the temperature and applied voltage to appropriate ranges.

[0009] That is, the lithium isotope concentration apparatus according to the present invention is configured as follows: having a processing tank divided into a first tank and a second tank, the second tank being used to extract lithium isotopes contained in the first tank in the form of lithium ions. 6 Li and 7 Recovery of Li containing Li in aqueous solution 6An aqueous solution of lithium ions with a higher isotope ratio of Li than the aqueous solution, comprising a lithium-ion conductive electrolyte membrane, porous electrodes, a power supply device, and a cooling device, wherein the lithium-ion conductive electrolyte membrane is used to separate the processing tanks; the porous electrodes are arranged to contact both sides of the lithium-ion conductive electrolyte membrane; the power supply device applies a voltage between the electrodes; and the cooling device cools the lithium-ion conductive electrolyte membrane. Furthermore, the multi-stage lithium isotope concentration apparatus of the present invention is configured by connecting two or more lithium isotope concentration apparatuses in an integrated manner with the processing tank, wherein the lithium-ion conductive electrolyte membranes of each lithium isotope concentration apparatus are separately arranged to separate the integrated processing tank into three or more tanks, the second tank of one of two adjacent lithium isotope concentration apparatuses also serves as the first tank of the other, and the cooling device cools the aqueous solution contained in at least one of the separated processing tanks.

[0010] According to the structure described, lithium ions in 6 Li + and 7 Li + The difference in migration rate is large at low temperatures, allowing them to move within the lithium-ion conductive electrolyte membrane. 6 Li moves more and is recycled.

[0011] The lithium isotope concentration method of this invention involves using a processing tank divided into a first tank and a second tank by a lithium-ion conductive electrolyte membrane, to extract lithium isotopes contained in the first tank from the second tank. 6 Li and 7 Recovery of Li containing Li in aqueous solution 6 A method for preparing an aqueous solution of lithium ions with a higher isotope ratio of Li than that of the aqueous solution. Furthermore, in the lithium isotope concentration method according to the present invention, the lithium-ion conductive electrolyte membrane is cooled to below 20°C, and a voltage is applied between electrodes of a porous structure disposed in such a manner that they are in contact with both sides of the lithium-ion conductive electrolyte membrane, with the first tank side being positive.

[0012] According to the method described above, lithium ions are made in 6 Li + and 7 Li + Under conditions of large differences in migration rates, they can move within the lithium-ion conductive electrolyte membrane, thereby enabling... 6 Li + More of it is moved and recycled. [Invention Effects]

[0013] The lithium isotope concentration apparatus and method according to the present invention can efficiently and safely recover lithium isotopes. 6 Li isotope ratios are higher in aqueous solutions. Furthermore, the multi-stage lithium isotope concentration apparatus according to the present invention can further improve… 6 Isotope ratio of Li. Attached Figure Description

[0014] Figure 1 This is a schematic diagram illustrating the structure of a lithium isotope concentration apparatus according to an embodiment of the present invention. Figure 2 This describes the electrodialysis of lithium ions. Figure 1 A schematic diagram of a lithium isotope concentration device is shown. Figure 3A This is an explanation Figure 1 A magnified view of the main part of the movement of lithium ions in the initial state during the electrodialysis of lithium ions in the lithium isotope concentration apparatus shown. Figure 3B This is an explanation Figure 1 A magnified view of the main part of the movement of lithium ions after the initial movement has just begun during the electrodialysis of lithium ions in the lithium isotope concentration apparatus shown. Figure 3C This is an explanation Figure 1 A magnified view of the main part of the movement of lithium ions during the electrodialysis process of lithium ions in the lithium isotope concentration apparatus shown. Figure 4 It is a model that illustrates ion conduction in electrolytes. Figure 5 It is a graph illustrating the dependence of applied voltage on the amount of lithium ions moving per unit time and the isotope ratio in the electrodialysis obtained through simulation. Figure 6A It is a graph illustrating the temperature dependence of the amount of lithium ions moving per unit time and the isotope ratio in the electrodialysis of lithium ions obtained through simulation. Figure 6B yes Figure 6A A magnified view of a portion of the image. Figure 7 This is a schematic diagram illustrating the structure of a multi-stage lithium isotope concentration apparatus according to an embodiment of the present invention. Figure 8 This is a graph showing the temperature dependence of lithium migration and lithium isotope separation coefficient in the examples and comparative examples. Figure 9 This is a graph showing the dependence of applied voltage on the amount of lithium movement and the lithium isotope separation coefficient involved in the embodiments and comparative examples. Detailed Implementation

[0015] Referring to the accompanying drawings, the manner in which the lithium isotope enrichment apparatus and method according to the present invention are described. In the drawings, for clarity, the size of certain elements is sometimes exaggerated, or the shape is sometimes simplified.

[0016] [Lithium Isotope Concentration Unit] like Figure 1 As shown, the lithium isotope concentration apparatus 10 according to the embodiments of the present invention includes a processing tank 1, an electrolyte membrane (lithium-ion conductive electrolyte membrane) 2, a first electrode 31 and a second electrode 32 (electrodes) covering each side of the electrolyte membrane 2, a power supply device 5, and a cooling device 6. The processing tank 1 is divided by the electrolyte membrane 2 into a supply tank (first tank) 11 containing an aqueous solution of Li (ASi) and a tank containing... 6 The lithium isotope concentration apparatus consists of two tanks: a recovery tank (second tank) 12 for the Li recovery aqueous solution ASi. The power supply 5 has a DC power supply, with its positive (+) terminal connected to the first electrode 31 located on the supply tank 11 side and its negative (-) terminal connected to the second electrode 32 located on the recovery tank 12 side. The cooling device 6 cools the electrolyte membrane 2 using the Li-containing aqueous solution ASi within the supply tank 11. Hereinafter, the elements constituting the lithium isotope concentration apparatus according to the embodiments of the present invention will be described.

[0017] Treatment tank 1 consists of a Li-containing aqueous solution containing ASi and 6 The material used for Li recovery is made of a material that will not corrode or deteriorate upon contact with the aqueous solution ASo. Furthermore, the treatment tank 1 only needs to have a volume corresponding to the required processing capacity; its shape and other characteristics are not particularly limited.

[0018] Electrolyte membrane 2 is an electrolyte with lithium-ion conductivity, preferably without electron conductivity. - Furthermore, in the Li-containing aqueous solution ASi, Li is present. + In the case of metal ions other than those present, it is preferable that the electrolyte membrane 2 does not conduct these metal ions. More preferably, a ceramic electrolyte possessing these properties is preferred. Specifically, lithium lanthanum titanium oxide (La) can be cited as an example. 2 / 3-x Li 3x TiO3 (also known as LLTO), etc. Such an electrolyte membrane 2 has lattice defects at a certain ratio. Because the size of these lattice defect sites is small, it does not conduct electricity with a diameter greater than that of Li. + Large metal ions. For example, in solid electrolytes like LLTO with a perovskite (ABO3) structure (A = Li, La or vacancy, B = Ti), a portion of the A sites have vacancies (A-site defects). Furthermore, as explained later in the section on lithium isotope enrichment methods, Li... + Infiltrating the A-position defect, Li +The defects at nearby A sites move between each other. Hereinafter, the sites that may contain Li, like the A site, will be called Li sites, and the Li sites with vacancies will be called Li site defects.

[0019] The first electrode 31 and the second electrode 32 are a pair of electrodes provided to apply voltage from both sides in a manner that makes contact with each side of the electrolyte membrane 2. The first electrode 31 and the second electrode 32 apply voltage over a large area of ​​the electrolyte membrane 2, and on the other hand, have a porous structure such as a mesh to ensure sufficient contact between the aqueous solutions ASi and ASo and the area of ​​each side of the electrolyte membrane 2. The first electrode 31 is provided on the side of the electrolyte membrane 2 on the supply tank 11 side (hereinafter, appropriately referred to as the surface), and has catalytic activity and electronic conductivity for the reaction of the following formula (1). It is formed of an electrode material that is stable when a voltage is applied in the Li-containing aqueous solution ASi, for example, platinum (Pt). The second electrode 32 is provided on the side of the electrolyte membrane 2 on the recovery tank 12 side (hereinafter, appropriately referred to as the back side), and has catalytic activity and electronic conductivity for the reaction of the following formula (2). It is formed by the reaction containing Li... + of 6 Electrode materials that are stable when a voltage is applied in an aqueous solution of Li for Li recovery are formed, for example, those formed from Pt. [Chemical Formula 1] 2Li + (electrolyte) + 2H₂O + 2e - -→2OH - +H2↑+2Li+(ASo)…(2)

[0020] The power supply device 5 is a DC power supply device, with its positive terminal connected to the first electrode 31 and its negative terminal connected to the second electrode 32, and a specified voltage V is applied.

[0021] Cooling device 6 is provided to maintain electrolyte membrane 2 at a specified temperature, using a Li-containing aqueous solution ASi or 6 The Li-recovery aqueous solution ASi is used to cool the electrolyte membrane 2. The cooling device 6 can be any known device for cooling liquids, preferably with temperature control functionality. In this embodiment, the cooling device 6 is an immersion type, where the pipe through which the refrigerant flows (refrigerant pipe) is immersed in the Li-containing aqueous solution ASi in the supply tank 11. The cooling device 6 only needs to maintain the electrolyte membrane 2 at a predetermined temperature; it is not necessary to use the Li-containing aqueous solution ASi... 6 The aqueous solution ASo used for Li recovery is at a uniform temperature. However, a stirring device may be included depending on the volume of the treatment tank 1. Regarding the temperature of the electrolyte membrane 2, it should be below 30°C, a temperature at which the aqueous solutions ASi and ASo will not freeze, for example, when... 6The aqueous solution ASo for Li recovery is kept above 0°C at the start of operation (electrodialysis start) of the lithium isotope concentration unit 10, assuming it is pure water. This will be explained in detail later. The aqueous solution ASi containing Li or... 6 The temperature of the Li recovery aqueous solution ASi is measured instead of the temperature of the electrolyte membrane 2. Similar to the treatment tank 1, the refrigerant pipe of the cooling device 6 is connected to the Li-containing aqueous solution ASi... 6 The material used for Li recovery, ASi, is made of a material that will not corrode or deteriorate upon contact with the aqueous solution, and its shape is not particularly specified. For example, to efficiently cool the electrolyte membrane 2, the refrigerant tube is bent in a planar shape to correspond to the size of the plate-shaped electrolyte membrane 2, and is located near the larger area of ​​the electrolyte membrane 2 and arranged in an opposing manner. Alternatively, the refrigerant tube can be inserted into both the supply tank 11 and the recovery tank 12, depending on the thickness of the electrolyte membrane 2. Furthermore, the cooling device 6 can also be configured such that the processing tank 1 has a double-layer structure (casing) with refrigerant flowing inside (the casing). Alternatively, it can be configured to use a pump to circulate the Li-containing aqueous solution ASi or... 6 The aqueous solution Aso used for Li recovery is circulated to the outside of treatment tank 1 and cooled by a heat exchanger.

[0022] ASi, containing Li in an aqueous solution, is a Li source. 7 Li and 6 Li cations 7 Li + , 6 Li + An aqueous solution, such as a lithium hydroxide (LiOH) aqueous solution, is used at the start of operation of the lithium isotope concentration unit 10, containing at a natural abundance ratio. 7 Li + , 6 Li + . 6 Li recovery aqueous solution ASo is used to contain large quantities of lithium ions (Li) recovered from Li-containing aqueous solutions ASi. + ,especially 6 Li + The aqueous solution, for example, is pure water, at the start of operation of the lithium isotope concentration unit 10. Furthermore, in this specification, in... 7 Li and 6 Li ( 7 Li + and 6 Li + In the absence of distinction between them, they are collectively referred to as Li (Li + ).

[0023] [Lithium Isotope Concentration Method] The lithium isotope concentration method according to embodiments of the present invention will be described. First, refer to... Figure 2 The electrodialysis of lithium ions performed in the lithium isotope concentration apparatus described in the embodiments will be explained. Furthermore, in Figure 2 The cooling device 6 is omitted in the lithium isotope concentration device 10 shown.

[0024] In the lithium isotope concentration device 10, when the power supply device 5 applies a positive voltage +V relative to the second electrode 32 to the first electrode 31, hydroxide ions (OH-) in the Li-containing aqueous solution ASi near the first electrode 31 are released. - The reaction of equation (3) occurs, causing electrons e to... - Emission is directed towards the first electrode 31, thereby producing water (H2O) and oxygen (O2). In the Li-containing aqueous solution ASi, as OH... - To reduce the charge and maintain charge balance, Li in the Li-containing aqueous solution ASi is reduced near electrolyte membrane 2. + The reaction of equation (4) moves into electrolyte membrane 2. Combining the reactions of equations (3) and (4), the reaction of equation (1) occurs near the first electrode 31. On the other hand, near the second electrode 32, through... 6 Li recovery uses aqueous solution ASO, H2O is supplied with electrons e - The reaction shown in equation (5) occurs, thereby producing hydrogen (H2) and OH. - .exist 6 Li is recovered in an aqueous solution of ASO, along with OH... - To maintain charge balance, an increase in Li in electrolyte membrane 2 occurs near electrolyte membrane 2. + The reaction of the following equation (6) is moved over. If the reactions of the following equation (5) and the following equation (6) are combined, the reaction of the following equation (2) occurs near the second electrode 32. [Chemical Formula 2] Li + (ASi)→Li + (electrolyte)…(4) 2H2O+2e - →2OH - +H2↑…(5) Li + (electrolyte)→Li + (ASo)…(6) 2Li + (electrolyte) + 2H₂O + 2e -→2OH - +H2↑+2Li + (ASo)…(2)

[0025] When these reactions occur, using an aqueous Li-containing solution ASi, an electrolyte membrane 2, and... 6 The Li recovered by aqueous solution ASo contains Li. + (Li + (ASi), Li + (electrolyte), Li + The electrochemical potential difference of (ASo) makes Li + From the Li-containing aqueous solution ASi, through the electrolyte membrane 2, to... 6 The Li-containing aqueous solution ASi moves to the first electrode 31 along with the electrons. - The amount of movement per unit time, from the second electrode 32 to 6 Li recovers electrons from aqueous solution ASO. - The greater the amount of movement per unit time, the faster these reactions occur. Therefore, the larger the voltage +V, the more Li moves from the first electrode 31 side to the second electrode 32 side in the electrolyte membrane 2. + The more electrons per unit time (mobility), the greater the mobility. However, in reality, when the voltage +V increases to a certain extent, the electrolyte membrane 2 also conducts electrons e. - Therefore, although Li + The mobility continues to increase, but the voltage dependence decreases. Here, refer to... Figures 3A-3C Detailed explanation of Li + Actions during passage through the electrolyte membrane 2. Figures 3A-3C This is an enlarged cross-sectional view of the vicinity of the electrolyte membrane 2 in the lithium isotope concentration device 10, showing partial contact between electrodes 31 and 32 and two sides of the electrolyte membrane 2. Additionally, in aqueous solutions of ASi and ASo, only those containing [specific components] are considered. 7 Li + , 6 Li + Use ○ to circle each one.

[0026] When no voltage is applied, such as Figure 3A As shown, 7 Li + , 6 Li + The sample is floated in a Li-containing aqueous solution ASi, and adsorption on the surface of electrolyte membrane 2 and detachment from the surface of electrolyte membrane 2 are alternately and repeatedly performed. Starting from this state, as... Figure 3BAs shown, a positive voltage is applied to the first electrode 31, and a negative voltage is applied to the second electrode 32. Furthermore, in the figure, positive charges are represented by + in circles, and negative charges are represented by - in circles. Thus, Li in the Li-containing aqueous solution ASi... + ( 7 Li + , 6 Li + The reaction described in equation (4) is intended to dissolve in the electrolyte membrane 2. At this time, Li adsorbed near the Li site defects on the surface of the electrolyte membrane 2... + The Li site defect is penetrated. Then, due to the electrodes 31 and 32, the electrolyte membrane 2 has a potential gradient on the back side that is lower than that on the surface, allowing the Li to penetrate the Li site defect on the surface. + The Li site defect near the deeper side of electrolyte membrane 2 jumps (jumps). Thus, Li... + Repeatedly moving from the Li site defect in electrolyte membrane 2 to the nearby Li site defect, ultimately as the reaction described in equation (6), such as Figure 3C As shown, the Li site defect on the back side moves to 6 Li is recovered in an aqueous solution of ASO.

[0027] Additionally, on the surface of electrolyte membrane 2, Li adsorbed near Li site defects + It moves deeper into the electrolyte membrane 2, thereby adsorbing another Li in its vicinity. + It moves over and dives into vacated Li site defects, or adsorbs new Li from Li-containing aqueous solutions (ASi). + And these Li + Similarly, it moves within electrolyte membrane 2. Furthermore, it moves through Li... + Moving within electrolyte membrane 2, the Li site defects are affected by Li. + Whether it is filled in or vacated again, the newly generated Li site defects on the surface of electrolyte membrane 2 enable the adsorbed Li on the surface to be filled in or vacated again. + It begins to move towards the back side.

[0028] Reference Figure 4 To further explain Li in detail + Interpositional movement (jumping) within electrolyte membrane 2. Figure 4 This is a model illustrating ion conduction in an electrolyte, where x represents the position along the thickness direction of electrolyte membrane 2, and E... p This represents potential energy. In electrolyte membrane 2, Li + ( 7 Li + , 6 Li + The Li site exists stably with minimal potential energy, but nearby Li sites are vacant (represented by dashed ○). When subjected to activation energy E...a At the above energy level, it is possible to overcome the energy barrier E between (jump) positions. m And move to that position defect (E) a =E D / 2+E m E D (Defect generation energy). Furthermore, it can be assumed that the ion undergoes thermal vibration at a frequency Γ0 at a location with minimal potential energy, and thus can jump at a frequency (jump 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 relatively small mass, and is 7 Li is 6 / 7 times, therefore the frequency Γ0 is 7 Li is (√(7 / 6)) times, as detailed below. The average moving velocity in electrolyte membrane 2 is 7 The speed of Li is (√(7 / 6)) times higher. Furthermore, for example, at a certain Li site defect relative to electrolyte membrane 2, two equidistant locations nearby exist respectively. 7 Li + and 6 Li + In this case, it is speculated that 6 Li + Redirect here first.

[0029] In addition, the Li sites in electrolyte membrane 2, i.e., in the ground state... 7 Li + , 6 Li + The potential energy rises to zero point oscillation hω I The quantity. Zero-point vibration hω I Dependent on isotopes, 6 Li + Compare 7 Li + Large. Similarly, in the excited state, 6 Li + Zero-point vibration hω S It is also larger. Therefore, its mass is greater than that of other substances. 7 Li + small 6 Li + In the ground state and excited state, considering the zero-point vibration hω I hω S Their potential energy is high. However, 6 Li + E is the energy barrier representing the potential difference between the excited state and the ground state. m Smaller (E) m ( 7 Li + )>E m (6 Li + )), that is, activation energy E a Smaller. As a result, 6 Li + Even if the energy received is higher 7 Li + Even small animals can jump. Li + The activation energy E in the energy received a The more remaining Li, the greater the amount of movement per unit time, i.e., the higher the mobility μ. Therefore, the larger the applied voltage +V, the greater the Li + The higher the migration rate, the better. Additionally, 6 Li + By 7 Li + A small voltage +V achieves the same activation energy E. a The remaining energy, and at this time, 6 Li + The mobility μ is higher than the frequency Γ0 by a certain amount. Figure 5 The figure shows the simulation per unit time. 6 Li + , 7 Li + Quantity of movement and moving Li + The voltage dependence of the isotope ratio is applied. In the simulation, the activation energy E according to the Maxwell-Boltzmann distribution is represented by a normal distribution. a The distribution was approximated. Specifically, for each... 6 Li + , 7 Li + According to the activation energy E a The probability density of a normal distribution with average value is calculated based on the energy received each time, exceeding the activation energy E. a (set up 6 Li + < 7 Li + ) of Li + The ratio of isotopes is calculated, and its cumulative value is multiplied by the frequency Γ0 ratio to determine the relative value of mobility μ. 7 Li + and 6 Li + The abundance ratio was calculated by setting it to 1:1 in order to simplify the simulation.

[0030] like Figure 5 As shown, 6 Li + , 7 Li + The mobility increases from 0 in an S-shaped curve as the applied voltage +V increases, relative to7 Li + Activation energy E a small 6 Li + The voltage shifts towards the side with a smaller +V value, and also increases by a factor exceeding the frequency Γ0. Furthermore, Figure 5 limμ represents the value per unit time. 6 Li + The limit of the amount of movement. Therefore, applying a voltage +V makes... 6 Li + The smaller the range of movement within electrolyte membrane 2, the better. 6 Li + Compared to 7 Li + It moves more. Moreover, when the applied voltage +V increases... 6 Li + , 7 Li + When the mobilities converge, the difference between them decreases, and the isotope ratio converges to (√(7 / 6)) / (1+√(7 / 6)). However, in practice, it is believed that when the voltage +V is increased, 6 Li + , 7 Li + The migration rate reaches Figure 5 Before reaching the limit shown, the voltage dependence decreases significantly. Specifically, as described above, when the voltage applied between the two sides of the electrolyte membrane 2 increases to a certain value, a portion of the transition metal ions constituting the electrolyte membrane 2 are reduced (e.g., if the electrolyte membrane 2 is LLTO, then Ti...). 4+ +e - →Ti 3+ Electrolyte membrane 2 conducts electrons e from the recovery tank 12 side to the supply tank 11 side. - As a result, most of the electrical energy provided is consumed by electrons. - The conduction consumption, therefore Li + The voltage dependence of Li mobility decreases. + The energy efficiency during movement decreases. Furthermore, due to the reduction of some of the transition metal ions constituting electrolyte membrane 2, the ionic radius of the reduced ions increases (e.g., if electrolyte membrane 2 is LLTO, then Ti...). 4+ <Ti 3+ ), used for Li + The bottleneck of movement widens, thus making the movement of Li... + of 6 The lithium isotope ratio decreases sharply. Additionally, due to the electrons (e) conducted in electrolyte membrane 2... - The resulting Joule heating causes the temperature of electrolyte membrane 2 to rise, therefore, as described later, the moving Li+ of 6 The Li isotope ratio decreases. Specifically, while it also depends on the electronic conductivity of the electrolyte membrane 2, electronic conductivity can be exhibited in the electrolyte membrane 2 when a voltage exceeding 2.0V is applied. Therefore, a voltage +V of 2.0V or less is preferred, and since a smaller applied voltage results in a larger isotope separation coefficient, a voltage +V of 1.5V or less is more preferred, and 1.0V or less is even more preferred. On the other hand, the lower limit of the voltage +V is not particularly specified, as long as it allows the Li isotope ratio to decrease. + It can move within the electrolyte membrane 2. For example, although it also depends on the electronic conductivity of the electrolyte membrane 2 or the hydrogen ion concentration of the aqueous solution ASi or ASo, it is preferably set in the range of 0.5V or higher. However, since the smaller the applied voltage +V, the more Li... + The lower the migration rate μ, the better the desired level is one that does not excessively reduce productivity.

[0031] Furthermore, the ion mobility μ is the relationship between the ion diffusion coefficient D and the following equation (7) (T: temperature (K), k: Boltzmann constant). The diffusion coefficient D, as shown in the following equation (8), is proportional to the hopping rate Γ (a: average distance between sites (hopping length), n...). c : carrier density, f: correlation coefficient determined by ions and their surroundings, d: diffusion field size). Furthermore, the frequency factor Γ0 of equation (8) is proportional to temperature T, as shown in equation (9). Additionally, (Z s vib / Z I vib The frequency factor Γ0 is inversely proportional to the square root of the mass number m, therefore it is also inversely proportional to the square root of the mass number m (h: Planck's constant, Z). s vib Phonon allocation function of saddle point, Z I vib : Phonon distribution function in the initial state, C1: constant). According to equations (8) and (9), the diffusion coefficient D is represented by equation (10). Moreover, according to equations (7) and (10), the ion mobility μ is represented by equation (11) (C2: constant). As shown in equation (11), the mass number m and activation energy E a smaller 6 Li + ion mobility μ ratio 7 Li + High. Moreover, the ion mobility μ depends on temperature T, and the degree of dependence is affected by the activation energy E. a The impact. [Mathematical Expression 1] kTμ=D…(7)

[0032] Based on equation (11), the relative temperature dependence is calculated per unit time. 7 Li + , 6 Li + Quantity of movement and moving Li + The isotope ratio, in Figure 6A The activation energy E is shown in the figure. a Is it set 7 Li + It is 0.30 eV. 6 Li + Calculated at 0.25 eV. Similar to the voltage-dependent simulation, the isotopic ratio is calculated by shifting the original value before... 7 Li + and 6 Li + The abundance ratio was calculated as 1:1. For example... Figure 6A As shown, 7 Li + , 6 Li + The mobility increases exponentially with increasing temperature, and the activation energy E a big 7 Li + The temperature dependence is greater. Therefore, as the temperature increases, the low mobility... 7 Li + With high mobility 6 Li + The ratio decreases. Specifically, for example... Figure 6A As shown, 6 The Li isotope ratio decreases sharply from around 1 in the low-temperature region where mobility is extremely low, and then decreases gradually with increasing temperature, converging to (√(7 / 6)) / (1+√(7 / 6)). Thus, the lower the temperature, the more Li migrates. + In 6 Li + The higher the ratio.

[0033] In this embodiment, the applicable temperature range is above the freezing point and below the boiling point of the aqueous solutions ASi and ASo. 6 The aqueous solution ASo for Li recovery is maintained at 0–100°C when the solution is pure water at the start of electrodialysis. Figure 6B The middle shows Figure 6A A magnified view of temperatures ranging from -50°C to 50°C. (See image below.) Figure 6B As shown, within the applicable temperature range of this embodiment,6 The temperature dependence of the Li isotope ratio is approximately linear, increasing at lower temperatures. Accordingly, the temperature of the electrolyte membrane 2 is preferably below 20°C, more preferably below 15°C, even more preferably below 10°C, and still more preferably below 5°C.

[0034] In the lithium isotope concentration method described in this embodiment, as the applied voltage time elapses, the Li remaining in the Li-containing aqueous solution ASi... + of 6 Li isotope ratio ( 6 Li / ( 7 Li+ 6 Li decreases, therefore the newly moved Li + of 6 The lithium isotope ratio decreases. Therefore, in order to concentrate more efficiently... 6 Li, for example, can be found in 6 The aqueous solution ASo used for Li recovery met the specified Li standards. + The concentration, or after a specified voltage application time, is adjusted, and the Li-containing aqueous solution ASi in the supply tank 11 is replaced. Alternatively, to increase the isotope separation coefficient, the voltage +V can be applied intermittently, or the reverse voltage -V′ (V > V′) can be applied alternately, in a manner where the isotope separation coefficient is high at the beginning of repeated voltage application (operation) (see Patent Document 2, Non-Patent Document 1). Regarding the period after electrodialysis... 6 Li recovery using aqueous solution ASO, for example, can be achieved by evaporating water to concentrate Li as needed, followed by the generation of lithium carbonate (Li₂CO₃) through bubbling with carbon dioxide (CO₂), causing it to precipitate, thereby recovering the lithium. 6 Li can be recovered. Alternatively, after the formation of lithium carbonate, lithium hydroxide (LiOH) can be generated in a supersaturated state through cooling or water evaporation, causing it to precipitate and thus recover the lithium. 6 Li is recycled.

[0035] (Modified Example) In the lithium isotope concentration method described in this embodiment, the lower the temperature of the electrolyte membrane 2, the higher the efficiency. 6 Li isotope ratio was used to recover it (see reference). Figure 6A , Figure 6B However, it requires an aqueous solution containing Li (ASi). 6 Li recovery using aqueous solution ASO is cooled above its freezing point in a way that prevents freezing. Therefore, aqueous solutions ASi, ASO, especially... 6The aqueous solution ASo for Li recovery can also contain a solute that does not permeate the electrolyte membrane 2, so that the freezing point is lowered to below 0°C. Such a solute is one in which the aqueous solution ASi or ASo will not corrode the electrolyte membrane 2 or electrodes 31, 32, etc. Specifically, examples include salts such as sodium chloride (NaCl), magnesium chloride (MgCl2), calcium chloride (CaCl2), and potassium chloride (KCl), or organic solvents such as ethylene glycol. As mentioned above, in order to recover from the end of electrodialysis... 6 Li recovery using aqueous solution ASO recovery 6 Li and carbon dioxide are bubbled, and in this case, sodium chloride, which does not produce precipitates (carbonates) other than lithium carbonate and has a significantly lower freezing point, is particularly preferred. Furthermore, 6 In the case where the aqueous solution ASo for Li recovery concentrates Li by evaporating water before bubbling carbon dioxide, it is preferable to remove the salts precipitated due to water reduction using conventional methods such as filtration before bubbling. Alternatively, for the recovery... 6 The Li recovery aqueous solution ASo can also selectively recover Li in pure water or the like, by performing conventional electrodialysis at a temperature above 0°C, such as room temperature, before carbon dioxide bubbling (see, for example, Japanese Patent Publication No. 2019-141807). According to this method, the electrolyte membrane 2 can be cooled to below 0°C, more preferably to below 0°C, thereby further improving… 6 Li isotopes can be concentrated more efficiently.

[0036] [Multi-stage lithium isotope concentration unit] The lithium isotope concentration device 10 of the present invention obtains lithium isotopes containing lithium in the recovery tank 12. 6 The Li isotope ratio is higher than that of the Li aqueous solution containing Li-Si in the supply tank 11. 6 Li recovery using aqueous solution (ASo). Therefore, by recovering this Li... 6 When the aqueous solution ASo for Li recovery is added to an empty supply tank 11, it is possible to obtain a solution containing Li. 6 Li aqueous solutions with a further higher isotopic ratio. Therefore, as Figure 7 As shown, by forming a cascade structure in which the recovery tank 12 of the lithium isotope concentration device 10 is integrated with the supply tank 11 of another lithium isotope concentration device 10, staged concentration is possible. 6Li. This multi-stage lithium isotope concentration apparatus 20 includes a processing tank 1A, four parallel electrolyte membranes (lithium-ion conductive electrolyte membranes) 2 spaced apart at intervals to divide the processing tank 1A into five tanks 11, 12, 13, 14, and 15 in one direction, a first electrode 31 and a second electrode 32 (electrodes) respectively covering each side of the electrolyte membranes 2, a power supply 50, and a cooling device 6A. The power supply 50 includes a power supply device 5 for each electrolyte membrane 2 connecting the electrodes 31 and 32 on both sides of the lithium isotope concentration apparatus 10 (see reference). Figure 1 The multi-stage lithium isotope concentrator 20 is configured to connect adjacent power supply units 5 in series. Furthermore, when voltage is applied intermittently, it is preferable to synchronize all power supply units 5. In the multi-stage lithium isotope concentrator 20, the second electrode 32 and the first electrode 31, disposed on opposite sides of two adjacent electrolyte membranes 2, are short-circuited by a conductor connection. The cooling device 6A has two refrigerant pipes for the input tanks 12 and 14 to cool the four electrolyte membranes 2. Furthermore, the number of refrigerant pipes and the structure of the cooling device 6A are not limited, as long as all electrolyte membranes 2 can be cooled to a specified temperature. Other elements are as described in the structure of the lithium isotope concentrator 10. That is, the multi-stage lithium isotope concentrator 20 is a structure in which four lithium isotope concentrators 10 are connected in such a way that each processing tank 1 is integrated into a processing tank 1A, and the recovery tank 12 of one of two adjacent lithium isotope concentrators 10 also serves as the supply tank 11 of the other.

[0037] The lithium isotope concentration method implemented by the multi-stage lithium isotope concentration device 20 is the same as the method implemented by the lithium isotope concentration device 10. In the figure, lithium isotope concentrations containing natural abundance ratios are added to the supply tank 11 at the left end. 7 Li, 6 Li-containing aqueous solution ASi is prepared, and pure water is added to other tanks 12, 13, 14, and 15. Positive voltages +V are applied through multiple power supplies of power supply unit 50. In the figure, Li... + Moving from left to right, the pure water in tanks 12, 13, 14, and 15 becomes purified water with different concentrations of... 6 Aqueous solutions of Li with different Li isotope ratios: AS1, AS2, AS3, ASo. 6 The isotopic ratios of Li increase in the order Asi < As1 < As2 < As3 < Aso. Therefore, even if Li + The isotope separation coefficient achieved by movement within an electrolyte membrane 2 is not large, and recovery is also possible. 6 Li has a high isotopic ratio, therefore it does not require low temperature and low voltage to oxidize Li. + The migration rate is drastically reduced, thereby increasing productivity.

[0038] In the multi-stage lithium isotope concentration device 20, there is no particular requirement for the number of electrolyte membranes 2 and the number of first electrodes 31 and second electrodes 32 provided for each electrolyte membrane 2. The more electrolyte membranes 2 there are, that is, the more lithium isotope concentration devices 10 are connected, the more lithium isotope can be recovered. 6 Li has a high isotope ratio. Additionally, in Figure 7 In this configuration, the lithium isotope concentration device 10 is connected in one direction and all adjacent electrolyte membranes 2,2 are arranged facing each other. However, for example, they can be connected at 90° bends at 1 and 2 locations and the adjacent electrolyte membranes 2,2 are arranged perpendicular to each other. Example

[0039] The foregoing has described the methods for implementing the present invention, including the lithium isotope enrichment apparatus and method. The following describes embodiments that demonstrate the effectiveness of the present invention. Furthermore, the present invention is not limited to these embodiments and methods; various modifications and alterations made based on these descriptions are naturally included within the scope of the present invention.

[0040] against Figure 1 The lithium isotope enrichment apparatus according to the embodiment of the present invention shown measures the change in the lithium isotope ratio by changing the applied voltage conditions.

[0041] (Construction of a lithium isotope concentration device) The lithium isotope enrichment device used 50mm×50mm, 0.5mm thick plate-shaped La... 0.57 Li 0.29 TiO3 (lithium-ion conductive ceramic LLTO, manufactured by Toho Titanium Co., Ltd., Japan) is used as the electrolyte membrane. Comb-shaped electrodes, 10 μm thick, 0.5 mm wide, and spaced 0.5 mm apart, are formed in the central area of ​​each of the two sides of the electrolyte membrane as the first and second electrodes. Leads for connecting to a power source are also formed on these electrodes. The first electrode, second electrode, and leads are formed by screen printing Pt paste onto the surface of the electrolyte membrane and firing it at 900°C for 1 hour in atmospheric conditions. The electrolyte membrane with the electrodes is installed in an acrylic plate processing tank, which is divided into a supply tank and a recovery tank. The processing tank is housed in a temperature-controlled thermostat to create a lithium isotope concentration device.

[0042] Add to the supply tank of the lithium isotope concentration unit 7 Li: 92.23 mol%, 6 Li: A 1 mol / L lithium hydroxide aqueous solution containing 7.77 mol% Li was used as the Li-containing aqueous solution. 150 ml of pure water was added to the recovery tank as... 6The lithium recovery solution was used to completely immerse the first and second electrodes. Then, the temperature of the lithium hydroxide aqueous solution and pure water in the treatment tank was adjusted to 20°C.

[0043] The power supply was connected to the first and second electrodes. After adjusting to the specified liquid temperature and allowing at least 12 hours to pass, the first electrode was used as the positive electrode, and a voltage of 2.0V was applied for 3600 seconds. During the voltage application, the current value was measured using an ammeter connected in series with the power supply, and the aqueous solutions in both the supply and recovery tanks were stirred. After the voltage was applied, the aqueous solution in the recovery tank was recovered, and the concentration of [unspecified substance] in the aqueous solution was determined using an inductively coupled plasma mass spectrometry (ICP-MS) device (Elan drc-e, PerkinElmer Co., Ltd.). 7 Li, 6 The amount of Li was measured. The supply and recovery tanks were replaced to change the liquid temperature, and a voltage of 2.0V was applied for 3600 seconds each time. The liquid temperature was adjusted in 5°C increments from 20°C to 50°C, and then adjusted to 0°C. Furthermore, at a liquid temperature of 20°C, a voltage of 1.0 to 2.0V was applied for 3600 seconds in 0.25V increments, and then again in 0.5V increments for 3600 seconds. After each voltage application, the concentration of Li in the aqueous solution recovered from the recovery tank was measured. 7 Li, 6 The amount of Li, and by 7 Li, 6 The amount of Li was calculated 6 Li isotope segregation coefficient. 6 The Li isotope separation coefficient is set as (the aqueous solution in the recovery tank after applying voltage) 6 Li / 7 Li) molar ratio) / (Li hydroxide aqueous solution in the supply tank before voltage application) 6 Li / 7 Li) molar ratio). In Figure 8 The text indicates an application time of 3600 seconds. 6 Li + Movement (hollow circle: ○) and 6 The temperature dependence curve of the Li isotope segregation coefficient (solid circle: ●) is shown in the figure. Figure 9 The graph shows its dependence on applied voltage.

[0044] like Figure 8 As shown, the lower the temperature, the better. 6 The higher the isotope segregation coefficient of Li, the better. 6 Li + The amount of movement decreases, but at 0°C it remains at about half of what it was at 25°C, so it can be considered that a sufficient amount can be recovered. Additionally, as... Figure 9 As shown, the lower the applied voltage, the better. 6The higher the isotope separation coefficient of Li, the more... 6 Li + The amount of movement decreases, becoming negligible at 0.5V. At 20℃ and 1.25V, 6 The isotope segregation coefficient of Li is equivalent to 0℃ and 2.0V, but 6 Li + The amount of movement is approximately 1 / 2, compared to that achieved by cooling. 6 Li isotope enrichment is less efficient than traditional methods. Therefore, it can be assumed that combining cooling and voltage control can improve efficiency. 6 The separation coefficient of Li isotopes is increased, thus improving efficiency. [Explanation of reference numerals in the attached figures]

[0045] 10: Lithium isotope concentration device; 20: Multi-stage lithium isotope concentration device; 1, 1A: Processing tank; 11: Supply tank (tank 1); 12: Recovery tank (tank 2); 2: Electrolyte membrane (lithium-ion conductive electrolyte membrane); 31: First electrode (electrode); 32: Second electrode (electrode); 5: Power supply device; 50: Power supply device; 6, 6A: Cooling device; ASi: Li-containing aqueous solution; ASo: 6 Li recovery using aqueous solution.

Claims

1. A lithium isotope concentration apparatus having a processing tank divided into a first tank and a second tank, wherein the second tank is used to extract lithium isotopes contained in the first tank in the form of lithium ions. 6 Li and 7 Recovery of Li containing Li in aqueous solution 6 An aqueous solution of lithium ions with a higher isotopic ratio of Li than the aqueous solution, characterized in that... The lithium isotope concentration device includes a lithium-ion conductive electrolyte membrane, porous electrodes, a power supply, and a cooling device. The lithium-ion conductive electrolyte membrane is used to separate the processing tank; the porous electrode is arranged to contact both sides of the lithium-ion conductive electrolyte membrane respectively; the power supply device applies voltage between the electrodes; and the cooling device cools the lithium-ion conductive electrolyte membrane.

2. The lithium isotope concentration apparatus according to claim 1, characterized in that, The power supply device applies voltage intermittently.

3. The lithium isotope concentration apparatus according to claim 1, characterized in that, The power supply device applies positive and negative voltages alternately.

4. The lithium isotope concentration apparatus according to any one of claims 1 to 3, characterized in that, The cooling device keeps the temperature of the lithium-ion conductive electrolyte membrane below 20°C.

5. The lithium isotope concentration apparatus according to any one of claims 1 to 3, characterized in that, The cooling device cools the aqueous solution contained in at least one of the first tank and the second tank.

6. A multi-stage lithium isotope concentration device, characterized in that it is constructed by connecting two or more lithium isotope concentration devices according to any one of claims 1 to 5 in an integrated manner with the processing tank, wherein... The lithium-ion conductive electrolyte membranes of the lithium isotope concentration device are configured to be separated from each other in such a way that the integrated processing tank is divided into three or more tanks. The second tank of one of the two adjacent lithium isotope enrichment units also serves as the first tank of the other. The cooling device cools the aqueous solution contained in at least one of the separated treatment tanks.

7. A method for concentrating lithium isotopes, comprising, in a processing tank divided into a first tank and a second tank by a lithium-ion conductive electrolyte membrane, using the second tank to extract lithium isotopes contained in the first tank in the form of lithium ions. 6 Li and 7 Recovery of Li containing Li in aqueous solution 6 The isotope ratio of Li is higher than that of the aqueous solution containing lithium ions. Its features are, The lithium-ion conductive electrolyte membrane is cooled to below 20°C, and a voltage is applied between the porous electrodes with the first groove side as positive, wherein the porous electrodes are arranged to contact both sides of the lithium-ion conductive electrolyte membrane respectively.

8. The lithium isotope concentration method according to claim 7, characterized in that, The aqueous solutions contained in the first tank and the second tank each have a freezing point of less than 0°C. The lithium-ion conductive electrolyte membrane is cooled to a temperature greater than the freezing point but less than 0°C, while the voltage is applied.

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