Method for suppressing formation of lithium carbonate, method for storing lithium hydroxide solution, method for producing lithium hydrogen solution, method for producing lithium hydroxide, and storage container for lithium hydroxide solution

Abstract

A method for suppressing the formation of lithium carbonate in a lithium hydroxide solution, the method comprising storing the lithium hydroxide solution in a storage container having an interior atmosphere with a lower CO2 concentration than air and having a positive pressure.

Description

Method for suppressing formation of lithium carbonate, method for storing lithium hydroxide solution, method for producing lithium hydroxide solution, method for producing lithium hydroxide, and storage container for lithium hydroxide solution ,

[0006] ,

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[0001] This specification describes a method for suppressing formation of lithium carbonate, a method for storing lithium hydroxide solution, a method for producing lithium hydroxide solution, a method for producing lithium hydroxide, and a storage container for lithium hydroxide solution.

[0002] For example, in processes for extracting metals from lithium-ion battery waste, various electronic devices, salt lake brine, ores, etc., a lithium salt solution may be obtained, and a lithium hydroxide solution may be prepared from the lithium salt solution.

[0003] As an example, in a process for recovering metals from lithium-ion battery waste, the battery powder of lithium-ion battery waste is leached with an inorganic acid such as sulfuric acid, and when a predetermined metal is separated from the metal-containing solution as the leachate by neutralization, solvent extraction, etc., a lithium salt solution such as a lithium sulfate solution may be obtained. Then, when the lithium sulfate solution is subjected to a hydroxylation treatment such as electrodialysis, a lithium hydroxide solution is obtained. The lithium hydroxide solution may be used as a pH adjuster during the above process or used for precipitation of lithium hydroxide by a crystallization operation. Examples of documents describing such processes include Patent Documents 1 to 3.

[0004] Japanese Patent Application Laid-Open No. 2024-053446, Japanese Patent Application Laid-Open No. 2024-537274, International Publication No. 2024 / 014521

[0005] By the way, if the lithium hydroxide solution is stored as it is in a simple container without any countermeasures, lithium carbonate may be formed during the storage. Lithium carbonate formed in the lithium hydroxide solution may cause problems or troubles in the process such as clogging the piping through which the lithium hydroxide solution is sent, and may also reduce the purity of lithium hydroxide obtained by a crystallization operation using the lithium hydroxide solution.

[0006] This specification provides a method for suppressing the formation of lithium carbonate in a lithium hydroxide solution, a method for storing a lithium hydroxide solution, a method for producing a lithium hydroxide solution, a method for producing lithium hydroxide, and a storage container for a lithium hydroxide solution.

[0007] The method for suppressing the formation of lithium carbonate described in this specification is a method for suppressing the formation of lithium carbonate in a lithium hydroxide solution, and involves storing the lithium hydroxide solution in a storage container that is under positive pressure and has an atmosphere of CO2 concentration lower than that of air.

[0008] The method for storing lithium hydroxide solution described in this specification involves storing the lithium hydroxide solution in the storage container described above, using the lithium carbonate generation suppression method described above.

[0009] The method for producing a lithium hydroxide solution described in this specification involves generating a lithium hydroxide solution from a lithium-containing solution containing anions of an inorganic acid and lithium ions, and then storing the lithium hydroxide solution in the storage container using the lithium carbonate generation suppression method described above.

[0010] The method for producing lithium hydroxide described in this specification involves using the above-mentioned method for suppressing the formation of lithium carbonate to precipitate lithium hydroxide from the lithium hydroxide solution inside the storage container, which serves as a crystallization vessel.

[0011] The storage container described in this specification is a storage container for lithium hydroxide solution, comprising: a container body for storing lithium hydroxide solution; a gas supply port provided in the container body that allows low CO2 gas, which has a CO2 concentration lower than that of air, to flow into the interior of the storage container; a gas outlet provided in the container body that allows the internal gas of the storage container to be discharged to the outside of the storage container; and a sealing mechanism that can maintain airtightness inside the storage container.

[0012] The method for suppressing the formation of lithium carbonate described in this specification can effectively suppress the formation of lithium carbonate in a lithium hydroxide solution.

[0013] This is a schematic diagram showing an example of a storage container that can be used in the lithium carbonate generation suppression method according to one embodiment. This is a schematic diagram showing another example of a storage container. This is a flow chart showing an example of treatment for lithium-ion battery waste that can be treated in the lithium carbonate generation suppression method according to one embodiment.

[0014] The following describes in detail the above-mentioned method for suppressing the generation of lithium carbonate, the method for storing lithium hydroxide solution, the method for producing lithium hydroxide solution, the method for producing lithium hydroxide, and embodiments of storage containers for lithium hydroxide solution.

[0015] One embodiment of the method for suppressing the formation of lithium carbonate is a method for suppressing the formation of lithium carbonate in a lithium hydroxide solution. In this method, the lithium hydroxide solution is stored in a storage container that is under positive pressure and has a CO2 concentration lower than that of air.

[0016] If a lithium hydroxide solution is stored in contact with air, carbon dioxide in the air may be absorbed into the lithium hydroxide solution, and lithium carbonate may be produced in the solution through a reaction between carbon dioxide and lithium ions. The lithium carbonate produced in the lithium hydroxide solution may clog the piping that carries the lithium hydroxide solution, and may also reduce the purity of the lithium hydroxide obtained by crystallization of the lithium hydroxide solution.

[0017] In contrast, in the above embodiment, the lithium hydroxide solution is stored in a storage container that has a CO2 concentration lower than that of air and is under positive pressure, thereby suppressing the reaction of lithium ions with carbon dioxide and the resulting formation of lithium carbonate. As a result, according to this embodiment, the formation of lithium carbonate in the lithium hydroxide solution can be effectively suppressed.

[0018] (Suppression of lithium carbonate generation) In the method for suppressing the generation of lithium carbonate in this embodiment, a storage container 1 such as the one shown in Figure 1 may be used.

[0019] The storage container 1 has a bottomed cylindrical or rectangular or other cylindrical container body 2 capable of storing lithium hydroxide solution LHS, and a gas supply port 3 and a gas outlet 4 provided on the upper side of the container body 2. The location of the gas supply port 3 and / or gas outlet 4 on the container body 2 is not limited to the upper wall as shown in the figure, but may be, for example, the side wall, but it is desirable that in most cases the location be above the liquid level when lithium hydroxide solution LHS is stored in the container body 2.

[0020] A gas supply pipe 5, connected to a gas supply source (not shown), is connected to the gas supply port 3. Low-CO2 gas is supplied from the gas supply source to the container body 2 via the gas supply pipe 5 and the gas supply port 3, as indicated by the arrows in Figure 1. This allows the gas supply port 3 to allow low-CO2 gas to flow into the storage container 1.

[0021] On the other hand, a gas discharge pipe 6 is connected to the gas outlet 4. The gas inside the storage container 1 can be discharged to the outside of the storage container 1 through the gas discharge pipe 6 via the gas outlet 4, as shown by the arrow in Figure 1.

[0022] Low CO2 gas refers to gas with a CO2 concentration lower than the CO2 concentration of the air surrounding the outside of the storage container 1 (for example, 410 ppm by volume). Low CO2 gas can be any gas with a CO2 concentration lower than air, and it is possible to use an inert gas such as nitrogen gas, but from the viewpoint of reducing costs, it is preferable to use low CO2 gas obtained by removing at least a portion of carbon dioxide from air. Such low CO2 gas can be obtained, for example, by a PSA (Pressure Swing Adsorption) type carbon dioxide removal device used when producing nitrogen gas. The CO2 concentration of the low CO2 gas can be, for example, less than 100 ppm by volume, preferably less than 30 ppm by volume, and more preferably less than 10 ppm by volume.

[0023] Furthermore, the storage container 1 shall have a sealing mechanism that makes the inside of the storage container airtight. In the illustrated example, the container body 2 has virtually no points of communication with the outside, except for the gas supply port 3, the gas outlet port 4, and the connection points to the concentration meter 9 and pressure gauge 10, which will be described later. On-off valves 7 and 8 are provided in the middle of the gas supply pipe 5 and the gas outlet pipe 6 as the sealing mechanism described above. In this case, the inside of the storage container can be made airtight by closing the on-off valves 7 and 8, respectively. Although not shown in the illustration, the container body may have a lid member, and when the lid member is closed, it may be configured so that the inside of the storage container can be made airtight by the sealing mechanism.

[0024] Furthermore, the storage container 1 may have a concentration meter 9 for measuring the CO2 concentration of its internal atmosphere and / or a pressure gauge 10 for measuring the internal pressure of the storage container 1. In this case, the concentration meter 9 can determine the CO2 concentration of the internal atmosphere in the storage container 1, and the pressure gauge 10 can determine the internal pressure of the storage container 1. The connection between the container body 2 and the concentration meter 9 or pressure gauge 10 can be located above the liquid level of the lithium hydroxide solution LHS on the upper wall or side wall, similar to the location where the gas supply port 3 and / or gas outlet 4 are provided, or it may be located in the middle of the gas outlet pipe 6.

[0025] Furthermore, the on-off valves 7 and 8 can be solenoid valves. In this case, the on-off valve 7 installed in the gas supply pipe 5 is electrically connected to the pressure gauge 10 and can be configured to be closed when the pressure is above a predetermined set pressure, but to open when the pressure falls below the set pressure. Also, the on-off valve 8 installed in the gas discharge pipe 6 is electrically connected to the concentration meter 9 and can be used to control the internal atmosphere of the storage container 1 so that it reaches a predetermined CO2 concentration.

[0026] To store lithium hydroxide solution LHS in such a storage container 1, for example, after putting lithium hydroxide solution LHS into the storage container 1, low CO2 gas can be supplied into the storage container 1 via the gas supply pipe 5 and gas supply port 3, and the internal gas of the storage container 1 can be discharged via the gas outlet 4 and gas discharge pipe 6. As a result, the air present in the storage container 1 is discharged and the storage container 1 is filled with low CO2 gas. In other words, the air inside the storage container 1 is purged with low CO2 gas.

[0027] Then, for example, by restricting the on / off valve 8 installed on the gas discharge pipe 6, the supply amount of low CO2 gas is made greater than the discharge amount of internal gas, and with the inside of the storage container 1 under positive pressure due to the supply of low CO2 gas, the storage container 1 is sealed with a sealing mechanism (by closing the on / off valves 7 and 8 in the illustrated example). This makes it possible to create an atmosphere inside the storage container 1 with a CO2 concentration lower than that of air, and under positive pressure (i.e., an internal pressure higher than 0 Pa).

[0028] By creating an atmosphere with a CO2 concentration lower than that of air inside the storage container 1, the reaction between lithium ions in the lithium hydroxide solution LHS and carbon dioxide in that atmosphere, and the resulting formation of lithium carbonate, can be suppressed compared to an atmosphere with a CO2 concentration similar to that of air. Furthermore, by maintaining positive pressure inside the storage container 1, the inflow of air from the outside is suppressed. As a result, the formation of lithium carbonate in the lithium hydroxide solution can be effectively suppressed.

[0029] The CO2 concentration in the internal atmosphere of the storage container 1 is preferably, for example, less than 100 ppm by volume, more preferably less than 30 ppm by volume, and particularly preferably less than 10 ppm by volume. In this case, since the CO2 concentration is sufficiently low, the formation of lithium carbonate is suppressed even more effectively. The CO2 concentration in the internal atmosphere can be measured by the concentration meter 9.

[0030] While the lithium hydroxide solution LHS is stored in the storage container 1, it is preferable to monitor the CO2 concentration of the internal atmosphere of the storage container 1 by, for example, measuring the CO2 concentration periodically, irregularly, or continuously using a concentration meter 9. If the monitoring reveals an increase in the CO2 concentration of the internal atmosphere, measures such as checking the airtightness of the storage container 1, purging with low-CO2 gas with the on / off valves 7 and 8 open can be taken.

[0031] The internal pressure of the storage container 1 is preferably 10 Pa or higher, and more preferably 100 Pa or higher. This is because such a high internal pressure sufficiently suppresses the intrusion of outside air, thereby continuously keeping the CO2 concentration in the internal atmosphere low.

[0032] While the lithium hydroxide solution LHS is stored in the storage container 1, it is preferable to monitor the internal pressure of the storage container 1 by, for example, measuring the internal pressure periodically, irregularly, or continuously using a pressure gauge 10. Depending on the internal pressure state that can be ascertained, if necessary, the airtightness of the storage container 1 can be checked, the internal pressure can be increased by opening the on / off valve 7 or supplying low CO2 gas from the gas supply port 3.

[0033] As described above, by storing the lithium hydroxide solution LHS in the storage container 1, the lithium hydroxide solution LHS can be stored for a predetermined period of time. In this case, for the reasons mentioned earlier, the generation of lithium carbonate during this storage period is effectively suppressed. In this case, the storage container 1 in which the lithium hydroxide solution LHS is stored corresponds to the storage container for the lithium hydroxide solution LHS.

[0034] Furthermore, in producing the lithium hydroxide solution, after generating the lithium hydroxide solution LHS from a lithium-containing solution containing inorganic acid anions and lithium ions by the hydroxylation method described later, the lithium hydroxide solution LHS can be stored in the storage container 1 as described above. In this case as well, the formation of lithium carbonate in the lithium hydroxide solution LHS produced by hydroxylation is effectively suppressed.

[0035] Furthermore, the method for suppressing the formation of lithium carbonate described above can also be used in crystallization to obtain lithium hydroxide (crystals) from lithium hydroxide solution LHS. In this case, by storing the lithium hydroxide solution LHS in a storage container 1, which serves as a crystallization vessel, as previously described, the formation of lithium carbonate in the lithium hydroxide solution LHS before, during, and after crystallization can be suppressed. Details of the crystallization operation will be described later.

[0036] Incidentally, as shown in Figure 2, the storage container 11 may include a container body 12 comprising two or more tanks 12a and 12b, and a connecting pipe 12c that connects these multiple tanks 12a and 12b in series from tank 12a, which is provided with a gas supply port 13, to tank 12b, which is provided with a gas outlet 14.

[0037] If there are multiple tanks 12a and 12b, multiple types of lithium hydroxide solutions LHS1 and LHS2 (for example, lithium hydroxide solutions obtained by electrodialysis or chemical conversion methods described later, lithium hydroxide solutions as crystallization solutions, etc.) with different components, concentrations, pH levels, etc., can be stored in each of the tanks 12a and 12b. Furthermore, since the multiple tanks 12a and 12b are connected by a connecting pipe 12c, the CO2 concentration in the internal atmosphere of each tank 12a and 12b can be reduced and the internal pressure increased in a single operation.

[0038] Each of the multiple tanks 12a and 12b can be equipped with a concentration meter 19a, 19b and a pressure gauge 20. In the illustrated example, a concentration meter 19a is provided in tank 12a, which is equipped with a gas supply port 13, while a concentration meter 19b and a pressure gauge 20 are provided in tank 12b, which is equipped with a gas outlet port 14. When the on / off valves 17 and 18 are controlled as solenoid valves, the concentration meter 19b of tank 12b can be electrically connected to the on / off valve 17 of the gas supply pipe 15, and the pressure gauge 20 of the same tank 12b can be electrically connected to the on / off valve 18 of the gas outlet pipe 16.

[0039] For example, due to frequent addition and removal of lithium hydroxide solution LHS2, the liquid level and internal pressure of the lithium hydroxide solution LHS2 fluctuate significantly. It is preferable to position the tank 12b that stores the lithium hydroxide solution LHS2 on the exhaust side of the series-connected tanks 12a and 12b, as shown in the illustrated example. For example, if a large amount of lithium hydroxide solution LHS1 or LHS2 is withdrawn from tank 12a or 12b at once, the inside of tank 12a or 12b may become negatively pressurized. If the negative pressure occurs in the exhaust-side tank 12b, backflow of gas from the exhaust-side tank 12b to the supply-side tank 12a is less likely to occur. In the storage container 11 illustrated in Figure 2, the tank 12b with the gas outlet corresponds to the exhaust-side tank 12b mentioned above.

[0040] The other components of the storage container 11 in Figure 2 can be substantially the same as those of the storage container 1 in Figure 1, so a further explanation will be omitted.

[0041] (Treatment of lithium-ion battery waste) The lithium carbonate generation suppression method, lithium hydroxide solution storage method, lithium hydroxide solution production method, lithium hydroxide production method, and storage container 1 described above may be used, for example, in the treatment of lithium-ion battery waste.

[0042] In the treatment of lithium-ion battery waste, as shown in Figure 3 as an example, pretreatment of the lithium-ion battery waste is performed to obtain battery powder, and then acid leaching, neutralization, extraction, hydroxide oxidation, and crystallization are carried out on the battery powder in this order. The details are described below.

[0043] The lithium-ion battery waste targeted is lithium-ion secondary batteries that can be used in mobile phones and various other electronic devices, and that have been discarded due to the battery product's lifespan, manufacturing defects, or other reasons. Recovering valuable metals from such lithium-ion battery waste is desirable from the perspective of effective resource utilization. Lithium-ion battery waste refers to lithium-ion batteries that are subject to recycling, regardless of whether the lithium-ion batteries are traded for a price, free of charge, or treated as industrial waste.

[0044] Lithium-ion battery waste has a housing containing aluminum as an exterior that wraps around it. Examples of such a housing include those made of only aluminum, as well as those containing aluminum and iron, aluminum laminate, etc. Further, the lithium-ion battery waste may contain, within the aforementioned housing, a positive electrode active material composed of a single metal oxide containing lithium and one selected from the group consisting of nickel, cobalt, and manganese, or a composite metal oxide containing two or more of them, etc., and may include an aluminum foil (positive electrode substrate) coated and fixed with, for example, polyvinylidene fluoride (PVDF) or other organic binders. Additionally, lithium-ion battery waste may contain copper, iron, etc. Further, inside the housing of the lithium-ion battery waste, there is usually a electrolytic solution in which an electrolyte such as lithium hexafluorophosphate is dissolved in an organic solvent. As the organic solvent, for example, ethylene carbonate, diethyl carbonate, etc. may be used.

[0045] In many cases, pretreatment is performed on lithium-ion battery waste. The pretreatment may include at least one of heat treatment, crushing, and sieving. Lithium-ion battery waste becomes battery powder through pretreatment. The heat treatment, crushing, and sieving of the pretreatment may be performed separately as needed, or may be performed in any order. Battery powder means powder in which some pretreatment is performed on lithium-ion battery waste and the positive electrode material components are separated and concentrated.

[0046] In heat treatment, for example, using a stationary furnace, a rotary kiln furnace, or other furnace, the above lithium-ion battery waste may be heated in an air atmosphere or an inert atmosphere within a temperature range of 450°C to 1000°C for 0.5 hours to 4 hours. Thereby, at least a part of the electrolytic solution is removed, and the organic binder may be decomposed. In crushing, using a crusher such as an impact type, the housing of the lithium-ion battery waste is destroyed, and the positive electrode active material is selectively separated from the aluminum foil coated with the positive electrode active material. In sieving, sieving is performed using a sieve with an appropriate mesh size.

[0047] The battery powder obtained in the pretreatment is leached with an acidic leaching solution containing sulfuric acid, hydrochloric acid, nitric acid or other inorganic acids by acid leaching. Thereby, a solution in which metals in the battery powder are dissolved (metal-containing solution) and a leaching residue that remains undissolved are obtained. Here, the treatment after acid leaching is also referred to as a wet treatment.

[0048] When the metal-containing solution obtained by acid leaching contains aluminum ions and / or iron ions, neutralization can be performed to raise the pH of the metal-containing solution and separate the neutralization residue to obtain a post-neutralization solution. The neutralization may include a dealuminumization step of raising the pH of the metal-containing solution to precipitate at least a part of the aluminum ions and an iron removal step of adding an oxidizing agent to further raise the pH. However, in the case where the metal-containing solution does not contain aluminum ions and / or iron ions, the dealuminumization step and / or the iron removal step may be omitted. Examples of the pH adjuster used in the neutralization include lithium hydroxide, sodium hydroxide, sodium carbonate, ammonia, etc., but it is particularly preferable to use the lithium hydroxide solution obtained after the hydroxylation described later.

[0049] After the metal-containing solution has undergone the above neutralization, each metal ion in the metal-containing solution can be extracted by a solvent extraction method. This may include, for example, extraction of manganese ions, extraction of cobalt ions, and extraction of nickel ions in this order. When aluminum ions remain in the metal-containing solution after neutralization, aluminum ions may also be extracted when extracting manganese ions. The lithium hydroxide solution obtained after the hydroxylation described later can be used to adjust the equilibrium pH in at least one of those extractions.

[0050] For the extraction of manganese ions, it is preferable to use a phosphate ester extractant (such as di-2-ethylhexyl phosphate (abbreviation: D2EHPA, for example, trade name: DP8R)). Alternatively, the extractant may be a mixture of the phosphate ester extractant and an oxime extractant (such as an aldoxime or one mainly composed of an aldoxime, specifically, for example, 2-hydroxy-5-nonylacetophenone oxime (trade name: LIX84), 5-dodecylsalicylaldoxime (trade name: LIX860), a mixture of LIX84 and LIX860 (trade name: LIX984), 5-nonylsalicylaldoxime (trade name: ACORGAM5640)). The equilibrium pH is preferably 2.3 to 3.5, more preferably 2.5 to 3.0.

[0051] After extracting manganese ions, cobalt ions can be extracted from the metal-containing solution. For the extraction of cobalt ions, it is preferable to use a solvent containing a phosphoric acid-based extractant, particularly a phosphonic acid ester-based extractant (especially 2-ethylhexyl 2-ethylhexylphosphonate (trade names: PC-88A, Ionquest 801), etc.). The equilibrium pH during extraction is preferably 5.0 to 6.0, more preferably 5.0 to 5.5.

[0052] After extracting cobalt ions, nickel ions can be extracted from the metal-containing solution. For nickel ion extraction, it is preferable to use a solvent containing a carboxylic acid extractant (particularly neodecanoic acid (such as Versatic Acid 10 (VA-10) manufactured by Shell Chemical Corporation)). The equilibrium pH during extraction is preferably 6.0 to 8.0, more preferably 6.8 to 7.2.

[0053] For solvents from which cobalt ions or nickel ions have been extracted, scrubbing can be performed as needed, followed by back-extraction using inorganic acids such as sulfuric acid, hydrochloric acid, or nitric acid. The pH may be set to 2.0 to 4.0 for back-extraction of cobalt ions and to 1.0 to 3.0 for back-extraction of nickel ions. Electrolysis and dissolution may be performed on the back-extracted nickel ion solution. Subsequently, the back-extracted solution can be heated to, for example, 40°C to 120°C to crystallize it, thereby obtaining cobalt salts such as sulfates and nickel salts.

[0054] Lithium-containing solutions, such as lithium sulfate solution, which are the post-extraction liquid after nickel ions have been extracted, can be subjected to hydroxide oxidation. In hydroxide oxidation, to obtain a lithium hydroxide solution from the lithium-containing solution, methods such as carbonation and chemical conversion using calcium hydroxide after producing lithium carbonate, chemical conversion using barium hydroxide, or electrodialysis can be employed.

[0055] In the case of carbonation and chemical conversion methods, a lithium carbonate solution is first obtained by adding a carbonate to a lithium-containing solution or by blowing in carbon dioxide. Then, in the so-called chemical conversion method, calcium hydroxide is added to the lithium carbonate solution, and a lithium hydroxide solution can be produced according to the reaction equation Li₂CO₃ + Ca(OH)₂ → 2LiOH + CaCO₃. Calcium ions that may remain in the solution can be removed using cation exchange resins or chelating resins.

[0056] When using barium hydroxide, a lithium hydroxide solution can be obtained by adding barium hydroxide to a lithium-containing solution and following the reaction Li₂SO₄ + Ba(OH)₂ → 2LiOH + BaSO₄. Barium that may dissolve in the solution at this time can be separated and removed using a cation exchange resin or chelating resin.

[0057] In electrodialysis, a lithium-containing solution is placed in the desalination chamber between the anion exchange membrane and the cation exchange membrane in a bipolar membrane electrodialysis machine. Pure water is then placed in the acid chamber between the bipolar membrane and the anion exchange membrane, and in the alkaline chamber between the cation exchange membrane and the bipolar membrane, and a voltage is applied between the electrodes. As a result, lithium ions in the lithium-containing solution in the desalination chamber move to the alkaline chamber, where the pure water is decomposed into hydroxide ions by the bipolar membrane, yielding a lithium hydroxide solution. In addition, anions of inorganic acids such as sulfate ions in the lithium-containing solution in the desalination chamber pass through the anion exchange membrane and move to the acid chamber. Furthermore, in electrodialysis, as a result of separating most of the lithium salts from the lithium-containing solution in the desalination chamber, a desalination solution that contains almost no lithium salts is obtained.

[0058] The lithium hydroxide solution obtained by hydroxide oxidation can be returned to the wet treatment as a pH adjuster, or it may be concentrated and then subjected to crystallization as needed. In crystallization, the lithium hydroxide solution (pre-crystallization solution) is stored in a crystallization tank, and crystallization operations such as heating and concentration or vacuum distillation are performed to precipitate lithium hydroxide. In the case of heating and concentration, a higher temperature during crystallization is preferable as it speeds up the process. However, after crystallization, the temperature at which the precipitate is dried should preferably be below 60°C to prevent the desorption of crystal water. This is because anhydrous lithium hydroxide from which crystal water has been desorbed is hygroscopic and difficult to handle. The lithium hydroxide produced by crystallization may be subjected to pulverization or other treatments to adjust its physical properties to the required level.

[0059] The steps preceding crystallization (the steps up to hydroxide, or, if concentration is performed after hydroxide, the steps up to concentration) may be continuous processes. On the other hand, crystallization may be a batch process performed when a certain amount of the pre-crystallization solution used for precipitation of lithium hydroxide has accumulated. Since the pre-crystallization solution (lithium hydroxide solution obtained by hydroxide, concentrated solution, etc.) and other lithium hydroxide solutions used in such batch processes as crystallization are used in relatively large quantities in a single batch process, the liquid level and internal pressure in the tank tend to fluctuate significantly when stored in a tank. For this reason, when using a storage container 11 as shown in Figure 2 for the lithium hydroxide solution used in a batch process, it is preferable to store the lithium hydroxide solution in the exhaust tank 12b of the multiple tanks 12a and 12b.

[0060] (Potential Contribution to SDGs) According to the embodiment described above, the formation of lithium carbonate in lithium hydroxide solution can be effectively suppressed, thereby reducing the occurrence of malfunctions in the metal recovery process of lithium-ion battery waste, lowering processing costs, and potentially yielding high-quality lithium hydroxide. For this reason, this embodiment has the potential to contribute to Goal 9 "Build resilient infrastructure, promote inclusive and sustainable industrialization and foster innovation" and Goal 12 "Ensure sustainable consumption and production patterns" of the United Nations-led Sustainable Development Goals (SDGs) by promoting waste reuse and improving resource utilization efficiency.

[0061] 1, 11 Storage container 2, 12 Container body 12a, 12b Tank 3, 13 Gas supply port 4, 14 Gas outlet port 5, 15 Gas supply pipe 6, 16 Gas outlet pipe 7, 8, 17, 18 On / off valves 9, 19a, 19b Concentration meter 10, 20 Pressure gauge 12c Connecting pipe LHS, LHS1, LHS2 Lithium hydroxide solution

Claims

1. A method for suppressing the formation of lithium carbonate in a lithium hydroxide solution, comprising storing the lithium hydroxide solution in a storage container that is under positive pressure and has a CO2 concentration lower than that of air.

2. The method for suppressing the generation of lithium carbonate according to claim 1, wherein the CO2 concentration of the internal atmosphere of the storage container is less than 30 ppm by volume.

3. The method for suppressing the generation of lithium carbonate according to claim 1, wherein the CO2 concentration of the internal atmosphere of the storage container is monitored while the lithium hydroxide solution is stored in the storage container.

4. The method for suppressing the generation of lithium carbonate according to claim 1, wherein the internal pressure of the storage container is 10 Pa or more.

5. The method for suppressing the generation of lithium carbonate according to claim 1, wherein the internal pressure of the storage container is monitored while the lithium hydroxide solution is stored in the storage container.

6. The method for suppressing the generation of lithium carbonate according to claim 1, wherein, when storing the lithium hydroxide solution in the storage container, the following steps are taken in this order: putting the lithium hydroxide solution into the storage container; supplying a low CO2 gas with a CO2 concentration lower than that of air into the storage container and discharging the internal gas of the storage container; and sealing the storage container while the inside of the storage container is under positive pressure due to the supply of the low CO2 gas.

7. The method for suppressing the generation of lithium carbonate according to claim 6, wherein the low CO2 gas used is a low CO2 gas obtained by removing at least a portion of carbon dioxide from air.

8. A method for storing a lithium hydroxide solution, comprising storing the lithium hydroxide solution in a storage container, which serves as a storage container, using the lithium carbonate generation suppression method described in any one of claims 1 to 7.

9. A method for producing a lithium hydroxide solution, comprising: generating a lithium hydroxide solution from a lithium-containing solution containing anions of an inorganic acid and lithium ions; and then storing the lithium hydroxide solution in a storage container using the lithium carbonate generation suppression method described in any one of claims 1 to 7.

10. A method for producing lithium hydroxide, comprising using the lithium carbonate formation suppression method described in any one of claims 1 to 7, wherein lithium hydroxide is precipitated from the lithium hydroxide solution inside the storage container, which serves as a crystallization vessel.

11. A storage container for lithium hydroxide solution, comprising: a container body for storing lithium hydroxide solution; a gas supply port provided in the container body, capable of introducing low-CO2 gas with a CO2 concentration lower than that of air into the storage container; a gas outlet provided in the container body, capable of discharging the internal gas of the storage container to the outside of the storage container; and a sealing mechanism capable of maintaining airtightness inside the storage container.

12. The storage container according to claim 11, wherein the sealing mechanism includes on / off valves provided on the gas supply pipe connected to the gas supply port and the gas discharge pipe connected to the gas discharge port.

13. The storage container according to claim 11 or 12, further comprising a concentration meter for measuring the CO2 concentration of the internal atmosphere of the storage container, and / or a pressure meter for measuring the internal pressure of the storage container.

14. The storage container according to claim 11 or 12, wherein the container body includes a plurality of tanks and a connecting pipe that connects the plurality of tanks in series from the tank having the gas supply port to the tank having the gas discharge port.

15. The storage container according to claim 14, wherein the tank provided with the gas outlet is used for storing a lithium hydroxide solution to be used in a batch process.

16. The storage container according to claim 15, wherein the tank provided with the gas outlet is used for storing the lithium hydroxide solution as a precrystallization liquid.

17. The storage container according to claim 11 or 12, wherein the storage container is a storage container or a crystallization vessel.

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