Electrodialysis method, sulfuric acid solution production method, lithium hydroxide solution production method, metal recovery method, and electrodialysis device

Abstract

This electrodialysis method is for generating an acid solution and an alkali solution from a metal-containing solution containing cations of an alkali metal and anions of an inorganic acid. The method includes: in an electrodialysis device 1, respectively supplying the metal-containing solution to a desalting chamber R1, an acid chamber supply liquid to an acid chamber R2, and an alkali chamber supply liquid to an alkali chamber R3; returning a desalted liquid flowing out from the desalting chamber R1 to the desalting chamber R1, returning an acid solution flowing out from the acid chamber R2 to the acid chamber R2, and returning an alkali liquid flowing out from the alkali chamber R3 to the alkali chamber R3 to thereby circulate the desalted liquid, the acid liquid, and the alkali liquid. During the circulation, at least a part of the acid liquid is replaced with a new acid chamber supply liquid and / or at least a part of the alkali liquid is replaced with a new alkali chamber supply liquid. The anion concentration of the inorganic acid in the acid liquid and / or the cation concentration of the alkali metal in the alkali liquid is reduced by the replacement.

Description

Electrodialysis method, method for producing sulfuric acid solution, method for producing lithium hydroxide solution, metal recovery method, and electrodialysis apparatus

[0001] This specification describes an electrodialysis method, a method for producing a sulfuric acid solution, a method for producing a lithium hydroxide solution, a method for recovering metals, and an electrodialysis apparatus.

[0002] In recent years, the recovery of valuable metals such as cobalt and nickel from lithium-ion battery waste discarded due to product lifespan, manufacturing defects, or other reasons has been widely considered from the perspective of effective resource utilization.

[0003] Methods for recovering metals from lithium-ion battery waste may include, for example, roasting or other prescribed dry treatments of the lithium-ion battery waste, and wet treatments of the battery powder obtained after such dry treatments.

[0004] In the wet process, metals such as cobalt, nickel, manganese, lithium, aluminum, and iron in the battery powder are leached with acid to obtain a metal-containing solution in which the metals have dissolved. Then, as described in Patent Document 1, for example, aluminum ions, iron ions, and manganese ions are removed sequentially or simultaneously from the metal-containing solution by neutralization or solvent extraction. After that, cobalt ions and nickel ions in the metal-containing solution are separated by solvent extraction. After the nickel ions are separated by extraction, a metal-containing solution with lithium ions remaining is obtained.

[0005] International Publication No. 2018 / 181816

[0006] In the aforementioned method for recovering metals from lithium-ion battery waste, electrodialysis can be performed to convert the metal salts dissolved in the metal-containing solution into other desired metal salts. In electrodialysis, the metal-containing solution is supplied to the desalination chamber of the electrodialysis machine, and pure water or similar liquids are supplied to the acid chamber and alkali chamber, respectively. As a result, the desalination solution flows out of the desalination chamber, the acid solution flows out of the acid chamber, and the alkali solution flows out of the alkali chamber.

[0007] In this type of electrodialysis method, improving current efficiency is a crucial issue from a cost reduction perspective. Conventional electrodialysis methods do not have sufficiently high current efficiency, and there is room for improvement.

[0008] This specification provides an electrodialysis method that can improve current efficiency, a method for producing a sulfuric acid solution, a method for producing a lithium hydroxide solution, a metal recovery method, and an electrodialysis apparatus.

[0009] The electrodialysis method described in this specification is an electrodialysis method for generating an acid solution and an alkaline solution from a metal-containing solution containing alkali metal cations and inorganic acid anions, comprising: supplying the metal-containing solution to the desalination chamber, the acid chamber supply solution to the acid chamber, and the alkaline chamber supply solution to the alkaline chamber using an electrodialysis apparatus; returning the desalination liquid flowing out of the desalination chamber to the desalination chamber, returning the acid solution flowing out of the acid chamber to the acid chamber, and returning the alkaline solution flowing out of the alkaline chamber to the alkaline chamber, thereby circulating the desalination liquid, the acid solution, and the alkaline solution, wherein at least a portion of the acid solution is replaced with a new acid chamber supply solution, and / or at least a portion of the alkaline solution is replaced with a new alkaline chamber supply solution during circulation, thereby reducing the concentration of inorganic acid anions in the acid solution and / or the concentration of alkali metal cations in the alkaline solution.

[0010] The method for producing the sulfuric acid solution described in this specification is to use the electrodialysis method described above.

[0011] The method for producing the lithium hydroxide solution described in this specification is to use the electrodialysis method described above.

[0012] The metal recovery method described in this specification is a method for recovering metal from lithium-ion battery waste, wherein at least a portion of the acid solution extracted by the exchange using the electrodialysis method described above is used as an acidic leachate and / or a back extract, and / or at least a portion of the alkaline solution extracted by the exchange is used as a pH adjuster.

[0013] The electrodialysis apparatus described in this specification is an electrodialysis apparatus used in an electrodialysis method for generating an acid solution and an alkaline solution from a metal-containing solution containing alkali metal cations and inorganic acid anions, comprising: a desalination chamber for supplying the metal-containing solution; an acid chamber for supplying an acid chamber supply liquid; and an alkaline chamber for supplying an alkaline chamber supply liquid; a desalination chamber circulation path for returning the desalination liquid flowing out of the desalination chamber back to the desalination chamber; an acid chamber circulation path for returning the acid solution flowing out of the acid chamber back to the acid chamber; and an alkaline chamber circulation path for returning the alkaline solution flowing out of the alkaline chamber back to the alkaline chamber, wherein the acid chamber circulation path and / or the alkaline chamber circulation path have branch paths that branch into two or more directions, and the branch paths are used for replacing at least a portion of the acid solution with a new acid chamber supply liquid, or replacing at least a portion of the alkaline solution with a new alkaline chamber supply liquid, the replacement which involves a decrease in the anion concentration of the inorganic acid in the acid solution or the cation concentration of the alkali metal in the alkaline solution.

[0014] According to the electrodialysis method, sulfuric acid solution production method, lithium hydroxide solution production method, metal recovery method, and electrodialysis apparatus described above, current efficiency can be improved.

[0015] This is a schematic diagram showing an electrodialysis apparatus according to one embodiment. This is a graph showing the change in sulfate ion concentration of the acid solution of the comparative example over time. This is a graph showing the change in sulfate ion concentration of the acid solution of the example over time.

[0016] The following describes in detail the electrodialysis method, the method for producing a sulfuric acid solution, the method for producing a lithium hydroxide solution, the metal recovery method, and embodiments of the electrodialysis apparatus described above. One embodiment of the electrodialysis method uses an electrodialysis apparatus to generate an acid solution and an alkaline solution from a metal-containing solution. This metal-containing solution is obtained by leaching metals in the battery powder of lithium-ion battery waste with an inorganic acid, and contains alkali metal cations and inorganic acid anions.

[0017] An electrodialysis apparatus is equipped with a desalination chamber, an acid chamber, and an alkali chamber. In the electrodialysis method, a metal-containing solution is supplied to the desalination chamber of the electrodialysis apparatus, an acid chamber supply solution to the acid chamber, and an alkali chamber supply solution to the alkali chamber. As a result, due to the potential difference resulting from the application of voltage between electrodes, alkali metal cations in the metal-containing solution move to the alkali chamber, and inorganic acid anions in the metal-containing solution move to the acid chamber, separating alkali metal cations and inorganic acid anions from the metal-containing solution. Consequently, in the desalination chamber, the metal-containing solution becomes a desalination solution, in the acid chamber, an acid solution containing inorganic acid anions is produced, and in the alkali chamber, an alkaline solution containing alkali metal cations is produced.

[0018] The desalination liquid flowing out of the desalination chamber is returned to the desalination chamber via a desalination chamber circulation path. Similarly, the acidic solution flowing out of the acid chamber is returned to the acid chamber via an acid chamber circulation path. The alkaline solution flowing out of the alkali chamber is returned to the alkali chamber via an alkali chamber circulation path. By circulating the desalination liquid, acidic solution, and alkaline solution in this manner, the desalination of the desalination liquid is sufficiently achieved, and the concentrations of the acidic and alkaline solutions can be increased. The acidic and alkaline solutions that have reached the predetermined concentrations can then be effectively used in other processes in the metal recovery method from lithium-ion battery waste, or in the recovery of alkali metals.

[0019] However, circulation presents a problem in that current efficiency decreases as the concentration of the acid and / or alkaline solution increases. The reason for this decrease in current efficiency is that, for example, focusing on the acid chamber side, as the concentration of the acid solution increases, the concentration gradient makes it more difficult for anions (such as sulfate ions) to move from the desalination chamber to the acid chamber. Also, as the concentration of the acid solution increases, hydrogen ions (H) move from the acid chamber to the desalination chamber. + The amount of lithium ions (Li) moving increases, and consequently the hydrogen ion concentration in the desalination chamber rises, the proportion of hydrogen ions in the total cations in the desalination chamber increases, and the amount of hydrogen ions moving from the desalination chamber to the alkali chamber also increases. As a result, lithium ions (Li) move from the desalination chamber to the alkali chamber. + This is because the amount of movement of the current decreases, which can reduce current efficiency.

[0020] Therefore, in the electrodialysis described above, at least a portion of the acid solution is replaced with a new acid chamber supply solution, and / or at least a portion of the alkaline solution is replaced with a new alkaline chamber supply solution during circulation. This replacement reduces the concentration of inorganic acid anions in the acid solution and / or the concentration of alkali metal cations in the alkaline solution. In other words, by performing the above replacement, the concentration of inorganic acid anions in the acid solution after replacement is lower than the concentration of inorganic acid anions in the acid solution before replacement, and / or the concentration of alkali metal cations in the alkaline solution after replacement is lower than the concentration of alkali metal cations in the alkaline solution before replacement. This improves the current efficiency of electrodialysis.

[0021] (Lithium-ion battery waste) The lithium-ion battery waste covered by this analysis consists of lithium-ion secondary batteries that can be used in mobile phones and other various electronic devices, and which 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 standpoint of effective resource utilization.

[0022] Lithium-ion battery waste has an outer casing containing aluminum. This casing may be made solely of aluminum, or it may contain aluminum and iron, aluminum laminate, etc. The lithium-ion battery waste may also contain a positive electrode active material made of a single metal oxide or a composite metal oxide containing two or more elements, including lithium and one element selected from the group consisting of nickel, cobalt, and manganese, or aluminum foil (positive electrode substrate) to which the positive electrode active material is coated and fixed with an organic binder such as polyvinylidene fluoride (PVDF). In addition, lithium-ion battery waste may contain copper, iron, etc. The casing of lithium-ion battery waste usually contains an electrolyte solution in which an electrolyte such as lithium hexafluoride phosphate is dissolved in an organic solvent. Examples of organic solvents used include ethylene carbonate and diethyl carbonate.

[0023] (Metal-containing solution) A metal-containing solution may be obtained, for example, by performing a dry treatment on the lithium-ion battery waste described above to obtain battery powder, then leaching the metal in the battery powder with an inorganic acid, and performing further wet treatment as necessary.

[0024] Dry processing to obtain battery powder from lithium-ion battery waste may include at least one of roasting, crushing, and sieving. Roasting, crushing, and sieving may be performed individually as needed, and may be performed in any order. Battery powder refers to powder obtained by separating and concentrating the positive electrode material components through some processing of lithium-ion battery waste. Battery powder may also be obtained as a powder in which the positive electrode material components are concentrated by crushing and sieving lithium-ion battery waste, with or without heat treatment.

[0025] In roasting, lithium-ion battery waste is heated in a stationary furnace or rotary kiln, for example, under an air atmosphere or an inert atmosphere such as nitrogen, at a temperature of 100°C to 1000°C for 0.5 to 4 hours. In crushing, to extract positive electrode material components from the housing of the lithium-ion battery waste, an impact-type crusher is used to destroy the housing and selectively separate the positive electrode material components from the positive electrode substrate. In sieving, sieving is performed using a sieve with an appropriate mesh size. As a result, aluminum and copper remain on the sieve, and battery powder with aluminum and copper removed to some extent is obtained below the sieve.

[0026] The battery powder described above is brought into contact with an acidic leachate of sulfuric acid, nitric acid, hydrochloric acid, or other inorganic acid. At this time, at least a portion of the acidic leachate can be an acid solution obtained by electrodialysis as described later (for example, a sulfuric acid solution). This yields a metal-containing solution containing alkali metal cations such as lithium ions and inorganic acid anions that were contained in the battery powder.

[0027] Metal-containing solutions may contain metal ions other than alkali metal cations, and may be subjected to wet processing for purposes such as separating these other metal ions. Such wet processing methods include neutralization and one- or multi-step solvent extraction.

[0028] In neutralization, for example, the pH of the metal-containing solution may be raised to 4.0 to 5.0 to precipitate aluminum ions, and then an oxidizing agent may be added to further raise the pH and raise the oxidation-reduction potential (ORP value, based on silver / silver chloride potential) to 300 mV to 900 mV to precipitate iron ions. In this case, an alkaline solution obtained by electrodialysis (for example, lithium hydroxide solution), as described later, can be used as a pH adjuster to raise the pH.

[0029] Subsequent solvent extraction may include the extraction of manganese ions, cobalt ions, and nickel ions in this order. In each extraction, a suitable extractant can be diluted with an organic solvent to form the solvent, and the metal ions can be extracted into the solvent after adjusting the pH to a predetermined equilibrium pH. Phosphate ester extractants and oxime extractants can be suitably used for manganese ion extraction, phosphonic acid ester extractants for cobalt ion extraction, and carboxylic acid extractants such as neodecanoic acid for nickel ion extraction. To adjust the equilibrium pH, an alkaline solution obtained by electrodialysis (e.g., lithium hydroxide solution) as described later can be used as a pH adjuster. For cobalt ion and nickel ion extraction, the solvent from which cobalt ions or nickel ions were extracted can be scrubbed as needed, and then back-extraction can be performed using a back-extract solution containing an inorganic acid such as sulfuric acid, hydrochloric acid, or nitric acid. Back-extraction may also be performed using a back-extract solution on the solvent from which manganese ions were extracted. As at least a portion of such a back-extract, an acid solution obtained by electrodialysis (e.g., sulfuric acid solution), as described later, can be used. Subsequently, if necessary, the solution obtained by back-extraction of cobalt ions or nickel ions can be further crystallized by heating and concentration to obtain cobalt salts such as sulfates and nickel salts, respectively.

[0030] In one example, the extract solution obtained after extracting nickel ions as described above may be used as a metal-containing solution for electrodialysis, as described below. This extract solution may be subjected to electrodialysis as a metal-containing solution after reducing or removing nickel ions, cobalt ions, manganese ions, magnesium ions, etc., by raising the pH or by ion exchange using resins such as cation exchange resins or chelating resins, if necessary. In this case, an alkaline solution obtained by electrodialysis (for example, lithium hydroxide solution) can be used as a pH adjuster to raise the pH.

[0031] The desalination solution obtained by the electrodialysis described below may be subjected to further treatment such as concentration or washing, as needed, before being subjected to electrodialysis again. In this case, the desalination solution corresponds to the metal-containing solution referred to herein.

[0032] (Electrodialysis) For electrodialysis, an electrodialysis apparatus 1 as illustrated in Figure 1 can be used. This electrodialysis apparatus 1 may be called a bipolar membrane electrodialysis apparatus, and the cell 1a is equipped with a desalination chamber R1 to which a metal-containing solution is supplied, an acid chamber R2 to which an acid chamber supply solution is supplied, and an alkali chamber R3 to which an alkali chamber supply solution is supplied. Here, as an example, the metal-containing solution is lithium ions (Li) as alkali metal cations. + ) as an anion of an inorganic acid, sulfate ion (SO4 2- This indicates cases that include sodium ions (Na), but it is not limited to this. + Other alkali metal cations such as (NO3) and nitrate ions (NO3) - ) or chloride ions (Cl - It may also be a metal-containing solution containing anions of other inorganic acids such as ).

[0033] More specifically, in the illustrated electrodialysis apparatus 1, a bipolar membrane 4, an anion exchange membrane 5, a cation exchange membrane 6, and a bipolar membrane 7 are sequentially disposed from the anode 2 side toward the cathode 3 side between the anode 2 and the cathode 3 in a cell 1a. Each of the bipolar membranes 4 and 7 is formed by laminating a cation exchange layer and an anion exchange layer. A desalination chamber R1 is defined between the anion exchange membrane 5 and the cation exchange membrane 6, an acid chamber R2 is defined between the bipolar membrane 4 and the anion exchange membrane 5, and an alkali chamber R3 is defined between the cation exchange membrane 6 and the bipolar membrane 7.

[0034] To perform electrodialysis with the electrodialysis apparatus 1, a predetermined voltage is applied between the anode 2 and the cathode 3, a metal-containing solution is supplied to the desalination chamber R1, and an acid chamber supply liquid such as pure water and an alkali chamber supply liquid are supplied to the acid chamber R2 and the alkali chamber R3, respectively. Then, lithium ions (Li + ) pass through the cation exchange membrane 6 and migrate into the alkali chamber R3. In the alkali chamber R3, water (H2O) is dissociated by the bipolar membrane 7 to generate hydroxide ions (OH - ), so a lithium hydroxide solution is obtained as an alkali liquid.

[0035] On the other hand, anions of inorganic acids in the metal-containing solution in the desalination chamber R1 pass through the anion exchange membrane 5 and migrate into the acid chamber R2. In the acid chamber R2, a sulfuric acid solution is produced as an acid liquid from the anions and hydrogen ions (H + ) generated from water (H2O) by the bipolar membrane 4.

[0036] In the desalination chamber R1, the metal-containing solution becomes a desalinated liquid after the lithium salt is separated into the acid chamber R2 side and the alkali chamber R3 side in the manner described above.

[0037] The acid solution obtained in the acid compartment R2 can be used, for example, as described above, as at least part of an acidic leachate for leaching metals from battery powder in a method for recovering metals from lithium-ion battery waste, or as at least part of a back-extraction solution used for back-extraction of a solvent from which cobalt ions, nickel ions or the like have been extracted. In addition, the alkaline solution obtained in the alkaline compartment R3 can be used as a pH adjuster in a method for recovering metals from lithium-ion battery waste, and may also be subjected to crystallization such as heating concentration or vacuum distillation to recover alkali metals such as lithium as metal salts such as lithium hydroxide. In such treatments and uses, acid solutions and alkaline solutions are sometimes required to have a high concentration of alkali metal cations (such as lithium ions) or a high concentration of inorganic acid anions (such as sulfate ions). In addition, alkali metal cations and inorganic acid anions may remain in the desalted solution obtained in the desalting compartment R1.

[0038] In electrodialysis, it is preferable to circulate the desalted solution, the acid solution and the alkaline solution for the purposes of increasing the concentration of the acid solution and the alkaline solution, and sufficiently performing desalination of the desalted solution. Specifically, the desalted solution flowing out of the desalting compartment R1 after passing through the desalting compartment R1 is returned to the desalting compartment R1, the acid solution flowing out of the acid compartment R2 after passing through the acid compartment R2 is returned to the acid compartment R2, and the alkaline solution flowing out of the alkaline compartment R3 after passing through the alkaline compartment R3 is returned to the alkaline compartment R3.

[0039] In order to enable such circulation of the liquid, the illustrated electrodialysis apparatus 1 is provided with a desalting compartment circulation path P1 connected to the inlet and outlet of the desalting compartment R1, an acid compartment circulation path P2 connected to the inlet and outlet of the acid compartment R2, and an alkaline compartment circulation path P3 connected to the inlet and outlet of the alkaline compartment R3.

[0040] Here, in the electrodialysis of the reference example, by continuously supplying water to tanks provided in the middle of the acid chamber circulation path P2 and the alkali chamber circulation path P3 while performing the above circulation, the overflow from the tanks may be continuously recovered. In this case, by adjusting the water supply amount according to the increase in concentration due to continuous electrodialysis, the concentration of the acid solution and alkali solution circulating in the electrodialysis apparatus 1 can be maintained without increasing, and a decrease in current efficiency can be suppressed compared to a case where the concentration increases. However, from the viewpoint of cost reduction, further improvement in current efficiency is desired.

[0041] The electrodialysis method of the present embodiment is characterized in that at least a part of the acid solution is replaced with a new acid chamber feed solution and / or at least a part of the alkali solution is replaced with a new alkali chamber feed solution in the middle of circulation, and the replacement reduces the concentration of inorganic acid anions in the acid solution and / or the concentration of alkali metal cations in the alkali solution. Thereby, the current efficiency of electrodialysis can be improved.

[0042] The term "replacement" as used herein means withdrawing at least a part of the acid solution and / or alkali solution in the electrodialysis apparatus 1, and supplying a new acid chamber feed solution and / or alkali chamber feed solution. In this replacement, the amount of the acid solution and / or alkali solution to be withdrawn is often equal to the amount of the new acid chamber feed solution and / or alkali chamber feed solution to be supplied, but they do not necessarily need to be equal in amount. This is because in electrodialysis, movement of water occurs along with movement of ions, and the volume of the acid solution and / or alkali solution changes (usually increases), so the liquid volume may be adjusted by replacement. For example, the ratio (W2 / W1) of the amount (W2) of the new acid chamber feed solution or alkali chamber feed solution to be supplied to the amount (W1) of the acid solution or alkali solution to be withdrawn may be 0.8 to 1.2, or may be 0.9 to 1.1.

[0043] The concentration of the acid chamber supply fluid is set lower than the concentration of the same type of acid solution circulating in the electrodialysis machine 1. This is to reduce the concentration of the acid solution after replacement. When replacing the acid solution, the difference in concentration between the acid solution circulating in the electrodialysis machine 1 and the new acid chamber supply fluid is not particularly limited, but the larger the difference in concentration, the lower the concentration of the acid solution after replacement can be. From this perspective, the acid chamber supply fluid may be pure water. However, in practice, pure water may not be used. For example, acid solution obtained from other electrodialysis may be used as the acid chamber supply fluid. Therefore, the concentration of the acid chamber supply fluid may be 70% or less, 50% or less, 30% or less, or 10% or less of the concentration of the acid solution circulating in the electrodialysis machine 1.

[0044] The same applies to the alkaline chamber supply solution. The concentration of the alkaline chamber supply solution is set lower than the concentration of the same type of alkaline solution circulating in the electrodialysis machine 1. This is to reduce the concentration of the alkaline solution after replacement. When replacing the alkaline solution, the difference in concentration between the alkaline solution circulating in the electrodialysis machine 1 and the new alkaline chamber supply solution is not particularly limited, but the larger the difference in concentration, the lower the concentration of the acid solution after replacement can be. From this viewpoint, the alkaline chamber supply solution may be pure water. However, in terms of operation, pure water may not be used. For example, alkaline solution obtained from other electrodialysis may be used as the alkaline chamber supply solution. Therefore, the concentration of the alkaline chamber supply solution may be 70% or less, 50% or less, 30% or less, or 10% or less of the concentration of the alkaline solution circulating in the electrodialysis machine 1.

[0045] When replacing at least a portion of the acid solution with a new acid chamber supply solution, it is preferable to adjust the amount of acid solution withdrawn so that the anion concentration (g / L) of inorganic acid in the acid solution at the end of the replacement is 50% or less, and furthermore 20% or less, of the anion concentration (g / L) of inorganic acid in the acid solution at the start of the replacement. Similarly, when replacing at least a portion of the alkaline solution with a new alkaline chamber supply solution, it is preferable to adjust the amount of alkaline solution withdrawn so that the cation concentration (g / L) of alkali metal in the alkaline solution at the end of the replacement is 50% or less, and furthermore 20% or less, of the cation concentration (g / L) of alkali metal in the alkaline solution at the start of the replacement. This allows for an even more effective improvement in current efficiency.

[0046] Here, "anion concentration of inorganic acid in the acid solution at the end of the exchange" and "cation concentration of alkali metal in the alkaline solution at the end of the exchange" may be the anion concentration of inorganic acid or the cation concentration of alkali metal at the end of the exchange, or they may be the anion concentration of inorganic acid or the cation concentration of alkali metal immediately after the end of the exchange. Similarly, "anion concentration of inorganic acid in the acid solution at the start of the exchange" and "cation concentration of alkali metal in the alkaline solution at the start of the exchange" may be the anion concentration of inorganic acid or the cation concentration of alkali metal at the start of the exchange, or they may be the anion concentration of inorganic acid or the cation concentration of alkali metal immediately before the start of the exchange. This is because it may be difficult to measure the concentration at the start and end of the exchange.

[0047] When replacing at least a portion of the acid solution with new acid chamber supply solution and / or at least a portion of the alkaline solution with new alkaline chamber supply solution, the amount replaced can be 20% or more, 50% or more, 70% or more, 80% or more, or 90% or more of the volume of circulating acid solution and / or alkaline solution (using the embodiment shown in Figure 1 as an example, the total amount in the electrodialysis machine 1, specifically the total amount in the acid chamber R2 or alkaline chamber R3, the acid chamber circulation path P2 or alkaline chamber circulation path P3, and the total amount in the storage tanks T2a and T2b or T3a and T3b), and the entire amount may also be replaced. The larger the amount replaced, the greater the decrease in concentration before and after the replacement, and thus the improved current efficiency. In calculating the above percentages, if the amount of acid solution or alkaline solution to be extracted (W1) and the amount of new acid chamber supply solution or alkaline chamber supply solution to be supplied (W2) are different, the larger amount is used as the amount to be replaced.

[0048] The time required for the exchange, from start to finish (exchange time), is not particularly limited, but it should be a time that allows for even a slight improvement in current efficiency through the exchange. From the perspective of improving current efficiency, the shorter the exchange time, the better. Therefore, the exchange time may be short. The concept of a short time varies depending on the conditions of electrodialysis, so it is difficult to specify a concrete time, but for example, the exchange time may be 10% or less of the time from the start to the end of the electrodialysis operation (operating time), or it may be 5% or less, 3% or less, or 1% or less. Alternatively, the exchange time may be 30 minutes or less, 20 minutes or less, 10 minutes or less, 5 minutes or less, or 1 minute or less.

[0049] In the illustrated embodiment, the acid chamber circulation path P2 and the alkali chamber circulation path P3 each have branching paths B2a and B2b and B3a and B3b that branch off in the middle. These acid chamber circulation path P2 and alkali chamber circulation path P3 each extend as a single path from their respective outlets in the direction of acid or alkali liquid flow, then branch off at branching point BP2 or BP3 to become branching paths B2a and B2b or branching paths B3a and B3b, and then merge into a single path at confluence point MP2 or MP3.

[0050] When such branching channels B2a and B2b, B3a and B3b are present, when circulating acidic or alkaline solutions, one of branching channels B2a and B2b or one of branching channels B3a and B3b is used, and when changing, the solution is passed through the other of branching channels B2a and B2b or the other of branching channels B3a and B3b, thus allowing branching channels B2a and B2b, B3a and B3b to be used for exchange.

[0051] Although not shown in the diagram, the branching path may branch into three or more paths. Also, if only the acid solution or the alkaline solution is to be replaced, it is not necessary to provide branching paths B2a and B2b and B3a and B3b in both the acid chamber circulation path P2 and the alkaline chamber circulation path P3, so the branching path B2a and B2b or B3a and B3b of the side that is not being replaced may be omitted.

[0052] However, even if there is a single acid chamber circulation path or alkali chamber circulation path that does not branch along the way, if there is a port along the way that allows for the withdrawal of acid solution or alkali solution and the supply of new acid chamber solution or alkali chamber solution, then replacement is possible. Therefore, the electrodialysis method of this embodiment is not limited to the electrodialysis apparatus shown in the figure, but can also be implemented in electrodialysis apparatuses in which the acid chamber circulation path or alkali chamber circulation path does not have branching paths. Even if the acid chamber circulation path or alkali chamber circulation path does not have branching paths, it is preferable to provide the storage tanks T2a or T2b and T3a or T3b described below and use them for supplying new acid chamber solution or alkali chamber solution.

[0053] It is desirable that each branch line B2a and B2b, and / or each branch line B3a and B3b, have storage tanks T2a and T2b, and / or storage tanks T3a and T3b, capable of storing liquid, as shown in the figure. This allows the acid and alkaline solutions withdrawn from the acid chamber circulation line P2 and alkali chamber circulation line P3, as well as new acid chamber supply liquid and alkali chamber supply liquid, to be stored in storage tanks T2a, T2b, T3a, and T3b, making their withdrawal and supply easier. In the illustrated example, a storage tank T1 is also provided in the middle of the desalination chamber circulation line P1.

[0054] In the example shown in Figure 1, branch lines B2a, B2b, B3a, and B3b are provided in both the acid chamber circulation path P2 and the alkali chamber circulation path P3, and storage tanks T2a, T2b, T3a, and T3b are located at each of the branch lines B2a, B2b, B3a, and B3b. However, it is not necessarily required to provide storage tanks T2a, T2b, T3a, and T3b for each branch line B2a, B2b, B3a, and B3b. For example, although not shown in the figure, it is possible to place one storage tank in the middle of at least one of the acid chamber circulation path and alkali chamber circulation path, and connect the piping as a branch line to that storage tank. In this case, one storage tank will be provided for each acid chamber circulation path and / or alkali chamber circulation path.

[0055] As described above, this embodiment performs a predetermined exchange during circulation. To perform the exchange during circulation, the exchange can be carried out without stopping the power supply and without stopping the flow of the circulating acid and / or alkaline solution. Alternatively, the flow of the circulating acid and / or alkaline solution can be temporarily stopped without stopping the power supply to perform the exchange, and then the flow can be restarted after the exchange.

[0056] In this embodiment, the predetermined exchange may be performed as a single event or intermittently. "Intermittently" means that multiple exchanges are performed at intervals from each other. The intervals between multiple exchanges may be constant or irregular. For example, the time from the end of the previous exchange to the start of the next exchange may be 30 to 360 minutes, but is not limited to this. Alternatively, a predetermined target concentration may be set, and the exchange may be performed each time that target concentration is reached. This configuration will be described separately as a modified example.

[0057] When the predetermined exchanges are performed intermittently, it is possible to lower the concentration of the acid solution and / or alkaline solution each time at least a portion of the acid solution and / or at least a portion of the alkaline solution are exchanged. As a result, the average concentration of the acid solution and / or alkaline solution tends to be lower overall throughout the electrodialysis process. Consequently, current efficiency can be improved compared to when exchanges are performed in single bursts. While such intermittent exchanges of at least one of the acid solution and alkaline solution can improve current efficiency, it is preferable to intermittently exchange both the acid solution and alkaline solution from the viewpoint of further improving current efficiency. The timing of the exchanges of the acid solution and alkaline solution may be simultaneous, or there may be a time interval between them.

[0058] When at least a portion of the acid solution is intermittently replaced with a new acid chamber supply solution, the average value of the inorganic acid anion concentration (g / L) in the acid solution is preferably 70% or less, more preferably 50% or less, and even more preferably 20% or less, of the inorganic acid anion concentration (g / L) in the acid solution at the start of at least one replacement cycle. When at least a portion of the alkaline solution is intermittently replaced with a new alkaline chamber supply solution, the average value of the alkali metal cation concentration (g / L) in the alkaline solution is preferably 70% or less, more preferably 50% or less, and even more preferably 20% or less, of the alkali metal cation concentration (g / L) in the alkaline solution at the start of at least one replacement cycle. This is because the lower the average value during electrodialysis, the greater the improvement in current efficiency. Here, the average value of the anion concentration (g / L) of the inorganic acid in the acid solution refers to the average value of the anion concentration (g / L) of the inorganic acid in the acid solution during electrodialysis, and the average value of the cation concentration (g / L) of the alkali metal in the alkaline solution refers to the average value of the alkali metal cation concentration (g / L) in the alkaline solution during electrodialysis. The average values ​​of the anion concentration (g / L) of the inorganic acid in the acid solution and the average value of the cation concentration (g / L) of the alkali metal in the alkaline solution can be determined by measuring the concentration of the acid solution flowing out of the acid chamber R2 and passing through the acid chamber circulation path P2, and the concentration of the alkaline solution flowing out of the alkaline chamber R3 and passing through the alkaline chamber circulation path P3, at predetermined timings during electrodialysis.

[0059] The predetermined timings are, from the start of electrodialysis operation until the first exchange, one point in time within ±10% of the start of operation, the start of the first exchange, and any intermediate points between these. From the first exchange until the final exchange, for each of the previous and next exchanges that occur chronologically, the predetermined timing is one point in time within ±10% of the end of the previous exchange, the start of the next exchange, and any intermediate points between these. From the final exchange until the end of operation, the predetermined timing is one point in time within ±10% of the end of the final exchange, the end of operation, and any intermediate points between these. For the concentrations measured at each of these timings, a time-weighted average is calculated, specifically, using the following formula (1), for each time point from the start of operation tk , and the concentration C at that time k The average concentration C is determined using the following method. However, if a simple average is used instead of a time-weighted average, the values ​​may shift and it may not be possible to calculate an accurate average concentration if the slope of the concentration increase changes between the previous and next exchanges. The anion concentration of inorganic acids is measured by neutralization titration. The cation concentration of alkali metals is measured using an ICP emission spectrometer SPS3300 manufactured by SII Nanotechnology Co., Ltd. or an equivalent instrument.

[0060]

[0061] The concentration of alkali metal cations in the metal-containing solution used for electrodialysis, typically lithium ion concentration, may be, for example, 1.0 g / L to 30.0 g / L. The flow rate per membrane area, i.e., linear velocity, of the desalted solution, acid solution, and alkaline solution circulated in the electrodialysis apparatus 1 may be, for example, 0.05 m / min to 1.00 m / min. The current density when a voltage is applied between the anode 2 and cathode 3 is, for example, 200 A / m². 2 ~1100 A / m 2 In some cases, the anion concentration of inorganic acids in the acid solution obtained by electrodialysis and withdrawn from the electrodialysis apparatus 1, typically the sulfate ion concentration, may be, for example, 30 g / L to 200 g / L, and the cation concentration of alkali metals in the alkaline solution withdrawn from the electrodialysis apparatus 1, typically the lithium ion concentration, may be, for example, 1 g / L to 25 g / L. The metal ion concentration can be measured using an ICP emission spectrometer SPS3300 manufactured by SII Nanotechnology Co., Ltd. or an equivalent device.

[0062] Next, a modified version of the electrodialysis method according to one embodiment will be described. In the modified version, a predetermined target concentration is set for the circulating acid solution and / or alkaline solution, and the solution is replaced each time the target concentration is reached. This makes it possible to improve current efficiency while obtaining the acid solution and / or alkaline solution of the target concentration. The target concentration that can be used as the basis for replacement may be set appropriately depending on the application of the acid solution and / or alkaline solution.

[0063] For example, the acid solution can be used as at least a portion of the acidic leachate in a metal recovery method, or as at least a portion of the back extract used in back extraction of a solvent from which cobalt ions or nickel ions have been extracted. In this case, if the acid solution is a sulfuric acid solution, the target concentration of sulfate ions may be set from the range of 30 g / L to 200 g / L, 60 g / L to 200 g / L, or 100 g / L to 200 g / L; if the acid solution is a hydrochloric acid solution, the target concentration of chloride ions may be set from the range of 10 g / L to 70 g / L, 30 g / L to 70 g / L, or 40 g / L to 70 g / L; and if the acid solution is a nitric acid solution, the target concentration of nitrate ions may be set from the range of 20 g / L to 130 g / L, 50 g / L to 130 g / L, or 80 g / L to 130 g / L.

[0064] Furthermore, the alkaline solution can be used as a pH adjuster in metal recovery methods or as a solution for crystallization. In this case, if the alkaline solution is a lithium hydroxide solution, the target lithium ion concentration may be set from the range of 1 g / L to 25 g / L, 5 g / L to 25 g / L, or 10 g / L to 25 g / L. If the alkaline solution is a sodium hydroxide solution, the target sodium ion concentration may be set from the range of 3 g / L to 85 g / L, 10 g / L to 85 g / L, or 30 g / L to 85 g / L.

[0065] In the operation of electrodialysis, the above-mentioned target concentration refers to the concentration used as the basis for exchanging the acid solution and / or alkaline solution, and the acid solution and / or alkaline solution can be exchanged when the target concentration is reached. However, since it is difficult to constantly measure the concentration during operation, there are circumstances where it is difficult to exchange the solution when the target concentration is reached. Therefore, in the modified version, each exchange can be performed when the concentration at the start of the exchange is within the range of target concentration ± 10%, preferably target concentration ± 5%. Furthermore, in the case of third-party implementation, the target concentration may not be determined or may not be set. In such cases, instead of the target concentration, the average values ​​of the concentrations of inorganic acid anions in the acid solution and alkali metal cations in the alkaline solution at the start of the exchange may be used. Specifically, in this embodiment, each exchange may be performed so that the concentration at the start of the exchange is within the range of the above average value ± 10%, preferably average value ± 5%. Since this average value can be estimated from past operational data, it is possible to perform electrodialysis in this form. Note that the modified version can also be used when performing a single exchange.

[0066] One embodiment of the method for producing a sulfuric acid solution uses the electrodialysis method described above. In this case, the metal-containing solution contains sulfate ions as anions of the inorganic acid, and the acid solution contains sulfate ions.

[0067] One embodiment of the method for producing a lithium hydroxide solution uses the electrodialysis method described above. In this case, the metal-containing solution contains lithium ions as alkali metal cations, and the alkaline solution contains lithium ions and hydroxide ions.

[0068] One embodiment of the metal recovery method is a method for recovering metal from lithium-ion battery waste, wherein at least a portion of the acid solution extracted by exchange using the electrodialysis method is used as the acidic leachate and / or back extract, and / or at least a portion of the alkaline solution extracted by exchange is used as the pH adjuster.

[0069] Next, we experimentally implemented the electrodialysis method described above and confirmed its effects, which are explained below. However, this explanation is for illustrative purposes only and is not intended to be an exhaustive limitation.

[0070] In both the examples and comparative examples, electrodialysis was performed on metal-containing solutions containing lithium ions and sulfate ions using a predetermined electrodialysis apparatus. Here, the metal-containing solution was supplied as the desalination solution, and pure water was supplied to the acid chamber and alkali chamber, respectively, as the acid chamber supply solution or alkali chamber supply solution. Furthermore, the desalination solution flowing out of the desalination chamber was returned to the desalination chamber, the acid solution flowing out of the acid chamber was returned to the acid chamber, and the alkali solution flowing out of the alkali chamber was returned to the alkali chamber, thereby circulating the desalination solution, acid solution, and alkali solution.

[0071] In both the comparative examples and the examples, two electrodialysis machines were connected, and the desalted liquid, which had undergone the first stage of desalting by circulating it in the first electrodialysis machine, was sent to the second electrodialysis machine and circulated in that machine to perform the second stage of desalting.

[0072] In the comparative example, an electrodialysis apparatus with almost the same configuration as that shown in Figure 1 was used, except that neither the acid chamber circulation path nor the alkali chamber circulation path had branching paths. In this comparative example, during electrodialysis, a new acid chamber supply solution (pure water) was continuously supplied to the storage tank of the acid chamber circulation path at a rate of 4.5 mL / sec, and the overflow from the storage tank was continuously recovered. As a result, in the first stage of desalination, the sulfate ion concentration of the acid solution passing through the acid chamber circulation path was maintained at a constant level of approximately 107 g / L, as shown in Figure 2. The amount of acid solution obtained by withdrawing it from the electrodialysis apparatus was 1.6 L. In the second stage of desalination, the sulfate ion concentration of the acid solution passing through the acid chamber circulation path remained constant at approximately 57 g / L. Note that the sulfate ions referred to here include bisulfate ions.

[0073] In this embodiment, an electrodialysis apparatus with almost the same configuration as that shown in Figure 1 was used, except that the alkaline chamber circulation path did not have a branching path. In the first stage of desalination in this embodiment, as shown in Figure 3, the acid solution was exchanged intermittently during circulation by withdrawing the acid solution from the acid chamber circulation path and supplying new acid chamber supply solution (pure water) to the acid chamber circulation path. In the first stage of desalination, the acid solution was exchanged when the sulfate ion concentration of the circulating acid solution reached 75 g / L ± 10%. In other words, the target sulfate ion concentration was set at 75 g / L. In each acid solution exchange, the ratio of the amount of new acid chamber supply solution supplied (W2) to the amount of acid solution withdrawn (W1) (W2 / W1) was approximately 0.8. As a result, the total amount of acid solution withdrawn from the electrodialysis apparatus was 2.6 L. Also, as shown in Figure 3, the average sulfate ion concentration in this embodiment was 46 g / L. In the second stage of desalination, the target sulfate ion concentration was set at 71 g / L.

[0074] As a result, the current efficiency of the comparative example was 56.2 for the first stage of desalination and 36.2 for the second stage of desalination. In contrast, the current efficiency of the example improved to 59.8 for the first stage of desalination and 43.4 for the second stage of desalination. The current efficiency referred to here was calculated using the formula: Current efficiency [%] = Li reduction in the desalination chamber [mol] × Faraday constant [C / mol] / (electric charge [C] × number of membrane pairs) × 100.

[0075] These results suggest that the electrodialysis method and electrodialysis apparatus described above may allow for improved current efficiency while obtaining acidic and / or alkaline solutions of a reasonably high concentration.

[0076] (Potential Contribution to SDGs) According to the embodiment described above, it is possible to improve current efficiency while obtaining acid and / or alkaline solutions of a reasonably high concentration, which may contribute to reducing processing costs in the recovery of metals from lithium-ion battery waste. For this reason, this embodiment may 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).

[0077] 1 Electrodialysis machine 1a Cell 2 Anode 3 Cathode 4 Bipolar membrane 5 Anion exchange membrane 6 Cation exchange membrane 7 Bipolar membrane B2a, B2b, B3a, B3b Branching paths BP2, BP3 Branching points MP2, MP3 Confluence point P1 Desalination chamber circulation path P2 Acid chamber circulation path P3 Alkali chamber circulation path R1 Desalination chamber R2 Acid chamber R3 Alkali chamber T1, T2a, T2b, T3a, T3b Storage tanks

Claims

1. An electrodialysis method for generating an acid solution and an alkaline solution from a metal-containing solution containing alkali metal cations and inorganic acid anions, comprising: supplying the metal-containing solution to a desalination chamber, an acid chamber supply solution to an acid chamber, and an alkaline chamber supply solution to an alkaline chamber using an electrodialysis apparatus; returning the desalination liquid flowing out of the desalination chamber to the desalination chamber, returning the acid solution flowing out of the acid chamber to the acid chamber, and returning the alkaline solution flowing out of the alkaline chamber to the alkaline chamber, thereby circulating the desalination liquid, the acid solution, and the alkaline solution; and replacing at least a portion of the acid solution with a new acid chamber supply solution and / or replacing at least a portion of the alkaline solution with a new alkaline chamber supply solution during the circulation, thereby reducing the concentration of inorganic acid anions in the acid solution and / or the concentration of alkali metal cations in the alkaline solution.

2. The electrodialysis method according to claim 1, wherein at least a portion of the acid solution is replaced with a new acid chamber supply solution, and the concentration of inorganic acid anions (g / L) in the acid solution at the end of the replacement is set to 50% or less of the concentration of inorganic acid anions (g / L) in the acid solution at the start of the replacement, and / or, at least a portion of the alkaline solution is replaced with a new alkaline chamber supply solution, and the concentration of alkali metal cations (g / L) in the alkaline solution at the end of the replacement is set to 50% or less of the concentration of alkali metal cations (g / L) in the alkaline solution at the start of the replacement.

3. The electrodialysis method according to claim 1 or 2, wherein at least a portion of the acid solution is intermittently replaced with a new acid chamber supply solution, and / or at least a portion of the alkaline solution is intermittently replaced with a new alkaline chamber supply solution.

4. The electrodialysis method according to claim 1 or 2, wherein at least a portion of the acid solution is intermittently replaced with a new acid chamber supply solution, and the average value of the anion concentration (g / L) of the inorganic acid in the acid solution is 70% or less of the anion concentration (g / L) of the inorganic acid in the acid solution at the start of at least one of the replacements, and / or, at least a portion of the alkaline solution is intermittently replaced with a new alkaline chamber supply solution, and the average value of the cation concentration (g / L) of the alkali metal in the alkaline solution is 70% or less of the cation concentration (g / L) of the alkali metal in the alkaline solution at the start of at least one of the replacements.

5. The electrodialysis method according to claim 1 or 2, wherein the metal-containing solution contains sulfate ions as anions of the inorganic acid, and the acid solution contains sulfate ions.

6. The electrodialysis method according to claim 1 or 2, wherein the metal-containing solution contains lithium ions as cations of the alkali metal, and the alkaline solution contains lithium ions and hydroxide ions.

7. The electrodialysis method according to claim 1 or 2, wherein the metal-containing solution is obtained by leaching metals from battery powder of lithium-ion battery waste with an inorganic acid.

8. A method for producing a sulfuric acid solution, comprising the electrodialysis method described in claim 5.

9. A method for producing a lithium hydroxide solution, comprising the electrodialysis method described in claim 6.

10. A method for recovering metals from lithium-ion battery waste, comprising using at least a portion of the acid solution extracted by the exchange method according to claim 1 or 2 as an acidic leachate and / or back extractate, and / or using at least a portion of the alkaline solution extracted by the exchange as a pH adjuster.

11. An electrodialysis apparatus for use in an electrodialysis method for generating an acid solution and an alkaline solution from a metal-containing solution containing alkali metal cations and inorganic acid anions, comprising: a desalination chamber for supplying the metal-containing solution; an acid chamber for supplying an acid chamber supply liquid; and an alkaline chamber for supplying an alkaline chamber supply liquid; a desalination chamber circulation path for returning the desalination liquid flowing out of the desalination chamber back to the desalination chamber; an acid chamber circulation path for returning the acid solution flowing out of the acid chamber back to the acid chamber; and an alkaline chamber circulation path for returning the alkaline solution flowing out of the alkaline chamber back to the alkaline chamber, wherein the acid chamber circulation path and / or the alkaline chamber circulation path have branch paths that branch into two or more, and the branch paths are used for the exchange of at least a portion of the acid solution with a new acid chamber supply liquid, or the exchange of at least a portion of the alkaline solution with a new alkaline chamber supply liquid, the exchange which involves a decrease in the anion concentration of the inorganic acid in the acid solution or the cation concentration of the alkali metal in the alkaline solution.

12. The electrodialysis apparatus according to claim 11, wherein each of the branch lines has a storage tank capable of storing liquid.

13. An electrodialysis apparatus according to claim 11 or 12, used in an electrodialysis method for generating an acid solution and an alkaline solution from a metal-containing solution containing sulfate ions as anions of the inorganic acid.

14. An electrodialysis apparatus according to claim 11 or 12, used in an electrodialysis method for generating an acid solution and an alkaline solution from a metal-containing solution containing lithium ions as cations of the alkali metal.

15. An electrodialysis apparatus according to claim 11 or 12, used in an electrodialysis method for generating an acidic solution and an alkaline solution from a metal-containing solution obtained by leaching metals in battery powder of lithium-ion battery waste with an inorganic acid.

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