Lithium recovery method and lithium recovery system

Abstract

This lithium recovery method for recovering lithium from a lithium-containing medium comprises: cultivating a salt-tolerant plant or a salt-resistant plant using the medium, and recovering the lithium concentrated in the body of the salt-tolerant plant or the salt-resistant plant, or the lithium discharged from the plant body.

Description

Lithium recovery method and lithium recovery system

[0001] The present disclosure relates to a lithium recovery method and system.

[0002] Demand for lithium has been increasing in recent years, and this trend is expected to continue. For example, lithium-ion batteries are used as the primary power source for electric vehicles. The widespread use of electric vehicles is being promoted to reduce greenhouse gas emissions, and demand is expected to continue to increase. However, lithium has problems such as unstable supply and environmental impacts, such as water and soil contamination, during the production process (see, for example, Non-Patent Document 1). Known sources of lithium resources are broadly divided into hydrospheres, such as continental salt lakes, brines, and seawater, and geospheres, such as lithium deposits. Two known lithium production methods are the concentration of "salt lake brines" from the hydrosphere and the purification of minerals such as "spodumene ore (spodumene pyroxene)" from the geosphere (see, for example, Non-Patent Document 2). These production processes require significant energy and cost, and consume large amounts of water. Therefore, expanding lithium production raises concerns about water shortages for agricultural and domestic use, for example. Furthermore, since by-products such as sodium sulfate are generated during the lithium refining process, there is a problem that wastewater generated during the lithium refining process pollutes water and soil. Therefore, there has been a demand for lithium production technology that can reduce the environmental burden described above while suppressing energy consumption. Furthermore, as a problem related to the environmental burden of lithium, there has been an environmental problem caused by waste generated from used lithium-ion batteries as a pollution source (see, for example, Non-Patent Document 3).

[0003] In addition to the lithium resource sources already mentioned, lithium is known to be contained in soil, mainly in clay minerals, at a concentration of about 7-200 ppm (see, for example, Non-Patent Document 4), and it is known that Japanese soil also contains 10-100 ppm of lithium (see, for example, Non-Patent Document 5). Looking at the lithium concentration in soil by region, it is 0.28-271 mg kg across Europe. －１(See, for example, Non-Patent Document 6), and in the topsoil of the United States, it is 1-300 mg kg －１ (See, for example, Non-Patent Document 7), and in Australia, it is 0.1-67.4 mg kg －１ (See, for example, Non-Patent Document 8), and in New Zealand, it is 0.08-92 mg kg －１ (For example, see Non-Patent Document 9). In China, the concentration of ammonium nitrate in the sediments of catchments is 5.27-400 mg kg －１ (For example, see Non-Patent Document 10), in the topsoil where there is underground lithium deposit, it is 211 mg kg －１ (See, for example, Non-Patent Document 11) lithium has been detected.

[0004] Conventional methods for recovering metals from soil include the use of plants known as hyperaccumulators, which accumulate specific metals at high concentrations (see, for example, Non-Patent Documents 12-15 and Patent Documents 1-6). More specifically, there are techniques known as phytoremediation, which utilizes the metal accumulation ability of plants such as hyperaccumulators to purify contaminated soil, and phytomining, which uses plants to recover rare metals present in trace amounts in soil. Phytoremediation is a low-cost, low-environmental-impact environmental remediation technology that removes contaminants from soil and other environments through plant absorption, accumulation, metabolism, decomposition, and other functions (see, for example, Non-Patent Documents 16-18). The target substances are organic pollutants such as heavy metals and dioxins, which are sources of contamination. Phytomining primarily targets high-value-added precious metals and rare metals. It involves adsorbing and accumulating the target metal ions from soil and other environments within plants, recovering the plants, and then extracting and refining the target metals.

[0005] JP 2011-45875 A JP 2007-92172 A JP 2006-159181 A JP 2006-75821 A JP 2004-275051 A JP 2002-336837 A

[0006] Japan Research Institute, Research Focus, "Lithium Production Issues Affecting the Global Shift to EVs," No. 2022-012; Shunzo Ishihara, "Lithium Granite Petrology and Pegmatite Resource Theory," Geological News, No. 670, pp. 27-45, June 2010; Wojciech Mrozik et al., "Environmental Impacts, Pollution Sources, and Pathway of Spent Lithium-ion Batterise," Energy Environ. Sci., 2021; Cannon, H.L. et al., "Lithium in Unconsolidated Sediments and Plants of the Basin and Range Province, Southern California and Nevada," 1975 (No. 918); United States Government Printing Office: Washington, DC, USA; Mitsutsune Ohta et al., "Soil Geochemical Map of Japan," Geochemistry, Vol. 57, pp. 247-278, 2023; Salminen, R. et al. Geochemical Atlas of Europe. Part 1 - Background information, methodology and maps, ISBN 9516909132 (2006).Smith, DB, Cannon, WF, Woodruff, LG, Solano, F. & Ellefsen, KJ Geochemical and Mineralogical Maps for Soils of the Conterminous United States. (2014).Caritat, P. d. & Cooper, M. National Geochemical Survey of Australia: The Geochemical Atlas of Australia. (2011).Robinson, B.H., Yalamanchali, R., Reiser, R. & Dickinson, N.M.Lithium as an emerging environmental contaminant: Mobility in the soil-plant system. Chemosphere 197, 1-6, doi:10.1016 / j.chemosphere.2018.01.012 (2018).Liu, H. et al. Concentration and distribution of lithium in catchment sediments of China: Conclusions from the China Geochemical Baselines project. Journal of Geochemical Exploration 215, 106540, doi:10.1016 / j.gexplo.2020.106540 (2020).P01Xu, Z., Liang, B., Geng, Y., Liu, T. & Wang, Q. Extraction of soils above concealed lithium deposits for rare metal exploration in Jiajika area: A pilot study. Applied Geochemistry 107, 142-151, doi:10.1016 / j.apgeochem.2019.05.018 (2019).Barbara Leitenmaier et al., "Compartmentation and complexation of metals in hyperaccumulator plants", Front. Plant Sci., 4, 374, 2013.Roger D. Reeves et al., "A global database for plants that hyperaccumulate metal and metalloid trace elements", New Phytol., 218, 407-411, 2017.Mitch M. Lasat, "Phytoextraction of Toxic Metals: A Review of Biological Mechanisms", J.Environ. Qual., 31, 109-120, 2002. Laurence Kavanagh et al., "Induced Plant Accumulation of Lithium", Geosciences, 2018, 8, 56. An Yan et al., "Phytoremediation: A Promising Approach for Revegetation of Heavy Metal-Polluted Land", Front. Plant Sci., 11, 359, 2020. Mitsutake Yoshida et al., "Current Status and Issues of Phytoremediation", Taisei Corporation Technology Center Bulletin, No. 38, 06, 2005. Xiaoqian Wang et al., "Phytoremediation for Contaminated Soil Remediation", Saitama Prefectural Environmental Science International Center Bulletin, No. 3, 114-123, 2004.

[0007] As described above, compared to conventional methods for producing lithium from lithium resource sources, there has been a demand for lithium purification technologies that can reduce energy consumption and costs while further mitigating the environmental impact, but such technologies have not been fully explored. While technologies for recovering specific metals from soil using hyperaccumulator plants are considered to be technologies that can at least reduce the environmental impact, no technologies for recovering lithium have been known. For example, Non-Patent Document 15 shows that lithium accumulation in plants of the Brassicaceae family can be induced by using chelating agents such as ethylenediaminetetraacetic acid (EDTA) and ethylenediamine-N,N'-disuccinic acid (EDDS). However, the feasibility of recovering lithium has not been fully explored.

[0008] The present disclosure can be realized as the following aspects. (1) According to one aspect of the present disclosure, there is provided a lithium recovery method for recovering lithium from a lithium-containing medium. This lithium recovery method includes cultivating a halophyte or halotolerant plant in the medium and recovering lithium concentrated within the plant body of the halophyte or halotolerant plant or lithium excreted from the plant body. According to this aspect of the lithium recovery method, lithium can be recovered from the medium by a very simple method of cultivating a halophyte or halotolerant plant in a lithium-containing medium and recovering lithium concentrated within the plant body or lithium excreted from the plant body. Therefore, lithium can be produced while reducing energy consumption, costs, and environmental impact. (2) In the lithium recovery method of the above aspect, the plant body may have salt glands, and lithium excreted from the salt glands may be recovered. This configuration enables highly efficient and sustainable lithium recovery while continuing the growth of the plant without damaging it, and by eliminating the need for processes such as plant recovery, dissolution, and extraction, it is possible to significantly reduce energy consumption, costs, and environmental impact. (3) In the lithium recovery method of the above aspect, the lithium released from the salt glands to the surface of the plant may be recovered using a suction device. This configuration enables a large amount of lithium to be recovered at once while suppressing the inclusion of impurities, thereby improving recovery efficiency. (4) In the lithium recovery method of the above aspect, the lithium released from the salt glands to the surface of the plant may be recovered by washing the surface of the plant with a washing solution. This configuration allows lithium to be recovered by the simple method of washing the surface of the plant. (5) In the lithium recovery method of the above aspect, lithium may be recovered from the plant having bicellular or multicellular salt glands as the salt glands. This configuration facilitates the operation of recovering lithium from the surface of the plant. (6) In the lithium recovery method according to the above aspect, Rhodes grass may be used as the halophyte or salt-tolerant plant.With this configuration, lithium can be easily recovered with higher efficiency. (7) In the lithium recovery method of the above aspect, soil containing 1 ppm or more and 1000 ppm or less of lithium may be used as the medium. With this configuration, lithium can be recovered from a lithium source that has been difficult to use in the past. (8) In the lithium recovery method of the above aspect, an aqueous solution containing 1 ppm or more and 1000 ppm or less of lithium may be used as the medium. With this configuration, lithium can be recovered from a lithium source that has been difficult to use in the past. (9) According to another aspect of the present disclosure, there is provided a lithium recovery system for recovering lithium from a lithium-containing medium. The lithium recovery system includes a cultivation unit that includes a halophyte or halotolerant plant and an aqueous medium that is an aqueous solution for cultivation, and that cultivates the halophyte or halotolerant plant using the aqueous medium, and an aqueous medium supply unit that supplies a lithium-containing liquid from which lithium is to be recovered to the cultivation unit as the aqueous medium. In this lithium recovery system, a halophyte or halotolerant plant is cultivated in the cultivation unit using an aqueous medium that is a lithium-containing liquid supplied from the aqueous medium supply unit. This makes it possible to recover lithium concentrated within the halophyte or halotolerant plant or lithium discharged from the plant, thereby recovering lithium from the aqueous medium while reducing energy consumption, costs, and environmental impact. (10) In the lithium recovery system of the above embodiment, the cultivation unit may hydroponically cultivate the halophyte or halotolerant plant using the aqueous medium. This configuration allows lithium to be recovered by the simple method of hydroponically cultivating the halophyte or halotolerant plant. (11) In the lithium recovery system of the above embodiment, the lithium-containing liquid may be a lithium-containing waste liquid generated in a lithium production process or a lithium recycling process. This configuration increases the lithium utilization efficiency.The present disclosure can be realized in various forms other than those described above, such as a method for recycling lithium, a method for recycling lithium-ion batteries, a method for purifying lithium-contaminated soil, a method for purifying lithium-containing wastewater, and a method for improving lithium production efficiency.

[0009] 1. A flowchart showing a lithium recovery method. 2. An explanatory diagram schematically showing an example of a lithium recovery system. 3. An explanatory diagram showing cultivation conditions and measurement results for Rhodes grass. 4. An explanatory diagram showing cultivation conditions and measurement results for plants other than Rhodes grass. 5. An explanatory diagram schematically showing the configuration of a hydroponic cultivation apparatus. 6. An explanatory diagram showing soil cultivation. 7. An explanatory diagram showing an optical microscope image of a cross section of a sixth leaf of Rhodes grass. 8. An explanatory diagram showing a secondary electron image of a cross section of a sixth leaf of Rhodes grass. 9. A photograph of Rhodes grass grown hydroponically 24 days after sowing. 10. An explanatory diagram showing the relationship between the dry weight of Rhodes grass and the LiCl concentration. 11. An optical photograph of the abaxial side of a leaf after addition of 2 mM LiCl. 12. An explanatory diagram showing the relationship between the amount of excreted salt and the amount of excreted Li and the LiCl concentration. 13. A diagram showing the relationship between the excreted salt Li concentration, the aboveground Li concentration, and the added LiCl concentration. 14. An explanatory diagram showing a photograph of Rhodes grass grown in Li-added soil 35 days later. 15. An explanatory diagram showing the measurement results of the aboveground dry weight and the amount of excreted Li after soil cultivation. Fig. 1 shows a photograph of a filter when salt is collected from leaves by a vacuum method. Fig. 2 shows a photograph of Nipponbare grown hydroponically 24 days after sowing. Fig. 3 shows the relationship between the dry weight of Nipponbare and LiCl concentration. Fig. 4 shows a photograph of ice plant grown in soil. Fig. 5 shows a photograph of okahijiki grown in soil.

[0010] A. Lithium Recovery Method: Figure 1 is a flowchart showing a lithium recovery method according to an embodiment of the present disclosure. When carrying out the lithium recovery method of this embodiment, first, a halophyte or halotolerant plant and a medium containing lithium are prepared (step T100). Hereinafter, "halophyte" and "halotolerant plant" will be collectively referred to as "halotolerant plant, etc.", and a "medium containing lithium" will be referred to as "Li-containing medium." Lithium can exist in various forms, such as lithium ions and lithium salts, but in the following description, these forms may be referred to as "lithium" without distinction.

[0011] Here, "halophytes" refers to plants (especially seed plants) that can tolerate relatively high salt concentrations, and "salt-tolerant plants" refers to plants that are resistant to growth inhibition up to a certain salt concentration. Plants are classified into three types: "salt-sensitive plants," "salt-tolerant plants," and "halophytes" based on their growth response to salt, particularly NaCl. Most plants belong to the "salt-sensitive" category and rapidly experience a decrease in growth or growth impairment in response to salt stress. "Salt-tolerant plants" can tolerate and maintain growth up to a certain level of salt stress, but if the stress exceeds this level, changes such as a decrease in growth, damage to leaf and stem morphology, and yellowing of the plant body are observed. "Halophytes" generally have the property of increasing their growth under salt stress levels that would reduce the growth of "salt-sensitive plants" or "salt-tolerant plants." Some species survive and continue to grow under salt stress levels up to the same salt concentration as seawater (approximately 3% NaCl). For example, the halophyte Salicornia glomerata achieves high tolerance to salt stress by accumulating excess salt in a part of the plant body, causing the tissues in that part, except for the vascular sheath, to wither and die.

[0012] At least some of these "salt-tolerant plants" possess organs called "salt glands." Salt glands are found in a variety of dicotyledonous and monocotyledonous plant species, and have been reported in over 50 species across 14 families (Front. Plant Sci. 8 1-20, 2017). The structure of salt glands varies by species, but they are broadly classified into three types: "saccular-hair salt glands," "multicellular salt glands," and "bicellular salt glands" (Jpn. J. Crop Sci., 90, 235-246, 2021).

[0013] "Saccular hair-type salt glands," also known as "bladder cells," are found in plants of the Amaranthaceae family, such as Chenopodium album and quinoa, and in plants of the Aizoaceae family, such as ice plant. Bladder cells are approximately 1,000 times larger than normal cells and accumulate high concentrations of salt within the cells. "Multicellular salt glands" are found in 11 other dicotyledonous families, including the mangrove tree Avicennia marina. "Bicellular salt glands" are found in grasses. Almost all grasses, except for the Pooideae subfamily, are known to have bicellular hairs in the epidermis of their aboveground parts. In particular, some in the Chloridoideae subfamily have been shown to function as salt glands, actively excreting salt (Front. Plant Sci. 8 1-20, 2017).

[0014] The lithium recovery method of this embodiment, as described below, involves cultivating a salt-tolerant plant or the like in a Li-containing medium, thereby recovering lithium from the salt-tolerant plant or the like in a Li-containing medium. The various salt-tolerant plants described above can be used as the salt-tolerant plant or the like for this purpose. Using a salt-tolerant plant or the like belonging to the Amaranthaceae family, which has a "saccular-hair-type salt gland," makes it possible to efficiently recover lithium concentrated in bladder cells. Furthermore, using a salt-tolerant plant or the like, such as mangrove marina, which has a "multicellular salt gland," or a salt-tolerant plant or the like belonging to the Poaceae subfamily, such as Rhodes grass (Chloris gayana Kunth), which has a "bicellular salt gland," allows relatively high concentrations of lithium-containing salts to be continuously secreted from the salt glands, and the secreted salts can be recovered. Therefore, highly efficient and sustainable lithium recovery is possible while significantly reducing energy consumption, costs, and environmental impacts, while continuing to grow the plant without damaging it.

[0015] In general, classifications such as "halophytes" and "halotolerant plants" are often evaluated based on their tolerance to sodium (Na) using NaCl or the like. It is particularly important that the "halotolerant plants, etc." used in the lithium recovery method of this embodiment have high tolerance to lithium (Li). From this perspective, Rhodes grass is particularly preferable as the "halotolerant plants, etc." This is because, although "halophytes" have higher tolerance to sodium (Na) than "halotolerant plants," Rhodes grass, which is a "halotolerant plant," has the property of being more tolerant to lithium (Li) than ice plant and seaweed, which are "halophytes," as will be described later.

[0016] As described above, the "salt-tolerant plants, etc." used in this embodiment may be those that have "saccular hair-type salt glands" and store lithium within their bodies, or those that have "multicellular salt glands" or "bicellular salt glands" and secrete lithium from the salt glands. The "salt-tolerant plants, etc." used in this embodiment are preferably plants that can grow while storing a certain amount of lithium (Li) within their bodies when cultivated in a Li-containing medium (Li-accumulating plants).

[0017] The "Li-containing medium" prepared together with the "salt-tolerant plant, etc." in step T100 of FIG. 1 is a medium containing lithium to be recovered. The "Li-containing medium" is a medium used to cultivate the "salt-tolerant plant, etc." as described below, and may be water or soil. The "Li-containing medium" may be, for example, soil containing 1 ppm to 1000 ppm of lithium, or an aqueous solution containing 1 ppm to 1000 ppm of lithium. The lithium concentration in the "Li-containing medium" may be adjusted as appropriate depending on the level of lithium tolerance of the "salt-tolerant plant, etc." used (including the degree to which the lithium concentration affects the growth rate) and the degree to which the lithium concentration affects the lithium concentration on the lithium concentration and lithium secretion ability of the "salt-tolerant plant, etc."

[0018] Such a "Li-containing medium" may be, for example, a lithium-containing waste liquid generated during lithium production by other lithium production methods. As in the case of producing lithium from hydrosphere lithium resources described above, lithium recovery from a lithium-containing liquid can be performed relatively easily by chemical methods, methods using adsorbents, or the like. However, it has been difficult to recover lithium from a lithium-containing liquid with a sufficiently high efficiency. Specifically, recovering more than 90% of lithium from hydrosphere lithium resources has been difficult from a cost perspective. Thus, after lithium is recovered from hydrosphere lithium resources by a conventional method, a lithium-containing waste liquid containing a relatively low concentration of lithium can be used as a "Li-containing medium." This can increase lithium production efficiency while suppressing cost increases, for example. Furthermore, by using such a lithium-containing waste liquid, the lithium concentration in the "Li-containing medium" can be appropriately suppressed, making it easier to recover lithium from a medium with a lithium concentration suitable for cultivating "salt-tolerant plants, etc."

[0019] Furthermore, the "Li-containing medium" may be lithium-containing wastewater generated during the recycling process of lithium from lithium-containing devices. For example, the recycling process for lithium-ion batteries involves dissolving metals through acid treatment and then recovering them through extraction. However, the efficiency of such metal recovery is known to be lower than that of other metal elements, e.g., 91-99% for nickel (Ni), 95-99% for cobalt (Co), and 94-99% for manganese (Mn), while the efficiency for lithium (Li) is 80-90% (Carbon Energy, 2, 6-43, 2020). As a result, a large amount of wastewater containing unrecovered lithium ions is discharged. Using such lithium-containing wastewater as the "Li-containing medium" can increase the lithium recycling efficiency. Furthermore, reducing the lithium concentration in the wastewater can reduce pollution of the wastewater receiving area.

[0020] Furthermore, the "Li-containing medium" may be a mineral with a relatively low lithium concentration, which has not traditionally been a target of mining, or soil containing such a mineral, among the aforementioned geospheric lithium resources. Generally, when mining lithium, minerals with higher lithium concentrations are prioritized, while minerals with lower lithium concentrations are postponed for recovery. Furthermore, minerals with lower lithium concentrations tend to have lower recovery efficiency relative to cost. By using minerals with a relatively low lithium concentration, such as those described above, as the "Li-containing medium," it becomes easier to recover lithium, which has traditionally been difficult to recover. Furthermore, by using minerals with a relatively low lithium concentration, such as those described above, the lithium concentration in the "Li-containing medium" can be appropriately reduced, facilitating lithium recovery from a medium with a lithium concentration suitable for the cultivation of "salt-tolerant plants, etc." Furthermore, if there is already soil contaminated with lithium due to the aforementioned lithium production or lithium recycling, such lithium-contaminated soil may be used as the "Li-containing medium."

[0021] Returning to FIG. 1 , after preparing the "salt-tolerant plants, etc." and the "Li-containing medium" in step T100, the "salt-tolerant plants, etc." are then cultivated using the "Li-containing medium" (step T110). When the "Li-containing medium" is soil, the "salt-tolerant plants, etc." can be cultivated by planting them directly in such soil. In this case, for example, the "salt-tolerant plants, etc." may be planted in a cultivation container containing the "Li-containing medium," or the "salt-tolerant plants, etc." may be planted in land containing lithium-contaminated soil as the "Li-containing medium." Alternatively, soil with a lower lithium concentration may be mixed with the soil serving as the "Li-containing medium" to adjust the lithium concentration in the soil, and then the "salt-tolerant plants, etc." may be cultivated. Furthermore, when using plants that have already been planted in land with a relatively low lithium concentration (for example, grasses such as Rhodes grass planted in a pasture) as the "salt-tolerant plants, etc.", the "Li-containing medium" may be mixed (plowed) into the soil (pasture, etc.) in which such "salt-tolerant plants, etc." are planted.

[0022] Generally, clay and humus in soil are negatively charged, so cations, including lithium ions, in the soil are adsorbed (base exchanged) and retained in the soil. Therefore, when cultivating "salt-tolerant plants, etc." in soil containing a "Li-containing medium" as described above, a chelating agent such as ethylenediaminetetraacetic acid (EDTA) or ethylenediamine-N,N'-disuccinic acid (EDDS) may be added to the soil to dissolve the lithium adsorbed in the soil and facilitate its absorption by the "salt-tolerant plants, etc." When using a chelating agent, EDDS is more preferable because of its biodegradability. Alternatively, an organic acid such as oxalic acid or citric acid may be added to the soil to dissolve lithium and facilitate its absorption by the "salt-tolerant plants, etc." Furthermore, instead of or in addition to adding an organic acid to the soil, a plant that releases organic acid from its roots may be planted together with the "salt-tolerant plants, etc." Various plants, such as legumes and grasses (including Rhodes grass), are known to secrete organic acids from their roots.

[0023] When the "Li-containing medium" is an aqueous medium such as the lithium-containing waste liquid described above, in step T110, the "salt-tolerant plants, etc." can be hydroponically cultivated using such an aqueous medium, or by diluting the aqueous medium as necessary. Here, "hydroponics" includes both a method using a solid medium such as hydroballs, rock wool, or coco peat instead of soil (hydroculture), and a method of cultivating plants using only a culture solution as a medium without using a solid medium. Furthermore, when cultivating "salt-tolerant plants, etc." using soil, the "Li-containing medium," which is an aqueous medium, may be used as the water supplied to the soil.

[0024] FIG. 2 is an explanatory diagram schematically illustrating an example of a lithium recovery system. The lithium recovery system 10 shown in FIG. 2 is an apparatus for cultivating salt-tolerant plants 20 and recovering lithium from the plants 20, and includes a cultivation unit 30 and an aqueous medium supply unit 40. The cultivation unit 30 includes the plants 20 and an aqueous medium 32, which is an aqueous solution for cultivation, and is used to cultivate the plants 20 using the aqueous medium 32. The cultivation unit 30 includes a container 34 for storing the aqueous medium 32, which can be distributed, and a substrate 36, which is disposed above the container 34 and serves as a substrate for planting the plants 20, and is made of a sponge or the like. The aqueous medium 32 is a lithium-containing liquid from which lithium is recovered, and is not particularly limited as long as it is a liquid capable of growing the plants 20. For example, the aqueous medium 32 may be the lithium-containing waste liquid described above. As shown in FIG. 2, the aqueous medium 32 contains dissolved and ionized lithium. The container unit 34 is provided with an inlet channel 33 through which the lithium-containing liquid used as the aqueous medium 32 flows into the container unit 34, and an outlet channel 34 through which the aqueous medium 32 flows out of the container unit 34. The aqueous medium supply unit 40 is a device that supplies the lithium-containing liquid, from which lithium is to be recovered, as the aqueous medium 32 to the cultivation unit 30, and is connected to the inlet channel 33. The configuration of the aqueous medium supply unit 40 is not particularly limited as long as it is capable of supplying the lithium-containing liquid, but it can be configured, for example, to include a tank that stores lithium-containing waste liquid and a pump that pumps the lithium-containing waste liquid from the tank to the inlet channel 33. Note that, as an example, the lithium recovery system 10 in FIG. 2 is provided with the cultivation unit 30 that performs hydroponic cultivation. However, a cultivation unit that performs soil cultivation may be provided instead of the cultivation unit 30 that performs hydroponic cultivation, or in addition to the cultivation unit 30 that performs hydroponic cultivation.

[0025] In step T110, the salt-tolerant plants are cultivated using the Li-containing medium, and the lithium in the Li-containing medium is absorbed by the salt-tolerant plants through their roots. If the salt-tolerant plants have, for example, saccular hair-type salt glands, the lithium taken up by the salt-tolerant plants from the Li-containing medium is concentrated and stored in the salt glands inside the plant. If the salt-tolerant plants have, for example, multicellular salt glands or bicellular salt glands, the lithium taken up by the salt-tolerant plants from the Li-containing medium is excreted from the salt glands on the surface of the plant. Figure 2 shows the excretion of lithium-containing salt 22 from the surface of the salt-tolerant plants 20.

[0026] After lithium has been concentrated and stored inside the salt-tolerant plant through cultivation in step T110, or after lithium-containing salts have been excreted from the plant, such lithium is recovered from the plant (step T120). When lithium has been stored in the "salt-tolerant plant, etc.", lithium can be recovered from the "salt-tolerant plant, etc." by, for example, drying the plant and then adding an acid such as sulfuric acid or nitric acid to turn the plant into a solution.

[0027] Furthermore, when lithium-containing salts are excreted from the surface of the "salt-tolerant plants, etc.", lithium can be recovered, for example, by sucking the excreted lithium-containing salts using a suction device. In this case, efficient recovery can be achieved, for example, by attaching a filter to cover the suction port of the suction device and capturing the sucked lithium-containing salts with the filter. Alternatively, when lithium-containing salts are excreted from the surface of the "salt-tolerant plants, etc.", lithium can be recovered by washing the surface of the plant with a cleaning solution such as water, dissolving the lithium-containing salts in the cleaning solution, and evaporating the water from the resulting cleaning solution. In particular, the method using the suction device described above is desirable because it is an extremely simple method with few steps, enables large-scale recovery processing at one time while suppressing the introduction of impurities, and easily increases recovery efficiency. When the "salt-tolerant plants, etc." have "multicellular salt glands" or "bicellular salt glands" and lithium-containing salts are excreted from the plant, the excretion of such lithium-containing salts is continuous. Therefore, in the lithium recovery system 10, by periodically recovering lithium by washing the plant body or using a suction device while appropriately supplying the lithium-containing liquid, it becomes possible to continuously recover lithium. Furthermore, it is possible to eliminate the need for steps such as recovering and dissolving the plant body for lithium recovery.

[0028] According to the lithium recovery method configured as described above, lithium can be recovered from the Li-containing medium by a very simple method of cultivating a "salt-tolerant plant, etc." using a "Li-containing medium" and recovering lithium from the plant body or the surface of the "salt-tolerant plant, etc." In other words, by having the "salt-tolerant plant, etc." absorb the lithium in the "Li-containing medium" through cultivation, lithium can be recovered from the plant body or the surface of the plant body. Therefore, this method can be a new lithium production method that can recover lithium while significantly reducing the environmental load associated with lithium recovery and reducing the amount of energy and cost required for lithium recovery compared to conventional methods using lithium resource sources in the hydrosphere or geosphere.

[0029] <Experimental Method> As shown in Figure 1, salt-tolerant plants were cultivated in Li-containing media (lithium-containing aqueous solution and lithium-containing soil), and lithium was recovered from the plants. The "salt-tolerant plants" used were the Catambora cultivar of Rhodes grass (Chloris gayana Kunth), a species of the Chloridoideae subfamily of the Poaceae family that possesses bicellular salt glands. The "halophytes" used were the ice plant (Mesembryanthemum crystallinum), which possesses sac-like hair-like salt glands, and the Japanese oak (Salsola komarovii), which is believed to lack salt glands. Furthermore, the "Nipponbare" (Oryza sativa L.), a member of the Poaceae family, was used as an example of a plant that does not belong to the "salt-tolerant plants" category. The plants were grown hydroponically, in soil, or both. Hydroponic cultivation is believed to eliminate the effects of lithium ion adsorption by soil.

[0030] Figures 3 and 4 are explanatory diagrams summarizing the conditions for cultivating plants and the measurement results for the cultivated plants. Figure 3 is an explanatory diagram for Rhodes grass, and Figure 4 is an explanatory diagram for plants other than Rhodes grass. Below, the cultivation method, lithium recovery method, and analysis method will be explained in order.

[0031] [Hydroponic cultivation of Rhodes grass] Rhodes grass seeds were soaked in 70% ethanol, washed with sterile water, then sterilized with a 3% aqueous solution of sodium hypochlorite, and then washed with sterile water. The sterilized seeds were sown on 1 / 2 MS (Murashige and Skoog) medium (pH 5.7, MES 0.5 g / L, agar 8 g / L) and grown at 25°C under light conditions for 12 hours (150 μmol m －２ ・s －１ The seeds were grown in an incubator set at 12 hours dark and 3 days dark. Three days after sowing, the germinated seeds were transplanted into a sponge soaked in a 1 / 2 MS medium solution (pH 5.7, MES 0.5 g / L). Six days after sowing, the sponge was placed in a hydroponic container containing a 1 / 2 MS medium solution, and hydroponic cultivation was initiated.

[0032] 5 is an explanatory diagram showing a schematic configuration of a hydroponic cultivation device 130 equipped with a sponge 136 into which germinated Rhodes grass plants have been transplanted. The hydroponic cultivation device 130 includes a container 134 for storing an aqueous medium 132, a sponge 136 serving as a substrate and positioned above the container 134 and into which germinated Rhodes grass plants 120 have been transplanted, and an evaporation prevention film 137 positioned above the sponge 136 to cover the opening of the container 134. As described above, the aqueous medium 132 at the start of hydroponic cultivation is a ½ MS medium solution.

[0033] After the start of hydroponic cultivation, LiCl was added to the culture solution (aqueous medium 132). LiCl addition was performed by replacing the aqueous medium 132 with the ½ MS medium solution containing LiCl 10 days after sowing, when the fifth leaf began to be extracted. The LiCl concentrations of the ½ MS medium solution were 0 mM (control), 0.1 mM, 0.2 mM, 0.4 mM, 0.6 mM, 0.8 mM, 1 mM, 2 mM, 4 mM, 6 mM, 8 mM, and 10 mM (1 mM Li = 6.94 ppm Li) (Samples No. 1 to 12 shown in Figure 3). The LiCl concentration of the ½ MS medium solution (aqueous medium 132) is also referred to as the "added LiCl concentration." One week after the LiCl addition, the aboveground parts of the Rhodes grass 120 plants were washed with pure water to remove salt excreted from the salt glands. Thereafter, the plants were again cultivated for one week using a 1 / 2 MS aqueous solution containing LiCl as the aqueous medium 132 (24 days after sowing), and then the discharged salts were recovered by the washing method described below.

[0034] [Soil Cultivation of Rhodes Grass] Rhodes Grass is cultivated in soil using petalite (LiAlSi ４ O １０The experiment was carried out using soil containing 22664 ppm Li (Li concentration: 22,664 ppm) to examine whether the discharged salt contained lithium. Specifically, petalite was added to a soil mixture of river sand and potting soil at a 1:1 (vol%) ratio, and two types of petalite-added soil were prepared by adjusting the lithium concentration of the soil to 22 ppm or 220 ppm (samples No. 13 and 14 shown in Figure 3). Rhodes grass was sown in 120 mL pots containing each of these soils, and the pots were then placed in containers containing 1 / 2 MS medium solution.

[0035] FIG. 6 is an explanatory diagram showing a schematic diagram of soil cultivation. The soil cultivation device 230 includes a pot 238 containing soil and a plant 220 planted in the soil, and a container 234 in which the pot 238 is placed and an aqueous medium 232 is arranged around the pot 238. As described above, Rhodes grass is used as the plant 220, the pot 238 contains petalite-added soil, and a 1 / 2 MS medium solution is used as the aqueous medium 232. The cultivation was carried out at 25°C under light conditions of 12 hours (150 μmol m －２ ・s －１ The Rhodes grass was grown in an incubator set under a dark condition of 12 hours. Thirty-five days after sowing, the excreted salt was collected by the washing method described below.

[0036] [Recovery of Exhausted Salt by Washing Method] The above-ground parts of the Rhodes grass 120 were washed with pure water, and the water in the washing water in which the salt excreted from the Rhodes grass had dissolved was evaporated, thereby recovering the excreted salt.

[0037] [Recovery of discharged salt by vacuum method] In addition to the washing method described above, a method of recovering discharged salt from Rhodes grass was also carried out by vacuum method. That is, a filter was attached to the aspirator so as to cover the suction port of the aspirator, and salt discharged onto the surface of the above-ground part of the Rhodes grass was directly sucked in by the aspirator and collected on the filter.

[0038] [Hydroponic Cultivation of Nipponbare] Nipponbare was hydroponically cultivated in the same manner and under the same conditions as Rhodes grass. The LiCl concentrations of the ½ MS medium solution used as the aqueous medium 132 were 0 mM (control), 0.2 mM, 1 mM, 2 mM, and 10 mM (samples 15 to 19 shown in FIG. 4).

[0039] [Cultivation of Ice Plant and Okahijiki in Li-added Soil] Ice plant and Okahijiki, known as halophytes, were cultivated in soil to which lithium had been added, and lithium tolerance was confirmed. Soil cultivation was carried out using an apparatus with a configuration similar to the soil cultivation apparatus 230 shown in FIG. 6. First, five seeds of each of the ice plant and Okahijiki were sown in pots 238 filled with soil to which no lithium had been added, and then the pots 238 were placed in containers 234 containing an aqueous 1 / 2 MS medium solution as the aqueous medium 232. Then, the pots were cultivated at 20°C under light conditions for 12 hours (150 μmol m －２ ・s －１ The plants were grown in an incubator set at 12 hours dark and 1 week dark. One week after sowing, the plants were thinned to one plant per pot, and from 28 days after sowing, they were cultivated for 40 days in a ½ MS medium solution (pH 5.7, MES 0.5 g / L) containing 1 mM LiCl. LiCl was added by transferring the pot 238 to a container 234 containing an aqueous medium 232 containing a ½ MS medium solution (pH 5.7, MES 0.5 g / L) containing 1 mM LiCl. The ice plant 28 days after sowing before the addition of LiCl was sample No. 20, the ice plant cultivated for 40 days after the addition of LiCl was sample No. 21, the okahijiki 28 days after sowing before the addition of LiCl was sample No. 22, and the okahijiki 28 days after the addition of LiCl was sample No. 23. 23 (see FIG. 4).

[0040] [Measurement of the amount of salt excreted] The weight of salt obtained by evaporating the washing solution used to wash the Rhodes grass to dryness was measured as the amount of salt excreted from the Rhodes grass. The Rhodes grass was washed on a plant-by-plant basis, and the amount of salt per plant in each sample was measured. The measurement results are shown as "amount of salt excreted (mg / plant)" in Figure 3 and Figure 12, which will be described later.

[0041] [Measurement of the Amount of Released Lithium and Calculation of the Lithium Concentration in the Discharged Salt] The amount of lithium released from Rhodes grass was measured using ion chromatography (IC). Specifically, the washing solution used to wash the Rhodes grass was evaporated to dryness, and the lithium ions contained in the resulting salt were quantitatively analyzed using IC. Rhodes grass was washed on a plant-by-plant basis, and the amount of released lithium per plant was measured for each sample. The measurement results are shown as "Li Released Amount (μg / plant)" in Figure 3 and Figures 12 and 15(B) described below. Furthermore, the lithium concentration in the discharged salt (Li concentration in discharged salt) was calculated by calculating the ratio of the "Li Released Amount (μg / plant)" to the "Amount of Discharged Salt (mg / plant)." The calculation results are shown as "Li Concentration (%) in Discharged Salt" in Figure 3 and Figure 13 described below.

[0042] [Measurement of dry weight of plant body] The plant body of each sample was divided into the above-ground part and the root part, dried, and the weight of each part was measured. The dry weight was measured on a plant-by-plant basis. The measurement results for the above-ground part are shown as "above-ground dry weight (mg / plant)" in Figures 3 and 4, and in Figures 10, 15(A), and 18 described below. The measurement results for the root part are shown as "root dry weight (mg / plant)" in Figures 10 and 18 described below.

[0043] [Measurement of Lithium Amount in Plants and Calculation of Lithium Concentration] For Samples 1, 3, 7, 8, 12, and 15-23, 0.1 g of dried plant aerial parts was added to 10 mL of 50% sulfuric acid, followed by 10 mL of 30% nitric acid. The temperature was raised to 300°C to extract the ions. The lithium content in the extract was then quantitatively analyzed by inductively coupled plasma optical emission spectroscopy (ICP-OES). The amount of lithium contained per plant aerial part was calculated from the measured value, and the percentage of the "aerial dry weight (mg / plant)" was calculated. For Rhodes grass (Samples 1, 3, 7, 8, and 12), measurements were performed on plants whose surfaces had been washed 24 days after sowing. The calculated results are shown as "aerial Li concentration (%)" in Figures 3, 4, and Figure 13 (described below).

[0044] [Optical Microscopy] The cross-sectional tissue of Rhodes grass leaves was observed using an optical microscope. A section 20-30 cm from the base of the sixth leaf of Rhodes grass plants grown in a lithium-free solution 24 days after sowing was sampled, immersed in a surfactant (Triton X-100, 0.5%), and fixed in 5% agarose. Then, slices of 100 μm thick were cut using a microslicer, stained with toluidine blue (0.05%), and tissue observation was performed.

[0045] [SEM Observation] Rhodes grass was observed using a scanning electron microscope (SEM). The sample for observing the shape of the salt glands was prepared using an ionic liquid (ethyl(2-hydroxyethyl)dimethylammonium methanesulfonate; C ７ H １９ NO ４ S) was diluted with ethanol and dropped onto the sample surface, and the sample was observed at an angle of 30° in a low vacuum atmosphere of 50 Pa.

[0046] <Experimental Results> [Structure of Salt Glands] Protruding structures formed by modified epidermal cells are present on the surfaces of above-ground plant parts, such as leaves and stems, and are collectively known as trichomes. Trichomes in the grass family are classified into three types: long trichomes (macrohairs); prickles (prickles with shorter, broader bases and sharper tips); and microhairs (microhairs), tiny, two-celled trichomes with dense cytoplasm. Functionally, trichomes are classified as secretory and non-secretory. Both macrohairs and prickles are non-secretory and are thought to function primarily as physical defenses against herbivory by animals and insects. On the other hand, microhairs are considered secretory because they have been confirmed to secrete small amounts of polysaccharides, proteins, minerals, and other substances in a wide range of plant subfamilies, including rice and maize. Although the role of trichomes in many plant species remains unclear, it has been shown that in some salt-tolerant species of the Polytrichomeae subfamily, they function as salt glands that actively excrete inorganic salts (Jpn. J. Crop Sci., 90, 235-246, 2021).

[0047] Figures 7 and 8 are explanatory diagrams showing images of a cross-section of the sixth leaf of Rhodes grass 24 days after sowing, grown in a culture medium without adding lithium. Figure 7 is an optical microscope image, where Figure 7(A) shows the adaxial salt gland, Figure 7(B) shows the abaxial salt gland, and Figure 7(C) shows an enlarged view of the salt gland. In the figures, arrows indicate the salt gland. Figure 8 is a secondary electron image, where Figure 8(A) shows the abaxial secondary electron image, and Figure 8(B) shows the salt gland. In the figures, arrows indicate the salt gland. The salt glands on the adaxial side of the leaf were located on the small veins (Fig. 7(A)), whereas those on the abaxial side were located between the veins (Fig. 7(B)). This distribution was consistent with the literature (Takao Oi et al., "MORPHOLOGY AND ULTRASTRUCTURE OF THE SALT GLANDS ON THE LEAF SURFACE OF RHODES GRASS (CHLORIS GAYANA KUNTH)", Int. J. Plant Sci., 173, 454-463, 2012). Furthermore, the large hairs were located on the same vein as the salt glands, whereas the sting hairs were located on a different vein (Fig. 8(A)). As shown in Fig. 7(C), the salt glands of Rhodes grass are bicellular, consisting of a basal cell and a cap cell. It is believed that ions transferred from the basal cell are excreted from the tip of the cap cell. In the backscattered electron image of the salt gland shown in FIG. 8(B), excreted salt was confirmed at the tip of the apical cell.

[0048] [Effect of Li Addition on Growth of Rhodes Grass] Figure 9 is an explanatory diagram showing photographs of Rhodes Grass grown hydroponically 24 days after sowing. The LiCl concentrations in the aqueous medium 132 used for hydroponic cultivation are 0 mM (control) in Figure 9(A), 2 mM in Figure 9(B), 4 mM in Figure 9(C), 6 mM in Figure 9(D), 8 mM in Figure 9(E), and 10 mM in Figure 9(F). The images show hydroponic cultivation in a container with an upper diameter of 13 cm.

[0049] 10 is an explanatory diagram showing the relationship between the dry weight per plant of the above-ground parts and roots of Rhodes grass grown by hydroponics 24 days after sowing and the concentration of LiCl added to the aqueous medium 132. As shown in FIG. 10, the addition of 2 mM or less of LiCl did not have a clear effect on the growth of Rhodes grass, whereas when the added LiCl concentration exceeded 2 mM, the growth rate of the above-ground parts and roots decreased almost in proportion to the added amount.

[0050] [Lithium excretion from salt glands] Figure 11 is an explanatory diagram showing an optical photograph of the abaxial side of a leaf after two weeks of hydroponic cultivation in an aqueous medium containing 2 mM LiCl. In the figure, the arrow indicates crystals formed when the excreted solution from the salt gland dried. Figure 12 is an explanatory diagram showing the relationship between the amount of excreted salt and Li excreted over the following week from a single Rhodes grass plant (the above-ground part of which was once washed with pure water to remove salts) grown hydroponically 17 days after sowing and the concentration of added LiCl.

[0051] As shown in Figure 12, when the added LiCl concentration was 0.4 mM or less, the amount of salt discharged did not change significantly with the added LiCl concentration. However, when the added LiCl concentration was 0.4 mM or more, the amount of salt discharged decreased with increasing added LiCl concentration. On the other hand, the amount of discharged Li was highest when the added LiCl concentration was 2 mM and decreased with increasing added LiCl concentration. As described above, it was confirmed that lithium was contained in the discharged salt when Rhodes grass was grown in a Li-containing aqueous solution.

[0052] [Analysis of Li Concentration in Aboveground Shoots and Exhausted Salt] Figure 13 shows the relationship between the lithium concentration in the exhaused salt (exhausted salt Li concentration) and the added LiCl concentration in hydroponically grown Rhodes grass plants 17 days after sowing, after washing the aboveground shoots with pure water. It also shows the relationship between the aboveground Li concentration and the added LiCl concentration 24 days after sowing. As shown in Figure 13, the aboveground Li concentration did not increase significantly with increasing added LiCl concentration. In contrast, the exhaused salt Li concentration tended to increase with increasing added LiCl concentration above 1 mM. For example, at an added LiCl concentration of 2 mM, the exhaused salt Li concentration (0.94%) was approximately 27 times higher than the aboveground Li concentration (0.04%). For example, recovery of rare metals by phytomining requires cutting down and burning the above-ground parts of the plant body. However, recovery of lithium excreted from salt glands of Rhodes grass and other plants may be more efficient if only the excreted salt is periodically collected.

[0053] [Li excretion from Rhodes grass grown in Li-added soil] Figure 14 is an explanatory diagram showing photographs of Rhodes grass grown in petalite-added soil 35 days after sowing. Figure 14(A) shows the results of cultivation in petalite-added soil with a Li concentration of 22 ppm, and Figure 14(B) shows the results of cultivation in petalite-added soil with a Li concentration of 220 ppm. Figure 15 is an explanatory diagram showing the measurement results of the dry weight of the aboveground parts (Figure 15(A)) and the amount of Li excreted (Figure 15(B)) of Rhodes grass grown in petalite-added soil 35 days after sowing.

[0054] 15, it was confirmed that lithium was excreted from the salt glands of Rhodes grass grown in petalite-added soil (Li-added soil) at both petalite addition amounts, i.e., 22 ppm and 220 ppm Li concentrations. This indicates that lithium can be recovered from soil by cultivating Rhodes grass in soil containing lithium and recovering lithium from the salt excreted by the salt glands.

[0055] [Recovery of discharged salt by vacuum method] Figure 16 is an explanatory diagram showing a photograph of a filter attached to a vacuum cleaner when salt was recovered from the surface of Rhodes grass leaves by vacuum method. As shown in Figure 16, recovery of discharged salt was observed, confirming that discharged salt can be recovered by vacuum method.

[0056] [Results of Hydroponic Cultivation of Rice Cultivar Nipponbare] Figure 17 is an explanatory diagram showing the state of Nipponbare grown by hydroponic cultivation 24 days after sowing. The LiCl concentration in the culture solution, which is the aqueous medium 132, is 0 mM (control) in Figure 17(A), 2 mM in Figure 17(B), and 10 mM in Figure 17(C). Here, the state of hydroponic cultivation using a container with an upper diameter of 13 cm is shown.

[0057] Figure 18 is an explanatory diagram showing the relationship between the dry weight of the aboveground shoots and roots per plant of Nipponbare (shown in Figure 17 ), i.e., Nipponbare grown hydroponically 24 days after sowing, and the added LiCl concentration in the culture solution used for hydroponic cultivation. Comparing the results for Nipponbare in Figure 18 with the results for Rhodes grass in Figure 10 , both the aboveground shoot dry weight and the root dry weight were nearly identical for Rhodes grass and Nipponbare when the added LiCl concentration was 0 mM. However, when the added LiCl concentration was 2 mM, Rhodes grass exhibited shoot dry weight and root dry weight nearly identical to those when the added LiCl concentration was 0 mM, whereas Nipponbare exhibited shoot dry weight and root dry weight reduced to approximately half of those when the added LiCl concentration was 0 mM. Thus, it was confirmed that Rhodes grass has higher lithium tolerance than Nipponbare, a fellow grass, when the added LiCl concentration was 2 mM.

[0058] [Results of soil cultivation of ice plant and hijiki] As shown in Figure 4, when the halophytes ice plant and hijiki were cultivated in soil, the addition of LiCl to the soil significantly increased the Li concentration in the aboveground parts, confirming that lithium had accumulated within the plant bodies (comparison between Samples No. 20 and 21, and between Samples No. 22 and 23). In other words, the halophytes ice plant and hijiki are known to accumulate sodium within their bodies and exhibit high sodium tolerance, but it was also confirmed that they can accumulate lithium, which is an alkali metal like sodium, within their bodies. Therefore, it is believed that lithium in the soil used for cultivation can be recovered by extracting lithium from the plant bodies.

[0059] Fig. 19 is a photograph of an ice plant grown in soil, and Fig. 20 is a photograph of a hijiki seaweed grown in soil. Fig. 19(A) and Fig. 20(A) show the results of samples without adding LiCl to the soil (samples No. 20 and 22), while Fig. 19(B) and Fig. 20(B) show the results of samples with 1 mM LiCl solution added to the soil and cultivated for 40 days (samples No. 21 and 23).

[0060] As shown in Figure 19(B), the addition of LiCl to the soil caused most of the leaves of the ice plant to wither and die, and as shown in Figure 20(B), the addition of LiCl to the soil also caused the leaves of the hijiki to turn yellow and show poor growth. Furthermore, as shown in Figure 4, the addition of LiCl to the soil significantly reduced the dry weight of the aboveground parts of both the ice plant and the hijiki, demonstrating growth inhibition (comparison between Samples No. 20 and 21, and between Samples No. 22 and 23). The ice plant and the hijiki are halophytes known to be able to grow in soil containing high concentrations of sodium ions. They are more sodium-tolerant than Rhodes grass, a salt-tolerant plant. However, Rhodes grass tended to have better tolerance to lithium ions.

[0061] The present disclosure is not limited to the above-described embodiments, and can be realized in various configurations without departing from the spirit thereof. For example, the technical features in the embodiments corresponding to the technical features in each aspect described in the Summary of the Invention section can be appropriately replaced or combined to solve some or all of the above-described problems or achieve some or all of the above-described effects. Furthermore, if a technical feature is not described as essential in this specification, it can be appropriately deleted.

[0062] The present disclosure can also be realized in the following forms. [Application Example 1] A lithium recovery method for recovering lithium from a lithium-containing medium, comprising cultivating a halophyte or halotolerant plant using the medium, and recovering lithium concentrated inside the plant body of the halophyte or halotolerant plant or lithium excreted from the plant body. [Application Example 2] The lithium recovery method according to Application Example 1, wherein the plant body has salt glands, and wherein the lithium excreted from the salt glands is recovered. [Application Example 3] The lithium recovery method according to Application Example 2, wherein the lithium excreted from the salt glands to the surface of the plant body is recovered using a suction device. [Application Example 4] The lithium recovery method according to Application Example 2, wherein the lithium excreted from the salt glands to the surface of the plant body is recovered by washing the surface of the plant body with a washing solution. [Application Example 5] The method for recovering lithium according to any one of Application Examples 2 to 4, wherein lithium is recovered from the plant having bicellular salt glands or multicellular salt glands as the salt glands. [Application Example 6] The method for recovering lithium according to any one of Application Examples 1 to 5, wherein Rhodes grass is used as the halophyte or salt-tolerant plant. [Application Example 7] The method for recovering lithium according to any one of Application Examples 1 to 6, wherein soil containing 1 ppm or more and 1000 ppm or less of lithium is used as the medium. [Application Example 8] The method for recovering lithium according to any one of Application Examples 1 to 6, wherein an aqueous solution containing 1 ppm or more and 1000 ppm or less of lithium is used as the medium. Application Example 9 A lithium recovery system for recovering lithium from a medium containing lithium, comprising: a cultivation unit including a halophyte or halotolerant plant and an aqueous medium that is an aqueous solution for cultivation, and for cultivating the halophyte or halotolerant plant using the aqueous medium; and an aqueous medium supply unit that supplies a lithium-containing liquid, from which lithium is to be recovered, to the cultivation unit as the aqueous medium.[Application Example 10] The lithium recovery system according to Application Example 9, wherein the cultivation unit hydroponically cultivates the halophyte or salt-tolerant plant using the aqueous medium. [Application Example 11] The lithium recovery system according to Application Example 9 or 10, wherein the lithium-containing liquid is a lithium-containing waste liquid generated in a lithium production process or a lithium recycling process.

[0063] DESCRIPTION OF SYMBOLS 10... Lithium recovery system 20... Salt-tolerant plants, etc. 22... Lithium-containing salt 30... Cultivation section 32, 132, 232... Aqueous medium 33... Inlet channel 34, 134... Container section 34... Outlet channel 36... Substrate 40... Aqueous medium supply section 120... Rhodes grass 130... Hydroponic cultivation device 136... Sponge 137... Evaporation prevention film 220... Plant 230... Soil cultivation device 234... Container 238... Pot

Claims

1. A method for recovering lithium from a medium containing lithium, comprising cultivating a halophyte or a salt-tolerant plant in the medium, and recovering lithium concentrated inside the plant body of the halophyte or the salt-tolerant plant or lithium excreted from the plant body.

2. A method for recovering lithium according to claim 1, wherein the plant body is provided with salt glands, and lithium excreted from the salt glands is recovered.

3. A method for recovering lithium according to claim 2, wherein the lithium excreted from the salt glands onto the surface of the plant body is recovered using a suction device.

4. A method for recovering lithium according to claim 2, wherein the surface of the plant body is washed with a washing solution to recover lithium excreted from the salt glands onto the surface of the plant body.

5. A method for recovering lithium according to claim 2, wherein lithium is recovered from the plant body having bicellular salt glands or multicellular salt glands as the salt glands.

6. The method for recovering lithium according to claim 5, wherein Rhodes grass is used as the halophyte or salt-tolerant plant.

7. The method for recovering lithium according to claim 1, wherein soil containing 1 ppm or more and 1000 ppm or less of lithium is used as the medium.

8. The method for recovering lithium according to claim 1, wherein an aqueous solution containing 1 ppm or more and 1000 ppm or less of lithium is used as the medium.

9. A lithium recovery system for recovering lithium from a medium containing lithium, comprising: a cultivation unit including a halophyte or halotolerant plant and an aqueous medium that is an aqueous solution for cultivation, and for cultivating the halophyte or halotolerant plant using the aqueous medium; and an aqueous medium supply unit that supplies a lithium-containing liquid, from which lithium is to be recovered, to the cultivation unit as the aqueous medium.

10. The lithium recovery system according to claim 9, wherein the cultivation section hydroponically cultivates the halophyte or salt-tolerant plant using the aqueous medium.

11. The lithium recovery system according to claim 9, wherein the lithium-containing liquid is a lithium-containing waste liquid generated in a lithium production process or a lithium recycling process.

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