Lithium sulfide production method and lithium recovery method

Abstract

Provided are a lithium sulfide production method and a lithium recovery method which have high production efficiency and with which lithium resources can be effectively used, said methods comprising a first contact treatment for bringing a lithium-containing liquid and a lithium extraction agent-containing liquid into contact, and a second contact treatment for bringing a lithium extract liquid obtained by means of the first contact treatment and a gas comprising hydrogen sulfide into contact.

Description

Method for producing lithium sulfide and method for recovering lithium

[0001] The present invention relates to a method for producing lithium sulfide and a method for recovering lithium.

[0002] With the recent rapid spread of information-related devices and communication devices such as personal computers, video cameras, and mobile phones, the development of batteries to be used as their power sources has become increasingly important. Among these batteries, lithium-ion batteries have attracted attention due to their high energy density. Currently available lithium-ion batteries use electrolytes containing flammable organic solvents, necessitating the installation of safety devices to suppress temperature rise during short circuits and improvements in structure and materials to prevent short circuits. In particular, for automotive applications, higher capacity and higher output are required, raising safety concerns regarding batteries using conventional electrolytes. In contrast, all-solid-state lithium batteries, which replace the electrolyte with a solid electrolyte and achieve a fully solid-state design, do not use flammable organic solvents within the battery, thereby simplifying safety devices and improving manufacturing costs and productivity. Furthermore, sulfide solid electrolytes are known as solid electrolytes for use in such all-solid-state lithium batteries.

[0003] Lithium sulfide is used as a raw material for sulfide solid electrolytes. Known methods for producing this lithium sulfide include, for example, a method using lithium hydroxide in which lithium hydroxide is reacted with hydrogen sulfide in a nonpolar organic solvent such as toluene (see, for example, Patent Document 1), and a method in which lithium is reacted with hydrogen sulfide without using a solvent (see, for example, Patent Document 2). Furthermore, a lithium ion battery recycling method has been proposed for recovering lithium from discarded lithium ion batteries, including roasting the lithium ion batteries at 500°C or less and under reduced pressure of 10 Pa or less, purifying the roasted powder, and treating the roasted powder with deionized water or a pH-adjusted acid to obtain a leachate by selectively leaching the lithium battery material portion of the roasted powder (see, for example, Patent Document 3).

[0004] JP 2010-163356 A JP 9-278423 A JP 2014-055312 A

[0005] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a method for producing lithium sulfide and a method for recovering lithium, which have high production efficiency and enable effective utilization of lithium resources.

[0006] The method for producing lithium sulfide according to the present invention is a method for producing lithium sulfide, comprising: a first contact treatment of bringing a lithium-containing solution into contact with a lithium extractant-containing solution; and a second contact treatment of bringing the lithium extract obtained by the first contact treatment into contact with a gas containing hydrogen sulfide.

[0007] Furthermore, the method for recovering lithium according to the present invention is a method for recovering lithium, comprising: a first contact treatment of contacting a lithium-containing solution with a lithium extractant-containing solution; and a second contact treatment of contacting the lithium extract obtained by the contact with a gas containing hydrogen sulfide.

[0008] According to the present invention, it is possible to provide a method for producing lithium sulfide and a method for recovering lithium, which have high production efficiency and enable effective utilization of lithium resources.

[0009] Hereinafter, an embodiment of the present invention (hereinafter, sometimes referred to as "the present embodiment") will be described. In this specification, the upper and lower limit values ​​of a range expressed by "greater than or equal to," "less than or equal to," and "to" can be arbitrarily combined, and the numerical values ​​in the examples can also be used as the upper and lower limit values.

[0010] (Findings Obtained by the Inventor to Achieve the Present Invention) As described above, as attention is growing on lithium-ion batteries, the demand for solid electrolytes used therein is also increasing, and a stable supply of lithium sulfide, which is a raw material for the solid electrolytes, is desired. Therefore, a wider range of lithium sources is being sought and studies are being conducted to ensure a more stable supply of lithium.

[0011] However, the methods described in Patent Documents 1 and 2 use lithium hydroxide as a raw material, and no consideration is given to other raw materials. The method described in Patent Document 3 is a method for recovering lithium from lithium ion batteries, and meets the demand for a wider range of lithium sources. However, although the method described in Patent Document 3 describes recovering lithium as lithium carbonate, no consideration is given to recovering lithium as lithium sulfide.

[0012] As mentioned above, lithium hydroxide is usually used as a raw material for lithium sulfide, and therefore, it is conceivable to prepare lithium hydroxide by crystallizing the extracted lithium into an aqueous solution, and then use the obtained lithium hydroxide as a raw material to prepare lithium sulfide. Alternatively, as in the method described in Patent Document 3, it is conceivable to prepare lithium carbonate, react the lithium carbonate with calcium hydroxide to obtain lithium hydroxide, and use this as a raw material for lithium sulfide. However, both methods involve many steps, and therefore there is room for improvement in terms of production efficiency.

[0013] The method described in Patent Document 3 above describes preparing lithium carbonate by blowing carbon dioxide into a leachate obtained by selectively leaching lithium by reacting deionized water or an acid with an adjusted pH with roasted powder of a lithium ion battery (Patent Document 3, Claim 1, Example 1, Description, Paragraph

[0018] , etc.). Patent Document 3 also describes supplying a crystallization stripping solution (aqueous solution) containing carbonate, bicarbonate, carbonate ions, etc., to obtain lithium carbonate in order to back-extract lithium ions from an oil phase containing an organic solvent such as kerosene and lithium ions into an aqueous phase (Patent Document 3, Claims 1 and 8, Example 5, Description, Paragraph

[0036] , etc.). Thus, the method described in Patent Document 3 is intended to recover lithium ions contained in the aqueous phase.

[0014] In response to this, the present inventors came up with the idea of ​​directly preparing lithium sulfide from a lithium-containing liquid extracted using a leached lithium extractant-containing liquid. When a gas containing hydrogen sulfide was supplied to the lithium-containing liquid, a reaction between lithium and hydrogen sulfide proceeded, making it possible to produce lithium sulfide. The lithium-containing liquid extracted using a lithium extractant-containing liquid is an oil phase, and directly recovering lithium contained in the oil phase and further converting it into lithium sulfide is not described in the above Patent Documents 1 and 2, nor Patent Document 3, and has not been considered at all.

[0015] According to the lithium sulfide production method of this embodiment, lithium sulfide can be produced through two contact treatments: a first contact treatment in which a lithium-containing liquid is contacted with a lithium extractant-containing liquid, and a second contact treatment in which a lithium extractant-containing liquid is contacted with a gas containing hydrogen sulfide. This allows lithium sulfide to be produced with high production efficiency. Furthermore, the lithium-containing liquid is not particularly limited as long as it contains lithium. For example, it is possible to use a liquid obtained by dissolving a lithium-containing material (e.g., a solid electrolyte) contained in waste materials such as processing components for lithium-ion batteries in an alkaline aqueous solution, or a liquid obtained by dissolving the lithium-containing material in an acidic aqueous solution containing various acids, such as inorganic and organic acids. This allows for a wider range of lithium sources and a more stable supply of lithium. Thus, the lithium sulfide production method and lithium recovery method of this embodiment can be methods that have high production efficiency and enable effective utilization of lithium resources.

[0016] (Regarding Various Forms of the Present Embodiment) A method for producing lithium sulfide according to a first form of the present embodiment is a method for producing lithium sulfide, comprising: a first contact treatment of bringing a lithium-containing liquid into contact with a lithium extractant-containing liquid; and a second contact treatment of bringing the lithium extract obtained by the first contact treatment into contact with a gas containing hydrogen sulfide.

[0017] According to the method for producing lithium sulfide of this embodiment, lithium sulfide can be produced by a very simple method in which a lithium extract solution obtained by contacting a lithium-containing solution with a lithium extractant-containing solution is brought into contact with a gas containing hydrogen sulfide. Furthermore, the lithium-containing solution is not particularly limited as long as it contains lithium, and therefore, for example, a solution derived from waste materials such as processing materials for lithium-ion batteries can be used. This makes it possible to search for a wider range of lithium sources and ensure a more stable supply of lithium, thereby enabling the effective use of lithium resources.

[0018] A second aspect of the present embodiment is the method for producing lithium sulfide of the first aspect, wherein the lithium extractant-containing liquid contains a lithium extractant and a hydrocarbon oil.

[0019] The lithium extractant-containing liquid may contain only the lithium extractant or may contain a hydrocarbon oil. Considering the need for more uniform and smooth contact in the first contact treatment, it is preferable to contain a hydrocarbon oil. Whether the lithium extractant-containing liquid is a liquid containing only the lithium extractant or a liquid containing both the lithium extractant and a hydrocarbon oil, lithium is present in the oil phase. Therefore, the second contact treatment involves contacting the lithium extractant, which forms the oil phase, with a gas containing hydrogen sulfide.

[0020] A method for producing lithium sulfide according to a third aspect of the present embodiment is the method for producing lithium sulfide according to the second aspect, further comprising separating lithium sulfide from the lithium sulfide-containing oil composition obtained by the second contact treatment.

[0021] By separating it in this way, lithium sulfide can be used as a product.

[0022] A fourth aspect of the present embodiment is a method for producing lithium sulfide according to any one of the first to third aspects, wherein the second contact treatment is carried out while blowing the gas containing hydrogen sulfide into a lithium extract.

[0023] There are no particular limitations on the method for contacting the lithium extract with the gas containing hydrogen sulfide in the second contact treatment. However, by performing the second contact treatment while blowing in the gas containing hydrogen sulfide, the lithium extract and the gas containing hydrogen sulfide can be brought into more uniform and efficient contact with each other, thereby improving production efficiency.

[0024] A fifth aspect of the present embodiment is a method for producing lithium sulfide according to any one of the first to fourth aspects, wherein the gas containing hydrogen sulfide is a gas containing hydrogen sulfide and an inert gas.

[0025] By using a gas containing hydrogen sulfide and an inert gas as the gas containing hydrogen sulfide, the second contact treatment can be carried out more uniformly and efficiently, thereby improving production efficiency.

[0026] A lithium recovery method according to a sixth aspect of the present embodiment is any one of the first to fifth aspects, wherein the second contact treatment is carried out while irradiating with ultraviolet light.

[0027] In the second contact treatment, contacting the lithium extract with a gas containing hydrogen sulfide while irradiating with ultraviolet light improves the separation efficiency when separating lithium sulfide from the fluid obtained by the second contact treatment, preferably a lithium sulfide-containing oil composition containing lithium sulfide and a hydrocarbon oil, etc., and therefore improves the effect of performing the second contact treatment, i.e., the efficiency of producing lithium sulfide.

[0028] A lithium recovery method according to a seventh aspect of the present embodiment is a lithium recovery method, comprising: a first contact treatment of contacting a lithium-containing solution with a lithium extractant-containing solution; and a second contact treatment of contacting the lithium extract obtained by the contact with a gas containing hydrogen sulfide.

[0029] As explained in the method for producing lithium sulfide according to the first embodiment, lithium sulfide can be produced from lithium contained in a lithium-containing solution by the extremely simple methods of the first contact treatment and the second contact treatment. That is, by the extremely simple methods of these two contact treatments, lithium contained in a lithium-containing solution can be recovered as lithium sulfide. Furthermore, the lithium-containing solution is not particularly limited as long as it contains lithium; for example, a solution derived from waste materials such as processing materials for lithium-ion batteries can be used. Therefore, it is possible to search for a wider range of lithium sources and ensure lithium more stably, thereby enabling the effective use of lithium resources.

[0030] [Method for Producing Lithium Sulfide] Hereinafter, a method for producing lithium sulfide according to the present embodiment will be described. The method for producing lithium sulfide according to the present embodiment is a method for producing lithium sulfide, comprising: a first contact treatment in which a lithium-containing liquid is brought into contact with a lithium extractant-containing liquid; and a second contact treatment in which the lithium extract obtained by the first contact treatment is brought into contact with a gas containing hydrogen sulfide.

[0031] (Lithium-Containing Liquid) The lithium-containing liquid used in the production method of this embodiment is not particularly limited as long as it contains lithium. In consideration of seeking a wider range of lithium sources, ensuring lithium more stably, and making effective use of lithium resources, examples of the lithium-containing liquid include concentrated water obtained by concentrating seawater, salt lake brine, mining wastewater, geothermal water, or a combination of these by means of evaporation or the like.

[0032] Examples of the lithium-containing liquid include lithium-containing liquids obtained from processing components of lithium secondary batteries. For example, lithium-containing liquids obtained by extraction from processing components of lithium secondary batteries containing a sulfide solid electrolyte or the like can be used. Representative examples of such lithium-containing liquids include aqueous solutions of sulfide solid electrolytes obtained by dissolving lithium-containing substances, such as sulfide solid electrolytes used in lithium secondary batteries, in an alkaline aqueous solution. Other examples include aqueous solutions of sulfide solid electrolytes obtained by dissolving them in an acidic aqueous solution containing various acids, such as inorganic acids and organic acids.

[0033] Here, preferred examples of the alkaline aqueous solution include aqueous solutions containing alkaline components such as sodium hydroxide, lithium hydroxide, potassium hydroxide, tetramethylammonium hydroxide, tetraethylammonium hydroxide, and calcium hydroxide. These alkaline components may be used alone or in combination of two or more. In consideration of the ease of dissolving the sulfide solid electrolyte, sodium hydroxide, potassium hydroxide, and calcium hydroxide are more preferred as the alkaline component. Furthermore, examples of the acidic aqueous solution include aqueous solutions containing various acids such as inorganic acids such as hydrochloric acid and sulfuric acid, and organic acids such as formic acid and acetic acid. These various acids may be used alone or in combination of two or more.

[0034] (Lithium Extractant-Containing Liquid: Extractant) The lithium extractant contained in the lithium extractant-containing liquid can be any compound capable of extracting lithium, without particular limitation. Representative examples of lithium extractants include phosphoric acid extractants such as tri-n-butyl phosphate, mono-2-ethylhexyl 2-ethylhexyl phosphonate, and di(2-ethylhexyl)phosphonic acid; oxime extractants such as 2-hydroxy-5-nonylacetophenone oxime, 5-dodecyl salicylaldoxime, and 5-nonyl salicylaldoxime; carboxylic acid extractants such as neodecanoic acid and naphthenic acid; ketone extractants such as methyl isobutyl ketone and dodecylphenyl-methyl-diketone; and amine extractants such as ethylenediaminetetraacetic acid. In the method for producing lithium sulfide of this embodiment, the lithium extractant is not limited to these examples, and any extractant capable of extracting lithium can be used. As the lithium extractant, one extractant can be used alone, or two or more extractants can be used in combination.

[0035] In the production method of this embodiment, the lithium extractant-containing liquid may contain only the lithium extractant, or may contain the lithium extractant and a diluent such as hydrocarbon oil. As described above, in order to ensure more uniform and smooth contact in the first contact treatment, it is preferable that the lithium extractant-containing liquid contain a diluent, and for example, it is preferable that the lithium extractant-containing liquid contain hydrocarbon oil as a diluent.

[0036] The hydrocarbon oil may be appropriately selected from solvent naphtha, kerosene, paraffinic solvents such as normal paraffin and isoparaffin, naphthenic solvents, aromatic solvents, petroleum ether, and the like.

[0037] When the lithium extractant-containing solution contains a lithium extractant and a diluent, the content of the lithium extractant may be 5% by mass or more and less than 100% by mass, preferably 10% by mass or more and 50% by mass or less, and more preferably 15% by mass or more and 40% by mass or less, based on the total amount of the extractant-containing solution. The same applies when the lithium extractant and organic solvent are contained.

[0038] The lithium extractant-containing liquid may also contain a modifier. As will be described later, the fluid obtained by the first contact treatment may have an oil phase and an aqueous phase. In this case, the use of a modifier can suppress the formation of a third phase caused by partial dissolution of the oil phase and the aqueous phase. This makes it possible to more efficiently extract a larger amount of lithium into the lithium extractant, thereby improving the production efficiency of lithium sulfide.

[0039] Preferred examples of the modifier include aliphatic alcohols such as hexanol, heptanol, octanol, nonanol, decanol, undecanol, and dodecanol. Other preferred examples include organic solvents such as hexane, octane, decane, dodecane, undecane, tridecane, decalin, cyclohexane, and decene. The carbon number of the aliphatic alcohol and organic solvent used as the modifier is preferably 6 or more, more preferably 8 or more, with the upper limit being preferably 16 or less, more preferably 14 or less, even more preferably 12 or less, and still more preferably 10 or less. The aliphatic alcohol may be linear or branched, with linear being preferred.

[0040] When the lithium extractant-containing liquid contains a lithium extractant, a diluent, and a modifier, the content of the lithium extractant based on the total amount of the lithium extractant-containing liquid is preferably 3% by mass or more, more preferably 5% by mass or more, and even more preferably 10% by mass or more, with an upper limit of preferably 40% by mass or less, more preferably 35% by mass or less, and even more preferably 30% by mass or less. The content of the diluent based on the total amount of the lithium extractant-containing liquid is preferably 50% by mass or more, more preferably 55% by mass or more, and even more preferably 60% by mass or more, with an upper limit of preferably 90% by mass or less, more preferably 85% by mass or less, and even more preferably 80% by mass or less. Furthermore, the content of the modifier based on the total amount of the lithium extractant-containing liquid is preferably 1% by mass or more, more preferably 5% by mass or more, and even more preferably 7.5% by mass or more, with an upper limit of preferably 20% by mass or less, more preferably 15% by mass or less, and even more preferably 12.5% ​​by mass or less.

[0041] (First Contact Treatment) The method of the first contact treatment for contacting the lithium-containing liquid with the lithium extractant-containing liquid is not particularly limited as long as it can contact the lithium-containing liquid with the lithium extractant-containing liquid. For example, a method of mixing the lithium-containing liquid and the lithium extractant-containing liquid in a reaction vessel equipped with a stirring blade may be used. In this case, for example, a method of dropping one of the lithium-containing liquid and the lithium extractant-containing liquid into the other while stirring the reaction vessel with a stirring blade may be used. Also, for example, a device equipped with a multistage extraction mixer settler and a Cottrell pump may be used.

[0042] Since the lithium extract obtained in the first contact treatment has an oil phase containing lithium, when the fluid obtained in the first contact treatment has an oil phase and an aqueous phase, it is preferable to separate the oil phase from the aqueous phase. The method for separating the oil phase from the aqueous phase is not limited as long as it can separate the oil phase from the aqueous phase, and may be, for example, centrifugal separation, decantation, or the like, or a method using a mixer settler or the like.

[0043] (Second Contact Treatment) The second contact treatment is a treatment in which the lithium extract obtained by the first contact treatment is brought into contact with a gas containing hydrogen sulfide. The method of the second contact treatment is not particularly limited as long as it can bring the lithium extract into contact with the gas containing hydrogen sulfide, and it is preferable to perform the second contact treatment while blowing in the gas containing hydrogen sulfide. In this case, the gas containing hydrogen sulfide is preferably supplied while bubbling, and is preferably supplied into the lithium extract as fine bubbles (for example, so-called microbubbles having a particle size of 1 μm to 100 μm, or so-called nanobubbles having a particle size of less than 1 μm). This allows for more uniform and efficient contact between the lithium extract and the gas containing hydrogen sulfide, thereby improving production efficiency.

[0044] For example, the second contact treatment can be easily carried out by using a reaction vessel equipped with stirring blades, which is preferably used in the first contact treatment, and which is provided at the bottom with a nozzle for supplying a gas containing hydrogen sulfide.

[0045] (Gas containing hydrogen sulfide) As the gas containing hydrogen sulfide, any gas containing at least hydrogen sulfide can be used without particular limitation, and for example, it is preferable to use hydrogen sulfide alone or a gas containing hydrogen sulfide and an inert gas. From the viewpoint of performing the second contact treatment more uniformly and efficiently, it is more preferable to use a gas containing hydrogen sulfide and an inert gas.

[0046] As the hydrogen sulfide, for example, commercially available hydrogen sulfide can be used as it is. The hydrogen sulfide may or may not be dehydrated, but from the viewpoint of further reducing the influence on the reaction, it is preferable that the water content is small, and the water content may be, for example, about 50 ppm by mass or less.

[0047] Examples of inert gases include rare gases such as helium, neon, and argon, nitrogen, and carbon dioxide. Of these, nitrogen is preferred from the viewpoint of being cheaper and more readily available.

[0048] The lithium extract obtained by the first contact treatment exhibits an oil phase containing lithium, as described above, to which a gas containing hydrogen sulfide is supplied. If the lithium extract is an aqueous phase, hydrogen sulfide dissolves in the extract, making it difficult for the reaction between lithium and hydrogen sulfide to proceed. In this regard, according to the method for producing lithium sulfide of the present embodiment, the reaction between lithium contained in the oil phase and hydrogen sulfide proceeds, and therefore the reaction proceeds more smoothly without being hindered by the dissolution of hydrogen sulfide. Therefore, according to the production method of the present embodiment, it is possible to produce lithium sulfide with high production efficiency.

[0049] In contrast, the method described in Patent Document 3 is intended to recover lithium ions contained in the aqueous phase, as described above. When hydrogen sulfide is supplied to the aqueous phase, it dissolves and does not contribute to the production of lithium sulfide by reaction with lithium. Therefore, although the method described in Patent Document 3 mentions supplying a carbonate or the like to obtain lithium carbonate, it can be said that the idea of ​​supplying hydrogen sulfide is not conceivable.

[0050] The lithium sulfide-containing oil composition obtained by the second contact treatment contains lithium sulfide and the hydrocarbon oil contained in the lithium extractant-containing liquid, and lithium sulfide precipitates. When lithium sulfide is used as a product, it is preferable to separate lithium sulfide from the lithium sulfide-containing oil composition obtained by the second contact treatment. Known methods such as solid-liquid separation and filtration can be used to separate lithium sulfide. Furthermore, to improve the yield of lithium sulfide, it is also possible to (i) contact the lithium sulfide-containing oil composition obtained by the second contact treatment with a lithium extractant-containing liquid and then with a gas containing hydrogen sulfide to increase the concentration of lithium sulfide in the lithium sulfide-containing oil composition, or (ii) heat the lithium sulfide-containing oil composition.

[0051] The second contact treatment is preferably carried out while irradiating with ultraviolet light. Carrying out the second contact treatment while irradiating with ultraviolet light promotes the separation of lithium sulfide from the fluid obtained by the second contact treatment, preferably the lithium sulfide-containing oil composition. As a result, the production efficiency of lithium sulfide is improved. The ultraviolet light to be irradiated can be any of various types of ultraviolet light, including long wavelength ultraviolet light (wavelength: 320 to 400 nm), medium wavelength ultraviolet light (wavelength: 280 to 320 nm), and short wavelength ultraviolet light (wavelength: 280 nm or less), with medium wavelength ultraviolet light (wavelength: 280 to 320 nm) being preferred.

[0052] The method of irradiating with ultraviolet light is not particularly limited as long as it can irradiate the fluid (preferably the lithium sulfide-containing oil composition) involved in the second contact treatment with ultraviolet light, and can be carried out using, for example, general-purpose equipment such as a high-pressure mercury lamp or a UV-LED device. The integrated light dose of ultraviolet light is preferably 1 mJ / cm. ２ More preferably, 5 mJ / cm ２ More preferably, 10 mJ / cm ２ or more, and the upper limit is preferably 500 mJ / cm ２ or less, more preferably 400 mJ / cm ２ More preferably, 300 mJ / cm or less ２ The following is the result.

[0053] [Method for recovering lithium] The method for recovering lithium of the present embodiment is a method for recovering lithium, comprising: a first contact treatment of contacting a lithium-containing solution with a lithium extractant-containing solution; and a second contact treatment of contacting the lithium extract obtained by the contact with a gas containing hydrogen sulfide.

[0054] The lithium-containing liquid, the lithium extractant-containing liquid, and the first contact treatment in which they are brought into contact with each other, as well as the lithium extractant, the gas containing hydrogen sulfide, and the second contact treatment in which they are brought into contact with each other, are as described in the above-mentioned method for producing lithium sulfide of the present embodiment.

[0055] The lithium sulfide obtained by the manufacturing method of this embodiment can be suitably used as a raw material for solid electrolytes. The obtained solid electrolyte can be suitably used in lithium ion secondary batteries, more specifically, in the solid electrolytic layer of an all-solid-state lithium ion secondary battery, or as a solid electrolyte to be mixed into a positive electrode or negative electrode composite. For example, an all-solid-state lithium ion secondary battery can be obtained by providing a positive electrode, a negative electrode, or a layer of solid electrolyte between the positive electrode and the negative electrode. Furthermore, lithium ion secondary batteries (all-solid-state lithium ion secondary batteries) are used in automotive applications, information-related devices and communication devices such as personal computers, video cameras, and mobile phones.

Claims

1. A method for producing lithium sulfide, comprising: a first contact treatment in which a lithium-containing solution is brought into contact with a solution containing a lithium extractant; and a second contact treatment in which the lithium extract obtained by the first contact treatment is brought into contact with a gas containing hydrogen sulfide.

2. The method for producing lithium sulfide according to claim 1, wherein the lithium extractant-containing liquid contains a lithium extractant and a hydrocarbon oil.

3. The method for producing lithium sulfide according to claim 2, wherein lithium sulfide is separated from the lithium sulfide-containing oil composition obtained by the second contact treatment.

4. The method for producing lithium sulfide according to any one of claims 1 to 3, wherein the second contact treatment is carried out while blowing the gas containing hydrogen sulfide into the lithium extract.

5. The method for producing lithium sulfide according to any one of claims 1 to 4, wherein the gas containing hydrogen sulfide is a gas containing hydrogen sulfide and an inert gas.

6. The method for producing lithium sulfide according to any one of claims 1 to 5, wherein the second contact treatment is carried out while irradiating with ultraviolet light.

7. A method for recovering lithium, comprising: a first contact treatment in which a lithium-containing solution is brought into contact with a solution containing a lithium extractant; and a second contact treatment in which the lithium extract obtained by the first contact treatment is brought into contact with a gas containing hydrogen sulfide.