Method for producing lithium hydroxide

Abstract

The present invention provides a method for producing lithium hydroxide which employs, as a source liquid, a wide variety of aqueous solutions containing lithium and which efficiently produces highly pure lithium hydroxide from the source liquid, said method comprising: first mixing for mixing an aqueous solution that contains lithium and at least one element other than lithium, and a base in a reaction tank with pH adjusted to 6-10; second mixing for mixing with pH adjusted to 12 or more; removing a hydroxide of the element other than lithium generated in the first mixing and the second mixing to obtain a lithium ion extraction liquid; using an electrochemical device having an Li-selectively permeable membrane to recover only lithium ions in a recovery solution from the lithium ion extraction liquid; and returning the lithium ion extraction liquid from which lithium ions have been recovered by the electrochemical device to the reaction tank and carrying out the pH adjustment.

Description

Technical Field

[0001] The present invention relates to a method for producing lithium hydroxide.

Background Art

[0002] With the rapid spread of information-related devices and communication devices such as personal computers, video cameras, and mobile phones in recent years, the development of batteries used as their power sources has been emphasized. Conventionally, electrolytes containing flammable organic solvents have been used for batteries used in such applications. However, by making the battery all-solid-state, a flammable organic solvent is not used inside the battery, the safety device can be simplified, and the manufacturing cost and productivity are excellent. Therefore, the development of a battery in which the electrolyte is replaced with a solid electrolyte layer has been carried out.

[0003] As a battery used in the above-mentioned applications, a lithium secondary battery or the like is used, and in recent years, its use in hybrid cars and electric vehicles developed in response to carbon dioxide emission regulations has also been studied. Therefore, it has become an urgent task to secure a lithium source more than ever, and as part of this, a technology for recovering lithium by recycling lithium secondary batteries has been developed (for example, see Patent Document 1).

[0004] In addition to the above recycling, from the viewpoint of more widely seeking a lithium source and more stably securing lithium, technologies for recovering lithium from salt lake brine using a manganese oxide compound as an adsorbent (for example, see Non-Patent Documents 1 and 2), technologies for recovering lithium by solar evaporation of brine (for example, see Non-Patent Documents 1 and 3), etc. have been disclosed.

[0005] As a solid electrolyte used in lithium secondary batteries and the like, sulfide solid electrolytes are known. Since sulfide solid electrolytes have high ionic conductivity, they are useful for increasing the output of batteries. Lithium sulfide is widely used as a raw material for producing sulfide solid electrolytes, and the demand for lithium hydroxide, which is a raw material for lithium sulfide, is increasing. As a method for producing lithium hydroxide, there is a method of electrolyzing an aqueous solution or suspension of lithium carbonate to generate an aqueous solution of lithium hydroxide through an ion exchange membrane (see, for example, Patent Document 2).

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Patent Document 2

Non-Patent Documents

[0007]

Non-Patent Document 1

Non-Patent Document 2

Non-Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0008] The technology described in Patent Document 1 recovers lithium ions from a stock solution containing lithium ions using a lithium ion conductor. However, with the increasing demand for lithium, an improvement in the efficiency of lithium recovery has been required more than ever. In addition, the technology described in Patent Document 2 limits the raw material of lithium hydroxide to lithium carbonate. To obtain lithium hydroxide using an aqueous solution containing other lithium as a raw material, further improvement is necessary. Furthermore, when obtaining lithium hydroxide by the technology described in Patent Document 2 and the like, since a dehydration step such as heating and concentration is required, the energy consumption is large, and reduction of such energy is necessary to obtain lithium at a lower cost.

[0009] Regarding the recovery of lithium from a wide range of aqueous solutions containing lithium, such as seawater and geothermal water, as a stock solution, it is also disclosed in Non-Patent Documents 1 to 3. However, in the technology using the adsorbent described in Non-Patent Document 1, after adsorbing lithium to the adsorbent, a base is added to remove impurities, so there is a problem that impurities derived from the base remain. Also, when trying to recover lithium from an aqueous solution with a low pH among the stock solutions, manganese oxide used as an adsorbent elutes, so there is a problem that it cannot be applied. In the technology using the adsorbent described in Non-Patent Document 2, since manganese oxide used as an adsorbent releases hydrogen ions when adsorbing lithium, the pH decreases and the adsorption of lithium is inhibited. In addition, the natural evaporation described in Non-Patent Documents 1 and 3 requires a long time for evaporation, so it is not efficient.

[0010] The present invention has been made in view of such circumstances, and an object thereof is to provide a method for efficiently producing high-purity lithium hydroxide from a wide range of aqueous solutions containing lithium as a stock solution.

Means for Solving the Problems

[0011] As a result of intensive studies to solve the above problems, the present inventors have found that the above problems can be solved by the following invention.

[0012] 1. A first mixing step of mixing an aqueous solution containing lithium and at least one element other than lithium with a base in a reaction vessel while adjusting the pH to 6 or more and 10 or less, and a second mixing step of mixing while adjusting the pH to 12 or more, and removing hydroxides of elements other than lithium generated by the first mixing and the second mixing to obtain a lithium ion extract; Recovering only lithium ions into a recovery solution from the lithium ion extract using an electrochemical device equipped with a Li selective permeable membrane, and Performing the pH adjustment by returning the lithium ion extract from which lithium ions have been recovered by the electrochemical device to the reaction vessel. A method for producing lithium hydroxide including the above steps. 2. The method for producing lithium hydroxide according to 1 above, wherein obtaining the lithium ion extract includes concentrating lithium ions. 3. The method for producing lithium hydroxide according to 2 above, wherein concentrating the lithium ions is performed by adsorbing the lithium ions using an adsorbent. 4. The method for producing lithium hydroxide according to 3 above, wherein the gas generated from the electrochemical device is used for desorbing the lithium ions adsorbed on the adsorbent. 5. The method for producing lithium hydroxide according to 4 above, wherein the gas is chlorine. 6. The method for producing lithium hydroxide according to any one of 1 to 5 above, further including separating lithium hydroxide from the recovery solution. 7. The method for producing lithium hydroxide according to 6 above, wherein the separation is performed by crystallization. 8. The method for producing lithium hydroxide according to any one of 1 to 7 above, wherein the at least one element other than lithium is at least one element selected from calcium, magnesium, strontium, manganese, iron, zinc, and lead. 9. The method for producing lithium hydroxide according to any one of 1 to 8 above, wherein the base is at least one selected from alkali metal hydroxides and alkaline earth metal hydroxides. 10. The method for producing lithium hydroxide according to any one of 1 to 9 above, wherein the Li selective permeable membrane contains an oxide or oxynitride containing lithium. 11. The method for producing lithium hydroxide according to any one of 3 to 10 above, wherein the adsorbent is at least one selected from a titanium oxide-based adsorbent, a manganese oxide-based adsorbent, and an antimony oxide-based adsorbent.

Advantages of the Invention

[0013] According to the present invention, it is possible to provide a method for efficiently producing high-purity lithium hydroxide from an aqueous solution containing lithium as a wide range of stock solutions.

Brief Description of the Drawings

[0014]

Figure 1

Figure 2

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Figure 5

Embodiments for Carrying Out the Invention

[0015] Hereinafter, a method for producing lithium hydroxide according to an embodiment of the present invention (hereinafter referred to as "this embodiment") will be described. Note that the method for producing lithium hydroxide according to an embodiment of the present invention is merely one embodiment of the method for producing lithium hydroxide of the present invention, and the present invention is not limited to the method for producing lithium hydroxide of this embodiment. Further, in this specification, lithium means both lithium and lithium ions, and shall be interpreted as appropriate as long as there is no technical contradiction.

[0016] [Method for Producing Lithium Hydroxide] The method for producing lithium hydroxide of this embodiment includes a first mixing in which an aqueous solution containing lithium and at least one element other than lithium and a base are adjusted to a pH of 6 or more and 10 or less and mixed in a reaction tank, and a second mixing in which the pH is adjusted to 12 or more and mixed. The method includes removing hydroxides of elements other than lithium generated by the first mixing and the second mixing to obtain a lithium ion extract, recovering only lithium ions from the lithium ion extract into a recovery solution using an electrochemical device equipped with a Li selective permeable membrane, and performing the pH adjustment by returning the lithium ion extract from which lithium ions have been recovered by the electrochemical device to the reaction tank.

[0017] In the production method of this embodiment, before selectively recovering lithium ions, by reacting an aqueous solution containing lithium and at least one element other than lithium (hereinafter sometimes simply referred to as "stock solution") with a base, elements other than lithium contained in the stock solution can be easily removed by forming hydroxides, and the content of lithium ions to be recovered contained in the lithium ion extract (hereinafter sometimes simply referred to as "extract") can be improved. Then, by improving the content of lithium ions in the lithium ion extract, lithium ions can be easily and selectively recovered, and it becomes possible to easily obtain high-purity lithium hydroxide with few impurities. In addition, an electrochemical device equipped with a Li selective permeable membrane can selectively recover lithium ions without any particular limitation as long as it is an aqueous solution containing lithium ions, regardless of the type of the stock solution. Therefore, by combining the removal of elements other than lithium as hydroxides as described above, it becomes possible to more easily produce high-purity lithium hydroxide for a wider range of stock solutions.

[0018] The production method of the present embodiment includes adjusting the pH in the reaction between the above-mentioned pH adjustment, that is, an aqueous solution (stock solution) containing lithium and at least one element other than lithium, and a base, using a lithium ion extract from which lithium ions have been recovered by an electrochemical device, specifically, returning it to the reaction tank for adjustment. Although lithium ions are recovered from the lithium ion extract by the electrochemical device, not all of them are recovered and some remain. The extract from which lithium ions have been recovered exhibits a high pH (alkaline). On the other hand, when elements other than lithium contained in the stock solution are made into hydroxides by the reaction of mixing the stock solution and the base, it becomes possible to easily remove the hydroxides by performing the reaction while adjusting the pH. Therefore, it becomes possible to efficiently produce lithium hydroxide. Thus, in order to use the extract from which lithium ions have been recovered for pH adjustment when reacting the stock solution and the base by mixing, by returning it to the reaction tank, pH adjustment can be performed without using a new chemical. As a result, the amount of chemical used and the amount of waste can be reduced. In addition, since it becomes easy to remove the hydroxide and the lithium ions remaining in the extract can be recovered, it becomes possible to efficiently produce lithium hydroxide.

[0019] In this way, according to the production method of the present embodiment, any aqueous solution containing lithium ions can be used as the stock solution without any particular limitation, and by efficiently recovering lithium ions from the stock solution, it becomes possible to efficiently produce high-purity lithium hydroxide.

[0020] (Mixing) In the production method of the present embodiment, an aqueous solution containing lithium and at least one element other than lithium, and a base are mixed while adjusting the pH in a reaction tank and reacted to form hydroxides of elements other than lithium. Here, the mixing while adjusting the pH is performed by a first mixing in which the pH is adjusted to 6 or more and 10 or less and then mixed, and a second mixing in which the pH is adjusted to 12 or more and then mixed. As a result, at least a part of the elements other than lithium can be removed, and a lithium ion extraction solution containing lithium ions with few impurities can be obtained.

[0021] An aqueous solution (stock solution) containing lithium and at least one element other than lithium is treated as a raw material for lithium hydroxide obtained by the production method of the present embodiment. Examples of the aqueous solution (stock solution) containing lithium and at least one element other than lithium include lithium-containing treated water extracted from a processing member of a lithium secondary battery. The lithium-containing treated water is not particularly limited as long as it is extracted from a processing member. For example, it may be extracted from a processing member of a lithium secondary battery containing a sulfide solid electrolyte, that is, lithium-containing treated water containing a sulfide solid electrolyte.

[0022] In addition, examples of the aqueous solution (stock solution) containing lithium and at least one element other than lithium include seawater, salt lake brine, mining wastewater, geothermal water, etc. In the production method of the present embodiment, these aqueous solutions can be used alone or in combination of multiple types.

[0023] Examples of the "element other than lithium" contained in the aqueous solution (stock solution) containing lithium and at least one element other than lithium include elements that can be contained in the above lithium-containing treated water, seawater, salt lake brine, mining wastewater, geothermal water, etc. Typically, Group 2 elements (alkaline earth metals) such as calcium, magnesium, and strontium; transition metals of Periods 4 to 5 of Groups 4 to 12 such as manganese, iron, and zinc; Group 14 elements such as lead, etc. can be mentioned. The stock solution may contain these elements alone or in combination of multiple types. In addition, the above stock solution may contain, as elements other than lithium, Group 1 elements (alkali metals) such as sodium and potassium, Group 13 elements such as boron, halogen elements such as chlorine, etc., but these elements are not removed from the stock solution as hydroxides in the same manner as lithium.

[0024] Examples of the base that is reacted by mixing with the above stock solution include inorganic bases and organic bases. From the viewpoint of easily removing the elements other than lithium as hydroxides and obtaining high-purity lithium hydroxide more efficiently, inorganic bases are preferred. Examples of the inorganic base preferably include hydroxides of alkali metals and alkaline earth metals. More specifically, alkali metal hydroxides such as sodium hydroxide and potassium hydroxide; alkaline earth metal hydroxides such as calcium hydroxide, magnesium hydroxide, and barium hydroxide can be mentioned. Among these, alkali metal hydroxides are preferred, and particularly sodium hydroxide is preferred. In addition, bases having hydrocarbon groups such as tetramethylammonium hydroxide and tetraethylammonium hydroxide (which can also be regarded as a kind of organic base) can also be mentioned.

[0025] In the production method of this embodiment, when the above stock solution and the base are mixed and reacted, hydroxides of the elements other than lithium, specifically, calcium hydroxide, magnesium hydroxide, strontium hydroxide, manganese hydroxide, iron hydroxide, zinc hydroxide, lead hydroxide, etc. can be removed.

[0026] The removal of these hydroxides is affected by the pH of the mixture of the aqueous solution serving as the above-mentioned stock solution and the base. As described above, pH adjustment is performed using the lithium ion extract in which lithium ions have been recovered by the electrochemical device. As described above, the pH adjustment needs to be carried out in two steps, adjusting the pH to 6 or more and 10 or less in the first mixing and adjusting the pH to 12 or more in the second mixing.

[0027] Regarding the fact that the removal of hydroxides is affected by pH, in the removal of hydroxides, the appropriate pH varies depending on the type thereof. For example, among the above-mentioned hydroxides, iron hydroxide, zinc hydroxide, and lead hydroxide are easily removed at a pH of 6 or more and 10 or less, and calcium hydroxide, magnesium hydroxide, strontium hydroxide, manganese hydroxide, iron hydroxide, and zinc hydroxide are easily removed at a pH of 12 or more. That is, for elements other than lithium, iron, zinc, and lead are easily removed at a pH of 6 or more and 8 or less, and calcium, magnesium, strontium, manganese, iron, and zinc are easily removed at a pH of 12 or more. Also, iron hydroxide and zinc hydroxide are easily removed in any pH range, that is, iron and zinc are easily removed in any pH range. In the production method of the present embodiment, in consideration of the influence by the above pH, adjustment to a pH of 6 or more and 10 or less in the first mixing and adjustment to a pH of 12 or more in the second mixing are carried out.

[0028] The mixing of the stock solution and the base needs to be carried out in two separate steps while changing the pH of the mixture of these stock solution and the base. Specifically, it is necessary to carry out the first mixing with pH adjustment to 6 or more and 10 or less and the second mixing with adjustment to pH 12 or more. It is preferable that the first mixing and the second mixing are carried out in this order, with the second mixing following the first mixing. By reacting in multiple steps in this way, elements that are easily removed as hydroxides in the pH range set in each step can be removed, so that the removal of hydroxides can be carried out efficiently.

[0029] The pH adjusted in the first mixing is preferably 6.5 or higher, more preferably 7.5 or lower, and particularly preferably 7. The pH of these mixtures is the adjustment target. Since the pH of the actual mixture fluctuates slightly above and below the adjustment target, the pH of the mixture may be within the range of pH ± 0.5 of the above adjustment target. For example, when the pH is 7, it means that the pH of the actual mixture is within the range of 6.5 or higher and 7.5 or lower. Within this range, the effect of the invention of efficiently producing high-purity lithium hydroxide from the stock solution can be obtained. Also, the pH adjusted in the second mixing is preferably 12 or higher, more preferably 12.5 or higher, still more preferably 13.5 or higher, and the upper limit is 14 or lower. The higher the pH adjusted in the second mixing, the more preferable it is, and it is particularly preferable to adjust it to 14.

[0030] The method of pH adjustment is not particularly limited as long as a lithium ion extract in which lithium ions are recovered by an electrochemical device is used. When reacting by mixing the stock solution and a base, the base is consumed, so the pH tends to decrease as the reaction proceeds. Therefore, pH adjustment may be performed while continuously supplying a lithium ion extract in which lithium ions are recovered by an electrochemical device, or may be performed intermittently.

[0031] Regarding the removal of hydroxides, the hydroxides of elements other than lithium described above do not dissolve in the mixture of the stock solution and the base and exist as solids, so the solids can be separated and removed. Separation of the hydroxides of elements other than lithium can be performed by various easy treatments such as suction filtration and decantation. The separation may also be performed by combining filtration and decantation.

[0032] (Concentrating lithium ions) In the manufacturing method of the present embodiment, in obtaining the lithium ion extraction liquid, it is preferable to include concentrating lithium ions. By including concentrating lithium ions, lithium hydroxide of higher purity can be efficiently manufactured. When precipitates other than lithium are generated by concentration, they may be used for the pretreatment of impurity removal.

[0033] Concentration of lithium ions can be carried out by methods such as evaporation of water, moisture removal using a reverse osmosis membrane, and adsorption of lithium ions using an adsorbent. However, it is preferable to carry out the concentration by adsorbing lithium ions using an adsorbent. By selectively adsorbing lithium ions with the adsorbent and then desorbing the lithium ions adsorbed on the adsorbent, lithium ions can be more easily concentrated, and lithium hydroxide of higher purity can be efficiently manufactured. The adsorption and desorption of lithium ions by the adsorbent can specifically be carried out by bringing the lithium ion extraction liquid into contact with the adsorbent to selectively adsorb the lithium ions contained in the extraction liquid onto the adsorbent. Next, by desorbing the lithium ions adsorbed on the adsorbent with an acid or the like, a lithium ion extraction liquid with reduced content of elements other than lithium and concentrated lithium ions is obtained.

[0034] Examples of the adsorbent include various adsorbents such as titanium oxide-based adsorbents such as lithium titanate, manganese oxide-based adsorbents such as lithium manganate, antimony oxide-based adsorbents such as lithium antimonate, hydrated aluminum oxide (Al2O3·xH2O, x>0), aluminum oxide-based adsorbents such as activated carbon composite hydrated aluminum oxide, and ion exchange resins. These can be used alone or in combination. From the viewpoint of more efficiently adsorbing lithium ions, a manganese oxide-based adsorbent is preferable. As the ion exchange resin, cation exchange resins such as weakly acidic cation exchange resins and strongly acidic cation exchange resins are preferable, and strongly acidic cation exchange resins having a sulfonic acid group as an exchange group are more preferable.

[0035] Examples of the acid used for desorbing lithium ions from the adsorbent include inorganic acids such as hydrochloric acid and nitric acid. In addition, as the acid used for desorption, a gas generated from the electrochemical device described later, preferably chlorine, can be used. For example, when the generated gas is chlorine, hydrogen chloride generated by reacting the generated chlorine with hydrogen is dissolved in water and used as an inorganic acid for desorption as hydrochloric acid. As a result, it is not necessary to supply a new inorganic acid such as hydrochloric acid, so that the amount of the drug used can be reduced, the amount of waste can also be reduced, and lithium hydroxide can be produced more efficiently.

[0036] (Recovery of lithium ions) The production method of the present embodiment includes recovering only lithium ions into a recovery liquid from a lithium ion extraction liquid using an electrochemical device equipped with a Li selective permeable membrane. "Recovering only lithium ions into the recovery liquid" means that the recovered ions do not substantially contain other ions than lithium ions, and the content of the other ions is at most 10% by mass or less, preferably 5% by mass or less, more preferably 3% by mass or less, still more preferably 1% by mass or less, and particularly preferably 0.5% by mass or less.

[0037] The recovery liquid used in the present embodiment is not particularly limited as long as it can dissolve lithium ions, and can be appropriately selected according to the finally obtained form of lithium. For example, pure water such as distilled water and ion-exchanged water is preferably used as the recovery liquid. In the manufacturing method of the present embodiment, the recovery liquid is supplied as water such as pure water or ion-exchanged water, and lithium ions are moved from the lithium ion extraction liquid obtained through the reaction by mixing the above-mentioned stock solution and base and the removal of hydroxide using an electrochemical device equipped with a Li selective permeable membrane to recover lithium ions, thereby obtaining a recovery liquid containing lithium ions (hereinafter sometimes simply referred to as "lithium ion-containing recovery liquid"). Next, after lithium hydroxide is generated from the lithium ion-containing recovery liquid by a treatment such as crystallization, a recovery liquid substantially free of lithium ions is obtained. The recovery liquid substantially free of lithium ions is obtained by removing lithium ions by crystallization from the lithium ion-containing recovery liquid obtained by recovering lithium ions from the lithium ion extraction liquid, and can be said to be a recovery liquid substantially free of lithium ions.

[0038] The lithium ion extraction liquid contains, in addition to lithium ions, "elements other than lithium" contained in the stock solution that were not removed in the reactions by mixing such as the first mixing and the second mixing, and anions such as chlorine. By using an electrochemical device, only lithium ions are recovered into the recovery liquid, and at the same time as this recovery, chlorine and the like contained in the extraction liquid are by-produced as a gas. Also, as gases other than chlorine, oxygen, hydrogen, etc. can also be by-produced. Among the gases generated from the electrochemical device, chlorine is preferable. This is because when chlorine is generated as a gas, as described above, it can be reacted with hydrogen to form hydrochloric acid and used as the acid used in the attachment and detachment from the adsorbent. Also, due to the recovery of lithium ions, the lithium ion extraction liquid after recovering lithium ions from the lithium ion extraction liquid contains "elements other than lithium" and the like contained in the stock solution that were not removed in the reactions by mixing such as the first mixing and the second mixing, and becomes a liquid having a high pH of about 12 to 14. The lithium ion extraction liquid from which lithium ions have been recovered is used, as described above, for pH adjustment in the reaction by mixing the stock solution and the base.

[0039] (Electrochemical device equipped with a Li selective permeable membrane) In the manufacturing method of this embodiment, when recovering lithium ions from the lithium ion extraction solution into the recovery solution, an electrochemical device equipped with a Li selective permeable membrane is used. The Li selective permeable membrane is a membrane having a function of moving lithium ions in the lithium ion extraction solution to the recovery solution, and is usually provided so as to partition the extraction solution and the recovery solution.

[0040] The Li selective permeable membrane is preferably composed of a Li selective permeable membrane body made of a super Li ion conductor (ion conductor) having a particularly high ion conductivity, and a Li adsorption layer formed as a thin layer on the extraction solution side thereof. When a super Li ion conductor is used as the Li selective permeable membrane body, the recovery efficiency of lithium can be increased by increasing the ionic current of lithium ions flowing between the electrodes. Here, lithium ions contained in an aqueous solution exist as lithium hydrated ions coordinated with water molecules around them. Therefore, in order to further increase the ionic current, it is effective to realize a situation where water molecules are easily removed at the surface of the Li selective permeable membrane (the interface between the Li selective permeable membrane and the extraction solution). For this reason, it is preferable that a Li adsorption layer that adsorbs lithium ions (excluding hydrates) in the lithium ion extraction solution is formed on the surface of the Li selective permeable membrane. That is, the Li selective permeable membrane is preferably surface Li adsorbed. As the Li adsorption layer, as will be described later, those formed by modifying the surface of the material constituting the Li selective permeable membrane are preferably mentioned.

[0041] Examples of the material constituting the Li selective permeable membrane body preferably include the following lithium-containing oxides, oxynitrides, etc. That is, the Li selective permeable membrane preferably contains the following lithium-containing oxides, oxynitrides, etc. Examples of the lithium-containing oxide include lanthanum lithium titanate: (Li x , La y )TiO z(Here, x = 3a - 2b, y = 2 / 3 - a, z = 3 - b, 0 < a ≤ 1 / 6, 0 ≤ b ≤ 0.06, x > 0) (hereinafter also referred to as "LLTO"), lithium lanthanum zirconate: Li7La3Zr2O 12 (hereinafter also referred to as "LLZO"), lithium lanthanum niobate: Li5La3Nb2O 12 , lithium lanthanum tantalate: Li5La3Ta2O 12 and the like can be mentioned. More specifically, as LLTO, Li 0.29 La 0.57 TiO3 (a ≈ 0.1, b ≈ 0) can be used.

[0042] These materials can be obtained, for example, as a sintered body obtained by mixing particles composed of this material with a sintering aid or the like and sintering at a high temperature (1000 °C or higher). In this case, the surface of the Li selective permeation membrane can also be configured as a porous body in which fine particles composed of LLTO are bonded (sintered), so that the effective area of the surface of the Li selective permeation membrane body can be increased. This is the same not only for LLTO but also for other lithium-containing oxides and oxynitrides described later.

[0043] As a super Li ion conductor that can be used as a material constituting the Li selective permeation membrane body, as a lithium-containing oxide, in addition to the above-mentioned LLTO, LLZO, etc., for example, Li 1+x+y Al x (Ti, Ge) 2-x Si y P 3-y O 12 (Here, 0 ≤ x ≤ 0.6, 0 ≤ y ≤ 0.6) (Li2O - Al2O3 - SiO2 - P2O5 - TiO2 - GeO2 system, hereinafter also referred to as "LASiPTiGeO") and the like can also be mentioned.

[0044] In addition, examples of the lithium-containing oxynitride include lithium phosphooxynitride (Li3PON, hereinafter also referred to as "LiPON"), nitride of LLTO (LLTON), nitride of LLZO (LLZON), nitride of LASiPTiGeO (LASiPTiGeON), and the like.

[0045] The above-mentioned super Li-ion conductors such as lithium-containing oxides and oxynitrides contain lithium as one of their constituent elements, and ionic conductivity is exhibited by the movement of lithium ions outside the crystal between lithium sites in the crystal. Lithium ions flow through the Li selective permeable membrane body, but sodium ions cannot flow through the Li selective permeable membrane. At this time, lithium ions (Li + ) conduct within the crystal, and hydrated lithium ions present in the extract together with lithium ions cannot enter the Li sites, so they do not conduct within the crystal. This is the same as the Li selective permeable membrane described in WO2015 / 020121.

[0046] Here, if a large amount of only lithium ions are adsorbed on the surface of the Li selective permeable membrane body by the Li adsorption layer, the water molecules of the lithium hydrated ions are removed during adsorption, leaving only lithium ions. Therefore, the conduction efficiency of lithium ions (ionic current flowing through the Li selective permeable membrane body) from the extract side (one main surface side) to the recovery liquid side (the other main surface side) in the Li selective permeable membrane body can be increased.

[0047] The Li selective permeable membrane preferably has an anode and a cathode joined thereto, and it is preferable that the anode is joined to the extract side (one main surface) of the Li selective permeable membrane and the cathode is joined to the recovery liquid side (the other main surface). With this configuration, one main surface on the extract side and the other main surface on the recovery liquid side of the Li selective permeable membrane are maintained at a certain positive potential and negative potential, respectively. As the materials for the anode and cathode, metal materials that do not cause an electrochemical reaction in the extract and the recovery liquid can be appropriately used respectively. Examples of such metal materials include SUS, Ti, Ti-Ir alloy, and the like.

[0048] Although the above materials used as the Li selective permeable membrane are solid, they are known to exhibit conductivity due to the flow of lithium ions in a form close to free electrons in the crystal. Therefore, when the anode is at a positive potential and the cathode is at a negative potential, among the lithium ions (positive ions) in the extraction liquid on the anode side, those that reach the cathode side of the Li selective permeable membrane flow from the anode side (extraction liquid) to the cathode side (recovery liquid) of the Li selective permeable membrane by ion conduction. The lithium ions that reach the cathode side of the Li selective permeable membrane are recovered in the recovery liquid. For this reason, after a predetermined time has elapsed, the lithium ion concentration in the extraction liquid decreases, and the lithium ion concentration in the recovery liquid increases.

[0049] The Li adsorption layer is formed as a thin layer on the surface of the Li selective permeable membrane main body by performing a chemical treatment on the Li selective permeable membrane main body. Specifically, it is formed by subjecting one main surface of the above Li selective permeable membrane main body (for example, LLTO) to an acid treatment, for example, exposing this surface to hydrochloric acid or nitric acid for 5 days. By this treatment, lithium, which is particularly easily oxidized among the constituent elements in the Li selective permeable membrane main body (for example, LLTO), is replaced by hydrogen in the acid, and an H 0.29 La 0.57 It is presumed that a substance layer (HLTO) with a composition close to LaTiO3 is formed. Here, the formation of the thin layer (HLTO) on the surface is supported by the fact that there are those having peaks different from those of the Li selective permeable membrane main body (for example, LLTO) from the X-ray diffraction results in WO2017 / 131051.

[0050] The H site in HLTO was originally a site where lithium enters, so H is particularly easily replaced by lithium ions and is difficult to be replaced by other ions (such as sodium ions). Therefore, HLTO functions as a Li adsorption layer. In addition, since HLTO is generated by the reaction with an acid, it is formed only on the outermost surface of the Li selective permeable membrane main body.

[0051] The electrochemical device equipped with a Li selective permeable membrane used in the manufacturing method of this embodiment has no particular limitation on other configurations as long as it is equipped with a Li selective permeable membrane. Figures 1 and 2 show a preferred embodiment of the electrochemical device used in the manufacturing method of this embodiment. From the perspective of improving the production efficiency of lithium hydroxide, the electrochemical device used in the manufacturing method of this embodiment preferably has a configuration shown in Figures 1 and 2, for example.

[0052] As the electrochemical device equipped with a Li selective permeable membrane, it preferably has at least a Li ion recovery tank 20 equipped with a Li selective permeable membrane 20c and a recovered liquid storage tank 21. The Li ion recovery tank 20 has an extract liquid tank 20a for storing a lithium ion extraction liquid and a recovered liquid tank 20b for storing a recovered liquid, and has a configuration partitioned by the Li selective permeable membrane 20c.

[0053] The recovered liquid storage tank 21 is used to receive recovered liquids such as pure water newly supplied and filtrate C discharged from the crystallization device 22. In addition, for example, until the concentration of lithium ions in the recovered liquid recovered from the extraction liquid in the Li ion recovery tank 20 rises to a certain concentration, a batch operation is performed to circulate the recovered liquid between the recovered liquid tank 20b and the recovered liquid storage tank 21, facilitating various operations such as circulating the recovered liquid at the start-up of the device, heating as necessary, and storing the recovered liquid once. Regarding the recovered liquid storage tank 21, from the perspective of corresponding to various operations, as a two-tank configuration, one of the tanks can be used as a tank for circulating the recovered liquid with the recovered liquid storage tank, and the other tank can be used as a tank for receiving new recovered liquid.

[0054] The recovered liquid storage tank 21 preferably has a temperature adjustment means 21a for adjusting the temperature of the recovered liquid. By having the temperature adjustment means 21a, the temperature inside the Li ion recovery tank 20 can be adjusted as necessary to promote the recovery of lithium ions, and it can also correspond to operations such as heating as necessary when manufacturing lithium hydroxide from the lithium ion-containing recovered liquid obtained by recovering lithium ions from the extraction liquid.

[0055] In the lithium ion recovery tank 20, since the lithium ion extraction liquid A2 from which lithium ions have been recovered is used for pH adjustment in the reaction by mixing the above-mentioned stock solution and the base, a discharge port is provided in the extraction liquid tank 20a of the Li ion recovery tank 20. The lithium ion extraction liquid A2 discharged from the discharge port of the extraction liquid tank 20a is returned to the reaction tank 10. When the adsorption / desorption device 11 is employed, chlorine generated preferably when recovering lithium ions from the lithium ion extraction liquid is used for desorbing the lithium ions adsorbed to the desorbent, and thus a chlorine discharge port is also provided in the extraction liquid tank 20a of the Li ion recovery tank 20.

[0056] Although not shown, in order to cope with various operations, for example, it may have an extraction liquid storage tank for storing the extraction liquid and a pump for feeding the extraction liquid to the extraction liquid tank 20a in the Li ion recovery tank 20.

[0057] (Various conditions for recovery) When recovering only lithium ions from the lithium ion extraction liquid to the recovery liquid, it is preferable to heat the recovery liquid. By heating, the recovery of lithium ions is promoted, and lithium hydroxide can be produced more efficiently. The adjusted temperature of the recovery liquid is preferably 50°C or higher, more preferably 60°C or higher, still more preferably 70°C or higher, and even more preferably 80°C or higher. As the upper limit, it is preferably 100°C or lower, more preferably 95°C or lower, and still more preferably 90°C or lower. Here, the adjusted temperature of the recovery liquid means the set value of the temperature during adjustment. Since the actual temperature of the recovery liquid or the like may fluctuate up and down around the set value, the actual temperature of the recovery liquid is considered to be included up to less than ±2.0°C. The same applies to the temperature of the extraction liquid described later.

[0058] When adjusted to the above temperature, the recovery of lithium ions is promoted. In addition, since the solubility of lithium ions increases due to the temperature rise of the recovery liquid, lithium ions are supplied from the extract by the increased amount, so that a larger amount of lithium ions can be recovered. Further, when separating lithium hydroxide from the lithium ion-containing recovery liquid from which lithium ions have been recovered from the extract, preferably by crystallization, by crystallizing the heated recovery liquid, it is also possible to produce lithium hydroxide while suppressing the energy consumption.

[0059] In this embodiment, the extract may be adjusted in pH. By adjusting the pH, lithium ions can be efficiently recovered. In this case, it is preferable to adjust the pH within the range of 12 or more and 14 or less. Note that setting the pH to 12 or more and 14 or less is the adjustment target. In this embodiment, for pH 12 or more and 14 or less, as the pH of the extract, a value of 11.5 or more and less than 12.5 for pH 12, and a value of 13.5 or more and less than 14.5 for pH 14 are included, which substantially means a range of 11.5 or more and less than 14.5.

[0060] When adjusting the pH of the extract in this embodiment, the means is not particularly limited. For example, it may be performed by a method of adding an alkaline aqueous solution to the extract. Further, the pH adjustment of the extract may be performed when recovering lithium ions in the recovery liquid, that is, lithium ions may be recovered in the recovery liquid while adjusting the pH of the extract, or may be performed in advance before recovering lithium ions in the recovery liquid.

[0061] As the alkaline component of the alkaline aqueous solution used for adjusting the pH of the extract, for example, the bases exemplified as those that can be used in the reaction with the above stock solution are preferably mentioned. Among them, sodium hydroxide is more preferable from the viewpoint of quickly adjusting the pH of the lithium ion extract.

[0062] Also, the extraction liquid may have its temperature adjusted in the same manner as the recovery liquid, specifically, it may be heated. This makes it easier to adjust the temperature of the recovery liquid and enables the recovery of lithium ions with high efficiency. When adjusting the temperature of the extraction liquid, the adjusted temperature may be within the adjustment range of the temperature of the above-mentioned recovery liquid.

[0063] (Separating lithium hydroxide) The method for producing lithium hydroxide according to this embodiment preferably includes separating lithium hydroxide from the recovery liquid as a method for producing lithium hydroxide from the recovery liquid. Specifically, in the production method of this embodiment, after recovering only lithium ions from the above-mentioned recovery liquid, lithium hydroxide is separated from the recovery liquid containing lithium ions (lithium ion-containing recovery liquid) obtained by recovering only lithium ions from the extraction liquid. As a result, lithium hydroxide can be obtained without requiring a dehydration step such as heating and concentration, so the energy consumption associated with the dehydration step and the like can be reduced, and a lithium source can be obtained more efficiently. The separation method is not particularly limited as long as lithium hydroxide can be obtained from the lithium ion-containing recovery liquid. For example, methods such as crystallization by cooling crystallization or evaporation crystallization are preferably mentioned.

[0064] (Cooling crystallization) In cooling crystallization, by heating the recovery liquid in the pre-stage of crystallization, the lithium ion content in the recovery liquid can be increased, and by creating a temperature difference, lithium ions can be recovered more efficiently. In the case of cooling crystallization, there is no particular limitation on the specific method as long as it is carried out by the usual cooling crystallization method. For example, it is preferably carried out while blowing an inert gas into the lithium ion-containing recovery liquid to maintain a positive pressure. By blowing in the inert gas, the formation of lithium carbonate (hereinafter, may be simply referred to as "carbonation") can be suppressed, and the production of lithium hydroxide by cooling crystallization is more promoted, so high-purity lithium hydroxide can be produced more efficiently.

[0065] When heating the recovery liquid in the stage prior to crystallization, the heating temperature is preferably 50°C or higher, more preferably 60°C or higher, and preferably 80°C or lower as the upper limit. When the heating temperature is within the above range, cooling crystallization can be performed more efficiently.

[0066] There is no particular limitation on the positive pressure, and it is usually sufficient to set it to about 0.1 to 30 kPa as the gauge pressure, and preferably 0.5 to 10 kPa from the viewpoint of performing freeze crystallization more efficiently. As the inert gas, nitrogen gas, argon gas, etc. may be used. The positive pressure may be adjusted by adjusting the supply and exhaust of the inert gas so that cooling crystallization is performed under positive pressure. From the viewpoint of suppressing carbonation, a gas containing oxygen may be used as long as the concentration of carbon monoxide, carbon dioxide, and hydrocarbon is 10 ppm or less. In order to obtain lithium hydroxide with higher purity, it is preferably 1 ppm or less, and more preferably 0.1 ppm.

[0067] In the case of cooling crystallization, from the viewpoint of performing cooling crystallization more efficiently, it is preferably performed while adjusting to 40°C or lower. From the same viewpoint, the crystallization temperature is preferably 35°C or lower, more preferably 30°C or lower, and still more preferably 25°C or lower. There is no particular limitation on the lower limit, but it may be set to exceed 0°C, and preferably 3°C or higher.

[0068] In the production method of this embodiment, when cooling crystallization is employed as the crystallization, it may include cooling the lithium ion-containing recovery liquid as necessary. By including cooling, the temperature of the lithium ion-containing recovery liquid can be actively adjusted to the above-preferred temperature, so that cooling crystallization can be performed more efficiently. Therefore, from the viewpoint of performing crystallization more efficiently, it is preferable to cool the lithium ion-containing recovery liquid and then perform crystallization. As a method for cooling the lithium ion-containing recovery liquid, either an air-cooling method or a water-cooling method may be adopted, and a cooler corresponding to the adopted method may be used.

[0069] (Evaporative Crystallization) In evaporation crystallization, since the recovered liquid is heated in the pre-crystallization stage, the energy required for evaporation can be suppressed. In the case of evaporation crystallization, there are no particular restrictions on the specific method as long as it is carried out by the usual evaporation crystallization method. For example, it is preferably carried out while adjusting the temperature to preferably 80°C or higher and 100°C or lower. From the viewpoint of performing evaporation crystallization more efficiently, the adjusted temperature is more preferably 85°C or higher, and even more preferably 90°C or higher.

[0070] From the viewpoint of performing evaporation crystallization more efficiently, evaporation crystallization is preferably carried out under a reduced-pressure atmosphere. By reducing the pressure, the water vapor generated in the system can be discharged, and this can be added to the filtrate or recovered liquid and recovered.

[0071] When reducing the pressure, there are no particular restrictions on the pressure, and it can usually be set as a vacuum pressure of about 0.05 to 10 kPa. From the viewpoint of performing evaporation crystallization more efficiently, it is preferably 0.1 to 5 kPa, and more preferably 0.2 to 1 kPa. Also, evaporation crystallization may be carried out while supplying an inert gas. In this case, as the inert gas, nitrogen gas, argon gas, etc. may be used. From the viewpoint of suppressing carbonation, a gas containing oxygen may be used as long as the concentration of carbon monoxide, carbon dioxide, and hydrocarbons is 10 ppm or less. In order to obtain lithium hydroxide with higher purity, it is preferably 1 ppm or less, and more preferably 0.1 ppm.

[0072] When performing the above crystallization in the production method of this embodiment, the filtrate generated by crystallization can be added to the recovered liquid. It is added to replenish the water in the recovered liquid in order to recover lithium ions from the recovered liquid as anhydrous lithium hydroxide or hydrated lithium hydroxide. By adding the filtrate to the recovered liquid and reusing it, the amount of fresh pure water supplied as the recovered liquid can be reduced, so that lithium hydroxide can be produced more efficiently. Note that the recovered liquid to which the filtrate is added is the recovered liquid used to transfer lithium ions from the extract, and is not a lithium ion-containing recovered liquid. In this embodiment, further, a heat exchanger that can utilize the exhaust heat of cooling crystallization and the surplus heat generated in evaporation crystallization for heating the recovery liquid can be provided. Thereby, the thermal efficiency can be further enhanced.

[0073] When evaporation crystallization is adopted, the pure water generated in evaporation crystallization can be easily reused by adding it to the filtrate or the recovery liquid, and the usage amount of new pure water can be reduced. Furthermore, compared with the case of newly supplying pure water, since there may be a case where the filtrate at a temperature higher than that of the new pure water can be reused, it becomes possible to produce lithium hydroxide more efficiently in terms of thermal energy. Also, in the case of cooling crystallization, a filtrate is also generated. Since the filtrate is obtained by crystallizing lithium hydroxide from a lithium-ion-containing recovery liquid, it can be said to be a recovery liquid from which lithium ions have been removed and that substantially does not contain lithium ions, but there may be a case where lithium ions contained in the recovery liquid are included. Therefore, in this case, the filtrate may not be pure water, but it can be reused by adding it to the recovery liquid, and the usage amount of new pure water can be reduced, so it becomes possible to produce lithium hydroxide more efficiently. Thus, in any case where cooling crystallization or evaporation crystallization is adopted as the crystallization, it is possible to reuse the filtrate generated in the crystallization by adding it to the recovery liquid.

[0074] When adding the filtrate to the recovery liquid, the filtrate may be heated as necessary. In the production method of this embodiment, by heating the filtrate and adding it to the recovery liquid, the temperature of the recovery liquid can be increased, the transfer of lithium ions from the extract to the recovery liquid can be promoted, and it becomes easier to recover lithium ions in the recovery liquid, so lithium hydroxide can be produced more efficiently. When heating the filtrate, it may be heated so that the temperature of the recovery liquid becomes a desired temperature. Also, for heating the filtrate, it is possible to use the exhaust heat of cooling crystallization and the surplus heat generated in evaporation crystallization, which are heat sources that can be used for heating the above-mentioned recovery liquid.

[0075] When adding the filtrate to the recovered liquid, although lithium ions may be contained in the filtrate as described above, impurities other than lithium ions are removed by the selective permeation membrane, so the filtrate can be reused without performing separate impurity removal.

[0076] When obtaining lithium hydroxide from the recovered liquid, the lithium hydroxide obtained by crystallization is usually lithium hydroxide monohydrate (LiOH·H2O). In the production method of the present embodiment, lithium hydroxide is separated from the filtrate by solid-liquid separation or the like, and the obtained lithium hydroxide can be used as it is according to the application, or can be further dehydrated and used. When dehydrating lithium hydroxide monohydrate, for example, it may be performed by ordinary drying such as heating or reduced pressure.

[0077] (Lithium Hydroxide Production Apparatus) FIGS. 1 and 2 are flowcharts showing a typical aspect of a lithium hydroxide production apparatus capable of performing the production method of lithium hydroxide of the present embodiment. In both figures, crystallization is assumed when separating lithium hydroxide from the recovered liquid. FIG. 1 is a flowchart when cooling crystallization is adopted, and FIG. 2 is a flowchart when evaporation crystallization is adopted.

[0078] The lithium hydroxide production apparatus shown in FIG. 1 includes a reaction tank 10 for mixing and reacting a stock solution and a base, a Li ion recovery tank 20 for recovering lithium ions, and a crystallization apparatus 22 as a separation apparatus for separating lithium hydroxide from the recovered liquid (lithium ion-containing recovered liquid B2) in which lithium ions are recovered in the Li ion recovery tank 20. In addition, an adsorption / desorption apparatus 11 using an adsorbent adopted as necessary, a hydrochloric acid preparation tank 12 for preparing hydrochloric acid to be supplied to the adsorption / desorption apparatus 11, a recovered liquid storage tank 21 for storing the recovered liquid, heat exchangers 23a, 23b, and 23c, and a drying apparatus 24 are provided.

[0079] As described above, the Li ion recovery tank 10 includes an extraction liquid tank 20a for storing the extraction liquid A1, a recovery liquid tank 20b for storing the recovery liquid B, and a Li selective permeable membrane 20c. The extraction liquid tank 20a and the recovery liquid phase 20b are partitioned by the Li selective permeable membrane 20c. The Li selective permeable membrane 20c is provided with a first electrode 20d (anode) on one main surface side (extraction liquid A1 side) and a second electrode 20e (cathode) on the other main surface side (recovery liquid B side). The recovery liquid storage tank 21 is provided with temperature adjusting means 21a capable of adjusting the temperature of the recovery liquid. Also, a pipe is provided for returning the lithium ion extraction liquid A2 from which lithium ions have been recovered from the extraction liquid tank 20a to the reaction tank 10.

[0080] The lithium hydroxide production apparatus shown in FIG. 2, similar to the production apparatus shown in FIG. 1, has a reaction tank 10, an adsorption / desorption apparatus 11, a hydrochloric acid preparation tank 12, a Li ion recovery tank 20, a recovery liquid storage tank 21 for storing the recovery liquid, a crystallization apparatus 22, heat exchangers 23a, 23b, and 23c, and a drying apparatus 24. The Li ion recovery tank 20 includes an extraction liquid tank 20a, a recovery liquid tank 20b, and a Li selective permeable membrane 20c. The Li selective permeable membrane 20c is provided with a first electrode 20d (anode) on one main surface side (extraction liquid A1 side) and a second electrode 20e (cathode) on the other main surface side (recovery liquid B side).

[0081] The production apparatus shown in FIG. 2 is different from the production apparatus of FIG. 1 in that, since the crystallization apparatus 22 employs evaporation crystallization, a recovery line is provided that uses the distilled water obtained by depressurizing the vapor generated from the crystallization apparatus 22 as the recovery liquid. In the Li ion recovery tank 20 of FIGS. 1 and 2, since oxygen and hydrogen can be generated in the extraction liquid tank 20a and the recovery liquid tank 20b by electrolysis of water, it is preferable to provide pipes and the like capable of exhausting and recovering them.

[0082] The reaction tank 10 is a tank in which the stock solution and the base are mixed, and in order to promote the reaction between the stock solution and the base, it is preferable that a stirrer is provided. The removal of the hydroxide generated by this reaction can be carried out by various filtrations such as suction filtration and decantation as described above. For example, filtration equipment and a tank for decantation may be provided between the reaction tank 10 and the adsorption and desorption device 11. Further, the reaction tank 10 may be provided with a discharge port for discharging the hydroxide generated by this reaction.

[0083] In FIGS. 1 and 2, in the reaction tank 10, the stock solution and the base are reacted by mixing, and the lithium ion extraction solution A0 obtained by removing the hydroxide is supplied to the adsorption and desorption device 11. The lithium ions contained in the extraction solution A0 are adsorbed, and the extraction solution A0' obtained by desorbing the lithium ions adsorbed on the adsorbent is supplied to the extraction solution tank 20a of the Li ion recovery tank 20. When the adsorption and desorption device 11 is not installed, the lithium ion extraction solution A0 discharged from the reaction tank 10 is directly supplied to the extraction solution tank 20a.

[0084] The reaction by mixing the stock solution and the base in the reaction tank 10 is carried out while adjusting the pH. For pH adjustment, as described above, preferably, the lithium ion extraction solution A2 from which lithium ions have been recovered from an electrochemical device having at least the Li ion recovery tank 20 equipped with the Li selective permeable membrane 20c and the recovery liquid storage tank 21 is used. Therefore, a pipe for sending the extraction solution A2 from the extraction solution tank 20a to the reaction tank 10 is provided in the electrochemical device, more specifically. A pump may be provided for sending the extraction solution A2, and a storage tank for temporarily storing the extraction solution A2 may also be provided.

[0085] When the adsorption and desorption device 11 is adopted, as described above, it is preferable to use chlorine generated when recovering lithium ions from the lithium ion extraction solution for desorbing the lithium ions adsorbed on the desorbent. When lithium ions are recovered from the lithium ion extraction solution in the lithium ion recovery tank 20, chlorine contained in the extraction solution is generated as a by-product. The generated chlorine D1 can be used as hydrochloric acid D2 in the hydrochloric acid preparation tank 12 and as an inorganic acid when desorbing lithium ions adsorbed on the adsorbent from the adsorbent in the adsorption and desorption device 11. Further, a storage tank may be provided to temporarily store the hydrochloric acid prepared in the hydrochloric acid preparation tank 12.

[0086] In the lithium ion recovery tank 20, the lithium ions contained in the extraction solution A1 are transferred from the extraction solution A1 to the recovery solution B1 using the Li selective permeable membrane 20c and recovered in the recovery solution B1. The recovery solution B1 is supplied as a lithium ion-containing recovery solution B2 to the crystallization device 22 via the recovery solution storage tank 21. In the manufacturing apparatus of FIGS. 1 and 2, a heat exchanger 23a for heating the lithium ion-containing recovery solution B2 to a predetermined temperature is provided. As the heat exchanger 23a, in addition to the shell and tube type heat exchanger using a medium as shown in FIG. 1, heat exchangers such as a jacket type and a heater type using electricity, a heat medium, etc. can be adopted. As the heat source, it is possible to use the exhaust heat of cooling crystallization, the surplus heat generated in evaporation crystallization, etc. The same applies to the heat exchangers 23b and 23c described later.

[0087] In the manufacturing apparatus of FIG. 1, lithium hydroxide crystallized in the crystallization apparatus 22 and the filtrate generated by crystallization are separated by solid-liquid separation or the like. The lithium hydroxide is further dried in the drying apparatus 24, and lithium hydroxide monohydrate (LiOH·H2O) is taken out as a product. Further, the filtrate C is heated as needed in the heat exchanger 23b together with newly supplied pure water as needed, and then, as a recovered liquid B0 substantially free of lithium ions, it passes through the recovered liquid storage tank 21, and after being heated as needed in the heat exchanger 23c as needed, it is supplied to the recovered liquid tank 20b of the Li ion recovery tank 20. Note that the fact that the recovered liquid B0 is substantially free of lithium ions means that if it does not contain the filtrate C, water such as pure water becomes the recovered liquid B0 and it contains none at all. Also, when it contains the filtrate C, although the filtrate C may contain lithium ions, the recovered liquid B1 stored in the recovered liquid tank 20b and the lithium ion-containing recovered liquid B2 supplied to the crystallization apparatus 12 are used to crystallize lithium hydroxide to remove lithium ions. Therefore, it means that the lithium ion content is low compared to these recovered liquids B1 and B2. Also, in the manufacturing apparatus of FIG. 2, since evaporation crystallization is employed, steam is discharged from the crystallization apparatus 22 by reducing the pressure or the like and cooled distilled water is recovered as the filtrate C. At the same time, since lithium hydroxide crystallized in the same manner as in the manufacturing apparatus of FIG. 1 and a liquid filtrate are generated, the liquid filtrate is also recovered as the filtrate C.

[0088] The Li ion recovery tank 20 may be in a form divided into an extraction liquid tank 20a and a recovered liquid tank 20b by a Li selective permeable membrane 20c in one tank, or may be in a form in which two tanks of the extraction liquid tank 20a and the recovered liquid tank 20b are connected via the Li selective permeable membrane 20c.

[0089] In the manufacturing apparatus of FIG. 1, the temperature adjustment is for the temperature of the recovered liquid in the recovery liquid tank 20b. To adjust the temperature of the recovered liquid B1 in the recovery liquid tank 20b, at least one of the heat exchangers 23b and 23c may be used before supplying the recovered liquid B0 to the recovery liquid tank 20b, or the temperature adjustment means 21a provided in the recovered liquid storage tank 21 may also be used. For example, when the manufacturing apparatus does not have the temperature adjustment means 21a, the temperature of the recovered liquid B0 at the outlet of at least one of the heat exchangers 23b and 23c is heated to be higher than a predetermined temperature, and the temperature of the recovered liquid in the recovery liquid tank 20b may be adjusted to the predetermined temperature. Also, when the temperature adjustment means 21a is provided and used, the temperature of the recovered liquid B0 at the outlet of the heat exchanger 23b does not have to be heated to the predetermined temperature. A temperature adjustment means corresponding to the temperature adjustment means 21a in the recovered liquid storage tank 21 may be provided in the recovery liquid tank 20b.

[0090] From the viewpoint of more reliably and stably adjusting the recovered liquid to a predetermined temperature, it is preferable to provide the temperature adjustment means 21a together with the heat exchanger 23b as shown in FIG. 1. Regarding the heat exchanger 23c, in addition to heating the recovered liquid B0, for example, when performing a batch operation in which the recovered liquid is circulated between the recovery liquid tank 20b and the recovered liquid storage tank 21 until the concentration of lithium ions contained in the recovered liquid B1 rises to a certain concentration, it is useful to provide it when adjusting the temperature of the recovered liquid in the recovery liquid tank 20b to a predetermined temperature.

[0091] Also, it is possible to adjust the temperature of the extract liquid as described above, and corresponding temperature heating means may be provided (not shown). In this case, similar to the recovered liquid, an extract liquid storage tank and a heat exchanger may be provided, and the extract liquid can be heated by the heat exchanger while circulating between the extract liquid tank 20a and the storage tank. Also, a heat exchanger may be provided in the extract liquid storage tank for heating, or a heat exchanger may be provided in the extract liquid tank 20a.

[0092] The manufacturing apparatus preferably includes a recovered liquid storage tank 21. By providing the recovery liquid storage tank 21, it becomes easier to perform a batch operation in which the recovery liquid is circulated between the recovery liquid tank 20b and the recovery liquid storage tank 21 until the concentration of lithium ions contained in the recovery liquid B1 as described above rises to a certain concentration. Also, various operations such as circulating and heating the recovery liquid at the start-up of the manufacturing apparatus and temporarily storing the filtrate as the recovery liquid and supplying it to the recovery liquid tank become possible. Further, by the combination of the heat exchanger 23c and the temperature adjusting means 21a, it becomes easier to heat the recovery liquid during the above-described batch operation and the circulation at the start-up of the manufacturing apparatus, and it is possible to more reliably and stably adjust the recovery liquid to a predetermined temperature.

[0093] The temperature adjusting means 21a is not particularly limited as long as it is means capable of adjusting the temperature of the recovery liquid. For example, it may be a heat exchanger or may be in the form of an air conditioner that heats the entire recovery liquid storage tank 21. When adopting a heat exchanger, there is no particular limitation on its type, and it may be appropriately selected according to the usage mode. Similar to the above-described heat exchangers 22a to c, for example, a shell and tube type heat exchanger using a medium, a jacket type heat exchanger using electricity, a heat medium, etc., a heater type heat exchanger, etc. can be adopted. In addition, when heating, as the heat source, it is possible to use the waste heat of cooling crystallization, the surplus heat generated in evaporation crystallization, etc.

[0094] When crystallization is adopted when separating lithium hydroxide from the lithium ion-containing recovery liquid B2, the crystallization apparatus 22 is preferably adopted. The crystallization apparatus 22 is an apparatus provided for crystallizing lithium hydroxide from the recovery liquid (lithium ion-containing recovery liquid) in which lithium ions are recovered in the Li ion recovery tank 20. For crystallization, for example, in the case of a batch operation in which the recovery liquid is circulated between the recovery liquid tank 20b and the recovery liquid storage tank 21 until the concentration of lithium ions contained in the above-described recovery liquid B1 rises to a certain concentration, after rising to the certain concentration, a part or all of the recovery liquid B1 may be withdrawn as the lithium ion-containing recovery liquid B2 and sent to the crystallization apparatus 22 for operation.

[0095] As described above, since the crystallization method employed in the crystallization apparatus 22 may be cooling crystallization, evaporation crystallization, or the like, an apparatus suitable for the form of crystallization may be adopted, and a commercially available crystallization apparatus may also be used. In addition, the crystallization apparatus 22 may be provided with an apparatus for separating the crystallized lithium hydroxide and the filtrate, such as a solid-liquid separation device, if necessary.

[0096] When cooling crystallization is adopted as the crystallization method, as in the manufacturing apparatus of FIG. 1, an inert gas supply line, a pressure control valve for exhausting according to the pressure in the crystallization apparatus 22, and an exhaust line for maintaining a positive pressure by supplying and exhausting an inert gas may be provided. When evaporation crystallization is adopted as the crystallization method, as in the manufacturing apparatus of FIG. 2, a pressure reducing device for discharging the filtrate generated in the apparatus as water vapor may be provided, and a cooling device for cooling the filtrate discharged as water vapor into a liquid filtrate, that is, distilled water, may also be provided.

[0097] The drying apparatus 24 is an apparatus for drying lithium hydroxide containing moisture that could not be completely separated by solid-liquid separation or the like after separating the crystallized lithium hydroxide and the filtrate in the crystallization apparatus 22 into lithium hydroxide monohydrate (LiOH·H2O) or anhydrous lithium hydroxide. The dryer used in the drying apparatus 24 may be appropriately selected according to the desired drying condition, scale, etc. For example, a heater such as a hot plate, a horizontal dryer having a heating means and a feeding mechanism, a horizontal vibration fluidized dryer, or a Henschel mixer or FM mixer commercially available that can dry while heating at about 50 to 140 °C and stirring under a reduced pressure atmosphere of usually about 1 to 80 kPa can also be used.

[0098] (Method for producing lithium sulfide) The lithium hydroxide obtained by the method for producing lithium hydroxide of the present embodiment can be used as a raw material for lithium sulfide. That is, the method for producing lithium hydroxide of the present embodiment can be applied to the method for producing lithium sulfide. Specifically, it can be applied to a method for producing lithium sulfide including producing lithium hydroxide by the method for producing lithium hydroxide of the above-described present embodiment and supplying hydrogen sulfide to the obtained lithium hydroxide.

[0099] When supplying hydrogen sulfide to lithium hydroxide, for example, lithium hydroxide and hydrogen sulfide gas are introduced into a reaction vessel and reacted while stirring or the like to obtain lithium sulfide. In this case, the lithium hydroxide may be a hydrate or an anhydride, and considering efficiency, it is preferable to react with hydrogen sulfide as a hydrate.

[0100] The reaction temperature between lithium hydroxide and hydrogen sulfide is usually preferably from 120°C to 300°C, more preferably from 140°C to 230°C, still more preferably from 150°C to 220°C, and even more preferably from 160°C to 210°C. When the reaction temperature is within the above range, the reaction is promoted, and high-purity lithium sulfide with a reduced amount of residual lithium hydroxide is easily obtained. Also, it is preferably from 1 hour to 60 hours, more preferably from 2 hours to 30 hours, and still more preferably from 6 hours to 20 hours. In this specification, the reaction time means the time for contacting hydrogen sulfide with lithium hydroxide to cause a reaction, and more specifically, the time from the start of supplying hydrogen sulfide to the stop of supplying hydrogen sulfide.

[0101] Also, it is possible to produce lithium sulfide by supplying hydrogen sulfide to the recovered liquid in the method for producing lithium hydroxide of the above-described present embodiment. There is no particular limitation on the method for supplying hydrogen sulfide. When supplying to the recovered liquid, hydrogen sulfide gas may be blown into the recovered liquid. When lithium sulfide and water are generated by the reaction between lithium hydroxide and hydrogen sulfide, the generated water is appropriately removed, and the blowing of hydrogen sulfide is stopped when substantially all the water has been removed to obtain lithium sulfide.

[0102] When supplying to the recovered liquid, hydrogen sulfide gas may be supplied to the crystallization device of the lithium hydroxide production apparatus described above, that is, hydrogen sulfide gas may be blown into the recovered liquid containing lithium ions for reaction, or the recovered liquid containing lithium ions may be separately supplied to a reaction vessel, and hydrogen sulfide gas may be blown into the reaction vessel for reaction in either a closed system (batch type) or a flow system.

[0103] The lithium sulfide thus obtained can be purified as necessary. The purification method is not particularly limited and may be carried out according to a conventional method.

Example

[0104] Next, the present invention will be specifically described by way of examples, but the present invention is not limited by these examples in any way.

[0105] (Measurement of element content) After collecting 1 mL of the sample in a fluororesin container, it was diluted with about 10 mL of ultrapure water, 5 mL of nitric acid was added and dissolved, and heated on a hot plate at 120 °C for 10 minutes. After cooling to room temperature, it was appropriately diluted according to the element concentration contained in the sample, and the content of various elements contained in the sample such as the lithium ion extract was measured by the calibration curve method or the standard addition method using an ICP emission spectroscopic analyzer (「5100 ICP - OES (model number)」, manufactured by Agilent Technologies, Inc.).

[0106] Preparation example (Preparation of stock solution) 3 L of geothermal water around the Salton Sea was stirred, allowed to stand for one week, and then the supernatant was collected as the stock solution (Table 1).

[0107] Example 1 (Preparation of lithium ion extract) 9 mL of the above stock solution (pH 2) was collected, 1 mL of 1 M aqueous sodium hydroxide solution was added, and the mixture was reacted by stirring to perform the first mixing (pH 7). After stirring, suction filtration was performed using a hydrophilic membrane filter (made of PTFE, pore size 0.45 μm) to carry out solid-liquid separation. 1 mL of the filtrate was collected in a fluororesin container, diluted with approximately 10 mL of ultrapure water, 5 mL of nitric acid was added and dissolved, and it was heated on a hot plate at 120 °C for 10 minutes. After cooling to room temperature, it was appropriately diluted according to the element concentration contained in the sample, and the content of the element was measured by the standard addition method using an ICP emission spectroscopic analyzer. The results are shown in Table 1. Next, 2 g of sodium hydroxide (granular) was added to 10 mL of the above filtrate (pH 7), and the mixture was reacted by stirring to perform the second mixing (pH 14). After stirring, suction filtration was performed using a hydrophilic membrane filter (made of PTFE, pore size 0.45 μm) to carry out solid-liquid separation, and a lithium ion extract was obtained. 1 mL of the obtained extract was collected in a fluororesin container, and the content of the element was measured by the standard addition method using an ICP emission spectroscopic analyzer in the same manner as above. The results are shown in Table 1.

[0108]

Table 1

[0109] From the above results, it was confirmed that iron, lead, and zinc were removed as hydroxides by the first mixing (pH 7), and calcium, iron, magnesium, manganese, strontium, and zinc were removed as hydroxides by the second mixing (pH 14).

[0110] (Lithium Ion Recovery Device) As the lithium ion recovery device used in the lithium ion recovery of Example 2, the recovery device shown in Figure 3 was used. The lithium ion recovery device shown in Figure 3 includes a Li separation membrane cell 30 equipped with a Li separation membrane 31 sandwiched between a positive electrode 32 and a negative electrode 33, a donor liquid tank 34, a donor liquid circulation pump 35, a recovered liquid tank 36, and a recovered liquid circulation pump 37. The Li separation membrane cell 30 has a structure in which a Li separation membrane laminate 31 (material: LLTО) inserted between current collectors (material: carbon) is sandwiched between a positive electrode 32 (material: platinum) and a negative electrode 33 (material: platinum). Electric power can be supplied to the positive electrode 32 and the negative electrode 33 by a constant voltage power source. By supplying electric power, Li ions are recovered from the stock solution in the positive electrode chamber to the recovered solution in the negative electrode chamber. The donor solution from which lithium ions are to be recovered is supplied to the donor solution tank 34 and can be circulated between the positive electrode chamber of the Li separation membrane cell 30 and the donor solution tank 34 by the donor solution circulation pump 35. Further, the recovered solution that recovers lithium ions from the donor solution is supplied to the recovered solution tank 36 and can be circulated between the negative electrode chamber of the Li separation membrane cell 30 and the recovered solution tank 36 by the recovered solution circulation pump 37.

[0111] Example 2 (Lithium Ion Recovery Test) In Example 1, lithium ions were recovered using the lithium ion extract obtained by the above second mixing. As the lithium ion recovery device, the device shown in FIG. 3 was used. In Example 1, 100 mL of the lithium ion extract obtained by the above second mixing was placed in the donor solution tank 34 as the donor solution to the lithium recovery device, and pure water was placed in the recovered solution tank 36 as the recovered solution. The donor solution was circulated using the donor solution circulation pump 35, and the recovered solution was circulated using the recovered solution circulation pump 37. When a voltage of 5 V was applied by a constant voltage power source, the current value flowing between the positive electrode and the negative electrode was measured, and the lithium recovery amount was measured. The maximum current value was 2.4 mA as shown in FIG. 4. After applying the voltage for 120 hours, the current value became almost 0, and the lithium recovery rate at that time was 30 mass% (recovery amount: 9.3 mg). Here, the lithium recovery rate means the ratio of the amount of lithium element in the recovered solution after lithium recovery to the amount of lithium element in the donor solution before lithium recovery. The change in the lithium recovery amount over time is shown in FIG. 5. Thus, it was found that lithium ions can be recovered from the lithium ion extract by using the recovery device shown in FIG. 3.

[0112] Example 3 (Reuse of the feed solution after lithium recovery) Since the feed solution from which lithium ions have been recovered (the lithium ion extract obtained in Example 1) has a high pH, it can be reused for adjusting the pH of the geothermal water used as the stock solution in Example 1. 10 mL of the feed solution (lithium extract, pH 14) after the lithium ion recovery test of Example 2 was added to 100 mL of the stock solution (geothermal water, pH 2), and the mixture was reacted by stirring to perform the first mixing (pH 7). After stirring, suction filtration was carried out using a hydrophilic membrane filter (made of PTFE, pore size 0.45 μm) to perform solid-liquid separation. 1 mL of the filtrate was collected in a fluororesin container, and the content of the elements was measured by the standard addition method using an ICP emission spectrometer (model number "5100 ICP-OES", manufactured by Agilent Technologies) in the same manner as in Example 1. The results are shown in Table 2. Next, 50 mL of the feed solution (lithium extract, pH 14) after the lithium ion recovery test of Example 2 was added to 10 mL of the above filtrate (pH 7), and the mixture was reacted by stirring to perform the second mixing (pH about 14). After stirring, suction filtration was carried out using a hydrophilic membrane filter (made of PTFE, pore size 0.45 μm) to perform solid-liquid separation, and a lithium ion extract was obtained. 1 mL of the obtained extract was collected in a fluororesin container, and the content of the elements was measured by the standard addition method using the above ICP emission spectrometer (model number "5100 ICP-OES", manufactured by Agilent Technologies) in the same manner as above. The results are shown in Table 2. From the above results, it was confirmed that the feed solution (lithium ion extract) from which lithium ions have been recovered can be reused for removing impurities by adjusting the pH of the geothermal water.

[0113]

Table 2

[0114] Example 4 (Production of lithium hydroxide) 100 mL of the lithium recovery solution obtained in the lithium ion recovery test of Example 2 was heated and concentrated at 100 °C on a hot plate under a nitrogen atmosphere until dry, and 9 mg of lithium hydroxide monohydrate (LiOH·H₂O) was obtained. As a result of measurement using an X-ray diffractometer (“D8 DISCOVER Plus” (trade name), manufactured by Bruker), since the obtained peaks were consistent with those of lithium hydroxide monohydrate (ICDD card number: 01-076-1073), it was confirmed that the obtained solid was lithium hydroxide monohydrate. Also, 5 mg of the obtained lithium hydroxide monohydrate was weighed into a fluororesin container, diluted with about 10 mL of ultrapure water, 5 mL of nitric acid was added and dissolved, and it was heated on a hot plate at 120 °C for 10 minutes. After cooling to room temperature, it was diluted, and the Li content was measured by the calibration curve method using an ICP emission spectrometer (“5100 ICP-OES” (model number), manufactured by Agilent Technologies, Inc.). As a result, it was 16.5% by mass, and it was confirmed that it was the same as the theoretical content of lithium hydroxide monohydrate (LiOH·H₂O).

[0115] Comparative Example 1 In Example 2 above, lithium ions were recovered in the same manner as in Example 1, except that the stock solution prepared in the preparation example was used without using the lithium ion extract obtained by the second mixing obtained in Example 1. When a voltage of 5 V was applied by a low-voltage power supply, the current value flowing between the positive and negative electrodes was measured, and the lithium recovery amount was measured. The maximum current value was 1.2 mA, and the current value 1 hour after the voltage was applied was 0.1 mA. The current value became almost 0 12 hours after the voltage was applied. The reason why the maximum current value in Comparative Example 1 is small is considered to be that since it was not mixed with a base by the first mixing and the second mixing, the influence of ions other than lithium ions and the reaction of lithium ions on the surface of the selective permeable membrane did not occur efficiently. From the above results, according to the method for producing lithium hydroxide of the present embodiment, since lithium ions can be efficiently recovered, it was confirmed that an aqueous solution containing lithium can be widely used as a stock solution, and high-purity lithium hydroxide can be efficiently produced from the stock solution.

Explanation of Symbols

[0116] 10. Reaction tank 11. Adsorption / desorption device 12. Hydrochloric acid preparation tank 20. Li ion recovery tank 20a. Extract tank 20b. Recovery liquid tank 20c. Li selective permeable membrane 20d. First electrode 20e. Second electrode 21. Recovery liquid storage tank 21a: Temperature control means 22. Crystallization device 23a. Heat exchanger 23b. Heat exchanger 23c. Heat exchanger 24. Drying device 30. Li separation membrane cell 31. Li separation membrane 32. Positive electrode 33. Negative electrode 34. Feed liquid tank 35. Feed liquid circulation pump 36. Recovery liquid tank 37. Recovery liquid circulation pump A0: Lithium ion extract A0’: Lithium ion extract (after adsorption / desorption) A1: Lithium ion extract (in the extract tank) A2: Lithium ion extract from which lithium ions have been recovered B0: Recovery liquid B1: Recovery liquid (in the recovery liquid tank) B2: Recovery liquid containing lithium ions C: Filtrate D1: Chlorine D2: Hydrochloric acid

Claims

1. First mixing, which involves adjusting the pH to 6 or higher and 10 or lower and mixing an aqueous solution containing lithium and at least one element other than lithium and a base in a reaction tank; and second mixing, which involves adjusting the pH to 12 or higher and mixing, and removing hydroxides of elements other than lithium generated by the first mixing and the second mixing to obtain a lithium ion extract; recovering only lithium ions into a recovery liquid using an electrochemical device equipped with a Li selective permeable membrane from the lithium ion extract; and performing the pH adjustment by returning the lithium ion extract from which lithium ions have been recovered by the electrochemical device to the reaction tank; A method for producing lithium hydroxide, comprising the above steps.

2. The method for producing lithium hydroxide according to claim 1, wherein obtaining the lithium ion extract includes concentrating lithium ions.

3. The method for producing lithium hydroxide according to claim 2, wherein concentrating the lithium ions is performed by adsorbing the lithium ions using an adsorbent.

4. The method for producing lithium hydroxide according to claim 3, wherein the gas generated from the electrochemical device is used for desorbing the lithium ions adsorbed to the adsorbent.

5. The method for producing lithium hydroxide according to claim 4, wherein the gas is chlorine.

6. The method for producing lithium hydroxide according to any one of claims 1 to 5, further comprising separating lithium hydroxide from the recovery liquid.

7. The method for producing lithium hydroxide according to claim 6, wherein the separation is performed by crystallization.

8. The method for producing lithium hydroxide according to any one of claims 1 to 7, wherein the at least one element other than lithium is at least one element selected from calcium, magnesium, strontium, manganese, iron, zinc, and lead.

9. The method for producing lithium hydroxide according to any one of claims 1 to 8, wherein the base is at least one selected from alkali metal hydroxides and alkaline earth metal hydroxides.

10. The method for producing lithium hydroxide according to any one of claims 1 to 9, wherein the Li selective permeable membrane contains an oxide or oxynitride containing lithium.

11. The method for producing lithium hydroxide according to any one of claims 3 to 10, wherein the adsorbent is at least one selected from a titanium oxide-based adsorbent, a manganese oxide-based adsorbent, an antimony oxide-based adsorbent, an aluminum oxide-based adsorbent, and an ion exchange resin.

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