Lithium salt extractant, composition, method for recovering lithium salt, and method for producing lithium salt

Abstract

To provide an extractant for selectively extracting lithium salt, a method for recovering lithium salt, and a method for producing lithium salt.SOLUTION: A lithium salt extractant comprises at least one selected from a group consisting of a compound represented by a general formula (1) and a compound represented by the general formula (2) (where X1, X2, X3 and X4 independently represent an oxygen atom, a sulfur atom, a sulfinyl group, a sulfonyl group, a carbonyl group, or an imino group).SELECTED DRAWING: None

Description

[Technical Field]

[0001] One embodiment of the present invention relates to a lithium salt extractant, a composition, a method for recovering lithium salts, and a method for producing lithium salts. [Background technology]

[0002] Electrochemical devices such as nonaqueous electrolyte secondary batteries, typified by lithium ion secondary batteries, and capacitors are widely used in small electronic devices, electric vehicles, hybrid vehicles, stationary power sources, etc., due to their excellent capacity characteristics, output characteristics, and life characteristics. In recent years, the rise of electric vehicles has led to an increasing demand for large lithium ion secondary batteries. Against this background, the consumption of lithium salts, which are raw materials for lithium ion secondary batteries, has been increasing.

[0003] Lithium salts are contained in seawater and salt lake brine, and can be recovered from these. For example, salt lake brine can be evaporated over a period of years in dry land with little rainfall, and sodium carbonate or the like is added to the concentrated brine to precipitate lithium ions as lithium carbonate, thereby recovering the lithium salt. Another example involves increasing the lithium ion concentration of salt lake brine using an ion exchange membrane, and then adding sodium carbonate or the like to the highly concentrated lithium ion aqueous solution to precipitate the lithium ions as lithium carbonate, thereby recovering the lithium salt. Lithium salts can also be recovered by crushing ores such as lepidolite and separating unwanted components with chemicals. Furthermore, because lithium salts are contained in wastewater from production lines for lithium secondary batteries and the like, methods for recovering them from wastewater are also being researched. Lithium salts can also be recovered from used lithium secondary batteries, but because impurities are also contained in them, methods for recovering lithium salts from waste materials are being researched.

[0004] As another example of a method for extracting and recovering lithium salts from brines, etc., chemicals capable of capturing lithium ions are being researched. One technique for recovering ions from solvents is to use anion receptors to capture anions in the solvent. The molecular structure of the anion receptor allows it to selectively capture the target ion species. Non-Patent Documents 1 and 2 disclose an anion receptor having a urea group at the 8,8'-position of a 2,2'-binaphthyl group. This anion receptor is capable of capturing free anions contained in a solvent.

[0005] Furthermore, it is also possible to extract a lithium salt from a solvent by capturing both the lithium ion and its counter ion with an ion receptor. Non-Patent Document 3 discloses the capture of LiCl using a strapped calix[4]pyrrole bearing a triazole as a lithium salt-selective receptor. Non-Patent Document 4 discloses that a heteroditopic macrocycle having halogen bonds and chalcogen bonds recognizes an ion pair of LiCl. [Prior art documents] [Non-patent literature]

[0006] [Non-Patent Document 1] S. Kondo, H. Sonoda, T. Katsu, and M. Unno, Sens. Actuators B, 160, 684-690 (2011). [Non-patent document 2] S. Kondo, M. Nagamine, S. Karasawa, M. Ishihara, M. Unno, and Y. Yano, Tetrahedron, 67, 943-950 (2011). [Non-patent document 3] Kyeong-Im Hong, et al., Chem. Commun., 2020,56, 10541-10544. [Non-patent document 4] Yuen Cheong Tse, et al., Chem. Commun., 2021, 57, 4950-4953. Summary of the Invention [Problem to be solved by the invention]

[0007] The anion receptors disclosed in Non-Patent Documents 1 and 2 have a structure in which the basic 2,2'-binaphthyl group is linked to rigid naphthyl groups via single bonds, resulting in a relatively rigid skeleton, and furthermore, the urea groups introduced at the 8,8'-positions are positioned appropriately, enabling them to capture anions. On the other hand, the anion receptors disclosed in Non-Patent Documents 1 and 2 tend to have low solubility in non-aqueous solvents due to the rigid structure resulting from the 2,2'-binaphthyl group. Non-Patent Documents 3 and 4 disclose receptors that capture LiCl in organic solvents, but the molecular structure of the receptor itself is complex, making it difficult to establish a synthesis procedure.

[0008] One object of the present invention is to provide an extractant that selectively extracts lithium salts. Another object of the present invention is to provide a simple method for extracting, recovering, or producing lithium salts. [Means for solving the problem]

[0009] The present invention provides the following. [1] A lithium salt extractant, which is at least one selected from the group consisting of compounds represented by the following general formula (1) and compounds represented by the following general formula (2): [ka] (In general formula (1), R 1 and R 2are each independently a hydrogen atom, an alkyl group, an aryl group, a heteroaryl group, an alkoxy group, a hydroxy group, or a group represented by —NHR′, R′ is a hydrogen atom, an alkyl group, an aryl group, a heteroaryl group, an alkoxy group, or a hydroxy group, and X 1 and X 2 are each independently an oxygen atom, a sulfur atom, a sulfinyl group, a sulfonyl group, a carbonyl group, or an imino group, n is an integer of 1 to 10, and multiple n's may be the same or different from each other, and in general formula (2), R 3 and R 4 are each independently a hydrogen atom, an alkyl group, an aryl group, a heteroaryl group, an alkoxy group, a hydroxy group, or a group represented by —NHR′, R′ is a hydrogen atom, an alkyl group, an aryl group, a heteroaryl group, an alkoxy group, or a hydroxy group, and X 3 and X 4 are each independently an oxygen atom, a sulfur atom, a sulfinyl group, a sulfonyl group, a carbonyl group, or an imino group, and m is an integer of 1 to 10.

[0010] [2] The lithium salt extractant according to [1], which is at least one selected from the group consisting of compounds represented by the following general formula (3) and compounds represented by the following general formula (4): [ka] (In the general formula (3), R 5 and R 6 are each independently a hydrogen atom, an alkyl group, an aryl group, a heteroaryl group, an alkoxy group, or a hydroxy group. In general formula (4), R 7 and R 8 are each independently a hydrogen atom, an alkyl group, an aryl group, a heteroaryl group, an alkoxy group, or a hydroxy group.

[0011] [3] In the general formula (3), R 5 and R 6are each independently an n-butyl group, a tert-butyl group, or a phenyl group, and in the general formula (4), R 7 and R 8 are each independently an n-butyl group, a tert-butyl group, or a phenyl group. [4] A composition comprising the lithium salt extractant according to any one of [1] to [3] and a non-aqueous solvent. [5] A method for recovering lithium salts using the lithium salt extractant according to any one of [1] to [3].

[0012] [6] A method for producing a lithium salt, comprising: a step of preparing a lithium salt-containing material; a step of preparing a mixture containing the lithium salt-containing material, the lithium salt extractant according to any one of [1] to [3], and a non-aqueous solvent; a step of subjecting the mixture to solid-liquid separation to obtain a separated liquid; and a step of contacting the separated liquid with water to obtain an aqueous lithium salt solution. [7] The method for producing a lithium salt according to [6], wherein the step of obtaining the lithium salt aqueous solution includes a step of mixing the separated liquid with water to precipitate and remove the lithium salt extractant. [8] The method for producing a lithium salt according to [6], wherein the step of obtaining the aqueous lithium salt solution comprises a step of separating the separated liquid into an aqueous phase and an oil phase by solvent extraction, and obtaining the aqueous lithium salt solution from the aqueous phase.

[0013] [9] The method for producing a lithium salt according to any one of [6] to [8], further comprising a step of recovering the lithium salt extractant after the step of obtaining the lithium salt aqueous solution.

[10] The method for producing a lithium salt according to any one of [6] to [9], comprising the step of supplying a carbonate source to the aqueous lithium salt solution to obtain lithium carbonate.

[11] The method for producing a lithium salt according to any one of [6] to

[10] , wherein the lithium salt-containing material is prepared by removing water from at least one selected from the group consisting of seawater and salt lake brine. [Effects of the Invention]

[0014] According to one embodiment of the present invention, an extractant that selectively extracts lithium salts can be provided, and a simple method for extracting, recovering, or producing lithium salts can be provided. DETAILED DESCRIPTION OF THE INVENTION

[0015] An embodiment of the present invention will be described below, but the present invention is not limited to the following examples.

[0016] "Lithium salt extractant" The lithium salt extractant according to one embodiment is characterized in that it is at least one selected from the group consisting of compounds represented by the following general formula (1) and compounds represented by the following general formula (2):

[0017] [ka]

[0018] (In general formula (1), R 1 and R 2 are each independently a hydrogen atom, an alkyl group, an aryl group, a heteroaryl group, an alkoxy group, a hydroxy group, or a group represented by —NHR′, R′ is a hydrogen atom, an alkyl group, an aryl group, a heteroaryl group, an alkoxy group, or a hydroxy group, and X 1 and X 2 are each independently an oxygen atom, a sulfur atom, a sulfinyl group, a sulfonyl group, a carbonyl group, or an imino group, n is an integer of 1 to 10, and multiple n's may be the same or different from each other, and in general formula (2), R 3 and R 4 are each independently a hydrogen atom, an alkyl group, an aryl group, a heteroaryl group, an alkoxy group, a hydroxy group, or a group represented by —NHR′, R′ is a hydrogen atom, an alkyl group, an aryl group, a heteroaryl group, an alkoxy group, or a hydroxy group, and X 3 and X 4are each independently an oxygen atom, a sulfur atom, a sulfinyl group, a sulfonyl group, a carbonyl group, or an imino group, and m is an integer of 1 to 10.

[0019] Hereinafter, the compound represented by general formula (1) and the compound represented by general formula (2) are also collectively referred to as a lithium salt extractant.

[0020] This lithium salt extractant can capture lithium salts in non-aqueous solvents and can be used to extract lithium salts from non-aqueous solvents. In particular, this lithium salt extractant is excellent at selectively capturing chloride ions liberated in non-aqueous solvents, and can be extracted in the form of lithium chloride (LiCl) by capturing chloride ions together with their counter ions, lithium ions.

[0021] Anion receptors with urea groups at the 8,8'-positions of a 2,2'-binaphthyl group have a rigid structure due to the 2,2'-binaphthyl group and have excellent anion-capturing ability due to the urea groups at both ends. This compound is shown in general formula (10) below.

[0022] [ka] (In general formula (10), R is an n-butyl group, a tert-butyl group, or a phenyl group.)

[0023] In contrast to the compound represented by general formula (10), the compound represented by general formula (1) has a structure in which the binaphthalene skeleton is replaced with a skeleton having an aliphatic chain and a heteroatom, and is thought to exhibit high solubility in non-aqueous solvents due to its flexible structure. The compound represented by general formula (2) has a structure in which the binaphthalene skeleton is replaced with an aliphatic chain, a heteroatom, and an aromatic chain, and is thought to exhibit high solubility in non-aqueous solvents due to its flexible structure. In the compound represented by general formula (1) and the compound represented by general formula (2), the amide bonds at both ends are expected to associate with anions, particularly chloride ions. Furthermore, in general formulas (1) and (2), R 1 ~R 4 are imino groups, and the introduction of urea groups at both ends is expected to further enhance the ability to associate with anions. On the other hand, due to their flexible structure, the ability to associate with anions tends to decrease. Considering their high solubility in organic solvents, adding these compounds to organic solvents at high concentrations makes it possible to efficiently capture anions from organic solvents. Furthermore, because they can be added to non-aqueous solvents at high concentrations, it is possible to reduce the amount of non-aqueous solvent used in extraction processes.

[0024] The compound represented by general formula (1) contains X 1 and X 2 The introduction of a heteroatom at the X position strengthens the interaction with the cation. 1 and X 2 It is believed that the introduction of an aliphatic chain of an appropriate length relative to the ionic radius of the lithium ion between the two molecules makes it possible to selectively capture lithium ions. In this way, a lithium ion and its counter ion, an anion, are captured within a single molecule, allowing it to function as an extractant for lithium salts. The compound represented by general formula (2) also exhibits a similar effect.

[0025] In general formula (1), R 1 and R 2are each independently a hydrogen atom, an alkyl group, an aryl group, a heteroaryl group, an alkoxy group, a hydroxy group, or a group represented by -NHR', and R' may be a hydrogen atom, an alkyl group, an aryl group, a heteroaryl group, an alkoxy group, or a hydroxy group. 1 and R 2 may be the same or different from each other.

[0026] R 1 and R 2 The alkyl group introduced as the alkyl group may be a linear or branched alkyl group, and may be chain-like or alicyclic. The alkyl group preferably has 1 to 20 carbon atoms, more preferably 1 to 8 carbon atoms, and even more preferably 1 to 4 carbon atoms. Examples of the alkyl group include chain-like alkyl groups such as methyl, ethyl, propyl, isopropyl, n-butyl, tert-butyl, sec-butyl, isobutyl, pentyl, hexyl, heptyl, octyl, isooctyl, 2-ethylhexyl, decyl, and dodecyl; and alicyclic alkyl groups such as cyclopentyl, cyclohexyl, and cycloheptyl, or groups in which at least one hydrogen atom of these groups is substituted with an alkyl group. Among these, chain-like alkyl groups are preferred, and alkyl groups having 1 to 4 carbon atoms are more preferred, with n-butyl and tert-butyl being even more preferred.

[0027] R 1 and R 2The aryl group introduced as the above preferably has 6 to 24 carbon atoms, more preferably 6 to 12 carbon atoms, and even more preferably 6 to 8 carbon atoms. This aryl group may be monocyclic, polycyclic, or fused, and may be a group having 1 to 4 aromatic rings or a group having 2 to 4 fused aromatic rings, preferably a group having one benzene ring. Examples of this aryl group include a phenyl group, a naphthyl group, an anthracenyl group, a phenanthrenyl group, a tetracenyl group, a biphenyl group, a terphenyl group, and a fluorenyl group. Among these, a phenyl group is preferred. These aryl groups may have at least one hydrogen atom substituted with an alkyl group, such as a phenyl group substituted with an alkyl group having 1 to 4 carbon atoms, specifically, a p-tolyl group, an m-tolyl group, and an o-tolyl group.

[0028] R 1 and R 2 The heteroaryl group introduced as the formula (I) is a group having carbon atoms and heteroatoms on the ring, and examples of the heteroatoms include a nitrogen atom, an oxygen atom, a sulfur atom, a silicon atom, a boron atom, and a phosphorus atom. The total number of carbon atoms and heteroatoms in this heteroaryl group is preferably 5 to 24, more preferably 6 to 12, and even more preferably 6 to 8. Examples of this heteroaryl group include groups having a 6-membered heteroaromatic ring such as pyridine or pyrazine, groups having a condensed heteroaromatic ring such as quinoline, isoquinoline, acridine or phenanthroline, and groups having a 5-membered heteroaromatic ring such as furan, pyrrole, or thiophene.

[0029] R 1 and R 2The alkyl group portion of the alkoxy group introduced as (I) may be a linear or branched alkyl group, and may be linear or alicyclic. This alkoxy group preferably has 1 to 20 carbon atoms, more preferably 1 to 8 carbon atoms, and even more preferably 1 to 4 carbon atoms. This alkoxy group is represented, for example, as -O-R', where R' represents an alkyl group, and specific examples are as described above for the alkyl group. More preferred examples of the alkoxy group having 1 to 4 carbon atoms include a methoxy group, an ethoxy group, a propoxy group, an isopropoxy group, an n-butoxy group, a tert-butoxy group, a sec-butoxy group, and an isobutoxy group.

[0030] R 1 and R 2 In the group represented by -NHR' introduced as 1 and R 2 Examples of the functional groups include those described above.

[0031] Preferably, R 1 and R 2 are each independently a hydrogen atom, an alkyl group having 1 to 20 carbon atoms, an aryl group having 6 to 24 carbon atoms, a heteroaryl group having 5 to 24 carbon atoms, an alkoxy group having 1 to 20 carbon atoms, a hydroxy group, or a group represented by -NHR'. Here, R' is preferably a hydrogen atom, an alkyl group having 1 to 20 carbon atoms, an aryl group having 6 to 24 carbon atoms, a heteroaryl group having 5 to 24 carbon atoms, an alkoxy group having 1 to 20 carbon atoms, or a hydroxy group. More preferably, R 1 and R 2are each independently a hydrogen atom, an alkyl group having 1 to 8 carbon atoms, an aryl group having 6 to 12 carbon atoms, a heteroaryl group having 6 to 12 carbon atoms, an alkoxy group having 1 to 8 carbon atoms, a hydroxy group, or a group represented by -NHR', and are preferably an alkyl group having 1 to 8 carbon atoms, a heteroaryl group having 6 to 12 carbon atoms, or a group represented by -NHR'. Here, R' is preferably a hydrogen atom, an alkyl group having 1 to 8 carbon atoms, an aryl group having 6 to 12 carbon atoms, a heteroaryl group having 6 to 12 carbon atoms, an alkoxy group having 1 to 8 carbon atoms, or a hydroxy group, and more preferably an alkyl group having 1 to 8 carbon atoms or a heteroaryl group having 6 to 12 carbon atoms. In a preferred example, R 1 and R 2 are each independently an alkyl group having 1 to 4 carbon atoms, an aryl group having 6 to 8 carbon atoms, or a group represented by -NHR' (wherein R' is an alkyl group having 1 to 4 carbon atoms or an aryl group having 6 to 8 carbon atoms), and are more preferably an n-butyl group, a tert-butyl group, a phenyl group, or a group represented by -NHR (wherein R' is an n-butyl group, a tert-butyl group, or a phenyl group). In a more preferred example, R 1 and R 2 At least one of R is a tert-butyl group or —NHR′ (where R′ is an n-butyl group), and more preferably R 1 and R 2 are both tert-butyl groups, or -NHR' (where R' is an n-butyl group).

[0032] In general formula (1), X 1 and X 2 may each independently be an oxygen atom (-O-), a sulfur atom (-S-), a sulfinyl group (-SO-), a sulfonyl group (-SO2-), a carbonyl group (-CO-), or an imino group (-NR-). In the imino group (-NR-), R may be a hydrogen atom or an alkyl group, preferably an alkyl group. The alkyl group of this imino group preferably has 1 to 10 carbon atoms, more preferably 1 to 6 carbon atoms, and even more preferably 1 to 4 carbon atoms. Preferably, X1 and X 2 are each independently an oxygen atom, a sulfur atom, a carbonyl group, or an imino group, more preferably an oxygen atom or a sulfur atom, and even more preferably an oxygen atom. 1 and X 2 are identical to each other, and preferably X 1 and X 2 are both oxygen atoms or sulfur atoms, and more preferably oxygen atoms.

[0033] In general formula (1), n ​​is preferably an integer of 1 to 10, more preferably 1 to 5, even more preferably 1 to 3, and most preferably 1 or 2.

[0034] An example of the compound represented by general formula (1) is R 1 and R 2 is a group represented by -NHR', and X 1 and X 2 is an oxygen atom and n=1. Specifically, it is a compound represented by the following general formula (3). In general formula (3), 5 and R 6 are each independently a hydrogen atom, an alkyl group, an aryl group, a heteroaryl group, an alkoxy group, or a hydroxy group. For details of each functional group, see the above R 1 and R 2 Examples of such problems include those described above.

[0035] [ka]

[0036] In general formula (3), R 5 and R 6 are each independently preferably an alkyl group, and the number of carbon atoms in the alkyl group is preferably 1 to 20, more preferably 1 to 10, even more preferably 1 to 8, and still more preferably 1 to 4. Specifically, R 5 and R 6are each independently preferably an n-butyl group, a tert-butyl group, or a phenyl group, and more preferably a tert-butyl group.

[0037] In general formula (2), R 3 and R 4 may each independently represent a hydrogen atom, an alkyl group, an aryl group, a heteroaryl group, an alkoxy group, a hydroxy group, or an -NHR' group. These functional groups are the same as those in R of the general formula (1) above. 1 and R 2 The details are as explained above in relation to general formula (1). X 3 and X 4 may each independently be an oxygen atom (-O-), a sulfur atom (-S-), a sulfinyl group (-SO-), a sulfonyl group (-SO2-), a carbonyl group (-CO-), or an imino group (-NR-). These functional groups are the same as those of X in the general formula (1) above. 1 and X 2 The details are as explained above in relation to general formula (1). m may be an integer of 1 to 10. m may be in the same range as n in the general formula (1) above, and the details are as explained in the general formula (1) above.

[0038] An example of the compound represented by general formula (2) is R 3 and R 4 is a group represented by -NHR', and X 3 and X 4 is an oxygen atom and m=1. Specifically, it is a compound represented by the following general formula (4). In general formula (4), 7 and R 8 are each independently a hydrogen atom, an alkyl group, an aryl group, a heteroaryl group, an alkoxy group, or a hydroxy group. For details of each functional group, see R in the general formula (1) above. 1 and R 2 Examples of such problems include those described above.

[0039] [ka]

[0040] In general formula (4), R 7 and R 8 are each independently preferably an alkyl group, and the number of carbon atoms in the alkyl group is preferably 1 to 20, more preferably 1 to 10, even more preferably 1 to 8, and still more preferably 1 to 4. Specifically, R 7 and R 8 are each independently preferably an n-butyl group, a tert-butyl group, or a phenyl group, and more preferably a tert-butyl group.

[0041] Specific compounds are listed below: In the structural formulas below, n-Bu represents an n-butyl group, t-Bu represents a tert-butyl group, and Ph represents a phenyl group.

[0042] [ka]

[0043] [ka]

[0044] Among the above compounds, from the viewpoint of good solubility in non-aqueous solvents due to the bis-ethoxyethyl structure, Compound 1a, Compound 1b, Compound 1c, Compound 1d, Compound 1e, and Compound 1f are preferred, Compound 1a, Compound 1b, and Compound 1c are more preferred, Compound 1a and Compound 1b are even more preferred, and Compound 1b is still more preferred. The above compounds may be provided alone or as a mixture.

[0045] "Method for synthesizing compounds" A method for synthesizing a compound represented by general formula (1) or a compound represented by general formula (2) will be described below. Note that the compound of one embodiment is not limited to a compound synthesized by the following synthesis method. The compound represented by general formula (1) or a compound represented by general formula (2) has a relatively simple molecular structure, and therefore the synthesis procedure is simple, and the compound can be synthesized in a one-step reaction from commonly used raw material compounds.

[0046] As examples of methods for synthesizing a compound represented by general formula (1) and a compound represented by general formula (2), methods for synthesizing a compound in which n=1 in general formula (1) and a compound in which m=1 in general formula (2) will be described. The method for synthesizing the compound represented by general formula (1) (n=1) and the compound represented by general formula (2) (m=1) can include introducing an isocyanic acid derivative, an carboxylic acid halide, or the like into a compound represented by the following general formula (5) and a compound represented by the following general formula (6), respectively. In general formulas (5) and (6), X 1 ~X 4 is as explained in the above general formula (1) and general formula (2).

[0047] [ka]

[0048] More specifically, an example of a method for synthesizing a compound represented by general formula (3) can include introducing an isocyanic acid derivative into the amino groups at both ends of 1,2-bis(2-aminoethoxy)ethane. An example of a method for synthesizing a compound represented by general formula (4) can include introducing an isocyanic acid derivative into the amino groups at both ends of 1,2-bis(2-aminophenoxy)ethane.

[0049] The isocyanic acid derivative is a compound represented by R"NCO. R" is R in general formula (3) or general formula (4). 5 ~R 8The details are as described above. Specific examples of the isocyanic acid derivative include alkyl isocyanates and aryl isocyanates. Examples of alkyl isocyanates include methyl isocyanate, ethyl isocyanate, propyl isocyanate, isopropyl isocyanate, n-butyl isocyanate, sec-butyl isocyanate, tert-butyl isocyanate, isobutyl isocyanate, pentyl isocyanate, hexyl isocyanate, and cyclohexyl isocyanate. Examples of aryl isocyanates include phenyl isocyanate.

[0050] This reaction can be carried out in various solvents, and examples of usable solvents include ketone solvents such as acetone, methyl ethyl ketone, and methyl isobutyl ketone; alcohol solvents such as methanol, ethanol, isopropanol, ethylene glycol, and diethylene glycol; ether solvents such as diethyl ether, diethylene glycol dimethyl ether, and tetrahydrofuran; amide solvents such as N,N-dimethylformamide and N,N-dimethylacetamide; ester solvents such as ethyl acetate and γ-butyrolactone; and water. Furthermore, the solvent may be a non-aqueous solvent used in the composition described below. After the reaction, the solvent and the like can be removed from the reaction mixture as needed, and the product can be obtained by filtration and drying. Alternatively, the product may be isolated by chromatography for further purification.

[0051] An example of a method for synthesizing 1,2-bis(2-aminophenoxy)ethane will be described. This synthesis method includes synthesizing 1,2-bis(2-nitrophenoxy)ethane using 2-nitrophenol as a starting material and amminating both terminal nitro groups of the 1,2-bis(2-nitrophenoxy)ethane. Specifically, 1,2-bis(2-nitrophenoxy)ethane can be obtained by reacting 2-nitrophenol with 1,2-dihalogenethyl. The reaction is preferably carried out in an organic solvent such as dimethylformamide (DMF), and a base such as KCO may be used. 1,2-bis(2-nitrophenoxy)ethane can be synthesized according to standard methods, and commercially available products may also be used. The nitro groups at both ends of 1,2-bis(2-nitrophenoxy)ethane can be aminated by a conventional method, but catalytic reduction is preferred. Specifically, the nitro groups can be reduced to amino groups by reducing 1,2-bis(2-nitrophenoxy)ethane with a catalyst such as palladium / carbon (Pd / C) under a reducing atmosphere such as hydrogen gas.

[0052] 1,2-bis(2-aminoethoxy)ethane can be synthesized according to a conventional method, and for example, a commercially available product may be used.

[0053] "composition" According to one embodiment, a composition including a lithium salt extractant and a non-aqueous solvent may be provided. The lithium salt extractant may be the lithium salt extractant according to one embodiment. This composition can be used for extracting a lithium salt. For example, by mixing this composition with a lithium salt-containing material containing a lithium salt, the lithium salt extractant can selectively capture the lithium salt from the lithium salt-containing material and dissolve the lithium salt in a non-aqueous solvent.

[0054] As the lithium salt to be extracted, various lithium salts can be used regardless of their solubility in non-aqueous solvents. Examples of lithium salts include lithium halides such as lithium chloride (LiCl), LiF, LiBr, and LiI, as well as Li2SO3, LiOH, Li2SO4, Li2CO3, Li3PO4, LiNO3, LiClO4, and LiRCOO (wherein R is an alkyl group having 1 to 4 carbon atoms, a phenyl group, or a naphthyl group). These salts are poorly soluble in non-aqueous solvents, but their solubility in non-aqueous solvents can be increased by using them in combination with the lithium salt extractant described above. Examples of lithium salts include LiPF6, LiBF4, LiFSI (lithium bisfluorosulfonylimide), LiTFSI (lithium bistrifluoromethanesulfonylimide), LiClO4, LiB(C6H5)4, LiCH3SO3, LiCF3SO3, LiN(SO2F)2, LiN(SO2CF3)2, LiN(SO2CF2CF3)2, etc. These salts exhibit some degree of solubility in non-aqueous solvents, but by using them in combination with the above-mentioned lithium salt extractant, the solubility in non-aqueous solvents can be further increased. The above lithium salts may be used alone or in combination of two or more.

[0055] The non-aqueous solvent is not particularly limited and various non-aqueous solvents can be used, and it is preferable that the non-aqueous solvent is capable of dissolving the lithium salt extractant. Examples of the non-aqueous solvent include cyclic carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate, and vinylene carbonate; chain carbonates such as dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, methyl propyl carbonate, butyl methyl carbonate, ethyl propyl carbonate, butyl ethyl carbonate, and dipropyl carbonate; cyclic carboxylic acid esters such as γ-butyrolactone; compounds having a nitrile group such as acetonitrile; chain ethers such as 1,2-dimethoxyethane and dimethoxymethane; tetrahydrofuran, 1,3 ether compounds such as cyclic ethers such as 1,4-dioxolane, 1,4-dioxane, 1,3-dioxane, and 2-methyltetrahydrofuran; chain carboxylic acid esters such as methyl acetate, ethyl acetate, methyl propionate, and ethyl propionate; compounds having a sulfonyl group such as sulfolane, propane sultone, 3-methylsulfolane, and 2,4-dimethylsulfolane; phosphate esters such as trimethyl phosphate and triethyl phosphate; methylene chloride, cyclopentanone, cyclohexylbenzene, 3-methyl-1,3-oxazolidin-2-one, and dimethyl sulfoxide. The non-aqueous solvent may be a compound having a substituent such as a fluorine atom or a chlorine atom, or may be a compound in which the above-mentioned non-aqueous solvent is substituted with a fluorine atom or a chlorine atom, such as a cyclic carbonate, a chain carbonate, an ether compound, or a chain carboxylic acid ester having one or more fluorine atoms or chlorine atoms, and specific examples thereof include fluoroethylene carbonate and chloroethylene carbonate.

[0056] The above-mentioned non-aqueous solvents may be used alone or in combination of two or more. When two or more non-aqueous solvents are used, the non-aqueous solvents become a mixture, and the solubility of the lithium salt tends to be increased. In addition, when two or more non-aqueous solvents are used, crystallization is less likely to proceed at low temperatures, and the composition can be suitably used for applications where the composition needs to be kept in a liquid state at low temperatures. When two or more non-aqueous solvents are used in combination, it is recommended to use a combination that forms a single phase in the composition.

[0057] The composition may be a non-aqueous composition, for example, a composition in which the water content is limited to 1% by mass or less, 0.5% by mass or less, or 0.1% by mass or less relative to the total amount of the composition, and may be substantially water-free. If the composition contains water, when extracting a water-soluble lithium salt, the lithium salt is less likely to be captured by the lithium salt extractant, and the amount dissolved in the non-aqueous solvent decreases, resulting in a problem of reduced recovery efficiency.

[0058] In one embodiment of the composition, the molar ratio of the lithium salt extractant to the non-aqueous solvent is preferably 0.1 or more, more preferably 0.5 or more, and even more preferably 1 or more. In one embodiment of the composition, the molar ratio of the lithium salt extractant to the non-aqueous solvent is preferably 200 or less, more preferably 100 or less, even more preferably 50 or less, and may be 30 or less, or 10 or less.

[0059] The compound represented by general formula (1) and the compound represented by general formula (2) each have a structure capable of capturing one lithium ion and counter ion per molecule. Therefore, lithium salts can be recovered within a range of one lithium ion per molecule of the compound represented by general formula (1) and the compound represented by general formula (2). The amount of lithium salt extractant used can be determined depending on the expected amount of lithium salt recovered.

[0060] The composition according to one embodiment may be a composition that is liquid at 30° C., and more preferably a composition that is liquid at 25° C. The composition according to one embodiment may be one that loses fluidity at lower temperatures and becomes gel-like or solid-like.

[0061] The composition of one embodiment can be used, for example, in a method for recovering lithium salts from lithium salt-containing materials and for producing lithium salts. In another example, the composition of an embodiment can be used in a method for recovering lithium salts from lithium salt-containing materials. In yet another example, the composition of an embodiment can be used in a method for adsorbing lithium salts from a lithium salt-containing material. In yet another example, the composition of an embodiment can be used in a method for adsorbing and removing lithium salts from a lithium salt-containing material. In yet another example, the composition of an embodiment can be used in a method for purifying lithium salts from a lithium salt-containing material. In yet another example, the composition of an embodiment can be used in a method for purifying lithium salts from a lithium salt-containing material to produce a highly concentrated lithium salt composition.

[0062] "Method of manufacturing lithium salts" According to one embodiment, there is provided a method for producing a lithium salt, the method including the steps of: preparing a lithium salt-containing material; preparing a mixture containing the lithium salt-containing material, a lithium salt extractant, and a non-aqueous solvent; performing solid-liquid separation of the mixture to obtain a separated liquid; and contacting the separated liquid with water to obtain an aqueous lithium salt solution. The lithium salt extractant according to one embodiment can be used as the lithium salt extractant.

[0063] The lithium salt-containing material is not particularly limited as long as it contains a lithium salt. The lithium salt-containing material is preferably a solid, and is preferably in a powder, crushed, particulate, or other form from the viewpoint of efficiency of dissolution or dispersion. The lithium salt-containing material is preferably water-free, and may be, for example, one in which the water content is limited to 1% by mass or less, 0.5% by mass or less, or 0.1% by mass or less relative to the total amount of the lithium salt-containing material, or one that is substantially water-free. If the lithium salt-containing material contains water, when extracting a water-soluble lithium salt, the lithium salt is difficult to capture by the lithium salt extractant, and the amount that dissolves in the non-aqueous solvent is reduced, resulting in a problem of reduced recovery efficiency. The lithium salt-containing material may be prepared in a dissolved or dispersed state in a non-aqueous solvent, and then mixed in this state with the lithium salt extractant and the non-aqueous solvent. The non-aqueous solvent used here may be any of the non-aqueous solvents described above for the non-aqueous solvent contained in the composition.

[0064] The lithium salt contained in the lithium salt-containing material may be the same as that described above for the lithium salt contained in the composition, and may be contained alone or in combination of two or more. It is preferable that the lithium salt contains a water-soluble lithium salt. The lithium salt-containing material may be a single component of lithium salt, may contain impurities in the single component of lithium salt, or may contain other components together with the lithium salt. The other components are not particularly limited, but include alkali metal salts, alkaline earth metal salts, transition metal salts, etc. Specific examples include sodium chloride, potassium chloride, magnesium chloride, calcium chloride, etc. These may be contained alone or in combination of two or more. In particular, methods for selectively recovering lithium salts from water-soluble alkali metal salts and alkaline earth metal salts in an aqueous medium are limited. Furthermore, alkali metal salts and alkaline earth metal salts that are poorly soluble in non-aqueous solvents are difficult to separate when the lithium salt is insoluble in the non-aqueous solvent. The lithium salt extractant according to one embodiment can capture the lithium salt and dissolve it in a non-aqueous solvent, making it possible to selectively recover the lithium salt from these salts.

[0065] Specifically, the lithium salt-containing material may be seawater or salt lake brine from which water has been removed; lithium salt-containing waste liquid or the like from which water and organic solvents have been removed; or material prepared by crushing rock salt. Water can be removed from seawater or salt lake brine by sun drying, boiling with heat, or the like. Furthermore, water can be removed from seawater or salt lake brine by heating after the lithium ion concentration has been increased by ion exchange membrane electrodialysis. Seawater and brines contain sodium ions, as well as magnesium ions, calcium ions, potassium ions, lithium ions, and other ions, which mainly form counterions with chloride ions. Because these chloride salts are water-soluble, it is difficult to selectively separate lithium salts from aqueous solutions. Furthermore, these chloride salts exhibit a tendency to be insoluble in non-aqueous solvents similar to lithium salts. However, by adding a lithium salt extractant to a non-aqueous solvent together with the lithium salt, the lithium salt is specifically captured by the lithium salt extractant and becomes soluble in the non-aqueous solvent, allowing other chloride salts to be removed by solid-liquid separation.

[0066] The content of the lithium salt contained in the lithium salt-containing material is not particularly limited, and the lithium salt can be recovered whether it is a small amount or a large amount. For example, the lithium salt content is preferably 0.1 to 100 mass %, more preferably 40 to 100 mass %, of the total amount of the lithium salt-containing material.

[0067] Next, a process for preparing a mixture containing a lithium salt-containing material, a lithium salt extractant, and a non-aqueous solvent will be described. The method for mixing these components is not particularly limited. These components may be added to a container all at once or in portions and mixed using a stirrer or the like. Alternatively, a composition containing a lithium salt extractant and a non-aqueous solvent may be prepared in advance, and the lithium salt-containing material may be added to this composition all at once or in portions and mixed. Heating the mixture can enhance reactivity. Heating is preferably performed at 30 to 100°C, more preferably at 50 to 100°C, and even more preferably at 80 to 100°C. The heating time may be appropriately determined depending on the scale of the reaction system, the heating temperature, the type and shape of the materials, etc., and may be, for example, 10 minutes to 5 hours, or 1 to 2 hours. Heating may be performed continuously or intermittently from the preparation of the mixture to the solid-liquid separation of the mixture. Since it is preferable that the lithium salt is sufficiently dissolved in the non-aqueous solvent during solid-liquid separation of the mixture, it is preferable to increase the temperature of the mixture during solid-liquid separation to enhance the solubility of the lithium salt.

[0068] In the mixture, the lithium salt extractant has a molar concentration of preferably 0.01 to 5 M, more preferably 0.5 to 1.0 M. In the mixture, the lithium salt-containing material varies depending on the expected amount of lithium salt contained therein, but is, for example, preferably 0.1 to 100 mass % of the total amount of the mixture, more preferably 40 to 100 mass %.

[0069] Next, the step of subjecting the mixture to solid-liquid separation to obtain a separated liquid will be described. The solid-liquid separation can be carried out by, for example, filtration, centrifugation, sedimentation, etc. In the filtration, filter paper, filter cloth, membrane filter, etc. can be used. When the lithium salt-containing material contains components other than the lithium salt and these components are not dissolved in the non-aqueous solvent, these components can be removed by solid-liquid separation. Since the solubility of the lithium salt in the non-aqueous solvent is promoted under heated conditions in the presence of the lithium salt extractant, the mixture may be heated during the separation step to maintain the solubility. The temperature at which the mixture is heated during the separation step is, for example, preferably 30 to 100°C, more preferably 50 to 100°C, and even more preferably 80 to 100°C.

[0070] Next, the step of contacting the separated liquid with water to obtain an aqueous lithium salt solution will be described. The separated liquid obtained after solid-liquid separation of the mixture contains a non-aqueous solvent, a lithium salt extractant that is soluble in the non-aqueous solvent, and a lithium salt that is captured by the lithium salt extractant and is soluble in the non-aqueous solvent. When this separated liquid is contacted with water, the lithium salt is released from the lithium salt extractant and extracted into the aqueous phase, thereby obtaining an aqueous lithium salt solution. Since components insoluble in the non-aqueous solvent are removed in the separation step, the resulting aqueous lithium salt solution is free from salts that are water-soluble but insoluble in the non-aqueous solvent, such as sodium chloride and potassium chloride. The lithium salt can be recovered by removing water from the lithium salt aqueous solution by evaporation under reduced pressure, etc. Alternatively, as will be described later, lithium ions contained in the lithium salt aqueous solution may be carbonated to precipitate lithium carbonate, which may then be recovered. Since the lithium salt extractant is water-insoluble, it is either dissolved in the non-aqueous solvent or, if the amount of water is large, precipitates as a precipitate and is not extracted into the aqueous phase. Therefore, after contacting the separation liquid with water and separating the aqueous phase, the lithium salt extractant can be recovered. This recovered lithium salt extractant can also be reused.

[0071] An example of the step of obtaining the lithium salt aqueous solution can include a step of mixing the separated liquid with water to precipitate and remove the lithium salt extractant. By mixing the separation liquid with water, the water-insoluble lithium salt extractant precipitates, and the water-soluble lithium salt dissolves in water and is contained in the supernatant. In this method, it is preferable to prepare a large amount of water relative to the separation liquid. For example, the volume of water is preferably 0.5 times or more, 5 times or more, or 10 times or more by volume relative to the separation liquid. On the other hand, from the viewpoint of preventing a decrease in the lithium salt concentration in the supernatant, the volume of water is preferably 100 times or less, 50 times or less, or 20 times or less by volume relative to the separation liquid. Depending on the type of nonaqueous solvent, the nonaqueous solvent is miscible with or separates from water. When the nonaqueous solvent is not miscible with water, the supernatant can be separated and recovered from the nonaqueous solvent, for example, due to the difference in specific gravity between the nonaqueous solvent and water. When the nonaqueous solvent is miscible with water, the nonaqueous solvent can be removed from the supernatant using, for example, an oil-water separator. Depending on the type of nonaqueous solvent, if the lithium salt can be recovered from the lithium salt aqueous solution even if the lithium salt aqueous solution contains a nonaqueous solvent, it is not necessary to remove the nonaqueous solvent from the supernatant. In this method, the lithium salt extractant can be recovered as a precipitate and can be reused after recovery.

[0072] Another example of the step of obtaining the lithium salt aqueous solution may include a step of separating the separated liquid into an aqueous phase and an oil phase by solvent extraction, and obtaining the aqueous phase as the lithium salt aqueous solution. When the non-aqueous solvent of the separation liquid is not miscible with water, water can be added to the separation liquid to separate it into an aqueous phase and an oil phase containing the non-aqueous solvent. The aqueous phase contains a water-soluble lithium salt, and the non-aqueous solvent contains a water-insoluble lithium salt extractant. This aqueous phase can be provided as an aqueous lithium salt solution. When the non-aqueous solvent of the separation liquid is miscible with water, water and a solvent that is not miscible with water but is miscible with the non-aqueous solvent can be added to the separation liquid to separate it into an aqueous phase and an oil phase. The aqueous phase contains a water-soluble lithium salt, and the non-aqueous solvent contains a non-aqueous solvent and a water-insoluble lithium salt extractant. The solvent that is not miscible with water but is miscible with the non-aqueous solvent may be appropriately selected depending on the type of non-aqueous solvent, and examples thereof include chloroform, toluene, and ethyl acetate. In this method, the lithium salt extractant is recovered as an oil phase, and therefore, the post-added separation solvent contained in the oil phase can be removed to recover a composition containing the lithium salt extractant and the non-aqueous solvent, which can be reused after recovery.

[0073] Next, the step of obtaining lithium carbonate by supplying a carbonate source to an aqueous lithium salt solution will be described. In one embodiment, the lithium salt aqueous solution can be provided as it is, or can be provided by supplying a carbonate source to the lithium salt aqueous solution to carbonate lithium ions, precipitating lithium carbonate, and recovering it as a solid. Carbonation can be achieved by adding sodium carbonate, potassium carbonate, or the like as a carbonate source to the lithium salt aqueous solution, or by supplying carbon dioxide gas to the lithium salt aqueous solution. [Example]

[0074] The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples.

[0075] "Test Example A" (Method for synthesizing compound 1b) The following compound 1b was synthesized. [ka]

[0076] (Synthesis method) A solution of 500 mg of 1,2-bis(2-aminoethoxy)ethane (obtained from Tokyo Chemical Industry Co., Ltd.) and 735 mg of tert-butyl isocyanate in 6 mL of tetrahydrofuran was refluxed under an argon atmosphere for 18 hours. The solution was cooled, and the resulting colorless solid was filtered by suction to obtain compound 1b (804 mg, 69%) represented by (1b) above. Mp 151-156°C. 1 H NMR (500 MHz, CDCl3) δ 5.46 (s, 2H), 5.15 (s, 2H), 3.75 (s, 4H), 3.56 (t,4H, J = 4.6 Hz), 3.31 (q, 4H, J = 4.6 Hz), 1.33 (s, 18H). 13 C NMR (126 MHz, CDCl3) δ158.2, 70.8, 70.2, 50.1, 40.0, 29.5.

[0077] (Method for recovering lithium salts) To a 9.0 mL vial, 0.5 M MeCN (acetonitrile), 1 M compound 1b, and the chloride salt in the ratio shown below were added. The mixture was then heated and stirred at 90°C for 1.5 hours. After stirring, the mixture was filtered through a cotton plug while maintaining the temperature to remove solids and obtain a filtrate. The filtrate was subjected to solvent extraction using a solvent containing chloroform (CHCl3):water (HO) = 20 mL:20 mL. The aqueous phase was removed and dried under reduced pressure by evaporation to obtain a colorless solid powder. Compound 1b was recovered in the CHCl3 oil phase.

[0078] The retention time (RT) of the obtained solid powder was evaluated using ion chromatography (IC). The amount of recovered LiCl was measured by calculating the concentration based on a separately prepared calibration curve using the area of ​​the peak corresponding to lithium ions in the chromatogram. The amount of recovered LiCl was then calculated from the concentration and the total volume. The recovery rate of LiCl was calculated from the amount of LiCl contained in the sample before extraction and the amount recovered. These results are shown in Table 1.

[0079] Ion chromatography measurement conditions Column: "PCT-301S" manufactured by DKK Toa Corporation Eluent: 1 mM tartaric acid Flow rate: 1.0mL / min Constant temperature bath temperature: 37℃ Injection volume: 5.0μL

[0080] The following compositions are expressed as molar ratios. (Example A1) Compound 1b:LiCl:NaCl=1:1:0 (Example A2) Compound 1b:LiCl:NaCl=1:0:1 (Example A3) Compound 1b:LiCl:NaCl=1:1:1 (Example A4) Compound 1b:LiCl:NaCl=1:1:10 (Example A5) Compound 1b:LiCl:NaCl=1:1:100 (Example A6) Compound 1b:LiCl:KCl =1:0:1 (Example A7) Compound 1b:LiCl:KCl =1:1:1 (Example A8) Compound 1b:LiCl:KCl =1:1:10

[0081] [Table 1]

[0082] From the above results, in Example A1, the recovery rate of LiCl from a sample containing only LiCl was 61.6%, and LiCl was efficiently recovered. In Examples A3 to A5, LiCl was efficiently recovered from a sample containing LiCl and NaCl at a recovery rate of 42.4% or more. In Examples A7 and A8, LiCl was efficiently recovered from a sample containing LiCl and KCl at a recovery rate of 58.8% or more. It can be seen that NaCl and KCl were not captured by Compound 1b, were not dissolved in MeCN, and were separated and removed as solids by cotton plug filtration.

[0083] "Test Example B" (Synthesis of Compound 1e) The following compound 1e was synthesized. [ka]

[0084] (Synthesis method) Under an argon atmosphere, tert-butyl isocyanate (0.65 mL, 5.51 mmol, 2.0 eq) was added in small portions via syringe to a solution of 1,2-bis(2-aminothio)ethane (499 mg, 2.77 mmol) in THF (10 mL) at room temperature. The reaction mixture was stirred at room temperature for 3 hours, cooled, and evaporated under reduced pressure. The residue was recrystallized from THF to give the product as a colorless solid. Yield: 470 mg, 45%. Melting point: 161.0-162.1 °C. 1H NMR (500 MHz, CDCl3) δ 5.13 (t, 2H, J = 5.5 Hz), 4.73 (s, 2H), 3.35 (dt, 2H, J1= 6.6, J2= 5.5 Hz), 3.78 (s, 4H), 2.69 (t, 4H, J = 6.6 Hz), 1.33 (s, 18). 13 C NMR (126 MHz, CDCl3) δ 157.6, 50.3, 40.0, 32.6, 32.1, 29.6.

[0085] When compound 1e, MeCN, and LiCl were mixed in a molar ratio of 1:6.4:1 and heated at 95°C, the mixture turned into a transparent solution in about 10 minutes. This indicates that compound 1e can capture and extract LiCl when heated.

[0086] (Synthesis of Compound 5b) The following compound 5b was synthesized. [ka]

[0087] (Synthesis method) Under an argon atmosphere, 1.8 mL (2.2 eq.) of tert-butylisocyanate was added to a THF solution (5.0 mL) of 1,8-octanediamine (997 mg, 6.91 mmol) at room temperature, and the mixture was refluxed for 1 hour. After cooling, ethyl acetate was added and the product was recrystallized to obtain the target compound as a white solid (2.327 g, 98%). Melting point: 200.4-201.4°C. 1 H NMR (500 MHz, CDCl3) δ 4.51 (bs, 4H), 3.10 (q, 4H, J= 6.9 Hz), 1.45 (quint, 4H, J = 6.9 Hz), 1.33 (s, 18H), 1.31 (m, 8H). 13 C NMR (126 MHz, CDCl3) δ 157.8, 50.3, 40.2, 29.9, 29.6, 28.7, 26.4.

[0088] Compound 5b, MeCN, and LiCl were mixed in a molar ratio of 1:6.4:1 and heated at 95°C for 1 hour, resulting in a solid-like mixture that did not liquefy. Compound 5b, MeCN, and LiCl were mixed in a molar ratio of 1:19.2:1 and heated at 95°C for 1 hour, resulting in a liquid but becoming cloudy and not dissolving. Compound 5b, MeCN, and LiCl were mixed in a molar ratio of 1:38.4:1 and heated at 95°C for 1 hour, resulting in no dissolution. This indicates that compound 5b does not have the ability to extract LiCl.

[0089] "Test Example C" Compound 1b was prepared in the same manner as in Test Example A above.

[0090] (Method for recovering lithium salts) To a 9.0 mL vial, 0.5 M MeCN, 1 M compound 1b, and the chloride salt in the ratio shown below were added. The mixture was then heated and stirred at 90°C for 1.5 hours. After stirring, the mixture was filtered through a cotton plug while maintaining the temperature to remove solids and obtain a filtrate. A 10-fold volume of water (HO) was added to the filtrate, and the filtrate was filtered with suction to obtain a filtrate. The filtrate was then dried under reduced pressure to obtain a colorless solid powder. Compound 1b precipitated upon the addition of water and was collected as a solid by suction filtration. The obtained solid powder was evaluated using ion chromatography (IC). The measurement conditions for ion chromatography were the same as those in Test Example A. The recovered amount and recovery rate of LiCl were determined using the same procedures as in Production Example A. The results are shown in Table 2.

[0091] (Example C1) Compound 1b:LiCl:NaCl=1:1:0 (Example C2) Compound 1b:LiCl:NaCl=1:1:50

[0092] [Table 2]

[0093] From the above results, the reprecipitation method in Example C1 achieved a 74% recovery rate of LiCl from a sample containing only LiCl, enabling efficient recovery of LiCl. In Example C2, LiCl was recovered at a 37% recovery rate from a sample containing LiCl and NaCl at a molar ratio of 1:50. The reason for the slightly lower recovery rate is thought to be that the mixture, which contains a large amount of NaCl relative to MeCN and LiCl, is mostly in a solid state, and the recovery rate was reduced during the procedure of extracting the liquid from this state using cotton plug filtration.

[0094] "Test Example D" Compound 1b was prepared in the same manner as in Test Example A above.

[0095] (Method for recovering lithium salts) To a 9.0 mL vial, 0.5 M MeCN, 1 M compound 1b, and the chloride salt in the proportions shown in Table 1 were added. The mixture was then heated and stirred at 90 °C for 1.5 h. After stirring, the mixture was filtered through a cotton plug while maintaining the temperature to remove solids and obtain a filtrate. The filtrate was subjected to solvent extraction using a solvent containing chloroform (CHCl3):water (HO) = 20 mL:20 mL (volume ratio). The aqueous phase was removed and dried under reduced pressure by evaporation to obtain a colorless solid powder. This solid powder was evaluated using ion chromatography (IC). Compound 1b was recovered in the CHCl3 oil phase. The obtained solid powder was evaluated using ion chromatography (IC) under the following measurement conditions. The amount and rate of recovered LiCl were determined using the same procedures as in Production Example A. The results are shown in Table 3. The amount of recovered MgCl was measured by calculating the concentration based on a separately prepared calibration curve using the area of ​​the peak corresponding to magnesium ions in the chromatogram. The amount of recovered LiCl was then calculated from the concentration and the total volume. The recovery rate of MgCl2 was calculated from the amount of MgCl2 contained in the sample before extraction and the amount recovered.

[0096] The following compositions are expressed as molar ratios. (Example D1) Compound 1b:LiCl:CaCl2:MgCl2=1:0:1:0 (Example D2) Compound 1b:LiCl:CaCl2:MgCl2=1:1:1:0 (Example D3) Compound 1b:LiCl:CaCl2:MgCl2=1:0:0:1 (Example D4) Compound 1b:LiCl:CaCl2:MgCl2=1:1:0:1 (Example D5) Compound 1b:LiCl:CaCl2:MgCl2=1:1:0:5

[0097] Ion chromatography measurement conditions Column: "PCT-301S" manufactured by DKK Toa Corporation Eluent: 5 mM tartaric acid and 1 mM dipicolinic acid Flow rate: 1.5mL / min Constant temperature bath temperature: 37℃ Injection volume: 5.0μl

[0098] [Table 3]

[0099] From the above results, in Example D2, LiCl was successfully separated and recovered from CaCl2. In Examples D4 and D5, LiCl was successfully separated and recovered from MgCl2. Since the tetrahedral ionic radius of Mg ions is close to that of Li ions, in Example D5, when the MgCl2 content was increased to 5M, some of the MgCl2 formed a complex with Compound 1b, resulting in the recovery of LiCl and MgCl2. On the other hand, when the MgCl2 content was 1M, this effect was small, and no MgCl2 was contained in the recovered product.

[0100] "Test Example E" Compound 1b was prepared using the same procedure as in Test Example A above. A mixture (solid) containing LiCl was prepared to replicate the ion concentration of the brine of a salt lake shown in Table 4. Sample 1 was a mixture of various chloride salts. Sample 2 was a mixture of various chloride salts, with the salts hydrated and evaporated in advance. A translucent gel was observed in Sample 2 when it was filtered through a cotton plug.

[0101] [Table 4]

[0102] (Method for recovering lithium salts) To a solution of 1.04 g of compound 1b in 1.0 mL of MeCN, 131 mg of a mixture containing LiCl was added and heated and stirred. The resulting mixture was filtered to separate the solids, yielding a filtrate. The resulting filtrate was added to five times the volume of water and filtered. K2CO3 was added to the aqueous phase for carbonate treatment, followed by filtration to obtain a colorless solid powder. After the first filtration, the MeCN phase contained compound 1b and LiCl trapped in it, and KCl and NaCl were removed as insoluble solids in the MeCN phase. After the second filtration, the water-insoluble compound 1b was removed as a solid by adding a large amount of water, yielding an aqueous lithium chloride solution. After the third filtration, Li2CO3 precipitated as a water-insoluble solid by carbonation, yielding 15 mg of Li2CO3 as a Li source.

[0103] The retention time (RT) of the obtained solid powder was evaluated using ion chromatography (IC). The recovered amount and recovery rate of LiCl were determined using the same procedures as in Production Example A. The recovered amount and recovery rate of MgCl were determined using the same procedures as in Production Example D. These results are shown in Table 5.

[0104] Ion chromatography measurement conditions Column: "PCT-301S" manufactured by DKK Toa Corporation Eluent: 5 mM tartaric acid and 1 mM dipicolinic acid Flow rate: 1.5mL / min Constant temperature bath temperature: 37℃ Injection volume: 5.0μL

[0105] [Table 5]

[0106] From the above results, it was possible to recover LiCl at a recovery rate of 60 mass% or more even under conditions that reproduced the brine of a salt lake. In Example E2, the recovery rate of MgCl2 was reduced by hydrating and evaporating the chloride salt in advance, which increased the selectivity for LiCl.

Claims

1. A lithium salt extractant which is at least one selected from the group consisting of compounds represented by the following general formula (1) and compounds represented by the following general formula (2): 【Chemical 1】 (In general formula (1), R １ and R ２ are each independently a hydrogen atom, an alkyl group, an aryl group, a heteroaryl group, an alkoxy group, a hydroxy group, or a group represented by —NHR′, where R′ is a hydrogen atom, an alkyl group, an aryl group, a heteroaryl group, an alkoxy group, or a hydroxy group, and X １ and X ２ are each independently an oxygen atom, a sulfur atom, a sulfinyl group, a sulfonyl group, a carbonyl group, or an imino group, n is an integer of 1 to 10, and multiple n's may be the same or different, In general formula (2), R ３ and R ４ are each independently a hydrogen atom, an alkyl group, an aryl group, a heteroaryl group, an alkoxy group, a hydroxy group, or a group represented by —NHR′, where R′ is a hydrogen atom, an alkyl group, an aryl group, a heteroaryl group, an alkoxy group, or a hydroxy group, and X ３ and X ４ are each independently an oxygen atom, a sulfur atom, a sulfinyl group, a sulfonyl group, a carbonyl group, or an imino group, and m is an integer of 1 to 10.

2. The lithium salt extractant according to claim 1, which is at least one selected from the group consisting of compounds represented by the following general formula (3) and compounds represented by the following general formula (4): 【Chemistry 2】 (In general formula (3), R ５ and R ６ are each independently a hydrogen atom, an alkyl group, an aryl group, a heteroaryl group, an alkoxy group, or a hydroxy group. ７ and R ８ are each independently a hydrogen atom, an alkyl group, an aryl group, a heteroaryl group, an alkoxy group, or a hydroxy group.

3. In the general formula (3), R ５ and R ６ are each independently an n-butyl group, a tert-butyl group, or a phenyl group, and in the general formula (4), R ７ and R ８ and each independently represent an n-butyl group, a tert-butyl group, or a phenyl group.

4. A composition comprising the lithium salt extractant of any one of claims 1 to 3 and a non-aqueous solvent.

5. A method for recovering lithium salts, which uses the lithium salt extractant according to any one of claims 1 to 3.

6. providing a lithium salt-containing material; preparing a mixture containing the lithium salt-containing material, the lithium salt extractant according to any one of claims 1 to 3, and a non-aqueous solvent; A step of subjecting the mixture to solid-liquid separation to obtain a separated liquid; and a step of contacting the separated liquid with water to obtain an aqueous lithium salt solution.

7. 7. The method for producing a lithium salt according to claim 6, wherein the step of obtaining the lithium salt aqueous solution includes a step of mixing the separated liquid with water to precipitate and remove the lithium salt extractant.

8. 7. The method for producing a lithium salt according to claim 6, wherein the step of obtaining the aqueous lithium salt solution comprises a step of separating the separated liquid into an aqueous phase and an oil phase by solvent extraction, and obtaining the aqueous lithium salt solution from the aqueous solution.

9. The method for producing a lithium salt according to claim 6 , further comprising the step of recovering the lithium salt extractant after the step of obtaining the lithium salt aqueous solution.

10. The method for producing a lithium salt according to claim 6 , further comprising the step of supplying a carbonate source to the aqueous lithium salt solution to obtain lithium carbonate.

11. The method for producing a lithium salt according to any one of claims 6 to 10, wherein the lithium salt-containing material is prepared by removing water from at least one selected from the group consisting of seawater and salt lake brine.

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