Lithium recovery agent, lithium recovery method, lithium recovery system, method for producing lithium-containing manganese oxide, and method for producing positive electrode active substance for lithium ion battery

Abstract

In the present invention, lithium can be easily and efficiently recovered from a lithium-containing starting liquid, using a lithium recovery agent containing an electricity-generating bacterium and a lithium intercalation material.

Description

Lithium recovery agent, lithium recovery method, lithium recovery system, method for producing lithium-containing manganese oxide, and method for producing positive electrode active material for lithium-ion battery

[0001] The present invention relates to a lithium recovery agent, a lithium recovery method, a lithium recovery system, a method for producing a lithium-containing manganese oxide, and a method for producing a positive electrode active material for a lithium ion battery.

[0002] Lithium (Li) is a resource in high demand as a raw material for lithium-ion secondary batteries and fuel for nuclear fusion reactors, and a stable and inexpensive extraction method is required. ＋ There are also hopes for low-cost recovery technology from discarded lithium secondary batteries that have reached the end of their life.

[0003] As one technique for recovering Li from seawater, etc., Non-Patent Documents 1 to 3 report the electrochemical lithium recovery method described below. First, a paint (kneaded mixture) is prepared by kneading a lithium adsorbent such as manganese oxide with a spinel structure that can selectively occlude lithium, a conductive additive such as carbon, and a binder such as polyvinylidene fluoride. This paint is applied to an electrode to produce a composite electrode. Then, lithium is recovered in the lithium adsorbent by passing electricity through the electrode using an electrochemical device such as a potentio-galvanostat.

[0004] S. Kim et al. , Environ. Sci. Technol. , 2020, 54, 9044-9051L. Wang et al. , Sustainable Energy Fuels, 2021, 5, 3124-3133J. Lee et al. , Phys. Chem. Chem. Phys. , 2013, 15, 7690-7695

[0005] However, the conventional lithium recovery methods disclosed in Non-Patent Documents 1 to 3 require a paint preparation (mixing) step and a coating step, and also require an electrochemical device for applying current to the electrodes. Thus, the conventional lithium recovery methods have had issues with the time and cost required for the complicated steps and equipment.

[0006] The present invention is intended to solve the above-mentioned problems. That is, one of the objects of the present invention is to provide a lithium recovery agent that can recover lithium simply and efficiently.

[0007] As a result of extensive research into achieving the above object, the inventors have found that the above object can be achieved by the following configuration.

[0008] [1] A lithium recovery agent for recovering lithium from a raw material solution containing lithium, the lithium recovery agent comprising: electric-generating bacteria; and a lithium intercalation material. [2] The lithium recovery agent according to [1], wherein the electric-generating bacteria is an iron-reducing bacterium. [3] The lithium recovery agent according to [2], wherein the electric-generating bacteria is a bacterium of the genus Shewanella or a bacterium of the genus Geobacter. [4] The lithium recovery agent according to any one of [1] to [3], wherein the lithium intercalation material is a compound containing a first transition metal. [5] The lithium recovery agent according to [4], wherein the first transition metal is at least one selected from the group consisting of manganese (Mn), vanadium (V), titanium (Ti), and iron (Fe). [6] The lithium recovery agent according to [5], wherein the lithium intercalation material is manganese dioxide having a spinel structure. [7] The lithium recovery agent according to any one of [1] to [6], wherein the lithium intercalation material is in the form of particles. [8] The lithium recovery agent according to any one of [1] to [7], further comprising an electron donor. [9] The lithium recovery agent according to [8], wherein the electric-generating bacterium is a bacterium of the genus Shewanella and the electron donor is lactate, or wherein the electric-generating bacterium is a bacterium of the genus Geobacter and the electron donor is acetate.

[10] The lithium recovery agent according to any one of [1] to [9], further comprising an electron mediator.

[11] The lithium recovery agent according to

[10] , wherein the electron mediator is a flavin.

[12] A method for recovering lithium, comprising contacting the lithium recovery agent according to any one of [1] to

[11] with the raw material solution.

[13] The method for recovering lithium according to

[12] , wherein electrons generated by the electric-generating bacterium are transferred to the lithium intercalation material.

[14] The method for recovering lithium according to

[12] or

[13] , comprising preparing a reaction solution containing the raw material solution and the lithium recovery agent, generating a precipitate containing the lithium recovery agent and the lithium in the reaction solution, and separating the precipitate from the reaction solution.

[15] The method for recovering lithium according to

[14] , wherein the raw material solution contains lithium ions introduced from the outside through a cation exchange membrane.

[16] A lithium recovery system comprising: a reaction vessel; and the lithium recovery agent according to any one of [1] to

[11] , disposed in the reaction vessel; wherein the raw material solution and the lithium recovery agent are in contact with each other in the reaction vessel.

[17] The lithium recovery system according to

[16] , which does not have a mechanism for passing electricity through the lithium recovery agent.

[18] The lithium recovery system according to

[16] , wherein the reaction vessel is provided with a cation exchange membrane for introducing lithium ions into the raw material solution from outside the reaction vessel.

[19] A method for producing a lithium-containing manganese oxide, comprising the lithium recovery method according to any one of

[12] to

[15] , wherein the lithium intercalation material is manganese dioxide.

[20] A method for producing a positive electrode active material for a lithium ion battery, comprising the lithium recovery method according to any one of

[12] to

[15] .

[0009] The present invention provides a lithium recovery agent that can recover lithium simply and efficiently.

[0010] 1 is a conceptual diagram illustrating the lithium recovery mechanism using the lithium recovery agent of this embodiment. FIG. 2 is a flowchart illustrating the lithium recovery method of this embodiment. FIG. 3 is a diagram illustrating the results of X-ray diffraction (XRD) measurement of manganese dioxide (before reaction) and the powder (after reaction) obtained in Experiment 1. FIG. 4 is a scanning electron microscope (SEM) photograph of the aggregates recovered in Experiment 1. FIG. 5 is a diagram illustrating the results of X-ray diffraction (XRD) measurement of manganese dioxide (before reaction) and the powder (after reaction) obtained in Experiment 2. FIG. 6 is a diagram illustrating the results of X-ray diffraction (XRD) measurement of the powder (after reaction) obtained in Experiment 3-1. FIG. 7 is a diagram illustrating the results of X-ray diffraction (XRD) measurement of the powder (after reaction) obtained in Experiment 3-2. FIG. 8 is a diagram illustrating the results of X-ray diffraction (XRD) measurement of the powder (after reaction) obtained in Experiment 3-3. FIG. 9 is a diagram illustrating the results of X-ray diffraction (XRD) measurement of the powder (after reaction) obtained in Experiment 3-4. FIG. 10 is a diagram illustrating the results of X-ray diffraction (XRD) measurement of the powder (after reaction) obtained in Experiment 3-5. 1 is a diagram showing the results of X-ray diffraction (XRD) measurement of the powder (after reaction) obtained in Experiment 3-6. 2 is a diagram showing the results of X-ray diffraction (XRD) measurement of the powder (after reaction) obtained in Experiment 4-1. 3 is a diagram showing the results of X-ray diffraction (XRD) measurement of the powder (after reaction) obtained in Experiment 4-2. 4 is a diagram showing the results of X-ray diffraction (XRD) measurement of the powder (after reaction) obtained in Experiment 4-3. 5 is a diagram showing the results of X-ray diffraction (XRD) measurement of the powder (after reaction) obtained in Experiment 4-4. 6 is a conceptual diagram illustrating a lithium recovery system of another embodiment. 7 is an image showing the setup of a demonstration test of the lithium recovery system. 8 is a comparison of an image (left) of a screw vial before immersion in a LiCl / PBS (10 mM) solution and an image (right) of the screw vial after immersion and reaction for 24 hours. 9 is a diagram showing the results of X-ray diffraction (XRD) measurement of the powder (after reaction) obtained in Experiment 6-1. 10 is a diagram showing the results of X-ray diffraction (XRD) measurement of the powder (after reaction) obtained in Experiment 6-2. FIG. 1 is a diagram showing the results of X-ray diffraction (XRD) measurement of the powder (after reaction) obtained in Experiment 6-3.

[0011] The present invention will be described in detail below. The following description of the constituent elements may be based on a representative embodiment of the present invention, but the present invention is not limited to such an embodiment. In this specification, a numerical range expressed using "to" means a range that includes the numerical values ​​before and after "to" as the lower and upper limits.

[0012] [Lithium Recovery Agent] The lithium recovery agent of this embodiment mainly includes electricity-generating bacteria and a lithium intercalation material. The lithium recovery agent of this embodiment comes into contact with a raw material solution containing lithium to recover lithium from the raw material solution.

[0013] <Electricity-generating bacteria> In this specification, the term "electric current-generating bacteria (current-generating bacteria)" refers to bacteria that have the ability to transfer electrons generated by the decomposition (metabolism) of an electron donor (organic substance) within the bacterial cell to an electron acceptor outside the bacterial cell (in this embodiment, a lithium intercalation material), i.e., the ability to perform extracellular electron transport (EET) (extracellular electron transfer ability).

[0014] Examples of current-generating bacteria include iron-reducing bacteria. Specific examples of iron-reducing bacteria include bacteria of the genus Shewanella and Geobacter. These power-generating bacteria are safe because they are not pathogenic, and are preferable because they grow quickly and therefore can produce sufficient effects even when initially introduced in small amounts. Examples of Shewanella species include Shewanella oneidensis, Shewanella loihica, Shewanella putrefaciens, and Shewanella algae. Examples of Geobacter species include Geobacter sulfurreducens and Geobacter metallireducens. The electric-generating bacteria may be known or unknown. These electric-generating bacteria may be used alone or in combination of two or more types as long as the effects of this embodiment are achieved.

[0015] <Lithium Intercalation Material> In this specification, the term "lithium intercalation material" refers to a material (host, matrix) into which lithium ions (guests) can be intercalated. Intercalation is a reversible chemical reaction in which another element (herein, lithium ions) enters the voids of a molecule, molecular group, or crystal (herein, lithium intercalation material).

[0016] The type (composition, crystal structure, shape, etc.) of the lithium intercalation material is not particularly limited and may be appropriately selected within the range in which the effects of this embodiment are exhibited. For example, the lithium intercalation material may be a compound containing a first transition metal, and examples of the first transition metal include manganese (Mn), vanadium (V), titanium (Ti), and iron (Fe). Specific examples of the compound include Mn ３ O ４ , Mn ２ O ３ , MnO ２ (Manganese dioxide), MnO ３ , Mn ２ O ７ Manganese oxides such as Fe ３ O ４ , Fe ２ O ３ Iron oxides such as V ２ O ５ , V.O. ２ Vanadium oxides such as TiO ２ Titanium oxides such as TiS ２ , FePO ４ Examples of the crystalline structure of the lithium intercalation material include layered rock salt type, spinel type, and olivine type. Examples of the lithium intercalation material include manganese dioxide, particularly manganese dioxide with a spinel structure (λ-type MnO ２ ) is preferred because it has high selectivity for lithium adsorption. Note that the lithium intercalation material may be used alone or in combination of two or more types as long as the effects of this embodiment are achieved.

[0017] The lithium intercalation material is preferably a powder (particles) from the viewpoint of increasing lithium recovery efficiency. The average particle size of the particles is not particularly limited and may be, for example, 5 nm to 500 μm, 50 nm to 9000 nm, or 100 nm to 300 nm. The "average particle size" can be determined, for example, by measuring the particle sizes of 100 randomly selected particles through electron microscope observation and averaging them (arithmetic mean).

[0018] <Other Components> The lithium recovery agent of this embodiment may be formed only from the power-generating bacteria and the lithium intercalation material, or may contain other components as long as the effects of this embodiment are achieved.

[0019] For example, the lithium recovery agent may further contain an electron donor (electron donor) that can be decomposed by the power-generating bacteria. As described above, the power-generating bacteria generate electrons by decomposing (metabolizing) organic matter (electron donor). However, when the raw material solution is seawater or other environmental samples, the raw material solution may already contain organic matter that can serve as an electron donor. Even in such cases, the lithium recovery efficiency can be improved by further including an electron donor in the lithium recovery agent.

[0020] The electron donor (electron donor) is not particularly limited in type or state, as long as it is a substance that can be decomposed (metabolized) by the electricity-generating bacteria contained in the lithium recovery agent and / or the bacteria contained in the raw material solution and can donate electrons to the electricity-generating bacteria. The electron donor may be in a solid, liquid, gaseous form, or a mixture thereof, and can be selected as appropriate depending on the specific form of the lithium recovery method. For example, when seawater is used as the raw material solution (or when a raw material solution is prepared from seawater), the original lithium (ion) content is low, for example, about 0.2 ppm.

[0021] In such cases, supplying a solid or gaseous electron donor to the raw material solution (reaction solution) can be more economically advantageous than supplying the electron donor as a liquid (liquid agent), since the amount used per recovered Li can be reduced. Specifically, using a solid or gas that can serve as an electron donor near the lithium recovery agent makes it possible to separate the seawater from the microorganisms and the lithium recovery agent, and allows for more efficient local (and continuous) lithium recovery.

[0022] Examples of such solid materials include metals such as magnesium and iron, and organic materials such as cellulose and polylactic acid. The form of the solid material is not particularly limited, and it may be in the form of particles or lumps. When the solid material is in the form of particles, the reaction tends to proceed more efficiently, and when the solid material is in the form of lumps, it is preferred because it can be more easily fixed in the vicinity of the lithium recovery agent.

[0023] Furthermore, when a gaseous electron donor is used, the gas may be supplied near the lithium recovery agent. For example, in the case of the secondary cooling system described above, an electrode may be placed near the lithium recovery agent, and hydrogen may be generated by electrolysis of cooling water. An example of a gaseous electron donor is hydrogen. Among the solid electron donors described above, metals (iron, magnesium, etc.) can generate hydrogen in the raw material liquid (reaction liquid), and therefore can serve as electron donors themselves, and can also serve as indirect electron donors by releasing hydrogen into the system.

[0024] Other examples of organic electron donors include lactates such as sodium lactate and acetates such as sodium acetate. It is preferable to appropriately select an electron donor that increases power generation efficiency based on the type of electric current-generating bacteria (electric-generating bacteria). For example, if the electric-generating bacteria is a Shewanella bacterium, lactate is preferred as the electron donor, and if the electric-generating bacteria is a Geobacter bacterium, acetate is preferred as the electron donor. Furthermore, as long as the effects of this embodiment are achieved, one type of electron donor may be used alone or two or more types may be mixed. The organic substance may be provided as a solid, a liquid (solution), or a mixture thereof. Furthermore, a polymer gel swollen with a solution in which the organic substance is dissolved can also be used as the electron donor. The swollen polymer gel gradually releases the organic substance into the reaction solution, allowing the reaction to proceed more efficiently.

[0025] Furthermore, for example, the lithium recovery agent may further contain an electron mediator. Electrons generated by the power-generating bacteria are transferred to an extracellular electron acceptor (lithium intercalation material) via an electron transfer protein present in the cell's outer membrane. The electron mediator activates the electron transfer protein and further promotes electron transfer to the lithium intercalation material. As a result, lithium recovery efficiency is improved, and recovery time (reaction time) can be shortened, for example. Examples of electron mediators include flavins and quinones. Flavins are a general term for derivatives of 7,8-dimethylisoalloxazine having a substituent at the 10th position, and include riboflavin (vitamin B2), FAD, and FMN. Quinones are aromatic organic compounds with a double bond and a cyclic diketone structure containing six carbon atoms, such as p-benzoquinone, o-quinone, and anthraquinone. These electron mediators may be used alone or in combination of two or more, as long as the effects of this embodiment are achieved.

[0026] The lithium recovery agent may further contain liquids (hereinafter referred to as "liquid components") including various inorganic salt buffer solutions such as boric acid, phosphate, and carbonate, water, physiological saline, cell culture medium, etc. For example, when the lithium recovery agent contains a cell culture medium, the number of electricity-generating bacteria can be increased by culturing them within the lithium recovery agent. As long as the effects of this embodiment are achieved, one type of liquid component may be used alone, or two or more types may be mixed and used.

[0027] The lithium recovery agent of this embodiment may be composed of a first agent containing the electric-generating bacteria and the above-mentioned liquid component, and a second agent containing a lithium intercalation material. The second agent may be composed only of the lithium intercalation material, or may further contain the above-mentioned liquid component. Furthermore, when the lithium recovery agent contains an electron donor, an electron mediator, etc., these components may be contained in the first agent and / or the second agent, or may be contained in other separate agents (e.g., a third agent and / or a fourth agent). The first agent, the second agent, and other agents may be stored in separate containers, and when using the lithium recovery agent, the first agent, the second agent, and other agents may be mixed with the raw material solution.

[0028] The ratio (proportion) of each component in the lithium recovery agent of this embodiment is not particularly limited, and can be adjusted appropriately within a range in which the effects of this embodiment are exhibited.

[0029] <Feedstock Solution> The feedstock solution is not particularly limited as long as it is a liquid containing lithium, and may be appropriately selected within a range that achieves the effects of this embodiment. Examples of feedstock solutions include seawater, salt lake brine, geothermal water, lithium-containing aqueous solutions obtained by recycling lithium ion batteries, mine drainage, and industrial wastewater, but it is preferable to use a feedstock solution that is not cytotoxic to the power-generating bacteria contained in the lithium recovery agent. Seawater has a low lithium concentration of approximately 0.025 mM, but is easily available in large quantities, making it an important lithium supply source. The lithium recovery agent of this embodiment can efficiently recover lithium even from feedstock solutions with low lithium concentrations, so seawater is suitable for this embodiment.

[0030] The lithium concentration of the raw material solution is not particularly limited, and the lithium recovery agent of this embodiment can be used with raw material solutions having a wide range of lithium concentrations, for example, from 0.01 mM to 50 mM, and can efficiently recover lithium even from raw material solutions with low lithium concentrations, for example, from 0.01 mM to 1 mM. The raw material solution may also contain an organic substance that can act as an electron donor (electron donor) and that can be decomposed by the power-generating bacteria. When the raw material solution contains a sufficient amount of electron donor (organic substance), the lithium recovery agent does not need to contain the electron donor, or the content of the electron donor can be reduced.

[0031] <Mechanism of Lithium Recovery> Fig. 1 shows a schematic diagram of a lithium recovery agent 100 in contact with a raw material solution 200 containing lithium. First, the electron donor 20 is decomposed (metabolized) in the electricity-generating bacteria 10 contained in the lithium recovery agent 100, and electrons e － The generated electron e － are transferred to an electron acceptor (lithium intercalation material) 40 outside the cell via an electron transfer protein 30 present in the outer membrane of the electricity-generating bacteria 10. This promotes electrochemical intercalation, in which lithium ions in the raw material solution are taken into the lithium intercalation material 40, and lithium (lithium ions Li ＋ ) is recovered. The inventors first discovered that the power-generating bacteria significantly promotes lithium intercalation, leading to the present invention. Furthermore, in the lithium recovery agent of this embodiment, the particles of the lithium intercalation material tend to form aggregates due to components derived from the power-generating bacteria during lithium recovery (reaction). This is thought to improve the conductivity and adhesion between the particles, further increasing the lithium recovery efficiency.

[0032] The lithium recovery agent of this embodiment can efficiently recover lithium by a simple method of contacting the agent with a raw material solution containing lithium (e.g., dispersing the agent in the raw material solution). Therefore, compared to the conventional methods disclosed in Non-Patent Documents 1 to 3, this method does not require a paint preparation (kneading) step or a coating step, and does not require the equipment required for these steps (e.g., a kneader, coater, dryer, etc.). Furthermore, electrochemical devices such as electrodes, wiring, and potentio-galvanostats are also not required. Furthermore, in this embodiment, the lithium intercalation material incorporating lithium forms aggregates with components derived from the power-generating bacteria and precipitates, making it easy to separate from the reaction solution. Thus, the lithium recovery agent of this embodiment is advantageous in terms of time and money, requires fewer steps and equipment, has a low environmental impact, and is highly applicable to mass production facilities.

[0033] For example, when manganese oxide is used as the lithium intercalation material, at least a portion of the manganese oxide is reduced by electrons transferred from the power-generating bacteria. ２ ) can be used to recover lithium ions, thereby converting manganese oxide lithium insertion compounds (e.g., Li ｘ Mn ２ O ４ , x = 0.4 to 2.0). The average oxidation number of manganese (Mn) in the manganese oxide lithium insertion compound is not particularly limited, but is, for example, +3 to +4. Note that the lithium ions incorporated into the manganese oxide are not reduced.

[0034] As described above, the lithium recovery agent of this embodiment has a metal recovery mechanism that is significantly different from recovery agents that recover metal ions in a raw material solution by directly reducing them. When recovering metal ions in a raw material solution by directly reducing them, there is a risk that metals other than the target metal contained in the raw material solution may also be reduced and recovered at the same time. In contrast, with the lithium recovery agent of this embodiment, electrons supplied by the power-generating bacteria are transferred to the lithium intercalation material, and lithium ions in the raw material solution are selectively incorporated into the lithium intercalation material. Therefore, even if the raw material solution contains metal ions other than lithium ions, the lithium recovery agent of this embodiment can selectively recover lithium ions.

[0035] The mechanism explained above is merely speculation and does not affect the scope of the present invention.

[0036] [Lithium Recovery System] A lithium recovery system 1000 shown in Fig. 1 will be described. The lithium recovery system 1000 includes a reaction vessel 300 and the lithium recovery agent 100 of this embodiment disposed in the reaction vessel 300. In the reaction vessel 300, the raw material solution 200 and the lithium recovery agent 100 come into contact with each other. As a result, lithium ions in the raw material solution are taken into the lithium intercalation material 40 (intercalation), and lithium (lithium ions Li ＋ ) is recovered.

[0037] The lithium recovery system 1000 does not need to have an energization mechanism (e.g., a power source, wiring, electrodes, etc.) for energizing the lithium recovery agent 100. This is because the power-generating bacteria 10 contained in the lithium recovery agent 100 can supply the lithium intercalation material with electrons necessary and sufficient for the lithium recovery reaction. Because the system does not have an energization mechanism, it can be manufactured and operated at low cost and has a low environmental impact.

[0038] 8 is a conceptual diagram of another embodiment of the lithium recovery system. The lithium recovery system 1100 includes a reaction vessel 300 and a lithium recovery agent 100 disposed in the reaction vessel 300. The reaction vessel 300 further includes a cation exchange membrane 400 for introducing lithium ions 130 into the raw material solution 200 from the outside.

[0039] The cation exchange membrane 400 is disposed in a pipe connecting the reactor 300 with a pipe 110 for secondary cooling water of the power plant, and introduces lithium ions 130 contained in the cooling water 210 in the external pipe 110 into the reactor 300. In this embodiment, the reactor 300 is installed midway along the pipe 110 for secondary cooling water of the power plant, but the installation location of the lithium recovery system of this embodiment is not limited to the above. For example, the reactor 300 may be immersed in a larger container (e.g., a water treatment tank) containing water containing lithium ions, or in a lake, marsh, ocean, or the like. The lithium recovery system of this embodiment easily maintains the inside of the reactor 300 in a condition suitable for lithium recovery (e.g., an anaerobic condition) and can more efficiently recover lithium even from low concentrations of lithium ions.

[0040] [Lithium Recovery Method] A lithium recovery method using the lithium recovery agent of this embodiment will be described. The lithium recovery method may be performed using the lithium recovery system 1000 (see FIG. 1) described above. The lithium recovery method includes a step of contacting the lithium recovery agent with a raw material solution (step S1 in FIG. 2). An example of the lithium recovery method will be described below with reference to the flowchart in FIG. 2.

[0041] First, a reaction solution containing a raw material solution and a lithium recovery agent is prepared (step S1 in FIG. 2), whereby the lithium recovery agent and the raw material solution come into contact with each other.

[0042] The reaction solution may be composed only of the raw material solution and the lithium recovery agent, or may contain other components as long as the effects of this embodiment are achieved. Examples of other components include liquids containing various inorganic salt buffers such as boric acid, phosphate, and carbonate, water, physiological saline, cell culture media, etc. (the "liquid components" described above).

[0043] The content (concentration) of each component in the reaction solution is not particularly limited and can be adjusted as appropriate within the range in which the effects of this embodiment are achieved. For example, the initial concentrations in the reaction solution may be in the following ranges: electricity-generating bacteria (OD value): 0.001 to 1, lithium intercalation material: 0.001 to 10 g / L, electron donor: 0 to 100 mM, electron mediator: 0 to 0.1 mM, lithium ion: 0.01 to 100 mM.

[0044] The pH of the reaction solution may be, for example, 5 to 8, or 6 to 8. If the pH of the reaction solution is set within the above range, the activity of the electricity-generating bacteria is activated, resulting in an improvement in the lithium recovery efficiency.

[0045] The method for preparing the reaction solution is not particularly limited, and for example, the raw material solution, the lithium recovery agent, and other components as necessary may be uniformly mixed by a known method. For example, the reaction solution may be prepared by continuously transferring lithium ions from a solution containing a lower concentration of lithium ions (i.e., from the outside) into the raw material solution through a cation exchange membrane.

[0046] Next, a precipitate is generated in the reaction solution (step S2 in FIG. 2). In the reaction solution, a reaction (intercalation) occurs in which lithium ions in the raw material solution are taken up by the lithium intercalation material. As a result, a precipitate containing the lithium recovery agent and the lithium taken up by the lithium recovery agent is generated, and the lithium in the raw material solution is recovered in the precipitate.

[0047] Here, the "reaction time" refers to the time from when the reaction solution is prepared (step S1 in FIG. 2 ) to when the precipitate is separated from the reaction solution (step S3 in FIG. 2 ), which will be described later. The reaction time can be adjusted as appropriate within a range that achieves the effects of this embodiment, and may be, for example, 10 minutes to 3 days, or 1 hour to 3 hours. If the reaction time is within the above range, the intercalation reaction will proceed sufficiently, and a precipitate containing a sufficient amount of lithium will be obtained. The temperature of the reaction solution during the reaction (reaction temperature) may be, for example, 4°C to 40°C, or 25°C to 30°C. If the reaction temperature is within the above range, the activity of the electricity-generating bacteria will be activated, resulting in improved lithium recovery efficiency. Furthermore, during the reaction (reaction time), the reaction solution may be left to stand, or may be shaken, stirred, etc.

[0048] Next, the precipitate is separated from the reaction solution (step S3 in FIG. 2). The separation method is not particularly limited, and general-purpose methods such as filtration and decantation can be used. In this embodiment, the lithium intercalation material aggregates to form a precipitate (aggregate) due to the action of the power-generating bacteria, and the precipitate (aggregate) tends to adhere to the bottom of the reaction vessel. This makes it easy to separate the precipitate from the supernatant.

[0049] As described above, the lithium recovery method of this embodiment allows for efficient recovery of lithium by a simple method of contacting a lithium recovery agent with a raw material solution. Unlike conventional methods (e.g., Non-Patent Documents 1 to 3), a step of applying electricity to the lithium recovery agent 100 is not required. The lithium recovery method of this embodiment is advantageous in terms of time and money, requires fewer steps and equipment, and therefore has a low environmental impact, and is highly applicable to mass production.

[0050] [Application of lithium recovery method] In the lithium recovery method of this embodiment, lithium (lithium ions) are recovered from the raw material solution, resulting in the production of a lithium intercalation material containing lithium ions. For example, when manganese oxide is used as the lithium intercalation material, the lithium ions in the raw material solution are recovered as a lithium-containing manganese oxide (manganese oxide lithium insertion compound). That is, the lithium recovery method of this embodiment can be applied to a method for producing a lithium-containing manganese oxide. In this production method, seawater or the like can be used as the lithium source (raw material solution), and by using electricity-generating bacteria, lithium-containing manganese oxide can be produced by a low-cost and simple method. The lithium-containing manganese oxide produced can be, for example, Li ｘ Mn ２ O ４ (x=0.4 to 2.0) The average oxidation number of manganese (Mn) is not particularly limited, but is, for example, +3 to +4.

[0051] Furthermore, lithium intercalation materials containing lithium ions (for example, the lithium-containing manganese oxide described above) can be used as positive electrode active materials for lithium-ion batteries. That is, the lithium recovery method of this embodiment can be applied to a method for producing positive electrode active materials for lithium-ion batteries. In this production method, seawater or the like can be used as a lithium source (raw material solution), and by using power-generating bacteria, positive electrode active materials for lithium-ion batteries can be produced in a low-cost and simple manner. In particular, lithium-containing manganese oxides have attracted attention as positive electrode materials for lithium-ion batteries because Mn is cheaper than Co, reserves are plentiful, and a stable supply is expected in the future.

[0052] The present invention will be described in more detail below with reference to examples. The materials, amounts used, ratios, treatment contents, treatment procedures, etc. shown in the following examples can be changed as appropriate without departing from the spirit of the present invention. Therefore, the scope of the present invention should not be construed as being limited by the examples shown below.

[0053] [Experiment 1] Lithium was recovered from a raw material solution (lithium aqueous solution) using a lithium recovery agent containing the following components: λ-MnO ２ The particles are LiMn with a spinel structure. ２ O ４ The lithium recovery agent was prepared by acid treatment. <Lithium recovery agent components> Electricity generating bacteria: Shewanella spp. Electron donor: Sodium lactate Intercalation material: Manganese dioxide with a spinel structure (λ-MnO ２ Particles, average particle diameter: 100 to 300 nm)

[0054] (1) Preparation of Reaction Solution First, an aqueous solution was prepared by dissolving lithium chloride and sodium lactate in a phosphate buffer solution (lithium chloride concentration: 50 mM, sodium lactate concentration: 50 mM). 0.05 g of manganese oxide particles was mixed with 50 mL of the prepared solution. Next, dissolved oxygen in the solution was removed by bubbling nitrogen, and Shewanella bacteria were introduced and the container was sealed to obtain a reaction solution. The Shewanella bacteria were added in an amount adjusted so that the optical density (OD value) when dispersed in 50 mL of the reaction solution was 0.3.

[0055] (2) Formation of precipitate The container was placed on a shaker in an incubator set at 30°C and shaken for 24 hours at a rotation speed of approximately 160 rpm. During this time, it was confirmed that a sheet-like aggregate (precipitate) consisting of manganese oxide particles and Shewanella bacteria was formed at the bottom of the container.

[0056] (3) Separation of Precipitate After 24 hours, the container was opened and the supernatant was removed (decantation) to recover the precipitate. The resulting precipitate was washed with a surfactant to remove microbial components, and then the water was removed in a dryer to obtain a powder.

[0057] <Evaluation> (1) Crystal structure evaluation The powder obtained in Experiment 1 was subjected to X-ray diffraction (XRD) measurement. The results are shown in Figure 3 as "After reaction." For comparison, λ-MnO ２ The profile of "Before reaction (λ-MnO ２ The results are shown in Figure 3. ２ ), all peaks after the reaction are the same as those before the reaction (λ-MnO２ ) shifted to a lower angle compared to the LiMn ion profile shown in the lower part of Figure 3 for reference. This indicates that the lattice size increased while maintaining the symmetry of the spinel structure after the reaction. This increase in lattice size suggests that the valence of the manganese ions decreased due to the electrochemical insertion of cations such as lithium into the crystal structure (intercalation). ２ O ４ (The average valence of manganese is +3.5).

[0058] (2) Composition Analysis The composition of the powder obtained in Experiment 1 was analyzed by inductively coupled plasma (ICP) emission spectrometry. As a result, the molar ratio of manganese to lithium in the powder (sample after reaction) was about Mn:Li = 2:0.6, and due to the influence of co-insertion of protons, etc., LiMn ２ O ４ Although the amount of lithium was less than that in the case of (Mn:Li=2:1), it was shown that a sufficient amount of lithium was recovered.

[0059] (3) Scanning Electron Microscope (SEM) Observation and Energy Dispersive X-ray Analysis (EDS) The pre-washed aggregates (precipitates) recovered by decantation in Experiment 1 were subjected to a dehydration and drying process to remove the microorganisms, after which morphological observation was performed using a scanning electron microscope (SEM). The results are shown in Figure 4. The majority of the aggregates consisted of manganese oxide particles, and the arrows in Figure 4 indicate the locations where the shape of Shewanella bacteria was clearly observed. Simultaneously with the SEM observation, manganese and carbon were mapped using energy dispersive X-ray analysis (EDS). These results also confirmed the presence of Shewanella bacteria at the arrow positions. Carbon was also detected around the Shewanella bacteria. From this, it is speculated that the microbial-derived components covering the aggregates ensure the conductivity and adhesiveness between the manganese oxide particles.

[0060] [Experiment 2] The final product, a powder, was obtained in the same manner as in Experiment 1, except that Shewanella bacteria was not used (not introduced into the container).

[0061] <Evaluation of Crystal Structure> X-ray diffraction (XRD) measurement was carried out on the powder obtained in Experiment 2 using the same method as in Experiment 1. The results are shown in Figure 5 as "After reaction". For comparison, λ-MnO ２ The profile of "Before reaction (λ-MnO ２ In contrast to the results of Experiment 1 (Fig. 3), the profile after the reaction showed a large attenuation of the peak intensity and a broad peak shape. This suggests that the crystallinity of manganese oxide has decreased, and there is a possibility that side reactions other than the lithium insertion reaction, which occurs while maintaining the crystalline framework structure, are occurring. In addition, the peak positions are also shown in the lower part of Fig. 5 for reference. ２ O ４ This suggests that the reaction was incomplete. Comparing the XRD results of Experiment 1 (Fig. 3) and Experiment 2 (Fig. 5) confirmed that the addition of Shewanella bacteria significantly promoted the electrochemical lithium insertion reaction (intercalation).

[0062] [Experiments 3-1 to 3-6] In practice, it is necessary to recover lithium from an environment with a low lithium concentration. Therefore, in Experiments 3-1 to 3-6, the lithium recovery characteristics from an aqueous solution with a low lithium concentration were evaluated.

[0063] In Experiments 3-1 to 3-6, the lithium concentrations in the reaction solutions were set to 20 mM, 10 mM, 5 mM, 2 mM, 1 mM, and 0.5 mM, respectively. Except for these, the final product, powder, was obtained in the same manner as in Experiment 1.

[0064] <Crystal structure evaluation and composition analysis> X-ray diffraction (XRD) measurement and composition analysis were performed on the powders obtained in Experiments 3-1 to 3-6 using the same method as in Experiment 1. The results of the X-ray diffraction (XRD) measurement are shown in Figures 6A to 6F. For comparison, Figures 6A to 6F also show the crystal structure of λ-MnO ２ The peak position of "λ-MnO ２ " is indicated by a vertical dashed line with a subscript.

[0065] As shown in Figures 6A to 6C, in Experiments 3-1 to 3-3 (lithium concentration: 5 to 20 mM), each peak (vertical dashed line without subscript) was observed to change from λ-MnO ２This is similar to the result of Experiment 1 (lithium concentration: 50 mM) shown in Figure 3, and suggests that lithium ions were electrochemically inserted into the manganese oxide crystal structure (intercalation).

[0066] On the other hand, in Experiments 3-4 to 3-6 (lithium concentration: 0.5 to 2 mM), the volume of the reaction solution was limited to 50 mL, so even if all the lithium in the reaction solution could be recovered, the amount of manganese oxide recovered was limited. ２ This suggests that the amount of lithium intercalation was reduced compared to Experiments 3-1 to 3-3 (lithium concentration: 5 to 20 mM).

[0067] However, the composition analysis revealed that in the low-lithium-concentration cases of Experiments 3-5 (FIG. 6E, lithium concentration: 1 mM) and 3-6 (FIG. 6F, lithium concentration: 0.5 mM), almost all of the lithium in the prepared reaction solution was recovered into manganese oxide (the error from the theoretical value was within 5%). This suggests that lithium can be recovered from a reaction solution with an initial lithium concentration of approximately 1 mM, for example, and that even after the reaction progresses and the lithium concentration further decreases, the intercalation reaction similarly proceeds sufficiently to enable lithium recovery. From the above, it was confirmed that lithium can be recovered with high efficiency even from a low-concentration lithium aqueous solution.

[0068] [Experiments 4-1 to 4-4] In Experiments 4-1 to 4-4, the lithium recovery characteristics were evaluated when the lithium recovery agent contained an electron mediator.

[0069] In Experiments 4-1 and 4-2, the experiments were conducted under the same conditions as Experiments 3-3 (lithium concentration in the reaction solution: 5 mM) and 3-2 (lithium concentration in the reaction solution: 10 mM), except that the reaction time was shortened to 3 hours, and a powder was obtained as the final product. Furthermore, in Experiments 4-3 and 4-4, the experiments were conducted under the same conditions as Experiments 4-1 and 4-2, except that the lithium recovery agent contained riboflavin as an electron mediator, and a powder was obtained as the final product. The riboflavin concentration in the reaction solution was 2 μM.

[0070] <Evaluation of Crystal Structure> X-ray diffraction (XRD) measurements were performed on the powders obtained in Experiments 4-1 to 4-4 using the same method as in Experiment 1. The results of the X-ray diffraction (XRD) measurements are shown in Figures 7A to 7D. For comparison, Figures 7A to 7D also show the crystal structure of λ-MnO ２ The peak position of "λ-MnO ２ " is indicated by a vertical dashed line with a subscript.

[0071] As shown in Figures 7A to 7D, in Experiments 4-3 (Figure 7C) and 4-4 (Figure 7D) using riboflavin, the observed peaks (vertical dashed lines without subscripts) were clearly differentiated from λ-MnO while maintaining their peak intensity, despite the short reaction time of 3 hours. ２ The peak position was clearly shifted to a lower angle side compared to that of the manganese oxide. This suggests that lithium ions were electrochemically inserted into the manganese oxide crystal structure (intercalation).

[0072] On the other hand, in Experiments 4-1 (FIG. 7A) and 4-2 (FIG. 7B) in which riboflavin was not used, λ-MnO ２ The peak shift from the peak position of was incomplete, suggesting that the amount of lithium intercalation was reduced compared to Experiments 4-3 and 4-4 in which riboflavin was used.

[0073] From the above results, it was confirmed that by using the electron mediator (riboflavin), lithium can be recovered from the raw material solution in a shorter time, that is, the lithium recovery efficiency is improved.

[0074] [Experiment 5] In Experiment 5, a powder as a final product was obtained in the same manner as in Experiment 1, except that seawater was used as the reaction liquid.

[0075] The Li concentrations of the seawater before the reaction (raw material liquid) and the seawater after the reaction (reaction liquid after Li recovery) used in Experiment 5 were measured by ICP emission spectroscopy. The results are shown below.

[0076]

[0077] From the results shown in Table 1, the lithium recovery rate can be calculated to be approximately 96 to 98% by weight. The results of Experiment 5 confirmed that lithium can be recovered at a high recovery rate even when seawater is used as the raw material solution.

[0078] [Experiment 6] A demonstration test of the lithium recovery system shown in Figure 8 was conducted. Figure 9A is an image showing the setup. A glass screw vial was immersed in an inverted position in a container (glass beaker) containing LiCl / PBS (10, 50 mM) solution. Note that for the purpose of explanation, the image has been partially edited, such as by removing the background.

[0079] The screw vial contained a PBS solution containing sodium lactate and a lithium recovery agent prepared in the same manner as in Experiment 1, except that it did not contain lithium chloride. As described above, this PBS solution did not initially contain LiCl (w / o LiCl). Furthermore, the opening of the screw vial was sealed with a cation exchange membrane instead of a screw cap.

[0080] Figure 9B compares an image of the screw vial before immersion in LiCl / PBS (10 mM) solution (left) with an image of the screw vial after immersion and reaction for 24 hours (right). The solution before immersion was reddish-brown, whereas the solution after reaction turned a darker brown. This is due to the interaction between lithium and λ-MnO ２ In FIG. 9B, the actual shades of red are displayed as shades of black.

[0081] 10A to 10C show the results (diffraction profiles) of powder X-ray diffraction (XRD) measurements performed in the same manner as in Experiment 1. Each figure corresponds to the following experiments: Fig. 10A: Experiment 6-1 (λ-MnO before immersion) ２10B: Experiment 6-2 (profile after immersion in 10 mM LiCl solution) FIG. 10C: Experiment 6-3 (profile after immersion in 50 mM LiCl solution)

[0082] Comparing the results of Experiment 6-2 (FIG. 10B) and Experiment 6-3 (FIG. 10C) with those of Experiment 6-1 (FIG. 10A), it is clear that λ-MnO ２ The peak due to LiMn shifted to the lower angle side. ２ O ４ This confirmed that the lithium ions introduced from the outside were recovered through the cation exchange membrane.

[0083] The lithium recovery agent of the present invention can recover lithium simply and efficiently. The recovered lithium can be used as a raw material for fuel for lithium ion secondary batteries and nuclear fusion reactors.

[0084] 10 Electric-generating bacteria 20 Electron donor 30 Electron transfer protein 40 Intercalation material 100 Lithium recovery agent 200 Raw material solution 300 Reaction vessel 1000 Lithium recovery system 110 Piping 130 Lithium ion 210 Cooling water 300 Reaction vessel 400 Cation exchange membrane 1100 Lithium recovery system

Claims

1. A lithium recovery agent for recovering lithium from a raw material solution containing lithium, comprising: Electricity-generating bacteria, A lithium intercalation material and a lithium recovery agent comprising:

2. The lithium recovery agent according to claim 1 , wherein the electric-power generating bacteria is an iron-reducing bacterium.

3. The lithium recovery agent according to claim 2 , wherein the electricity-generating bacteria is a bacterium of the genus Shewanella or a bacterium of the genus Geobacter.

4. The lithium recovery agent according to any one of claims 1 to 3, wherein the lithium intercalation material is a compound containing a first transition metal.

5. The lithium recovery agent according to claim 4, wherein the first transition metal is at least one selected from the group consisting of manganese (Mn), vanadium (V), titanium (Ti), and iron (Fe).

6. The lithium recovery agent according to claim 5, wherein the lithium intercalation material is manganese dioxide having a spinel structure.

7. The lithium recovery agent according to any one of claims 1 to 3, wherein the lithium intercalation material is in the form of particles.

8. The lithium recovery agent according to any one of claims 1 to 3, further comprising an electron donor.

9. The electric-generating bacterium is a Shewanella bacterium, and the electron donor is a lactate salt, or The lithium recovery agent according to claim 8 , wherein the electricity-generating bacteria is a Geobacter bacterium, and the electron donor is an acetate salt.

10. The lithium recovery agent according to any one of claims 1 to 3, further comprising an electron mediator.

11. The lithium recovery agent according to claim 10, wherein the electron mediator is a flavin.

12. A method for recovering lithium, comprising contacting the lithium recovery agent according to any one of claims 1 to 3 with the raw material liquid.

13. The method for recovering lithium according to claim 12, wherein the electrons generated by the electricity-generating bacteria are transferred to the lithium intercalation material.

14. preparing a reaction solution containing the raw material solution and the lithium recovery agent; generating a precipitate containing the lithium recovery agent and the lithium in the reaction solution; The method for recovering lithium according to claim 12, further comprising separating the precipitate from the reaction solution.

15. The method for recovering lithium according to claim 14, wherein the raw material solution contains lithium ions introduced from the outside through a cation exchange membrane.

16. 1. A lithium recovery system comprising: A reaction vessel; The lithium recovery agent according to any one of claims 1 to 3, which is disposed in the reaction vessel; The lithium recovery system, wherein the raw material liquid and the lithium recovery agent are contacted in the reaction vessel.

17. 17. The lithium recovery system according to claim 16, which does not have a mechanism for passing electricity through the lithium recovery agent.

18. 17. The lithium recovery system according to claim 16, wherein the reaction vessel is provided with a cation exchange membrane for introducing lithium ions into the raw material solution from outside the reaction vessel.

19. The lithium recovery method according to claim 12, The method for producing a lithium-containing manganese oxide, wherein the lithium intercalation material is manganese dioxide.

20. A method for producing a positive electrode active material for a lithium ion battery, comprising the lithium recovery method according to claim 12.