Method for recovering lithium

Abstract

The present invention provide a means for reducing the cost of waste liquid treatment in a technique for recovering lithium from a lithium ion-containing aqueous solution. According to the present invention, there is provided a lithium recovery method for recovering lithium from a lithium ion-containing aqueous solution, the lithium recovery method comprising: obtaining a mixture containing a gas hydrate from a gas and the lithium ion-containing aqueous solution; obtaining a lithium ion concentrated aqueous solution (1) by separating the gas hydrate from the mixture; and recovering lithium from the lithium ion concentrated aqueous solution (1).

Description

How to recover lithium

[0001] The present invention relates to a method for recovering lithium, and more particularly to a method for recovering lithium from an aqueous solution containing lithium ions.

[0002] Lithium (Li) is widely used in batteries such as lithium-ion secondary batteries, in the ceramics industry as an additive for pottery and glass, and as a moisture absorbent for air conditioning equipment, flux in continuous casting, and as a raw material for grease. In recent years, the consumption of lithium has been on the rise due to the expanding demand for automobile batteries and other products, and this has led to a demand for technologies to recover lithium resources.

[0003] Chinese Patent Application Publication No. 110527849 discloses a continuous lithium enrichment system using a hydrate method, which is intended to recover lithium resources from seawater, salt lake brine, etc. The document describes that the system includes a lithium solution circulation system and a cyclopentane circulation system, and that the lithium solution and cyclopentane are mixed and cooled in a hydrate reactor to obtain a hydrate and a concentrated lithium-containing solution. The document also describes that the produced hydrate solid is maintained in the reactor, and the concentrated lithium-containing solution is returned to the lithium solution circulation system to increase the lithium concentration in the lithium solution, thereby obtaining a lithium-containing solution with a desired concentration.

[0004] According to the technology described in the above document, the lithium concentration in a lithium solution can be increased by separating water from the lithium solution as a hydrate (a hydrate of cyclopentane, also called cyclopentane hydrate). When the hydrate is heated, it separates into two phases: a cyclopentane phase and an aqueous phase. While the cyclopentane phase can be recycled to the cyclopentane circulation system, the aqueous phase is unnecessary and is therefore discarded as waste liquid. Furthermore, the solution obtained after recovering lithium from a concentrated lithium-containing solution is also unnecessary and is discarded as waste liquid. However, these waste liquids contain residual cyclopentane, which is environmentally hazardous, and therefore must be removed from the waste liquid before disposal. Such waste liquid treatment is costly (in terms of money, time, and / or labor), ultimately leading to increased lithium recovery costs.

[0005] Therefore, an object of the present invention is to provide a means for reducing the cost of waste liquid treatment in a technique for recovering lithium from an aqueous solution containing lithium ions.

[0006] The present inventors have conducted extensive research to solve the above-mentioned problems, and as a result, have found that the above-mentioned problems can be solved by separating water contained in a lithium ion-containing aqueous solution by gas hydration in concentrating the lithium ion-containing aqueous solution, thereby completing the present invention.

[0007] That is, one aspect of the present invention is a method for recovering lithium from a lithium ion-containing aqueous solution, the method comprising: obtaining a mixture containing a gas hydrate from a gas and the lithium ion-containing aqueous solution; separating the gas hydrate from the mixture to obtain a lithium ion-enriched aqueous solution (1); and recovering lithium from the lithium ion-enriched aqueous solution (1).

[0008] Hereinafter, embodiments of the present invention will be described, but the technical scope of the present invention should be determined based on the claims and is not limited to the following embodiments.

[0009] One aspect of the present invention is a method for recovering lithium from a lithium ion-containing aqueous solution, the method comprising the steps of obtaining a mixture containing gas hydrate from a gas and the lithium ion-containing aqueous solution (hereinafter also referred to as a “gas hydrate production step (A)” or “step (A)”), separating the gas hydrate from the mixture to obtain a lithium ion-enriched aqueous solution (1) (hereinafter also referred to as a “gas hydrate separation step (B)” or “step (B)”), and recovering lithium from the lithium ion-enriched aqueous solution (1) (hereinafter also referred to as a “lithium ion recovery step (C)” or “step (C)”). This aspect makes it possible to reduce waste liquid treatment costs in a technology for recovering lithium from a lithium ion-containing aqueous solution.

[0010] Hereinafter, each step of the lithium recovery method according to the present embodiment will be described in detail.

[0011] The present embodiment relates to a method for recovering lithium from a lithium-ion-containing aqueous solution. The lithium-ion-containing aqueous solution to be recovered can be any water containing dissolved lithium ions, such as brine (e.g., seawater, salt lake water, geothermal brine, hot spring water, etc.), a lithium-ion-containing aqueous solution obtained during the recycling process of lithium-containing products (e.g., lithium-ion batteries (LiBs)), concentrated seawater that is a by-product of seawater desalination, or concentrated seawater that is a by-product of soda salt production. The following is an example of a method for obtaining a lithium-ion-containing aqueous solution from LiBs. First, the LiBs are inactivated by heat treatment or the like and then crushed to remove materials derived from the casing, resin, and current collector metal. The remaining positive electrode active material, negative electrode active material, and black mass (concentrated slag containing nickel, manganese, cobalt, lithium, etc.) derived from the electrolyte are brought into contact with water, and the lithium is dissolved in the water, thereby obtaining a lithium-ion-containing aqueous solution. Other elements than lithium, such as nickel, manganese, and cobalt, are insoluble in water, so they are recovered separately by hydrometallurgy, in which the black mass obtained after dissolving lithium in water is dissolved in an acid solution to extract the metal ions.

[0012] The concentration of lithium ions contained in the lithium ion-containing aqueous solution is not particularly limited, but is preferably 10 －５ mol / kg or more 10 －１ mol / kg or less, more preferably 10 －５ mol / kg or more 10 －２ mol / kg or less, and more preferably 10 －５ mol / kg or more 10 －３ mol / kg or less.

[0013] Conventionally, it has not been easy to separate alkali metal ions (monovalent cations) from alkaline earth metal ions (divalent cations) and recover only the alkali metal ions. However, in the lithium recovery method according to the present embodiment (particularly, in the step (A)), ２ Using a gas containing CO ２ According to the lithium recovery method that generates a hydrate of lithium, lithium can be easily recovered from a lithium ion-containing aqueous solution that contains alkaline earth metal ions. Therefore, in a preferred embodiment of the lithium recovery method of the present invention, the lithium ion-containing aqueous solution contains at least one selected from alkaline earth metal ions (magnesium ions, calcium ions, strontium ions, barium ions, beryllium ions, and radium ions). More preferably, the lithium ion-containing aqueous solution contains at least one selected from magnesium ions, calcium ions, strontium ions, and barium ions. Even more preferably, the lithium ion-containing aqueous solution contains magnesium ions and / or calcium ions.

[0014] <Gas Hydrate Formation Step (A)> In step (A), a mixture containing gas hydrate is obtained from a gas and the lithium ion-containing aqueous solution. Gas hydrate is an ice-like solid substance in which a gas is trapped inside a cage-like structure of water molecules. Generally, the water constituting the cage structure is called the "host," and the gas trapped inside the cage structure is called the "guest." Gas hydrate can be produced by applying low-temperature and high-pressure conditions in the presence of water and gas. In this specification, "gas" refers to a substance that is in a gaseous state at room temperature and normal pressure (25°C, 1 atm (101,325 Pa)). According to the method of this embodiment, using a gas as the guest makes it easier to separate the guest and water compared to using cyclopentane, which is a liquid at room temperature and normal pressure, and therefore reduces the cost of waste liquid treatment.

[0015] The type of gas used in step (A) is not particularly limited, but may be, for example, hydrocarbon, carbon dioxide (CO ２ ), oxygen (O ２ ), nitrogen (N ２ ), argon (Ar), krypton (Kr), xenon (Xe), hydrogen sulfide (H ２ Specific examples of hydrocarbons include methane, ethane, propane, n-butane, iso-butane, ethylene, 1-butene, 2-butene, and isobutene. These gases may be used alone or in combination of two or more. Among these gases, CO ２ and preferably contains CO ２ It is preferable that CO ２ When using CO ２ It is a hydrate. ２ In addition, when the lithium ion-containing aqueous solution contains alkaline earth metal ions, the cost of recovering lithium can be reduced by using CO ２ The use of the above method also has the advantage that alkaline earth metal ions can be easily separated as carbonates.

[0016] To enable the production of gas hydrate under higher temperature and lower pressure conditions (milder conditions), it is also preferable to produce the hydrate in the presence of a helping guest substance in addition to water (host) and gas (guest). From the viewpoint of further reducing the cost of waste liquid treatment, it is preferable that the helping guest substance is gaseous at room temperature and normal pressure. Note that although helping guest substances that are liquid at room temperature and normal pressure (e.g., cyclopentane, tetrahydrofuran, methylcyclohexane, etc.) are known, from the viewpoint of further reducing the cost of waste liquid treatment, it is preferable not to add a substance that is liquid at room temperature and normal pressure to the system in step (A).

[0017] The specific method for producing gas hydrate from gas and water in the lithium ion-containing aqueous solution is not particularly limited, and any known method for producing gas hydrate can be appropriately adopted. ２ Using CO ２ The following method can be used to generate hydrate: First, a lithium ion-containing aqueous solution and CO ２ Then, the mixture is subjected to low-temperature and high-pressure conditions to prepare a mixed solution. ２ At this time, CO hydrate is generated in the mixed liquid. ２ The low-temperature, high-pressure condition may be subjected to a low-temperature, high-pressure condition while continuing to supply CO ２ In the phase equilibrium diagram of a hydrate system, there are no particular limitations as long as the temperature and pressure are lower than the phase equilibrium conditions. ２ , gaseous CO ２ , CO ２ The quadruple point at which the four phases of hydrate can coexist is a temperature of 10.5°C and a pressure of 4.46 MPa (44.0 atm).

[0018] In step (A), the gas is CO ２ and the gas hydrate comprises CO ２ In the case of a gas hydrate, the pH of the mixture containing the gas hydrate is preferably 9 or less, more preferably less than 7. If the pH of the mixture is high, lithium carbonate (Li２ CO ３ ) and lithium bicarbonate (LiHCO ３ The precipitation of lithium salts may lead to a decrease in the lithium recovery efficiency, so it is preferable to control the pH of the mixture so that it does not become too high (preferably so that the pH does not exceed 9, more preferably so that the pH does not become 7 or higher). By adjusting the pH of the mixture to 9 or less, lithium carbonate (Li ２ CO ３ By adjusting the pH of the mixture to less than 7, the precipitation of lithium carbonate (Li ２ CO ３ ) plus lithium bicarbonate (LiHCO ３ ) can also be suppressed, thereby further improving the lithium recovery efficiency. The lower limit of the pH of the mixture is not particularly limited, but is preferably 1 or more, more preferably 2 or more, and even more preferably 3 or more. The pH of the mixture is determined by the CO 2 concentration for generating gas hydrate. ２ It is possible to control the amount of the oxygen supplied by adjusting the amount of the oxygen supplied.

[0019] Gas is CO ２ and the gas hydrate comprises CO ２ In the case where the lithium ion-containing aqueous solution is a hydrate and contains at least one selected from alkaline earth metal ions, in step (A), ２ When hydrate is formed, alkaline earth metal carbonates (e.g., MgCO ３ , CaCO ３ , SrCO ３ , BaCO ３ , BeCO ３ , RaCO ３ ) may precipitate. Therefore, the mixture may contain a carbonate of an alkaline earth metal. In this case, in the gas hydrate separation step (B) described below, it is preferable to remove the carbonate from the mixture in addition to separating the gas hydrate from the mixture.

[0020] In step (A), gas hydrate is produced from the water and gas in the lithium ion-containing aqueous solution. Furthermore, the production of gas hydrate enriches the lithium ions in the lithium ion-containing aqueous solution. Thus, step (A) produces a mixture containing gas hydrate (more specifically, a mixture of gas hydrate and a lithium ion-enriched aqueous solution).

[0021] <Gas Hydrate Separation Step (B)> In step (B), the gas hydrate is separated from the mixture to obtain a lithium ion-enriched aqueous solution (1). The separation operation may be performed under low-temperature and high-pressure conditions, but can also be performed under room temperature and normal pressure. The specific separation method is not particularly limited, and known solid-liquid separation techniques can be appropriately adopted. When the density of the gas hydrate is lower than the density of the lithium ion-enriched aqueous solution (1), a sherbet-like gas hydrate floats in the mixture. In this case, the gas hydrate and the lithium ion-enriched aqueous solution (1) can be easily separated by extracting the gas hydrate from the top of the mixture or extracting the lithium ion-enriched aqueous solution (1) from the bottom of the mixture. In addition, the hydrate can be separated more quickly by using centrifugation or squeezing techniques.

[0022] The concentration of lithium ions contained in the lithium ion concentrated aqueous solution (1) is not particularly limited, but is preferably 10 －４ mol / kg or more, more preferably 10 －４ mol / kg or more and 10 mol / kg or less, and more preferably 10 －３ mol / kg or more and 10 mol / kg or less, and particularly preferably 10 －２ mol / kg or more and 10 mol / kg or less, and most preferably 10 －１ mol / kg or more and 10 mol / kg or less.

[0023] <Lithium Ion Recovery Step (C)> In step (C), lithium is recovered from the lithium ion-enriched aqueous solution (1). The form of lithium recovered in step (C) may be any of lithium ions, lithium compounds, and metallic lithium, and is not particularly limited. In the lithium ion recovery step using a lithium ion conductor described below, lithium is recovered as a lithium ion recovery aqueous solution. Herein, the term "lithium ion recovery aqueous solution" refers to an aqueous solution containing substantially only lithium ions as metal ions. The content of metal ions other than lithium ions in the lithium ion recovery aqueous solution is preferably 3 mol % or less, more preferably 1 mol % or less, and even more preferably 0.1 mol % or less (lower limit: 0 mol %), relative to the total number of moles of metal ions. Furthermore, the lithium ion recovery aqueous solution may be converted into various lithium compounds (e.g., lithium carbonate or lithium hydroxide) and then recovered. That is, according to one aspect of the present invention, a method for producing a lithium ion recovery aqueous solution is provided, including the lithium recovery method according to this aspect. Furthermore, according to another aspect of the present invention, a method for producing a lithium compound (e.g., lithium carbonate or lithium hydroxide) is provided, including the lithium recovery method according to this aspect.

[0024] [Lithium ion recovery step (C1) using a lithium ion conductor] A preferred embodiment of the lithium recovery method of the present invention involves recovering lithium from the lithium ion concentrated aqueous solution (1) (step (C)), by disposing the lithium ion concentrated aqueous solution (1) on one main surface of a lithium ion conductor and disposing recovery water on the other main surface, and allowing lithium ions contained in the lithium ion concentrated aqueous solution (1) to permeate from the one main surface to the other main surface, thereby obtaining a lithium ion recovery aqueous solution. Hereinafter, the lithium ion recovery step having the above configuration will also be simply referred to as "step (C1)." According to this step (C1), a highly pure lithium ion recovery aqueous solution can be obtained.

[0025] The lithium ion conductor is not particularly limited as long as it has the function of selectively transmitting lithium ions. Examples of such lithium ion conductors include those described in Japanese Patent No. 6818334 (corresponding to the specification of U.S. Patent Application Publication No. 2019 / 0032230) as represented by Formula 1: (Li ｘ , La ｙ ) TiO ｚ (where x=3a-2b, y=2 / 3-a, z=3-b, 0<a≦1 / 6, 0≦b≦0.06, x>0) or lithium lanthanum titanate (LLTO) having a composition of formula 2: Li １＋ｘ＋ｙ Al ｘ (Ti, Ge) ２－ｘ Si ｙ P ３－ｙ O １２ (where 0≦x≦0.6, 0≦y≦0.6) Li-substituted NASICON (Na Super Ionic Conductor) crystals are known. From the viewpoint of durability and robustness, Li ０．２９ La ０．５７ TiO ３ LLTO having a composition of (in the above formula 1, a≈0.1, b≈0) is preferred. From the viewpoint of the extraction rate of lithium ions, a Li-substituted NASICON-type lithium ion conductor is preferred.

[0026] In step (C1), a lithium ion-enriched aqueous solution (1) is placed on one main surface of a lithium ion conductor, and recovery water is placed on the other main surface. More specifically, for example, in a dialysis tank consisting of two compartments separated by a lithium ion conductor, the lithium ion-enriched aqueous solution (1) is placed in one compartment (hereinafter also referred to as the "first compartment"), and recovery water is placed in the other compartment (hereinafter also referred to as the "second compartment"). Here, from the viewpoint of recovering high-purity lithium, the recovery water is preferably water that contains little or no impurities (pure water (resistivity of about 1 to 10 MΩ cm) or ultrapure water (resistivity of more than about 10 MΩ cm)). The pure water and ultrapure water may be RO water, deionized water, or distilled water.

[0027] Using the dialysis tank described above, lithium ions contained in the lithium ion-enriched aqueous solution (1) are permeated from one main surface side to the other main surface side. From the viewpoint of improving the lithium recovery rate, the permeation is preferably performed in an electrodialysis mode. That is, according to a preferred embodiment, in the step (C1), an anode is disposed on the one main surface side (first chamber), a cathode is disposed on the other main surface side (second chamber), and a voltage is applied between the two electrodes. In this case, it is preferable to dispose the anode in contact with the one main surface and the cathode in contact with the other main surface. This significantly improves the migration rate of lithium ions from one main surface side (first chamber) to the other main surface side (second chamber). Note that electrodialysis typically involves the electrolysis of water (anodic reaction: 2H ２ O → O ２ +4H ＋ +4e － , or 4OH － →O ２ +2H ２ O+4e － ; Cathodic reaction: 2H ＋ +2e － →H ２ ) by oxygen (O ２ ) and hydrogen (H ２ ) can be produced as a by-product. Also, if the aqueous solution contains chloride ions, chlorine may be produced instead of oxygen.

[0028] It is also possible to perform dialysis without applying voltage by utilizing the energy of the difference in lithium ion concentration between one main surface side (first chamber) and the other main surface side (second chamber) (reverse electrodialysis mode). In this case, the lithium ion migration speed is slower than in electrodialysis, but electrical energy can be extracted because a potential difference occurs between one main surface side (first chamber) and the other main surface side (second chamber).

[0029] According to the lithium recovery method of this embodiment, by performing step (C1) using the lithium ion-enriched aqueous solution (1) obtained by steps (A) and (B), the migration rate of lithium ions in the lithium ion conductor in step (C1) is increased, thereby improving the lithium recovery efficiency. In the past, in lithium recovery methods using lithium ion conductors (such as the aforementioned LLTO and Li-substituted NASICON-type crystals), a method of increasing the applied voltage in electrodialysis mode has been investigated in order to improve the lithium ion migration rate. However, with conventional methods, even if the voltage is increased, the lithium ion migration rate sometimes cannot be sufficiently improved. This is thought to be due to the fact that, as the voltage increases, electronic conduction occurs in the lithium ion conductor, reducing the current efficiency and increasing the power consumption for water electrolysis. On the other hand, according to the recovery method of this embodiment, by using the lithium ion-enriched aqueous solution (1) in step (C1), the migration rate of lithium ions can be significantly improved without increasing the applied voltage. Note that sun drying is also a conceivable method for concentrating a lithium ion-containing aqueous solution. However, with the sun-drying method, the concentration process, which would normally take one to two years, can be completed in just a few days by generating and separating gas hydrates, making it possible to recover larger amounts of lithium in a shorter period of time.

[0030] In step (C1) (particularly when permeation is performed in electrodialysis mode), when the pH of the lithium ion-enriched aqueous solution (1) obtained in step (B) is less than 7, it is preferable to adjust the pH of the lithium ion-enriched aqueous solution (1) to 7 or higher before disposing the lithium ion-enriched aqueous solution (1) on one of the main surfaces (the first chamber). That is, in a preferred embodiment of the lithium recovery method of the present invention, recovering lithium from the lithium ion-enriched aqueous solution (1) includes: adjusting the pH of the lithium ion-enriched aqueous solution (1) when the pH is less than 7 to obtain a lithium ion-enriched aqueous solution (2) having a pH of 7 or higher; disposing the lithium ion-enriched aqueous solution (2) on one of the main surfaces of a lithium ion conductor and disposing recovery water on the other main surface; and allowing the lithium ions contained in the lithium ion-enriched aqueous solution (2) to permeate from the one main surface to the other main surface to obtain a lithium ion-enriched aqueous solution. This configuration can further improve the lithium recovery efficiency. In a system in which hydrogen ions and lithium ions coexist, the selective permeability of lithium ions in the lithium ion conductor may be reduced. In particular, when permeation is performed in electrodialysis mode, hydrogen ions are generated as water is electrolyzed at the anode on the main surface side (first chamber) (anode reaction: 2H ２ O → O ２ +4H ＋ +4e － Therefore, the problem of the selective permeability of lithium ions in the lithium ion conductor is likely to become apparent. By setting the pH at 7 or higher, the reaction of hydroxide ions at the anode to generate oxygen and water (4OH － →O ２ +2H ２ O+4e －) is more likely to proceed, and the anode reaction is less likely to proceed, thereby suppressing the generation of hydrogen ions. This improves the selective permeability of lithium ions in the lithium ion conductor, and as a result, the lithium ion recovery efficiency can be improved. In order to further improve the lithium ion recovery efficiency, when the pH of the lithium ion-enriched aqueous solution (1) is less than 9, it is more preferable to adjust the pH of the lithium ion-enriched aqueous solution (1) to 9 or more; when the pH of the lithium ion-enriched aqueous solution (1) is less than 12, it is even more preferable to adjust the pH of the lithium ion-enriched aqueous solution (1) to 12 or more.

[0031] As a specific method for adjusting (raising) the pH, it is preferable to adopt a method of adding sodium hydroxide or potassium hydroxide to the lithium ion concentrated aqueous solution (1). The lithium ion conductor can selectively transmit lithium ions even when sodium ions or potassium ions coexist with lithium ions. In addition, sodium or potassium carbonates and hydrogen carbonates have a higher solubility than lithium carbonates and hydrogen carbonates, and therefore have the advantage of being less susceptible to adverse effects due to salt precipitation. In addition, from the viewpoint of suppressing the precipitation of lithium carbonate or lithium hydrogen carbonate, it is preferable to add sodium hydroxide or potassium hydroxide dissolved in the lithium ion concentrated aqueous solution (1). ２ It is also preferred to adjust (raise) the pH by removing CO ２ Specific methods for removing the lithium ion-enriched aqueous solution (1) include reducing the pressure, heating, and CO ２ Examples of the method include bubbling a gas other than the above (air, oxygen, nitrogen, argon, etc.) or evaporating water in the lithium ion-enriched aqueous solution (1).

[0032] From the viewpoint of suppressing the precipitation of lithium carbonate or lithium hydrogen carbonate, regardless of the pH of the lithium ion concentrated aqueous solution (1), CO ２That is, in a preferred embodiment of the method for recovering lithium from the lithium ion-enriched aqueous solution (1), the recovery of lithium from the lithium ion-enriched aqueous solution (1) is carried out by removing CO ２ to obtain a lithium ion concentrated aqueous solution (3), and disposing the lithium ion concentrated aqueous solution (3) on one main surface side of a lithium ion conductor and disposing recovery water on the other main surface side, and allowing the lithium ions contained in the lithium ion concentrated aqueous solution (3) to permeate from the one main surface side to the other main surface side, thereby obtaining a lithium ion recovery aqueous solution. ２ and the gas hydrate comprises CO ２ In the case of a hydrate, lithium carbonate or lithium hydrogen carbonate is likely to precipitate, and therefore, by configuring step (C1) as described above, it is preferable to suppress the precipitation of these lithium salts. ２ The specific method for removing the above is as described above.

[0033] The following embodiments are also included within the scope of the present invention: Item 1: A method for recovering lithium from a lithium ion-containing aqueous solution, the method comprising: obtaining a mixture containing a gas hydrate from a gas and the lithium ion-containing aqueous solution; separating the gas hydrate from the mixture to obtain the lithium ion-enriched aqueous solution (1); and recovering lithium from the lithium ion-enriched aqueous solution (1); Item 2: A method for recovering lithium from a lithium ion-enriched aqueous solution (1) in which the gas is CO ２ and the gas hydrate comprises CO ２Item 3: The method according to Item 1 or 2, wherein the mixture has a pH of 9 or less; Item 4: The method according to Item 3, wherein the mixture has a pH of less than 7; Item 5: The method according to any one of Items 1 to 4, wherein the lithium ion-containing aqueous solution contains at least one ion selected from magnesium ions, calcium ions, strontium ions, barium ions, beryllium ions, and radium ions; Item 6: The method according to any one of Items 1 to 5, wherein recovering lithium from the lithium ion-enriched aqueous solution (1) comprises disposing the lithium ion-enriched aqueous solution (1) on one main surface side of a lithium ion conductor and disposing recovery water on the other main surface side, and allowing lithium ions contained in the lithium ion-enriched aqueous solution (1) to permeate from the one main surface side to the other main surface side, thereby obtaining a lithium ion-recovered aqueous solution; Item 7: The method according to any one of Items 1 to 5, wherein recovering lithium from the lithium ion-enriched aqueous solution (1) comprises arranging the lithium ion-enriched aqueous solution (1) and an anode on one main surface side of a lithium ion conductor, arranging recovery water and a cathode on the other main surface side, and applying a voltage between the anode and the cathode to permeate lithium ions contained in the lithium ion-enriched aqueous solution (1) from the one main surface side to the other main surface side, thereby obtaining a lithium ion-enriched aqueous solution; Item 8: The method according to any one of Items 1 to 5, wherein recovering lithium from the lithium ion-enriched aqueous solution (1) comprises adjusting the pH of the lithium ion-enriched aqueous solution (1) when the pH is less than 7 to obtain a lithium ion-enriched aqueous solution (2) having a pH of 7 or higher, and arranging the lithium ion-enriched aqueous solution (2) on one main surface side of a lithium ion conductor, arranging recovery water on the other main surface side, and permeating lithium ions contained in the lithium ion-enriched aqueous solution (2) from the one main surface side to the other main surface side, thereby obtaining a lithium ion-enriched aqueous solution;Item 9: The method according to any one of Items 1 to 5, wherein recovering lithium from the lithium ion-enriched aqueous solution (1) includes adjusting the pH of the lithium ion-enriched aqueous solution (1) when the pH is less than 7 to obtain a lithium ion-enriched aqueous solution (2) having a pH of 7 or more, and arranging the lithium ion-enriched aqueous solution (2) and an anode on one main surface side of a lithium ion conductor and arranging recovery water and a cathode on the other main surface side, and allowing lithium ions contained in the lithium ion-enriched aqueous solution (2) to permeate from the one main surface side to the other main surface side to obtain a lithium ion-enriched aqueous solution; Item 10: The method according to any one of Items 1 to 5, wherein recovering lithium from the lithium ion-enriched aqueous solution (1) includes recovering CO from the lithium ion-enriched aqueous solution (1); ２ 6. The method according to any one of Items 1 to 5, comprising: removing the lithium ion-enriched aqueous solution (3) from the lithium ion conductor; disposing the lithium ion-enriched aqueous solution (3) on one main surface side of the lithium ion conductor and disposing recovery water on the other main surface side; and allowing the lithium ions contained in the lithium ion-enriched aqueous solution (3) to permeate from the one main surface side to the other main surface side, thereby obtaining a lithium ion recovery aqueous solution.

[0034] This application is based on International Patent Application PCT / JP2023 / 027031, filed on July 24, 2023, the disclosure of which is incorporated by reference in its entirety.

Claims

1. A method for recovering lithium from a lithium ion-containing aqueous solution, comprising: obtaining a mixture containing a gas hydrate from a gas and the lithium ion-containing aqueous solution; separating the gas hydrate from the mixture to obtain a lithium ion-enriched aqueous solution (1); and recovering lithium from the lithium ion-enriched aqueous solution (1).

2. The gas is CO ２ and the gas hydrate comprises CO ２ The method for recovering lithium according to claim 1, wherein the lithium is a hydrate.

3. The method for recovering lithium according to claim 1 or 2, wherein the pH of the mixture is 9 or less.

4. The method for recovering lithium according to claim 3, wherein the pH of the mixture is less than 7.

5. The method for recovering lithium according to claim 1 or 2, wherein the lithium ion-containing aqueous solution contains at least one ion selected from the group consisting of magnesium ions, calcium ions, strontium ions, barium ions, beryllium ions and radium ions.

6. The method for recovering lithium from the lithium ion concentrated aqueous solution (1) according to claim 1 or 2, comprising disposing the lithium ion concentrated aqueous solution (1) on one main surface side of a lithium ion conductor, disposing recovery water on the other main surface side, and allowing the lithium ions contained in the lithium ion concentrated aqueous solution (1) to permeate from the one main surface side to the other main surface side to obtain a lithium ion recovery aqueous solution.

7. The method for recovering lithium from the lithium ion concentrated aqueous solution (1) according to claim 1 or 2, comprising: adjusting the pH of the lithium ion concentrated aqueous solution (1) when the pH is less than 7 to obtain a lithium ion concentrated aqueous solution (2) having a pH of 7 or more; and arranging the lithium ion concentrated aqueous solution (2) on one main surface side of a lithium ion conductor, arranging recovery water on the other main surface side, and allowing the lithium ions contained in the lithium ion concentrated aqueous solution (2) to permeate from the one main surface side to the other main surface side to obtain a lithium ion recovery aqueous solution.

8. Recovering lithium from the lithium ion concentrated aqueous solution (1) comprises: ２ to obtain a lithium ion concentrated aqueous solution (3); and disposing the lithium ion concentrated aqueous solution (3) on one main surface side of a lithium ion conductor and disposing recovery water on the other main surface side, and allowing lithium ions contained in the lithium ion concentrated aqueous solution (3) to permeate from the one main surface side to the other main surface side, thereby obtaining a lithium ion recovery aqueous solution.