Method for treating lithium-ion-containing aqueous solution

Abstract

[Problem] To efficiently obtain, from a lithium-ion-containing aqueous solution containing anions, a lithium-ion-containing aqueous solution which has a reduced content of anions other than hydroxide ions. [Solution] This method for treating lithium-ion-containing aqueous solution uses an electrodialyzer equipped with a raw-solution tank separated from adjacent tanks on both sides by a cation-exchange membrane and an anion-exchange membrane respectively, a first adjoining tank which adjoins the raw-solution tank with the cation-exchange membrane interposed therebetween, and a second adjoining tank which adjoins the raw-solution tank with the anion-exchange membrane interposed therebetween, wherein: a lithium-ion-containing aqueous solution which contains lithium ions, cations other than lithium ions, and anions is put in the raw-solution tank; water or an aqueous solution is put in the first adjoining tank and the second adjoining tank; a voltage is applied between a cathode inside the first adjoining tank and an anode inside the second adjoining tank; and, while the pH of the liquid inside the raw-solution tank is kept at 10.5 or higher, lithium ions inside the raw-solution tank are caused to move into the first adjoining tank through the cation-exchange membrane.

Description

Method for treating aqueous solution containing lithium ions

[0001] The present invention relates to a method for treating a lithium ion-containing aqueous solution, for obtaining a lithium ion-containing aqueous solution having a reduced anion content from a lithium ion-containing aqueous solution containing components derived from used lithium ion batteries or the like, by electrodialysis.

[0002] In the recycling process for recovering valuable metals from used lithium-ion batteries, the batteries are subjected to heat treatment and crushing / sorting processes to separate base metals such as aluminum, iron, and copper from the remaining powder called black mass. Black mass contains large amounts of rare metals such as nickel, cobalt, and lithium and is used as a smelting material. There are several methods for recovering lithium from this black mass, and one possible method is to selectively recover lithium ions from the various ions contained in the aqueous leachate of black mass using electrodialysis.

[0003] As a method for selectively recovering lithium ions from a lithium ion-containing solution containing cations other than lithium ions by electrodialysis, for example, Patent Document 1 discloses a technology employing a three-electrode system in an electrodialysis method using a lithium ion conductive electrolyte membrane (LLTO). This technology is said to be able to suppress the flow of electrons that attempt to permeate the lithium ion conductive electrolyte membrane in the opposite direction to the lithium ions when the electrolysis potential is increased, thereby enabling improved productivity in selectively recovering lithium ions.

[0004] Patent No. 7103626

[0005] The technology described in Patent Document 1 could also be used to selectively recover lithium ions from black mass aqueous leachates. However, the inventors' experiments showed that when the technology described in Patent Document 1 was applied to black mass aqueous leachates, it was not always easy to maintain rapid lithium ion migration through the lithium ion conductive electrolyte membrane (LLTO). This was thought to be because the black mass aqueous leachates derived from used lithium-ion batteries contain many anions other than hydroxide ions, and these anions are not easily reduced on the electrode surface. Therefore, to solve this problem, it is effective to pretreat the black mass aqueous leachate to produce a lithium ion-containing solution with a reduced content of anions other than hydroxide ions.

[0006] As a pretreatment method, it was thought that the well-known electrodialysis method using a cation exchange membrane would be effective. That is, it was thought that by transferring lithium ions and other cations present in the aqueous leachate of black mass through a cation exchange membrane into an aqueous solution in a separate tank, it would be possible to obtain a lithium ion-containing solution with a reduced content of anions other than hydroxide ions. However, this method presented a new problem: the cation exchange membrane was prone to clogging, making it difficult to continue electrodialysis using the cation exchange membrane.

[0007] An object of the present invention is to provide an electrodialysis technique that can obtain a lithium ion-containing aqueous solution with a reduced content of anions other than hydroxide ions from a lithium ion-containing aqueous solution that also contains anions other than hydroxide ions (for example, an aqueous leachate of black mass derived from used lithium ions) while continuing electrodialysis using a cation exchange membrane.

[0008] When attempting to transfer cations from the water leachate of black mass to a separate tank by electrodialysis using a cation exchange membrane, the problem of clogging of the membrane was encountered, as mentioned above. Investigation of the clogging substance revealed that it was aluminum hydroxide Al(OH). ３It was found that the main component of the black mass leachate is aluminum. Since black mass obtained by treating used lithium-ion batteries contains a large amount of residual aluminum derived from the aluminum foil of the current collector, aluminum is also present in the aqueous leachate of the black mass. In aqueous solutions, aluminum tends to exist as ions in low and high pH ranges, and as aluminum hydroxide in intermediate pH ranges. The aqueous leachate of black mass is usually alkaline. After extensive research, the inventors discovered that by adjusting the pH of the solution to be treated to maintain it in a predetermined high pH range, clogging of the cation exchange membrane caused by the precipitation of aluminum hydroxide can be prevented, and cations can be efficiently transferred from the aqueous leachate of black mass to a separate tank. Based on this finding, the following invention is disclosed in this specification.

[0009] [1] A method for treating a lithium-ion-containing aqueous solution using an electrodialysis apparatus comprising a stock solution tank separated from an adjacent tank by a cation exchange membrane and a first adjacent tank adjacent to the stock solution tank via the cation exchange membrane, with electrodes provided in the first adjacent tank and the stock solution tank, respectively; storing a lithium-ion-containing aqueous solution containing lithium ions, cations other than lithium ions, and anions in the stock solution tank, and storing water or an aqueous solution in the first adjacent tank; connecting the electrode in the first adjacent tank to a power source so that the electrode in the first adjacent tank serves as a cathode and the electrode in the stock solution tank serves as an anode, and applying a voltage between the electrodes; maintaining the pH of the solution in the stock solution tank at a value such as 10.5 or higher at which precipitation of aluminum hydroxide does not occur, and transferring the lithium ions in the stock solution tank through the cation exchange membrane into the first adjacent tank, thereby obtaining a lithium-ion-containing aqueous solution in the first adjacent tank with a reduced content of anions other than hydroxide ions. [2] A method for treating a lithium-ion-containing aqueous solution using an electrodialysis apparatus comprising a stock solution tank separated from adjacent tanks on either side by a cation exchange membrane and an anion exchange membrane, a first adjacent tank adjacent to the stock solution tank via the cation exchange membrane, and a second adjacent tank adjacent to the stock solution tank via the anion exchange membrane, with electrodes provided in the first and second adjacent tanks, wherein the stock solution tank is filled with a lithium-ion-containing aqueous solution containing lithium ions, cations other than lithium ions, and anions, and the first and second adjacent tanks are filled with water or an aqueous solution, and the electrodes in the first and second adjacent tanks are connected to a power source so that the electrode in the first adjacent tank serves as a cathode and the electrode in the second adjacent tank serves as an anode, thereby applying a voltage between the electrodes, and maintaining the pH of the solution in the stock solution tank at 10.5 or higher, thereby transferring the lithium ions in the stock solution tank through the cation exchange membrane into the first adjacent tank, thereby obtaining a lithium-ion-containing aqueous solution in the first adjacent tank with a reduced content of anions other than hydroxide ions. [3] The method for treating a lithium ion-containing aqueous solution according to the above [1] or [2], wherein the lithium ion-containing aqueous solution contained in the concentrate tank contains aluminum dissolved therein.[4] The method for treating a lithium ion-containing aqueous solution according to any one of [1] to [3] above, wherein the lithium ion-containing aqueous solution contained in the concentrate tank is an aqueous solution containing a water leachate of black mass, which is a powder containing metal derived from used lithium ion batteries. [5] The method for treating a lithium ion-containing aqueous solution according to any one of [1] to [4] above, wherein the pH of the solution in the concentrate tank is maintained at 10.5 or higher by introducing the lithium ion-containing aqueous solution into the concentrate tank from the outside.

[0010] According to the present invention, it is possible to efficiently obtain a lithium ion-containing aqueous solution in which the content of anions other than hydroxide ions has been reduced from a lithium ion-containing aqueous solution containing anions and aluminum, such as the aqueous leachate of black mass derived from used lithium ion batteries, by electrodialysis using a cation exchange membrane while avoiding clogging of the cation exchange membrane. The obtained lithium ion-containing aqueous solution can be suitably used in processes such as the direct recovery of lithium ions using a lithium ion conductive electrolyte membrane (LLTO).

[0011] 1 is a diagram illustrating a typical cross-sectional structure of an electrodialysis device using a cation exchange membrane that can be applied to the present invention, and a mode of use thereof. 2 is a diagram illustrating a typical cross-sectional structure of an electrodialysis device using a cation exchange membrane and an anion exchange membrane that can be applied to the present invention, and a mode of use thereof. 3 is a diagram illustrating a typical cross-sectional structure of an electrodialysis device using a cation exchange membrane and an anion exchange membrane that can be applied to the present invention, and a mode of use thereof. 4 is a diagram illustrating a typical cross-sectional structure of an electrodialysis device using a cation exchange membrane and an anion exchange membrane that can be applied to the present invention, and a mode of use thereof. 5 is a diagram illustrating a typical cross-sectional structure of an electrodialysis device using a cation exchange membrane and an anion exchange membrane that can be applied to the present invention, and a mode of use thereof. 6 is a diagram illustrating a typical cross-sectional structure of an electrodialysis device using a cation exchange membrane and an anion exchange membrane that can be applied to the present invention, and a mode of use thereof. 7 is a diagram illustrating a typical cross-sectional structure of an electrodialysis device using a cation exchange membrane and an anion exchange membrane that can be applied to the present invention, and a mode of use thereof. 8 is a diagram illustrating a typical cross-sectional structure of an electrodialysis device using a cation exchange membrane and an anion exchange membrane that can be applied to the present invention, and a mode of use thereof. 9 is a diagram illustrating a typical cross-sectional structure of an electrodialysis device using a cation exchange membrane and an anion exchange membrane that can be applied to the present invention, and a mode of use thereof. 10 is a diagram illustrating a typical cross-sectional structure of an electrodialysis device using a cation exchange membrane and an anion exchange membrane that can be applied to the present invention, and a mode of use thereof.

[0012] Figure 1 shows a typical cross-sectional structure and usage example of an electrodialysis apparatus using a cation exchange membrane that can be applied to the present invention. A treatment tank 100 includes a raw solution tank 10 and a first adjacent tank 11, which are adjacent to each other via a cation exchange membrane 1. An electrode 31 and an electrode 32 are installed in the first adjacent tank 11 and the raw solution tank 10, respectively. The electrodes 31 and 32 are connected to a power source 30.

[0013] FIG. 2 shows a typical cross-sectional structure and exemplary usage of an electrodialysis apparatus using cation and anion exchange membranes that can be used in the present invention. The treatment tank 100 is partitioned by a cation exchange membrane 1 and an anion exchange membrane 2. The treatment tank 100 includes a raw solution tank 10 located between the cation exchange membrane 1 and the anion exchange membrane 2, a first adjacent tank 11 adjacent to the raw solution tank 10 via the cation exchange membrane 1, and a second adjacent tank 12 adjacent to the raw solution tank 10 via the anion exchange membrane 2. The first adjacent tank 11 and the second adjacent tank 12 are equipped with electrodes 31 and 32, respectively. The electrodes 31 and 32 are connected to a power source 30. In the embodiment shown in FIG. 2 using an anion exchange membrane, anions contained in the solution in the raw solution tank 10 can be selectively passed through the anion exchange membrane 2 and collected in the second adjacent tank 12, allowing the solution in the second adjacent tank 12 after treatment to be utilized as an acid solution.

[0014] In the electrodialysis apparatus having the configuration shown in FIGS. 1 and 2 , when treating a lithium ion-containing aqueous solution in an amount larger than the amount of liquid that can be contained in the raw solution tank 10, an external container containing the same liquid as the lithium ion-containing aqueous solution contained in the raw solution tank 10 can be prepared, and the liquid can be circulated between the raw solution tank 10 and the external container using a device such as a tube pump, thereby making it possible to subject a larger amount of the lithium ion-containing aqueous solution to electrodialysis treatment.

[0015] Furthermore, when a large amount of lithium ions is transferred from the source solution tank 10 to the first adjacent tank 11 by electrodialysis, if the lithium ion concentration of the solution contained in the first adjacent tank 11 rises above a certain level, a higher voltage may be required to transfer the lithium ions from the source solution tank 10 to the first adjacent tank 11, or cations may precipitate beyond their solubility, ultimately making it difficult to transfer the lithium ions from the source solution tank 10 to the first adjacent tank 11. To avoid this, as described above, an external container containing the same solution as the solution contained in the first adjacent tank 11 may be prepared, and the solution may be circulated between the first adjacent tank 11 and the external container using a device such as a tube pump, thereby suppressing an increase in the lithium ion concentration of the solution contained in the first adjacent tank 11. Using this method, it is possible to electrodialyze a larger amount of lithium ion-containing aqueous solution.

[0016] 3 and 4 show schematic examples of electrodialysis apparatuses having the configurations shown in FIGS. 1 and 2, respectively, in which the liquid in the tank is circulated between the tank and an external container, and their usage modes. Pipes 60a and 60b are provided between the stock solution tank 10 and the external container 50, and liquid can be circulated between the stock solution tank 10 and the external container 50 using a pump 70, such as a tube pump. Pipes 61a and 61b are provided between the first adjacent tank 11 and the external container 51, and liquid can be circulated between the first adjacent tank 11 and the external container 51 using a pump 71, such as a tube pump.

[0017] The method for treating a lithium ion-containing aqueous solution of the present invention will be described below using the electrodialysis apparatus configuration shown in Figures 1 and 2 as an example. Known cation exchange membranes such as CSE (trade name "Neosepta", manufactured by Astom Corporation) and CMVN (trade name "Selemion", manufactured by AGC Engineering Co., Ltd.) can be used as the cation exchange membrane 1, as well as new cation exchange membranes that may be developed in the future. Known anion exchange membranes such as ASE (trade name "Neosepta", manufactured by Astom Corporation) can be used as the anion exchange membrane 2, as well as new anion exchange membranes that may be developed in the future.

[0018] The electrode 31 converts electrons from the power supply 30 into hydrogen ions H ＋ Hydrogen gas H ２ The electrode 32 functions as a "cathode" that generates hydroxide ions OH in the solution, and can be made of a material (e.g., nickel) that is corrosion-resistant to the lithium ion-containing aqueous solution. － and other anions to form oxygen gas O ２ and chlorine gas Cl ２ The anode functions as an "anode" that generates the gas, and can be made of an insoluble material (such as platinum).

[0019] The raw liquid tank 10 contains a lithium ion-containing aqueous solution 20, which is the liquid to be treated. This lithium ion-containing aqueous solution 20 contains lithium ions, cations other than lithium ions, and anions. In particular, an aqueous solution containing an aqueous leachate of black mass, which is a powder containing metals derived from used lithium ion batteries, is a suitable target for the lithium ion-containing aqueous solution 20. The term "aqueous solution containing an aqueous leachate of black mass" refers to either the aqueous leachate of black mass itself or a mixture of water or an aqueous solution and the aqueous leachate of black mass. Aluminum is usually dissolved in an aqueous solution containing an aqueous leachate of black mass.

[0020] The first adjacent tank 11 contains water or an aqueous solution 21 for receiving cations such as lithium ions from the lithium ion-containing aqueous solution 20, which is the liquid to be treated. In the initial state before the start of electrodialysis, the water or aqueous solution 21 may be an aqueous solvent (e.g., pure water). After the start of electrodialysis, the water or aqueous solution 21 becomes an aqueous solution containing cations such as lithium ions.

[0021] 2, the second adjacent tank 12 contains water or an aqueous solution 22 for receiving anions from the lithium ion-containing aqueous solution 20, which is the liquid to be treated. In the initial state before the start of electrodialysis, the water or aqueous solution 22 may be an aqueous solvent (e.g., pure water). After the start of electrodialysis, the water or aqueous solution 22 becomes an aqueous solution containing anion components.

[0022] During electrodialysis, it is preferable to stir the liquids contained in the stock liquid tank 10, the first adjacent tank 11, and in the embodiment of Figure 2, the second adjacent tank 12. Stirring methods include mechanical stirring using a stirrer or rotating blades provided in each tank, as well as a method in which the liquid in the tank is circulated and moved by an external pump.

[0023] After initial solutions are placed in the raw solution tank 10, the first adjacent tank 11, and, in the embodiment shown in FIG. 2, the second adjacent tank 12, the electrodes 31 and 32 are connected to a power source 30 so that the cathode and anode, respectively, are anodes, and a voltage is applied between the electrodes to perform electrodialysis. The voltage applied between the electrodes is set to a potential difference sufficient to allow water electrolysis to proceed smoothly between the electrodes, i.e., sufficient to generate hydrogen gas from the cathode electrode 31 and oxygen gas from the anode electrode 32. The raw solution tank 10 contains the lithium ion-containing aqueous solution 20 to be treated. While the voltage is applied, a lithium ion-containing aqueous solution, such as an aqueous solution containing black mass leachate, may be continuously or intermittently introduced into the raw solution tank 10 via a path connected to an external tank. In this case, the introduction of the solution may also be used to adjust the pH, as described below. The lithium ion concentration of the lithium ion-containing aqueous solution 20 to be treated during electrodialysis is not particularly limited, but may be set within a range of 10 mg / L or more and saturation concentration or less.

[0024] When electrodialysis is performed by applying a voltage between the electrodes 31 and 32, lithium ions and other cations contained in the lithium ion-containing aqueous solution 20, which is the liquid to be treated, pass through the cation exchange membrane 1 in the direction indicated by arrow 41 in Fig. 1 , and move from the raw solution tank 10 to the first adjacent tank 11. In the embodiment of Fig. 2 , anions contained in the lithium ion-containing aqueous solution 20 pass through the anion exchange membrane 2 in the direction indicated by arrow 42 in Fig. 1 , and move from the raw solution tank 10 to the second adjacent tank 12. The temperature of the liquid during electrodialysis is not particularly limited as long as it can be maintained in a liquid state in each tank, but it is preferably maintained in the range of 10 to 80°C, for example.

[0025] The lithium ion-containing aqueous solution 20 to be treated typically exhibits an alkaline pH of 10.5 or higher. When the electrodialysis described above is performed, the pH of the solution in the raw solution tank 10 decreases with the migration of cations and anions unless pH adjustment is performed. The inventors' studies have found that when the pH of the solution in the raw solution tank 10 falls below 10.5, solid substances primarily composed of aluminum hydroxide are likely to form in the solution. These solid substances then adhere to the cation exchange membrane 1, causing clogging of the cation exchange membrane 1. Therefore, in the present invention, the pH of the lithium ion-containing aqueous solution 20 in the raw solution tank 10 is adjusted to maintain the pH at 10.5 or higher, thereby preventing clogging of the cation exchange membrane 1. It is more preferable to adjust the pH to maintain the pH at 10.8 or higher.

[0026] The pH in this specification is measured using a pH meter calibrated with an appropriate buffer solution according to the pH range to be measured, based on JIS Z8802:2011. The pH values ​​described in this specification are values ​​measured by a pH meter compensated by a temperature-compensating electrode and directly read under the temperature conditions of the liquid. In the examples described below, pH was measured using a portable pH / ORP / ion meter Five Easy F20 and a pH measurement electrode LE438 manufactured by METTLER TOLEDO.

[0027] An example of a method for adjusting the pH of the liquid in the stock solution tank 10 to maintain the pH at or above the predetermined value is to periodically introduce a new lithium ion-containing aqueous solution into the stock solution tank 10 from the outside via a circulation path or the like during electrodialysis to maintain a high pH. Alternatively, electrodialysis may be temporarily stopped before the pH of the liquid in the stock solution tank 10 falls below the predetermined value, and a portion or all of the liquid in the stock solution tank 10 is removed. An amount of new lithium ion-containing aqueous solution equivalent to the amount of removed liquid is then introduced into the stock solution tank 10 to sufficiently increase the pH of the liquid in the stock solution tank 10, and then electrodialysis may be resumed. In either case, it is preferable to periodically monitor the pH of the liquid in the stock solution tank 10 during electrodialysis as needed. An alkaline solution or alkali may be introduced in addition to the lithium ion-containing aqueous solution, or an alkaline solution or alkali may be introduced instead of the lithium ion-containing aqueous solution.

[0028] By continuing electrodialysis while maintaining the pH of the liquid in the raw liquid tank 10 at a predetermined value or higher, a lithium ion-containing aqueous solution with a reduced anion content can be obtained in the first adjacent tank 11 without replacing the cation exchange membrane 1 for an extended period of time. The water or aqueous solution 21 in the first adjacent tank 11 can be recovered as a lithium ion-containing aqueous solution with a reduced anion content after the lithium ion concentration in the first adjacent tank 11 is adjusted to a level suitable for use in the next step (e.g., a direct lithium ion recovery step using a lithium ion-conductive electrolyte membrane) by electrodialysis. Examples of recovery methods include recovering the entire amount of the liquid in the first adjacent tank 11 after stopping electrodialysis, or recovering the liquid by continuously or intermittently discharging it to the outside during electrodialysis. In the latter case, an aqueous solvent (e.g., pure water) in an amount corresponding to the amount of the discharged liquid can be replenished into the first adjacent tank 11 as needed during electrodialysis.

[0029] Example 1 An electrodialysis apparatus having the configuration shown in Figure 4 (the configuration shown in Figure 2 plus a circulation function with an external container) was prepared. A CSE (trade name "Neosepta", manufactured by Astom Corporation) was used as the cation exchange membrane 1, and an ASE (trade name "Neosepta", manufactured by Astom Corporation) was used as the anion exchange membrane 2. The volumes of the stock solution tank 10, first adjacent tank 11, and second adjacent tank 12 were all approximately 0.13 L. The stock solution tank 10 and an external container 50 with a volume of approximately 2 L were connected by a conduit 60 made of polypropylene tubing. During electrodialysis, the liquids contained in the stock solution tank 10 and the external container 50 were circulated at a circulation flow rate of 50 mL / min using a tube pump 70. The first adjacent tank 11 and an external container 51 having a capacity of approximately 2 L were connected by a conduit 61 made of the same tube as above, and during the electrodialysis treatment, the liquids contained in the first adjacent tank 11 and the external container 51 were circulated at a circulation flow rate of 50 mL / min using a tube pump 71. The electrode 31 was a nickel plate, and the electrode 32 was a platinum plate.

[0030] An aqueous leachate of black mass, a powder derived from used lithium-ion batteries, was prepared. This leachate was analyzed for cations using a calibration curve method with an inductively coupled plasma optical emission spectrometer (ICP-OES, Optima 7000DV, manufactured by PerkinElmer Co., Ltd.), and for anions using a calibration curve method with an ion chromatograph (Eco IC, manufactured by Metrohm AG). The results confirmed that this black mass leachate was a lithium-ion-containing aqueous solution containing the main ions at the concentrations shown in Table 1. Hereinafter, this black mass leachate will be referred to as the "raw material solution."

[0031]

[0032] A total of 2 L of the above raw material solution was placed in the raw material tank 10 and the external container 50, and a total of 2 L of pure water was placed in the first adjacent tank 11 and the external container 51. Furthermore, 130 mL of pure water was placed in the second adjacent tank 12. The liquid in each of the raw material tank 10, the first adjacent tank 11, and the second adjacent tank 12 was stirred using a stirrer, and electrodialysis was performed by applying a 10 V DC voltage between the electrodes 31 and 32 from an external power source 30, with electrode 31 serving as the cathode and electrode 32 serving as the anode, respectively. The liquid temperature in each tank was maintained at 20°C. During electrodialysis, the pH of the liquid in the raw material tank 10 (hereinafter referred to as the "liquid to be treated") was measured approximately every 12 hours. The pH of the liquid to be treated (raw material solution) before the start of electrodialysis was 11.5.

[0033] After the start of electrodialysis, the pH of the treated liquid gradually decreased and reached pH 10.8 on the 12th day after the start of electrodialysis. At this time, the Li concentration in the first adjacent tank 11 was 850 mg / L. Visual observation revealed no solid precipitation in the raw liquid tank 10 or the external container 50. At this time, electrodialysis was interrupted, the entire amount of the treated liquid in the raw liquid tank 10 and the external container 50 was discharged, and 2 L of the above-mentioned raw liquid was newly introduced into the raw liquid tank 10 and the external container 50. In this manner, the pH of the treated liquid was adjusted by introducing a new lithium ion-containing aqueous solution (raw liquid) from the outside into the raw liquid tank 10 and the external container 50. Thereafter, electrodialysis was resumed under the above-described conditions. The pH of the treated liquid gradually decreased and reached pH 10.8 again on the 22nd day after the initial start of electrodialysis. Even at this time, no solid precipitation was observed in the raw liquid tank 10. When the pH of the liquid to be treated again reached 10.8, electrodialysis was terminated, and the liquid in the first adjacent tank 11 and the external container 51 was recovered. This liquid is called the "cation dialysate."

[0034] (Anion / Lithium Ion Concentration Ratio) As can be seen from Table 1 above, the aqueous leachate (raw material solution) of black mass contains various anions. Here, the "anion / lithium ion concentration ratio" expressed by the following formula (1) is used as an index of the concentration ratio (mass ratio) of the main anions contained in the aqueous solution to lithium ions. Anion / lithium ion concentration ratio = ([F － ]+[Cl － ]+[SO ４２－ ]+[PO ４ ３－ ]+[Al(OH) ４ ２－ ]) / [Li ＋ ] ... (1) Here, the value of the concentration (mg / L) of the ion written in the [ ] in formula (1) is substituted for the corresponding part. The anion / lithium ion concentration ratio of the above raw solution is 0.48. On the other hand, when the above cation dialysis solution was analyzed in the same manner as the above raw solution, the cation dialysis solution was found to have a Li ＋ The anion concentration was 1700 mg / L, and the anion / lithium ion concentration ratio was 0.0013. By the electrodialysis method with pH adjustment described above, it was possible to obtain, in the first adjacent tank 11 and the external container 51, an aqueous solution containing lithium ions (cation dialysate) in which the anion content was significantly reduced compared to that of the feed solution, without causing clogging of the cation exchange membrane.

[0035] Comparative Example 1 Electrodialysis was performed using the same equipment and raw material solution as in Example 1, with the exception that the capacity of the external container 51 connected to the first adjacent tank 11 was 1 L and a total of 1 L of pure water was placed in the first adjacent tank 11 and the external container 51. However, in this example, electrodialysis was continued without interruption from the initial start of electrodialysis until the pH of the liquid to be treated in the raw liquid tank 10 decreased to 10.2. Specifically, the pH of the liquid to be treated reached 10.2 on the 10th day after the start of electrodialysis. The reason for the larger pH decrease per hour in Comparative Example 1 compared to Example 1 is presumably because the amount of pure water placed in the first adjacent tank 11 and the external container 51 was smaller than in Example 1, resulting in a higher lithium ion concentration in the liquid in the first adjacent tank 11 and the external container 51 during electrodialysis than in Example 1, thereby accelerating the migration of lithium ions to the first adjacent tank 11. Visual observation revealed the deposition of solid material in the raw liquid tank 10 at this point. Furthermore, the solid material was observed adhering to part of the surface of the cation exchange membrane 1, and it was thought that if electrodialysis were continued in this state, the solid material would clog the cation exchange membrane 1. Therefore, electrodialysis was terminated when the pH of the treated liquid reached 10.2. The solid material was sampled and analyzed, and it was confirmed to be composed primarily of aluminum hydroxide. As can be seen from this example, in the electrodialysis of a lithium ion-containing aqueous solution containing various ions, such as the aqueous leachate of black mass, it is difficult to perform electrodialysis using the same cation exchange membrane for a long period of time unless the pH of the treated liquid is adjusted to maintain a high pH.

[0036] REFERENCE SIGNS LIST 1 Cation exchange membrane 2 Anion exchange membrane 10 Raw liquid tank 11 First adjacent tank 12 Second adjacent tank 20 Lithium ion-containing aqueous solution as the liquid to be treated 21 Water or aqueous solution for receiving cations 22 Water or aqueous solution for receiving anions 30 Power source 31, 32 Electrodes 50, 51 External container 60a, 60b, 61a, 61b Pipes 70, 71 Pump 100 Treatment tank

Claims

1. A method for treating an aqueous solution containing lithium ions, comprising: a raw solution tank separated from an adjacent tank by a cation exchange membrane; and a first adjacent tank adjacent to the raw solution tank via the cation exchange membrane; and an electrodialysis device provided with electrodes in the first adjacent tank and the raw solution tank, wherein the raw solution tank is provided with a lithium ion-containing aqueous solution containing lithium ions, cations other than lithium ions, and anions; the first adjacent tank is provided with water or an aqueous solution; the electrode in the first adjacent tank is connected to a power source so that the electrode in the first adjacent tank serves as a cathode and the electrode in the raw solution tank serves as an anode, and a voltage is applied between the electrodes; and while maintaining the pH of the solution in the raw solution tank at 10.5 or higher, the lithium ions in the raw solution tank are transferred through the cation exchange membrane into the first adjacent tank, thereby obtaining an aqueous solution containing lithium ions in which the content of anions other than hydroxide ions has been reduced in the first adjacent tank.

2. A method for treating a lithium-ion-containing aqueous solution, comprising: an electrodialysis apparatus comprising a raw solution tank separated from adjacent tanks on either side by a cation exchange membrane and an anion exchange membrane, a first adjacent tank adjacent to the raw solution tank via the cation exchange membrane, and a second adjacent tank adjacent to the raw solution tank via the anion exchange membrane, the first and second adjacent tanks each equipped with an electrode; storing a lithium-ion-containing aqueous solution containing lithium ions, cations other than lithium ions, and anions in the raw solution tank; storing water or an aqueous solution in the first and second adjacent tanks; connecting both electrodes to a power source so that the electrode in the first adjacent tank serves as a cathode and the electrode in the second adjacent tank serves as an anode, and applying a voltage between the both electrodes; and transferring the lithium ions in the raw solution tank through the cation exchange membrane into the first adjacent tank while maintaining the pH of the liquid in the raw solution tank at 10.5 or higher, thereby obtaining a lithium-ion-containing aqueous solution in the first adjacent tank in which the content of anions other than hydroxide ions has been reduced.

3. The method for treating an aqueous solution containing lithium ions according to claim 1 or 2, wherein the aqueous solution containing lithium ions contained in the concentrate tank contains aluminum dissolved therein.

4. The method for treating a lithium-ion-containing aqueous solution according to claim 1 or 2, wherein the lithium-ion-containing aqueous solution contained in the concentrate tank is an aqueous solution containing a water leachate of black mass, which is a powder containing metal originating from used lithium-ion batteries.

5. A method for treating an aqueous solution containing lithium ions according to claim 1 or 2, wherein the pH of the solution in the raw solution tank is maintained at 10.5 or higher by introducing an aqueous solution containing lithium ions from outside into the raw solution tank.

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